Increasing Substrate Temperature Research Articles

Interplay of transport mechanisms during the evaporation of a pinned sessile water droplet

Droplet evaporation has been intensively investigated in past decades owing to its emerging applications in diverse fields of science and technology. Yet the role transport mechanisms has been the subject of a heated debate, especially the presence of Marangoni flow in water droplets. This work aims to draw a clear picture of the switching transport mechanisms inside a drying pinned sessile water droplet in both the presence and absence of thermocapillarity by developing a comprehensive model that accounts for all pertinent physics in both phases as well as interfacial phenomena at the interface. The model reveals a hitherto unexplored mixed radial and buoyant flow by shedding light on the transition from buoyancy induced Rayleigh flow to the radial flow causing coffee ring effect. Predictions of the model excellently match previous experimental results across varying substrate temperatures only in the absence of Marangoni flow. When thermocapillarity is accounted for, strong surface flows shape the liquid velocity field during most of the droplet lifetime and the model starts to overestimate evaporation rates with increasing substrate temperature.

Mott variable range hopping transport in thermal evaporated vanadyl 2, 3 naphthalocyanine thin films

Thin films of Vanadyl 2, 11, 20, 29, Tetra Tert-Butyl 2,3 Naphthalocyanines [VTTBNc] are prepared by means of Vacuum evaporation technique. The effect of thickness and substrate heating on electrical, optical, structural and surface morphological characteristics of the thin films are studied by means of various characterization techniques like DC electrical conductivity, UV–visible absorption spectra, X-ray Diffractogram (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Electrical conductivity studies of thin film samples show an exponential variation with a negative temperature coefficient of resistance. Transport property like density of states near Fermi level decreases and hopping distance increase with the increase in thickness and substrate temperature.

Structural, optical and morphological evolution of Ga2O3/Al2O3 (0001) films grown at various temperatures by pulsed laser deposition

This study systematically investigated the structural, optical, and morphological evolution of Gallium oxide (Ga2O3) films deposited at different substrate temperatures on Al2O3(0001) using pulsed laser deposition (PLD). The thickness of the Ga2O3 films was standardized in order to eliminate its effect on the film properties. The effect of substrate temperature from room temperature to 600 °C on the film's transmittance, crystalline structure, chemical composition and surface morphology, was explored. The plasma species generated during the deposition of the PLD process were monitored and analyzed employing in situ optical emission spectroscopy. The deposition rate of the films decreased with increasing substrate temperature. X-ray photoelectron spectroscopy was used to detect both Ga3+ and Ga + oxidation states in all prepared films, which indicated substoichiometric Ga2O3 films deficient in oxygen. The percentage of non-lattice oxygen decreased with increasing substrate temperature. At optimal condition, mono-crystaline β-Ga2O3 was produced with a high visible and near-infrared transmittance, large grain size and smooth surface, which is suitable for the application in high-performance power electric devices and photoelectronic devices.

The effect of substrate temperature on the critical velocity in microparticle impact bonding

A number of nascent coating and micromanufacturing processes involve particles sprayed at a high velocity, which impact a substrate, deform, and adhere. Successful bonding between the particles and the substrate requires impact velocities higher than the so-called critical adhesion velocity. This critical velocity is influenced by the temperature of the substrate, a variable that we isolate in this work by conducting single-particle impacts on a variable-temperature substrate for three systems (Al–Al, Sn–Sn, and Ti–Ti) with particles individually selected within a narrow size distribution. Our results quantitatively connect the increase in substrate temperature to a significant lowering of the critical velocity, which we attribute to the lower dynamic strength of the thermally softened substrate. The data are generally consistent with expectations for bonding being controlled by a hydrodynamic process of jetting upon impact.

Effect of temperature on the growth of TiN thin films by oblique angle sputter-deposition: A three-dimensional atomistic computational study

Kinetic Monte Carlo (kMC) atomistic computations using MODENA code were employed to simulate the growth of columnar TiN thin films under oblique angle deposition geometry. The influence of substrate temperature (300, 400 and 500 K) on the morphology (column tilt angle, average layer density, compactness, surface roughness) of the layers was studied by varying the inclination angle α of the substrate from 5° to 85° with respect to the centerline of the source. Two types of simulations were considered in this work: the first one assumes a collimated flux (CF) of incident particles and the second one grasps the angular distribution of sputtered Ti particles to closely mimic the magnetron sputtering (MS) conditions. The formation of separated columns with high aspect ratio, and tilted in the direction of the incident particles flux, is observed for α ≥ 35° for the two types of particle flux. The column width and tilt angle, the average layer density and the compactness of the TiN films are found to increase with increasing substrate temperature, due to enhanced surface diffusion. The column tilt angle β increases from 3° to 60° with increasing α for the CF case, while it saturates to approx. 35° when the MS distribution is considered. The relationship between β and α, and their temperature dependence, are discussed and compared to experimental results obtained on sputter-deposited TiN films, as well as with other results and models reported in the literature. The code also reproduces morphological features common to most films produced at glancing angles, such as column broadening with increasing thickness and their anisotropic aggregation (bundling association) in the transverse direction.

Controllable preparation and electrochemical properties of In-situ annealed LiCoO2 films with a specific crystalline orientation on stainless steel substrates

The crystallization characteristics of LiCoO2 (LCO) thin films are key factors that affect the electrochemical properties of films. In this paper, in-situ annealed LCO films with a specific crystalline orientation were prepared on stainless steel (SS) substrates by radio-frequency (RF) magnetron sputtering. The effects of the high-temperature pretreatment of the SS substrate, substrate temperature and sputtering power on the crystallization and electrochemical properties of the LCO films were investigated in detail. It was found that the structure of the SS substrate was transformed from the γ phase to the δ phase after the high-temperature pretreatment, and the crystallization orientation of the LCO films could be induced by the different SS phase structures. The crystallization characteristics of the LCO films were also clearly influenced by the substrate temperature. The crystallization orientation changed from the (003) orientation to the (101) orientation when the temperature increased to a high degree, but too high of a substrate temperature (such as 600 °C) ruptured the films. The discharge specific capacity of the LCO films increased with an increasing substrate temperature, showing a capacity of 53.8 μAh cm−2 μm−1 at 550 °C and exhibiting good cycling stability. At this temperature, the crystal orientation could be controlled by adjusting the sputtering power to avoid rupturing the thin films, thereby achieving high-quality LCO films with a specific orientation. The LCO films prepared at 120 and 200 W showed obvious (101) and (003) preferred orientations, respectively. The galvanostatic charge-discharge tests showed that the (101) preferred orientation film exhibited a large initial discharge capacity of 57 μAh cm−2 μm−1, but its cycling performance was poor. The (003) preferred orientation delivered a superior cycling performance with an initial discharge capacity of 55.6 μAh cm−2 μm−1 and a capacity retention of 72% after 150 cycles. Cyclic voltammetry and electrochemical impedance spectroscopy measurements showed that the (101) preferred orientation was more conducive to the full infiltration of the electrolyte and the transport of lithium ions, but the stability of the structure and surface was poor and the impedance clearly increased during cycling. The (003) preferred orientation exhibited better structural and surface stability and exhibited better lithium-ion diffusion after repeated electrochemical processes.

Additive manufacturing of high strength near β titanium alloy Ti-55511 by engineering nanoscale secondary α laths via in-situ heat treatment

In addition to the great merits of producing three-dimensional complex components from metallic powders in additive manufactured parts, the microstructural features can be tailored by the intrinsic heat treatment (IHT), i.e., cyclic re-heating without any additional post-treatment of the printed samples. Here we report that the microstructural configurations can be widely manipulated in an additive manufactured Ti-5Al-5Mo-5V-1Cr-1Fe (Ti-55511) near β titanium alloy, with an emphasis on the effect of IHT on the in-situ precipitation of α phase. The typical as-printed samples consist of prior-β grains, coarse primary α (α I ) colony and nanoscale secondary α (α II ) laths. Based on automatic quantitative image analysis, the increase of substrate temperature has a remarkable impact on accelerating the precipitation of nanoscale α II laths, while suppressing the precipitation kinetics of the primary α colony, and the corresponding volume fraction of α II laths increases from only 2% to more than 40%, resulting in a tensile strength increment from 900 MPa to 1200 MPa. The enhanced strength derives from those extremely fine α II laths in terms of boundary strengthening. The findings in this work provide a strategy of strengthening additively manufactured components by taking advantage of one step intrinsic heat treatment.

Nanoindentation and Photoluminescence Studies of Hydrogenated Boron Carbon Nitride Thin Films

Nanoindentation and photoluminescence (PL) studies were performed on hydrogenated boron carbon nitride thin films deposited using radio frequency magnetron sputtering. Dual target sputtering from B4C and BN targets was used to deposit films. The variation in the composition of films was studied using energy-dispersive X-ray spectroscopy. The influence of hydrogen gas and substrate temperature on the mechanical properties was investigated using nanoindentation measurements. Photoluminescence studies were performed on films deposited under varying hydrogen content and different deposition temperatures. The films deposited in this study exhibited hardness of 6–22 GPa and Young’s modulus of 125–140 GPa. PL spectra demonstrated two prominent emission peaks around 499 nm and 602 nm for the deposited films. Increasing the hydrogen gas ratio in the films induced PL peak shifts to longer wavelengths. Emission spectra shifted to long wavelength with increasing substrate temperature. The emission peak position shifted from 499 nm to 544 nm and from 602 nm to 655 nm as a function of substrate temperature. For the first time, BCNH based thin films PL behavior at low temperature (77 K) has been characterized in this study. The BCNH thin films show a rare phenomenon of negative thermal quenching of emission.

Effect of high-enthalpy atmospheric plasma spraying parameters on the mechanical and wear resistant properties of alumina ceramic coatings

Over the past decade, alumina ceramic coatings have become promising candidates for anti-wear and anti-corrosion applications owing to their excellent mechanical properties, such as chemical inertness and high temperature resistance, high hardness, and high abrasion resistance. In this work, alumina ceramic coatings are prepared via high-enthalpy atmospheric plasma spraying. The effect of plasma spraying parameters should be paid to attention, such as spraying power, powder feeding rate, and initial substrate temperature, on the mechanical and wear characteristics of the obtained coatings. According to the results, the increase in the plasma spraying power allows one to substantially reduce the porosity of coatings and in turn improves the wear resistance. The use of the higher powder feeding rates enables one to achieve the lower density and adhesion of coatings, which is due to the rising amount of unmolten particles. Finally, an increase in the initial substrate temperature reduces to a large extent the defects of the coating by decreasing the quenching stress, which enhances their mechanical properties. A decrease in the porosity of the coating is beneficial to improve the wear resistance.

Effects of substrate temperature and intermediate layer on adhesion, structural and mechanical properties of coaxial arc plasma deposition grown nanodiamond composite films on Si substrates

Low-temperature fabrication of nanodiamond films on untreated silicon substrates, which are preferred substrates and widely employed in industry, can extend nanodiamond film applications, for instance in biosensing and miniaturization technologies. For its realization, the weak adhesion of nanodiamond films on silicon substrates due to insufficient atomic interdiffusion at the interfaces is a serious issue that needs to be overcome. In the present study, coaxial arc plasma deposition (CAPD) grown nanodiamond films were fabricated at low temperatures on silicon substrates. The effects of the substrate temperature, which is an important parameter in the CAPD nanodiamond film growth process, were structurally and physically investigated. It was found that the films softened with increasing substrate temperature and atomic interdiffusions at interfaces between the films and substrates were activated, which resulted in the formation of SiC at the interfaces. On the other hand, the films fabricated directly on silicon at room temperature were exfoliated due to the poor adhesion and high residual stress. Consequently, intermediate layers that were fabricated at elevated substrate temperatures were employed to improve the adhesion strength of nanodiamond films on silicon substrates. This way, the atomic interdiffusion at the interfaces could be promoted and the residual stress in the films was relieved. In the second stage, the films were fabricated on the intermediate layers at different temperatures. It has shown that the top layer films fabricated at low temperature gained distinctive mechanical and structural properties. By applying this strategy, several micrometres of hard nanodiamond films can be fabricated on Si substrates without easily being peeled off.

Temperature induced dynamics of water confined between graphene and MoS2.

Water trapped between MoS2 and graphene assumes a form of ice composed of two planar hexagonal layers with a non-tetrahedral geometry. Additional water does not wet these ice layers but forms three-dimensional droplets. Here, we have investigated the temperature induced dewetting dynamics of the confined ice and water droplets. The ice crystals gradually decrease in size with increasing substrate temperature and completely vanish at about 80 °C. Further heating to 100 °C induces changes in water droplet density, size, and shape through droplet coalescence and dissolution. However, even prolonged annealing at 100 °C does not completely dry the interface. The dewetting dynamics are controlled by the graphene cover. Thicker graphene flakes allow faster water diffusion as a consequence of the reduction of graphene's conformity along the ice crystal's edges, which leaves enough space for water molecules to diffuse along the ice edges and evaporate to the environment through defects in the graphene cover.

Liquid antimony pentachloride as oxidant for robust oxidative chemical vapor deposition of poly(3,4-ethylenedioxythiophene) films

The oxidative chemical vapor deposition (oCVD) process is investigated to produce poly (3,4-ethylenedioxythiophene) (PEDOT) thin films on 10 cm diameter Si wafers, involving the SbCl5 liquid oxidant. Process/structure/properties correlations are thoroughly studied, including the influence of the SbCl5/EDOT ratio, substrate temperature (Tsub), total pressure and deposition duration, on the thickness, composition, morphology, spatial uniformity of the films, and on their electrical conductivity and optical transmittance. The electrical conductivity of the films increases by decreasing the oxidant/EDOT ratio and by increasing the substrate temperature. Such increase of substrate temperature results in the decrease of the deposited mass and thickness. Films uniformity and electrical conductivity are improved by decreasing the total pressure. Operating at 75 Pa results in films of equal and uniform thickness deposited on substrates located all over the deposition chamber, proving the potential of the PEDOT-SbCl5 oCVD process to be scaled up over larger surfaces. The absence of post deposition liquid rinsing allows developing a full dry process, which is of interest to coat sensitive substrates and can thus be implemented for the processing of devices requiring durable, transparent, conductive PEDOT thin films, in particular in the field of optoelectronics.

Generation mechanism and suppression method of landing error of two successively deposited metal droplets caused by coalescence and solidification

Accurate deposition of metal droplets is crucial to limit geometrical defects in metal droplet-based 3D printing. However, unpredictable movements of the droplets displaced from the original landing location due to surface tension-driven flow before it is hindered by solidification, named landing error, lead to broken traces, irregular waved surfaces, or collapsed structures. In the present work, the effect of solidification at the early-time coalescence of two deposited metal droplets on the landing error was revealed. High-speed images were presented to observe coalescence dynamics. A volume of fluid (VOF) based numerical model was developed to analyze the generation mechanism of the landing error. An interesting phenomenon is observed that the second droplet absorbs more mass from the first droplet to form a bigger spherical crown with the increase of substrate temperature, resulting in the distinct final shapes. Inspired by this, a mass conservation model was proposed to predict the dependence of the landing error on substrate temperature. Metal droplets overlapping experiments were further conducted to verify the model and establish the relationship between the landing error and the substrate temperature. Predictions agreed well with experimental results. Finally, a strategy of increasing the thermal conductivity of the substrate to suppress the landing error at high substrate temperatures was proposed, which significantly expanded the processing window of the accurate deposition. This work can provide useful theoretical and experimental guidance for accurate printing of high-quality lines or patterns by utilizing metal droplets.

Droplet Evaporation on a Hydrophobic Photothermal Conversion Substrate

Use of the photothermal effect to control droplet evaporation shows great promise in various applications. Droplet evaporation initiated by direct photothermal conversion between light and fluid is limited by the interaction between the wavelength and fluid type. Here, we report laser-induced sessile droplet evaporation on a hydrophobic photothermal conversion substrate formed by embedding Ti₂O₃ particles into polydimethylsiloxane. Our results indicated that the photothermal conversion substrate could efficiently convert light energy into heat to enable droplet evaporation on it. Unlike droplet evaporation actuated by direct photothermal conversion, in which higher interface temperature was located at the laser projection region, the droplet evaporation on the photothermal conversion substrate showed higher temperature near the triple-phase contact line because of heat transfer from the substrate to the droplet and small heat transfer resistance resulting from small height at the edge. Due to the increased substrate temperature, the droplet evaporation on the photothermal conversion substrate could exhibit a relatively stable and long-term constant contact angle mode even under the localized heating effect. Moreover, by controlling the laser beam position, droplet evaporation could exhibit a directional long-term constant contact angle mode. The obtained results will be helpful for the design and operation of droplet microfluidics based on the photothermal conversion substrate.

Influence of Substrate Temperature on Electrical and Optical Properties of Hydrogenated Boron Carbide Thin Films Deposited by RF Sputtering

Amorphous hydrogenated boron carbide films were deposited on silicon and glass substrates using radio frequency sputtering. The substrate temperature was varied from room temperature to 300 °C. The substrate temperature during deposition was found to have significant effects on the electrical and optical properties of the deposited films. X-ray photoelectron spectroscopy (XPS) revealed an increase in sp2-bonded carbon in the films with increasing substrate temperature. Reflection electron energy loss spectroscopy (REELS) was performed in order to detect the presence of hydrogen in the films. Metal-insulator-metal (MIM) structure was developed using Al and hydrogenated boron carbide to measure dielectric value and resistivity. Deposited films exhibited lower dielectric values than pure boron carbide films. With higher substrate deposition temperature, a decreasing trend in dielectric value and resistivity of the films was observed. For different substrate temperatures, the dielectric value of films ranged from 6.5–3.5, and optical bandgap values were between 2.25–2.6 eV.

Properties of Eu-doped YVO4 thin films grown on glass substrates by radio-frequency magnetron sputtering

The effects of substrate temperature on the structural, morphological and luminescent properties of YVO4:Eu3+ phosphor thin films were investigated using X-ray diffraction, field emission scanning electron microscopy, photoluminescence spectrometry and ultraviolet–visible spectrophotometry. YVO4:Eu3+ thin films were grown on glass substrates using a radio-frequency magnetron sputtering technique at varying substrate temperatures of 25–400 °C. All thin films exhibited a strongly (200) preferred orientation. The optical transmittance spectra indicated an average transmittance higher than 86.5% in the range of 400–1100 nm. Regardless of the substrate temperature, five emission bands centered at 542, 598, 622, 656 and 705 nm, respectively, were observed for all thin films. The maximum excitation and emission spectra were observed at a substrate temperature of 400 °C. A red shift of the band gap energy was observed with increasing substrate temperature. The intensity of the red emission from 5D0 → 7F2 (622 nm) electric dipole transition was stronger than that of the orange emission due to 5D0 → 7F1 (598 nm) magnetic dipole transition, which indicates the presence of more Eu3+ ions in sites without inversion symmetry. Therefore, substrate temperature plays an important role in the growth of red-emitting YVO4:Eu3+ thin films for solid-state lighting and electroluminescent devices.

Out-of-Plane Thermal Expansion Coefficient and Biaxial Young’s Modulus of Sputtered ITO Thin Films

This paper proposes a measuring apparatus and method for simultaneous determination of the thermal expansion coefficient and biaxial Young’s modulus of indium tin oxide (ITO) thin films. ITO thin films simultaneously coated on N-BK7 and S-TIM35 glass substrates were prepared by direct current (DC) magnetron sputtering deposition. The thermo-mechanical parameters of ITO thin films were investigated experimentally. Thermal stress in sputtered ITO films was evaluated by an improved Twyman–Green interferometer associated with wavelet transform at different temperatures. When the heating temperature increased from 30 °C to 100 °C, the tensile thermal stress of ITO thin films increased. The increase in substrate temperature led to the decrease of total residual stress deposited on two glass substrates. A linear relationship between the thermal stress and substrate heating temperature was found. The thermal expansion coefficient and biaxial Young’s modulus of the films were measured by the double substrate method. The results show that the out of plane thermal expansion coefficient and biaxial Young’s modulus of the ITO film were 5.81 × 10−6 °C−1 and 475 GPa.

Development of Co-Based Amorphous Composite Coatings Synthesized by Laser Cladding for Neutron Shielding.

Advanced amorphous coatings consisting of Co-based metallic glasses with ultrahigh strength (6 GPa) and high microhardness (up to 17 GPa) can significantly improve the surface properties of matrix materials. However, the intrinsic brittleness of Co-based metallic glasses can lead to the initiation of microcracks caused by the inevitable generation of thermal stress during the laser cladding process, which severely limits the potential application. In this paper, the methods of increasing substrate temperature and fabricating composite coatings with the addition of toughened Fe powders were adopted to inhibit the generation of microcracks in the Co55Ta10B35 amorphous coatings. Moreover, neutron shielding performances of the cladding coatings with high B content were investigated with a wide range of neutron energy (wavelength: 0.15–0.85 nm). The results indicate that the fully amorphous coating and composite ones can be fabricated successfully. The increase in the substrate temperature and the addition of Fe powders can effectively inhibit the initiation and propagation of microcracks. The fully Co-based amorphous coating with high B content (35 at.%) can exhibit excellent neutron shielding performance. With the addition of Fe powders, the neutron shielding performance is reduced gradually due to the dilution effect of B in the composite cladding coatings, but the microcrack will be completely restrained.

An Investigation of Spray Deposited CdO Films and CdO/p-Si Heterojunction at Different Substrate Temperatures

In this study, CdO films were successfully obtained by using a homemade chemical spray pyrolysis technique. The crystal structures of the CdO thin films improved due to an increase in the substrate temperature when the spray time was kept constant. Additionally, CdO film deposited at 250°C exhibited amorphous crystal structure. The surface morphology of the samples was evaluated by scanning electron microscope (SEM) and it was observed that well-defined granules started to be clearly seen when the substrate temperature increased. Optical properties of CdO films were also investigated by using an ultraviolet–visible (UV–Vis) spectrophotometer, and the optical band gap of CdO varied from 2.57 eV to 2.73 eV with increasing substrate temperature. The electrical performance of the CdO films in the Au/CdO/p-Si device were determined by I–V measurements. According to the results, it was found that diode parameters depend on the changing properties of CdO in terms of the substrate temperature.

Photoresponse characteristics from vacuum deposited thin film of copper phthalocyanine: dependence on grain size

An organic photodetector (PD) is fabricated with single layer thin film of copper phthalocyanine (CuPc) on glass substrate. The thermal deposition of CuPc film on the substrate was realized under high vacuum and at different substrate temperature (room temperature, 40 ◦C, 70 ◦C, 100 ◦C). The comparison of photoresponse characteristics of CuPc thin film deposited under different conditions showed good improvement with increase in the substrate temperature, and the best performances being observed for the film deposited at substrate temperature of 100 ◦C. The thin film of CuPc characterized through X-ray diffraction (XRD) spectroscopy and atomic force microscopy (AFM) clearly indicated that with increase in substrate temperature, the grain size of CuPc film increased, which improved the crystallinity and hence the photoconductivity of the device. The CuPc thin film based PD displayed stable and reproducible photoswitching characteristics under white light irradiation, with photocurrent modulation by varying in input optical power. The highest photo to dark current ratio and responsivity of the devices was calculated to be, ca. 6.5 and 7.1 mA-W−1 at low optical power, ca. 14.5 mW-cm−2.