Showing papers by "Nathan S. Lewis published in 1993"
TL;DR: In this article, a theoretical model is developed to describe the basic currentvoltage properties of semiconductor contacts, with emphasis on the contrasts between ideal and observed behavior, using the concepts from this model, the characteristics of a variety of SINR contacts are evaluated.
Abstract: Critical comparisons are drawn between the basic electrical properties of semiconductor/metal, semiconductor/liquid, and semiconductor/conducting polymer junctions. A theoretical model is developed to describe the basic current-voltage properties of semiconductor contacts, with emphasis on the contrasts between ideal and observed behavior. Using the concepts from this model, the characteristics of a variety of semiconductor contacts are evaluated. The discussion focuses on the following semiconductors: Si, GaAs, InP, and II-VI compounds based on the Cd-(chalcogenide) materials.
35 citations
TL;DR: In this paper, a spin-cast of poly-RCOT (R = alkyl, tert-butoxy, trimethylsilyl, and p-X-phenyl) was used to obtain reversible electrochemistry for both reductive and oxidative doping.
Abstract: : High molecular weight, amorphous, partially substituted polyacetylenes (poly-RCOT) have been prepared using the ring-opening metathesis polymerization of substituted cyclooctetraenes. Spin-cast films of these polymers yielded unusually sharp, well-defined reversible electrochemistry for oxidative and reductive doping processes. As the substituent on the polymer chain was varied (R = alkyl, tert-butoxy, trimethylsilyl, and p-X-phenyl), the potentials for oxidative and reductive doping changed by 0.3 V. In addition, the separation between the oxidative and reductive doping processes varied from 1.66 V to > 2.0 V. Coulometry suggested that the reversible doping step represented a transfer of 1 electron for every 13-15 double bonds of the polymer. In contrast, the electrochemistry of predominantly- cis poly-RCOT films was irreversible, and indicated the presence of an electrochemical cis-trans isomerization on the first voltammetric sweep through either reductive or oxidative doping. Spectroelectrochemical studies indicated that the electrochemically doped poly- RCOT materials R=sec-butyl, (CH3)3Si) possessed mid-gap transitions at energies of 0.8-0.9 eV. The redox chemistry of the soluble, poly-RCOT (R=sec-butyl, (CH3) 3Si) species in CH2Cl2 solution was also investigated. Voltammetric studies showed that both the reductive and oxidative doping processes were chemically irreversible, and indicated that the dissolved polymers were electroactive over a wide range of potentials.
31 citations
TL;DR: The role of the chemisorbed metal in the n-GaAs/M/KOH-Se[sup [minus]]/2[minus](aq) system is, therefore, best described as catalyzing interfacial charge transfer at the semiconductor/liquid interface, as opposed to establishing a semiconductor or metal or semiconductor-insulator/metal contact that is exposed to, but not influenced by, the electrolyte solution.
Abstract: The current-voltage properties of n-GaAs photoanodes have been evaluated in KOH-Se[sup [minus]]/2[minus]/(aq), CH[sub 3]CN-Fe[sup +]/0, and CH[sub 3]CN-MV[sup 2+]/+ solutions. Chemisorption of transition-metal ions (Rh[sup III], Co[sup III], Ru[sup III], Os[sup III]) onto n-GaAs has been shown previously to effect improved photoanode behavior for n-GaAs/KOH-Se[sup [minus]]/2[minus](aq) contacts, but it is not clear whether the chemisorbed metal forms a buried semiconductor/metal junction or results in a hybrid semiconductor/metal/liquid contact. After chemisorption of transition-metal ions, n-GaAs photoanodes displayed different open circuit voltages in contact with each electrolyte solution investigated. The role of the chemisorbed metal in the n-GaAs/M/KOH-Se[sup [minus]]/2[minus](aq) system is, therefore, best described as catalyzing interfacial charge transfer at the semiconductor/liquid interface, as opposed to establishing a semiconductor/metal or semiconductor/insulator/metal contact that is exposed to, but not influenced by, the electrolyte solution. 65 refs., 6 figs., 2 tabs.
22 citations
TL;DR: In this paper, the luminescence decay dynamics of thin epilayer GaAs samples under high level injection conditions were monitored in contact with KOHSe^(-/2-)(aq) solutions.
Abstract: n-GaAs/KOHSe^(-/2-)(aq) contacts have been studied using real time photoluminescence decay techniques. This system is of interest because metal ion chemisorption improves the steady-state current-voltage properties of GaAs/KOH-Se^(-/2-)(aq)/Pt cells, yielding 16% efficiency under simulated 1-sun illumination conditions. In this work, the luminescence decay dynamics of thin epilayer GaAs samples under high level injection conditions were monitored in contact with KOHSe^(-/2-)(aq) solutions. The photoluminescence signals decayed more rapidly after metal ion chemisorption than after a fresh etch, indicating that the metal ion treatment induced a more active recombination and/or charge-transfer process than the etch. A finite-difference simulation was used to model the decays and to extract a minority carrier surface recombination velocity, S_(min), for these systems. For etched GaAs surfaces, S_(min) = 5 X 10^3 cm s^(-1), while GaAs surfaces that had been etched and then exposed to 0.010 M Co(NH_3)_6^(3+) (pH = 11) solutions displayed S_(min) = 2 X 10^5 cm s^(-1). Qualitatively similar behavior was observed for Rh-, Ru-, and Os-treated GaAs surfaces as well. These data are fully consistent with prior suggestions that the primary effect of metal ion chemisorption is to increase the rate of hole transfer to the Se^(-/2-)(aq) electrolyte, as opposed to decreasing surface recombination processes at the GaAs/liquid contact.
16 citations
TL;DR: In this article, small signal photocurrent transients have been measured for n-Si/CH_3OH-Me_2Fc^(+/0)/Pt cells and they decayed in <10 µs and were limited by the series resistance of the cell in combination with the space charge capacitance of the semiconductor.
Abstract: Small signal photocurrent transients have been measured for n-Si/CH_3OH-Me_2Fc^(+/0)/Pt, n-Si/Au/CH_3OH-Me_2Fc^(+/0)/Pt, n-Si/Pt/NaOH(aq)/Ni(OH)_2/Ni, n-TiO_2/NaOH(aq)/Ni(OH)_2/Ni, and n-TiO_2/NaOH(aq)-Fe(CN)_6^(3-/4-)/Pt cells. Even though the radio-frequency and microwave conductivity signals for photoexcited n-Si/CH_3OH-Me_2Fc^(+/0) contacts persist for > 100 µs, the photocurrent transients for these interfaces decayed in <10 µs and were limited by the series resistance of the cell in combination with the space-charge capacitance of the semiconductor. An equivalent circuit model is presented and physically justified in order to explain this behavior. The model is also used to elucidate the conditions under which photocurrent transients at semiconductor electrodes can be expected to yield information regarding the faradaic charge-transfer rate across the semiconductor/liquid interface.
14 citations
01 Jan 1993
7 citations
TL;DR: In this paper, animals are being produced on subjects such as: atomic and molecular orbitals, lattices, VSPER, nucleophilic substitution, stereochemistry, sigma and pi bonding, and many more.
Abstract: Animations are being produced on subjects such as: atomic and molecular orbitals, lattices, VSPER, nucleophilic substitution, stereochemistry, sigma and pi bonding, and many more
3 citations