Liquid-phase Growth Research Articles

Phase control and growth of Y123 and Y124 crystals below 600 °C by molten KOH flux

Phase formation temperatures of YBa2Cu3O7−δ (Y123), YBa2Cu4O8 (Y124) and Y2Ba4Cu7O15 (Y247) in a system containing molten KOH have been studied with respect to partial oxygen pressure. At the low oxygen partial pressure of approximately 10−5–10−4atm, crystalline Y123 phase was generated at as low as 550°C with the superconducting transition temperature above 90K. In the air atmosphere, Y124 phase was formed below 600°C and Y123/Y124 phase boundary was observed approximately 775°C. At the oxygen pressure of 1atm, Y247 was formed between the regions of Y123 and Y124 formation. Phase formation relation among Y123, Y124 and Y247 is similar to that of the conventional system without KOH, however, phase boundary sifts toward lower temperature by 50–150°C in the KOH contained system. The morphology of the obtained crystals indicates that they grew by the liquid phase growth mode. The process with the molten KOH has a potential to fabricate superconducting liquid phase epitaxial films at very low temperatures below 600°C.

Laser-activated gold catalysts for liquid-phase growth of cadmium selenide nanowires.

A laser-activated-catalyst (LAC) technique was developed to grow CdSe nanowires in liquid medium at room temperature. The gold catalysts dispersed in the precursor solution were activated by a pulsed laser so as to decompose the precursor and catalyse the nanowire growth simultaneously. The LAC technique can achieve accurate positioning of nanowires, which is beneficial for device fabrication.

Thermoelectric Properties of Cu-Doped n-Type Bi2Te2.85Se0.15 Prepared by Liquid Phase Growth Using a Sliding Boat

N-type Bi2Te2.85Se0.15 thermoelectric materials were prepared by liquid phase growth (LPG) using a sliding boat, a simple and short fabrication process for Bi2Te3-related materials. Cu was selected as a donor dopant, and its effect on thermoelectric properties was investigated. Thick sheets and bars of CuxBi2 Te2.85Se0.15 (x=0–0.25) of 1–2mm in thickness were obtained using the process. X-ray diffraction patterns and scanning electron micrographs showed that the in-plane direction tended to correspond to the hexagonal c-plane, which is the preferred direction for thermoelectric conversion. Cu-doping was effective in controlling conduction type and carrier (electron) concentration. The conduction type was p-type for undoped Bi2Te2.85Se0.15 and became n-type after Cu-doping. The Hall carrier concentration was increased by Cu-doping. Small resistivity was achieved in Cu0.02Bi2Te2.85Se0.15 owing to an optimized amount of Cu-doping and high crystal orientation. As a result, the maximum power factor near 310K for Cu0.02Bi2Te2.85Se0.15 was approximately 4×10−3W/K2m and had good reproducibility. Furthermore, the thermal stability of Cu0.02Bi2Te2.85Se0.15 was also confirmed by thermal cycling measurements of electrical resistivity. Thus, n-type Bi2Te2.85Se0.15 with a large power factor was prepared using the present LPG process.

Ultrathin nickel hydroxide and oxide nanosheets: synthesis, characterizations and excellent supercapacitor performances.

High-quality ultrathin two-dimensional nanosheets of α-Ni(OH)2 are synthesized at large scale via microwave-assisted liquid-phase growth under low-temperature atmospheric conditions. After heat treatment, non-layered NiO nanosheets are obtained while maintaining their original frame structure. The well-defined and freestanding nanosheets exhibit a micron-sized planar area and ultrathin thickness (<2 nm), suggesting an ultrahigh surface atom ratio with unique surface and electronic structure. The ultrathin 2D nanostructure can make most atoms exposed outside with high activity thus facilitate the surface-dependent electrochemical reaction processes. The ultrathin α-Ni(OH)2 and NiO nanosheets exhibit enhanced supercapacitor performances. Particularly, the α-Ni(OH)2 nanosheets exhibit a maximum specific capacitance of 4172.5 F g−1 at a current density of 1 A g−1. Even at higher rate of 16 A g−1, the specific capacitance is still maintained at 2680 F g−1 with 98.5% retention after 2000 cycles. Even more important, we develop a facile and scalable method to produce high-quality ultrathin transition metal hydroxide and oxide nanosheets and make a possibility in commercial applications.

Liquid-phase growth of platinum nanoparticles on molybdenum trioxide nanosheets: an enhanced catalyst with intrinsic peroxidase-like catalytic activity.

A facile method for the synthesis of metal nanostructure-decorated two-dimensional (2D) semiconductor nanosheets was developed. The solution-processable molybdenum trioxide (MoO3) nanosheet was used as a template for direct liquid-phase growth of platinum nanoparticles (Pt NPs) under ambient conditions. Results show that the Pt NPs with sizes of 1-3 nm were uniformly grown on the MoO3 surface. Importantly, the Pt-MoO3 hybrid nanomaterial exhibits an enhanced peroxidase-like catalytic activity compared to the MoO3 nanosheet, Pt NPs, and their physical mixture under the same conditions. As a proof-of-concept application, the Pt-MoO3 hybrid nanomaterial was used as a high-efficiency peroxidase-mimic for ultrasensitive colorimetric detection of glucose in serum samples. This work provides a promising strategy for design and development of biomimetic catalysts by smart assembly of different dimensional nanomaterials.

Effect of predeformation on the transition from hexagonal phase to square phase near the melting point using phase field crystal method

The two-mode phase field crystal (PFC) method is used to calculate the phase diagram. And in this paper it is used to simulate the effects of predeformation degree and isothermal temperature on the hexagonal grain boundary evolution and on the hexagonal/square phase transition. Results show that when there is no predeformation in the initial phase, the grain boundary defect causes the pre-melting around the melting point; predeformation increases and the interaction between deformation and defects induces the pre-melting around the melting point; and the predeformation further increases, deformation induces liquid phase and square phase simultaneously at the distortion place. The bigger the predeformation and the closer to melting point the maintained temperature, the more obvious the growth of liquid phase is; on the contrary, the square phase grows obviously. The distortion energy is released with time and the phase of grain finally becomes square phase. It can be concluded that keeping the hexagonal phase isothermal near the melting temperature, the liquid phase appears at the grain boundary or at the other defects because the predeformation leads to the increase of atom activity, thus increasing atom disorder degree. Then with the release of distortion energy, the grain phase finally transforms into an equilibrium square phase. In this way the hexagonal/square transition time is extended.

Liquid phase growth of bulk GaSe crystal implemented with the temperature difference method under controlled vapor pressure

GaSe crystal has been expected as one of the promising nonlinear optical crystals for highly efficient terahertz (THz) wave generation. However there are several reasons why it is difficult to grow the bulk crystals with high quality. To overcome some difficulties, the temperature difference method under controlled vapor pressure (TDM-CVP) is applied for crystal growth. According to this method, stoichiometric composition can be controlled by the application of Se vapor during crystal growth. Crystal growth is carried out at a constant growth temperature without any mechanical disturbance or vibration. It is also noticed that lower temperature growth enables the reduction of point defect concentration in equilibrium. In this article, surface morphology is observed by an optical microscope using the Nomarski interference method. To identify polytypes of grown crystals, backscattered Raman spectra were measured. X-ray diffraction confirmed the polytypes and single crystalline phase. Infrared (λ=1μm) and terahertz wave (1–3THz) transmittance measurements were performed to calculate the absorption coefficient in these wavelength regions. From these results, it is shown that the grown crystals have shown ε-type single phase and the absorption coefficients of grown crystals have been improved according to the increase of applied Se vapor pressure during crystal growth.

Preparation of Microporous Silicone Rubber Membrane with Tunable Pore Size via Solvent Evaporation-Induced Phase Separation

Silicone rubber membrane with ordered micropores in the surface was prepared by means of the solvent evaporation-induced phase separation. A ternary solution including liquid silicone rubber precursor, liquid paraffin, and hexane was cast to form a film with a two-phase structure after the hexane was evaporated. The micropores were generated by removing liquid paraffin phase in the cured silicone rubber film. The effects of the liquid paraffin concentration, casting temperature, initial casting solution thickness, air circulation, and addition of surfactant Span-80 on the pore structure in the membrane surface were investigated. The average pore size increases with increasing liquid paraffin concentration or the initial casting solution thickness. The formation of pore structure in the membrane surface is related to the phase separation and thus the phase separation process of the casting solution surface was in situ observed using the digital microscope. The formation mechanism of pore is attributed to a nucleation, growth, and coalescence process of liquid paraffin phase in the membrane surface.

Thermoelectric Properties of Bi0.5Sb1.5Te3 Prepared by Liquid-Phase Growth Using a Sliding Boat

A liquid-phase growth process using a graphite sliding boat was applied for synthesis of p-type Bi0.5Sb1.5Te3. The process lasted only 60 min, including rapid heating for melting, boat-sliding, and cooling. Thick sheets and bars of 1 mm and 2 mm in thickness having preferable crystal orientation for thermoelectric conversion were successfully prepared by the process. Control of carrier concentration was attempted through addition of excess tellurium (1 mass% to 10 mass%) to optimize the thermoelectric properties of the material. The Hall carrier concentration was found to be decreased by addition of excess tellurium. The electrical resistivity and Seebeck coefficient varied depending on the carrier concentration. As a result, the maximum observed power factor near 300 K was 4.4 × 10−3 W/K2m, with corresponding Hall carrier concentration of 4.6 × 1025 m−3. Thus, thermoelectric properties were controllable by addition of excess tellurium, and a large power factor was thus obtained through a simple and short process.

Processes in phase boundary region during liquid phase growth

AbstractThe behavior of components within the phase boundary region during liquid phase growth is the subject of the present article. Based on the supposition that the phase boundary is a structured region, repeating the periodicity of the substrate, the distribution of different components within the phase boundary is considered. Assuming that the value of the supersaturation at the upper end of the phase boundary defines the growth rate of the compound, a relation has been derived, concerning the extension of the phase boundary. The case of liquid phase epitaxial growth of GaAs is considered and an effort for evaluation of the phase boundary extension is undertaken. The linear dependence of the stationary growth rate on the cooling rate, predicted previously, is proved experimentally.

Effect of Coke Breeze Addition Timing on Sintering Operation

For the purpose of reducing specific coke breeze consumption, we examined the influence which the morphology of coke breeze and pseudo-particles structure have on sintering quality. As a means to control the morphology of coke breeze in pseudo-particles, we delayed the timing of coke breeze addition in granulation process of sintering materials. As a result, when we added more coke breeze in the latter stage of granulation, we noticed that granulating property as well as permeability were improved. Also, much of coke breeze stayed on the surface layer of pseudo-particles or in free particle, which led to improved quality and burn through speed (abbreviated as BTS).When we added the entire charge of coke breeze in the latter stage, combustion quality of coke breeze was improved. However, conduction and accumulation of heat turned down, which resulted in deteriorating yield due to the exhaust heat loss.Therefore, we searched for a ratio of the second-stage addition favorable for improving yield by making a higher raw material bed.With the second-stage addition at 50%, we were able to build a higher raw material bed through improvement in sinter quality and permeability, while maintaining good BTS. As a result, expanded area in the sintering bed with temperature at 1200°C or higher led to liquid phase growth, which finally enabled the reduction in coke breeze consumption without causing deterioration in both yield and shutter index.

Amorphization of silicon induced by nanodroplet impact: A molecular dynamics study

The hypervelocity impact of electrosprayed nanodroplets on crystalline silicon produces an amorphous layer with a thickness comparable to the droplet diameters. The phase transition is puzzling considering that amorphization has not been observed in macroscopic shock compression of silicon, the only apparent difference being the several orders of magnitude disparity between the sizes of the macroscopic and nanodroplet projectiles. This article investigates the physics of the amorphization by modeling the impact of a nanodrop on single-crystal silicon via molecular dynamics. The simulation shows that the amorphization results from the heating and subsequent melting of a thin layer of silicon surrounding the impact area, followed by an ultrafast quenching with cooling rates surpassing 1013 K/s. These conditions impede crystalline growth in the supercooled liquid phase, which finally undergoes a glass transition to render a disordered solid phase. The high temperature field near the impact interface is a localized effect. The significantly different temperatures and cooling rates near the surface and in the bulk explain why amorphization occurs in nanodroplet impact, while it is absent in macroscopic shock compression. Since these high temperatures and ultrafast quenching rates are likely to occur in other materials, nanodroplet impact may become a general amorphatization technique for treating the surfaces of most crystalline substrates.

Liquid phase growth of graphene on silicon carbide

We developed a novel method to produce graphene on silicon carbide (SiC) at a temperature as low as 1000°C. The method is based on liquid phase growth (LPG) of graphene mediated by liquid gallium, which acts not only as a flux to store carbon dissolved from a surface of SiC when heated, but also as a catalyst to promote the formation of graphene on SiC when cooled. Our experimental results revealed that gallium-treated SiC substrates are coated with uniform and continuous graphene films. The LPG method is able to supply graphene films consisting of one to several hundreds of layers, depending on heating temperatures. Our approach can not only provide an alternative way to form graphene natively on SiC, but will also bring a technological breakthrough in industrial applications of graphene, e.g. the realization of graphene-on-insulator substrates.

Complete Response to EPOCH in a Patient With HIV and Extracavitary Primary Effusion Lymphoma Involving the Colon: A Case Report and Review of Literature

Introduction Primary effusion lymphoma (PEL) is a rare malignancy that accounts for 5% of HIV-related non-Hodgkin lymphoma (NHL). It usually presents as a lymphomatous growth in liquid phase within various body cavities such as the pleural, pericardial, and peritoneal spaces. Although extracavitary tumors can occur in PEL, they do so rarely but may be histologically indistinguishable from PEL. PEL s also defined by the expression of Kaposi sarcoma–associated heresvirus (KSHV) (also known as human herpesvirus 8 [HHV8]) in

Growth mechanism during selective epitaxy of p-doped SiC using VLS transport

ABSTRACTSince a few years, VLS transport is studied not only for homoepitaxial SiC growth but also for SiC selective epitaxial growth (SEG). In this approach, a stacking of silicon and aluminum layers is deposited on the substrate and patterns are created by photolithography. Upon melting, the Al-Si liquid droplets are fed by propane to obtain the SEG of p-doped SiC. In this work, the growth mechanisms were deeper investigated, in particular the influence of the carrier gas (H2 or Ar) and the growth temperature. SEG experiments showed higher growth rates than those measured in the standard configuration (nonselective growth). Moreover, the SiC layers exhibited step-bunched areas characteristic of liquid phase growth but also areas with morphological features due to a disruption of the step-bunching growth mode.

N incorporation and photoluminescence in In-rich InGaAsN grown on InAs by liquid phase epitaxy

Dilute nitride InGaAsN layers with high In content have been grown on InAs substrates by liquid phase epitaxy using GaN as a precursor for N in the growth solution. Photoluminescence (PL) was obtained in the mid-infrared spectral range at temperatures between 4 and 300 K. Although Ga increases the InAs bandgap, the strong band anti-crossing effect from the N incorporation resulted in an overall bandgap reduction of 11 meV compared with InAs. The temperature-dependent PL exhibited a complicated behaviour and showed an anomalous increase in intensity from 190 K to room temperature. This was due to the formation in a complex defect which behaves as a non-radiative recombination centre and prevents radiative band–band recombination at temperatures <190 K. Above this temperature the PL increases as band–band transitions become allowed. The formation of this defect requires the presence of both Ga and N and becomes de-activated after a high-temperature anneal. Raman spectroscopy confirmed the presence of phonon modes associated with In–N and Ga–N bonds confirming the incorporation of N using liquid phase growth.

Formation of Bi4Ti3O12 One-Dimensional Structures by Solid-State Reactive Diffusion. From Core−Shell Templates to Nanorods and Nanotubes

One-dimensional nanostructures are usually fabricated using liquid-phase chemical methods or growth from the vapor phase. A different approach is proposed in this investigation. Using two different kinds of reactive templates with core−shell structure obtained using colloidal chemistry methods, we fabricated for the first time Bi4Ti3O12 nanorods and nanotubes by means of solid-state reactions. The intimate contact of the parent compounds in the core−shell template resulted in low reaction temperatures (500−600 °C), overcoming the morphological instability problem of one-dimensional (1D) templates. As the formation of bismuth titanate is dominated by the coupled ambipolar diffusion of Bi3+ and O2− ions through the titanate layer, the final morphology, nanorod or nanotube, is determined by the relative arrangement of the parent compounds in the core−shell template. When the bismuth precursor is located in the shell region and the core is a single-crystal TiO2 nanowire, formation of a single-crystal Bi4Ti3O12 nanorod occurs by a topochemical reaction. Opposite, when the shell corresponds to nanocrystalline TiO2 and the core to the bismuth precursor, the reaction leads to a porous nanorod or a nanotube depending on the template thickness. The development of the central cavity is ascribed to the coalescence of Kirkendall porosity and the effect of mechanical stresses accumulated during the reaction. The present results indicate that a careful control of the solid-state reactions at the nanoscale can be achieved by means of reactive templates with core−shell structure thus providing an effective tool for the design and the large-scale fabrication of a variety of nano-objects with different dimensionalities.

Fundamental study for solvent growth of silicon carbide utilizing Fe-Si melt

Fe-Si melt is a candidate for use as an alloy solvent for rapid liquid phase growth of SiC because of the high solubility of carbon in molten iron. In this work, the equilibrium phase relationship between SiC and the liquid phase of the Fe-Si-C system was investigated at 1523 K by the phase equilibration technique, and was further studied with the thermodynamic calculation. It was found that Fe- 36 mol% Si melt equilibrates with SiC at the temperature and possesses the higher carbon solubility than silicon-based melt. The first trial of the SiC crystal growth experiment was then carried out with Fe- 36 mol% Si melt by means of temperature difference method, and formation of SiC layer was obtained on the graphite substrate. Accordingly, it was found possibility for rapid growth of SiC by the solvent growth method with Fe- 36 mol% Si melt.

Equilibrium Phase Relationship between SiC and a Liquid Phase in the Fe-Si-C System at 1523&amp;ndash;1723 K

Fe-Si melt is a candidate for use as an alloy solvent for rapid liquid phase growth of SiC because of the high solubility of carbon in molten iron. In this work, the equilibrium phase relationship between SiC and the liquid phase of the Fe-Si-C system was studied to determine the optimal composition of a high SiC content solvent. The solubility of carbon in molten silicon was examined and the thermodynamic properties of the liquid phase in the Si-C system were reassessed. The phase relationship between SiC and Fe-Si melt was investigated by the equilibration technique at 1523–1723 K. It was found that Fe-36 mol% Si alloy equilibrates with SiC at the corresponding temperatures. The equilibrium phase relationship between SiC and various compositions of Fe-Si melts was studied by using thermodynamic calculations. The results indicated that SiC is far more soluble in iron-rich Fe-Si melt than in silicon-rich melt. The Fe-Si melt of Fe-36 mol% Si composition possessing high SiC solubility should be a suitable solvent for rapid liquid phase growth of SiC. [doi:10.2320/matertrans.MRA2008404]

Mechanisms of Grain Size Evolution during Aluminum Spray Forming

A numerical approach is implemented to analyze the evolution of grain size during spray forming of 5083 Al. The evolution of grain size is investigated at two different thicknesses corresponding to 400 °C and 602 °C on the deposited material’s surface. Nucleation behavior and nuclei growth in individual droplets are computed during the flight and deposition stages. Based on the measured temperature history, nuclei coarsening during slow solidification of remaining liquid phase and grain growth during solid-state cooling are analyzed in detail. The calculated results indicate bimodal and relatively uniform grain morphology corresponding to the deposited material’s surfaces with 400 °C and 602 °C, respectively.