Transmission-reflection studies

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. 

When light is directed onto a sample it may either be transmitted or reflected. Hence, one can obtain the spectra by either transmission or reflection. Since some of the light is absorbed and the remainder is reflected, study of the diffuse reflected light can be used to measure the amount absorbed. However, the low efficiency of this diffuse reflectance process makes it extremely difficult to measure 120) and it was speculated that infrared diffuse reflection measurements would be futile 120). Initially, an integrating sphere was used to capture all of the reflected light121) but more recently improved diffuse reflectance cells have been designed which allow the measurement of diffuse reflectance spectra using FT-IR instrumentation 122). 

There are several major areas of interfacial phenomena to which infrared spectroscopy has been applied that are not treated extensively in this volume. Most of these areas have established bodies of literature of their own. In many of these areas, the replacement of dispersive spectrometers by FT instruments has resulted in continued improvement in sensitivity, and in the interpretation of phenomena at the molecular level. Among these areas are the characterization of polymer surfaces with ATR (127-129) and diffuse reflectance (130) sampling techniques transmission IR studies of the surfaces of powdered samples with adsorbed gases (131-136) alumina(137.138). silica (139). and catalyst (140) surfaces diffuse reflectance studies of organo- modified mineral and glass fiber surfaces (141-143) metal overlayer enhanced ATR (144) and spectroelectrochemistry (145-149). 

Fig. 26. Transmission and reflection study with a Fourier spectrometer, a) background spectrum and interferogram b) sample spectrum and interferogram c) ratio of both spectra (reflectivity of CdCr2Sc4 in this example). —These data were obtained with a Beckman-RIIC Fourier spectrometer FS 720 with a Fourier transform computer FTC 300 attached to it...

A study of the feasibility of using infrared methods was conducted by the American Oil Company. Their results indicated that infrared studies of electrode surfaces by transmission or direct-reflection methods appear less promising than the internal-reflection technique. Even under favorable conditions, multiple internal-reflection studies (using germanium and silicon) proved... 

Since the initial report by Drs. Sperling and de Vries and their colleagues, inherited superactivity of PRPP synthetase has become established as an unusual cause of purine overproduction, hyperuricemia, and gout in man. To date, detailed investigations of 7 families with superactive PRPP synthetase have been published, and I am aware of 4 additional families currently under study. In each family, the index cases have been males, and where studied, the patterns of inheritance of the enzyme aberrations have been consistent with X-linked transmission, reflecting the apparent structural basis of superactivity in each defective enzyme. 

Kaynak, A., Unsowrth, J., Glout, R., Mohan, A. S., and Bears, G. R, A study of microwave transmission, reflection, absorption and shielding effectiveness of conducting polypyrrole films, J. Appl, Polym. ScL, 54, 269-278 (1994). 

SNOM can be applied in a range of modes including transmission, reflectance, and emission. Such techniques are likely to be coupled to electrochemical studies in the future. The spatial resolution of such imaging makes the possibility of interrogating potential control of single molecules a reality. 

A small-size target specimen will often need to be removed from a matrix in which it is buried by using a knife, scalpel, or needle in an appropriate and safe manner, depending on the conditions surrounding it. If the target specimen is covered by a layer of some other material this may need to be scraped off Infrared microscopic measurements are utilized in many areas of study. In order to satisfy the various needs, in addition to straightforward transmission measurements, various types of reflection measurements such as specular reflection, attenuated total reflection (ATR), and transmission-reflection measurements (described later) can be performed with an infrared microscope designed for such purposes. 

A DIGILAB 14B/D Fourier Transform infrared spectrometer was utilized to obtain 1 cm resolution spectra over the 4000 to 600 cm region for copolyether-urethane-urea, polyether-urethane, polypropylene glycol. Urethane I, Urethane II and Urea I. The sample chamber was allowed to come to equilibrium with a continuous nitrogen purge prior to data collection of 250 scans per sample for transmission studies and 1000 scans per sample for internal reflectance studies. 

Absorption spectroscopy provides a means to study particular details about a monolayer. Transmission spectroscopy is difficult because the film, which is thin, absorbs little. Gaines [1] describes multiple-pass procedures for overcoming this problem. Reflection spectroscopy in the UV-visible range has been reported for lipid monolayers [150,151] and in the IR range for oleic acid [152]. 

The use of DRIFTS for the characterization of surfaces has to date been limited, but has recently been used for applications in fields as diverse as sensors development [12], soils science [13], forensic chemistry [14], corrosion [15], wood science [16] and art [F7]. Given that there is in general no reason for preferring transmission over difilise reflectance in the study of high-area powder systems, DRIFTS is likely to become much more popular in the near fiiture. 

The ordered structure and molecule orientation in the monolayers, as suggested by the Hardy model, have been studied by various means. Electron diffraction techniques, for example, including both reflection and transmission, have been employed to examine the molecular orientation of adsorbed monolayers or surface hlms. The observations from these studies can be summarized as follows [3]. 

The Fe-B nanocomposite was synthesized by the so-called pillaring technique using layered bentonite clay as the starting material. The detailed procedures were described in our previous study [4]. X-ray diffraction (XRD) analysis revealed that the Fe-B nanocomposite mainly consists of Fc203 (hematite) and Si02 (quartz). The bulk Fe concentration of the Fe-B nanocomposite measured by a JOEL X-ray Reflective Fluorescence spectrometer (Model JSX 3201Z) is 31.8%. The Fe surface atomic concentration of Fe-B nanocomposite determined by an X-ray photoelectron spectrometer (Model PHI5600) is 12.25 (at%). The BET specific surface area is 280 m /g. The particle size determined by a transmission electron microscope (JOEL 2010) is from 20 to 200 nm. 

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