Imaging Aqueous-processable

FIGURE 6.3 Atomic force microscopy images of silk films formed from reprocessed fibroin of B. mori. Two modes of processing are shown, all aqueous process (top), and methanol-induced 3-sheet transition... 

The potendal of the AFM to enhance the characterization of bioerodible polymers, and biomaterials in general, stems from ability of the instrument to obtain veity high resolution images from uncoated polymer. samples within aqueous environments. Therefore, it has become possible to image dynamic processes like surface erosion and protein adsorption which are fundamental to the mechanisms of drug delivery and biocompatibility. 

There is nothing uncommon about the equipment components used in the semi-aqueous process. They are the pumps, filters, tanks with cove comets, spray nozzles, etc., noted as "Best" in Chapter 7 " of Ref. 1. The image of Figure 3.9 shows one such apparatus in which that process is practiced. 

For in situ investigations of electrode surfaces, that is, for the study of electrodes in an electrochemical environment and under potential control, the metal tip inevitably also becomes immersed into the electrolyte, commonly an aqueous solution. As a consequence, electrochemical processes will occur at the tip/solution interface as well, giving rise to an electric current at the tip that is superimposed on the tunnel current and hence will cause the feedback circuit and therefore the imaging process to malfunction. The STM tip nolens volens becomes a fourth electrode in our system that needs to be potential controlled like our sample by a bipotentiostat. A schematic diagram of such an electric circuit, employed to combine electrochemical studies with electron tunneling between tip and sample, is provided in Figure 5.4. To reduce the electrochemical current at the tip/solution... 

Fig. 13.13 Photographs of sonoluminescence from NaCl aqueous solution sonicated at 135 kHz in a cylindrical beaker (a). Image (a) was digitally processed to obtain the red component (b), which corresponds to Na atom emission, and the blue component (c), which corresponds to continuum emission [41] (Reprinted from the Japan Society of Applied Physics. With permission)...

In the example of Fig. 7.15 [43j rhodium particles have been deposited by spin coat impregnation of a Si02/Si substrate with an aqueous solution of rhodium trichloride. After drying, the particles were reduced in hydrogen. The images show samples prepared at three different rotation speeds in the spin coating process, but with concentrations adjusted such that each sample contains about the same amount of rhodium atoms. The particles prepared at high rotation speeds are smaller, which... 

One of the most significant applications of STM to electrochemistry would involve the application of the full spectroscopic and imaging powers of the STM for electrode surfaces in contact with electrolytes. Such operation should enable the electrochemist to access, for the first time, a host of analytical techniques in a relatively simple and straightforward manner. It seems reasonable to expect at this time that atomic resolution images, I-V spectra, and work function maps should all be obtainable in aqueous and nonaqueous electrochemical environments. Moreover, the evolution of such information as a function of time will yield new knowledge about key electrochemical processes. The current state of STM applications to electrochemistry is discussed below. 

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