Crystalline Growth Research Articles

Revisiting scaling of calcium sulfate in membrane distillation: Uncertainty of crystal-membrane interactions

Scaling of calcium sulfate (CaSO4) is a stumbling block to the development of membrane distillation (MD), which holds promise for the treatment of saline water/wastewater. Despite increasing efforts made to understand the scaling behavior of CaSO4 in a process of MD and thereby develop strategies for mitigating the negative effects, considerable uncertainty remains about occurrence of the wetting and structural damage that could result from the strong crystal-membrane interactions. This study combined experimental and theoretical approaches to corroborate that a higher degree of supersaturation could be achieved by concentrating the CaSO4 in the feed at a faster rate; the elevated supersaturation would be in favor of exerting substantially high crystallization pressure on the membrane structures. In particular, the theoretical analysis established two dimensionless groups for measuring the relative importance of the concentration effect and quantifying the essential role played by the crystalline growth, respectively. In addition to alleviating the uncertainty, this study would be beneficial to the design of MD processes with improved scaling resistance.

In-situ electrodeposited Ag/Cu for electrochemical reduction of acetic acid to nanodiamond under ambient conditions

Carbon nanostructured materials such as nanodiamonds and graphene are useful for various applications, but their low-energy production technologies remain an important challenge to overcome. Herein, the electrochemical reduction of acetic acid using in-situ electrodeposited Ag/Cu to nanocrystalline carbon products was investigated as a function of AgNO3 concentrations in the presence of water and [BMIM]+[BF4]- ionic liquid. Under the conditions used, the deposited Ag clusters could become negatively charged and were responsible for the reduction of acetic acid and the consequent crystalline carbon growth. Increasing Ag concentrations did not only result in higher amounts of Ag being deposited but also created significant local pressure on the atomistic level, where the crystalline carbon was formed, resulting in the re-ordering of carbon atoms into nanodiamond structure. The presence of nanodiamond with average crystallite size 27 nm was clearly evidenced by XRD, Raman, XPS, and TEM-EDX-SAED. The in-situ electrochemical reduction has shown to be an effective ultra-low energy strategy to produce crystalline solid carbon under ambient conditions.

Enhanced Photoresponse of High Crystalline Bi2Se3 Thin-Films Using Patterned Substrates.

High-quality Bi2Se3 thin films with topological insulating properties at room temperature have recently attracted much attention as one of the promising materials for realizing innovative electronic and optoelectronic devices. Here, we report the high crystallinity growth of Bi2Se3 thin films on a patterned sapphire substrate (PSS) by using a vapor-phase transport deposition with minimizing thermal dissociation of Se atoms vaporized in Bi2Se3 powder. This PSS not only reduces the large dislocation of heterogeneously grown Bi2Se3 on a sapphire substrate but also induces enhanced light absorption in the visible to near-infrared (IR) ranges compared to Bi2Se3 on planar sapphire substrates. Thus, the Bi2Se3 thin film laterally grown on the PSS reveals uniform surface properties and high crystallinity in the rhombohedral lattice phase with a full width at half maximum of 0.06° for the XRD (003) peak. Also, the photoresponse of the fabricated IR conversion device using Bi2Se3/PSS heterostructure exhibits excellent performance and high reliability with no degradation after continuous switching. As a result, the device constructed with the Bi2Se3/PSS exhibits one order of magnitude higher NIR induced-photocurrent and 1-2 orders of magnitude faster photo-switching than that with Bi2Se3/Al2O3. Such an enhancement in the device performance of Bi2Se3/PSS is confirmed by the increased absorption spectra in visible and NIR ranges and the improved light absorption distribution.

Synthesis of calcium aluminate nanoflakes for degradation of organic pollutants

Calcium aluminate nanoflakes possessing a single crystalline orthorhombic Ca5Al6O14 phase and a thickness of about 50 nm were synthesized via a simple route. The elements O, Al, and Ca were confirmed in the nanoflakes by element mapping and X-ray photoelectron spectroscopy. Formation and growth of the nanoflakes can be explained by a nucleation and crystalline growth process. The nanoflakes exhibit a band gap of 3.87 eV which entails good photocatalytic activity towards gentian violet which, in aqueous solution at a concentration of 10 mg L−1, can be entirely degraded within 100 min upon irradiation of a 175 W mercury lamp using 1 g L−1 calcium aluminate nanoflakes as catalyst. The reaction rate constant is 0.032 min−1 which is six times higher than that using calcium aluminate nanostructures obtained from different conditions. The nanoflakes are recoverable and possess good stability for the gentian violet degradation.

Effect of Calcination Temperature on the Properties of Nanotitania-Based Extrudates from an Industrial Raw Material

Titanium dioxide is an important material for catalytic reactions as a promoter, support, catalyst, and additive. In this paper, titania extrudates were prepared from industrial raw material by an extrusion method and then calcined at different temperatures. Results show that there are nanostructures with anatase phase from 450o to 850oC because the presence of SO4 2– delays the formation of rutile nucleation up to 950oC,and the morphology is irregular and smooth at 950oC. The SO4 2– ions and crystallinegrowth affect the properties of titania extrudates at various calcination temperatures. At temperatures below 650oC, the effect of SO4 2–removal is more than the effect of crystalline growth on the properties of the extrudates. But at temperatures above 650oC, the effect of crystal growth is dominant because of mobility of atoms, although more sulfate ions are exited. It decreases open pore volume and increases strength and attrition resistance.

Retraction Note to: Crystalline growth of tungsten trioxide (WO3) nanorods and their development as an electrochemical sensor for selective detection of vitamin C

Retraction Note to: Crystalline growth of tungsten trioxide (WO3) nanorods and their development as an electrochemical sensor for selective detection of vitamin C

Epitaxial CdSe/PbSe Heterojunction Growth and MWIR Photovoltaic Detector

A novel Epitaxial Cadmium Selenide (CdSe) on Lead Selenide (PbSe) type-II heterojunction photovoltaic detector has been demonstrated by Molecular Beam Epitaxy (MBE) growth of n-type CdSe on p-type PbSe single crystalline film. The use of Reflection High-Energy Electron Diffraction (RHEED) during the nucleation and growth of CdSe indicates high-quality single-phase cubic CdSe. This is a first-time demonstration of single crystalline and single phase CdSe growth on single crystalline PbSe, to the best of our knowledge. The current-voltage characteristic indicates a p-n junction diode with a rectifying factor over 50 at room temperature. The detector structure is characterized by radiometric measurement. A 30 μm × 30 μm pixel achieved a peak responsivity of 0.06 A/W and a specific detectivity (D*) of 6.5 × 108 Jones under a zero bias photovoltaic operation. With decreasing temperature, the optical signal increased by almost an order of magnitude as it approached 230 K (with thermoelectric cooling) while maintaining a similar level of noise, achieving a responsivity of 0.441 A/W and a D* of 4.4 × 109 Jones at 230 K.

Cooperative Calcium Phosphate Deposition on Collagen-Inspired Short Peptide Nanofibers for Application in Bone Tissue Engineering.

In recent years, immense attention has been devoted over the production of osteoinductive materials. To this direction, collagen has a dominant role in developing hard tissues and plays a crucial role in the biomineralization of these tissues. Here, we demonstrated for the first time the potential of the shortest molecular pentapeptide domain inspired from collagen toward mineralizing hydroxyapatite on peptide fibers to develop bone-filling material. Our simplistic approach adapted the easy and facile route of introducing the metal ions onto the peptide nanofibers, displaying adsorbed glutamate onto the surface. This negatively charged surface further induces the nucleation of the crystalline growth of hydroxyapatite. Interestingly, nucleation and growth of the hydroxyapatite crystals lead to the formation of a self-supporting hydrogel to construct a suitable interface for cellular interactions. Furthermore, microscopic and spectroscopic investigations revealed the crystalline growth of the hydroxyapatite onto peptide fibers. The physical properties were also influenced by this crystalline deposition, as evident from the hierarchical organization leading to hydrogels with enhanced mechanical stiffness and improved thermal stability of the scaffold. Furthermore, the mineralized peptide fibers were highly compatible with osteoblast cells and showed increased cellular biomarkers production, which further reinforced the potential application toward effectively fabricating the grafts for bone tissue engineering.

Investigation of natural gas hydrate formation and slurry viscosity in non-emulsifying oil systems

At a later stage of oilfield development, there will be more free water in the pipeline, which may engender the phase inversion of water-in-oil emulsions, thereby augmenting the risk of hydrate plugging. In a novel 30 L high-pressure autoclave, the effects of wax content, water cut, temperature, initial pressure, and rotation speed on hydrate crystallization nucleation and slurry viscosity were examined. Results demonstrated that in systems with wax content greater than or equal to 2 wt%, at the onset of the swift hydrate growth stage, the aggregation of wax and hydrate will impair the gelling structure of wax-containing oil, inducing an abrupt fall in slurry viscosity. Consideration is given to the solubility fluctuation of the natural gas in oil, and an empirical prediction formula for gas consumption during hydrate formation in wax-containing systems is established. The presence of wax hinders the crystalline nucleation and growth of hydrates. Notwithstanding, the hydrate slurry viscosity of the wax-containing system is greater because the wax-hydrate aggregates have a more conspicuous effect on the slurry viscosity than the hydrate volume fraction. The water cut of 70% is a critical upper limit, above which the viscosity of hydrate slurry would increase dramatically. Higher rotation speed and initial pressure can significantly enhance the viscosity of hydrate slurries, but their effects on the hydrate nucleation induction time are more perplexing.

Relation between chemical reduction and crystalline growth in mixtures of low-dimensional NiO and reduced graphene oxide

The carbothermal and graphenothermal reduction of metal oxide and graphite or graphene systems are critical for obtaining pure metals and designing new energy materials. However, the nano-level differences between these processes have not been investigated in detail. Herein, we investigate the relationship between crystalline growth and chemical reduction during the heat-treatment of reduced graphene oxide (RGO) and NiO nanoparticles. The heat-treated RGO/NiO mixtures exhibit complex interactions. Below a critical NiO concentration, the crystalline growth of RGO and NiO take precedence. Above this threshold, drastic Ni formation occurs by the chemical reduction of NiO. This demonstrates a concentration-dependent competitive relationship between chemical reduction and crystalline growth. Two factors require further study, namely, the low-dimensional shape/contact-dependent chemical reactivity between RGO and NiO, and the thermodynamic size-dependent driving force for crystalline growth of individual RGO and NiO crystals.

Synthesis of Colloidal GaN and AlN Nanocrystals in Biphasic Molten Salt/Organic Solvent Mixtures under High-Pressure Ammonia.

Group III nitrides are of great technological importance for electronic devices. These materials have been widely manufactured via high-temperature methods such as physical vapor transport (PVT), chemical vapor deposition (CVD), and hydride vapor phase epitaxy (HVPE). The preparation of group III nitrides by colloidal synthesis methods would provide significant advantages in the form of optical tunability via size and shape control and enable cost reductions through scalable solution-based device integration. Solution syntheses of III-nitride nanocrystals, however, have been scarce, and the quality of the synthesized products has been unsatisfactory for practical use. Here, we report that incorporating a molten salt phase in solution synthesis can provide a viable option for producing crystalline III-nitride nanomaterials. Crystalline GaN and AlN nanomaterials can be grown in a biphasic molten-salt/organic-solvent mixture under an ammonia atmosphere at moderate temperatures (less than 300 °C) and stabilized under ambient conditions by postsynthetic treatment with organic surface ligands. We suggest that microscopic reversibility of monomer attachment, which is essential for crystalline growth, can be achieved in molten salt during the nucleation and the growth of the III-nitride nanocrystals. We also show that increased ammonia pressure increases the size of the GaN nanocrystals produced. This work demonstrates that use of molten salt and high-pressure reactants significantly expands the chemical scope of solution synthesis of inorganic nanomaterials.

Synthesis of Tungsten Oxide Nanoflakes and Their Antibacterial and Photocatalytic Properties

This current work revealed a single-step fabrication of tungsten oxide nanoflakes (WO3 NFs) with the help of Terminalia arjuna bark extract. Bioactive phytoconstituents of T. arjuna bark extract were involved in the nucleation process and promoted the material crystalline growth in a particular direction. The as-prepared sample thermal decomposition was analyzed by TG/DTG. The as-prepared sample was annealed at 300 °C for 2 h, and the annealed sample was characterized by UV-Vis-DRS, FTIR, Raman, XRD, SEM, EDX, and TEM. Synthesized WO3 samples showed a monoclinic phase of the flake-like structure with lengths of 25~230 nm and diameters of 25~120 nm. The WO3 NFs were evaluated against S. aureus and E. coli. Over 3 mg concentrations of WO3 NFs outperform the positive control in antibacterial activity. The pseudo-first-order kinetics of the WO3 NFs enhanced the photocatalytic performance of methylene blue (MB). These results prove that WO3 NFs have sustainable performance in antibacterial and MB degradation applications.

Preparation and characterization of foamed concrete using a foaming agent and local mineral resources from Burkina Faso

The paper describes lightweight-foamed concretes (LFC) that were formulated from cement, natural sand, and foam from a foaming agent with densities of 600 and 700 kg/m3. The identified mineral phases in the cement are alite, belite, Celite, ferrite, calcite, and gypsum. The obtained foamed concretes have a porosity varying from 29.17 to 37.14 vol%, a thermal conductivity below 0.2 W/m.K, and a mechanical strength greater than 2 MPa. At 28 days setting, the relative quantities of crystalline and amorphous phases were identified by XRD and DTA/TG. These techniques allowed to show the importance of the carbonation process and hydrated phases formation on the macroscopic strength increase. The microstructural characterization by image analyses evidences that when the density decreases, growth of both crystalline and amorphous phases in the bubble walls during setting is a mean of compensating the role of density in strength.

Crystalline organic thin films for crystalline OLEDs (II): weak epitaxy growth of phenanthroimidazole derivatives.

The ordered molecular arrangement of crystalline organic semiconductors facilitates high carrier mobility and light emission in organic light-emitting diode (OLED) devices. It has been demonstrated that the weak epitaxy growth (WEG) process is a valuable crystallization route for fabricating crystalline thin-film OLEDs (C-OLEDs). Recently, C-OLEDs based on crystalline thin films of phenanthroimidazole derivatives have exhibited excellent luminescent properties such as high photon output at low driving voltage and high power efficiency. Achieving effective control of organic crystalline thin film growth is crucial for the development of new C-OLEDs. Herein, we report the studies on morphology structure and growth behavior of the phenanthroimidazole derivative WEG thin films. The oriented growth of WEG crystalline thin films is determined by channeling and lattice matching between the inducing layer and active layer. Large-size and continuous WEG crystalline thin films can be obtained by controlling the growth conditions.

Root cause for the difference in photovoltaic parameters of perovskite solar cells prepared by one- and two-step processes

Benefiting from good solubility of metal halide perovskites, low-temperature solution processes (including one- and two-step spin-coating) have become the most common approach for perovskite solar cells (PSCs). However, one confusing issue is that what are specifically effective strategies for the one-step process may not be applicable for the two-step process, and vice versa. Herein, the PSCs with the same perovskite composition and device configuration were prepared by one- and two-step processes, respectively. The results indicated that high performance PSCs with comparable power conversion efficiency over 22% were achieved by both methods, while the detailed photovoltaic parameters varied greatly depending on the one- or two-step process. Compared to the one-step counterpart, the two-step processed PSCs exhibit lower open-circuit voltage and fill factor, but superior short-circuit current, which was in-depth interpreted in terms of the crystalline growth mode, optical properties, defect types, and carrier transport mechanisms related to a perovskite film surface (including a top and a bottom surface). Understanding the root cause for such differences would be central toward identifying what is really crucial for further producing high performance PSCs.

Ultrafast Temporal-Spatial Dynamics of Phase Transition in N-Doped Ge2Sb2Te5 Film Induced by Femtosecond Laser Pulse Irradiation.

Element-doped phase change material (PCM) could improve the performances, e.g., better thermal stability, higher electrical resistance, and faster crystallization speed; thus, the influence of the doping element needs to be further investigated. In this paper, a femtosecond laser, which could realize the ultrafast phase transition rate of PCM between amorphization and crystallization, was used to explore the properties of nitrogen-doped Ge2Sb2Te5 (GST), and a bond effect was proposed. The pure GST and different nitrogen contents of doped GST films were investigated by femtosecond laser pulse excitation through a pump-probe shadowgraph imaging technique. The results showed that the element-doped films could change photon absorption because of the increase in free carriers. This caused the faster rate of reflectivity to change in the irradiated area by the laser beam as the more nitrogen doped. When the nitrogen content increased, the crystallization evolution became harder because it enhanced the bond effect, which suppressed crystalline grain growth and improved the thermal stability. Based on the analysis in the paper, the desired performances of PCMs, e.g., ultrafast dynamics, crystallization evolution, and thermal stability, could be controlled according to the demands by modifying the bond effect.

Effect of annealing in the formation of well-crystallized and textured SrFe12O19 films grown by RF magnetron sputtering

We have studied the influence of the annealing treatment on the crystalline growth of SrFe12O19 previously deposited on Si (100) substrates using radio frequency (RF) magnetron sputtering. For this goal, two grown films, with and without ex situ heating step, have been analyzed and compared to determine the differences in their structural, compositional, and magnetic properties. The results obtained by the different analysis techniques, in particular Mössbauer spectroscopy together with EXAFS and XANES data, suggest that the as-grown film is composed of nanocrystalline maghemite nanoparticles and amorphous strontium oxide. Specifically, Mössbauer spectroscopy results pointed out the presence of Fe3+ cations occupying octahedral and tetrahedral sites with hyperfine magnetic fields 49.3 T and 44.2 T, respectively, characteristic of a spinel-related structure. A strontium hexaferrite canonical structure with a c-axis orientation in the sample plane was found for the annealed film.Graphical abstract

Influence of growth temperature on microstructural and electromagnetic properties of nickel thin films

Nickel thin films were grown on quartz substrates in ultra‐high vacuum at laser fluence of 98 J/cm2 using pulsed laser deposition. Effects of substrate temperature on the electromagnetic properties of the films were investigated. XRD data reveal crystalline growth at substrate temperature (Ts) of 500°C. Roughness of the thin films at Ts of 100°C was noted as 8 nm which was decreased to 3 nm at 500°C. Coercive field and electrical resistivity were decreased from 10 to 5 mT and 0.71 to 0.064 μΩ‐m, respectively, at higher substrate temperature. Magnetoresistance for both modes of configuration and Hall mobility were decreased, while carrier density and Hall coefficient showed opposite behavior with increased substrate temperature.

Sticking together: Mechanisms of quartz synneusis in high-silica magma

The formation of crystal clusters by synneusis (magmatic sintering) affects a wide range of magmatic systems from olivine clusters in komatiite to quartz clusters in high-silica granite. A common feature of synneusis in any mineral phase is the alignment of neighbouring crystals in certain lower-energy orientation relationships. However, the underlying mechanisms involved with both the alignment of crystals in lower-energy orientations and the binding of crystal clusters are not well understood. In the absence of mechanisms that bind crystals together upon contact, the same hydrodynamic forces that may bring crystals together can in theory also serve to disaggregate clusters. Here I use cathodoluminescence imaging and crystal orientation data from quartz clusters in high-silica granite to show that i) rapid crystalline neck growth along attachment surfaces and ii) grain rotation are two mechanisms that reduce the grain boundary energy of crystal clusters while increasing clusters’ shear strength. The continued crystallization of sintered phases as the magmatic body cools further cements crystal pairs and resists cluster disaggregation. Together these mechanisms underpin both the formation and preservation of large crystal clusters in dynamic magmatic environments.

2D materials-assisted heterogeneous integration of semiconductor membranes toward functional devices

Heterogeneous integration techniques allow the coupling of highly lattice-mismatched solid-state membranes, including semiconductors, oxides, and two-dimensional materials, to synergistically fuse the functionalities. The formation of heterostructures generally requires two processes: the combination of crystalline growth and a non-destructive lift-off/transfer process enables the formation of high-quality heterostructures. Although direct atomic interaction between the substrate and the target membrane ensures high-quality growth, the strong atomic bonds at the substrate/epitaxial film interface hinder the non-destructive separation of the target membrane from the substrate. Alternatively, a 2D material-coated compound semiconductor substrate can transfer the weakened (but still effective) surface potential field of the surface through the 2D material, allowing both high-quality epitaxial growth and non-destructive lift-off of the grown film. This Perspective reviews 2D/3D heterogeneous integration techniques, along with applications of III–V compound semiconductors and oxides. The advanced heterogeneous integration methods offer an effective method to produce various freestanding membranes for stackable heterostructures with unique functionalities that can be applied to novel electrical, optoelectronic, neuromorphic, and bioelectronic systems.