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Title: (Electron transfer rates at semiconductor/liquid interfaces)

Abstract

Work has focused on several aspects of the fundamental chemistry and physics semiconductor/liquid junction behavior. These projects have been directed primarily towards GaAs/liquid contacts, because GaAs/liquid systems provide high energy conversion efficiencies and offer an opportunity to gain mechanistic understanding of the factors that are important to control in an efficient photoelectrochemical energy conversion system.

Authors:
Publication Date:
Research Org.:
California Inst. of Tech., Pasadena, CA (United States). Div. of Chemistry and Chemical Engineering
Sponsoring Org.:
USDOE; USDOE, Washington, DC (United States)
OSTI Identifier:
7237506
Report Number(s):
DOE/ER/13932-T2
ON: DE92018559
DOE Contract Number:
FG03-88ER13932
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 14 SOLAR ENERGY; LIQUIDS; INTERFACES; PHOTOCURRENTS; TIME DEPENDENCE; SEMICONDUCTOR MATERIALS; SURFACES; PASSIVATION; AMINES; CHEMISORPTION; DYE LASERS; ELECTROCHEMICAL ENERGY CONVERSION; GALLIUM ARSENIDES; PHOTOELECTROCHEMICAL CELLS; PROGRESS REPORT; RECOMBINATION; THIOLS; ARSENIC COMPOUNDS; ARSENIDES; CHEMICAL REACTIONS; CONVERSION; CURRENTS; DOCUMENT TYPES; ELECTRIC CURRENTS; ELECTROCHEMICAL CELLS; ENERGY CONVERSION; EQUIPMENT; FLUIDS; GALLIUM COMPOUNDS; LASERS; LIQUID LASERS; MATERIALS; ORGANIC COMPOUNDS; ORGANIC SULFUR COMPOUNDS; PNICTIDES; SEPARATION PROCESSES; SOLAR EQUIPMENT; SORPTION; 400400* - Electrochemistry; 400500 - Photochemistry; 140505 - Solar Energy Conversion- Photochemical, Photobiological, & Thermochemical Conversion- (1980-)

Citation Formats

Lewis, N.S.. (Electron transfer rates at semiconductor/liquid interfaces). United States: N. p., 1992. Web. doi:10.2172/7237506.
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Lewis, N.S.. (Electron transfer rates at semiconductor/liquid interfaces). United States. doi:10.2172/7237506.
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Lewis, N.S.. Wed . "(Electron transfer rates at semiconductor/liquid interfaces)". United States. doi:10.2172/7237506. https://www.osti.gov/servlets/purl/7237506.
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@article{osti_7237506,
title = {(Electron transfer rates at semiconductor/liquid interfaces)},
author = {Lewis, N.S.},
abstractNote = {Work has focused on several aspects of the fundamental chemistry and physics semiconductor/liquid junction behavior. These projects have been directed primarily towards GaAs/liquid contacts, because GaAs/liquid systems provide high energy conversion efficiencies and offer an opportunity to gain mechanistic understanding of the factors that are important to control in an efficient photoelectrochemical energy conversion system.},
doi = {10.2172/7237506},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Wed Jan 01 00:00:00 EST 1992},
month = {Wed Jan 01 00:00:00 EST 1992}
}
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Technical Report:
View Technical Report (0.88 MB)
DOI:  10.2172/7237506
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  • Work has focused on several aspects of the fundamental chemistry and physics semiconductor/liquid junction behavior. These projects have been directed primarily towards GaAs/liquid contacts, because GaAs/liquid systems provide high energy conversion efficiencies and offer an opportunity to gain mechanistic understanding of the factors that are important to control in an efficient photoelectrochemical energy conversion system.

  • The primary focus of this research was to develop new spectroscopies applicable to the study of carrier dynamics at semiconductor surfaces. The progress made during the tenure of this grant includes the development of three novel techniques for surface studies: Surface Restricted Transient Grating Spectroscopy, Surface Acoustic Wave (SAW) spectroscopy, and Surface Space-charge Electro-optic Sampling. Further, these techniques were then applied to the study of carrier dynamics at n-TiO{sub 2} and n-GaAs interfaces. The primary results were that hole carrier reaction dynamics at TiO{sub 2} surfaces involves thermalized hole carriers at the surface on 100 psec time scales. A largemore » effective hole mass of TiO{sub 2} is found m{sub h} greater than 3m{sub e} which negates any possibility of hot hole transfer. In contrast, the studies at n-GaAs (100) surfaces found hole carrier transfer to be faster than 30 psec and appears to be direct, without the intermediacy of surface states. The hole carrier transport to the surface is found to be faster than 300 fsec and approaches the ballistic limit for transport. Therefore, the hole carriers do arrive with large amounts of excess energy at the surface. These results indicate that at least some fraction of the hole carriers are transferring unthermalized. The importance of this in solar energy collection is that this work supports, at least from a fundamental standpoint, the possibility of exploiting hot carriers to avoid thermal energy loss mechanisms and enhance conversion efficiency. These studies are the first to provide direct time resolved (not diffusion limited) studies of surface reaction dynamics. In addition, the approach provides the highest possible resolution for studying surface reactions in the time domain. The specific results for both TiO{sub 2} and GaAs surface will be discussed below. 32 refs., 1 fig.« less

  • The major emphasis of this research program has been to determine the mechanism of electron transfer at an abrupt phase discontinuity defined by a conducting surface. The key issue is the strength of the electronic coupling between the delocalized band states and the electronic levels of an adsorbed molecule on the surface. The use of semiconductor liquid junctions provides an ideal system for addressing this question. Optical excitation at above band gap wavelengths can be used to prepare the system at the adiabatic crossing point for electron transfer, i.e., directly at the transition state. This method enables a femtosecond viewmore » of the time evolution of the transition state. In the past year, we have examined the carrier reaction dynamics at (100) GaAs single crystal surfaces. The major focus has been on determining the fundamental surface state trapping rate constants at oxide induced surface states. This is the main competing channel for direct interfacial charge transfer and needs to be fully characterized. The key question in the case of surface state trapping are: (1) What is the mechanism of electronic coupling between surface traps and the band states and (2) What is the time scale for the trapping. 5 refs.« less

  • To study the dynamics of surface electron transfer processes, three, highly surface specific, optical probes have been developed in conjunction with semiconductor liquid junctions: surface restricted transient gratings, optically generated surface acoustic waves, and in-situ electro-optic sampling of surface space charge fields. These three optical probes have been employed to measure interfacial carrier population dynamics, interface structure and carrier thermalization, and surface transport respectively at TiO/sub 2/(001) and GaAs(100) interfaces. 3 refs., 3 figs.

  • No abstract prepared.