Spectral analysis of the structure of ultradispersed diamonds

The structure of ultradispersed diamonds (UDD) is studied by spectral methods. The presence of diamond crystal phase in the UDD is found based on x-ray analysis and Raman spectra. The Raman spectra also show sp²-and sp³-hybridized carbon. Analysis of IR absorption spectra suggests that the composition of functional groups present in the particles changes during the treatment. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 4, pp. 524–528, July–August, 2008.     

Raman active collective mode in underdoped cuprates

We report experimental observation of Bardasis–Schrieffer-type s-symmetry collective mode in the d-wave high T_c superconductors. The mode persists above T_c in the pseudogap phase of the underdoped superconductors — direct spectroscopic evidence of the correlations in the particle–particle channel above T_c.     

Growth and raman scattering of aluminium gallium orthophosphate piezoelectric crystals

A new series of non-ferroelectric crystals, the piezoelectric solid solution aluminium gallium orthophosphate Al_1-xGa_xPO₄ (AGP, 0 < x < 1) system has been successfully developed by a hydrothermal method. The AGP crystal with X = 0.10 shows a phase transition temperature T_−β = 587 ± 3 °C with a cell parameters A = b = 0.49386(3) and C = 1.09563(2) nm. Raman spectra including directional dispersion in AGP are similar to those from -AIPO4 and -quartz crystals, indicating all of them belong to an isomorphic family, the short-range interaction being dominant in AGP. Comparison with -AIPO4 crystals, there exists an apparent red shift of the mode frequency and a smaller TO/LO mode splitting of the E species in the AGP crystals.     

Inelastic scattering of hot electrons in n-GaAs/AlAs types I and II multiple quantum wells doped with silicon

We have studied the dependence of hot electron scattering rate on temperature in n-GaAs/AlAs types I and II multiple quantum wells. For a sample with well width 37 Å, which is on the borderline between types I and II band alignment, the increase of the temperature in the range 6–80 K leads to the strong decrease of the hot electron scattering rate. We explain this result by ionization of donors and transfer of cold electrons from the Γ-valley of GaAs to the X-valley of AlAs.     

Multivariable structural characterization of semicrystalline polymer blends by small‐angle light scattering

A new multi‐variable‐measurement approach for characterizing and correlating the nanoscale and microscale morphology of crystal‐amorphous polymer blends with melt‐phase behavior is described. A vertical small‐angle light scattering (SALS) instrument optimized for examining the scattering and light transmitted from structures ranging from 0.5 to 50 μm, thereby spanning the size range characteristic of the initial‐to‐late stages of thermal‐phase transitions (e.g., melt‐phase separation and crystallization) in crystal‐amorphous polymer blends, was constructed. The SALS instrument was interfaced with differential scanning calorimetry (DSC), and simultaneous SALS/DSC/transmission measurements were performed. We show that the measurement of transmitted light and SALS under H_V (cross‐polarized) optical alignments during melting can be used to reliably measure the thermodynamic (e.g., crystal melting and melt‐phase separation temperatures) and structural variables (e.g., crystalline fraction within the superstructures and volume fraction of superstructures) necessary for describing the multiphase behavior of crystal‐amorphous blends in one combined measurement. We also evaluate the orientation correlations of crystalline volume elements within the superstructures. Our results indicate that simultaneous measurement of transmitted light can provide a reliable estimate of the total scattering from density and orientation fluctuations and the melt‐phase separation temperature of polymer blends. For solution‐cast poly(?‐caprolactone)/poly(D,L‐lactic acid) blends, our multivariable measurements during melting provide the parameters necessary to generate a crystal–liquid and liquid–liquid phase diagram and characterize the solid‐state morphology. This opens up the challenge to explore use of our vertical SALS instrument as a rapid and convenient method for developing structure–property relationships for crystal‐amorphous polymer blends. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2714–2727, 2002     

Appearance of pseudo-band-gaps in a disordered quantum wire array

The density of states and the conductivity are calculated in lateral superlattices with disorder in the period within a self-consistent Born approximation. Although the potential loses its periodicity on average due to disorder, it leads to an opening up of a pseudo-band-gap and modifies the conductivity perpendicular to the superlattice even qualitatively, when the energy reaches the zone boundary.     

The dynamical properties of Rydberg hydrogen atom near a metal surface

The dynamical properties of Rydberg hydrogen atom near a metal surface are presented by using the methods of phase space analysis and closed orbit theory. Transforming the coordinates of the Hamiltonian, we find that the phase space of the system is divided into vibrational and rotational region. Both the Poincaré surface of section and the closed orbit theory verify the same conclusion clearly. In this paper we choose the atomic principal quantum number asn=20. The dynamical character of the exited hydrogen atom depends sensitively on the atom-surface distanced. Whend is sufficiently large, the atom-surface potential can be expressed by the traditional van der Waals force and the system is integrable. Whend becomes smaller, there exists a critical valued _c. Ford>d _c, the system is near-integrable and the motion is regular. While chaotic motion appears ford<d _c, and the system tends to be non-integrable. The trajectories become unstable and the electron might be captured onto the metal surface.     

Electrons from target and projectile ionization in simple collision systems

Summary Absolute double differential cross-sections for target ionization and projectile electron loss were determined in collisions of H⁺, H₂ ⁺,³He⁺ and³He⁺⁺ ions (0.4 to 2.0 Me V/u) with He and Ar gas targets at electron emission angles from 0° up to 60°. The experimental results are qualitatively well described by plane-wave Born approximations including screening of the projectile in target ionization and of the target atom in the case of electron loss.

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Riassunto Sono state determinate le sezioni d’urto doppie differenziali assolute per la ionizzazione del bersaglio e la perdita dell’elettrone proiettile in collisioni di ioni H⁺, H ₂ ⁺ ,³He⁺ e³He⁺⁺ (da 0.4 a 2.0 Me V/u) con bersagli di gas He e Ar ad angoli di emissione degli elettroni da 0° a 60°. I risultati sperimentali sono qualitativamente ben descritti dalle approssimazioni di Born per onde piane che comprendono la schermatura del proiettile nella ionizzazione del bersaglio e dell’atomo bersaglio nel caso di perdita dell’elettrone.

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Резюме Определяются абсолютные дважды дифференшиальные поперечные сечения для ионизации мишени и потери электровов налетающими частишами при соударениях ионов H⁺, H ₂ ⁺ ,³He⁺ и³He⁺⁺ (от 0.4 до 2.0 Me V/u) в случае газовых Не и Ar мишеней при углах эмиссии электронов от 0° до 60°. Экспериментальные результаты качественно хорощо описываются с помощью плоско-волнового борновского приближения, включая экранирование налетающей частицы при ионизации мишени в случае потери электрона.