MoS2(1-x)Te2x, the alloy of MoS2 and MoTe2 was fabricated with just co-sputtering and the combination of co-sputtering with following thermal treatment in chalcogen ambient. Phase separation, where MoTe2 was segregated rather than S and Te being uniformly distributed, was observed for some samples. From the physical structure evaluation using XRD, it was shown that the samples that was sulfurized after unintentional oxidation during shelf time exhibited no phase separation. It was suggested that oxidation of Mo or amorphous nature of the film at the chalcogenization stage may prevent the phase separation. In addition, some samples were stored in desiccator for stability evaluation. It was revealed that the samples undergo oxidation to different extent depending on the carrier gas used in tellurization. Finally, the bandgap and band structure was evaluated for samples with different Te concentration. The bandgap showed bowing behavior for different Te concentration with the bowing parameter b = -1.21 eV. Combined with the bandgap evaluation, the valence analysis with XPS showed that the band structure shifted according to the Te concentration. The shift in bandgap allows flexible band alignment which is expected to expand the materials applicability.

Zinc Oxide (ZnO) has been shown to exhibit semiconducting and piezoelectric dual properties. This has led to a large commercial demand on ZnO for optoelectronics that operate at the blue-ultraviolet regions. Consequently, varying techniques have been devised to create different nanostructures of ZnO. Here, the single step synthesis of ZnO nanostructures was performed on Si(100) substrates with a thin ZnO seed-layer. A modified chemical vapor deposition (CVD) method was developed to accomplish the structure formation. Sb doping of the structures in the gas phase was performed to study its effects on structure and optoelectronic properties. Different structures were realized including nanofilaments, nanoparticles, microflowers, nanorods, nanotubes, and nanocolumns. Only nanorods/columns, and nanotubes are shown in this work. Morphology was examined using scanning electron microscopy (SEM). Energy-dispersive X-ray spectroscopy (EDS) and X-ray powder diffraction (XRD) were used for structural studies. Optoelectronic properties were explored using room-temperature photoluminescence (PL) spectroscopy. PL data show the relative decrease in the number of defects and increase in crystal quality upon increasing reaction time. Significant structural effects were also observed upon doping. Some structural defects might be attributed to the diffusion of Sb ions into the lattices of ZnO, replacement of Zn by Sb, and ionic radii difference. These stacking faults are most likely the reason behind the dominance and broadening of DLE peak.

Bulk production by Chemical Vapor Deposition (CVD) of ultra-long Carbon Nanotubes (CNTs) with lengths greater than several centimeters is desirable for materials applications, but is not presently feasible. A principal reason for this limitation is cessation of CNT growth due to erosion of the nano-sized catalyst particles from which the CNTs nucleate and grow: at elevated CVD growth temperatures, atoms of catalytic metal detach and diffuse away from the particles, resulting in erosion and eventual deactivation of the particles. Recently, a novel idea was introduced to slow this diffusion and erosion by including heavy refractory metals with the catalyst metals in the nanoparticles. Here are presented recent and ongoing investigations into this method. The metal system investigated uses iron as catalyst and rhenium as diffusion inhibitor. Results show that inclusion of Re in the catalyst particles will substantially increase the catalysts particle lifetimes, and hence the growth time of the CNTs produced. These results are compared to previous results obtained using the iron/molybdenum system of catalyst/inhibitor.

Theoretical calculations and experimental observations show MoTe2 is a type II Weyl semimetal, along with many members of transition metal dichalcogenides family. We have grown highly crystalline large-area MoTe2 thin films on Si/SiO2 substrates by chemical vapor deposition. Very uniform, continuous, and smooth films were obtained as confirmed by scanning electron microscopy and atomic force microscopy analyses. Measurements of the temperature dependence of longitudinal resistivity and current–voltage characteristics at different temperature are discussed. Unsaturated, positive quadratic magnetoresistance of the as-grown thin films has been observed from 10 to 200 K. Hall resistivity measurements confirm the majority charge carriers are hole.

We demonstrated that single-walled carbon nanotubes (SWCNTs) grew from Ir catalysts by an alcohol catalytic chemical vapor deposition (ACCVD) method using a gas source-type CVD system. At an ethanol pressure of 1×10−1 Pa at 800°C, vertically aligned SWCNTs (VA-SWCNTs) were grown on SiO2/Si substrates. As the growth time became longer, the VA-SWCNT became thicker, and it reached almost 5 μm for a growth time of 180 min. The Raman spectroscopy results showed that the diameters of the grown SWCNTs were mainly distributed below 1.1 nm, indicating that the SWCNTs grown from Ir catalysts had small diameters compared with those from other metal catalysts.

We have demonstrated the high yield (∼900 μm) and highly single-wall selective (>95%) growth of carbon nanotube (CNT) forest using aluminium nitride (AlN) as a catalyst underlayer. Such high efficiency and single-wall selectivity have not been previously reported using this underlayer system. Evaluation with transmission electron microscopy showed that the average diameter of the grown carbon nanotubes was ∼3.0 nm, which is similar to those grown on alumina underlayers. In addition, characterization of the catalyst/underlayer system using atomic force microscopy and X-ray photoelectron spectroscopy suggests that neither Ostwald ripening along the surface nor catalyst subsurface diffusion into the AlN underlayer are severely occurring at the growth temperature, leading to the creation of the stable and dense small nanoparticle array to achieve an efficient growth of single-wall CNTs.

Catalytic growth of substantial amounts of Carbon Nanotubes (CNTs) to lengths greater than 1 – 2 cm is currently limited by several factors, including especially the deactivation of the catalyst particles due to erosion of catalyst atoms from the catalyst particles at elevated CNT growth temperatures. Inclusion of refractory metals in the CNT growth catalyst has recently been proposed as a method to prevent this catalytic particle erosion and deactivation, allowing the CNT to grow for greater times and reach substantially greater lengths. Here are presented results of recent investigations into this method. The system investigated employs Molybdenum as the erosion inhibitor and Iron as the CNT growth catalyst. Results show that inclusion of Mo leads to substantially longer catalyst particle lifetimes.

Recently, the millimetre-scale, highly efficient growth of single-wall carbon nanotube (SWCNT) forests from iron (Fe) catalysts has been reported through the annealing of the magnesia (MgO) underlayer. Here, we report the modulation of the CNT yield (height) and average number of CNT walls for a Fe/MgO catalyst system through the collective effects of initial Fe amount and MgO annealing temperature. Our results revealed the existence of a well-defined region for high yield SWCNT forest growth in the domain of deposited Fe thickness and MgO annealing temperature. Through topographic examinations of the catalyst surface using atomic force microscopy, we confirmed that our results stem from the collective effects of increased amounts of surface-bound Fe through the amount of deposition and suppression of Fe subsurface diffusion, together govern the amount of surface-bound catalyst. The combination of these mechanisms determined the final nanoparticle size, density, and stability and could explain the three distinctly defined regions: low yield SWCNT growth, high yield SWCNT growth, and high yield multiwall CNT growth. Furthermore, we explained the observed borders between these three regions.

During decomposition of copper formate, a volatile intermediate is formed, that can be utilized to fabricate conductive copper lines for electrical interconnections. By the method called Reactive Transfer Printing (RTP), a pattern of copper (II) formate was printed, and placed adjacent to a second surface; decomposition of the printed pattern led to a transfer of copper to the second substrate. It was found that the yield of the transfer process improved due to presence of several carboxylic acids which are liquid with a high boiling point. Furthermore we found that the transport of copper starts at a lower temperature than previously reported, indicating that the first decomposition step of copper formate is related to the catalytic decomposition of formic acid on a copper surface. The findings enable printing of conductive copper patterns onto the interior surface of a glass vessel.

Thin film tin sulphide (SnS) was deposited on to molybdenum (Mo) substrates using metal organic chemical vapor deposition at 470°C using tetraethyltin and ditertiarybutylsulfide as precursors. In situ mass spectroscopy was used to study the exhaust gas species downstream of the reaction zone. The precursor vapor carrier gas was either nitrogen or hydrogen, thin film SnS only forming when the latter was used. Mass spectroscopy determined that hydrogen sulfide was being produced and playing a critical role in the vapor phase reaction process and adsorption of tin and sulfur on to the Mo surface. As-grown grain sizes were determined by scanning electron microscopy and were observed to be large averaging around 2 microns across. X-ray diffraction showed the films to be single phase SnS without any parasitic Sn2S3 or SnS2 phases, with a small amount of MoS2 also being detected.

Growth of single-walled carbon nanotube (SWCNT) was achieved by an alcohol catalytic chemical vapor deposition (CVD) mechanism that was conducted in a high vacuum using Ru catalysts. By optimizing the ethanol pressure, SWCNTs can grow in a wide range of temperature between 500 °C and 900 °C. Both the yield and crystalline quality of SWCNTs reached their maxima at 700 °C. Significantly, the SWCNT growth was achieved even at 450 °C, which was much lower than the growth temperatures that were required for SWCNT growth using Ru catalysts previously. Raman measurements exhibited that the diameter distribution of the SWCNTs that were grown at 450 °C was quite narrow and (11, 4) nanotubes were dominant. The observations of transmission electron microscope (TEM) suggested that the size of the Ru particles were larger than the diameter of SWCNT. Such a relation was similar to the relation observed in the growth of SWCNTs using Pt catalysts.

The chemical-vapor deposition conditions for the growth of pure boron (PureB) layers on silicon at temperatures as low as 400°C were investigated with the purpose of optimizing photodiodes fabricated with PureB anodes for minimal B-layer thickness, low dark current and chemical robustness. The B-deposition is performed in a commercially-available Si epitaxial reactor from a diborane precursor. In-situ methods commonly used to improve the cleanliness of the Si surface before deposition are tested for a deposition temperature of 450°C and PureB layer thickness of 3 nm. Specifically, high-temperature baking in hydrogen, and exposure to HCl are tested. Both material analysis and electrical diode characterization indicate that these extra cleaning steps degrade the properties of the PureB layer and the fabricated diodes.

Although Pb-based perovskite solar cells already achieve power conversion efficiencies (PCE) beyond 20 %, the use of toxic Pb is causing considerable environmental concern. As a consequence, a variety of alternative cations have been investigated to replace Pb2+ in the perovskite structure. Methylammonium bismuth iodide (MA3Bi2I9, MBI) has shown promising results for environmentally benign and chemically stable devices. While the PCE of MBI-based solar cells are still comparably low, structural improvements have been made by using chemical vapor deposition (CVD). CVD allows for the well-controlled formation of coherent and dense MBI layers in contrast to solution-processing. In this work, CVD as a possible MBI fabrication method for efficient and size-scalable solar cells is discussed. The precursors MA iodide (MAI) and Bi iodide (BiI3) are deposited in an alternating deposition process forming the desired MBI perovskite on the heated substrate. Substrate temperatures as well as deposition times of each precursor are varied with the aim of forming coherent and dense MBI layers. Optimized films are further processed to solar cell prototypes and compared with solution-processed reference devices. The results reveal that CVD possesses great potential to enable the manufacture of MBI photovoltaic (PV) devices processed in a solvent-free environment.

Transition metal dichalcogenide (TMDC) monolayers like MoS2 are promising materials for future electronic applications. Large-area monolayer MoS2 samples for these applications are typically synthesized by chemical vapor deposition (CVD) using MoO3 reactants and gas-phase sulfur precursors. Recent experimental studies have greatly improved our understanding of reaction pathways in the CVD growth process. However, atomic mechanisms of sulfidation process remain to be fully elucidated. In this work, we present quantum-mechanically informed and validated reactive molecular dynamics (RMD) simulations for CVD synthesis of MoS2 layers using S2 precursors. Our RMD simulations clarify atomic-level reaction pathways for the sulfidation of MoO3 surfaces by S2, which is a critical reaction step for CVD synthesis of MoS2 layers. These results provide a better understanding of the sulfidation process for the scalable synthesis of defect-free MoS2 and other TMDC materials.

In situ X-ray absorption near edge structure (XANES) measurements were conducted to elucidate the chemical states of Co and Ni catalysts during single-walled carbon nanotube (SWCNT) growth via chemical vapor deposition (CVD). XANES spectra indicated that both Co and Ni catalysts partially oxidized before heating. It was found that Co catalysts formed carbides during the SWCNT growth. In contrast, Ni catalysts remained metallic state even after the SWCNT growth had begun. These results indicate that during SWCNT growth, carbon atoms dissolve into Co particles, whereas for Ni particles, they diffuse on the surface region. It was concluded that the growth mechanisms of SWCNTs formed by CVD differed for either Co or Ni catalyst.

In this study, we examined the limitations in growth temperatures for single-walled carbon nanotube (SWNT) forest synthesis using a water (H2O) growth enhancer as highlighted by a dramatic decrease in growth efficiency at high temperatures. Comparative synthesis using a carbon monoxide (CO) growth enhancer demonstrated a wider temperature window for SWNT forest synthesis. We found that SWNT forests taller than 100 μm could not been synthesized above 850 °C by using H2O, but by using CO, tall (>800 μm) forests could be synthesized at growth temperatures exceeding 900 °C. The dependency of H2O concentration showed that H2O, itself, was the cause for the reduced growth efficiency observed at higher temperatures. In contrast, increased CO concentrations did not result in any drop in the carbon nanotube (CNT) yield across the entire temperature range. While a severe drop of CNT yield above 950 °C was observed when CO was used, the origin was found to stem from catalyst particle aggregation enhanced by diffusion on the surface rather than CO itself. Therefore, the ability to synthesize at higher growth temperatures is advantageous when using more stable carbon feedstocks, such as methane.

When the size and spacing of catalyst nanoparticles are well controlled on a substrate, carbon nanotubes (CNTs) can grow and assemble into a unique, vertically aligned structure frequently called a “forest.” Long, aligned, and pure CNTs can easily be synthesized in simple or highly complex configurations. First reported in 1996, CNT forests have been shown to be unique and useful forms of CNTs, as they have spurred the development of novel processes and applications and in addition, served as test beds for investigations into CNT growth mechanisms. This article provides an overview of two decades of research in this area.

Catalysts play essential roles in the chemical vapor deposition of single-wall carbon nanotubes (SWCNTs). In this article, we summarize studies on catalysts for the structure-controlled growth and mass production of SWCNTs, discussing the main progress and the remaining challenges.

The union of the unique diamond properties with steel (most common substrate material) provides a new solution for machine parts under critical mechanical conditions and severe environmental. However, CVD diamond coating directly on steel comes with several issues. The fundamental reasons for the lack of adhesion are an iron catalytic effect, the high carbon solubility in iron and high mismatch in thermal expansion coefficient of diamond and steel. The use of interlayer may solve these issues acting as a diffusion barrier, for both iron and carbon, and match thermal expansion coefficients. Several articles describe the PVD deposition or electroplated interlayer. In the present study, the diamond film coated steel with an intermediate barrier deposited by laser cladding process. In this novel technique, laser irradiation melts the powder (preplaced) and the substrate surface to create the coating on a steel substrate. We used the SiC/Ti and SiC/Cu powder mixtures to create the intermediate barrier. Diamond film deposition was carried out in an HFCVD reactor (Hot Filament Chemical Vapor Deposition). The samples characterization included X-ray Diffraction (XRD); Field Emission Gun - Scanning Electron Microscopy (FEG-SEM) and Raman Scattering Spectroscopy (RSS). Results showed that laser incidence dissociated partially the SiC powder, forming FeSi, Cu3Si phases. Further, the composite layer assisted the high thermal stress relief in steel/diamond interface.

Next-generation electronic devices are expected to demonstrate greater utility, efficiency and durability. Meanwhile, plastics such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN) and variety of poly(para-xylylene) polymers enable transformational advantages to device shape, flexibility, weight, transparency and recyclability. Exhibiting a combination of outstanding mechanical, electrical, optical, and chemical properties of graphene with the plastic substrates could propose ideal material for the future flexible electronics. Chemical vapor deposition (CVD) allows cost-effective fabrication of a high-quality large-area graphene films, however, the critical issue is clean and noninvasive transfer of the films onto a desired substrate. The water-based delamination of CVD grown graphene on Cu can be considered as a “green” transfer process utilizing only hot deionized water. We investigated a method requiring only two essential steps: coating of 6-inch monolayer CVD graphene with transparent and flexible polymer, and Cu delamination in hot water. Proposed method is inexpensive, reproducible, environmentally friendly, waste-free and suitable for large-scale, high quality graphene. The transfer process demonstrated films with enhanced charge carrier mobility, high uniformity, free of mechanical defects, and sheet resistance as low as ∼50 Ω/sq with 96.5 % transparency at 550 nm wavelength.