Use Of Single Crystals Research Articles

High sensitivity dual-mode ratiometric optical thermometry based on Ce3+/Mn2+ co-doped LiYF4 single crystal

Serial dual-emitting single crystals LiYF4: 0.5Ce3+/αMn2+ (α = 0, 0.05, 0.1, 0.3, 0.5, and 1.0) samples were synthesized by a reformative Bridgman technique. A comprehensive investigation was carried out to systematically analyze the crystal structure, energy transfer mechanism, luminescence properties, and temperature-dependent sensing capabilities. The single crystal exhibits distinct dual broadband emissions, with peaks at 373 nm attributed to the transition from 5d to 4f of Ce3+ ions and 555 nm assigned to the transition from 4T1g(4G) to 6A1g(4S) level of Mn2+ ions. The optical properties of the Ce3+/Mn2+ co-doped LiYF4 single crystal were studied in relation to temperature, with a focus on enabling precise optical temperature measurements. The research revealed a relative sensitivity of 0.995 % K−1 at 498 K and temperature resolution of 0.03 K at 498 K, indicating the potential of LiYF4: Ce3+/Mn2+ single crystals for use in highly sensitive optical thermometry applications. These findings highlight the crystal suitability for the development of temperature sensing devices with enhanced sensitivity and resolution.

MAPb(Br1–xClx)3 Hybrid Perovskite Materials for Direct X-ray Detection

The study and development in recent years of hybrid (organic–inorganic) halide perovskite materials have given them an unprecedented opportunity for direct ionizing radiation detection, given their large attenuation coefficient and sufficient charge carrier mobility lifetime product. The use of single crystals, considered as model materials, allows us to investigate their intrinsic properties. Characterizations under X-ray illumination of detector devices based on methylammonium lead tribromide (MAPbBr3) single crystals, obtained by optimized growths, show good sensitivity but high dark current density. To improve this critical parameter, while using MAPbBr3 as the base material, we employ anion engineering within the halide elements. We present here mixed halide perovskite crystals, with bromide partially replaced with chloride, obtained through optimized growths using modified inverse temperature crystallization in dimethylformamide, leading to high-quality single crystals of the general formula MAPb(Br1–xClx)3. Six chlorine contents are targeted and carefully determined experimentally via energy-dispersive X-ray analysis and X-ray powder diffraction. For each composition, several crystals are synthesized and used to prepare X-ray detection devices. Their optoelectronic properties are determined under standard X-ray medical conditions and hint at the existence of an optimal composition. MAPb(Br0.85Cl0.15)3 exhibits the best sensitivity with a value of S ≈ 3 μC mGyair–1 cm–2 for RQA5 spectral quality and the lowest dark current density with a value of Jdark ≈ 22 nA mm–2, both recorded at a 50 V mm–1 electric field. This sensitivity value doubles our own MAPbBr3 single crystal device and is higher than that of CsI(Tl)- or a-Se-based flat panels. The present work broadens the benefits and drawbacks of employing halide engineering in perovskite materials to improve the optoelectronic performance under high-energy radiation.

Growing indium antimonide single crystals with a diameter of 100 mm by the modified Chochralsky method

At present, all over the world there is a tendency to increase the diameters of single crystals of both elementary semiconductors and semiconductor compounds. There are reports indicating the use of single crystals of III-V semiconductors with a diameter of four to six inches. So far, indium antimonide single crystals up to 75 mm in diameter have been obtained in Russia.Indium antimonide is the element base of the broadest field of solid-state electronics — optoelectronics. On its basis, linear and matrix photodetectors are manufactured, operating in the spectral wavelength range of 3-5 microns, which are used as a viewing element in thermal imaging systems.In this work, we selected the thermal growth conditions and obtained indium antimonide single crystals 100 mm in diameter in the crystallographic direction [100]. The solution of this problem has made it possible to significantly increase the yield of suitable photodetectors.Single crystals 100 mm in diameter were grown by the Czochralski method in a two-stage process. The design of the graphite heating unit was enlarged and matched to a working crucible with a diameter of 150 millimeters and a load of 4.5-5 kg.The Van der Pauw method was used to measure the electrical properties of the obtained single crystals, which corresponded to the standard parameters of undoped indium antimonide. Using an optical microscope, the etching pits were counted using the 9-field method. The dislocation density in crystals with a diameter of 100 mm was ≤ 100 cm-2 and corresponded to the values ​for crystals of 50 mm.

Growth of single crystals in the (Na1/2Bi1/2)TiO3\u2013(Sr1\u2013xCax)TiO3 system by solid state crystal growth

Ceramics based on (Na1/2B1/2)TiO3 are promising candidates for actuator applications because of large strains generated by an electric field-induced phase transition. For example, the (1−x)(Na1/2Bi1/2)TiO3-xSrTiO3 system exhibits a morphotropic phase boundary at x = 0.2–0.3, leading to high values of inverse piezoelectric constant d*33, which can be further improved by the use of single crystals. In our previous work, single crystals of (Na1/2B1/2)TiO3-SrTiO3 and (Na1/2B1/2)TiO3-CaTiO3 were grown by the solid state crystal growth technique. Growth in the (Na1/2B1/2)TiO3-SrTiO3 system was sluggish whereas the (Na1/2B1/2)TiO3-CaTiO3 single crystals grew well. In the present work, 0.8(Na1/2Bi1/2)TiO3-0.2(Sr1−xCax)TiO3 single crystals (with x = 0.0, 0.1, 0.2, 0.3, 0.4) were produced by the solid state crystal growth technique in an attempt to improve crystal growth rate. The dependence of mean matrix grain size, single crystal growth distance, and electrical properties on the Ca concentration was investigated in detail. These investigations indicated that at x = 0.3 the matrix grain growth was suppressed and the driving force for single crystal growth was enhanced. Replacing Sr with Ca increased the shoulder temperature Ts and temperature of maximum relative permittivity Tmax, causing a decrease in inverse piezoelectric properties and a change from normal to incipient ferroelectric behavior.

Direct Assessment of Ultralow Li+ Jump Rates in Single Crystalline Li3N by Evolution‐Time‐Resolved 7Li Spin‐Alignment Echo NMR

AbstractDiffusion processes of small cations and anions play important roles in many applications such as batteries and sensors. Despite the enormous progress we have witnessed over the past years in characterizing the irregular movement of ions such as Li+, new methods able to sharpen our view and understanding of fast and slow diffusion phenomena are steadily developed. Still, very few techniques are, however, available to directly sense extremely slow Li+ diffusion processes. Here, we took advantage of 1D evolution‐time resolved 7Li spin‐alignment echo NMR that is able to probe the extremely slow interlayer Li+ hopping process in layer‐structured Li3N, which served as a model substance for our purposes. The use of single crystals enabled us to study this translational process without being interfered by the fast intralayer Li+ motions. At 318 K the corresponding jump rate of interlayer dynamics turned out to be in the order of 2500(200) s−1 resulting in a diffusion coefficient as low as 1×10−17 m2 s−1, which is in excellent agreement with results from literature. The method, comparable to 1D and 2D NMR exchange spectroscopy, relies on temporal fluctuations of electric interactions the jumping ions are subjected to. 7Li single crystal 1D SAE NMR offers new opportunities to precisely quantify slow Li+ diffusion processes needed to validate theoretical models and to develop design principles for new solid electrolytes.

Influence of Ca2+ and Zr4+ codoping on the optical characteristics of Gd3Al2Ga3O12:Ce single-crystal

Scintillation materials that can convert absorbed high-energy particles into photons of visible radiation find many applications, in particular in modern methods of medical imaging. Gd3Al2Ga3O12 : Ce is promising single crystal for use as a detecting crystal element of the positron emission tomographs due to its unique properties: high density, high light output, radiation hardness, etc. However, its scintillation kinetics currently limit the use of this crystal. Changing of these kinetics by codoping becomes a priority task, which is considered in many papers. The literature data analysis showed that the optical characteristics of such codoped crystals were not well enough studied or were not investigated at all. In this regard, the spectral dependences of transmission, absorption and reflection are measured using optical spectroscopy for Gd3Al2Ga3O12:Ce, Gd3Al2Ga3O12 : Ce,Ca and Gd3Al2Ga3O12 : Ce,Zr. Dispersion dependences of refractive in dices are obtained by approximating the refractive indices measured using the Brewster method. The approximation was carried out using the Cauchy equation. The material constants of this equation are estimated.

Germanium-doped silicon (sige) as a material for the manufacture of power semiconductor devices resistant to secondary cosmic radiation

The problem of unpredictable failure of power semiconductor devices can be solved by using technologies that increase their radiation resistance. The use of single crystals of germanium doped silicon slows down the degradation of the characteristics of devices when exposed to ionizing radiation, which is an alternative to scarce and expensive GaAs, GaN, SiC, used for these purposes. The impact of secondary cosmic radiation may be responsible for the degradation of the electrophysical parameters of silicon single crystals during their long-term storage, as well as for the decrease in the operating efficiency of semiconductor solar energy converters.

Europium concentration effects on the scintillation properties of Cs4SrI6:Eu and Cs4CaI6:Eu single crystals for use in gamma spectroscopy

Recently discovered scintillators Cs4SrI6:Eu and Cs4CaI6:Eu have shown promising properties for gamma-ray detection in homeland security applications, with <4% energy resolution (at 662 keV) and light yields above 50,000 ph/MeV. However, a thorough investigation of the effects of europium concentration has not yet been conducted. In this work, Eu2+ concentration was varied from 0.5 mol% to 9 mol%, and Ø7 mm single crystals were grown from the melt via the vertical Bridgman method. Scintillation performance was evaluated as a function of Eu2+ concentration to determine the optimal amount. The observed trend was improved energy resolution and higher light yield with increasing Eu2+ concentration up to 7 mol%. The best energy resolution achieved was 3.2% for Cs4SrI6:Eu 7% and 3.6% for Cs4CaI6:Eu 7%. Their respective light yields were 71,000 ph/MeV and 69,000 ph/MeV.

Effect of Composition on the Growth of Single Crystals of (1-x)(Na1/2Bi1/2)TiO3-xSrTiO3 by Solid State Crystal Growth.

The (1−x)(Na1/2Bi1/2)TiO3-xSrTiO3 (NBT-100xST) system is a possible lead-free candidate for actuator applications because of its excellent strain vs. electric field behaviour. Use of single crystals instead of polycrystalline ceramics may lead to further improvement in piezoelectric properties but work on single crystal growth in this system is limited. In particular, the effect of composition on single crystal growth has yet to be studied. In this work, single crystals of (NBT-100xST) with x = 0.00, 0.05, 0.10 and 0.20 were grown using the method of Solid State Crystal Growth. [001]-oriented SrTiO3 single crystal seeds were embedded in (NBT-100xST) ceramic powder, which was then pressed to form pellets and sintered at 1200 °C for 5 min–50 h. Single crystal growth rate, matrix grain growth rate and sample microstructure were examined using scanning and transmission electron microscopy. The results indicate that the highest single crystal growth rate was obtained at x = 0.20. The mixed control theory of grain growth is used to explain the single crystal and matrix grain growth behaviour.

First point-spread function and x-ray phase-contrast imaging results with an 88-mm diameter single crystal.

In this study, we report initial demonstrations of the use of single crystals in indirect x-ray imaging with a benchtop implementation of propagation-based x-ray phase-contrast imaging. Based on single Gaussian peak fits to the x-ray images, we observed a four times smaller system point-spread function (PSF) with the 50-µm thick single crystal scintillators than with the reference polycrystalline phosphor/scintillator. Fiber-optic plate depth-of-focus and Al reflective-coating aspects are also elucidated. Guided by the results from the 25-mm diameter crystal samples, we report additionally the first results with a unique 88-mm diameter single crystal bonded to a fiber optic plate and coupled to the large format CCD. Both PSF and x-ray phase-contrast imaging data are quantified and presented.

Zircon - A possible indicator of mass transfer in deformation zones: A solution for the Roffna gneiss controversy (Suretta nappe, Switzerland)

This paper proposes a simple volume (mass) balancing technique as a means to assess the volume loss and tectonic flattening of mylonitic shear zones. The method involves counting the number of zircon crystals in oriented polished thin sections, analyzed subsequently in the electron microprobe, using the BSEI mode, and a spectrometer setup for detection of the element Zr. Here we present an application to the Roffna gneiss (Eastern Switzerland), a porphyritic granite of Permian origin, which has been metamorphosed and transformed into a phengitic schist under low-grade metamorphic conditions. Mass balances for this material have produced controversial interpretations, in that a first analysis of chemical data of wall rock and mylonite suggested an isochoric mylonitic transition event, while a dramatic volume loss of some 50% in the course this process was inferred after a re-evaluation of the same data. Electron-microscopy of zircon crystals that were retrieved from rocks which had undergone different degrees of deformation revealed only minor alterations and mechanical damage of single grains. This stability of zircon justified the use of single crystals, and in consequence of the element Zr, as passive markers in determining volume (mass) changes during deformation. Results obtained by this method allow us to confirm that the deformation of the Roffna gneiss involved a volume loss of 29 ± 6%, accompanied by chemical alterations. Deformation-induced mobility changes of various elements lead to small gains in Mg and Cr but significant losses Si, Al, Na, Ca, and Sr during the metamorphic event. All other elements, including the REE, underwent no substantial long-range transport.

First direct comparative test of single crystal rhodium and molybdenum mirrors for ITER diagnostics

All optical and laser diagnostics in ITER will use mirrors to observe the plasma radiation. In the ITER environment, mirrors may become contaminated with plasma impurities hampering the performance of corresponding diagnostics. An in-situ mirror cleaning is proposed, which relies on ion sputtering of the contaminants and the affected mirror material. Previous research demonstrated the advantages of single crystal (SC) molybdenum (Mo) under sputtering conditions over polycrystalline concepts. Recently, the first single crystal rhodium (Rh) mirrors became available and tests have been started at the Forschungszentrum Jülich.In a direct test, SC Rh and SC Mo mirrors were exposed under identical conditions in steady-state helium plasmas in the linear plasma device PSI 2. The energy of impinging ions was ∼100eV matching conditions expected in the in-situ cleaning system in ITER. During exposure, molybdenum mirrors lost 420–500nm due to sputtering. Rhodium mirrors lost about 1μm. Exposure corresponded to 50–100 cleaning cycles in ITER. Nevertheless, rhodium mirrors have preserved their specular reflectivity, showing the maximum degradation of less than 7% at 250nm. Molybdenum mirrors demonstrated a moderate decrease of specular reflectivity of 12–25%. Results open new perspectives for the use of single crystals in ITER diagnostics.

Synthesis of carbon nanotubes on the surface of the field cathode of X-ray tube

Carbon nanotubes are unique materials being actively investigated in the development of X-ray tubes with a field cathode. The so-called cold-ray tubes. Our contribution in this direction is the use of single crystals W for the anodes and cathodes as substrates. Here are the structures we obtained carbon nanotubes with the catalysts and directly on the surface of tungsten. The report presents results of studies of carbon nanotubes (CNT) formation on metal substrates W and Ni. X-ray microprobe analysis revealed the presence of 8 at. % carbon. Average density of the powder was measured as 5.1 ± 0.1 g/cm3. Calculations have shown that this value corresponds to the density of the carbon content of 8 at. %.

Hexagonal-Rod Growth Mechanism and Kinetics of the Primary Cu6Sn5 Phase in Liquid Sn-Based Solder

A hexagonal-rod growth mechanism is proposed to describe the growth behavior of the primary Cu6Sn5 phase in liquid Sn-based solder. After Sn-6.5 at.%Cu solder had been maintained at 250°C for 10 h, a large number of hexagonal-rod-type Cu6Sn5 grains were found to have separated within it. Our observations show that these hexagonal rods had side facets in the \(\{ 10\overline{1} 0\}_{\mathrm{\eta} }\) family and round ends close to the {0002}η family. Moreover, the nucleation of the hexagonal rods was studied, and the corresponding growth kinetics found to be governed by a Cu-supply-controlled mechanism rather than an interfacial-reaction-controlled or Cu-diffusion-limited mechanism. More importantly, the anisotropic growth of the Cu6Sn5 phase was confirmed to be the dominant reason for production of these primary hexagonal rods with high aspect ratio. This may represent an avenue for synthesis of nanosized Cu6Sn5 single crystals for use as anode materials in lithium-ion batteries. Additionally, our Cu6Sn5 hexagonal-rod growth mechanism may provide insight into morphological and kinetic studies on interfacial Cu6Sn5 grains and similar intermetallics.

Ferroelectric, Thermal, and Magnetic Characteristics of Praseodymium Malonate Hexahydrate Crystals

Gel-grown single crystals of [Pr2(C3H2O4)3(H2O)6] exhibit remarkably flat habit faces, the most predominant being {110}. High-resolution x-ray diffraction analysis showed that the crystals are free from structural grain boundaries, which is the key requirement for single crystals for use in the microelectronics industry to serve as low-dielectric-constant ferroelectric material. The dielectric behavior recorded on {110} planes of single crystals shows that the crystal is ferroelectric with transition temperature Tc = 135°C, which differs from the Curie–Weiss temperature T0 by 2°C (T0 < Tc). Material in pellet form is shown to exhibit slightly different dielectric behavior. Polarization versus electric field confirms the ferroelectric behavior of the material. The dielectric behavior is also supported by the results of thermal studies, viz. thermogravimetric analysis (TGA), differential thermal analysis (DTA), and differential scanning calorimetry (DSC). The magnetic susceptibility and magnetic moment are calculated to be 30.045 × 10−6 emu and 3.092 BM, respectively.

Dielectric relaxation in YMnO3 single crystals

We have investigated the origin of the dielectric relaxation in YMnO3 single crystals. Two distinct dielectric relaxation features were observed at low (200⩽T⩽373K) and high (300⩽T⩽450K) temperatures. Analysis of our detailed frequency, electrode and thickness dependent dielectric measurements and ac conductivity data as well as the use of single crystals allow us to get a comprehensive picture of these relaxations. The low temperature relaxation is attributed to the Maxwell–Wagner type effects originating from the dipoles at the surface while the high temperature one is suggested to originate from hopping of charge carriers resulting from the second ionization of oxygen vacancies.

Mounting a thermocouple of type E onto a Cu single crystal for use in a magnetically sensitive environment below 77 K

Type E thermocouples show magnetic effects at liquid nitrogen temperature and below. This may cause trouble in experiments that are sensitive to magnetic stray fields like nuclear magnetic resonance, photoemission or high resolution electron energy loss spectroscopy. Here, a solution for the temperature measurement of a single crystal is presented. The authors weld a copper rod onto the back side of the single crystal, thereby relocating the sensitive sample from the thermocouple attachment position. They show that it is possible to measure the crystal temperature at the end of the rod while significantly reducing the ferromagnetic influence due to the increased distance.

Characteristics of a planar-type Cd0.9Zn0.1Te radiation detector grown by using the low-pressure bridgman method

An indium-doped (7 ppm) Cd0.9Zn0.1Te single crystal for use in room-temperature radiation detectors has been grown using a low-pressure Bridgman (LPB) furnace at the Korea Atomic Research Institute. The single crystal has a (111) orientation and a high resistivity of ∼1 × 1012 Ω·cm. In addition, the mobility-lifetime products of the electrons and hole are 4.2 × 10−4 cm2/V and 5 × 10−5 cm2/V, respectively. These values are simply derived by using a Hecht and a neural equation and 5 MeV alpha particles emitted from an 241Am alpha source. To characterize the Cd0.9Zn0.1Te grown by using the LPB method, we fabricated planar detectors with volume of 10 × 10 × 2.5 mm3 from a 2-inch-diameter Cd0.9Zn0.1Te ingot.

Observation of Annealing-Induced Doping in TiO2 Mesoporous Single Crystals for Use in Solid State Dye Sensitized Solar Cells

Mesoporous single crystals (MSCs) of TiO2 are promising materials for more efficient dye sensitized solar cells and other energy conversion or storage devices, since they combine high surface area with large crystalline domain size. In this work, we investigate the charge transport properties of TiO2 MSCs after annealing them within a confining template at temperatures from 500 to 850 °C. We observe that higher anneal temperatures do not change the crystal phase, as in nanocrystalline TiO2, but do influence the MSC absorption spectrum in a manner consistent with the signature of increased oxygen-vacancy defects. By comparing MSC film conductivity in vacuum and in air, we infer that these anneal-induced defects increase the background charge density in TiO2. Subsequently, we measure higher effective mobility in annealed MSCs using transient mobility spectroscopy (TMS), consistent with higher anneal temperatures filling sub-bandgap trap states by n-doping TiO2. Finally, we measure faster charge transport ra...

An In-Situ Electrochemical Cell for Neutron Diffraction Studies of Phase Transitions in Small Volume Electrodes of Li-Ion Batteries

The design and performance of a novel in-situ electrochemical cell that greatly facilitates the neutron diffraction study of complex phase transitions in small volume electrodes of Li-ion cells, is presented in this work. Diffraction patterns that are Rietveld-refinable could be obtained simultaneously for all the electrodes, which demonstrates that the cell is best suited to explore electrode phase transitions driven by the lithiation and delithiation processes. This has been facilitated by the use of single crystal (100) Si sheets as casing material and the planar cell configuration, giving improved signal-to-noise ratio relative to other casing materials. The in-situ cell has also been designed for easy assembly and to facilitate rapid experiments. The effectiveness of cell is demonstrated by tracking the neutron diffraction patterns during the charging of graphite/LiCoO2 and graphite/LiMn2O4 cells. It is shown that good quality neutron diffraction data can be obtained and that most of the finer details of the phase transitions, and the associated changes in crystallographic parameters in these electrodes, can be captured.