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Time-Resolved Radio Frequency Conductivity (TRRFC) Studies of Charge-Carrier Dynamics in Aqueous Semiconductor Suspensions

Herrmann, Hartmut and Martin, Scot T. and Hoffmann, Michael R. (1995) Time-Resolved Radio Frequency Conductivity (TRRFC) Studies of Charge-Carrier Dynamics in Aqueous Semiconductor Suspensions. Journal of Physical Chemistry, 99 (45). pp. 16641-16645. ISSN 0022-3654. doi:10.1021/j100045a025.

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The time-resolved radio-frequency conductivity (TRRFC) method provides a useful tool for in situ measurements of charge carrier dynamics in aqueous suspensions of semiconductor particles. In this report, the effects of pH on surface states of ZnO and the effects of hole scavengers (2-propanol) are examined. The experimental results are interpreted in terms of surface mediated recombination processes, in which holes are trapped in a fast process by surficial sites on the ZnO. Recombination rates appear to be governed by the reaction rate of electrons with surface-trap sites. At higher pH (i.e., pH 12), electrostatic repulsion due to a negatively charged ZnO surface leads to slower surface recombination rates compared to lower pH (Le., pH 7) conditions. Addition of a hole scavenger significantly decreases the absolute charge-carrier concentration as detected by TRRFC. This decrease is attributed to the loss of trapped surface holes or surface-bound OH due to oxidation of the hole scavenger. When 2-propanol is used as a solvent, the holes react in a fast step with the solvent at the semiconductor interface within the time resolution of the experiment. The observed TRRFC signal is then due to electrons which are thought to be predominantly transferred to dissolved oxygen (O_2) leading to the formation of hydroperoxyl radicals (HO_2) and subsequently hydrogen peroxide (H_2O_2).

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Herrmann, Hartmut0000-0001-7044-2101
Hoffmann, Michael R.0000-0001-6495-1946
Additional Information:© 1995 American Chemical Society. Received: November 15, 1994; In Final Form: July 25, 1995. The authors are grateful for the loan of radiofrequency components from Prof. N.S. Lewis, the help of Prof D. P. Weitekamp's group (especially John Marohn) with radio frequency components, and the use of the excimer laser by Prof. G. A. Blake. Financial support for this project is provided by the Advanced Research Project Agency (AFWA) and the Office of Naval Research (ONR) {NAV 5 HFMNN0001492J1901). We are grateful to Drs. Ira Skumick and Harold Guard for their generous support and encouragement. S.T.M. is supported by a National Defense Science and Engineering Graduate Fellowship. H.H. wishes to thank NATO and Deutscher Akademischer Austauschdienst (DAAD) for support. We thank the reviewers of this paper for their stimulating comments.
Funding AgencyGrant Number
Defense Advanced Research Projects Agency (DARPA)UNSPECIFIED
Office of Naval Research (ONR)NAV 5 HFMNN0001492J1901
National Defense Science and Engineering Graduate (NDSEG) FellowshipUNSPECIFIED
North Atlantic Treaty Organization (NATO)UNSPECIFIED
Deutscher Akademischer Austauschdienst (DAAD)UNSPECIFIED
Issue or Number:45
Record Number:CaltechAUTHORS:20150810-083411057
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Official Citation:Time-Resolved Radio Frequency Conductivity (TRRFC) Studies of Charge-Carrier Dynamics in Aqueous Semiconductor Suspensions Hartmut Herrmann, Scot T. Martin, and Michael R. Hoffmann The Journal of Physical Chemistry 1995 99 (45), 16641-16645 DOI: 10.1021/j100045a025
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:59331
Deposited By: Ruth Sustaita
Deposited On:10 Aug 2015 18:32
Last Modified:10 Nov 2021 22:18

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