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.     

Zeeman effect in α-quartz

The helical crystal structure in α-quartz acts as the natural micro-solenoids for an electromagnetic wave passing through them, producing a longitudinal magnetic field in the direction of the optical axis. The longitudinal magnetic field further induces the Larmor frequency for the rotation of the bound electrons. The calculated Larmor frequency was experimentally confirmed by monitoring a line splitting of the infrared OH-band in the transmission spectra of α-quartz. A shift in the resonance frequency of the OH-band is equal to the Larmor frequency induced by the natural Zeeman effect.     

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.     

Theory of anisotropic hyperfine interactions in π-electron radicals

Anisotropic proton hyperfine interactions in π-electron radicals are approximated by a magnetic dipole interaction between each proton and an electron spin magnetization that is distributed in 2s and 2p Slater atomic orbitals centred on carbon atoms.     

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.     

Location and associated hyperfine properties of μ+ in La2CuO4

The location of the positive muon used as a probe in highT _c systems is investigated using the unrestricted Hartree-Fock cluster procedure. Our calculations indicate that ⁺ is located in thea–c plane at a distance of 1.08 Å from the apical oxygen at a ⁺-O(a)-Cu angle of 25°. The hyperfine field at this site is also calculated. Our results show the importance of including the local contact and dipolar contributions to the hyperfine field which arise from the unpaired electron spin distribution in the vicinity of the muon.     

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 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.     

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.     

Multi-level relaxation model for describing the M?ssbauer spectra of single-domain particles in the presence of quadrupolar hyperfine interaction

A multi-level stochastic model taking into account the magnetic anisotropy, precession and diffusion of the uniform magnetization of single-domain particles is developed in order to describe the M?ssbauer absorption spectra of an ensemble of magnetic nanoparticles in the presence of quadrupolar hyperfine interaction with an arbitrary orientation of its principal axes. This model allows one to take into account physical mechanisms for forming the hyperfine structure in a real situation and can be easily realized even on a personal computer. In particular, now one can numerically describe qualitative features of temperature evolution of the M?ssbauer spectral shape from a 'symmetric' magnetic sextet to a quadrupolar doublet of lines, which has been observed in a large number of experimental spectra of (57)Fe nuclei in magnetic nanoparticles for almost half a century.     

Theory of the 2S–2P Lamb shift and 2S hyperfine splitting in muonic hydrogen

The 7σ$7\sigma$ discrepancy between the proton rms charge radius from muonic hydrogen and the CODATA-2010 value from hydrogen spectroscopy and electron-scattering has caused considerable discussions. Here, we review the theory of the 2S–2P Lamb shift and 2S hyperfine splitting in muonic hydrogen combining the published contributions and theoretical approaches. The prediction of these quantities is necessary for the determination of both proton charge and Zemach radii from the two 2S–2P transition frequencies measured in muonic hydrogen; see Pohl et al. (2010) [9] and Antognini et al. (2013) [71].     

RF-μSR study of muonium charge states and dynamics in Si

The radio frequencySR technique developed at TRIUMF was used to measure the temperature dependence of the diamagnetic muon, Mu, and Mu^* amplitudes in silicon between 10 K and 500 K. Six samples doped with phosphorus (n-type) and boron (p-type) in the concentration range 10¹¹ to 10¹⁵ cm^–3 were studied. In pure Si a very good fit over the whole temperature range is obtained from a model that includes the ionization of Mu^* and Mu to a bond centered ⁺ followed at high temperature by charge exchange involving Mu.     

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.     

Exploration of hyperfine interaction between constituent quarks via η productions

The elastic-scattering reaction ³⁶Ar + α was studied using the Thick Target Inverse Kinematics technique. Data were taken at a beam energy of 150 MeV in a reaction chamber filled with ⁴He gas, corresponding to the excitation region of 12–20 MeV in ⁴⁰Ca. Using a simplified R -matrix method of analysis energies, widths and spin assignments were obtained for 137 resonances. The structure is discussed within the concept of α-cluster structure in the quasi-continuum of ⁴⁰Ca and is compared to other nuclei in the same mass region.     

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.     

Spectrum of b-baryons: color hyperfine interaction vs. experiment

I discuss several recent highly accurate theoretical predictions for masses of baryons containing the b quark,especially Ωb （ssb） very recently reported by CDF.I also point out an approximate effective supersymmetry between heavy quark baryons and mesons and provide predictions for the magnetic moments of Λc and Λb .Proper treatment of the color-magnetic hyperfine interaction in QCD is crucial for obtaining these results.     

Non-perturbative treatment of hyperfine interaction in charmonium; a clue to understanding the pseudoscalars?

We give arguments that the wave function of η _c is relativistic and strongly localized while that of η _c , though non-relativistic, looks quite different from what is naively expected. This has consequences for the overlap integrals with ψ and ψ′ and may solve the problems associated with magnetic transitions. The hadronic width of η _c is expected around 20 MeV, that of η _c ^′ can become very small.     

Critical exponentβ for hyperfine fields in nickel

The magnetic hyperfine fields for⁶³Ni,⁶⁶Cu, and⁶⁷Zn nuclei in nickel metal have been measured by means of perturbed-ray angular distribution techniques at different temperatures up to 1 K below the Curie temperature,T _C . The temperature dependence of the fields can be very well fitted by (1—T/T _C ) with best values=0.322(16) for⁶³NiNi, = 0.427(42) for⁶⁶CuNi, and=0.427(14) for⁶⁷ZnNi respectively. The differences between these exponents indicate that there could be probe atom dependent deviations from proportionality between hyperfine field and bulk magnetization in the critical region.Work performed in partial fulfillment of the requirements for a doctorate in physics at the Freie Universität, Berlin     

Mössbauer study of the magnetic and electric hyperfine interaction of dilute57Fe impurities in rare earth metal hosts

The hyperfine interaction of dilute⁵⁷Fe in the rare earth (RE)metals Gd to Lu was investigated by Mössbauer measurements with⁵⁷Co doped RE sources. In all hosts well split, 2-lines spectra were observed at room temperature, with slight asymmetries of the line intensities in some cases. The quadrupole splitting eQV_zz/2 increases from 0.29 mm/sec for Gd to 0.50 mm/sec for Tb, and decreases by less than 10 % between Tb and Lu. Only about 10 % of the corresponding electric fieldgradient (EFG) can be accounted for by the ionic EFG on a substitutional RE site. The temperature dependence of the EFG was measured in the case of Tb. No variation within 3 percent was found between 300 K and 700 K. Measurements of the magnetic hyperfine interaction at low temperatures were carried out in Tb. The saturation field of⁵⁷Fe in this host is H_hf(FeTb;4.2 K)=25(2) KOe. The temperature dependence of the magnetic hyperfine field does not follow the host magnetization (T_c=220K) but vanishes at about 80 K. Similar anomalies of H_hf(T) have previously been observed for other transition element impurities in the RE ferromagnets.     

Cross-sectional study of femtosecond laser bulk modification of crystalline α-quartz

Bulk irradiation of crystalline α-quartz was performed with ∼170-fs laser pulses with a wavelength of 800 nm focused below the sample surface. Investigations were carried out using transmission electron microscopy on a cross-sectional specimen prepared using focused ion beam techniques. We observed alternating amorphous–crystalline structures with sharp transitions and associated density changes, surrounded by a highly strained crystalline structure. The alternating sub-surface structures are parallel to the laser’s electric field polarization and exhibit a spacing which is close to the laser wavelength in air. Cracking was also observed in the near proximity of these structures.