STEP SCANNING

Although very detailed, fundamental information is available from ultrafast TRIR methods, significant expertise in femtosecond/picosecond spectroscopy is required to conduct such experiments. TRIR spectroscopy on the nanosecond or slower timescale is a more straightforward experiment. Here, mainly two alternatives exist step-scan FTIR spectroscopy and conventional pump-probe dispersive TRIR spectroscopy, each with their own strengths and weaknesses. Commercial instruments for each of these approaches are currently available. 

In conventional nanosecond pump-probe dispersive TRIR experiments, also described previously, kinetic data are collected at one frequency at a time. These data can then be used to construct a series of time-resolved IR spectra. Thus, in the dispersive experiment kinetic data are used to construct spectra, and in the step-scan experiment spectral data are used to derive kinetics. 

Figure 4.16. Experimental setting of the combined femtosecond pulsed laser and step scan IR spectrometer (left) and modifications of the infrared interferogram after the laser pulse (right) [187].

Seguin, E., Thibault-Starzyk, F. and Arnolds, H. (2006) Coupling step scan IR and pulsed laser for operando at 33ns in catalysis, proceedings of operando - II Second international congress on operando spectroscopy, Toledo (Spain), 23-27 April, 2006. 

This procedure can only be applied for a Kratky camera with zero-dimensional detector. It shows the value of this classical step-scan device for studies of scattering in absolute intensity units. 

X-ray diffraction was done using a Siemens D-500 diffractometer utilizing CuKa radiation (1.406 A). The data were collected as step scans, with a step size of 0.05° 29 and a count time of 2 s/step between 10° and 80° 29. 

Vasenkov, S. and Frei, H. (2000). Time-resolved study of acetyl radical in zeolite NaY by step-scan FT-IR spectroscopy. J. Phys. Chem. A 104, 4327 4332... 

Step-growth reactions, 24 16 Step-scan ftir photoacoustic analysis, 19 564... 

Figure 3. Schematic of present and potential future optical lithography systems (a) Perkin Elmer Micralign (10), (b) Bell Labs printer (11), (c) reduction step-and-repeat (Censor, Electromask, GCA, Optimetrix, Philips), (d) IX step-and-repeat (Ultratech), (e) IX stripe scan, and (f) reduction step-scan, R indicates object and image orientations. Lenses are indicated only schematically. (Reproduced with permission from Ref. 30)...

E.N. Lewis, RJ. Treado, R.C. Reeder, G.M. Story, A.E. Dowrey, C. Marcott and I.W. Levin, Fourier transform step-scan imaging interferometry high-definition chemical imaging in the infrared spectral region. Anal. Ghent., 67, 3377-3381 (1995). 

Figure 11. SIMS step scan analysis of the interfacial substrate surface between the initial scribe and the edge of the delaminated zone coating and test conditions as in Figure 10.

Figure 13. SIHS step scan analysis of a portion of the zone of...

Figure 4 Step-scan FTIR spectra of 1-naphthyl acetate photodissociation and carbonyl species). (Adapted from Ref. 56.)...

Ganguly J., Bhattacharya R.N., and Chakraborty S. (1988) Convolution effect in the determination of compositional profiles and diffusion coefficients by microprobe step scans. Am. Mineral. 73, 901-909. 

Application of nLFP techniques in the IR region has been available for well over a decade. In one approach, laser diodes are used to generate the monitoring beam and a fast IR detector employed. Alternatively, a step-scan spectrometer uses the same methodologies employed by normal Fourier transform infrared (FTIR) spectrometers, but spectral capture is much faster. 

E Acquisition with Step Scanning F Calibration of Spectra... 

The processes involved in data acquisition and the considerations relevant to obtaining appropriate data for deconvolution are nearly identical for both continuous scanning and step scanning instruments. Where no specific distinction is noted, no differences are significant at the current state of the deconvolution art. Sampling, aliasing, and other details of the data-acquisi-tion process can be analyzed using the methods discussed in Chapter 1. 

In our operations, we often establish step-scan parameters as if we were continuously scanning. Because continuous scanning requirements are more demanding, no problems arise using this approach. 

For chemically stable systems for which time resolution is not needed, Clausen etal. (52) obtained excellent spectral quality by combining normal EXAFS with XRD simply by recording the two data sets sequentially for the catalyst sample in the same setup. In this approach (Fig. 9) a diffractometer was mounted between the first and second ionization chambers in a standard EXAFS spectrometer setup, and the EXAFS was then recorded by step-scanning the monochromator through the energy region of interest (33). The XRD pattern can be acquired at the most convenient wavelength,... 

X-ray absorption spectroscopic measurements were carried out at the storage ring DORIS III (HASYLAB DESY, Hamburg, Germany) at the EXAFS II beam line, which was equipped with a Si (111) double-crystal monochromator. All spectra were recorded at room temperature in a step-scanning mode. For data analyses the program WinXAS [17] was used. 

Several improvements to the basic data collection algorithm have been made. Perhaps the most significant is the use of the step-scan technique, versions of which were developed in 1969 for our computerized diffractometer, and simultaneously elsewhere. 

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