Vapor Transport Method Research Articles

Effect of CuS buffer layer on the structural and optical properties of TeO2 nanowires: a comparative study

The current work concerns with the effects of cupper sulfide (CuS) buffer layer on morphological, structural and optical properties of tellurium dioxide (TeO2) nanostructured thin films synthesized by vapor transport method. Single crystalline tetragonal TeO2 crystallographic phase with enhanced peak intensity and crystallinity for CuS/TeO2 film are observed by x-ray diffraction analysis. Scanning electron microscopy examinations revealed small rod-like morphology for TeO2 and randomly oriented nanowires morphology for CuS/TeO2 samples. The estimated optical band gap energies were 3.78 and 3.63 eV for TeO2 and CuS/TeO2 nanostructured films, respectively. The photoluminescence of CuS/TeO2 film was enhanced and red-shifted from 450 to 455 nm by the presence of CuS layer. The effective charge carrier life times were 0.14 ns and 1.92 ns for TeO2 and CuS/TeO2 films, respectively. These results could be beneficial for optoelectronic devices such as light emitting devices.

Ultrasensitive and broadband polarization-sensitive topological insulator photodetector induced by element substitution

Topological insulators are considered as one of the preferred materials for high-performance optoelectronic devices due to their small bulk bandgaps and ultra-high carrier mobility. However, the existence of their unique Dirac like surface states makes the corresponding optoelectronic devices to have high dark current, and the logic circuit cannot be turned off effectively. Opening the surface state gap by element doping is an effective means to achieve high performance of devices. Here, we design and prepare single crystal Bi2Se2.15S0.85 nanowires by a facile iodine-assisted chemical vapor transport method and a fabricated individual Bi2Se2.15S0.85 nanowire based photodetector. The devices exhibit remarkable photoresponse over the broadband wavelength ranging from ultraviolet C (275 nm) to near-infrared (1310 nm) with the low dark current of 10−12 A. They show superior optoelectrical properties with an ultrafast response speed of 170 ns, detectivity of 9.35 × 1011 Jones, a competitive responsivity of 1.31 A/W, and superb stability to keep great photoresponse for at least one year, which are superior to the reported photodetectors. Additionally, benefiting from the anisotropic crystal structure of Bi2Se2.15S0.85, the devices also display good polarization detection performance in a wide spectral range from 266 nm to 1064 nm with a dichroic ratio of 1.81 at 360 nm.

Dopant‐Induced Giant Photoluminescence of Monolayer MoS2 by Chemical Vapor Transport

AbstractSubstitutional doping of 2D transition metal dichalcogenides (TMDCs) has been recognized as a promising strategy to tune their optoelectronic properties for a wide array of applications. However, controllable doping of TMDCs remains a challenging issue due to the natural doping of these materials. Here, the controllable growth of Ti‐doped MoS2 monolayers is demonstrated via the chemical vapor transport method, and the atomic embedded structure is confirmed by scanning transmission electron microscope with a probe corrector measurements. Furthermore, the grown Ti‐doped MoS2 monolayer exhibits giant photoluminescence (PL), 85‐fold stronger than a pristine MoS2 monolayer prepared by the same method. The giant PL enhancement is attributed to dopant‐induced O‐Ti‐S units and improved interaction between the monolayer and the mica substrate, increasing the photoluminescence quantum yield and facilitating radiation recombination. The successful growth of Ti‐doped MoS2 monolayer and the improvement of its optical and electrical properties by Ti doping may provide a promising method to engineer the optoelectronic properties of 2D TMDCs materials.

Molybdenum disulfide homogeneous junction diode fabrication and rectification characteristics

The chemical vapor transport method was used in this research to synthesize MoS2 bulk. Through mechanical exfoliation, we limited the thickness of MoS2 flakes from 1 to 3 μm. In order to fabricate a p–n homogeneous junction, we used oxygen plasma treatment to transform the MoS2 characteristics from n-type to p-type to fabricate a p–n homogenous junction and demonstrate the charge neutrality point shift from −80 to +102 V successfully using FET measurement. The MoS2 p–n homogeneous junction diode showed an excellent p-n characteristic curve during the measurements and performed great rectifying behavior with 1–10 Vpp in the half-wave rectification experiment. This work demonstrated that MoS2 flake had great potential for p-n diodes that feature significant p–n characteristics and rectifying behavior.

Black Phosphorus: Fundamental Properties and Influence of Impurities Induced by Its Synthesis.

Black phosphorus (BP) has been among the most widely explored materials in recent years because of its exceptional properties. A vapor transport method using tin and iodide as mineralizers was used to synthesize large crystals which can be used for fundamental physical characterization including electrical and heat transport and heat capacity. This method is compared to other reported procedures (high-pressure crystal growth and mercury catalysis) which are broadly used and the most dominant procedures for the obtainment of bulk layered BP. In addition, we have investigated any possible impurities which could have been introduced by synthesis and their possible incorporation into BP and their influence on the physical properties of BP.

(Digital Presentation) Earth-Abundant Copper-Based Electrode Materials for Li-Ion Storage

Lithium-ion batteries (LIBs) find their use in almost all applications starting from electronic gadgets to grid energy storage and hybrid electric vehicles. In this direction, the development of high-capacity anodes is crucial to fulfil the increasing energy demand. To evaluate the Li+ ion storage performance, we have synthesized an earth-abundant copper-based electrode material, Cu3PS4, using the chemical vapor transport (CVT) method from the constituent elements Cu, P, and S in a 3:1:4 ratio. It has an enargite-type structure and has a layered-type morphology (Figure 1a). A high capacity of 970 mAh g-1 is obtained at 0.1 A g-1 current density. The electrode is amenable for high discharge rates up to 5 A g-1, and at a discharge rate of 1 A g-1, the cell can be cycled 5000 times with 90% capacity retention. The high electrochemical performance of the material is related to the conversion reaction as probed by in situ Raman spectroscopy (Figure 1b) and surface-controlled capacitive contribution due to the formation of a polymeric film over the electrode surface. A full cell with LiCoO2 cathode results in a large number of cycles with stable performance. Further improvement is achieved by forming a composite with an organic polymer, polybenzimidazole. The composite electrode delivers almost double the capacity of the pristine electrode. Other studies on the use of the electrode material to multivalent ion storage based on Mg2+, Zn2+, and Al3+ are in progress.Reference D. Tripathy and S. Sampath, J. Power Sources 2020, 478, 229066. Figure 1. (a) Unit cell structure and SEM image of Cu3PS4 and (b) in situ Raman spectra of the electrode after discharge. Figure 1

Cation‐Alloying‐Induced Blue‐Shifted and Wide‐Spectrum Polarization‐Sensitive Photodetection in Quasi‐1D SbBiS3

Polarization-Sensitive Photodetection In article number 2200061, Juehan Yang, Qun Xu, Zhongming Wei, and co-workers successfully obtain SbBiS3 single crystal via the chemical vapor transport method. The theoretical calculation results reveal that the band gap widening and the optical absorption blue shift of SbBiS3 are caused by cationic alloying. The cover image describes that the SbBiS3-based photodetector implement a wide-spectrum polarization-sensitive response.

Chemically Synthesized Alq3 and Ni-doped Alq3 Nanorods for Spintronics Applications

In this research we demonstrate the synthesis of pristine tris(8-hydroxyquinoline) aluminium (Alq3) and nickel-doped Alq3 nanorods as well as their characterization. The thermal vapour transport method was used to synthesize nanomaterials in the morphology of nanorods. The surface morphology was studied using scanning electron microscopy (SEM). The structural properties were analyzed using X-ray diffraction. UV-Visible and photoluminescence (PL) spectroscopy were used to examine the optical characteristics. Doping of Ni introduced ferromagnetic properties in the Alq3 and also retained its semiconductor properties. Ni-doped Alq3 nanorods are useful for the development of spintronics devices.

Synthesis, Crystal Growth, and Annealing of CdSxSe1-x and Cr:CdS0.8Se0.2 Single Crystals.

Mid-infrared laser in the 2-5 μm wavelength region is in the atmospheric transmission window range, and hence, it has important application prospects in the fields of optoelectronic countermeasures, space communication, environmental remote sensing, and molecular spectroscopy. One of the most promising technological approaches to achieve mid-infrared laser output is based on direct lasing of transition-metal (TM)-doped II-VI chalcogenide crystals. In this work, CdSxSe1-x and Cr:CdS0.8Se0.2 polycrystals were synthesized by a chemical vapor synthesis method from a stoichiometric mixture of vacuum-sublimed CdS and CdSe. The structure of the synthesized products was analyzed by X-ray diffraction (XRD). Using these synthesized products, CdSxSe1-x and Cr:CdS0.8Se0.2 single crystals were grown by the physical vapor transport (PVT) method. After annealing, the band gap becomes smaller and the transmission range widens to 17 μm. The composition of the single crystals was determined by energy-dispersive spectrometry (EDS) mapping and XPS, and it was found to be uniform throughout the ingot. In addition, the absorption peak maximum for the Cr2+ ion in the Cr:CdS0.8Se0.2 crystal is at 1.84 μm.

Cation‐Alloying‐Induced Blue‐Shifted and Wide‐Spectrum Polarization‐Sensitive Photodetection in Quasi‐1D SbBiS3

Quasi‐1D ternary semiconductors have attracted considerable attention recently because of their additional bandgap engineering deriving from the variable stoichiometry. Herein, SbBiS3single crystals are successfully synthesized by chemical vapor transport (CVT) method. The basic characterizations combined with theoretical calculations reveal that SbBiS3semiconductor has an intrinsically low symmetry structure and in‐plane anisotropy of optical absorption. Significantly, the bandgap of SbBiS3shows a blue‐shifted compared to the bandgaps of binary Sb2S3and Bi2S3. Moreover, the quasi‐1D SbBiS3‐based photodetector shows a wide‐spectrum photosensitivity (360–1064 nm), a fast response speed (τrise≈ 10 μs andτdecay ≈ 94 μs) at 532 nm, a high photoresponsivity (6.82 A W−1) at 360 nm. In addition, the photodetector exhibits an anisotropic photocurrent ratio up to 1.12 at 808 nm. The work demonstrates the SbBiS3prepared by cationic alloy is a promising candidate for the application of polarized optoelectronics.

Peak thermal conductivity measurements of boron arsenide crystals

Recent experiments have validated prior theories of unusual high thermal conductivity $(\ensuremath{\kappa})$ in boron arsenide (BAs) and revealed large $\ensuremath{\kappa}$ variation associated with extended and point defects in the samples. The peak $\ensuremath{\kappa}$ provides valuable insights into the competition between intrinsic phonon-phonon scattering processes and extrinsic boundary and defect scattering processes in BAs. However, prior measurement methods have not been able to measure the peak $\ensuremath{\kappa}$ because of fundamental and technical limitations. Here, we report peak $\ensuremath{\kappa}$ measurements of BAs crystals synthesized under different conditions with source materials of different purities via a vapor transport method. For three representative samples, the measured $\ensuremath{\kappa}$ peak appears at temperatures between 120 and 150 K and varies from $410\ifmmode\pm\else\textpm\fi{}60\phantom{\rule{0.16em}{0ex}}\mathrm{W}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ to $830\ifmmode\pm\else\textpm\fi{}100\phantom{\rule{0.16em}{0ex}}\mathrm{W}\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$. The measured thermal conductivities agree with theoretical calculations across the full temperature range. The similar calculated and measured peak temperatures helps to narrow down the boundary scattering mean free path to be around 4 \ensuremath{\mu}m in two samples and 5 \ensuremath{\mu}m in another, while the variation of the peak magnitude reveals a one-order-of-magnitude difference in the strength of point defect scattering. The phonon-defect scattering behavior correlates well with the measured electronic Raman scattering background, the impurity concentrations revealed by secondary ion mass spectroscopy, and the Hall concentration and mobility of the $p$-type samples except for an anomalously high hole concentration that appears in one sample, which indicates nonuniform impurity distribution. The observed correlation clarifies the origins of extrinsic phonon scattering mechanisms in BAs crystals.

Advances in 200 mm 4H SiC Wafer Development and Production

200 mm diameter n-type 4H SiC wafers were produced from bulk crystals grown using a physical vapor transport (PVT) method. The configuration of the growth cell was modified to both allow for the growth of larger crystals with respect to the standard 150 mm process, and to induce a thermal environment necessary to increase the mass deposition rate. A 25% increase in deposition rate was achieved relative to the standard process. The resulting wafers exhibited resistivity uniformity comparable to commercial 150 mm product. Optical and x-ray techniques were used to evaluate wafer quality, and revealed surface and bulk crystal defect densities acceptable for epilayer growth.

Brief Introduction to Single Crystal Growth Techniques

This article aims to introduce several synthesis methods to grow single-crystalline samples, which are widely used in experimental condensed matter physics studies. In order to understand the crystal growth in high-temperature melts, the concept of congruent/incongruent melting is explained based on a binary phase diagram. Then principles and practices of the Czochralski, flux-growth, and floating-zone growth methods are described. In addition, the chemical vapor transport method is briefly mentioned.

Review of Sublimation Growth of SiC Bulk Crystals

The review on bulk growth of SiC includes a basic overview on the widely used physical vapor transport method for processing of 4H-SiC boules as well as the discussion of three current research topics: (a) Sublimation bulk growth of large area, freestanding cubic SiC, (b) in-situ Visualization of the PVT Process using 2D and 3D X-ray based imaging and (c) prediction of dislocation formation and motion in SiC using a continuum model of dislocation dynamics (CDD).

Highly Sensitive Photodetector Based on the n-Si/p-GaSe Vertical Heterojunction

Photodetectors based on two-dimensional materials and their van der Waals (vdW) heterojunctions usually have excellent optoelectronic performance and great potential applications. Herein, gallium (Aladdin, particles, 99.999% trace metal basis), selenium (Aladdin, powder, 99.999% trace metal basis), and iodine (Alfa Aesar, 99.999% trace metal basis) are the raw materials for the growth of gallium selenide (GaSe) single crystals by the chemical vapor transport method, in which iodine is the transport agent. Subsequently, GaSe nanoflakes are exfoliated from the grown bulk GaSe crystals by mechanical exfoliation. The n-Si/p-GaSe van der Waals vertical heterojunctions have been designed and fabricated for photodetection, which show good characteristics including a high responsivity of 1.74 A/W and a fast response/recovery time of 48 μs/88 μs under zero bias owing to their type-II band structure and built-in electric field. The results indicate that n-Si/p-GaSe vdW vertical heterojunctions are promising candidates in future ultrafast optoelectronic devices.

Crystal Growth and Characterization of ZrSiS-Type Topological Dirac Semimetals

WHM materials (W = Zr/Hf, H = Si/Ge/Sn, M = S/Se/Te) represent a large family of topological semimetals, which have attracted intensive interest since they are considered to be good candidates for studying various topological states. Here, we report the crystal growth, characterization, and electronic properties of HfSiS, ZrGeS, and ZrGeSe. All samples were prepared by a chemical vapor transport method with I2 as a transport agent, and the growth conditions were optimized. X-ray diffraction (XRD) measurements showed that the as-grown crystals crystallized in a PbFCl-type layered structure. They all showed metallic behavior from temperature-dependent resistivity measurements and the carrier densities were estimated to be in the order of 1021 cm−3. A large magnetoresistance of up to 1200% and an obvious Shubnikov–de Hass (SdH) oscillation were observed for HfSiS.

Ultrafast-response and broad-spectrum polarization sensitive photodetector based on Bi1.85In0.15S3 nanowire

Alloying of semiconductors is a good strategy to manipulate their electronic band structures, which can broaden the photoresponse range of the corresponding optoelectronic devices. In addition, building a Schottky diode and improving the crystal quality of the channel semiconductor can improve the photoresponse speed of the optoelectronic device. Here, we report the design and preparation of Bi1.85In0.15S3 nanowires by a facile chemical vapor transport method. The individual Bi1.85In0.15S3 nanowire photodetectors realize excellent photoresponse in a broadband range from solar-blind deep ultraviolet (266 nm) to near-infrared (830 nm), and the obtained maximum external photoresponsivity of 95.99 A/W and detectivity of about 3.52×1011 Jones at 638 nm. Furthermore, the photodetectors also exhibit the ultrafast photoresponse speed with the rise time of 190 ns and the fall time of 180 ns, owing to the high crystal quality and the Schottky contacts between the Au electrodes and nanowires. In addition, the photoresponse of photodetectors is polarization angle sensitive in a broadband range from 266 to 808 nm, and the obtained maximum dichroic ratio is 3.54 at 808 nm, which results from the structural anisotropy of the Bi1.85In0.15S3 crystal. These performances are superior to the reported Bi2S3, In2S3, and other Bi or In sulfide nanowire photodetectors. The results render (BixIn1−x)2S3 photodetectors have significant application potentials in multifunctional optoelectronics and electronics.

Enhanced Optical Response of Zinc-Doped Tin Disulfide Layered Crystals Grown with the Chemical Vapor Transport Method.

Tin disulfide (SnS2) is a promising semiconductor for use in nanoelectronics and optoelectronics. Doping plays an essential role in SnS2 applications, because it can increase the functionality of SnS2 by tuning its original properties. In this study, the effect of zinc (Zn) doping on the photoelectric characteristics of SnS2 crystals was explored. The chemical vapor transport method was adopted to grow pristine and Zn-doped SnS2 crystals. Scanning electron microscopy images indicated that the grown SnS2 crystals were layered materials. The ratio of the normalized photocurrent of the Zn-doped specimen to that of the pristine specimen increased with an increasing illumination frequency, reaching approximately five at 104 Hz. Time-resolved photocurrent measurements revealed that the Zn-doped specimen had shorter rise and fall times and a higher current amplitude than the pristine specimen. The photoresponsivity of the specimens increased with an increasing bias voltage or decreasing laser power. The Zn-doped SnS2 crystals had 7.18 and 3.44 times higher photoresponsivity, respectively, than the pristine crystals at a bias voltage of 20 V and a laser power of 4 × 10−8 W. The experimental results of this study indicate that Zn doping markedly enhances the optical response of SnS2 layered crystals.

On the Absorption and Photoluminescence Properties of Pure ZnSe and Co-Doped ZnSe:Eu3+/Yb3+ Crystals

Co-doped Zinc selenide (ZnSe) is a promising material because of a high photoluminescence efficiency and wide spectral range emission in the visible region. In this work, ZnSe and Eu3+/Yb3+ co-doped ZnSe crystals were grown by the chemical vapour transport method. Photoluminescence and optical measurements revealed the effect of trivalent rare earth Eu3+/Yb3+ ions on the emission of new lines with enhancement intensity. In the photoluminescence spectrum, some sharp and intense lines were observed that allow for the possibility of covering a broad emission range. Moreover, the optical measurement showed a lower bandgap compared to that of pure ZnSe bulk crystal. This material is suitable for developing optoelectronic devices, which can emit light in the visible and near infrared range with an improved emission efficiency and wide tunability.

One-step synthesis of FeSe0.45Te0.55 single crystals without excess Fe content

Excess interstitial Fe atoms in as-grown FeSe1−xTex single crystals are unavoidable in the self-flux growing procedure. As harmful defects to the study of superconductivity and Majorana fermions, the excess Fe atoms are usually removed by the post-annealing procedure. This two-step method is mostly used to obtain high quality FeSe1−xTex single crystals in present studies. Here, we carried out a one-step way to synthesize FeSe1−xTex single crystals without excess Fe content using a chemical vapor transport method. By combining transport measurement, magnetic measurement, and local scanning tunneling microscopy measurement, we prove that there is no excess Fe content in our one-step grown FeSe0.45Te0.55 single crystals. This work provides a new convenient way to obtain pure FeSe0.45Te0.55 single crystals and may be helpful to better study this exotic material.