Rastered mode

As opposed to XPS, AES signals typically exhibit complex structure, and sometimes require elaborate data treatment. Also, AES does not easily provide information on oxidation states, as XPS does. On the other hand, AES is often acquired by using easy-to-focus electron beams as the excitation source, and can therefore be used in a rastering mode for the microanalysis of nanosized spots... 

It may be taken for granted that analysis for all elements on a catalyst support work equally well. We have performed experiments on many different catalysts and have found that elements such as Cl, K, Na, and S are very sensitive to the electron beam. Cl and S appear to volatilize in the vacuum while K and Na move away from the incident beam. This is especially true when the beam is spotted directly onto the particle versus using the less damaging raster mode. Examples of how elemental analyses of a BaS0A, zeolite, and NaCl particles vary as a function of time are shown in Figure 5. 

Aside from the freedom to choose the primary ion beam type, impact energy, impact angle, and impact current, there exist nnmerous modes under which these can be operated. For starters, the primary ion beam, or beams, can be directed at the sample s surface over some predefined area ranging from < 1 pm to > 10,000 pm. This can be directed in a stationary mode or the rastered mode. 

Rastered mode describes scanning of a focnsed primary ion beam over some predefined area over the sample. In this mode, the beam spot size must be substantially smaller than the analyzed area and instantaneous dead-time effects associated with primary beam rastering must be considered (see Section 4.2.3.3.3.2). 

In the raster mode, all voxels in a cubic volume that contains the microstructure are scanned by the actual/virtual laser focal spot, depending on having the shutter ON (actual)/OFF (virtual). In the vector mode, the laser focus directly traces the profile to be defined. Figure 31a and b respectively illustrate how a character s could be scanned with the two modes. Apparently the vector mode requires a smaller number of voxels. Depending on the structures, variations and combinations of these two basic modes could be used. 

In the spectrum acquisition mode the probe is either fixed in the spot mode or raster scanned over a small area at high magnification and a complete spectrum acquired. A typical spectrum is shown in Figure 2. 

The results shown in Figure 6 above are an example of this mode of analysis, but include additional information on the chemical states of the Si. The third most frequently used mode of analysis is the Auger mapping mode, in which an Auger peak of a particular element is monitored while the primary electron beam is raster scanned over an area. This mode determines the spatial distribution, across the surface, of the element of interest, rather than in depth, as depth profiling does. Of course, the second and third modes can be combined to produce a three-dimensional spatial distribution of the element. The fourth operational mode is just a subset of the third mode a line scan of the primary beam is done across a region of interest, instead of rastering over an area. 

Figure 40. Operating modes for electron beam systems left — raster scan coupled with continuous table motion right — vector scan, step and repeat.

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]. 

In the classical contact mode (Fig. 6a) AFM measures the hard-sphere repulsion forces between the tip and the sample. As a raster-scan drags the tip over the sample surface, the detector measures the vertical deflection of the cantilever, which indicates the local sample height. A feedback loop adjusts the position of the cantilever above the surface as it is scanned and monitors the changes in the surface height, generating a 3D image—a decisive advantage of AFM over TEM [3]. 

These structures were recorded by a vectorial focal spot scanning in a spiral-by-spiral method rather in a raster layer-by-layer mode using a PZT stage. Such spiral structures fabricated in SU-8 have optical spot bands in near-lR [24], telecommunication [25], and 2-5 pm-IR region [26] or can be used as templates for Si infiltration [11]. It is obvious, that direct laser scanning is well suited for defect introduction into 3D PhC, as demonstrated in resin where a missing rod of a logpUe structure resulted in the appearance of a cavity mode in an optical transmission spectriun [27]. 

Micro-XRF uses a monochromatic X-ray beam focused to a few microns in diameter. The principle is the same as for the XRF system discussed earlier. A typical analytical mode is to raster the sample under the X-ray beam to produce element maps of the samples. This technique is used to determine bulk compositions of IDPs and the material in the Stardust tracks. 

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