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Characterization of conducting GaAs multilayers by infrared spectroscopy at oblique incidence (1990)

Grosse, P. ; Harbecke, B. ; Heinz, B. ; [et al.]

Springer

Applied physics 50 (1990), S. 7-12

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ISSN: 1432-0630

Keywords: 78.20 ; 78.65

Source: Springer Online Journal Archives 1860-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics

Notes: Abstract The electrical and geometric properties of GaAs multilayer structures are measured nondestructively by infrared reflectance spectroscopy (50–5000 cm−1). Using oblique incidence and both s- and p-polarizations of the probing beam, carrier concentration and thickness of the epitactic films as well as the carrier concentration of the GaAs substrate are determined. The main structures in the spectra are due to phonon reststrahlen bands, Fabry-Perot interferences and the zeros of the dielectric function leading to dips in the reflectance (Berreman Mode). The results compare favorably with a depth-resolved secondary ion mass spectrometric (SIMS) sample analysis. The range of applicability of the method is discussed.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00323946

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1H NMR and molecular mechanics studies of epimeric ethyl esters of 20(R, S)-hydroxy-23-norcholanoic acids (1991)

Maier, M. S. ; Seldes, A. M. ; Gros, E. G.

Chichester : Wiley-Blackwell

Organic Magnetic Resonance 29 (1991), S. 137-142

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ISSN: 0749-1581

Keywords: 20(R,S)-Hydroxy-23-norcholanoic acid derivatives ; 1H NMR ; Pyridine-induced shifts ; Molecular mechanics calculations ; Chemistry ; Analytical Chemistry and Spectroscopy

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology

Notes: Proton chemical shifts for the C-18, C-21, —CO2CH2CH3 and —CO2CH2CH3 protons of epimeric ethyl esters of 20(R,S)-hydroxy-23-norcholanoic acids were measured in deuteriochloroform and pyridine-d5. The observed solvent shifts due to specific OH - pyridine hydrogen-bonded complexes allowed the quantification of the epimeric mixtures by analysis of the pyridine-d5 1H NMR spectra. The main features of the pyridine-induced shifts are rationalized in terms of the preferred conformations for the 20R- and 20S-epimers, which are predicted by molecular mechanics calculations.

Additional Material: 3 Ill.