The aluminum centers in α-quartz

A review of the research literature dealing with the role of aluminum centers in α-quartz is presented, covering the developments of the last twenty years. The primary techniques (dielectric measurements, electron paramagnetic resonance and optical spectroscopy) have led to quite a detailed understanding of the structure and radiation chemistry of the centers in terms of aluminum ions at silicon sites, with various possibilities for nearby interstitial cations and electron holes on neighboring oxygen atoms.     

First-principles investigations of proton generation in α-quartz

Proton plays a key role in the interface-trap formation that is one of the primary reliability concerns, thus learning how it behaves is key to understand the radiation response of microelectronic devices. The first-principles calculations have been applied to explore the defects and their reactions associated with the proton release in α-quartz, the well-known crystalline isomer of amorphous silica. When a high concentration of molecular hydrogen(H_2) is present, the proton generation can be enhanced by cracking the H_2 molecules at the positively charged oxygen vacancies in dimer configuration. If the concentration of molecular hydrogen is low, the proton generation mainly depends on the proton dissociation of the doublyhydrogenated defects. In particular, a fully passivated E_2' center can dissociate to release a proton barrierlessly by structure relaxation once trapping a hole. This research provides a microscopic insight into the proton release in silicon dioxide, the critical step associated with the interface-trap formation under radiation in microelectronic devices.     

Luminescence of ion-irradiated α-quartz

Optical functionality of materials used in devices is the basis of modern photonics. It depends on selected photoactive impurities or low-dimensional structures, which can be tailored by ion implantation. The present survey covers cathode-luminescence spectroscopy performed after Ge, Ba, Na, Rb and Cs ion implantation in α-quartz, in connection with dynamic, laser-induced and chemical epitaxy of the surface layers amorphized during the ion irradiation. The correlations, which emerged for various luminescence bands, ion species and thermal processing methods, allows one to classify the bands into ion-specific and intrinsic ones. The microstructural properties measured by ion beam analysis and transmission electron microscopy will be combined with the luminescence data, and the role of photoactive defects in quartz and nanoparticles of the implants will be discussed. The technologically most attractive case of double Rb/Ge implantation will be highlighted, which combines the achievement of full chemical epitaxy (due to the alkali ions) and a high light output (due to Ge atoms). Finally, some investigations suggested to better understand the interplay between nanostructure and light emission in ion-doped quartz and the enormous potential for photonic application will be outlined.     

Molecular dynamics simulation of latent track formation in α-quartz

The latent ion track in α-quartz is studied by molecular dynamics simulations. The latent track is created by depositing electron energies into a cylindrical region with a radius of 3nm. In this study, the electron stopping power varies from 3.0keV/nm to 12.0keV/nm, and a continuous latent track is observed for all the simulated values of electron stopping power except 3.0keV/nm. The simulation results indicate that the threshold electron stopping power for a continous latent track lies between 3.0keV/nm and 3.7 keV/nm. In addition, the coordination defects produced in the latent track are analyzed for all the simulation conditions, and the results show that the latent track in α-quartz consists of an O-rich amorphous phase and Si-rich point defects. At the end of this paper, the influence of the energy deposition model on the latent track in α-quartz is investigated. The results indicate that different energy deposition models reveal similar latent track properties. However, the values of the threshold electron stopping power and the ion track radius are dependent on the choice of energy deposition model.     

The Zeeman effect for helium atom

The g-factors of the 23P, 21P, and 33P states of the helium atom are calculated by using the vatiational wave functions constructed from the linear combinations of Slater-type basis sets. The relativistic corrections to order α2(a.u.) and the effect of the motion of the center of mass are treated by using first-order perturbation theory. Most of our predicted results are in good agreement with recent results of Yan and Drake, which were obtained by using the wave functions with doubled Hylleraas coordinates. Based on the analysis of the convergence pattern in our calculation, we believe that our predicted value of the δgL-factor for 33P state in 4He, 2.914 15×10-7, ought to be reasonable and accurate, although there are no corresponding experimental data available in the liteature yet to be compared with.     

Second-order Zeeman effect of theX−B transition in molecular iodine

Saturated absorption spectroscopy was applied to study the line shape of the molecular iodineX( = 0,J = 13,15) B( = 43,J = 12, 16) transition ( = 514.5 nm) in a transversal magnetic field as high as 0.51 T. The Zeeman structure of several hyperfine structure (hfs) components was completely resolved and a detailed study of the second-order Zeeman shift and splitting was made. The anisotropic Magnetic Susceptibility (MS) of the molecular iodine both in theB(43) (X = 7.3 ± 1 × 10^–34 J/Oe²) and theX(0) [ = (0.6 ± 1) × 10^–34 J/Oe²] states as well as the isotropic MS difference [0 –o = (2 ± 0.2) × 10^–34 J/Oe²] was measured.     

Theory for position of muonium in α-quartz and associated hyperfine interaction

The electronic structures and hyperfine interactions of muonium and hydrogen in -quartz are investigated by the unrestricted Hartree-Fock cluster procedure. The muonium is found to be trapped near the center of the line joining two silicon atoms. On including vibrational effects, the muon hyperfine constant comes out as 1.09 times that for free muonium, this ratio being larger than unity and smaller than for protons in trapped hydrogen, both features being in agreement with experiment.Briefly reported in Abstract at the American Physical Society meeting in New Orleans, March 1988. See Bull. Am. Phys. Soc. 33 (1988) 770.     

UV cathodoluminescence of crystalline α-quartz at low temperatures

Two luminescence bands in the UV range were detected in crystalline α-quartz under electron beam excitation (6 kV, 3-5 μA). One band is situated at 5 eV and could be observed in pure samples. Its intensity increases with cooling below 100 K and undergoes saturation below 40 K alongside a slow growth with the time of irradiation at 9 K. The decay curve of the band at 5 eV contains two components, a fast (<10 ns) and a slow one in the range of 200 μs. The photoluminescence band at 5 eV with a similar temperature dependence was found in previously neutron-irradiated crystalline α-quartz. Therefore, the band at 5 eV was attributed to host material defects in both irradiation cases. The creation mechanism of such defects by electrons, the energy of which is lower than the threshold for a knock-out mechanism of defect creation, is discussed. Another band at 6 eV, containing subbands in different samples, appears in the samples containing aluminum, lithium and sodium ions. This luminescence is ascribed to a tunnel radiative transition in an association of (alkali atom)⁰-[AlO₄]⁺ that is formed after the trapping of an electron and a hole by Li⁺ (or Na⁺) and AlO₄.     

Susceptibility versus density change of neutron irradiated α-quartz

The paramagnetism of neutron irradiated α-quartz single crystals is given versus the relative density decrease of the specimens. There clearly exists a relation between the radiation induced susceptibility and density change. The precise correlation, however, depends on experimental conditions, amongst which the irradiation temperature may be.     

The hydrothermal growth of α-quartz and the nature of the physico-chemical defects detected in the resulting crystal

Abstract

The development of α-quartz for high frequencies devices leads to a strong reduction of the thickness of the piezoelectric sheet. Such a thickness is comparable to the size of the defects. Consequently, the main objective for the improvement of the performances of α-quartz used as a piezoelectric material is to reduce the density of physico-chemical defects.

Our work has been focussed in two directions:

(i) the identification of different physico-chemical defects using the overlap of different techniques (X-ray topography, IR spectroscopy, Cathodoluminescence, Thermo-luminescence, EPR,…)

(ii) attempts at improving the correlations between the different parameters governing the hydrothermal crystal growth of a-quartz and the nature or the density of defects.     

α-quartz as a substrate in thermal phonon radiation

Using the mechanical strong anisotropic-quartz, measurements of radiation temperature as a function of phonon radiation power were performed for gold and copper radiators evaporated on theX- orZ-crystal face, respectively. The comparison with theoretical model calculations of phonon transmission across the interface yields agreement with the isotropic/anisotropic acoustic mismatch model. A strong increase in radiation temperature in comparison to linear emission models is observed at temperatures above about 40 K. We suppose that this effect is due to phonon back-scattering which leads to a back-heating of the metal film.Supported by Bundesministerium für Forschung und Technologie     

Analysis of the Zeeman effect on D_α spectra on the EAST tokamak

Based on the passive spectroscopy,the D_α atomic emission spectra in the boundary region of the plasma have been measured by a high resolution optical spectroscopic multichannel analysis(OSMA) system in EAST tokamak.The Zeeman splitting of the D_α spectral lines has been observed.A fitting procedure by using a nonlinear least squares method was applied to fit and analyze all polarization π and ±σ components of the D_α atomic spectra to acquire the information of the local plasma.The spectral line shape was investigated according to emission spectra from different regions(e.g.,low-field side and high-field side) along the viewing chords.Each polarization component was fitted and classified into three energy categories(the cold,warm,and hot components) based on different atomic production processes,in consistent with the transition energy distribution by calculating the gradient of the D_α spectral profile.The emission position,magnetic field intensity,and flow velocity of a deuterium atom were also discussed in the context.     

Influences of neutral oxygen vacancies and E′_1 centers on α-quartz

Our calculations demonstrate that the concentration of neutral oxygen vacancies can affect the geometrical structrue,electronic structure, and optical properties of α-quartz. Moreover, the distribution of the neutral oxygen divacancy can also exert some influence on the properties of α-quartz. The dissimilarity and similarities are presented in the corresponding density of state(DOS) and absorption spectrum. In addition, when a higher defect concentration is involved in α-quartz,the influence of E1 center on the geometry of α-quartz becomes more significant. However, the introduction of an E1 center barely results in any improvement compared with the influence produced by the corresponding neutral defect.     

Rotational Rydberg states of polar molecules: Hund’s classification and Zeeman effect

The rotational Rydberg states of polar molecules, which arise as a result of the interaction of a Rydberg electron with core rotations, are considered. A large number of angular momenta in the core-electron system lead to a considerably greater number of possible coupling schemes of these momenta compared to the number of schemes determined by the classical five Hund’s cases for lower excited electron states of molecules. As a result of such detailed Hund’s classification, more than 30 different coupling schemes (Hund’s subcases) are constructed for rotational Rydberg states of molecules. The conditions of their realization are indicated in terms of the relative quantities of intramolecular interactions, for which analytical estimates are presented. For a large number of subcases, analytical expressions for the molecular matrix elements are found. These expressions can be useful in classification of the experimental spectra of highly excited molecules. As an application, for each of the subcases considered, analytical expressions are given, which describe the linear Zeeman effect and the Paschen-Back effect.     

Acousto-electric effect in bone

In the present work,acoustoelectric effect in bone has been investi-gated.Rectangular bone samples prepared from the middiaphysis of the wallof animal bone are exposed by ultrasonic field having frequency of 2.5 MHz.The bone matrix changes under ultrasound exposure which results into the gen-eration of potential in bone.The present study may be helpful in the develop-ment of acousto-electric devices.     

Polarization effect in parametric amplifier

With the rapid development of optical communicationwideband optical amplifier has always been the topic ointensive study. Optical parametric amplifier (OPA) is apotential candidate for future optical amplification dueto its wide bandwidth outside the erbium-doped fibeamplifier (EDFA) amplification bandwidth[1]. Parametric amplification is based on four-wave-mixing (FWMphenomenon and is polarization-dependent if it is nocarefully configured. If the signal and the pumps do noshare the same s…     

Aharonov-Bohm effect in spherical billiard

Using Gutzwiller's periodic orbit theory,we study the quantum level density of a spherical billiard in the presence of a magnetic flux line added at its center,especially discuss the influence of the magnetic flux strength on the quantum level density.The Fourier transformed quantum level density of this system has allowed direct comparison between peaks in the level density and the length of the periodic orbits.For particular magnetic flux strength,the amplitude of the peaks in the level density decreased and some of the peaks disappeared.This result suggests that Aharonov-Bohm effect manifests itself through the cancellation of periodic orbits.This phenomenon will provide a new experimental testing ground for exploring Aharonov-Bohm effect.     

Observation of Electromagnetically Induced Transparency in a Zeeman—Sublevel System in Rubidium Atomic Vapour

We observed electromagnetically induced transparency (EIT) in a Zeeman-sublevel system using rubidium atomic vapour at the temperature of 75~C, in which the width of the EIT signal is only 0.6 MHz. Two different methods were performed to observe the EIT signal in our experiment.     

Experimental Test of Alternating-Current Zeeman Interference Effect in Ramsey Separated Oscillating Fields

An experimental test of ac Zeeman effect in an optically pumped caesium beam frequency standard is reported and analysed. An interference pattern of the atomic energy level shift as a function of the applied microwave field near the atomic transition frequency was observed. It was superimposed on the dispersion lineshape of a normal ac Zeeman effect. This effect was analysed with the atomic wavefunction phase analysing method.