Satellite lines in the optical spectrum of Mn2+ in rare earth double nitrate crystals

Satellite lines have been observed in the spectra of Mn²⁺ in crystals of lanthanum manganese double nitrate and praseodymium manganese double nitrate doped with impurity ions on Mn²⁺ sites and rare-earth sites. The lattice sites in the neighbourhood of the Mn²⁺ ions which must be occupied by impurity ions to produce satellite lines have been identified. Besides the satellite lines a common line shift was observed, which was concentration dependent.Project of the Sonderforschungsbereich Festkörperspektroskopie Darmstadt-Frankfurt supported by the Deutsche Forschungsgemeinschaft.     

Mössbauer study of 57Fe in GaAs and GaP following 57Mn+ implantation

Ion implantation provides a precise method of incorporating dopant atoms in semiconductors, provided lattice damage due to the implantation process can be annealed and the dopant atoms located on regular lattice sites. We have undertaken ⁵⁷Fe emission Mössbauer spectroscopy measurements on GaAs and GaP single crystals following implantation of radioactive ⁵⁷Mn^?+? ions, to study the lattice sites of the implanted ions, the annealing of implantation induced damage and impurity–vacancy complexes formed. The Mössbauer spectra were analyzed with four spectral components: an asymmetric doublet (D1) attributed to Fe atoms in distorted environments due to implantation damage, two single lines, S1 assigned to Fe on substitutional Ga sites, and S2 to Fe on interstitial sites, and a low intensity symmetric doublet (D2) assigned to impurity–vacancy complexes. The variations in the extracted hyperfine parameters of D1 for both materials at high temperatures (T?> 400 K) suggests changes in the immediate environment of the Fe impurity atoms and different bonding mechanism to the Mössbauer probe atom. The results show that the annealing of the radiation induced damage is more prominent in GaAs compared to GaP.     

The magnetic properties of Eu nanoclusters formed in NaCl crystals during plastic deformation and aggregation

Plastic deformation of aged crystals and diffusion-controlled aggregation of Eu²⁺ ions in freshly quenched NaCl: Eu crystals causes the formation of complexes bound by exchange interaction. The solution of large-sized precipitates by quenching followed by impurity aggregation results in the nucleation of magnetically sensitive clusters comprising few atoms. A constant magnetic field with induction 5 T increases the probability of the transition of magnetically sensitive clusters from the high-to low-spin metastable state and induces changes in their atomic structure.     

Specific features in the generation and motion of dislocations in heat-treated silicon wafers

The specific features in the generation and motion of dislocations in silicon single-crystal wafers after different heat treatments are investigated by the four-point bending technique. It is demonstrated that annealing of silicon single-crystal wafers at a temperature of 450°C leads to their substantial hardening as compared to the postgrowth state. The oxygen-containing precipitates and precipitate dislocation pileups formed in the silicon wafer bulk during multistage heat treatment are efficient heterogeneous nucleation sites of dislocations under the action of thermal or mechanical stresses. It is found that the multistage heat treatment of the silicon wafers under conditions providing the formation of an internal getter within their bulk results in considerable disordering of the wafer structure. The inference is made that the formation of the defect state in the crystal lattice of silicon and the strength characteristics of silicon wafers substantially depend on the temperature-time schedules of the low-temperature stage of multistage heat treatment.     

Local environment and oxidation state of a Mn impurity in SrTiO3 determined from XAFS data

The local environment and oxidation state of a Mn impurity in strontium titanate doped with 3% Mn were studied by X-ray absorption fine structure spectroscopy. The effect of the synthesis conditions on the incorporation of the impurity into A and B sites was studied. It was established that Mn ions substituting for Ti are in the Mn⁴⁺ oxidation state and are on-center. Mn ions substituting for Sr are in the Mn²⁺ oxidation state and off-center, and are displaced from the lattice site by 0.32 Å absorption near the edge structure can be used to determine the ratio of Mn atoms incorporated into A and B sites in the lattice.     

Lattice location of implanted As in ZnO

Radioactive ⁷³As ions were implanted into a ZnO single crystal at room temperature with 60 keV up to a fluence of 2×10¹³ cm⁻². Subsequently, the angular emission channeling patterns of emitted conversion electrons were recorded by means of a position-sensitive detector in the as-implanted state and following annealing up to 900 C, and were compared to simulated emission yields for a variety of different lattice sites. We find that As does not occupy substitutional O sites, but mainly occupies the substitutional Zn sites. The fraction of As on O sites was at most a few per cent. Arsenic in ZnO is thus an interesting example of an impurity in a semiconductor where the major impurity lattice site is determined by atomic size and electronegativity rather than its position in the periodic system. Possible consequences with respect to the role of arsenic as a p-type dopant in ZnO are being discussed.     

Microhardness studies on melt-grown single-phase mixed (NaK)Cl and solution-grown two-phase NaClKCl crystals

Microhardness studies were carried out on melt-grown (NaK)Cl crystals. The quenching strains and the difference in the ionic sizes of the cations constituting the mixed system introduced large numbers of defects, viz. dislocations, grain boundaries, etc. The etching experiments and supplementary X-ray studies clearly revealed that the Na⁺ or K⁺ ions are precipitated at the dislocation sites. These phase particles strongly interact with dislocations so as to obstruct the mobility of the latter contributing to the hardening mechanism. Results are compared with solution-grown two-phase mixed NaClKCl pure NaCl and pure KCl crystals.     

Internal strain and the ferroelectric transition in ferroelastic NH4HSO4 crystals as studied by EPR of VO2+ impurity probes

The ferroelectric phase transition and its relation to the spontaneous strain in ferroelastic NH₄HSO₄ crystals were investigated using VO²⁺ ions as an EPR probe. The impurity ions were found to be interstitially trapped at sites surrounded by crystallographically inequivalent NH₄⁺ and SO₄^2? ions. The polar VO²⁺ axes exhibited temperature-dependent displacements in two distinct directions with different energies. The differential properties of VO²⁺ ions in NH₄HSO₄ crystals were used to verify the presence of internal stress in the ferroelastic phases, and the corresponding strain was studied in the range between ?120 and + 100°C. The results indicate that the ferroelectric phase transition occurs as a consequence of lattice instability caused by the internal strain. At the second-order structural transition a dipolar lattice emerges in the crystal and the spontaneous polarization appears as a result of internal entropy transfer to the strained lattice.     

Spectroscopy of radiation-induced and structural defects in garnet crystals with V and Cr impurity ions

The optical absorption spectra of crystals with garnet structure (A₃B₂C₃O₁₂), containing V or Cr impurity ions, before and after oxidation annealing, γ irradiation, and coactivation with Ca and Mg ions have been experimentally and theoretically investigated. It is shown that V³⁺ and Cr⁴⁺ ions are incorporated into both octahedral and tetrahedral sites of the garnet lattice. The absorption spectra and energy level diagrams of impurity ions are identified.     

Atomistic sliding mechanisms of the Σ=5 symmetric tilt grain boundary in bcc iron

Atomistic computer simulations were performed to investigate the mechanisms of grain-boundary sliding in bcc Fe using molecular statics and molecular dynamics with embedded-atom method interatomic potentials. For this study we have chosen the Σ?=?5, (310)[001] symmetrical tilt boundary with tilt angle θ?=?36.9°. Sliding was determined to be governed by grain-boundary dislocation activity with Burgers vectors belonging to the displacement shift complete lattice. The sliding process was found to occur through the nucleation and glide of partial grain-boundary dislocations, with a secondary grain-boundary structure playing an important role in the sliding process. Interstitial impurities and vacancies were introduced into the grain boundary to study their role as nucleation sites for the grain-boundary dislocations. While vacancies and H interstitials act as preferred nucleation sites, C interstitials to not.     

Molecular dynamics analysis of impurity ions behavior in β″-Al2O3

The effects of foreign impurity ions in the conduction plane on the β″-Al₂O₃ lattice have been analyzed by molecular dynamics. As impurity ions, K and Ca ions were chosen and Na sites in the conduction plane were replaced with these ions. Results are summarized as follows: (1) The β″-Al₂O₃ lattice expands perpendicular to the conduction plane when K ions are doped; (2) Ca ions do not contribute to expansions of the β″-Al₂O₃ lattice; (3) both K and Ca ions reduce the mean square displacement of Na ions, which can be attributed to decreased Na ion diffusion.     

2.5MeV的He+离子辐照316L不锈钢中氦泡的形核与生长研究

利用透射电子显微镜分析了0.3—0.5T_m温区（T_m为材料溶点）316L奥氏体不锈钢经高剂量氦离子辐照后辐照损伤峰区氦泡的形成行为.实验结果支持氦泡的双原子形核模型，并证实氦泡的形成主要受制于自间隙子/氦置换机制扩散.材料中高密度位错的存在显著增强氦泡形核并抑制氦泡生长.与前人低剂量辐照实验结果的比较表明0.3—0.5T_m温区氦泡形核机制不随辐照剂量或剂量率发生显著变化． 关键词：     

Hyperfine interactions of111Cd in ion-implanted face centered cubic cobalt

The magnetic-dipole and electric-quadrupole hyperfine interactions of¹¹¹Cd probes in fcc cobalt after implantation of radioactive¹¹¹In⁺ ions have been investigated by PAC measurements with fast BaF₂ detectors. Six different sites of the probe atoms could be distinguished and characterized by their hyperfine parameters and annealing behaviour. Besides the substitutional site, three sites are assigned to In-vacancy complexes which are formed athermally in the implantation process or by thermally-activated trapping of lattice defects in annealing stage III. The remaining two sites are attributed to In located in stacking faults or hcp regions of the host. Systematic trends of impurity hyperfine fields in defect sites become evident from a comparison with other impurity-host combinations. The temperature dependence of the magnetic hyperfine fields has been measured between 20 K and 390 K. Large differences found for the various sites are discussed.     

EPR Spectroscopy of Impurity Thulium Ions in Yttrium Orthosilicate Single Crystals

The frequency-field and orientation dependences of the electron paramagnetic resonance (EPR) spectra are measured for impurity Tm³⁺ ions in yttrium orthosilicate (Y₂SiO₅) single crystals by stationary EPR spectroscopy in the frequency range of 50–100 GHz at 4.2 K. The position of the impurity ion in the crystal lattice and its magnetic characteristics are determined. The temperature dependences of the spin–lattice and phase relaxation times are measured by pulse EPR methods in the temperature range of 5–15 K and the high efficiency of the direct single-phonon mechanism of spin–lattice relaxation is established. This greatly shortens the spin–lattice relaxation time at low temperatures and makes impurity Tm³⁺ ions in Y₂SiO₅ a promising basis for the implementation of high-speed quantum memory based on rare-earth ions in dielectric crystals.     

Near-neighbour interactions in iron based alloys

Time differential perturbed angular correlation experiments were carried out using¹¹¹Cd probe nuclei to measure the change in conduction electron polarization at different lattice sites due to scattering around an impurity atom.     

Studies on the origin of the 3400 cm region infrared bands of synthetic and natural α-quartz

Boron was incorporated into synthetic quartz thereby producing, by perturbing an OH vibration, an i.r. band at 3594 cm^?1 whose absorption coefficient varies with boron content. The present study was not able to confirm the correlations of i.r. bands with alkali ions as reported by others. Ions such as Al³⁺, Y³⁺, Yi⁴⁺ and Be²⁺ produced no new, sharp absorption bands in the i.r. spectra. The conclusion was reached that the impurity perturbation of the OH vibration was strongly influenced by the impurity site and that probably the tunnel sites were more important than interstitial or lattice sites. Mass spectrometric analyses of sixteen crystals are reported. I.R. spectra of natural quartz, non-doped synthetic quartz and boron-doped synthetic quartz are presented.     

A phototropic center and distribution of the chromium impurity in rare-earth garnet crystals

Crystals of two types, namely, Gd₃Sc₂Al₃O₁₂ doped by Ca²⁺ and Cr³⁺ ions and Gd₃Sc₂Ga₃O₁₂ doped by Nd³⁺ and Cr³⁺, are studied using x-ray diffraction. In order to elucidate how an impurity is embedded in the lattice, its effect on the electron density distribution and microstrains of the crystal lattice is investigated. It is shown that chromium ions can occupy the lattice sites located predominantly in the octahedral environment of the oxygen ligands.     

Micromechanics of the transition from intergrain to intragrain deformation in nanomaterials

A micromechanism of the transition from intergrain sliding to intragrain glide by nucleation and emission of lattice partial dislocations at grain-boundary dislocations is proposed and described theoretically. The energy characteristics of this process are calculated. It is shown that the nucleation of lattice partial dislocations is energetically efficient and can occur athermally (without the energy barrier) under conditions of the action of ultrahigh mechanical stresses. The critical stresses required for the athermal nucleation and emission of dislocations are calculated.     

The electrical activity of phosphorus channelled into silicon

The electrical activity of phosphorus ions, implanted at energies between 40 and 400 keV along the 〈110〉 axis of silicon crystals, has been measured as a function of depth, following a 700°C anneal. The electrical activity, determined by differential electrical sheet conductivity measurements combined with anodic stripping, was found to be close to 100 per cent in both pulled and float-zoned material. In some cases it was possible to compare carrier concentration and impurity ion distributions within the same specimen, implanted with a mixed dose of P³¹ and Pa³².

By radioactive tracer techniques it has been shown that de-channelling of phosphorus ions is significantly greater in certain dislocation-free crystals than in other, dislocated silicon crystals. Scanning X-ray diffractometer measurements reveal considerably more lattice strain in the former. It is proposed that both effects may arise from vacancy clustering, together with associated decoration by impurity atoms, as a result of the absence of sinks provided by a few dislocations.

The degree of channelling of P³² in epitaxially-grown 〈111〉 silicon has been found to exceed that in high-quality bulk-grown crystals. The consequences of this observation, combined with the high electrical activity of channelled phosphorus, are considered briefly.     

X-Ray standing wave analysis of bismuth implanted in Si(110)

Perfect crystal silicon samples implanted with 60 KeV Bi atoms along the [110] surface normal direction were analyzed with X-ray standing waves. Two reflection orders, (220) and (440) were used with synchrontron radiation to study systematically the impurity distribution function at 5 different doses ranging from 0.6 to 10×10¹⁴ Bi atoms/cm². The analysis reveals the substitutional Bi position connected with a lattice expansion and the formation of precipitates at higher Bi doses as well as estimates for the Bi vibrational amplitude.