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Raman spectroscopy of the hydrogen bond in the associates H2OxHNO3 and (HNO3)2NO3(-). Evans windows

100%

Potier A. , Potier J. , Herzog M. H. , Herzog J. F.

1998

tom Vol. 72, nr 2

292-301

The discontinuous shifts of Raman lines with the concentration between 500 and 2600 cm(-1) in solutions of HNO3-H2O and KNO3-HNO3 show the formation of the associates H2OxHNO3 and (HNO3)2xNO3(-). The study of the 2000-3600 cm(-1) range enhances the complexity of the OH' spectra with the occurrence of Evans windows, owing to the formation of hydrogen bonds in the two associates.

Charge-sensitive vibrational modes in the (EDT-TTF-OX)2AsF6 chiral molecular conductors

88%

Olejniczak I. , Frąckowiak A. , Matysiak J. , Madalan A. , Pop F. , Avarvari N.

Open Physics

2014

tom 12

nr 3

215-220

Infrared and Raman spectra of three chiral molecular conductors (EDT-TTF-OX)2AsF6, comprising of two salts based on enantiopure EDT-TTF-OX donor molecules and one based on their racemic mixture, have been measured as a function of temperature. In the frequency range of the C=C stretching vibrations of EDT-TTF-OX, charge-sensitive modes are identified based on theoretical calculations for neutral and oxidized EDT-TTF-OX using density functional theory (DFT) methods. The positions of C=C stretching modes in both Raman and infrared spectra of the (EDT-TTF-OX)2AsF6 materials are analyzed assuming a linear relationship between the frequency and charge of the molecule. The charge density on the EDTTTF-OX donor molecule is estimated to be +0.5 in all investigated materials and does not change with temperature. Therefore we suggest, that M-I transition observed in (EDT-TTF-OX)2AsF6 chiral molecular conductors at low temperature is not related to the charge ordering mechanism.

Determination of the LO phonon energy by using electronic and optical methods in AlGaN/GaN

88%

Celik O. , Tiras E. , Ardali S. , Lisesivdin S. , Ozbay E.

Open Physics

2012

tom 10

nr 2

485-491

The longitudinal optical (LO) phonon energy in AlGaN/GaN heterostructures is determined from temperature-dependent Hall effect measurements and also from Infrared (IR) spectroscopy and Raman spectroscopy. The Hall effect measurements on AlGaN/GaN heterostructures grown by MOCVD have been carried out as a function of temperature in the range 1.8-275 K at a fixed magnetic field. The IR and Raman spectroscopy measurements have been carried out at room temperature. The experimental data for the temperature dependence of the Hall mobility were compared with the calculated electron mobility. In the calculations of electron mobility, polar optical phonon scattering, ionized impurity scattering, background impurity scattering, interface roughness, piezoelectric scattering, acoustic phonon scattering and dislocation scattering were taken into account at all temperatures. The result is that at low temperatures interface roughness scattering is the dominant scattering mechanism and at high temperatures polar optical phonon scattering is dominant.