Porous silicon stabilization thermal oxidation

A number of studies has been attempted to stabilize porous silicon low-temperature oxidation in a controlled way [1-3], surface modification of silicon nanocrystallites by chemical [4] or electrochemical [5] procedures etc. Rapid thermal processing (RTP) is thought to be a shortcut method of the PS stabilization for a number of purposes. However, there is no data about RTP influence on the PS structure. Therefore, the study of lattice deformations of PS layers after RTP is of great interest. In the present work. X-ray double-crystal diffractometry was used to measure lattice deformations of PS after RTP of millisecond and second durations. 

Arguably, the simplest method to stabilize the porous silicon surface is oxidation. A popular technique is to use ozone to rapidly generate a Si-OH capped surface with a thin oxide layer. Alternatively, thermal treatment in air (400-800 °C) is used to generate thicker oxide layers (Pap et al. 2004). Surface hydroxyl groups can be further reacted with silanes, which can further stabilize the surface against hydrolytic attack, as well as provide a means of attaching functional groups to the... 

Furthermore, results obtained with respect to the thermal stability of the pore structure in porous silicon carbide and the stability towards air, hydrogen or steam of the surface of a silicon oxynitride powder indicate that the stability of high surface area non-oxidic materials can be promising with respect to potential application in catalysis. 

Petrova-Koch V, Muschik T, Kux A et al (1992) Rapid-thermal-oxidized porous Si-the superior photoluminescent Si. Appl Phys Lett 61 943-945 Porter LA, Choi HC, Ribbe AE et al (2002) Controlled electroless deposition of noble metal nanoparticle films on germanium surfaces. Nano Lett 2 1067-1071 Rabinal MK, Mulimani BG (2007) Transport properties of molecularly stabilized porous silicon schottky junctions. New J Phys 9 440-448... 

Bsiesy et al. (1991) believe that electrochemical oxidation of PSi has the following advantages (1) electrochemical oxidation of porous silicon can be achieved easily and (2) it is possible to oxidize either the lower part of the porous layer, or the whole depth, at a level which depends on the exchanged charge. This method therefore appears to be more attractive than thermal oxidation when incomplete oxidation is required. In particular, such a requirement appears during silicon (or other material) epitaxy on porous silicon. These processes generally involve temperatures above 400 °C and porous silicon must be stabilized by a preoxidation step in order to conserve its very thin microstructure. If this preoxidation is achieved by thermal oxidation, there is also oxide growth on top of the sample, which must be eliminated before subsequent epitaxy. Electrochemical oxidation, with an appropriate choice of experimental conditions, can lead to oxidation limited to the inner part of the porous layer. 

The template removal step, needed to achieve porous materials, is one of the most critical points. In contrast to silica, other compositions are usually more sensitive to thermal treatments and calcination can result in breakdown of the mesostructures. Hydrolysis, redox reactions, or phase transfonnarions to the thermodynamically preferred denser crystalline phases account for this lower thermal stability. Many of the transition metal-based mesostruetured materials synthesized in the presence of cationic surfactants collapse during thermal treatments. The poor thermal stability observed could be due to the different 0x0 chemistry of the metals compared to silicon. Several oxidation states of the metal centers may be responsible for oxidation and/or reduction during calcination. In addition, incomplete condensation of the framewoik is possible. 

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