Vapor-solid Process Research Articles

Temperature-controlled synthesis of novel boron nanofibers by laser ablation technique

The synthesis of boron nanofibers (BNFs) at different temperatures using the double-pulsed laser ablation (DPLA) technique were reported. Q-switched Nd: YAG laser with 532 and 1064 nm dual beam wavelengths of laser used to ablate a solid boron target. A vapor–solid process at a furnace temperature and pressure supported boron 'nanofibers' growth with the active metal catalysts of 1 % Ni and 1 % Co in a quartz tube furnace in flowing argon (Ar) gas. The crystalline phase purity of the synthesized BNFs at 950, 1050, and 1150 °C were determined by X-ray diffraction (XRD), and the results from XRD confirm that each BNF is preferentially grown in the c-axis (100) direction of alpha boron (α-B). Electron microscopy revealed that each BNF exhibit a length of 1–5 μm and a diameter width of 5–100 nm, while the elemental chemical compositional nature of the BNFs is identified from energy dispersive X–ray spectroscopy (EDX). Image analysis shows the average diameter of each BNF synthesized to be 23.10, 19.13, and 16.09 nm. The lattice distance of each BNF is found to be 0.40, 0.39, and 0.38 nm, respectively. Fingerprint Raman spectroscopy revealed the fundamental vibrational modes of BNFs at Eg and A1g.

Synthesis and growth mechanism of silicon-based nanostructures from polysiloxane via CVD process

The work is concerned with the deposition of ceramic layers of various morphologies, containing silicon and nitrogen, from a polysiloxane precursor in the chemical vapor deposition (CVD) process. The experiments involved the saturation of nitrogen as a gaseous carrier with polysiloxane molecules in the CVD reaction. Saturated nitrogen was supplied to the reaction zone and depending on the synthesis temperature (1000–1800 °C) and the concentration of resin in gas phase, various nanocrystalline and amorphous deposits were obtained on graphite foil, including polygranulated SiOC powders, fibrous layers composed of nanofibers (NFs) containing silicon and nitrogen, nanochains and composite fibrous components. The morphology, structure and chemical composition of the deposits formed in the CVD reaction changed with increasing temperature. Above 1300 °C, oxygen in the silicon oxycarbide deposits was gradually replaced by nitrogen, creating SiN bonds. The dominant phase in the deposits obtained in the temperature range of 1700–1800 °C were two-phase silicon oxynitride NFs. The core of these NFs consisted of a polycrystalline structure surrounded by an amorphous shell. These structures grew preferentially in the [111] direction through heterogeneous nucleation in the vapor-solid process (VS). The changes in deposits morphology were influenced by the CVD temperature and the resin content in the gas carrier. The activation energy of the crystallization process of silicon oxynitride nanofibers was approximately 96 kJ/mol.

Study of NiO-NiMn2O4-Patterned Surfaces Fabricated by a Vapor–Solid Process

Study of NiO-NiMn₂O₄-Patterned Surfaces Fabricated by a Vapor–Solid Process

Enhancing grain growth of caesium-formamidinium-based lead halide perovskite thin films through PbI2 precursor engineering in vapor-solid reaction

Vapor-solid reaction methods are highly regarded as potential solutions for large-scale production of perovskite thin films due to their scalability, compatibility with silicon tandem technology, and lack of solvents. However, the limited penetration of organic vapor through the solid inorganic film results in a slow growth rate of perovskite, leading to poor crystallinity and small grain size. This high defect density in the grain boundaries hinders the enhancement of device performance. In this study, we used 1,3-diaminoguanidine monohydrochloride as an additive in the PbI2 precursor films, which effectively improved perovskite grain growth in the vapor-solid reaction process. After optimization, we achieved high-quality perovskite thin films with a large grain size exceeding 5 μm. Notably, solar devices based on these large-grain perovskite thin films achieved a high power conversion efficiency up to 21.13%.

Synthesis of a highly conductive coordination polymer film via a vapor-solid phase chemical conversion process.

A novel vapor-solid phase chemical conversion process is reported here to synthesise high-quality films of the conductive coordination polymer (c-CP) Ag5BHT (BHT = benzenehexanothiolate), which has the potential to be applied for the synthesis and processing of c-CP electronic devices. This approach involves reacting a silver oxide precursor and an H6BHT linker in an isopropanol solvent vapor atmosphere to obtain Ag5BHT thin films with controllable thickness (100-300 nm). The as-synthesized Ag5BHT thin films exhibit conductivities as high as 10 S cm-1. Additionally, under field-effect modulation, these nanofilms demonstrate remarkably high charge mobility (38 cm2 v-1 s-1).

Contact between water vapor and silicate surface causes abiotic formation of reactive oxygen species in an anoxic atmosphere

Spontaneous generation of reactive oxygen species (ROS) in aqueous microdroplets or at a water vapor-silicate interface is a new source of redox chemistry. However, such generation occurs with difficulty in liquid water having a large ionic strength. We report that ROS is spontaneously produced when water vapor contacts hydrogen-bonded hydroxyl groups on a silicate surface. The evolution of hydrogen-bonded species such as hydroxyl groups was investigated by using two-dimensional, time-resolved FT-IR spectroscopy. The participation of water vapor in ROS generation is confirmed by investigating the reaction of D2O vapor and hydroxyl groups on a silicate surface. We propose a reaction pathway for ROS generation based on the change of the hydrogen-bonding network and corresponding electron transfer onto the silicate surface in the water vapor-solid contact process. Our observations suggest that ROS production from water vapor-silicate contact electrification could have contributed to oxidation during the Archean Eon before the Great Oxidation Event.

Synthesis of ZnO nanowires by thermal chemical vapor deposition technique: Role of oxygen flow rate

Novel catalyst-free synthesis of hierarchical zinc oxide (ZnO) nanowires (NWs) by atmospheric pressure thermal chemical vapor deposition (TCVD) technique and the impact of different oxygen (O2) flow rates (25, 50, 75, and 100 mL/min) on the optical behavior, crystalline structure, emission response, and surface morphology of the prepared samples were studied in detail. The hierarchical ZnO NWs were characterized by ultraviolet–visible (UV–Vis) spectrophotometer, X-ray diffraction (XRD), photoluminescence (PL) spectroscopy, and field emission scanning electron microscope (FESEM) measurements. The physical characteristics of the samples were found to be intensely influenced by the O2 flow rate. UV–Vis spectrophotometer measurements indicated that the optical energy gap (Eg) of the samples varies from 3.24 eV to 3.10 eV with regulating O2 flow rates from 25 to 100 mL/min. XRD analyses confirmed that all the prepared samples were polycrystalline in nature with hexagonal wurtzite-type crystal structure and a strong preferential direction along the (002) plane. Photoluminescence results revealed that oxygen vacancies were the major defects causing the blue emissions. Besides, the higher flow rate of O2 (100 mL/min) was efficient in decreasing the number of oxygen vacancies accountable for wide visible emission band intensity. FESEM images demonstrated a high density of hierarchical ZnO NWs with diameters ranging from 33 ± 2 nm to 88 ± 5 nm. Based on the FESEM observations, the potential growth mechanism of the hierarchical ZnO NWs was a vapor-solid (VS) process. Our simple systematic process for growth and characterization may provide toward the development of the hierarchical ZnO NWs-based gas sensors.

Branched MgO Nanowires Synthesized by Thermal Evaporation Method in Air at Atmospheric Pressure

MgO nanowires with a branched structure were fabricated using a thermal evaporation method in air at atmospheric pressure. The branched MgO nanowire was made up of two parts: a primary central nanowire trunk and lots of secondary nanowire branches. The branched MgO nanowires had a 4-fold symmetrical structure. The secondary nanowire branches grew perpendicular on the four side facets of the central nanowire trunks with square cross-sections. The nanowire branches also grew in a single row and were vertically well aligned in the same direction with each other. The scanning electron microscopy images of the branched nanowires grown at 1000<sup>o</sup>C showed that the diameter of branches gradually decreased along the growth direction and no catalyst particle was found at the tips of the branches, indicating that the branches were grown by a vapor-solid process. For the branched nanowires grown at 1150<sup>o</sup>C, spherical particles which were shown to be catalysts were observed at the tips of the branches. The chemical analysis by energy dispersive spectroscopy showed that the spherical particles were composed of Mg and O elements. These results suggest that the branches’ growth resulted from a self-catalyzed vapor-liquid-solid process. The structural characterization by X-ray diffraction confirmed that the branched MgO nanowires had a cubic lattice structure. The room temperature cathodoluminescence spectra of the branched MgO nanowires exhibited a very strong visible emission which was associated with oxygen vacancies.

Reduced NiO nanostructures grown on nickel foam by anodization and heat treatment for oxygen evolution reaction

A straightforward, cost-effective, and direct approach is developed to fabricate NiO nanostructures directly supported on nickel foams using only an annealing treatment in combination with a short-term anodization process and a reduction process before and after the heat treatment. The vapor-solid growth process is proposed as a possible mechanism for the growth of the NiO nanostructures. The oxygen evolution reaction (OER) activities of the fabricated electrodes were examined employing electrochemical measurements in 1.0 ​M NaOH. Among the fabricated electrodes, the nanoleaf-like NiO electrocatalysts composed of ultra-small NiO nanoparticles were shortly exposed to an alkaline solution at a voltage of 50 ​V (anodization) prior to the thermal annealing and followed by the reduction in NaBH4 exhibited the best electrocatalytic performance towards OER compared to the electrodes synthesized in the absence of reduction and solely by thermal annealing. The NiO nanoleaves delivered a current density of 135 ​mA/cm2 at 1.6 ​V potential versus the reversible hydrogen electrode (RHE) under alkaline conditions.

High-loaded nanobelt-array/nanobelt-microsphere multilayer Li4Ti5O12 self-supported on Ti foils for high-performance lithium ion battery

A high-loaded porous nanobelt-constructed multilayer hierarchical Li4Ti5O12 nanostructure (NBMH-LTO) is prepared via a hydrothermal process with the presence of NaF. This novel NBMH-LTO contains a nanobelt array layer directly grown on the Ti substrate and upper hollow microsphere-layers consisting of nanobelts. The self-standing Li4Ti5O12 nanobelts on conductive Ti foil can be directly used as anode in flexible and foldable lithium ion batteries without using conductive additives or binders. Furthermore, N-doped NBMH-LTO (NBMHNLTO) electrode is successfully obtained via a simple vapor-solid reaction process between NBMH-LTO and NH3, and it exhibits a high areal capacity of 0.71 mAh cm−2 at 0.1 mA cm−2 and excellent rate/cyclic performance. Additionally, the NBMHNLTO electrode also displays excellent performance at low temperature, after 100 cycles at -20 °C (1 mA cm−2), the capacity retention rate can reach to 98.6%. The enhanced performance of NBMHNLTO can be attributed to its high active materials load benefited from the new synthesis strategy, good electronic connection profited from the unique 3D network of nanbelts, and the further improved electron conductivity due to the presence of Ti3+in nanobelts.

Study of Sn doped NiO microwires with waveguiding behaviour grown by a vapor-solid process

Sn-doped NiO microwires with tailored structure of defects, optical properties and waveguiding behaviour were fabricated by a one-step vapor-solid method. The presence of metallic Sn or SnO2 in the precursor mixture favours the formation of elongated microstructures with singular morphologies. This geometry, not explored so far, provides an increased surface to volume ratio and a characteristic morphology, which is of potential interest in a wide range of surface properties and optoelectronic functionalities. In this work, the structural, compositional, electronic and optical properties of the microwires have been analyzed as a function of Sn precursor. Depending on the employed Sn precursor, the optical properties such as their luminescence or waveguiding behaviour can be tailored. In some of the analysed microwires a red laser can be guided along the microstructure. This behaviour has not been previously reported for NiO so far, hence increasing the functionality and applicability of this material.

One dimensional Au-ZnO hybrid nanostructures based CO2 detection: Growth mechanism and role of the seed layer on sensing performance

Abstract In the present research, hybrid Au-ZnO one-dimensional (1-D) nanostructures were grown on silicon substrates with an Al-doped ZnO (AZO) seed layer (Ultrasonic Spray Pyrolysis: USP grown) and no seed layer (NSL) using two different catalytic gold films of 2 nm and 4 nm, respectively. Consequently, such 1-D nanostructures growth was associated with the vapor-liquid-solid (VLS) and vapor-solid (VS) processes. Scanning electron microscopy (SEM) imaging analysis confirms that heat treatment triggered Au nanoparticles nucleation with varying diameters. The Au nanoparticles size and underneath seed layer texture strongly affect the morphology and aspect ratio of 1-D ZnO nanostructures. The seed layer (1-D USP) sample resulted in the growth of longer nanowires (NWs) with a high aspect ratio. The NSL sample showed the formation of nanorods (NRs) with a low aspect ratio mainly via VS growth process. X-ray diffraction (XRD), X-Ray photoelectron spectroscopy (XPS), and photoluminescence (PL) analysis also revealed the differences in the NWs and NRs properties and confirmed VLS and VS growth mechanisms. CO2 gas sensing performance at different concentrations was demonstrated, and NWs with seed layer showed a relatively higher sensing response. In contrast, NSL samples (NRs) exhibited two times faster response. A detailed gas sensing mechanism with different CO2 adsorption modes based on properties of 1-D nanostructures has been discussed. Currently, CO2 sensing and capturing are critical topics in the green transition framework. The present work would be of high significance to the scientific field of NW growth and fulfill the urgent need for CO2 gas sensing.

Formation of NiO/SnO2 p-n heterostructures grown by a single-step process based on a vapor–solid method

Fabrication of p-n heterostructures in low dimensional structures has been considered one of the most promising strategies to develop optoelectronic devices with enhanced applicability in photocatalysis or solar cells, among other fields of research, although it is still a challenging task. Different approaches have been used in the fabrication of p-n heterostructures, usually involving expensive processing and subsequent growth stages. In this work, NiO/SnO2 heterostructures formed by SnO2 micro and nanowires grown on NiO grains, have been fabricated in a single step following a vapor–solid process which avoids the use of catalyst or external substrates.

Preparation of SiC nanowires on graphite paper with silicon powder

In this study, a novel and catalyst-free preparation method of SiC nanowires (SiC NWs) was proposed. A slurry prepared by mixing silicon powder with ethyl cellulose and methanol was uniformly coated on a graphite paper, which was then kept in vacuum furnace at different temperature to form SiC NWs. The phases, microstructure and the formation mechanism of SiC NWs was investigated. It was found that the SiC NWs was formed with a vapor-solid process, during which the silicon powder particles were gradually sublimated and reacted with C provided by graphite paper to form 3C-SiC NWs. With increasing holding temperature, high amounts of SiC NWs with a large diameter was obtained, and the micro-morphology of which changed from flocculent into curvilinear, and finally linear nanowires.

Preparation, doping modulation and field emission properties of square-shaped GaN nanowires

GaN nanomaterials, as one of the most important third-generation semiconductor materials, have attracted wide attention. In this study, GaN nanowires with square cross section were successfully prepared by microwave plasma chemical vapor deposition system. The diameters of nanowires are from 300 to 500 nm and the lengths from 15 to 20 μm. The results show that the cross section of nanowires could be transformed from triangle into square by adjusting the ratio of Mg to Ga in source materials. X-ray diffraction(XRD)result indicate that the structure of GaN nanowires are agree with the hexagonal wurtzite. X-ray photoelectron spectroscopy (XPS) rusult show that a certain amount of Mg and O impurities incoporated in the square-shaped GaN nanowires. Transmission electron microscopy (TEM) result suggested that square-shaped GaN nanowires had high crystallinity with a growth direction of [<inline-formula><tex-math id="M500">\begin{document}$0\bar 110$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="16-20200445_M500.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="16-20200445_M500.png"/></alternatives></inline-formula>]. The ratio of source materials- and time-depented growth mechanism was also studied. It was suggested that the transformation of the cross section from triangle to square structure should be derived from the growth mechanism change from vapor-liquid-solid(VLS)process to vapor-solid(VS)process. The doped Mg increased the growth rate of the nanowires sidewalls, which led to a symmetrically growth of GaN nanowires along the twin boundaries. GaN nanowires gradually transformed to square structure by auto-catalytic growth. Moreover, the property of field emission were further investigated. The results showed that the turn-on electric field of square-shaped GaN nanowires was 5.2 V/m and a stable field emission property at high electric field. This research provides a new method for the preparation of square-shaped GaN nanowires and a prospective way for the design and fabrication of novel nano-scale devices.

Laser assisted synthesis of inorganic fullerene like MoS2-Au nanohybrid and their cytotoxicity against human monocytic (THP-1) cells

Here in, we report the investigation of the immunotoxicity of gold nanoparticles decorated on inorganic fullerene like MoS2 nanostructure (IFMoS2- AuNPs) on the THP-1 immune cell line. The MoS2 nanoparticle with fullerene like nanostructure (IFMoS2) was synthesized by double pulsed laser-assisted chemical vapour deposition (LCVD) method from bulk MoS2 at the temperature of 700 °C. The MoS2 inorganic fullerene-like nanoparticles grown by vapour-solid process (VS). The surface of the IFMoS2 was decorated with gold nanoparticles (AuNPs) to develop the semiconductor biocompatibility interface. The IFMoS2 are typically with diameters 20–50 nm as observed from the electron microscopy analysis. The stability of IFMoS2-AuNPs were examined by dynamic light scattering (DLS) and zeta potential measurements. The decoration of AuNPs on IFMoS2 surface was analyzed by UV–Vis, FTIR, PXRD, FESEM, EDX with elemental mapping and HRTEM measurement. The in vitro cytotoxicity evaluation of the FMoS2-AuNPs was determined on acute monocytic leukemic cells (THP-1) in which cell viability, caspase activity (CASP -3&7/CASP -8/CASP -9) and cell- structural changes were assessed. From FESEM revealed that IFMoS2-AuNPs induced apoptosis in THP-1 cells. Further, THP-1 cell viability markedly decreased at higher IFMoS2-AuNPs concentrations (65–100 μg/ml), indicating its potential as a chemotherapeutic agent in the treatment of human monocytic leukemia.

Formation mechanism and properties of nanorod-structured ZnO films prepared by pyrolysis of Zn acetate films

Nanorod-structured ZnO (NR-ZnO) films were formed on glass substrates by thermal treatment of Zn acetate films in a closed-type tube furnace. The formation mechanism of the NR-ZnO films is proposed as follows: the volatile Zn acetate was vaporized from the top region of the Zn acetate films; the mixture of ZnO and Zn acetate groups in the intermediate region acted as a seed layer; and ZnO NRs were grown in the intermediate region via the vapor-solid process of the volatile groups. The as-formed NR-ZnO films exhibited a wurtzite crystal structure with strong c-axis orientation. The optical bandgap of the film was ∼3.27 eV, and photoluminescence emissions centered at 3.10, 2.98, and 2.81 eV were observed. The diffuse and specular transmittance values of the film were ∼95% and 59% at 550 nm, respectively. This difference originated from the structure of the NRs, which increased the light path length in the films.

Synthesis and formation mechanism of α-Si3N4 single-crystalline nanowires via direct nitridation of H2-treated SiC fibres

Silicon nitride (Si3N4) nanowires were synthesised using H2-treated SiC fibres as raw materials and a graphite cylinder as the substrate at 1500 °C in N2 atmosphere. The nanowires were characterised by X-ray photoelectron spectroscopy, chemical analysis, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The results showed that the Si3N4 nanowires have diameters ranging from a few tens to hundreds of nanometres and lengths of several hundred micrometres. The preferred growth direction of the nanowires was (010), and the nanowires comprised single-crystalline α-Si3N4. In addition, the formation mechanism of Si3N4 nanowires was discussed. The free silicon in the H2-treated SiC fibres was found to react with N2 to form Si3N4 nanowires, leading us to speculate that the growth mechanism involves a vapour-solid process.

Catalyst-Free Vapor Phase Growth of Ultralong SnSe Single-Crystalline Nanowires

Herein, high quality ultralong tin selenide (SnSe) nanowires (NWs) have been synthesized via physical vapor deposition (PVD) without catalyst. The length of the synthesized SnSe NWs are hundreds of microns and even up to one millimeter, while the mean diameter is about 270 nm, and the aspect ratio of ultralong SnSe NWs can be over 3000. The microstructural characterizations indicate that the SnSe NWs are well-crystallized single crystals with growth direction along the normal {011} planes. The formation of the SnSe NWs is addressed by an oriented one-dimensional growth driven by the dynamic factors in the vapor–solid process. The near-infrared optical band gap of the SnSe NWs has been determined.

Morphology control, electronic properties and evolution of light emission in faceted indium oxide structures

In2O3 micro-rods consisting of In2O3 rods with pyramid-like shape structures on top were synthesized on Au-catalyzed quartz substrates, via a vapor–solid process by a controlled vapor transport method. It was found that the Au catalyst and vapor–solid mechanism played an important role in the growth process and the growth phenomena in these structures were found to be in agreement with the preferential growth directions. The morphology and the structural evolution of the structure were successfully controlled and examined during the synthesis process. The controlled synthesis has made it possible for the In2O3 pyramid to be obtained either as an individual structure or as a cap on top of an In2O3 rod. In2O3 pyramids and In2O3 micro-rods were prepared at 900 and 1000 °C, respectively, and their electronic and room-temperature photoluminescence properties have been investigated. Current–voltage measurements were performed on a single In2O3 micro-rod in the temperature range 300–400 K and good quality ohmic contacts were obtained. Furthermore, the conductance of the In2O3 micro-rod has been found to increase slightly with increasing temperature, as revealed by temperature-dependent measurements. Photoluminescence measurements showed that In2O3 pyramids exhibited a UV luminescence band centered at 366 nm, while light emissions covering nearly the whole blue region have been observed in In2O3 micro-rods. The present work will enrich synthesis science and strongly indicates that processing conditions, as well as the morphology evolution control, are effective ways of fabricating In2O3-based tunable light-emitting devices. Furthermore, the faceted In2O3 microcrystal synthesized in this work may be promoted as pyramidal In2O3 microcavity, due to its unique shape that may allow multiple internal reflections of light at the titled pyramid facets.