Local and Electronic Structure of Siloxene
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Local and electronic structure of siloxene Ernst Z. Kurmaeva) and Sergei N. Shamin Institute of Metal Physics, Russian Academy of Sciences-Ural Division, 620219 Yekaterinburg GSP-170, Russia
David L. Ederer Department of Physics, Tulane University, New Orleans, Louisiana 70118
Ursula Dettlaff-Weglikowska and J¨org Weber Max-Planck-Institut f¨ur Festk¨orperforschung, Heisenbergstrasse 1, 70569 Stuttgart, Germany (Received 7 July 1997; accepted 10 September 1998)
Silicon L2,3 x-ray emission spectra (XES) of siloxene powder samples prepared according to W¨ohler and Kautsky (W¨ohler and Kautsky siloxene) are presented. The results are compared with the Si L2,3 spectra of the reference compounds a-Si, c-Si, SiO2 , and SiOx . A close similarity of the electronic structure of W¨ohler siloxene to that of a-SiO0.43 : H and of Kautsky siloxene to that of a-SiO0.87 : H is found. We determine the number of oxygen atoms per Si atom at ,0.5 in W¨ohler siloxene and ,0.8 in Kautsky siloxene. The relative concentrations are in good agreement with the results of infrared absorption measurements on the same samples.
I. INTRODUCTION
Light-emitting, silicon-based materials are very attractive for an integration with silicon microelectronics in optoelectronic devices.1 Crystalline silicon (c-Si) is not suited for visible light emission, due to the small indirect band gap of about 1.1 eV. An efficient visible luminescence at room temperature from Si is, however, possible by drastic changes in the band structure. Different methods were pursued in the past to modify the band structure of c-Si: amorphous Si alloys with a high degree of structural disorder (a-SiHx , a-SiCx , a-SiOx , a-SiNx ), quantum confinement in crystallites of ˚ [porous silicon (p-Si)], or by the reduction of 10–20 A the dimensionality in silicon backbone materials [e.g., planar silane (SiH)n , linear polysilanes (SiH2 )n , siloxene (Si6 O3 H6 )n ]. Siloxene exhibits a strong visible (yellowgreen) photoluminescence2,3 and it is considered as an alternative material for Si-based luminescent devices. Siloxene has attracted considerable interest due to the controversial discussion on the origin of the strong visible photoluminescence from porous silicon. It has been proposed that the visible luminescence of porous silicon originates from a siloxene contamination.4,5 Two ideal modifications of siloxene are shown schematically in Fig. 1. On the left-hand side of the Si-planar structure [Si6 H62x (OH)x ]n for x 3 is given. This modification consists of planes in which the silicon atoms form covalently bonded puckered layers similar to the (111) plane of c-Si and OH groups. The crystal
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Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 14, No. 4, Apr 1999
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structure of Si planar is verified experimentally only for samples which were prepared according to the procedure given by W¨ohler6 (so-called “as prepared” W¨ohler silo
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