Search results for "Spectral"
showing 10 items of 3116 documents
CEMS Study of 57Fe Implanted in Diamond
2002
Conversion electron Mossbauer (CEMS) measurements have been made on a diamond sample implanted with 70 keV 57Fe to a dose of 5 × 1014 cm−2. CEMS spectra were collected in the as-implanted state and after annealing the diamond up to 1470 K. The lower temperature spectra were consistently fitted with three symmetric doublets. With annealing the areal fractions of two of the doublets increased to 44% and 48 %, respectively, while that of the third doublet decreased to be replaced by a single line component with isomer shift δ = 0.0 mm/s. Comparison of the observed isomer shifts with recent in-beam Mossbauer measurements and theoretical calculations allow us to attribute the singlet to intersti…
Positron Annihilation with Electrons of Admixture Atoms in Some Binary Nickel Alloys
2005
Weighted difference curves have been shortly presented as a proper tool allowing to analyze in another way two-detector Doppler spectra regarding positron annihilation with admixture electrons in some nickel alloys. The analysis of low and middle momentum parts of Doppler spectra for investigated alloys reflects the annihilation of positrons with admixture electrons. There is no distinct signal of annihilations with admixture electrons from the positron lifetime data for well-annealed samples.
Numerical and experimental investigation of short Au nanorods
2014
The plasmonic properties of Au nanorods (NRs) have been investigated theoretically and experimentally, a system that is of high current interest in relation to various nanophotonics applications. The non-aligned NRs arrays were formed by a seed-mediated growth method that relies on the reduction of metal salt by a weak reduction agent in the presence of preformed metallic seed nanoparticles. We applied the finite-element method to calculations of absorption spectra from gold NRs supported in an aqueous solution. Comparison to experimentally measured spectra is found in a good agreement.
Linear and Angular Distyrylpyrazines with Terminal Donor Groups: Synthesis, Solvatochromism, and Acidochromism of the Electronic Spectra
2011
A series of linear and angular distyrylpyrazines and lateral donor groups has been prepared by aldol condensation between dimethylpyrazines and the appropriate aromatic aldehyde. The optical absorption and emission properties of these systems were studied in different solvents and media. The materials display a strong solvatochromism of the emission that is reflected by large red shifts of their fluorescence emission maxima on increasing the solvent polarity. This behaviour suggests a highly polar emitting state, which is characteristic of compounds that undergo an internal charge transfer upon excitation. Upon protonation, the UV-vis spectra are altered, and the fluorescence intensity of t…
Photothermal excitation setup for a modified commercial atomic force microscope
2014
High-resolution imaging in liquids using frequency modulation atomic force microscopy is known to suffer from additional peaks in the resonance spectrum that are unrelated to the cantilever resonance. These unwanted peaks are caused by acoustic modes of the liquid and the setup arising from the indirect oscillation excitation by a piezoelectric transducer. Photothermal excitation has been identified as a suitable method for exciting the cantilever in a direct manner. Here, we present a simple design for implementing photothermal excitation in a modified Multimode scan head from Bruker. Our approach is based on adding a few components only to keep the modifications as simple as possible and …
Water orientation and hydrogen-bond structure at the fluorite/water interface
2016
AbstractWater in contact with mineral interfaces is important for a variety of different processes. Here, we present a combined theoretical/experimental study which provides a quantitative, molecular-level understanding of the ubiquitous and important CaF2/water interface. Our results show that, at low pH, the surface is positively charged, causing a substantial degree of water ordering. The surface charge originates primarily from the dissolution of fluoride ions, rather than from adsorption of protons to the surface. At high pH we observe the presence of Ca-OH species pointing into the water. These OH groups interact remarkably weakly with the surrounding water and are responsible for the…
Angular dependence of recombination luminescence-detected EPR in a ZnO crystal
2015
Angular dependency of electron paramagnetic resonance, optically detected by UV-excited recombination luminescence (RL-EPR), was measured for nominally pure ZnO single crystals. Observed magnetic resonances belong to the broad yellow RL band with slow decay centred at 610 nm, which is characteristic of untreated ZnO crystals. In the sample, irradiated with the 266 nm UV laser, an additional RL band centred at 740 nm appears, which has considerably faster decay time than the yellow one. This RL band is characteristic of the luminescence of Fe3+ ions in the ZnO crystals. It could be observed only after the UV laser treatment. No RL-EPR signal was detected for this RL band. Our spectral simula…
Direct observation of Drude behavior in the heavy-fermion by broadband microwave spectroscopy
2005
Abstract Previous optical studies on the heavy-fermion system UPd 2 Al 3 down to frequencies of about 1 cm - 1 ( = 30 GHz ) revealed a well-pronounced pseudogap at low frequencies (below 3 cm - 1 ) that was attributed to magnetic correlations. Thus, the optical conductivity at even lower frequencies is of notable interest because the Drude roll-off (the high-frequency characteristic of a metal which will give information on the quasiparticle dynamics) remained hidden at extremely low frequencies. Using a novel cryogenic broadband microwave spectrometer employing the Corbino geometry we have studied the complex optical conductivity of UPd 2 Al 3 thin films in the frequency range from 45 MHz …
Soft mode in PMN–PSN ceramics
2008
Various ordered and disordered (1–x)Pb(Mg1/3Nb2/3)O3 –x Pb(Sc1/2Nb1/2)O3 (PMN–PSN) ceramics were studied by THz transmission spectroscopy in the temperature range of 10–300 K. It is found that the dielectric relaxation dominates in the spectra in higher temperatures, T > 170 K. In contrast, below 150 K, the strength of relaxation becomes so weak that the phonon contribution can be separated. The phonon contributribution in the investigated frequency range (200 GHz–2 THz) is presumably caused by the E component of the Last mode. The component exhibits hardening on cooling in all investigated ceramics and its critical temperature in ferroelectric PMN–PSN ceramics (x = 1, 0.95) is lower than t…
Coherent aspects of the local dipolar field in echo dynamics: A spectral narrowing effect.
1996
We have measured the spectral content of the echo radiation emitted by a two-level spin system ([${\mathrm{AlO}}_{4}$${]}^{0}$ centers in quartz), after a two-pulse excitation sequence, ${\mathrm{\ensuremath{\theta}}}_{1}$-\ensuremath{\tau}-${\mathrm{\ensuremath{\theta}}}_{2}$. In general, the experimental spectral shapes reproduce qualitatively those calculated for an inhomogeneous system of noninteracting spins. However, we found that in certain ranges of the sequence parameters (${\mathrm{\ensuremath{\theta}}}_{1}$, ${\mathrm{\ensuremath{\theta}}}_{2}$, and \ensuremath{\tau}) the widths of the experimental spectra are less than expected by a factor that amounts up to 0.5. The observed na…