Optical properties, spectroscopy reflectivity

Doornbos RMP, Lang R, Aalders MC, Cross FW, Sterenborg HJCM. The determination of in vivo human tissue optical properties and absolute chromophore concentrations using spatially resolved steady-state diffuse reflectance spectroscopy. Physics in Medicine and Biology 1999, 44, 967-981. 

These coefficients have the dimension of reciprocal length (Mills, 1988), in this context, cm Kubelka and Munk (1931) described the optical properties of pigments by employing the parameters a and r. The Kubelka-Munk theory is the basis of diffuse reflection spectroscopy (Sec. 6.4). We have extended the Kubelka-Munk approach in order to describe the Raman scattering of crystal powders (Schrader and Bergmann, 1967). The results can also be applied to liquids and transparent solids. The procedure is as follows ... 

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. 

Spectroscopy is in general terms the science that deals with the interaction of electromagnetic radiation with matter in particular, it can be said to be the investigation of the optical properties, i. e. the transmission or reflection, of a sample within a certciin spectral range. These properties are studied as a function of the wavelength or frequency of the incident electromagnetic radiation. The spectral range mainly under consideration here is the infrared. 

As everyone knows, the optical properties of a material are expressed in two optical constants, the refractive index n and the absorption coefficient x. It is the purpose of spectroscopy to determine experimentally one or both of these optical constants as a function of frequency. This can be done by measuring reflection or transmission. If we were able to measure amplitudes or electrical fields (magnitude and phase) in an optical investigation, it would generally be possible to deduce both optical constants from one measurement of either reflection or transmission. However, we are only able to measure intensities where the magnitude of the field is determined and the phase information is lost. Thus, in general, from one item of information only one optical constant is obtained, and two measurements are necessary to determine both. There are a few exceptions to this rule, e.g. the... 

Otto, A. (1975). Spectroscopy of Surface Polaritons by Attenuated Total Reflection. In Seraphin, B. O (Ed.), Optical Properties of Solids, New Developments. North-Holland, Amsterdam, p. 677. 

Spectroscopies such as UV-visible absorption and phosphorescence and fluorescence detection are routinely used to probe electronic transitions in bulk materials, but they are seldom used to look at the properties of surfaces [72]. As with other optical techniques, one of the main problems here is the lack of surface discrimination, a problem that has sometime been b q)assed by either using thin films of the materials of interest [73, 74], or by using a reflection detection scheme. Modulation of a parameter, such as electric or magnetic fields, stress, or temperature, which affects the optical properties of the sample and detection of the AC component of the signal induced by such periodic changes, can also be used to achieve good surface sensitivity [75]. This latter approach is the basis for techniques such as surface reflectance spectroscopy, reflectance difference spectroscopy/reflectance anisotropy spectroscopy, surface photoadsorption... 

Bermudez V M 1992 Infrared optical properties of dielectric/metal layer structures of relevance to reflection absorption spectroscopy J. Vac. Sci. Technol. A 10 152-7... 

Growth of multilayer periodic Z nS/ZnSe h eterostructures b y m etallorganic c hemical vapor deposition, their optical properties examined by ellipsometry and traditional spectroscopy are described. The results obtained evidence that the structures proposed are promising as efficient Bragg reflectors for blue semiconductor lasers. Reflection coefficient higher than 90% in the blue-green spectral range have been obtained. 

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... 

Two types of high electron mobility transistors (HEMTs) with 2D electron gas were made from AlGaN/GaN heterostructures grown by MOCVD on Si (111) substrates, and their electrical DC properties were compared. Optical study, namely photoluminescence, photoreflection and reflection spectroscopy of the structures was performed. The strain values in GaN layers (6.6 and 1.7 kBar) and electric field strength near the heterointerface (470 and 270kV/cm) were determined. A correlation between the HEMTs DC characteristics and the optical properties of GaN layers was demonstrated. 

In early in-situ infrared spectroscopy studies of catalyst supported on reflective Au substrates, it was recognized that spectral bands develop distortions due to anomalous optical effects as the catalyst coverage becomes greater than a few monolayers [17, 18, 158]. Different procedures were adopted to ensure that catalyst coverages on Au remained low [15, 17, 18, 157, 158]. Related to these efforts are experiments that examine the electrochemical and optical properties of nanostructured metal electrodes prepared by chemical, vapor, or electrochemical deposition methods (cf. Refs. [79, 137, 141, 170-179] and references therein). Much of the work in this area has targeted SEIRAS measurements. 

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