Beryllium Single Crystals Research Articles

Research on microlaser aided machinability of single crystal Beryllium cutting based on molecular dynamics

Research on microlaser aided machinability of single crystal Beryllium cutting based on molecular dynamics

Electronic structure of thin epitaxial Be films on Si(111)

We show that single crystal films of Be can be grown on Si(111) substrates, exhibiting nearly identical surface electronic bandstructure to that found on the pristine Be(0001) surface of bulk Be. Segregation of silicon atoms into the film causes strong doping of the surface states. For sufficiently thin films, the quality and uniformity are sufficient to observe well-defined quantum well states. In addition to making single-crystal beryllium more accessible for future studies, thin film growth of beryllium on high-resistivity silicon substrates may open up new possibilities to investigate earlier suggestions of surface superconductivity.

Influence of temperature on the cutting performance of single-crystal beryllium: a molecular dynamics simulation investigation

Influence of temperature on the cutting performance of single-crystal beryllium: a molecular dynamics simulation investigation

Atomic-Layer Deposition of Single-Crystalline BeO Epitaxially Grown on GaN Substrates.

We have grown a single-crystal beryllium oxide (BeO) thin film on a gallium nitride (GaN) substrate by atomic-layer deposition (ALD) for the first time. BeO has a higher thermal conductivity, bandgap energy, and dielectric constant than SiO2. As an electrical insulator, diamond is the only material on earth whose thermal conductivity exceeds that of BeO. Despite these advantages, there is no chemical-vapor-deposition technique for BeO-thin-film deposition, and thus, it is not used in nanoscale-semiconductor-device processing. In this study, the BeO thin films grown on a GaN substrate with a single crystal showed excellent interface and thermal stability. Transmission electron microscopy showed clear diffraction patterns, and the Raman shifts associated with soft phonon modes verified the high thermal conductivity. The X-ray scan confirmed the out-of-plane single-crystal growth direction and the in-plane, 6-fold, symmetrical wurtzite structure. Single-crystalline BeO was grown on GaN despite the large lattice mismatch, which suggested a model that accommodated the strain of hexagonal-on-hexagonal epitaxy with 5/6 and 6/7 domain matching. BeO has a good dielectric constant and good thermal conductivity, bandgap energy, and single-crystal characteristics, so it is suitable for the gate dielectric of power semiconductor devices. The capacitance-voltage (C-V) results of BeO on a GaN-metal-oxide semiconductor exhibited low frequency dispersion, hysteresis, and interface-defect density.

Electrodynamic characteristics of berillium oxide in the submillimeter-infrared band

Single-crystal beryllium oxide has been studied by submillimeter-infrared spectroscopy and nonlinear optics methods in the wavenumber range of 2–5000 cm–1 in the temperature interval of 80–300 K. With the aid of computation models, the dispersion parameters of phonons and nonresonance absorption bands have been determined. The mechanisms responsible for dielectric loss in the terahertz band have been revealed. It has been shown that the decisive contribution is made by low-frequency dipole excitations, including two-phonon difference processes, and this contribution exceeds the phonon contribution by two orders of magnitude. Coherent anti-Stokes Raman scattering has been used to determine the coefficients of absorption by polaritons of the low-frequency dispersion branch.

Shock wave compression of hexagonal-close-packed metal single crystals: Time-dependent, anisotropic elastic-plastic response of beryllium

Understanding and modeling the response of hcp metals to high stress impulsive loading is challenging because the lower crystal symmetry, compared to cubic metals, results in a significantly more complex material response. To gain insight into the inelastic deformation of hcp metals subjected to high dynamic stresses, shock wave compression of single crystals provides a useful approach because different inelastic deformation mechanisms can be examined selectively by shock compression along different crystal orientations. As a representative example, we report, here, on wave propagation simulations for beryllium (Be) single crystals shocked along the c-axis, a-axis, and several low-symmetry directions to peak stresses reaching 7 GPa. The simulations utilized a time-dependent, anisotropic material model that incorporated dislocation dynamics, deformation twinning, and shear cracking based descriptions of inelastic deformation. The simulation results showed good overall agreement with measured wave profiles for all the different crystal orientations examined [Pope and Johnson, J. Appl. Phys. 46, 720 (1975)], including features arising from wave mode coupling due to the highly anisotropic inelastic response of Be. This good agreement demonstrates that the measured profiles can be understood in terms of dislocation slip along basal, prismatic, and pyramidal planes, together with deformation twinning along {101¯2} planes. Our results show that the response of shocked Be single crystals involves the simultaneous operation of multiple, distinct inelastic deformation mechanisms for all orientations except the c-axis. For shocked c-axis Be, the measured wave profiles do not provide good discrimination between pyramidal slip and other inelastic deformation mechanisms, such as shear cracking. The findings presented here provide insight into the complex inelastic deformation response of shocked Be single crystals and are expected to be useful for other hcp crystals. More broadly, the present work demonstrates the potential of shock wave propagation along low-symmetry directions to examine, and discriminate between, different inelastic deformation mechanisms in crystalline solids.

The Dynamics of Thermal Expansion in Single Crystal Beryllium from Nanosecond X-Ray Irradiation

Single crystals of beryllium were illuminated with nanosecond X-ray pulses generated from laser irradiated (~1.5 × 1014 W/cm2) gold targets. The characteristic gold M-band centered at 2.5 keV was measured by time-integrated transmission grating spectroscopy and a time-resolved (spectrally integrated) X-ray photodiode through beryllium targets of various thickness. Approximately decaying exponential temperature profiles were predicted to be induced in 100- and 160-μm-thick single crystal targets producing nearly instant surface motion as measured by free surface velocity interferometry. This temperature profile gave rise to free surface (opposite to drive laser surface) velocity histories in a c-axis single crystal and a (10[overbar]10) single crystal in which large initial acceleration gave way to lower (ramped) acceleration due to the internal temperature gradient. A smooth rise to the peak velocity was then followed by a sharp release originating from the free surface nearest to the laser drive. Differences between the velocities in each of these regions were found between the two single crystals investigated, which were due to the thermal expansion properties as a function of direction (including plasticity). These results can be used to predict the behavior of preheated polycrystalline targets relevant to instability seeding in inertial confinement fusion ablators.

Angular dependence of the Knight shift, electric field gradient, and spin-lattice relaxation time of 9Be NMR in beryllium metal

Angular dependences of 9Be NMR (±1/2) and (±1/2 ⇔ ±3/20 transition frequencies are measured in a single-crystal beryllium metal plate in a field of 7.04T. The isotropic Kiso and anisotropic Kaniso components of the Knight shift are determined. The measured values of Kiso and T1 are considered in terms of the contact, polarization, and orbital contributions.

Giant parametric amplification of the nonlinear response in a single crystal of beryllium in a quantizing magnetic field

The nonlinear response to an ac magnetic field with and without parametric pumping was studied experimentally on a rod-like beryllium single crystal at low temperatures in a quantizing magnetic field applied parallel to the hexagonal axis. At low temperatures (⩽3K) giant parametric amplification of the nonlinear response is observed in narrow windows near de Haas-van Alphen (dHvA) beating antinodes, where the amplitude of the magnetic oscillations is maximal. This effect is of threshold character with respect to the amplitude of the dHvA oscillations and occurs as a result of a diamagnetic phase transition of a strongly correlated electron gas into nonuniform state, with the formation of Condon domain structure. It is shown that the nonuniform phase appears periodically in a magnetic field. The components of the rectified signal field reproduce the envelope of H-T critical curves and can be used for reconstruction of diamagnetic phase diagrams.

Relationships Between Metal-Metal Bonding and Crystallographic Pitting in hcp Metals

The orientation dependence of pit propagation in single-crystal beryllium (Be) is compared to observations for single-crystal zinc (Zn). Pits formed on the prism planes of both Be and Zn were characterized by interiors which had crystallographically oriented, parallel plates of unattacked material. In Be, the orientation of the unattacked material had a 90° asymmetry with respect to those formed in Zn. To explain this difference, the electron density distribution for low index planes in Be and Zn was analyzed. A conceptual model for crystallographic pit propagation that considers the role of orientation dependent metal-metal bonding is introduced.

Experimental study of the deformation near a notch tip in copper and copper–beryllium single crystals

The plastic deformation around a notch tip within ductile single crystal material was investigated experimentally. Moiré microscopy was used to measure the strain field on the surface of bending samples of Orientation II with a notch on the (0 1 0) plane and its tip along the [ 1 ̄ 0 1] direction. The results of tests conducted on copper and copper–beryllium single crystals are compared to analytical solutions, numerical calculations, and prior experiments on samples of Orientation I with a notch on the (1 0 1) plane and its tip along the [1 0 1 ̄ ] direction. Distinct sectors with sharp sector boundaries are observed in experiments as were predicted analytically by Rice (Mech. Mater. 6 (1987) 301). However, Rice predicted that both Orientations I and II would give rise to the same sectors. It is found that experimental results for these two orientations differ and neither set of results agree with the analytical solution. In both orientations, the sector boundaries do not exclusively correspond to angles at which slip and kink can occur in these crystallographic orientations. The experiments also lead to the conclusion that some sectors in the deformation field remain elastic even after large amounts of deformation have occurred elsewhere. Based on the optical observations and strain measurements, a stress field is presented for Orientation II.

An inelastic X-ray spectrometer with 2.2 meV energy resolution

We present a new spectrometer at the Advanced Photon Source for inelastic X-ray scattering with an energy resolution of 2.2 meV at an incident energy of 21.6 keV. For monochromatization, a nested structure of one silicon channel cut and one ‘artificial’ channel cut is used in forward-scattering geometry. The energy analysis is achieved by a two-dimensional focusing silicon analyzer in backscattering geometry. In the first demonstration experiments, elastic scattering from a Plexiglas TM sample and two dispersion curves in a beryllium single crystal were measured. Based on these data sets, the performance of the new spectrometer is discussed.

Phase diagram for Condon domains in beryllium

Recent μSR data on the Condon domain state in a beryllium single crystal at external fields H∥[0001] showed serious disagreement with the predictions for phase boundaries based on standard Lifshitz–Kosevich (LK) theory. In search of a realistic phase diagram, the susceptibility χ a ( B, T) is calculated in the frame of a model beyond the ‘quadratic’ LK formula and consistent with available information on the Fermi surface.

Formation of mixed layers and compounds on beryllium due to C + and CO + bombardment

Compound formation on a clean beryllium single crystal (0 0 0 1) during bombardment with 5 keV C + and 3 and 5 keV CO + ions is studied by means of in situ X-ray photoelectron spectroscopy (XPS). In combination with in situ Rutherford backscattering analysis (RBS), TRIDYN computer simulation, and measurements of the weight change of the sample due to the bombardment, models for the sample composition changes and erosion mechanisms are derived for both ion species. In the case of C + bombardment a carbon layer builds up on top of the beryllium. The transition region from pure beryllium to pure carbon consists partly of Be 2C and the beryllium erosion stops as the covering carbon layer develops. During CO + bombardment a deposition/erosion equilibrium is established. After initial C and O accumulation, the beryllium substrate is covered by a ternary mixture layer of about 10 nm thickness containing BeO, elementary carbon and C–O compounds. Be 2C is present only at low fluences and before the equilibrium is established. The erosion of beryllium proceeds and a chemical erosion process limits the deposited amounts of carbon and oxygen via emission of CO.

Factors Influencing the Transition from Metastable to Stable Pitting in Single-Crystal Beryllium

The pitting potential of single-crystal beryllium in 0.01 M sodium chloride decreased with crystallographic orientation in the order Orientations which were associated with the lowest and were characterized by crystallographically oriented parallel plates of unattacked Be on the pit interior and square pit walls. While pit geometries in the (0001) surface appeared to be random, corrosion propagation was often in the and families of directions. Potentiostatic current/time data revealed that metastable pitting was characterized by two types of transients: (i) transients with a lifetime <1 s, similar in shape to the current/time data observed in the repassivation process, and (ii) transients whose lifetimes lasted 5-140 s and were associated with physical damage on the sample surface. The nucleation frequency of repassivation events was directly proportional to passive current density and inversely proportional to applied anodic potential. Although the frequency and magnitude of damage events increased with increasing applied anodic potential for any given orientation, the total accumulated damage was greatest for orientations with the highest Prepassivation resulted in a decrease in the frequency of repassivation events but had only minimal effect on the frequency and magnitude of the damage events. The results are discussed in terms of physical bulk metal properties as well as critical pitting environments (i.e., ohmic and mass transport models). © 2000 The Electrochemical Society. All rights reserved.

Compositional variation and precipitate structures of copper–beryllium single crystals grown by the Bridgman technique

The Bridgman technique was used to produce Cu–1.8 wt% Be single crystals. The growth methodology is presented and optimal growth conditions for the production of CuBe single crystals utilizing the Bridgman technique were determined. The influence of material purity, the temperature profile, and the translation rate on the crystal growth process are discussed. The as-grown single-crystal material produced was investigated with optical microscopy, scanning electron microscopy, X-ray diffraction, and spectrometry techniques. Segregation of impurities and alloying elements occurred as a consequence of recrystallization and resulted in a variation of composition over the length of the single crystals grown. The compositional variation was characterized for crystals that underwent single and double solidification passes. Structures occurring at multiple length scales were documented throughout the single crystal material. Precipitate structures consisting of β- and γ-phases in a Cu-rich α-matrix were identified. Structures aligned with the {1 0 0} planes of the parent phase were also observed.

Anomalous compressibility and magnetostriction of beryllium under the conditions of diamagnetic domain formation

Magnetostriction oscillations are measured for a single-crystal beryllium sample shaped like a plate perpendicular to the direction of the magnetic field. In the range of 2–5 T at a temperature of 1.5 K, i.e., in the region of diamagnetic domain formation (Condon domains), the striction signal has the saw-tooth shape corresponding to the alternation of homogeneous and nonhomogeneous (domain) states. The formation of the domain structure is accompanied by an anomalous increase in compressibility; the oscillations in this coefficient are more than one hundred times greater than the value given by the standard theory. An analysis of the results indicates that the domain wall width should increase with increasing plate thickness.

Combined ion and electron spectroscopy study of the surface reactions of beryllium with carbon

Surface reactions of evaporated carbon on a clean metallic beryllium single crystal (0 0 0 1) are investigated in situ by means of X-ray photoelectron spectroscopy and Rutherford backscattering spectrometry. The carbon is deposited at room temperature. The resulting films are successively heated to temperatures between 473 and 873 K in steps of 100 K and analyzed after each step. The as-deposited films consist of Be 2C at the beryllium/carbon interface, and of a mixture of graphitic and disordered carbon on top. At elevated temperatures carbidization takes place between 473 and 673 K and leads to a homogeneous layer of Be 2C on top of the beryllium. The Be 2C bulk photoelectron energies are found to be 282.7 eV for C 1s and 113.0 eV for Be 1s, respectivley.

Diamagnetic domains in beryllium observed by muon-spin-rotation spectroscopy

Dia- and paramagnetic (Condon) domains were observed in single crystal beryllium for applied fields $\mathit{H}||[0001]$ of 1--3 T, at temperatures $T=0.1--3$ K, by muon-spin-rotation $(\ensuremath{\mu}\mathrm{SR})$ spectroscopy at PSI. On varying H, the domains with magnetization parallel and opposite to $\mathit{H}$ reappear in each de Haas--van Alphen period $\ensuremath{\Delta}H,$ detected by the doublet splitting in the precession frequency spectrum. As H varies within the ``domain section'' $\ensuremath{\delta}H$ of a dHvA cycle, the domain inductions ${B}_{1}{,B}_{2}$ stay constant, while the volume fractions of the para- and diamagnetic regions vary linearly. The beat in the susceptibility amplitude $a(B)=4\ensuremath{\pi}{(dM/dB)}_{\mathrm{max}},$ with a period of $\ensuremath{\approx}33\ensuremath{\cdot}\ensuremath{\Delta}H,$ allowed us to determine ${B}_{i}$ and $\ensuremath{\delta}H$ for different regimes. As a increases by a factor of $\ensuremath{\approx}3,$ the sections $\ensuremath{\delta}H$ grow, $|{B}_{2}\ensuremath{-}{B}_{1}\stackrel{\ensuremath{\rightarrow}}{|}\ensuremath{\Delta}H,$ and the uniform state between two domain sections shows an increasingly strong diamagnetism, $\ensuremath{-}4\ensuremath{\pi}\ensuremath{\chi}\ensuremath{\gg}1.$ The domains persist up to $T\ensuremath{\approx}3$ K and at fields down to $H\ensuremath{\approx}1$ T. On varying H, a slight ``field overheating'' was observed. The domain area in the phase diagram is much larger than expected, while other predictions of the theory proved to be qualitatively correct.

Observation of diamagnetic domains in beryllium

We have observed diamagnetic domains (Condon domains) in a beryllium single crystal in magnetic fields H⩽3 T (H∥[0001]) at liquid-helium temperatures. The formation of the domain structure was determined according to magnetic-breakdown quantum oscillations of the resistance thermoelectric power as well as according to the splitting of the resonance peak of the free spin precession frequency of muons (µSR). The alternation of a uniform state (with one µSR peak) and a state with domain structure (with two peaks) is consistent as regards the periodicity with the de Haas-van Alphen effect, the period is ΔH≅78 Oe, and the range of existence of domains and the difference in their magnetizations are ΔB=4πΔM=B2−B1≅30 Oe.