Use Of Single Crystals Research Articles

Micropillar compression deformation of single crystals of the intermetallic compound ζ-FeZn13

The deformation behavior of the ζ phase in the Fe–Zn system has been investigated by micropillar compression tests at room temperature with the use of single crystals with 13 different crystal orientations prepared by the focused ion beam method. Two different slip systems, {110}〈11¯2〉 and (100)[001], are observed to operate. The critical resolved shear stresses (CRSS) value for {110}〈11¯2〉 slip is more than three times smaller than that for (100)[001] slip. From the anisotropy in CRSS for these two slip systems, {110}〈11¯2〉 slip is predicted to operate for most crystal orientations, except for a narrow orientation region around [3¯05] where (100)[001] slip operates. The CRSS for {110}〈11¯2〉 slip shows an inverse power-law scaling against the specimen size with an exponent of −0.517. The bulk CRSS value for {110}〈11¯2〉 slip is estimated to be 62–76MPa by taking into account the specimen size effects of CRSS. The reasons why {110}〈11¯2〉 slip with a rather long Burgers vector (0.7700nm) is selected as the easiest slip system are discussed in terms of the nature of atomic bonding in the crystal structure, especially the rigid atomic bonding within an Fe-centered Zn12 icosahedron (for slip plane selection), and the energetic barrier height along the slip direction and the resultant possible dissociation schemes (for slip direction selection). Some implications are made on how the deformability of the ζ phase can be improved in the textured coating layer in galvannealed steels based on the results obtained.

The electrochemical characterization of copper single-crystal electrodes in alkaline media

The use of single-crystals in electrochemistry requires careful characterization of the surface structure. This paper addresses the characterization of Cu single-crystals using blank cyclic voltammetry in alkaline media. The adsorption and desorption of OH species in the underpotential region of Cu2O formation in alkaline media occur at different potentials on Cu(111) and Cu(100), whereas OH adsorption on Cu(110) is not observed in this potential region. This allows for a direct distinction of the Cu(hkl) basal planes. The adsorption of OH on Cu(111) induces a reconstructed adlayer on the surface. On Cu(322), a stepped surface with 5 atom wide (111) terraces, OH adsorption is observed in the same potential range as on Cu(111), but on Cu(322) reconstruction does not seem to take place. This is explained by the fact that the unit cell of the reconstructed layer is much larger than the (111) terrace width of Cu(322) and, therefore, reconstruction cannot take place. Cu(911), having 5 atom wide (100) terraces, exhibits the same voltammetric features as Cu(100), but with a lower intensity. This is explained by the lower amount of (100) terraces present on this surface.

Impurities in zone-refining anthracene crystals

Over the past five decades, paramount interest had been given to the synthesis of single crystals for use as scintillators in nuclear radiation detection field. Organic semiconductors are in principle less costly and of light weight, providing real potential as improved radiation detectors. However, challenges remain in the crystal growth and purification of the neutron detection material whereby the residual impurity will result in formation of excitation trap quenching the light yield within the host crystal. In this study, single crystals of anthracene up to 10cm had been grown from the melt based on a self-designed, inexpensive and versatile zone refining apparatus. Platelets cut from these crystals by applying wire saw were tested for purity and perfection by Powder X-ray Diffraction (XRD), Laser Desorption Ionization-Time of Flight Mass Spectrometry (LDI-ToF MS), Fourier-Transform Infrared Spectroscopy (FT-IR), Atomic Force Microscopy (AFM) and fluorescence measurement. The results of characterization studies revealed that impurities within commercial anthracene powder such as carbazole and 9,9′bianthryl have been reduced effectively as indicated by LDI-ToF MS analysis. Meanwhile the photoluminescence analysis had clearly demonstrated higher photon energies derived from the pure crystal as compared to those of commercial material with higher content of impurities where free excitons during their localization surrender part of its energy to the surroundings.

Increasing 13C CP-MAS NMR Resolution Using Single Crystals: Application to Model Octaethyl Porphyrins

Octaethyl porphyrin (OEP) and its Ni and Zn derivatives are considered as model compounds in biochemical, photophysical, and fossil fuel chemistry. They have thus been investigated by high-resolution solid-state (13)C NMR using powders, but peak assignment has been difficult because of large line widths. Arguing that a significant cause of broadening might be the anisotropic bulk magnetic susceptibility, we utilized single crystals in our (13)C cross-polarization magic angle spinning (CP-MAS) measurements and observed a nearly 2-fold line narrowing. This enhanced resolution enabled us to assign chemical shifts to each carbon for all the three compounds. The new assignments are now in agreement with X-ray structural data and allowed us to probe the motional dynamics of the methyl and methylene carbons of the OEP side chains. It is apparent that the use of single crystals in (13)C CP-MAS measurements has a significantly wider impact than previously thought.

Inkjet printing of single-crystal films

The use of single crystals has been fundamental to the development of semiconductor microelectronics and solid-state science. Whether based on inorganic or organic materials, the devices that show the highest performance rely on single-crystal interfaces, with their nearly perfect translational symmetry and exceptionally high chemical purity. Attention has recently been focused on developing simple ways of producing electronic devices by means of printing technologies. 'Printed electronics' is being explored for the manufacture of large-area and flexible electronic devices by the patterned application of functional inks containing soluble or dispersed semiconducting materials. However, because of the strong self-organizing tendency of the deposited materials, the production of semiconducting thin films of high crystallinity (indispensable for realizing high carrier mobility) may be incompatible with conventional printing processes. Here we develop a method that combines the technique of antisolvent crystallization with inkjet printing to produce organic semiconducting thin films of high crystallinity. Specifically, we show that mixing fine droplets of an antisolvent and a solution of an active semiconducting component within a confined area on an amorphous substrate can trigger the controlled formation of exceptionally uniform single-crystal or polycrystalline thin films that grow at the liquid-air interfaces. Using this approach, we have printed single crystals of the organic semiconductor 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C(8)-BTBT) (ref. 15), yielding thin-film transistors with average carrier mobilities as high as 16.4 cm(2) V(-1) s(-1). This printing technique constitutes a major step towards the use of high-performance single-crystal semiconductor devices for large-area and flexible electronics applications.

Large signal electromechanical properties of low loss (1−x)Pb(Mg1/3Nb2/3)O3−xPbTiO3 single crystals

The use of single crystals based on the solid solution (1−x)Pb(Mg1/3Nb2/3)O3−xPbTiO3 (PMNT) has been demonstrated in many piezoelectric devices, but the low mechanical quality factor has limited its use in high power projector applications. In this work, 33-mode properties of PMNT single crystals with various modifications were evaluated to see if self-heating may be reduced by decreasing the mechanical and electrical losses within the active material. Three modifications were evaluated: incorporating ternary components, adding acceptor dopants, or orienting the crystal along different crystallographic directions. The electromechanical properties of these modified crystals were evaluated under increasing levels of dynamic strain. The results suggest that modified single crystal PMNT may improve the source level from a projector while reducing thermal effects from self-heating, making them appropriate for high power applications.

Magnetic and electronic properties ofEu1−xSrxMnO3(0.3<x<0.7)single crystals

Among versatile perovskite manganites showing colossal magnetoresistance (CMR), ${\text{Eu}}_{1\ensuremath{-}x}{\text{Sr}}_{x}{\text{MnO}}_{3}$ around $x\ensuremath{\sim}0.4$ shows the ferromagnetic metal with the lowest transition temperature $(\ensuremath{\sim}40\text{ }\text{K})$ due to the narrowest one-electron bandwidth and hence is readily subject to the drastic phase changes with variations in temperature, magnetic field, and hole doping $(x)$. We have investigated the variation in the electronic state with $x$ with use of single crystals. As $x$ increases, the ferromagnetic metal at $0.38\ensuremath{\le}x\ensuremath{\le}0.47$ changes to a spin-glasslike insulator at $0.48\ensuremath{\le}x\ensuremath{\le}0.5$, the layered antiferromagnetic (A-type) state at $0.51\ensuremath{\le}x<0.6$, and the chained antiferromagnetic (C-type) state at $0.6\ensuremath{\le}x$, respectively. Due to the increased disorder upon alloying of Eu/Sr, the charge/orbital ordering with the modulation vector (0, $q$, 0) with $q=1/2$ in the orthorhombic $Pbnm$ setting (${a}_{0}\ensuremath{\sim}{b}_{0}\ensuremath{\sim}{c}_{0}/\ensuremath{\surd}2\ensuremath{\sim}\ensuremath{\surd}2{a}_{\text{p}}$, ${a}_{\text{p}}$ being the lattice parameter of the pseudocubic lattice) cannot be formed in a long range but remains short ranged. In the vicinity of $x=0.5$, an application of an external magnetic field removes such short-range charge/orbital ordering $(q=1/2)$ to cause an insulator to metal transition or CMR. In a broad range of $x$ $(0.55\ensuremath{\le}x\ensuremath{\le}0.59)$, the critical temperature for the layered antiferromagnetic state is relatively lowered and alternatively the charge/orbital ordering with $q\ensuremath{\sim}1/3$ becomes to be visible. It has also been found that the modulation is temperature dependent; commensurate with $q\ensuremath{\sim}1/3$ upon the transition while incommensurate with $q>1/3$ at low temperatures.

Aurivillius-type ceramics, a class of high temperature piezoelectric materials: Drawbacks, advantages and trends

Abstract The obtention of reliable and high performance piezoelectric ceramics for uses at high temperatures is still an open issue in the field of electroceramics. The materials used nowadays for such applications present limitations due to different causes: low piezoelectric coefficients, difficulties in processing that lead to the necessary use of single crystals, high cost of raw materials and more. In this sense, an increasing interest in materials with the so-called Aurivillius-type structure has occurred during recent years, due to their relatively high piezoelectric coefficients and high ferro–paraelectric phase transition temperature. However, some difficulties must be overcome, such as processing for obtaining highly dense ceramics and determining their real piezoelectric behaviour at high temperature. In this work, a review of the processing and properties of ceramics with this structure is shown. Effects of the use of precursors obtained by an alternative route mechanical activation on the microstructure are explained. A complete piezoelectric characterization at working temperatures (>300 °C), barely found in the literature, is also shown. The effects of trapped charges in the dielectric permittivity and in the piezoelectric radial resonance are also discussed.

Principles of deformation in single crystals of two different orientations processed by equal-channel angular pressing

The use of single crystals in equal-channel angular pressing provides an opportunity for critically examining the deformation characteristics without including any artifacts due to the presence of grain boundaries. This paper presents an overview of recent experiments in which crystals of high-purity aluminum and copper were pressed through one pass in ECAP using crystals having two different initial orientations: a 0° orientation where the {1 1 1} slip plane lies parallel to the theoretical shear plane and the 〈1 1 0〉 slip direction lies parallel to the shear direction and a 20° orientation where the crystal is rotated about a horizontal axis by 20° in a clockwise sense. The experimental results show good agreement between these two materials but some variations arise because of the difference in the strain hardening rate for the two materials.

Evaluation of Melt-Grown, ZnO Single Crystals for Use as Alpha-Particle Detectors

As part of an ongoing investigation of the scintillation properties of zinc-oxide-(ZnO)-based scintillators, several melt-grown, ZnO single crystals have been characterized using alpha-particle excitation, infrared reflectance, and room temperature photoluminescence. The crystals, grown by Cermet, Inc., using an oxygen-pressurized melt-growth process, were doped with Group 1 elements (Li), Group 2 elements (Mg), Group 3 elements (Ga, In) and lanthanides (Gd, Er, Tm). The goals of these studies are to better understand the scintillation mechanisms associated with various members of the ZnO scintillator family and to then use this knowledge to improve the radiation detection capabilities of ZnO-based scintillators. One application for which ZnO is particularly well suited as a scintillator is as the associated particle detector in a deuterium-tritium (D-T) neutron generator. Application requirements include the exclusion of organic materials, outstanding timing resolution, and high radiation resistance. ZnO:Ga and ZnO:In have demonstrated fast (subnanosecond) decay times with relatively low light yields, and ZnO(Ga) has been used in a powder form as the associated particle detector for a D-T neutron generator. Four promising candidate materials, ZnO, ZnO:Ga, ZnO:In,Li, and ZnO:Er,Li, were identified in this study. These four samples demonstrated sub-nanosecond decay times and alpha-particle-excited- luminescence comparable to BC-400 fast plastic scintillator. The ZnO:Mg,Ga, ZnO:Gd, and ZnO:Li samples demonstrated appreciable slow (microsecond) decay components that would be incompatible with high-counting-rate applications.

Crystal Orientations Near Welds in High RRR Niobium With Very Large Grains

Superconducting radio frequency (SRF) cavities made of single crystal niobium are under development for use in charged particle accelerators. Use of single crystals may simplify manufacturing and reduce cost, as well as improve properties over the currently used fine grain niobium material. However, the processes of forming by deep drawing, and subsequent welding of the formed parts to assemble the cavity, might lead to recrystallization in regions of high strain or curvature near the weld. Orientation imaging microscopy (OIM) was used to assess these possibilities in some preliminary experiments. A sample of single crystal niobium strip was arbitrarily bent and electron beam (EB) heated across one end to simulate welding. The bent sample had no more than 14% strain, and it did not exhibit definitive recrystallization near or away from the EB heated area. Another sample was prepared by halving a large grain niobium bicrystal across the boundary of two grains, flipping one half and EB welding the halves back together, such that the weld had three different grain misorientations along its length, including two triple points. There was no formation of new orientations along the weld where it joined two crystal orientations. However, some new orientations solidified where the weld encountered three different grain orientations. This preliminary data is encouraging, suggesting that minimal generation of new grain orientations during EB welding may be practical. However, more work with different orientations and strains is needed to determine how tolerant Nb is for maintaining a flat solidification interface and resisting recrystallization.

Ambipolar Light‐Emitting Transistors of a Tetracene Single Crystal

AbstractThe first ambipolar light‐emitting transistor of an organic molecular semiconductor single crystal, tetracene, is demonstrated. In the device configuration, electrons and holes injected from separate magnesium and gold electrodes recombined radiatively within the channel. By varying the applied voltages, the position of the recombination/emission zone could be moved to any position along the channel. Because of the changes made to the device structure, including the use of single crystals and polymer dielectric layers and the adoption of an inert‐atmosphere fabrication process, the set of materials that can be used for light‐emitting transistors has been expanded to include monomeric molecular semiconductors.

Use of single crystal and soft piezoceramics for alleviation of flow separation inducedvibration in a smart helicopter rotor

Dynamic stall and flow separation induced vibration alleviation is investigated using singlecrystal and soft piezoceramic-induced shear actuation. PZT-5H performs well to reducevibration at cruise speed (about 50%) but fails to achieve a substantial vibration reduction(about 20%) at high speed forward flight because dynamic stall and flow separation requirea larger stroke for vibration reduction. -induced shear actuation is found to generate a larger stroke and eventually a highervibration reduction (about 60–70%) at both cruise and high speed flight. It is observed thatthe controller performs satisfactorily up to a noise level of 20% in the sensed data.Optimum placement of actuators along the span, as well as the eventualities of actuatorfailure and degradation are also addressed.

The effect of Nb and W alloying additions to the thermal expansion anisotropy and elastic properties of Mo5Si3

The directional thermal expansion and elastic properties of Mo5Si3, (Mo0.8Nb0.2)5Si3, and (Mo0.85W0.15)5Si3 have been studied as a function of temperature through the use of single crystals. Thermal expansion anisotropy was reduced by Nb and W alloying. The decrease in thermal expansion anisotropy by Nb alloying was only found to occur at low temperatures, and thermal expansion anisotropy of (Mo0.8Nb0.2)5Si3 was similar to that for the other two compounds at 800 °C. Values for the polycrystalline Young’s, bulk, and shear moduli calculated from the measured single-crystal elastic constants are reduced by Nb alloying, and increased by W alloying at all temperatures studied. The elastic modulus E was calculated for the orientations between [100]-[001] and [100]-[010]. In contrast to the effects of Nb on thermal expansion anisotropy, Nb alloying increased the E[001]/E[100] elastic anisotropy.

Precipitate effects on the mechanical behavior of aluminum copper alloys: Part II. Modeling

This work focuses on a new hardening formulation accounting for precipitate-induced anisotropy in a binary aluminum-copper precipitation-hardened alloy. Different precipitates were developed upon aging at 190°C and 260°C, and corresponding work hardening characteristics were predicted for single and polycrystals. The use of single crystals facilitated the demonstration of the effect of precipitates on the flow anisotropy behavior. Pure aluminum was also studied to highlight the change in deformation mechanisms due to the introduction of precipitates in the matrix. The influence of precipitate-induced anisotropy on single-crystal flow behavior was clearly established, again relating to the precipitate character. Simulations are presented for several single-crystal orientations and polycrystals, and they display good agreement with experiments. The work demonstrates that precipitate-induced anisotropy can dominate over the crystal anisotropy effects in some cases.

SILICON CARBIDE WITHOUT DEFECTS

ALONG-SOUGHT METHOD to grow defect-free silicon carbide (SiC) single crystals for use as semiconductor wafers has been developed by a team of Japanese researchers. The technology advance means that SiC could now begin to be used as a more durable replacement for standard silicon semiconductors in a range of electronic devices for high-power, highfrequency, and high-temperature applications. Silicon carbide has been studied since the 1950s as a potential replacement for silicon in certain electronic devices. One lingering problem has been that SiC does not have a liquid phase, so the standard technique of controlled solidification of a liquid, used to make silicon and other semiconductors, can't be used. Instead, a vapor deposition method in which SiC is sublimed onto a seed crystal is used. But this technique leads to misalignment of some SiC molecular layers, introducing lattice defects that interfere with performance and have limited the material's use. Daisuke Nakamura and Kazumasa Takatori ...

Dimensionality Changes in Crystalline Complexes Induced by Exposure to Air: Solid-State Studies Using Single Crystal and Powder X-ray Diffraction Methods

When they come into contact with air, coordination compounds can often change their appearance. For instance, the colour of the compound can change as transparent crystals become opaque microcrystalline solids. This visible transformation of the compound is frequently accompanied by structural modifications due to loss of solvent molecules or in the reverse case, the reaction with water from the air. Often, the dimensionality of the structures also varies and this aspect is demonstrated for three pairs of copper(II) complexes (1D ? 0D, 1D ? 2D and 3D ? 2D). The complementary use of single crystal and powder X-ray diffraction methods is indispensable for the evaluation of these structural changes.

A comparison of single crystal versus ceramic piezoelectric materials for acoustic applications

For nearly fifty years, piezoelectric ceramics (primarily from the PZT family) have been the materials of choice as the active elements in sound projectors and receivers, medical ultrasound probes, etc. There is currently great interest in the materials community in the use of newly discovered single crystal relaxor ferroelectric materials as a replacement in applications that currently utilize piezoelectric ceramics. The salient features of single crystal piezoelectrics are strains an order of magnitude larger than are achievable in PZT and electromechanical coupling coefficients on the order of 90 percent. This presentation will provide a more thorough comparison of the physical and piezoelectric properties of single crystal piezoelectrics versus conventional PZT piezoceramics. This will hopefully provide the transducer designer with a better understanding of the pros and cons in the use of single crystals. In addition, a brief review of single crystal synthesis procedures will be described. Finally, some acoustic devices utilizing both single crystals and piezoceramics will be compared. [Work supported by DARPA and ONR Code 321-TS.]

Effects of Zn addition and thermal annealing on yield phenomena of CdTe and Cd0.96Zn0.04Te single crystals by nanoindentation

Mechanical yield phenomena in CdTe and CdZnTe single crystals for use as radiation detectors were studied by nanoindentation, since dislocations can act as electrically active levels that would impact device performance. The initial deformation behavior prior to yielding is elastic for as-grown crystals, indicating that rapid dislocation nucleation is the controlling mechanism for the observed yield point. Zn doping increases the stress required for initiating plastic deformation from 0.76 GPa in CdTe to 1.29 GPa in CdZnTe, and increases the flow stress of the material from solid solution hardening. Thermal annealing leads to plastic loading at very low loads, suggesting that annealing CdZnTe generates a low but increased density of dislocations in the bulk material.

Point-contact spectroscopy in MgB 2 single crystals in magnetic field

We present the results of a spectroscopic study of state-of-the-art MgB 2 single crystals, carried out by using a modified point-contact technique. The use of single crystals allowed us to obtain point contacts with current injection either parallel or perpendicular to the ab-planes. The effect of magnetic fields up to 9 T on the conductance spectra of these contacts is here thoroughly studied, for both B parallel and perpendicular to the ab-planes. The complete thermal evolution of the upper critical field of the π band is determined for the first time, and quantitative information about the upper critical field of the σ band and its anisotropy is obtained. Finally, by exploiting the different effect of a magnetic field applied parallel to the ab-planes on the two band systems, the partial contributions of the σ and π bands to the total conductance are obtained separately. Fitting each of them with the standard BTK model yields a great reduction of the uncertainty on Δ σ and Δ π, whose complete temperature dependence is obtained with the greatest accuracy.