Vapor Transport Method Research Articles

Preparation of Indium Tin Oxide Nanowires by Using physical-vapor-transport method

This paper presents a physical-vapor-transport method for the growth of Indium Tin Oxide (ITO) nanowires. ITO nanowires were successfully fabricated by physical vapor transport method using gold nanoparticles as catalyst prepared by two methods. The effects of holding temperature and catalyst on the growth of ITO nanowires were investigated. The experimental results show that the longer ITO nanowires can be grown by increasing the holding temperature at 850 °C, increasing the proportion of carbon powder, and using gold nanoparticles catalyst with smaller particle size. The longest ITO nanowire we fabricated is as long as 45 μm. Our experiments show that the density and diameter of ITO nanowires can be controlled by controlling the density and diameter of gold nanoparticle catalysts. The smaller the nanoparticle diameter is, the easier it is to grow long ITO nanowires.

Infrared photodetector based on 2D monoclinic gold phosphide nanosheets yielded from one-step chemical vapor transport deposition

Infrared detection by binary phosphides is of great interest due to their high carrier mobility, excellent stability, and high absorbance coefficient, as they have a wide range of applications in civil and military fields. As the only metastable phase in gold phosphide, Au2P3 has attracted great attention in fundamental research and optoelectronic applications. Here, we synthesized high-quality and environmentally stable Au2P3 nanosheets through a modified facile one-step mineralization-assisted chemical vapor transport method. Through systematic infrared photoluminescence characterizations, it is found that the as-synthesized Au2P3 nanosheets display an impressive mid-infrared luminescence band centered at about 6.64 μm (0.187 eV) at room temperature. Furthermore, Au2P3-based self-powered photodetectors display outstanding infrared detection performance with D* = 2.9 × 1010 Jones at 1550 nm and D* = 1.9 × 108 Jones at 2611 nm, respectively. Our results suggest that the synthesized Au2P3 nanosheets could be promising candidates for future chip-based infrared nanophotonic and optoelectronic circuitry.

Molybdenum Oxide Nanoparticle Aggregates Grown by Chemical Vapor Transport.

In this study, the advanced chemical vapor transport (CVT) method in combination with the quenching effect is introduced for creating molybdenum oxide nanoparticle arrays, composed of the hierarchical structure of fine nanoparticles (NPs), which are vertically grown with a homogeneous coverage on the individual carbon fibers of carbon fiber paper (CFP) substrates. The obtained molybdenum oxide NPs hold a metastable high-temperature γ-Mo4O11 phase along with a stable α-MoO3 phase by the quenching effect. Furthermore, such a quenching effect forms thinner and smaller nanoparticle aggregates by suppressing the growth and coalescence of primary particles. The molybdenum oxide nanoparticle aggregates are prepared using two different types of precursors: MoO3 and a 1:1 (mol/mol) mixture of MoO3 and activated carbon. The results characterized using X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy show that the relative amount of α-MoO3 to γ-Mo4O11 within the prepared NPs is dependent on the precursor type; a lower amount of α-MoO3 to γ-Mo4O11 is obtained in the NPs prepared using the mixed precursor of MoO3 and carbon. This processing–structure landscape study can serve as the groundwork for the development of high-performance nanomaterials in various electronic and catalytic applications.

Anisotropic Magnetoresistance Effect of Intercalated Ferromagnet FeTa3S6

Intercalated transition metal dichalcogenides have been widely used to study the magnetic and magnetoelectric transport properties in a strong anisotropic and spin–orbit coupling environments. In this study, ferromagnetic FeTa3S6 (also known as Fe1/3TaS2) single crystals were grown by using the chemical vapor transport method, and its magnetic and magnetoelectric transport properties were measured. The results show that FeTa3S6 has ferromagnetic ordered below 37K, with sharp switching of magnetization, butterfly-shaped double-peak magnetoresistance and anomalous Hall effect, and the magnetization and resistance have strong anisotropy. When a magnetic field is oriented parallel to the c-axis, the magnetoresistance exceeds 10% at a temperature of 10K, and negative magnetoresistance is generated when the magnetic field is larger than the switching field. When the direction of the magnetic field of 9T rotates from out-of-plane to in-plane, the anisotropic magnetoresistance exceeds 40%, and the angle-dependent Hall resistance presents a novel trend, which may be due to the existence of a topological Hall effect or other magnetic structures in the FeTa3S6 thin film. When the magnetic field of 9T rotates in the ab-plane of the sample, the in-plane anisotropic magnetoresistance conforms to the form of sin2φ. The experimental results of this study provide important information for the study of magnetic and magnetoelectric transport properties of intercalated transition metal dichalcogenides.

Effect of cerium impurity on the stable growth of the 4H-SiC polytype by the physical vapour transport method

Effect of cerium impurity in the SiC source material on the 4H-SiC growth was investigated. 4H-SiC crystals were grown on 6H-SiC crystal seeds by physical vapor transport and using the open seed backside method. Cerium is the impurity used for promotion of the 4H polytype nucleation. The optimal amount of CeO2 for the growth of 4H-SiC with a good crystalline quality and without undesired 15R- and 6H-SiC inclusions was identified. The open seed backside method combined with the presence of cerium impurity in the growth chamber were more effective for the crystal growth process due to a lower degradation of the backside surface of the grown crystal.

Defect-Induced Luminescence Quenching of 4H-SiC Single Crystal Grown by PVT Method through a Control of Incorporated Impurity Concentration

The structural defect effect of impurities on silicon carbide (SiC) was studied to determine the luminescence properties with temperature-dependent photoluminescence (PL) measurements. Single 4H-SiC crystals were fabricated using three different 3C-SiC starting materials and the physical vapor transport method at a high temperature and 100 Pa in an argon atmosphere. The correlation between the impurity levels and the optical and fluorescent properties was confirmed using Raman spectroscopy, X-ray diffraction, inductively coupled plasma atomic emission spectroscopy (ICP-OES), UV-Vis-NIR spectrophotometry, and PL measurements. The PL intensity was observed in all three single 4H-SiC crystals, with the highest intensities at low temperatures. Two prominent PL emission peaks at 420 and 580 nm were observed at temperatures below 50 K. These emission peaks originated from the impurity concentration due to the incorporation of N, Al, and B in the single 4H-SiC crystals and were supported by ICP-OES. The emission peaks at 420 and 580 nm occurred due to donor–acceptor-pair recombination through the incorporated concentrations of nitrogen, boron, and aluminum in the single 4H-SiC crystals. The results of the present work provide evidence based on the low-temperature PL that the mechanism of PL emission in single 4H-SiC crystals is mainly related to the transitions due to defect concentration.

Vapor transport growth of MnBi2Te4 and related compounds

Motivated by fine tuning of the magnetic and topological properties of MnBi2Te4 via defect engineering, in this work, we report the crystal growth of MnBi2Te4 and related compounds using vapor transport method and crystal characterization by measuring elemental ratio, magnetic and transport properties, and scanning tunneling microscopy. For the growth of MnBi2Te4 single crystals, I2, MnI2, MnCl2, TeCl4, and MoCl5 are all effective transport agents; chemical transportation occurs faster in the presence of iodides than chlorides. We further successfully grow MnSb2Te4, MnBi2−xSbxTe4, and Sb-doped MnBi4Te7 crystals. A small temperature gradient< 20∘C between the hot and cold ends of the growth ampoule is critical for the successful crystal growth of MnBi2Te4 and related compounds. Compared to flux grown crystals, vapor transported crystals tend to be Mn stoichiometric, and Sb-bearing compositions have more Mn/Sb site mixing. The vapor transport growth provides a new materials synthesis approach to fine tune the magnetic and topological properties of these intrinsic magnetic topological insulators where controlling defects is vital.

2D FeOCl: A Highly In-Plane Anisotropic Antiferromagnetic Semiconductor Synthesized via Temperature-Oscillation Chemical Vapor Transport.

2D van der Waals (vdW) transition-metal oxyhalides with low symmetry, novel magnetism, and good stability provide a versatile platform for conducting fundamental research and developing spintronics. Antiferromagnetic FeOCl has attracted significant interest owing to its unique semiconductor properties and relatively high Néel temperature. Herein, good-quality centimeter-scale FeOCl single crystals are controllably synthesized using the universal temperature-oscillation chemical vapor transport (TO-CVT) method. The crystal structure, bandgap, and anisotropic behavior of the 2D FeOCl are explored in detail. The absorption spectrum and electrical measurements reveal that 2D FeOCl is a semiconductor with an optical bandgap of ≈2.1eV and a resistivity of ≈10-1 Ω m at 295 K, and the bandgap increases with decreasing thickness. Strong in-plane optical and electrical anisotropies are observed in 2D FeOCl flakes, and the maximum resistance anisotropic ratio reaches 2.66 at 295 K. Additionally, the lattice vibration modes are studied through temperature-dependent Raman spectra and first-principles density functional calculations. A significant decrease in the Raman frequencies below the Néel temperature is observed, which results from the strong spin-phonon coupling effect in 2D FeOCl. This study provides a high-quality low-symmetry vdW magnetic candidate for miniaturized spintronics.

Effect of chemical doping on memristive behavior of VO2 microcrystals

Strongly correlated oxides, such as vanadium dioxide that undergoes a sharp metal-insulator transition when triggered by different stimuli, are of high relevance for novel electronic devices. In this work, we show the variation in threshold voltage of memristor behavior with systematic doping of tungsten (W) in VO2 crystals grown by the vapor transport method. Chemical doping effects on metal insulator transition are further correlated with Raman spectroscopy studies and differential scanning calorimetry studies. Furthermore, bi-polar threshold switching of VO2 memristor behavior is demonstrated in VO2 microcrystals with different contents of W. Threshold voltage for electrical triggering in W doped VO2 is reduced to about 0.547 V from 2.27 V of undoped VO2.

Characterization of prismatic slip in PVT-grown AlN crystals

The most frequently observed deformation mechanism in wurtzite aluminum nitride (AlN) grown by the physical vapor transport (PVT) method is basal plane slip. However, prismatic slip also takes place in such crystals. In this study, prismatic slip is observed in a 50 mm commercial AlN substrate wafer, leading to a sixfold symmetric BPD pattern in the wafer. Prismatic dislocations cross slip on to basal plane and multiply there, increasing the dislocation density of the wafer. A radial thermal model is established to explore the origin of the unevenly distributed dislocations. The unevenly distributed resolved shear stress across the whole radial area of the boule during PVT growth caused by radial thermal gradients offers driving force for the activation of the three sets of prismatic slip systems, producing nonuniform dislocation distribution in the boule and thus the wafer. Both experimental observations and theoretical calculations of the critical resolved shear stress (CRSS) correlate well with the model results, revealing that controlling radial thermal gradients is critical for lowering dislocation density and enhancing the crystal quality using PVT growth method.

High-Performance Photodetectors Based on the 2D SiAs/SnS2 Heterojunction.

Constructing 2D heterojunctions with high performance is the critical solution for the optoelectronic applications of 2D materials. This work reports on the studies on the preparation of high-quality van der Waals SiAs single crystals and high-performance photodetectors based on the 2D SiAs/SnS2 heterojunction. The crystals are grown using the chemical vapor transport (CVT) method and then the bulk crystals are exfoliated to a few layers. Raman spectroscopic characterization shows that the low wavenumber peaks from interlayer vibrations shift significantly along with SiAs’ thickness. In addition, when van der Waals heterojunctions of p-type SiAs/n-type SnS2 are fabricated, under the source-drain voltage of −1 V–1 V, they exhibit prominent rectification characteristics, and the ratio of forwarding conduction current to reverse shutdown current is close to 102, showing a muted response of 1 A/W under excitation light of 550 nm. The light responsivity and external quantum efficiency are increased by 100 times those of SiAs photodetectors. Our experimental results enrich the research on the IVA–VA group p-type layered semiconductors.

Numerical Analysis of Dislocation Density of SiC Crystals Tilted from [0001] Toward [12¯10]$[ {1\bar 210} ]$ and [11¯00]$[ {1\bar 100} ]$ Grown by Physical Vapor Transport

AbstractA 3D and time‐dependent analysis of dislocation density using the Alexander–Haasen model to estimate the plastic deformation of tilted angle growth of 4H–SiC single crystals during crystal growth and cooling processes grown using the physical vapor transport method is performed. The growth direction is set to tilt from [0001] toward and to fabricate wafers to stabilize polytype during crystal growth of the epitaxial layer. The maximum dislocation density in SiC crystals increases as the tilted angle increases, whereas von Mises stress, which is one of the measures of dislocation density, decreases. The calculated results show dislocation density distribution in the crystal grown in [0001] exhibits six‐folded symmetry, whereas that in the crystal grown in the tilt direction from [0001] toward and exhibits asymmetric distribution.

Comparative Study of Bulk and Nanoengineered Doped ZnSe

Chromium- and cobalt-doped zinc selenide nanoparticles were synthesized using a low-temperature reactive solution growth method. The morphological and optical characteristics were compared to those of doped zinc selenide (ZnSe) bulk crystals grown by the physical vapor transport (PVT) method. We observed agglomeration of particles; however, the thioglycerol capping agent has been shown to limit particle grain growth and agglomeration. This process enables doping by addition of chromium and cobalt salts in the solution. A slightly longer refluxing time was required to achieve cobalt doping as compared with chromium doping due to lower refluxing temperature. The nanoparticle growth process showed an average particle size of approximately 300 nm for both Cr- and Co-doped zinc selenide. The optical characterization of Co:ZnSe is ongoing; however, preliminary results showed a very high bandgap compared to that of pure ZnSe bulk crystal. Additionally, Co:ZnSe has an order of magnitude higher fluorescence intensity compared to bulk Cr:ZnSe samples.

ZnO nanostructured materials and their potential applications: progress, challenges and perspectives.

Extensive research in nanotechnology has been conducted to investigate new behaviours and properties of materials with nanoscale dimensions. ZnO NPs owing to their distinct physical and chemical properties have gained considerable importance and are hence investigated to a detailed degree for exploitation of these properties. This communication, at the outset, elaborates the various chemical methods of preparation of ZnO NPs, viz., the mechanochemical process, controlled precipitation, sol–gel method, vapour transport method, solvothermal and hydrothermal methods, and methods using emulsion and micro-emulsion environments. The paper further describes the green methods employing the use of plant extracts, in particular, for the synthesis of ZnO NPs. The modifications of ZnO with organic (carboxylic acid, silanes) and inorganic (metal oxides) compounds and polymer matrices have then been described. The multitudinous applications of ZnO NPs across a variety of fields such as the rubber industry, pharmaceutical industry, cosmetics, textile industry, opto-electronics and agriculture have been presented. Elaborative narratives on the photocatalytic and a variety of biomedical applications of ZnO have also been included. The ecotoxic impacts of ZnO NPs have additionally been briefly highlighted. Finally, efforts have been made to examine the current challenges and future scope of the synthetic modes and applications of ZnO NPs.

Layered transition metal chalcogenophosphate towards air-stable visible light photodetection

Two-dimensional (2D) multiple-element layered transition metal chalcogenophosphates (TMCPs) have received tremendous attention due to their excellent carrier mobility, and absorption coefficient, displaying great potential for optoelectronic applications. Here, the novel high-quality manganese nickel phosphorous sulfur (Mn0.24Ni0.76PS3) crystals are obtained by using chemical vapor transport (CVT) method. Further, thin flakes of Mn0.24Ni0.76PS3 are achieved and employed to prepare photodetectors. Impressively, the prepared photodetectors exhibit excellent photo-response in visible light region, such as on/off ratio, and response time, a responsivity up to 10.4 mA W−1 and a detectivity of 1.31 × 108 Jones, demonstrating great potential for future air-stable visible light photodetection.

Growth of p-type 4H-SiC single crystals by physical vapor transport using p-type SiC powder

In this study, a novel Al doping method was used to grow p-type SiC. p-Type 4H-SiC crystals were grown by a physical vapor transport (PVT) method using p-type SiC powder.

Controllable growth of centimetre-sized UTe2 single crystals by the chemical vapor transport method

UTe2 single crystals were grown using the chemical vapor transport method, possessing standard lattice parameters and good single crystallinity, and the effects of various growth parameters on the crystal morphology were explored.

Stability & durability of self-driven photo-detective parameters based on Sn1-β Sb β Se (β = 0, 0.05, 0.10, 0.15, 0.20) ternary alloy single crystals.

In the present investigation Sn1-β Sb β Se crystals are grown using the direct vapor transport method. The crystals after growth were analyzed by EDAX and XPS to confirm the elemental composition. The surface morphological properties were studied by scanning electron microscope, confirming a flat surface and layered growth of the Sn1-β Sb β Se crystals. The structural properties studied by X-ray diffraction and high-resolution transmission electron microscopy confirm the orthorhombic structure of the grown Sn1-β Sb β Se crystals. The Raman spectroscopic measurements evince the presence of B2g and Ag vibration modes. The PL intensity peak at ∼400 nm to 500 nm confirms the energy band gap. The indirect energy band gap of 1.18 eV was evaluated using Tauc plot by employing UV-visible spectroscopy making it a promising candidate for optoelectronic and photonic applications. The pulse photo response of pure and doped samples was studied under a monochromatic source of wavelength 670 nm and intensity of 30 mW cm-2 at zero biasing voltage firstly on day one and then the same samples were preserved for 50 days and the stability of the photodetectors was observed. Photodetector parameters such as rise time, decay time, photocurrent, responsivity, sensitivity, and detectivity were observed, and evaluated results are presented in this article.

Growth of hexagonal boron nitride (hBN) on silicon carbide substrates by the physical vapor transport method

The possibility of growing hexagonal boron nitride (hBN) of high structural perfection on hexagonal silicon carbide (SiC) substrates using the physical vapor transport method is demonstrated. The results obtained indicate that this method is promising for the formation of large-area high-quality hBN/SiC heterostructures in the course of one technological process, which have a high potential for device applications. Keywords: hexagonal boron nitride, high-temperature sublimation from the gas phase, Raman spectroscopy, photoluminescence.

Giant coercivity in single crystal Ta&lt;sub&gt;3&lt;/sub&gt;FeS&lt;sub&gt;6&lt;/sub&gt; film

Van der Waals (vdW) layered ferromagnetic materials provide a unique platform for fundamental spintronic research, and have broad application prospects in the next-generation spintronic devices. In this study, we synthesize high-quality single crystals of vdW intrinsic ferromagnet Ta&lt;sub&gt;3&lt;/sub&gt;FeS&lt;sub&gt;6&lt;/sub&gt; by the chemical vapor transport method. We obtain thin layer samples of Ta&lt;sub&gt;3&lt;/sub&gt;FeS&lt;sub&gt;6&lt;/sub&gt; with thickness values ranging from 19 to 100 nm by the mechanical exfoliation method, and find that their corresponding Curie temperatures are between 176 and 133 K. The anomalous Hall measurement shows that the Ta&lt;sub&gt;3&lt;/sub&gt;FeS&lt;sub&gt;6&lt;/sub&gt; has out-of-plane ferromagnetism with the coercivity reaching 7.6 T at 1.5 K, which is the largest value in those of the layered vdW ferromagnetic materials reported so far. In addition, we observe that the reversal polarity of the hysteresis loop changes sign with temperature increasing. Our work provides an opportunity to construct stable and miniaturized spintronic devices and present a new platform for studying spintronics based on van der Waals magnetic materials.