Inhomogeneities In Crystals Research Articles

Influence of crystal field inhomogeneities on the spontaneous and laser tuning emission of a Nd3+-doped Li2O-BaO-Al2O3-P2O5 glass

The present work focuses on the spectroscopic and laser properties of Nd3+ in a Li2O-BaO-Al2O3-P2O5 aluminophosphate glass which includes Judd-Ofelt calculation, stimulated emission cross-section of the 4F3/2→4I11/2 emission laser transition, lifetime of the 4F3/2 state and quantum efficiency. Site-selective laser spectroscopy and stimulated emission under selective excitation has been performed to determine the crystal field inhomogeneity at the Nd3+ site together with its broadening effect on the spontaneous and laser emissions. However, a much narrowed laser emission has been achieved by using an intracavity tilting plate which acts as a tunable optical filter to adjust the laser wavelength.

Nano-positive up negative down in binary oxide ferroelectrics

Ferroelectric HfO2 and ZrO2-based materials are promising candidates for next-generation ferroelectric devices, but their characterization is challenging due to complex factors such as crystal phases, degradation mechanisms, and local inhomogeneities. In this work, we propose a novel nanosized positive-up-negative-down (PUND) method to assess the ferroelectric response of doped-HfO2. This method is based on actual current probing and is immune to most electrostatic artifacts that plague other electrical atomic force microscopy (AFM) techniques. We demonstrate the PUND method’s ability to induce ferroelectric switching in Si-doped HfO2 and investigate the distinctive PUND response obtained for individual grains. We also extract the polarization charge based on a direct estimate of the tip–sample contact area. The proposed PUND method is a significant innovation as it is a method to combine the high spatial resolution of AFM with the immunity to electrostatic artifacts of current probing. This makes it a powerful tool for studying ferroelectric materials at the nanoscale, where local inhomogeneities and other effects can have a significant impact on their behavior. The PUND method is also notable for its ability to extract polarization charge based on a direct estimate of the tip–sample contact area. This is a significant improvement over previous methods, which often relied on indirect or approximate estimates of the contact area. Overall, the PUND method is a novel and innovative technique that offers significant advantages for the characterization of ferroelectric materials at the nanoscale. It is expected to have a major impact on the research and development of next-generation ferroelectric devices.

Quantitative Mineralogy of Planetary Silicate Ternary Mixtures Using Raman Spectroscopy

AbstractA 532‐nm‐excited lunar Raman spectrometer (LRS) has been selected as a scientific payload of the Chang'e‐7 mission, exploring mineralogy assemblages in the lunar south polar region. However, the quantification of dark‐colored silicate minerals via Raman spectroscopy is an urgent requirement for upcoming Raman applications in future lunar and planetary explorations. Therefore, we conducted detailed laboratory studies on the Raman quantification of lunar silicate minerals using ternary mixtures of feldspar, olivine, and augite. Quantitative models were established employing the observed linear relationship between Raman integrated intensities and mineral proportions. The significant correlation coefficients (>0.94) and small RMSE (≤4.20 wt.%) confirmed the performance of these models. A series of methods (multipoint sampling, multispectral averaging, peak area extraction, and spectral parameter ratios) were jointly used to ensure that the models were not significantly affected by crystal orientation, chemical inhomogeneity, and instruments. Factors (σ2/σ1) describing the relative Raman scattering cross sections were introduced to calibrate the Raman counts. Our results indicated that the relative Raman scattering efficiency of feldspar, olivine, and augite is 1.4:2.4:1, which can be used to improve the quantitative accuracy of the point‐counting method if polymineralic mixing spectra are dominant. The models were validated across different samples using laboratory mixtures and lunar soil (CE5C0600). The lithology of the Chang'e‐5 soils is basaltic/gabbroic according to the quantitative mineralogy returned from our models that is consistent with the results from traditional methods. This research will be of particular significance for accurately determining the mineral abundances for Chang'e‐7 and other planetary missions. As such, crucial information can be inferred to understand the geological evolution of the exploration regions.

High-precision FoM measurement setup for Ti:sapphire crystals.

The figure of merit (FoM) of Ti:sapphire (Ti:Sa) crystals is a generally used means to evaluate the quality of the crystals. Despite the importance of Ti:Sa, the question of FoM measurement precision stayed out of focus, while the commercially available spectrometers provide unsatisfactory 3σ precision reaching ±60%. In this paper, we present a setup for a single-pass high-precision transmission measurement for three different wavelengths (532, 780, and 1560nm) based on Nd:YAG and Er:YAG lasers. A synchronous detection via a double integrated sphere enabled us to achieve the transmission uncertainty of 0,01-0,03%. With the presented setup, we show that it is possible to determine the FoM values with 3σ precision of ±7,5%. Owing to the high FoM precision, we were able to trace spatial inhomogeneities of an unannealed Ti:Sa crystal produced by a commercial manufacturer Crytur. Our measurements demonstrate that the FoM values can be significantly affected by the crystal inhomogeneities and angular mismatch between the c axis of the Ti:Sa and polarization orientation.

The Effect of Ne+ Ion Implantation on the Crystal, Magnetic, and Domain Structures of Yttrium Iron Garnet Films

The mechanism of the influence of crystal inhomogeneities on the magnetic and domain microstructures of functional materials based on yttrium iron garnet heterostructures is an important subject of investigation due to the aim to predict parameters for manufacturingpurposes. A study of the structural and magnetic characteristics of a set of yttrium iron garnet films grown on gadolinium–gallium garnet substrate is presented. High-resolution X-ray diffractometry, Mössbauer spectroscopy, MFM, as well as ion implantation simulation and X-ray diffraction simulation were used together to determine the features of the effect of Ne+ ion implantation with different dose rates on the samples. The simulation of ion implantation with E = 82 keV showed energy loss profiles of Ne ions with subsequent defect formation up to amorphization of near-surface layers at high doses. Implantation creates two magnetically non-equivalent types of tetrahedrally located Fe3+ ions, which leads to a rotation of the total magnetic moment relative to the film surface and a change in the width of the magnetic domain stripes.

Electrical Transport and Magnetic Properties of High-Quality Sr x Bi2Se3 Single Crystals Obtained by Annealing

Topological insulator Bi2Se3 becomes topological superconductors by doping Cu or Sr. These materials attract much interest because of the nematic state showing two-fold symmetry when the magnetic field is applied parallel to ab-plane. In this study, single crystals of Sr x Bi2Se3 (0.1 ≤ x ≤ 0.3) were grown by the self-flux method followed by annealing process, which improved superconducting properties. Using these high-quality samples, in-plane magnetic-field-angle dependence of resistivity was measured. The result showed two-fold symmetry and indicated the existence of nematic domains. In addition, magnetoresistance as a function of in-plane field direction was measured and is discussed with regard to crystal inhomogeneity. These results help us to perform future experiments of direct visualization of nematic domains.

Исследование взаимосвязи механических напряжений, оптической неоднородности и концентрации кислорода в кристаллах германия

The radial distribution of mechanical stress, optical inhomogeneity and oxygen concentration in Sb-doped germanium crystals grown by the Czochralski method with diameter of 200 mm and resistivity from 10.5 to 18.5 Ω·cm were studied. It was found that residual stress calculated from the data of X-ray structural analysis correlates with results of numerical simulation of thermoelastic stress and interrelates with optical inhomogeneity and concentration of oxygen presented in the atomically dispersed state in germanium.

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The radial distribution of mechanical stress, optical inhomogeneity and oxygen concentration in Sb-doped germanium crystals grown by the Czochralski method with diameter of 200 mm and resistivity from 10.5 to 18.5 Ω·cm were studied. It was found that residual stress calculated from the data of X-ray structural analysis correlates with results of numerical simulation of thermoelastic stress and interrelates with optical inhomogeneity and concentration of oxygen presented in the atomically dispersed state in germanium.

Photo-e.m.f. at a metal/layered n-InSe semiconductor contact under heating conditions of current carriers by an electric field

The features of the photo-e.m.f. are experimentally studied on the metal/n-InSe contact under conditions of heating the current carriers by an electric field in the temperature range of T0 =77÷350 K. The dependences of the photo-e.m.f. (Uph ) value have been measured in the absence of and under the condition of heating the current carriers , as well as the value of from the wavelength (λ) and light intensity (I), heating electric field strength (Ê), time (τ), temperature (T0 ), the initial value of the dark resistivity (ρD0 at 77K) n-InSe. It has been established that the heating of current carriers by an electric field significantly affects the magnitude and behavior of the photo-e.m.f. characteristics on the metal/n-InSe contact. The nature of this effect depends on T0,ρD0, I. The value of significantly exceeds the value of . With an increase in Ê, the value of AUph increases linearly (ΔUph~Ê) at relatively small Ê, and the dependence of ΔUph (Ê) reaches saturation at higher Ê. The value of ΔUph decreases with increasing ρD0 , at relatively small Ê. With an increase in ρD0 , the relaxation time of the photo-e.m.f. also increases when turned off the pulse of the electric field. The obtained experimental results are explained on the basis of the dependence of the photo-e.m.f. on the metal/n-InSe contact on the effective temperature of heated current carriers (Te ), considering the effect of the spatial inhomogeneity of n-InSe crystals on the photo-e.m.f. and on the process of heating the current carriers.

Modeling and simulation of the lateral photovoltage scanning method

The goal of this paper is to model and simulate the lateral photovoltage scanning (LPS) method which detects inhomogeneities in semiconductor crystals. Our drift-diffusion model is based on the semiconductor device equations combined with an implicit boundary condition which models a volt meter. To validate our 2D and 3D finite volume simulations, we use theory developed by Tauc [1] to derive three analytical predictions which our simulation results corroborate, even for anisotropic 2D and 3D meshes. Our code runs about two orders of magnitudes faster than earlier implementations based on commercial software [2]. It also performs well for small doping concentrations which previously could not be simulated at all due to numerical instabilities. We present a convergence study which shows that the LPS voltage converges quadratically. Finally, our simulations provide experimentalists with reference laser powers for which meaningful voltages can still be measured. For higher laser power the screening effect does not allow this anymore.

Temporal prepulse contrast degradation in high-intensity CPA lasers from anisotropy of amplifier gain media.

We present a study of the temporal prepulse contrast degradation of high focused intensity pulses produced in CPA laser systems due to imperfections in amplifier design, alignment of amplifier components, and crystal inhomogeneity. Using an extended cross-polarized imaging technique, we demonstrate the presence of multiple crystal domains inside Ti:sapphire slabs with ≈10cm diameter. The results of our numerical calculations show that crystalline c-axis orientation inhomogeneity caused by these crystal domains can lead to the generation of prepulses with a relative contrast of >10-10 within several picoseconds before the main pulse. In a multiple-slab amplifier head configuration sometimes used in high-repetition-rate systems, the misalignment of the crystalline c-axes of the amplifier slab with respect to each other can lead to the generation of prepulses with relative contrast as high as 10-6, depending on the magnitude of misalignment.

Formation and Characterization of Concentration Inhomogeneities in Melt-Grown Crystals

Formation and Characterization of Concentration Inhomogeneities in Melt-Grown Crystals

Direct visualization of anionic electrons in an electride reveals inhomogeneities.

Electrides are an unusual family of materials that feature loosely bonded electrons that occupy special interstitial sites and serve as anions. They are attracting increasing attention because of their wide range of exotic physical and chemical properties. Despite the critical role of the anionic electrons in inducing these properties, their presence has not been directly observed experimentally. Here, we visualize the columnar anionic electron density within the prototype electride Y5Si3 with sub-angstrom spatial resolution using differential phase-contrast imaging in a scanning transmission electron microscope. The data further reveal an unexpected charge variation at different anionic sites. Density functional theory simulations show that the presence of trace H impurities is the cause of this inhomogeneity. The visualization and quantification of charge inhomogeneities in crystals will serve as valuable input in future theoretical predictions and experimental analysis of exotic properties in electrides and materials beyond.

МАКРОСКОПІЧНА НЕОДНОРІДНІСТЬ ОПТИЧНИХ, ДІЕЛЕКТРИЧНИХ І ФОТОДІЕЛЕКТРИЧНИХ ВЛАСТИВОСТЕЙ КРИСТАЛІВ ZnSe

The subject matter of study in the article is the optical, dielectric and photodielectric properties of ZnSe crystals containing macroscopic structural inhomogeneities. The goal of this work is to study large-scale inhomogeneities in ZnSe crystals, which is important for determining the suitability of their application in technology. The tasks to be solved are: in a crystalline ZnSe ingot of cylindrical shape in the optical range at perpendicular to the light flux orientation of the sample axis to detect macroscopic inhomogeneities and establish their relationship with the features of the dielectric properties of the local regions of the ZnSe ingot; to investigate the influence of nonmonochromatic light flux on the distribution of dielectric parameters along the axis of the ZnSe ingot containing areas of macroscopic inhomogeneities. The problems were solved by the following methods: the homogeneity of the zinc selenide ingot was studied by the polarization-optical photoelasticity method; the photometry method was used to study the intensity distribution of the light scattered by the sample perpendicular to its axis; the dielectric properties of a crystalline ZnSe ingot were investigated by the capacitive method. The following results were obtained. In ZnSe crystals regions of three types were found: isotropic, weakly anisotropic, and anisotropic. Sharp changes in the intensity of scattered light are observed in the region of large-scale optical inhomogeneity, and light scattering in this region occurs anisotropically. The angular dependences of C and tgδ at an electric field frequency of 1 kHz are obtained for the region of large-scale optical anisotropy. The changes in dielectric parameters under the action of nonmonochromatic light along the sample axis are measured. Conclusions. It was found that ZnSe crystals are characterized by large-scale inhomogeneities of the investigated properties. A close relationship is noted between the optical and electrophysical properties, which is probably due to the mutual influence of two-dimensional and point defects on the formation of a defect structure during the growth and further cooling of the crystal.

Application of Glow Discharge Mass Spectrometry for the Monitoring of Dopant Distribution in Optical Crystals Grown by TSSG Method

Direct analysis of matrix and admixture elements in non-conducting crystals is a relevant analytical task in terms of quality assurance of optical materials. The current study aimed to develop a method capable to assess the inhomogeneity of optical crystals with sufficient sensitivity. K1−xRbxTiOPO4 (x = 0.002 and 0.05) and KGd1−yNdy(WO4)2 (y = 0.05) were grown using the top-seeded solution growth method (TSSG). The samples were analyzed by microsecond direct current pulsed glow discharge time-of-flight mass spectrometry (µs-PDC TOF GDMS). The data were compared with the results obtained by scanning electron microscope-energy dispersive X-ray spectroscopy (SEM EDX) and spectrophotometry and validated by the analysis of certified reference material. Sample glow discharge sputtering and analysis were optimized and implemented in real samples. Sample coating with a silver layer and sample pressing in the metallic matrix were proposed to ensure effective sputtering for K1−xRbxTiOPO4 and KGd1−yNdy(WO4)2, respectively. Using the designed method, the inhomogeneity of the dopant’s distribution was demonstrated along the growth axis and in the case of K1−xRbxTiOPO4, also in the growth sectors of different faces. The designed method is applicable for the direct analysis of optical crystal and may be implemented in quality assurance in the manufacturing of optical materials.

Manganese-Doping-Induced Quantum Confinement within Host Perovskite Nanocrystals through Ruddlesden-Popper Defects.

The concept of doping Mn2+ ions into II–VI semiconductor nanocrystals (NCs) was recently extended to perovskite NCs. To date, most studies on Mn2+ doped NCs focus on enhancing the emission related to the Mn2+ dopant via an energy transfer mechanism. Herein, we found that the doping of Mn2+ ions into CsPbCl3 NCs not only results in a Mn2+‐related orange emission, but also strongly influences the excitonic properties of the host NCs. We observe for the first time that Mn2+ doping leads to the formation of Ruddlesden–Popper (R.P.) defects and thus induces quantum confinement within the host NCs. We find that a slight doping with Mn2+ ions improves the size distribution of the NCs, which results in a prominent excitonic peak. However, with increasing the Mn2+ concentration, the number of R.P. planes increases leading to smaller single‐crystal domains. The thus enhanced confinement and crystal inhomogeneity cause a gradual blue shift and broadening of the excitonic transition, respectively.

Електронні характеристики квантових точок СdS, що містять дефекти

Using the density functional theory and the generalized gradient approximation, we calculated the atomic structure, the density of electronic states, and the optical absorption spectra of CdS quantum dots containing intrinsic defects — a cadmium vacancy VCd and an interstitial sulfur atom SI, and substitutional impurities — zinc and copper in place of the atom cadmium — ZnCd and CuCd, respectively. The calculations were performed for the Cd33S33 cluster corresponding to the so-called “magic” size of the quantum dot. This size has a minimum of dangling bonds at the surface and allows the using of such a cluster without the passivation. The structural relaxation during the formation of such defects and the distribution of the wave function of the state corresponding to the top of the valence band are analyzed in details. It has been shown that the cadmium vacancy forms local states in the band gap of CdS nanocrystals, and can serve as centers of radiative recombination. Other defects form energy levels in the depths of the valence band or near its top, but whose energy positions do not correspond to the band maxima in the experimental photoluminescence spectra of CdS quantum dots, both undoped and doped with zinc. The calculated optical absorption spectra demonstrate a strong peak in the region of fundamental absorption of CdS for a cluster containing a substitutional impurity of CuCd, in contrast to other systems where no such peaks are observed. In addition, the replacement of the cadmium atom with copper leads to a decrease in the number of chemical bonds to three and, accordingly, to the largest relaxation among the systems studied. This feature is caused by the crystal structure inhomogeneity of copper sulfide CuxS, which, depending on stoichiometry, can be either a semiconductor or a metal.

Nondestructive evaluation of homogeneity of Mn-doped 0.23Pb(In1/2Nb1/2)O3–0.48Pb(Mg1/3Nb2/3)O3–0.29PbTiO3 single crystals via resonant ultrasound spectroscopy

Ultrahigh electromechanical coupling factors and piezoelectric strain coefficients of relaxor-based single crystals make them materials of choice for next-generation electroacoustic transducers. Thus far, the compositional homogeneity problem of relaxor-based single crystals has not been completely solved. To promote the application of these crystals, methods for evaluating their quality and uniformity using nondestructive processes are urgently needed. In this study, resonant ultrasound spectroscopy (RUS) was employed for the nondestructive evaluation (NDE) of the property inhomogeneity of relaxor-based single crystals for the first time. A inhomogeneous rectangular parallelepiped [0 0 1]c poled Mn-doped 0.23Pb(In1/2Nb1/2)O3–0.48Pb(Mg1/3Nb2/3)O3–0.29PbTiO3 (23PIN-48PMN-29PT) single crystal sample and a homogeneous lead zirconate titanate (PZT-8) sample were evaluated via RUS. Furthermore, the evaluation results were verified by cutting the 23PIN-48PMN-29PT sample into four smaller samples and measuring the elastic constants , , and ; dielectric constants ; and piezoelectric constant d33 for each sample (including the PZT-8 sample).

Microscopic characterization of bulk damage resistance of DKDP nonlinear crystals

DKDP nonlinear crystals in ICF drivers are susceptible to laser-induced bulk damage, therefore it is significant important to characterize bulk damage in order to prevent, reduce, and/or manage bulk damage. This work presents a method evaluating the bulk damage resistance of DKDP crystals, directly providing pinpoints density, size distribution, and three-dimensional (3D) distribution of pinpoints. This technique can be used for characterizing the crystal inhomogeneity, and the result demonstrates that crystal inhomogeneity have a strong and negligible impact on pinpoints density and the size distribution of pinpoints respectively, suggesting two distinct energy deposition mechanisms governing the damage initiation and the growth of the pinpoints.

Bi3+ Heterovalent Doping in APbBr3 Lead Halide Perovskite Single Crystals: Urbach Tail and Photon Recycling Effect

We focused on Bi3+ as a promising candidate for donor impurity in lead halide perovskites and fabricated electron-doped CH3NH3PbBr3 single crystals. Room-temperature optical measurement revealed the increase in Urbach tail and suppression of photon recycling effect by Bi doping, which results in photoluminescence (PL) blue shift. Furthermore, we conducted optical reflectance and PL measurements at cryogenic temperature, where the thermal broadening is supressed. At low temperature, exciton dominates the optical properties and the photon recycling effect is negligible. From the PL intensity and spectral width, we quantitatively evaluated the impact of Bi-doping on crystal inhomogeneity.