In Transmission Mode

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... 

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).

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. 

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. 

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... 

Figure 3.9 Conceptual view of tandem mass spectrometry with a tandem-inspace triple quadrupole mass analyzer." The first mass analyzer (Ql) selects the precursor ion of interest by allowing only it to pass, while discriminating against all others. The precursor ion is then fragmented, usually by energetic collisions, in the second quadrupole (q2) that is operated in transmissive mode allowing all fragment ions to be collimated and passed into the third quadrupole (Q3). Q3 performs mass analysis on the product ions that compose the tandem mass spectra and are rationalized to a structure.

Based on the way the interferometer is configured, CCMI sensors can be categorized into two groups, namely the Mach-Zehnder interferometer (MZI) type and the Michelson interferometer (MI) type. The MZI sensor works in transmission mode, i.e., the transmitted interference signal is detected. The MI sensor works in reflection mode, where the light passes the interferometer twice and the reflected interference signal is detected. 

The use of parallel beam optics as a means for determining the polymorphic composition in powder compacts has been discussed [45]. In this study, compressed mixtures of known polymorphic composition were analyzed in transmission mode, and the data were processed using profile-fitting software. The advantage of using transmission, rather than the reflectance, is that the results were not sensitive to the... 

During crystallization procedures, undesirable oiling-out (i.e. liquid-liquid demixing) may occur. A UV-vis study of such systems with highly dispersed vesicles, or crystals, in transmission mode will capture... 

The NIR monitoring was done off-line using a Eoss NIRSystems Model 6500 analyzer in transmission mode and a quartz cuvette with 0.5-mm path length. The spectra had 10-nm wavelength resolution with data... 

Structural information of LB films has also been obtained from FTIR studies. In the carboxylate form of the fatty acid, the relative intensities of the vs(C02-) and va(C02-) signals are dependent on the orientation of the chain axis. The dipole moments of the vs(C02-) and va(C02 ) stretches are parallel to and perpendicular to the chain axis, respectively. In transmission mode the electric vector of the IR radiation interacts strongly with dipole moments parallel to the substrate. This means that in transmission mode the vs(C02-) will be most intense, and the va(C02-) the weakest, for films with the chain axis perpendicular to the substrate. The opposite is true for the FTIR-RA mode. There is general consensus that in M-FA films the chain axis is approximately perpendicular to the substrate while the protonated form of the acid after exposure to H2S has a tilt relative to the substrate. Further discussion of FTIR as an investigative tool into the reaction of M2+-FA films with dihydrogen chalcogenides is given in later sections. 

This work demonstrated a number of new results and opportunities for ultrafast XAS 1) it is possible to work with highly dilute solutions in transmission mode without dramatic loss of signal-to-noise ratio. This is very promising as one can envision the study of samples, for which large concentrations are impossible to reach. Biologically relevant samples are usually investigated in solutions with up to 1 mmol/1 concentration, and we therefore can envision such studies on the ultrafast time scales in the near future. 2) It is possible to scan the time delay between the laser pump pulse and the x-ray probe pulse, and therefore follow the evolution of the system from the start. 3) It also demonstrated the operation of an optical-x-ray cross-correlator (Fig. 6.b). The time resolution is not a limiting factor and the experiments are feasible with sources of shorter x-ray pulses, provided the flux is not too low. 

Vanadium K-edge XANES measured in transmission mode at 15 K showed that the attached V complex (2) maintained its square pyramidal conformation with a V=0 bond (Figure 2.2a). Curve-fitting analysis of V K-edge EXAFS Fourier transforms (Figure 2.2b) provided local structure information on the supported V complex (2) with an unsaturated conformation, which differs from that of the V-monomer precursor (1). The EXAFS curve-fitting was performed in the R-space with two shells short V=0 and long V—O bonds. A V=0 bond was observed at 0.157 0.001 nm,... 

Figure 17.13. Stacked C (Is) NEXAFS spectra of NOM from various sources and environments showing molecular-level structural and compositional heterogeneity. The spectra were recorded in transmission mode (fungi, bacteria, fresh charcoal, black C particle from Liang et al., 2006 black-C rich humic substance from Solomon et al., 2007b litter J. Lehmann, unpubl. data).

The 1.7% Co2+ ZnO DMS-QDs in Figure 34 were also examined by Zeeman spectroscopy in transmission mode. An average band-edge Zeeman shift of 53 cm 1/7 over the range of 0-7 T ( Fig. 35) was measured. The Zeeman data were analyzed in the mean-field approximation using Eq. 11, where x is the dopant mole fraction and (Sz) is the expectation value of the Sz operator of the spin Hamiltonian. 7/oa and iVop quantify the exchange interactions between the dopant and unpaired spins in the conduction (CB) and valence bands (VB), respectively (19, 159-161). 

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