Scanning electron microscopy limitations

Perhaps the most significant complication in the interpretation of nanoscale adhesion and mechanical properties measurements is the fact that the contact sizes are below the optical limit ( 1 t,im). Macroscopic adhesion studies and mechanical property measurements often rely on optical observations of the contact, and many of the contact mechanics models are formulated around direct measurement of the contact area or radius as a function of experimentally controlled parameters, such as load or displacement. In studies of colloids, scanning electron microscopy (SEM) has been used to view particle/surface contact sizes from the side to measure contact radius [3]. However, such a configuration is not easily employed in AFM and nanoindentation studies, and undesirable surface interactions from charging or contamination may arise. For adhesion studies (e.g. Johnson-Kendall-Roberts (JKR) [4] and probe-tack tests [5,6]), the probe/sample contact area is monitored as a function of load or displacement. This allows evaluation of load/area or even stress/strain response [7] as well as comparison to and development of contact mechanics theories. Area measurements are also important in traditional indentation experiments, where hardness is determined by measuring the residual contact area of the deformation optically [8J. For micro- and nanoscale studies, the dimensions of both the contact and residual deformation (if any) are below the optical limit. 

Some limitations of optical microscopy were apparent in applying [247—249] the technique to supplement kinetic investigations of the low temperature decomposition of ammonium perchlorate (AP), a particularly extensively studied solid phase rate process [59]. The porous residue is opaque. Scanning electron microscopy showed that decomposition was initiated at active sites scattered across surfaces and reaction resulted in the formation of square holes on m-faces and rhombic holes on c-faces. These sites of nucleation were identified [211] as points of intersection of line dislocations with an external boundary face and the kinetic implications of the observed mode of nucleation and growth have been discussed [211]. 

Scanning electron microscopy is commonly used to study the particle morphology of pharmaceutical materials. Its use is somewhat limited because the information obtained is visual and descriptive, but usually not quantitative. When the scanning electron microscope is used in conjunction with other techniques, however, it becomes a powerful characterization tool for pharmaceutical materials. 

Immunolabel samples either before or after fixation. Any size gold can be used for scanning electron microscopy. The size of the gold particles is limited by the resolution of the instrument. 

Limited evidence from microsurgical ablation experiments suggests that semio-chemicals are perceived by the external scapular setae (Leal el al., 1989f). The morphology of the setae has been characterized by scanning electron microscopy (Leal and Mochizuki, 1990). 

With improvements in the preparation of more active HDS catalysts, MoS2 crystallites became smaller, and traditional physical techniques for characterization such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) became limited. In fact, today s best catalysts do not exhibit XRD patterns, and the active catalyst particles can no longer be observed directly by TEM. Thus, new techniques were required to provide structural information about Co(Ni)-Mo-S catalysts. As modern surface science characterization procedures evolved, they were immediately applied to the study of CoMoSx-based... 

The main inconvenience of the ERDs construction is the lack of reproducibility. Due to the tiny electrode surfaces, small variations imply big changes. The sealing between the electrode surface and the insulator material is very crucial for obtaining a well-defined electrode surface and low noise. Their characterization can be achieved by different techniques [17]. Scanning electron microscopy (SEM) is suitable for UMEs but not for smaller ERDs. Information about ERD dimensions can be obtained from the experimental (by chronoamperometry or cyclic voltammetry) and theoretical response in well-defined electrochemical systems [5]. Moreover, this electrochemical characterization shows several limitations when ERDs approach the low nanometric scale [8,14,36]. 

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