U.S. patent application number 15/180596 was filed with the patent office on 2016-09-29 for analysis device, analysis method, optical element and electronic apparatus for analysis device and analysis method, and method of designing optical element.
The applicant listed for this patent is Seiko Epson Corporation. Invention is credited to Mamoru SUGIMOTO.
Application Number | 20160282266 15/180596 |
Document ID | / |
Family ID | 50190332 |
Filed Date | 2016-09-29 |
United States Patent
Application |
20160282266 |
Kind Code |
A1 |
SUGIMOTO; Mamoru |
September 29, 2016 |
ANALYSIS DEVICE, ANALYSIS METHOD, OPTICAL ELEMENT AND ELECTRONIC
APPARATUS FOR ANALYSIS DEVICE AND ANALYSIS METHOD, AND METHOD OF
DESIGNING OPTICAL ELEMENT
Abstract
An analysis device includes an optical element which includes a
metal layer, a light transmitting layer on the metal layer, and a
plurality of metal particles on the light transmitting layer
arranged at a first interval P1 in a first direction and arranged
at a second interval P2 in a second direction intersecting the
first direction, P1<P2.ltoreq.Q+P1, a light source which
irradiates incident light of linearly polarized light in the first
direction onto the optical element, and a detector which detects
light emitted from the optical element. Where Q represents the
interval between diffraction gratings.
Inventors: |
SUGIMOTO; Mamoru; (Chino,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Seiko Epson Corporation |
Tokyo |
|
JP |
|
|
Family ID: |
50190332 |
Appl. No.: |
15/180596 |
Filed: |
June 13, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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14194903 |
Mar 3, 2014 |
9389178 |
|
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15180596 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N 21/554 20130101;
G01N 21/658 20130101; G01N 21/553 20130101; G01N 21/65 20130101;
G01N 21/01 20130101; G01N 21/21 20130101; Y10T 29/49826
20150115 |
International
Class: |
G01N 21/552 20060101
G01N021/552; G01N 21/65 20060101 G01N021/65; G01N 21/21 20060101
G01N021/21 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 5, 2013 |
JP |
2013-042666 |
Claims
1. An analysis device comprising: an optical element which includes
a metal layer, a light transmitting layer provided on the metal
layer to transmit light, and a plurality of metal particles
arranged on the light transmitting layer at a first interval P1 in
a first direction and arranged at a second interval P2 in a second
direction intersecting the first direction; wherein
P1<P2.ltoreq.Q+P1; wherein Q represents an interval between
diffraction gratings given by: (.omega./c){.di-elect cons..di-elect
cons.(.omega.)/(.di-elect cons.+.di-elect
cons.(.omega.))}.sup.1/2=.di-elect cons..sup.1/2(.omega.)/.di-elect
cons.)sin .theta.+2m.pi./Q(m=.+-.1,.+-.2, . . . ); and wherein an
angular frequency of a localized surface plasmon excited in a metal
particle column is .omega., a dielectric constant of a metal
constituting the metal layer is .di-elect cons.(.omega.), a
dielectric constant around the metal layer is .di-elect cons.,
light speed in a vacuum is c, and an irradiation angle of incident
light which is an inclination angle of incident light from a
thickness direction of the light transmitting layer is .theta..
2. The analysis device according to claim 1, wherein 60 nm
P2.ltoreq.1310 nm.
3. The analysis device according to claim 1, wherein 60 nm
P2.ltoreq.660 nm.
4. The analysis device according to claim 1, wherein 60 nm
P1.ltoreq.120 nm.
5. The analysis device according to claim 1, wherein a size of the
metal particles in the first direction is D and 30
nm.ltoreq.D.ltoreq.72 nm.
6. The analysis device according to claim 1, wherein a size of the
metal particles in a height direction is T and 4
nm.ltoreq.T.ltoreq.20 nm.
7. The analysis device according to claim 1, wherein the light
transmitting layer is a dielectric layer in which a height
direction of the metal particles is a thickness direction, and a
thickness of the dielectric layer is G and 20 nm.ltoreq.G.ltoreq.60
nm.
8. The analysis device according to claim 1, further comprising a
detector which detects light emitted from the optical element,
wherein the detector detects Raman scattering light enhanced by the
optical element.
9. The analysis device according to claim 1, further comprising a
light source which irradiates incident light of linearly polarized
light in the first direction onto the optical element, wherein the
light source irradiates incident light having a wavelength greater
than a size in a height direction and a size in the first direction
of the metal particles onto the optical element.
10. An analysis method comprising: providing an optical element;
wherein the optical element includes a metal layer, a light
transmitting layer provided on the metal layer to transmit light,
and a plurality of metal particles arranged at a first interval P1
in a first direction and arranged at a second interval P2 in a
second direction intersecting the first direction on the light
transmitting layer, wherein P1<P2.ltoreq.Q+P1; wherein incident
light of linearly polarized light in the first direction is
irradiated onto the optical element; and wherein Q represents an
interval between diffraction gratings given by:
(.omega./c){.di-elect cons..di-elect cons.(.omega.)/(.di-elect
cons.+.di-elect cons.(.omega.))}.sup.1/2=.di-elect
cons..sup.1/2(.omega.)/.di-elect cons.)sin
.theta.+2m.pi./Q(m=.+-.1,.+-.2, . . . ); and wherein an angular
frequency of a localized surface plasmon excited in a metal
particle column is .omega., a dielectric constant of a metal
constituting the metal layer is .di-elect cons.(.omega.), a
dielectric constant around the metal layer is .di-elect cons.,
light speed in a vacuum is c, and an irradiation angle of incident
light which is an inclination angle of incident light from a
thickness direction of the light transmitting layer is .theta..
11. A method of manufacturing an optical element comprising:
providing a light transmitting layer on a metal layer to transmit
light; and providing a plurality of metal particles on the light
transmitting layer arranged at a first interval P1 in a first
direction and arranged at a second interval P2 in a second
direction intersecting the first direction, wherein
P1<P2.ltoreq.Q+P1; wherein Q represents an interval between
diffraction gratings given by: (.omega./c){.di-elect cons..di-elect
cons.(.omega.)/(.di-elect cons.+.di-elect
cons.(.omega.))}.sup.1/2=.di-elect cons..sup.1/2(.omega.)/.di-elect
cons.)sin .theta.+2m.pi./Q(m=.+-.1,.+-.2, . . . ); and wherein an
angular frequency of a localized surface plasmon excited in a metal
particle column is .omega., a dielectric constant of a metal
constituting the metal layer is .di-elect cons.(.omega.), a
dielectric constant around the metal layer is .di-elect cons.,
light speed in a vacuum is c, and an irradiation angle of incident
light which is an inclination angle of incident light from a
thickness direction of the light transmitting layer is .theta..
12. A method of manufacturing an optical element comprising:
providing a light transmitting layer; and providing a plurality of
metal particles on the light transmitting layer arranged at a first
interval in a first direction and arranged at a second interval in
a second direction intersecting the first direction, wherein the
metal particles are arranged in a matrix in the first and second
directions such that a localized surface plasmon and a propagated
surface plasmon occur.
13. An electronic apparatus comprising: the analysis device
according to claim 8; a calculation unit which calculates
diagnostic information based on detection information from the
detector; a storage unit which stores the diagnostic information;
and a display unit which displays the diagnostic information.
14. The electronic apparatus according to claim 13, wherein the
diagnostic information includes information relating to the
presence and/or absence or the amount of at least one bio-related
material selected from a group consisting of bacteria, viruses,
protein, nucleic acids, and antigens and/or antibodies, or at least
one compound selected from inorganic molecules and organic
molecules.
15. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation patent application of U.S.
application Ser. No. 14/194,903 filed Mar. 3, 2014, which claims
priority to Japanese Patent Application No. 2013-042666 filed Mar.
5, 2013, both of which are expressly incorporated by reference
herein in their entireties.
BACKGROUND
[0002] 1. Technical Field
[0003] The present invention relates to an analysis device, an
analysis method, an optical element and an electronic apparatus for
an analysis device and an analysis method, and a method of
designing an optical element.
[0004] 2. Related Art
[0005] In the fields of environment, food, public safety, and the
like including the medical and health field, there is a demand for
a sensing technique which detects trace substances quickly and
simply with high sensitivity and high precision. There are a wide
variety of trace substances to be detected, and include, for
example, bio-related materials, such as bacteria, viruses, protein,
nucleic acids, and various antigens/antibodies, and various
compounds including inorganic molecules, organic molecules, and
polymers. In the related art, while trace substances are detected
by sampling, analysis, and parsing, since a dedicated device is
required and an inspection worker needs to be skilled, the analysis
in this situation is difficult. For this reason, it takes a lot of
time (several days or more) for an inspection result to be
obtained. Thus, there is a great need for quick and simple
detection, and therefore, it is desirable to develop a sensor which
can meet this need.
[0006] For example, from expectations of comparative ease of
integration and less influence by an inspection and measurement
environment, there is a growing interest in a sensor which uses
surface plasmon resonance (SPR), or a sensor which uses
surface-enhanced Raman scattering (SERS).
[0007] For the purpose of sensing with higher sensitivity, as an
example of a sensor element having a structure which realizes a
hybrid mode, in which both modes of a localized surface plasmon
(LSP) and a propagated surface plasmon (PSP) are resonated
simultaneously, OPTICS LETTERS, Vol. 34, No. 3, 2009, 244-246
suggests a sensor element, called GSPP (Gap type Surface Plasmon
Polariton). OPTICS LETTERS, Vol. 30, No. 24, 2005, 3404-3406
describes the fundamental matters of electromagnetic coupling of
LSP and PSP, and discloses an element having a configuration in
which LSP and PSP interfere with each other constructively
(International Publication No. 2009/002524 and International
Publication No. 2005/114298).
[0008] The sensor disclosed in International Publication No.
2009/002524 has a layer in which nanoparticles formed on a
substrate made of a dielectric are arranged regularly in a lattice
shape. The particle layer is an array in which a particle size is 2
nm to 200 nm, if the particles are arranged in a square lattice
shape, the particles are arranged at an interval between particles
of 50 nm to several .mu.m, and if the particles are arranged so as
to form a diffraction grating, the particles are arranged in a row
at an interval of 1 nm to 10 nm and at an interval between rows of
equal to or greater than 0.1 .mu.m.
[0009] The sensor disclosed in International Publication No.
2005/114298 has a vapor deposition layer which is called a
resonance mirror on a substrate and is made of silver, gold, or
aluminum to have a thickness of 200 nm to 500 nm. Then, the sensor
has a dielectric layer which is called a light transmitting layer
formed on the vapor deposition layer to have a thickness of smaller
than 50 nm, and a particle layer which is called a nanoparticle
layer formed on the dielectric layer and has particles of gold,
silver, or the like arranged therein. The particle layer is an
array in which the particle size is 50 nm to 200 nm, and the
particles are arranged regularly at even intervals between
particles from an interval smaller than the wavelength of incident
light to an interval obtained by adding 0 nm to 20 nm to the
particle size.
[0010] However, in the sensors disclosed in International
Publication No. 2009/002524 and International Publication No.
2005/114298, the relationship between the wavelength or
polarization sate of incident light and the arrangement of the
array is not taken into consideration, and for this reason, a
sufficient signal amplification degree is not necessarily
obtained.
[0011] Although OPTICS LETTERS, Vol. 34, No. 3, 2009, 244-246 and
OPTICS LETTERS, Vol. 30, No. 24, 2005, 3404-3406 suggest a system
which uses the interaction between the localized surface plasmon
and the propagated surface plasmon, there is a problem in that Hot
Spot Density (HSD) is low.
SUMMARY
[0012] An advantage of some aspects of the invention is that it
provides an optical element with a large enhancement degree of
light based on plasmon to be excited by light irradiation and high
HSD, and a method of designing an optical element. Another
advantage of some aspects of the invention is that it provides an
analysis device and an electronic apparatus including the optical
element, and an analysis method.
[0013] An aspect of the invention is directed to an analysis device
including an optical element which includes a metal layer, a light
transmitting layer provided on the metal layer to transmit light,
and a plurality of metal particles arranged at a first interval in
a first direction and arranged at a second interval in a second
direction intersecting the first direction on the light
transmitting layer, a light source which irradiates incident light
of linearly polarized light in the same direction as the first
direction onto the optical element, and a detector which detects
light emitted from the optical element, in which the arrangement of
the metal particles of the optical element satisfies the
relationship of Expression (1).
P1<P2.ltoreq.Q+P1 (1)
[0014] Here, P1 represents the first interval, P2 represents the
second interval, and Q represents the interval between diffraction
gratings given by Expression (2) when an angular frequency of a
localized surface plasmon excited in the metal particle column is
.omega., a dielectric constant of a metal constituting the metal
layer is .di-elect cons.(.omega.), a dielectric constant around the
metal layer is .di-elect cons., light speed in a vacuum is c, and
an irradiation angle of incident light which is an inclination
angle of incident light from a thickness direction of the light
transmitting layer is .theta..
(.omega./c){.di-elect cons..di-elect cons.(.omega.)/(.di-elect
cons.+.di-elect cons.(.omega.))}.sup.1/2=.di-elect
cons..sup.1/2(.omega.)/.di-elect cons.)sin
.theta.+2m.pi./Q(m=.+-.1,.+-.2, . . . ) (2)
[0015] According to this analysis device, an optical element with a
large enhancement degree of light based on plasmon and high HSD is
provided, whereby it is possible to easily perform detection and
measurement of trace substances.
[0016] In the analysis device according to the aspect of the
invention, the interval P2 may satisfy the relationship of 60
nm.ltoreq.P2.ltoreq.1310 nm.
[0017] According to the analysis device of this configuration,
since an optical element with a larger enhancement degree of light
based on plasmon is provided, it is possible to more easily perform
detection and measurement of trace substances.
[0018] In the analysis device according to the aspect of the
invention, the interval P2 may satisfy the relationship of 60
nm.ltoreq.P2.ltoreq.660 nm.
[0019] According to the analysis device of this configuration,
since an optical element with a larger enhancement degree of light
based on plasmon is provided, it is possible to more easily perform
detection and measurement of trace substances.
[0020] In the analysis device according to the aspect of the
invention, the interval P1 may satisfy the relationship of 60
nm.ltoreq.P1.ltoreq.120 nm.
[0021] According to the analysis device of this configuration,
since an optical element with a larger enhancement degree of light
based on plasmon is provided, it is possible to more easily perform
detection and measurement of trace substances.
[0022] In the analysis device according to the aspect of the
invention, the size D of the metal particles in the first direction
may satisfy the relationship of 30 nm.ltoreq.D.ltoreq.72 nm.
[0023] According to the analysis device of this configuration,
since an optical element with a larger enhancement degree of light
based on plasmon is provided, it is possible to more easily perform
detection and measurement of trace substances.
[0024] In the analysis device according to the aspect of the
invention, the size T of the metal particles in a height direction
may satisfy the relationship of 4 nm.ltoreq.T.ltoreq.20 nm.
[0025] According to the analysis device of this configuration,
since an optical element with a larger enhancement degree of light
based on plasmon is provided, it is possible to more easily perform
detection and measurement of trace substances.
[0026] In the analysis device according to the aspect of the
invention, the light transmitting layer may be a dielectric layer
in which a height direction of the metal particles is a thickness
direction, and the thickness G of the dielectric layer may satisfy
the relationship of 20 nm.ltoreq.G.ltoreq.60 nm.
[0027] According to the analysis device of this configuration,
since an optical element with a larger enhancement degree of light
based on plasmon is provided, it is possible to more easily perform
detection and measurement of trace substances.
[0028] In the analysis device according to the aspect of the
invention, the detector may detect Raman scattering light enhanced
by the optical element.
[0029] According to the analysis device of this configuration,
since an optical element with a larger enhancement degree of light
based on plasmon is provided, it is possible to enhance Raman
scattering light and to easily perform measurement of trace
substances.
[0030] In the analysis device according to the aspect of the
invention, the light source may irradiate incident light having a
wavelength greater than the size T in the height direction and the
size D in the first direction of the metal particles onto the
optical element.
[0031] According to the analysis device of this configuration,
since it is possible to further extract the capability of an
optical element with a large enhancement degree of light based on
plasmon, it is possible to easily perform detection, measurement,
and the like of trace substances.
[0032] Another aspect of the invention is directed to an optical
element which is provided in the analysis device according to the
aspect of the invention and onto which linearly polarized light in
the same direction as the first direction is irradiated.
[0033] This optical element has a large enhancement degree of light
based on plasmon.
[0034] Still another aspect of the invention is directed to an
analysis method which irradiates incident light onto an optical
element and detects light emitted from the optical element with the
irradiation of incident light to analyze an object stuck to the
surface of the optical element, in which the optical element
includes a metal layer, a light transmitting layer provided on the
metal layer to transmit light, and a plurality of metal particles
arranged at a first interval in a first direction and arranged at a
second interval in a second direction intersecting the first
direction on the light transmitting layer, the metal particles of
the optical element are arranged so as to satisfy the relationship
of Expression (1), and incident light of linearly polarized light
in the same direction as the first direction is irradiated onto the
optical element.
P1<P2.ltoreq.Q+P1 (1)
[0035] Here, P1 represents the first interval, P2 represents the
second interval, and Q represents the interval between diffraction
gratings given by Expression (2) when an angular frequency of a
localized surface plasmon excited in the metal particle column is
.omega., a dielectric constant of a metal constituting the metal
layer is .di-elect cons.(.omega.), a dielectric constant around the
metal layer is .di-elect cons., light speed in a vacuum is c, and
an irradiation angle of incident light which is an inclination
angle of incident light from a thickness direction of the light
transmitting layer is .theta..
(.omega./c){.di-elect cons..di-elect cons.(.omega.)/(.di-elect
cons.+.di-elect cons.(.omega.))}.sup.1/2=.di-elect
cons..sup.1/2(.omega./.di-elect cons.)sin
.theta.+2m.pi./Q(m=.+-.1,.+-.2, . . . ) (2)
[0036] According to this analysis method, since an optical element
with a large enhancement degree based on plasmon and high HSD is
used, it is possible to easily detect and measure trace
substances.
[0037] Yet another aspect of the invention is directed to a method
of designing an optical element, in which the optical element
includes a metal layer, a light transmitting layer provided on the
metal layer to transmit light, and a plurality of metal particles
arranged at a first interval in a first direction and arranged at a
second interval in a second direction intersecting the first
direction on the light transmitting layer, and the metal particles
are arranged so as to satisfy the relationship of Expression
(1).
P1<P2.ltoreq.Q+P1 (1)
[0038] Here, P1 represents the first interval, P2 represents the
second interval, and Q represents the interval between diffraction
gratings given by Expression (2) when an angular frequency of a
localized surface plasmon excited in the metal particle column is
.omega., a dielectric constant of a metal constituting the metal
layer is .di-elect cons.(.omega.), a dielectric constant around the
metal layer is .di-elect cons., light speed in a vacuum is c, and
an irradiation angle of incident light which is an inclination
angle of incident light from a thickness direction of the light
transmitting layer is .theta..
(.omega./c){.di-elect cons..di-elect cons.(.omega.)/(.di-elect
cons.+.di-elect cons.(.omega.))}.sup.1/2=.di-elect
cons..sup.1/2(.omega.)/.di-elect cons.)sin
.theta.+2m.pi./Q(m=.+-.1,.+-.2, . . . ) (2)
[0039] According to this design method, it is possible to design an
optical element with a large enhancement degree of light based on
plasmon and high HSD.
[0040] Still yet another aspect of the invention is directed to a
method of designing an optical element, in which the optical
element includes a metal layer, a light transmitting layer provided
on the metal layer to transmit light, and a plurality of metal
particles arranged at a first interval in a first direction and
arranged at a second interval in a second direction intersecting
the first direction on the light transmitting layer, and the metal
particles are arranged in a matrix in the first direction and the
second direction such that a localized surface plasmon and a
propagated surface plasmon occur.
[0041] According to this design method, it is possible to design an
optical element with a large enhancement degree of light based on
plasmon.
[0042] Further, another aspect of the invention is directed to an
electronic apparatus including the analysis device according to the
aspect of the invention, a calculation unit which calculates
diagnostic information such as health and medical information on
the basis of detection information from the detector, a storage
unit which stores the health and medical information, and a display
unit which displays the health and medical information.
[0043] According to this electronic apparatus, the electronic
apparatus includes an optical element with a large enhancement
degree of light based on plasmon, whereby it is possible to easily
detect trace substances and provide high-precision health and
medical information.
[0044] In the electronic apparatus according to the aspect of the
invention, the health and medical information may include
information relating to the presence/absence or the amount of at
least one bio-related material selected from a group consisting of
bacteria, viruses, protein, nucleic acids, and antigens/antibodies,
or at least one compound selected from inorganic molecules and
organic molecules.
[0045] According to the electronic apparatus of this configuration,
it is possible to provide useful health and medical
information.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] Embodiments of the invention will be described with
reference to the accompanying drawings, wherein like numbers
reference like elements.
[0047] FIG. 1 is a perspective view schematically showing an
optical element of an embodiment.
[0048] FIG. 2 is a schematic view when the optical element of the
embodiment is viewed from a thickness direction of a light
transmitting layer.
[0049] FIG. 3 is a schematic view of a cross-section perpendicular
to a first direction of the optical element of the embodiment.
[0050] FIG. 4 is a schematic view of a cross-section perpendicular
to a second direction of the optical element of the embodiment.
[0051] FIG. 5 is a schematic view when the optical element of the
embodiment is viewed from the thickness direction of the light
transmitting layer.
[0052] FIG. 6 is a graph of a dispersion relation representing
dispersion curves of incident light and gold.
[0053] FIG. 7 is a graph showing the relationship between a
dielectric constant of Ag and a wavelength.
[0054] FIG. 8 is a graph showing a dispersion relation of a
dispersion curve of a metal, a localized surface plasmon, and
incident light.
[0055] FIG. 9 is a schematic view when an optical element of a
modification example of the embodiment is viewed from a thickness
direction of a light transmitting layer.
[0056] FIG. 10 is a schematic view of an analysis device of an
embodiment.
[0057] FIG. 11 is a schematic view of an electronic apparatus of an
embodiment.
[0058] FIG. 12 is a schematic view showing an example of a model
according to an experimental example.
[0059] FIG. 13 is a schematic view showing a model according to an
experimental example.
[0060] FIG. 14 is a graph showing excitation wavelength dependence
of hybrid plasmon according to an experimental example.
[0061] FIG. 15 is a graph of a dispersion relation according to an
experimental example.
[0062] FIG. 16 is a graph showing the relationship between an
enhancement degree and an interval according to an experimental
example.
[0063] FIG. 17 is a graph of a dispersion relation according to an
experimental example.
[0064] FIG. 18 is a graph showing the relationship between a Raman
scattering enhancement degree and an interval according to an
experimental example.
[0065] FIG. 19 is a graph showing the relationship between an
enhancement degree and an interval according to an experimental
example.
[0066] FIG. 20 is a graph showing the relationship between a Raman
scattering enhancement degree and an interval according to an
experimental example.
[0067] FIGS. 21A and 21B are schematic views showing an example of
a model according to an experimental example.
[0068] FIG. 22 is a diagram showing a hot spot intensity
distribution upon polarization in a first direction.
[0069] FIG. 23 is a diagram showing a hot spot intensity
distribution upon polarization in a first direction.
[0070] FIG. 24 is a graph showing the relationship between an
enhancement degree and the number of Ag particles according to an
experimental example.
[0071] FIG. 25 is a graph showing the relationship between a Raman
scattering enhancement degree and the number of Ag particles
according to an experimental example.
[0072] FIG. 26 is a graph showing the relationship between an
enhancement degree and the number of Ag particles according to an
experimental example.
[0073] FIG. 27 is a graph showing the relationship between a Raman
scattering enhancement degree and the number of Ag particles
according to an experimental example.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0074] Hereinafter, some embodiments of the invention will be
described. In the following embodiments, an example of the
invention will be described. It should be noted that the invention
is not limited to the following embodiments, and various
modifications may be carried out within a scope not departing from
the gist of the invention. Not all configurations described below
are essential to the invention.
1. OPTICAL ELEMENT
[0075] FIG. 1 is a schematic view of a cross-section of an optical
element 100 of this embodiment. FIG. 2 is a schematic view when the
optical element 100 of this embodiment is viewed in plan view
(viewed from a thickness direction of a light transmitting layer).
FIGS. 3 and 4 are schematic views of a cross-section of the optical
element 100 of this embodiment. FIG. 5 is a schematic view when the
optical element 100 of this embodiment is viewed from the thickness
direction of the light transmitting layer. The optical element 100
of this embodiment includes a metal layer 10, metal particles 20,
and a light transmitting layer 30.
1.1. Metal Layer
[0076] The metal layer 10 is not particularly limited insofar as a
metal surface which does not transmit light is provided, and for
example, may have a thick plate shape or a shape of a film, a
layer, or a membrane. For example, the metal layer 10 may be
provided on a substrate 1. In this case, the substrate 1 is not
particularly limited, and it is preferable that the substrate 1 is
less likely to affect a propagated surface plasmon excited in the
metal layer 10. As the substrate 1, for example, a glass substrate,
a silicon substrate, a resin substrate, or the like may be used.
The shape of the surface of the substrate 1 on which the metal
layer 10 is provided is not particularly limited. If a regular
structure is formed on the surface of the metal layer 10, the
substrate may have a surface corresponding to the regular
structure, and if the surface of the metal layer 10 is a plane, the
surface of the substrate may be a plane. In the example of FIGS. 1
to 5, the metal layer 10 is provided on the surface (plane) of the
substrate 1.
[0077] Here, although the expression of "plane" is used, the
related expression does not indicate a mathematically strict plane
which is flat (smooth) with no slight unevenness. For example, the
surface has unevenness due to constituent atoms or unevenness due
to a secondary structure (crystal, grain aggregate, grain boundary,
or the like) of a constituent material, and is not a strict plane
from a microscopic viewpoint. However, even in this case, from a
more macroscopic viewpoint, unevenness is less noticeable, and the
surface is observed to such an extent that the surface may be
referred to as a plane. Accordingly, in this specification, it is
assumed that, when the surface is recognizable as a plane from a
more macroscopic viewpoint, the surface is referred to as a
plane.
[0078] In this embodiment, the thickness direction of the metal
layer 10 coincides with the thickness direction of the light
transmitting layer 30 described below. In this specification, the
thickness direction of the metal layer 10 or the thickness
direction of the light transmitting layer 30 may be referred to as
a depthwise direction, a height direction, or the like upon
description of the metal particles 20 described below. For example,
if the metal layer 10 is provided on the surface of the substrate
1, the normal direction of the surface of the substrate 1 may be
referred to as a thickness direction, a depthwise direction, or a
height direction.
[0079] For example, the metal layer 10 can be formed using a
method, such as vapor deposition, sputtering, casting, machining,
or the like. If the metal layer 10 is provided on the substrate 1,
the metal layer 10 may be provided on the entire surface of the
substrate 1 or may be provided on a part of the surface of the
substrate 1. The thickness of the metal layer 10 is not
particularly limited insofar as the propagated surface plasmon is
excited in the metal layer 10, and for example, can be equal to or
greater than 10 nm and equal to or smaller than 1 mm, preferably,
equal to or greater than 20 nm and equal to or smaller than 100
.mu.m, and more preferably, equal to or greater than 30 nm and
equal to or smaller than 1 .mu.m.
[0080] The metal layer 10 is made of a metal in which there are an
electric field given by incident light and an electric field such
that a polarization induced by the electric field vibrates in an
inverse phase, that is, a metal which can have a dielectric
constant such that, if a specific electric field is given, a real
part of a dielectric function has a negative value (has a negative
dielectric constant), and a dielectric constant of an imaginary
part is smaller than the absolute value of the dielectric constant
of the real part. Examples of a metal which can have a dielectric
constant in a visible light region include gold, silver, aluminum,
copper, platinum, an alloy thereof, and the like. The surface of
(the end surface in the thickness direction) the metal layer 10 may
or may not have a specific crystal plane.
[0081] The metal layer 10 has a function of causing a propagated
surface plasmon to be generated in the optical element 100 of this
embodiment. Light is incident on the metal layer under the
following conditions, whereby the propagated surface plasmon is
generated near the surface (the end surface in the thickness
direction) of the metal layer 10. In this specification, a quantum
of vibration in which vibration of electric charges near the
surface of the metal layer 10 and electromagnetic waves are coupled
is called surface plasmon plariton (SPP). The propagated surface
plasmon generated in the metal layer 10 can interact (hybrid) with
a localized surface plasmon generated in the metal particles 20
described below under certain conditions.
1.2. Metal Particle
[0082] The metal particles 20 are provide to be separated from the
metal layer 10 in the thickness direction. The metal particles 20
may be arranged to be spatially separated from the metal layer 10,
and other substances, such as an insulator, a dielectric, and a
semiconductor, may be provided between the metal particles 20 and
the metal layer 10 in a single layer or a plurality of layers. In
the example of FIGS. 1 to 5 of this embodiment, the light
transmitting layer 30 is provided on the metal layer 10, and the
metal particles 20 are formed on the light transmitting layer 30,
whereby the metal layer 10 and the metal particles 20 are arranged
to be separated in the thickness direction of the light
transmitting layer.
[0083] The shape of the metal particles 20 is not particularly
limited. For example, the shape of the metal particles 20 may be a
circular shape, an elliptical shape, a polygonal shape, an
undefined shape, or a combined shape thereof when projected in the
thickness direction of the metal layer 10 or the light transmitting
layer 30 (in plan view from the thickness direction), or may be a
circular shape, an elliptical shape, a polygonal shape, an
undefined shape, or a combined shape thereof when projected in a
direction orthogonal to the thickness direction. In the example of
FIGS. 1 to 5, although all the metal particles 20 are drawn in a
columnar shape having a center axis in the thickness direction of
the light transmitting layer 30, the shape of the metal particles
20 is not limited thereto.
[0084] The size T in the height direction of the metal particles 20
indicates the length of a zone when the metal particles 20 can be
cut by a plane perpendicular to the height direction, and is equal
to or greater than 1 nm and equal to or smaller than 100 nm. The
size in a first direction orthogonal to the height direction of the
metal particles 20 indicates the length of a zone when the metal
particles 20 can be cut by a plane perpendicular to the first
direction, and is equal to or greater than 5 nm and equal to or
smaller than 200 nm. For example, if the shape of the metal
particles 20 is a columnar shape with the height direction as a
center axis, the size (the height of the column) in the height
direction of the metal particles 20 is equal to or greater than 1
nm and equal to or smaller than 100 nm, preferably, equal to or
greater than 2 nm and equal to or smaller than 50 nm, more
preferably, equal to or greater than 3 nm and equal to or smaller
than 30 nm, and still more preferably, equal to or greater than 4
nm and equal to or smaller than 20 nm. If the shape of the metal
particles 20 is a columnar shape with the height direction as a
center axis, the size (the diameter of the bottom surface of the
column) in the first direction of the metal particles 20 is equal
to or greater than 10 nm and equal to or smaller than 200 nm,
preferably, equal to or greater than 20 nm and equal to or smaller
than 150 nm, more preferably, equal to or greater than 25 nm and
equal to or smaller than 100 nm, and still more preferably, equal
to or greater than 30 nm and equal to or smaller than 72 nm.
[0085] Although the shape and material of the metal particles 20
are arbitrary insofar as a localized surface plasmon is generated
by irradiation of incident light, examples of a material in which a
localized surface plasmon can be generated by light near visible
light include gold, silver, aluminum, copper, platinum, an alloy
thereof, and the like.
[0086] The metal particles 20 can be formed by, for example, a
method which performs patterning after a thin film is formed by
sputtering, vapor deposition, or the like, a microcontact print
method, a nanoimprint method, or the like. The metal particles 20
may be formed by a colloid chemical method, and may be arranged at
a position to be separated from the metal layer 10 by an
appropriate method.
[0087] The metal particles 20 have a function of causing a
localized surface plasmon to be generated in the optical element
100 of this embodiment. Incident light is irradiated onto the metal
particles 20 under the following conditions, whereby the localized
surface plasmon can be generated around the metal particles 20. The
localized surface plasmon generated in the metal particles 20 can
interact (hybrid) with the propagated surface plasmon generated in
the metal layer 10 under certain conditions.
1.3. Arrangement of Metal Particles
[0088] As shown in FIGS. 1 to 5, a plurality of metal particles 20
are arranged to constitute metal particle columns 21. The metal
particles 20 are arranged in the first direction orthogonal to the
thickness direction of the metal layer 10 in the metal particle
columns 21. In other words, the metal particle columns 21 have a
structure in which a plurality of metal particles 20 are arranged
in the first direction orthogonal to the height direction. If the
metal particles 20 have a longitudinal shape (an anisotropic
shape), the first direction in which the metal particles 20 are
arranged may not coincide with the longitudinal direction. The
number of metal particles 20 which are arranged in one metal
particle column 21 may be plural, and preferably, is equal to or
greater than 10.
[0089] The interval of the metal particles 20 in the first
direction in the metal particle columns 21 is defined as an
interval P1 (see FIGS. 2 to 5). The interval P1 indicates the
inter-center distance (pitch) of two metal particles 20 in the
first direction. If the metal particles 20 have a columnar shape
with the thickness direction of the metal layer 10 as a center
axis, the inter-particle distance of two metal particles 20 in the
metal particle columns 21 is equal to a length obtained by
subtracting the diameter of the column from the interval P1. If the
inter-particle distance is small, there is a tendency that the
effect of the localized surface plasmon acting between the
particles increases, and an enhancement degree increases. The
inter-particle distance may be equal to or greater than 5 nm and
equal to or smaller than 1 .mu.m, preferably, equal to or greater
than 5 nm and equal to or smaller than 100 nm, and more preferably,
equal to or greater than 5 nm and equal to or smaller than 30
nm.
[0090] The interval P1 of the metal particles 20 in the first
direction in the metal particle columns 21 is equal to or greater
than 10 nm and equal to or smaller than 1 .mu.m, preferably, equal
to or greater than 20 nm and equal to or smaller than 800 nm, more
preferably, equal to or greater than 30 nm and equal to or smaller
than 780 nm, and still more preferably, equal to or greater than 50
nm and equal to or smaller than 700 nm.
[0091] Although the metal particle columns 21 are constituted by a
plurality of metal particles 20 arranged at the interval P1 in the
first direction, the distribution, intensity, and the like of the
localized surface plasmon generated in the metal particles 20 also
depend on the arrangement of the metal particles 20. Accordingly,
the localized surface plasmon which interacts with the propagated
surface plasmon generated in the metal layer 10 is a localized
surface plasmon taking into consideration the arrangement of the
metal particles 20 in the metal particle columns 21, as well as a
localized surface plasmon generated in the single metal particle
20.
[0092] As shown in FIGS. 1 to 5, the metal particle columns are
arranged at an interval P2 in a second direction intersecting the
thickness direction of the metal layer 10 and the first direction.
The number of metal particle columns 21 arranged may be plural, and
preferably, is equal to or greater than 10.
[0093] Here, the interval of adjacent metal particle columns 21 in
the second direction is defined as the interval P2. The interval P2
indicates the inter-center distance (pitch) of two metal particle
columns 21 in the second direction. If the metal particle columns
21 are constituted by a plurality of columns 22, the interval P2
indicates the distance between the position of a center of a
plurality of columns 22 in the second direction and the position of
a center of a plurality of columns 22 of an adjacent metal particle
column 21 in the second direction (see FIG. 9).
[0094] The interval P2 between the metal particle columns 21 is set
under conditions described in "1.3.1. Propagated Surface Plasmon
and Localized Surface Plasmon", and for example, may be equal to or
greater than 10 nm and equal to or smaller than 10 .mu.m,
preferably, equal to or greater than 20 nm and equal to or smaller
than 2 .mu.m, more preferably, equal to or greater than 30 nm and
equal to or smaller than 1500 nm, still more preferably, equal to
or greater than 60 nm and equal to or smaller than 1310 nm, and
particularly preferably, equal to or greater than 60 nm and equal
to or smaller than 660 nm.
[0095] The angle between a line in the first direction in which the
metal particle columns 21 extend and a line which connects two
closest metal particles 20 respectively belonging to adjacent metal
particle columns 21 is not particularly limited, and may be a right
angle. For example, as shown in FIG. 2, the angle between both
lines may be a right angle, or as shown in FIG. 5, the angle
between both lines may not be a right angle. That is, if the
arrangement of the metal particles 20 when viewed from the
thickness direction is regarded as a two-dimensional lattice with
the positions of the metal particles 20 as lattice points, an
irreducible fundamental unit lattice may have a rectangular shape
or a parallelogram shape. If the angle between the line in the
first direction in which the metal particle columns 21 extend and
the line which connects two closest metal particles 20 respectively
belonging to adjacent metal particle columns 21 is not a right
angle, the interval between two closest metal particles 20
respectively belonging to adjacent metal particle columns 21 may be
defined as the interval P2.
1.3.1. Propagated Surface Plasmon and Localized Surface Plasmon
[0096] First, the propagated surface plasmon will be described.
FIG. 6 is a graph of a dispersion relation representing dispersion
curves of incident light and gold.
[0097] Usually, even if light is irradiated onto the metal layer 10
at an incidence angle (irradiation angle .theta.) of 0 to 90
degrees, the propagated surface plasmon is not generated. For
example, this is because, if the metal layer 10 is made of Au, as
shown in FIG. 6, a light line and a dispersion curve of SPP of Au
have no intersection point. Even if the refractive index of a
medium through which light passes changes, since SPP of Au changes
depending on an ambient refractive index, there is no intersection
point. In order to cause the propagated surface plasmon with an
intersection point to be generated, there is a method in which a
metal layer is provided on a prism like the Kretschmann
arrangement, and the wavenumber of incident light increases with
the refractive index of the prism, or a method in which the
wavenumber of a light line increases with a diffraction grating.
FIG. 6 is a graph showing a so-called dispersion relation (the
vertical axis is an angular frequency [.omega.(eV)], and the
horizontal axis is a wave vector [k(eV/c)]).
[0098] The angular frequency .omega.(eV) on the vertical axis of
the graph of FIG. 6 has a relationship of .lamda.
(nm)=1240/.omega.(eV), and can be converted to wavelength. The wave
vector k(eV/c) on the horizontal axis of the graph has a
relationship of k(eV/c)=2.pi.2/[.lamda. (nm)/100]. Accordingly, for
example, if .lamda.=600 nm, k=2.09 (eV/c). The irradiation angle is
the irradiation angle of incident light, and is the inclination
angle from the thickness direction of the metal layer 10 or the
light transmitting layer 30 or from the height direction of the
metal particles 20.
[0099] Although FIG. 6 shows the dispersion curve of SPP of Au, in
general, when the angular frequency of incident light incident on
the metal layer 10 is .omega., light speed in a vacuum is c, the
dielectric constant of a metal constituting the metal layer 10 is
.di-elect cons.(.omega.), and an ambient dielectric constant is
.di-elect cons., the dispersion curve of SPP of the metal is given
by Expression (3).
K.sub.SPP=.omega./c[.di-elect cons..di-elect
cons.(.omega.)/(.di-elect cons.+.di-elect cons.(.omega.))].sup.1/2
(3)
[0100] When the irradiation angle of incident light, that is, the
inclination angle from the thickness direction of the metal layer
10 or the light transmitting layer 30 or from the height direction
of the metal particles 20 is .theta., the wavenumber K of incident
light which passes through virtual diffraction gratings having an
interval Q can be expressed by Expression (4).
K=n(.omega./c)sin .theta.+m2.pi./Q(m=.+-.1,.+-.2, . . . ) (4)
[0101] This relationship appears as a line, instead of a curve, on
the graph of the dispersion relation.
[0102] Note that n is an ambient refractive index, when an
extinction coefficient is .kappa., a real part .di-elect cons.' and
an imaginary part .di-elect cons.'' of a relative dielectric
constant .di-elect cons. at a frequency of light are respectively
given by .di-elect cons.'=n.sup.2-.kappa..sup.2 and .di-elect
cons.''=2n.kappa., and if an ambient medium is transparent, since
.kappa.0, .di-elect cons. is a real number, becomes .di-elect
cons.=n.sup.2, and is given by n=.di-elect cons..sup.1/2.
[0103] In the graph of the dispersion relation, if the dispersion
curve (Expression (3)) of SPP of the metal and the line (Expression
(4)) of diffracted light have an intersection point, the propagated
surface plasmon is excited. That is, if the relationship of
K.sub.SPP=K, the propagated surface plasmon is excited in the metal
layer 10.
[0104] Accordingly, Expression (2) is obtained from Expression (3)
and Expression (4).
(.omega./c){.di-elect cons..di-elect cons.(.omega.)/(.di-elect
cons.+.di-elect cons.(.omega.))}.sup.1/2=.di-elect
cons..sup.1/2(.omega.)/.di-elect cons.)sin
.theta.+2m.pi./Q(m=.+-.1,.+-.2, . . . ) (2)
[0105] It is understood that, if the relationship of Expression (2)
is satisfied, the propagated surface plasmon is excited in the
metal layer 10. In this case, in the example of SPP of Au of FIG.
6, change in .theta. and m can cause change in the slope and/or
slice of the light line, and it is possible to cause the line of
the light line to intersect the dispersion curve of SPP of Au.
[0106] Next, the localized surface plasmon will be described.
[0107] The condition for causing the localized surface plasmon to
be generated in the metal particles 20 is given by the following
expression using a real part of a dielectric constant.
Real[.di-elect cons.(.omega.)]=-2.di-elect cons. (5)
[0108] If the ambient refractive index n is 1, since .di-elect
cons.=n.sup.2-.kappa..sup.2=1, Real [.di-elect
cons.(.omega.)]=-2.
[0109] FIG. 7 is a graph showing the relationship between the
dielectric constant of Ag and wavelength. For example, although the
dielectric constant of Ag is as shown in FIG. 7, and the localized
surface plasmon is excited at a wavelength of about 400 nm, if a
plurality of Ag particles are close to each other in a nano order
or if the Ag particles and the metal layer 10 (Au film or the like)
are arranged to be separated by the light transmitting layer 30
(SiO.sub.2 or the like), the peak wavelength of the localized
surface plasmon is red-shifted (shifted to a long wavelength side)
by the effect of the gap. Although the shift amount depends on
dimension, such as Ag diameter, Ag thickness, Ag particle interval,
or light transmitting layer thickness, for example, a wavelength
characteristic that the localized surface plasmon has a peak at 500
nm to 900 nm is exhibited.
[0110] Unlike the propagated surface plasmon, the localized surface
plasmon is plasmon which has no speed and does not move, and if the
localized surface plasmon is plotted in the graph of the dispersion
relation, the slope is zero, that is, .omega./k=0.
[0111] FIG. 8 is a graph showing a dispersion relation of a
dispersion curve of a metal, a localized surface plasmon, and
incident light. The optical element 100 of this embodiment
electromagnetically couples the propagated surface plasmon and the
localized surface plasmon, thereby obtaining an extremely large
enhancement degree of an electric field. That is, the optical
element 100 of this embodiment has a feature that the intersection
point of the line of diffracted light and the dispersion curve of
SPP of the metal in the graph of the dispersion relation is not set
to an arbitrary point, and both intersect near a point at which the
greatest or maximum enhancement degree is given in the localized
surface plasmon generated in the metal particles 20 (metal particle
columns 21) (see FIG. 8).
[0112] In other words, in the optical element 100 of this
embodiment, it is designed such that, in the graph of the
dispersion relation, the line of diffracted light passes near the
intersection point of the dispersion curve of SPP of the metal and
the angular frequency (a line parallel to the horizontal axis
marked with LSP on the graph of the dispersion relation of FIG. 8)
of incident light giving the greatest or maximum enhancement degree
in the localized surface plasmon generated in the metal particles
20 (metal particle columns 21).
[0113] Here, if converted to wavelength, near the intersection
point refers to within the range of a wavelength having a length of
about .+-.10% of the wavelength of incident light, or within the
range of a wavelength having a length of about .+-.P1 (the interval
of the metal particles 20 in the metal particle columns 21) of the
wavelength of incident light.
[0114] In Expressions (3), (4), and (2), although the condition
that the propagated surface plasmon is excited when the angular
frequency of incident light incident on the metal layer 10 is
.omega. has been described, in order to cause interaction (hybrid)
of the localized surface plasmon and the propagated surface
plasmon, in the optical element 100 of this embodiment, win
Expressions (3), (4), and (2) becomes the angular frequency of
incident light giving the greatest or maximum enhancement degree in
the localized surface plasmon generated in the metal particles 20
(metal particle columns 21) or an angular frequency near the
angular frequency of incident light.
[0115] Accordingly, when the angular frequency of the localized
surface plasmon which is excited in the metal particle columns 21
is .omega., if Expression (2) is satisfied, it is possible to cause
a hybrid of the localized surface plasmon and the propagated
surface plasmon.
[0116] Accordingly, when the angular frequency of the localized
surface plasmon generated in the metal particle column 21 having
the metal particles 20 arranged at the interval P1 is .omega., if
the line of diffracted light (order m) which is incident on the
virtual diffraction gratings having the interval Q at the
irradiation angle .theta. and is diffracted passes near the
position of .omega. of the dispersion curve of SPP of the metal in
the graph of the dispersion relation (if Expression (2) is
satisfied), it is possible to cause a hybrid of the localized
surface plasmon and the propagated surface plasmon, and to obtain
an extremely large enhancement degree. In other words, in the graph
of the dispersion relation shown in FIG. 8, the slope and/or slice
of the light line changes to change the light line so as to pass
near the intersection point of SPP and LSP, whereby it is possible
to cause a hybrid of the localized surface plasmon and the
propagated surface plasmon, and to obtain an extremely large
enhancement degree.
1.3.2. Interval P2
[0117] The interval P2 between the metal particle columns 21 is set
as follows. When vertical incidence (incidence angle .theta.=0) is
made and first-order diffracted light (m=0) is used, if the
interval P2 is set as the interval Q, Expression (2) can be
satisfied. However, the interval Q at which Expression (2) can be
satisfied by the incidence angle .theta. and the order m of
diffracted light to be selected has a width. Although it is
preferable that the incidence angle .theta. in this case is the
inclination angle from the thickness direction to the second
direction, the incidence angle may be the inclination angle in a
direction including the component of the first direction.
[0118] Accordingly, the range of the column interval P2 which can
cause a hybrid of the localized surface plasmon and the propagated
surface plasmon is given by Expression (6) taking into
consideration the presence near the intersection point (the width
of .+-.P1).
Q-P1P2.ltoreq.Q+P1 (6)
[0119] Although the interval P2 is the interval between the metal
particle columns 21 in the second direction, in regard to the
interval between two metal particles 20 belonging to adjacent metal
particle columns 21, the line which connects these metal particles
20 can be inclined with respect to the second direction by a method
of selecting two metal particles 20. That is, two metal particles
20 belonging to adjacent metal particle columns 21 can be selected
so as to have an interval longer than the interval P2. In FIG. 2,
an auxiliary line for describing this is drawn, and two metal
particles 20 which are separated at a distance longer than the
interval P2 in a direction inclined with respect to the second
direction can be selected from adjacent metal particle columns 21.
As described above, since adjacent metal particle columns 21 are
the same metal particle column 21, the arrangement of the metal
particles 20 when viewed from the thickness direction may be
regarded as a two-dimensional lattice with the positions of the
metal particles 20 as lattice points. In the two-dimensional
lattice, there is an interval (diffraction grating) longer than the
interval P2.
[0120] Accordingly, in the matrix of the metal particles 20
arranged at the interval P1 and the interval P2, diffracted light
by diffraction gratings having an interval greater than the
interval P2 can be expected. For this reason, an inequality
expression on the left side of Expression (6) can be defined as
P1<P2. In other words, in Expression (6), even if the column
interval P2 is smaller than Q-P1, since there may be diffraction
gratings having the interval Q at which Expression (2) can be
satisfied, it is possible to cause a hybrid of the localized
surface plasmon and the propagated surface plasmon. Therefore, the
interval P2 may be a value smaller than Q-P1, and it should suffice
that the relationship of P1<P2 is satisfied.
[0121] From above, if the interval P2 between the metal particle
columns 21 in the optical element 100 of this embodiment satisfies
the relationship of Expression (1), it is possible to cause a
hybrid of the localized surface plasmon and the propagated surface
plasmon.
P1<P2.ltoreq.Q+P1 (1)
1.4. Light Transmitting Layer
[0122] The optical element 100 of this embodiment has the light
transmitting layer 30 which separates the metal layer 10 from the
metal particles 20. In FIGS. 1, 3, and 4, the light transmitting
layer 30 is drawn. The light transmitting layer 30 may have a shape
of a film, a layer, or a membrane. The light transmitting layer 30
is provided on the metal layer 10. Accordingly, it is possible to
separate the metal layer 10 from the metal particles 20.
[0123] The light transmitting layer 30 can be formed by, for
example, a method, such as vapor deposition, sputtering, CVD, or
various kinds of coating. The light transmitting layer 30 may be
provided on the entire surface of the metal layer 10 or may be
provided on a part of the surface of the metal layer 10. The
thickness of the light transmitting layer 30 is not particularly
limited insofar as the propagated surface plasmon of the metal
layer 10 and the localized surface plasmon of the metal particles
20 can interact with each other, and even in a thick gap structure
using a higher-order interference effect, the effects can be
obtained. The thickness of the light transmitting layer 30 can be,
for example, equal to or greater than 1 nm and equal to or smaller
than 1 .mu.m, preferably, equal to or greater than 5 nm and equal
to or smaller than 500 nm, more preferably, equal to or greater
than 10 nm and equal to or smaller than 100 nm, still more
preferably, equal to or greater than 15 nm and equal to or smaller
than 80 nm, and particularly preferably, equal to or greater than
20 nm and equal to or smaller than 60 nm.
[0124] The light transmitting layer 30 may have a positive
dielectric constant, and may be formed of, for example, SiO.sub.2,
Al.sub.2O.sub.3, TiO.sub.2, a polymer, ITO (Indium Tin Oxide), or
the like. The light transmitting layer 30 may be made of a
dielectric. The light transmitting layer 30 may have a plurality of
layers of different materials.
[0125] If the light transmitting layer 30 is provided, since there
is a case where the excitation peak frequency of the localized
surface plasmon generated in the metal particles 20 is shifted, it
is desirable to take this into consideration in obtaining the peak
excitation wavelength of the localized surface plasmon upon setting
of the interval P2.
1.5. Other Configurations and Modification
1.5.1. Overlayer
[0126] The optical element 100 of this embodiment may have an
overlayer as desired. Though not shown, the overlayer may be formed
so as to cover the metal particles 20. The overlayer may also be
formed so as to expose the metal particles 20 and to cover other
configurations.
[0127] For example, the overlayer has a function of mechanically
and chemically protecting the metal particles 20 or other
configurations from the environment. The overlayer may be formed by
a method, for example, vapor deposition, sputtering, CVD, various
kinds of coating, or the like. The thickness of the overlayer is
not particularly limited. The material of the overlayer is not
particularly limited, and the overlayer may be formed of, for
example, a metal, such as ITO, Cu, or Al, a polymer, or the like,
as well as an insulator, such as SiO.sub.2, Al.sub.2O.sub.3, or
TiO.sub.2. It is desirable that the thickness of the overlayer is
thin so as to be equal to or smaller than several nm.
[0128] If the overlayer is provided, similarly to the light
transmitting layer 30, since there is a case where the excitation
peak frequency of the localized surface plasmon generated in the
metal particles 20 is shifted, it is desirable to take this into
consideration in obtaining the peak excitation wavelength of the
localized surface plasmon upon setting of the column interval
P2.
1.5.2. Modification
[0129] FIG. 9 is a schematic view when an optical element 200
according to a modification example is viewed from the thickness
direction. The metal particle columns 21 may have a plurality of
columns 22. The columns 22 have a plurality of metal particles 20
arranged at the interval P1 in the first direction, and are the
same as the metal particle columns 21. Accordingly, all of a
plurality of columns 22 are parallel to the first direction. The
angle between a line in the first direction which connects two
adjacent metal particles 20 of the same column 22 and a line which
connects the closest metal particles 20 among the metal particles
20 belonging to adjacent columns 22 is not particularly limited,
and may or may not be a right angle. In the example shown in the
drawing, a case where the angle between both lines is a right angle
is described.
[0130] Here, the interval between adjacent columns 22 is defined as
an interval P3 (see FIG. 9). The interval P3 indicates the
inter-center distance (pitch) between two columns 22 in the second
direction. The interval P3 may have the relationship of P3 P1 with
respect to the interval P1 between the metal particles 20 in the
first direction.
[0131] If the metal particle columns 21 have columns 22 of a (where
a is an integer equal to or greater than 2), the metal particle
columns 21 have a width of (a-1)P3 in the second direction, and
have a maximum of (a-1)P1. Accordingly, in this case, there is a
limit to the minimum value of the interval P2, and the minimum
value of the interval P2 becomes aP3<P2. In the example shown in
the drawing, the metal particle columns 21 have two columns 22, the
metal particle columns 21 have a maximum of the width of P1 in the
second direction, and the minimum value of the interval P2 becomes
2P3<P2.
[0132] Even in the optical element 200 according to the
modification example, similarly to the optical element 100, it is
possible to enhance light with a very high enhancement degree on
the basis of plasmon to be excited by light irradiation.
1.6. Method of Designing Optical Element
[0133] The optical element 100 of this embodiment has the
above-described structure, and hereinafter, a method of designing
an optical element will be specifically described.
[0134] First, an optical element is designed including selecting
the interval P2 such that the line of diffracted light of the
localized surface plasmon generated in the metal particle column 21
intersects near the intersection point of the dispersion curve of
the metal constituting the metal layer 10 and the angular frequency
[.omega.(eV)] of light giving the peak of the localized surface
plasmon excited in the metal particles 20 (metal particle columns
21) arranged at the interval P1 in the graph (the vertical axis is
an angular frequency [.omega.(eV)] and the horizontal axis is a
wave vector [k(eV/c)]) of the dispersion relation (see FIG. 8).
[0135] A method of designing the optical element of this embodiment
includes the following process.
[0136] The excitation wavelength dependence of the localized
surface plasmon in the metal particles 20 (metal particle columns
21) is examined, and the wavelength at which the greatest or
maximum localized surface plasmon is generated in the metal
particles 20 (in this specification, this is referred to as a peak
excitation wavelength) is recognized. As described above, although
the localized surface plasmon changes depending on the material,
shape, and the arrangement of the metal particles 20, the
presence/absence of other configurations, or the like, the peak
excitation wavelength can be obtained by measurement or
computation.
[0137] The dispersion curve of the metal constituting the metal
layer 10 is recognized. This curve may be obtained from the
literature or the like depending on the material of the metal layer
10, or may be obtained by computation. From the left side of
Expression (2), it is understood that the dispersion relation
changes with the ambient refractive index .di-elect cons. of the
metal layer 10.
[0138] The obtained peak excitation wavelength and the dispersion
curve are plotted in the graph (the vertical axis is an angular
frequency [.omega.(eV)] and the horizontal axis is a wave vector
[k(eV/c)]) of the dispersion relation. At this time, the peak
excitation wavelength of the localized surface plasmon becomes a
line parallel to the horizontal axis on the graph. Though described
above, since the localized surface plasmon is plasmon which has no
speed and does not move, if the localized surface plasmon is
plotted in the graph of the dispersion relation, the slope
(.omega./k) becomes zero.
[0139] The incidence angle .theta. of incident light and the order
m of diffracted light to be used are determined, the value of Q is
obtained from Expression (2), and the interval P2 is selected so as
to satisfy the condition of Expression (1). Then, the metal
particle columns 21 are arranged.
[0140] If at least the above-described process is performed to set
the interval P1 and the interval P2, since LSP and PSP are in an
interaction (hybrid) state, it is possible to design an optical
element having a very large enhancement degree.
1.7. Enhancement Degree
[0141] With the mesh position of FDTD computation, the magnitude
relationship between an electric field Ex in an X direction (first
direction) and an electric field Ez in a Z direction (thickness
direction), that is, a vector changes. If linearly polarized light
in the X direction is used as excited light, the electric field Ey
in the Y direction (second direction) is nearly negligible. For
this reason, the enhancement degree can be recognized using the
square root of the sum of the squares of Ex and Ez, that is,
SQRT(Ex.sup.2+Ez.sup.2). With this, it is possible to perform
comparison of the scalars of local fields.
[0142] The SERS (Surface Enhancement Raman Scattering) effect is
expressed by Expression (a) using hot spot density (HSD) as SERS EF
(Enhancement Factor) when an electric field enhancement degree at a
wavelength of excited light is Ei, and an electric field
enhancement degree at a wavelength after Raman scattering is
Es.
SERS EF=Ei.sup.2Es.sup.2HSD (a)
[0143] Here, for example, since a scattering wavelength is 638 nm,
and the difference between the scattering wavelength and the
excitation wavelength is equal to or smaller than 40 nm, Stokes
scattering equal to or smaller than 1000 cm.sup.-1 at the
excitation wavelength of 600 nm can be approximated as follows
(Emax is the greatest enhancement degree).
Ei.sup.2Es.sup.2.apprxeq.Emax.sup.4
[0144] Accordingly, Expression (a) can be substituted with
Expression (b).
SERS EF=Emax.sup.4HSD (b)
[0145] That is, it can be considered that SERS (Surface Enhancement
Raman Scattering) is obtained by multiplication of hot spot density
and the fourth power of the electric field enhancement degree by
plasmon.
[0146] In an experimental example described below, in regard to
Expression (b), HSD is normalized, and Expression (c) is defined
and shown.
SERS EF=(Ex.sup.4+Ez.sup.4)/Unit Area (c)
[0147] If the enhancement degree of the optical element 100 is
considered, it is desirable to take into consideration so-called
hot spot density (HSD). That is, the enhancement degree of light by
the optical element 100 depends on the number of metal particles 20
per unit area of the optical element 100.
[0148] In the optical element 100 of this embodiment, the interval
P1 and the interval P2 are set such that the relationship of
Expressions (1) and (2) is satisfied. However, if HSD is taken into
consideration, the SERS enhancement degree of the optical element
100 is proportional to (Ex.sup.4+Ez.sup.4)/(P1P2).
1.8. Incident Light
[0149] The wavelength of incident light incident on the optical
element 100 is not limited insofar as the localized surface plasmon
is generated and the relationship of Expression (2) is satisfied,
and electromagnetic waves including ultraviolet light, visible
light, and infrared light may be used. In this embodiment, incident
light is linearly polarized light. In this embodiment, incident
light is linearly polarized light whose electric field is in the
same direction as the first direction (the extension direction of
the metal particle columns 21) of the optical element 100 (see
FIGS. 1 to 5). With this, it is possible to obtain a very large
enhancement degree of light by the optical element 100.
[0150] The optical element 100 of this embodiment has the following
features.
[0151] The optical element 100 of this embodiment can enhance light
with a very high enhancement degree and high HSD on the basis of
plasmon to be excited by light irradiation. Since the optical
element 100 of this embodiment has a high enhancement degree, for
example, the optical element 100 of this embodiment can be used in
a sensor which quickly and simply detects bio-related materials,
such as bacteria, viruses, protein, nucleic acids, or various
antigens/antibodies, or various compounds including inorganic
molecules, organic molecules, and polymers with high sensitivity
and high precision in the field of medicine and health,
environment, food, public safety, and the like. For example, the
enhancement degree when an antibody is coupled to the metal
particles 20 of the optical element 100 of this embodiment may be
obtained, and the presence/absence or the amount of an antigen may
be examined on the basis of change in enhancement degree when the
antigen is coupled to the antibody. The enhancement degree of light
of the optical element 100 of this embodiment can be used to
enhance Raman scattering light of trace substances.
2. ANALYSIS DEVICE
[0152] FIG. 10 is a diagram schematically showing a main part of an
analysis device 1000 of this embodiment.
[0153] The analysis device 1000 of this embodiment includes the
above-described optical element 100, a light source 300 which
irradiates incident light of linearly polarized light in the same
direction as the first direction onto the optical element 100, and
a detector 400 which detects light emitted from the optical element
100. The analysis device 1000 of this embodiment may include other
appropriate configurations (not shown).
2.1. Optical Element
[0154] The analysis device 1000 of this embodiment includes the
optical element 100. Since the optical element 100 is the same as
the above-described optical element 100, detailed description will
not be repeated.
[0155] The optical element 100 serves an operation to enhance light
and/or an operation as a sensor in the analysis device 1000. The
optical element 100 may be used in contact with a sample to be
analyzed by the analysis device 1000. The arrangement of the
optical element 100 in the analysis device 1000 is not particularly
limited, and the optical element 100 may be installed on a stage or
the like on which an installation angle or the like is
adjustable.
2.2. Light Source
[0156] The analysis device 1000 of this embodiment includes the
light source 300. The light source 300 irradiates incident light
onto the optical element 100. The light source 300 is arranged so
as to irradiate linearly polarized light (linearly polarized light
in the same direction as the first direction) in the first
direction (the direction in which the metal particles 20 are
arranged and the direction in which the metal particle columns 21
extend) of the optical element 100 (see FIG. 10). The incidence
angle .theta. of incident light irradiated from the light source
300 may appropriately change in accordance with the excitation
conditions of the surface plasmon of the optical element 100. The
light source 300 may be installed in a goniometer or the like.
[0157] Light irradiated from the light source 300 is not
particularly limited insofar as the surface plasmon of the optical
element 100 can be excited, and electromagnetic waves including
ultraviolet light, visible light, and infrared light may be used.
Light irradiated from the light source 300 may or may not be
coherent light. Specifically, as the light source 300, a light
source in which a wavelength selection element, a filter, a
polarizer, and the like are appropriately provided in a
semiconductor laser, a gas laser, a halogen lamp, a high-pressure
mercury vapor lamp, a xenon lamp, or the like may be used.
[0158] Light from the light source 300 becomes incident light, and
enhanced light is emitted from the optical element 100.
Accordingly, it is possible to perform amplification of Raman
scattering light of the sample or detection of a substance
interacting with the optical element 100.
2.3. Detector
[0159] The analysis device 1000 of this embodiment includes the
detector 400. The detector 400 detects light emitted from the
optical element 100. As the detector 400, for example, a CCD
(Charge Coupled Device), a photomultiplier tube, a photodiode, an
imaging plate, or the like may be used.
[0160] It should suffice that the detector 400 is provided at a
position at which light emitted from the optical element 100 can be
detected, and the positional relationship with the light source 300
is not particularly limited. The detector 400 may be installed in a
goniometer or the like.
2.4. Analysis Method
[0161] An analysis method of this embodiment which irradiates
incident light onto the above-described optical element 100,
detects light emitted from the optical element 100 with irradiation
of incident light, and analyzes an object stuck to the surface of
the optical element 100 is performed by irradiating incident light
of linearly polarized light onto the optical element 100 in the
same direction as the first direction (the direction in which the
metal particles 20 are arranged and the direction in which the
metal particle columns 21 extend).
3. ELECTRONIC APPARATUS
[0162] An electronic apparatus 2000 of this embodiment includes the
above-described analysis device 1000, a calculation unit 2010 which
calculates health and medical information on the basis of detection
information from the detector 400, a storage unit 2020 which stores
the health and medical information, and a display unit 2030 which
displays the health and medical information.
[0163] FIG. 11 is a schematic view showing the configuration of the
electronic apparatus 2000 of this embodiment. The analysis device
1000 is the analysis device 1000 described in "2. Analysis Device",
and detailed description will not be repeated.
[0164] The calculation unit 2010 is, for example, a personal
computer or a personal digital assistance (PDA), receives the
detection information (signal or the like) transmitted from the
detector 400, and performs calculation based on the detection
information. The calculation unit 2010 may control the analysis
device 1000. For example, the calculation unit 2010 may control the
output, position, or the like of the light source 300 of the
analysis device 1000 or may control the position or the like of the
detector 400. The calculation unit 2010 can calculate the health
and medical information on the basis of the detection information
from the detector 400. The health and medical information
calculated by the calculation unit 2010 is stored in the storage
unit 2020.
[0165] The storage unit 2020 is, for example, a semiconductor
memory, a hard disk drive, or the like, and may be constituted
integrally with the calculation unit 2010. The health and medical
information stored in the storage unit 2020 is transmitted to the
display unit 2030.
[0166] The display unit 2030 is constituted by, for example, a
display board (liquid crystal monitor or the like), a printer, an
illuminant, a speaker, or the like. The display unit 2030 performs
display or gives an alarm on the basis of the health and medical
information or the like calculated by the calculation unit 2010
such that the user can recognize the content.
[0167] The health and medical information may include information
relating to the presence/absence or the amount of at least one
bio-related material selected from a group consisting of bacteria,
viruses, protein, nucleic acids, and antigens/antibodies or at
least one compound selected from inorganic molecules and organic
molecules.
4. EXPERIMENTAL EXAMPLES
[0168] Hereinafter, although the invention will be further
described in connection with experimental examples, the invention
is not limited to the following examples. The following examples
are a simulation by a computer.
4.1. Computation Model
[0169] FIG. 12 is a schematic view showing the basic structure of a
model for use in a simulation.
[0170] In all models used for computation of an experimental
example, a dielectric layer (SiO.sub.2) film was formed on Au
(metal layer) which was thick enough to prevent transmission of
light. The thickness of the dielectric layer was fixed to 20 nm, 50
nm, or 60 nm. Metal particles arranged on the dielectric layer were
Ag, and were a column with the thickness direction of the
dielectric layer (SiO.sub.2) as a center axis, the size (the
diameter of the bottom surface) of the column was 30 nm, 32 nm, or
72 nm, and the height of the column was 4 nm to 20 nm.
[0171] FDTD soft Fullwave manufactured by CYBERNET SYSTEMS CO.,
LTD. was used for computation. The condition of a used mesh was a 1
nm minimum mesh, and the computation time cT was 10 atm.
[0172] The ambient refractive index n was 1, and incident light was
linearly polarized light in the same direction as the first
direction (X) with vertical incidence from the thickness direction
(Z) of the metal layer or the light transmitting layer.
[0173] In a model having Ag particles arranged in a line at an
interval of 60 nm in the second direction (X), a near field
characteristic was computed on the top surface of the SiO.sub.2
film below the Ag particles, and it was understood that an electric
field vector was greatly changed with the arrangement of YeeCell.
Accordingly, since it is found that, if an electric field is
described by scalar, the effect of the position of YeeCell
decreases, and a value at a substantially maximum enhancement
position (hot spot) substantially became equal in the X direction
and the Z direction, in this experimental example, it is assumed
that the enhancement degree is expressed by SQRT
(Ex.sup.2+Ez.sup.2). Here, Ex represents electric field intensity
in a polarization direction (first direction) of incident light,
and Ez represents electric field intensity in the thickness
direction. In this case, electric field intensity in the second
direction is small and thus not taken into consideration.
4.2. Experimental Example 1
[0174] FIG. 13 is a diagram schematically showing a model used in
Experimental Example 1.
[0175] While the thickness of the dielectric layer was 50 nm, the
size (the diameter of the bottom surface) of the column of the Ag
particles having a columnar shape was 30 nm, the interval P1 of the
Ag particles in the first direction was fixed to 60 nm, and the
interval P2 of the Ag particle columns in the second direction was
changed to 60 nm, 480 nm, 540 nm, 600 nm, 660 nm, and 720 nm,
excitation wavelength dependence of a near file was examined. Here,
the diameter of the bottom surface of the Ag particles was 30 nm.
The result is shown in FIG. 14.
[0176] Referring to FIG. 14, it was found that, when the interval
P2 was 480 nm, 540 nm, 600 nm, 660 nm, and 720 nm, the peak
excitation wavelength was 610 nm. In the respective cases, the
enhancement degree was 100.9, 101.8, 101.1, 95.1, and 94.4.
[0177] In contrast, it was found that, when the interval P2 was 60
nm (that is, P1=P2), the peak excitation wavelength was about 620
nm, and the enhancement degree was about 58.7. The reason for which
the peak excitation wavelength becomes 620 nm is considered that,
since the distance between the Ag particles in the second direction
is 60 nm, red-shift occurs due to the localized surface
plasmon.
[0178] From this, it was found that, when the interval P2 was 480
nm, 540 nm, 600 nm, 660 nm, and 720 nm, a significantly large
enhancement degree is exhibited compared to when the interval P2 is
60 nm. When the interval P2 was 480 nm to 720 nm, in particular,
when the interval P2 is 540 nm and 600 nm, the reason that a larger
enhancement degree is exhibited can be explained by a graph (FIG.
15) of a dispersion relation.
[0179] That is, the reason is considered that, if the interval P2
is 540 nm and 600 nm, this is closer to the intersection point of
the peak excitation wavelength (610 nm) of the localized surface
plasmon of the Ag particles and SPP of Au in the graph of the
dispersion relation of FIG. 15.
[0180] With this experimental example, it was found that, even if
the interval P2 was changed, the peak excitation wavelength of the
localized surface plasmon was not changed, and a hybrid with the
propagated surface plasmon of the Au layer was attained and a high
enhancement degree was obtained depending on the size of the
interval P2.
4.3. Experimental Example 2
[0181] A simulation was performed in the same manner as in
Experimental Example 1, except that the thickness of the dielectric
layer was 60 nm, and the size (the diameter of the bottom surface)
of the Ag particles having a columnar shape was 32 nm.
[0182] According to this model, the peak excitation wavelength was
633 nm. SQRT(Ex.sup.2+Ez.sup.2) at this time was 67.9. Hereinafter,
as shown in Experimental Example 1, since the peak excitation
wavelength was not changed by the interval P2, the peak excitation
wavelength was fixed to 633 nm, and the interval P2 was a
variable.
[0183] While the interval P1 of the Ag particles in the first
direction was fixed to 60 nm, and the interval P2 of the Ag
particle columns in the second direction was changed, change of the
enhancement degree with respect to the interval P2 was obtained.
The result is shown in FIG. 16.
[0184] Referring to FIG. 16, as the interval P2 became larger from
60 nm, the enhancement degree immediately increased, and the
enhancement degree had a maximum value at 600 nm. If the interval
P2 became larger, while the enhancement degree slightly decreased,
the enhancement degree increased while a high enhancement degree
was maintained, and had two peak values when the interval P2 was
1200 nm.
[0185] From this, it is understood that the Ag particles and the Au
film interact with each other. It was found that, a hybrid with the
propagated surface plasmon of the Au layer was attained and a high
enhancement degree was obtained depending on the size of the
interval P2.
[0186] Referring to FIG. 16, for example, even in a region where
the interval P2 was small, for example, the interval P2 was 120 nm
(93.1), it was understood that a significantly large enhancement
degree 1.37 times the enhancement degree (67.9) when the interval
P2 was 60 nm was obtained. The reason is considered that two
effects of interaction of SPP of Au and LSP and a hot spot density
effect (the effect of concentrating an electric field on a small
hot spot if hot spot density decreases) are combined.
[0187] Another reason is considered that the Ag particles can be
selected such that the interval between two Ag particles belonging
to adjacent Ag particle columns is longer than the interval P2 by a
way to select two Ag particles. Accordingly, it is considered that
there is a grating interval (diffraction grating) longer than the
interval P2, and diffracted light by diffraction gratings having
the interval occurs. Specifically, as shown in FIG. 2, it is
considered that the propagated surface plasmon between diffraction
gratings of an oblique component exhibits an enhancement effect if
the interval of the diffraction gratings satisfies 600 nm, and
resonance (hybrid) with the localized surface plasmon of the metal
particles occurs.
[0188] FIG. 17 shows a graph of a dispersion relation of this
experimental example. Referring to FIG. 17, it is confirmed that an
intersection point with SPP of Au is near 600 nm, and the
enhancement degree has a maximum value at the interval P2=600
nm.
[0189] The reason for which the peak of the enhancement degree is
present at the interval P2=1200 nm is considered that a multiple of
a wavenumber 2.pi./1200 corresponding to 1200 nm becomes equal to a
wavenumber 27.pi./600 corresponding to 600 nm.
[0190] In this experimental example, since the excitation
wavelength was 633 nm, the enhancement degree when the interval
P2=600 nm was 134.5 and had the highest value close to two times
the enhancement degree (67.9) when the interval P2=60 nm.
4.4. Experimental Example 3
[0191] If both energy of excitation light and energy of scattering
light are utilized, Raman scattering is proportional to the fourth
power of an enhanced electric field. That is, it is that Raman
scattering is proportional to .di-elect cons..sup.4. Accordingly,
when the interval P1=60 nm and the interval P2=600 nm of
Experimental Example 2, (134.5/67.9).sup.4=15.39. However, in this
case, since the number of metal particles per unit area becomes
1/10 compared to when the interval P1=60 nm and the interval P2=60
nm, the Raman scattering enhancement degree can be estimated as
1/10=1.54. That is, in Experimental Example 2, it is possible to
obtain a high Raman scattering enhancement degree of 54%.
[0192] Accordingly, the vertical axis of FIG. 16 of Experimental
Example 2 was normalized as (Ex.sup.4+Ez.sup.4)/(P1P2) with hot
spot density and plotted in FIG. 18.
[0193] From the plot of FIG. 18, the Raman effect is supposed, and
by comparison with the sum of the fourth power per unit area, it is
found that a high value in a wide range of 60 nm<P2.ltoreq.660
nm is obtained compared to when the interval P1=60 nm and the
interval P2=60 nm.
[0194] For example, the value of (Ex.sup.4+Ez.sup.4)/(P1P2) was
17133729 when P1=60 nm and P2=60 nm, and was 35522039 when P1=60 nm
and P2=240 nm.
4.5. Experimental Example 4
[0195] A simulation was performed in the same manner as in
Experimental Example 1, except that the thickness of the dielectric
layer was 20 nm, the size (the diameter of the bottom surface) of
the column of the Ag particles having a columnar shape was 72 nm,
the height of the column was 20 nm, and the interval P1 was 120
nm.
[0196] The peak excitation wavelength of the localized surface
plasmon of this model was 633 nm. As shown in FIG. 19, as in
Experimental Example 1 and Experimental Example 2, if the interval
P2 became larger, the enhancement degree increased. In this
experimental example, the enhancement degree had a maximum value at
P2=600 nm corresponding to a wavenumber as the intersection point
of SPP of Au and the peak excitation wavelength of LSP in the graph
of the dispersion relation.
[0197] As a result of plotting with the value of
(Ex.sup.4+Ez.sup.4)/(P1P2) (FIG. 20), it was found that a high
value in a wide range of 120 nm<P2.ltoreq.840 nm was obtained
compared to a case where the interval P1=120 nm and the interval
P2=120 nm.
4.6. Experimental Example 5
[0198] When the metal particle columns have a plurality of columns,
a simulation was performed using the following model.
[0199] FIGS. 21A and 21B show a computation model in which the
thickness of the dielectric layer is 60 nm, the size (the diameter
of the bottom surface) of the column of the Ag particles having a
columnar shape is 32 nm, the height of the column is 4 nm, and the
interval P1 is 60 nm. FIG. 22 shows a hot spot distribution in a
near field when one column of Ag particles is excluded (FIG. 21B).
A region used for computation was indicated by a broken line in the
drawing. The peak excitation wavelength is 633 nm.
[0200] A left view of FIG. 22 shows Ex and Ez of a model in which
the interval P2=600 nm. A wavenumber in which a nine-line model
occurs becomes a 600 nm pitch. A middle view of FIG. 22 shows a hot
spot intensity distribution. A right view of FIG. 22 shows a
distribution when the interval P1=60 nm and the interval P2=60 nm.
Ex (64) and Ez (21) of the interval P1=the interval P2=60 nm were
drawn as an auxiliary line in the middle view of FIG. 22. A model
of the interval P2=600 nm exceeded a value when the interval P1=the
interval P2=60 nm in all hot spots.
[0201] FIG. 23 shows a comparison result of when the interval P1=60
nm and the interval P2=600 nm and when the interval P1=600 nm and
the interval P2=60 nm in a three-line model. The direction of the
polarization of excitation light is the same first direction. That
is, this is synonymous with a case where the polarization direction
of linearly polarized light is the first direction and a case where
the polarization direction of the linearly polarized light is the
second direction when the interval P1=60 nm and the interval P2=600
nm.
[0202] Referring to FIGS. 22 and 23, it was found that, in a case
of linearly polarization in the first direction, variation in
intensity distribution by the positions of the hot spots was
significantly reduced. For this reason, it is understood that this
optical element can be suitably used as a concentration sensor.
[0203] A simulation was performed with the increased number of
excluded Ag particle columns, and it was thus found that hot spot
intensity was enhanced compared to a model with no Ag particle
columns excluded. The result was collectively shown in FIG. 24. An
error bar on a bar graph of FIG. 24 represents a distribution by
the positions of the hot spots, and in case of number of Ag
particle columns is one and two, it is understood that there is few
distribution of intensity.
[0204] The Raman enhancement degree per unit area taking into
consideration a decrease in hot spot density (HSD) with the
exclusion of the Ag particle columns is estimated, and the
graphical result of the Raman enhancement degree is shown in FIG.
25. Referring to FIG. 25, the Raman enhancement degree has a
maximum value when the number of Ag particle columns is around 2 to
5 and is about two times compared to a model with no Ag particle
columns excluded.
4.7. Experimental Example 6
[0205] A simulation was performed in the same manner as in
experimental Example 5, except that the thickness of the dielectric
layer was 20 nm, the size (the diameter of the bottom surface) of
the column of the Ag particles having a columnar shape was 72 nm,
the height of the column was 20 nm, and the number of Ag particle
columns to be arranged was 5. The peak excitation wavelength is 633
nm.
[0206] The result is shown in FIGS. 26 and 27. Referring to FIGS.
26 and 27, a simulation was performed with the increased number of
excluded Ag particle columns, and it was thus found that hot spot
intensity was enhanced compared to a model with no Ag particle
columns excluded.
[0207] The Raman enhancement degree per unit area taking into
consideration a decrease in hot spot density (HSD) with the
exclusion of the Ag particle columns is estimated, and from the
graphical result of the Raman enhancement degree (FIG. 27), it is
found that, the Raman enhancement degree has a maximum value when
the number of Ag particle columns is 2 and is about three times
compared to a model with no Ag particles excluded.
[0208] The invention is not limited to the foregoing embodiments,
and various modifications may be made. For example, the invention
includes the substantially same configuration (for example, a
configuration having the same functions, method, and result, or a
configuration having the same object and effects) as the
configurations described in the embodiments. The invention also
includes a configuration in which a non-essential portion in the
configurations described in the embodiments is substituted. The
invention also includes a configuration in which the same
functional effects as the configurations described in the
embodiments can be obtained or a configuration in which the same
object as the configurations described in the embodiments can be
attained. The invention also includes a configuration in which a
known configuration is added to the configurations described in the
embodiments.
* * * * *