Search results for " vibration"
showing 10 items of 296 documents
Raman and infrared studies ofLa1−ySryMn1−xMxO3(M=Cr, Co, Cu, Zn, Sc or Ga): Oxygen disorder and local vibrational modes
2006
We present results of our study of polarized Raman scattering and infrared reflectivity of rhombohedral ceramic La1-ySryMn1-xMxO3 manganites in the temperature range between 77 and 320 K. In our samples, a part of the Mn atoms is substituted by M = Cr, Co, Cu, Zn, Sc, or Ga with x in the range 0-0.1. The hole concentration was kept at the optimal value of about 32% by tuning the Sr content y. We have monitored distortions of the oxygen sublattice by the presence of broad bands in the Raman spectra, the increase of dc resistivity extracted from the infrared reflectivity, and the change of the critical temperature of the ferromagnetic transition. Our results support the idea that these proper…
Temperature- and Magnetic-Field-Dependent Longitudinal Spin Relaxation in Nitrogen-Vacancy Ensembles in Diamond
2011
We present an experimental study of the longitudinal electron-spin relaxation time (T1) of negatively charged nitrogen-vacancy (NV) ensembles in diamond. T1 was studied as a function of temperature from 5 to 475 K and magnetic field from 0 to 630 G for several samples with various NV and nitrogen concentrations. Our studies reveal three processes responsible for T1 relaxation. Above room temperature, a two-phonon Raman process dominates, and below, we observe an Orbach-type process with an activation energy, 73(4) meV, which closely matches the local vibrational modes of the NV center. At yet lower temperatures, sample dependent cross relaxation processes dominate, resulting in temperature …
Depth profiling of optical and vibrational properties in GaN/AlN quantum dot superlattices
2009
Spatially resolved confocal μ-Raman and μ-photoluminescence experiments were performed to analyze the vibrational and optical properties of GaN/AlN quantum dots as a function of depth. Two approaches have been followed. First, spectra were taken by defocusing the microscope objective at various depths on the sample surface. In a second set of experiments a bevel at an angle of 20° with respect to the surface normal was prepared by mechanical polishing of the surface, and spectra were taken across the bevel. The E2h vibrational modes ascribed to the GaN QDs and the AlN spacer redshift towards the surface, indicating the progressive relaxation of the QDs and a considerable increase of the ten…
Structural and luminescence properties of GaN nanowires grown using cobalt phthalocyanine as catalyst
2015
Catalyst free methods have usually been employed to avoid any catalyst induced contamination for the synthesis of GaN nanowires with better transport and optical properties. Here, we have used a catalytic route to grow GaN nanowires, which show good optical quality. Structural and luminescence properties of GaN nanowires grown by vapor-liquid-solid technique using cobalt phthalocyanine as catalyst are systematically investigated as a function of various growth parameters such as the growth temperature and III/V ratio. The study reveals that most of the nanowires, which are several tens of microns long, grow along [101¯0] direction. Interestingly, the average wire diameter has been found to …
Evaluation of the influence of light-curing units on the degree of conversion in depth of a bulk-fill resin.
2020
Background It is known that bulk-fill have been widely studied and used by dentists in the clinic. However, the use of light-curing units that do not have the ability to adequately light-cure these materials at the appropriate depth can affect their clinical performance. The aim of this study was evaluating the influence of 5 different light curing units (LCUs) on the degree of conversion (DC) of a bulk-fill resin at depths of 0 to 4 mm and determined the effect of using 20s exposure and 40s. Material and methods Cylinders of composite were made in a stainless steel matrix (n=10). The specimens were exposed from the top surface using 5 LCUs: Valo® Cordless (VA); Radii Plus (RA); Emitter.D (…
<title>Vibrational spectra of tungsten oxides with different lattice topology</title>
1997
It is determined that vibrations of linear chains -O-W-O-W- in tungsten-oxygen network are rather independent. The value of vibrational frequency is determined by asymmetry of O equals W - O bonds.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
Identification Techniques I
2012
Infrared (IR) and Raman spectroscopy have a high potential for characterisation of material. Extensive series of wet chemical analysis may be substituted by a single spectroscopic measurement followed by detailed chemometric data evaluation. Topics of this chapter are: (i) basics of IR and Raman spectroscopy, (ii) the registration of “correct” spectra, and (iii) spectra evaluation. Dedicated applications in the area of conservation science are collected in separate chapters. The infrared (IR) spectrum is often called the fingerprint of a substance. An IR spectrum identifies a substance like a human fingerprint. Due to their origin the features of an IR spectrum are bands, not peaks. They in…
Vibrational modes and strain in GaN/AlN quantum dot stacks: dependence on spacer thickness
2007
We have investigated the influence of spacer thickness on the vibrational and strain characteristics of GaN/AlN quantum dot multilayers (QD). The Raman shift corresponding to the E2h vibrational mode related to the QDs has been analyzed for AlN thicknesses ranging from 4.4 nm to 13 nm, while the amount of GaN deposited in each layer remained constant from sample to sample. It is shown that there is a rapid blue shift of the GaN vibrational mode with spacer thickness when its value is smaller than 7 nm while it remains almost constant for thicker spacers. A rapid increase of the Raman line-width in the thicker samples is also observed. The experimental behavior is discussed in comparison wit…
Influence of external stretching on hydrogen electromigration in Pd and PdCu, PdAg alloys
2005
Influence of external stretching of Pd and Pd77Cu23 and Pd77Ag23 alloys on hydrogen electromigration in these systems was investigated. The electro-resistivity method was applied in the investigations. It was found that in order to furnish a full description of the kinetics and dynamics transport of hydrogen in the externally applied electric field to samples in the state of elastic and plastic stretching, it is not sufficient to provide a functional dependence of two commonly used parameters (diffusion coefficient D and effective valence Zeff) on degree of deformation. To describe the electromigration in these conditions a mathematical model was applied, which assumes the existence of two …
On the flexural vibrations of sandwich plates
1995
A simplified approach to sandwich plate free vibrations, based on the superposition method, can provide approximations to the lowest modes for various boundary conditions, showing a characteristic influence of the bending-shear stiffness ratio.