Differential reflection spectroscopy

In fact, with the very recent addition of differential reflection spectroscopy (DRS) to the suite of applicable technologies, as described in Chapter 15, we now have the possibility of sensing trace quantities of explosives where they are most often found in the environment, adsorbed to solid surfaces. Technologies that can, like DRS, locate these traces in situ offer a very different way to approach the problem. There have been several recent attempts to do this in situ detection from some distance away. To date the DRS seems the most successful. It has demonstrated detection at a range of a few meters. 

REMOTE SENSING OF EXPLOSIVE MATERIALS USING DIFFERENTIAL REFLECTION SPECTROSCOPY... 

Hummel, R. E. Differential reflectance spectroscopy in analysis of surfaces, in R. A. Meyers, Ed. Encyclopedia of Analytical Chemistry, Wiley, Chichester, 2000, p. 9047-9071. 

Chapter 15, Differential Reflection Spectroscopy for Detection of Explosive Materials, describes a quite different type of technology that became available just as this book was in press. It is different from all the others described herein because it seeks to remotely locate and identify the explosive molecules in situ, whereas all the other trace sensing technologies require that some molecules be taken into the apparatus, ingested, in order to be sensed. This approach presents exciting possibilities, but is just emerging, with no field experience yet. 

The structures were grown in an ultra high vacuum (UHV) chamber VARIAN with a base pressure of 2-10 °Torr equipped with differential reflectance spectroscopy (DRS) [3] for a study of optical properties of the samples. Samples were cut from n-type 0.3 D cm Si(l 11) substrates. The silicon was cleaned by flashes at 1250 °C (7 times). Surface purity was controlled by AES. RDE was carried out at 500 °C, 550 °C, and 600 °C. The Cr deposition rate was about 0.04 nm/min controlled by a quartz sensor. An additional annealing during 2 min at 700 °C was done for all samples before the growth of silicon epitaxial cap layer. 

UV-VISIBLE reflectance spectroscopy is used to investigate the optical properties of metal surfaces and its change with electrode potential, to detect surface states at the metal-electrolyte interface. Differential reflectance spectroscopy gives information on surface reactions or adsorbate formation. 

Growth experiments were carried out in two ultra high vacuum (UHV) cambers with sublimation sources of Si, Fe and Cr and quartz sensors of film thickness. Optical properties of the samples were studied in UHV chamber VARIAN (210 10Torr) equipped with differential reflectance spectroscopy (DRS) facilities. The samples surface was studied in the second UHV chamber (1 -10 9 Torr) equipped with LEED optics. Si(100) and Si(l 11) wafers were used as substrates for different series of the growth experiments. For the growth of silicide islands, metal films of 0.01-1.0 nm were deposited onto silicon surface. Silicon overgrowth with the deposition rate of 3-4 nm/min was carried out by molecular beam epitaxy (MBE) at 600-800 °C for different substrates. The samples were then analyzed in situ by LEED and ex situ by HRTEM and by... 

Gale, R.J., Sefaja, J. and Fleischmann, M. (1981) Modulated differential reflectance spectroscopy of lead dioxide films during growth. Analytical Chemistry, 53,1457. 

McIntyre, J.D.E. and Aspnes, D.E. (1971) Differential reflection spectroscopy of very thin surface Aims. Surf Set, 24,417-434. 

In a systematic study, the deposition of thin Ag overlayers on a Cu(lll) electrode was investigated by electroreflectance and differential reflectance spectroscopy, employing an optical thin-layer cell (Figure Figure 55... 

The deposition of metals onto semiconductor electrodes is sensitively monitored by differential reflectance spectroscopy because of the vast differences in the optical constants of metals and semiconductors. " Figure 58 illustrates the reflectance changes, R/R, for a ZnO electrode (which is an... 

The initial stages, notably the formation of a monolayer on a foreign substrate at underpotentials, were mainly studied by classical electrochemical techniques, such as cyclic voltammetry [8, 9], potential-step experiments or impedance spectroscopy [10], and by optical spectroscopies, e.g., by differential reflectance [11-13] or electroreflectance [14] spectroscopy, in an attempt to evaluate the optical and electronic properties of thin metal overlayers as function of their thickness. Competently written reviews on the classic approach to metal deposition, which laid the basis of our present understanding and which still is indispensable for a thorough investigation of plating processes, are found in the literature [15-17]. 

To overcome the limitation of detecting only a color change in the sensing colloidal crystal films, we apply a differential spectroscopy measurement approach coupled with the multivariate analysis of differential reflectance spectra. In differential spectroscopy, the differential spectrum accentuates the subtle differences between two spectra. Thus, in optical sensing, when the spectral shifts are relatively small, it is well accepted to perform measurements of the differential spectral response of sensing films before and after analyte exposure6 19. Therefore, the common features in two spectra of a sensing film before and after analyte exposure cancel and the differential spectrum accentuates the subtle differences due to analyte response. 

Overall it is quite clear, that a combination of epr spin-probes, UV-vis reflectance spectroscopy, size exclusion and intrazeolite oxidation experiments are able to effectively differentiate those organometallic-zeolite impregnations which place metal guests within the internal voids of the zeolite compared to those on the external surface of the zeolite lattice. 

We already know that PM-IRRAS combines Fourier transform mid-IR reflection spectroscopy with fast PM of the incident beam (ideally between p- and s-linear states) and with two-channel electronic and mathematical processing of the detected signal in order to get a differential reflectivity spectrum AR/... 

We will first describe briefly the main experimental techniques coupled with electrochemical methods Infrared Reflectance Spectroscopy (IRS), Electrochemical Quartz Crystal Microbalance (EQCM), Differential Electrochemical Mass Spectrometry (DEMS), Chemical Radiotracers and High Performance Liquid Chromatography (HPLC). 

Neville, G. A., Beckstead, H. D. and Shurvell, H. F. (1992). Utility of Fourier transform Raman and Fourier transform infrared diffuse reflectance spectroscopy for differentiation of polymorphic spirolactone samples. J. Pharm. Set, 81, 1141-6. [129, 132]... 

Abbreviations CCK, cholecystokinin RNase. ribonuclease G-protein, guanine nucleotide binding protein GPCR, G-protein-coupled receptor. SDS sodium dodecylsulfate, CTAH. hexadecyltrimethyl ammonium hydroxide DMPC. di-myristoylphosphatidylcholine DPPC, di-palmitoylphosphatldylcholine CMC, critical micellar concentration SUV, small unilamellar vesicles CD, circular dichroism NMR, nuclear magnetic resonance hs-DC, high sensitivity differential scanning calorimetry IR-ATR, infrared attenuated total reflection spectroscopy NOE, nuclear Overhauser effect MD, molecular dynamics DMSO, dimethylsulfoxide TFE, trifluoroethanol for abbreviations of peptides see tables land 2, and fig. 11. 

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