Preparation Of Single Crystals Research Articles

Crystal growth, structure, and optical properties of new quaternary chalcogenide nonlinear optical crystal AgGaGeS4

AgGaGeS4 is a new quaternary chalcogenide nonlinear optical crystal in application to converting a 1.064 μm Nd:YAG laser to 4–11 μm mid-IR output. It has been clearly demonstrated a high laser damage threshold, 50 MW cm−2 at 1.064 μm, which makes it a promising material for high-power and sustained laser frequency conversion. However, the preparation of the AgGaGeS4 single crystal has been perplexed by the complex multiple chemical reactions, high vapor pressure and large undercooling degree. In this work, a unique cooling process is used to modify the vapor transport with mechanical oscillation method for higher quality polycrystal. Besides, diverse ways have respectively addressed the pivotal issues of crystal growth process by the Bridgman method, such as the degree of supercooling, growth rate and control of decomposition at high temperature. Eventually, we have obtained the AgGaGeS4 crystal and the maximum size is Φ30 mm × 50 mm. In addition, the non-polarization Raman spectra were recorded at room temperature with a 532 nm laser beam excitation source. The main vibration frequencies present around 107, 323 and 355 cm−1, and the relationship between the structure and lattice vibrational properties is also discussed and analyzed in detail. The crystal performs a good homogeneity and high transparency in the 0.5–11.5 μm spectral range, especially the absorption coefficient of annealed AgGaGeS4 wafer that ranges from 0.01 cm−1 to 0.05 cm−1 in 0.9–10 μm after annealing, which illustrate it suitable for further optical experiments and the comprehensive applications. Besides, the band gap changes from 2.787 eV to 2.805 eV after annealing. At last, the surface damage threshold is about 103 MW·cm−2 which is two times more than report, and the body damage threshold is about 132 MW·cm−2.

(Invited) 2D Materials: Crystal Growth for Future Device Structures

The isolation of graphene, now over decade ago, has given rise to the revitalization of an old full set of materials, two-dimensional materials (2DM), which have exceptional electrical, chemical and physical properties. Some of the materials under investigation in addition to graphene are hexagonal boron nitride (h-BN), semiconducting, metallic, and superconducting transition metal dichalcogenides (TMD) with a general chemical formula, MX2 where M is for example equal to Mo, W, Ta, Nb, Zr, Ti, and X = S, Se and Te, and others. While graphene is a material with many exceptional properties and h-BN is an excellent 2D insulator, TMD materials provide what neither graphene nor h-BN can, bandgap engineering that, in principle, can be used to create new devices that cannot be fabricated with h-BN and graphene alone. There is hope that 2DM can be integrated to fabricate numerous device types for many applications ranging from inkjet-printed circuits, photonic applications, flexible electronics, and high-performance electronics. However, to fully realize the benefits of these materials, the community will have to work together to define new device structures, device integration schemes, and materials growth processes to help the semiconductor industry make progress toward meeting the original goals of the International Technology Roadmap for Semiconductors (ITRS). A number of deposition/growth techniques have been used to prepare large area graphene, such as growth on SiC through the evaporation of Si at high temperatures, precipitation of carbon from metals, and catalytic chemical vapor deposition on Cu and Pt. Direct growth of good quality graphene on dielectrics/semiconductors other than SiC with reasonable properties has also been reported recently on Ge. Due to its insulating nature and compatibility with graphene and TMDs, the preparation of large area h-BN is also being developed on both metals and dielectrics. Transition metal dichalcogenides, however, present altogether different opportunities and difficulties in the preparation of low defect density large area single crystals. Vapor transport, chemical vapor deposition (CVD), and molecular beam epitaxy (MBE) are being developed to produce these materials for initial studies of materials physics and device fabrication. In addition, there is some effort in performing simulations to guide growth for both CVD and MBE growers. Therefore, there is an opportunity here to have the crystal growers and the modeling community collaborate to develop high quality materials and processes. A number of devices structures are currently under evaluation to take advantage of the basic properties of graphene, bi-layer graphene, h-BN and TMDs. Some of the devices are based on tunneling phenomena while others are based on excitonic phenomena. In this presentation I will present the state of the art results of graphene, h-BN, and a few TMD materials and their prospects for future electronic device applications.

Bulk single crystal growth and sample surface preparation of catalytic NaAu2

Here in we have grown bulk single crystals of NaAu2 for the first time to enable surface studies on the nature of the (111) bulk surface. This intermetallic compound exhibits surprisingly high catalytic activity for CO oxidation, a benchmark reaction. Theory predicts NaAu2 to be the most thermodynamically stable composition in the Na-Au binary phase diagram and NaAu2 has been seen to preferentially form in experiments containing Na and Au which supports this prediction. The (111) surface was also predicted to be the most stable and is nearly bulk-terminated making single crystal samples prepared with this crystallographic orientation a fitting choice. The crystal quality and surface composition of the metallographically prepared surface was determined by x-ray diffraction methods in addition to optical and electron microscopy.

Preparation and characterization of Tb1-xNdxVO4 single crystals for optical isolators

High optical quality Tb1-xNdxVO4 (TNV) single crystal with dimensions of Ø29 × 39 mm3 was grown by the Czochralski (Cz) technique. Powder X-ray diffraction analysis was performed, indicating that as-grown crystal belongs to tetragonal system. The optical and magneto-optical properties have been investigated in detail. TNV possesses very high transmittance, especially in the near-infrared region. The Verdet constant of TNV at 1064 nm reaches 71 rad m−1T−1, 78% larger than that of reference compound TGG. The high magneto-optical figure of merit and extinction ratio also reveal the superior magneto-optical performances of TNV in comparison with TGG. Measurements of thermal conductivity and laser-induced damage threshold (LIDT) were also carried out. These features make Tb1-xNdxVO4 a potential candidate for magneto-optical applications in the near-infrared (NIR) region.

The OCS method of seeding point detection using visible vision for large-diameter sapphire single crystal growth via the Kyropoulos method

The seeding process is vital in the preparation of large-diameter sapphire single crystal. It is the key to detect the seeding point during the seeding process. The OCS method is proposed in the paper to detect the seeding point. The OCS method improves the detection method of spoke pattern center proposed by Churl Min Kim, based on this, and the convergence model of spoke pattern center is fitted, so that the real seeding point is detected. In the experiment, the OCS method is verified by comparing with the traditional manual seeding method (operated by skilled seeding technologists) and the method proposed by Churl Min Kim. The OCS method has the same effect as the traditional artificial seeding method and can reduce the number of attempts in a single seeding experiment. Compared with the method proposed by Churl Min Kim, the OCS method can meet the needs of actual industrial production in terms of the number of successful seeding, the number of seeding attempts and the average seeding time.

Electronic structure and exciton shifts in Sb-doped MoS2 monolayer

The effective manipulation of excitons is important for the realization of exciton-based devices and circuits, and doping is considered a good strategy to achieve this. While studies have shown that 2D semiconductors are ideal for excitonic devices, preparation of homogenous substitutional foreign-atom-doped 2D crystals is still difficult. Here we report the preparation of homogenous monolayer Sb-doped MoS2 single crystals via a facile chemical vapor deposition method. A and B excitons are observed in the Sb-doped MoS2 monolayer by reflection magnetic circular dichroism spectrum measurements. More important, compared with monolayer MoS2, the peak positions of two excitons show obvious shifts. Meanwhile, the degeneration of A exciton is also observed in the monolayer Sb-doped MoS2 crystal using photoluminescence spectroscopy, which is ascribed to the impurity energy levels within the band-gap, confirmed by density function theory. Our study opens a door to developing the doping of 2D layered transition metal dichalcogenides with group-V dopants, which is helpful for the fundamental study of the physical and chemical properties of transition metal dichalcogenides.

Получение и свойства монокристаллов CdCr2S4

Получение и свойства монокристаллов CdCr2S4

Europium-doped Lu2O3 phosphors prepared by a sol-gel method

Cubic lutetium sesquioxide (Lu2O3) presents a suitable host material because of its favourable properties including chemical and phase stability. Lu2O3 has a wide band gap (> 5.5 eV) and its doping with lanthanide ions, which behave as activators, gives rise to some unique optical properties. Also, due to a high effective atomic number (Zeff = 68.8) and high density (9.42 g/cm3) of the Lu2O3 host, providing high stopping power for ionizing radiation, it has also attracted attention as a scintillator material. Since optical properties are affected by both crystal structure and morphology, which depend strongly on the synthesis method and conditions employed, many different methods have been studied for its synthesis. However, due to high melting temperature of Lu2O3 (2490 °C), the preparation of single crystals is difficult. In our work, we prepared polycrystalline samples of Eu:Lu2O3 using a sol-gel route based on the Pechini polycondensation. We tested three europium doping concentrations, two different annealing regimes were examined as well. The influence of mentioned parameters on photoluminescent and radioluminescent properties was established. Our samples proved that the used synthesis method can be used for further research of Lu2O3 doped with other rare-earth metals.

The Phosphine Oxide Route toward Lead Halide Perovskite Nanocrystals.

We report an amine-free synthesis of lead halide perovskite (LHP) nanocrystals, using trioctylphosphine oxide (TOPO) instead of aliphatic amines, in combination with a protic acid (e.g., oleic acid). The overall synthesis scheme bears many similarities to the chemistry behind the preparation of LHP thin films and single crystals, in terms of ligand coordination to the chemical precursors. The acidity of the environment and hence the extent of protonation of the TOPO molecules tune the reactivity of the PbX2 precursor, regulating the size of the nanocrystals. On the other hand, TOPO molecules are virtually absent from the surface of our nanocrystals, which are simply passivated by one type of ligand (e.g., Cs-oleate). Furthermore, our studies reveal that Cs-oleate is dynamically bound to the surface of the nanocrystals and that an optimal surface coverage is critical for achieving high photoluminescence quantum yield. Our scheme delivers NCs with a controlled size and shape: only cubes are formed, with no contamination with platelets, regardless of the reaction conditions that were tested. We attribute such a shape homogeneity to the absence of primary aliphatic amines in our reaction environment, since these are known to promote the formation of nanocrystals with sheet/platelet morphologies or layered phases under certain reaction conditions. The TOPO route is particularly appealing with regard to synthesizing LHP nanocrystals for large-scale manufacturing, as the yield in terms of material produced is close to the theoretical limit: i.e., almost all precursors employed in the synthesis are converted into nanocrystals.

Preparation and characterization of single crystals of tetrakis(4-(5,5-dimethyl-2-phenyl-1,3-dioxan-2-yl)phenyl)germane

A novel tetrakis(4-(5,5-dimethyl-2-phenyl-1,3-dioxan-2- yl)phenyl)germane (2) was synthesized by the reaction of germanium(IV) tetrachloride with 4-(5,5-dimethyl-2-phenyl-1,3-dioxan-2-yl)phenyllithium. Colorless plate-shaped single crystals obtained from recrystallization in ether were characterized by the single-crystal X-ray diffraction. The organogermanium compound was crystallized in a noncentrosymmetric nonpolar tetragonal space group, I-4, and classified as a porous molecular material owing to the presence of two types of distinct channels as a result of intermolecular hydrogen bonding. Compound 2 exhibits a differential gas adsorption property. The powder second-harmonic generating (SHG) measurements indicate that compound 2 shows a SHG efficiency 10 times greater than those of α-SiO2 and type-1 nonphase-matchable.

Anisotropic Optoelectronic Properties of Melt-Grown Bulk CsPbBr3 Single Crystal.

All-inorganic perovskite CsPbBr3 has been considered as one of the star semiconductors due to its inspiring optoelectronic properties and higher stability than the organic-inorganic hybrid counterparts. The preparation of large-size single crystals with low trap density and the performance optimization on the devices still challenge the commercial application of this material. Here the large transparent CsPbBr3 single crystal (ϕ 24 mm × 90 mm) was grown by a modified Bridgman method. With the determination of crystallographic directions, the anisotropic optoelectronic properties were investigated for the first time. The result shows a high electron mobility (11.61 cm2/(V s)) along the b axis, one order of magnitude higher than that along the c axis. Moreover, the photoresponse measurement yields a high responsivity (5.83 A/W) and external quantum efficiency (1360%) on the (001) plane irradiated by the 532 nm laser diode with 1 mW/cm2 under 10 V bias, which is a 305% enhancement compared with the (010) plane. Our study on anisotropic optoelectronic properties of CsPbBr3 will provide a significant approach to enhance the performance of single-crystalline devices.

Structural Chemistry of Halide including Thallides A8Tl11X1−n (A = K, Rb, Cs; X = Cl, Br; n = 0.1–0.9)

A8Tl11 (A = alkali metal) compounds have been known since the investigations of Corbett et al. in 1995 and are still a matter of current discussions as the compound includes one extra electron referred to the charge of the Tl117− cluster. Attempts to substitute this additional electron by incorporation of a halide atom succeeded in the preparation of single crystals for the lightest triel homologue of the group, Cs8Ga11Cl, and powder diffraction experiments for the heavier homologues also suggested the formation of analogous compounds. However, X-Ray single crystal studies on A8Tl11X to prove this substitution and to provide a deeper insight into the influence on the thallide substructure have not yet been performed, probably due to severe absorption combined with air and moisture sensitivity for this class of compounds. Here, we present single crystal X-Ray structure analyses of the new compounds Cs8Tl11Cl0.8, Cs8Tl11Br0.9, Cs5Rb3Tl11Cl0.5, Cs5.7K2.3Tl11Cl0.6 and K4Rb4Tl11Cl0.1. It is shown that a (partial) incorporation of halide can also be indirectly determined by examination of the Tl-Tl distances, thereby the newly introduced cdd/cdav ratio allows to evaluate the degree of distortion of Tl117− clusters.

Preparation of Fine Single Crystals of Rutheno-Cuprates by the Self-Flux Method with Alumina Boats

We investigate the single crystal growth of rutheno-cuprates, which are known to be magnetic superconductors. We attempted the single crystal growth of two systems, RuSr2GdCu2O8−δ (RuGd-1212) and RuSr2(Gd,Ce)2Cu2O10−δ (RuGd-1222), by the self-flux method with alumina boats. Fine cubic crystals of RuGd-1212 with a side length of approximately 5 μ m were obtained by slow cooling from 1350 to 940 ∘C. Plate-like RuGd-1222 crystals with a smooth plane were obtained at the surface of the precursor pellet. RuGd-1222 was more stable at high temperatures than RuGd-1212 and was also superconductive, but its superconductivity weakened as the cooling rate decreased. This weakening was induced by decomposition. Therefore, high-quality RuGd-1222 single crystals were difficult to obtain, and we failed to extract only the smooth planar crystal part. As a modified synthesis technique, we mixed a precursor containing Ru–Sr–Gd–Ce flux with RuGd-1222 powders and gradually cooled the mixture from 1350 to 1090 ∘C. A plate-like RuGd-1222 sample with a smooth surface and a size of 70 × 30μm2 was obtained from the side surface of the precursor pellet. By this technique, we could separate the planar crystal part. Semiquantitative composition analysis confirmed this planar crystal as a RuGd-1222 phase. The X-ray diffraction peak suggested the (0014) plane, implying that the plate-like precipitates are c-axis-oriented RuGd-1222 single crystals.

Preparation of Cu2Sn1-xGexS3 bulk single crystals by chemical vapor transport with iodine

Bulk crystals of monoclinic Cu2Sn1−xGexS3 were prepared by chemical vapor transport with iodine. The samples were investigated using electron-probe microanalysis, transmission electron microscopy, Raman spectroscopy and X-ray diffraction (XRD). All of the samples had a Cu-rich and S-poor composition. As the Ge content increased, the XRD peaks shifted to higher angle, the Raman peaks shifted to higher wavenumber, and the lattice constants decreased. Selected-area electron diffraction patterns showed that the samples were single crystal and had a monoclinic structure.

Optimization of crystal growth and properties of γ-CuI ultrafast scintillator by the addition of LiI

Large-sized γ-CuI single crystals with ultrafast scintillation property were grown in LiI acetonitrile solvent through evaporation technique. The LiI exhibits unique properties to γ-CuI single crystal preparation. One is that it increases the solubility of CuI in the solvent, which gives rise to a largest-sized (23 × 14 × 2 mm3) single crystal with the high optical transmission (over 60%) in the wavelength region of 435–800 nm. The other feature is that it acts as an effective isoelectronic dopant and improves the molar ratio of copper to iodine, which greatly enhances the near-band-edge emissions (411 and 432 nm) and suppresses the broadband emission (680 nm). The decay time of the fast emission under pulsed X-ray excitation is shorter than 450 ps. The results will give a guidance for optimizing the properties of γ-CuI single crystal as an ultrafast scintillator.

A comparison of the thermal decomposition mechanism of wurtzite AlN and zinc blende AlN

The sublimation route is one of the primary and most significant methods for the synthesis of an aluminum nitride (AlN) single crystal. Its long synthesis time and high reaction temperature, however, limit the production of its commercial product. In this work, we applied HSC Chemistry 6 software, ab initio molecular dynamics, and X-ray diffraction to investigate the thermal decomposition of AlN. We calculated the decomposition temperatures of AlN under vacuum and simulated the decomposition mechanism of AlN by the ab initio molecular dynamics method. According to the thermodynamic calculations, the decomposition temperature of AlN decreased following a decrease in the system pressure. The ab initio molecular dynamics results indicated that wurtzite-type AlN (w-AlN) was decomposed by the layer-by-layer mechanism and followed a decomposition reaction equation of AlN → Al(g) + 0.29N2(g) + 0.42N(g), which originated from the inequality sp3 hybridization. The zinc-type AlN (z-AlN) decomposed from the surface to interior of the structure because of the equality of the sp3 hybridization, and the z-AlN decomposition reaction equation followed AlN → Al(g) + 0.5N2(g). The AlN decomposition experiments further verified that Al(g) was the product of the wurtzite-type AlN thermal decomposition. This work can provide valuable information for the preparation of the AlN single crystal.

Confined-solution process for high-quality CH3NH3PbBr3 single crystals with controllable morphologies

Solution processes have shown excellent potential for application to the growth of single-crystal materials. We have developed a confined-solution method for the preparation of single crystals with a controlled morphology. By confining the precursor solution within a micrometer-thick cavity and then controlling the saturation by adjusting the temperature gradient and fluid flow, high-quality CH3NH3PbBr3 single crystals with tunable morphologies could be obtained. The morphologies of the CH3NH3PbBr3 can be adjusted from sub-square centimeter-scale thin sheets that are square or rectangular, to one-dimensional wires with lengths in the order of centimeters, simply by changing the temperature. The thicknesses of the CH3NH3PbBr3 sheets could be adjusted from hundreds of nanometers to tens of microns. The CH3NH3PbBr3 sheets feature very clean surfaces with an atomic-scale roughness. This simple strategy provides a means of growing high-quality single crystals with clean surfaces, which realize high levels of performance when applied to devices. Open image in new window

Preparation of fine single crystals of magnetic superconductor RuSr2GdCu2O8−δ by partial melting

In this study, fine uniform RuSr2GdCu2O8−δ (RuGd-1212) single crystals have been successfully prepared by partial melting. Synthesis temperature could be lowered to a value not exceeding the decomposition temperature of RuGd-1212 using the Sr–Gd–Cu–O flux. The crystals grown by alumina boats are cubic, which coincides with the result of a previous study of RuGd-1212 single crystals using platinum crucibles. The single crystals were up to 15 × 15 × 15 µm3 in size and their lattice constants were consistent with those of polycrystalline samples reported previously. Although the present size of single crystals is not sufficient for measurements, the partial melting technique will be beneficial for future progress of research using RuGd-1212 single crystals. Appropriate nominal composition, sintering atmosphere, and temperature are essential factors for growing RuGd-1212 single crystals.

Seeded growth of boron arsenide single crystals with high thermal conductivity

Materials with high thermal conductivities are crucial to effectively cooling high-power-density electronic and optoelectronic devices. Recently, zinc-blende boron arsenide (BAs) has been predicted to have a very high thermal conductivity of over 2000 W m−1 K−1 at room temperature by first-principles calculations, rendering it a close competitor for diamond which holds the highest thermal conductivity among bulk materials. Experimental demonstration, however, has proved extremely challenging, especially in the preparation of large high quality single crystals. Although BAs crystals have been previously grown by chemical vapor transport (CVT), the growth process relies on spontaneous nucleation and results in small crystals with multiple grains and various defects. Here, we report a controllable CVT synthesis of large single BAs crystals (400–600 μm) by using carefully selected tiny BAs single crystals as seeds. We have obtained BAs single crystals with a thermal conductivity of 351 ± 21 W m−1 K−1 at room temperature, which is almost twice as conductive as previously reported BAs crystals. Further improvement along this direction is very likely.

Design and Development of Instrumentations for the Preparation of Platinum Single Crystals for Electrochemistry and Electrocatalysis Research Part 3: Final Treatment, Electrochemical Measurements, and Recommended Laboratory Practices

In this contribution, which is the final paper in a topic-focused series of three papers, we report on the development of experimental methodology that is applied to acquire cyclic voltammetry (CV) profiles for hemispherical Pt(111), Pt(110), and Pt(100) as well as polyoriented monocrystalline Pt electrodes. The paper describes an effective, multi-step procedure for cleaning of electrochemical and annealing glassware. The procedure comprises a four-step process for cleaning glassware and a three-step process for cleaning Viton and Teflon parts to minimize any contamination that can originate from these setup components. The contribution also outlines general laboratory practices that need to be followed in order to maintain clean conditions for conducting electrochemical experiments. The paper discusses a thermal treatment methodology that consists of two steps, namely flame-based annealing and induction-based annealing. The application of this approach produces reproducible, clean, defect-free, and atomically-ordered Pt surfaces. The complete procedure of Pt electrode annealing, cooling in a controlled atmosphere, protecting with a droplet of water, and transferring to an electrochemical cell allows one to conserve a metallic character of the electrode surface (it does not form any oxide during the transfer) while maintaining an atomic order. In addition, the paper describes the design and operation of a multi-component electrochemical workstation, which is employed in measurements on platinum electrochemistry and electrocatalysis. The paper presents and discusses the hanging meniscus configuration that is used to maintain an electrolytic contact between a monocrystalline Pt electrode and an aqueous electrolyte solution. Finally, the contribution presents CV profiles for hemispherical Pt(111), Pt(110), and Pt(100) as well as polyoriented, monocrystalline Pt electrodes, which are characteristics of high-quality electrodes and clean experimental conditions. These results validate the instrumentation described in the series of papers and the laboratory practices developed in the course of our research.