Transmission modes

Monolayers can be transferred onto many different substrates. Most LB depositions have been perfonned onto hydrophilic substrates, where monolayers are transferred when pulling tire substrate out from tire subphase. Transparent hydrophilic substrates such as glass [18,19] or quartz [20] allow spectra to be recorded in transmission mode. Examples of otlier hydrophilic substrates are aluminium [21, 22, 23 and 24], cliromium [9, 25] or tin [26], all in their oxidized state. The substrate most often used today is silicon wafer. Gold does not establish an oxide layer and is tlierefore used chiefly for reflection studies. Also used are silver [27], gallium arsenide [27, 28] or cadmium telluride wafer [28] following special treatment. 

In many ways the nanocrystal characterization problem is an ideal one for transmission electron microscopy (TEM). Here, an electron beam is used to image a thin sample in transmission mode [119]. The resolution is a sensitive fimction of the beam voltage and electron optics a low-resolution microscope operating at 100 kV might... 

The PLM can be used in a reflection or a transmission mode. With either mode, light of various wavelengths from ultraviolet to infrared, polarized or unpolarized, is used to yield a wide variety of physical measurements. With just ordinary white light, a particle or any object detail down to about 0.5 p.m (500 nm) in diameter can be observed to detect shape, size, color, refractive index, melting point, and solubiUty in a group of solvents, all nondestmetively. Somewhat larger particles yield UV, visible, or IR absorption spectra. 

In the studies described above, the samples were supported in low atomic weight matrices, melted in situ, and measured in transmission mode. Similarly, second... 

Figure 16-28. Oocl-OPV5 111 its nenialic phase ai I 8) C. Left polari/ed-light optical micrograph (scale ban SO pm Zeiss pliolomieroscopc). Right X-ray dillraclioii scan (0-20 scanning in transmission mode. CuKu radiation. /.= 1.5418 A).

The reaction on the catalyst surface was followed by in situ i.r. spectroscopy using a Bruker IFS88 FTIR spectrometer for the characterisation of sorbed species and mass spectroscopy for the analysis of gas phase. The state of Pt was further investigated by in situ X-ray absorption spectroscopy (Daresbury, UK, beamline 9.1, transmission mode, Si(220) monochromator, Pt-Lj, edge). Details of catalyst characterisation techniques are reported elsewhere [13,14]. 

In situ XRD spectra were collected on beam line X18A at the National Synchrotron Light Source (NSLS) located at Brookhaven National Laboratory (BNL). The X-ray wavelength (X) was 1.195 A. The step size of the 29 scan was 0.02° in the regions with Bragg reflections and 0.05° in the regions without reflections. The XRD spectra were collected in the transmission mode (Liu et al., 2004). 

Fig. 3.19 Schematic illustration of the measurement geometry for Mossbauer spectrometers. In transmission geometry, the absorber (sample) is between the nuclear source of 14.4 keV y-rays (normally Co/Rh) and the detector. The peaks are negative features and the absorber should be thin with respect to absorption of the y-rays to minimize nonlinear effects. In emission (backscatter) Mossbauer spectroscopy, the radiation source and detector are on the same side of the sample. The peaks are positive features, corresponding to recoilless emission of 14.4 keV y-rays and conversion X-rays and electrons. For both measurement geometries Mossbauer spectra are counts per channel as a function of the Doppler velocity (normally in units of mm s relative to the mid-point of the spectrum of a-Fe in the case of Fe Mossbauer spectroscopy). MIMOS II operates in backscattering geometry circle), but the internal reference channel works in transmission mode...

Conversion electron Mossbauer spectroscopy (CEMS) measurements with back scattering geometry have the merit that spectra can be obtained from a sample with much less isotope content compared with transmission measurements. Another merit is that a sample, deposited on a thick substrate, could be measured, and that because of the limited escape depth of the conversion electrons, depth-selective surface studies are possible. The CEMS technique was found to be best applicable to specimens of 10-100 pg Au cm, i.e., about two orders of magnitudes thinner than required for measurements in transmission mode [443]. This way (1) very thin films of gold alloys, as well as laser- and in beam-modified surfaces in the submicrometers range of depth [443], and (2) metallic gold precipitates in implanted MgO crystals [444] were investigated. 

Spectroscopic evaluation of the catalysts. The UV-Vis spectra of the Jacobsen Co-salen catalysts were collected in the transmission mode on a CARY-3E UV-Vis spectrophotometer by dissolving the catalysts in epichlorohydria The Co K-edge (7709 eV) X-ray absorption near edge stracture, XANES, of Jacobsen s Co-salen catalyst was collected during the HKR reaction at beamline XIO-C at National Synchrotron Light Source (NSLS), Brookhaven National Lab, Upton, NY. 

Figure 57.11. The HRTEM of the CA53 aetivated at 110°C for 120 min in both the transmission mode (A) and the diffraetion mode at a wide lens aperture (B) (30).

In a transmission mode instrument, the Nd YAG laser beam is focussed on the back side surface of thin samples (<1 pm thick). A spot diameter of 0.5 pm is possible, and commercial instruments of this configuration have been used primarily for biomedical and particle analysis applications. 

The most extensive study of the nickel oxide electrode is that of McBreen et a/.,83 who employed an in situ cell in a transmission mode (see cell in Fig. 17). The study of nickel oxide is complicated by the numerous species present and their interconversion. McBreen... 

In transmission mode a spatial resolution of about 15-20 pm can be achieved with infrared microscopes [32]. This is generally sufficient to properly identify such as small impurities, inclusions, gels or single components of multilaminate foils. Similar to Raman spectroscopy, line profiles or maps over larger sample areas can be performed. 

With real data, a more scientifically valid approach would be to correct the nonlinearity from physical theory. In the current case, for example, a scientifically valid approach would be to convert the data to transmission mode, subtract the stray light and reconvert to absorbance the nonlinear wavelengths would have become linear again. There are, of course, several things wrong with this procedure, all of them stemming from the fact that this data was created in a specific way for a specific purpose, not necessarily to be representative of real data ... 

Fig. 10 a Co K-edge XAS spectrum for CoP collected in transmission mode, showing the approximate regions where XANES and EXAFS features are observed and the assignment of dipolar and quadrupolar transitions, b EXAFS (x) vs. k curve, c Fourier transform of EXAFS... 

Fig. 21 a Normalized As K-edge XANES spectra for FeAs and some FeAsi j,Py members, measured in transmission mode, b Orbital projections of conduction states calculated from FeAs and FeAso.5oPo.50 (the Fermi edge is at OeV). Reprinted with permission from [61]. Copyright Elsevier... 

The Fe K-edge spectra were recorded in the transmission mode and a metallic iron foil spectrum was measured simultaneously with each sample spectrum for energy calibration. X-ray absorption spectra for each sample were collected from 7,520 to 8,470 eV, with a step size of 0.40 eV and acquisition times of ca. 68 s per sample. Measuring each sample, in turn, and repeating... 

Due to the opaque nature of most solids, investigations that use some type of electronic spectroscopy as a means of characterization cannot be performed in the transmission mode. Studies performed in the solid state therefore must make... 

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