Vapor Deposition Method Research Articles

Synthesis and characterization of thermally-evaporated CdS thin-films

Cadmium sulfide (CdS) thin films (thickness: 200 nm) were grown over silicon (Si) substrate via thermal evaporation deposition method, where the ultimate pressure and deposition rate were 1 × 10−6 torr and 1.0-1.2 Å/sec, respectively. X-ray diffraction established polycrystalline films with a hexagonal crystal structure and preferred orientation (002). The energy dispersive analysis of X-ray has recognized pure and stoichiometric films. The uniform, dense and smooth films with low roughness (1.4 nm) appeared in atomic force microscopy. The scanning electron microscopy characterization has recognized a continuous and defects-free film (like cracks, pinholes and overhang) with a uniform distribution of interconnected nanoparticles (size: 24.5–35.1 nm). The good adhesion of the film was confirmed via a scotch tape test. Ellipsometry revealed that the grown CdS film has a refractive index of 2.42–2.45. Thus, polycrystalline CdS film with hexagonal phase (highly stable, wide bandgap, high transmission, environmentally tolerable, and good mechanical strength) could be utilized as a suitable window material and passivation agent in the fabrication of solar cell and infrared detector, respectively.

Bright Soliton and Bright–Dark Soliton Pair in an Er-Doped Fiber Laser Mode-Locked Based on In2Se3 Saturable Absorber

The output power in ultrafast fiber lasers is usually limited due to the lack of a versatile saturable absorber with high damage threshold and large modulation depth. Here we proposed a more efficient strategy to improve the output energy of erbium-doped fiber laser based on indium selenide (In2Se3) prepared by using the physical vapor deposition (PVD) method. Finally, stable mode-locked bright pulses and triple-wavelength dark–bright pulse pair generation were obtained successfully by adjusting the polarization state. The average output power and pulse energy were 172.4 mW/101 nJ and 171.3 mW/100 nJ, which are significantly improved compared with the previous work. These data demonstrate that the PVD-In2Se3 can be a feasible nonlinear photonic material for high-power fiber lasers, which will pave a fresh avenue for the high-power fiber laser.

Low-Temperature Chemical Vapor Deposition Growth of MoS2 Nanodots and Their Raman and Photoluminescence Profiles

We report on the growth of an ordered array of MoS2 nanodots (lateral sizes in the range of ∼100–250 nm) by a thermal chemical vapor deposition (CVD) method directly onto SiO2 substrates at a relatively low substrate temperature (510–560°C). The temperature-dependent growth and evolution of MoS2 nanodots and the local environment of sulfur-induced structural defects and impurities were systematically investigated by field emission scanning electron microscopy, micro-Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) techniques. At the substrate temperature of 560°C, we observed mostly few-layer MoS2, and at 510°C, multilayer MoS2 growth, as confirmed from the Raman line shape analysis. With reduced substrate temperature, the density of MoS2 nanodots decreases, and layer thickness increases. Raman studies show characteristic Raman modes of the crystalline MoS2 layer, along with two new Raman modes centered at ∼346 and ∼361 cm−1, which are associated with MoO2 and MoO3 phases, respectively. Room temperature photoluminescence (PL) studies revealed strong visible PL from MoS2 layers, which is strongly blue-shifted from the bulk MoS2 flakes. The strong visible emission centered at ∼ 658 nm signifies a free excitonic transition in the direct gap of single-layer MoS2. Position-dependent PL profiles show excellent uniformity of the MoS2 layers for samples grown at 540 and 560°C. These results are significant for the low-temperature CVD growth of a few-layer MoS2 dots with direct bandgap photoluminescence on a flexible substrate.

Ultrasmooth Organic Films Via Efficient Aggregation Suppression by a Low-Vacuum Physical Vapor Deposition.

Organic thin films with smooth surfaces are mandated for high-performance organic electronic devices. Abrupt nucleation and aggregation during film formation are two main factors that forbid smooth surfaces. Here, we report a simple fast cooling (FC) adapted physical vapor deposition (FCPVD) method to produce ultrasmooth organic thin films through effectively suppressing the aggregation of adsorbed molecules. We have found that thermal energy control is essential for the spread of molecules on a substrate by diffusion and it prohibits the unwanted nucleation of adsorbed molecules. FCPVD is employed for cooling the horizontal tube-type organic vapor deposition setup to effectively remove thermal energy applied to adsorbed molecules on a substrate. The organic thin films prepared using the FCPVD method have remarkably ultrasmooth surfaces with less than 0.4 nm root mean square (RMS) roughness on various substrates, even in a low vacuum, which is highly comparable to the ones prepared using conventional high-vacuum deposition methods. Our results provide a deeper understanding of the role of thermal energy employed to substrates during organic film growth using the PVD process and pave the way for cost-effective and high-performance organic devices.

Effect of carbon nanotubes produced by using different methods on electrical and optical properties of zinc oxide–carbon nanotube composite

Abstract In this study, carbon nanotubes, which were produced by using chemical vapour deposition and mechano-thermal methods, were combined with zinc oxide matrix at different ratios and the effects of the nanotubes on electrical and optical properties of zinc oxide were examined. It was observed that electrical conductivity of zinc oxide at room temperature increased with the increase in the reinforcement rate both in carbon nanotube reinforced samples produced by using chemical vapour deposition and those produced by using the mechano-thermal method. Carbon nano-tube reinforced samples produced by using chemical vapour deposition yielded relatively better results for the same reinforcement rate.

Growth of Metal Oxide Nanostructures by Thermal Oxidation of Metals Under Influence of External Electric Fields and Electric Current Flow

Thermal oxidation of metals in a furnace or a hot plate is a simple and low‐cost method to grow nanowires and other nanostructures of oxides of technological interest. In comparison with evaporation–deposition techniques based on vapor–solid (VS) or vapor–liquid–solid (VLS) mechanisms, thermal oxidation is a more direct and easy technique but does not normally lead to the formation of complex heterostructures or ternary oxides. Application of an external electric field at the sample during thermal oxidation has been used to improve the control of the nanowire dimensions, or final concentration on the starting metal surface. Other approach to grow oxide nanowires during the oxidation process is to heat the sample by Joule effect by the flow of a high‐density electric current in a metal wire. Joule heating has been found to reduce the growth time, typically some hours in thermal oxidation or evaporation–deposition methods, to few seconds or minutes. Herein, the results of representative articles on nanowire growth during thermal oxidation under the presence of an electric field and on the growth during Joule heating are summarized in the frame of mechanisms of stress relaxation‐driven ion diffusion and of thermally assisted electromigration.

A strategy of adopted Co4S3/Co2P2O7 composite grew on carbon paper to enhance the efficient of dye-sensitized solar cells

Metal phosphates have shown good hydrogen evolution reaction catalytic ability, but as counter electrode (CE) materials they are rarely used in dye-sensitized solar cell (DSSC). A strategy that introduction of Co2P2O7 as a “collaborator” to improve the catalytic performance of Co4S3 for the DSSC. The Co4S3/Co2P2O7 film grew on carbon paper (CP) was synthesized by using a hydrothermal route and vapor deposition method, and served as platinum-free (Pt-free) CE for DSSC. The composite materials of Co4S3/Co2P2O7 has many advantages of unique spherical morphology, large special surface area, more active sites and fast reaction kinetics for the reduction of I−/I3−. Under optimal conditions, a DSSC based on the Co4S3/Co2P2O7/CP CE achieves a high power conversion efficiency of 8.99%, which is comparable to that of the Pt (7.49%) and CoS1.097/CP (8.18%) CEs. The results indicate that the Co4S3/Co2P2O7/CP CE with the advantages of efficient and facile synthesis is a promising alternative to the expensive Pt CE for the DSSCs in the future.

The new concept of thermal barrier coatings with Pt + Pd/Zr/Hf-modified aluminide bond coat and ceramic layer formed by PS-PVD method

AbstractThermal barrier coatings (TBCs) are widely used for protection of gas turbine parts from high temperature and corrosion. In the present study, the new concept of TBCs with three-element-modified aluminide coatings was presented. In the first stage, the Pt and Pd were electroplated on MAR M247 nickel superalloy. In the next stage, the low-activity CVD aluminizing process with Zr or Hf doping was conducted. The ceramic layer containing yttria-stabilized zirconia was obtained by the plasma spray physical vapour deposition (PS-PVD) method. The microscopic examination showed the formation of aluminide coating containing up to 5 at% of Pt and 10 at% of Pd in (Ni, Pt, Pd)Al solid solution. The small concentration of Hf and Zr in diffusion zone of aluminide bond coat was noted as well. The outer ceramic layer was characterized by columnar structure typically formed during the PS-PVD process. The obtained results showed that the new concept of TBCs formed using new processes might be an attractive alternative to conventional coatings produced using the expensive electron beam physical vapour deposition (EB-PVD) method.

Effect of Different Deposition Pressure on Diamond Films Deposited by Hot Filament Chemical Vapor Deposition.

A hot filament chemical vapor deposition (HFCVD) method was adopted to deposit diamond films at deposition pressures ranging from 2-6 kPa. The effects of deposition pressure on the deposition rate, phase structure, and microstructure of diamond films were investigated. The surface morphology, grain size, micro-structure, and growth rate of the diamond films were analyzed using scanning electron microscopy, X-ray diffraction (XRD), and Raman spectrometry. The experimental results showed that granules on the surface exhibited increasingly compact structure with increasing deposition pressure. The diamond films deposited at various pressures have good compactness, and the particles on the film surfaces are arranged in an ordered manner. All films exhibited orientation along the (111) plane, which was the significant characteristic XRD peak of each diamond film. The (111) peak intensity was the strongest for the film prepared at 2 kPa deposition pressure. Overall, the deposition rate and grain size decreased with increasing deposition pressure, provided other deposition conditions remained unchanged. However, the densification of the microstructure and the nucleation density increased with increasing deposition pressure. Secondary nucleation became more pronounced as deposition pressure increased, and grain size decreased as nucleation density increased.

Investigation of UV, ns-laser damage resistance of hafnia films produced by electron beam evaporation and ion beam sputtering deposition methods

Laser-induced damage in coating materials with a high index of refraction, such as hafnia, limits the performance of high power and high energy laser systems. Understanding the underlying physics responsible for laser damage holds the key for developing damage-resistant optical films. Previous studies have reported a substantial difference in laser damage onset for hafnia films produced by different deposition methods, yet the underlying mechanisms for the observed difference remain elusive. We combined laser damage testing with analytical characterizations and theoretical simulations to investigate the response of hafnia films produced by electron (e-) beam evaporation vs ion beam sputtering (IBS) methods upon UV ns-laser exposure. We found that e-beam produced hafnia films were overall more damage resistant; in addition, we observed a polarization anisotropy associated with the onset of damage in the e-beam films, while this effect was absent in the latter films. The observed differences can be attributed to the stark contrast in the pressure inside the pores inherent in both films. The high pressure inside the IBS-induced nanobubbles has been shown to reduce the threshold for laser-induced plasma breakdown leading to film damage. The polarization effects in the e-beam coatings can be related to the asymmetric electric field intensification induced by the columnar void structure. Our findings provide a fundamental basis for developing strategies to produce laser damage-resistant coatings for UV pulsed laser applications.

Mechanism of vertically arrays of carbon nanotubes by camphor based catalysed in-situ growth

In this study, a growth mechanism of vertically aligned carbon nanotubes (VACNT) on a nanostructured porous silicon template (NPSiT) was proposed based on the experimental observations obtained. Camphor oil and ferrocene (Fe) were used as a carbon source and a catalyst, respectively. The NPSiT was optimised and used as a template to synthesise VACNT. The VACNT was synthesised on NPSiT by using a double thermal chemical vapour deposition (DTCVD) method. The synthesis was also performed via a floated method in a DTCVD reactor by using an in-situ catalyst in the absence of any catalysts pre-treatment. Each of the growth mechanisms was proposed based on the TEM images obtained at different synthesis conditions. From the results, a mixed top and bottom growth model was proposed for the growth mechanism of VACNT at the pores and pillars. On the contrary, the tip growth model was proposed for the growth inside the pores, while the valley growth model was proposed for the growth within the pillars of NPSiT. Furthermore, a mixed tip and valley growth model was proposed based on the location of Fe particles.

The water resistance enhanced strategy of Mn based SCR catalyst by construction of TiO2 shell and superhydrophobic coating

The Mn-based catalyst with hollow spherical structure was prepared by hydrothermal method and used for selective catalytic reduction (SCR) of NO with NH3. Mn-based catalysts exhibit excellent de-NOx performance at low-temperature, but narrow operating temperature window and poor water resistance restrict its application. Effectively expanding the operating temperature window and improving the H2O resistance of the Mn-based catalyst are the keys to industrial application. In this article, the H-MnO2 catalyst was prepared by hydrothermal method and modified by kinetic adsorption and vapor deposition methods. The TiO2 layer can effectively limit the excessive redox performance and improve the acidity of the catalyst surface, the NO conversion above 90% at 140–380 °C of H-MnO2@TiO2 catalyst. The phenyltrimethoxysilane was deposited on the surface of the H-MnO2@TiO2 catalyst by vapor deposition method. The NO conversion rate of the H-MnO2@TiO2@HL catalyst exceeds 80% in the temperature range of 180–380 °C. When the H2O was introduced, the NO conversion rate increases from 70% to 85% at 180 °C. The in situ DRIFTs results showed NH3 and NO could be adsorbed and activated on the catalyst surface, and the catalytic reaction follows Langmuir-Hinshelwood (L-H) mechanism. Under the presence of H2O, the NH4+ bonding to Brønsted acid sites were inhibited but the NH3 bonding to Lewis acid site was almost unaffected. In summary, through two-step modification, the operating temperature window and water resistance of Mn-based catalysts are effectively improved. It can be seen that a reasonable structure design can effectively improve the comprehensive performance of the catalyst.

Deposition of YSZ Layer by PS-PVD on Different Materials

Plasma Spray Physical Vapour Deposition (PS-PVD) method was designed for production of ceramic layer on nickel superalloys. In typical process before deposition the base material is heated by plasma up to 900 °C. In present article the yttria stabilized zirconia (YSZ) was deposited on low melting point materials: 2017A-type aluminium alloy and Cu-ETP copper. The influence of power current, process time and powder feed rate on structure and thickness of obtained coatings was analysed. During first deposition process the overheating of Al-sample was observed and as result the power current was decreased to 1600 A. In the next experimental the approx. 5 mm thick dense coating was formed. During experimental processes of YSZ deposition on copper the thickness of coating increased from approx. 5 to 22 mm. The copper-oxide layer was formed under ceramic layer. The microscopic assessment showed the difficulties in formation of columnar ceramic layer on use base materials. The obtained coating was characterized by dense structure as a result of lower plasma energy during process. The increasing of power current is not possible in the case of overheating of base material.

Thermal Barrier Coating Deposited Using the PS-PVD Method on TiAl-Nb-Mo Intermetallic Alloy with Different Types of Bond Coats

TiAl intermetallics can be considered an alternative for conventional nickel superalloys in the high-temperature application. A TBC (Thermal Barrier Coatings) with ceramic topcoat with columnar structure obtained using EB-PVD (electron beam physical vapour deposition) is currently used to protect TiAl intermetallics. This article presents the new concept and technology of TBC for TiAl intermetallic alloys. Bond coats produced using the slurry method were obtained. Si and Al nanopowders (70 nm) were used for water-based slurry preparation with different composition of solid fraction: 100 wt.% of Al, 50 wt.% Al + 50 wt.% Si and pure Si. Samples of TNM-B1 (TiAl-Nb-Mo) TiAl intermetallic alloy were used as a base material. The samples were immersed in slurries and dried. The samples were heat treated in Ar atmosphere at 1000 °C for 4 h. The outer ceramic layer was produced using the new plasma spray physical vapour deposition (PS-PVD) method. The approximately 110 μm thick outer ceramic layers contained yttria-stabilised zirconium oxide. It was characterised by a columnar structure. Differences in phase composition and structures were observed in bond coats. The coatings obtained from Al-contained slurry were approximately 30 μm thick and consisted of two zones: the outer contained the TiAl3 phase and the inner zone consisted of the TiAl2 phase. The second bond coat produced from 50 wt.% Al + 50 wt.% Si slurry was characterised by a similar thickness and contained the TiAl2 phase, as well as titanium silicides. The bond coat formed from pure-Si slurry had a thickness < 10 μm and contained up to 20 at % of Si. This suggests the formation of different types of titanium silicides and Ti-Al phases. The obtained results showed that PS-PVD method can be considered as an alternative to the EB-PVD method, which is currently applied for deposition a columnar structure ceramic layer. On the other hand, the use of nanopowder for slurry production is problematic due to the smaller thickness of the produced coating in comparison with conventional micro-sized slurries.

Revisiting the problem of crystallisation and melting of selenium

In this paper, we study the structure of the solid selenium (Se) formed by the vapor deposition method. We provide direct visual evidence that faceted crystal-like shapes obtained from vapor phase deposition are a self-assembly of linear strands that have a persistence length of 10 μm. These strands are held together by weak forces and can easily be separated. These chains occasionally get entangled to form chiral structures and often meander about destroying long range orientation and translation order in a continuous manner. Moreover, it is easy for the long strands of linear chains to slide past the neighboring ones, and hence the system has a large concentration of disinclination like defects in addition to the defects caused by the entanglement of the chains. Like organic polymers, the obtained Se structures also exhibit a spread in the melting temperature. This spread is closely related to the density of the sub-structures present in the system. The infrared imaging shows that these structures heat up in an inhomogeneous manner and the cross polarized images show that the process of melting initiates in the bulk.

Pulsed Laser Deposition of Epitaxial Non-Doped PbTiO3 Thin Films from PbO–TiO2 Mosaic Targets

PbTiO3 (PTO) suffers from difficulty in preparing high-density robust bulk ceramics, which in turn has been a bottleneck in thin films growth with physical vapor deposition (PVD) methods. In the present work, we prepared non-doped PTO thin films by a pulsed laser deposition (PLD) method with either a single PTO target or a mosaic target consisting of PbO and TiO2 pie-shaped pieces. On the PTO single target, laser irradiation caused selective ablation of Pb, resulting in Ti-rich cone-shaped pillar structure on the surface, whereas the irradiated surface of PbO and TiO2 pieces was smoother. Epitaxial PTO films deposited on SrTiO3 (001) substrates from the pie-chart targets with PbO:TiO2 areal ratio from 3:5 to 5:3 resulted in composition, crystallinity, flatness, and ferroelectric properties almost independent of the areal ratio. The averaged composition of each film was close to stoichiometric, suggesting a compositional self-control mechanism. For growing epitaxial and high-quality non-doped PTO films, a PbO–TiO2 pie-chart target is advantageous in easiness of handling and stable surface structure.

Effect of the chemical vapor deposition condition on the electrochemically catalytic efficiency for hydrogen evolution reaction in MoS2 nanoparticles

Introduction: Using the metal organic chemical vapor deposition (MOCVD) method, we have synthesized the MoS2 nanoparticles on graphite foil substrates employed as the electrochemical working electrodes with highly efficient electrocatalysis for hydrogen evolution reaction (HER).
 Methods: The morphological and structural properties of the as-grown MoS2 materials were demonstrated by field emission scanning electron microscope (FESEM) and Raman spectroscopies, while their elemental components were investigated by X-ray photoelectron spectroscopy (XPS).
 Results: The optimum growth time was acquired to be 11 hours. Thereby such obtained electrode exhibited the maximum HER activity with onset over the potential of 220 mV versus reversible hydrogen electrode (RHE), and the Tafel slope of 66 mV per decade (mV/dec).
 Conclusion: Our results suggest a good technique for the research of high-efficient HER electrocatalyst based on atomic-thickness layered materials.

Photocatalytic Synthesis of Urea (CO2/N2/H2O) on Coal-Based Carbon Nanotubes with the Fe-Core-Supported Ti3+-TiO2 Composite Catalyst

In this study, carbon nanotubes with Fe cores (Fe-CNTs) were successfully prepared by the vapor deposition method, which used raw coal as a carbon source. The brookite crystal Ti3+-doped TiO2 (Ti3+...

Nanorods over wettable and defect sights

Study of wetting and nonwetting surfaces is very significant in various fields of science. Stability of self-assembled wettable layers over any surface is vital in that respect. The generation and then detection of defect sites on such surfaces is also ominously important. In this study, self-assembled monolayers of PFDTS (1H,1H,2H,2H-perfluorodecyltrichlorosilane) molecules on silicon-wafer have been created by vapour deposition method. Due to fluorinated tail of PFDTS molecule, the nature of surface will become hydrophobic. Such hydrophobic surface normally leaves no deposits, except at a single point over the surface. Defect sights on PFDTS region produces confined areas on the hydrophobic surface with different wettability. Such sights will facilitate narrowed deposition of nanoparticles within the hydrophobic defects. These fluidic deposits will facilitate nanoscale interactions and drying capillaries to play their role within such regions. Hydrophobic regions without defects show clean surface with no deposition of nanoparticles, whereas close-packed gold nanorods have been observed within the confined defect regions on PFDTS.

Improving the Photovoltaic Performance of Flexible Solar Cells with Semitransparent Inorganic Perovskite Active Layers by Interface Engineering.

Inorganic perovskite CsPbBr3 has broad application prospects in photovoltaic windows, tandem cells, and other fields due to its intrinsic semitransparency, excellent photoelectric properties, and stability. In this work, a high-quality semitransparent CsPbBr3 film was prepared by a sequential vacuum evaporation deposition method without high-temperature annealing and successfully used as the active layer of flexible perovskite solar cells (F-PSCs) for the first time, achieving a power conversion efficiency (PCE) of 5.00%. By introducing an energy-level buffer layer of Cu2O between CsPbBr3 and Spiro-OMeTAD, the champion PCE has been further improved to 5.67% owing to the reduction of electron-hole recombination and enhanced charge extraction. The optimized devices present higher stability, which can maintain more than 95% of the initial efficiency even after continuous heating at 85 °C for 240 h. Moreover, the F-PSCs also exhibit excellent mechanical durability, and 90% of the original PCE can be retained after 1000 bending cycles at a curvature radius of 3 mm.