Search Results (70)

The Ostwald ripening process in 3D and 2D systems has been studied in great detail over decades. In the application to surface nanoislands and nanodroplets, it is usually assumed that the capture coefficients of adatoms by supercritical nanoparticles of size $s$ scale as $s^{\alpha }$, where the growth index $\alpha$ is smaller than unity. Here, we study theoretically the Ostwald ripening of 3D and 2D nanoparticles whose capture coefficients scale linearly with $s$. This case includes submonolayer surface islands that compete for the flux of highly diffusive adatoms upon termination of the material influx. We obtain analytical solutions for the size distributions using the Lifshitz–Slezov scaled variables. The distributions over size $s$ and radius $R$ are monotonically decreasing, and satisfy the normalization condition for different values of the Lifshitz–Slezov constant $c$. The obtained size distributions satisfy the Family–Vicsek scaling hypothesis, although the material influx is switched off. The model is validated by fitting the monotonically decreasing size distributions of Au nanoparticles that serve as catalysts for the vapor–liquid–solid growth of III-V nanowires on silicon substrates. Full article

A3B5 nanowires are usually grown via the vapor-liquid-solid mechanism. Species from the vapor are incorporated into the nanowires using a catalyst droplet. Typically, the droplet is a low-melting-point eutectic alloy of catalyst and group III metal. This growth imposes a set of limitations on the heterostructure formation and doping. Axial A3B5 heterostructure nanowires obtained via an interchange of group III metals suffer from blurring and kinking. Amphoteric dopants such as Si could act as donors and acceptors, leading to electron-to-hole ratio oscillations along the nanowire. To overcome these limits, the growth with a catalyst, which could dissolve both components of the nanowire, is studied. Tin has a eutectic with both components, As and Ga. This makes the growth of GaAs nanowires with a tin catalyst different from that with standard catalysts. Nanowire growth occurs with at least two types of catalysts, Ga-rich and Ga-poor (As-rich). This article aims to study the nanowire growth with an Sn catalyst. For the first time, the growth of GaAs nanowires using a tin catalyst by molecular beam epitaxy is shown. Tin can serve as a catalyst not only for the chemical growth of GaAs nanowires but also as a nucleation site for their growth. Both compositions of the catalyst are observed. The annealing of a thin film of tin on a Si and GaAs substrate has also been studied. At temperatures below 450 °C, small metal droplets form, while tin dissolves into the substrate at higher temperatures. Full article

Greenhouses are crucial for maintaining an ideal temperature and humidity level for plant growth; however, attaining ideal levels remains a challenge. Energy-efficient and sustainable alternatives are needed because traditional temperature/humidity control practices and vapor compression air conditioning systems depend on climate conditions and harmful refrigerants. Advanced alternative technologies like evaporative cooling and desiccant dehumidification have emerged that maintain the ideal greenhouse temperature and humidity while using the least amount of energy. This study reviews direct evaporative cooling, indirect evaporative cooling, and Maisotsenko-cycle evaporative cooling (MEC) systems and solid and liquid desiccant dehumidification systems. In addition, integrated desiccant and evaporative cooling systems and hybrid systems are reviewed in this study. The results show that the MEC system effectively reduces the ambient temperature up to the ideal range while maintaining the humidity ratio, and both dehumidification systems effectively reduce the humidity level and improve evaporative cooling efficiency. The integrated systems and hybrid systems have the ability to increase energy efficiency and controlled climatic stability in greenhouses. Regular maintenance, initial system cost, economic feasibility, and system scalability are significant challenges to implement these advanced temperature and humidity control systems for greenhouses. These findings will assist agricultural practitioners, engineers, and researchers in seeking alternate efficient cooling methods for greenhouse applications. Future research directions are suggested to manufacture high-efficiency, low-energy consumption, and efficient greenhouse temperature control systems while considering the present challenges. Full article

Narrow-gap InN is a desirable candidate for near-infrared (NIR) optical communication applications. However, the absence of lattice-matched substrates impedes the fabrication of high-quality InN. In this paper, we employed Molecular Beam Epitaxy (MBE) to grow nanostructured InN with distinct growth mechanisms. Morphological and quality analysis showed that the liquid phase epitaxial (LPE) growth of hexagonal InN nanopillar could be realized by depositing molten In layer on large lattice-mismatched sapphire substrate; nevertheless, InN nanonetworks were formed on nitrided sapphire and GaN substrates through the vapor-solid process under the same conditions. The supersaturated precipitation of InN grains from the molten In layer effectively reduced the defects caused by lattice mismatch and suppressed the introduction of non-stoichiometric metal In in the epitaxial InN. Photoluminescence and electrical characterizations demonstrated that high-carrier concentration InN prepared by vapor-solid mechanism showed much stronger band-filling effect at room temperature, which significantly shifted its PL peak to higher energy. LPE InN displayed the strongest PL intensity and the smallest wavelength shift with increasing temperature from 10 K to 300 K. These results showed enhanced optical properties of InN nanostructures prepared on large lattice mismatch substrates, which will play a crucial role in near-infrared optoelectronic devices. Full article

Two-dimensional WSe₂ nanosheets have received increasing attention due to their excellent optoelectronic properties. Solid precursors, such as WO₃ and Se powders, have been extensively employed to grow WSe₂ nanosheets by the chemical vapor deposition (CVD) method. However, the high melting point of WO₃ results in heterogeneous nucleation sites and nonuniform growth of the WSe₂ nanosheet. By dissolving WO₃ powder in a NaOH solution, we report a facile and uniform growth of monolayer and bilayer WSe₂ nanosheets on a SiO₂/Si substrate at a large scale using liquid precursor by the CVD method. The size and thickness of the WSe₂ nanosheets were controlled by modulating the precursor concentration and growth temperature. The as-prepared monolayer and bilayer WSe₂ nanosheets were well characterized by optical microscopy, atomic force microscopy, and Raman and photoluminescence spectroscopy. With the increase in precursor concentration, the size of the monolayer WSe₂ increased up to 120 μm. Bilayer WSe₂ nanosheets were grown at higher temperatures. The photosensitivity of the bilayer WSe₂ was one order of magnitude higher than that of the monolayer WSe₂. The carrier mobility, specific detectivity, photoresponsivity, and external quantum efficiency of the bilayer WSe₂ were about two orders of magnitude higher than those of the monolayer WSe₂. Our method opens up a new avenue to grow monolayer and bilayer WSe₂ for optoelectronic applications. Full article

Cavitation is a dynamic process characterized by the formation, growth, and collapse of vapor or gas vacuoles in liquids or at the liquid–solid interface, initiated by a local pressure drop. This phenomenon releases concentrated energy through microjet impacts and shock waves, leading to a violent exchange of energy with the surrounding environment. While cavitation is often perceived as detrimental, certain aspects can be harnessed for practical applications. Relevant studies have shown that cavitating jets provide high operating efficiencies, reduce energy consumption per unit, and have the potential for waste treatment. This paper presents three types of cavitating jets: central body cavitation, oscillatory cavitation, and shear cavitation. Additionally, the formation process of a cavitating jet and the effects of various factors on jet performance are discussed. Following an in-depth examination of the cavitation phenomena, subsequent chapters explore the applications of cavitating jets in material surface enhancement, cleaning, and energy exploration. Furthermore, recommendations for future research on cavitating jets are provided. This paper provides a comprehensive literature review on cavitating jets. Full article

This study investigates the growth of gallium arsenide nanowires, using lead as a catalyst. Typically, nanowires are grown through the vapor–solid–liquid mechanism, where a key factor is the reduction in the nucleation barrier beneath the catalyst droplet. Arsenic exhibits limited solubility in conventional catalysts; however, this research explores an alternative scenario in which lead serves as a solvent for arsenic, while gallium and lead are immiscible liquids. Liquid lead easily dissolves in Si as well as in GaAs. The preservation of the catalyst during the growth process is also addressed. GaAs nanowires have been grown by molecular beam epitaxy on silicon Si (111) substrates at varying temperatures. Observations indicate the spontaneous doping of the GaAs nanowires with both lead and silicon. These findings contribute to a deeper understanding of the VLS mechanism involved in nanowire growth. They are also an important step in the study of GaAs nanowire-doping processes. Full article

Compositional control over vapor–liquid–solid III–V ternary nanowires based on group V intermix (VLS IIIV_xV_1−x NWs) is complicated by the presence of a catalyst droplet with extremely low and hence undetectable concentrations of group V atoms. The liquid–solid and vapor–solid distributions of IIIV_xV_1−x NWs at a given temperature are influenced by the kinetic parameters (supersaturation and diffusion coefficients in liquid, V/III flux ratio in vapor), temperature and thermodynamic constants. We analyze the interplay of the kinetic and thermodynamic factors influencing the compositions of VLS IIIV_xV_1−x NWs and derive a new vapor–solid distribution that contains only one parameter of liquid, the ratio of the diffusion coefficients of dissimilar group V atoms. The unknown concentrations of group V atoms in liquid have no influence on the NW composition at high enough levels of supersaturation in liquid. The simple analytic shape of this vapor–solid distribution is regulated by the total V/III flux ratio in vapor. Calculating the temperature-dependent desorption rates, we show that the purely kinetic regime of the liquid–solid growth occurs for VLS IIIV_xV_1−x NWs in a wide range of conditions. The model fits the data well on the vapor–solid distributions of VLS InP_xAs_1−x and GaP_xAs_1−x NWs and can be used for understanding and controlling the compositions of any VLS IIIV_xV_1−x NWs, as well as modeling the compositional profiles across NW heterostructures in different material systems. Full article

The development of low-cost and low-power gas sensors for reliable NO₂ gas detection is important due to the highly toxic nature of NO₂ gas. Herein, initially, SnO₂ nanowires (NWs) were synthesized through a simple vapor–liquid–solid growth mechanism. Subsequently, different amounts of SnO₂ NWs were composited with MoS₂ nanosheets (NSs) to fabricate SnO₂ NWs/MoS₂ NS nanocomposite gas sensors for NO₂ gas sensing. The operation of the sensors in self-heating mode at 1–3.5 V showed that the sensor with 20 wt.% SnO₂ (SM-20 nanocomposite) had the highest response of 13 to 1000 ppb NO₂ under 3.2 V applied voltage. Furthermore, the SM-20 nanocomposite gas sensor exhibited high selectivity and excellent long-term stability. The enhanced NO₂ gas response was ascribed to the formation of n-n heterojunctions between SnO₂ NWs and MoS₂, high surface area, and the presence of some voids in the SM-20 composite gas sensor due to having different morphologies of SnO₂ NWs and MoS₂ NSs. It is believed that the present strategy combining MoS₂ and SnO₂ with different morphologies and different sensing properties is a good approach to realize high-performance NO₂ gas sensors with merits such as simple synthesis and fabrication procedures, low cost, and low power consumption, which are currently in demand in the gas sensor market. Full article

Due to the very efficient relaxation of elastic stress on strain-free sidewalls, III–V nanowires offer almost unlimited possibilities for bandgap engineering in nanowire heterostructures by using material combinations that are attainable in epilayers. However, axial nanowire heterostructures grown using the vapor–liquid–solid method often suffer from the reservoir effect in a catalyst droplet. Control over the interfacial abruptness in nanowire heterostructures based on the group V interchange is more difficult than for group-III-based materials, because the low concentrations of highly volatile group V atoms cannot be measured after or during growth. Here, we develop a self-consistent model for calculations of the coordinate-dependent compositional profiles in the solid and liquid phases during the vapor–liquid–solid growth of the axial nanowire heterostructure ${\mathrm{A}}_{{\mathrm{x}}_0}{\mathrm{B}}_{1-{\mathrm{x}}_0}\mathrm{C}/{\mathrm{A}}_{{\mathrm{x}}_1}{\mathrm{B}}_{1-{\mathrm{x}}_1}\mathrm{C}$ with any stationary compositions ${\mathrm{x}}_0$ and ${\mathrm{x}}_1$. The only assumption of the model is that the growth rates of both binaries AC and BC are proportional to the concentrations of group V atoms A and B in a catalyst droplet, requiring high enough supersaturations in liquid phase. The model contains a minimum number of parameters and fits quite well the data on the interfacial abruptness across double heterostructures in GaP/GaAs_xP_1−x/GaP nanowires. It can be used for any axial III–V nanowire heterostructures obtained through the vapor–liquid–solid method. It forms a basis for further developments in modeling the complex growth process and suppression of the interfacial broadening caused by the reservoir effect. Full article

Alzheimer’s disease (AD) is a progressive neurodegenerative disease characterized by the accumulation of amyloid beta (Aβ) plaques in the brain. Aβ_1–42 is the main component of Aβ plaque, which is toxic to neuronal cells. Si nanowires (Si NWs) have the advantages of small particle size, high specific surface area, and good biocompatibility, and have potential application prospects in suppressing Aβ aggregation. In this study, we employed the vapor–liquid–solid (VLS) growth mechanism to grow Si NWs using Au nanoparticles as catalysts in a plasma-enhanced chemical vapor deposition (PECVD) system. Subsequently, these Si NWs were transferred to a phosphoric acid buffer solution (PBS). We found that Si NWs significantly reduced cell death in PC12 cells (rat adrenal pheochromocytoma cells) induced by Aβ_1–42 oligomers via double staining with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and fluorescein diacetate/propyl iodide (FDA/PI). Most importantly, pre-incubated Si NWs largely prevented Aβ_1–42 oligomer-induced PC12 cell death, suggesting that Si NWs exerts an anti-Aβ neuroprotective effect by inhibiting Aβ aggregation. The analysis of Fourier Transform Infrared (FTIR) results demonstrates that Si NWs reduce the toxicity of fibrils and oligomers by intervening in the formation of β-sheet structures, thereby protecting the viability of nerve cells. Our findings suggest that Si NWs may be a potential therapeutic agent for AD by protecting neuronal cells from the toxicity of Aβ_1–42. Full article

Silicone monomers are the basic raw materials for the preparation of silicone materials. The secondary dust generated during the preparation of silicone monomer by the Rochow–Müller method is a fine particulate waste with high silicon content. In this paper, the physical and chemical properties of silicon powder after pretreatment were analyzed, and an experimental study was conducted on the use of silicon dust in the preparation of Si₃N₄, a nitrogen enhancer for steelmaking, by direct nitriding method in order to achieve the resourceful use of this silicon dust. Furthermore, the thermodynamics and kinetics of the nitriding process at high temperatures were analysed using FactSage 8.1 software and thermogravimetric experiments. The results indicate that after holding at a temperature range of 1300~1500 °C for 3 h, the optimal nitriding effect occurs at 1350 °C, with a weight gain rate of 26.57%. The nitridation of silicon dust is divided into two stages. The first stage is the chemical reaction control step. The apparent activation energy is 2.36 × 10⁵ kJ·mol⁻¹. The second stage is the diffusion control step. The silicon dust growth process is mainly controlled by vapor–liquid–solid (VLS) and vapor–solid (VS) mechanisms. Full article

Over the last ten years, the discovery of topological materials has opened up new areas in condensed matter physics. These materials are noted for their distinctive electronic properties, unlike conventional insulators and metals. This discovery has not only spurred new research areas but also offered innovative approaches to electronic device design. A key aspect of these materials is now that transforming them into nanostructures enhances the presence of surface or edge states, which are the key components for their unique electronic properties. In this review, we focus on recent synthesis methods, including vapor–liquid–solid (VLS) growth, chemical vapor deposition (CVD), and chemical conversion techniques. Moreover, the scaling down of topological nanomaterials has revealed new electronic and magnetic properties due to quantum confinement. This review covers their synthesis methods and the outcomes of topological nanomaterials and applications, including quantum computing, spintronics, and interconnects. Finally, we address the materials and synthesis challenges that need to be resolved prior to the practical application of topological nanomaterials in advanced electronic devices. Full article

The broad and fascinating properties of nanowires and their synthesis have attracted great attention as building blocks for functional devices at the nanoscale. Silicon and germanium are highly interesting materials due to their compatibility with standard CMOS technology. Their combination provides optimal templates for quantum applications, for which nanowires need to be of high quality, with carefully designed dimensions, crystal phase, and orientation. In this work, we present a detailed study on the growth kinetics of silicon (length 0.1–1 $\mathsf{\mu }$m, diameter 10–60 nm) and germanium (length 0.06–1 $\mathsf{\mu }$m, diameter 10–500 nm) nanowires grown by chemical vapor deposition applying the vapour–liquid–solid growth method catalysed by gold. The effects of temperature, partial pressure of the precursor gas, and different carrier gases are analysed via scanning electron microscopy. Argon as carrier gas enhances the growth rate at higher temperatures (120 nm/min for Ar and 48 nm/min H${}_2$), while hydrogen enhances it at lower temperatures (35 nm/min for H${}_2$ and 22 nm/min for Ar) due to lower heat capacity. Both materials exhibit two growth regimes as a function of the temperature. The tapering rate is about ten times lower for silicon nanowires than for germanium ones. Finally, we identify the optimal conditions for nucleation in the nanowire growth process. Full article

Coalescence of nanowires and other three-dimensional structures into continuous film is desirable for growing low-dislocation-density III-nitride and III-V materials on lattice-mismatched substrates; this is also interesting from a fundamental viewpoint. Here, we develop a growth model for vertical nanowires which, under rather general assumptions on the solid-like coalescence process within the Kolmogorov crystallization theory, results in a morphological diagram for the asymptotic coverage of a substrate surface. The coverage is presented as a function of two variables: the material collection efficiency on the top nanowire facet $a$ and the normalized surface diffusion flux of adatoms from the NW sidewalls $b$. The full coalescence of nanowires is possible only when $a=1$, regardless of $b$. At $a>1$, which often holds for vapor–liquid–solid growth with a catalyst droplet, nanowires can only partly merge but never coalesce into continuous film. In vapor phase epitaxy techniques, the NWs can partly merge but never fully coalesce, while in the directional molecular beam epitaxy the NWs can fully coalesce for small enough contact angles of their droplets corresponding to $a=1$. The growth kinetics of nanowires and evolution of the coverage in the pre-coalescence stage is also considered. These results can be used for predicting and controlling the degree of surface coverage by nanowires and three-dimensional islands by tuning the surface density, droplet size, adatoms diffusivity, and geometry of the initial structures in the vapor–liquid–solid, selective area, or self-induced growth by different epitaxy techniques. Full article