Raster-scan mode

Laser scanning is the step needed to convert pre-designed CAD patterns into real structures. Two basic modes for direct laser scanning can be utilized, raster-scan mode and vector-scan mode, of which the concepts are illustrated in Figs. 31a, b. 

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.

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]. 

In the scanning mode the electron beam focused on the sample is scanned by a set of deflection coils. Backscat-tered electrons or secondary electrons emitted from the sample are detected. As the electron beam passes over the surface of the sample, variations in composition and topology produce variations in the intensity of the secondary electrons. The raster of the electron beam is synchronized with that of a cathode ray tube, and the detected signal then produces an image on the tube. 

The first method [87,88] uses a matrix form of the Beer-Lambert absorption law in a transmission mode. A 2-D material sample is raster-scanned by a pulsed, tunable THz source to generate an N rows x L columns image matrix [/] where N is the number of THz frequencies used and L is the number of pixels. The values of [/] are the measured total absorbance at each pixel. Separate absorption experiments with known materials of interest establish the THz spectra both graphically and through the N x M spectra matrix [S], where M is the number of components. The collection of species can include non-agent materials that can affect the absorptions for example, barrier materials with spectra that are typically weakly frequency dependent. The spatial patterns of the agents are contained in the M x L matrix [P], The values of [P] effectively contain agent concentration information. 

Mapping the transihons across boundaries between botanical parts in wheat and corn, shown as A-E on the wheat sechon (Figure 7.3a) and F-J on the corn kernel (Figure 7.3b), was accomplished in a raster scan procedure. This was achieved in a transmission mode between the hme that the IRps instrument was installed, and 1995. Spectra from each mapping experiment yielded functional group images... 

Figure 15.2 shows the different types of EBLs, along with their writing strategies. This figure also illustrates how the exposure tool has evolved from being a tool that used a Gaussian beam (in raster scan or vector scan mode) to print one pixel at a time on the wafer, to one that used a shaped beam (with fixed or variable shape) to print one pixel at a time on the wafer, then to one that used a shaped beam to project and print an entire cell or character at a time on the wafer, and then to one... 

AFM measures attractive or repulsive forces between a probe and the sample. In the repulsive contact mode, the tip of the probe is attached to a cantilever. Vertical deflections of the cantilever caused by surface variations are monitored as a raster scan drags the tip over the sample. This imaging mode is used to study hard samples and provides images with angstrom resolution. If the sample is soft, a noncontact mode is preferred. 

The PUs microstructure can be also investigated by means of atomic force microscopy (AFM). Phase images obtained via AFM, enable visual representation of the PUs microphase separated morphology. AFM records the surface topography of materials by measuring attractive or repulsive forces between the probe and the sample. Vertical deflections caused by surface variations are monitored as a raster scan drugs a fine tip over the sample. A detailed description of different modes in AFM technology has been described in [195]. 

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