U.S. patent application number 10/205397 was filed with the patent office on 2003-01-30 for ultrafine particles and method and apparatus for producing the same.
Invention is credited to Fujimoto, Hiroshi.
Application Number | 20030019327 10/205397 |
Document ID | / |
Family ID | 19061020 |
Filed Date | 2003-01-30 |
United States Patent
Application |
20030019327 |
Kind Code |
A1 |
Fujimoto, Hiroshi |
January 30, 2003 |
Ultrafine particles and method and apparatus for producing the
same
Abstract
The present invention provides a method of producing ultrafine
particles by vaporization comprising: vaporizing a target by
sputtering; causing particles that fly from the target by
vaporization to be deposited on an oil surface; and recovering the
oil on which the flown particles have deposited to obtain
individually dispersed ultrafine particles.
Inventors: |
Fujimoto, Hiroshi;
(Kanagawa, JP) |
Correspondence
Address: |
Platon N. Mandros
BURNS, DOANE, SWECKER & MATHIS, L.L.P.
P.O. Box 1404
Alexandria
VA
22313-1404
US
|
Family ID: |
19061020 |
Appl. No.: |
10/205397 |
Filed: |
July 26, 2002 |
Current U.S.
Class: |
75/331 ;
204/192.12; 204/192.15; 204/298.15; 204/298.28 |
Current CPC
Class: |
Y10S 977/888 20130101;
B22F 9/12 20130101 |
Class at
Publication: |
75/331 |
International
Class: |
B22F 009/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 27, 2001 |
JP |
2001-228521 |
Claims
What is claimed is:
1. A method of producing ultrafine particles by vaporization
comprising: vaporizing a target by sputtering; causing particles
that fly from the target by vaporization to be deposited on an oil
surface; and recovering the oil on which the flown particles have
deposited to obtain individually dispersed ultrafine particles.
2. The method according to claim 1, wherein the oil surface is a
fluidized oil surface prepared by fluidizing an oil.
3. The method according to claim 2, wherein the fluidized oil
surface is formed on the surface of a rotating substrate.
4. The method according to claim 2, wherein the fluidized oil
surface is formed on the surface of an inclined substrate.
5. The method according to claim 1, wherein the target is a
multi-element compound.
6. The method according to claim 5, wherein the multi-element
compound contains at least one of the metals in the 4th to the 6th
periods in the periodic table.
7. The method according to claim 5, wherein the multi-element
compound contains at least one element selected from the elements
of the groups III, IV, V and VI in the 4th to the 6th periods in
the periodic table.
8. Ultrafine particles obtained by the method according to claim
1.
9. A method of producing ultrafine particles by vaporization
comprising: vaporizing a target by sputtering; cooling and
solidifying particles that fly from the target by vaporization; and
recovering the flown particles that have been solidified by cooling
to obtain individually dispersed ultrafine particles.
10. The method according to claim 9, wherein the flown particles
are cooled and solidified by a cooled substrate.
11. The method according to claim 9, wherein the flown particles
are cooled and solidified after a vaporized medium has been
modified or adsorbed to the surfaces of the flown particles.
12. The method according to claim 10, wherein the flown particles
are cooled and solidified after a vaporized medium has been
modified or adsorbed to the surfaces of the flown particles.
13. The method according to claim 9, wherein the target is a
multi-element compound.
14. The method according to claim 13, wherein the multi-element
compound contains at least one of the metals in the 4th to the 6th
periods in the periodic table.
15. The method according to claim 9, wherein the multi-element
compound contains at least one element selected from the elements
of the groups III, IV, V and VI in the 4th to the 6th periods in
the periodic table.
16. Ultrafine particles obtained by the method according to claim
9.
17. An apparatus for producing ultrafine particles by vaporization
comprising: means for vaporizing a target by sputtering; an oil on
which particles that fly from the target by vaporization are
deposited; and means for recovering the oil on which the flown
particles have deposited.
18. An apparatus for producing ultrafine particles by vaporization
comprising: means for vaporizing a target by sputtering; means for
cooling and solidifying particles that fly from the target by
vaporization; and means for recovering the flown particles that
have been solidified by cooling.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to ultrafine particles, and to
a method and an apparatus for producing the same. As used herein,
the term "ultrafine particle" refers to fine particles having an
average particle size ranging from 1 nm to 50 nm, that is,
so-called "nano size particles" (occasionally referred to as "nano
particles").
[0003] 2. Description of the Related Art
[0004] Conventionally, various methods of producing ultrafine
particles have been researched. Since nano particles having an
average particle size of below dozens of nano meters cannot be
obtained by grinding, build-up methods have been used. Primary
examples of build-up methods can be divided into gas phase methods,
such as condensation by evaporation and vapor phase reaction, and
liquid phase methods, such as precipitation and desolvation.
[0005] As an example of a liquid phase method, Japanese Patent
Application Laid-Open (JP-A) No. 2000-54012 discloses a method of
forming, through reduction, magnetic nano crystals made of metals,
intermetallic compounds and alloys. Although it is possible to
obtain ultrafine particles having a relatively uniform particle
size, the method has limitations in that raw materials must be
dissolved as a solution and only a compound having a stoichiometric
composition ratio is obtained.
[0006] When the gas phase method is used, a thin film can
relatively easily be formed. However, various procedures are needed
to recover a product in the form of nano particles. For example,
JP-A No. 2001-35255 introduces silver or oxygen using in-gas
evaporation to obtain nano particles of silver oxide. The Journal
of Crystal Growth 45 (1978), pp. 490 to 494, proposes a method of
producing ultrafine particles of higher purity by vacuum
evaporation on a rheological oil surface (VEROS method). In this
method, resistance overheating or an electron beam is used as the
evaporation source. However, although these methods are suitable
for forming particles made of a single-element of noble metals, it
is difficult to produce ultrafine particles made of two or more
metal elements. It is also the case that there is no effective way
of producing nano particles of alloys having an arbitrary
composition.
[0007] In the VEROS method described above, resistance overheating,
an electron beam or the like is used for vaporization. In this
method, when a multi-element base target is used, a problem arises
in that, timing of evaporation may shift depending on a difference
in a vapor pressure, whereby only giving single-element particles
and failing to produce composite particles. In order to solve this
problem, it is conceivable to use ion beams as vaporizing means to
vaporize a multi-element base target having the form of molecules
or an alloy. However, in this case, vaporization efficiency is poor
and the apparatus cost is high. Further, these methods require a
relatively high vacuum. In order to individually disperse fine
particles, it is necessary to either discharge the vaporized
molecules from the system before aggregation occurs or protect the
surface, and for this purpose, a medium that adheres to the
surfaces of particles must be present in the vacuum system.
Consequently, there are problems in that the degree of vacuum is
decreased and the vaporizing means cannot function in an ordinary
manner.
[0008] As stated above, it is difficult to obtain nano size
particles having a variety of compositions and applicable to
various objects by liquid phase methods, and such nano size
particles cannot be obtained by gas phase methods such as a CVD
method. Because particles aggregate to form a film within one to
several seconds even if ordinary sputtering is used, there is
currently no specific method capable of producing nano size
particles.
[0009] Moreover, when arranging nano particles in the form of a
film, it is effective to coat a colloidal solution of nano
particles. However, it is necessary to select a dispersing medium
and a coating equipment suited for particle constituent elements.
Although gas phase methods are known in which fine particles are
recovered by causing vaporized particles to adhered to a dispersion
medium, there is the problem that the particles easily coagulate
when their concentration is high. There has also been a demand for
a method of readily producing a stable colloidal solution of nano
particles.
SUMMARY OF THE INVENTION
[0010] An object of the present invention is to solve the
aforementioned problems associated with the prior art and to attain
the following object. That is, an object of the invention is to
provide a method and an apparatus for readily producing
individually dispersed ultrafine particles having an arbitrary
composition and an arbitrary composition ratio and a colloidal
solution thereof at a low cost, and to provide ultrafine particles
that are obtained by the method and the apparatus.
[0011] The aforementioned problems are solved by the following
means.
[0012] A first aspect of the invention is a method of producing
ultrafine particles by vaporization comprising: vaporizing a target
by sputtering; causing particles that fly from the target by
vaporization to be deposited on an oil surface; and recovering the
oil on which the flown particles have deposited to obtain
individually dispersed ultrafine particles.
[0013] A second aspect of the invention is a method of producing
ultrafine particles by vaporization comprising: vaporizing a target
by sputtering; cooling and solidifying particles that fly from the
target by vaporization; and recovering the flown particles that
have been solidified by cooling to obtain individually dispersed
ultrafine particles.
[0014] A third aspect of the invention is an apparatus for
producing ultrafine particles by vaporization comprising: means for
vaporizing a target by sputtering; an oil on which particles that
fly from the target by vaporization are deposited; and means for
recovering the oil on which the flown particles have deposited.
[0015] A fourth aspect of the invention is an apparatus for
producing ultrafine particles by vaporization comprising: means for
vaporizing a target by sputtering; means for cooling and
solidifying particles that fly from the target by vaporization; and
means for recovering the flown particles that have been solidified
by cooling.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a schematic structural view showing a first
embodiment of an apparatus for producing ultrafine particles of the
present invention.
[0017] FIG. 2 is a schematic structural view showing a second
embodiment of an apparatus for producing ultrafine particles of the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] First and second embodiments of the present invention are
described in detail below. An apparatus for producing ultrafine
particles of the invention, the ultrafine particles of the
invention, and a method of producing the ultrafine particles of the
invention are also described.
[0019] First Embodiment
[0020] The method according to the first embodiment of the
invention is a method of producing ultrafine particles by
vaporization comprising: vaporizing a target by sputtering; causing
particles that fly from the target by vaporization to be deposited
on an oil surface; and recovering the oil on which the flown
particles have deposited to obtain individually dispersed ultrafine
particles.
[0021] In the method of producing ultrafine particles according to
the first embodiment of the invention, multi-element based
ultrafine particles can be produced by employing sputtering for
vaporization (vaporizing means). Further, particles can be flown
normally in the presence of a medium such as an oil even under
vacuum. By causing particles to be deposited on an oil surface,
individually dispersed ultrafine particles can readily be obtained
without causing aggregation of the particles. Therefore, by the
method of producing ultrafine particles according to the first
embodiment, individually dispersed ultrafine particles having an
arbitrary composition and an arbitrary composition ratio or a
colloidal solution thereof can stably be obtained, in a simple
manner and at a low cost.
[0022] In the method of producing ultrafine particles according to
the first embodiment of the invention, suitable examples of the oil
to form an oil surface include silicone-based oils having a boiling
point of 200.degree. C. or more, .alpha.-terpineol, hydrocarbons
having 6 or more carbon atoms and alcohols having a high boiling
point. Various additives may be included in these oils. Preferable
examples of the additive include alkylphosphine oxides,
alkylphosphines and the compounds containing at least one selected
from --SH, --CN, --NH.sub.2, --SO.sub.2OH, --SOOH, --OPO(OH).sub.2
and --COOH. Among them, alkylphosphine oxides and the compounds
containing at least one selected from --SH and --COOH are
preferable. It is appropriate that the oil has been deaerated.
[0023] In the method of producing ultrafine particles according to
the first embodiment of the invention, it is preferable that the
oil surface is formed on a substrate (a flat plate) such that a
suitable oil thin film can readily be formed. The substrates are
preferably made of metals or resins which have been smooth-treated.
The substrates are selected from the materials that are adaptable
to the oil used. It is particularly preferable if an oil thin film
is formed uniformly on a substrate and can be fluidized at an
arbitrary speed as described later. Therefore, for the purpose of
controlling the surface tension of the substrate, it is preferable
to perform surface treatment of the substrate as necessary.
[0024] In the method of producing ultrafine particles according to
the first embodiment of the invention, it is preferable that the
oil surface is a fluidized oil surface obtained by fluidizing an
oil, from the standpoints of recovering an oil efficiently and
obtaining individually well-dispersed ultrafine particles. By
causing particles to be deposited on the fluidized oil surface,
particle growth can be suppressed, whereby ultrafine particles
having a minute and uniform particle size can readily be obtained.
As the method of fluidizing an oil, i.e., the method of forming a
fluidized surface, the method to form the fluidized surface on a
rotating substrate surface, the method to form the fluidized
surface on an inclined substrate, and the like are suitably used.
These methods may be used in combination. As used herein, the term
"inclined" of the inclined substrate means that a vertical line on
the substrate surface is inclined with respect to the gravity
direction.
[0025] In case of forming a fluidized surface on the surface of a
rotating substrate, when a substrate processed to have the shape of
a disk is rotated, an oil can uniformly be fluidized to achieve a
preferable fluidized oil surface in a simple manner. The rotational
speed of the rotating substrate preferably ranges from about 10 rpm
to about 500 rpm. An oil is preferably supplied from a position
substantially around the center of the rotating shaft of the
rotating substrate, and the supply is continuously maintained
without interruption. The oil feeding speed is preferably from 0.01
ml/min to 2 ml/min per unit area of the rotating substrate. The
fluidized oil surface may be formed either at the upper surface
(the surface provided opposite to the gravity direction: in this
case sputtering is conducted in the direction of downward) or at
the lower surface (the surface provided in the gravity direction:
in this case sputtering is conducted in the direction of upward) of
the rotating substrate. It is more preferable to form a fluidized
surface on the upper surface of the rotating substrate. If a
fluidized oil surface is formed at the lower surface of the
rotating substrate, there may arise a problem that an oil drops on
a vaporizing means to cause pollution or other troubles depending
on a low rotational speed and physical properties of an oil (e.g.,
low viscosity). Besides, if conducted downwardly, sputtering can
release flown particles more efficiently. From the standpoints, it
is preferable to form a fluidized oil surface on the upper surface
of the rotating substrate.
[0026] In case of forming a fluidized oil surface on an inclined
substrate surface, it is suitable that oil supply is carried out
such that an oil can spread over an entire surface of the inclined
substrate. For example, it is preferable to supply an oil such that
the oil can flow from the upper end to the lower end of the
inclined substrate.
[0027] Suitably, a substrate is cooled in both of the rotating
substrate method and the inclined substrate method described above.
A substrate may be cooled in the same manner as conducted by a
cooling method (means) described in the second embodiment below.
Water may be used as a cooling medium.
[0028] In the method of producing ultrafine particles according to
the first embodiment of the invention, when the above-described
rotating substrate method is employed, an oil on which flown
particles (ultrafine particles) have deposited can be recovered,
for example, in such a manner that particles that collided
(deposited) to the fluidized oil surface of the rotating substrate
surface are flown to the periphery by a centrifugal force caused by
rotation of the rotating substrate, and the oil flown outside of
the periphery and including the particles is captured by a member
which protects the substrate periphery and then the oil is
collected to one site. In the inclined substrate method, an oil
that has dropped on the lower end of the inclined substrate may be
stored in a tank and the like. In both of the above-described
rotating substrate method and inclined substrate method, an oil may
be supplied in a circulating mode. That is, the oil recovered at an
oil recovering portion can be delivered, for circulation, to an oil
feeding portion such that the oil can be continuously used until
ultrafine particles (flown particles) reach a predetermined
concentration.
[0029] The recovered oil may be concentrated by vacuum or vacuum
heating, as necessary. Further, after recovered, the oil may
preferably be replaced with other organic solvents (e.g., organic
solvents having a lower boiling point than that of the oil, such
as, toluene, xylene, hexane, alcohols having 6 or less carbon
atoms) depending on use purposes. The concentration rate may vary
and range from about 10 to 40% by weight, depending on the
composition of ultrafine particles and the solvent used.
[0030] The first embodiment of an apparatus suitably used for the
method of producing ultrafine particles according to the invention
is illustrated below, referring to a drawing.
[0031] The apparatus for producing ultrafine particles shown in
FIG. 1 comprises a sputtering device 12 for vaporization
(vaporizing means) and a rotating substrate 14 capable of rotating
to form a fluidized oil surface in a vacuum chamber 10. The
sputtering device 12 has, for example, a target (not shown) having
a necessary composition previously prepared by calcination, and
additionally, a shutter 16 in the vacuum chamber 10. The rotating
substrate 14 has a vacant structure to which a cooling medium is
introduced from a cooling medium inlet 18, to cool the rotating
substrate 14 from inside. Regions around the periphery of the
rotating substrate 14 are covered with a protecting member 20. To
serve as the particle recovering means, the protecting member 20 is
connected with an oil recovering tube 22 in the shape of a float,
and the oil recovering tube 22 is further connected with an oil
recovering tank 24 outside of the vacuum chamber 10. In the
vicinity of the rotating shaft of the rotating substrate 14, an oil
feeding tube 26 is arranged to enable an oil supplied to the upper
surface near the rotating shaft of the rotating substrate 14. The
oil feeding tube 26 is connected with an oil feeding tank 28
outside of the vacuum chamber 10. And to the oil feeding tank 28,
an evacuating tube 30 is connected. Rotation of the rotating
substrate 14 is controlled by a motor 32.
[0032] In an apparatus for producing ultrafine particles shown in
FIG. 1, a cooling medium is introduced from the cooling medium
inlet 18 to cool the rotating substrate 14. Rotation of the
rotating substrate 14 is controlled by the motor 32, and an oil is
continuously supplied, through the oil feeding tube 26, to a
position around the rotating shaft of the rotating substrate 14
from the oil feeding tank 28, to thereby form a fluidized oil
surface. In this operation, an oil has previously been deaerated
through an evacuating tube 30. The shutter 16 provided for the
sputtering device 12 is opened to expose a target (not shown) to
the vacuum chamber 10 to initiate sputtering. In the initial
period, the oxides present on the surface of the target are
eliminated and then sputtering is commenced. The flown particles
reach the fluidized oil surface formed on the upper surface of the
rotating substrate 14, fly away to the periphery by a centrifugal
force together with a fluidized oil, are captured by the protecting
member 20, and then are collected to the oil recovering tank 24
through the oil recovering tube 22. Thus, ultrafine particles can
be obtained. The recovered oil containing the flown particles
(ultrafine particles) may be concentrated and replaced, as
necessary, to give a desired colloidal product.
[0033] Second Embodiment
[0034] The method according to the second embodiment of the
invention is a method of producing ultrafine particles by
vaporization comprising: vaporizing a target by sputtering; cooling
and solidifying particles that fly from the target by vaporization;
and recovering the flown particles that have been solidified by
cooling to obtain individually dispersed ultrafine particles.
[0035] In the method of producing ultrafine particles according to
the second embodiment of the invention, multi-element based
ultrafine particles can be produced by employing sputtering for
vaporization (vaporizing means). Further, particles can be flown
normally in the presence of a medium such as a vaporized medium
even under vacuum. By cooling and solidifying the flown particles,
individually dispersed ultrafine particles can readily be recovered
without causing aggregation of the particles. Therefore, by the
method of producing ultrafine particles according to the second
embodiment, individually dispersed ultrafine particles having an
arbitrary composition and an arbitrary composition ratio or a
colloidal solution thereof can stably be obtained, in a simple
manner and at a low cost.
[0036] In the method of producing ultrafine particles according to
the second embodiment of the invention, in order to perform cooling
and solidifying (cooling and solidifying means), for example, a
substrate is cooled (a cooled substrate is provided) and the
particles flown by sputtering are frozen on the surface of the
cooled substrate. In order to cool the substrate, a cooling medium
such as liquid nitrogen, liquid carbon dioxide and super-cooled
water may be used. By cooling the substrate in such a manner, the
flown particles (ultrafine particles) are cooled and solidified
(frozen) to cause deposition thereof on the surface of the
substrate. Preferably, cooling of the substrate is conducted, for
example, by inside cooling in which a cooling medium is circulated
into the substrate in order to efficiently deposit the flown
particles on the surface of the substrate. The substrate may be
rotated at a relatively low speed.
[0037] In the method of producing ultrafine particles according to
the second embodiment of the invention, it is preferable to use and
mediate a vaporized medium. That is, when the substrate is cooled
for solidifying the particles, a vaporized medium is adsorbed to
the surface of the flown particles (cooling and solidifying means)
for modifying the surface, and then the flown particles are cooled
and solidified. For use as the vaporized medium, solvents having a
relatively low boiling point are preferable. For example, organic
solvents having a boiling point of 200.degree. C. or lower are
preferable, and more preferable are the organic solvents having a
boiling point of 150.degree. C. or lower. Alcohols are particularly
preferable. Cooling of the flown particles is accelerated by
contacting the particles with a vaporized solvent. Since the
vaporized solvent is adsorbed to the surface of the particles for
modification thereof, the flown particles are frozen and deposited
on the surface of the substrate together with the vaporized
solvent. The flown particles (ultrafine particles) are prevented
from aggregating with additional particles that will be flown
later, by an effect of the vaporized solvent adsorbed to the
particle surface, to thus produce ultrafine particles having a
small particle size and a narrower particle size distribution. It
is also preferable to use, together with the vaporized medium, an
adsorbent having a different adsorbing force to the surface of
flown particles such that the adsorbent can contact with the flown
particles. Suitable examples of the adsorbent include
alkylphosphine oxides, alkylphosphines and the compounds containing
at least one selected from --SH, --CN, --NH.sub.2, --SO.sub.2OH,
--SOOH, --OPO(OH).sub.2 and --COOH. Among them, alkylphosphine
oxides and the compounds containing at least one selected from --SH
and --COOH are preferable. More specifically, as a lipophilic
adsorbent, adsorbing compounds containing a substituent having a
total of 6 or more carbon atoms, preferably 8 to 40 carbon atoms,
such as an octyl group, a decyl group, a dodecyl group and a
hexadecyl group can be used. As a hydrophilic adsorbing agent,
adsorbing compounds having a substituent or a hydrophilic group
having 6 or less carbon atoms (e.g., --SO.sub.3M, --COOM in which M
represents a hydrogen atom, an alkali metal atom, an ammonium
molecule and the like) can suitably be used. The fact that the
surface of the flown particles (ultrafine particles) is adsorbed by
a vaporized medium or an adsorbent can be confirmed by high
resolution TME, such as FE-TEM to find that a specified distance is
left between the particles, or by chemical analysis.
[0038] In the method of producing ultrafine particles according to
the second embodiment of the invention, the flown particles
(ultrafine particles) solidified by cooling (frozen) can be
recovered, for example, by the following procedure. When a
substrate is cooled by liquid nitrogen and the like, the flown
particles are frozen and deposited on the substrate surface, after
which sputtering and the liquid nitrogen supply are halted, vacuum
is leaked, the substrate is rotated with gradually raising the
temperature to cause the deposited particles (ultrafine particles)
adhered by the vaporized solvent to be molten and flown away to the
periphery by a centrifugal force, then to be captured by a
protecting member arranged around the periphery of the substrate,
and finally to be collected to one site.
[0039] The second embodiment of an apparatus suitably used for the
method for producing ultrafine particles according to the invention
is illustrated below, referring to FIG. 2. Members having the same
functions as those in an apparatus shown in FIG. 1 are designated
by the same symbols.
[0040] The apparatus for producing ultrafine particles shown in
FIG. 2 comprises a sputtering device 12 for vaporization
(vaporizing means) and a rotating substrate (a cooled substrate) 14
capable of rotating and of cooling and solidifying the flown
particles in a vacuum chamber 10, and additionally, a vaporized
medium inlet 34 to introduce a vaporized medium into the vacuum
chamber 10. The sputtering device 12 has, for example, a target
(not shown) having a necessary composition previously prepared by
calcination, and additionally, a shutter 16 in the vacuum chamber
10. The rotating substrate 14 has a vacant structure to which a
cooling medium is introduced from a cooling medium inlet 18, to
cool the rotating substrate 14 from inside. Regions around the
periphery of the rotating substrate 14 are covered with a
protecting member 20. To serve as the particle recovering means,
the protecting member 20 is connected with a recovering tube 22 in
the shape of a float, and the recovering tube 22 is further
connected with a recovering tank 24 outside of the vacuum chamber
10. Rotation of the rotating substrate 14 is controlled by a motor
32.
[0041] In an apparatus for producing ultrafine particles shown in
FIG. 2, a cooling medium is introduced from the cooling medium
inlet 18 to cool the rotating substrate 14. A vaporized medium is
introduced into the vacuum chamber 10 from a vaporized medium inlet
34. The rotating substrate 14 is rotated by a motor at a low speed
of, for example, about 10 to 30 rpm. The shutter 16 provided for
the sputtering device 12 is opened to expose a target (not shown)
to the vacuum chamber 10 to initiate sputtering. In the initial
period, the oxides present on the surface of the target are
eliminated and then sputtering is commenced. The particles flown by
sputtering are brought into contact with a vaporized medium to
cause surface modification or surface adsorption by the vaporized
medium, and then are frozen and deposited on the upper surface of
the cooled rotating substrate 14. Thereafter, introduction of the
cooling medium from the cooling medium inlet 18 is halted. At the
time when the frozen and deposited substance starts melting, the
rotational speed of the rotating substrate 14 is increased. The
frozen deposit is molten and then flown away to the periphery by a
centrifugal force caused by rotation of the rotating substrate 14,
and is captured by a protecting member 20, and thereafter is
collected to a collecting tank 24 via a collecting tube 22. Thus,
ultrafine particles can be obtained. Further, the flown particles
(ultrafine particles)--containing molten deposit recovered can be
concentrated and then replaced, as necessary, to give a desired
colloidal product.
[0042] The procedures which are common to the first and second
embodiments of the invention are described below.
[0043] In the method of producing ultrafine particles of the
invention, sputtering can be conducted by conventionally known
methods. Sputtering may be conducted without any restriction, in
the direction of upwardly, downwardly and in the left and right
directions. In the invention, "downward" means the gravity
direction, and "upward" means the opposite direction.
[0044] In the method of producing ultrafine particles of the
invention, the target may be any of single-element compounds and
multi-element compounds of two or more elements. According to the
present invention, it is possible to produce preferable ultrafine
particles made of multi-element compounds consisting of two or more
elements. Specifically, various composite materials can be used,
not to mention of ordinarily used metals, intermetallic compounds
or sulfides, and silicon and the oxides thereof. Further, when
silver, gold, copper, zinc, iron, cobalt, chromium, nickel,
aluminum, as well as chalcogen compounds such as indium, antimony,
tellurium and the composite compounds thereof are used, an
advantageous effect of the present invention can be exhibited. As
the multi-element compound, the oxides and sulfides containing at
least one of the metals in the 4th to the 6th periods in the
periodic table or the oxides and sulfides of a multi-metal
consisting of two or more metals are preferable, and multi-element
compounds containing the elements of the groups III, IV, V and VI
in the 4th to the 6th periods in the periodic table (at least one
element selected from the groups of 13, 14, 15 and 16 according to
IUPAC, 1989, inorganic chemical nomenclature, revised version) are
more preferable. More specifically, the oxides and sulfides of
magnesium, aluminum, silicon, titanium, vanadium, manganese,
copper, zinc, gallium, strontium, yttrium, zirconium, silver,
indium, cesium, barium and the like, or the oxides and sulfides of
the composite material thereof, or multi-element compounds
containing silver, germanium, indium, antimony, tellurium and the
like in an arbitrary composition ratio are preferable. In the
invention, ultrafine particles made of metal multi-element
compounds having a stoichiometrically non-applicable composition
ratio can readily be produced.
[0045] It is preferable in the invention that the distance between
a target and an oil surface (or a substrate surface for deposition)
can arbitrarily be varied. By varying the distance, particle sizes
and surface modification levels may be controlled, whereby
applicability of the ultrafine particles can be enlarged.
[0046] In the method of the invention, it is possible to produce
ultrafine particles having an arbitrary composition and an
arbitrary composition ratio, so long as sputtering can be
implemented for a given composition. Therefore, ultrafine particles
obtained by the method of the invention (ultrafine particles of the
invention) can be applied and used in various fields. For example,
in optical recording materials, metal chalcogen compounds are used
as the recording material. If the metal chalcogen compounds are
used in the form of ultrafine particles produced by the present
invention, recording sensitivity and recording density can be
improved. A functional film can also be obtained by using the
ultrafine particles of the invention. A metal chalcogen compound
used for optically recording has a composition of Ag, In, Sb and
Te, or Ge, Sb and Te, each included in non-stoichiometric ratio.
Therefore, it is difficult to formulate the components into a
single particle by synthesis. However, ultrafine particles can be
produced by the method of the present invention if the calcinated
metal chalcogen compound is used as a target for sputtering.
[0047] The ultrafine particles obtained by the invention may be
included in a layer used for a dielectric material layer which is a
constituent element of the optical recording material
(particularly, DVD disk). Besides, the ultrafine particles of the
invention may be used in a functional layer, in addition to a
recording layer and a dielectric material layer.
[0048] Furthermore, the obtained ultrafine particles of the
invention may be used in the form of a colloidal solution in an
organic solvent. Alternatively, a hydrophilic solvent may be
replaced to produce a hydrophilic colloidal solution. These
colloidal solutions can be spin-coated or web-coated, to give a
thinner film.
EXAMPLES
[0049] The present invention is described further in detail below
with reference to the following examples, but it is to be
understood that the invention is not limited to the examples.
Example 1
[0050] Ultrafine particles (nano particles) were produced as
follows by using an apparatus shown in FIG. 1. In order to produce
a target for sputtering, metals of Ag, In, Sb and Te were
calcinated at a weight ratio of 1:1:18:7 and the produced target
was placed in the sputtering apparatus 12 using a 4-inch backing
plate. As the rotating substrate 14, a vacant substrate in the form
of disc having a diameter of about 30 cm was produced and rotated
at a rotational speed of 450 rpm using the motor 32 while
water-cooling was provided by introducing cooling water from the
cooling medium inlet 18. .alpha.-Terpineol was deaerated for use as
an oil, and then supplied through the oil feeding tube 26 to the
upper surface of the rotating substrate 14 at a feeding speed of 30
ml/min. In the sputtering device 12, an RF high-rate electric
source and a 4-inch planar magnetron-type cathode were used. Inside
the vacuum chamber 10, a diffusion pump and a rotary pump were
arranged to control the degree of vacuum for sputtering.
[0051] Ten minutes after the particle production started, an
interval of 3 minutes was provided, and this procedure was repeated
three times, to thus perform sputtering for a total of 30 minutes.
The particles dispersed in about 700 ml of the recovered oil were
observed by a transmission-type electron microscope TEM, to find
that nano particles had an average particle size ranging from 3 to
8 nm.
[0052] The composition of one particle was investigated by using
EF-TEM, to reveal the presence of four elements Ag, In, Sb and
Te.
Example 2
[0053] Ultrafine particles (nano particles) were produced as
follows by using an apparatus shown in FIG. 2. In order to produce
a target for sputtering, metals of Ag, In, Sb and Te were
calcinated at a weight ratio of 1:1:18:7 and the produced target
was placed in the sputtering apparatus 12 using a 4-inch backing
plate. As the rotating substrate 14, a vacant substrate in the form
of disc having a diameter of about 30 cm was produced and rotated
at a rotational speed of 450 rpm using the motor 32 while
water-cooling was provided by introducing cooling water from the
cooling medium inlet 18. 1-ethoxy-2-propanol containing about 0.1%
of sodium mercaptosuccinate and having been vaporized to a degree
capable of sputtering was introduced from the vaporized medium
inlet 34 into the vacuum chamber. In the sputtering device 12, an
RF high-rate electric source and a 4-inch planar magnetron-type
cathode were used. Inside the vacuum chamber 10, a diffusion pump
and a rotary pump were arranged to control the degree of vacuum for
sputtering.
[0054] Five minutes after the particle production started, an
interval of 1 minute was provided, and this procedure was repeated
five times, to thus perform sputtering for a total of 25 minutes.
Thereafter, Ar was introduced into the vacuum chamber 10 to raise
the pressure to a normal pressure, and the liquid nitrogen supply
was halted. When the frozen deposit on the rotating substrate 14
started melting, a rotational speed of the rotating substrate 14
was increased to 250 rpm, and the molten deposit was recovered.
[0055] The particles present in a dispersion (molten deposit) were
observed by a transmission-type electron microscope TEM, to confirm
that nano particles having an average particle size ranging from 3
to 8 nm could be produced, as obtained in Example 1. This
dispersion did not cause precipitation and excellent colloidal
conditions were maintained even after 7 hours at an ordinary
temperature.
[0056] The composition of one particle was investigated by using
EF-TEM, to reveal the presence of four elements Ag, In, Sb and
Te.
Example 3
[0057] Ultrafine particles (nano particles) were produced in a
similar manner as in Example 2 except that in place of sodium
mercaptosuccinate, polyvinylpyrrolidone having a molecular weight
of 1600, sodium citrate and a hydrolyzate of tetraethoxy
orthosilicate (TEOS) were used, respectively. The obtained
multi-element base nano particles maintained excellent
dispersibility.
Example 4
[0058] Ultrafine particles (nano particles) were produced in a
similar manner to Example 1 except that a calcinated metal made of
Ge, Sb and Te at a weight ratio of 2:3:5 was used as a target for
sputtering. The resultant ultrafine particles were observed by
EF-TEM, to find that the three elements were included in a particle
at approximately the same proportion as above. The average particle
size ranged from 3 to 9 nm.
[0059] As described above, the present invention can provide a
method and an apparatus for stably producing individually dispersed
ultrafine particles having an arbitrary composition and an
arbitrary composition ratio or a colloidal solution thereof in a
simple manner and at a low cost, and also provide the ultrafine
particles obtained by the method and the apparatus.
* * * * *