Insulating samples

The operation of the STM depends on the conduction of electrons between tip and sample. This means, of course, that insulating samples are, in general, not accessible to STM investigations. Nevertheless, a large body of work [32] dealing with STM characterization of thin organic films on conducting substrates is now in... 

A disadvantage of AES is that the intense electron beam easily causes damage to sensitive materials (polymers, insulators, adsorbate layers). Charging of insulating samples also causes serious problems. 

SNMS is suitable for quantitative element depth profiling of metallic and electrically insulating samples. Laser-SNMS enables the additional acquisition of 2D element distributions with HF-plasma SNMS bulk analysis is also feasible. 

The ratio Db/Da is a so-called relative sensitivity factor D. This ratio is mostly determined by one element, e. g. the element for insulating samples, silicon, which is one of the main components of glasses. By use of the equation that the sum of the concentrations of all elements is equal to unity, the bulk concentrations can be determined directly from the measured intensities and the known D-factors, if all components of the sample are known. The linearity of the detected intensity and the flux of the sputtered neutrals in IBSCA and SNMS has been demonstrated for silicate glasses [4.253]. For SNMS the lower matrix dependence has been shown for a variety of samples [4.263]. Comparison of normalized SNMS and IBSCA signals for Na and Pb as prominent components of optical glasses shows that a fairly good linear dependence exists (Fig. 4.49). 

Another approach is to hold the insulating sample in place by means of a thin metal plate or foil which has a small (3 mm) hole in it. This will provide improved electrical contact near the analysis area and minimizes the exposed area of insulating material. 

Following the extraction, the undissolved solid material is then filtered out and the filtrate analyzed. Examples of this would be soil samples to be analyzed for metals, such as potassium or iron, and polymer him or insulation samples to be analyzed for formaldehyde residue. The extracting liquid may or may not be aqueous. Soil samples being analyzed for metals, for example, utilize aqueous solutions of appropriate... 

A rather large negative MR, with a substantial anisotropy, has been observed in reentrant insulating samples with high x (Oiwa et al. 1998b Katsumoto et al. 1998). A destruction of bound magnetic polarons, as invoked in an earlier work on (In.Mn)As... 

As with all other techniques, the method has limitations, some of which are as follows. Data collection is slow, quantitative analysis requires one to several hours after an overnight pumpdown prior to analysis. The method has relatively poor lateral resolution. Sample charging effects may pose a problem with insulating samples. 

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