Photoluminescent Silicon in Nanoporous Aluminium Oxide
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Corresponding author Prof. Dr. G.Schmid, Dr. A.Heilmann, Th. Sawitowski, Institut fdr Anorganische Chemie, Universitat Essen, Universititsstr. 5-7, D - 45117 Essen, Germany, E-mail: [email protected], phone:+49-201-183-2054, fax:+49-201-183- 2402 Prof. Dr. P. Jutzi, A. Klipp, FakultAt fir Chemie, Universitat Bielefeld, Universitttsstr. 25, D - 33615
Bielefeld, Germany [§]
Prof. Dr. U. Kreibig, R Neuendorf, 1.Physikalisches Institut, RWTH Aachen, D - 52026 Aachen
ABSTRACT Thermal decomposition of a metastable silane in nanoporous alumina leads to the formation of luminescent silicon nanostructures. While varying the pore size of the transparent membranes the luminescence can be shifted from 504 rim up to 537 nm by building up a sheet-like structure of siloxene on the inner pore surface. INTRODUCTION Nanoporous aluminium oxide membranes have variously been used to generate nanosized particles of different materials [1-3]. Here we report on the formation of photoluminescent siloxenes by spontaneous decomposition of silanes in the channels of aluminiutm oxide membranes. This method opens novel and simple routes to stable light-emitting systems. The use of nanoporous aluminium oxide membranes allows control of two decisive factors: the size of the photoluminescent system and the chemistry on its surface. In addition alumina membranes offer a tremendous increase of surface compared with usual two- dimensional arrays. Assuming an averaged number of 1010 pores per cm 2 a membrane of that size with 40 nm pores and 1 gim in thickness has an inner surface of 13 cm 2 . EXPERIMENT The alumina membranes are formed as described by anodization of aluminium in polyprotic acids [4-6]. The pore diameter is mainly a function of the applied voltage (about 1.0 - 1.2 nm per V) and can be varied between 5 rm and 250 nm. The thickness of the membranes depends on the anodization time. Using high purity aluminium the resulting membranes are transparent between 350 um and the near infrared region. Thermal decomposition of Cp*SiH 3 (Cp* = pentamethyl cyclopentadienyl) has already been used for CVD processes to generate Si containing films [7-8]. Using alumina membranes heat treatment up to 800*C of a vacuum filled membrane in nitrogen atmosphere leads to the formation of Cp*H, H2 and Si. While organic products and most of the hydrogen leave the pores immediately, the silicon atoms will spontaneously react with the OH groups of the pore surfaces to give stable AI-O-Si interactions. By this process siloxene-like structure are formed on the pore walls (Fig. 1).
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Mat. Res. Soc. Symp. Proc. Vol. 486 ©1998 Materials Research Society
Siloxene layer
Figure 1:
Sketch of a piece of siloxene on the pore wall of nanoporous aluminium oxide
The presence of hydrogen causes Si-H bonds on the Si surface, Si-OH bond formation is possible also. The amount of silicon present in the pore is easily be determined by the pore size and the silicone content in the silane. So by varying the pore diameter different amount of silicon
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