Substrate Temperature Research Articles

Molecular Dynamics Study of Substrate Temperature and Incident Energy Influence on the Crystallization Behavior of Alumina Thin Film Deposition Process

Molecular Dynamics Study of Substrate Temperature and Incident Energy Influence on the Crystallization Behavior of Alumina Thin Film Deposition Process

Epitaxial growth of single unit-cell superconducting β-Bi2Pd

Bismuth-based binary alloy β-Bi2Pd has recently been suggested as a connate topological superconductor with immense promise for Majorana zero modes. However, the epitaxial thin films down to the ultimate level of single unit-cell have been challenging. Here, we employed the state-of-the-art molecular beam epitaxy to prepare single unit-cell superconducting β-Bi2Pd films with lateral dimensions of hundreds of nanometers. Utilizing in situ scanning tunneling microscopy/spectroscopy, we uncover evidence of anisotropic superconductivity whose spectra are well fit by anisotropic s-wave gap functions and demonstrate that the epitaxial growth of β-Bi2Pd films relies substantially on the substrate temperature, flux ratio, growth rate, and coverage. The high-quality epitaxial films provide a promising platform to investigate the topological superconductivity at the two-dimensional limit.

Enhanced crystallinity of (Sr,Ba)Nb2O6 films on sapphire and alumina substrates

Barium-strontium niobate in thin film form can be considered as a prospective ferroelectric material for microwave applications due to high dielectric nonlinearity. Its performance is linked to film structure quality, and one method to achieve high-quality films on microwave substrates goes through the process of annealing. (Sr,Ba)Nb2O6 films of good crystallinity were formed on sapphire and alumina substrates by magnetron sputtering. The processes of recrystallization of films on single- and polycrystalline substrates under the conditions of ex situ annealing at temperatures of 1100–1200 °C were studied. Highly (00l) oriented films on sapphire substrate were obtained by the deposition in oxygen atmosphere at a substrate temperature of 900 °C with post-growth annealing in air at an annealing temperature of 1150 °C.

Crystallization-Based Modification of Ammonium Perchlorate Heat Release.

Composite propellants use the decomposition of crystalline oxidizers, such as ammonium perchlorate (AP), to produce oxidizing species that can combust with fuels. Controlled crystal microstructure must be leveraged to tailor reactivity to minimize the use of exotic energetic materials. This work uses meniscus-guided coating (MGC) to fabricate films of AP with a high degree of control over the AP crystal microstructure. Exploring a wide range of crystallization parameters resulted in film thickness ranging from 200 nm to 14 μm, particle size ranging from 18 to 110 μm, variable preferential orientation with respect to the substrate, and relative defect density ranging from 2.74 × 105 to 6.78 × 105 μm-3. Increasing coating blade speed and substrate temperature within the MGC process shifts the preferential orientation of the AP crystals from predominantly exhibiting (002) and (210) crystal planes parallel to the substrate to (200)/(011) crystal planes parallel to the substrate. This shift in orientation is accompanied by an increase in defect density, which is shown to increase the heat release from the low-temperature decomposition regime and decrease the heat release from the high temperature regime. These results demonstrate the ability to use recrystallization, defect density control, and orientation control to tune the heat release profiles of energetic materials to augment propellant performance.

Towards ZnO-Based Near-Infra-Red Radiation Detectors: Performance Improvement via Si Nanoclusters Embedment

Si nanoparticles embedded in a ZnO matrix were produced by a sequential deposition of ZnO/Si/ZnO layers, by radio frequency sputtering. Sample growth temperatures of 25 °C, 300 °C, and 500 °C were used to deposit ZnO/Si/ZnO layers on soda lime glass and p-type silicon substrates; ZnO layers were deposited by reactive radio-frequency sputtering employing a mixture of Ar/O2, with a ratio of 66/33, as working atmosphere. The type of substrate and the growth temperature affect the first ZnO layer roughness, promoting the formation of silicon nanoparticles, matrix characteristics, and as consequence, spectral response. The roughness of the initial ZnO layer is transferred to the top layer of ZnO, and it can be tailored between 65 and 370 Å, depending on the sample growth temperature. Transmission electron microscopy show that substrate temperature mainly affects the density of silicon nanoparticles rather than their size. ZnO/Si/ZnO films deposited on p-type silicon substrate were processed and photosensors were obtained, showing a selective response in the 950 to 1150 nm wavelength range, making them suitable candidates for near infrared detectors.

Study of selective etching of TaN with respect to SiOCH dielectrics using SiF4 plasma processes

TaN is used as a Cu diffusion barrier during metal interconnect formation to enable modern chip fabrication. In this study, the selective removal of TaN with respect to SiOCH dielectrics is explored using neutral dominant plasmas containing pure SiF4 or with O2 or H2 additives. SiF4 is studied because the Si-containing gas has been historically used to deposit Si-based films, but the gas also contains F capable of volatilizing Ta. This work explores the possibility of enabling both selective etching of TaN and selective deposition on SiOCH. SiF4 discharges are impacted by the addition of O2 and H2 gases; exhibiting significantly different deposition and etching regimes. The substrate temperature plays a critical role in modulating the TaN etching versus deposition window compared to SiOCH. Through this work, selective etching of TaN with respect to SiOCH is achieved.

Influence of magnetron sputtering process parameters on the morphology of palladium thin films: An empirical study

Abstract The heightened initial energy of deposited atoms during the magnetron sputtering process alters the conventional rules of structure zone transformation for film morphology, posing challenges in fabricating Pd films with specific morphologies. This study aims to elucidate the impacts of substrate temperature and sputtering power on the morphology of Pd films and to determine the magnetron sputtering process parameters for preparing Pd films within a typical structure zone. Pd thin films were fabricated by using magnetron sputtering under varying substrate temperatures and sputtering powers. The morphologies of the films were examined through Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). With increasing substrate temperature, the structure zone of Pd films transitions from Zone T to Zone 2, and subsequently to Zone 3. Given that initial energy enhances the diffusion capability of deposited atoms, the threshold temperature for structural zone transformation of Pd films prepared by magnetron sputtering is lower than the critical value suggested by the Structure Zone Model (SZM). While sputtering power does not critically affect the structure zone of Pd films, it influences grain size and preferred orientation. The substrate temperature is the decisive factor affecting the structural zone of thin films, with the critical temperature for structure zone transformation in magnetron sputtering being lower than that proposed by the Structural Zone Model (SZM). Furthermore, the research has determined the magnetron sputtering process parameters necessary for fabricating Pd thin films with specific structure zones. This study paves the way for subsequent enhancements in the hydrogen sensitivity of palladium thin film sensors through morphology control.

INITIATED CHEMICAL VAPOR DEPOSITION (iCVD) OF POLY(ACRYLIC ACID): A COMPARISON BETWEEN CONTINUOUS AND CLOSED-BATCH iCVD APPROACHES

In this study, poly(acrylic acid) (PAA) thin films were deposited on silicon wafer and glass surfaces by initiated chemical vapor deposition (iCVD) method using di-tert-butyl peroxide (TBPO) as the initiator and acrylic acid (AA) as the monomer. During iCVD, two different precursor feeding approaches, namely continuous and closed-batch, were employed. The effects of substrate temperature and the precursor feeding approaches on the deposition rates and surface morphology of the films were investigated. The highest deposition rates for the continuous and closed-batch iCVD approaches were found as 26.1 nm/min and 18.6 nm/min, respectively, at a substrate temperature of 15 °C. FTIR analysis of the films deposited by both approaches indicated high structural retention of the monomer during the polymerization. AFM results indicated that, PAA thin films possessed low RMS roughness values of 2.76 nm and 1.84 nm using continuous and closed-batch iCVD, respectively. Due to the slightly higher surface roughness of the film deposited under continuous iCVD, that film exhibited a lower water contact angle of 16.1° than the film deposited in closed-batch iCVD. In terms of monomer utilization ratio, closed-batch system was found to be more effective, which may help to minimize the carbon footprint of iCVD process.

Stability Properties of Inverted Organic Solar Cells Prepared with a ZnO Buffer Layer

Organic solar cells (OSCs) of inverted structure (IOSC) were designed to enhancement the solar cell efficiency and stability in organic based solar cell. IOSC was built with the structure of Au/P3HT:PCBM/ZnO/ITO. ZnO thin layers were fabricated on ITO electrodes using the unbalanced magnetron sputtering method. ZnO layer is used as the buffer layer in this structure to prevent oxidation by UV light to the interface of the organic layer and reduce the energy barrier, allowing electron to be easily transferred between the ITO energy level and the organic acceptor energy level (LUMO). ZnO films are also used as a barrier layer to prevent hole injection from P3HT due to the lack of charge carrier recombination. XRD results exhibited that the particle size in ZnO layers increased as the substrate temperature increased. The conversion efficiency of IOSC improved with increasing ZnO substrate temperature. Moreover, compared to the existing device, the IOSC using a ZnO buffer layer was in a stable state for a longer period of time. After about 7 days, it woas found that the Voc of the hybrid solar cells remained almost constant over time and under all conditions. As a result, the ZnO film in the OSC plays an important role for protecting the organic layer of OSCs and enhancing the efficiency.

Statistical Optimization and Purification of Cellulase Enzyme Production from Trichosporon insectorum

Enzymatic degradation of cellulosic biomass represents the most sustainable and environmentally friendly method for producing liquid biofuel, widely utilized in various commercial processes. While cellulases are predominantly produced by bacteria and fungi, the enzymatic potential of cellulase-producing yeasts remains significantly less explored. In this study, the yeast strain Trichosporon insectorum, isolated from the gut of the coprophagous beetle Gymnopleurus sturmii, was utilized for cellulase production in submerged fermentation. A central composite design was employed to optimize cellulase production, with substrate concentration, temperature, and pH as dependent variables. The highest CMCase activity of 0.71 IU/mL was obtained at 1% substrate concentration, pH 5, and an incubation temperature of 40 °C for 72 h of fermentation using cellulose as a carbon source. For FPase production, the high value was 0.23 IU/mL at 0.5% CMC, pH 6, and an incubation temperature of 40 °C for 72 h. After purification, the enzymes produced by T. insectorum represent 39% of the total proteins. The results of this study offer an alternative strategy for utilizing various carbon sources, both soluble (CMC, carboxymethylcellulose) and insoluble (cellulose), to efficiently produce cellulase for the degradation of lignocellulosic materials. This approach holds promising benefits for sustainable waste management.

Synthesis of Sn-ZnO nanostructures on MgO by hybrid pulsed laser ablation and RF magnetron sputtering tandem system for CO gas-sensing application

An exceptional method of incorporating Sn ions into Zinc Oxide (ZnO) using a tandem system of Pulsed Laser Deposition (PLD) and Radio-Frequency Magnetron Sputtering (RFMS) to synthesize and functionalize ZnO nanostructures is demonstrated in this study for gas-sensing application. The RFMS power was varied up to 50 W to sputter a pure Sn metal target, while simultaneously or successively growing ZnO nanostructures on a templated MgO < 0001 > substrate and on an Au-plated Al2O3 gas sensor, via PLD process at the substrate temperature of 700 °C in 100–500 millitorr oxygen/argon gas background. The morphologies of the grown Sn-ZnO nanostructures were characterized by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and X-ray Diffraction (XRD), and while their chemical/oxidation states and optical properties were analyzed by X-ray photospectroscopy (XPS) and photoluminescence (PL), respectively. For simultaneous deposition, the resulting (0002)-dominated 2D grain-like ZnO nanostructures were influenced by the interaction of the dynamic PLD plasma with static RFMS plasma at different powers. For successive growth, at 50 W-RF power, a remarkable increase in the sensor response to 50-ppm carbon monoxide (CO) gas was observed at 250 °C, which could be attributed to the creation of more adsorption sites in the Sn-ZnO depletion region caused by the replacement of some Zn sites with Sn ions in the ZnO matrix. This study, therefore, exhibits the viability of this hybrid system to design, synthesize, and functionalize Sn-ZnO nanomaterials, either by simultaneous/successive deposition, for gas-sensing applications.

Preparation and Characterization Studies of CU2SnS3 Thin Film using Ultrasonic Spray Pyrolysis Technique for Solar Cell Application

Low-cost ternary chalcogenide is produced using technologies like ultrasonic pyrolysis spray method. A thin film of Cu2SnS3 which is doused with the substrate of glass temperature by altering the temperature from 330 C to 550 C. As the temperature increases, the amorphous phase of the thin layer of Cu2SnS3 crystal structure is discovered to shift to tetragonal phase. Using this above technique Cu2SnS3 chalcogenide thin film were deposited at temperature of substrate, varying from 300 C to 550 C in increment of 50 C, utilizing affordable, computerized pyrolysis using ultrasonic spray processes. When films are generated at 500 C for the substrate the The tetragonal phase of Cu2SnS3 is produced in highly crystalline films. Higher temperature of substrate results in the develop the binary phase SnS2.650.4 nm is discovered to be the typical film thickness. So, by using pyrolysis technique the attributes of the thin-film Cu2SnS3 is studied in solar cell.

Deposition temperature-mediated growth of helically shaped polymers and chevron-type graphene nanoribbons from a fluorinated precursor

Graphene nanoribbons (GNRs) of precise size and shape, critical for controlling electronic properties and future device applications, can be realized via precision synthesis on surfaces using rationally designed molecular precursors. Fluorine-bearing precursors have the potential to form GNRs on nonmetallic substrates suitable for device fabrication. Here, we investigate the deposition temperature-mediated growth of a new fluorine-bearing precursor, 6,11-diiodo-1,4-bis(2-fluorophenyl)-2,3-diphenyltriphenylene (C42H24F2I2), into helically shaped polymer intermediates and chevron-type GNRs on Au(111) by combining scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory simulations. The fluorinated precursors do not adsorb on the Au(111) surface at lower temperatures, necessitating an optimum substrate temperature to achieve maximum polymer and GNR lengths. We compare the adsorption behavior with that of pristine chevron precursors and discuss the effects of C-H and C-F bonds. The results elucidate the growth mechanism of GNRs with fluorine-bearing precursors and establish a foundation for future synthesis of GNRs on nonmetallic substrates.

Effects of salinity and temperature on the icing of sessile saltwater droplets on solid surfaces

The icing of sessile seawater droplets on solid surfaces holds significant importance in scientific research and freeze desalination technology. Nevertheless, the statistical characteristics and underlying mechanisms of this phenomenon remain insufficiently understood. In this study, we experimentally investigate the statistical characteristics of the icing of seawater droplets on solid surfaces, and couple with the molecular dynamics method to reveal the influence of salinity and substrate temperature on the icing. It is found that the nucleation time of seawater droplets on solid surfaces exhibits stochasticity, while it follows a normal distribution. With increasing salinity or surface temperature, the distribution range of the nucleation time becomes broader and more dispersed. Both the average nucleation time and the average freezing time of seawater droplets increase with increasing salinity or temperature; the former is due to an elevating nucleation energy barrier, and the latter stems from an increasing ice-salt solution interfacial free energy (the energy required to freeze the salt solution into a unit area of ice). Our findings enhance the comprehension of the characteristics and fundamental mechanisms of the icing of seawater droplets on solid surfaces, offering valuable insights for the development of freeze desalination technology.

Capture zone scaling in 2D Ge island nucleation on Si(111)-(7 × 7) at elevated temperatures

Recently we have studied the concentration N2D of 2D Ge island nucleated on large-scale Si(111)-(7 × 7) terraces at 550 − 650 °C as function of the substrate temperature T and Ge deposition rate R [J. Cryst. Growth. 531 (2020) 125347], where we have shown that N2D(R) dependence is characterized by a power law with scaling exponent χ = 1 ± 0.1. However, in the frames of classical Venables rate-equation approach, the obtained range of χ values do not allow one to unambiguously determine the critical nucleus size i, since χ = 1 ± 0.1 can be attributed to both diffusion limited (DL) and attachment limited (AL) growth regimes. In order to determine an exact i size and growth kinetics, in this work, we have investigated the scaled capture-zone distribution (CZD) of nucleated 2D Ge islands on the same Ge/Si(111)-(7 × 7) samples and described it by the generalized Wigner distribution Pβ=aβAβexp-bβA2, where Pβ is the probability density of getting into some region of capture zone values, A is normalized Voronoi cell area for 2D island, β=iχ is scaling parameter directly related to the critical nucleus size i. It has been shown that the kinetics of 2D Ge island nucleation on the wide Si(111)-(7 × 7) terraces at elevated temperatures should procced under AL growth kinetics with i = 3–5 particles.

Diamond coatings on copper surfaces through interface engineering

To address the challenges posed by the significant thermal stress and limited affinity of diamond coatings on copper (Cu) substrates, we developed a method combining femtosecond (fs) laser texturing with the application of a nickel (Ni) interlayer. This technique was utilized for adhesion enhancement of diamond coatings on Cu. By varying the deposition duration and microgrid depth through multiple fs laser scanning passes, it is possible to attain well-adhered diamond coatings on Cu substrates. These coatings demonstrate an outstanding quality factor of 93.4% and an average grain size of 5.5 μm. The enhanced adhesion results from the synergistic reinforcement of the mechanical interlock and anchoring mechanisms facilitated by the textured surface, further bolstered by the presence of the Ni interlayer. Moreover, the shape of the texture significantly influences the deposition outcome. Single-crystal diamonds with an average grain size of 10 μm were achieved on sharp microgrids at a substrate temperature of 550 °C. This work is expected to offer a general approach for deposition of diamond coatings on metallic materials with enhanced adhesion.

CuxS films as photoelectrodes for visible-light water splitting

Copper sulfides are appealing semiconductors for optoelectronics applications requiring visible-light activity, such as solar water splitting, due to their relatively low band gaps and earth-abundance. This study investigates the effect of deposition conditions, including substrate temperature and background gas pressure, on the characteristics and photoelectrochemical performance of copper sulfide (CuxS) films grown by pulsed laser deposition (PLD) on Si (100) substrates. The results reveal that varying the deposition parameters influences the crystalline phases, morphology, and optoelectronic properties of the films. For deposition at room temperature, the films exhibited covellite CuS phase, while elevated deposition temperatures (250 °C and 500 °C) led to the formation of Cu1.8S and Cu2S phases, resulting in narrowing of the band gap, with the increased temperature also enhancing the film crystallinity and surface roughness. As a result of the changes in film morphology and crystal structure, photocurrent density magnitudes increased with higher deposition temperatures, reaching 0.747 mA/cm2 at −0.8 V for films deposited at 500 °C under vacuum, at least an order of magnitude higher than reported in comparable previous studies of the photoelectrochemical performance of CuxS. Background gas pressure only slightly affected the photocurrent density, with changes in photoactivity also correlating with changes in film roughness and band gap. The results demonstrate the good visible-light activity and behavior of CuxS as a stand-alone photoelectrode material, with tunability based on the fabrication conditions, suggesting their potential use in photoelectrochemical and other solar energy conversion applications.

Fabrication of TiN metal hard masks via very-high-frequency-direct-current superimposed sputtering

In high-end logic devices, TiN films have attracted increasing attention as metal hard masks (MHMs) for scaling trenches and vias of Cu back-end of line. In this study, we investigated the application of very-high-frequency-direct-current (VHF)-DC superimposed magnetron sputtering for fabricating TiN MHM films and compared these films with TiN MHM films deposited via DC magnetron sputtering. The X-ray diffraction (XRD) pattern of deposited TiN MHs showed crystalline orientations corresponding to the (111), (200), and (220) orientations of NaCl TiN. The films deposited using DC magnetron sputtering exhibited high density (<5.2 g/cm³) and significant compressive stress (1.477 GPa) when the TiN film thickness ranged from 29 to 30 nm. The films deposited via VHF-DC superimposed sputtering exhibited a higher density (5.25 g/cm³) and tensile stress (0.928 GPa). As revealed by XRD, the films deposited via DC sputtering exhibited the (111) crystal orientation, whereas those deposited via VHF-DC superimposed sputtering exhibited the (200) crystal orientation. The film deposited by VHF-DC superimposed sputtering at a frequency of 60 MHz and a substrate temperature of 350 °C exhibited good resistivity (93.0–143.3 μΩ cm). Furthermore, the TiN films exhibited exceptional smoothness with a surface roughness of less than 0.5 nm. These results show that VHF-DC superimposed sputtering is a promising technique for fabricating TiN-based MHMs.

Internal flow in freezing and non-freezing water droplets at freezing temperatures

By comparing freezing and non-freezing water droplets with Particle Image Velocimetry (PIV), this paper aims to further advance the knowledge of the internal movement in deposited water droplets. The experiments are carried out at substrate temperatures below 0 °C, and the onset of the freezing process is controlled by the structure of the plate. Results show similar flow patterns for the freezing and non-freezing case, indicating that the phase change is not the initial driving force of the internal movement or the directional change phenomena. The phase change will, however, decrease the volume of the liquid and generate a difference in heat transfer and temperature, hence introducing a faster decrease in velocity and sooner directional velocity change. In the non-freezing case, a stagnated period at the beginning of the internal movement is observed before the decrease in velocity.

Synthesis and gasochromic hydrogen sensing properties of sodium tungsten bronze films by atmospheric flame vapor deposition

This study explores the gasochromic hydrogen sensing capabilities of Pd-coated NaxWO3 thin films prepared via Flame Vapor Deposition (FVD) on soda-lime glass substrates. Employing an oxy-hydrogen generator and varying substrate temperatures (100–450 °C) were investigated. X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) revealed a transition from Na0.1WO3 to Na2W6O19 phases, increased crystallite size (5.4–35.5 nm), and morphological changes from porous to dense structures with temperature. The films exhibited good optical transparency (70–95%) in the visible and near-infrared, with the sample deposited at 350 °C (S350) showing the maximum transmittance. The gasochromic hydrogen sensing performance of Pd/NaxWO3 films was evaluated. The sensor response increased with operating temperature, reaching an optimal performance at 300 °C. The sample S350 exhibited the fastest response (51 s) and recovery (30 s) times with a linear calibration curve limit of detection (LOD) of 46 ppm. Repeated cycling tests indicated stable and reversible performance. Finally, the sensing mechanism was described.