Growth silicon oxides

Many theories on the formation mechanisms of PS emerged since then. Beale et al.12 proposed that the material in the PS is depleted of carriers and the presence of a depletion layer is responsible for current localization at pore tips where the field is intensified. Smith et al.13-15 described the morphology of PS based on the hypothesis that the rate of pore growth is limited by diffusion of holes to the growing pore tip. Unagami16 postulated that the formation of PS is promoted by the deposition of a passive silicic acid on the pore walls resulting in the preferential dissolution at the pore tips. Alternatively, Parkhutik et al.17 suggested that a passive film composed of silicon fluoride and silicon oxide is between PS and silicon substrate and that the formation of PS is similar to that of porous alumina. 

When the surface is completely covered by an oxide film, dissolution becomes independent of the geometric factors such as surface curvature and orientation, which are responsible for the formation and directional growth of pores. Fundamentally, unlike silicon, which does not have an atomic structure identical in different directions, anodic silicon oxides are amorphous in nature and thus have intrinsically identical structure in all orientations. Also, on the oxide covered surface the rate determining step is no longer electrochemical but the chemical dissolution of the oxide.1... 

S. Jin, Q. Li, and C. Lee, Direct growth of amorphous silicon oxide nanowires and crystalline silicon nanowires from silicon wafer, Phys. Status Solidi A—Appl. Res. 188, Rl—R2 (2001). 

It appears that di-coordinated oxygen configurations such as backbond and dimer-bridge are the most stable forms and play a significant role in the initial growth of silicon oxide film. 

An important point is that the micro- and nanopowders consisting of pyramidal crystallites (prepared by grinding silicon waste from semiconductor manufacturing) and single-crystal Si are identical in the temperature variation of the silicon oxide growth rate. At the same time, the nanopowders prepared via silane decomposition in an rf plasma and the micropowders consisting of spherical crystallites differ markedly in the temperature variation of the oxidation rate. The nanopowders are less sensitive to the oxidation temperature. 

There are many types of silicon oxides such as thermal oxide, CVD oxide, native oxide, and anodized oxide. Only native oxide and anodic oxide are directly relevant in the context of this book. Anodic oxide film, which is involved in most of the electrochemical processes on silicon electrodes, has not been systematically understood, partly due to its lack of application in mainstream electronic device fabrication, and partly due to the great diversity of conditions under which anodic oxide can be formed. On the other hand, thermal oxide, due to its importance in silicon technology, has been investigated in extremely fine detail. This chapter will cover some aspects of thermal oxide such as growth kinetics and physical, electrical, and chemical properties. The data on anodic oxide will then be described relative to those of thermal oxide. 

The electrical properties of silicon oxide play a critical role in many phenomena on sihcon electrodes, particularly in the growth of anodic films. Anodic oxides can... 

With this OAG approach, highly pure, ultra-long and uniform-sized SiNWs in bulk-quantity could be synthesized by either laser ablation or thermal evaporation of silicon powders mixed with silicon oxide or silicon monoxide only [23-28]. Section 10.2 discusses the physical chemistry aspects of the OAG. Transmission electron microscopic data and theoretical calculations are used to describe the nuclea-tion and the growth of SiNWs via the OAG process. 

Silicon oxide is a critical source material in the oxide-assisted growth as described above. It also plays important roles, as is well known, in many fields such as electronics, optical communications, and thin-film technology. Our recent finding of silicon oxide in the synthesis of silicon nanowires, as we reviewed in the previous part of this chapter, would extend further the important new application of silicon oxide. 

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