Calibration grating

Various types of calibration gratings for examination of lateral and vertical non-linearity of the SPM scanner, detection of angular distortions are developed. Mentioned characteristics are related with electro-mechanical parameters of scanning probe microscope positioning system. Necessity of check these parameters occurs not so freqently due to high level of widely used SPM models. 

The interior of bulk samples can be revealed by fracture, freeze fracture, or (cryo-/ultra)microtoming. These techniques are well established in electron microscopy and require substantial training to ensure that the knives used do not introduce scratches and other artefacts. Unlike in SEM or TEM analysis, however, it is very well possible to analyze the trimmed specimen instead of the very thin sections removed (cryofacing). This loosens the constraint of ultrathin sections in many applications. Care has to be taken that the sample to be imaged is not significantly thicker or thinner than the calibration grating used for scanner calibration (see Sect. 2.2.5)... 

If a flattening is necessary, it must be properly executed high and low features must be excluded from the analysis (see corresponding software manuals for exact procedures). In Fig. 2.36, an AFM height image of a calibration grating is shown, in which parts of the square shaped depressions were excluded from the calculation (as is advised). In the lower two rows, this has not been done on purpose. As a result, a vertical profile would show elevated areas between the depressions that are an artefact of the data processing. 

Fig. 2.36 AFM height image in which the upper part of the image was properly flattened, while for the lower parts the depressions were not excluded from the analysis. The calibration grating is of course devoid of elevated squares (compare also Fig. 2.28a)...

Fig. 2.41 Bearing analysis of AFM height image of calibration grating displaying the depth distribution (middle) and the cumulative distribution of depths (right)...

Figure 4. Images of Calibration Grating TGZ01 no g-control and using (7-contiol a), b) with a diamond tip c), d) with an AFM cantilever tip.

Figure 1. (a) Surface rendered topographic AFM image of calibration grating displaying tip geometry, (b) Profile of calibration grating and radius of curvature measurement. 

In Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), a gaseous, solid (as fine particles), or liquid (as an aerosol) sample is directed into the center of a gaseous plasma. The sample is vaporized, atomized, and partially ionized in the plasma. Atoms and ions are excited and emit light at characteristic wavelengths in the ultraviolet or visible region of the spectrum. The emission line intensities are proportional to the concentration of each element in the sample. A grating spectrometer is used for either simultaneous or sequential multielement analysis. The concentration of each element is determined from measured intensities via calibration with standards. 

Thanks are due David Kurtz for providing the Fenvalerate data and stimulating my interest in the detection-calibration problem. Helpful discussions with John Mandel concerning the Fenvalerate data set are also gratefully acknowledged. 

Many diffuse-reflectance instruments are available. Some employ several interference filters to provide narrow bands of radiation. Others are equipped with grating monochromators. Ordinarily, calibration is often a stringent requirement as samples must be acquired of the material for analysis that contain the range of analyte concentrations likely to be encountered. It may be useful to grind solid samples to a reproducible particle size. Equations are developed and used for the analysis. Once method development has been completed and validated, solid samples can be analyzed in a few minutes. Accuracy and precision are reported to be of 1 to 2% relative. 

---