Liquid-phase Growth Research Articles

Observing Growth and Dissolution of Cuprous By Liquid Cell TEM

Metal oxides has attracted great attention due to the widely applications, which are commonly used in semiconductor industry due to their excellent physical and chemical properties. Also, it exhibits variety of structures. Among various metal oxides, cuprous (Cu2O, copper (I) oxide) is regarded as one of the most promising materials. It is cheap, earth-abundant, and nontoxic; therefore, it can be applied in catalysis, sensor, solar cell and p-type semiconductor. However, the redox reaction of cuprous is still uncertain, which strongly influent its size, morphology, and nanostructure. In this work, the growth and dissolution of cuprous were observed via in situ liquid cell transmission electron microscopy (TEM). The study of cuprous nanoparticles formation, such as kinetics analysis, nucleation, growth, and reduction reaction in liquid phase can be achieved. In the cuprous growth, dendrite shape agglomeration dispersed everywhere inside the chip at the beginning. Few minutes later, the accumulation of copper ions resulted in a rapidly growth of cuprous nanostructures. The results indicated that the electron beam reduced the precursor which led the copper ions transfer into copper (I) oxide. Whereas in the cuprous dissolution, the cubic shape dissolved in specific {100} planes, and finally fully disappeared. The dissolution is resulted from the higher dose of electron exposure, the radiation-damage-caused vacancies accumulated and formed porous checkerboard-like nanostructure. The growth/dissolution results were systemically analyzed through the viewpoint of kinetics and dynamics. The direct observation of the dynamic process sheds light on the preparation of metal oxide by redox reaction method and extends the study of reaction kinetics. Figure 1

One-pot size-controlled growth of graphene-encapsulated germanium nanocrystals

To realize graphene-encapsulated semiconductor nanocrystals (NCs), an additional graphene coating process, which causes shape destruction and chemical contamination, has so far been inevitable. We report herein one-pot growth of uniform graphene-germanium core–shell nanocrystals (Ge@G NCs) in gram scale by the addition of methane as a carbon source during the thermal pyrolysis of germane. The methane plays a critical role in the growth of the graphene shell, as well as in the determination of the nucleation density and diameter of the NCs, similar to a surfactant in the liquid-phase growth of monodisperse NCs. By adjusting the gas ratio of precursors, a mixture of germane and methane, we can control the size of the Ge@G NCs in the range of ∼5–180 nm. The Ge@G NCs were characterized by various microscopic and spectroscopic tools, which indicated that the Ge core is single crystalline, and is completely covered by the graphene shell. We further investigated the merits of the graphene shell, which can enhance the electrical conductivity of nanocrystalline materials.

Lightly doped n-type tensile-strained single-crystalline GeSn-on-insulator structures formed by lateral liquid-phase crystallization

A tensile-strained single-crystalline n-type GeSn-on-insulator structure was demonstrated by lateral liquid-phase crystallization of an Sb-doped GeSn layer, and the diffusion and activation behaviors of Sb atoms in a liquid-phase-grown GeSn wire were investigated. A photoluminescence-based study revealed that a substantial amount of Sb was swept out during the liquid-phase growth of the GeSn wire. A thin-film transistor based on an Sb-doped GeSn wire on a quartz substrate exhibited n-channel accumulation-mode operation, and the temperature dependence of field-effect mobility revealed that the single-crystalline GeSn wire is a lightly doped n-type (∼1017 cm−3). The combination of Sb-doped n-type and undoped p-type GeSn wires would be an ideal platform for GeSn-based optoelectronic integration.

Brine formation via deliquescence by salts found near Don Juan Pond, Antarctica: Laboratory experiments and field observational results

The observed darkening of water tracks near Don Juan Pond (DJP) as well as the formation of wet patches elsewhere in the McMurdo Dry Valleys is attributed at least partially to deliquescence, a process by which salts absorb atmospheric water vapor and form brine, coupled with liquid-phase growth when the atmospheric relative humidity exceeds the water activity. Here we perform laboratory experiments to investigate the temperature and relative humidity conditions necessary for deliquescence to occur in calcium chloride-rich sediments collected from the DJP watershed. We use a Raman microscope equipped with an environmental cell to study both deliquescence and efflorescence (recrystallization) of the soluble salt component of DJP soils between −30 and +15 °C. In this temperature range, we find that the soluble salt component of the DJP sediments begins to deliquesce between 19 and 46% RH, slightly higher than the deliquescence relative humidity of the primary pure component, calcium chloride. We find a limited hysteresis between deliquescence and efflorescence, but much greater supersaturation of the salt brine can occur at temperatures above 0 °C. The relative humidity conditions were varied either slowly (over ∼8 h) to observe near-equilibrium phases or rapidly (over <1 h) to better mimic Antarctic conditions and no differences in deliquescence relative humidity or efflorescence relative humidity were noted. The results of this work can help predict when deliquescence could be actively occurring in the soils near Don Juan Pond and explain darkening of the salt pan after a high humidity period. In tandem with field data, our experimental results suggest that brines can be generated near Don Juan Pond via deliquescence frequently during the southern summer and autumn. Additionally, the soluble salts may persist in the aqueous phase continuously for several months during the southern summer. This work also suggests that salt deliquescence could be impacting the year-round hydrological cycle of the DJP watershed. Steep-sloped water tracks found near DJP have been suggested as a terrestrial analog for recurring slope lineae on Mars, for which salt deliquescence is a proposed formation mechanism. Therefore, understanding the formation of deliquescent brines in a hyper-arid region on Earth may have relevance to Mars.

Liquid phase growth of GaSe1−xTex mixed crystals by temperature difference method under controlled vapor pressure

GaSe crystal is one of a group of nonlinear optical (NLO) crystals expected to be utilized as a highly efficient generators of terahertz waves. However, GaSe has some drawbacks that limit it from further application. Firstly, it has poor crystallinity and, secondly, the layers are prone to exfoliation. In this work, crystal growth was carried out at a constant low temperature under a controlled Se vapor pressure to improve the crystallinity. In addition, Te was added in order to grow mixed crystals to improve the bonding forces between the layers. X-ray fluorescence was used to measure the Te composition in the grown crystals. Red shifts of the excitation peaks were found from photoluminescence with increasing Te composition, indicating that mixed crystals were successfully grown. The lattice constant, c, was calculated from the results of X-ray diffraction and was shown to have an almost linear dependence on Te composition.

Electrical property and structural analysis of amphoteric impurity Ge doped GaSe crystal grown by liquid phase growth

In order to improve conversion efficiency of THz wave generation, Germanium (Ge)-doped gallium selenide (GaSe) single crystals have been grown by Temperature Difference Method under Controlled Vapor Pressure (TDM-CVP). In this article, electrical property and lattice constant of Ge doped GaSe (GaSe:Ge) crystal are compared with that of not-intentionally doped GaSe crystal. Compared with non-doped GaSe crystal, carrier concentration p was decreased by Ge-doping (not-intentionally doped GaSe p=3.2×1015cm−3 at 255K, GaSe:Ge p=4.9×1014cm−3 at 255K). In addition, it has been confirmed that lattice constant of GaSe crystal increased with doping Ge concentration increased.

Templated assembly of metal nanoparticle films on polymer substrates

We report on directed self-assembly of ordered, vapor-deposited gallium nanoparticles on surface-relief-structured polymer substrates. Grating templates impose periodic order in one dimension, most effectively when the grating half-period is of the order of the mean unperturbed center-to-center particle spacing for a given mass-thickness of Ga. Self-organized order also emerges in the perpendicular direction as a consequence of the liquid-phase particles' nucleation, growth, and coalescence on the ridges of the grating pattern in relative isolation from the adjacent slots, and vice versa.

Transition metal doping of GaSe implemented with low temperature liquid phase growth

Our group works on improving the conversion efficiencies of terahertz (THz) wave generation using GaSe crystals. The operating principle is based on difference frequency generation (DFG) which has the advantages such as high output power, a single tunable frequency, and room temperature operation. In this study, GaSe crystals were grown by the temperature difference method under controlled vapor pressure (TDM-CVP). It is a liquid phase growth method with temperature 300°C lower than that of the Bridgman method. Using this method, the point defects concentration is decreased and the polytype can be controlled. The transition metal Ti was used to dope the GaSe in order to suppress free carrier absorption in the low frequency THz region. As a result, a deep acceptor level of 38meV was confirmed as being formed in GaSe with 1.4at% Ti doping. Compared with undoped GaSe, a decrease in carrier concentration (~1014cm−3) at room temperature was also confirmed. THz wave transmittance measurements reveal the tendency for the absorption coefficient to increase as the amount of dopant is increased. It is expected that there is an optimum amount of dopant.

Liquid-phase growth of few-layered graphene on sapphire substrates using SiC micropowder source

We demonstrated direct synthesis of graphene films consisting of a few layers (few-layered graphene) on sapphire substrates by liquid-phase growth (LPG), using liquid Ga as the melt and SiC micropowder as the source material. When the dissolution temperature was above 700°C, almost all Si atoms of SiC diffused into the Ga melt and only carbon atoms remained at the interface beneath the liquid Ga. Above 800°C, X-ray photoelectron spectra showed that most of the remaining carbon was graphitized. When the dissolution temperature was 1000°C, Raman spectra showed that few-layered graphene films grew on the sapphire substrates.

Ferronickel particle formation during the carbothermic reduction of a limonitic laterite ore

Attempts to economically extract nickel from the nickeliferous laterite ores face a number of challenges, including a limited ability to beneficiate the ore prior to processing. One method to address this issue would be to reduce the ore at moderate temperatures to form a ferronickel alloy, which could then be selectively recovered to form a nickel concentrate. The current work explores the effects of varying coal, elemental sulphur and pyrite additions and temperatures in the range of 1000–1200°C on the formation of ferronickel alloy particles in a limonitic ore. It was observed that a small sulphur addition (⩽4%) yielded a significant increase in the average size of the ferronickel particles formed during reduction. A decrease in the average nickel grade of the ferronickel particles, resulting from the increased metallization of iron, was also observed in the presence of sulphur. The ferronickel particle morphology and distribution of sulphur in the reduced ore are consistent with a liquid-phase growth mechanism driven by the FeFeS eutectic at 988°C.

Top Seeded Solution Growth of 4H-SiC Bulk Crystal Using Graphite Block for Long-Term Growth

Solution growth method of SiC is assumed to be a promising technique to grow high quality SiC bulk crystal. Solution growth of SiC are based on the liquid phase growth from an incongruent melt composed of Si and C. Among various solution growth techniques, top seeded solution growth (TSSG) method for SiC has been widely studied for a next generation SiC growing technique. In TSSG method, the crystal growth on seed crystals is accomplished by the precipitation of solid SiC from C dissolved a Si melt on a seed crystal located at the top of the liquid. Because of the low solubility of C in liquid Si, SiC crystal growth on seed crystals using TSSG involves the use of a Si-rich Si-C solution. Therefore, in the TSSG method, high C solubility is required to increase the growth rate of SiC. Hence, there have been lots of studies how to increase the C solubility of Si melt. Eventually, several metallic solvents were proved to enhance the carbon solubility, so that the growth rate of SiC using TSSG were remarkably increased up to 2 mm/h. So, it is very optimistic to increase the thickness of grown crystal. However, TSSG has critical issue to increase crystal thickness because the C is supplied from the graphite crucible which is also the reservoir of Si melt. As growing time goes, therefore, the crucible will be dissolved to Si melt and the dissolved carbon will be consumed to grow single crystalline SiC crystal. Eventually, the thickness of SiC grown layer will be limited the volume size of graphite crucible. The reduction of graphite crucible will bring about the change of temperature distribution in the solid and liquid inside the reactor. Mechanical failure during crystal growth could be happened. Therefore, in this study, we applied a graphite block inside graphite crucible for elongate the growing time limit using graphite crucible for TSSG. Several graphite blocks with different design and materials properties were evaluated using finite element analysis using COMSOL multiphysics. The simulated results were then applied to the real experimental growth using small seed samples. Finally, the durability of graphite crucible and the crystal quality were comparatively evaluated with and without graphite blocks using several characterizations techniques.

Using priority growth orientation of crystallite of the Monte Carlo method to study the process of crystal nucleation and growth in liquid phase

The technique of “crystallite growth preferred orientation” was presented based on the Monte Carlo (MC) simulations of grain growth, and its factor was used to establish a lattice coordinate tracking method. The nucleation and growth of crystal from the liquid phase throughout the whole simulation were examined. Changes in solid fraction and crystallite size were counted via simulation by lattice tracking. Results showed that the established model could properly reflect crystallite nucleation and growth. The model was also determined capable of accurately estimating the number of solid phase fraction and achieving change in crystallite size by the lattice tracking method. The change in solid fraction and MC step (MCS) satisfied the [Formula: see text] curve during simulation. The crystallite growth index was 0.477, which was relatively close to the theoretical value of 0.5.

Assessment of solid state and liquid phase sintering models by comparison of isothermal densification kinetics in W and W-Cu systems

The role of liquid phase and grain growth during the intermediate stage of sintering is investigated by comparing the isothermal densification rate of the tungsten skeleton in two systems: solid-state sintered W and liquid-phase sintered W-10wt%Cu. Densification curves at 1380 °C, i.e. well after completion of capillary rearrangement in W-Cu, are confronted to the predictions of a model that considers a single representative grain size with quasi-equilibrium interfaces and a monotonic increase in grain size and coordination with density. In both systems, the densification mechanism is taken to be governed by W diffusion along grain boundaries. For system W-Cu, a phenomenological law is proposed to allow accounting for the decrease in liquid surface curvature during funicular filling of the pores by the liquid-phase. The kinetics of grain growth is described via current literature model. Good agreement is demonstrated between experimental measurements and model predictions when relying on material parameter values given in literature. In system W-Cu, the detrimental effect of the decrease in dihedral angle is, at the beginning of the funicular stage, compensated by the contribution to sintering stress brought about by the concave curvature of liquid/vapour interface. The sensitivity of computational results to model hypotheses and material parameters is assessed. The most influential parameters are diffusivities along W grain boundaries and along W/vapour and W/Cu interfaces.

Artemisinin production by plant hairy root cultures in gas- and liquid-phase bioreactors.

Alternative biotechnological protocol for large-scale artemisinin production was established. It featured enhanced growth and artemisinin production by cultivation of hairy roots in nutrient mist bioreactor (NMB) coupled with novel cultivation strategies. Artemisinin is used for the treatment of cerebral malaria. Presently, its main source is from seasonal plant Artemisia annua. This study featured investigation of growth and artemisinin production by A. annua hairy roots (induced by Agrobacterium rhizogenes-mediated genetic transformation of explants) in three bioreactor configurations-bubble column reactor, NMB and modified NMB particularly to establish their suitability for commercial production. It was observed that cultivation of hairy roots in a non-stirred bubble column reactor exhibited a biomass accumulation of 5.68 g/l only while batch cultivation in a custom-made NMB exhibited a higher biomass concentration of 8.52 g/l but relatively lower artemisinin accumulation of 0.22 mg/g was observed in this reactor. A mixture of submerged liquid-phase growth (for 5 days) followed by gas-phase cultivation in nutrient mist reactor operation strategy (for next 15 days) was adopted for hairy root cultivation in this investigation. Reasonably, high (23.02 g/l) final dry weight along with the artemisinin accumulation (1.12 mg/g, equivalent to 25.78 mg/l artemisinin) was obtained in this bioreactor, which is the highest reported artemisinin yield in the gas-phase NMB cultivation.

Optimization of the Homogenization Heat Treatment of Nickel-Based Superalloys Based on Phase-Field Simulations: Numerical Methods and Experimental Validation

A method for predicting the fastest possible homogenization treatment of the as-cast microstructure of nickel-based superalloys is presented and compared with experimental results for the single-crystal superalloy ERBO/1. The computational prediction method is based on phase-field simulations. Experimentally determined compositional fields of the as-cast microstructure from microprobe measurements are being used as input data. The software program MICRESS is employed to account for multicomponent diffusion, dissolution of the eutectic phases, nucleation, and growth of liquid phase (incipient melting). The optimization itself is performed using an iterative algorithm that increases the temperature in such a way that the microstructural state is always very close to the incipient melting limit. Maps are derived allowing describing the dissolution of primary γ/γ′-islands and the elimination of residual segregation with respect to temperature and time.

Microstructure and magnetic properties of low-temperature-fired NiCuZn ferrites with SiO2–CaO–Na2O–K2O glass

The low-temperature-fired NiCuZn ferrites with SiO2–CaO–Na2O–K2O (SCNK) glass additives are prepared by the conventional solid-state reaction method. The effects of SCNK glass additives on sintering behavior, microstructures and magnetic properties of NiCuZn ferrites are also investigated. Results show that SCNK glass additives overtly improve the densification of samples through the formation of liquid phase and grains growth promotion. The appropriate SCNK glass additives not only can noticeably increase the initial permeability (μi) and saturation flux density (Bs), but also can obviously reduce the remanent flux density (Br) and coercive filed strength (Hc). However, too much glass additives will deteriorate the magnetic properties. In summary, 0.2 wt% SCNK glass added in NiCuZn ferrite shows excellent magnetic properties: μi = 648.18 (100 kHz), Bs = 166.21 mT, Br = 83.57 mT and Hc = 39.38 A m−1.

Low power optical limiting studies on nanocrystalline benzimidazole thin films prepared by modified liquid phase growth technique

In the present work, benzimidazole (BMZ), a well known nonlinear optical material, thin films were deposited using the modified liquid phase growth technique at different solution temperatures. The prepared samples were subjected to spectral, structural and surface analyses. Linear optical properties and third-order optical nonlinearity of the deposited BMZ thin films were analysed using UV–visible–NIR spectrum and Z-scan technique, respectively. The experimental results show that the BMZ films exhibit reverse saturable absorption and positive nonlinearity at 650 nm CW laser of power 5 mW. The measured third-order nonlinear susceptibility of the films is about 10−10 esu. Optical limiting studies were performed using the same laser source and the potentiality of the BMZ films is reported.

Detached Melt Nucleation during Diffusion Brazing of a Technical Ni-based Superalloy: A Phase-Field Study

Advanced solidification processes like welding, soldering, and brazing are often characterized by their specific solidification conditions. But they also may include different types of melting processes which themselves are strongly influenced by the initial microstructures and compositions of the applied materials and therefore are decisive for the final quality and mechanical properties of the joint. Such melting processes are often not well- understood because - compared to other fields of solidification science - relatively little research has been done on melting by now. Also, regarding microstructure simulation, melting has been strongly neglected in the past, although this process is substantially different from solidification due to the reversed diffusivities of the involved phases. In this paper we present phase-field simulations showing melting, solidification and precipitation of intermetallic phases during diffusion brazing of directionally solidified and heat-treated high-alloyed Ni- based gas turbine blade material using different boron containing braze alloys. Contrary to the common belief, melting of the base material is not always planar and can be further accompanied by detached nucleation and growth of a second liquid phase inside the base material leading to polycrystalline morphologies of the joint after solidification. These findings are consistent with results from brazed laboratory samples, which were characterized by EDX and optical microscopy, and can be explained in terms of specific alloy thermodynamics and inter-diffusion kinetics. Consequences of the gained new understanding for brazing of high- alloyed materials are discussed.

Freeze enrichment protocol based on voltammetric probing of liquid-phase growth in frozen aqueous electrolyte solutions.

Voltammetry of the reversible redox couple, Fe(CN)6(4-)/Fe(CN)6(3-), using a microdisc electrode, is employed to probe the dynamic process of the growth of the liquid phase (LP) in frozen aqueous NaCl solutions. Critical factors are the temperature history of a frozen sample and a freeze-concentration ratio. When the temperature is directly set to the working temperature after freezing at -25.0 °C, CV measurements are often impossible at high concentration ratios. Even if measurements are possible, the shapes of the CVs and the currents change with time over 3 h. Combined measurements of CV and chronoamperometry clearly indicate that the growth of the LP near the working electrode is responsible for these phenomena. The development of an LP along the electrode surface leads to a change in the shape of the CV due to an increase in the contribution from the radial diffusion. When the LP mainly grows orthogonal to the electrode surface, the peak-shaped CV representing linear diffusion is maintained over several hours. In contrast, when the temperature of a frozen sample increases up to -2.0 °C for annealing, reproducible cyclic voltammograms (CVs) are always measured at temperatures higher than -18 °C. This procedure allows us to handle frozen solutions as a deterministic system rather than a stochastic one. The present results strongly suggest that annealing of frozen samples is critical for successful uses of the freeze enrichment of trace solutes. Up to 1000-fold enrichments for voltammetric measurements are demonstrated by the proposed procedure involving an annealing step.

Solid–Liquid Diffusion and Phase Growth Kinetics in Mg-Ca Binary System

The solid–liquid diffusion between Mg and Mg-10 at.% Ca alloy was studied at a temperature range of 570°C to 630°C for 10, 20, 30min, respectively. Only one compound, Mg2Ca, was observed in the diffusion couples. As the diffusion time increased, the dendritic structure of the diffusion layer became coarser. The thickness of the diffusion layer had an exponential relation to the experimental temperature. The Mg2Ca phase was observed to follow parabolic growth with diffusion time, which suggested that the growth of the Mg2Ca phase was controlled by diffusion mechanism. The activation energy was determined to be 111.28 kJ/mol.