Search results for "Spectroscopy"
showing 10 items of 10293 documents
External-ion accumulation in a Penning trap with quadrupole excitation assisted buffer gas cooling
1994
Abstract A pulsed ion beam from an external source is injected into a Penning trap and accumulated by repeatedly lowering during ion capture to prevent the ions already captured from escaping. For the same reason the newly captured ions have to be cooled, which achieved by buffer gas collisions. To prevent radial on loss, the ions are exposed to azimuthal quadrupole excitation. By choosing the appropriate frequency (range) this method (selective quadrupole excitation assisted capture and centering (SQUEACE) allows a mass selection during the capture process and leads to a centering of those ions in the Penning trap. The multiple ion bunch capture results in a significant improvement in sign…
ESR study of the liposome membrane physical parameters in the heating-cooling cycles.
1998
Abstract Changes of dynamic and structural parameters of egg yolk lecithin (EYL) liposome membranes in the heating-cooling cycles have been studied using the E S R spin probe method. The investigations were conducted in the range of temperatures from -18 °C to +60 °C. It has been found that in the range of temperatures -15 °C to +45 °C in both the heating and the cooling run the spectroscopic parameters changed practically along the same curve (reversible changes). However, after exceeding this range of temperatures one of the parameters (partition coefficient of the spin probe 2,2,6,6 -tetramethylpiperidine -1-oxyl; TEMPO) changed along a closed curve, showing the phenomenon of thermal h…
Short range ordering and phase separation in rapidly quenched Ni80 57Fe1P19 amorphous alloys solution treated at different temperatures
1990
Abstract Electrochemical measurements and Mossbauer spectroscopy were used to study a rapidly quenched Ni80 57Fe1P19 amorphous alloy solution treated between 920 and 1500 °C. Different short range orderings were shown in amorphous alloys solution treated at different temperatures. This finding can be associated with phase separation occurring in the liquid state. This phase separation can be inherited in slightly relaxed amorphous state.
Structural modifications induced by electron irradiation in SiO2 glass: Local densification measurements
2009
We report a study on the structural modifications induced in amorphous silicon dioxide (a-SiO2) by electron irradiation in the dose range from 1.2?103 to 5?106?kGy. This study has been performed by investigating the properties of the 29Si hyperfine structure of the E '? center by electron paramagnetic resonance (EPR) spectroscopy. Our data suggest that the structural modifications induced by irradiation take place through the nucleation of confined high-defective and densified regions statistically dispersed into the whole volume of the material. In addition, we have estimated that in the high dose limit (D?105?kGy) the degree of densification associated to the local (within the defective r…
Raman study of strain in GaN/AlN quantum dot multilayered structures
2005
Raman spectroscopy has been used to investigate self-assembled stacks of GaN/AlN quantum dots with increasing number of periods. The E2H phonon modes associated to GaN and AlN are clearly resolved with visible excitation, and their energies allow the simultaneous monitoring of the dot and barrier strain states. The compression of the quantum dots is evidenced by a shift of the E2H phonon mode of circa 29 cm–1 to higher energies with respect to its relaxed value. The strain of the AlN spacer is found to be correlated to that of the dot, with an increase in its tensile component for the samples with fewer periods and a partial relaxation for samples over 50 periods. Additionally, resonant eff…
The electron beam induced short lived absorption in PLZT optical ceramics
2013
Abstract The short lived absorption induced by a pulsed electron beam in the led–lanthanum–zirconate–titanate (PLZT) optical ceramics was studied. The measured absorption spectrum covers 1.1–2.9 eV energy range and consists of several strongly overlapping peaks. The rise of the absorption is delayed with respect to the excitation pulse, due to charge carrier migration before trapping at centers responsible for the absorption. The formation rate of absorption centers and decay rate of absorption depend on the photon energy. The kinetics of short lived absorption varies over spectrum and can be approximated with a stretched exponent. The stretched exponent parameters indicate that the local d…
Molecular dynamics in low-molar and polymeric ferroelectric liquid crystals
1991
Broadband dielectric spectroscopy covering the frequency range from 10−1 Hz to 109 Hz was employed to study the molecular dynamics in low-molar and polymeric ferrroelectric liquid crystals. At frequencies below 106 Hz the ferroelectric modes, soft and Goldstone mode are observed. In the frequency regime from 106 Hz to 109 Hz a fast relaxation process is found, which is assigned to the hindered rotation of the mesogens around their long molecular axis. It turns out that the molecular dynamics is not principally different between low-molar and polymeric systems.
Delayed-neutron spectroscopy with 3He spectrometers
1977
Abstract The characteristics of a 3 He ionization chamber for high-resolution spectroscopy of β-delayed neutrons have been examined. The detector response function is given in the energy range 0.019–2.77 MeV. A considerably improved energy resolution has been achieved by minimizing effects due to pulse summing, detection of scattered neutrons, and microphonics, and is most evident in the low-energy part of the spectra.
Raman Spectroscopy and Low-Temperature Transport Measurements of Individual Single-Walled Carbon Nanotubes with Varying Thickness
2009
We have investigated two metallic and one semiconducting individual single-walled carbon nanotubes (SWNT) and one bundle of two semiconducting nanotubes with a diameter range 1.1−2.9 nm with Raman spectroscopy and low-temperature electric transport measurements. With these two methods, we obtain mutually independent measurements on the basic properties of a specific nanotube. In particular, we obtain data on metallic and semiconducting properties. Evidence of a small band gap for one metallic tube was obtained. For the semiconducting SWNTs with diameters of 2.7−2.9 nm, a special resonance condition was observed which causes an anomalous intensity ratio for the two components of the G-band. …
Differential Cross Sections and Product Rovibrational Distributions for (16)O + (32)O2 and (18)O + (36)O2 Collisions.
2015
We report rotationally resolved opacity functions, product rotational distributions, and differential cross sections for the (16)O + (16)O(16)O (v = 0,j = 1) → (16)O(16)O (v' = 0,j') + (16)O and (18)O + (18)O(18)O (v = 0,j = 1) → (18)O(18)O (v' = 0,j') + (18)O collisions calculated by a time-independent quantum mechanical method employing one of the latest potential energy surface of ozone [ Dawes ; et al. J. Chem. Phys. 2013 , 139 , 201103 ]. The results obtained for both collisional systems in the energy range 0.001-0.2 eV are examined, and interesting mass scaling effects have been discovered. The shapes of product angular distributions suggest a transition from an indirect to a direct s…