As-grown Crystals Research Articles

Single crystal growth and characterization of new Zintl phase Ca9Zn3.1In0.9Sb9

Complex Zintl phases have yielded a large variety of promising new thermoelectric materials. In this study we report the discovery of the new Zintl phase Ca9(Zn1–xInx)4Sb9 (x ​~ ​0.9), needle-like crystals of which were serendipitously obtained from an In- and Sb-rich flux. Although its composition is reminiscent of Ca9Zn4+xSb9, an excellent thermoelectric material with zT ​> ​1, the substitution of In on the Zn site leads to the formation of an entirely new structure type. Single crystal X-ray diffraction revealed a structure characterized by TSb4 tetrahedra (T ​= ​statistically disordered Zn and In atoms) and ZnSb3 triangular units, which share common corners to form [T4Sb9]18− polyanions. The average structure was found to have hexagonal symmetry. The valence electron count in this heavily-disordered structure appears to follows the Zintl-Klemm rules, suggesting semiconducting behavior. Single crystal electrical conductivity and Seebeck coefficient measurements support this conclusion, suggesting that the as-grown crystals are degenerate p-type semiconductors.

Growth of ZnTe crystal via directional solidification method and study of its mechanical properties

In this work, several ZnTe single crystals were successfully prepared from the mole ratio of Zn/Te = 2:8, through a directional solidification method. It is found the as-grown ZnTe single crystal has standard F43m cubic structure and excellent composition homogeneity. The infrared transmittance is tested about 50% in range of 500–4000 cm−1 wavenumber. The microhardness Hv on (110) plane is analyzed unfixed, which changes from 79.71 to 48.41 MPa under a load P of 0.01–1.0 kg. The Hv-P dependence could be theoretically explained based on Kick’s law and the Meyer index n is calculated to be 1.76. Besides, ZnTe single crystal demonstrates an outstanding fracture toughness as none crack is discovered on the crystal surface even under the maximum 1.0 kg applied load. The above results indicate ZnTe single crystal is quite a type of soft but ductile material, which might give valuable reference for crystal processing or application in the future.

Effect of malachite green dye doping in tristhiourea zinc (II) sulphate single crystal—a potential nonlinear optical material

Tristhiourea zinc (II) sulphate (ZTS) is a semi-organic and highly nonlinear optical material used for second harmonic generation (SHG) and other nonlinear optical (NLO) applications. The good quality of pure ZTS (PZTS) and 0.05 mol% and 0.1 mol% malachite green (MG) dye-doped ZTS crystals were harvested by employing low cost effective slow evaporation solution growth technique. The as-grown crystals were subjected to different characterization techniques to see the effect of MG doping on structural, mechanical, thermal, optical and NLO properties. The sharp and intense peaks observed in powder X-ray diffraction and high-resolution X-ray diffraction of PZTS and doped ZTS confirmed the good crystalline quality of pure and doped ZTS. A comparison of FT-IR spectroscopy studies of pure and doped crystals confirmed the incorporation of MG dopant in ZTS from the observation of shifting of various absorption bands. The optical bandgap energies and cut off wavelengths for pure and doped ZTS crystals were studied using UV–Vis.-NIR spectroscopy over an extended spectral range of 200–1100 nm at room temperature. The photoluminescence study revealed that microscopic defects like vacancies and self interstitials are reduced. Thermal stability of the grown crystals were studied by thermogravimetric analysis and found that the thermal stability is not affected much by doping. Vicker’s hardness test was employed to pure and MG-doped ZTS crystals and elucidated that the doped ZTS crystals were found to be slightly softer than pure ZTS. The frequency dependent dielectric constants i.e. ɛr (real), ei (imaginary), dielectric loss (tan δ) and ac electrical conductivity (σac) of pure and doped ZTS crystals were studied by subjecting the grown crystals with impedance analyzer. To observe the NLO property, the grown crystals were subjected to Kurtz powder technique. The results of SHG studies expounded that the SHG efficiency was increased by 2.75 times with MG doping in ZTS crystals.

Growth of Very Large MoS2 Single Crystals Using Out-Diffusion Transport and Their Use in Field Effect Transistors

Monolayer molybdenum disulfide (MoS2) is an attractive 2D material with a wide range of potential applications in the field of electronics and optoelectronics. To obtain the best performance, it is very necessary to grow large area single crystals of MoS2 (single domain) to avoid the effects of grain boundaries, but is exceptionally challenging to do this. Here, we report a novel method which we call out-diffusion vapor transport to grow large area single crystal monolayer MoS2 using an otherwise conventional chemical vapor deposition system. In this method, microchannels were created on the boat to significantly limit the region where MoOx vapor can react with S vapor to form crystals. This growth method resulted in triangular monolayer MoS2 single crystals up to ∼640 μm on a side grown on an oxidized silicon substrate, the largest crystals reported to date. Most of these crystals were multilayer at the center. This common feature has been identified in the literature as partially reduced transition metal oxide nucleates a second layer. We also achieved fully monolayer MoS2 single crystals up to ∼450 μm on a side, the largest demonstrated without the MoOx. Fabricated field effect transistors (FET) using MoS2 monolayer crystal as the active layer demonstrate a conventional n-type behavior, room-temperature mobility up to 45.5 cm2 V−1 s−1 and a maximum ON-Current (ION)/OFF-current (IOFF) ratio of 1.8 × 107. Raman and Photoluminescence results indicate that the as-grown large area monolayer crystals have high crystalline quality and uniformity with minimal defects, a finding that is consistent with the high electron mobility. This research work provides a superior technique to grow large-area high-quality single-crystal monolayer MoS2 without resorting to exotic equipment or techniques.

Dipole relaxation process and giant dielectric permittivity in Eu3+-doped CdMoO4 single crystal

Single crystal of Eu3+-doped cadmium molybdate (Cd0.9268▯0.0244Eu0.0488MoO4, where ▯ denotes cationic vacancies) has been successfully grown by the Czochralski method in air and under 1 MPa. X-ray diffraction analysis indicates that as-grown single crystal exhibits tetragonal scheelite-type structure (a = b = 5.16188(14) Å; c = 11.2080(5) Å; space group I41/a). Eu3+ ions do not show long-range order and they are randomly distributed in CdMoO4 framework substituting Cd2+ ones. UV–vis diffuse reflectance measurements revealed very close optical band gap (Eg) values, i.e. ∼1.74 eV along [100] and [001] crystallographic directions that are twice smaller than Eg of microcrystalline pure CdMoO4 as well as powder Eu3+-doped single crystal. Magnetic and electrical studies of Eu3+-doped cadmium molybdate single crystal showed a paramagnetic and n-type semiconducting behaviour with the metal-insulator transition above 350 K along both crystallographic directions. Dielectric results analysis using the Cole-Cole fit function revealed that the dipole relaxation process has different time scale depending on the crystallographic direction and exhibits Arrhenius temperature dependence for both studied directions. This fact is accompanied by the colossal dielectric permittivity with εr > 8⋅103. The above results are considered in the framework of narrow europium multiplets of energy comparable to thermal energy.

Electronic Transport Properties of Nb1–xTaxSb2 Single-Crystal Semimetals Grown by a Chemical Vapor Transport Based High-Throughput Method

In quantum materials, the Fermi surface and physical behaviors are particularly sensitive to the crystal quality and composition, while it is difficult to obtain a large quantity of quasi-continuous stoichiometric ratio high-quality single crystals quickly, which seriously restricts the research efficiency and scientific achievement transformation. In the past decade, the rise of high-throughput technologies has brought new opportunities to the exploration and mechanism cognition of topological quantum materials. Taking Nb1–xTaxSb2 (NTS) topological semimetals as an example, here we propose a high-throughput single-crystal growth and design method based on chemical vapor transport (CVT) for high-melting-point transition-metal dichalcogenide materials, which intends to accelerate the crystal synthesis and the research efficiency by the influence of different proportions on the properties of the quantum systems. We have successfully grown Nb1–xTaxSb2 single crystals of various proportions (x = 0, 0.1, 0.2, 0.3, 0.5, 0.7, 0.8, 0.9, 1) in one pot at one time with the help of a CVT-based high-throughput method. Then, we systematically study the effect of composition on its crystallographic and magnetotransport properties. First, the excellent crystallographic quality and element uniformity of the produced NTS were verified via X-ray diffraction, energy dispersive X-ray spectroscopy, and transmission electron microscopy. Later, we performed temperature- and angle-dependent resistivity measurements on the as-grown NTS crystals under magnetic fields up to B = 9 T and found the following. (1) The resistivity of all NTS crystals decreases monotonically with decreasing temperature from T = 300 K under zero magnetic field and displays resistivity plateaus below T = 10 K. (2) Upon application of a magnetic field larger than 3 T the resistivity shows a significant upturn in the low-temperature regions for NbSb2 and TaSb2. This resistivity upturn, however, is rapidly suppressed with an increase in x from 0 to 0.5, completely disappears for x = 0.5, and recovers with a further increase in x from 0.5 to 1. (3) All NTS crystals show anisotropic parabolic-like magnetoresistance behaviors with no sign of saturation. (4) The magnetoresistance highly depends on the Nb:Ta ratio and reaches a minimum value when the Nb:Ta ratio is 1. An analysis of the results reveals that the degree of Nb:Ta atomic disorder and the electron–hole compensation could account for the doping-dependent magnetotransport behaviors. In conclusion, our method does have high-throughput characteristics, and the results not only provide further insight into the electronic transport properties of the NTS family but also give a reliable reference for other similar systems, which may promote the opening of a new chapter of a high-throughput research mode in quantum materials.

Third order nonlinear optical, spectral, luminescence, mechanical strength and electrical properties of d – Alanine bulk crystals

Abstract Optical quality d - Alanine bulk crystals were grown by slow evaporation technique. The grown crystal is confirmed by single crystal XRD. The functional parameters are analysed by the FTIR and powder XRD implicates its crystalline nature. The optical constants of the as-grown crystal were determined from the uv visible spectral studies. The third order nonlinear refractive index and nonlinear absorption coefficient of the grown crystal were measured by Z-scan studies. The third order nonlinear susceptibility was found to be 2.2545 х 10−6 esu which seems to be fairly high. The Photoluminescence spectra reveal the emission bands for d -Alanine crystals. The hardness testing was accomplished by Vickers and Knoop testing to determine the Young's Modulus of the crystal. The d.c. conductivity of the grown crystal was measured by the complex impedance analysis wherein the obtained plot in the form of semicircle finds application in Debye relaxation for materials having large dc conductivity.

Study on precipitates in AgGaSe2 single crystal grown by vertical gradient freezing method

In this study, AgGaSe2 single crystal was successful grown by vertical gradient freezing method. Meanwhile, the precipitates on AgGaSe2 single crystal were investigated by x-ray photoelectron spectroscopy (XPS). This technique was recommended as a practicable method to study the precipitates while they are difficult to be detected by other measurements owing to their components and fairly low content. In addition, Energy Disperse Spectroscopy (EDS) and x-ray diffraction (XRD) were employed to characterize the quality of the as-grown AgGaSe2 single crystal. The EDS results indicate a slight deviation from stoichiometric ratio along growth defects. The XRD results manifest that AgGaSe2 crystal has single phase and high purity. The XPS results indicate that precipitates exist on as-grown AgGaSe2 single crystal mainly in the form of Ga2Se3. Ga2O3 and Ag2O were detected by XPS on the polished surface of the as-grown crystal wafer which was regarded as an oxide layer. The study on precipitates may provide important reference for growth process improvement and post-treatment to obtain high quality AgGaSe2 single crystal.

Crystal growth and thermal annealing of AgGaGe5Se12 crystal

AgGaGe5Se12 is a new quaternary nonlinear optical crystal which is applied to laser frequency conversion, especially converting 1.064 µm light to mid-IR range. In this work, we have synthesized the AgGaGe5Se12 polycrystal by the two-zones temperature method. By the modified Bridgman method, we have grown high-quality AgGaGe5Se12 single crystal 30 mm in diameter and 50 mm in length. The structure refinement was carried out by the Rietveld method. Besides, the XRS results were analyzed by comparing with AgGaGeS4 and AgGaGe5S12. In addition, the non-polarized Raman spectra were recorded and the intense peaks were observed at 200 and 232 cm−1. The peaks were attributed to corner-sharing (CS) and edge-sharing (ES) clusters. At last, the crystal was characterized by a high transparency in the 0.6–15 µm spectral range and the absorptions at 3.4 and 7 µm, observed in the as-grown crystal, have been eliminated after annealing. Thus, AgGaGe5Se12 is appropriate for further optical experiments and more comprehensive applications.

Synthesis, growth, structural, optical, thermal and mechanical properties of bis-benzotriazole trichloroacetic acid single crystals

The potential organic bis-benzotriazole trichloroacetic acid (BBTCA) single crystal was formed by slow evaporation of solvents by solution-growth method. The structural parameters and crystalline perfection of BBTCA crystal was confirmed by single crystal X-ray diffraction and powder X-ray diffraction analyses. The BBTCA crystal belongs to the crystal system monoclinic with the space group of P21/c. Various functional groups and corresponding modes of vibrations were identified by using FTIR spectrum. The optical transparency window of the grown BBTCA crystal was studied by UV–Vis–NIR spectroscopy. Photoluminescence study indicates that the broad band emissions occurred at near band edge of the visible region. In TG-DTA, thermal behaviour reveals that BBTCA is thermally stable up to 130°C. The dielectric properties of BBTCA with respect to frequency were investigated with various temperatures. Third-order nonlinearities and mechanical behaviour of as-grown BBTCA crystal were tested by Z-scan experiment and Vicker’s hardness test.

Volume Gallium Oxide Crystals Grown from Melt by the Czochralski Method in an Oxygen-Containing Atmosphere

Results of successful experiments on the growth of gallium oxide (β-Ga2O3) crystals by the Czochralski method are reported. The influence of growth atmosphere on the crystalline perfection of obtained material has been studied. It established that high-quality transparent optical crystals can be obtained provided the atmosphere contains about 5 vol % oxygen. As-grown β-Ga2O3 crystals were characterized by X-ray diffraction and optical transmission measurements.

Growth and characterization of ZnTe single crystal via a novel Te flux vertical Bridgman method

In this work, an II–VI group semiconductor zinc telluride (ZnTe) single crystal is prepared by a novel vertical Bridgman method using Te as flux. The initial mole ratio of Zn/Te = 3:7 is designed for raw material synthesis. ZnTe polycrystalline combined with rich Te is effectively fabricated through rocking technique at 1100 °C. A Φ 25 mm × 65 mm ZnTe boule is successfully grown under a ~ 40 °C·cm−1 temperature gradient with a growth speed of 5 mm·day−1. The as-grown ZnTe crystal has a standard 1:1 stoichiometric ratio and pure F43m phase structure. The maximum transmittance perpendicular to (110) plane is about 64%, and the band gap (Eg) is tested to be 2.225 eV. Terahertz (THz) examination results demonstrate that the time of the highest THz signal is around 17 ps and the frequency of the highest THz transmission is about 0.78 THz, implying that the ZnTe crystal grown by the present Te flux vertical Bridgman method has a good feasibility for THz application.

Identifying Native Point Defects in the Topological Insulator Bi2Te3.

We successfully identified native point defects that occur in Bi2Te3 crystals by combining high-resolution bias-dependent scanning tunneling microscopy and density functional theory based calculations. As-grown Bi2Te3 crystals contain vacancies, antisites, and interstitial defects that may result in bulk conductivity and therefore may change the insulating bulk character. Here, we demonstrate the interplay between the growth conditions and the density of different types of native near-surface defects. In particular, scanning tunneling spectroscopy reveals the dependence on not only the local atomic environment but also on the growth kinetics and the resulting sample doping from n-type toward intrinsic crystals with the Fermi level positioned inside the energy gap. Our results establish a bias-dependent STM signature of the Bi2Te3 native defects and shed light on the link between the native defects and the electronic properties of Bi2Te3, which is relevant for the synthesis of topological insulator materials and the related functional properties.

Spectroscopic and continuous-wave laser properties of Er:GdScO3 crystal at 2.7 µm

Er:GdScO3 crystal was grown by the edge-defined film-fed (EFG) method for the first time. The rocking curve showed that the as-grown crystal has a high crystalline quality. The peak absorption cross section at 980 nm is 0.38×10−20 cm2 with full width at half maximum (FWHM) of 19.5 nm and the peak emission cross section at 2720 nm is 0.93×10−20 cm2 with FWHM of 149.0 nm. The fluorescence lifetimes of 4I11/2 and 4I13/2 were fitted to be 2.24 ms and 4.57 ms, respectively. At inversion ratio P≥0.5, the positive local peak of gain cross-section at 2.7 µm was obtained. Continuous-wave laser operation of Er:GdScO3 crystal was demonstrated. The maximum output power of 863 mW was obtained with a slope efficiency of 11.25%. The results indicated that Er:GdScO3 crystal is a potential laser material for 2.7 µm laser.

Structural, optical, spectroscopic and thermal investigations on novel semi-organic nonlinear optical material - Potassium boro-oxalate single crystal

In this work, a new semi-organic nonlinear optical material of Potassium boro-oxalate (KBO) is synthesized and subsequently a single crystal of size 7 × 5 × 3 mm3 is grown from the aqueous solution by slow evaporation technique at ambient temperature. Characterizations are performed on the single crystals to study the structural, thermal, linear and nonlinear optical (NLO) properties of the as-grown single crystals. Crystal and molecular structure of KBO are solved by direct method and further refinement is performed by full-matrix least-square method employing SHELXL-2014 software. Single crystal X-ray diffraction (SXRD) studies revealed that the grown crystal associates to triclinic crystal family with non-centrosymmetric space group P1. The Fourier transform infrared (FTIR) spectrum reflected the presence of various functional groups in the title compound. The Ultraviolet-visible-near infrared (UV-VIS-NIR) absorption and transmission spectrum are recorded to capture the suitability of the grown single crystals for various optical and NLO applications. The thermal decomposition and thermal stability of the KBO single crystals up to 187°C are investigated by TGA-DTG (Thermo Gravimetric - Differential Thermo Gravimetric), TGA-DTA (Thermo Gravimetric-Differential Thermal analysis) and DSC (Differential Scanning Calorimetry) curves. Kurtz-Perry powder technique is employed to explore the SHG (Second Harmonic Generation) efficiency of the KBO single crystals. SHG efficiency of KBO is found to be comparable to KDP.

Studies of crystal growth, structural, spectral and optical properties of solution grown 2-phenylethylaminium p-nitrophenolate monohydrate single crystals for efficient nonlinear optical applications

2-phenylethylaminium p-nitrophenolate monohydrate (2PPNP) single crystals were grown by evaporation of solvent method. Defect free 2PPNP crystal was subjected to single X-ray diffraction analysis and revealed the unit cell parameters, packing style. The molecular geometrical parameters, molecular orbital, first order hyperpolarizability, MEP map, Mulliken atomic charges and thermodynamic properties of 2-phenylethylaminium p-nitrophenolate monohydrate crystal were theoretically investigated by DFT calculations. FTIR, FT-Raman and NMR studies encompasses its functional components precisely to confirm the compound as 2PPNP. Optical transparency of the as-grown crystals was studied by using UV-Vis spectrum and it shows the transparency in the entire visible region. Photo-excitation of 2PPNP was examined to understand its light emitting behavior. Thermal stability of the grown was examined by TG-DTA analysis to understand the withstanding temperature of 2PPNP and its various endothermic reactions. Microhardness property of 2PPNP was evaluated upto 100 g indentation load and results are analyzed. The Z-scan study was made for the polished 2 mm thick 2PPNP defect free single crystal to evaluate its third-order nonlinearity for knowing the usefulness to optoelectronic applications.

The micro-pulling-down growth of Eu3+-doped Y3Al5O12 and Y3ScAl4O12 crystals for red luminescence

Abstract We report on the comparative growth and spectroscopy of Eu3+-doped Y3Al5O12 (YAG) and Y3ScAl4O12 crystals grown by the micro-pulling-down (μ-PD) method. The structure of the as-grown crystals was determined by X-ray diffraction (XRD) and Raman spectroscopy. The absorption spectra of the crystals are dominated by a strong line centered at 395 nm, matching well with the emission of commercial ultraviolet laser diodes. The Eu:YAG and Eu:Y3ScAl4O12 crystals exhibit strongest red emission centered at 710 nm and the full width at half maximum (FWHM) was calculated to be 2.03 and 3.19 nm, respectively. The fluorescence decay curves of 5D0 levels were measured and discussed. All the results indicate that the Eu:YAG and Eu:Y3ScAl4O12 crystals are promising candidates for red luminescent/laser materials.

Organic Broadband THz Generators Optimized for Efficient Near-Infrared Optical Pumping.

New organic THz generators are designed herein by molecular engineering of the refractive index, phonon mode, and spatial asymmetry. These benzothiazolium crystals simultaneously satisfy the crucial requirements for efficient THz wave generation, including having nonlinear optical chromophores with parallel alignment that provide large optical nonlinearity; good phase matching for enhancing the THz generation efficiency in the near‐infrared region; strong intermolecular interactions that provide restraining THz self‐absorption; high solubility that promotes good crystal growth ability; and a plate‐like crystal morphology with excellent optical quality. Consequently, the as‐grown benzothiazolium crystals exhibit excellent characteristics for THz wave generation, particularly at near‐infrared pump wavelengths around 1100 nm, which is very promising given the availability of femtosecond laser sources at this wavelength, where current conventional THz generators deliver relatively low optical‐to‐THz conversion efficiencies. Compared to a 1.0‐mm‐thick ZnTe crystal as an inorganic benchmark, the 0.28‐mm‐thick benzothiazolium crystal yields a 19 times higher peak‐to‐peak THz electric field with a broader spectral bandwidth (>6.5 THz) when pumped at 1140 nm. The present work provides a valuable approach toward realizing organic crystals that can be pumped by near‐infrared sources for efficient THz wave generation.

Thermally stimulated dislocation generation in silicon crystals grown by the Float-Zone method

Based on own previous studies on dislocation generation in FZ- silicon crystals and in order to verify the location and conditions of dislocation generation and spreading, in the current work we present results from a model experiment using a measurement set-up close to the FZ process. Here, an as-grown dislocation-free FZ crystal with a diameter of 20 mm was exposed to temperature-induced strains. No mechanical surface treatment or sample preparation were applied and no mechanical stress was induced during measurement. The crystal was stepwise heated up in the temperature range from 700 °C till 1180 °C controlled by a pyrometric system. The crystal was cut into several samples and analyzed by Lateral Photovoltage Scanning (LPS), photoluminescence (PL) and etch pit density (EPD) as well as the lifetime (MDP) were measured. Our experimental results show that there is an indication that the dislocation density and the lifetime show an inverse behavior depending on the temperature increase in the investigated range. Therefore, this basic correlation known from the literature was confirmed. The area of dislocations generation and its spreading behavior could be revealed. Possible origins and correlations are discussed.

Growth, thermal, and polarized spectroscopic properties of Nd:CeF3 crystal for dual-wavelength lasers

A Nd:CeF3 crystal was grown successfully by the vertical Bridgman method. The polarized optical properties were investigated for the first time. Based on the Judd–Ofelt theory, the spectral parameters of Nd3+ were studied in detail by using the spectrum of the as-grown crystal. The peak absorption cross-section of σ-polarization at 791 nm is 1.59 × 10−20 cm2, the full width at half maximum (FWHM) is 10 nm. The peak emission cross-section of σ-polarization at 1070 nm is approximately 2.53 × 10−20 cm2, and the three peaks that make up the broadband peak have comparable value. The measured 4F3/2 level fluorescence lifetime is 0.406 ms. Moreover, segregation coefficient of Nd3+, thermal diffusivity coefficient, and thermal conductivity were also measured. We propose that the Nd:CeF3 crystal may be a promising material for 1 μm dual-wavelength laser applications.