AFM application for in situ study of adsorption processes
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HE 8th INTERNATIONAL WORKSHOP ON BEAM INJECTION ASSESSMENT OF MICROSTRUCTURES IN SEMICONDUCTORS, JUNE 11–14, 2006, ST. PETERSBURG, RUSSIA
AFM Application for in situ Study of Adsorption Processes1 E. A. Sosnov, S. A. Belova, and A. A. Malygin St. Petersburg State Technological Institute, St. Petersburg, 198013 Russia Submitted September 12, 2006; accepted for publication October 3, 2006
Abstract—Comparison of calculated and experimental data allows us to assume the following mechanism of H2O adsorption in dynamic conditions at high temperature: during the adsorption of the first portions of sorbate on the silica gel surface, the thin film of water overlaps the access to intrapore space and the adsorption proceeds only on the exterior surface of the sorbent. PACS numbers: 68.08.-p, 68.15.+e, 68.37.Ps, 82.33.Ln, 82.70.Gg DOI: 10.1134/S1063782607050016
1. INTRODUCTION The invention of scanning tunneling (1981), and later atomic force microscopy (AFM) (1986)—methods with high sensitivity and resolution—has made possible the direct examinations of topography and the physicochemical properties of solid surfaces. Modern developments in scanning probe microscopy methodology allow the expansion of the sphere of investigations, including carrying out the direct study of physical processes leakage at the surface of solids. This work is devoted to the investigation by AFM methods in situ of water vapor adsorption on wide-porous silica gels in dynamic regimes. The silica gel ShSKG and indicator vanadium-containing silica gel IVS-1 received by processing of ShSKG by VOCl3 vapors by the molecular layering method [1, 2] were studied. As is known, IVS-1 shows indicator properties in relation to H2O vapors (color transition in the adsorbate quantities interval a H2 O = 0−12 mmol/g: white–yellow–orange–red–claret with wide gamma of the intermediate color nuances [3]). This allows estimation of the quantity of adsorbed waters by silica gel metachromatism. The specified property of indicator silica gel, in spite of the fact that the water vapor adsorption velocity of IVS-1 surpasses the analogous parameter for ShSKG [4], has been used for estimation of the adsorbate quantity of ShSKG silica gel, yielding a slightly overestimated value.
with the use of NSG-01 cantilever upon water adsorption from air onto the surface of silica gel spherical particles (∅2.5–3.0 mm). For decreasing of the water vapor adsorption velocity, the sorbent, recycled at 400°C within 2 h [4], was placed on a preheated SPM objective table where the matrix temperature 130 ± 2°C was supported. 3. RESULTS AND DISCUSSION The topography of initial silica gel ShSKG before water vapor adsorption is shown in Fig. 1a. The analysis of topography has shown that the homogeneous globular structure with a medial globule size of 180– 200 nm is observed at the silica gel surface. At the same time, the calculation of structural characteristics of a silica gel (see table) allows the estimation of the size of a single globule at ~10 nm. This calculation has been carried out on a pr
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