Sample non-conductive

Because polymers are typically non-conductive, sample charging can occur and has to be compensated carefully, e. g. by use of a low-energy electron-flood gun, to avoid line-shape distortion and misinterpretation of the measurements. 

The advantages of LA are now well-known - no sample preparation is needed, conducting and non-conducting samples of arbitrary structure can be analyzed directly, spatial resolution up to a few microns can be obtained, high vacuum conditions are not required, rapid simultaneous multi-element analysis is possible, and it is possible to obtain complete analytical information with a single laser pulse. A brief overview of the potential and limitations of LA will be given in this chapter. 

Samples suitable for SEM measurements include most solids which are stable under vacuum (metals, ceramics, polymers, minerals). Samples must be less than 2 cm in diameter. Non-conducting samples are usually coated with a thin layer of carbon or gold in order to prevent electrostatic charging. 

A thin metallic layer (e.g., Au) deposited on geological sample is helpful before direct mass spectrometric measurements because in SIMS charging effects occur due to the sputtering process of non-conducting samples. 

The main purpose of the invention of the first SFM was to extend the imaging capabilities of STM to non-conductive samples [64]. This was enabled by sensing electromagnetic forces that act in the near field of the surface (Fig. la). In prac-... 

Figure 3. Photoelectron energy balance - Non-conductive sample.

We have found that quite consistent data can be reproducibly obtained with non-conductive samples such as zeolites by performing careful gold deposition under vacuum (10 torr) of layers with thickness of the order of 20 A. The binding energy scale may then be referenced to Au4f = 84.0 eV and the other emissions are not overly attenuated. 

Samples to be used in dc discharges must be electrically conducting. Metals, alloys and even semiconductors work quite well in this mode. Non-conducting samples must be mixed with a conducting matrix such as pure copper or silver and pressed into a suitable form. On the other hand, an rf discharge allows non-conducting samples to be handled directly, thereby avoiding the need for matrix modification. 

It affords direct analysis of both conducting and non-conducting samples (the latter requires using an rf source or mixing with a conductive matrix if a dc source is employed) ... 

The gliding spark, which is formed through an hf discharge superimposing sparks along the surface of electrically non-conducting samples, can also ablate... 

For the case of both electrically conducting and electrically non-conducting samples, laser ablation combined with AAS may be useful. In this case AAS measurements can be performed directly at the laser plume. Measurement of the non-element specific absorption will be very important, because of the presence of particles, molecules and radicals as well as due to the emission of continuum radiation. In addition, the absorption measurements should be made in the apprppriate zones. When applying laser ablation for direct solids sampling, the atomic vapor produced can also be led into a flame for AAS work, as has previously been described by Kantor et al. [299] in their early work. 

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