Low Substrate Temperature Research Articles

Deposition Mechanism and Characterization of Plasma-Enhanced Atomic Layer-Deposited SnOx Films at Different Substrate Temperatures.

The promising functional tin oxide (SnOx) has attracted tremendous attention due to its transparent and conductive properties. The stoichiometric composition of SnOx can be described as common n-type SnO2 and p-type Sn3O4. In this study, the functional SnOx films were prepared successfully by plasma-enhanced atomic layer deposition (PEALD) at different substrate temperatures from 100 to 400 °C. The experimental results involving optical, structural, chemical, and electrical properties and morphologies are discussed. The SnO2 and oxygen-deficient Sn3O4 phases coexisting in PEALD SnOx films were found. The PEALD SnOx films are composed of intrinsic oxygen vacancies with O-Sn4+ bonds and then transformed into a crystalline SnO2 phase with increased substrate temperature, revealing a direct 3.5–4.0 eV band gap and 1.9–2.1 refractive index. Lower (<150 °C) and higher (>300 °C) substrate temperatures can cause precursor condensation and desorption, respectively, resulting in reduced film qualities. The proper composition ratio of O to Sn in PEALD SnOx films near an estimated 1.74 suggests the highest mobility of 12.89 cm2 V−1 s−1 at 300 °C.

Pseudostoichiometric and oxygen deficient MoOx for efficient sensing of H2S and CO at relatively low operating temperature and analyte concentrations

Pseudostoichiometric molybdenum oxide (MoOx) thin films were deposited on glass substrates using radio frequency magnetron sputtering from sintered molybdenum trioxide (MoO3) target at relatively low substrate temperature in inert (Ar) atmosphere. Structural, morphological, and electrical properties of the deposited films were studied thoroughly, followed by detailed investigations on the sensing performance of the same toward two hazardous and toxic gases, hydrogen sulfide (H2S) and carbon monoxide (CO); specifically at low operating temperature and with low concentrations. Good response percentages with satisfactory response and recovery time were obtained for both the gases. These might be attributed to the presence of oxygen deficient and well distributed nanostructures on the surface of the film that facilitate gas adsorption/anchoring and promotes the charge transfer reactions on the surface of the semiconductor. Furthermore, extensive sensing measurements and post-sensing structural characterization were carried out, which revealed long-term stability of the sensing platform.

Characterization and electrochromic properties of NiO thin films prepared using a green aqueous solution by pulsed spray pyrolysis technique

Nickel acetylacetonate of 0.2 M aqueous solution is used to synthesize (NiO) thin films by pulsed spray pyrolysis method onto glass substrates. Structural and morphological properties of the deposited films were examined using (XRD) and (FESEM) techniques. The results revealed that at low substrate temperatures and short spray time, the obtained films were amorphous, whereas the films deposited at higher temperatures and long spray time has a cubic phase. Cross-sectional FESEM is used to properly estimate films thicknesses. The energy band gap is calculated to be 3.52–3.89 eV using optical spectrum measurements. Electrochromic properties of NiO films deposited on FTO working electrode substrates are measured in a three-electrode cell containing KOH with Ag/AgCl reference electrode at a scan rate of 20 mV/s. The charge density increases with the thickness, and it is 98.0 mC/cm2 at the thickness of 360 nm after 30-min deposition time at 400 °C and for most of the samples the film stability increases after cycling.Graphical abstract

Flowing Gas Experiments Reveal Mechanistic Details of Interfacial Reactions on a Molecular Level at Knudsen Flow Conditions

Knudsen flow experiments and its interpretation in terms of adsorption/desorption kinetics as well as quantitative uptake on substrates of interest is presented together with the description of critical design parameters of the Knudsen Flow Reactor (KFR). Hitherto focused almost exclusively on the uptake phase exposing a virgin substrate to interacting gases, we now extend the experiment and its interpretation to the desorption phase at ambient temperature. We present analytical expressions for different experimental situations in terms of adsorption (ka), desorption (kd) and effusion (ke) rate constants. The measurement of kd leads to surface residence times (1/kd) obtained under the same experimental conditions as the uptake (ka) that results in the determination of the Langmuir equilibrium constant KL = ka/kd. We emphasize the interaction of semivolatile organic probe gases and small polar molecules with amorphous carbon and mineral dust materials at ambient temperatures. The latter leads to a molecular characterization scheme based on the use of up to ten different reactive probe gases. After saturation of the uptake of each probe gas this results in a reactivity map of the interface. Several examples are used to underline the broad applicability of the technique such as the silver/air (Ag) interface and the reactivity of TiO2 materials towards uptake of CO2 and CH3OH. Following characterization of several types of amorphous carbon a model incorporating several structural elements in agreement with the reactive gas titration is proposed. For instance, an interface that is at the same time weakly basic and strongly reducing is composed of pyrones and hydroquinones whose simultaneous occurrence leads to stable free radicals that may play a role in atmospheric chemistry (EPFR). The question is raised what makes an interface hydrophobic in terms of surface functional groups when interacting with small polar molecules such as H2O(D2O), HCl, NO2 and NH2OH. Multidiagnostic studies of heterogeneous reactions are enabled using stirred-flow reactors (SRF) that are a logical extension of the KFR approach thus relaxing the Knudsen flow requirements. Previous work using SRF on low-temperature substrates such as H2O ices is highlighted that may be of interest to the exoplanetary and space sciences community.

High-Efficiency of PVD Coating Process by Applying an Additional Rotation

This article analyzes PVD coatings (physical vapor deposition—the coating material is vaporized and deposited by sputtering or arc evaporation, and PVD coatings are applied at lower substrate temperatures and thus can be applied to a wider range of substrates) applied to samples which are located in a fixture. This fixture enables additional rotation of the sample via the coating process. The fixture allows an increase of coated tools in one batch, and therefore an increase of the current capacity of the coating machine. The introductory section of the article describes the process of product design, including its modifications. The experimental section is focused on the functionality checking of the proposed design. The coating process was carried out on a machine named INNOVA. To guarantee the correct coating application during the process, it is necessary to research the coating thickness and the chemical composition of the samples and compare these results with the results of samples which were coated without using a designed fixture. Round bars with a diameter of 10 mm were chosen as test samples. On these samples, a FUTURA monolayer was applied on a TiAlN base. Chemical composition and coating thickness were evaluated using a scanning electron microscope (SEM). Using a fixture with a fourth rotation, the same chemical composition and coating thickness were achieved as those samples which were coated in a process without the use of a fourth rotation. Therefore, it was possible to confirm a capacity increase of the coating machine.

Interlayer-Assisted Growth of Si-Based All-Inorganic Perovskite Films via Chemical Vapor Deposition for Sensitive and Stable X-ray Detection.

All-inorganic perovskites are considered as preferred materials for next-generation X-ray detectors. However, preparing high-quality thick films by traditional solution-based methods remains challenging due to the low solubility of the precursors. In this work, chemical vapor deposition technology is employed to grow Si-based all-inorganic cesium-lead-bromide perovskite thick films. By introducing a SnO2 nanocrystal interlayer onto the Si substrate to facilitate the heterogeneous nucleation of the perovskite, we are able to grow high-quality films with a smooth surface and compact grains at a relatively low substrate temperature of 260 °C. The resultant X-ray detectors exhibit a decent sensitivity of 2930 μC Gyair-1 cm-2, a small dark current density of 1.5 nA cm-2, and a low detection limit of 120 nGyair s-1. Moreover, the devices show excellent biasing stability with a record small baseline drift of 4.6 × 10-9 nA cm-1 s-1 V-1 under a large electric field of 1100 V/cm among all perovskite polycrystalline film-based detectors ever reported.

Numerical Simulation of Residual Stress and Deformation in Wire Arc Additive Manufacturing

In this paper, multi-layer and multi-pass arc additive manufacturing experiments were carried out on the Q345 substrate using Y309L welding wire. Based on MSC. Marc software, a thermal-elastic-plastic finite element method was developed to numerically simulate the temperature field, stress field, and deformation during the additive manufacturing process. The effects of the substrate thickness and interpass temperature on the temperature field, stress field, and deformation were discussed. The results indicated that the deposition materials at different positions experienced different thermal cycles, which might lead to the non-uniform microstructure and mechanical properties within the workpiece. The interpass temperature and the thickness of the substrate influenced the residual stress distribution in the additive manufactured structure. A low interpass temperature and thin substrate was able to effectively reduce the tensile residual stress. The thick substrate resulted in a small angular deformation of the substrate during the additive manufacturing process.

Source/Drain Activation for Flexible Poly-Si Nanoscale pFETs with a Laser-Buffer Layer by CO2 laser Annealing

A laser-buffer layer of SiO2/W/SiO2 with a high reflectivity at 10.6 μm enables CO2 laser treatment for the source/drain dopant activation of poly-Si nanoscale field-effect transistor (nano-FET) (Wch/Lg = 70/70 nm) on the flexible polyimide substrate. The laser-buffer layer thermally modified by CO2 laser reduces the sheet resistance of the source/drain to 1.4 kΩ/sq. at low laser energy of 15 W and low substrate temperature of 125 °C. The flexible nano-FET (nano-fFET) exhibits a subthreshold swing (S.S) of 84 mV/dec. and a low drain-induced barrier lowering of 202 mV/V at a bending radius of 10 mm. Low degradation rate of S.S and threshold voltage (Vth) for single- and multi-channel nano-fFETs arises from oxide-trap predomination after long time hot-carrier stress as demonstrated by a ΔVth power-factor of ∼0.2.

HiPIMS obtained carbon nano-coatings on copper foil and their thermal conductivity

To prevent overheating of high-power electronic devices, effective cooling and thermal management is a key issue. Owing to the extraordinarily high thermal conductivity of graphene structure in nature, an approach for growth of carbon nano-coating with multiplex layer architecture on copper foil by using high power impulse magnetron sputtering (HiPIMS), as an alternative to the conventional chemical vapor deposition process, is reported for heat-spreading purposes. For successful deposition, a high peak current of 600 A with a short pulse of 30 μs at a relatively low substrate temperature of 600 °C was applied. Moreover, growth mechanisms without and with applying copper for Cu/carbon (Cu/C) nano-coating periodic deposition are revealed and discussed. Based on the measurement results using Angstrom's method, under optimum deposition time, the HiPIMS prepared carbon nano-coating with multiplex layer architecture, which contains in-plane-oriented multilayer graphene structure and the following out-of-plane-oriented turbostratic graphene structure, can enhance the heat spreading ability of the copper foil, reaching a thermal diffusivity value of 1.05 cm2/s. For Cu/C nano-coating periodic deposition, copper can act as catalyzing ingredient to inhibit amorphous carbon formation and promote the crystalline graphene-like structure growth, resulting in a further increase in the thermal diffusivity up to 1.21 cm2/s, twice that of the bare copper foil.

Laser-Assisted Growth of Carbon-Based Materials by Chemical Vapor Deposition

Carbon-based materials (CBMs) such as graphene, carbon nanotubes (CNT), highly ordered pyrolytic graphite (HOPG), and pyrolytic carbon (PyC) have received a great deal of attention in recent years due to their unique electronic, optical, thermal, and mechanical properties. CBMs have been grown using a variety of processes, including mechanical exfoliation, pulsed laser deposition (PLD), and chemical vapor deposition (CVD). Mechanical exfoliation creates materials that are irregularly formed and tiny in size. On the other hand, the practicality of the PLD approach for large-area high-quality CMB deposition is quite difficult. Thus, CVD is considered as the most effective method for growing CBMs. In this paper, a novel pulsed laser-assisted chemical vapor deposition (LCVD) technique was explored to determine ways to reduce the energy requirements to produce high quality CBMs. Different growth parameters, such as gas flow rate, temperature, laser energy, and deposition time were considered and studied thoroughly to analyze the growth pattern. CBMs are grown on Si and Cu substrates, where we find better quality CBM films on Cu as it aids the surface solubility of carbon. Raman spectroscopy confirms the presence of high-quality PyC which is grown at a temperature of 750 °C, CH4 gas flow rate of 20 sccm, a laser frequency of 10 Hz, and an energy density of 0.116 J/cm2 per pulse. It is found that the local pulsed-laser bombardment helps in breaking the carbon-hydrogen bonds of CH4 at a much lower substrate temperature than its thermal decomposition temperature. There is no significant change in the 2D peak intensity in the Raman spectrum with the further increase in temperature which is the indicator of the number of the graphene layer. The intertwined graphene flakes of the PyC are observed due to the surface roughness, which is responsible for the quenching in the Raman 2D signal. These results will provide the platform to fabricate a large area single layer of graphene, including the other 2D materials, on different substrates using the LCVD technique.

Fabrication of Cu&lt;sub&gt;2&lt;/sub&gt;ZnSnS&lt;sub&gt;4&lt;/sub&gt; (CZTS) thin films by ultrasonic spray pyrolysis at a low substrate temperature and effect of tin concentration on the characteristics of the CZTS thin films

Cu2ZnSnS4 (CZTS) thin films are fabricated on glass substrates using the spray pyrolysis method with different concentrations of Sn content were studied in this research work. All the CZTS thin films are fabricated at substrate temperature 200°C to minimize the formation of secondary phases. Here, we show how the variation in Sn content concentration influences the optical and structural properties of the CZTS thin films. The XRD patterns reveal that the concentration of Sn content has to be optimized to minimize the formation of secondary phases for a fixed substrate temperature. In turn, the band gap of the CZTS films is highly influenced by the formation of secondary phases. We have found that the films prepared from the precursor solution with 1.8 mM concentration of Sn content have the best crystal structure and an optical band gap of 1.55 eV. The CZTS thin films also have good carrier concentrations ranging from 4.2×1019 to 22.9×1020 cm-3. Bangladesh J. Sci. Ind. Res. 57(1), 1-6, 2022

Surface Conductivity and Preferred Orientation of TiN Film for Ti Bipolar Plate

The properties of thin films are often influenced by the crystal’s preferred orientation. In the present study, we report the strong dependence of surface conductivity on the preferred orientation of TiN film that acts as the coating material for Ti bipolar plate. The preferred orientation of TiN film is successfully controlled along the (111) or (200) planes by adjusting the N2 flow rate or Ti substrate temperature during the deposition process via DC (direct current) reactive magnetron sputtering. Small N2 flow rate of 3 to 6 sccm or low substrate temperature (e.g., 25 °C) facilitates the growth of TiN films along the (111). The (111) preferred orientated TiN films show much lower interfacial contact resistance (ICR) than the (200) preferred orientated films. A considerably low ICR value of 1.9 mΩ·cm2 at 140 N/cm2 is achieved at the N2 flow of 4 sccm and the substrate temperature of 25 °C.

Crystalline quality of GaAs1−x Bi x grown below 250 °C using molecular beam epitaxy

This study revealed the crystalline quality of the dilute bismide alloy GaAs1−x Bi x grown on a GaAs(001) substrate below 250 °C using molecular beam epitaxy. The substrate temperature and As flux played a dominant role in tuning the crystal structure between amorphous and single crystalline GaAs1−x Bi x , as well as in the Bi introduction in GaAs below 250 °C. Sample characterization demonstrated a substrate temperature of 250 °C produced single crystalline ∼200 nm thick GaAs0.982Bi0.018 with clear X-ray diffraction fringes, while the lower substrate temperature of 180 °C yielded an amorphous film. Rutherford backscattering spectrometry showed sufficient As supply at the growing surface provides uniform Bi distribution.

Ultrathin Ge epilayers on Si produced by low-temperature PECVD acting as virtual substrates for III-V / c-Si tandem solar cells

Ultrathin (20 nm) epitaxial films of germanium are deposited on crystalline silicon wafers, to act as virtual substrates for the growth of III-V materials, opening a low-cost approach to tandem solar cells. Such ultrathin layers allow for material cost reduction, along with the possibility of using the silicon wafer as the bottom cell in tandem devices. A simple plasma-enhanced chemical vapor deposition (PECVD) process at 175 °C has been optimized to deposit these heteroepitaxial germanium films, which grow directly on the silicon wafers without any intermediate silicon-germanium alloy. Thanks to an in-situ plasma cleaning step prior to Ge epitaxy, the films can sustain high-temperature annealing in vacuum (up to 800 °C) without any delamination. The suitability of the germanium heteroepitaxial films as virtual substrates is analyzed by depositing III-V layers on them by conventional growth methods like chemical beam epitaxy (CBE) and metalorganic chemical vapor deposition (MOCVD). The properties of the GaAs films deposited on the virtual substrates are comparable in terms of roughness, microstructure, and crystallinity to these of the III-V layers co-deposited on c-Ge wafers, pointing at the effectiveness of the ultrathin c-Ge epitaxial layers to act as virtual substrates for III-V epitaxial growth. Moreover, growing the c-Ge layers on c-Si substrates with 5° miscut avoids the formation of antiphase domains. These substrates are finally used to demonstrate proof of concept tandem solar cells, proving the suitability of our low temperature and ultrathin virtual substrate approach.

Evidence of sp2-like Hybridization of Silicon Valence Orbitals in Thin and Thick Si Grown on α-Phase Si(111)√3 × √3R30°-Bi.

One-monolayer (ML) (thin) and 5-ML (thick) Si films were grown on the α-phase Si(111)√3 × √3R30°-Bi at a low substrate temperature of 200 °C. Si films have been studied in situ by reflection electron energy loss spectroscopy (REELS) and Auger electron spectroscopy, as a function of the electron beam incidence angle α and low-energy electron diffraction (LEED), as well as ex situ by grazing incidence X-ray diffraction (GIXRD). Scanning tunneling microscopy (STM), and scanning tunneling spectroscopy (STS) were also reported. The REELS spectra, taken at the Si K absorption edge (~1.840 KeV), reveal the presence of two distinct loss structures attributed to transitions 1s→π* and 1s→σ* according to their intensity dependence on α, attesting to the sp2-like hybridization of the silicon valence orbitals in both thin and thick Si films. The synthesis of a silicon allotrope on the α-phase of Si(111)√3 × √3R30°-Bi substrate was demonstrated by LEED patterns and GIXRD that discloses the presence of a Si stack of 3.099 (3) Å and a √3 × √3 unit cell of 6.474 Å, typically seen for multilayer silicene. STM and STS measurements corroborated the findings. These measurements provided a platform for the new √3 × √3R30° Si allotrope on a Si(111)√3 × √3 R30°-Bi template, paving the way for realizing topological insulator heterostructures from different two-dimensional materials, Bi and Si.

MEMS Piezoresistive Pressure Sensor Based on Flexible PET Thin-Film for Applications in Gaseous-Environments

This experimental study presents the operation of pressure sensors made from low-temperature flexible substrates. Design, simulation, fabrication, and characterization are carried out with a number of fabricated flexible pressure devices. Simulations are used to optimize the sensor parameters such as the geometrical shape, electrical potential output, sensitivity and working-range of the sensor, thus predicting the sensing behavior before fabrication. The behaviour of the devices are simulated by using COMSOL Multiphysics. The pressure structure consists of a substrate of polyethylene terephthalate (PET) thin-film used as a diaphragm. A thin layer of indium tin oxide (ITO) on the PET substrate is obtained and used as a first conductive metallic track. Subsequently, nichrome (NiCr 80/20 wt%) alloy material was deposited by electron beaming to generate four piezoresistors with thickness of 50 nm that can be used to detect resistance change using a Wheatstone bridge when the sensor is exposed to different working pressures. Aluminum metallic tracks of 200 nm in thickness are deposited by sputtering in order to connect the four piezoresistors. A working range of pressure is applied from 0 kPa to 130 kPa. Resistivity and sensitivity measured values were <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.37 \times 10^{-3}\, {\Omega }$ </tex-math></inline-formula> -cm and 6.365 mV/kPa respectively. All simulations and experimental results showed that the sensor characteristics are favorable for applications where the pressure is below 130 kPa.

Pulsed Laser Ablation: A Facile and Low-Temperature Fabrication of Highly Oriented n-Type Zinc Oxide Thin Films

Eco-friendly and facile zinc oxide (ZnO) synthesis of zinc-oxide-based nanomaterials with specific properties is a great challenge due to its excellent industrial applications in the field of semiconductors and solar cells. In this paper, we report the production of zinc oxide thin films at relatively low deposition temperature employing a simple and non-toxic method at low substrate temperature: pulsed laser ablation, as a first step for developing a n-ZnO/p-Si heterojunction. Single-phase n-type zinc oxide thin films are confirmed by an X-ray diffraction (XRD) pattern revealed by the maximum diffraction intensity from the (002) plane. Absorbance measurements indicate an increase in the band gap energy close to the bulk ZnO. A 350 °C substrate temperature led to obtaining a highly porous film with high crystallinity and high bandgap, showing good premises for further applications.

Terraced and 3D Pyramid-Shaped Polymer Single Crystal via Low Temperature-Assisted Microfluidic Technology.

3D pyramidal polymer single crystals provide spatial gradient variations within the crystal molecules, and these variations facilitate the study of the relationship between structure and properties within the molecules of various complexes with anisotropic structures. As described herein, a low-temperature-assisted microfluidic pore channeling approach is proposed to prepare structurally ordered polymer single crystals. A mixture of dichloromethane and dimethyl sulfoxide is used as a prepolymer, and a liquid microfluidic technique is employed to grow the end-functionalized polymers into 3D polymer single crystals. Through the ordered growth of single crystals, a personalized pyramidal pattern with a homogeneous structure is formed. To evaluate the mesh node density, low-temperature growth time and substrate type are also investigated. Rectangular, pyramidal, and dendritic patterns are synthesized via low-temperature single crystal growth. This work shows that low temperature-assisted microfluidics provides a novel means to tune the 3D structure of polymer single crystals.

Growth of nanoporous high-entropy oxide thin films by pulsed laser deposition

High-entropy oxides (HEO) with entropic stabilization and compositional flexibility have great potential application in batteries and catalysis. In this work, HEO thin films were synthesized by pulsed laser deposition (PLD) from a rock-salt (Co0.2Ni0.2Cu0.2Mg0.2Zn0.2)O ceramic target. The films exhibited the target’s crystal structure, were chemically homogeneous, and possessed a three-dimensional (3D) island morphology with connected randomly shaped nanopores. The effects of varying PLD laser fluence on crystal structure and morphology were explored systematically. Increasing fluence facilitates film crystallization at low substrate temperature (300 °C) and increases film thickness (60–140 nm). The lateral size of columnar grains, islands (19 nm to 35 nm in average size), and nanopores (9.3 nm to 20 nm in average size) increased with increasing fluence (3.4 to 7.0 J/cm2), explained by increased kinetic energy of adatoms and competition between deposition and diffusion. Additionally, increasing fluence reduces the number of undesirable droplets observed on the film surface. The nanoporous HEO films can potentially serve as electrochemical reaction interfaces with tunable surface area and excellent phase stability.Graphical abstract

Structural, Morphological, Vibrational and Optical Properties of GaN Films Grown by Reactive Sputtering: The Effect of RF Power at Low Working Pressure Limit

This work reports the properties of GaN films grown onto c-Si (100) at relatively low substrate temperature (400°C) by reactive magnetron sputtering. The study depicts the effect of working pressure and RF power on the GaN film structural, vibrational and optical properties characterized by X-ray diffraction, atomic force and scanning electron microscopies, Raman spectroscopy and spectroscopic ellipsometry. Unusual low pressure deposition condition (0.40 Pa) was achieved by using a separated argon inlet directed to the Ga target surface, resulting in improved crystalline quality of the films. In this condition, the preferential crystalline orientation, the surface morphology and the optical gap of the GaN films show a strong dependence on the RF power applied to the Ga target, where low RF power (30-60 W) was responsible for increasing the c-axis orientation and the optical gap, while higher RF power (75-90 W) decreased the overall crystal quality and increased the surface roughness.