Atomic force microscopy surface measurements

Scanning tunnelling microscopy, scanning electrochemical microscopy, and AFM-surface potential measurements have also been used to investigate Nafion films. Scanning electrochemical microscopy reveals a domain-like structure containing circular features ca. 1-2 nm in diameter made up of a conductive center (presumed to be ion-rich regions) surrounded by a much less conductive zone. " Atomic force microscopy surface potential measurements detect features that were interpreted as ion channels in Nafion membranes. The size of the claimed ion channels was... 

Zhang JX, Ebbens S, Chen XY, et al. Determination of the surface free energy of crystalline and amorphous lactose by atomic force microscopy adhesion measurement. Pharm Res 2006 23(2) 401 07. 

The area per n-alkanethiol in a complete monolayer on a gold surface is 0.21 nm per molecule. This value does not depend on the chain length, at least not for the molecules HDT, ODT, and ECT used in this work. The packing density (/Omi) is obtained by inverting this value and equals 4.608 x 10 molecules/cm. From atomic force microscopy (AFM) measurements on the sputtered gold of 30 nm thickness used in this work, we assume a roughness factor of fJ = 1.1. The surface concentration of the complete monolayer in g cm can now be calculated... 

To monitor their surface plasmon absorption, UV-visible absorption spectra were obtained for all LbL films produced using a Cary 50 UV-visible spectrometer. Atomic force microscopy (AFM) measurements were performed on a Digital Instruments NanoScope IV operating in tapping mode with a n+-... 

Experimentally, rupture forces in biological systems can be measured with atomic force microscopy, surface force apparatus, optical tweezers, or the biomembrane force probe technique. Each of these methods operates on different time.scales and gives additional insights into the dynamics strength of biological bonds (see Ref. 75). Since none of these methods yields details on the atomic level, this is a nice application for molecular dynamics. 

With the application of atomic force microscopy in measuring surface forces, it became possible to detect the bridging of individual polymer chains. In particular polyelectrolytes adsorbing to charged surfaces in aqueous medium have been studied [1414—1418]. Peeling a strongly adsorbed polyelectrolyte from a surface is similar to... 

AFM Atomic force microscopy [9, 47, 99] Force measured by cantilever deflection as probe scans the surface Surface structure... 

The most popular of the scanning probe tecimiques are STM and atomic force microscopy (AFM). STM and AFM provide images of the outemiost layer of a surface with atomic resolution. STM measures the spatial distribution of the surface electronic density by monitoring the tiumelling of electrons either from the sample to the tip or from the tip to the sample. This provides a map of the density of filled or empty electronic states, respectively. The variations in surface electron density are generally correlated with the atomic positions. 

Kelly T W ef a/1998 Direct force measurements at polymer brush surfaces by atomic force microscopy Macromoiecuies 31 4297-300... 

A wide variety of measurements can now be made on single molecules, including electrical (e.g. scanning tunnelling microscopy), magnetic (e.g. spin resonance), force (e.g. atomic force microscopy), optical (e.g. near-field and far-field fluorescence microscopies) and hybrid teclmiques. This contribution addresses only Arose teclmiques tliat are at least partially optical. Single-particle electrical and force measurements are discussed in tire sections on scanning probe microscopies (B1.19) and surface forces apparatus (B1.20). 

Advances have been made in directly measuring the forces between two surfaces using freshly cleaved mica surfaces mounted on supports (15), and silica spheres in place of the sharp tip of an atomic force microscopy probe (16). These measurements can be directly related to theoretical models of surface forces. 

Atomic force microscopy (AFM) or, as it is also called, scanning force microscopy (SFM) is based on the minute but detectable forces - of the order of nano Newtons -between a sharp tip and atoms on the surface. The tip is mounted on a flexible arm, called a cantilever, and is positioned at a subnanometre distance from the surface. If the sample is scanned under the tip in the x-y plane, it feels the attractive or repulsive force from the surface atoms and hence it is deflected in the z-direction. The deflection can be measured with a laser and photo detectors as indicated schematically in Fig. 4.29. Atomic force microscopy can be applied in two ways. 

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