ISSN:0021-2148    

DOI:10.1002/ijch.199300001

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe effect of size on the electronic structure of semiconductor clusters is discussed and the evolution of the absorption spectrum with cluster size is quantitatively modeled using pseudopotentials.

ISSN:0021-2148    

DOI:10.1002/ijch.199300002

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThis article reviews recent experiments on the band edge luminescence of 32‐Å‐diameter, near‐wurtzite CdSe particles. Time, wavelength, and polarization resolution of the emission reveal a complex kinetics where the hole is mobile on the surface. A model is outlined involving strong resonance between three‐dimensional quantized internal states and the intrinsic surface states due to reconstruction. The hole appears to localize on the surface within abou

ISSN:0021-2148    

DOI:10.1002/ijch.199300003

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractGaAs quantum dots have been prepared by reacting gallium acetylacetonate with trimethylsilylarsine in triethylene glycol ether at 216 K. The colloidal dispersion of GaAs nanocrystals has been characterized by transmission electron microscopy, electron diffraction, ultrafiltration, optical absorption and photoluminescence spectroscopy, and transient pump‐probe spectroscopy; the spectral data were also fitted to a model that accounts for the size‐dependent optical properties of a Gaussian distribution of particle sizes. Our results indicate that the spectral region above 470 nm can be assigned solely to GaAs nanocrystals having a mean diameter of 40.0 Å with a standard deviation of 9.7 Å. The origin of spectral features below 470 nm has not yet been determined conclus

ISSN:0021-2148    

DOI:10.1002/ijch.199300004

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractA study of the dynamics of the electronic states of CdS semiconductor clusters grown in situ in reversed micelles via picosecond pump‐probe technique reveals efficient transient bleaching of the excitonic absorption. This effect is attributable mainly to hole localization near the trapped electron, with no evidence of electron ejection (forming a solvated electron) detectable despite the apparent proximity of the cluster to the included water pool. Bleaching efficiency is cluster‐size dependent, and recovery kinetics are governed by the nature of the particle surface. Similar decay behavior is observed in cluster fluorescence. Generally, the decay is characterized by two components, the faster attributed to recombination of a mobile, detrapped electron with a trapped hole, and the slower to an exchange interaction between trapped carriers. The observed strong multiexponentionality of the decay results from a distribution in trap energy levels, as well as from a distribution of distances between traps on the cluster surface. By varying preparation conditions, particles of different sizes with different surface defects can be grown in reversed micelles in a reproducible way so that their electronic properties can be control

ISSN:0021-2148    

DOI:10.1002/ijch.199300005

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractWe report that two 10‐Å [Cd20S13(SPh)22]−8clusters may be fused together to form a 13‐Å CdS cluster, which shows a sharp absorption peak at 370 nm and a luminescence peak at 390 nm. This is supported by the concentration dependence of the absorption spectra, the luminescence‐excitation spectra, the capillary zone electrophoresis separation, the electrochemical measurement, and the powder X‐ray data. This cluster fusion process occurs naturally in solution at high concentrations of [Cd20S13(SPh)22]−8. It can also be induced electrochemically by a two‐electron oxidation process. We also show that capillary zone electrophoresis and electrochemical synthesis are two useful new techniques for obtaining monodisperse CdS clusters. Their potentials and limitation

ISSN:0021-2148    

DOI:10.1002/ijch.199300006

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractMethodologies for the in situ generation of size‐quantized semiconductor particulate films (SQSPFs) are described. Cadmium, zinc, lead, and copper sulfides have been generated from their divalent metal ion precursors electrostatically attached to well‐compressed, negatively charged monolayers by the infusion of hydrogen sulfide. Cadmium selenide has been generated at positively charged dioctadecyldimethylammonium bromide monolayers floating on an aqueous subphase which contained appropriate concentrations of sodium selenosulfate and cadmium nitrilotriacetate. SQSPFs have been characterized by absorption spectra, electron microscopy, scanning tunneling microscopy, X‐ray diffraction, and electrochemical measurements. Evidence is presented for the oriented growth and preparation‐dependent rectification behavior of

ISSN:0021-2148    

DOI:10.1002/ijch.199300007

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractSurface modification as well as size control of CdS colloids in acetonitrile has been achieved with mercaptoethylamine (MEA). The CdS emission yield increases as it interacts with the surface modifier. A decrease in the hole‐trapping yield was observed in optically excited CdS colloids which were modified with MEA. Use of such surface modifiers in bridging a semiconductor colloid with a gold colloid has also been demonstrate

ISSN:0021-2148    

DOI:10.1002/ijch.199300008

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractSeveral methods for the control of semiconductor particle sizes, in particular in the quantum size regime, are surveyed. Rational choice of solvent polarity, reaction temperature, concentration of reactants, solution pH, and counterions will determine the size and size distribution of the particles. Sizes of colloidal particles formed in microheterogeneous environments will often be predetermined by the dimensions of the micropores and cavities within the network of the medium. This is the situation in zeolite and clay cavities, and in polymer networks. Self‐aggregation of amphiphillic molecules often generates microdomains which may be utilized to direct the particle precursors or the particles themselves into these domains and thus limit their growth. Finally, complexation at the surface of the particles may limit and control the growth processes of the particles. The latter approach also allows functional modification of the particles' surfac

ISSN:0021-2148    

DOI:10.1002/ijch.199300009

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractOptical properties of extremely small metal chalcogenide particles that exhibit quantization effects have been examined. For extremely small semiconductor clusters with low effective carrier mass, optical absorption edges are shifted by several volts as a result of quantization effects that increase the effective bandgap of particles. Injection of electrons or holes into quantized semiconductor colloidal particles was studied by the pulse radiolysis technique. The reducing potential of photogenerated carriers was found to be greatly enhanced in quantized semiconductor particles, compared to the corresponding bulk material. Excess electrons trapped on the surface lead to a blue‐shift in the absorption edge of colloids. The appearance of this shift depends critically on the method of colloid preparation. The presence of OH−ions in PbS, CdS, and CdTe colloidal solutions blocks the sites where electrons are trapped and shortens the lifetime of bleaching, whereas in a slightly acidic solution long‐lived bleaching was observed. Different spectroscopic properties were found for hole excess and OH adducts of hydrous titanium oxides as a consequence of the existence of different environmental conditions of Ti(IV) atoms at the surface. The position where hole injection occurs lies in the mid‐gap level of 25

ISSN:0021-2148    

DOI:10.1002/ijch.199300010

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY