Process for preparing a nanocrystalline material

Details Process for preparing a nanocrystalline material Process for preparing a nanocrystalline material

1998-09-09

2002-04-30

Griffin, Steven P. (Department: 1754)

Chemistry of inorganic compounds

Treating mixture to obtain metal containing compound

Group va metal or arsenic

C423S092000, C423S101000, C423S122000, C423S509000, C423S566100

Reexamination Certificate

active

06379635

ABSTRACT:

The present invention relates to a process. In particular, the present invention relates to a process for synthesising nanocrystalline materials, such as nanocrystalline CdSe.
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. (D. Duonghong et al.,
J. Am. Chem. Soc
. 1982, 104, 2977, R. Rossetti et al.,
J. Chem. Phys
., 1984, 80, 4464, A. Henglein,
Chem. Rev
., 1989, 89, 1861, M. L. Steigerwald and L. E. Brus,
Acc. Chem. Res
., 1990, 23, 183, Y. Wang and N. Herron,
J. Phys. Chem
. 1991, 95, 49, H. Weller,
Adv. Mater
. 1993, 5, 88, A. Hagfeldt and M. Gratzell,
Chem. Rev
. 1995, 95, 49, L. E. Brus,
J. Chem. Phys
. 1984, 80, 4403, L. Brus,
J. Phys. Chem
. 1986, 90, 2555, P. E. Lippens and M. Lannoo,
Phys. Rev
. B 1989, 39, 10935 and Y. Nosaka,
J. Phys. Chem
. 1991, 95, 5054.)
Interest in research into new synthetic routes for semiconductor nanocrystallites is now enhanced as devices based on such materials have been fabricated. (V. L. Colvin, et al., Nature 1994, 39, 10935, B. O. Dabbousi et al.,
Appl. Phys. Lett
., 1995, 66, 1317 and R. S. Urquhart et al.,
Langmuir
, 1995, 11, 1127.) A number of synthetic methods have been reported for the preparation of a wide range of semiconductor nanoparticles (D. Duonghong et al.,
J. Am. Chem. Soc
. 1982, 104, 2977, R. Rossetti et al.,
J. Chem. Phys
., 1984, 80, 4464, A. Henglein,
Chem. Rev
., 1989, 89, 1861, M. L. Steigerwald and L. E. Brus,
Acc. Chem. Res
., 1990, 23, 183, Y. Wang and N. Herron,
J. Phys. Chem
. 1991, 95, 49, H. Weller,
Adv. Mater
. 1993, 5, 88, A. Hagfeldt and M. Gratzell,
Chem. Rev
. 1995, 95, 49, Y. Wang and N. Herron,
J. Phys. Chem
. 1987, 91, 257, H. J. Watzke and J. N. Fendler,
J. Phys. Chem
., 1987, 91, 854, P. C. Sercel et al.,
Appl. Phys. Lett
. 1992, 61, 696, V. Sankaran et al.,
Chem. Mater
. 1993, 5, 1133, A. Mews et al.,
J. Phys. Chem
. 1994, 98, 934, O. V. Salata et al.,
Appl. Phys. Lett
. 1994, 65, 189, M. L. Steigerwald et al.,
J. Am. Chem. Soc
. 1998, 110, 3046, A. R. Kortan et al.,
J. Am. Chem. Soc
. 1990, 112, 1327 and J. G. Brerman et al.,
J. Am. Chem. Soc
. 1989, 111, 4141.)
Known processes for preparing nanocrystalline materials, such as nanocrystalline CdSe, have included arrested precipitation in micelles (M. L. Steigerwald et al) or the reaction of molecular species at high temperature in organic solvents. (A. R. Kortan et al.,
J. Am. Chem. Soc
. 1990, 112, 1327, J. G. Brenman et al.,
J. Am. Chem. Soc
. 1989, 111, 4141, C. B. Murray et al.
J. Am. Chem. Soc
., 1993, 115, 8706 and J. E. Bowen Katari et al.,
J. Phys. Chem
. 1994, 98, 4109.)
In more detail, Murray et al 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
3
)
2
Cd in TOP (tri-n-octylphosphine) into a hot solution of TOP containing Se (TOPSe and TOP). Alternatively, any one of (TMS)
2
S (bis(trimethylsilyl)sulphide), (TMS)
2
Se (bis(trimethylsilyl)selenide), and (BDMS)
2
Te (bis(tert-butyldimethylsilyl)tellurium) may be used instead of TOPSe.
In the Murray process (CH
3
)
2
Cd is chosen as the only Cd source. Moreover, Murray et al state that (TMS)
2
Se or TOPSe and TOPTe are selected as chalcogen sources with TOPSe and TOPTe preferred due to their ease of preparation and their stability.
Chemical reactions in TOPO (tri-n-octylphosphine oxide) are also described by (C. B. Murray et al.). These processes have been used to prepare nanocrystallites of II/VI semiconductors (V. L. Colvin et al, B. O. Dabbousi et al, C. B. Murray et al and J. E. Bowen Katari et al.). In this instance, TOPO is used as dispersing medium and a metal source (e.g Cd(CH
3
)
2
) and a chalcogenide source (e.g. TOPSe) are injected into the hot TOPO (typically at 250° 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. (C. B. Murray et al and J. E. Bowen Katari et al.)
A refinement of the Murray process has been proposed by (J. E. Bowen Katari et al). 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
3
)
2
Cd is then added. The resultant (CH
3
)
2
Cd/Se solution is then added to a heated solution of TOPO.
As with the Murray process, in the Katari process (CH
3
)
2
Cd is chosen as the only Cd source.
There are however problems associated with the prior art processes for preparing nanocrystalline materials. For example, both the Murray process (C. B. Murray et al) and the Katari process (J. E. Bowen Katari et al) involve the use of hazardous chemicals, in particular (CH
3
)
2
Cd. In this regard, (CH
3
)
2
Cd is toxic, volatile and extremely difficult to handle. Moreover, on exposure to air it undergoes spontaneous combustion.
Aside from using the hazardous compound Cd(CH
3
)
2
(V. L. Colvin et al and B. O. Dabbousi et al) to prepare nanocrystalline CdSe, other workers have used the equally hazardous H
2
Set (R. S. Urquhart et al) for the synthesis of the CdSe.
The present invention seeks to overcome the problems associated with the prior art processes for making nanocrystalline materials.
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.
According to a second aspect of the present invention there is provided a nanocrystalline material obtained by the process of the present invention.
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.
Preferably the metal ion is a divalent metal ion or a trivalent metal ion.
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.
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.
Preferably the second ion is or is part of a thiol-carbamate group or a seleno-carbamate group.
Preferably the second ion is or is part of a dithiol-carbamate group or a diseleno-carbamate group.
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.
Preferably the organic group is an alkyl group, which may be substituted and/or unsaturated.
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.
Preferably the organic group is a di-C
1-6
alkyl group and/or the thio group is a dithio group or a diseleno group.
Preferably the organic group is a diethyl group.
Preferably the dispersing medium is at a temperature of 250° C. or more, preferably about from 300° C. to 350° C.
Preferably the dispersing medium passivates the surface of the nanocrystalline material.
Preferably the dispersing medium is TOPO, or a related coordinating medium, including combinations thereof. Another dispersing medium could be TBP.
Preferably the nanocrystalline materia

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