Precursor Growth Research Articles

Preparation and dye separation performance of ZIF-67/mesoporous silica ceramic nanofiltration membrane by liquid phase epitaxy (LPE) growth method

Ceramic membrane plays an important role in separation process with advantages of high thermal and chemical resistances, but its applications on the nanofiltration are restricted because of the limitation of pore size. In this study, a commercial tubular ceramic membrane with pore diameter of 0.1 μm was firstly coated with mesoporous silica substrates, in which ZIF-67 nanocrystals were generated layer-by-layer inside the mesochannels via liquid phase epitaxy growth method. The open pore size of ceramic membrane can be precisely controlled by increasing the growth cycles of ZIF-67 nanocrystals. The influence of preparation conditions on the dye separation was investigated, including growth cycles, precursor concentration, and molar ratio of Co2+/2-methylimidazole (Co2+/Hmim). Under the optimized conditions, the rejection of methylene blue, methyl orange, chromium black T, rhodamine B, acid fuchsin, and Congo red were in the range of 92–99 % with membrane fluxes of 0.45–0.73 L m−2 h−1. Bovine serum albumin solution was used to evaluate the anti-fouling abilities of the ceramic membrane. The flux recovery ratio, which was calculated according to the ratio between the water permeance after washing and before filtration, was 52.3 % with the flux decline rate of 66.3 %.

Chemical identification of new particle formation and growth precursors through positive matrix factorization of ambient ion measurements

Abstract. In the lower troposphere, rapid collisions between ions and trace gases result in the transfer of positive charge to the highest proton affinity species and negative charge to the lowest proton affinity species. Measurements of the chemical composition of ambient ions thus provide direct insight into the most acidic and basic trace gases and their ion–molecule clusters – compounds thought to be important for new particle formation and growth. We deployed an atmospheric pressure interface time-of-flight mass spectrometer (APi-ToF) to measure ambient ion chemical composition during the 2016 Holistic Interactions of Shallow Clouds, Aerosols, and Land Ecosystems (HI-SCALE) campaign at the United States Department of Energy Atmospheric Radiation Measurement facility in the Southern Great Plains (SGP), an agricultural region. Cations and anions were measured for alternating periods of ∼ 24 h over 1 month. We use binned positive matrix factorization (binPMF) and generalized Kendrick analysis (GKA) to obtain information about the chemical formulas and temporal variation in ionic composition without the need for averaging over a long timescale or a priori high-resolution peak fitting. Negative ions consist of strong acids including sulfuric and nitric acid, organosulfates, and clusters of NO3- with highly oxygenated organic molecules (HOMs) derived from monoterpene (MT) and sesquiterpene (SQT) oxidation. Organonitrates derived from SQTs account for most of the HOM signal. Combined with the diel profiles and back trajectory analysis, these results suggest that NO3 radical chemistry is active at this site. SQT oxidation products likely contribute to particle growth at the SGP site. The positive ions consist of bases including alkyl pyridines and amines and a series of high-mass species. Nearly all the positive ions contained only one nitrogen atom and in general support ammonia and amines as being the dominant bases that could participate in new particle formation. Overall, this work demonstrates how APi-ToF measurements combined with binPMF analysis can provide insight into the temporal evolution of compounds important for new particle formation and growth.

Thermal decomposition of trimethylindium and indium trisguanidinate precursors for InN growth: An abinitio and kinetic modeling study.

Indium nitride (InN) is an interesting material for future electronic and photonic-related applications, as it combines high electron mobility and low-energy band gap for photoabsorption or emission-driven processes. In this context, atomic layer deposition techniques have been previously employed for InN growth at low temperatures (typically <350 °C), reportedly yielding crystals with high quality and purity. In general, this technique is assumed to not involve any gas phase reactions as a result from the time-resolved insertion of volatile molecular sources into the gas chamber. Nonetheless, such temperatures could still favor the precursor decomposition in the gas phase during the In half-cycle, therefore altering the molecular species that undergoes physisorption and, ultimately, driving the reaction mechanism to pursue other pathways. Thence, we herein evaluate the thermal decomposition of relevant In precursors in the gas phase, namely, trimethylindium (TMI) and tris(N,N'-diisopropyl-2-dimethylamido-guanidinato) indium (III) (ITG), by means of thermodynamic and kinetic modeling. According to the results, at T = 593K, TMI should exhibit partial decomposition of ∼8% after 400s to first generate methylindium and ethane (C2H6), a percentage that increases to ∼34% after 1h of exposure inside the gas chamber. Therefore, this precursor should be present in an intact form to undergo physisorption during the In half-cycle of the deposition (<10s). On the other hand, the ITG decomposition starts already at the temperatures used in the bubbler, in which it slowly decomposes as it is evaporated during the deposition process. At T = 300 °C, the decomposition is a fast process that reaches 90% completeness after 1s and where equilibrium, at which almost no ITG remains, is achieved before 10s. In this case, the decomposition pathway is likely to occur via elimination of the carbodiimide ligand. Ultimately, these results should contribute for a better understanding of the reaction mechanism involved in the InN growth from these precursors.

Resolidified Chalcogen Precursors for High-Quality 2D Semiconductor Growth.

Two-dimensional (2D) semiconductors including transition metal dichalcogenides (TMDCs) have gained attention in optoelectronics for their extraordinary properties. However, the large amount and locally distributed lattice defects affect the optical properties of 2D TMDCs, and the defects originate from unstable factors in the synthesis process. In this work, we develop a method of pre-melting and resolidification of chalcogen precursors (sulfur and selenium), namely resolidified chalcogen, as precursor for the chemical vapor deposition growth of TMDCs with ultrahigh quality and uniformity. Taking WS2 as an example, the monolayer WS2 shows uniform fluorescence intensity and a small full-width at half-maximum of photoluminescence peak at low temperatures with an average value of 13.6±1.9 meV. The defect densities at the interior and edge region are both low and comparable, i.e., (9±3)×1012 cm-2 and (10±4)×1012 cm-2 , indicating its high structural quality and uniformity. This method is universal in growing high quality monolayer MoS2 , WSe2 , MoSe2 , and will benefit their applications.

Resolidified Chalcogen Precursors for High‐Quality 2D Semiconductor Growth

AbstractTwo‐dimensional (2D) semiconductors including transition metal dichalcogenides (TMDCs) have gained attention in optoelectronics for their extraordinary properties. However, the large amount and locally distributed lattice defects affect the optical properties of 2D TMDCs, and the defects originate from unstable factors in the synthesis process. In this work, we develop a method of pre‐melting and resolidification of chalcogen precursors (sulfur and selenium), namely resolidified chalcogen, as precursor for the chemical vapor deposition growth of TMDCs with ultrahigh quality and uniformity. Taking WS2 as an example, the monolayer WS2 shows uniform fluorescence intensity and a small full‐width at half‐maximum of photoluminescence peak at low temperatures with an average value of 13.6±1.9 meV. The defect densities at the interior and edge region are both low and comparable, i.e., (9±3)×1012 cm−2 and (10±4)×1012 cm−2, indicating its high structural quality and uniformity. This method is universal in growing high quality monolayer MoS2, WSe2, MoSe2, and will benefit their applications.

Atomic layer deposition of MoOx thin films using Mo(iPrCp)2H2 and O3

This work studied the growth of molybdenum oxide thin films with thermal atomic layer deposition (ALD) using Mo(iPrCp)2H2 and O3 as precursors. Growth parameters were determined by varying growth temperature and precursor dose times. ALD growth was exhibited in a temperature range of 100–200 °C. The growth per cycle ranged from 1.3 to 1.7 Å/cycle with a standard uniformity parameter of &amp;lt;5%. Attempts to grow films using H2O as an oxygen source showed no significant growth. Film properties were measured using spectroscopic ellipsometry, x-ray reflectivity, x-ray diffraction, x-ray photoelectron spectroscopy, and infrared spectroscopy.

Continuous Large Area Monolayered Molybdenum Disulfide Growth Using Atmospheric Pressure Chemical Vapor Deposition.

The growth of large crystallite continuous monolayer materials like molybdenum disulfide (MoS2) with the desired morphology via chemical vapor deposition (CVD) remains a challenge. In CVD, the complex interplay of various factors like growth temperatures, precursors, and nature of the substrate decides the crystallinity, crystallite size, and coverage area of the grown MoS2 monolayer. In the present work, we report about the role of weight fraction of molybdenum trioxide (MoO3), sulfur, and carrier gas flow rate toward nucleation and monolayer growth. The concentration of MoO3 weight fraction has been found to govern the self-seeding process and decides the density of nucleation sites affecting the morphology and coverage area. A carrier gas flow of 100 sccm argon results in large crystallite continuous films with a lower coverage area (70%), while a flow rate of 150 sccm results in 92% coverage area with a reduced crystallite size. Through a systematic variation of experimental parameters, we have established the recipe for the growth of large crystallite atomically thin MoS2 suitable for optoelectronic devices.

Effect of the Growth Interruption on the Surface Morphology and Crystalline Quality of MOCVD-Grown h-BN

Hexagonal boron nitride (h-BN) is one promising material class for applications in DUV optoelectronics due to the layered structure and ultra-wide bandgap. The synthesis of h-BN with smooth surface morphology and high quality on dielectric substrates is the key to construct efficient functional devices thereon. In this study, we reported wafer-scale h-BN on c-plane sapphire substrates by metal organic chemical vapor deposition utilizing the flow modulation epitaxy (FME) with growth interruptions. The effect of the growth interruption location within FME on the surface morphology and crystalline quality of h-BN films was systematically investigated. The interruption after the TEB injection could promote the mobility of B adatoms, and the interruption after the NH3 injection could further relieve the passivation of N terminal growth fronts and mitigate the parasitic gas-phase reaction between growth precursors. By simultaneously employing interruptions after TEB and NH3 injections, the growth rate of h-BN increased significantly from 0.16 nm/min to 4.76 nm/min, and the surface roughness of 2-nm-thick h-BN was reduced to 0.587 nm. In addition, h-BN grown with an interruption solely after the NH3 injection presented the best crystallinity because the relatively slow growth rate reduced the possibility of impurity incorporation.

Phase-Controllable Growth of Air-Stable SnS Nanostructures for High-Performance Photodetectors with Ultralow Dark Current.

The epitaxial growth of low-dimensional tin chalcogenides SnX (X = S, Se) with a controlled crystal phase is of particular interest since it can be utilized to tune optoelectronic properties and exploit potential applications. However, it still remains a great challenge to synthesize SnX nanostructures with the same composition but different crystal phases and morphologies. Herein, we report a phase-controlled growth of SnS nanostructures via physical vapor deposition on mica substrates. The phase transition from α-SnS (Pbnm) nanosheets to β-SnS (Cmcm) nanowires can be tailored by the reduction of growth temperature and precursor concentration, which originates from a delicate competition between SnS-mica interfacial coupling and phase cohesive energy. The phase transition from the α to β phase not only greatly improves the ambient stability of SnS nanostructures but also leads to the band gap reduction from 1.03 to 0.93 eV, which is responsible for fabricated β-SnS devices with an ultralow dark current of 21 pA at 1 V, an ultrafast response speed of ≤14 μs, and broadband spectra response from the visible to near-infrared range under ambient condition. A maximum detectivity of the β-SnS photodetector arrives at 2.01 × 108 Jones, which is about 1 or 2 orders of magnitude larger than that of α-SnS devices. This work provides a new strategy for the phase-controlled growth of SnX nanomaterials for the development of highly stable and high-performance optoelectronic devices.

Impact of synthesis temperature and precursor ratio on the crystal quality of MOCVD WSe2 monolayers

Structural defects in transition metal dichalcogenide (TMDC) monolayers (ML) play a significant role in determining their (opto)electronic properties, triggering numerous efforts to control defect densities during material growth or by post-growth treatments. Various types of TMDC have been successfully deposited by MOCVD (metal-organic chemical vapor deposition), which is a wafer-scale deposition technique with excellent uniformity and controllability. However, so far there are no findings on the extent to which the incorporation of defects can be controlled by growth parameters during MOCVD processes of TMDC. In this work, we investigate the effect of growth temperature and precursor ratio during MOCVD of tungsten diselenide (WSe2) on the growth of ML domains and their impact on the density of defects. The aim is to find parameter windows that enable the deposition of WSe2 ML with high crystal quality, i.e. a low density of defects. Our findings confirm that the growth temperature has a large influence on the crystal quality of TMDC, significantly stronger than found for the W to Se precursor ratio. Raising the growth temperatures in the range of 688 °C to 791 °C leads to an increase of the number of defects, dominating photoluminescence (PL) at low temperatures (5.6 K). In contrast, an increase of the molar precursor ratio (DiPSe/WCO) from 1000 up to 100 000 leads to less defect-related PL at low temperatures.

Effect of Al4B2O9 and Al18B4O33 whiskers synthesized in situ on the evolution of microstructure and mechanical properties of white fused alumina and Cubitron glass-ceramic composites

The present paper reports on the influence of in situ crystallization of aluminum borate whiskers on the evolution of the microstructure and mechanical properties of electrocorundum (white fused alumina) and microcrystalline alumina (Cubitron 321™) glass-ceramic porous composites. The investigated composites were obtained by sintering the white fused alumina (WFA) and Cubitron 321™ abrasive grains, glass-ceramic bond and various amounts of precursor for whisker growth. The results showed that in the presented technology, the crystallization of the composite reinforcing phases proceeds differently in both types of composites, which affects their microstructure and mechanical properties. An increase in the mechanical tensile strength of 36% was observed for both types of composites; however, depending on the type of abrasive grain, the composites with the highest tensile strength differed in the amount of whisker precursor added. A significant increase in the Young's modulus values was also observed for composites containing 40 wt% precursor: by 45% for WFA and by 52% for Cubitron 321™.

A Review of Recent Progress in β‐Ga2O3 Epitaxial Growth: Effect of Substrate Orientation and Precursors in Metal–Organic Chemical Vapor Deposition

Gallium oxide (Ga2O3) is a highly promising ultrawide‐bandgap semiconductor for power electronics that emerged about a decade ago. Epitaxial growth Ga2O3 at the small scale is demonstrated. In order to develop scalable manufacturing of high‐performance epitaxial structures, in‐depth understanding of the fundamental growth processes, control parameters, and mechanism is imperative. This review discusses the recent progress in epitaxial growth of β‐Ga2O3 films and highlights challenges in obtaining high growth rate, low defects, and high carrier mobilities. Compared with the other epitaxy methods, metal–organic chemical vapor deposition (MOCVD) offers a wider growth window and precursor selection option, to minimize the tradeoff between crystal quality and growth rate. Growth rate is inversely proportional to temperature, within a certain temperature window, because of the unavoidable premature gas‐phase reactions and desorption of the highly volatile gallium suboxide (Ga2O) at elevated temperatures. Growth defects, background impurity incorporation, and carrier mobilities can be affected by the choice of MOCVD precursors, nucleation, and adsorption/desorption/diffusion of adatoms on substrate surfaces of different orientations, including the effect of growing on cleavage and noncleavage planes. This review summarizes the current status of the epitaxial growth of β‐Ga2O3 and analyzes the major factors that enhance mobility and reduce background doping concentration. The insights gained help advance the manufacturability of device‐grade epitaxial thin films.

Reactive Characteristics of Novel Core‐Shell Al−CuO Microspheres Prepared by Alcohol‐Thermal Treatment of Cu(OH)2

AbstractIn this study, core‐shell structured Al@CuO energetic microspheres are prepared through the alcohol‐thermal method. CuO is grown in situ around superfine Al powder, and Cu(OH)2 powder is used directly as the precursor for CuO growth. The effects of reaction temperature and reaction time on the chemical transformation as well as coating quality are investigated by using scanning electron microscopy, transmission electron microscopy and X‐ray diffraction. More importantly, the transformation of Cu(OH)2 into CuO during alcohol‐thermal process is tentatively discussed. And the growth mechanisms of CuO are speculated, which mainly consist of the continuous dissolution of Cu(OH)2, the transformation of dissolved Cu(OH)2 to CuO which happens at a lower temperature than that of dry Cu(OH)2 powder, and the heterogeneous nucleation and growth of CuO. The prepared Al@CuO energetic microspheres are compared with physically mixed Al/CuO counterparts by using thermal analysis, electric ignition and constant‐volume combustion tests. Benefiting from the improved interfacial contact quality, Al@CuO energetic microspheres show overall enhanced reaction characteristics in terms of reaction onset temperature, heat release, apparent activation energy, ignition delay, burning time and pressurization rate.

Kinetics of Catalyst-Free and Position-Controlled Low-Pressure Chemical Vapor Deposition Growth of VO2 Nanowire Arrays on Nanoimprinted Si Substrates.

In the present article, the position-controlled and catalytic-free synthesis of vanadium dioxide (VO2) nanowires (NWs) grown by the chemical vapor deposition (CVD) on nanoimprinted silicon substrates in the form of nanopillar arrays was analyzed. The NW growth on silicon nanopillars with different cross-sectional areas was studied, and it has been shown that the NWs' height decreases with an increase in their cross-sectional area. The X-ray diffraction technique, scanning electron microscopy, and X-ray photoelectron spectroscopy showed the high quality of the grown VO2 NWs. A qualitative description of the growth rate of vertical NWs based on the material balance equation is given. The dependence of the growth rate of vertical and horizontal NWs on the precursor concentration in the gas phase and on the growth time was investigated. It was found that the height of vertical VO2 NWs along the [100] direction exhibited a linear dependence on time and increased with an increase in the precursor concentration. For horizontal VO2 NWs, the height along the direction [011] varied little with the growth time and precursor concentration. These results suggest that the high-aspect ratio vertical VO2 NWs formed due to different growth modes of their crystal faces forming the top of the growing VO2 crystals and their lateral crystal faces related to the difference between the free energies of these crystal faces and implemented experimental conditions. The results obtained permit a better insight into the growth of high-aspect ratio VO2 NWs and into the formation of large VO2 NW arrays with a controlled composition and properties.

Mechanisms of promotion in the heterotrophic growth of Chlorella vulgaris by the combination of sodium acetate and hydrolysate of broken rice

In order to reduce the culture cost and increase the growth rate of heterotrophic Chlorella vulgaris, the effects of hydrolysate of broken rice (HBR) combined with sodium acetate on its growth were evaluated. Results showed that the addition of 0.4 g/L of sodium acetate could stabilize the pH of the medium via the co-metabolism of acetate, ammonia and nitrate by Chlorella vulgaris. Meanwhile, isocitrate lyase activity increased threefold, which further promoted the glyoxylate cycle and the citric acid cycle, which finally provided more energy and metabolic precursors for cell growth. The biomass production (5.04 g/L), biomass productivity (1.65 g/L/day) and protein content (64.14 %) were 1.56, 1.81 and 1.77 times higher than the glucose group. This study demonstrated that HBR combined with sodium acetate could effectively promote the heterotrophic metabolism of microalgae, which provided scientific basis and guidance for industrial production of high-value products using Chlorella vulgaris as a fermentation platform.

Dual-metal precursors for the universal growth of non-layered 2D transition metal chalcogenides with ordered cation vacancies

Dual-metal precursors for the universal growth of non-layered 2D transition metal chalcogenides with ordered cation vacancies

Study Of Soot Aggregate Formation And Oxidation In A Swirled Stratified Premixed Ethylene/Air Flame

Soot particles are one of the main causes of today's pollution because of their negative contribution to global warming and human health. Aviation is one of the domains dealing with soot reduction as the new engine concepts are developed to reduce fuel consumption and global emissions. Despite the fact that most combustion devices used for air transportation operate at high pressure (e.g., aircraft gas turbines up to 40 bar), our understanding of soot formation and oxidation in such conditions is not yet at an appropriate level, as there is still a fundamental lack of experimental data and corresponding predictive models in the literature. Thus, the objective of the current study is to evaluate soot formation and oxidation processes in stratified, swirled, premixed ethylene/air flames examined with a variety of laser diagnostics designed to simultaneously measure soot particle and soot precursor 2D-distributions, as well as the flame structure and the aerodynamic field. For that, the SIRIUS burner was selected because of its ability to produce flames with topologies similar to those encountered in aircraft combustors. Soot particle distributions are measured by Planar Laser-induced incandescence (PLII) diagnostic. The flame structure is obtained by detecting the hydroxyl radicals (OH) with Planar laser-induced fluorescence (PLIF). A second PLIF diagnostic is also used to investigate the production of polycyclic aromatic hydrocarbons (PAH) with the detection of two benzene rings molecules which are recognized as good precursors of soot nucleation and growth. Finally, the particle Image Velocimetry (PIV) diagnostic is used for measuring the velocity distributions. These laser diagnostics are coupled together in order to obtain cross-correlations between several scalar parameters playing a determining role in the soot formation/consumption processes. The experimental results collected at atmospheric pressure are reviewed and critically assessed. A scenario describing the link between the soot inception, growth, aggregation and oxidation processes is proposed by analyzing velocity, OH, PAHs and soot distributions. In particular, the data reveal the presence of distinct regions for these processes. Incipient soot production zone is strongly function of specific local conditions of velocity, PAH concentration, and strain rate encountered at the interface of the internal recirculation zone and the fuel/air jet. The central part of the inner recirculation zone in which large structures move at low velocities provides suitable conditions for the aggregation of nascent soot particles while an oxidation region located in the upper zone of the internal recirculation zone favors the consumption of soot.

Dual-metal precursors for the universal growth of non-layered 2D transition metal chalcogenides with ordered cation vacancies

Two-dimensional (2D) transition metal chalcogenides (TMCs) are promising for nanoelectronics and energy applications. Among them, the emerging non-layered TMCs are unique due to their unsaturated dangling bonds on the surface and strong intralayer and interlayer bonding. However, the synthesis of non-layered 2D TMCs is challenging and this has made it difficult to study their structures and properties at thin thickness limit. Here, we develop a universal dual-metal precursors method to grow non-layered TMCs in which a mixture of a metal and its chloride serves as the metal source. Taking hexagonal Fe1–xS as an example, the thickness of the Fe1–xS flakes is down to 3 nm with a lateral size of over 100 μm. Importantly, we find ordered cation Fe vacancies in Fe1–xS, which is distinct from layered TMCs like MoS2 where anion vacancies are commonly observed. Low-temperature transport measurements and theoretical calculations show that 2D Fe1–xS is a stable semiconductor with a narrow bandgap of ∼60 meV. In addition to Fe1–xS, the method is universal in growing various non-layered 2D TMCs containing ordered cation vacancies, including Fe1–xSe, Co1–xS, Cr1–xS, and V1–xS. This work paves the way to grow and exploit properties of non-layered materials at 2D thickness limit.

Selective area growth of β-Ga2O3 by HCl-based halide vapor phase epitaxy

We demonstrated selective area growth of β-Ga2O3 by HCl-based halide vapor phase epitaxy on SiO2-masked (001) and (010) β-Ga2O3 substrates. Perfect growth selectivity was achieved under the presence of HCl etching gas in addition to the growth precursors. In both substrate cases, (100) facet dominated the grown shapes owing to their smallest surface energy density. High-aspect-ratio structures having (100) sidewall facets were observed for the stripe windows along [010] and [001] directions on the (001) and (010) substrates, respectively. These structures may be applicable to trenches and fins used for β-Ga2O3-based power devices.

A Heat-Liquefiable Solid Precursor for Ambient Growth of Perovskites with High Tunability, Performance and Stability.

Halide perovskites are intensively studied for applications in optoelectronic devices because of their outstanding properties and relatively low cost. However, the common precursor solutions for perovskite fabrication are rather unstable in the presence of moisture and oxygen, limiting the large-scale low-cost production of perovskite. Herein, water is used counterintuitively to formulate an ambient stable perovskite precursor, which is peculiar in that it is solid at room temperature but becomes a liquid at 75°C. The non-fluidity of the precursor stemmed from the water-assisted intermediate fiber assembly, conferring high damp air stability. Yet the heat-liquefiability made the precursor highly processible for perovskite growth, and when guided by polyvinyl pyrrolidone coordination with Pb2+ , the perovskite can preferentially grow along the [200] direction, significantly improving the film quality. To demonstrate the utility of the precursor, it has been used to fabricate self-driven halide perovskite photodetectors, which exhibited a low noise current of 2.0× 10-14 AHz-1/2 , a high specific detectivity up to 1.4 × 1013 Jones, and high stability of 20days of operation with only <5% external quantum efficiency decay. This type of solid-liquid convertible precursor opens up new opportunities for wider applications of perovskites.