Chemical Vapor Transport Method Research Articles

Mixed Insulating State for van der Waals CoPS3

Large-scale high-quality van der Waals CoPS3 single crystals are synthesized using a chemical vapor transport (CVT) method. The crystallographic structure and electronic properties of this layered material are systematically studied using different spectroscopic methods (XPS, NEXAFS, and resonant photoelectron spectroscopy) accompanied by density functional theory (DFT) calculations. All experimental and theoretical data allow assignment of this material to the class of mixed Mott-Hubbard/charge-transfer insulator with Udd ≅ Δ. All obtained results can enrich the information on the new class of van der Waals materials, transition metal phosphorus trichalcogenides, and help to further effectively exploit their electronic, optical, and transport properties, which are important for adopting this kind of materials into different application areas, such as spintronics and catalysis.

Novel High Current-Carrying Quasi-1D Material: Nb2 PdS6.

A quasi-one-dimensional van der Waals metallic nanowire Nb2 PdS6 is synthesized, and its electrical characteristics are analyzed. The chemical vapor transport method is applied to produce centimeter-scale Nb2 PdS6 crystals with needle-like structures and X-ray diffraction (XRD) confirms their high crystallinity. Scanning transmission electron microscopy reveals the crystal orientation and atomic arrangement of the specific region with atomic resolution. The electrical properties are examined by delaminating bulk Nb2 PdS6 crystals into a few nanometer-scale wires onto 100 nm-SiO2 /Si substrates using a mechanical exfoliation process. Ohmic behavior is confirmed at the low-field measurements regardless of their thickness variation, and 4.64nm-thick Nb2 PdS6 shows a breakdown current density (JBD ) of 52 MA cm-2 when the high electrical field is delivered. Moreover, with further exfoliation down to a single atomic chain, the JBD of Nb2 PdS6 is predicted to have a value of 527 MA cm-2 . The breakdown of Nb2 PdS6 proceeds due to the Joule heating mechanism, and the Nb2 PdS6 nanowires are well fitted to the 1D thermal dissipating model.

Artificial Neural Network Identification of GeSe-Based Two-Color Polarization-Sensitive Photodetector

For low-dimensional materials, the in-plane anisotropy of their structure can realize the detection of polarized light. This characteristic can be utilized to fabricate polarization-sensitive photodetectors without polarizers. It is conductive to the miniaturization and integration of devices. As a typical IV-VI group material, GeSe is easy to be synthesized by chemical vapor transport method, and has obvious response to the light in the visible and near-infrared band. In this study, a GeSe-based polarization-sensitive photodetector was fabricated. The sensitivity of GeSe to the polarization angle of light in the visible and near-infrared bands was explored. And a program was used to perform large-scale imaging. The polarized light response in the visible and near-infrared bands was compared and analyzed by artificial neural network.

Chemical Vapor Transport Synthesis of Cu(VO)2(AsO4)2 With Two Distinct Spin-1/2 Magnetic Ions.

A new copper vanadyl arsenate, Cu(VO)2(AsO4)2, was synthesized via the chemical vapor transport method. Cu(VO)2(AsO4)2 adopts an original structure type. It is characterized by layers formed by edge-sharing and corner-sharing V-centered octahedra resulting in a unique topology that was hitherto not reported for vanadates. Single CuO6 octahedra connect vanadate layers into a rigid framework. The thermal expansion of the framework studied by the single-crystal HT X-ray diffraction is reported. The magnetic behavior of Cu(VO)2(AsO4)2 shows an interplay of ferromagnetic V4+-V4+ and antiferromagnetic Cu2+-V4+ interactions that result in a ferrimagnetic long-range order below TC = 66 K.

Visible light photodetectors based on multilayered O-doped BiI3 nanoflakes with ultrahigh sensitivity

Recently, BiI3 was discovered as a promising 2D semiconductor materials for photovoltaic and photodetector device, due to its suitable bandgap, high optical absorption coefficient, excellent electron mobility, and low carrier concentration. However, as so far, only the CVD/PVD grown BiI3 nanoflakes/films have been reported. Here, we firstly synthesized the O-doped BiI3 (OBI) bulk crystals via chemical vapor transport (CVT) method, and then systematically studied the electrical and optoelectronic properties of exfoliated multi-layer OBI nanoflakes. Back-gated field-effect transistor fabricated on the multi-layer OBI nanoflakes with van der Waals (vdW) bottom electrode contact exhibited n-type semiconducting characteristics. In addition, exfoliated multi-layer OBI based photodetector demonstrates an excellent photoresponse with good reproducibility at room-temperature for visible wavelengths, including a high photo-to-dark current ratio (2.16 ×104), a remarkable photoresponsivity (850 mA W−1), a fast response speed (rise/decay time of 3.2/2.9 ms), and a high specific detectivity (9.85 ×1012 Jones), which is favored by the ultralow dark current (∼30 fA). These results indicated that the OBI crystals have great potential for future applications in highly sensitive and ultrafast visible-light photodetector.

Nonlinear optical properties and photoexcited carrier dynamics of MnPS3 nanosheets.

Here, we systematically report on the preparation of high-quality few-layered MnPS3 nanosheets (NSs) by chemical vapor transport (CVT) and mechanical stripping method, and its carrier dynamics and third-order nonlinear optical properties were studied. Using the classical technique of open aperture Z-scan, a typical phenomenon of saturable absorption (SA) was observed at 475 nm, which indicates that the material is expected to be used as a saturable absorber in ultrafast lasers. The typical phenomenon of reverse saturation absorption (RSA) is observed at 800 and 1550 nm, which shows its potential in the field of broadband optical limiting. Compared with graphene, BP, MXene, MoS2 and other typical two-dimensional materials, MnPS3 NSs has a higher modulation depth. Using the non-degenerate transient absorption spectroscopy technology at room temperature, a slower cooling process of thermal carrier of MnPS3 was observed. Moreover, the carrier lifetime can be tuned according to the wavelength. This work is of great significance to the improvement of MnPS3 based devices, and lays a foundation for the application of MnPS3 in short-wavelength photovoltaic cell, photoelectric detection and other fields.

Temperature dependence of band shifts induced by impurity ionization in ZrTe5

The topological phase transition in ${\mathrm{ZrTe}}_{5}$ remains a challenge for its sensitivity to the structural parameters and carrier densities. One important issue is that the temperature dependence of the band shifts has been reported controversially. Using angle-resolved photoemission spectroscopy, we study the temperature evolution of the band structures of ${\mathrm{ZrTe}}_{5}$ with samples prepared by chemical vapor transport and flux methods. We find two distinct types of band shift with temperature, one monotonically moving downward to high binding energies with the increase of temperature and another one moving downward first and then reversely upward. By assuming ${\mathrm{ZrTe}}_{5}$ is a semiconductor with a limited amount of impurities, we analyze the temperature-induced ionization of the impurities and chemical potential shift to interpret the discrepant experimental observations. In this scenario, the discrepancies in band structures and the controversial results on temperature-dependent band shifts can be reconciled in a unified picture.

Colloidal Synthesis of Zirconium Disulphide Nanostructures and their Stability Against Oxidation

AbstractThe need to exploit the exotic properties of ZrS2 synthesized via colloidal means is imperative. For almost a decade now there has been no literature on the colloidal synthesis of ZrS2 nanomaterials. Meanwhile, several publications are available on other methods of synthesis mostly chemical vapour transport (CVT) and chemical vapour deposition (CVD). The synthesized bulk material from the CVT method is further subjected to exfoliation (mechanical or liquid) to obtain mono or few‐layers of ZrS2. With the colloidal method, there is a possibility of the oxide being formed during the synthesis of ZrS2 and likely destabilization of the nanomaterial after synthesis on exposure to ambient environment. In this study, both the heat up and hot injection methods were employed to fabricate various morphologies of ZrS2 nanomaterials. The metal and sulphur precursors were dissolved in a mixture of octadecene (ODE) and oleic acid (OA); and refluxed at a temperature of 290 °C in the presence of nitrogen gas. ODE served the role of non‐coordinating solvent, while OA served as the capping agent. Nanorods, nanospheres and nanosheets were obtained from the heat up method. Meanwhile, the hot injection approach produced nanosheets and nanospheres with well noticeable hollow centres. Powder X‐ray diffractometer (PXRD) validated the formation of the ZrS2 hexagonal phase with traces of oxides of zirconium, ZrO2. The peak of S2p was conspicuously absent while the Zr3d peak was well noticeable in the XPS spectra. XPS and EDS measurements confirmed the replacement of the sulphur atom by the O atom on the surface of the nanomaterials. Only one exciton peak was observed for the absorption spectra from both the heat up and hot injection methods; and thermal thermogravimetry analysis (TGA) revealed three plateaux of decomposition of the nanomaterials.

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.

(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.

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.

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.

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.