Kinetic contrast in atomic force microscopy
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Kinetic Contrast in Atomic Force Microscopy D. V. Sheglov and A. V. Latyshev Institute of Semiconductor Physics, Siberian Division, Russian Academy of Sciences, Novosibirsk, 630090 Russia e-mail: [email protected]; [email protected] Received May 22, 2007
Abstract—The mechanism of the formation of phase contrast in atomic force microscopy (AFM) is studied for various conditions of an oscillating tip interacting with the surface. A phase shift is detected in oscillations of the resonating AFM tip during its interaction with the substrate surface when the AFM tip moves over the surface. We substantiate kinetic mechanism of the formation of phase contrast in AFM, which is initiated when the velocity of the AFM tip moving over the substrate surface increases as a result of increasing friction force. A dependence of the kinetic contrast in AFM on the effective roughness of the surface is discovered. Images of the distribution of copper impurity over the silicon surface under atmospheric conditions are obtained using the method of kinetic phase contrast in AFM. PACS numbers: 68.37.Ps, 68.35.Bs, 81.40.Pq DOI: 10.1134/S1063776108020039
1. INTRODUCTION It is well known that atomically clean surfaces of semiconductors and metals extracted from an ultrahigh vacuum chamber are coated with a natural oxide layer. However, in spite of the presence of the film consisting of natural oxide and contaminants present on the silicon surface under atmospheric conditions, atomic force microscopy (AFM) makes it possible to visualize on the surface single atomic steps with the height of an interplanar spacing (0.31 nm on Si(111) [1] and 0.14 nm on Si(100) [2]). Consequently, in the course of its formation, natural oxide replicates morphological features of the surface such as atomic steps several angstroms in height. Moreover, it was shown recently that AFM under atmospheric conditions makes it possible to visualize elements of a relief 0.08 nm in height on the step surface of Si(111) [3]. Such a substantial breakthrough in the diagnostics of structural processes on the surface has become possible after the discovery of semicontact scanning of the surface by an oscillating AFM tip [4]. The semicontact AFM technique involves the detection of amplitude and phase shift in resonant oscillations of the tip during its interaction with the surface [5]. The AFM method applied for detecting phase shift in tip oscillations is known as the phase contrast technique. Phase shift in the oscillations of an AFM tip as a result of its interaction with the surface depends on many parameters, including stiffness, chemical composition, and the presence of oxide and absorbing layer of water. Physical regularities governing phase shift have not been studied comprehensively, which complicates correct interpretation of information on the surface
obtained using this method [6, 7]. It was shown in [8] that the changes in the phase signal during the time when the tip approaches the surface can be described by the model taking into ac
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