Rastersondengestützte Untersuchung der elektrochemischen Abscheidung von Element- und Verbindungshalbleitern aus ionischen Flüssigkeiten
Final Report Abstract
In this report we demonstrate that semiconducting silicon, Gadoped silicon and grey selenium can be made by electrodeposition in the air and water stable ionic liquid [Py1,4]TFSA. The wide electrochemical and thermal windows of the employed ionic liquid allow the electrodeposition of elemental silicon and grey selenium, respectively. The electrodeposition of silicon was investigated in the ionic liquid [Py1,4]TFSA containing SiCl4 on highly oriented pyrolytic graphite (HOPG) and Au(111) at room temperature. The liquid itself exhibits on HOPG and on Au(111) an electrochemical window of 4 V and of 5 V respectively, which is limited in the anodic regime by the degradation of HOPG or by gold oxidation and in the cathodic regime by the irreversible reduction of the organic cation and maybe some anion breakdown. Upon addition of SiCl4 a main reduction process begins at -1.6 V vs. Fc/Fc+ (on HOPG) and at -1.8 V vs. Fc/Fc+ (on Au(111)), which is correlated to the electrodeposition of elemental semiconducting silicon. The results show that a thin layer of very small clusters/crystallites forms first, followed by crystallite agglomerates that finally lead to a 500 - 1000 nm thick silicon layer. In situ STM results reveal that the Au(111) surface is subject to a restructuring/reconstruction at electrode potentials more negative than the open circuit potential (OCP) both in the case of the pure ionic liquid and in the presence of SiCl4. Si deposition on a reconstructed typical Au(111) surface starts on the terraces. Initially small 150 - 450 pm high islands grow at -1.7 V vs. Fc/Fc+. With time these islands slowly grow covering the whole of the surface by a few nanometer thick layer after a while. This layer has a band gap of 1.0 ± 0.2 eV, typical for silicon. The electrochemical doping of Si by Ga should be feasible from our preliminary results. The electrodeposition of selenium was investigated in the ionic liquid [Py1,4]TFSA containing 0.1 M SeCl4 on platinum substrate at variable temperatures. The presented results show that at temperatures ≥ 100 oC grey selenium can be electrodeposited as single phase in the ionic liquid [Py1,4]TFSA.
Publications
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Electrochem. Commun., 2004, 6, 510
S. Zein El Abedin, N. Borissenko, F. Endres
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J. Phys. Chem. B, 2006, 110, 6250
N. Borisenko, S. Zein El Abedin, F. Endres
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Z. Phys. Chem., 2006, 220, 1377
F. Endres, S. Zein El Abedin, N. Borisenko
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Electrochim. Acta, 2007, 52, 2746
S. Zein El Abedin, A. Y. Saad, H. K. Farag, N. Borisenko, Q. X. Liu, F. Endres
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Z. Phys. Chem., 2007, 221, 1407
F. Endres, S. Zein El Abedin
