Half-width Of Line Research Articles

Interfacial characterization of nanocrystalline alloys

Nanocrystalline FeCuSiB alloys with grain sizes in the range 25–90 nm were obtained by crystallization of the amorphous alloy. The results of Mössbauer spectroscopy showed that, owing to the presence of a large number of interfaces which were thought to lack ordering as well as interface expansion, the Fe atoms in the interfaces show a wide distribution and a low s-electron density, which is manifested in large values of the half-linewidth (HLW) and isomer shift (IS). Microhardness measurements indicate that the variation in microhardness of nanocrystalline FeCuSiB alloys with respect to the average grain size is in good agreement with the variations in HLW and IS.

Microstructures and mechanical properties of amorphous hydrogenated carbon-nitrogen films

Amorphous hydrogenated carbon-nitrogen (a-C:N:H) films have been deposited on glass, silicon and aluminium substrates by r.f.-plasma-enhanced chemical vapour deposition using C 2H 2 and N 2 gas mixtures in the plasma reactor. An enhanced nitrogen partial pressure leads to a decrease in the hydrogen content and an increase in the nitrogen content of the films as shown by combustion analysis and the IR absorption coefficients for the N-H, C-N and C-H stretching modes. The existence of nitrile groups in a-C:N:H films explains the reduced hardness and stress of the films with increasing nitrogen content. Further, decreases in the optical band gap by 0.5 eV and in the halfwidth of the electron spin resonance line down to 2.5 G are observed, as well as increases in the density of states at the Fermi level by one order of magnitude and in the d.c. conductivity by five orders of magnitude. Temperature-dependent conductivity measurements are consistent with a hopping mechanism around the Fermi level in the temperature range from 170 to 400 K and confirm that the density of states at the Fermi level is the most important parameter for d.c. conductivity. The measurements demonstrate the inefficiency of doping of a-C:H films with nitrogen.

Transmission Mössbauer spectroscopy and x-ray diffraction studies on the structure of nanocrystalline Fe-Cu-Si-B alloys

Nanocrystalline Fe-Cu-Si-B alloys with grain sizes of 25–90 nm were synthesized by crystallization of the amorphous alloy. Two nanocrystalline phases of α-Fe(Si) and Fe2B were observed in all tested samples. Transmission Mössbauer spectroscopy investigation on the structure of nanocrystalline Fe-Cu-Si-B alloys showed that Si atoms are completely and substitutionally dissolved in Fe bcc lattice and the arrangement of the Si atoms in the α-Fe(Si) phase shows short range order (SRO), whereas 8.5–9.7 at. % of the B atoms were found as Fe2B and the remainder were located in the interfaces. When grains grow larger, the arrangement of the Si atoms in the α-Fe(Si) phase changes. Interestingly, x-ray diffraction results reveal that the lattice constant of α-Fe(Si) phase decreases rapidly with grain coarsening. Based on the thermodynamic analysis, the changes in the lattice constant of the α-Fe(Si) phase and SRO of Si atoms in bcc Fe lattices were attributed to the lattice expansion as a result of the variation of vacancy concentration in α-Fe(Si) solid solution. Meanwhile, owing to the interface contribution, the alloy with small grain size is found to exhibit large values of half linewidth (HLW) and isomer shift (IS) in the Mössbauer spectra. The results from electrical resistivity measurements agree and confirm the strong effects of the lattice distortion and interfaces.

The lattice structure of nanocrystalline Fe-Cu-Si-B alloys

Nanocrystalline Fe-Cu-Si-B alloys with different grain sizes were synthesized by crystallization of an amorphous alloy. Two nanophases, α-Fe(Se) and Fe 2B, were noticed in all samples. XRD results reveal that the lattice constant of the α-Fe(Si) phase increases; the a-axis is elongated and the c-axis is shortened in the Fe 2B phase upon reducing the grain size. Based on the thermodynamic analysis, the changes in the lattice parameters were attributed to the solution of vacancies in the above two phases. Owing to the lattice distortion of the α-Fe(Si) and Fe 2B phases, the crystallite with small size is found to exhibit a disordered character to some extent, which is manifested by large values of the half linewidth (HLW) and isomer shift (IS) of various Fe configurations in the Mössbauer parameters.

Collisional Narrowing and Spectral Shift in CARS Spectra of Molecular Nitrogen and Oxygen at Pressures up to 2500 bar and Temperatures of 850 K

AbstractVibrational‐rotational CARS spectra of molecular nitrogen and oxygen at high densities and temperatures are recorded using a scanning CARS‐spectrometer. Measurements are performed at pressures up to 2500 bar and temperatures up to 850 K. The spectral line position and halfwidth of the fully collapsed Q‐branch are determined for pure N2, O2, N2/O2 mixtures and Ar/O2 mixtures. Comparisons of the experimental data with different theoretical models for the rotational energy transfer are also presented. Three quantum mechanical approaches (MEG‐, ECS‐, PEG‐laws) are compared with a classical description of the relaxation process treating the angular momentum as a continuous variable.

Effect of γ-ray irradiation on the electrical conductivity of β-PbF 2

Effect of γ-ray irradiation on polycrystalline β-PbF 2 was investigated by X-ray, Raman scattering and electrical conductivity. With an increase in the dose of γ-ray irradiation, the half line width of Raman peak increased, suggesting the formation of Frenkel defects. On the other hand, the electrical conductivity decreased with an increase in the irradiation dose. The motion of the formed interstitial F - ions is presumed to be hindered by unidentified defects formed simultaneously by the irradiation.

Exciton-polariton light absorption in bulk GaAs and semiconductor superlattices

A comparative study of the temperature dependence of the absorption edge has been performed with thin single-crystal wafers of bulk GaAs and multilayer quantum-size GaAs/Ga0.3Al0.7As structures with the well and barrier thicknesses La=Lb approximately=135 Å in the temperature range T=4-300 K. The total number of periods was N>20. The authors consider the quantity K*, which is proportional to the integral absorption coefficient calculated as a product of the line halfwidth and the optical density at the exciton band maximum. In bulk samples K* shows a sharp increase by nearly an order of magnitude, up to T* approximately= 110 K, and then remains roughly constant. The temperature T* may be considered as critical for the excitonic polariton-mechanical exciton transition. A similar behaviour of K* was observed for superlattices with a slightly increasing integral absorption up to a temperature of T* approximately=20 K. This fact is considered as evidence for the polariton nature of light absorption at T

Exciton localization in Cd1−xMnxTe and its dependence on the strong magnetic field

Abstract The magneto-photo-luminescence in Cd1−xMnxTe(x = 0.13−0.4) was investigated in magnetic fields up to 43 T by a pulsed magnet at T = 4.2 K. Significant behaviour of exciton peak intensity, half-line width and spectral line shape of the exciton emission band was observed and interpreted in terms of free magnetic polaron effect depending on the magnetic field and manganese concentration.

N-ethyl- N-nitrosourea induced brain tumors in rats monitored by nuclear magnetic resonance imaging, plasma proton nuclear magnetic resonance spectroscopy and microscopy

Characteristic slow growing brain gliomas were induced in rats by a single subcutaneous injection of N-ethyl-N-nitrosourea (ENU) within 24 h of birth. A parallel control group of rats was injected with saline. Seven treated rats developed gliomas within 2 years. Periodic nuclear magnetic resonance imaging (MRI) of the brain in 3-mm slices at 1.5 Tesla and monthly plasma sampling for proton magnetic resonance spectroscopy (MRS) at 360 MHz were started 6 months after the injection of ENU. In the MRS experiments, the Fossel index, average of the line widths of the methylene and methyl peaks at 360 MHz, was determined from half-line widths of methyl and methylene peaks at 0.8 ppm and 1.3 ppm. In five of the ENU injected animals that developed histologically verified brain tumors, these were also observed by MRI without contrast agents. There was no consistent correlation between the imaged tumors and the Fossel index obtained through MRS during the course of the study where repeated observations were performed on individual animals, nor was there any consistent statistical difference in the Fossel index between ENU-treated and control animals. The results of this study demonstrate that slowly developing carcinogen-induced brain tumors in rats can be successfully and reliably monitored non-invasively by MRI but not by MRS of plasma.

Phonons in Ca2-xSrxCuO3 (x=0, 0.2 and 0.4): Raman and infrared spectroscopy, and lattice dynamics calculation

The polarized Raman spectra of Ca2CuO3, Ca1.8Sr0.2CuO3 and Ca1.6Sr0.4CuO3 single crystals and the IR transmission spectra of Ca2CuO3 and Ca1.6Sr0.4CuO3 have been measured. The frequencies of all Gamma -point phonons of Ca2CuO3 have been determined on the basis of assignment of the one-phonon Raman (Ag) and IR lines to definite normal modes and calculations of the lattice dynamics. The line assignment is consistent with earlier results for Ca1.8Sr0.2CuO3 as well as with the line shifts upon substitution of Sr for Ca. The intensive broad lines in the (bb)-polarized Raman spectra of both Sr-free and Sr-substituted samples (in addition to the two Ag lines already assigned) have been attributed to resonantly enhanced two-phonon scattering involving modes related to motions of Cu and/or O(2) atoms. A coincidence has been found between most of the line frequencies and half-widths in the (bb)-polarized Raman spectra and some of the maxima in the two-phonon density of states as obtained from lattice dynamics calculations.

Intensity and linewidth measurements in the 13.7 μm fundamental bands of 12C 2H 2 and 12C 13CH 2 at planetary atmospheric temperatures

The absolute intensities and collision-broadened half-widths of several lines in the P-, Q-, and R-branches of the v 5-fundamental band of 12C 2H 2 have been measured at various temperatures between 147 and 295 K employing the Doppler-limited spectral resolution (∼10 -4 cm -1) of a tunable diode laser spectrometer. The absolute intensities of R(5), R(7), R(9), and R(20) in the same fundamental belonging to 12C 13CH 2 have also been measured at 294 K. The temperature dependence of the collision-broadened half-width has been determined for some of the lines broadened by planetary atmospheric gases, namely, He, Ar, H 2, and N 2. Four self-broadened linewidths of 12C 2H 2, as well as three H 2-broadened linewidths and a self-broadened half-width of 12C 13CH 2, have also been retrieved from our measurements.

Peculiarities of magnetic resonance in organic ferromagnet of pyrolyzed polyacrylonitrile

Electron paramagnetic and ferromagnetic resonances in a powder of polyacrylonitrile (PAN) pyrolyzed in a temperature range from 873 to 1273 K have been measured at ∼9 GHz. It has been ascertained that the paramagnetic spin concentration diminishes from 5.5 × 1020 to 2.1 × 1019 spins/cm3 and the half-width of an absorption line decreases from 0.35 to 0.21 mT with an increase of pyrolysis temperature from 873 to 1073 K. The magnetization dependence upon the magnetizing field strength in these specimens is found to contain a falling branch. In the pyrolysis temperature range from 1073 to 1273 K the data of the magnetic resonance and those obtained with the help of a vibromagnetometer have shown the formation of a ferromagnetic phase in the pyro-PAN.

Additive Effect of Salts on the Bactericidal Action of Ethanol towards Escherichia coli and State of Solution

The additive effect of salts on the bactericidal action of ethanol towards Escherichia coli was investigated.The salts NaCl, KCl, LiCl and CaCl2 had no effect on the bactericidal action of 10% ethanol solution but enhanced that of a 20% solution. Their effects were proportional to the concentration of the added salts in the ethanol solution, and increased in the order of LiCl, KCl, NaCl, and CaCl2.Differential scanning calorimetry (DSC) thermograms during the heating process were remarkably changed by addition of NaCl. KCl, LiCl, or CaCl2 to aqueous solutions of ethanol. Half line widths of the water oxygen signal in the 17O nuclear magnetic resonance (17O NMR) spectra were also remarkably broadened by addition of NaCl, KCl, and CaCl2 to 20% ethanol solution, implying a decrease in the degree of molecular freedom. The signal of the hydroxyl proton in the 1H NMR spectra was shifted to lower magnetic field in the presence of NaCl, KCl and CaCl2, indicating that the proton was hydrogen-bonded.It is suggested that the additive effect of salts on the bactericidal action of ethanol towards Escherichia coli might be enhanced through hydrogen-bonding and hydration interactions between water, salts and ethanol.

A lineshape fitting model for 1H NMR spectra of human blood plasma

A lineshape fitting model was constructed for classifying the overlapping information in the 1H NMR spectrum of human blood plasma. A reliable assignment of the overlapping fatty acid (-CH2-)n and -CH3 resonances of the various lipoproteins (VLDL, very low density lipoprotein; LDL, low density lipoprotein; HDL high density lipoprotein) is introduced, and for the first time detailed characteristics (chemical shifts, half linewidths, and relative intensities) of the individual lipoprotein components were obtained directly from the whole plasma spectrum. This was achieved by combining the constructed lineshape fitting model and the proper 400 MHz proton NMR measurements from blood plasma of a healthy donor, from fractions of the different lipoproteins, and from plasma samples in which the lipoprotein fractions were separately added. The results suggest fair promise of future applications of the rapid and easy NMR analysis of lipoprotein distribution in various research and clinical situations.

Magnetic phase transition and short range order in Nd 2BaCuO 5

Optical spectra of the “brown phase” Nd 2BaCuO 5 accompanying the high- T c superconductor NdBa 2Cu 3O 7− x have been measured. A magnetic phase transition at T c=7.5 K has been found from the temperature dependences of the spectral line splittings and halfwidths. A short range order present up to 10 T c is supposed to be connected with the quasi-one-dimensional character of magnetism in Nd 2BaCuO 5.

Diode laser measurements of Kr-broadened linewidths in the ν_1 band of OCS

Kr-broadened halfwidths of twenty-eight lines in the nu(1) band of OC(32)S have been measured from absorption spectra recorded at room temperature with a tunable diode laser spectrometer. The results are compared to values calculated on the basis of the Anderson-Tsao-Curnutte theory and an improved semiclassical impact model developed by Robert and Bonamy. Both theories have been applied from a Smith-Giraud-Cooper intermolecular potential by considering the potential coefficients as adjustable parameters. Moreover, an atom-atom interaction model was used in the latter theory.

The influence of NaX zeolite particle size on crystallinity measured by the XRD method

The degree of crystallinity of NaX zeolite samples, previously determined by X-ray diffraction ( DC XRD), was measured by a series of methods (i.r. spectroscopy, specific area, and ion-exchange measurements). For NaX zeolite samples, crystallized with various amounts of added “seed” SASS, it was found that 1. (a) There were no significant changes in the position, number, and half-width of the diffraction lines. 2. (b) Only slight changes in the shape of the i.r. spectra, chemical composition, specific area, and ion-exchange capacity occurred. 3. (c) There was only a slight decrease in the intensity of the diffraction peaks caused by the increase of SASS up to 20%. 4. (d) With the addition of more than 20% SASS, there was a sharp decrease in the intensity of the diffraction lines, and on the basis of this a sudden decrease in DC XRD a decrease of the mean particle size, as well as a decrease in the fraction of particles of dimensions less than 1 μm. The decrease in degree of crystallinity DC XRD is explained by the mosaic structure of zeolites and extinction effects that lead to a decrease in the intensity of the diffraction lines due to the decrease in the dimensions of mosaic blocks and increase in the angle of disorder.

Spectral characteristics of HeI 10830 A line in the quiet chromosphere

We describe preliminary results of the observation of the HeI 10830 AD line in the quiet chromosphere in 1986 and 1987 with the newly installed Reticon system on the solar spectrograph of Purple Mountain Observatory. We found: (1) The HeI 10830 A line has an emission maximum outside the solar limb. The maximum intensity in 1987 was definitely greater than the maximum in 1986. (2) The maximum intensity was roughly proportional to the line half-width. (3) The line half-width in coronal hole regions wasclearly smaller than in non-hole regions and was independent of the emission intensity. (4) The line half-width before the emission maximum is basically a constant, mostly with a tendency of increasing outward, the height at which the change begins depends on the optical thickness. (6) The emission maximum only correlates positively with the monthly smoothed sunspot number and there is no trace of it correlating with the 1–8 A X-ray flux or the intensity of the coronal green line above the observed point. We also give preliminary results of fitting our calculated theoretical profiles to the observed profile. The uniform model cannot give a good fit; a simple two-layer model not only greatly improved the fit, it also gave a reasonable absorption profile for solar disk observation. There seems no need for assuming a 20 km/s horizontal turbulence field, as many authors have done.

FM characteristics and compact modules for coherent semiconductor lasers coupled to an external cavity

Measured FM responses of a semiconductor laser optically coupled off-axis to a confocal Fabry-Perot cavity are discussed. It was found that this cavity acted as a frequency discriminator and as a phase comparator for slow and fast frequency fluctuations, respectively. The crossover between them was determined by a half linewidth of the cavity. On the basis of these investigations, two kinds of coherent semiconductor laser modules were constructed. External Fabry-Perot cavities were made by using an optical fiber and a hemispherical microlens. The linewidths of these lasers were less than 25 kHz. >

Spectroscopic investigation of a low current arc in pure fluorine

A pure fluorine 10-A DC arc has been operated in an Al/sub 2/O/sub 3/ tube of 18 mm diameter at atmospheric pressure. This arc was used to perform radially resolved spectroscopic end-on measurements in the visible and UV-spectral regions. An excitation temperature of 7800 K on the arc axis was determined from the intensity of atomic fluorine lines, and an ion density of 1.7*10/sup 21/ m/sup -3/ was determined from the half-width of the contamination line H/sub beta /. A Boltzmann plot of the affinity continuum in the UV-spectral region yields two groups of electrons. A group of hot electrons is characterized by a temperature that agrees with the excitation temperature, and a group of cold electrons has a temperature in accordance to the gas temperature of 4000 K. The absolute intensity of the affinity continuum gives and electron density of 1.3*10/sup 20/ m/sup -3/ on the arc axis, which is lower than the density of both positive and negative ions in the discharge. From the difference between the electron and gas temperature, an elastic collision cross section between the electrons and F-atoms of 2*10/sup -20/ m/sup 2/ is determined. >