Atomic force microscopy devices

L.M. Do, E.H. Han, Y. Niidome, and M. Fujihira, Observation of degradation processes of A1 electrodes in organic electroluminescence devices by electroluminescence microscopy, atomic force microscopy, scanning electron microscopy, and Auger electron spectroscopy, J. Appl. Phys., 76 5118-5121, 1994. 

A number of methods are available for the characterization and examination of SAMs as well as for the observation of the reactions with the immobilized biomolecules. Only some of these methods are mentioned briefly here. These include surface plasmon resonance (SPR) [46], quartz crystal microbalance (QCM) [47,48], ellipsometry [12,49], contact angle measurement [50], infrared spectroscopy (FT-IR) [51,52], Raman spectroscopy [53], scanning tunneling microscopy (STM) [54], atomic force microscopy (AFM) [55,56], sum frequency spectroscopy. X-ray photoelectron spectroscopy (XPS) [57, 58], surface acoustic wave and acoustic plate mode devices, confocal imaging and optical microscopy, low-angle X-ray reflectometry, electrochemical methods [59] and Raster electron microscopy [60]. 

Another device that yields results of the same kind as STM is atomic force microscopy (AFM) (Binning, 1986). This avoids dependence on an electron stream (which cannot be obtained from insulators)58 and relies on the actual interatomic forces between a microtip and nearby surface atoms. The forces experienced at a given point by the tip are sensed by a cantilever spring. The movements of this are slight, but they can be measured by means of interf erometry and in this way the movement of the tip can be quantified. The sensitivity of the atomic force microscope is less than that of STM, but its action is independent of the electrical conductivity of the surface and it is therefore to be preferred over STM, particularly for studies in bioelectrochemistiy. 

The substrate surface smoothness is critical to TFT performance. Device fabrication processes basically duplicate and/or worsen the surface roughness, which leads to smaller pentacene grains and results in deterioration of pentacene channel mobility. Atomic-force microscopy was used to characterize the surface roughness. Figure 15.21 shows an AFM image of our PET substrate surface before any process. The mean-square roughness and peak-to-valley roughness are 10 A and 90 A,... 

Figure 18.11 illustrates atomic force microscopy (AFM) pictures of gold-covered silica substrates covered with composite particles. These particles were immobilised by the simultaneous electropolymerisation of pyrrole. Thus, even traditional MAA-EDMA copolymer particles can readily be electrically connected to an electrode, thereby obtaining close contact between the transducer and the recognition sites within the polymer. The device is being developed into an amperometric morphine sensor. 

In the case of carbon black, the aggregates are distributed in the matrix rather than individual particles, it is therefore important in some applications (e.g., conductive plastics) to evaluate the distance between these aggregates. It is now possible to measure these distances by atomic force microscopy coupled with straining device. There is a linear relationship between the parallel distance between aggregates dispersed in SBR and strain value. For 10 phr of N 234, the mean distance between aggregates varied in a range from 1.85 to 3.42 jm. For practical purposes, a modified equation [5.4] is used to determine the interaggregate distance ... 

Exact measurements turned out difficult, however, as the manipulation of such tiny objects led to experimental problems. The performance of tensile tests, for example, requires a device to clamp objects just a few nanometers thick. The employment of two atomic force microscopy (AFM) tips movable against each other proved its worth here (Figure 3.45). 

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