Crystal Pieces Research Articles

Unique Optical Periodicity Assembly of Discrete Dendritic Lamellae and Pyramidal Single Crystals in Poly(ε-caprolactone).

A unique zig-zag banded morphology poly(ε-caprolactone) (PCL), crystallized at high Tc = 46-47 °C and confined in thin films (<1 μm), is found to be assembled of parallel cogrowth of two totally crystal entities: edge-on dendritic lamellar protrusion from surfaces and flat-on pyramidal single crystals. The alternating PCL optical bands are assembled as flat-on single crystals aligned as straight dendrites as a valley band in series with edge-on branches as a ridge band, leading to a unique assembly mechanism of periodic optical rings where these two crystal pieces are assembled in series. Detailed assembly mechanisms are proposed to explain how the composite bands in the PCL aggregates are correlated to optical birefringence periodicity. By techniques of melt crystallization via periodic species drainage, PCL single crystals could be prepared and tailor-made to a variety of nanopatterns as templates for applications.

Rapid crystal growth of triple-layered cuprate superconductor HgBa2Ca2Cu3O8+δ by cesium chloride additional method

We have developed the rapid growth method for HgBa2Ca2Cu3O8+δ (Hg-1223) by using a sealed quartz tube technique with a small amount of cesium chloride (CsCl). Our results suggested that a small amount of CsCl works as a flux during the crystal growth of Hg-1223. The developed method achieved the growth of the Hg-1223 single crystal pieces in 4 h. Furthermore, the grown single crystals showed high purity. The developed method is useful for application purposes such as high transition-temperature (T c) superconducting cable.

Rainbow in the dark. The identification of diagnostic projectile impact features on rock crystal

Over the last years, functional analyses and projectile fracture analyses on non-chert tools are becoming widespread and are drawing more attention in the archaeological literature. The actual tendencies of conducting holistic studies of the archaeological sites and their materials is allowing to obtain a better quality of data and a better understanding of the subsistence patterns of hunter-gatherer societies. In this way, rock crystal and other types of minerals and rocks of the quartzose group are getting a significant presence in the literature. In this paper, we intend to address a comprehensive approach, both macroscopic and microscopic, to an assemblage of experimental rock crystal projectiles to shed light on the identification of the diagnostic features of the use of small rock crystal pieces as projectile points. Aiming to avoid misidentifications, we did not only follow a sequential experiment design, but also carried out a comparative analysis between impact fractures and knapping fractures, marks from bipolar knapping on an anvil, and intentional bending fractures. Besides, in the elaboration of the experimental projectile assemblage we used different sets of targets to document possible differences in the quantity and disposition of the wear impact traces.

Crystal growth and Ce3+ concentration optimization in Tl2LaCl5: An excellent scintillator for the radiation detection

High effective atomic number (70) and density (5.17 g/cm3) among the known halide scintillators with excellent scintillation performance make Tl2LaCl5 (TLC) a new potential candidate for X- and γ-ray detection. The preliminary scintillation performance of TLC was reported earlier for small crystal pieces without any detail information of synthesis, crystal growth optimization conditions and Ce3+ doping concentration, which are investigated in this study. The newly developed melt rotation technique was found to be the best one for the synthesis of TLC and probably for other Tl-based compounds among the known melting techniques. Pure and nominal Ce3+ concentration of 1%, 3%, 5%, 7% and 10% TLC crystals were grown with two zones vertical Bridgman technique in two different type of homemade furnaces and found the optimum thermal gradient, pulling and cooling rate as 25 °C/cm, 0.5 mm/h and 20 °C/h, respectively. The best energy resolution of ∼3.3% (FWHM) and light yield of ∼82,000 ph/MeV were obtained for TLC:3%Ce3+ under 662 keV γ-rays excitation. The promising scintillation performance of TLC revealed that this crystal could be used in Positron Emission Tomography (PET), environmental radiation monitoring and homeland security applications.

Improvement of the Productivity in the Process to Eliminate Paint in Glass Products

The aim of the present investigation is the formulation of a remover that can eliminate paint in products made of glass that do not fulfill the quality control of the painting so that they can be repainted. The types of paint it is desired to remove from glass are the following ones: "shiny translucent", "shiny hiding", "matte type frost" and "metallic". Nowadays, the crystal pieces are unpainted by being burned in an oven at 600 °C and later they are submerged in an acid diluted at 5% remover so that they could finally be manually carved. After the manual carving the pieces are ready to be painted again. The paint remover that is presented in this work is capable of eliminating the painting of pieces of crystal without having them being burned in the oven at 600°C. The remover possesses the following characteristics: it is not inflammable, it has low toxicity and it has a low environmental impact compared with other removers. The time, cost and workforce used to take the paint off the pieces of glass with this remover is lower compared with the traditional methods.

A micromachined piezoelectric microgripper for manipulation of micro/nanomaterials.

Micro/nanomaterials and devices have attracted great interest in recent years because of their extensive application prospects in almost all kinds of fields. However, the manipulations of the material at the micro/nanoscale, such as the separation or transfer of a micro/nano-object in the process of assembling micro/nanodevices, are quite difficult. In this paper, we present a micromachined micro-gripper made of photoresist material (SU-8) and driven by piezoelectric Pb(Mg,Nb)O3-PbTiO3 single crystal pieces. In order to keep two grasping jaws of the micro-gripper operating in the same plane at the micro/nanometer scale, a fine circular flexure hinge was fabricated for elastically connecting them together. After introducing the interface effect, the relationship between the opening stroke of two jaws and the applied voltage was developed and then confirmed by finite element simulation. The micro-gripper was finally installed on a six degree of freedom stage for performing a pick-up, release, and transfer manipulation of a 2 μm ZnO micro-fiber. The presented piezoelectric micro-gripper shows a great potential for the precise manipulation of a single piece of micro/nanomaterial for micro/nanodevices' assembling.

Nuevos datos sobre la temprana difusión del ajedrez en los Pirineos, y una reflexión sobre las piezas de Àger = New evidences on the early spread of chess in the Pyrenees, and a consideration about the Àger set.

The oldest documents revealing the spread of chess in medieval Christian Europe come from the Catalan counties and the Eastern Pyrenees. The aim of this paper is to add two new documentary evidences which confirm the presence of rock crystal chess pieces both in the abbey of Santa Maria de Ripoll and in the cathedral of Roda de Isabena. Additionally, the present study tries to reexamine our current knowledge regarding the exceptional set of pieces coming from the collegiate church of Sant Pere in Ager, suggesting it may have been a donation from one of the descendants of Arnau Mir de Tost, who were the viscounts of Ager of the Cabrera family and later became counts of Urgell.

3D Imaging of Twin Domain Defects in Gold Nanoparticles.

Topological defects are ubiquitous in physics and include crystallographic imperfections such as defects in condensed matter systems. Defects can determine many of the material's properties, thus providing novel opportunities for defect engineering. However, it is difficult to track buried defects and their interfaces in three dimensions with nanoscale resolution. Here, we report three-dimensional visualization of gold nanocrystal twin domains using Bragg coherent X-ray diffractive imaging in an aqueous environment. We capture the size and location of twin domains, which appear as voids in the Bragg electron density, in addition to a component of the strain field. Twin domains can interrupt the stacking order of the parent crystal, leading to a phase offset between the separated parent crystal pieces. We utilize this phase offset to estimate the roughness of the twin boundary. We measure the diffraction signal from the crystal twin and show its Bragg electron density fits into the parent crystal void. Defect imaging will likely facilitate improvement and rational design of nanostructured materials.

Pr3+:BaY2F8 Crystal Nanoparticles (24 nm) Produced by High-Energy Ball Milling: Spectroscopic Characterization and Comparison with Bulk Properties

Nanocrystals (NC) of Pr3+:BaY2F8 with average diameter of 24 nm have been successfully prepared by high-energy ball milling. The method is versatile, easily scalable, and does not require the use of surfactants or catalysts. NC were prepared starting from high quality single crystal pieces, and their spectroscopic features are analyzed and compared with those of a single bulk crystal. Under 445 nm excitation, we recorded the 10 K and room temperature emission spectra of the two samples. The spectra show the same peak positions and width, and this means that the milling process does not introduce substantial modifications to the crystal structure. Besides, there are strong differences in the relative intensity of the lines emitted toward different lower lying levels in the two samples. In particular, the high-energy transitions seem to be hyper intense in the NC with respect to the bulk sample. On the contrary, the emission lines that end at excited levels are less intense in the NC. In addition, the time evolution of the 3P0 decay shows striking differences between the nanosized materials and the bulk sample. Despite the exponential decay of the latter luminescence (τ = 43 μs), NC possess a strong nonlinear component with a lifetime much shorter than in the bulk. Calculations show that nearly 89% of the excited ions contribute to the short-time decay, which is attributed to ions residing near the NC surface.

Development of Materials Integration for Laser Gain Media: Single Crystals and Ceramic (Polycrystalline) Materials and Applications

A study of the fundamental issues of materials integration for wafer bonding offers new pathways for achieving photonic materials with unique properties. First, the bonding of single crystal oxide crystals (YAG and yttria, for example) with different compositions and even different orientations is shown to critically depend upon several important parameters. A detectable level of subsurface damage usually accompanies the polishing of these crystals. We studied chemical mechanical polishing (CMP) of these oxide crystals to provide surfaces which exhibit sub-nm roughness, and the absence of subsurface damage. These surfaces are then activated and we use XPS and other surface sensitive techniques to assess the state of the surface after different processes. Next, we demonstrate that we can significantly reduce the bonding time and temperature to attach two single crystal pieces based on these improved polishing techniques. These techniques also apply to polycrystalline (ceramic) materials as well.Second, we demonstrate wafer bonding for polycrystalline laser gain media. Two issues are important here. First, the grain composition – and hence chemistry – may be different than the bulk composition / chemistry. Under ideal conditions, the grain boundaries may simply be regions of misorientation and be nearly atomically abrupt. The second issue is that the different grain orientations present on a surface may (i) exhibit different hardnesses and / or (ii) different chem-mech polishing rates. Therefore, the issues of chemistry are more important than is the case with single crystal materials. We determined that the best combination of solution chemistry and polishing parameters involves the use of the SUBA 500 (yellow) pad and the same applied force as for the single crystal YAG. For many combinations of force, chemistry, and pad material, a clear delineation of the grain boundaries was revealed. However, we were able to achieve a set of polishing conditions for which the boundaries are not preferentially etched. These surfaces also proved to be damage-free and were able to show a high fraction of bonded interface (>90%) on 50 mm diameter gain media disks.

Skeletal isomerization of tetradecane catalyzed by TON-type zeolites with a fragmented core–shell structure

TON-type zeolites with a core–shell structure were synthesized by crystal overgrowth of an aluminum-free TON-type zeolite on an aluminum-containing TON-type zeolite in the presence of fluoride ion, which was used as a mineralizing reagent to restrain the formation of defects. The core–shell structured zeolite showed greater selectivity for skeletal isomerization in tetradecane hydroisomerization because the acid sites on the external surface of needle-shaped crystals were passivated to inhibit cracking. Breaking the needle-shaped crystals of the core–shell structure to create shorter crystal pieces effectively enhanced the catalytic activity and selectivity for isomerization because new pore entrances were formed.

Experimental and theoretical studies of donor–acceptor scintillation from PbI2

We report on the scintillation properties of undoped PbI2, and PbI2 doped with La, Cu, Ag, and Te. X-ray luminescence spectra were recorded at 7K and the time responses for 80ps pulses of X-rays were recorded from 14K to 150K. Samples were irregularly shaped crystal pieces that ranged from 300 to 1000μm in size. We found that at 14K the undoped samples had a fast emission at 520nm (0.18eV below the band edge) and a total light output of about 40,000photons/MeV. 10% of this light appears in the first ns, which is 5 times greater than LSO and 1.5 times greater than LaBr3:Ce. 50% of the light appears in the first 100ns. The luminosity decreased dramatically as the temperature was increased above 40K, consistent with a non-radiative path that has an activation energy of 3.8meV. Doping with the donor La3+ only slightly changed these scintillation properties. Doping with the donor La3+ and the deep acceptors Cu+, Ag+, and Te2– produced primarily slow donor–acceptor emissions at peak wavelengths of 605, 653, and 800nm, respectively. The luminosity of the samples doped with La3+ and Cu+ depended strongly on the La3+ concentration, demonstrating its role as an electron donor. First-principles band structure calculations showed (1) that the donor level depth of an isolated iodine vacancy is about 0.8eV, too deep to explain the 520nm emission wavelength, and (2) that a donor–acceptor pair consisting of a spatially associated iodine vacancy donor and a lead vacancy acceptor has shallower donor and acceptor depths that are consistent with the 520nm emission wavelength.

Influence of the atmosphere on the growth of LiYF4 single crystal fibers by the micro‐pulling‐down method

AbstractMicro‐pulling‐down growth of LiYF4 single crystal fibers have been performed under different gas atmospheres using stoichiometric LiYF4 single crystal pieces from prior Czochralski experiments as starting material. Completely transparent and phase pure LiYF4 single crystal fibers could be obtained after evacuation of the recipient to 2×10‐6 mbar and subsequent filling with pure (99.995%) CF4 gas. Using a gas mixture of 5% CF4 in Argon or pure 5N Argon leads to the formation of micro crystallites of oxofluorides on the surface. Evacuating only to 3 × 10‐3 mbar leads, independently of atmosphere, to completely white fibers that are heavily contaminated with oxofluorides. DSC measurements of the completely transparent fiber grown under pure CF4 atmosphere reveal congruent melting behavior. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Growth and Characterization of BaGa4S7: A New Crystal for Mid-IR Nonlinear Optics

The new nonlinear optical (NLO) crystal BaGa4S7 for the mid-infrared (IR) has been grown by a Bridgman-Stockbarger technique. Polycrystalline materials with stoichiometric composition were synthesized from BaS, Ga, and S as the initial materials by solid-state reactions. The ultraviolet (UV) and IR transmittance of the crystal was determined with polished crystal pieces. The UV and IR optical absorption edges were found to be at 350 nm and 13.7 μm, respectively. From optical measurements of second harmonic generation on powders, the NLO coefficient d33 was determined to be 12.6 pm/V. The laser damage threshold of a single crystal reached about 1.2 J/cm2 at 1.064 μm. The Vickers-hardness value of the crystal is 327.5 HV5, which is equivalent to Mohs’ hardness of about 5.

Crystal Growth and Defect Characterization of AlN Single Crystals

In this paper, we report results from seeded AlN PVT growth experiments carried out using SiC seeds. The purpose of the experiments was to understand the morphology and crystalline quality of PVT AlN crystals grown under the crystal growth environments investigated. AlN single crystal films of 120-650μm in thickness were grown and freestanding AlN single crystal pieces up to 4×5mm2 were obtained. Surface morphologies and crystal defects in these AlN single crystals were studied using optical microscopy. Selected AlN single crystals were studied using a high-resolution triple-axis X-ray diffraction technique and a Synchrotron White Beam X-ray Diffraction Topography technique. Defects identified in AlN crystals are cracks, dislocations, grain boundaries and crystallite inclusions.

Development of portable CdZnTe spectrometers for remote sensing of signatures from nuclear materials

Room temperature cadmium zinc telluride (CZT) gamma-ray spectrometers are being developed for a number for years for medical, space and national security applications where high sensitivity, low operating power and compactness are indispensable. The technology has matured now to the point where large volume (several cubic centimeters) and high energy resolution (approximately 1% at 660 eV) of gamma photons, are becoming available for their incorporation into portable systems for remote sensing of signatures from nuclear materials. The straightforward approach of utilizing a planar CZT device has been excluded due to the incomplete collection arising from the trapping of holes and causing broadening of spectral lines at energies above 80 keV, to unacceptable levels of performance. Solutions are being pursued by developing devices aimed at processing the signal produced primarily by electrons and practically insensitive to the contribution of holes, and recent progress has been made in the areas of material growth as well as electrode and electronics design. Present materials challenges are in the growth of CZT boules from which large, oriented single crystal pieces can be cut to fabricate such sizable detectors. Since virtually all the detector grade CZT boules consist of several grains, the cost of a large, single crystal section is still high. Co-planar detectors, capacitive Frisch-grid detectors and devices taking advantage of the small pixel effect, are configurations with a range of requirements in crystallinity and defect content and involve variable degrees of complexity in the fabrication, surface passivation and signal processing. These devices have been demonstrated by several research groups and will be discussed in terms of their sensitivity and availability. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Performance of the new pyrolytic graphite analyser bank on the near-backscattering spectrometer IRIS on the ISIS pulsed source

The pyrolytic graphite (PG) analyser bank on the IRIS high-resolution quasi-elastic/low-energy inelastic neutron scattering spectrometer at ISIS has been upgraded. While the original analyser utilised a 6-row by 225-column array of graphite crystals cooled to 30 K, the new design is comprised of 4212 crystal pieces (18 rows by 234 columns). In addition, the graphite is now cooled close to liquid-helium temperature to further improve the sensitivity of the spectrometer. In this paper, the performance of the newly upgraded instrument is determined by comparing resolution measurements collected from the complete IRIS spectrometer before and after modification.

Specific relationship between blood lead and air lead in the crystal industry.

The main objective of the study was to establish the consequences of exposure to crystal dust on blood lead level in workers employed in hand-finishing and grinding crystal pieces. The second objective was to research a relationship between ambient air lead and blood lead. A study conducted in eastern France on 131 subjects occupationally exposed to an aerosol containing crystal particles involved personal measurements of atmospheric exposure to lead, determination of blood lead and, by questionnaire, collection of personal data on exposure characteristics, state of health and level of hygiene of survey volunteers. Initial analysis showed that differences in exposure at the workplace corresponded to differences in blood lead in the operators. There was definitely a potential risk of overexposure to lead, but the existence of this risk was not confirmed by level of blood lead concentrations and, moreover, no clinical signs of lead poisoning in the employees exposed were revealed. The existence of a relationship between personal air (PbA) and blood lead (PbB) levels in grinders and polishers was demonstrated. This relationship, of the form log PbB=2.064+0.181 x log PbA, turns out to be different from those provided by previously published models, which were developed from studies conducted in lead-acid battery manufacturing plants and form the basis of national regulations. Thus, chronic exposure at 100 microg/m(3) of lead at a crystal-grinding workshop corresponds to a mean PbB level of 270 microg/l, whereas the recognized models estimate 350 to 500 microg/l. This study revealed a specific risk for these categories of exposed individuals. The origin of the descriptive model obtained for the lead exposure/ PbB level relationship raises, through the example of lead, the more general problem of the need to take into account differentiation of chemical substances containing the same element in biological monitoring.

Interfacial Reactions in Thin Film and Bulk Iron/Silicon Couples

ABSTRACTInitial phase formation in thin film and bulk Fe/Si couples has been investigated using transmission and scanning electron microscopy (TEM and SEM). For the thin film couples, ≈165 nm of Fe was deposited by electron beam evaporation onto &lt;111&gt; oriented Si substrates. SiO2 capping layers (≈100nm thick) were used to protect the Fe from oxidation during subsequent annealing. Bulk diffusion couples were fabricated by clamping together polycrystalline Fe pieces and &lt;111&gt; oriented single crystal Si pieces and sealed in evacuated (≈10-4 torr) quartz capsules. Annealing of thin film couples was done at temperatures ranging from 300°C to 500°C for up to several hours. Bulk couples were annealed at 700°C for up to ≈1000hrs.Interfacial reactions were detected in as deposited thin film couples. A layer =5nm thick was identified, through electron diffraction, as poorly crystalline off-stoichiometric Fe3Si. Iron was the major diffuser during the formation of Fe3Si. During annnealing off-stoichiometric Fe3Si transformed to stoichiometric Fe3Si. FeSi was the next phase to form - initially detected after annealing at 300°C for 3 hrs. Similar results were obtained for bulk couples. The first phase to form was ordered stoichiometric Fe3Si (initially detected after 7 hrs), followed by FeSi (≈23 hrs) and then FeSi2 (&gt;200 hrs). The formation behavior of these phase is discussed.

Growth of EuO crystals by a solution sintering process

A method of growing cm3-sized single crystals of EuO with better homogeneity than previously obtainable was developed. The starting materials are either Eu203 powder plus metal - or EuO pre-grown crystal pieces plus metal - charges. The growth takes place from solution within a small temperature interval of 5 to 10°C at the growth temperature. At the growth temperatures of 1780, 1820 and 1740°C for the growth of stoichiometric - slightly oxygen-rich and slightly metal-rich - samples, solid EuO is in equilibrium with a metal-rich Eu1-xOx solution and a gas phase. The ratio of solid EuO to EU1_xOx solution has been varied from 9:1 to 4:1. Variations in homogeneity and stoichiometry are confirmed by specific heat measurements around 70 K at the para-to-ferro-magnetic phase transition. The structural perfection measured by γ-ray diffractometry reveals a mosaic spread of subgrain orientations of about 0.5°.