U.S. patent application number 15/305154 was filed with the patent office on 2017-02-09 for electronic device comprising nanogap electrodes and nanoparticles.
The applicant listed for this patent is FONDS DE L'ESPCI - GEORGES CHARPAK, NEXDOT. Invention is credited to Benoit DUBERTRET, Emmanuel LHUILLIER.
Application Number | 20170040120 15/305154 |
Document ID | / |
Family ID | 54322686 |
Filed Date | 2017-02-09 |
United States Patent
Application |
20170040120 |
Kind Code |
A1 |
LHUILLIER; Emmanuel ; et
al. |
February 9, 2017 |
ELECTRONIC DEVICE COMPRISING NANOGAP ELECTRODES AND
NANOPARTICLES
Abstract
An electronic device includes a substrate and at least two
electrodes spaced by a nanogap, wherein the at least two electrodes
are bridged by at least one nanoparticle and wherein the at least
one nanoparticle has an overlap area with the at least two
electrodes higher than 2% of the area of the at least one
nanoparticle. A method of manufacturing the electronic device and
the use of the electronic device in photodetector, transistor,
phototransistor, optical modulator, electrical diode, photovoltaic
cell or electroluminescent component are also described.
Inventors: |
LHUILLIER; Emmanuel; (Paris,
FR) ; DUBERTRET; Benoit; (Paris, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NEXDOT
FONDS DE L'ESPCI - GEORGES CHARPAK |
Paris
Paris |
|
FR
FR |
|
|
Family ID: |
54322686 |
Appl. No.: |
15/305154 |
Filed: |
April 22, 2015 |
PCT Filed: |
April 22, 2015 |
PCT NO: |
PCT/EP2015/058729 |
371 Date: |
October 19, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14258245 |
Apr 22, 2014 |
|
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15305154 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B82Y 10/00 20130101;
H01L 21/02628 20130101; H01L 29/22 20130101; H01L 51/5221 20130101;
H01L 21/02568 20130101; H01L 29/0665 20130101; H01L 31/022408
20130101; H01L 51/5206 20130101; H01L 21/02551 20130101; H01L
29/413 20130101; H01L 51/56 20130101; H01L 21/02601 20130101; H01L
21/28 20130101; H01G 9/2054 20130101; Y02E 10/542 20130101; H01L
31/112 20130101; H01G 9/205 20130101; H01L 29/0673 20130101; H01L
33/06 20130101; H01S 5/1067 20130101 |
International
Class: |
H01G 9/20 20060101
H01G009/20; H01L 21/28 20060101 H01L021/28; H01L 29/41 20060101
H01L029/41; H01L 51/56 20060101 H01L051/56; H01L 51/52 20060101
H01L051/52; H01L 31/0224 20060101 H01L031/0224 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 22, 2014 |
EP |
14165507.6 |
Claims
1-16. (canceled)
17. An electronic device comprising a substrate and at least two
electrodes spaced by a nanogap, wherein the at least two electrodes
are bridged by at least one nanoparticle and wherein the at least
one nanoparticle has an overlap area with the at least two
electrodes higher than 2% of the area of the at least one
nanoparticle.
18. The electronic device according to claim 17, wherein the at
least one nanoparticle has an overlap area with each of the at
least two electrodes higher than 1% of the area of the at least one
nanoparticle.
19. The electronic device according to claim 17, wherein the
nanogap has a size (d) ranging from 0.1 nanometer to 1 000
nanometers.
20. The electronic device according to claim 17, wherein the
nanogap has a length (L) ranging from 1 nanometer to 10
millimeters.
21. The electronic device according to claim 17, wherein the at
least one nanoparticle is a large quantum dot, a nanosheet, a
nanorod, a nanoplatelet, a nanoplate, a nanowall, a nanodisk, a
nanotube, a nanoribbon, a nanobelt or a nanowire.
22. The electronic device according to claim 17, wherein the at
least one nanoparticle is a semiconductor nanoplatelet.
23. The electronic device according to claim 17, further comprising
an electrolyte on the at least one nanoparticle.
24. A method of manufacturing an electronic device, said electronic
device comprising a substrate and at least two electrodes spaced by
a nanogap, wherein the at least two electrodes are bridged by at
least one nanoparticle and wherein the at least one nanoparticle
has an overlap area with the at least two electrodes higher than 2%
of the area of the at least one nanoparticle; the method comprising
the steps of: a) formation on a substrate of at least two
electrodes spaced by a nanogap ranging from 0.1 nanometer to 1 000
nanometers; b) preparation of colloidal nanoparticles; c)
nanoparticle's ligand exchange procedure; d) deposition of at least
one nanoparticle onto the nanogap wherein the at least one
nanoparticle has an overlap area with the at least two electrodes
spaced by a nanogap higher than 2% of the area of the at least one
nanoparticle; e) nanoparticle's ligand exchange procedure if not
performed at step c); and f) deposition of an electrolyte.
25. The method of manufacturing an electronic device according to
claim 24, wherein the method of formation on a substrate of at
least two electrodes spaced by a nanogap is selected from
electromigration, electrodeposition, mechanically controlled break
junctions, e-beam lithography, self-alignment methods, lift-off
methods, shadowing methods, on-wire lithography, nanotube
masks.
26. The method of manufacturing an electronic device according to
claim 24, wherein the method of deposition of at least one
nanoparticle onto the nanogap is selected from drop casting, spin
coating, dip coating, spray casting, screen printing, inkjet
printing, sputtering techniques, evaporation techniques,
electrophoretic deposition, gravure printing, flexographic printing
or vacuum methods.
27. The method of manufacturing an electronic device according to
claim 24, wherein the nanoparticle is a semiconductor
nanoplatelet.
28. The electronic device according to claim 17, wherein a pn
junction is formed between the at least two electrodes.
29. A product comprising the electronic device, said electronic
device comprising a substrate and at least two electrodes spaced by
a nanogap, wherein the at least two electrodes are bridged by at
least one nanoparticle and wherein the at least one nanoparticle
has an overlap area with the at least two electrodes higher than 2%
of the area of the at least one nanoparticle; wherein the product
is a photodetector, a transistor, a phototransistor, an optical
modulator, an electrical diode, a light-emitting diode, a laser, a
photovoltaic solar cell or an electroluminescent component.
Description
FIELD OF INVENTION
[0001] The present invention relates to the field of nanotechnology
and especially to a device comprising nanogap electrodes and
nanoparticles. The present invention also pertains to processes for
preparing said device and to applications in photodetection using
said device.
BACKGROUND OF INVENTION
[0002] The use of colloidal quantum dots (CQD) in optoelectronic
devices requests both the fine control of their optical and
transport properties. Transport in a CQD film is a multiscale
process where hopping process occur at the nanoparticle scale and
film morphology (cracks . . . ) is playing a role at the
micrometric scale. Consequently not only the inter-particle tunnel
barrier needs to be tune to adjust the coupling but a good long
scale ordering is also requested. Atomic-ligand passivation (such
as S.sup.2-, SCN.sup.- or Cl.sup.- and metal chalcogenides ligands)
do address the shortening and lowering of the inter-particle tunnel
barrier but they generally request polar solvent which come at the
price of a more limited range of method to build the nanoparticle
film. With such passivation the film remains strongly disordered.
In disordered film the photo-activated carrier still need to
perform a random walk to reach the electrodes which typically
included hundred to thousand steps. To avoid this inefficient
transport process several strategies have been developed among
which the realization of QD-graphene hybrid to uncouple the
absorption from the transport process or the use of nanogap.
[0003] With a nanometer long channel, capable of accommodating
nanoparticles, the nanoparticle can be directly connected to the
electrodes which avoid the post absorption diffusion transport of
the carrier and its trapping. Moreover the short transport length
reduced the transit time which tend to increase the photoconductive
gain of the device.
[0004] To realize these nanogaps several methods have been proposed
including e-beam lithography, self-alignment method,
electromigration or shadowing methods. In spite of this interest
quantum dots remain tricky to connect to the electrodes and a poor
overlap is obtained while using a spherical particle which size is
of the same order of magnitude of the gap size.
[0005] One of the object of the present invention is thus to use
nanoplatelets for connecting nanogap electrodes.
[0006] Motivation for nanogap based photodetector is first the
increase of the gain. In a photodetector the responsivity, i.e. the
ability of the active material to convert the light photon flux
into a current expressed in A.W.sup.-1; is proportional to the
product of the internal quantum efficiency by the gain R.eta.g. The
gain is itself the ratio of the photocarrier lifetime .tau. divided
by the transit time .tau..sub.transit, where the transit time is
the time for a photogenerated charge to reach the electrode:
g = .tau. .tau. transit . ##EQU00001##
The internal quantum efficiency is the ratio of the number of
charger carriers collected by the electronic device to the number
of photons absorbed by the active material. The smallest the
spacing between the electrodes the shortest the time for the
carrier to reach the electrodes. As a consequence reducing the
electrodes spacing from a few micrometers to a few nanometers
potentially increases the gain by a factor 1 000.
[0007] Other motivation for nanogap based photodetector is the fact
that the volume reduction of the nanoparticle makes that it is
easier to get rid of the defect of the film morphology. Indeed for
micrometer scale film is common to observe crack formation into the
film. These cracks in particular tend to be formed when a ligand
exchange procedure on film is processed.
[0008] Another attractive aspect for nanogap based photodetector is
the fact that transport is no longer driven by hopping.
Consequently the noise level is not as high as the one associated
with hopping transport.
[0009] Finally another interest of this geometry of device is to
build electroluminescent system based on colloidal QD. So far most
of the effort to build Led using colloidal nanoparticle as active
material rely on the encapsulation of a thin layer of nanoparticle
between one hole and one electron injection layer. However the p
type layer is generally a conductive polymer. This solution
presents two main drawbacks which are (i) a limited lifetime of the
device and (ii) a device which can not be used in the infrared (IR)
due to the high absorption of the organic layer. In order to build
IR operating electroluminescent device it is thus very appealing to
avoid any organic material. The nanogap or nanotrench of the
invention which can be operated in the high electric field regime
allows to apply energy drop per particle of the order of the band
edge energy which is the requested condition to achieve
electroluminescence. Coupling a nanotrench with a narrow band gap
material such as lead or mercury chalcogenides is consequently a
possible path to build organic free IR emitting device.
[0010] Consequently the use of nanoplatelets for connecting nanogap
electrodes could lead to outstanding properties, such as
responsitivity and/or specific detectivity, which have not been
reported until now in the prior art.
SUMMARY
[0011] This invention thus relates to an electronic device
comprising a substrate and at least two electrodes spaced by a
nanogap, wherein the at least two electrodes are bridged by at
least one nanoparticle and wherein the at least one nanoparticle
has an overlap area with the at least two electrodes higher than 2%
of the area of the at least one nanoparticle.
[0012] According to one embodiment, the at least one nanoparticle
has an overlap area with each of the at least two electrodes higher
than 1% of the area of the at least one nanoparticle.
[0013] According to one embodiment, the nanogap has a size d
ranging from 0.1 nanometer to 1 000 nanometers, preferably from
0.25 nanometer to 500 nanometers, more preferably from 1 nanometer
to 100 nanometers, even more preferably from 10 nanometers to 80
nanometers.
[0014] According to one embodiment, the nanogap has a length L
ranging from 1 nanometer to 10 millimeters, preferably from 5
nanometers to 1 millimeter, more preferably from 10 nanometers to
100 micrometers, even more preferably from 50 nanometers to 10
micrometers.
[0015] According to one embodiment, the at least one nanoparticle
is a large quantum dot, a nanosheet, a nanorod, a nanoplatelet, a
nanoplate, a nanowall, a nanodisk, a nanotube, a nanoribbon, a
nanobelt or a nanowire. According to a preferred embodiment, the at
least one nanoparticle is a semiconductor nanoplatelet.
[0016] According to one embodiment, the electronic device further
comprises an electrolyte on the at least one nanoparticle.
[0017] The present invention also relates to a method of
manufacturing the electronic device of the present invention, the
method comprising the steps of: [0018] a) formation on a substrate
of at least two electrodes spaced by a nanogap ranging from 0.1
nanometer to 1 000 nanometers; [0019] b) preparation of colloidal
nanoparticles; [0020] c) optionally, nanoparticle's ligand exchange
procedure; [0021] d) deposition of at least one nanoparticle onto
the nanogap wherein the at least one nanoparticle has an overlap
area with the at least two electrodes spaced by a nanogap higher
than 2% of the area of the at least one nanoparticle; [0022] e)
nanoparticle's ligand exchange procedure if not performed at step
c); and [0023] f) optionally deposition of an electrolyte.
[0024] According to one embodiment, the method of formation on a
substrate of at least two electrodes spaced by a nanogap is
selected from electromigration, electrodeposition, mechanically
controlled break junctions, e-beam lithography, self-alignment
methods, lift-off methods, shadowing methods, on-wire lithography,
nanotube masks.
[0025] According to one embodiment, the method of deposition of at
least one nanoparticle onto the nanogap is selected from drop
casting, spin coating, dip coating, spray casting, screen printing,
inkjet printing, sputtering techniques, evaporation techniques,
electrophoretic deposition, gravure printing, flexographic printing
or vacuum methods.
[0026] The present invention also relates to an electronic device
wherein a pn junction is formed between the at least two
electrodes.
[0027] According to one embodiment, the electronic device of the
present invention is used as photodetector, transistor or
phototransistor. According to one embodiment, the electronic device
of the present invention is used as optical modulator. According to
one embodiment, the electronic device of the present invention is
used as an electrical diode, a photovoltaic solar cell or an
electroluminescent component.
[0028] The present invention also relates to a light-emitting
device and laser comprising an electronic device according to the
invention.
DEFINITIONS
[0029] In the present invention, the following terms have the
following meanings: [0030] As used herein the singular forms "a",
"an", and "the" include plural reference unless the context clearly
dictates otherwise. [0031] The term "about" is used herein to mean
approximately, roughly, around, or in the region of. When the term
"about" is used in conjunction with a numerical range, it modifies
that range by extending the boundaries above and below the
numerical values set forth. In general, the term "about" is used
herein to modify a numerical value above and below the stated value
by a variance of 20 percent. [0032] "Active material" refers to the
material (usually a semiconductor) which carrier density and or
electronic state will be tuned by the application of a bias over
the electrodes. [0033] "Aspect ratio" refers generally to the ratio
of the lengths in the different dimensions. The aspect ratio of the
nanogap refers herein to the ratio of the length of the nanogap L
(i.e. to the width of the ends of the at least two electrodes
spaced by the nanogap or equivalently the length of the side of the
at least two electrodes in contact with the gap) to the distance or
width between the at least two electrodes spaced by the nanogap d
(also referred herein as the nanogap size). Thus within the present
invention the aspect ratio refers to L/d, see FIG. 1. [0034]
"Nanogap" refers herein to spacing, at the nanometer scale, between
at least two electrodes. Alternatively the term nanotrench might be
also used to describe the same. [0035] "Nanogap electrodes" refers
to at least two electrodes spaced by at least one nanogap. "Nanogap
electrodes" and "at least two electrodes spaced by a nanogap" are
used interchangeably throughout the specification. [0036] "Nanogap
size" refers herein to the width of the gap or equivalently to the
median inter-electrodes distance d, see FIG. 1. [0037] "Nanogap
length" refers to the length of each electrode L, see FIG. 1.
[0038] "Nanoparticle" refers to a particle of any shape having at
least one dimension in the 0.1 to 100 nanometers range. [0039]
"Projected area" of a nanoparticle refers to the area defined by
the projection of the surface of the nanoparticle on the plane
defined by the surface of the at least two electrodes spaced by a
nanogap in contact with the nanoparticle.
DETAILED DESCRIPTION
[0040] This invention relates to an electronic device comprising a
substrate and at least two electrodes spaced by a nanogap.
According to a preferred embodiment, the at least two electrodes
spaced by a nanogap are bridged by at least one nanoparticle and
the at least one nanoparticle has an overlap area with the at least
two electrodes spaced by a nanogap higher than 5% of the area of
the at least one nanoparticle.
[0041] The device of the present invention comprises a substrate on
which the at least two electrodes spaced by a nanogap are formed,
manufactured and/or deposited.
[0042] According to a first embodiment, the substrate is formed
from silicon, silicon dioxide, aluminum oxide, sapphire, germanium,
gallium arsenide, an alloy of silicon and germanium, indium
phosphide, indium tin oxide, fluorine doped tin oxide, graphene,
glass and its derivative, plastic materials or any material that a
person skilled in the art would find suitable.
[0043] According to a second embodiment, the substrate is formed
from ZnS, ZnSe InP, CdZnTe, ZnTe, GaAs, GaSb, or mixture
thereof.
[0044] According to an embodiment, the substrate is formed from
undoped semiconductor. According to another embodiment, the
substrate is formed from slightly doped semiconductor.
[0045] According to an embodiment, the substrate is formed from
non-conducting polymer.
[0046] According to an embodiment, the substrate is formed from an
insulating material. According to a preferred embodiment, the
substrate is formed from an oxide material acting as an electronic
insulator. According to another embodiment, the substrate comprises
at least two layers with an oxide layer on the top, acting as an
electronic insulator, such as for example SiO.sub.2 layer on a Si
layer.
[0047] According to an embodiment, the substrate is rigid.
According to another embodiment, the substrate is flexible and/or
stretchable.
[0048] According to an embodiment, the substrate is
transparent.
[0049] According to an embodiment, the substrate is transparent in
a wavelength window compatible with the absorption spectrum of the
at least one nanoparticle. Compatible means herein that the
substrate is at least partly transparent in the range of wavelength
wherein the at least one nanoparticle is absorbing. Partly
transparent means herein that the substrate has a transmittance of
at least 50%, preferably at least 75%, more preferably at least
90%.
[0050] According to an embodiment, the substrate is transparent in
the visible, i.e. in a wavelength range from about 380 nanometers
to about 750 nanometers.
[0051] According to an embodiment, the substrate is transparent in
the ultraviolet range of wavelength, i.e. in a wavelength range
from about 10 nanometers to about 380 nanometers.
[0052] According to an embodiment, the substrate is transparent in
the infrared range of wavelength, i.e. in the wavelength range from
about 750 nanometers to about 1 000 000 nanometers, preferably from
about 750 nanometers to about 50 000 nanometers, more preferably
from about 750 nanometers to about 3 000 nanometers.
[0053] According to one embodiment, the substrate is partly
transparent in the visible and/or in the ultraviolet range of
wavelength and/or in the infrared range of wavelength.
[0054] According to an embodiment, the substrate transparency
window is at least 1 nanometer large, preferably at least 10
nanometers large and more preferably above 50 nanometers large.
[0055] According to an embodiment, the substrate is transparent in
two wavelength windows compatible with the absorption spectrum of
the at least one nanoparticle.
[0056] According to an embodiment, the substrate transparency
window is made of several windows in order to fit the absorption
spectrum of the multicolor detector, preferably of several narrow
transparency windows i.e. of at most 50 nm large.
[0057] According to an embodiment, the substrate is used as back
gating. In said embodiment, the substrate is preferentially formed
from a conducting contact coated with a dielectric layer, said
dielectric contact being formed from silicon dioxide, hafnium
dioxide, non-conducting polymer such as PMMA or any other
dielectric layer that one skilled in the art would find
suitable.
[0058] The electronic device of the present invention comprises
nanogap electrodes (i.e. at least two electrodes spaced by a
nanogap).
[0059] According to a first embodiment, the device comprises 2, 3,
4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15 electrodes spaced by at
least one nanogap. According to an embodiment, the nanogap is
positioned between 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15
electrodes.
[0060] According to an embodiment, wherein the device comprises
three electrodes, one of them is used as a gate electrode for
tuning the carrier density between the two other nanogap electrodes
(i.e. in the active material bridging the two other electrodes: the
source and the drain electrodes).
[0061] According to an embodiment, the device comprises several
electrodes (for example 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14
or 15 electrodes) forming several nanogaps (for example 1, 2, 3, 4,
5, 6, 7, 8, 9, 10, 11, 12, 13 or 14 nanogaps) in parallel.
[0062] According to an embodiment, the device comprises several
electrodes (for example 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14
or 15 electrodes) forming an array of nanogap.
[0063] According to an embodiment, as illustrate in FIG. 2, the
nanogap has a straight shape. According to another embodiment, the
nanogap has a serpentin shape. According to an embodiment, the
geometry of the nanogap comprises curved edges. According to one
embodiment, the at least two electrodes spaced by a nanogap are
interdigitated.
[0064] According to an embodiment, the nanogap has an aspect ratio
L/d ranging from 1 to 10.sup.9, from 100 to 10.sup.9, from 200 to
10.sup.9, from 500 to 10.sup.9, from 1 000 to 10.sup.9, from 10 000
to 10.sup.9, from 10 to 10.sup.8, from 100 to 10.sup.7, from 1 000
to 10.sup.7, from 10 to 10.sup.6, or from 100 to 10.sup.5.
[0065] According to an embodiment, the nanogap has an aspect ratio
L/d ranging from 1, 10, 100, 200, 500, 1 000, 10.sup.4 for the
lower value to up to 10.sup.5, 10.sup.6, 10.sup.7, 10.sup.8,
10.sup.9 for the higher value.
[0066] According to an embodiment, the optical area of the device
ranges from 10.sup.-16 m.sup.2 to 0.1 m.sup.2, more preferably
10.sup.-14 M.sup.2 to 10.sup.-7 m.sup.2, more preferably from
10.sup.-13 m.sup.2 to 10.sup.-8m.sup.2 and even more preferably
from 10.sup.-11 M.sup.2 to 9.times.10.sup.-9 m.sup.2.
[0067] According to an embodiment, the size d of the nanogap ranges
from 0.1 nanometer to 1 000 nanometers, from 0.1 to 500 nanometers,
from 0.1 nanometer to 200 nanometers, from 0.1 nanometers to 100
nanometers, from 1 nanometers to 100 nanometers or from 10 to 100
nanometer.
[0068] According to an embodiment, the size d of the nanogap is
larger than 1 nm, larger than 2 nm, larger than 5 nm, larger than
10 nm, larger than 25 nm, larger than 50 nm.
[0069] According to an embodiment, the size d of the nanogap is
less than 1 000 nanometers, less than 200 nanometers, preferably
less than 100 nanometers, more preferably less than 75 nanometers,
even more preferably less than 50 nanometers.
[0070] According to one embodiment, the depth of the nanogap ranges
from 0.1 nm to 10 .mu.m, preferably from 0.1 nm to 1 .mu.m, more
preferably from 1 nm to 100 nm.
[0071] According to an embodiment, the length L of the nanogap
ranges from 1 nanometer to 10 millimeters, from 5 nanometers to 1
millimeter, from 10 nanometers to 100 micrometers or from 100
nanometers to 100 micrometers. According to an embodiment, at least
one of the nanogap electrodes is not tapered or pointed. According
to an embodiment, the nanogap electrodes are not tapered or
pointed.
[0072] According to an embodiment, the nanogap electrodes are
formed from metal such as gold, silver, palladium, platinum,
copper, titanium, tungsten, aluminum, silver or iron.
[0073] According to an embodiment, the nanogap electrodes are
formed form transparent conducting layer made for example from
transparent conducting oxides such as indium tin oxide, fluorine
doped tin oxide, zinc oxide, doped zinc oxide.
[0074] According to an embodiment, the nanogap electrodes are
formed from non-doped semiconductor or doped semiconductor such as
ZnS, ZnSe InP, CdZnTe, ZnTe, GaSb, Si, Sn, Ge, GaAs, AlGaAs, InAs,
InP, InGaAs, or mixture thereof.
[0075] According to an embodiment, the nanogap electrodes are
formed from carbon based materials. According to an embodiment, the
nanogap electrodes are not formed from carbon based materials.
[0076] According to an embodiment, the nanogap electrodes are
formed from the same material. According to another embodiment, the
nanogap electrodes are formed from two different materials.
[0077] According to an embodiment, the material forming the at
least two electrodes spaced by a nanogap is homogeneous. According
to another embodiment, the material forming the at least two
electrodes spaced by a nanogap is structured of different
layers.
[0078] In an embodiment, the nanogap electrodes do not comprise an
insulator coating.
[0079] In an embodiment, the electrodes are coupled to a plasmonic
resonator.
[0080] In an embodiment, the absorption or emission of the system
is boosted by coupling the active material with a plasmonic
structure.
[0081] In an embodiment, a metallic minor is deposited below the
transport electrodes and reflects the non-absorbed light toward the
active material. This material can be made of Au, Al, Ag.
[0082] In an embodiment, the plasmonic structure used to boost the
optical performance of the device use the contact electrodes to
build a resonator.
[0083] In an embodiment, the spacing of the electrodes is tuned in
order to obtain a plasmonic resonance close to the band edge energy
of the optically active material.
[0084] The electronic device of the present invention comprises at
least two electrodes spaced by a nanogap and bridged by at least
one nanoparticle. According to an embodiment, in the device of the
present invention each of the at least one nanoparticle bridges at
least two electrodes spaced by a nanogap.
[0085] According to an embodiment, in the device of the present
invention the at least one nanoparticle is used as the active
material.
[0086] According to an embodiment, the at least one nanoparticle
bridging the at least two electrodes spaced by a nanogap has at
least 2% of its projected area overlapping with the at least two
electrodes spaced by a nanogap (i.e. the at least one nanoparticle
has an overlap area with the at least two electrodes spaced by a
nanogap higher than 2% of the area of the at least one
nanoparticle). According to an embodiment the at least one
nanoparticle bridging the at least two electrodes spaced by a
nanogap has at least 5% of its projected surface overlapping with
the at least two electrodes spaced by a nanogap. According to an
embodiment, the at least one nanoparticle bridging the at least two
electrodes spaced by a nanogap has at least 10% of its projected
surface overlapping with the at least two electrodes spaced by a
nanogap. According to an embodiment, the at least one nanoparticle
bridging the at least two electrodes spaced by a nanogap has at
least 20% of its projected surface overlapping with the at least
two electrodes spaced by a nanogap.
[0087] According to an embodiment, the at least one nanoparticle
bridging the at least two electrodes spaced by a nanogap has at
least 1% of its projected area overlapping with each of the at
least two electrodes spaced by a nanogap (i.e. the at least one
nanoparticle has an overlap area with each of the at least two
electrodes spaced by a nanogap higher than 1% of the area of the at
least one nanoparticle). According to an embodiment the at least
one nanoparticle bridging the at least two electrodes spaced by a
nanogap has at least 2.5% of its projected surface overlapping with
each of the at least two electrodes spaced by a nanogap. According
to an embodiment, the at least one nanoparticle bridging the at
least two electrodes spaced by a nanogap has at least 5% of its
projected surface overlapping with each of the at least two
electrodes spaced by a nanogap.
[0088] According to an embodiment, the at least one nanoparticle
bridging the at least two electrodes spaced by a nanogap has at
least 10% of its projected surface overlapping with each of the at
least two electrodes spaced by a nanogap.
[0089] According to an embodiment, the at least one nanoparticle
bridging the at least two electrodes spaced by a nanogap is for
example nanocrystal, nanosphere, nanocube, nanosheet, nanorod,
nanoplatelet, nanoplate, nanoprism, nanowall, nanodisk,
nanoparticle, nanopowder, nanotube, nanotetrapod, nanotetrahedron,
nanoribbon, nanobelt, nanowire, nanoneedle, nanocube, nanoball,
nanocoil, nanocone, nanopiller, nanoflower, quantum dot or
combination thereof.
[0090] According to an embodiment, the at least one nanoparticle
bridging the at least two electrodes spaced by a nanogap is a large
quantum dot (i.e. a quantum dot having a diameter of at least 10
nanometers, at least 15 nanometers, at least 20 nanometers, at
least 25 nanometers, at least 30 nanometers, at least 40
nanometers, at least 50 nanometers, at least 75 nanometers, or at
least 100 nanometers).
[0091] According to an embodiment, the at least one nanoparticle
bridging the at least two electrodes spaced by a nanogap has any
shape suitable for bridging at least two electrodes spaced by a
nanogap, e.g. nanosheet, nanorod, nanoplatelet, nanoplate,
nanowall, nanodisk, nanowire, nanoribbon, nanobelt, nanoneedle and
the like.
[0092] According to an embodiment, the at least one nanoparticle is
0D, 1D, and 2D nanoparticle.
[0093] In the present application, the term nanoplatelet has the
same meaning as nanosheet, 2D-nanoparticle or quasi
2D-nanoparticle.
[0094] According to a preferred embodiment, the at least one
nanoparticle bridging the at least two electrodes spaced by a
nanogap is a nanoplatelet or nanosheet. According to an embodiment,
the at least one nanosheet has a thickness of about 0.3 nm to about
10 mm, about 0.3 nm to about 1 mm, about 0.3 nm to about 100 .mu.m,
about 0.3 nm to about 10 .mu.m, about 0.3 nm to about 1 .mu.m,
about 0.3 nm to about 500 nm, about 0.3 nm to about 250 nm, about
0.3 nm to about 100 nm, about 0.3 nm to about 50 nm, about 0.3 nm
to about 25 nm, about 0.3 nm to about 20 nm, about 0.3 nm to about
15 nm, about 0.3 nm to about 10 nm, about 0.3 nm to about 5 nm.
[0095] According to an embodiment, the at least one nanosheet has a
lateral dimensions (length and/or width) of at least 1.5 times its
thickness. According to an embodiment, the lateral dimensions of
the at least one nanosheet are at least 2, 2.5, 3, 3.5, 4, 4.5, 5
times larger than its thickness. According to an embodiment, the
lateral dimensions of the nanosheet are from at least 0.45 nm to at
least 50 mm.
[0096] According to an embodiment, the lateral dimensions of the
nanosheet are ranging from at least 2 nm to less than 1 m, from 2
nm to 100 mm, from 2 nm to 10 mm, from 2 nm to 1 mm, from 2 nm to
100 .mu.m, from 2 nm to 10 .mu.m, from 2 nm to 1 .mu.m, from 2 nm
to 100 nm, from 2 nm to 10 nm.
[0097] According to an embodiment, the at least one nanoparticle
bridging the at least two electrodes spaced by a nanogap have an
homogeneous composition.
[0098] According to an embodiment, as illustrated in FIGS. 1 and 3,
several nanoparticles bridge the at least two electrodes spaced by
a nanogap (for example 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 10.sup.2,
10.sup.3, 10.sup.4, 10.sup.5, 10.sup.6, 10.sup.7, 10.sup.10,
10.sup.15, 10.sup.20, 10.sup.23 nanoparticles).
[0099] According to an embodiment, at least 2 nanoparticles bridge
the at least two electrodes spaced by a nanogap. According to an
embodiment, at least 3, 4, 5, 6, 7, 8, 9, 10, 10.sup.2, 10.sup.3,
10.sup.4, 10.sup.5, 10.sup.6, 10.sup.7, 10.sup.10, 10.sup.15,
10.sup.20 or 10.sup.23 nanoparticles bridge the at least two
electrodes spaced by a nanogap.
[0100] According to an embodiment, a film of nanoparticles, such as
a film of nanoplatelets, bridges the at least two electrodes spaced
by a nanogap. According to an embodiment, the film of nanoparticle
bridging the at least two electrodes spaced by a nanogap has a
thickness ranging from 0.1 nm to 100 .mu.m, preferably ranging from
1 nm to 1 .mu.m and more preferably from 2 nm to 200 nm.
[0101] According to an embodiment, the active material comprising
at least one nanoparticle is implemented into a film of
nanoparticles. According to an embodiment, the film of
nanoparticles is obtained from colloidal nanoparticles. According
to an embodiment, the active material does not comprise a film of
nanoparticles.
[0102] According to an embodiment, the at least one nanoparticle of
the invention is inorganic, colloidal and/or crystalline.
[0103] According to an embodiment, the at least one nanoparticle of
the invention comprises a semi-conductor from group IV, group
IIIA-VA, group IIA-VIA, group IIIA-VIA, group IA-IIIA-VIA, group
IIA-VA, group IVA-VIA, group VIB-VIA, group VB-VIA, or group
IVB-VIA.
[0104] According to an embodiment, the at least one nanoparticle of
the invention comprises a material MxEy, wherein: [0105] M is
selected from Zn, Cd, Hg, Cu, Ag, Al, Ga, In, Si, Sn, Ge, Pb, Sb,
Sn, Pd, Fe, Au, Ti, Bi, W, Mo, V or a mixture thereof; [0106] E is
selected from O, S, Se, Te, N, P, As or a mixture thereof; and
[0107] x and y are independently a decimal number from 0 to 5, at
the condition that when x is 0, y is not 0 and inversely.
[0108] According to an embodiment, the material MxEy comprises
cationic element M and anionic element E in stoichiometric ratio,
said stoichiometric ratio being characterized by values of x and y
corresponding to absolute values of mean oxidation number of
elements E and M respectively.
[0109] According to an embodiment, the at least one nanoparticle of
the invention comprises a material MxNyEz, wherein: [0110] M is
selected from Zn, Cd, Hg, Cu, Ag, Al, Ga, In, Si, Sn, Ge, Pb, Sb,
Sn, Pd, Fe, Au, Ti, Bi, W, Mo, V or a mixture thereof; [0111] N is
selected from Zn, Cd, Hg, Cu, Ag, Al, Ga, In, Si, Sn, Ge, Pb, Sb,
Sn, Pd, Fe, Au, Ti, Bi, W, Mo, V or a mixture thereof; [0112] E is
selected from O, S, Se, Te, N, P, As or a mixture thereof; and
[0113] x, y and z are independently a decimal number from 0 to 5,
at the condition that when x is 0, y and z are not 0, when y is 0,
x and z are not 0 and when z is 0, x and y are not 0.
[0114] According to one embodiment, the at least one nanoparticle
of the invention is made of a quaternary compound such as InAlGaAs,
ZnAgInSe or GaInAsSb.
[0115] According to an embodiment, the at least one nanoparticle
comprises a material selected from Si, Ge, Sn, CdS, CdSe, CdTe,
ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, PbS, PbSe, PbTe, CuInS.sub.2,
CuInSe.sub.2, AgInS.sub.2, AgInSe.sub.2, CuS, Cu.sub.2S, Ag.sub.2S,
Ag.sub.2Se, Ag.sub.2Te, InN, InP, InAs, InSb, In.sub.2S.sub.3,
Cd.sub.3P.sub.2, Zn.sub.3P.sub.2, Cd.sub.3As.sub.2,
Zn.sub.3As.sub.2, ZnO, AN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb,
FeS.sub.2, TiO.sub.2, Bi.sub.2S.sub.3, Bi.sub.2Se.sub.3,
Bi.sub.2Te.sub.3, MoS.sub.2, WS.sub.2, VO.sub.2, and alloys and
mixtures thereof.
[0116] According to a preferred embodiment, the at least one
nanoparticle is selected in the group comprising: CdSe, CdTe, CdS,
HgTe, PbSe, PbS, PbTe and the core/shell structures such as
CdSe/CdS, CdSe/CdZnS, CdSe/ZnS, CdTe/CdS/CdZnS, CdS/ZnS, PbS/CdS,
PbSe/CdS.
[0117] According to an embodiment, the at least one nanoparticle
bridging the at least two electrodes spaced by a nanogap has an
alloy--such as HgCdTe--, a gradient, a core shell or core-crown
structure.
[0118] According to an embodiment, the at least one nanoparticle
presents a heterostructure, which means that the at least one
nanoparticle of the invention is partially coated by at least one
layer of inorganic material.
[0119] According to an embodiment, the at least one nanoparticle
has a core/shell structure, i.e. the core is totally coated by at
least one layer of inorganic material.
[0120] According to another embodiment, the at least one
nanoparticle comprises a core totally coated by a first layer of
inorganic material, said first layer being partially or totally
surrounded by at least one further layer of inorganic material.
[0121] According to an embodiment, the core and the at least one
layer of inorganic material are composed of the same material or
are composed of different materials.
[0122] According to an embodiment, the core and the at least one
layer of inorganic material comprise a semi-conductor from group
IV, group IIIA-VA, group IIA-VIA, group IIIA-VIA, group
IA-IIIA-VIA, group IIA-VA, group IVA-VIA, group VIB-VIA, group
VB-VIA, or group IVB-VIA.
[0123] According to an embodiment, the core and the at least one
layer of inorganic material comprise a material MxEy, wherein:
[0124] M is selected from Zn, Cd, Hg, Cu, Ag, Al, Ga, In, Si, Sn,
Ge, Pb, Sb, Pd, Fe, Au, Ti, Bi, W, Mo, V or a mixture thereof;
[0125] E is selected from O, S, Se, Te, N, P, As or a mixture
thereof; and [0126] x and y are independently a decimal number from
0 to 5, at the condition that when x is 0, y is not 0 and
inversely.
[0127] According to an embodiment, the material MxEy comprises
cationic element M and anionic element E in stoichiometric ratio,
said stoichiometric ratio being characterized by values of x and y
corresponding to absolute values of mean oxidation number of
elements E and M respectively.
[0128] According to an embodiment, the core and the at least one
layer of inorganic material comprise a material MxNyEz, wherein:
[0129] M is selected from Zn, Cd, Hg, Cu, Ag, Al, Ga, In, Si, Sn,
Ge, Pb, Sb, Sn, Pd, Fe, Au, Ti, Bi, W, Mo, V or a mixture thereof;
[0130] N is selected from Zn, Cd, Hg, Cu, Ag, Al, Ga, In, Si, Sn,
Ge, Pb, Sb, Sn, Pd, Fe, Au, Ti, Bi, W, Mo, V or a mixture thereof;
[0131] E is selected from O, S, Se, Te, N, P, As or a mixture
thereof; and [0132] x, y and z are independently a decimal number
from 0 to 5, at the condition that when x is 0, y and z are not 0,
when y is 0, x and z are not 0 and when z is 0, x and y are not
0.
[0133] According to one embodiment the core and the at least one
layer of inorganic material is made of a quaternary compound such
as InAlGaAs, ZnAgInSe or GaInAsSb.
[0134] According to an embodiment, the core and the at least one
layer of inorganic material comprise a material selected from Si,
Sn, Ge, Sn, CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, PbS,
PbSe, PbTe, CuInS.sub.2, CuInSe.sub.2, AgInS.sub.2, AgInSe.sub.2,
CuS, Cu.sub.2S, Ag.sub.2S, Ag.sub.2Se, Ag.sub.2Te, InN, InP, InAs,
InSb, In.sub.2S.sub.3, Cd.sub.3P.sub.2, Zn.sub.3P.sub.2,
Cd.sub.3As.sub.2, Zn.sub.3As.sub.2, ZnO, AlN, AlP, AlAs, AlSb, GaN,
GaP, GaAs, GaSb, FeS.sub.2, TiO.sub.2, Bi.sub.2S.sub.3,
Bi.sub.2Se.sub.3, Bi.sub.2Te.sub.3, MoS.sub.2, WS.sub.2, VO.sub.2,
and alloys and mixtures thereof.
[0135] According to an embodiment, the at least one nanoparticle is
oriented with respect to the at least two electrodes spaced by a
nanogap. According to an embodiment, the at least one nanoparticle
is not randomly arranged on the nanogap electrodes. According to an
embodiment, the at least one nanoparticle is randomly arranged on
the nanogap electrodes.
[0136] According to an embodiment, the at least one nanoparticle
bridging the at least two electrodes spaced by a nanogap has a size
equal to the nanogap size. According to an embodiment, the at least
one nanoparticle bridging the at least two electrodes spaced by a
nanogap has a size larger than the nanogap size.
[0137] According to an embodiment, the at least one nanoparticle
bridging the at least two electrodes spaced by a nanogap has a size
of at least 10 nm, preferably at least 15 nm, more preferably at
least 30 nm. According to an embodiment, the at least one
nanoparticle bridging the at least two electrodes spaced by a
nanogap has a size ranging from about 0.1 nm to about 1 000 nm,
preferably from about 1 nm to about 200 nm, more preferably from
about 5 nm to about 100 nm, even more preferably from about 10 nm
to about 75 nm.
[0138] According to an embodiment, the at least one nanoparticle is
further coated by an organic capping, agent, an inorganic capping
agent, or mixture thereof. According to an embodiment, the at least
one nanoparticle has a surface chemistry made of organic ligand
such as for example an alkyl chain connected to a thiol, amine,
acid and/or phosphine function.
[0139] According to an embodiment, the at least one nanoparticle
has a surface chemistry made of ions such as S.sup.2-, OH.sup.-,
HS.sup.-, Se.sup.2-, NH.sup.2-, Te.sup.2-, SCN.sup.-, Br.sup.-,
I.sup.-, Cd.sup.2+, NH.sub.4.sup.+, Hg.sup.2+, Cl.sup.-, Zn.sup.2+,
Pb.sup.2+, or mixture thereof.
[0140] According to an embodiment, the at least one nanoparticle
has a surface chemistry made metal chalcogenides.
[0141] According to an embodiment, the at least one nanoparticle is
not selected from carbon based nanoparticle such as carbon
nanotubes (multi-walled or single-walled) or graphene. According to
an embodiment, the at least one nanoparticle is not selected from
silver nanoparticle. According to an embodiment, the at least one
nanoparticle is not selected from silicon nanoparticle. According
to an embodiment, the at least one nanoparticle is not selected
from aluminum nanoparticles, preferably not selected from aluminum
quantum dot. According to an embodiment, the at least one
nanoparticle does not comprise a semiconductor selected from group
III-V, more preferably the at least one nanoparticle is not
selected from GaAs.
[0142] According to an embodiment, the at least one nanoplatelet is
not prepared by exfoliation of the corresponding layered bulk
crystals.
[0143] According to an embodiment, the electronic device of the
present invention does not comprise a nitrogenous material disposed
or coated on the at least one nanoparticle.
[0144] According to an embodiment, the electronic device of the
present invention does not comprise composite made of semiconductor
material and plasmonic nanoparticles.
[0145] According to an embodiment, the nanogap accommodates
biological or chemical molecules. According to an embodiment, the
nanogap does not accommodate biological or chemical molecules.
[0146] According to an embodiment, the nanogap does not accommodate
at least one nanoparticle; the at least one nanoparticle bridges
the at least two electrodes spaced by a nanogap.
[0147] According to an embodiment, the at least one nanoparticle is
not positioned between the at least two electrodes spaced by a
nanogap; the at least one nanoparticle bridges the at least two
electrodes spaced by a nanogap.
[0148] According to an embodiment, the nanoparticle bridging the
nanotrench covered at least 1%, at least 2% , at least 5%, at least
10%, at least 25%, at least 30%, at least 40%, at least 50%, at
least 75%, at least 80%, at least 90% or about 100% of the
nanotrench area.
[0149] According to an embodiment, the at least one nanoparticle
does not comprise a bridging molecule.
[0150] According to an embodiment, the nanotrench contains more
than 1 bridging nanoparticle, more preferably more than 2 bridging
nanoparticles, more preferably more than 5 bridging nanoparticles,
more preferably more than 10 bridging nanoparticles and even more
preferably more than 100 bridging nanoparticles.
[0151] According to an embodiment, the electronic device of the
invention is not used to conduct tunnel spectroscopy.
[0152] According to an embodiment, the nanotrench contains more
than 2 bridging nanoparticles, and is not used to conduct tunnel
spectroscopy.
[0153] According to an embodiment, the nanoparticles have
absorption and/or photoconduction properties in the X ray and/or in
the UV and/or in the visible and/or in the infrared.
[0154] According to an embodiment, the nanoparticles have
absorption and/or photoconduction properties in the near infrared,
and/or in the mid infrared and/or in the long wavelength infrared
and/or in the far infrared and or in the THz.
[0155] According to an embodiment, the nanoparticles have
absorption and/or photoconduction properties from about 750
nanometers to about 1 000 000 nanometers, preferably from about 750
nanometers to about 50 000 nanometers, more preferably from about
750 nanometers to about 10 000 nanometers.
[0156] According to an embodiment, the nanoparticles are not
metallic nanoparticles.
[0157] According to an embodiment, the nanoparticles are
semiconductor nanoparticles.
[0158] According to an embodiment, the electronic device of the
present invention comprises at least one electrolyte: electrolyte
gating is performed to tune the carrier density of the at least one
nanoparticle bridging the at least two electrodes spaced by a
nanogap.
[0159] According to an embodiment, solid, polymer, gel, ion-gel or
liquid electrolytes may be implemented, preferably gel or solid
electrolytes.
[0160] According to an embodiment, the contact between the
electrolyte and the nanogap electrodes is prevented by the active
material (i.e. by the at least one nanoparticle).
[0161] According to an embodiment, the contact between the
electrolyte and the first and second electrodes is prevented by the
active material (i.e. by the at least one nanoparticle).
[0162] According to an embodiment, the electrolyte can be in the
form of an aqueous solution of a dissolved ionic chemical compound
(or compounds), a non-aqueous solution of a dissolved ionic
chemical compound (or compounds), a polymer electrolyte, a gel
electrolyte, a solid electrolyte or a molten salt electrolyte.
[0163] According to an embodiment, the electrolyte comprises a
matrix and ions. According to a preferred embodiment, the
electrolyte comprises a polymer matrix.
[0164] According to an embodiment, the polymer matrix of the
electrolyte comprises polystyrene, poly(N-isopropyl acrylamide),
polyethylene glycol, polyethylene, polybutadiene, polyisoprene,
polyethylene oxide, polyethyleneimine, polymethylmethacrylate,
polyethylacrylate, polyvinylpyrrolidone, polypropylene glycol,
polydimethylsiloxane, polyisobutylene, or a blend/multiblocks
polymer thereof.
[0165] According to an embodiment, the electrolyte comprises ions
salts. According to an embodiment, the polymer matrix is doped with
ions salts. According to said embodiments, the ions salts is LiCl,
LiBr, LiI, LiSCN, LiClO.sub.4, KClO.sub.4, NaClO.sub.4, ZnCl.sub.3,
ZnCl.sub.4.sup.2-, ZnBr.sub.2, LiCF.sub.3SO.sub.3, LiPF.sub.6,
LiASF.sub.6, LiN(SO.sub.2CF.sub.3).sub.2,
LiC(SO.sub.2CF.sub.3).sub.2, LiBF.sub.4, NaBPh.sub.4, NaCl, NaI,
NaBr, NaSCN, KCl, KBr, KI, KSCN, LiN(CF.sub.3SO.sub.2).sub.2, or
mixture thereof.
[0166] According to an embodiment, the electrolyte comprises
material that contains mobile ions of lithium, sodium, potassium,
ammonium, hydrogen, copper, silver or mixture thereof.
[0167] According to an embodiment, the electrolyte comprises
polymers and/or glasses, including but not limited to PEG, PEO,
PVDF, PET, PTFE, FEP, FPA, PVC, polyurethane, polyester, silicone,
some epoxies, polypropylene, polyimide, polycarbonate,
polyphenylene oxide, polysulfone, calcium magnesium aluminosilicate
glasses, E-glass, alumino-borosilicate glass, D-glass, borosilicate
glass, silicon dioxide, quartz, fused quartz, silicon nitride,
silicon oxynitride, or mixture thereof.
[0168] According to an embodiment, the electrolyte comprises ionic
liquid. According to an embodiment, the polymer matrix and the ions
are replaced by a polymerizable ionic liquid.
[0169] According to an embodiment, the at least one nanoparticle
surface chemistry is chosen to be a counterion of one of the ions
of the electrolyte.
[0170] According to an embodiment, the nanoparticle surface
chemistry is chosen so that the at least one nanoparticle and the
electrolyte can form a redox reaction.
[0171] According to an embodiment, at least one ion from the
electrolyte can reversibly give one or more electron(s) to the
active material (i.e. the at least one nanoparticle) as in redox
based reactions.
[0172] Examples of pairs of nanoparticle surface chemistry/ion
include but is not limited to: OH.sup.-/Li.sup.+,
OH.sup.-/Na.sup.+, OH.sup.-/K.sup.+, OH.sup.-/NH.sub.4.sup.+,
OH.sup.-/any ammonium ion, OH.sup.-/any ionic liquid,
O.sup.2-/Li.sup.+, O.sup.2-/Na.sup.+, O.sup.2-/K.sup.+,
O.sup.2-/NH.sub.4.sup.+, O.sup.2-/any ammonium ion, O.sup.2-/any
ionic liquid, HS.sup.-/Li.sup.+, HS.sup.-/Na.sup.+,
HS.sup.-/K.sup.+, HS.sup.-/NH.sub.4.sup.+, HS.sup.-/any ammonium
ion, HS.sup.-/any ionic liquid, SCN.sup.-/Li.sup.+,
SCN.sup.-/Na.sup.+, SCN.sup.-/K.sup.+, SCN.sup.-/NH.sub.4.sup.+,
SCN.sup.-/any ammonium ion, SCN.sup.-/any ionic liquid,
NH.sub.2.sup.-/Li.sup.+, NH.sub.2.sup.-/Na.sup.+,
NH.sub.2.sup.-/K.sup.+, NH.sub.2.sup.-/NH.sub.4.sup.+,
NH.sub.2.sup.-/any ammonium ion, NH.sub.2.sup.-/any ionic liquid,
S.sup.2-/Li.sup.+, S.sup.2-/Na.sup.+, S.sup.2-/K.sup.+,
S.sup.2-/NH.sub.4.sup.+, S.sup.2-/any ammonium ion, S.sup.2-/any
ionic liquid, Se.sup.2-7Li.sup.+, Se.sup.2-/Na.sup.+,
Se.sup.2-/K.sup.+, Se.sup.2-/NH.sub.4.sup.+, Se.sup.2-/any ammonium
ion, Se.sup.2-/any ionic liquid, Te.sup.2-/Li.sup.+,
Te.sup.2-/Na.sup.+, Te.sup.2-/K.sup.+, Te.sup.2-/NH.sub.4.sup.+,
Te.sup.2-/any ammonium ion, Te.sup.2-/any ionic liquid,
Cl.sup.-/Li.sup.+, Cl.sup.-/Na.sup.+, Cl.sup.-/K.sup.+,
Cl.sup.-/NH.sub.4.sup.+, Cl.sup.-/any ammonium ion, Cl.sup.-/any
ionic liquid, Br.sup.-/Li.sup.+, Br.sup.-/Na.sup.+,
Br.sup.-/K.sup.+, Br.sup.-/NH.sub.4.sup.+, Br.sup.-/any ammonium
ion, Br.sup.-/any ionic liquid, I.sup.-/Li.sup.+, I.sup.-/Na.sup.+,
I.sup.-/K.sup.+, I.sup.-/NH.sub.4.sup.+, I.sup.-/any ammonium ion,
I.sup.-/any ionic liquid, any metal-chalcogenide/Li.sup.+, any
metal-chalcogenide/Na.sup.+, any metal-chalcogenide/K.sup.+, any
metal-chalcogenide/NH.sub.4.sup.+, any metal-chalcogenide/any
ammonium ion, any metal-chalcogenide/any ionic liquid,
Cd.sup.2+/Cl.sup.-, Cd.sup.2+/Br.sup.-, Cd.sup.2+/I.sup.-,
Cd.sup.2+/SO4.sup.2-, Cd.sup.2+/ClO.sub.4.sup.-,
Cd.sup.2+/BF.sub.4.sup.-, Cd.sup.2+/NO.sub.3.sup.-, Cd.sup.2+/any
ionic liquid, Pb.sup.2+/Cl.sup.-, Pb.sup.2+/Br.sup.-,
Pb.sup.2+/I.sup.-, Pb.sup.2+/SO4.sup.2-, Pb.sup.2+/ClO.sub.4.sup.-,
Pb.sup.2+/BF.sub.4.sup.-, Pb.sup.2+/NO.sub.3.sup.-, Pb.sup.2+/any
ionic liquid, Zn.sup.2+/Cl.sup.-, Zn.sup.2+/Br.sup.-,
Zn.sup.2+/I.sup.-, Zn.sup.2+/SO4.sup.2-, Zn.sup.2+/ClO.sub.4.sup.-,
Zn.sup.2+/BF.sub.4.sup.-, Zn.sup.2+/NO.sub.3.sup.-, Zn.sup.2+/any
ionic liquid, Hg.sup.2+/Cl.sup.-, Hg.sup.2+/Br.sup.-,
Hg.sup.2+/I.sup.-, Hg.sup.2+/SO4.sup.2-, Hg.sup.2+/ClO.sub.4.sup.-,
Hg.sup.2+/BF.sub.4.sup.-, Hg.sup.2+/NO.sub.3.sup.-, Hg.sup.2+/any
ionic liquid, NH.sub.3/CI.sup.-, NH.sub.3.sup.+/Br.sup.-,
NH.sub.3/I.sup.-, NH.sub.3/SO4.sup.2, NH.sub.3/ClO.sub.4,
NH.sub.3.sup.+/BF.sub.4.sup.-, NH.sub.3.sup.+/NO.sub.3.sup.-,
NH.sub.3.sup.+/any ionic liquid.
[0173] According to an embodiment, the electrolyte is transparent
in a wavelength window compatible with the absorption spectrum of
the at least one nanoparticle. Compatible means herein that the
substrate is at least partly transparent in the range of wavelength
wherein the at least one nanoparticle is absorbing. Partly
transparent means herein that the substrate has a transmittance of
at least 50%, preferably at least 75%, more preferably at least
90%.
[0174] According to an embodiment, the electrolyte is transparent
in the visible, i.e. in a wavelength range from about 380
nanometers to about 750 nanometers.
[0175] According to an embodiment, the electrolyte is transparent
in the ultraviolet range of wavelength, i.e. in a wavelength range
from about 10 nanometers to about 380 nanometers.
[0176] According to an embodiment, the electrolyte is transparent
in the infrared range of wavelength, i.e. in the wavelength range
from about 750 nanometers to about 1 000 000 nanometers, preferably
from about 750 nanometers to about 50 000 nanometers, more
preferably from about 750 nanometers to about 3 000 nanometers.
[0177] According to an embodiment, the electrolyte transparency
window is at least 1 nm large, preferably at least 10 nm large and
more preferably above 50 nm large.
[0178] According to one embodiment, the substrate is partly
transparent in the visible and/or in the ultraviolet range of
wavelength and/or in the infrared range of wavelength.
[0179] According to an embodiment, the electrolyte is transparent
in two wavelength windows compatible with the absorption spectrum
of the at least one plurality of nanoparticle.
[0180] According to an embodiment, the electrolyte transparency
window is made of several windows in order to fit the absorption
spectrum of the multicolor detector, preferably of several narrow
transparency windows i.e. of at most 50 nm large.
[0181] According to one embodiment, the nanogap has an aspect ratio
L/d ranging from 1 to 10.sup.9, from 100 to 10.sup.9, from 200 to
10.sup.9, from 500 to 10.sup.9, from 1 000 to 10.sup.9, from 10 000
to 10.sup.9, from 10 to 10.sup.8, from 100 to 10.sup.7, from 1 000
to 10.sup.7, from 10 to 10.sup.6, or from 100 to 10.sup.5; in
addition, at least 1, 2, 3, 4, 5, 6, 7, 8,9, 10, 10.sup.2,
10.sup.3, 10.sup.4, 10.sup.5, 10.sup.6, 10.sup.7, 10.sup.10,
10.sup.15, 10.sup.20, 10.sup.23 nanoparticles bridge the at least
two electrodes spaced by a nanogap and said nanoparticle bridging
the nanogap covers at least 1%, at least 2% , at least 5%, at least
10%, at least 25%, at least 30%, at least 40%, at least 50%, at
least 75%, at least 80%, at least 90% or about 100% of the nanogap
area.
[0182] According to an embodiment, the manufacturing process for
preparing the electronic device of the present invention comprises
two main steps: [0183] nanogap electrodes fabrication, [0184]
deposition of the at least one nanoparticle onto the nanogap and
nanoparticle's ligand exchange after or before deposition on the
nanogap, and [0185] optionally, electrolyte deposition.
[0186] More precisely, the manufacturing process for preparing the
electronic device of the present invention comprises: [0187] a) the
fabrication of the at least two electrodes spaced by a nanogap onto
a substrate, [0188] b) the preparation of colloidal nanoparticles,
[0189] b') optionally, the nanoparticle's ligand exchange step in
solution, [0190] c) the deposition of at least one nanoparticle
onto the nanogap wherein the at least one nanoparticle has an
overlap area with the at least two electrodes spaced by a nanogap
higher than 5% of the area of the at least one nanoparticle, [0191]
c') if step b') is not implemented, nanoparticle's ligand exchange
step, [0192] d) optionally, the electrolyte deposition on the
active material (i.e. on the at least on nanoparticle), and [0193]
e) optionally, the deposition of a further electrode on the
electrolyte.
[0194] According to an embodiment, the steps b), b'), c), c') may
be implemented more than once with different nanoparticles.
[0195] According to an embodiment, the at least two electrodes of
step a) are at least a source and a drain electrodes and the
further electrode of step e) is a gate electrode.
[0196] According to one embodiment, the at least two electrodes are
processed with a gas treatment before step c).
[0197] According to one embodiment, the at least two electrodes are
treated with molecules such as short-chain alkane thiols to improve
the adhesion of the at least one nanoparticle before step c).
[0198] According to one embodiment, the at least two electrodes are
treated with a coating for passivating the surface of the at least
two electrodes before step c).
[0199] According to an embodiment, the at least two electrodes are
annealed before step c) at a temperature ranging from 100.degree.
C. to 1 000.degree. C.
[0200] According to an embodiment, the component in progress is
annealed before step d) at low temperature, typically below
400.degree. C., or below 300.degree. C., or below 200.degree. C.,
or below 100.degree. C.
[0201] According to one embodiment, the at least one nanoparticles
bridging the nanogap electrodes is obtained by a process which
fuses smaller nanoparticles, such as a chemical process or an
annealing step.
[0202] According to one embodiment, the nanogap bridged by at least
one nanoparticle is exposed to an atomic layer deposition or a
chemical bath deposition step.
[0203] According to an embodiment, for narrow band gap material,
nanoparticle's ligand exchange is performed, after deposition, in
the active material comprising at least one nanoparticle or on the
nanoparticles in solution prior to the deposition of at least one
nanoparticle, preferably, after deposition, in the active material
comprising at least one nanoparticle.
[0204] According to an embodiment, the film of nanoparticle can be
treated with a ligand exchange procedure made on the film of
nanoparticle. A solution of short ligand such as etandithiol for
example at 1% in volume in ethanol is prepared. The nanoparticles,
capped with their long ligand as from the synthesis, under a film
form are dipped for 30s in the short ligand solution and finally
rinsed in pure solvent such as alcohol or acetonitrile.
[0205] According to an embodiment, the nanoparticle can be treated
with a ligand exchange procedure directly on the solution. A
solution of ions such as S.sup.2- or CI.sup.- for example is
prepared at 1% in mass in polar solvent such as N methyl formamide.
This solution is mixed with the nanoparticle in non-polar solvent
such as toluene or hexane. The two phases are strongly mixed and
sonicated. A phase transfer occurs and the nanoparticles get capped
with the short ligand and dispersed in the polar phase. This
solution can now be directly used to build conductive device.
[0206] According to an embodiment, for wide band gap material
nanoparticle' s ligand exchange is performed, after deposition, in
the active material comprising at least one nanoparticle or on the
nanoparticles in solution prior to the deposition of at least one
nanoparticle, preferably on the nanoparticles in solution prior to
the deposition.
[0207] According to an embodiment, nanoparticle' s ligand exchange
improves the conduction properties of the active material.
[0208] According to an embodiment, the method of fabrication of the
nanogap electrodes is selected from electromigration,
electrodeposition, mechanically controlled break junctions, e-beam
lithography methods, self-alignment methods, lift-off methods,
shadowing methods, on-wire lithography, nanotube masks.
[0209] According to an embodiment, the at least one nanoparticle
bridging the at least two electrodes spaced by a nanogap is
deposited using conventional deposition techniques, including for
example, drop casting, spin coating, dip coating, spray casting,
inkjet printing, screen printing, sputtering techniques,
evaporation techniques, electrophoretic deposition, vacuum methods,
gravure printing, flexographic printing or any other means that a
person skilled in the art would find appropriate.
[0210] According to an embodiment, the at least two electrodes
spaced by a nanogap are made of the same material.
[0211] According to an embodiment, the at least two electrodes
spaced by a nanogap are made of gold.
[0212] According to an embodiment, the at least two electrodes
spaced by a nanogap are made of Au, Ag, Ti, Cr, Pd, Pt, Cu, Ni, Al,
Fe and their alloy.
[0213] According to an embodiment, the at least two electrodes
spaced by a nanogap are made of Si, Ge, GaAs, InP and their
alloy.
[0214] According to an embodiment, each electrode composing the
nanogap can be made with a layered structure such as Ti/Au.
[0215] According to an embodiment, each electrode composing the
nanogap includes a layer which role is to favor the contact of the
top material onto the substrate. This layer is typically made of Ti
or Cr.
[0216] According to an embodiment, the thickness of each electrode
ranges from 1 nm to 1 mm, more preferably from 30 nm to 1
.mu.m.
[0217] According to an embodiment, the at least two electrodes
spaced by a nanogap are made of different materials.
[0218] According to an embodiment, the at least two electrodes
spaced by a nanogap are made of two different materials such as
Al/Pt, Al/Au, Ag/Au, Ag/Pt.
[0219] According to an embodiment, the device made of two asymetric
electrodes presents a diode behavior (asymetric IV curve), see FIG.
9.
[0220] According to an embodiment, the electrolyte is deposited
using any printing methods that a person skilled in the art would
find appropriate, such as for example spin coating or dip coating,
or drop casting.
[0221] According to an embodiment, in use, the bias applied between
the at least two electrodes spaced by a nanogap is below 100 V,
preferably below 10 V, more preferably below 5 V.
[0222] According to an embodiment, in use, the current flowing
between the at least two electrodes spaced by a nanogap is ranging
from 1 fA to 1 A, preferably from 1 pA to 1 mA.
[0223] According to an embodiment, the device is operated in air.
According to an embodiment, the device is operated under inert
atmosphere. According to an embodiment, the device is operated
under vacuum.
[0224] According to an embodiment, the device is operated at a
temperature ranging from 0 K to 400 K, preferably from 4 K to 350
K, more preferably from 77 K to 300 K.
[0225] According to an embodiment, using nanogap based electrodes
bridged by nanoparticles, especially by nanoplatelets, instead of
conventional micrometric spaced electrodes unexpectedly improves
the responsivity performance.
[0226] According to an embodiment, the electronic device of the
present invention has a responsivity ranging from 1 A.W.sup.-1 to
10.sup.9 A.W.sup.-1, from 1 A.W.sup.-1 to 10.sup.8 A.W.sup.-1, from
1 A.W.sup.-1 to 10.sup.7 A.W.sup.-1, from 1 A.W.sup.-1 to 10.sup.6
A.W.sup.-1, preferably from 1 A.W.sup.-1 to 10.sup.5 A.W.sup.-1,
more preferably from 1 A.W.sup.-1 to 10.sup.4 A.W.sup.-1, even more
preferably from 100 A.W.sup.-1 to 5 000 A.W.sup.-1.
[0227] According to an embodiment, the electronic device of the
present invention has a responsivity of at least 1 A.W.sup.-1,
preferably at least to 20 A.W.sup.-1, more preferably at least 50
A.W.sup.-1, even more preferably at least 100 A.W.sup.-1.
[0228] According to an embodiment, the electronic device of the
present invention has an electron mobility ranging from 10.sup.-6
cm.sup.2V.sup.-1s.sup.-1 to 10.sup.4 cm.sup.2v.sup.-1s.sup.-1,
preferably from 10.sup.-2 cm.sup.-2v.sup.-1s.sup.-1.
[0229] According to an embodiment, the electronic device of the
present invention has a specific detectivity of at least 10.sup.7
cm.Hz.sup.1/2W.sup.-1 (also called "Jones"), preferably at least
10.sup.10 Jones, more preferably at least 10.sup.12 Jones, even
more preferably at least 10.sup.13 Jones.
[0230] According to an embodiment, the electronic device of the
present invention has a response time smaller than 100
milliseconds, preferably smaller than 10 milliseconds, more
preferably smaller than 0.1 milliseconds, even more preferably
smaller than 0.01 milliseconds.
[0231] According to an embodiment, the device of the present
invention can also be attractive for other application than
photoconduction: thanks to the small gap it is very easy to apply a
very large bias (10.sup.8 V.m.sup.-1 can easily be obtained). This
large electric field can be used to obtain Stark effect in the
bridging nanoparticle. Indeed under an applied electric field the
quantum state tend to be shifted in energy. In particular a shift
and a bleach of the optical feature are expected. This effect can
be used to build an optical modulator.
[0232] According to an embodiment, the electronic device of the
present invention is used in biological imaging, photodetectors,
photovoltaic devices, transistors, stark modulators, light emission
devices, quantum-dot lasers, or solar cells.
[0233] According to an embodiment, the device is used as optical
modulator.
[0234] According to an embodiment, the device is used as
photodetector.
[0235] According to an embodiment, the device is used as single
pixel photodetector.
[0236] According to an embodiment, several devices (i.e. several
nanogaps) are used to build a several pixels detector.
[0237] According to an embodiment, are used to build an array of
detecting pixel used for instance as a focal plane array.
[0238] According to an embodiment, the device is not used as a
switch.
[0239] In one embodiment the gate electrode is grounded and a
source and drain bias with different sign is applied.
[0240] In one embodiment the gate electrode is grounded and a pn
junction is formed between the drain and source nanogap
electrodes.
[0241] In one embodiment, a pn junction is formed between two of
the nanogap electrodes and this electronic device may be used as a
LED or as a photodetector operating in photovoltaic mode.
[0242] According to an embodiment, the device used as photodetector
is operated in the visible range of wavelength. According to
another embodiment, the device used as photodetector is operated in
the infrared range of wavelength. According to another embodiment,
the device used as photodetector is operated in the ultraviolet
range of wavelength. According to another embodiment, the device
used as photodetector is operated in the X-ray range of
wavelength.
[0243] According to an embodiment, the device is used to form a
diode. According to an embodiment, the device is used for
manufacturing an electrical diode.
[0244] According to an embodiment, the device used as a diode is
the active element of a photovoltaic solar cell. According to an
embodiment, the device is used for manufacturing a photovoltaic
solar cell or an electroluminescent component.
[0245] According to an embodiment, the device used as a diode is
the active element of a light emitting diode.
[0246] According to an embodiment, the device used as a light
emitting diode is the component of a lighting device.
[0247] According to an embodiment, the device used as a light
emitting diode is the component of a display.
[0248] According to an embodiment, the device is used as
transistor. According to an embodiment, the device is used as
phototransistor.
[0249] According to an embodiment, the device is used as a
nonlinear component of an electrical circuit.
[0250] According to an embodiment, the device is used as a chemical
sensor. According to an embodiment, the chemical sensitivity of the
device is obtained by the presence of the detecting element acting
as a dopant. According to an embodiment, the device used as a
chemical sensor is sensitive to the concentration of a species
diluted in a solvent used as electrolyte. According to an
embodiment, the device used as a chemical sensor present some
selectivity properties related to the surface chemistry of the at
least one nanoparticle used to bridge the at least two electrodes
spaced by a nanogap.
[0251] According to an embodiment, the device is used to obtain
electroluminescence from the at least one nanoparticle bridging the
at least two electrodes spaced by a nanogap.
[0252] According to an embodiment, the device is used to obtain
stimulated light emission from the at least one nanoparticle
bridging the at least two electrodes spaced by a nanogap.
[0253] According to an embodiment, the device is as a gain material
of a laser.
[0254] It should be understood that the spatial descriptions (e.g.,
"above", "below", "up", "down", "top", "bottom", "on", "under",
etc.) made herein are for purposes of illustration only, and that
devices of the present invention can be spatially arranged in any
orientation or manner that one skilled in the art could easily
implemented.
BRIEF DESCRIPTION OF THE DRAWINGS
[0255] FIG. 1 is a scheme of the electronic device according to one
embodiment of the present invention.
[0256] FIG. 2 is a scanning electron microscopy picture of nanogaps
at three different scales.
[0257] FIG. 3 is a scanning electron microscopy picture of nanogaps
coated with CdTe nanoplatelets at three different scales.
[0258] FIG. 4 shows the current as a function of time under a
constant drain-source bias in the electronic device according to
one embodiment of the present invention wherein the nanogap
electrodes are bridged with CdSe/CdS nanoplatelets. The square
response corresponds to light illumination. The response time of
the electronic device is faster than 0.1 second.
[0259] FIG. 5 shows the current as a function of drain bias under
incident light power in the electronic device according to one
embodiment of the present invention wherein the nanogap electrodes
are bridged with CdSe/CdS nanoplatelets.
[0260] FIG. 6 shows the current as a function of gate bias under
incident light power in the electronic device according to one
embodiment of the present invention wherein the nanogap electrodes
are bridged with CdSe/CdS nanoplatelets. The gating is made by
LiClO.sub.4 in PEG as electrolyte.
[0261] FIG. 7a is a scheme of the energy diagram of the electronic
device according to one embodiment of the present invention under
zero drain bias for conduction and valence band.
[0262] FIG. 7b is a scheme of the conduction band diagram of the
electronic device according to one embodiment of the present
invention under different drain bias.
[0263] FIG. 8 is an image of a nanogap and the electroluminescent
signal (indicated by the arrow) located at the nanotrench
level.
[0264] FIG. 9 represents the current vs voltage for a nanogap made
of Au and Al contact spaced by 70 nm and connected using CdSe/CdS
Nanoplatelets.
REFERENCES
[0265] N Nanoparticle(s)
[0266] E Electrode(s)
[0267] d Nanogap size--Inter-electrode distance
[0268] L Nanogap length--Length of the electrode
EXAMPLES
[0269] The present invention is further illustrated by the
following examples.
[0270] Nanoparticle Synthesis:
[0271] CdSe Nanoplatelets
[0272] In a first step Cadmium myristate (Cd(Myr).sub.2) is
prepared. In a typical synthesis 240 mg of Cd(Myr).sub.2, 25 mg Se
powder are mixed in 30 ml of ODE, the solution degased under vacuum
for 20 minutes at room temperature. Then the atmosphere is switch
to Argon and the temperature is set to 240.degree. C. At
204.degree. C. 40 mg of Cd(OAc).sub.2 are quickly added. The
reaction is performed 12 minutes at 240.degree. C. After this, the
solution is cooled down. The precipitation of the nanoplatelets is
done by adding ethanol. After centrifugation the obtained solid is
redispersed in hexane. The cleaning procedure is repeated three
times.
[0273] CdTe Nanoplatelets
[0274] In a first step Cadmium propanoate (Cd(Prop).sub.2) is
prepared by mixing 1.036 g of CdO in 10 ml of propionic acid under
Argon for 1 hour. Then the flask is open to air and the temperature
risen to 140.degree. C. up to the point the volume get divided by a
factor two. The whitish solution is precipitated by addition of
acetone. After centrifugation the solid is dried under vacuum for
24 hours. In the glove box 1M TOPTe is prepared by stirring 2.55 g
of Te pellets in 20 ml of TOP for four days at room temperature. In
a three necks flask 0.13 g of Cd(Prop).sub.2, 160 .mu.m of oleic
acid and 10 ml ODE are degased for 90 minutes at 95.degree. C. Then
the atmosphere is switched to Argon and the temperature risen to
210.degree. C. 0.2 mL of 1M TOPTe is quickly injected in the flask.
After 20 minutes the reaction is quenched by adding 1 mL of oleic
acid and cooling down the flask at room temperature. The cleaning
process is done by adding Ethanol to precipitate the CdTe
nanoplatelets. The solid obtained after centrifugation is
redispersed in hexane. This procedure is repeated three times.
[0275] CdSe/CdS Nanoplatelets
[0276] Two procedures can be performed to obtain a CdS shell on
CdSe core. In a first procedure 30 mg of NaSH are mixed in 4 ml of
N methyl formamide (NMFA) in a 20 mL vial up to dissolution. Then
500 .mu.L of the CdSe core in solution in hexane are added in the
vial. The solution is stirred until a complete transfer of the
nanoparticles in the nmFA phase. Then 500 .mu.l of 0.2 M cadmium
acetate in nmFA are added in the vial. The reaction is performed
for 1 hour at room temperature under stirring. Precipitation is
ensured by addition of ethanol. After centrifugation the obtained
solid is dispersed in nmFA. The cleaning step is repeated a second
time. As an alternative procedure to grow the shell it is possible
to dissolve 30 mg of Na.sub.2S are mixed in 2 ml of nmFA in a 4 mL
vial up to dissolution. The core are then precipitated by addition
of acetonitrile to remove the excess of sulfide and redispersed in
nmFA. Then 500 .mu.l of 0.2 M cadmium acetate in nmFA are added in
the vial. After the almost immediate reaction the excess of
precursors is removed by precipitation of the nanocrystals with a
mixture of toluene and acetonitrile (5:1). The solid obtained by
centrifugation is redisolved in nmFA. The procedure is repeated 3.5
times. The final nanoparticles are stored in nmFA.
[0277] Spherical CdSe Quantum Dots
[0278] In a three necks flask, 8 ml of ODE, 1.5 g of TOPO and 0.75
ml of Cd(OA).sub.2 at 0.5 M in oleic acid are degased for 30
minutes under vacuum. Then under argon flow, the temperature is set
at 280.degree. C. and a mixture of 3 ml of oleylamine and 4 ml of
TOPSe at 1 M in TOP are quickly injected at 300.degree. C. while
the temperature is set at 280.degree. C. After 8 minutes, the
reaction is stopped and the quantum dots are precipitated twice
with ethanol and resuspended in hexane.
[0279] PbS Spherical Quantum Dots
[0280] In a three necks flask, we introduce 0.9 g lead oxide and
40mL of oleic acid. The mixture is degased for 1 h at 100.degree.
C. under vacuum and then heated under Argon at 150.degree. C. for
three hours. In the glove box 0.4 mL of Bis(trimethylsilyl)sulfide
(TMSS) are mixed in 20 mL of octadecene (ODE). In a 100 mL three
necks flask, 12 ml of the lead oleate (PbOA) mixture previously
prepared are quickly degased at 100.degree. C. and then heated at
150.degree. C. under Argon. 6 mL of the solution of TMSS in ODE are
quickly injected to the flask and the reaction performed for 3
minutes. Finally the solution is quickly cooled to room
temperature. The solution is precipitated by adding ethanol and
centrifuged for 5 minutes at 3000 rpm. The solid is redispersed in
toluene. The cleaning step is repeated a second time. At the third
cleaning, selective precipitation is performed to separate the
different size.
[0281] HgTe spherical quantum dots
[0282] In the glove box a 1 M solution of trioctylphosphine
telluride (TOPTe) is prepared by a slow stirring of Te powder in
trioctylphosphine (TOP). In a three neck flask 135 mg of HgCl.sub.2
and 7.4 g of octadecylamine are degased under vacuum for 1 hour at
120.degree. C. The atmosphere is then switch to Argon and the
solution heated at 80.degree. C. 0.5 ml of the 1 M TOPTe are
quickly injected and the reaction is performed at the same
temperature for 5 minutes. The solution is quenched by a quick
addition of dodecanthiol. Finally the flask is cooled down to room
temperature. The obtained dark solution is then split between two
centrifuge tubes filled with a 10% in volume mixture of dodecathiol
(DDT) in tetrachloroethylene (TCE) and a droplet of TOP. The
solution is precipitated by addition of methanol. After
centrifugation the solid is dried and redispersed in chloroform.
The cleaning is step is repeated three times.
[0283] CdS Nanorods
[0284] In the glove box, 0.18 g of sulfur powder are stirred in 20
ml of TOP up to dissolution and formation of trioctylphosphine
sulfide (TOPS). The final solution is reddish. In a 100 ml three
necks flask, 0.23 g of CdO, 0.83 g of n-tetradecylphosphonic acid
(nTDPA) and 7 g of trioctylphosphine oxide (TOPO) are degased under
vacuum for two hours at 80.degree. C. Then the flask is switch
under Argon and the temperature risen up to 340.degree. C. Above
300.degree. C. the solution turns colorless. After 5 minutes the
flask is cooled to 300.degree. C., every two minutes 0.4 ml of the
TOPS mixture is injected. The color of the solution turn yellowish
after 30 minutes and this color will increase up to the end. Once
all the TOPS have been injected the heating mantle is removed and
the flask quickly cooled down. Around 70.degree. C. some toluene is
added to avoid the TOPO solidification.
[0285] The cleaning process is repeating three times by
precipitating the rods by adding ethanol and redispersing them in
toluene.
[0286] Nano Gap Fabrication:
[0287] Self-Aligned Method
[0288] On a Si/SiO.sub.2 wafer, a first electrode is prepared
either using standard optical lithography or electron beam
lithography. In a typical preparation AZ 5214-E resist is deposit
by spin coating on the wafer. The wafer is then baked for 90 s at
110.degree. C. A first UV exposure using the lithography mask is
performed for a couple second. Then the film is further bake at
125.degree. C. for 2 minutes. Finally we process to metal
deposition. The electrodes are made of a layer of Ti (2 nm), a
layer of gold (30 nm) and a layer of Cr (30 nm). Lift off process
is then made to remove the resist by dipping the wafer in acetone.
The wafer is then cleaned using isopropanol and a plasma O.sub.2
etching is conducted for 5 minutes. The electrodes are cooked in
air at 250.degree. C. for 30 minutes in order to convert the Cr
into chromium oxide. In a second step a second electrodes is
prepared using the same ligthography method in a geometry which
allow an overlap with the first electrode. For metal deposition we
evaporate a Ti layer (2 nm) and a gold layer (30 nm). The chromium
oxide layer acts as a shadow mask and a nanometer size gap is
formed between the two electrodes. After a lift off step and a
cleaning step, the top chromium oxide layer of the first electrodes
is etched using a chromium etchant solution. A final step of
cleaning with acetone and isopropanol is performed.
[0289] E-Beam Lithography Method
[0290] On a Si/SiO.sub.2 wafer, a polyemtehyl metacrylate polymer
is deposited and cooked at 165.degree. C. to remove the excess of
solvent. Using electron beam lithography, two electrodes are
designed and allows in a second step the evaporation of metals
(typically 3 nm of Cr and 30 nm of gold). After a lift off
procedure the nanogap is formed.
[0291] Tilted Evaporation Method
[0292] On a Si/SiO.sub.2 wafer, a first electrode is prepared
either using standard optical lithography or electron beam
lithography. In a typical preparation AZ 5214 E resist is deposit
by spin coating on the wafer. The wafer is then baked for 90 s at
110.degree. C. A first UV exposure using the lithography mask is
performed for a couple second. Then the film is further bake at
125.degree. C. for 2 minutes. We then process to metal deposition
by evaporating Ti (2 nm) and a layer of gold (30 nm). A second
pattern is prepared using the same lithography procedure. The
second metallic evaporation is made while the sample is tilted in
order that the first electrode shadows some part of the second
pattern. This shadow effect allows the formation of nanogap at the
scale of a few tenth nanometers.
[0293] Nanoparticle Ligand Exchange and Depositions for
Photodetection --1.sup.st Strategy
[0294] The nanoparticles initially dispersed in a non-polar solvent
can be spincoated onto the nanogap in a glove box. The film is then
heated on a hot plate to remove the excess of solvent at 90.degree.
C. The device is then dipped into a solution of short ligand such
as ethandithiol ou 1.4 diaminobutane at 1% in ethanol for 1 minute.
The film is then rinced in pure ethanol for 20 s and finally dried
under nitrogen flow.
[0295] Nanoparticle Ligand Exchange and Depositions for
Photodetection--2.sup.nd Strategy
[0296] The nanoparticles initially dispersed in a non-polar solvent
are mixed with a solution of Na.sub.2S in N-methyl formamide (1% in
weight). After strong sonication the particle switch of phase and
are transferred in the polar phase. The initial and now clear non
polar phase is discarded. The polar phase is then cleaned two other
times by adding hexane. The nanoparticles are precipitated by
addition of an alcohol. The obtained pellet is redispersed in fresh
N-methyl formamide. This solution is then dropcasted onto the
nanogap on a hot plate at 100.degree. C. The heating is performed
until a complete removal of the solvent.
[0297] Electrolyte Preparation
[0298] The electrolyte is a mixture of polyethylene glycol (PEG) or
polyethylene oxide (PEO) with a given molar weight and ions. The
molar ratio between the cation and the oxygen is taken equal to 16.
For a typical electrolyte 50 mg of LiClO.sub.4 and 230 mg of PEG
(MW=6000 g.mol.sup.-1) are heated together at 150.degree. C. on a
hot plate in the glove box. For higher PEG/PEO molar weight the
mixture is heated at 200.degree. C. Processing the electrolyte in
air has not lead to any noticeable change. The electrolyte can then
be brushed on the at least one nanoparticle onto the nanogap by
softening it at 90.degree. C.
[0299] Responsivity:
[0300] A nanogap where CdSe/CdS nanoplatelets coated with S.sup.2-
capping ligands have been bridged is characterized at room
temperature under primary vacuum. The applied drain source is 2 V.
The sample is illuminated using a 405 nm with a power between 1 and
50 mW corresponding to a flux into the nanogap of 1 to 50 nW. The
obtained photoresponse is 3 kA.W.sup.-1.
[0301] Pn Junction Formation:
[0302] HgTe quantum dots are capped using S.sup.2- ligands, using a
phase transfer method using Na.sub.2S precursor dissolved in
N-methyl formamide. The nanoparticle solution is dropcasted on
nanogap electrodes. Electroltrolyte made of LiClO.sub.4 dissolved
in PEG (M.sub.w=6000 g.mol.sup.-1) is brushed on the nanoparticle
film, while the electrolyte has been soften at 90.degree. C. A gate
electrode is deposited on the electrolyte and grounded. A source
bias of 2V compared to the gate is applied and a drain bias of -2V
compared to the gate is also applied while using a two channel
sourcemeter. The whole system is frozen by cooling the system to a
temperature below the freezing point of the electrolyte. Then a
stable pn junction is formed showing a current-voltage
characteristic of a diode.
[0303] Measurement Condition in View of FIGS. 4-6:
[0304] The samples are characterized under vacuum. A drain source
bias between 0 and 5 V is applied. Light illumination results from
a 405 nm laser source operated with a power ranging from 0.15 mW
and 50 mW. All measurements are made at room temperature.
[0305] Electroluminescence Signal:
[0306] On a 50 nm size nanogap device a solution of nanoplatelets
(CdSe/CdS is dropcasted). The electrodes are connected to a current
source (keithely 2634). As soon the applied bias overcome the band
edge energy we start observing a luminescent signal which spatially
overlap with the nanogap, see FIG. 8.
* * * * *