U.S. patent application number 09/043258 was filed with the patent office on 2001-06-28 for process for preparing a nanocrystalline material.
This patent application is currently assigned to Paul O'Brien. Invention is credited to O'BRIEN, PAUL, TRINDADE, TITO.
Application Number | 20010005495 09/043258 |
Document ID | / |
Family ID | 10780775 |
Filed Date | 2001-06-28 |
United States Patent
Application |
20010005495 |
Kind Code |
A1 |
O'BRIEN, PAUL ; et
al. |
June 28, 2001 |
PROCESS FOR PREPARING A NANOCRYSTALLINE MATERIAL
Abstract
A process for preparing a nanocrystalline material comprising at
least a first ion and at least a second ion different from the
first ion, and wherein at least the first ion is a metal ion, is
described. The process comprises contacting a metal complex
comprising the first ion and the second ion with a dispersing
medium suitable to form the nanocrystalline material and wherein
the dispersing medium is at a temperature to allow formation by
pyrolysis of the nanocrystalline material when contacted with the
metal complex.
Inventors: |
O'BRIEN, PAUL; (ESSEX,
GB) ; TRINDADE, TITO; (ICHAVO, PT) |
Correspondence
Address: |
THOMAS J KOWALSKI
FROMMER LAWRENCE & HAUG
745 FIFTH AVENUE
NEW YORK
NY
10151
|
Assignee: |
Paul O'Brien
|
Family ID: |
10780775 |
Appl. No.: |
09/043258 |
Filed: |
September 9, 1998 |
PCT Filed: |
August 9, 1996 |
PCT NO: |
PCT/GB96/01942 |
Current U.S.
Class: |
423/87 ;
257/E33.005; 423/101; 423/122; 423/509; 423/566.1; 423/92 |
Current CPC
Class: |
C01B 32/15 20170801;
C01P 2004/64 20130101; C01G 15/00 20130101; C01B 25/08 20130101;
C01P 2002/70 20130101; C01P 2004/22 20130101; B82Y 30/00 20130101;
H01L 31/1828 20130101; C01P 2006/60 20130101; C01P 2002/84
20130101; B82Y 40/00 20130101; Y02E 10/543 20130101; C01B 17/20
20130101; H01L 33/18 20130101; C01P 2002/85 20130101; H01L 31/032
20130101; C01P 2004/04 20130101; C01G 9/08 20130101; H01L 33/20
20130101; C01G 11/02 20130101; C01B 19/007 20130101; C01P 2002/80
20130101; C01P 2006/34 20130101 |
Class at
Publication: |
423/87 ; 423/92;
423/101; 423/122; 423/509; 423/566.1 |
International
Class: |
C01G 021/00; C01G
011/00; C01G 015/00; C01G 009/00; C01F 007/00; C01G 013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 15, 1995 |
GB |
9518910.6 |
Claims
1. A process for preparing a nanocrystalline material comprising at
least a first ion and at least a second ion different from the
first ion, and wherein at least the first ion is a metal ion, the
process comprising contacting a metal complex comprising the first
ion and the second ion with a dispersing medium suitable to form
the nanocrystalline material and wherein the dispersing medium is
at a temperature to allow formation by pyrolysis of the
nanocrystalline material when contacted with the metal complex.
2. A process according to claim I wherein the metal ion is a
divalent metal ion or a trivalent metal ion.
3. A process according to claim 1 or claim 2, wherein the metal ion
is selected from a cadmium ion, a zinc ion, a lead ion, a mercury
ion, an indium ion and a gallium ion, including combinations
thereof.
4. A process according to any one of the preceding claims wherein
the second ion is selected from an oxide ion, a selenide ion, a
sulphide group, a phosphide group or an arsenide ion, or
combinations thereof.
5. A process according to any one of the preceding claims, wherein
the second ion is or is part of a thiol-carbamate group or a
seleno-carbamate group.
6. A process according to claim 5, wherein the second ion is or is
part of a dithiol-carbamate group or a diseleno-carbamate
group.
7. A process according to any one of the preceding claims, wherein
the metal complex additionally comprises an organic group and/or a
thio group.
8. A process according to claim 7, wherein the organic group is an
alkyl group, which may be substituted and/or unsaturated.
9. A process according to claim 7 or claim 8, wherein the organic
group is a dialkyl group, which may be substituted and/or
unsaturated, and/or wherein the thio group is a dithio group.
10. A process according to claim 9, wherein the organic group is a
di-Cl.sub.1-6alkyl group and/or the thio group is a dithio group or
a diseleno group.
11. A process according to claim 10, wherein the organic group is a
diethyl group.
12. A process according to any one of the preceding claims, wherein
the dispersing medium is at a temperature of 250.degree. C. or
more, preferably about from 300.degree. C. to 350.degree. C.
13. A process according to any one of the preceding claims, wherein
the dispersing medium passivates the surface of the nanocrystalline
material.
14. A process according to any one of the preceding claims, wherein
the dispersing medium is TOPO, or a related coordinating medium,
including combinations thereof.
15. A process according to any one of the preceding claims, wherein
the nanocrystalline material comprises or is selected from any one
of cadmium selenide, cadmium sulphide, zinc selenide, zinc
sulphide, indium phosphide and gallium arsenide, including ternary
and quaternary combinations thereof.
16. A process according to any one of the preceding claims, wherein
the nanocrystalline material is cadmium selenide.
17. A process according to any one of the preceding claims, wherein
the metal complex is diethyl diselenocarbamato cadmium or dithio
diselenocarbamato cadmium, or related mixed alkyl complexes
thereof.
18. A nanocrystalline material obtained by the process according to
any one of the preceding claims.
19. A device comprising a nanocrystalline material according to
claim 18.
20. A device according to claim 19 wherein the device is an optical
device.
21. A device according to claim 19 or claim 20 wherein the device
is any one of a non-linear optic device, a solar cell or an
LED.
22. A device according to any one of claims 19 to 21 wherein the
device is an LED.
23. A process substantially as described herein.
Description
[0001] The present invention relates to a process. In particular,
the present invention relates to a process for synthesising
nanocrystalline materials, such as nanocrystalline CdSe.
[0002] Nanocrystalline materials, which are sometimes referred to
as nanoparticles, Q-particles, quantum dots or nanocrystallites,
have been recognised as suitable systems for studying the
transition from the molecular to the macrocrystalline level and
have been extensively studied in the recent years..sup.1-11
[0003] Interest in research into new synthetic routes for
semiconductor nanocrystallites is now enhanced as devices based on
such materials have been fabricated. .sup.12-14 A number of
synthetic methods have been reported for the preparation of a wide
range of semiconductor nanoparticles..sup.1-7,15-23
[0004] Known processes for preparing nanocrystalline materials,
such as nanocrystalline CdSe, have included arrested precipitation
in micelles.sup.21 or the reaction of molecular species at high
temperature in organic solvents..sup.22-25
[0005] In more detail, Murray et al .sup.22 report on the
preparation of CdE (where E is S, Se or Te) by the pyrolysis of two
organometallic reagents by injection into a hot coordinating
solvent. In particular, the Murray process involves injecting a
solution of (CH.sub.3).sub.2Cd in TOP (tri-n-octylphosphine) into a
hot solution of TOP containing Se (TOPSe and TOP). Alternatively,
any one of (TMS).sub.2S (bis(trimethylsilyl)sulp- hide),
(TMS).sub.2Se (bis(trimethylsilyl)selenide), and (BDMS).sub.2Te
(bis(tert-butyldimethylsilyl)tellurium) may be used instead of
TOPSe.
[0006] In the Murray process (CH.sub.3).sub.2Cd is chosen as the
only Cd source. Moreover, Murray et al state that (TMS).sub.2Se or
TOPSe and TOPTe are selected as chalcogen sources with TOPSe and
TOPTe preferred due to their ease of preparation and their
stability.
[0007] Chemical reactions in TOPO (tri-n-octylphosphine oxide) are
also described by Murray.sup.24. These processes have been used to
prepare nanocrystallites of II/VI semiconductors.sup.12,13,24,25.
In this instance, TOPO is used as dispersing medium and a metal
source (e.g Cd(CH.sub.3).sub.2) and a chalcogenide source (e.g.
TOPSe) are injected into the hot TOPO (typically at 250.degree. C.)
to form CdSe nanocrystallites. The size distribution of the
semiconductor can be controlled by the temperature of heating
during the synthesis and by size selective precipitation of the
final material..sup.24,25
[0008] A refinement of the Murray process has been proposed by
Katari et al.sup.23. As with the Murray process, in the Katari
process CdE is prepared by the pyrolysis of two organometallic
reagents by injection into a hot coordinating solvent. In the
Katari process Se is dissolved in TBP (tributylphosphine) to which
(CH.sub.3).sub.2Cd is then added. The resultant
(CH.sub.3).sub.2Cd/Se solution is then added to a heated solution
of TOPO.
[0009] As with the Murray process, in the Katari process
(CH.sub.3).sub.2Cd is chosen as the only Cd source.
[0010] There are however problems associated with the prior art
processes for preparing nanocrystalline materials. For example,
both the Murray process (ibid) and the Katari process (ibid)
involve the use of hazardous chemicals, in particular
(CH.sub.3).sub.2Cd. In this regard, (CH.sub.3).sub.2Cd is toxic,
volatile and extremely difficult to handle. Moreover, on exposure
to air it undergoes spontaneous combustion.
[0011] Aside from using the hazardous compound
Cd(CH.sub.3).sub.2.sup.12,1- 3 to prepare nanocrystalline CdSe,
other workers have used the equally hazardous H.sub.2Se.sup.14 for
the synthesis of the CdSe.
[0012] The present invention seeks to overcome the problems
associated with the prior art processes for making nanocrystalline
materials.
[0013] According to a first aspect of the present invention there
is provided a process for preparing a nanocrystalline material
comprising at least a first ion and at least a second ion different
from the first ion, and wherein at least the first ion is a metal
ion, the process comprising contacting a metal complex comprising
the first ion and the second ion with a dispersing medium suitable
to form the nanocrystalline material and wherein the dispersing
medium is at a temperature which allows formation of the
nanocrystalline material by pyrolysis when contacted with the metal
complex.
[0014] According to a second aspect of the present invention there
is provided a nanocrystalline material obtained by the process of
the present invention.
[0015] According to a third aspect of the present invention there
is provided a device comprising a nanocrystalline material obtained
by the process of the present invention.
[0016] Preferably the metal ion is a divalent metal ion or a
trivalent metal ion.
[0017] Preferably the metal ion is selected from a cadmium ion, a
zinc ion, a lead ion, a mercury ion, an indium ion and a gallium
ion, including combinations thereof.
[0018] Preferably the second ion is selected from an oxide ion, a
selenide ion, a sulphide group, a phosphide group or an arsenide
ion, or combinations thereof.
[0019] Preferably the second ion is or is part of a thiol-carbamate
group or a selenocarbamate group.
[0020] Preferably the second ion is or is part of a
dithiol-carbamnate group or a diselenocarbamate group.
[0021] Preferably the metal complex additionally comprises an
organic group and/or thio group. The organic group can be an alkyl
group or an aryl group, which may be substituted.
[0022] Preferably the organic group is an alkyl group, which may be
substituted and/or unsaturated.
[0023] Preferably the organic group is a dialkyl group, which may
be substituted and/or unsaturated, and/or wherein the thio group is
a dithio group.
[0024] Preferably the organic group is a di-C.sub.1-.sub.6alkyl
group and/or the thio group is a dithio group or a diseleno
group.
[0025] Preferably the organic group is a diethyl group.
[0026] Preferably the dispersing medium is at a temperature of
250.degree. C. or more, preferably about from 300.degree. C. to
350.degree. C.
[0027] Preferably the dispersing medium passivates the surface of
the nanocrystalline material.
[0028] Preferably the dispersing medium is TOPO, or a related
coordinating medium, including combinations thereof. Another
dispesing medium could be TBP.
[0029] Preferably the nanocrystalline material comprises or is
selected from any one of cadmium selenide, cadmium sulphide, zinc
selenide, zinc sulphide, indium phosphide and gallium arsenide,
including ternary and quaternary combinations thereof.
[0030] Preferably the nanocrystalline material is cadmium
selenide.
[0031] Preferably the metal complex is diethyl diselenocarbamato
cadmium or dithio diselenocarbamato cadmium, or related mixed alkyl
complexes thereof.
[0032] Preferably the device is an optical device.
[0033] Preferably the device is any one of a non-linear optic
device, a solar cell or an LED.
[0034] Preferably the device is an LED.
[0035] Preferably the device is a blue LED.
[0036] The present invention is therefore based on the surprising
finding that nanocrystalline materials can be prepared by using as
a reactant a metal complex which provides at least two of the ions
of the nanocrystalline material. The process of the present
invention is therefore very different to the Murray process (ibid)
and the Katari process (ibid) wherein in each of those processes it
is necessary to use two independent sources to provide at least two
of the ions of the nanocrystalline material. Thus, the use of a
molecular precursor containing both elements in the present process
provides an attractive route to metal selenides, especially if a
large scale preparation is anticipated.
[0037] The present invention is further advantageous over the prior
art processes as it does not rely on the use of hazardous chemicals
such as (CH.sub.3).sub.2Cd.
[0038] The present invention is further advantageous as it provides
a low cost route to prepare photovoltaic materials and
optoelectronic materials, preferable examples of which include
non-linear optic devices, solar cells and LEDs.
[0039] Thus the present invention shows that a single source can be
used in a dispersing medium, such as TOPO, to replace the use of
the hazardous metal alkyls. In a highly preferred embodiment, the
present invention provides the synthesis of CdSe nanocrystallites
using methyl diethyldiselenocarbamato cadmium (II) MeCddsc:
[(CH.sub.3)CdSe.sub.2CN(C.- sub.2H.sub.5).sub.2].sub.2) as a
precursor. The synthetic method of this preferred embodiment is
diagrammatically illustrated in FIG. 1, which makes no efforts to
represent a mechanistic pathway.
[0040] Even though the pathway shown in FIG. 1 is for the synthesis
of CdSe it is to be understood that the process of the present
invention is useful for preparing a series of nanocrystalline
materials.
[0041] Examples of nanocrystalline materials that can be prepared
using an appropriate single molecule precursor can be represented
by the general formulae A and B as shown below.
M.sup.IIE GENERAL FORMULA A
[0042] wherein M is Zn, Cd, Hg or a divalent transition metal; and
wherein E is O, S, Se, P, or As.
M.sup.IIII.sub.xE.sub.y GENERAL FORMULA B
[0043] wherein M is Al, In, Ga or a trivalent transition metal; and
wherein E is O, S, Se, P, or As; and wherein x and y are
appropriate intergers.
[0044] Formulae A and B also encompass related ternary systems.
[0045] Therefore, examples of nanocrystalline materials other than
cadmium selenide include cadmium sulphide, zinc selenide, zinc
sulphide, indium phosphide and gallium arsenide.
[0046] The general formula of the metal complex for use in the
process of the present invention can be represented as:
ML.sub.n FORMULA I
[0047] wherein M represents a metal ion; L represents one or more
ligands which need not be the same; n represents the valency of the
metal; and wherein M is the first ion of the nanocrystalline
material and at least one L provides the second ion for the
nanocrystalline material.
[0048] Typically M is a divalent metal ion or a trivalent metal
ion, such as any one of cadmium, zinc, lead, mercury, indium
gallium, including combinations thereof.
[0049] Typically L is any one of an oxide ion, a selenide ion, a
sulphide group, a phosphide group or an arsenide ion, or
combinations thereof. More in particular L is or is part of any one
of a thiol-carbamate group or a seleno-carbamate group such as a
dithiol-carbamate group or a diseleno-carbamate group.
[0050] In a preferred embodiment, at least one L is an organic
group and/or a thio group. If at least one L is an organic group
then preferably that organic is an alkyl group, which may be
substituted and/or unsaturated, such as a C.sub.1-10 (preferably
C.sub.1-6, more preferably C.sub.1-4) alkyl group, which may be
substituted and/or unsaturated.
[0051] Preferably, at least one L is a dialkyl group, which may be
substituted and/or unsaturated, and/or wherein the thio group is a
dithio group. Preferably, the organic group is a di-C.sub.1-6 alkyl
group and/or the thio group is a dithio group or a diseleno group.
In a highly preferred embodiment, at least one L is a diethyl
group.
[0052] Typical general formulae for suitable metal complexes
containing at least one organic group for use as single molecule
precursors in the process of the present invention are shown below
as Formula II (for metals that are divalent) and as Formula III
(for metals that are trivalent):
[R.sup.II-M.sup.II-(E.sub.xCNRR.sup.1).sub.y].sub.z FORMULA II
[(R.sup.II)(R.sup.III)-M.sup.III-(E.sub.xCNRR.sup.1).sub.y].sub.z
FORMULA III
[0053] wherein R, R.sup.1, R.sup.II and R.sup.III independently
represent an aryl or alkyl group as defined above, which may be
substituted and/or unsaturated; M.sup.II is a divalent metal ion;
M.sup.III is a trivalent metal ion; E is any one of an oxide ion, a
selenide ion, a sulphide group, a phosphide group or an arsenide
ion, or combinations thereof (such as, by way of example,
--O--S--); x is an integer, preferably 2; y is an integer; and z is
an integer, usually 1 or 2.
[0054] As mentioned above, a highly preferred metal complex
containing at least one organic group for use as a single molecule
precursor in the process of the present invention is methyl
diethyldiselenocarbamato cadmium (II) (MeCddsc) wherein R is
C.sub.2H.sub.5; R.sup.1 is C.sub.2H.sub.5; R.sup.II is (CH.sub.3);
M is Cd.sup.II; E is Se; x is 2; y is 1; and z is 2.
[0055] However, other preferred metal complexes containing at least
one organic group for use as single molecule precursors in the
process of the present invention include
M-(E.sub.2CNAlk.sub.2).sub.n FORMULA IV
[0056] wherein n is 2 for metals such as zinc, cadmium and lead; n
is 3 for metals such as gallium or indium; E is S or Se; and A is
an aryl or alkyl group, preferably ethyl; including carbamate (i.e.
O-donors) thereof: and either
R.sup.II-M-(E.sub.2CNA.sub.2).sub.n FORMULA V
[0057] or
(R.sup.II).sub.n-M-(E.sub.2CNA.sub.2) FORMULA VI
[0058] wherein n is 1 for metals such as zinc, cadmium and lead; n
is 2 for metals such as gallium or indium; E is S or Se; A is an
aryl or an alkyl group, preferably ethyl; and R.sup.II is
independently selected from an alkyl or aryl group as defined
above, such as methyl.
[0059] Other possible metal complexes for use as single molecule
precursors in the process of the present invention include related
thiolates, thiophosphinates or phosphinochalcogens and related
selenium containing compounds.
[0060] The present invention will now be described only by way of
examples. In the examples, reference is made to the attached
Figures wherein
[0061] FIG. 1 is a scheme of the synthetic method of CdSe
nanocrystallites using a single source;
[0062] FIG. 2 is an optical absorption spectrum of CdSe
nanocrystallites dispersed in toluene (fraction 3)--the inset shows
the particle size distribution of the same sample as determined by
TEM; and
[0063] FIG. 3 is a fluorescence emission spectra of size
fractionated CdSe (Xexc = 465 nm).
Experimental
1. Preparation of nanocrystalline cadmium selenide
[0064] 1.1 MeCddsc was synthesised by the comproportionation
reaction.sup.27 between Cd(CH.sub.3).sub.2 (Epichem) and
bisdiethyldiselenocarbamato cadmium (II) in dry toluene, at room
temperature, using Schlenk techniques and a nitrogen atmosphere.
The TOPO (90%, Aldrich) was purified using the method described in
the literature..sup.28 The identity of MeCddsc and the purity of
TOPO were checked by .sup.1H nmr and IR spectroscopy and melting
point measurements.
[0065] 1.2 MeCddsc (0.5 mmol) was placed in 10 ml of TOP (98%,
Aldrich) and the mixture formed was filtered after which was
injected in 30 g of TOPO at 200.degree. C. The temperature of the
solution was then raised to 250.degree. C. and heated for half an
hour. The deep red solution that formed was allowed to cool down to
75.degree. C. after which a large excess of dry CH.sub.3OH (BDH)
was added. A flocculate precipitate formed and was isolated by
centrifugation and redispersed in toluene, any insoluble material
was then discarded. The toluene was pumped off under vacuum
(10.sup.-2 Torr) to give a deep red material which was washed with
CH.sub.3OH. The solid was redispersed in toluene to give solutions
with a Port wine red colour which remained optically clear for
weeks. Size selective precipitation was performed by adding
CH.sub.3OH to this solution until turbidity was observed followed
by centrifugation the solid. This procedure was successively
applied to the supernatant solutions obtained during the
fractionation process until no optical absorption was detected.
[0066] 1.3 The toluene solutions containing the nanocrystallites
were characterised by optical absorption spectroscopy (Philips PU
8710 spectrophotometer) and fluorescence emission spectroscopy
(Perkin Elmer LS50 luminescence spectrometer), at room temperature.
The fluorescence spectra were normalized with the maximum set to
one hundred. The X-ray powder diffraction experiments were
performed using a Philips 1130 X-ray generator and a Guinier
camera. Conventional transmission electron microscopy (TEM) of the
nanocrystallites was performed using a JEOL-JEM 1200 EX II scanning
and transmission electron microscope, operating at 100 kV, on
samples deposited over carbon coated copper grids. The histogram
was obtained after measuring the diameter of around 300
nanoparticles shown on the TEM images. High resolution transmission
electron microscopy (HRTEM) was performed using a JEOL FX 2000
instrument, operating at 200 kV, on samples deposited over carbon
coated copper grids.
[0067] 1.4 The optical absorption spectrum of a toluene solution
containing nanodispersed CdSe obtained from the thermal
decomposition of MeCddsc is shown in FIG. 2. The absorption edge of
the spectrum is clearly blue shifted in relation to the bulk band
gap of CdSe (716 nm, 1.73 eV) suggesting the presence of
nanoparticles with sizes below the bulk exciton dimensions of CdSe.
The maximum observed in the optical spectrum of nanodispersed CdSe
has been associated with the lowest energy electronic transition
occurring in the CdSe nanocrystallites..sup.21-25
[0068] 1.5 The emission fluorescence spectra of different size
fractionated samples of CdSe are depicted in FIG. 3. The size
selective precipitation is based on the fact that the largest
particles are the first to precipitate, due to the stronger Van der
Waals interactions, on the addition of a non-solvent to the
nanodispersed material. Using this procedure it is possible to
obtain initial solid fractions richer in larger particles as
compared with the later fractions. The maximum of the emission band
in FIG. 3 is gradually blue shifted as the size distributions
become weighted of smaller dimensions particles. Such shifts on the
band edge (FIG. 2) and band maximum (FIG. 3) in the absorption and
emission spectra, respectively, have been reported as an evidence
of quantum size effects..sup.1-7
[0069] 1.6 The fluorescence spectrum of fraction 3 corresponds to
the optical absorption spectrum in FIG. 2. The emission band
maximum is observed at a wavelength close to the absorption edge of
the optical spectrum (band edge emission); the typical red emission
due to the recombination of charge carriers on deep traps located
at the particles surface was not detected. These results suggest
that surface coverage with TOPO molecules should have occurred on
the CdSe nanocrystallites..sup.2,24-26 The energy dispersive
analysis X-ray results (EDAX) for CdSe nanocrystallites (after
several washings with methanol) still show the presence of
phosphorous, suggesting that the TOPO molecules are quite firmly
bond to the CdSe nanocrystallites.
[0070] 1.7 The dark red powder obtained from the synthesis gave an
X-ray diffraction pattern consistent with hexagonal CdSe. The TEM
image of the fraction 3 of CdSe giving the spectra in FIG. 2 and
FIG. 3 was studied. The mean particle diameter of the
nanocrytalline material was found to be 51.9.+-.7.4 Angstroms. The
TEM results show that the CdSe nanocrystallites are approximately
spherical and close to monodispersed. On the basis of the effective
mass approximation.sup.4 the excitonic peak located at 568 nm (2.18
eV) suggests the presence of CdSe nanoparticles with a diameter
close to 57 Angstroms, discrepancies between the experimentally
measured particle diameter and the predictions of the effective
mass approximation have been reported by other authors..sup.24
[0071] 1.8 The crystallinity of the CdSe nanoparticles was
confirmed by HRTEM. The HRTEM images showed the typical hexagonal
pattern of the wurtzite structure for some of the particles in
agreement with the X-ray powder diffraction results. The analysis
of several images are consistent with the presence of some CdSe
nanocrystallites with stacking faults. This type of defect for CdSe
nanocrystallites has been reported by other authors.sup.24.
Alivisatos et al..sup.25 reported the synthesis of CdSe
nanocrystallites, using a TOPO method at higher temperatures for
which no stacking faults were detected.
2. Preparation of nanocrystalline indium sulihide
[0072] 2.1 Initially Me.sub.2InS.sub.2CNEt.sub.2 was prepared by a
comproportionation reaction between stoichiometric amounts of
tris(diethyldithiocarbarmato)indium(III) (5.7 g, 10.2 mmol) and
trimethylindium (3.3 g) in toluene (40 mL). The mixture was stirred
at room temperature for half an hour and then heated to 50.degree.
C. and stirred for further 10 min. On concentration, white crystals
settled out from the clear solution (7.90 g, 88%), mp 84.degree.
C.
[0073] 2.2 The compound prepared by the process of 2.1 was then
used to replace MeCddsc in Section 1.2 (supra). The product,
nanocrystalline indium sulphide, was then analysed using the
methods outlined in Sections 1.4-1.8 (supra).
3. Preparation of nanocrystalline gallium sulhide
[0074] 3.1 Initially Me.sub.2GaS.sub.2CNEt.sub.2 was prepared by a
comproportionation reaction between stoichiometric amounts of
tris(diethyldithiocarbarmato)gallium(III) and trimethylgallium in
toluene (40 mL). The mixture was stirred at room temperature for
half an hour and then heated to 50.degree. C. and stirred for
further 10 min. On concentration, crystals settled out from the
solution.
[0075] 3.2 The compound prepared by the process of 3.1 was then
used to replace MeCddsc in Section 1.2 (supra). The product,
nanocrystalline gallium sulphide, was then analysed using the
methods outlined in Sections 1.4-1.8 (supra).
4. Preparation of other precursors for the preparation of
nanocrystalline indium sulphide and nanocrystalline gallium
sulphide
[0076] 4.1 The precursor molecules described in Sections 2.1 and
3.1 could be respectively replaced with
Et.sub.2InS.sub.2CNEt.sub.2, Np.sub.2InS.sub.2CNEt.sub.2,
Et.sub.2GaS.sub.2CNEt.sub.2, and Np.sub.2GaS.sub.2CNEt.sub.2. In
this regard these compounds were prepared by the following general
protocol, which refers to the preparation of Et.sub.2InS.sub.2CNEt,
though of course the other compounds are prepared by use of similar
and appropriate reactants.
[0077] 4.2 Et.sub.2InS.sub.2CNEt.sub.2 was prepared by adding
sodium diethyldithiocarbarmate (2.73 g, 15.97 mmol) to a solution
of chlorodiethylindium (3.33 g, 15.97 mmol) in ether (60 mL) and
stirred for 12 h at room temperature. A white solid (NaCl) formed
during the reaction which was removed by filtration. The colourless
filtrate containing the product was evaporated to dryness under
vacuum. The solid product contained traces of salt and was
dissolved in petroleum spirits (60-80.degree. C.) and filtered. The
filtrate, on concentration, gave white crystals of
diethyldiethyldithiocarbamatoindium (III) (3.33 g, 65%), mp
57.degree. C.
[0078] 4.3 As mentioned above, Np.sub.2InS.sub.2CNEt.sub.2 was
prepared in a similar manner and was obtained as a white
crystalline solid (2.97 g, 70%), mp 44.degree. C.
[0079] 4.4 As mentioned above, Et.sub.2GaS.sub.2CNEt.sub.2 (4.51 g,
75%) and Np.sub.2GaS.sub.2CNEt.sub.2 (3.25 g. 72%), both liquids,
were prepared in a similar manner.
[0080] 4.5 The compounds of 4.1 to 4.4 were then used to replace
MeCddsc in Section 1.2 (supra). The respective nanocrystalline
products were then analysed using the methods outlined in Sections
1.4-1.8 (supra).
5. Preparation of nanocrystalline zinc sulphide
[0081] 5.1 Initially [Zn[S.sub.2CNMe.sup.1Pr].sub.2].sub.2 was
prepared as follows. A mixture of "zinc hydroxide" (4.77 g, 48
mmol), N-methylisopropylamine (10 ml, 96 mmol) and carbon
disulphide (5.76 ml, 96 mmol) were suspended in ethanol and stirred
at ca. 60.degree. C. for 2 hours. On cooling, the reaction mixture
was filtered affording a white solid which was then dried at room
temperature in vacuo and recrystallised from acetone. Yield 11.7 g,
67.6%.
[0082] 5.2 The compound prepared by the process of 5.1 was then
used to replace MeCddsc in Section 1.2 (supra). The product,
nanocrystalline zinc sulphide, was then analysed using the methods
outlined in Sections 1.4-1.8 (supra).
6. Preparation of nanocrystalline cadmium sulphide
[0083] 6.1 Initially [Cd[S.sub.2CNMe.sup.1Pr].sub.2].sub.2 was
prepared as follows. A mixture of cadmium hydroxide,
N-methylisopropylamine and carbon disulphide were suspended in
ethanol and stirred at ca. 60.degree. C. for 2 hours. On cooling,
the reaction mixture was filtered affording a solid which was then
dried at room temperature in vacuo and recrystallised from
acetone.
[0084] 6.2 The compound prepared by the process of 6.1 was then
used to replace MeCddsc in Section 1.2 (supra). The product,
nanocrystalline cadmium sulphide, was then analysed using the
methods outlined in Sections 1.4-1.8 (supra).
7. Preparation of nanocrystalline zinc arsenide
[0085] 7.1 Initially [Zn[As.sub.2CNMe.sup.1Pr].sub.2].sub.2 was
prepared by appropriately adapting the process of Section 5.1
(supra).
[0086] 7.2 The compound prepared by the process of 7.1 was then
used to replace MeCddsc in Section 1.2 (supra). The product,
nanocrystalline zinc arsenide was then analysed using the methods
outlined in Sections 1.4-1.8 (supra).
8. Preparation of nanocrystalline cadmium arsenide
[0087] 8.1 Initially [Cd[As.sub.2CNMe.sup.1Pr].sub.2].sub.2 was
prepared by appropriately adapting the process of Section 6.1
(supra).
[0088] 8.2 The compound prepared by the process of 8.1 was then
used to replace MeCddsc in Section 1.2 (supra). The product,
nanocrystalline cadmium arsenide was then analysed using the
methods outlined in Sections 1.4-1.8 (supra).
9. Preparation of further nanocrystalline materials
[0089] 9.1 The following compounds were used to replace MeCddsc in
Section 1.2 (supra). The respective nanocrystalline materials were
then analysed using the methods outlined in Sections 1.4-1.8
(supra).
[0090] 9.2 The following commentary describes the preparation of
(C.sub.5H.sub.11).sub.2GaP.sup.tBu.sub.2, however the process can
be appropriately adapted for the preparation of
(C.sub.5H.sub.11).sub.2Indiu- mP.sup.tBu.sub.2,
(C.sub.5H.sub.11).sub.2GalliunAsBu.sub.2, and
(C.sub.5H.sub.11).sub.2IndiumAsBu.sub.2.
[0091] 9.3 To prepare (C.sub.5H.sub.11).sub.2GaP.sup.tBu.sub.2,
LiP.sup.tBu.sub.2 was initially prepared by the addition of
HP.sup.tBu.sub.2(5 g, 33.4 mmol) to a stirred solution of
.sup.nBuLi (14.24 cm.sup.3 of 2.5 M solution in hexanes, 35.6 mmol)
diluted further with petroleum spirits (60-80.degree. C., 50
cm.sup.3, 0.degree. C.). The solution was left to stir overnight,
concentrated, and then left to crystallise.
(C.sub.5H.sub.11).sub.2GaCl(2) (2.56 g, 10.34 mmol) was dissolved
in ether (60 cm.sup.3) and stirred at 0.degree. C.
LiP.sup.tBu.sub.2 (1.57 g, 10.33 mmol) was slowly added and the
mixture was allowed to reach ambient temperature. After stirring
overnight, the solvent was removed under vacuum leaving a white
solid. Petroleum spirits (60-80.degree. C.) (30 cm.sup.3) were
added to the solid. After decanting the supernatant, the solution
was concentrated and left to crystallise at --25.degree. C.
Colourless, triangular shaped crystals formed, yield 3.12 g, (84
%), m.p. 81.degree. C.
10. Summary
[0092] The results reported here clearly show that nanocrystalline
materials such as nanocrystalline MeSe can be easily prepared from
molecular compounds such as MeCddsc. Moreover, these prepared
nanocrystalline materials can be used as or in high quality
semiconductors.
[0093] Other modifications of the present invention will be
apparent to those skilled in the art.
REFERENCES
[0094] 1. D. Duonghong, J. Ramsden and M. Gratzell, J. Am. Chem.
Soc. 1982,104, 2977.
[0095] 2. R. Rossetti, J. L. Ellison, J. M. Gibson and L. E. Brus,
J Chem. Phys., 1984, 80, 4464.
[0096] 3. A. Henglein, Chem. Rev., 1989, 89, 1861.
[0097] 4. M. L. Steigerwald and L. E. Brus, Acc. Chem. Res., 1990,
23, 183.
[0098] 5. Y. Wang and N. Herron, J Phys. Chem. 1991, 95, 525.
[0099] 6. H. Weller, Adv. Mater. 1993, 5, 88.
[0100] 7. A. Hagfeldt and M. Gratzell, Chem. Rev. 1995, 95, 49.
[0101] 8. L. E. Brus, J Chem. Phys. 1984, 80, 4403.
[0102] 9. L. Brus, J Phys. Chem. 1986, 90, 2555.
[0103] 10. P. E. Lippens and M. Lannoo,Phys. Rev.B 1989, 39,
10935.
[0104] 11. Y. Nosaka, J Phys. Chem. 1991, 95, 5054.
[0105] 12. V. L. Colvin, M. C. Schiamp, A. P. Alivisatos, Nature
1994, 370, 354.
[0106] 13. B. O. Dabbousi, M. G. Bawendi, O. Onitsuka and M. F.
Rubner, Appl. Phys. Lett., 1995, 66, 1317.
[0107] 14. R. S. Urquhart, D. Neil Furlong, T. Gengenbach, N. J.
Geddes and F. Grieser, Langmuir, 1995, 11, 1127.
[0108] 15. Y. Wang and N. Herron, J Phys. Chem. 1987, 91, 257.
[0109] 16. H. J. Watzke and J. N. Fendler, J. Phys. Chem. 1987, 91,
854.
[0110] 17. P. C. Sercel, W. A. Saunders, H. A. Atwater, K. J.
Vahala, and R. C. Flagan, Appl. Phys. Lett. 1992, 61, 696.
[0111] 18. V. Sankaran, J. Yue, R. E. Cohen, R. R. Schrock and R.
J. Silbey, Chem. Mater., 1993, 5, 1133.
[0112] 19. A. Mews, A. Eychmuller, M. Giersig, D. Schooss and H.
Weller, J. Phys. Chem. 1994, 98, 934.
[0113] 20. O. V. Salata, P. J. Dobson, P. J. Hull and J. L.
Hutchison, Appl. Phys. Lett. 1994, 65, 189.
[0114] 21. M. L. Steigerwald, A. P. Alivisatos, J. M. Gibson, T. D.
Harris, R. Kortan, A.
[0115] M. Muller, A. M. Thayer, T. M. Duncan, D. C. Douglas and L.
E. Brus, J. Am. Chem. Soc. 1988, 110, 3046.
[0116] 22. A. R. Kortan, R. Hull, R. L. Opila, M. G. Bawendi, M. L.
Steigerwald, P. J. Carroll and L. E. Brus, J Am. Chem. Soc. 1990,
112, 1327.
[0117] 23. J. G. Brenman, T. Siegrist, P. J. Carroll, M.
Stuczynski, L. E. Brus and M. L. Steigerwald, J Am. Chem. Soc.
1989, 111, 4141.
[0118] 24. C. B. Murray, D. J. Norris and M. G. Bawendi, J Am.
Chem. Soc., 1993, 115, 8706.
[0119] 25. J. E. Bowen Katari, V. L. Colvin and A. P. Alivisatos, J
Phys. Chem. 1994, 98, 4109.
[0120] 26. N. Chestnoy, T.D. Harris, R. Hull, and L.E. Brus, J
Phys. Chem., 1986, 90, 3393.
[0121] 27. M. B. Hursthouse, M. Azad Malik, M. Motevalli and P.
O'Brien, Polyhedron, 1992, 11, 45.
[0122] 28. G. W. Mason, S. McCarthy and D. F. Peppard, J Inorg.
Nuclear Chem., 1960, 12, 315.
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