Singlecrystalline semiconductor electrodes modified with monolayer protected gold clusters

1. Institute of Ohysical Chemistry “Ilie Murgulescu” Singlecrystalline semiconductor electrodes modified with monolayer protected gold clusters ID_35/2008: Research Project sponsored by the National University Research Council - Executive Agency for Higher Education and Research Funding (CNCSIS-UEFISCSU) No 500/2009. Project Director: Dr. Valentina Lazarescu

2. Project Summary • The poor chemical stability of semiconducting surfaces along with their high density of surface states is considered one of the major impediments in developing large scale device applications. Therefore, much effort has been done in order to improve the electronic properties of these surfaces by their chemical modification. Thiol self-assembled monolayers turned out to be among the most promising candidates. An extensive research has been lately focused on Au clusters embedded in a thiolate monolayer, the so-called monolayer protected clusters, interest in this field being justified by the potential utility of these materials in biochemistry, chemical sensors and microelectronic device fabrication. The design of such structures with specific functions and properties is possible only by understanding the mechanism of the electronic interactions and their role in the self-assembly process. This project explores the effects of the self-assembled monolayers formed by 4,4'-thiobisbenzenethiol and colloidal Au on the electronic properties of GaAs(hkl) and Si(hkl) electrodes as reflected in their electrochemical and non-linear optical properties. Our team has a good expertise in studying the surface state-and field-effects at semiconductor/solution interface by Electrochemical Impedance Spectroscopy and Second Harmonic Generation. Information concerning the passivation efficiency supplied by cyclic voltammetry with stationary and rotating disc electrodes combined with that referring to the organic layer conductivity and transport properties explored by Scanning Electrochemical Microscopy (technique capable of probing surface reactivity of materials at microscopic scales) provide a deep insight into this complex interface architecture. AFM/STM and XPS studies will furnish further data on surface morphology and chemical composition. SHG and SECM investigations will be performed within the existing cooperation framework, at Ulm University and Rennes University, respectively.

3. Reserch Team

4. Budget

5. Project objectives in 2009 • Preparation and characterization of GaAs(hkl) electrodes modified with 4,4’thio-bis-benzenethiol (TBBT) • Studies on the TBBT effects on the electronic properties of the GaAs(hkl) electrodes by electrochemical impedance spectroscopoy (EIS) • Evaluation of the redox properties of the TBBT-modified GaAs(hkl) electrodes

6. Scientific contributions based on the results obtained in 2009 • 1. V. Lazarescu, R. Scurtu, M.F. Lazarescu, A.M. Toader, E. Volanschi, Passivation Effects of 4, 4’ Thio-bis-benzene-thiolate Adsorbed Layers on Semiconducting Electrodes, oral presentation at 60th Annual Meeting of the International Society of Electrochemistry, Beijing, 15-22 Aug. 2009, invited for publication in Electrochimica Acta • 2. Rareş Scurtu, Mihail Lăzărescu, Valentina Lăzărescu, Surface States- and Field-Effects at Bare and Thiolate Covered GaAs(111)A Electrodes, poster presented at 60th Annual Meeting of the International Society of Electrochemistry, Beijing, 15-22 Aug. 2009 • 3.V. Lazarescu, R. Scurtu, M. F. Lazarescu, A. M. Toader, E. Volanschi, E. Santos, H. Jones, G. Götz, P. BäuerleSurface States- and Field Effects at Thiolate-Covered GaAs(110) Electrodes,oral presentaion at 5th Kurt Schwabe Symposium, Erlangen, 24-28 Mai 2009 • 4 V. Lazarescu, R. Scurtu, M. F. Lazarescu, A. M. Toader, E. Volanschi, E. SantosSHG- and EIS-investigations on thiolate-covered GaAs(110) electrodes,oral presentation at Journees d’Electrochimie, Sinaia, 6-10 iulie 2009 • 5. A. M. Toader, M. Lăzărescu, V. Lăzărescu, E. Volanschi, L'électrochimie de l'hémine sur des électrodes de GaAs fonctionnalisées avec 4,4thiobisbenzènethiol,poster at Journees d’Electrochimie Sinaia,6-10 iulie 2009