Search results for "SPECTRA"
showing 10 items of 3542 documents
Luminescent silicon nanocrystals produced by near-infrared nanosecond pulsed laser ablation in water
2014
Abstract We report the investigation of luminescent nanoparticles produced by ns pulsed Nd:YAG laser ablation of silicon in water. Combined characterization by AFM and IR techniques proves that these nanoparticles have a mean size of ∼3 nm and a core–shell structure consisting of a Si-nanocrystal surrounded by an oxide layer. Time resolved luminescence spectra evidence visible and UV emissions; a band around 1.9 eV originates from Si-nanocrystals, while two bands centered at 2.7 eV and 4.4 eV are associated with oxygen deficient centers in the SiO 2 shell.
Residual crystalline silicon phase in silicon-rich-oxide films subjected to high temperature annealing
2002
Structural properties of silicon rich oxide films (SRO) have been investigated by means of micro-Raman spectroscopy and transmission electron microscopy (TEM). The layers were deposited by plasma enhanced chemical vapor deposition using different SiH4/O2 gas mixtures. The Raman spectra of the as-deposited SRO films are dominated by a broad band in the region 400-500 cm-1 typical of a highly disordered silicon network. After annealing at temperatures above 1000°C in N2, the formation of silicon nanocrystals is observed both in the Raman spectra and in the TEM images. However, most of the precipitated silicon does not crystallize and assumes an amorphous microstructure. © 2002 The Electrochem…
Characterization of SiPM properties at liquid nitrogen temperature
2016
SiPM operation at cryogenic temperatures fails for many common devices. A particular type with deep channels in the silicon substrate instead of quenching resistors was thoroughly characterized from room temperature down to liquid nitrogen temperature by illuminating it with low light levels. The devices were mounted in vacuum with the temperature stabilized to allow long-term operation. SiPM signals from a LED pulser were acquired with single-pixel resolution. Generalized fits to the charge collection spectra were used to extract properties like single-pixel gain, inter-pixel variation, breakdown voltage, and photon detection efficiency. With these measurements a deeper investigation of th…
EPR study of Ce3+ luminescent centers in the Y2SiO5 single crystalline films
2017
Abstract The work reports results of EPR investigation of the Ce3+ incorporation in the Y2SiO5 and (Y,La)2SiO5 single crystalline films (SCFs), grown by liquid phase epitaxy method. The Ce3+ content determined from EPR spectra varied between 0.49 and 0.65 at. % in Y2SiO5 SCFs and strongly increased up to 1.9 at. % in (Y,La)2SiO5 SCF, suggesting a positive role of the La dopant in the incorporation of the Ce3+ ions into Y2SiO5 host. The EPR study showed the presence of only one type of Ce3+ centers (Ce1) corresponding to the localization of Ce3+ ions in the seven–fold coordinated positions of the Y2SiO5 host. No Ce2 center spectra (six-fold coordinated Ce3+ positions) were detected in films …
Inelastic Light Scattering Contribution to the Study of the Onset of Sintering of a Nanopowder
2017
International audience; The onset of the sintering of 5 nm ZrO2 and TiO2 nanoparticles is investigated by various methods including inelastic light scattering. A special attention is paid to low-frequency Raman spectra where scattering from confined acoustic vibrations and quasielastic scattering manifest. Significant changes are observed between samples sintered at different temperatures or applied forces. A detailed analysis of the spectra enables to follow the variation of the size of the nanoparticles, the surface area, and the formation of internanoparticles necks in the sintered materials. Finally, low-frequency scattering is shown to be more sensitive to the onset of sintering than m…
Modelling and analysis of the influence of solar spectrum on the efficiency of photovoltaic modules
2021
Abstract The article presents the influence of changes in the solar radiation spectrum distribution on the properties of various photovoltaic modules, with particular emphasis on the scattered component. We compared the relative efficiency of the photovoltaic modules based on various semiconductor absorbers during bright and sunny, and cloudy summer days. Additionally, we presented the impact of the module tilt angle on the magnitude of the surface incident scattered component and on the efficiency of the module. The solar spectra for various weather conditions were estimated using specialised computer programmes,such as SolarSpectrum or SMARTS2, and we present here the validation results f…
Microwave Fourier Transform Spectroscopy of Rovibrational Transitions in the ν 2 /ν 4 Dyads of Methane- 12 C and - 13 C
1987
The ν2/ν4 dyad-dyad spectra of 12CH4 and 13CH4 molecules in the (8÷20) GHz region have been predicted including line strengths. All transitions with γmax > 810-12 cm-1 have been observed directly using a MWFT spectrometer: six F-type transitions for 12CH4 and nine for 13CH4.
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…
Influence of nanoscale order–disorder transitions on the magnetic properties of Heusler compounds for spintronics
2017
Modifications in nanoscale chemical order are used to tune the magnetic properties, namely T-C, of Co2FeSixAl1-x (0 < x < 1). High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) with Z-contrast reveals nanoscale regions of L2(1) order within a B2 matrix in the off-stoichiometry samples. Perhaps surprisingly, the latter, more chemically disordered structure, exhibits a higher T-C. Upon annealing, the off-stoichiometry samples become more homogeneous with the fraction of L2(1) order decreasing. The short-range order was also investigated using X-ray absorption fine structure (XAFS) measurements at the Co and Fe K edges. Since the local atomic environments of C…
Infrared spectroscopy of ruthenium tetroxide and high-resolution analysis of the ν3 band
2015
Abstract RuO 4 is a heavy tetrahedral molecule which has practical uses for several industrial fields. Due to its chemical toxicity and the radiological impact of its 103 and 106 isotopologues, the possible remote sensing of this compound in the atmosphere has renewed interest in its spectroscopic properties. New, higher resolution FTIR spectra have been recorded at room temperature, using an isotopic pure sample of 102 RuO 4 and a sample with all stable isotopes present in natural abundance. We reinvestigate here the strong ν 3 stretching fundamental region and perform new assignments and effective Hamiltonian parameter fits for the five main isotopologues ( 99 RuO 4 , 100 RuO 4 , 101 RuO …