Thin Crystal Plates Research Articles

Thermal Tuning of Vibration Band Gaps in Thin Phononic Crystal Plates with Nitinol

Vibration band structures of thin phononic crystal plates (PCPs) with square array and graphite array of nitinol inserts are calculated by the plane wave expansion (PWE) method. The influences of filling fraction are considered when investigating the effects of the varying temperature on the band gaps. Vibration band gaps of these PCPs can be tuned by changing temperature. This study will be useful in designing PCPs with tunable gaps.

Anisotropy and the optimal aspect ratio of a bent crystal

A thin bent rectangular crystal plate can be used as the second crystal in a double-crystal monochromator to focus sagittally a wide synchrotron X-ray beam. When bent in the sagittal direction, the plate also bends in the tangential direction (so-called anticlastic bending), which can adversely affect the diffracted beam. It is known that the undesirable anticlastic deformation can be minimized if the plate aspect ratio (length to width) is optimized. The present study investigates the influence of crystal material anisotropy and shows that ignoring it in the design of a sagittally bent crystal can lead to a significant underestimation of anticlastic deformation. For example, analysis shows that the optimal aspect ratio for a simply supported bent Si(220) plate ranges from 2.13 to 2.82 depending on the in-plane orientation of the cut rectangular plate. Treating silicon as isotropic with material properties in the literature leads to a plate design with an optimal aspect ratio of 2.36 and a plate with significant anticlastic bending.

Synthesis and catalytic properties of titanium containing extra-large pore zeolite CIT-5

Titanium containing extra-large pore zeolite CIT-5 (IZA code: CFI) was successfully prepared by direct synthesis using Cab-O-Sil M5 and titanium(IV) butoxide in the presence of LiOH. N-Methylsparteinium hydroxide was used as a structure directing agent. The product crystallized into thin plate crystals with an approximate size of 20×5×0.2μm. The lowest achieved Si/Ti ratio was 23. The necessary duration of hydrothermal synthesis increased with increasing concentration of Ti in the reaction mixture from 11 days (Si/Ti=63 in product) to 17 days (Si/Ti=36) at 155°C. Prepared Ti-CFI samples exhibit BET surface areas in the range of 308–346m2/g and micropore volumes of 0.094–0.097cm3/g. CFI possesses extra-large pores (14-ring, 7.2×7.5Å) accessible for bulky molecules, therefore, Ti-CFI is a useful catalyst for epoxidation of double bonds in bulky molecules used in perfumery and pharmacy. The Ti-CFI samples proved to be catalytically active in epoxidation of 1-octene, cyclooctene, α-pinene, and norbornene with hydrogen peroxide as oxidation agent.

Amplitude evolution equation and transient effects in piezoelectric crystal resonators

We study transient effects in AT-cut quartz plate thickness-shear mode acoustic wave resonators. Mindlin's equations for thin crystal plates are employed. Based on the relatively slow evolution of the vibration amplitude compared to the high-frequency thickness-shear vibration, a first-order differential equation governing the amplitude evolution is obtained. The equation allows simple and accurate solutions for transient processes in quartz resonators. A few numerical examples of resonator startup and turning off are given. The equation can be applied to other transient processes in crystal resonators such as driving voltage fluctuations and generalized to resonator-based acoustic wave sensors.

Implantation cochléaire sous-anesthésie locale avec sédation : étude de 13 cas

Czochralski grown Ce and Gd-doped Y3Al5O12 (Ce,Gd:YAG) single crystal demonstrated superior performance features in a new concept of white LED where it is used as thin single crystal phosphor plates (SCPPs). New SCPP-based white LED realizes epoxy resin free package, which allows to eliminate the photodegradation issue of the organic material. Optical, thermal and electrical properties of SCPPs and SCPP-based white LEDs are discussed with the powder phosphor and commercial LED reference. SCPPs showed significantly higher values and better stability under the high temperatures, irradiation and current. Quantum efficiency was found to be as high as 93%.

Two Systems of [DabcoH2]2+/[PipH2]2+–Uranyl–Oxalate Showing Reversible Crystal-to-Crystal Transformations Controlled by the Diammonium/Uranyl/Oxalate Ratios in Aqueous Solutions ([DabcoH2]2+ = 1,4-Diazabicyclo-[2.2.2]-octaneH2 and [PipH2]2+ = PiperazineH2)

We present here two systems of [dabcoH2]2+–uranyl–oxalate and [pipH2]2+–uranyl–oxalate in which [dabcoH2]2+ and [pipH2]2+ are cations of doubly protonated 1,4-diazabicyclo-[2.2.2]-octane (dabco) and piperazine (pip), respectively. Each system yielded two different crystals and showed the reversible crystal-to-crystal transformations between them in aqueous solutions, controlled by the ratio of reactants or building blocks in the reaction systems. The four compounds in pairs are [dabcoH2][UO2(C2O4)2(H2O)]·2H2O (dabco1) and [dabcoH2][(UO2)2(C2O4)3(H2O)2]·2H2O (dabco2), and [pipH2][UO2(C2O4)2(H2O)]·4H2O (pip1) and [pipH2][(UO2)2(C2O4)3(H2O)2]·2H2O (pip2). Besides the cations and lattice water, dabco1 and pip1 contain mononuclear anions of [UO2(C2O4)2(H2O)]2–, whereas dabco2 and pip2 possess dinuclear anions of [(UO2)2(C2O4)3(H2O)2]2–, and in all structures, the uranium ion shows a pentagonal bipyramid environment made up of equatorial oxalate, water, and apical oxygen. The needle crystals of dabco1 belong to the chiral space group P6522. In the structure, the [UO2(C2O4)2(H2O)]2– anions form anionic helixes along the 65 axis and they are further linked by N–H···O hydrogen bonds between the interhelix [dabcoH2]2+ cation and oxalates of the anion. Disorder of lattice water and the [dabcoH2]2+ cation is observed in dabco1. The thin plate crystals of pip1 in space group P1̅ possess a lamellar structure, with dense layers of [pipH2]2+·2[UO2(C2O4)2(H2O)]2– pillared by other crystallographically unique [pipH2]2+ cations, and the structure contains lattice water forming branched zigzag water chains. Block crystals of dabco2 and pip2, in monoclinic space groups C2/c and P21/c, respectively, are of similar layer-like structures, possessing the dinuclear [(UO2)2(C2O4)3(H2O)2]2– anion with one tetradentate oxalate bridge. The anions and ammonium cations form chains by N–H···O hydrogen bonds between them and then further form stacked layers via O–H···O hydrogen bonds among the coordinated and lattice water and the oxalate ligands. The ratio of diammonium/uranyl/oxalate in the reaction systems controlled the final outcomes and the occurrence of transformation, no transformation, and reverse transformation. The thermal stability; UV–vis, IR, and Raman spectra; and luminescence were also investigated.

Design of a diamond-crystal monochromator for the LCLS hard x-ray self-seeding project

As the result of collaborations between the Advanced Photon Source (APS), Argonne National Laboratory, and the Linac Coherent Light Source (LCLS) at SLAC National Accelerator Laboratory, we have designed and constructed a diamond crystal monochromator for the LCLS hard x-ray self-seeding project. The novel monochromator is ultrahigh-vacuum compatible to meet the LCLS linear accelerator vacuum environmental requirement. A special graphite holder was designed for strain-free mount of the 110-μm thin synthetic diamond crystal plate provided by Technological Institute for Super-hard and Novel Carbon Materials of Russia (TISNCM). An in-vacuum multi-axis precision positioning mechanism is designed to manipulate the thin-film diamond holder with resolutions and stabilities required by the hard x-ray self-seeding physics. Optical encoders, limit switches, and hardware stops are established in the mechanism to ensure system reliability and to meet the accelerator personal and equipment safety interlock requirements. Molybdenum shields are installed in the monochromator to protect the encoders and associated electronics from radiation damage. Mechanical specifications, designs, and preliminary test results of the diamond monochromator are presented in this paper.

Diamond crystal optics for self-seeding of hard X-rays in X-ray free-electron lasers

We report design, fabrication, and results of X-ray topography characterization of thin synthetic type IIa diamond crystal plates and crystal-holder assemblies developed for the Hard X-ray Self-Seeding project at the Linac Coherent Light Source. The goal of the project was to achieve generation of fully coherent hard X-rays using the self-seeding concept and the single-crystal diamond wake monochromator [Geloni et al., J. Mod. Opt. 58, 1391 (2011)]. High crystal quality, crystal thickness of ≈0.1–0.2mm and strain-free crystal mount were the main requirements. Nearly defect-free diamond plates of (001) orientation, with thicknesses of 0.1mm and 0.15mm, and of a trapezoidal shape were fabricated and preliminarily evaluated. The plates were further characterized using X-ray topography. These tests helped to minimize strain in crystals induced by mounting in crystal holders and to determine defect-free crystal regions. Self-seeding experiments were conducted at the Linac Coherent Light Source using the diamond plates and crystal-holder assemblies selected by our studies. Fully coherent 8.33-keV X-rays with 5×10−5 relative bandwidth were produced [Amann et al., Nat. Photonics 6, 693 (2012)].

Properties of Czochralski grown Ce,Gd:Y3Al5O12 single crystal for white light-emitting diode

Czochralski grown Ce and Gd-doped Y3Al5O12 (Ce,Gd:YAG) single crystal demonstrated superior performance features in a new concept of white LED where it is used as thin single crystal phosphor plates (SCPPs). New SCPP-based white LED realizes epoxy resin free package, which allows to eliminate the photodegradation issue of the organic material. Optical, thermal and electrical properties of SCPPs and SCPP-based white LEDs are discussed with the powder phosphor and commercial LED reference. SCPPs showed significantly higher values and better stability under the high temperatures, irradiation and current. Quantum efficiency was found to be as high as 93%.

Amino-acid based coordination polymers

Five new transition metal–amino acid coordination polymers, including two copper compounds 1D-{Cu(d-α-PhGly)2} (1), 1D-{Cu(l-Trp)2} (2) and three cadmium compounds 2D-{Cd(d-Leu)2} (3) 2D-{Cd(d-Phe)2} (4) and 2D-{[Cd(d-Phe)(4,4′-bipy)H2O][NO3]} (5) are structurally characterized (PhGly=phenylglycinato, Trp=tryptophanato, Leu=leucinato, Phe=phenylalaninato in enantiopure form, 4,4′-bipy=4,4′-bipyridine). Single crystals were obtained by slow diffusion of the metal salt and the ligand in a water–methanol mixture. The enantiopure amino acetate ligands led to homochiral crystallization of 1–5 in the non-centrosymmetric space group P21. Characterization by single-crystal X-ray diffraction, infrared and Raman spectroscopy showed that the copper compounds 1 and 2 form twofold helices around the 21 screw axis and the cadmium compounds 3–5 yield two-dimensional coordinative layers also with twofold helices around the 21 axes for 3 and 4. The Cu-amino-acetate/carboxlyate helices are connected by N–H···O hydrogen bonds and very long Cu⋯O–carboxylate contacts to supramolecular 2D layers. Crystal packings of 2D layer structures in 1–4 show a separation of the hydrophobic alkyl groups from the hydrophilic M-amino-carboxylate region. Charge-assisted Cu(+)⋯(−)O interactions and N–H···(−)O hydrogen-bonding interactions in the hydrophilic region are the driving force of “hydrophobic exterior layer” formation with a hydrophilic interior exposing the hydrophobic alkyl groups to the exterior. Stacking of the layers occurs through weak van der Waals interactions between the alkyl groups. This correlates with the crystal morphology, with formation of thin crystal plates along the stacking direction.In 5 the Cd-μ-amino carboxylate-κN,O:O′ units with a pentagonal–bipyramidal Cd atom form strands, and these strands are then joined through the rigid 4,4′-bipy linkers to a coordinative 2D layer. The nitrate anions connect these layers with charge-assisted (aqua)O–H···(−)O(nitrate) and (amino)N–H···(−)O(nitrate) hydrogen bonds to a supramolecular 3D network.

Encapsulation of Keggin-type anions in reduced molybdenum–iron-type Keplerates as a general phenomenon

Upon standing in air at room temperature, acidified aqueous solutions (pH 2) obtained by dissolving sodium molybdate, iron(II) chloride, acetic acid and potassium dodecatungstoborate led to the formation of greenish thin plate crystals (1) containing discrete clusters. Upon drying 1 at room temperature crosslinking of the clusters occurs in a solid-state reaction which leads to compound 2. Based on crystallographic studies of 1 and on extensive physical characterization (vibrational, NMR, Mössbauer spectra and magnetic susceptibility measurements) of 2, it was shown that compounds 1 and 2 contain reduced spherical {Mo72Fe30} Keplerate-type shells encapsulating non-reduced tungstoborate Keggin-type anions. The properties and structures of these compounds are compared to related hybrid structures containing in principle easier reducible molybdophosphate or molybdosilicate cores. According to the results the present type of encapsulation can be considered as a general phenomenon.

Hydrophobic-exterior layer structures and magnetic properties of trinuclear copper complexes with chiral amino alcoholate ligands

The trinuclear secondary building unit (SBU) {Cu3(μ-L)4X2} constructed from chelating and alcoholate-O-bridging chiral amino alcoholate (amino alkoxido, μ-L) and terminal halide ligands (X) gives rise to two-dimensional (2D) homochiral supramolecular polymers through the bridging action of the halide ligand. Compounds 2D-[Cu3(μ-L)4(μ3-X)2] {X = Br (1 to 4), X = Cl (5, 6); L = amino-ethanolate (1, 5), (R)-2-amino-propan-1-olate (2), (R)-2-amino-butan-1-olate (ab) (3, 6), (R)-2-amino-2-phenyl-ethanolate (4)} were synthesized from 2-amino alcohol, LH with CuBr2 or CuCl2, respectively, in the presence of triethylamine (TEA). The crystal packing of isomorphous 2D-[Cu3(μ-L)4(μ3-X)2] shows a separation of the hydrophobic alkyl from the hydrophilic amino-/alcoholate-/Cu–Br-region. Charge-assisted Cu(2+)⋯(−)Br- and hydrogen-bonding interactions in the hydrophilic region are the driving force of “hydrophobic exterior layer” formation with a hydrophilic interior exposing the hydrophobic alkyl groups to the exterior. Stacking of the layers through weak van-der-Waals interactions between the alkyl groups correlates with formation of thin crystal plates along the stacking direction. A lower ligand concentration yields both dinuclear and mononuclear SBUs in one-dimensional (1D-) homochiral coordination polymers 1D-[{Cu2(μ-ab)2Br2}2{(μ3-Br)Cu(abH)2Br}{(μ3-Br)Cu(abH)(CH3OH)Br}] (7) and 1D-[{Cu2(μ-ab)2Cl2}2{(μ3-Cl)Cu(abH)(CH3CH2OH)Cl}2] (8). In {[Cu(rac-abH)(rac-ab)H2O]ClO4}2 (9) two SBUs combine through charge assisted H-bonds to a dimeric unit. Temperature dependent magnetic susceptibility measurements of 1 and 3 show ferromagnetic coupling but no magnetic ordering. However, at temperatures lower than 3 K an onset of long-range magnetic ordering can be observed. AC magnetic measurements in the range of 1.9 K to 5 K at different frequencies show that the long range magnetic ordering is achieved at lower temperatures than that. Correlation of magnetic coupling with the Cu–O–Cu angle is in agreement with the structural parameters of 1 and 3. Very good agreement between experimental and DFT calculated J,j coupling constants shows that the interaction between the terminal copper(II) ions in these linear trinuclear SBUs is operative and it cannot be neglected.

Morphological transition in crystallization of Si from undercooled melt

Using CO2 laser equipped electro-magnetic levitator, we carried out the crystallization of Si at undercoolings from 0 K to 200 K. From the point of the interface morphologies, the relationship between growth velocities and undercoolings was classified into two regions, I and II, respectively. In region I where the undercooling is approximately less than 100 K, needle-like thin plate crystals whose interface consists of faceted plane were observed. In region II, the morphology of growing crystals changed to massive dendrites. Although the interface morphologies look quite different between region I and II, the growth velocities are expressed by two dimensional (2D) nucleation-controlled growth model, and at undercoolings larger than 150 K, the growth velocities asymptotically close to the analysis of the mono-parametric linear kinetics growth model. In this stage, the kinetic coefficient of 0.1 m/sK is equivalent to that derived by the diffusion-controlled growth model. This result means that with increase of undercooling, the rate-determining factor changes from 2D nucleation on the faceted interface to random incorporation of atoms on the rough interface.

5.4 GHz Lamb Wave Resonator on LiNbO3 Thin Crystal Plate and Its Application

A cognitive radio system operating at frequencies from 400 MHz to 6 GHz requires tunable filters with a wide variable frequency range. Wide band resonators are required to realize such tunable filters consisting of resonators. However, it is difficult to fabricate a very high frequency and wide band resonator, such as 6 GHz and wider than 10%, respectively. The first antisymmetric (A1) mode of a Lamb wave on a LiNbO3 thin plate or film having a high velocity and a large electromechanical coupling factor is a suitable wave for fabricating an ultrawide band and high frequency resonator. This time, we attempted to fabricate a higher frequency Lamb wave resonator on a thin LiNbO3 single-crystal plate instead of the LiNbO3 film, though it has been considered difficult to form a very thin LiNbO3 crystal plate. A new one-port Lamb wave resonator showed a high frequency in the 5 GHz range, a wide bandwidth of 12%, and a high impedance ratio of 62 dB at resonant and antiresonant frequencies. Moreover, we applied the resonator to a ladder-type tunable filter, and obtained the tunable range of 9% from 5.58 to 6.06 GHz theoretically.

Low-frequency band gaps in one-dimensional thin phononic crystal plate with periodic stubbed surface

Using supercell plane wave expansion method, the Lamb wave band structure of one-dimensional thin plate with periodic stubs is investigated. The numerical results show that flat bands will appear and band gap can exist in a low-frequency domain. The position of the flat bands and width of the low-frequency Lamb wave band gap can be tuned by the stub height, plate thickness and filling fraction. The band gap is obtained by opening the folding points of the same plate modes not the crossing point of different plate mode when the stub height is small.

Negative refraction experiments with guided shear-horizontal waves in thin phononic crystal plates

This paper presents the experimental evidence of negative refraction of a guided ultrasonic shear-horizontal wave in a phononic crystal plate, a thin aluminum plate with periodically spaced circular holes. Unlike bulk wave experiments, guided-wave experiments allow the full measurement of negatively refracted waves propagating into a base aluminum plate from the phononic crystal plate. The present guided-wave experiments were conducted with the planar solenoid array-type orientation-adjustable patch-type magnetostrictive transducer having good beam directivity. An effective technique to estimate negative refraction angles from the experimental measurements is suggested, yielding values in good agreement with theoretically calculated angles.

ローレンツ電顕法によるスキルミオン格子の観察

The formation of a triangular lattice of the topological spin textures (skyrmions) is suggested by recent neutron scattering studies on B20-type helical magnets. We have observed the real-space image of the skyrmion lattice in Fe0.5Co0.5Si by Lorentz transmission electron microscopy. Besides the perfect hexagonal arrangement of skyrmions, we have observed the disordered or isolated skyrmions as well as the coexistence with helical spin order. Furthermore, we have found that the skyrmion lattice is quite stable over a wide temperature region in a thin crystal plate with its thickness smaller than the skyrmion lattice constant.

Siの過冷凝固におけるTwin-related ⇔ Twin-free遷移

Using CO2 laser equipped electro-magnetic levitator, we carried out the crystallization of Si at undercoolings from 0 K to 200 K. From the point of the interface morphologies, the relationship between growth velocities and undercoolings was classified into two regions, Iand II, respectively. In regionIwhere the undercooling is approximately less than 100 K, thin plate crystals whose interface consists of faceted plane were observed. In region II, the morphology of growing crystals changed to massive dendrites. Although the interface morphologies in region II look quite different from that in regionI, the growth velocities are expressed by two dimensional (2D) nucleation-controlled growth model, and at undercoolings larger than 150 K, the growth velocities asymptotically close to the analysis of the mono-parametric linear kinetics growth model. In this stage, the kinetic coefficient of 0.1 m/sK is equivalent with that derived by the diffusion-controlled growth model. This result means that with increase of undercooling, the rate-determining factor changes from 2D nucleation on the faceted interface to random incorporation of atoms on the rough interface.

Near room-temperature formation of a skyrmion crystal in thin-films of the helimagnet FeGe

The skyrmion, a vortex-like spin-swirling object, is anticipated to play a vital role in quantum magneto-transport processes such as the quantum Hall and topological Hall effects. The existence of the magnetic skyrmion crystal (SkX) state was recently verified experimentally for MnSi and Fe(0.5)Co(0.5)Si by means of small-angle neutron scattering and Lorentz transmission electron microscopy. However, to enable the application of such a SkX for spintronic function, materials problems such as a low crystallization temperature and low stability of SkX have to be overcome. Here we report the formation of SkX close to room temperature in thin-films of the helimagnet FeGe. In addition to the magnetic twin structure, we found a magnetic chirality inversion of the SkX across lattice twin boundaries. Furthermore, for thin crystal plates with thicknesses much smaller than the SkX lattice constant (as) the two-dimensional SkX is quite stable over a wide range of temperatures and magnetic fields, whereas for quasi-three-dimensional films with thicknesses over as the SkX is relatively unstable and observed only around the helical transition temperature. The room-temperature stable SkX state as promised by this study will pave a new path to designing quantum-effect devices based on the controllable skyrmion dynamics.

High-frequency lamb wave device composed of MEMS structure using LiNbO3 thin film and air gap

High-frequency devices operating at 3 GHz or higher are required, for instance, for future 4th generation mobile phone systems in Japan. Using a substrate with a high acoustic velocity is one method to realize a high-frequency acoustic or elastic device. A Lamb wave has a high velocity when the substrate thickness is thin. To realize a high-frequency device operating at 3 GHz or higher using a Lamb wave, a very thin (less than 0.5 μm thick) single-crystal plate must be used. It is difficult to fabricate such a very thin single crystal plate. The authors have attempted to use a c-axis orientated epitaxial LiNbO(3) thin film deposited by a chemical vapor deposition system (CVD) instead of using a thin LiNbO(3) single crystal plate. Lamb wave resonators composed of a interdigital transducer (IDT)/the LiNbO(3) film/air gap/base substrate structure like micro-electromechanical system (MEMS) transducers were fabricated. These resonators have shown a high frequency of 4.5 and 6.3 GHz, which correspond to very high acoustic velocities of 14,000 and 12,500 m/s, respectively, have excellent characteristics such as a ratio of resonant and antiresonant impedance of 52 and 38 dB and a wide band of 7.2% and 3.7%, respectively, and do not have spurious responses caused by the 0th modes of shear horizontal (SH(0)) and symmetric (S(0)) modes.