Thermal Vapor Deposition Research Articles

Conformality of PVD shell layers on GLAD-nanorods investigated by Monte Carlo simulations

The quality of the shell coating around nanorods is critical in device applications. Conventional physical vapor deposition (PVD) techniques can be utilized for highly conformal shell coating formation in core-shell structure devices. To identify scalable fabrication techniques for conformal shell coatings, Monte Carlo (MC) simulations of PVD growth were performed under different atomic flux distributions and angles on arrays of glancing angle deposition (GLAD) nanorods, which were also generated by MC simulations. We investigated the conformality of PVD films (shell) around GLAD rod arrays (core) and analyzed the thickness uniformity of the shell layer across the sidewalls of rods. Our results show that Angular Flux-Normal Angle (A-NAD), which might correspond to high-pressure sputter deposition at normal incidence (HIPS at θ = 0o) can generate better conformal shell coating compared to others. In Uniform Flux-Normal Angle technique (U-NAD), which corresponds to a thermal evaporation deposition, the growth suffers from poor sidewall coverage. In addition, introducing a small angle to the flux also improves the shell conformality. Therefore, high-pressure sputter deposition technique is expected to provide superior conformality for a catalyst or semiconductor coating around base nanorods, for example for fuel cell and solar cell applications, with the help of obliquely incident atoms of the HIPS flux.

Fabrication of pre-wetting induced superamphiphobic meshes for on-demand oil-water separation of light or heavy oil-water mixtures

In this study, a facile approach was proposed to fabricate superamphiphobic meshes for on-demand separating light or heavy oil and water mixtures after pre-wetting process. The micro-nano hierarchical structures on superamphiphobic stainless steel mesh were fabricated via vacuum thermal evaporation and chemical deposition. Low surface energy was acquired by modification with perfluorooctanoic acid. The effect of reaction time on wettability was investigated to obtain the optimal parameters of fabricating samples exhibiting superhydrophobicity and superoleophobicity simultaneously. The wettability of superamphiphobic meshes was controlled by the liquids of pre-wetting process. The superamphiphobic surfaces pre-treated with ethanol and water were used to separate the mixtures of light oil and water, while the meshes sequentially pre-soaked with ethanol and oil to separate the mixtures of heavy oil and water. The separation efficiency of up to 98 % was found even after multiple cycles. The fabricated superamphiphobic surfaces can avoid contamination and achieve on-demand oil-water separation without any external forces, which will have promising potential for application in oil-water separation.

Strategy for sensitive and selective NO2 detection at low temperatures utilizing p-type TeO2 nanowire-based sensors by formation of discrete n-type ZnO nanoclusters

Heterostructured nanomaterials have been extensively studied for gas sensing applications because of their unique properties. In this study, we synthesized heterostructured nanomaterials consisting of p-type TeO2 (p-TeO2) NWs and discrete n-type ZnO (n-ZnO) nanoclusters (NCs) to detect NO2 gas molecules. These nanomaterials were synthesized via thermal evaporation and atomic layer deposition (ALD) techniques and then systematically investigated for NO2 sensing capabilities with regard to operating temperature, NO2 response, response/recovery times, and selectivity. The successful formation of discrete n-ZnO NCs depending on ALD conditions was observed via scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and these nanomaterials were characterized by energy dispersive spectrometry (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The NO2 response of the p-TeO2 NW sensors was considerably enhanced through the formation of discrete n-ZnO NCs. In addition, the synthesized sensors showed good NO2 selectivity in comparison with interfering gases such as SO2, CO, and C2H5OH. Herein, the enhanced NO2 sensing mechanisms of p-TeO2 NWs by formation of discrete n-ZnO NCs will be discussed in detail. We also believe that the formation of discrete n-ZnO NCs is an effective way to enhance NO2 sensing capabilities of p-TeO2 NW-based gas sensors.

Cost‐Effective Green Synthesis of Boron‐Rich Carbide Coatings for Infrared Windows and Night‐Vision Optics

The increasing demand for infrared (IR) window materials for various applications in optical imaging systems necessitates the development of cost‐effective green techniques. Herein, the synthesis of refractory boron carbide (BC) using castor oil, as carbon precursor, and the preparation of IR transparent films by thermal vapor deposition technique is reported. Films are prepared with 1:3, 1:4, and 1:5 ratios of boric acid and castor oil, respectively. The X‐ray diffraction (XRD) and Fourier‐transform IR (FTIR) analyses reveal the structure of films prepared to be BC. The morphology of the films is analyzed by the atomic force microscopy (AFM) technique, and its dependence on precursor's ratio is also studied. The spectroscopic characterization by the ultraviolet–visible–near IR (UV–vis–NIR) transmittance study reveals the potential of the films for IR window applications. The bandgap energy of the BC films determined from the Tauc plot yields a value of 2.33 eV. The absorption coefficient, extinction coefficient, refractive index, dissipation factor, and optical conductivity are also studied from the reflectance and transmittance data.

Plasma spray–physical vapor deposition toward advanced thermal barrier coatings: a review

Plasma spray–physical vapor deposition (PS–PVD) is a unique technology that enables highly tailorable functional films and coatings with various rare metal elements to be processed. This technology bridges the gap between conventional thermal spray and vapor deposition and provides a variety of coating microstructures composed of vapor, liquid, and solid deposition units. The PS–PVD technique serves a broad range of applications in the fields of thermal barrier coatings (TBCs), environmental barrier coatings (EBCs), oxygen permeable films, and electrode films. It also represents the development direction of high-performance TBC/EBC preparation technologies. With the PS–PVD technique, the composition of the deposition unit determines the microstructure of the coating and its performance. When coating materials are injected into a nozzle and transported into the plasma jet, the deposition unit generated by a coating material is affected by the plasma jet characteristics. However, there is no direct in situ measurement method of material transfer and deposition processes in the PS–PVD plasma jet, because of the extreme conditions of PS–PVD such as a low operating pressure of ~ 100 Pa, temperatures of thousands of degrees, and a thin and high-velocity jet. Despite the difficulties, the transport and transformation behaviors of the deposition units were also researched by optical emission spectroscopy, observation of the coating microstructure and other methods. This paper reviews the progress of PS–PVD technologies considering the preparation of advanced thermal barrier coatings from the perspective of the transport and transformation behaviors of the deposition units. The development prospects of new high-performance TBCs using the PS–PVD technique are also discussed.

Thin-Film Solar Cells with 19% Efficiency by Thermal Evaporation of CdSe and CdTe

CdTe-based solar cells exhibiting 19% power conversion efficiency were produced using widely available thermal evaporation deposition of the absorber layers on SnO2-coated glass with or without a t...

Extreme ultraviolet photon conversion efficiency of tetraphenyl butadiene.

Extreme ultraviolet (EUV) radiation can be converted to visible light using tetraphenyl butadiene (TPB) as a phosphor. 1 µm films of TPB were prepared using thermal vapor deposition of the pure material and by spin coating suspensions of TPB in high-molecular-weight polystyrene/toluene solutions. Calibrated sources and detectors were used to determine the effective photon conversion efficiency of the films for incident EUV radiation in the wavelength range of $125\;{\rm nm}\le\lambda\le 200\;{\rm nm}$125nm≤λ≤200nm. After exposure to atmosphere, the efficiency of the vapor-deposited films decreased significantly, while the efficiency of the spin-coated films remained unchanged. The production of TPB films by spin coating offers the advantages of simplicity and long-term stability.

Sn-Doped CdS Nanowires with Low-Temperature Lasing by CW-Laser Excitation

Sn-doped CdS nanowires, with the inside coexisting Sn(II)S, Sn2(III)S3, and Sn(IV)S2 identified by in situ Raman and XPS spectra, are grown via a simple thermal evaporation deposition technique. It...

Unique Layer-Doping-Induced Regulation of Charge Behavior in Metal-Free Carbon Nitride Photoanodes for Enhanced Performance.

Photoinduced charge carrier behavior is critical in determining photoelectrocatalytic activity. In this study, a unique layer-doped metal-free polymeric carbon nitride (C3 N4 ) photoanode is fabricated by using one-pot thermal vapor deposition. With this method, a photoanode consisting of a phosphorus-doped top layer, boron-doped middle layer, and pristine C3 N4 bottom layer, was formed as a result of the difference in thermal polymerization kinetics associated with the boron-containing H3 BO3 -melamine complex and the phosphorus-containing H3 PO4 -dicyandiamide complex. This layer-doping fabrication strategy effectively contributes to the formation of dual junctions that optimizing charge carrier behavior. The ternary-layer C3 N4 photoanode exhibits significantly enhanced photoelectrochemical water oxidation activity compared to pristine C3 N4 , with a record photocurrent density of 150±10 μA cm-2 at 1.23 V vs. RHE. This layer-doping strategy provides an effective means for design and fabrication of photoelectrodes for solar water oxidation.

Feasibility Study of an Adaptive-Pressure Plasma Coating Process—Part 1: Model Description

Thermal barrier coatings for gas turbine engines are mainly produced by electron beam physical vapor deposition or atmospheric plasma spray depending on the thermomechanical loading of engine components. This study deals with the numerical design of a two-step thermal plasma-aided physical vapor deposition process capable of efficiently evaporating the coating material processed in the plasma jet and of producing a strain-tolerant coating microstructure from vapor phase condensation. The system involved a high-pressure chamber and a low-pressure chamber connected by an expansion nozzle. The objective was to achieve the highest deposition efficiency for a given plasma specific enthalpy. The numerical simulations based on computational fluid dynamics and direct simulation Monte Carlo models projected the effect of the process geometry and operating conditions on the gas flow fields, powder vaporization efficiency and nucleation/growth phenomena in the gas phase. For a targeted powder feed rate, they allowed to determine the length of the high-pressure chamber, the diameter of the expansion nozzle and other dimensions of the deposition system. The expansion nozzle that linked the two chambers was the crucial component of the process, and the predictions made it possible to select the geometry and process operating parameters that avoided its clogging and/or melting

Enhanced visible light photocatalytic activity of g-C3N4 decorated ZrO2-x nanotubes heterostructure for degradation of tetracycline hydrochloride

Photocatalytic degradation is considered as a promising strategy to address the environmental threat caused by antibiotics abuse. Visible light driven g-C3N4 decorated ZrO2-x nanotubes heterostructure photocatalysts for antibiotic degradation were successfully synthesized by anodic oxidation and following a thermal vapor deposition method. Compared with pure g-C3N4 or ZrO2-x nanotubes, the composite photocatalysts exhibited more extended visible light response and higher separation rate of photo-generated electron-holes pairs. The optimized heteroctructure with 7.1 wt.% g-C3N4 exhibited 90.6% degradation of tetracycline hydrochloride (TC-H) under 1 h visible light irradiation. The mainly active species of TC-H degradation were photo-generated h+ and O2-. The pathway of charge migration in the g-C3N4/ZrO2-x NTs system was also studied and a possible photocatalytic mechanism was proposed for TC-H degradation. Constructing the g-C3N4/ZrO2-x nanotubes heterostructure is anticipated to be an effective strategy for photocatalytic degradation of antibiotics.

Epitaxial growth of Ag-Cu bimetallic nanoparticles via thermal evaporation deposition

The epitaxial growth of silver on copper benefits carriers' transport across interfaces and is thus important for opto-electronic applications and catalysis. Cu-Ag bimetallic nanoparticles have long been fabricated using chemical methods. The epitaxial growth of silver on copper has been rarely reported. In this study, we demonstrate the fabrication of Cu-Ag bimetallic nanoparticle with a configuration of silver epitaxial growth on copper via thermal evaporation deposition in vacuum, in which not only the oxidation of copper is reduced but also contamination is avoided. Meanwhile, a core-shell-like bimetallic nanoparticle with a copper core and a silver shell is also fabricated. The configurations of the two kinds of Cu-Ag bimetallic nanoparticles were explored by analyzing the changes of the X-ray photoelectron spectra, high resolution transmission electron microscopy images, diffraction rings, and glancing angle X-ray diffraction patterns with the increasing amount of silver and copper. A model of lattice matching between silver on copper was also established for the epitaxial Cu-Ag bimetallic nanoparticle. The layered epitaxial bimetallic nanoparticle show strong anti-oxidation effect and obvious localized surface plasmon resonance damping of Ag nanoparticles, suitable for applications requiring anti-oxidation and low absorbance.

High-Performance Self-Powered Ultraviolet Photodetector Based on Nano-Porous GaN and CoPc p-n Vertical Heterojunction.

Gallium nitride (GaN) is a superior candidate material for fabricating ultraviolet (UV) photodetectors (PDs) by taking advantage of its attractive wide bandgap (3.4 eV) and stable chemical and physical properties. However, the performance of available GaN-based UV PDs (e.g., in terms of detectivity and sensitivity) still require improvement. Fabricating nanoporous GaN (porous-GaN) structures and constructing organic/inorganic hybrids are two effective ways to improve the performance of PDs. In this study, a novel self-powered UV PD was developed by using p-type cobalt phthalocyanine (CoPc) and n-type porous-GaN (CoPc/porous-GaN) to construct a p–n vertical heterojunction via a thermal vapor deposition method. Under 365 nm 0.009 mWcm−2 light illumination, our device showed a photoresponsivity of 588 mA/W, a detectivity of 4.8 × 1012 Jones, and a linear dynamic range of 79.5 dB, which are better than CoPc- and flat-GaN (CoPc/flat-GaN)-based PDs. The high performance was mainly attributed to the built-in electric field (BEF) generated at the interface of the CoPc film and the nanoporous-GaN, as well as the nanoporous structure of GaN, which allows for a higher absorptivity of light. Furthermore, the device showed excellent stability, as its photoelectrical property and on/off switching behavior remained the same, even after 3 months.

Large-area, liftoff nanoporous GaN distributed Bragg reflectors: Fabrication and application

Abstract A facile one-step electrochemical etching based on NaNO3 solution was developed for use in the chemical lift-off nanoporous- (NP-) GaN distributed Bragg reflectors (DBRs) over a macroscopic area (>1 cm2). The reflectivity of the lift-off DBR mirror is ~85%, which is far lower than that (~97%) of the NP-GaN DBR on the sapphire substrate. The decrease should be attributed to light scattering due to higher roughness in the lift-off mirror. To study its possible applications, tris(8-hydroxyquinoline) aluminum (III) (Alq3) thin film was grown on transferred NP-GaN DBR mirror onto silicon substrate via a thermal evaporation deposition. Compared to the reference Alq3 thin film, the photoluminescence of the Alq3 thin film on the transferred mirror presents significant enhancement and slight blue-shift, which should be attributable to reflectivity enhancement by the DBR and inner channel surface in the DBR mirror, respectively.

Role of ionization fraction on the surface roughness, density, and interface mixing of the films deposited by thermal evaporation, dc magnetron sputtering, and HiPIMS: An atomistic simulation

The effect of ionization fraction on the epitaxial growth of Cu film on Cu (111) substrate at room temperature is explored. Three deposition methods, thermal evaporation, dc magnetron sputtering (dcMS), and high power impulse magnetron sputtering (HiPIMS) are compared. Three deposition conditions, i.e., fully neutral, 50% ionized, and 100% ionized flux were considered thermal evaporation, dcMS, and HiPIMS, respectively, for ∼20000 adatoms. It is shown that higher ionization fraction of the deposition flux leads to smoother surfaces by two major mechanisms, i.e., decreasing clustering in the vapor phase and bicollision of high energy ions at the film surface. The bicollision event consists of local amorphization which fills the gaps between islands followed by crystallization due to secondary collisions. The bicollision events are found to be very important to prevent island growth to become dominant and increase the surface roughness. Regardless of the deposition method, epitaxial Cu thin films suffer from stacking fault areas (twin boundaries) in agreement with recent experimental results. Thermal evaporation and dcMS deposition present negligible interface mixing while HiPIMS deposition presents considerable interface mixing.

Preferentially oriented CuCdS2 thin films and thickness effects on structural, optical and electrical properties

Copper cadmium sulfide (CuCdS2) thin films were deposited via thermal evaporation deposition technique. Crystallinity and adhesive nature of the thin films were improved at the substrate temperature of 300 °C. CuCdS2 thin films possess nanocrystalline nature with hexagonal structure and its grain size increased from 20 to 37 nm with respect to deposition time. Linear increment in the thickness with respect to deposition time ensued preferential orientation along (002) plane. Raman spectra explained the vibrational modes of CuCdS2 nanoparticles and thin films. The intensity ratio between LO and 2LO peaks (I2LO/ILO) increased with grain size. Optical studies revealed that the transmission retained 30–60% in blue to green band region and reached maximum value in yellow–red band. Band gap values vary between 2.1 and 2.4 eV, and the expansion attributed to confinement of charges. Atomic force microscopy images showed that the films acquired nanocrystallinity with definite boundaries between the grains and grain sizes increased from 18 to 32 nm. Grains were grown as spikes during a longer deposition period and average surface roughness of the films was increased with grain size. Morphology of the surface grains tended to grow in circular shape to minimize the surface free energy. Oxidation states of the elements were found using X-ray photoelectron spectroscopy and stoichiometry of all the CuCdS2 films could be explained as 1:1:2 for Cu:Cd:S. Electrical studies revealed that all the films had p-type semiconducting nature. Resistivity values of the films are found in the order of 10−2 Ω; concomitant with the thickness it decreased to 10−3. Bulk concentration values lay in the range of 1019–1020. Photoconductivity measurements showed that the p–n junction of CuCdS2/n-Si had rectifying nature.

Visible surface diffusion of gold nanostructures on a paper at room temperature through localized surface plasmon resonance

ABSTRACTWe visually observed color changes of discontinuous gold surfaces on paper substrates through localized surface plasmon resonance (LSPR) at room temperature due to surface diffusion of gold nanostructures. Isolated nanoparticles and an uncompleted nanosheet of gold were obtained by thermal vapor deposition. After preservation for 8 months in air at room temperature, the particle sizes and shapes remarkably changed with color changes. The surface diffusion of the discontinuous gold on the paper would be derived from solid-state dieting, resulting in the growth of the nanosheet defect and coalescence of the nanoparticles. This is due to the total energy minimization of the surfaces of gold nanostructures and the paper and the interface between gold and the paper.

АВТОМАТИЗИРОВАННОЕ НАПЫЛЕНИЕ АМОРФНЫХ ХАЛЬКОГЕНИДНЫХ СЛОЕВ

The results of the application of automation in obtaining chalcogenide layers with new properties are given. Such parameters of the thermal vapour deposition process as evaporator temperature or power were automatically controlled. The moments of the opening and closing of the valve were established experimentally in order to ensure a uniform deposition rate of the layers. The criterion for evaluating the uniform speed was the data of optical control of the thickness of the applied layers. As an example, diagrams of the behavior of the evaporator temperature are given, which are set using a control program and implemented in real time. As a result, layers with reproducible parameters and doubled dynamic range of photo-structural changes in the refractive index were obtained. Automated technology is applied for deposition with uniform speed of film axicons on rotating substrates through a mask of a special shape, providing a linear radial change in layer thickness.

Sb2Se3 thin films fabricated by thermal evaporation deposition using the powder prepared via mechanical alloying

Sb2Se3 based thin film solar cells have recently drawn a growing research interest. In the work, Sb2Se3 thin films were deposited on BK7 glass substrates by thermal evaporation at room-temperature. The Sb2Se3 powder was prepared by mechanical alloying method. It can found that the prepared Sb2Se3 powder has single Sb2Se3 crystal structure with slight Sb-excess. The influence of the evaporation current on the micro-structure of the films was investigated. The results show that the thin films have the similar contents as the Sb2Se3 powder, but have amorphous structure. After annealing, the crystallinity of the Sb2Se3 thin films has single Sb2Se3 phase with well-crystallized and smooth surface. The optical band gap of Sb2Se3 thin films deposited at 120 A is 1.26 eV, indicating that the thin film has good optical property.

Optical properties of ZnO/MgF2 bilayer thin films prepared by PVD technique

Zinc Oxide (ZnO) is considered as one of the best materials already used as a window layer in solar cells due to its antireflective capability. The ZnO/MgF2 bilayer thin film is more efficient as antireflective coating. In this work, ZnO and ZnO/MgF2 thin films were deposited on glass substrate using pulsed laser deposition and thermal evaporation deposition methods. The optical measurements indicated that ZnO thin layer has an energy gap of (3.02 eV) while ZnO/MgF2 bilayer gives rise to an increase in the energy gap. ZnO/MgF2 bilayer shows a high energy gap (3.77 eV) with low reflectance (1.1-10 %) and refractive index (1.9) leading to high transmittance, this bilayer could be a good candidate optical material to improve the performance of solar cell window.