Thermal Deposition Research Articles

Electrically heated monolithic catalyst for in-situ hydrogen production by methanol steam reforming

Electrification of conventionally combustion-heated reactors has the potential to reduce CO2 emissions and provide a flexible and compact heat supply. In this paper, multi-segment helical FeCrAl substrates were arranged in tube-shell form with insulation by honeycomb ceramics to obtain the electrically heated monolithic catalyst (EHMC) substrate, followed by thermal treatment and catalyst deposition to obtain the EHMC. The start-up and catalytic performance of the EHMC at different reaction conditions were studied experimentally. The results showed that the desired temperature of 275 °C could be reached in 29 s with a uniform temperature distribution by supplying a current of 2 A in air atmosphere. Compared with the commercial granular catalyst under external heating condition, the EHMC showed better catalytic activity due to higher methanol conversion and similar CO concentration at low reaction temperature. Furthermore, when the methanol conversion was 90%, the GHSV of the EHMC was 5.54 times that of the commercial granular catalyst, indicating that the EHMC can operate at higher GHSV owing to the enhanced mass and heat transfer ability.

Influence of dust purge hole on thermal performance and particle deposition of a turbine blade with ribbed internal cooling channel

Influence of dust purge hole on thermal performance and particle deposition of a turbine blade with ribbed internal cooling channel

Rapid fabrication of the Au hexagonal cone arrays for SERS applications

This study performed trace detection using surface-enhanced Raman scattering (SERS) on Au hexagonal cone arrays (Au-HCAs). Uniform porous anodized aluminum oxide (AAO) templates were used, and an Ag film with a cone cavity was prepared using a thermal deposition technique. Next, a series of homogeneous Au-HCAs were prepared controllably via electrodeposition growth technology. The prepared Au-HCAs were used as SERS substrates, and according to the experimental results, the optimal electrodeposition time is 600 s. At this time, Au-HCAs had the highest SERS activity. The detection limit of R6G was 10−9 M, exhibiting high reproducibility and high uniformity at 10−6 M, indicating that Au-HCAs had good stability. Moreover, a good linear correlation between the Raman intensity and the molecular concentration endowed Au-HCAs with good quantitative analysis ability. Therefore, the Au-HCAs exhibited great potential for qualitative and quantitative detection.

Study on the influence of dust accumulation on the photothermal performance of a trough solar system based on space-time factors in alpine areas

Based on the dust accumulation and distribution characteristics of concentrator surfaces in alpine regions, a comparative experimental platform for measuring the energy flux density of the focal plane and thermal performance was developed in this study. By combining theory and experimentation, the influence of time (dust deposition density) and space (concentrator tilt angle) on the dust distribution characteristics and photothermal performance of a trough solar system was studied. The optical loss caused by concentrator dust was evaluated based on the intercept factor, while the thermodynamic loss caused by dust was evaluated based on the collecting efficiency and exergy efficiency. The results demonstrate that concentrator dust at a tilt angle of 60° will lead to a maximum center shift of 1.66 mm of the focal plane. Importantly, the inconsistency between thermal performance and dust deposition density indicates that the dust distribution characteristics caused by tilt angle have a significant influence on the thermal performance of the system. Comparatively, an increase in dust deposition density from 0 to 2.46 g/m2 leads to a 20.58% relative reflectivity loss, together with 48.30% and 55.08% reductions in the collecting efficiency and exergy efficiency, respectively. This study revealed the influence of space–time factors on dust distribution characteristics and photothermal performance, which can provide design ideas regarding dust removal for the application of trough solar systems in alpine areas.

Temperature measurement and simulation analysis of heaterless hollow cathode during start-up process

Monochromatic radiation thermometry is used to quantify temperature distribution during the start-up process for a heaterless hollow cathode. A transparent cathode is designed to facilitate the transmission of thermally and spontaneously radiated photons from the interior of the structure and their reception by the detection equipment. The relative radiation intensities can be obtained by the developed measurement equipment, which consists of an scientific complementary metal oxide semiconductor camera and a 780 nm narrow-band filter, and then transformed into temperature distributions calibrated by a two-color pyrometer. The current and voltage characteristics of the anode and keeper and plasma image captured by the high-speed camera are used to analyze the thermal evolution mechanism. A 2D extended fluid model coupling with a thermal model is also developed and used to help clarify the thermal deposition variation at different locations. These results provide further support for the hypothesis that thermal deposition of ions and electrons, thermal conduction, and thermal radiation all affect the rate of change in temperature of various components.

Triggering Shock Wave Positions by Patterned Energy Deposition

The problem considered in this work is shock wave (SW) positioning control in shock-dominated flows. Experiments are conducted to investigate the triggering effect of patterned near-surface electrical discharges on SW reflection from plane walls. In the wind tunnel, M=4, P0 = 4 bar, a solid wedge SW generator is mounted on the upper wall. Q-DC filamentary electrical discharges were arranged on the opposite wall, so that the SW from the wedge impinged on the plasma filaments that are arranged flow-wise in either a row of three or a single central filament. Within the supersonic flow, narrow subsonic areas are actuated by electrical discharge thermal deposition, resulting in pressure redistribution, which, in turn, relocates the reflection of impinging SW to a predefined position. Mie scattering, schlieren imaging, and wall pressure measurements are used to explore the details of plasma-SW interaction. Using Mie scattering, the three-dimensional shape of the SW structure is mapped both before and after electrical discharge activation. Plasma-based triggering mechanisms are described in terms of the physical principles of flow control and a criterion for determining the effectiveness of the flowfield control.

Atomic layer deposition of oxide coatings on porous metal and polymer structures fabricated by additive manufacturing methods (laser-based powder bed fusion, material extrusion, material jetting)

Complex porous 316 L stainless steel, Ti-6Al-4V, Ti-6Al-7Nb, ULTEM™ 1010 and MED610™ polymer structures were produced with additive manufacturing methods. The structures were surface functionalized by atomic layer deposition of titanium, zinc and zirconium oxide coatings with a thickness between 14 and 43 nm. Deep and narrow structures with aspect ratios >10 could be coated. Titanium oxide films are mostly amorphous when plasma-assisted deposition is used and contain nanocrystalline anatase when deposited by thermal atomic layer deposition. The deposited titanium oxide grains ranged in size from ∼20 to 60 nm. In interior parts of the fractured porous polymer model structures with pore sizes of 1–2 mm, both thermal and plasma-assisted titanium oxide thin films and partly delamination were detected. X-ray photoelectron spectroscopy analysis revealed almost stoichiometric composition and dominance of the Ti (IV) oxidation state at a 250 °C deposition temperature. Zinc oxide coatings in porous polymer model structures partly delaminate as well, while adhesion and homogeneity is higher for printed Ti-6Al-7Nb lattice structures with a 0.5-mm mesh size. Zirconium oxide coatings on Ti-6Al-4V lattice structures with a 0.8-mm mesh size are comparable to zinc oxide coatings but are mostly crystalline. This is attributed to the relatively high, 300 °C deposition temperature. The findings demonstrate potential but also limitations of combined additive manufacturing and atomic layer deposition for medicine and energy production applications. In addition, the results confirm previous studies that metallic and polymeric substrate materials and process conditions strongly influence the coating structure and composition, and individual development of each intended application is required.

Dry heterometallic resist processing based on thermal sublimation deposition and development

A negative tone heterometallic ring resist (HRR) based on a supramolecular assembly [ NH2(allyl)2 ] [ Cr7NiF8(piv)16 ] with previously demonstrated resolution down to sub 10-nm lines is evaluated in terms of its flexibility to be processed either “wet” (spin cast and solvent developed) or “dry” (deposition and development by vacuum sublimation). The implemented sublimation hardware fits easily in the wafer load-lock chamber of extreme ultraviolet and electron beam exposure systems dedicated to research and development activities and allows for HRR films to be uniformly deposited or developed in the same vacuum environment. The HRR shows a sublimation rate dependence on temperature that obeys a Clausius–Clapeyron relation, with thermal stability up to 275°C. Flood exposures of the HRR show identical sensitivity between wet- and dry-deposited films, whereas contrast degradation is observed when dry development is initiated by increasing the temperature prior to system pump down. A modified sublimation setup allows for the dry development of exposed HRR samples inside the electron beam tool without breaking vacuum. In this case, nominally patterned 25 nm L/S are identically resolved at 30 keV for wet- or dry-developed HRR.

Evaluating the Topological Surface Properties of Cu/Cr Thin Films Using 3D Atomic Force Microscopy Topographical Maps

In the present work, Cu/Cr thin films were deposited on substrates of a different nature (Si, Glass, Bk7, and ITO) through a thermal evaporation deposition method. Non-contact atomic force microscopy (AFM) was used to obtain 3D AFM topographical maps of the surface for the Cu/Cr samples. Various analyses were carried out to obtain crucial parameters for the characterization of the surface features. In particular, Minkowski functionals (including the normalized Minkowski volume, the Minkowski boundary, and the Minkowski connectivity) and studies of the spatial microtexture by fractal and multifractal analyses were carried out. Different roughness parameters (including arithmetical mean height, root mean square height, skewness, kurtosis, fractal dimension, Hurst coefficient, topographical entropy, and fractal lacunarity) were quantified in these analyses for the comparison of the surface morphology of the different samples. All the samples displayed non-Gaussian randomly rough surfaces, indicating the presence of multifractal features.

Synthesis and Characterization of Silica–Tantala Microporous Membranes for Gas Separations Fabricated Using Chemical Vapor Deposition

Composite membranes consisting of microporous tantalum-doped silica layers supported on mesoporous alumina substrates were fabricated using chemical vapor deposition (CVD) in both thermal decomposition and counter-flow oxidative deposition modes. Tetraethyl orthosilicate (TEOS) was used as the silica precursor and tantalum (V) ethoxide (TaEO) as the tantalum source. Amounts of TaEO from 0 mol% to 40 mol% were used in the CVD gas mixture and high H2 permeances above 10−7 mol m−2 s−1 Pa−1 were obtained for all conditions. Close examination was made of the H2/CH4 and O2/CH4 selectivities due to the potential use of these membranes in methane reforming or partial oxidation of methane applications. Increasing deposition temperature correlated with increasing H2/CH4 selectivity at the expense of O2/CH4 selectivity, suggesting a need to optimize membrane synthesis for a specific selectivity. Measured at 400 °C, the highest H2/CH4 selectivity of 530 resulted from thermal CVD at 650 °C, whereas the highest O2/CH4 selectivity of 6 resulted from thermal CVD at 600 °C. The analysis of the membranes attempted by elemental analysis, X-ray photoelectron spectroscopy, and X-ray absorption near-edge spectroscopy revealed that Ta was undetectable because of instrumental limitations. However, the physical properties of the membranes indicated that the Ta must have been present at least at dopant levels. It was found that the pore size of the resultant membranes increased from 0.35 nm for pure Si to 0.37 nm for a membrane prepared with 40 mol% Ta. Similarly, an increase in Ta in the feed resulted in an increase in O2/CH4 selectivity at the expense of H2/CH4 selectivity. Additionally, it resulted in a decrease in hydrothermal stability, with the membranes prepared with higher Ta suffering greater permeance and selectivity declines during 96 h of exposure to 16 mol% H2O in Ar at 650 °C.

Front Cover: Mesoporous Silica Supported Highly Dispersed GaN Catalysts Synthesized by Thermal Atomic Layer Deposition for Propane Dehydrogenation (ChemCatChem 19/2022)

The Front Cover depicts the propane dehydrogenation (PDH) reaction on the supported gallium nitride (GaN) catalyst. In their Research Article, Hao Feng and co-workers report a novel method of synthesizing high surface area GaN catalysts supported on mesoporous silica (MCM-41) using thermal atomic layer deposition (ALD). GaN nanoparticles are uniformly dispersed on the surface of MCM-41 with ordered channel structures. Properties of highly dispersed GaN species were studied by various microscopic and spectroscopic techniques. In PDH reaction, the ALD GaN/MCM-41 catalysts demonstrated excellent activity and selectivity. More information can be found in the Research Article by Hao Feng and co-workers .

Impact of an ortho-cyano group on photophysical properties and performance of OLEDs based on D-A–A type pyrazine push-pull system

A series of novel D–A–A push-pull systems based on a 2-cyanopyrazine acceptor core bearing various electron-donating fragments are synthesized and investigated. The effect of the cyano group on the spectral-luminescent properties of molecules in solvents of different polarities and films obtained by thermal vacuum deposition has been investigated. Fast and delayed luminescence was studied at room temperature and 77K. The energy gap between the S1 and T1 states is estimated. The reasons for the weak thermally activated delayed fluorescence are discussed. It has been found that increasing the efficiency of light-emitting organic diodes up to 20 times took place when a cyano group introduces into fluorophores.

Green upconversion improvement of TiO2 codoped Er3+-Yb3+ nanoparticles based thin film by adding ALD-Al2O3 for silicon solar cell applications

This paper investigates the upconversion luminescence modification of codoped nanoparticles with lanthanides ions based thin films through adding a coating. First, these nanoparticles based thin films composed of Er3+-Yb3+ co-doped anatase-TiO2 are prepared using spin coating technique supported by a design of experiment (DOE) approach with the Hadamard matrix of order 4 to improve the deposition conditions. For the coating step, different thicknesses of Al2O3 layer are realised by thermal atomic layer deposition (T-ALD) onto the surface of Er3+-Yb3+ co-doped anatase-TiO2 nanoparticles based thin films. The results show that the ALD-Al2O3 coating can benefit the luminescence properties of the upconversion nanoparticles based thin films. Thin ALD-Al2O3 (10 nm) coated stack exhibits similar upconversion luminescence as the uncoated nanoparticles based film but insures also their stability. Meanwhile, for 100 nm ALD-Al2O3 coating, enhancement of the upconversion green emission by 98% at the expense of the red emission compared to uncoated sample is observed. This results are promising to be applied in photovoltaics field.

Optimization of the corrosion performance of Ni-SiC coatings through flash heating

Flash heating is an effective thermal deposition technique for additively applying high performance coatings with the possibility of on-site coating application. This research analyzes the corrosion performance of coatings developed by flash heating using a two-cubed full factorial design of processing conditions such as gas flow rate, coating composition, and current on corrosion rate. Using a 95 % confidence interval, it was found that the gas flow rate and the combination of composition and current had statistically significant effects on corrosion performance with p-values of 0.0015 and 0.0067, respectively. The optimal corrosion performance was found to occur at a gas flow rate of 12–14 cfh, composition of 70 wt% Ni and 30 wt% SiC, and a plasma current of 140 A. These parameters resulted in a corrosion rate of 20.4 μA/cm2. This is a reduction of 96.6 % compared to the carbon steel substrate and 90.9 % compared to the worst-performing Ni-SiC coating in terms of corrosion rate. This research enables the prediction and optimization of corrosion performance of Ni-SiC coatings when fabricated by flash heating.

Effect of thermal treatment and deposition conditions of ZnO by radio frequency sputtering on the photovoltaic response of CdTe solar cells

ZnO thin films grown by radio frequency sputtering were studied as a function of the experimental parameters: source power, chamber deposition pressure, substrate temperature and oxygen partial pressure; in addition to post-deposition thermal treatment. The ZnO thin films were characterized by stylus profilometry, optical measurements, electrical resistivity, X-ray diffraction, energy dispersive spectroscopy and scanning electron microscopy. Current-voltage and external quantum efficiency measurements were performed on the CdS/CdTe-based solar cell. In the case of ZnO/CdS thin films with a high-temperature thermal treatment, an increment in transmittance was observed in the ZnO wavelength region. With the incorporation of the ZnO thin film in the front contact of the solar cell, we obtained a photovoltaic efficiency of 7.4%, with the following optimal deposition conditions: 230 W source power, 2.67 Pa of deposition pressure and 300°C for the substrate temperature with a thermal treated of 450 °C for ZnO/CdS thin films. While a photovoltaic efficiency of 6.0% was obtained, when the ZnO/CdS was thermal treated at 500°C with the ZnO deposited at 140 W source power, 1.33 Pa deposition pressure and 250 °C for the substrate temperature. Finally, a photovoltaic efficiency of 10% was achieved for CdTe solar cells with ZnO thin film by combining the experimental conditions and the thermal treatment described above.

Nanosecond pulsed plasma assisted combustion of ammonia-air mixtures: Effects on ignition delays and [formula omitted] emission

Computational investigation of plasma assisted combustion of ammonia-air mixtures in constant volume and constant pressure reactors are conducted, to determine the impact of operating conditions on ignition delays and NOx emissions. Due to the lack of a chemical kinetic mechanism for plasma discharge of ammonia (NH3)/air mixtures, a mechanism has been assembled in this work using well-validated plasma reactions of NH3 with O2 and N2, alongside plasma kinetics of air from the literature. The impact of the reduced electric field (E/N), equivalence ratio, pressure, pulse frequency and the energy density on the ignition delays and NO/NO2 emission is discussed. At lower E/N, vibrational-to-translational (VT) relaxation of the vibrational states of NH3 and N2 is observed to play a dominant role in the gas heating process on account of the higher vibrational energy contribution. The ignition event is observed to be faster for fuel-lean mixture (ϕ = 0.5) compared to stoichiometric and fuel-rich (ϕ = 1.2) conditions owing to the lower consumption of OH radicals through the reactivity-inhibiting reaction NH3+OH→NH2+H2O between plasma pulses for leaner mixtures. Nevertheless, the fuel-lean mixture is observed to exhibit higher production of NOx than stoichiometric and fuel-rich mixtures, resulting from plasma chemistry involving oxygen radical and electronic excited states of N2. At the higher pressure of 3 atm, the pressure dependent recombination reaction H+O2+M→HO2+M is found to delay the ignition by limiting the reactive radicals compared to the corresponding 1 atm case. Higher rates of collisional quenching at higher pressures during the inter-pulse gaps resulted in lesser amount of electronically excited states of N2 and O2, which resulted in lower production of air-bound NOx during the pulses. Pulse frequency and energy density per pulse are seen to exhibit an inversely proportional effect on the ignition delay times. Most importantly, a faster ignition and lower production of NOx is observed in the case of plasma discharges compared to thermal energy deposition, owing to the enhanced production of OH radicals and the reforming of NH3 to produce N2 with plasma, respectively. Interesting roles of fuel-radicals such as NH2 and NH in both producing and reducing NO at different instants have also been discussed.

The Effect of Deposition Conditions on Heterointerface‐Driven Band Alignment and Resistive Switching Properties

AbstractTitanium nitride and hafnium oxide stack have been widely used in various resistive memory elements since the materials are complementary‐metal‐oxide‐semiconductor compatible. The understanding of the interface properties between the electrode and the oxide is important in designing the memory behavior. To bridge this understanding, HfOx grown using plasma enhanced atomic layer deposition (PEALD) and thermal atomic layer deposition (TALD) are compared, in terms of band alignment and electrical performances in the HfOx/PEALD TiN stacks. X‐ray photoelectron spectroscopy reveals a thicker interfacial TiO2 layer in the PEALD HfOx/TiN stack whose interface resembles more to the PEALD HfOx/TiO2 interface (conduction band offset ΔEC = 1.63 eV), whereas the TALD HfOx stack interface resembles more to the TALD HfOx/TiN interface (ΔEC = 2.22 eV). The increase in the forming voltage and the early onset of reverse filament formation (RFF) in the I–V measurements for the PEALD HfOx stack confirms the presence of the thicker interfacial layer; the early onset of RFF is likely related to a smaller ΔEC. The findings show the importance of understanding the intricate details of the material stack, where ΔEC difference and the presence of a thicker TiO2 interfacial layer due to different deposition procedures affect the device performance.

Core–Shell Structures Prepared by Atomic Layer Deposition on GaAs Nanowires

GaAs nanowire arrays have been prepared by anodization of GaAs substrates. The nanowires produced on (111)B GaAs substrates were found to be oriented predominantly perpendicular to the substrate surface. The prepared nanowire arrays have been coated with thin ZnO or TiO2 layers by means of thermal atomic layer deposition (ALD), thus coaxial core–shell hybrid structures are being fabricated. The hybrid structures have been characterized by scanning electron microscopy (SEM) for the morphology investigations, by Energy Dispersive X-ray (EDX) and X-ray diffraction (XRD) analysis for the composition and crystal structure assessment, and by photoluminescence (PL) spectroscopy for obtaining an insight on emission polarization related to different recombination channels in the prepared core–shell structures.

Pyroelectric and Ferroelectric Properties of Hafnium Oxide Doped with Si via Plasma Enhanced ALD

Devices based on ferroelectric hafnium oxide are of major interest for sensor and memory applications. In particular, Si-doped hafnium oxide layers are investigated for the application in the front-end-of-line due to their resilience to high thermal treatments. Due to its very confined doping concentration range, Si:HfO2 layers based on thermal atomic layer deposition often exhibited a crossflow pattern across 300 mm wafer. Here, plasma enhanced atomic layer deposition is explored as an alternative method for producing Si-doped HfO2 layers, and their ferroelectric and pyroelectric properties are compared.

Development of friction stir powder deposition process for repairing of aerospace-grade aluminum alloys

This paper presents development of a novel friction stir powder deposition (FSPD) process for potential repairing applications of aerospace-grade aluminum alloy AA6061-T6. Powder form of the deposition material was thermo-mechanically processed at a temperature below its melting point. Influence of various process parameters on thermal cycles, deposition quality, deposition height, microstructure, and mechanical properties have been studied. Higher degree of deformation resulted in a dynamically recrystallized fine-grained microstructure which gave better mechanical properties. EDS study revealed uniform distribution of the major alloying elements throughout the deposition. Best quality deposition showed maximum microhardness and wear rate 0.84 and 1.07 times respectively than the substrate AA6061-T6 alloy. FSPD process is found to be capable of depositing maximum height of 0.45 mm, maximum deposition efficiency of 22% with an energy consumption of 73.7 J/mm 3 per unit deposition material consumption. Moreover, it used current in the range of 5-7 Ampere. This research shows that FSPD process can provide considerable cost and energy savings over fusion-based additive manufacturing processes making it a viable alternative for repairing aerospace-grade aluminum alloys. • Developed friction-stir powder deposition as a solid-state AM process for aerospace-grade Al alloys. • Max. deposition height: 0.45 mm; deposition efficiency: 22%; Avg. peak temperature: 293 °C. • Higher deformation gave dynamically recrystallized fine-grained microstructure. • Uniform distribution of alloying elements in the deposition. • Deposition microhardness and wear rate are 0.84 and 1.07 times than substrate AA6061-T6.