Lattice Dilation Research Articles

Electronic structure of hydrogen and muonium in Al, Mg and Cu

The electronic structure of hydrogen and muonium in simple metals is investigated. The spherical solid model potential is used for the discrete lattice and the Blatt correction for lattice dilation. The proton and muon are kept at the octahedral sites in the fcc and hcp lattices and self-consistent non-linear screening calculations are carried out. The scattering phase shifts, electronic charge density, effective impurity potential, self-energy, charge transfer, residual resistivity and Knight shift are calculated. The spherical solid potential changes the scattering character of impurity. The phase shifts are found slowly converging. The scattering is more prominent in Al than in Mg and Cu. The virtual bound states of proton and muon are favoured in all the three metals. The calculated value of residual resistivity for CuH is in good agreement with the experimental value. The results for Knight shift forμ + in Cu and Mg are in reasonable agreement with the experimental values while those forμ + in Al are lower than the experimental value. The analytical expressions for effective impurity potential and electronic charge density are suggested.

Exciton luminescence in Si1−xGex/Si heterostructures grown by molecular beam epitaxy

Coherent Si1−xGex alloys and multilayers synthesized by molecular beam epitaxy (MBE) on Si(100) substrates have been characterized by low-temperature photoluminescence (PL) spectroscopy and transmission electron microscopy (TEM). Phonon-resolved transitions originating from excitons bound to shallow impurities were observed in addition to a broad band of intense luminescence. The broad PL band was predominant when the alloy layer thickness was greater than 40–100 Å, depending on x and the strain energy density. The strength of the broad PL band was correlated with the areal density (up to ∼109 cm−2) of strain perturbations (local lattice dilation ∼15 Å in diameter) observed in plan-view TEM. Thinner alloy layers exhibited phonon-resolved PL spectra, similar to bulk material, but shifted in energy due to strain and hole quantum confinement. Photoluminescence excitation spectroscopy, external quantum efficiency, time-resolved PL decay, together with the power and temperature dependence of luminescence intensity, have been used to characterize Si1−xGex/Si heterostructures exhibiting both types of PL spectra. The role of MBE growth parameters in determining optical properties was investigated by changing the quantum well thickness and growth temperature. The transition from phonon-resolved, near-band-gap luminescence in thin layers to the broad PL band typical of thick layers is discussed in terms of a strain energy balance model which predicts a ‘‘transition thickness’’ which decreases with increase in x.

Structural Properties of H‐Implanted InP Crystals

H has been implanted in crystals at the energy and at different doses ranging from . The depth dependence of the elastic lattice strain has been investigated by high resolution x‐ray diffractometry. The implantation produces a lattice dilation. The strain increases with increasing depth, reaches the maximum at about 0.75 μm, and then decreases rapidly; moreover the maximum strain is proportional to the dose. No extended crystal defects have been detected by transmission electron microscopy up to . At a buried amorphous layer 28 nm in thickness has been observed at the same depth where the strain is maximum. The thickness of the amorphous layer increases by further increasing the dose and reaches a value of about 0.18 μm for .

Voltage and temperature dependence of silicon high-order Laue zone line positions

Abstract Two fast-electron quantum states are highly excited for crystal orientations close to the Si zone axis, manifesting themselves as pairs of lines associated with each high-order Laue zone (HOLZ) reflection. The electron wave-vector k is determined from absolute positions of deficit lines in the zeroth-order beam, where full account is taken of dynamically induced displacements compared with positions determined from kinematic (geometrical) theory. Geometrie results approximate experiment provided that k is modified by Δk, equivalent to a voltage shift ΔE. The two excited Bloch states provide an independent assessment of Δk. Changes in HOLZ line position with inereasing temperature are due to delocalization of the projected potential and corresponding shifts in eigenvalues. The displacement of HOLZ lines due to thermal lattice dilation is three times smaller than shifts due to delocalization of the elastic potential. A nominal 300 kV accelerating voltage of a Philips CM30 electron microscope i...

Elastic instability of crystals caused by static atom displacement: A mechanism for solid-state amorphization.

During the solid-state amorphization process, there have been a number of observations showing a large lattice dilatation and softening of shear elastic constants. Based on these reports, the amorphization mechanism was modeled by introducing static displacement of atoms that caused lattice strain. The calculation indicated that a crystalline structure became unstable at a critical strain value. Qualitative agreement was obtained between the calculated and experimental values of the changes in the shear elastic constant and the lattice parameter at the instability point

The impact of lattice dilation on deep states in MBE GaAs

Deep level transient spectroscopy (DLTS) of n-type, molecular beam epitaxially grown GaAs has revealed a large increase in the concentrations of the characteristics deep electron traps, known as M states, with erbium doping. Total M trap concentrations in excess of 5 × 10 15 cm -3 are measured for a moderate erbium doping level of 1 × 10 18 cm -3. These high M trap concentrations can be increased by a further two orders of magnitude by growth upon strained, more heavily erbium-doped material. Dilation of the GaAs matrix, arising in this case from the presence of the large Erbium atoms and ErAs precipitates in the lattice, is believed to play a major role in the creation of these characteristics MBE defects.

SiGe/Si Quantum Wells by MBE : A Photoluminesence Study

AbstractStrained Sil-xGex quantum wells and multi-quantum wells, synthesized by solid source ebeam evaporated MBE on Si(100) substrates have been studied by low temperature photoluminescence (PL) spectroscopy. Phonon resolved transitions originating from excitons bound to shallow impurities in Sil-xGex layers were observed over the temperature range 2K to 100K and used to characterize Sil-xGex/Si heterostructures. Thin Sil-xGex quantum wells exhibited phonon-resolved PL spectra, similar to bulk material, but shifted in energy due to strain, quantum well width and Ge fraction. In single quantum wells confinement shifts up to ∼200 meV were observed (1.2 nm wells with x = 0.38) and NP linewidths down to 1.37 meV were obtained. The confinement shifts were modeled by hole confinement in Sil-xGex wells. An annealing study was performed to investigate the role of Si-Ge interdiffusion on luminescence. Both the geometrical shape and optical emission of the quantum well were found to significantly change through intermixing. In addition to near edge luminescence a broad band of intense luminescence was obtained from several Sil-xGex/Si heterostructures. Some layers exhibited both types of PL spectra. However, the broad PL band (peak energy ∼120meV below the strained bandgap) was predominant when the alloy layer thickness was greater than 2 - 10nm, depending on x, growth temperature, and substrate surface preparation. The strength of the broad PL band was correlated with the areal density of strain perturbations (∼109cm−2 per quantum well corresponding to a spacing of 300nm in the plane of the well; local lattice dilation ∼ 1.5 nm in diameter) observed in plan-view TEM. The first few wells of MQW exhibited only band edge luminescence as was revealed by etching off the upper MQW periods. In addition, post growth anneals at temperatures in the range 700°C to 1100°C were found to enhance band edge luminescence, while the broad luminescence band decayed to zero intensity. Interdiffusion at these these temperatures has been shown to dramatically change the QW shape and consequently interfacial asperities would be expected to disappear, consequently only shallow phonon resolved luminescence is observed in PL after annealing. The influence of PL measurement parameters such as excitation power density and PL sample temperature on the relative strengths of band edge versus broad band luminescence were also consistent with the presence of exciton traps at sites of reduced bandgap.

Microstructural change and its influence on fission gas release in high burnup UO 2 fuel

The microstructural change of UO 2 fuel pellets (burnup: 6–83 GWd/t), base irradiated under LWR conditions, has been studied by detailed postirradiation examinations. The lattice parameter near the fuel rim in the irradiated UO 2 increased with burnup and appeared to become constant beyond about 50 GWd/t. This lattice dilation was mainly due to the accumulation of radiation induced point defects. Moreover, the dislocation density in the UO 2 matrix developed progressively with burnup, and eventually the tangled dislocations organized many sub-grain boundaries in the highest burnup fuel of 83 GWd/t. This sub-grain structure induced by accumulated radiation damage was compatible in appearance with SEM fractography results which revealed sub-divided grains of sub-micron size in as-fabricated grains. The influence of burnup on 85Kr release from the UO 2 fuels has been examined by means of a postirradiation annealing technique. The higher fractional release of high burnup fuels was mainly due to the burnup dependence of the fractional burst release evolved on temperature ramp. The fractional burst release was represented in terms of the square root of burnup from 6 to 83 GWd/t.

Very hard solid-solution-type tungsten-carbon coatings deposited by reactive magnetron sputtering

Tungsten-carbon coatings have been deposited on stainless steel substrates by reactive magnetron sputtering in ArCH 4 mixtures. The composition of coatings was determined by electron microprobe analyses. Only the cubic α-W phase with an expanded lattice parameter was detected by X-ray diffraction in the W-C coatings containing less than 25 at% of carbon. Since the lattice dilatation of the α-W phase increased with increasing carbon content these coatings were assumed to be tungsten-carbon solid solutions. The dilatation of the W crystal lattice and Vickers hardness of the solid-solution-type W-C coatings were measured as functions of the carbon concentration. A lattice dilatation-microhardness relationship was established.

Lattice Parameter Changes in High Dose Ion-Implanted, Pulsed Laser Annealed GaAs:Si

ABSTRACTDouble crystal x-ray diffraction has been used to examine the lattice parameter changes which occur in heavily Si-doped GaAs obtained by ion implantation of 28Si at 180 keV with doses up to 1 x 1016/cm2. The heavily damaged, implanted layer was pulsed laser annealed with single pulses from a 10 ns dye laser operating at 728 nm with an energy density of up to 0.9 J/cm2. Plasmon Raman scattering was used at the center of the laser-annealed spots to determine the free electron concentration which reached ∼4 × 1019/cm3. Double crystal rocking curves were obtained for <400> reflections from the pulsed laser annealed area and from the surrounding as-implanted region. The results show a dilation of the lattice of up to 0.5% in the as-implanted region and in the laser-annealed region a dilation of 0.025%. The residual lattice dilation after annealing is interpreted in terms of a dilation due to free carriers and a (smaller) contraction due to the Si atomic size effects.

Broad Band vs Phonon Resolved Luminescence in Si1−xGex/Si Heterostructures Grown by Molecular Beam Epitaxy

ABSTRACTSi1−xGex alloys and multilayers synthesized by solid source MBE on Si(100) substrates have been characterized by low temperature photoluminescence (PL) spectroscopy and transmission electron microscopy (TEM). Phonon resolved transitions originating from excitons bound to shallow impurities were observed in addition to a broad band of intense luminescence. PL spectroscopy over the temperature range 2K to 100K has been used to characterize Si1−xGex/Si heterostructures exhibiting both types of PL spectra. Thin alloy layers exhibited phonon-resolved PL spectra, similar to bulk material, but shifted in energy due to strain and hole quantum confinement. In single quantum wells confinement shifts up to ∼200 meV were observed (1.2 nm wells with x = 0.38) and NP linewidths down to 1.37 meV were obtained. However, the broad PL band (peak energy ∼120meV below the strained bandgap) was predominant when the alloy layer thickness was greater than 2 – 10nm, depending on x, growth temperature, and substrate surface preparation. The strength of the broad PL band was correlated with the areal density of strain perturbations (∼109cm−2 per quantum well; local lattice dilation ∼1.5 nm in diameter) observed in plan-view TEM. The role of MBE growth parameters in determining optical properties was investigated by changing growth temperature, substrate preparation procedures and exploring the effect of surface passivation in a hydrogen ambient. In addition, post growth anneals at temperatures in the range 700°C to 1 100°C were carried out, where interdiffusion removes interfacial asperities and the broad luminescence band decays to zero intensity.

Lattice dilation acrossn-InP-substrates and its influence on material properties of InP/InGaAsP- double-heterostructures

Precise measurements of lattice parameter and photoluminescence were performed across InP-substrates and InP/InGaAsP-DHS. They show a lattice dilation in a region with enriched free carrier concentration if strongn-type doped InP-substrates of faceted 〈111〉-grown LEC-crystals were used. Strain gradients and mismatch problems have to take into consideration.

Hydrogen-solute interaction in nickel-based dilute alloys studied by internal friction technique

The internal friction has been measured for dilute NiM alloys (M = Ti, Si, Co, Cr, Cu, Fe, Mn, Pd, V) containing hydrogen over a temperature range from 60 to 400 K. An internal friction peak due to the interaction between substitutional solute atoms and interstitial hydrogen atoms (SI peak, SIP) is observed around 160K except for the NiCo alloy. Detailed measurements have been performed on the NiTi alloy; the binding energy for the TiH pair; evaluated from the solute and hydrogen concentration dependence of the peak height, is smaller than 2 kJ/mol. The relaxation strength of the SIP is comparable to the Snoek peaks in b.c.c. metals, and is closely related to the dilatation of the host Ni lattice by alloying. Below 120 K, a background internal friction is observed in specimens which show the SIP. The background is explained in terms of the magnetomechanical damping accompanied by the hydrogen reorientation around solute atoms under a static stress due to magnetostriction.

Lattice distortion of solute atoms in metals studied by x-ray-absorption fine structure.

The analysis of the x-ray-absorption fine structure (XAFS) yields information about the local atomic arrangement of the absorbing atom. The technique was used to study systematically the lattice dilatation or compression caused by substitutional impurity atoms in the fcc metals Al, Cu, Ni, Pd, and Ag and the bcc metals Fe, Nb, and V. Measuring XAFS spectra at the {ital K} and {ital L} edges of a variety of metals, interatomic distances, coordination numbers, and Debye-Waller factors were determined. Using experimentally determined amplitudes and phases from appropriate model compounds, the accuracy of the analysis is about 0.5% for nearest-neighbor distances and about 10% for coordination numbers and Debye-Waller factors. For the 61 systems investigated, shifts of the first-neighbor-shell distance of up to 10 pm are found, while the shifts of higher shells are generally small. Systematic variations within the rows of the Periodic Table are observed, indicating the importance of electronic effects. The results are discussed in comparison with lattice-parameter measurements and band-structure calculations.

X-ray diffraction study of Fe/MgO multilayered films with an enhanced magnetization

Fe atoms in Fe(16 AA)/MgO(60 AA) multilayered films, prepared in UHV conditions, have been identified as having the same BCC structure as for the bulk specimens, using X-ray diffraction. The lattice parameter for the Fe atoms was found to be larger than the bulk value by 1.0%. Such a lattice dilation is related to the enhancements in magnetization and hyperfine field of Fe atoms in Fe/MgO multilayered films.

Optical energy-gap variation and deformation potentials in CuInTe2

Values of optical energy gap E0 as a function of pressure P up to 3 GPa at room temperature, and as a function of temperature T in the range 10–300 K at atmospheric pressure were obtained by optical-absorption measurements on samples of CuInTe2. It was shown that in this pressure range, E0 varies linearly with P, dE0/dP having a value of 2.2×10−2 eV/GPa. The variation of E0 with T was fitted well by a simple Manoogian–Leclerc equation of the form E0(0) − E0(T) = UT + Vφ (coth φ/2T−1). Both dE0/dP and U can be related to (dE0/dT)2, the lattice dilation contribution to the variation of the energy gap with temperature, and the values obtained in the two cases showed good agreement. The Vφ term can be related to (dE0/dT)1, the energy-gap variation due to electron-phonon interaction. From the values of (dE0/dT)1 and (dE0/dT)2, values were determined for the acoustic deformation potentials of the conduction band Ce and of the valence band Ch.

Neutron powder diffusion study of the fast-ion transition and specific heat anomaly in beta -lead fluoride

A powder sample of beta -PbF2 has been studied by neutron diffraction using the high resolution powder diffractometer at the Rutherford-Appleton Laboratory. Rietveld profile refinements have been performed on data collected at roughly 100 temperatures from ambient to well above the transition to the fast-ion phase, which occurs at Tc approximately 710 K. The lattice parameter, a0(T), the concentration of Frenkel defects, and thermal parameters for both the fluorine and the lead ions have been determined as a function of temperature. Precise values of a0(T) enable the linear expansivity to be calculated, for which there is a pronounced peak centred on Tc. It is possible to calculate contributions to the specific heats, Cp, from harmonic and anharmonic lattice vibrations, Frenkel disorder an lattice dilation; a broad peak is obtained centred on Tc, which is in good agreement with the directly determined experimental data.

Numerical modeling of superlattice x-ray-scattering intensities.

We describe a one-dimensional x-ray-scattering model that includes discrete layer-thickness fluctuations and interfacial diffusion in the kinematical approximation. We demonstrate the use of the model in an analysis of the out-of-plane scattering intensities of epitaxial Co-Au and Co-Cu superlattices. In the case of Co-Au superlattices, the experimental data show that interfacial diffusion is limited to a two-monolayer region, and that layer-thickness fluctuations are of order \ifmmode\pm\else\textpm\fi{}1 monolayer. The superlattice features in Co-Cu superlattice measurements are shown to arise from lattice-spacing modulations and are insensitive to composition modulation. The measured intensities are consistent with Co-Cu interfaces which are 2 monolayers thick. A dilation of the Co lattice in the direction of growth is observed for both Co-Au and Co-Cu superlattices. We speculate that the expansion is due to a slightly reduced density of atoms in an imperfectly stacked structure.

Real-time x-ray studies of strain kinetics in InxGa1-xAs quantum-well structures.

A new time-resolved x-ray method of probing the kinetics of interfacial strains in semiconductor heterostructures is presented. High-resolution synchrotron-radiation measurements of the strain relaxation during rapid thermal annealing show that the lattice dilation of an as-grown quantum-well structure is relieved cooperatively by a series of sluggish discontinuous transitions. Well-defined metastable states of strain are observed between the transitions.

Oxygen Potentials and Lattice Parameter of Irradiated BWR Fuels.

The oxygen potentials and lattice parameter of oxide fuels (UO2 and UO2-2 w/0Gd2O3) irradiated in commercial BWRs have been measured by using a solid electrolyte galvanic cell technique and X-ray diffractometry. The fuel burn-up was 13–30 GWd/t for the former measurements and 6–35 GWd/t for the latter. The oxygen potentials at 750°C for irradiated UO2 ranged from −420 kJ/mol at the fuel rim to −480 kJ/mol at the fuel center. The corresponding values for irradiated U02-2 w/0Gd2O3 ranged from −460 to −540 kJ/mol. The lattice parameter near the fuel rim in the irradiated UO2 increased with burn-up, and was distinctly larger than that at the fuel center. This lattice dilatation was mainly due to the accumulation of radiation defects, not to a decrease in O/M ratio, and was almost recovered after the annealing at 1,600°C for 5 h.