Hot Substrate Research Articles

The pivotal role of copper on the structural and optical parameters of ZnS thin films for optoelectronic applications

In this research, using chemical spray pyrolysis technology, Zn1-xCuxS doped (0.0, 0.02, 0.04, 0.06, 0.08 and 0.10 at.%) thin films were grown on a hot glass substrate with a substrate temperature of 275 °C, the thickness is about 110 nm. The spray solutions contain Zn(CH3COO)2•2H2O, SC(NH2)2 and CuCl2•2H2O with molar concentration 0.1 M/L. Energy Dispersion Analysis X-rays (EDAX) sets the initial processing components. The structure of the films was investigated by XRD pattern, and it was found that the films were polycrystalline with a cubic phase for Zn1-xCuxS at (x = 0, 0.02, 0.04 at.%) and mixed cubic and hexagonal phases for (x = 0.06, 0.08 and 0.10 at.%) with a small trace of (CuS). The micro-structural (lattice strain, e, and the crystallite's size, Dv) parameters for the pure and treated films were determined. The transmission spectrum envelope method is used to calculate the film thickness and refractive index. The estimated optical band gap of pure ZnS and ZnS:Cu is a direct transition, and decreases from 3.44 eV to 3.32 eV as the Cu concentration increases. The dielectric constants (ε1 and ε2), dispersion parameters (Eo, Ed), high-frequency dielectric constants, (ε∞), carrier concentration (N/m*) and plasma resonance frequency (ωp) were calculated. According to the changes of the microstructure parameters, the changes of all the optical parameters are discussed for applications in optoelectronics.

Leidenforst Motion: Leidenfrost Motion of Water Microdroplets on Surface Substrate: Epitaxy of Gallium Oxide via Mist Chemical Vapor Deposition (Adv. Mater. Interfaces 6/2021)

The Leidenforst motion of diluted water micro-droplets on hot flat substrates enables the growth of α-Ga2O3 thin films via mist chemical vapor deposition. The incident probability, incident angle, lifetime, and gliding distance of the microdroplets at surface vicinity determine the growth behaviors of the epilayer. More details can be found in article number 2001895 by Minh-Tan Ha, Si-Young Bae and co-authors.

Efficient removal of 2-chlorophenol from aqueous solution using TiO2 thin films/alumina disc as photocatalyst by pulsed laser deposition

Pulsed laser deposition facilitates the epitaxial deposition and growth of TiO2 at low temperature on hot substrate. In this study, nanosized nitrogen-doped TiO2 thin films were deposited on fabricated alumina disc-shaped and glass substrates. Textural properties of the fabricated disc and alumina disc-supported TiO2 were investigated using N2 adsorption–desorption isotherms, field emission scanning electron microscopy (FESEM), X-ray diffraction and Fourier transform infrared (FTIR) spectroscopy. FESEM showed the presence of single crystals of TiO2 on the alumina disc. FTIR showed the presence of octahedral TiO2 and different hydroxyl groups on the surface which is responsible for the photoactivity and also showed the functional groups adsorbed on the catalyst surface after the photocatalytic degradation. The concentration of 2-chlorophenol and the photo-redox intermediate products as a function of irradiation time was determined. The concentration of the produced chloride ion during the photocatalytic degradation was determined by an ion chromatography. The results showed that the photocatalytic activity of the catalyst decreased upon cycling. The obtained results were compared with nanostructured TiO2 supported on glass substrate. Higher efficiency of 100% degradation was achieved for TiO2/Al2O3 catalyst, whereas about 70% degradation of 2-CP was achieved using TiO2/glass. Different photointermediates of 2-CP degradation have been identified for each cycle. The difference of intermediates is supported by the adsorbed fragments on the catalyst surface.

Aging Response in Selective Laser Melted AlSi10Mg Alloy as Function of Distance from the Substrate Plate

Selective Laser Melting (SLM) builds a metallic part in a layer-by-layer mode with growth occurring along the vertical axis. Metallic powder layers are melted by a laser beam by programmed scan sequences inducing specific mechanical properties in the as-built samples according to process parameters. Post heat treatments are usually performed to optimise the mechanical behaviour. In this work, the effects induced by heat treatments at 175°, 200° and 225°C on SLMed bars of Al10SiMg were investigated as function of distance from the substrate plate. The bars were 300 mm height and in the as-built condition, Vickers microhardness and tensile strength decreased along the built direction, while the elongation increased from the bottom to the top of the billet. After heat treatments, Vickers microhardness resulted lower of 10HV at the top of the bar compared to its bottom in contact with the hot substrate; microhardness decreased with time at constant temperature compared to the as-built. Tensile properties showed variations of 50 MPa and 1% elongation between the top and the bottom of the billet when aging was performed at 175°C for 4h; the strength and ductility gradients were reduced to 20 MPa and 0,5% respectively by increasing the aging time to 6h. Microstructure investigations performed by scanning electron microscopy confirmed the different evolution of Silicon particles and precipitated particles at different height of the bars.

Investigating the residual stress in additive manufacturing of repair work by directed energy deposition process on SS316L hot rolled steel substrate

The aim of this research is to conduct a systematic investigation of the directed energy deposition of stainless steel 316L powder in order to evaluate and investigate residual stresses caused by the laser deposition process. In metal additive manufacturing, predicting residual stress is critical for ensuring the quality of the fabricated part. Stainless steel 316L cubes were prepared by directed energy deposition process on hot rolled steel substrate for the repair work purpose. To evaluate the effect of the residual stress of sandwich samples, which can be compressive or tensile. Also, to investigate the residual stresses developed on the interface region for between the directed energy deposition, and hot rolled steel sample. Finally, it is found that the residual stresses on the hot rolled steel surfaces in the compressive stress (-855 MPa), on other hand compressive stress has obtained in the directed energy deposition surface (-822 MPa). The residual stresses were determined experimentally using X-Ray Diffraction (XRD) residual stress measurements.

A sandwich-like structural model revealed for quasi-2D perovskite films

Quasi-2D perovskite films deposited on hot substrates are shown to possess a sandwich-like, large-n/small-n/large-n phase distribution profile in the orthogonal direction. This structure facilitates both exciton funneling to the film surfaces and efficient charge carrier transport.

Thermophobic Leidenfrost.

We report that a volatile liquid deposited on a hot substrate with a gradient of temperature does not only levitate (Leidenfrost effect), but also spontaneously accelerates to the cold. This thermophobic effect is also observed with sublimating solids, and we attribute it to the ability of temperature differences to tilt (slightly) the base of the "object", which induces a horizontal component to the levitating force. This scenario is tested by varying the drop size (with which the acceleration increases) and the substrate temperature (with which the acceleration decreases), showing that the effect can be used to control, guide and possibly trap the elusive Leidenfrost drops.

The Impact of Nanofluids on Droplet/Spray Cooling of a Heated Surface: A Critical Review

Cooling by impinging droplets has been the subject of several studies for decades and still is, and, in the last few years, the potential heat transfer enhancement obtained thanks to nanofluids’ use has received increased interest. Indeed, the use of high thermal conductivity fluids, such as nanofluids’, is considered today as a possible way to strongly enhance this heat transfer process. This enhancement is related to several physical mechanisms. It is linked to the nanofluids’ rheology, their degree of stabilization, and how the presence of the nanoparticles impact the droplet/substrate dynamics. Although there are several articles on droplet impact dynamics and nanofluid heat transfer enhancement, there is a lack of review studies that couple these two topics. As such, this review aims to provide an analysis of the available literature dedicated to the dynamics between a single nanofluid droplet and a hot substrate, and the consequent enhancement or reduction of heat transfer. Finally, we also conduct a review of the available publications on nanofluids spray cooling. Although using nanofluids in spray cooling may seem a promising option, the few works present in the literature are not yet conclusive, and the mechanism of enhancement needs to be clarified.

Gradient wick channels for enhanced flow boiling HTC and delayed CHF

Liquid supply to wick structures of flow boiling surfaces is fundamentally restricted by the capillary limit at which the pressure drop of the wicked liquid surpasses texture-amplified capillary forces. Gradient wick structures partially decouple permeability and capillary pressure, thereby delaying the capillary limit. In this study, gradient wick channels facilitating out-of-plane liquid delivery are introduced to postpone the capillary limit and thus enhance the two-phase flow boiling heat transfer coefficient (HTC) and delay critical heat flux (CHF). Here, the permeability of the gradient wick channels is augmented by large-pore-size meshes employed near the bulk fluid while capillary pressure is maximized by small-pore-size meshes utilized near the hot boiling surface. This combination of wick structures enables to preferentially guide the cooling liquid, deionized water, from the far-field cold liquid toward the bottom hot substrate. The spatial distribution of individual gradient wick channels promotes separate liquid-vapor pathways, thus facilitating the vapor escape process. Experiments conducted here reveal that the flow boiling performance metrics of the proposed heat sink leveraging the gradient wick channels outperform those of the homogenous wick channels and solid fin channels. The proposed heat sink demonstrates a strong liquid mass flux dependency due to a combination of convective boiling and amplified wickability effects. The enhanced convective boiling could be related to surface roughness, a high number of active nucleation sites, and a large surface area available through tortuous passages of wick channels. At higher mass flow rates, effective capillary pressure available for out-of-plane wicking action also increases, thereby further boosting the wickability effect and associated heat transfer processes. This could meaningfully delay the CHF. In fact, the CHF limit was not observed on the gradient wick channel surfaces in the mass flux and wall superheat range studied. The experimental results indicated a maximum heat flux of 870 W/cm2 with a gradient wick channel heat sink, a 60% improvement compared with a plain copper surface. Furthermore, a maximum HTC of 1000 kW/m2-K at a wall superheat of 3 °C was observed, a three-fold enhancement compared with that of the plain surface. The proposed gradient wick channel topology offers new pathways for designing innovative surface technologies with high heat removal capabilities, thereby potentially improving the energy economy in myriad modern energy applications.

Application of a large-scale molecular dynamics approach to modelling the deposition of TiO2 thin films

The previously developed large-scale molecular dynamics approach is applied to high-performance parallel modelling the deposition of TiO2 thin films. The largest simulated clusters reach 40 nm in size with about two million atoms. The surface roughness and porosity of normally deposited films with a flux of high and low energy atoms for cold and hot substrates are investigated. The formation of separate nanostructures in high-energy glancing angle deposited films is studied. The averaged structural parameters of the elongated pores in these films are determined using the original Monte Carlo based method. The difference between the main components of the refractive index tensor of glancing angle deposited TiO2 thin films is calculated.

Influence of deposition temperature on microstructure formation of Ti-Al-C-N ceramic coatings prepared via pulsed-DC PACVD

Ti-Al-C-N coatings were deposited on AISI H13 hot work tool steel substrates using PACVD method at deposition temperatures of 350, 425 and 500 °C. The results showed that synthesized nanostructured coatings consist of Ti-rich fcc-(Ti,Al)(C,N) and w-AlN nano-grains as well as an amorphous carbon nitride (a-CNx) phase. Increasing of the deposition temperature from 350 °C to 500 °C enhanced the intensity ratio of Disordered peak (ID) to Graphite peak (IG) from 0.94 to 1.13, respectively which is attributed to the increased graphitization of a-CNx phase. Rising the deposition temperature from 350 °C to 425 °C decreased the crystallite size from 11 to 9 nm, while further temperature increase to 500 °C generated larger crystallites of 13 nm. Layers of 2.33, 1.63 and 2.02 μm thickness were developed at different temperatures of 350, 425 and 500 °C, respectively. This behavior caused by increasing the temperature was originated from two competitive factors; the reduction of growth rate induced by more intense ion sputtering and the increase of growth rate induced by grain growth. Another result obtained by increasing the temperature from 350 °C to 500 °C was noticed as a 40% higher surface roughness due to more intense ion sputtering effect and grain growth. Finally, the highest micro-hardness value was measured as 4240 ± 53 HV0.01 for the coating deposited at 425 °C associated with the smallest crystallite size.

Electroless Ni-P Plating of Carbon Steel via Hot Substrate Method and Comparison of Coating Properties with those for Conventional Method

In this study, Ni-P electroless coating was deposited on carbon steel by a new method called SLHS (substrate local heating system) which makes a higher rate of deposition possible without the risk of decomposition of electroless baths. The effects of pH and temperature on plating rate, composition, surface morphology, hardness and corrosion of the coating in SLHS condition (Tsub = 190 °C, Tbath = 80 °C) were investigated. In addition, the impact of heat-treatment at 400 °C for 1 h on hardness, morphology and microstructure was also studied. Samples prepared by this method were characterized by Scanning Electron Microscopy/Energy-Dispersive x-ray analysis, Light Microscope and x-ray diffraction. They were then submitted to Vickers microhardness and tribological tests. The deposition rates of electroless nickel (EN) coating were first estimated by weight gain method and then by light and scanning electron microscopy. Electrochemical Impedance Spectroscopy (EIS), Tafel polarization and salt spray tests were then used to evaluate the corrosion properties of the coatings. The study shows that maximum deposition rates for conventional and SLHS samples were approximately 20 µm/h and 32 µm/h, respectively. This increase in the plating rate reduces the phosphorus level by nearly 1.5 wt.% for SLHS sample. The corrosion resistance of SLHS sample is improved in comparison to the conventional one.

A comparison of three shoe sole impression lifting methods at high substrate temperatures.

Footwear impressions are a common form of evidence found at crime scenes, and the accurate recovery and recording of such impressions is critical for shoe sole comparison and identification. The lifting of shoe sole impressions from hot surfaces (>30°C/86°F) and in hot environments has received little attention in the literature, particularly in relation to the recovery of class and randomly acquired characteristics (RACs) required for accurate comparisons. This study addressed this knowledge gap by comparing the performance of three common impression lifters (gelatin, adhesive, and vinyl static cling film) at recovering shoe sole impressions in dust from hot flooring substrates. Dry origin dust shoe sole impressions were made on ceramic tile, galvanized metal, and laminated wood flooring using a shoe that possessed two RACs and five class characteristics present on the sole. Substrates were left in direct full sun for five hours during a summer day prior to lifting. Performance was measured by the proportion of RACs and class characteristics visible in each lifted impression. Results demonstrated that the vinyl static cling film tested performed poorly across all substrates, particularly for metal (23.8% marks recovered), including notable shrinkage of the lifted impression. In contrast, adhesive (~96% marks recovered over all substrates), and to a lesser extent gelatin (~85%), lifts were highly successful on hot substrates. These data suggest that adhesive lifts can consistently and accurately recover shoe sole impressions from hot substrates. This study contributes critical information for crime scene examiners to improve and expand evidence recovery in hot environments.

Tailoring the Surface Morphology and the Crystallinity State of Cu- and Zn-Substituted Hydroxyapatites on Ti and Mg-Based Alloys.

Titanium-based alloys are known as a “gold standard” in the field of implantable devices. Mg-based alloys, in turn, are very promising biocompatible material for biodegradable, temporary implants. However, the clinical application of Mg-based alloys is currently limited due to the rapid resorption rate in the human body. The deposition of a barrier layer in the form of bioactive calcium phosphate coating is proposed to decelerate Mg-based alloys resorption. The dissolution rate of calcium phosphates is strongly affected by their crystallinity and structure. The structure of antibacterial Cu- and Zn-substituted hydroxyapatite deposited by an radiofrequency (RF) magnetron sputtering on Ti and Mg–Ca substrates is tailored by post-deposition heat treatment and deposition at increased substrate temperatures. It is established that upon an increase in heat treatment temperature mean crystallite size decreases from 47 ± 17 to 13 ± 9 nm. The character of the crystalline structure is not only governed by the temperature itself but relies on the condition such as either post-deposition treatment, where an amorphous calcium phosphate undergoes crystallization or instantaneous crystalline coating growth during deposition on the hot substrate. A higher treatment temperature at 700 °C results in local coating micro-cracking and induced defects, while the temperature of 400–450 °C resulted in the formation of dense, void-free structure.

Controlling of c-axis position of ZnO nano-crystalline films deposited at various substrate temperature by ultrasonic spray method

In this paper, ZnO thin films were elaborated onto hot glass substrates by ultrasonic spray pyrolysis technique. The solution contains zinc acetate dehydrate mixed with methanol with solution concentration equals 0.1 mol/L. The effect of the substrate temperature on the properties of ZnO was investigated. All films deposited were characterized by various techniques such as X-ray diffraction to examine the films structure and UV-Visible spectroscopy to determine the optical proprieties. The obtained results show that films are polycrystalline at hexagonal shape type wurtzite in structure. The crystallite size is varied between 10.36 and 71.1 nm, the optical transmission leads to 90% in visible rang, the optical band gap is varied from 3.22 to 3.28 eV and the electrical resistivity is found between 1.42 Ω cm and 17.60 Ω cm. The elaborated films have UV emission located at 380 nm.

Hot aluminum substrate induced hexagonal‐tetragonal phase transitions in InSe and performance of Al/InSe/Cu2O pn tunneling devices

AbstractIn the current study, we have considered the induced phase transitions in Al/InSe thin film substrates and employing them for fabrication of InSe/Cu2O tunneling channels. The InSe substrates are observed to prefer the transition from the hexagonal γ‐In2Se3 to the rarely observed tetragonal InSe. The phase transitions are obtained by the thermally assisted diffusion of aluminum, which was already kept at 250°C in a vacuum media of 10−5 mbar before the compensation of InSe. The tetragonal InSe also induced the crystallization of orthorhombic Cu2O with acceptable level of lattice matching along the a‐axis. The Al/InSe/Cu2O/Au heterojunctions, which are electrically analyzed are observed to exhibit rectifying features with the current conduction being dominated by electric fields assisted thermionic emission (tunneling) through a barrier of width of 5.5 to 14.0 nm and barrier height of 0.19 to 0.30 eV. The ac analyses of the capacitance and conductance spectra of this device have shown that it can exhibit high/low capacitance and frequency dependent conductance switching modes at 0.12 GHz in addition to negative capacitance effect in the range of 0.12 to 1.80 GHz. The features of the device are promising as they indicate the suitability of the device for fabrication of field effect transistors, memory devices, and ultrafast switches.

Ultrasonic Spray Pyrolysis of Antimony‐Doped Tin Oxide Transparent Conductive Coatings

AbstractTransparent conducting oxides are fundamental for the fabrication of optoelectronic devices including touchscreen displays, solar cells, and light emitting diodes. However, they mostly rely on rare elements and expensive vacuum‐based deposition methods that negatively affect the overall cost of optoelectronics. Here, a detailed investigation on the synthesis of antimony‐doped tin oxide films using an ultrasonic spray coating system is presented. High‐quality, crystalline SnO2 films are deposited via decomposition of metal precursors sprayed directly onto hot (>400 °C) substrates. Doping is easily achieved by adding the dopant salt to the spray solution, and the presence of the dopant atoms heavily influences the optical, electrical, and structural properties of SnO2. These coatings are characterized using a comprehensive suite of techniques including X‐ray diffraction, electron microscopy, X‐ray and ultraviolet photoelectron spectroscopies, Hall effect measurements, optical spectroscopy in the visible and near infrared, and atomic force microscopy, in order to elucidate the relationship between the synthetic conditions and functional properties. Through a careful optimization process, Sb‐doped SnO2 coatings showing transmittance values in the visible spectrum between 80% and 90%, and sheet resistances of 10–20 Ω/sq−1 are achieved. Such values are suitable for immediate applications of these Sb‐doped SnO2 films as high‐performance transparent conductors.

An integrated, optofluidic system with aligned optical waveguides, microlenses, and coupling prisms for fluorescence sensing.

An improved, laser-induced fluorescence-based micro-optical biosensor was designed and fabricated, with cyclic olefin copolymer (COC) optical waveguides, a poly(methyl methacrylate) (PMMA) fluidic substrate with an array of microlenses, and a COC coupling prism integrated with the waveguide substrate or cover plate. The double-sided hot embossed fluidic substrate had sampling zone microchannels on the bottom and microlenses on the top. Dissolved COC injected into polydimethylsiloxane (PDMS) lost molds embedded the waveguides in the PMMA cover plate and formed the integrated coupling prism. The embedded COC waveguide was flycut down to 50 μm. The cover plate and shallow, 1:20 aspect ratio, microchannels were thermal fusion bonded using a pressure-assisted boiling point control system, without sagging. The large COC prism coupled better to the waveguide. The highest intensity evanescent excitation of the waveguide was obtained near the critical angle. The maximum signal-to-noise ratio (SNR) was 119 and the lowest detection limit was 7.34 × 10-20 mol at a SNR of 2 for a 100 μm wide by 50 μm deep waveguide. The microlenses highly focused the fluorescent radiation in the sampling zone. The microfabricated waveguide enables rapid, low-cost detection of fluorescent samples with high SNR, a low detection limit, and high sampling efficiency.

Precise thickness profile measurement insensitive to spatial and temporal temperature gradients on a large glass substrate.

When manufacturing glass substrates for display devices, especially for large-sized ones, the time-varying spatial temperature gradient or distribution on the samples is remarkably observed. It causes serious degradation of thickness measurement accuracy due to the combination of thermally expanded thickness and temperature-dependent refractive index. To prevent or minimize the degradation in thickness measurement accuracy, the temperature distribution over an entire glass substrate has to be known in real time in synchronization with the thickness measurement to specify the refractive index of the sample based on an exact mathematical model of the temperature-dependent refractive index. In this paper, a measurement method for determining the thickness profile of a large glass substrate regardless of precise measurement of temperature distribution and the mathematical model of the refractive index was demonstrated. The widely used glass substrates with nominal thicknesses of 0.6 mm and 1.3 mm were measured at room and high temperatures. Through comparison of thickness profiles of hot glass substrates having large temperature gradients and those estimated through thermal expansion of thickness profiles measured at room temperature, it was confirmed that the proposed method can provide highly reliable thickness measurement results under such challenging conditions, unlike simple calculation from the optical thickness using the well-known refractive index.

High resolution digital image correlation for microstructural strain analysis of a stainless steel repaired by Directed Energy Deposition

Deformations within a microstructural gradient zone of stainless steel repaired specimens are investigated. The repair, added material by Directed Energy Deposition over a hot rolled sheet substrate, was tested in monotonic tensile experiments. In situ tests, scanning electron microscope images combined with high resolution digital image correlation and electron backscatter diffraction maps, permitted to monitor the local strain distribution. The strain distribution is homogeneous in the substrate and exhibits a heterogeneous pattern in the printed part with localization correlating spatially with the position of interlayers. The vicinity of the interface has smaller strains and exhibits larger hardness.