Silicon desorption kinetics

Gupta, P., Colvin, V.L. and George, S.M. (1988) Hydrogen desorption kinetics from monohydride and dihydride species on silicon surfaces , Phys. Rev. B 37, 8234. 

In the 1970s and 1980s both the clean and H-covered Si surfaces were characterized by diffraction and spectroscopic methods, but only in the last decade have there been reproducible studies of chemical kinetics and dynamics on well-characterized silicon surfaces. Despite the conceptual simplicity of hydrogen as an adsorbate, this system has turned out to be rich and complex, revealing new principles of surface chemistry that are not typical of reactions on metal surfaces. For example, the desorption of hydrogen, in which two adsorbed H atoms recombine to form H2, is approximately first order in H coverage on the Si(lOO) surface. This result is unexpected for an elementary reaction between two atoms, and recombi-native desorption on metals is typically second order. The fact that first-order desorption kinetics has now been observed on a number of covalent surfaces demonstrates its broader significance. 

In early measurements of desorption kinetics, Kleint et al. [23] and Belyakov et al. [24] reported that desorption of H2 from the Si(lll) surface follows second-order kinetics with an activation barrier of 42 kcal/mol. Second-order kinetics was also reported on silicon films with the same activation barrier and on Si(lOO) with an activation barrier of 46 kcal/mol [25]. None of these surfaces were well-characterized, and coverages were unknown. Despite the similarity among these results, they have not been confirmed in more recent work. Several authors have commented on possible problems with this early work, ranging from poor surface preparation to inaccurate measurement methods [26-28]. 

In view of the many important applications in semiconductor technology, the interaction of hydrogen with silicon surfaces has been intensively studied. Recombinative H2 desorption from Si(100)-2 x 1 follows first-order kinetics89, unusual when compared with the second-order kinetics observed for H2 desorption from Si(lll)-7 x 7. The measured activation barriers for the desorption of H2 on Si(100) range from 45 to 66 kcalmol-189 90. 

Gupta et al. [20] found second-order kinetics for desorption from the dihydride phase on porous silicon. The corresponding activation energy from isothermal measurements is 43 kcal/mol. The TPD experiments of Flowers et al. [40] on Si(100)-2 X 1 also showed that desorption from the dihydride was second order, with an activation energy of 47 kcal/mol. This result is derived from a model that estimates the equilibrium density of dihydrides as a function of coverage and temperature. This model has been criticized... 

Brash and ten Hove (27) have shown that the early plasma protein adsorption and desorption events occur more slowly and can be more readily examined if the plasma is diluted. Using this approach, we found that exposure of each of the methacrylate polymers to 1% plasma (Fig. 4C) resulted in fibrinogen binding which showed maxima after 1 to 3 minutes of exposure followed by decreases in bound fibrinogen to an apparent plateau at less than 0.1 ug/cm. These kinetics are similar to those reported by Brash and ten Hove i2J) for glass, siliconized glass and polyethylene. 

A similar kinetic analysis clarities the other specific etching mechanisms and can be applied for sputtering, as well as for ion energy-driven etching limited by the formation and desorption of etch product, which takes place in the case of silicon etching by F atoms (Lieberman Lichtenberg, 1994). 

The application of IR spectroscopy to organic sorbates has been primarily limited to gas-phase a orption kinetics and gas-phase catalysis (21). The usefrilness of IR for investigating sorption/desorption processes in situ, has been demonstrated for the selectivity of conformer adsorption at mineral surfaces (22). Strong absorption of H O vibrational modes by IR radiation has been a major hindrance in the application of IR spectroscopy to study organic sorption at aqueous-mineral interfaces. Attenuated total reflectance-IR (ATR-IR) spectroscopy and the use of DjO in the aqueous phase minimizes the water absorption problem. Figure 3 details the ATR setup used in this study. Clay pastes were loaded into Teflon plaques and clamped to both sides of a vertical ATR prism. Silicon sealant around the edges of the plaques prevented water evaporation during extended data collection times (up to 2 days). The area of the D O... 

Nichols, K.P., Azoz, S., Gardeniers, H.J.G.E. (2008) Enzyme Kinetics by Directly Imaging a Porous Silicon Microfluidic Reactor Using Desorption/Ionization on Silicon Mass Spectrometry. (2008) Anal. Chem. 80 8314-8319. 

Ruano GD, Ferron J, Arce RD, Koropecki RR (2011) Kinetics of electron induced desorption of hydrogen in nanostmctured porous silicon. Phys Status Solidi (a) 208(6) 1453-1457 Salonen J, Laine E (1996) The quenching and recovery of photoluminescence in porous silicon. J Appl Phys 80(10) 5984-5985... 

Nichols KP, Azoz S, Gardeniers HJGE (2008) Enzyme kinetics by directly imaging a porous silicon microfluidic reactor using desorption/ionizahon on silicon mass spectrometry. Anal Chem 80(21) 8314-8319... 

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