U.S. patent application number 14/866044 was filed with the patent office on 2017-03-30 for synthesis method for controlling antimony selenide nanostructure shapes.
The applicant listed for this patent is Sharp Laboratories of America (SLA), Inc.. Invention is credited to Alexey Koposov.
Application Number | 20170088422 14/866044 |
Document ID | / |
Family ID | 58286193 |
Filed Date | 2017-03-30 |
United States Patent
Application |
20170088422 |
Kind Code |
A1 |
Koposov; Alexey |
March 30, 2017 |
Synthesis Method for Controlling Antimony Selenide Nanostructure
Shapes
Abstract
Methods are provided for controlling the shape of antimony
selenide (Sb.sub.2Se.sub.3) synthesized nanostructures. The method
dissolves an antimony (III) salt in a first amount of carboxylic
acid, forming an antimony precursor. In one aspect, antimony (III)
chloride is dissolved in oleic acid. Separately, selenourea is
dissolved in oleylamine, forming a selenium precursor. The antimony
precursor is combined with the selenium precursor to form a first
solution and cause a reaction. The reaction is quenched with a
solvent having a low boiling point. In response to quenching the
reaction in the first solution, antimony selenide nanorods are
formed, having a length in the range of 150-200 nanometers (nm) and
a diameter in the range of 20 to 30 nm. Related methods can be used
to create, shorter nanorods, nanocrystals, and hollow
nanospheres.
Inventors: |
Koposov; Alexey; (Vancouver,
WA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sharp Laboratories of America (SLA), Inc. |
Camas |
WA |
US |
|
|
Family ID: |
58286193 |
Appl. No.: |
14/866044 |
Filed: |
September 25, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C01P 2004/16 20130101;
C01B 19/007 20130101; H01L 31/0272 20130101; H01L 31/035209
20130101; C01P 2006/40 20130101; H01L 31/035227 20130101; C01P
2004/64 20130101; C01P 2004/34 20130101; H01L 31/032 20130101 |
International
Class: |
C01B 19/00 20060101
C01B019/00; H01L 31/0352 20060101 H01L031/0352; H01L 31/0272
20060101 H01L031/0272 |
Claims
1. A method for controlling the shape of antimony selenide
(Sb.sub.2Se.sub.3) nanostructures, the method comprising: providing
antimony (III) salt; dissolving the antimony (III) salt in a first
amount of carboxylic acid, forming an antimony precursor;
dissolving selenourea in oleylamine, forming a selenium precursor;
combining the antimony precursor with the selenium precursor to
form a first solution; causing a reaction; quenching the reaction
with a solvent having a low boiling point; and, in response to
quenching the reaction in the first solution, forming antimony
selenide nanorods, having a length in a range of 150-200 nanometers
(nm) and a diameter in a range of 20 to 30 nm.
2. The method of claim 1 wherein, dissolving the antimony (III)
salt in the first amount of carboxylic acid includes dissolving at
a temperature in a range of 130 to 170.degree. C.
3. The method of claim 1 wherein, dissolving selenourea in
oleylamine includes dissolving at a temperature in a range of 180
to 220.degree. C.
4. The method of claim 1 wherein dissolving the antimony (III) salt
in the first amount of carboxylic acid includes dissolving antimony
(III) chloride in oleic acid.
5. The method of claim 1 wherein forming the first solution
includes forming the first solution at a temperature in a range of
160 to 200.degree. C.
6. The method of claim 1 wherein forming the antimony precursor
includes dissolving, proportionally, 200 milligrams (mg) of
antimony (III) chloride in 3 milliliters (mL) of oleic acid at 150
degrees C.; wherein forming the selenium precursor includes
dissolving, proportionally, 100 mg of selenourea with 1 mL of
oleylamine at 200 degrees C., and then cooling to 100 degrees C.;
wherein forming the first solution includes heating the antimony
precursor to 180 degrees C. and injecting it into the selenium
precursor kept at the 100 degree C. temperature; wherein causing
the reaction includes stirring the first solution for 10 seconds;
and, wherein quenching the reaction includes adding toluene to the
first solution.
7. The method of claim 1 further comprising: prior to quenching,
adding phosphine oxide to the first solution, forming a second
solution; in response to quenching the reaction in the second
solution, forming antimony selenide nanocrystals having a size in a
range of 1 to 5 nm.
8. The method of claim 7 wherein adding phosphine oxide to the
first solution includes combining phosphine oxide, the antimony
precursor, and the selenium precursor at a temperature in a range
of 80 to 120.degree. C.
9. The method of claim 7 wherein adding phosphine oxide to the
first solution includes adding tri-n-octylphosphine (TOPO) to the
first solution.
10. The method of claim 9 wherein forming the antimony precursor
includes dissolving, proportionally, 200 mg of antimony (III)
chloride in 3 mL of oleic acid at 150 degrees C.; wherein forming
the selenium precursor includes dissolving, proportionally, 100 mg
of selenourea with 1 mL of oleylamine at 200 degrees C., and then
cooling to 100 degrees C.; wherein forming the first solution
includes heating the antimony precursor to 100 degrees C. and
injecting it into the selenium precursor kept at the 100 degree C.
temperature; and wherein adding TOPO to the first solution includes
adding, proportionally, 0.75 grams (g) of TOPO.
11. The method of claim 1 further comprising: adding 1-octadecene
(ODE) and oleylamine to the antimony precursor, creating a first
amount of a first modified antimony precursor; wherein combining
the antimony precursor with the selenium precursor includes
combining the first modified antimony precursor with a second
amount of selenium precursor to form a third solution; and, in
response to quenching the reaction in the third solution, forming
antimony selenide hollow spheres having an outside diameter in a
range of 5 to 15 nm.
12. The method of claim 11 wherein combining the first amount of
first modified antimony precursor with the second amount of
selenium precursor includes combining at a temperature of in a
range of 180 to 200 degrees C.
13. The method of claim 11 wherein creating the first amount of
first modified antimony precursor includes combining,
proportionally, 0.132 g of antimony (III) chloride, 0.72 mL of
oleylamine, 0.56 mL of oleic acid, and 6.3 mL of ODE, heating at a
temperature of 130 degrees C. for 30 minutes, and then heating to
180 degrees C.; wherein forming the selenium precursor includes
dissolving, proportionally, 0.16 g of selenourea with 1.25 mL of
oleylamine at 150 degrees C., and then cooling to 100 degrees C.;
wherein forming the third solution includes keeping the selenium
precursor at 100 degrees C. and injecting it into the 180 degree C.
temperature first modified antimony precursor; and, wherein
quenching the reaction includes adding hexane to the third
solution.
14. The method of claim 11 wherein, combining the antimony
precursor with the selenium precursor includes combining the first
amount of first modified antimony precursor with a third amount of
selenium precursor, greater than the second amount, to form a
fourth solution; in response to quenching the reaction in the
fourth solution, forming antimony selenide nanoparticles having
diameter in a range of 5 to 15 nm.
15. The method of claim 14 wherein creating the first amount of
first modified antimony precursor includes combining,
proportionally, 0.132 g of antimony (III) chloride, 0.72 mL of
oleylamine, 0.56 mL of oleic acid, and 6.3 mL of ODE, heating at a
temperature of 130 degrees C. for 300 minutes, and then heating to
180 degrees C.; wherein forming the selenium precursor includes
dissolving, proportionally, 0.2 of selenourea with 1.25 mL of
oleylamine at 150 degrees C., and then cooling to 100 degrees C.;
wherein forming the third solution includes keeping the selenium
precursor at 100 degrees C. and injecting it into the 180 degree C.
temperature first modified antimony precursor; and, wherein
quenching the reaction includes adding hexane to the third
solution.
16. The method of claim 1 wherein forming the antimony precursor
includes dissolving the antimony (III) salt in a second amount of
carboxlic acid, greater than the first amount; the method further
comprising: adding ODE to the antimony precursor to create a second
modified antimony precursor; wherein combining the second modified
antimony precursor with the selenium precursor includes forming a
fifth solution; and, in response to quenching the reaction in the
fifth solution, forming antimony selenide nanorods, having a length
in a range of 30 to 50 nm, and a diameter in a range of 5 to 15 nm.
17 The method of claim 16 wherein, forming the second modified
antimony precursor includes combining, proportionally, 0.132 g of
antimony (III) chloride, 0.56 mL of oleic acid, and 6.3 mL of ODE,
heating at a temperature of 130 degrees C. for 30 minutes, and then
heating to 180 degrees C.; wherein forming the selenium precursor
includes dissolving, proportionally, 0.16 of selenourea with 1.25
mL of oleylamine at 150 degrees C., and then cooling to 100 degrees
C.; wherein forming the fifth solution includes keeping the
selenium precursor at 100 degrees C. and injecting it into the 180
degree C. temperature antimony precursor; and, wherein quenching
the reaction includes adding hexane to the fifth solution.
18. A method for synthesizing antimony selenide (Sb.sub.2Se.sub.3)
nanocrystals, the method comprising: providing antimony (III) salt;
dissolving the antimony (III) salt in carboxylic acid, forming an
antimony precursor; dissolving selenourea in oleylamine, forming a
selenium precursor; combining the antimony precursor with the
selenium precursor to form a first solution; adding phosphine oxide
to the first solution, forming a second solution; causing a
reaction; quenching the reaction with a solvent having a low
boiling point; and, in response to quenching the reaction in the
second solution, forming antimony selenide nanocrystals having a
size in a range of 1 to 5 nanometers (nm).
19. A method for synthesizing antimony selenide (Sb.sub.2Se.sub.3)
nanostructures, the method comprising: providing antimony (III)
salt; dissolving the antimony (III) salt in carboxylic acid with
oleylamine and 1-octadecene (ODE), forming an antimony precursor;
dissolving selenourea in oleylamine, forming a first amount of
selenium precursor; combining the antimony precursor with the first
amount of selenium precursor to form a first solution; causing a
reaction; quenching the reaction with a solvent having a low
boiling point; and, in response to quenching the reaction in the
first solution, forming antimony selenide hollow spheres having an
outside diameter in a range of 5 to 15 nanometers (nm).
20. The method of claim 19 wherein combining the antimony precursor
with the selenium precursor includes combining the antimony
precursor with a second amount of selenium precursor, greater than
the first amount of selenium precursor; in response to quenching
the reaction in the first solution, forming antimony selenide
nanoparticles having a diameter in a range of 5 to 15 nm.
21. A method for synthesizing antimony selenide (Sb.sub.2Se.sub.3)
nanorods, the method comprising: providing antimony (III) salt;
dissolving the antimony (III) salt in carboxylic acid with
1-octadecene (ODE), forming an antimony precursor; dissolving
selenourea in oleylamine, forming a selenium precursor; combining
the antimony precursor with the selenium precursor to form a first
solution; causing a reaction; quenching the reaction with a solvent
having a low boiling point; and, in response to quenching the
reaction in the first solution, forming antimony selenide nanorods,
having a length in a range of 30 to 50 nanometers (nm), a diameter
in a range of 5 to 15 nm.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention generally relates to methods of chemical
synthesis and, more particularly, to methods for synthesizing
antimony selenide nanostructures in a variety of shapes.
[0003] 2. Description of the Related Art
[0004] In the current development of modern photovoltaics there is
a significant demand for new materials that can potentially act as
a substitute for conventional silicon. Such research and
development has given rise to the cadmium telluride (CdTe) and
copper indium gallium selenide (CIGS) solar cells, based on thin
films technology. Moreover, hybrid organic/inorganic perovskite
materials have recently emerged as sensitized architectures as a
result of the constant search and evaluation of new materials as
absorbers in solar cells.
[0005] Among the materials offering promise in the fabrication of
solar cells, antimony--based chalcogenides represent a special
subgroup. In comparison to many other materials, antimony--based
chalcogenides are relatively non-toxic, earth abundant, and quite
stable. The nature of their binary composition should suggest
relatively simple antimony sulfide and antimony selenide
preparation and handling methods. The physical properties of
antimony chalcogenides, particularly the positions of the
conduction and valence bands relative to the band structures of
conventional electron and hole transporting materials, make them
appealing candidates for photovoltaics. In addition, antimony
sulfide has the advantage of an optical band gap of around 1.6
electronvolts (eV), making this material an almost ideal candidate
for the tandem solar cells. In contrast, antimony selenide is a
narrower band gap semiconductor material suitable as an absorber in
single junction solar cells.
[0006] In particular, the most common application of antimony
sulfide and antimony selenide relies on a sensitized architecture
involving the mesoporous titania scaffold. Such a mesoscopic
architecture provides some tolerance to the materials quality.
Moreover, the band structure of both antimony semiconductors allows
for the fabrication of solid sensitized solar cells. Such a device
structure permits a device photovoltaic performance of up to 8.4%.
However, as of yet, thin film antimony selenide solar cells have
not demonstrated such efficiency. It is currently assumed that the
poorer performance of antimony selenide is due to the defect states
formed during the materials preparation or poor interface
formation, even though selenide has been shown to produce
significant photocurrents (ACS Appl. Mater. Interfaces, 2014, 6
(4), pp 2836-2841).
[0007] Due to the seemingly simple methods of preparation suggested
by the binary nature of the material, the most common approaches
for the formation of the antimony selenide have included the
electrodeposition of both elements, or a chemical bath deposition.
In both cases, the forming materials are initially amorphous and
require an additional annealing step for conversion into a
crystalline semiconductor phase. Those techniques generally provide
materials with the diminished quality, resulting in the poor
performances in solar cells, which mostly originates from the
random distribution of the crystallites and defects within the
absorber material of a solar cell.
[0008] It would be advantageous if antimony chalcogenide structures
could be fabricated with a greater detail of control over their
shapes and crystallinity.
SUMMARY OF THE INVENTION
[0009] Antimony chalcogenides such as antimony sulfide, antimony
selenide, and antimony telluride have shown promise as materials
for the fabrication of the solar cells. However, the conventional
methodologies for their preparation have resulted in a poor quality
of the materials, often due lack of control. Disclosed herein are
methods that permit the production of various antimony chalcogenide
nanostructures having a high quality, suitable for potential
application in photovoltaics or other similar fields. In addition,
these synthetic methods can potentially be used to prepare light
emitting nanostructures based on antimony
sulfide/selenide/telluride, for use in lighting and display
applications.
[0010] Accordingly, a method is provided for controlling the shape
of antimony selenide (Sb.sub.2Se.sub.3) nanostructures. The method
dissolves an antimony (III) salt in a first amount of carboxylic
acid, forming an antimony precursor. In one aspect, antimony (III)
chloride is dissolved in oleic acid. Separately, selenourea is
dissolved in oleylamine, forming a selenium precursor. The antimony
precursor is combined with the selenium precursor to form a first
solution and cause a reaction. The reaction is quenched with a
solvent having a low boiling point. In response to quenching the
reaction in the first solution, antimony selenide nanorods are
formed, having a length in the range of 150-200 nanometers (nm) and
a diameter in the range of 20 to 30 nm.
[0011] In one aspect prior to quenching, phosphine oxide (e.g.,
tri-n-octylphosphine (TOPO)) is added to the first solution,
forming a second solution. Then, in response to quenching the
reaction in the second solution, antimony selenide nanocrystals are
formed having a size in a range of 1 to 5 nm.
[0012] In another aspect, 1-octadecene (ODE) and oleylamine are
added to the antimony precursor, creating a first amount of a first
modified antimony precursor. The first modified antimony precursor
is combined with a second amount of selenium precursor to form a
third solution. Then, in response to quenching the reaction in the
third solution, antimony selenide hollow spheres are formed having
an outside diameter in a range of 5 to 15 nm.
[0013] Alternatively, if the first amount of first modified
antimony precursor is combined with a third amount of selenium
precursor, greater than the second amount, a fourth solution is
formed. In response to quenching the reaction in the fourth
solution, antimony selenide nanoparticles are formed having a
diameter in a range of 5 to 15 nm.
[0014] In another variation, the antimony precursor is formed by
dissolving the antimony (III) salt in a second amount of carboxlic
acid, greater than the first amount, and adding ODE to create a
second modified antimony precursor. The second modified antimony
precursor is combined with the selenium precursor to form a fifth
solution. Then, in response to quenching the reaction in the fifth
solution, antimony selenide nanorods are formed, having a length in
the range of 30 to 50 nm, and a diameter in the range of 5 to 15
nm.
[0015] Additional details of the above-summarized synthesis methods
are presented below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIGS. 1 and 2 are drawings representing TEM images of a
sample of Sb.sub.2Se.sub.3 (0620) at low magnification (FIG. 1) and
at high magnification (FIG. 2) showing the lattice fringes.
[0017] FIG. 3 is a flowchart illustrating a method for controlling
the shape of antimony selenide (Sb.sub.2Se.sub.3)
nanostructures.
[0018] FIG. 4 is a drawing representing the TEM analysis of
antimony selenide sample 0702.
[0019] FIG. 5 is a drawing representing a TEM image of
Sb.sub.2Se.sub.3 sample 0927 showing a hollow nanosphere.
[0020] FIG. 6 is a drawing representing a TEM image of an antimony
selenide nanorod.
[0021] FIG. 7 is a flowchart summarizing the steps depicted in FIG.
2.
[0022] FIG. 8 is a flowchart illustrating a method for synthesizing
antimony selenide (small) nanocrystals.
[0023] FIG. 9 is a flowchart illustrating a method for synthesizing
antimony selenide nanostructures.
[0024] FIG. 10 is a flowchart illustrating a method for
synthesizing antimony selenide (short) nanorods.
DETAILED DESCRIPTION
[0025] Different approaches can be applied for the selective
synthesis of antimony selenide nanostructures. Although not
explicitly described, similar principles can be applied towards the
preparation of antimony sulfide or antimony telluride. It should be
noted that the methods disclosed herein are the first known example
of the direct colloidal chemical synthesis of antimony
chalcogenides. The selective preparation is based upon the proper
choice of the starting material as well as reaction media.
Different surfactants, present in the reaction solution, which can
be specifically introduced or obtained through the decomposition of
the precursors, dictate the growth of the nanostructures in
particular directions. Herein is presented the preparation of the
nanorods, nanocrystals, and nano-hollow spheres.
[0026] One procedure for antimony selenide nanorod preparation can
be described as follows: a 200 mg of antimony (III) chloride is
dissolved in 3 milliliters (mL) of oleic acid at 150.degree. C. In
a separate vial, 100 milligrams (mg) of selenourea
(SeC(NH.sub.2).sub.2) is dissolved in 1 mL of oleylamine at
200.degree. C. Upon forming a dark red solution, the vial is cooled
down to 100.degree. C. Then, antimony precursor is heated to about
180.degree. C. and the selenium precursor is quickly injected into
the reaction mixture. After 10 seconds the reaction is quenched by
the additional of 5 mL of toluene. The product (sample 0620) of the
reaction is an ensemble of nanorods, which is unambiguously
confirmed by transmission electron microscope (TEM).
[0027] As used herein, quenching is a rapid cooling treatment that
prevents the occurrence of low-temperature processes, such as phase
transformations, by only providing a narrow window of time in which
a reaction is both thermodynamically favorable and kinetically
accessible. It is the quenching process that stops the formation of
the antimony selenide reaction at the stage of a particular
tailored nanostructure. A (chemical) reaction is a process that
leads to the transformation of one set of chemical substances to
another. Classically, chemical reactions encompass changes that
only involve the positions of electrons in the forming and breaking
of chemical bonds between atoms, with no change to the nuclei (no
change to the elements present), and can often be described by a
chemical equation. The substance (or substances) initially involved
in a chemical reaction are called reactants or reagents. Chemical
reactions are usually characterized by a chemical change, and they
yield one or more products, which usually have properties different
from the reactants.
[0028] A colloid is one of three primary types of mixtures, with
the other two being a solution and suspension. A colloid is a
solution that has particles, ranging between 1 and 1000 nanometers
in diameter, that are able to remain evenly distributed throughout
the solution. These are also known as colloidal dispersions because
the substances remain dispersed and do not settle to the bottom of
the container. In colloids, one substance is evenly dispersed in
another. The substance being dispersed is referred to as being in
the dispersed phase, while the substance in which it is dispersed
is in the continuous phase.
[0029] A precursor is a compound that participates in the chemical
reaction that produces another compound.
[0030] A product is a substance that is formed during a chemical
reaction.
[0031] Carboxylic acids are oxoacids having the structure
RC(.dbd.O)OH. The term is used as a suffix in systematic name
formation to denote the --C(.dbd.O)OH group including its carbon
atom.
[0032] FIGS. 1 and 2 are drawings representing TEM images of a
sample of Sb.sub.2Se.sub.3 (0620) at low magnification (FIG. 1) and
at high magnification (FIG. 2) showing the lattice fringes. TEM
analysis reveals the formation of the nanorods of antimony
selenide. As used herein, a nanorod is defined as having a shape
with a length greater than its other two dimensions. The
cross-section is defined by the crystal structure of the material.
The crystallinity of the final material was found to be perfect
(FIG. 2). The sizes of the nanorods estimated by TEM images average
150-200 nm in length and 25 nm in width. Some smaller nanorods were
also found with a length of about 50 nm. The growth of the nanorods
can be controlled by the reaction time and the ratio of the
reactants. A variation of the temperature in such a procedure leads
to either bulk-type precipitate (at higher temperatures) or the
formation of an amorphous material (at lower temperatures).
[0033] FIG. 3 is a flowchart illustrating a method for controlling
the shape of antimony selenide (Sb.sub.2Se.sub.3) nanostructures.
Although the method is depicted as a sequence of numbered steps for
clarity, the numbering does not necessarily dictate the order of
the steps. It should be understood that some of these steps may be
skipped, performed in parallel, or performed without the
requirement of maintaining a strict order of sequence. Generally
however, the method follows the numeric order of the depicted
steps. However, as explained in more detail below, different
nanostructures require slight modifications to the methods
described immediately below. The method starts at Step 200.
Long Nanorods (Micro-Rods)
[0034] Step 202 provides antimony (III) salt. Step 204 dissolves
the antimony (III) salt in a first amount of carboxylic acid (e.g.,
oleic acid), forming an antimony precursor. In one aspect, the
antimony (III) salt is dissolved at a temperature in the range of
130 to 170.degree. C. As used herein, the dissolution of a solid
(e.g., an antimony (III) salt) into a liquid or other solvent is a
process by which these original solid state become a solute
(dissolved component), forming a solution of the solid in the
original solvent. In the case of a crystalline solid dissolving in
a liquid, crystalline structure must disintegrate such that the
separate atoms, ions, or molecules are released. Step 206 dissolves
selenourea in oleylamine, forming a selenium precursor. In one
aspect, selenourea is dissolved in oleylamine at a temperature in
the range of 180 to 220.degree. C.
[0035] Step 208 combines the antimony precursor with the selenium
precursor to form a first solution. In one aspect, Step 208 forms
the first solution at a temperature in. a range of 160 to
200.degree. C. Step 210 causes a reaction. Step 212 quenches the
reaction with a solvent having a low boiling point. Step 214, in
response to quenching the reaction in the first solution, forms
antimony selenide nanorods, having a length in the range of 150-200
nm and a diameter in the range of 20 to 30 nm.
[0036] More explicitly, Step 204 may form the antimony precursor by
dissolving, proportionally, 200 mg of antimony (III) chloride in 3
mL of oleic acid at 150 degrees C. Step 206 may form the selenium
precursor by dissolving, proportionally, 100 mg of selenourea with
1 mL of oleylamine at 200 degrees C., and then cooling to 100
degrees C. Step 208 may form the first solution by heating the
antimony precursor to 180 degrees C. and injecting it into the
selenium precursor kept at the 100 degree C. temperature. Step 210
helps cause the reaction by stirring the first solution for 10
seconds, and Step 212 quenches the reaction by adding toluene to
the first solution.
Small Nano Crystals
[0037] As an alternative to the synthesis procedure used for the
preparation of antimony selenide nanorods, sample 0702 was prepared
at lower temperature (about 100.degree. C.) with the addition of
tri-n-octylphosphine oxide (TOPO) (0.75 g) in the reaction. TOPO is
a well-known surface ligand used for the preparation of the quantum
dots, which was expected to suppress nanorod formation and growth.
After quenching, no precipitation or any sign of aggregation was
observed.
[0038] Phosphines are PH.sub.3, and compounds are derived from it
by substituting one, two, or three hydrogen atoms with hydrocarbyl
groups R.sub.3P, RPH.sub.2, R.sub.2PH, and R.sub.3P (R.noteq.H) are
called primary, secondary, and tertiary phosphines, respectively.
One specific phosphine is named as a substituted phosphane, e.g.
CH.sub.3PH.sub.2 methylphosphane. Phosphine oxides are compounds
having the structure R.sub.3P.dbd.O mesomer-arrow
R.sub.3P.sup.+--O.sup.-.
[0039] FIG. 4 is a drawing representing the TEM analysis of
antimony selenide sample 0702. The analysis reveals that the
reaction mixture consists of: a) extra-small nanocrystals with a
size of 1-2 nm, and b) a significant amount of the amorphous
aggregates which were seen during antimony selenide synthesis. A
nanocrystal is a material particle having at least one dimension
smaller than 100 nanometers (a nanoparticle) and composed of atoms
in either a single- or poly-crystalline arrangement. The results
confirmed that low temperatures and the addition of TOPO are the
key factors in preparing this type of nano-material. Thus, the
modification of the standard procedure (Steps 202 to 214) by the
addition of TOPO leads to inhibited growth of the forming
particles. This result also suggests that TOPO may he a good
passivating ligand for nanoparticles of that type. To summarize, by
adding or eliminating TOPO, either nanorods or ultra-small
nanoparticles of antimony selenide can be synthesized.
[0040] Returning to FIG. 3, prior to quenching (Step 212), Step 209
adds phosphine oxide (e.g., tri-n-octylphosphine (TOPO)) to the
first solution, forming a second solution. In response to quenching
the reaction in the second solution, Step 216 forms antimony
selenide nanocrystals having a size in a range of 1 to 5 nm. For
example, Step 209 adds phosphine oxide to the first solution by
combining phosphine oxide, the antimony precursor, and the selenium
precursor at a temperature in a range of 80 to 120.degree. C.
[0041] In one aspect, Step 204 forms the antimony precursor by
dissolving, proportionally, 200 mg of antimony (III) chloride in 3
mL of oleic acid at 150 degrees C. Step 206 may form the selenium
precursor by dissolving, proportionally, 100 mg of selenourea with
1 mL of oleylamine at 200 degrees C., and then cooling to 100
degrees C. Step 208 may form the first solution by heating the
antimony precursor to 100 degrees C. and injecting it into the
selenium precursor kept at the 100 degree C. temperature. Step 209
adds, proportionally, 0.75 grams (g) of TOPO to the first
solution.
[0042] Alternatively, 0.132 grams (g) of antimony(III) chloride,
0.72 mL of oleylamine, 0.56 mL of oleic acid, and 6.3 mL of
1-octadecene (ODE) were placed in 3-neck round bottom flask
equipped with the stirring bar and thermocouple in the glovebox.
The flask was closed, removed from the glovebox and heated under
vacuum at 130.degree. C for 30 minutes using a heating mantle. The
reaction was pumped and purged three times with nitrogen (N.sub.2)
and the temperature was slowly raised to 150.degree. C. under
vacuum, then switched to N.sub.2 and heated to 180.degree. C. At
this time the solution appeared clear. Meanwhile, a solution
containing 0.15 g of selenourea in 1.25 mL of oleylamine was
prepared in the glovebox at 150.degree. C. The selenium
(Se)-containing precursor was quickly injected into the reaction
flask at 180.degree. C and the reaction was immediately quenched by
the injection of 3 mL of hexane. The reaction mixture (sample 0919)
was analyzed by scanning TEM (STEM). Due to the presence of the
excess ligand, TEM did not provide any reliable information, but
STEM images showed the presence of the ultra-small nanocrystals
around 1 nm size.
Hollow Spheres
[0043] To obtain nanocrystals of a larger size or different shape,
the injection temperature was lowered to 170.degree. C. and the
reaction time was extended to 10 seconds (sample 0927), which
technically should improve the growth of the material, although too
low of a temperature may promote the formation of amorphous
material. The TEM images revealed the formation of hollow
microspheres with a diameter of about 10 nm.
[0044] FIG. 5 is a drawing representing a TEM image of
Sb.sub.2Se.sub.3 sample 0927 showing a hollow nanosphere. Among the
hollow nanospheres a few nanocrystals were found as well as the
bi-product of the reaction (not shown on the figure). The prepared
sample can be purified by the addition of ethanol and the resulting
precipitated particles can be dispersed in toluene.
[0045] Returning to FIG. 2, Step 205a adds 1-octadecene (ODE) and
oleylamine to the antimony precursor, creating a first amount of a
first modified antimony precursor. Then, Step 208 combines the
first modified antimony precursor with a second amount of selenium
precursor to form a third solution. In response to quenching the
reaction in the third solution, Step 218 forms antimony selenide
hollow spheres having an outside diameter in a range of 5 to 15 nm.
As used herein, a hollow sphere or hollow nanosphere has a
spherical shape with an outside diameter, an antimony selenide
shell, and a hollow inside diameter. The inside and outside
diameters are in the range of 1 to 100 nm, with the inside diameter
being at least 1 nm smaller than the outside diameter.
[0046] In one aspect, Step 208 combines the first amount of first
modified antimony precursor with the second amount of selenium
precursor at a temperature of in the range of 180 to 200 degrees C.
In another aspect, creating the first amount of first modified
antimony precursor in Step 205a includes combining, proportionally,
0.132 g of antimony (III) chloride, 0.72 mL of oleylamine, 0.56 mL
of oleic acid, and 6.3 mL of ODE, heating at a temperature of 130
degrees C. for 30 minutes, and then heating to 180 degrees C. Step
206 forms the selenium precursor by dissolving, proportionally,
0.16 g of selenourea with 1.25 mL of oleylamine at 150 degrees C.,
and then cooling to 100 degrees C. Step 208 forms the third
solution by keeping the selenium precursor at 100 degrees C. and
injecting it into the 180 degree C. temperature first modified
antimony precursor, and Step 212 quenches the reaction by adding
hexane to the third solution.
Larger Nanocrystals
[0047] In order to facilitate the formation of nanocrystals or
quantum dots of antimony selenide, the amount of selenium precursor
was increased to 200 mg and, using the same conditions, sample 1018
was prepared. The results obtained by TEM showed the formation of
the nanoparticles of a size of around 10 nm. Thus, Step 208
combines the first amount of first modified antimony precursor with
a third amount of selenium precursor, greater than the second
amount, to form a fourth solution. In response to quenching the
reaction in the fourth solution, Step 220 forms antimony selenide
nanoparticles having a diameter in a range of 5 to 15 nm.
[0048] In one aspect, creating the first amount of first modified
antimony precursor (Step 205a) includes combining, proportionally,
0.132 g of antimony (III) chloride, 0.72 mL of oleylamine, 0.56 mL
of oleic acid, and 6.3 mL of ODE, heating at a temperature of 130
degrees C. for 30 minutes, and then heating to 180 degrees C. Step
206 forms the selenium precursor by dissolving, proportionally, 0.2
g of selenourea with 1.25 mL of oleylamine at 150 degrees C., and
then cooling to 100 degrees C. Step 208 forms the third solution by
keeping the selenium precursor solution at 100 degrees C. and
injecting it into the 180 degree C. temperature first modified
antimony precursor, and Step 212 quenches the reaction by adding
hexane to the third solution.
Short Nanorods
[0049] FIG. 6 is a drawing representing a TEM image of an antimony
selenide nanorod. By eliminating the oleylamine in the initial
mixture and increasing the amount of oleic acid, sample 1026 was
prepared. TEM images of the sample revealed nanorods with about a
10 nm diameter and about 30-50 nm in length. The elemental
composition of sample 1026 was obtained using energy-dispersive
X-ray spectroscopy (EDX). Thus, the presence of oleylamine allows
for control the morphology to enable the formation of nanocrystals.
Such a discovery allows for the controlled growth of antimony
selenide nanocrystals. The composition of the nanorods was measured
using EDX and found to he Sb.sub.2Se.sub.4.8, which suggests that
the surface of the nanorods was Se-rich.
[0050] In this aspect Step 204 forms the antimony precursor by
dissolving the antimony (III) salt in a second amount of carboxlic
acid, greater than the first amount, and Step 205b adds ODE to
create a second modified antimony precursor. Step 208 combines the
second modified antimony precursor with the selenium precursor and
forms a fifth solution. In response to quenching the reaction in
the fifth solution, Step 222 forms antimony selenide nanorods,
having a length in the range of 30 to 50 nm, a diameter in the
range of 5 to 15 nm.
[0051] In one aspect, Steps 204 and 205b can be merged so that the
second modified antimony precursor is formed by combining,
proportionally, 0.132 g of antimony (III) chloride, 0.56 mL of
oleic acid, and 6.3 mL of ODE, heating at a temperature of 130
degrees C. for 30 minutes, and then heating to 180 degrees C. Step
206 forms the selenium precursor by dissolving, proportionally,
0.16 of selenourea with 1.25 mL of oleylamine at 150 degrees C.,
and then cooling to 100 degrees C. Step 208 forms the fifth
solution by keeping the selenium precursor at 100 degrees C. and
injecting it into the 180 degree C. temperature antimony precursor.
Step 212 quenches the reaction by adding hexane to the fifth
solution.
[0052] In summary, the combination of oleic acid and oleylamine is
important for the control of the particle size and morphology. In
particular, increasing the amount of oleic acid with respect to
oleylamine, leads to the formation of the nanorods instead of
nanocrystals. Evaluations were made where the amount of oleylamine
was made significantly higher than in the original (long nanorod)
procedure. The amount of oleylamine loaded into the reaction
mixture was doubled, and the reaction was carried out in the
exactly same fashion as before. The samples prepared by this
procedure were analyzed by TEM, which revealed that under the same
conditions, the presence of the additional.
[0053] amount of oleylamine significantly inhibits the growth of
the nanoparticles.
[0054] Thus, the present disclosure demonstrates the tunability of
the synthetic route for the preparation of antimony selenide
nanoparticles. Although not explicitly demonstrated, the same
synthesis procedures can be used for the preparation of the
antimony sulfide and antimony telluride as well.
[0055] FIG. 7 is a flowchart summarizing the steps depicted in FIG.
2. Step 700 represents the standard procedure for the formation of
the longer nanorods (Steps 202 to 214, FIG. 2), which may also be
referred to as micro-rods. If TOPO is added in Step 702,
nanocrystalline seeds, which are defined as nanocrystals with a
size of 1-2 nm, are formed in Step 704 (Steps 202 to 216, FIG. 2).
If octadecene is made the primary solvent in Step 706, the result
is hollow spheres (nanospheres) in Step 708 (Steps 202 to 218, FIG.
2). By increasing the selenium precursor in Step 710, the result is
nanocrystals in Step 712 (Steps 202 to 220, FIG. 2). The
nanocrystals of Step 712 are larger in size than those formed in
Step 704. By eliminating oleylamine and increasing the oleic acid
in the Step 714, the result is the nanorods of Step 716 (Steps 202
to 222, FIG. 2). The nanorods of Step 716 are smaller than the ones
formed using the standard procedure of Step 700.
[0056] FIG. 8 is a flowchart illustrating a method for synthesizing
antimony selenide (small) nanocrystals. The method begins at Step
800. Step 802 provides antimony (III) salt. Step 804 dissolves the
antimony (III) salt in carboxylic acid, forming an antimony
precursor. Step 806 dissolves selenourea in oleylamine, forming a
selenium precursor. Step 808 combines the antimony precursor with
the selenium precursor to form a first solution. Step 810 adds
phosphine oxide to the first solution, forming a second solution.
Step 812 causes a reaction. Step 814 quenches the reaction with a
solvent having a low boiling point. Step 816, in response to
quenching the reaction in the second solution, forms antimony
selenide nanocrystals having a size in a range of 1 to 5 nm. More
explicit details of this method have been presented above.
[0057] FIG. 9 is a flowchart illustrating a method for synthesizing
antimony selenide nanostructures. The method begins at Step 900.
Step 902 provides antimony (III) salt. Step 904 dissolves the
antimony (III) salt in carboxylic acid with oleylamine and ODE,
forming an antimony precursor. Step 906 dissolves selenourea in
oleylamine, forming a first amount of selenium precursor. Step 908
combines the antimony precursor with the first amount of selenium
precursor to form a first solution. Step 910 causes a reaction.
Step 912 quenches the reaction with a solvent having a low boiling
point. In response to quenching the reaction in the first solution.
Step 914 forms antimony selenide hollow spheres having an outside
diameter in a range of 5 to 15 nm.
[0058] In one aspect, Step 908 combines the antimony precursor with
a second amount of selenium precursor, greater than the first
amount of selenium precursor. In response to quenching the reaction
in the first solution, Step 916 forms antimony selenide
nanoparticles having a diameter in a range of 5 to 15 nm. More
explicit details of this method have been presented above.
[0059] FIG. 10 is a flowchart illustrating a method for
synthesizing antimony selenide (short) nanorods. The method begins
at Step 1000. Step 1002 provides antimony (III) salt. Step 1004
dissolves the antimony (III) salt in carboxylic acid with ODE,
forming an antimony precursor. Step 1006 dissolves selenourea in
oleylamine, forming a selenium precursor. Step 1008 combines the
antimony precursor with the selenium precursor to form a first
solution. Step 1010 causes a reaction. Step 1012 quenches the
reaction with a solvent having a low boiling point. In response to
quenching the reaction in the first solution, Step 1014 forms
antimony selenide nanorods, having a length in a range of 30 to 50
nm, diameter in a range of 5 to 15 nm.
[0060] Antimony selenide synthesis methods have been provided that
permit the shape of the resulting nanostructures to be "tuned".
Examples of particular experiments and component ratios have been
presented to illustrate the invention. However, the invention is
not limited to merely these examples. Although antimony selenide
structures are described in detail, the methods also apply to
antimony sulfide and antimony telluride structure synthesis. Other
variations and embodiments of the invention will occur to those
skilled in the art.
* * * * *