Film Deposition Research Articles

Effect of SiO2 Layer Thickness on SiO2/Si3N4 Multilayered Thin Films

Silicon nitride (Si3N4) materials are widely used in the electronics, optoelectronics, and semiconductor industries, with Si3N4 thin films exhibiting high densities, high dielectric constants, good insulation performance, and good thermal and chemical stability. However, direct deposition of Si3N4 thin films on glass can result in considerable tensile stress and cracking. In this study, magnetron sputtering was used to deposit a Si3N4 thin film on glass, and a silicon dioxide (SiO2) thin film was introduced to reduce the Si3N4 binding force and stress. The effect of the SiO2 layer thickness on the SiO2/Si3N4 multilayered thin film was explored. The results indicated that the introduction of the SiO2 layer could improve the weak adhesion characteristics of Si3N4 thin films. Moreover, sputtering the SiO2 layer to 150 nm resulted in the highest hardness and transmittance of the SiO2/Si3N4 multilayered thin films. The findings of this study lay a solid foundation for the application of Si3N4 thin films on glass.

Self-powered broadband photodetectors based on Bi2O2Se with asymmetric contact areas

Self-powered broadband photodetectors are widely used in military reconnaissance, outdoor environmental sensing, wearable medical monitoring. Current commercial broadband photodetectors based on conventional materials are structurally complex, high cost, and external power consumption. 2D materials emerge as promising candidates for the development of novel photodetectors with superior performances. The construction of self-powered photodetectors predominantly employs the heterostructures or metal–semiconductor–metal (MSM) configurations, which still suffer from either multiple steps of material growth, transferring, alignment or various photolithography, film deposition techniques. Herein, a simple and effective asymmetric contact strategy is proposed to fabricate Bi2O2Se-based self-powered broadband photodetectors with asymmetric Au contact areas. The photodetector exhibits excellent performance under 350–1150 nm illumination. The responsivity is as high as 1.38, 4.76, and 0.63 A/W under 350, 550, and 1050 nm, respectively, which are much higher than those of the previously reported self-powered photodetectors based on Bi2O2Se nanosheets. Meanwhile, the self-powered photodetector has a high external quantum efficiency of 1073.16 % at 550 nm. In addition, the photodetector has excellent stability in the air and enables both imaging and optical communication. Owing to the simple architecture, cost-effectiveness, straightforward manufacturing process, and impressive performance, the proposed self-powered photodetectors hold considerable promise for future applications.

Investigation of amorphous-SiC thin film deposition by RF magnetron sputtering for optical applications

Silicon carbide (SiC) is a rapidly emerging material for photonic applications, thanks to its exceptional optical properties. To be used as a waveguide, SiC thin films must be deposited directly on silica at low temperature. Amorphous SiC films were deposited by RF magnetron sputtering using a single source of high-purity polycrystalline SiC. A systematic study of the chemical, structural and optical properties of the films was carried out, using a combination of XRD, XPS, SIMS, spectroscopic ellipsometry, Raman spectroscopy and UV–Vis absorption spectroscopy. The aim was to link deposition conditions to film properties. By exploring a three-parameter space (RF power, substrate temperature, pressure), we have demonstrated that RF power is the main parameter which controls the entire deposition process and film properties. By simply adjusting the RF plasma power between 150 and 450 W, it is possible to adjust the refractive index at a wavelength of 1.5 μm in the range 2.50–2.75 and vary the bandgap from 2.5 to 1.7 eV. This is attributed to a slight variation in film composition, particularly in terms of Si/C ratio and C–C bond concentration.

Effects of Rapid Heat Treatments on the Properties of Cu2O Thin Films Deposited at Room Temperature Using an Ammonia-Free SILAR Technique

We report herein the analysis of the properties of copper(I) oxide thin films deposited by an optimized ammonium-free successive ion layer adsorption and reaction (SILAR) technique. The Cu2O thin film deposition process was carried out at room temperature using copper acetate monohydrate, sodium citrate as complexing agent, and hydrogen peroxide as precursors of copper and oxygen ions, respectively. The harmless and easy-to-handle sodium citrate replaces the volatile NH4OH commonly employed as complexing agent in the SILAR technique for the deposition of metal oxide thin films. The optical, structural, morphological, and electrical properties of the as-deposited Cu2O thin films were studied as a function of the number of cycles during deposition, as well as their modifications produced by the effect of rapid thermal annealing (RTA) in vacuum in a temperature range of 200–250°C for 1 min, 3 min, and 5 min. The as-deposited thin films had cubic crystalline structure corresponding to the Cu2O phase as determined by x-ray diffraction (XRD), with a direct energy bandgap of 2.43–2.51 eV depending on the number of cycles, and electrical resistivity of the order of 103 Ω cm. The XRD and x-ray photoelectron spectroscopy (XPS) analysis of the Cu2O thin films treated by RTA demonstrated an increase of the crystal size with time and temperature of the RTA and reduction effects from Cu2+ to Cu1+ oxidation states. On the other hand, the RTA treatments also decreased their energy bandgap to 2.38 eV and electrical resistivity to 102 Ω cm. The high energy bandgap values of the Cu2O thin films were attributed to quantum confinement effects produced by their small crystal size in the range of 3.6–8.6 nm.Graphical

Lead-free methyl ammonium tin iodide perovskite thin film growth in single step via plasma enhanced chemical vapour deposition technique and its optoelectronic properties

In the present work, lead free methyl ammonium tin iodide (CH3NH3SnI3 or MASnI3) perovskite thin films have been deposited via single step plasma enhanced chemical vapour deposition (PECVD) technique. In our earlier work, we reported lead based methyl ammonium lead iodide (CH3NH3PbI3 or MAPbI3) perovskite thin film deposition in 2-step, using sputtering technique for the PbI2 thin films and PECVD technique for CH3NH3I (MAI) thin films. Similarly, CH3NH3SnI3 perovskite thin films are deposited in this work using PECVD technique in single step. Lead is substituted with tin due to its toxic behaviour, environmental and health related issues. CH3NH3SnI3 perovskite is doped n-type via changing the molar ratio of SnI2 and CH3NH3I. SnI2/CH3NH3I ratio is changed from 0.33 to 2 to study the n-type doping of CH3NH3SnI3 perovskite. Deposited CH3NH3SnI3 perovskite thin films are deposited over p-type silicon wafer to make n-type doped n-CH3NH3SnI3/p-Si heterojunction photodiode.

Intrinsic doping and ageing of indium oxide thin films

Indium oxide (In2O3) is one of the most used materials for the synthesis of transparent electronics devices and currently tin-doped indium oxide (ITO) dominates the field of Transparent Conductive Oxides for most applications, from ICT to photovoltaics. In this work we present a study on the responses of indium oxide upon the formation, and stabilization, of point defects induced with different methods. After the deposition of In2O3 thin films via RF magnetron sputtering, treatments such as Ion Implantation (I.I.), Ultraviolet (UV) irradiation and Sun exposure were employed to generate oxygen vacancies as intrinsic dopants. Both I.I. and UV irradiations significantly improved the electrical conductivity of films, increasing the carrier density by up to 3 orders of magnitude. Moreover, after I.I. also the crystalline quality of the films was enhanced.To monitor the stability of oxygen vacancies upon exposure to ambient atmosphere, the ageing of samples was followed and recorded for a couple of weeks, reporting a fast and strong degradation of electrical properties. As a facile strategy to counteract the sheet resistance increase, samples were encapsulated in an ultra-thin (≈10 nm) SiO2 layer deposited via sputtering. Irradiated and encapsulated films retained a much lower sheet resistance throughout the observation time, preserving the samples conductivity.

Two-step preparation of methylammonium lead triiodide perovskite film via electrospray deposition of methylammonium iodide solution for solar cell applications

Solution-processable perovskite solar cells (PSCs) have the potential to revolutionize solar cell technology by enabling low power generation costs via low-cost device fabrication. However, most existing research regarding PSCs relies on the spin-coating method, which is not conducive to large-area film deposition. Therefore, the development of an alternative deposition method for perovskite films has become increasingly important for commercialization, for which electrospray deposition is a promising technique. This study investigates the two-step preparation of methylammonium lead triiodide (MAPbI3) perovskite films via the electrospray deposition of a methylammonium iodide (MAI) solution on a spin-coated PbI2 film. The gradual conversion of PbI2 to MAPbI3 with increasing MAI deposition time was revealed, accompanied by an increase in the size of the perovskite crystals. In addition, PSCs were successfully fabricated by electrospraying MAI, achieving a considerable power conversion efficiency of 7.86 % at the optimal MAI deposition time.

Nanoscopic catalyst-loaded porous metal oxide hollow frameworks using porous block copolymer templates for high performance formaldehyde sensors

Porous and hollow nanostructures functionalized with nanoscopic catalysts have attracted considerable interest in a wide range of applications depending on surface reactions. In this study, we present an efficient and versatile synthetic strategy of porous metal oxide hollow frameworks (HFs) decorated with noble metal nanoparticles (NPs). The key lies in the use of porous and bicontinuous polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) microparticles as templates, which feature pores on the order of several hundred nanometers in size. Homogeneous Pt loading on the surface of the porous microparticles is achieved through the preferential adsorption of Pt precursors onto the P4VP block via electrostatic interactions. Subsequent SnO2 thin film deposition and calcination ultimately yield honeycomb-like SnO2 HFs with macropores and uniform distribution of Pt NPs. The Pt NP-loaded SnO2 HFs exhibit exceptional formaldehyde (HCHO) sensing capabilities, characterized by remarkable sensitivity (31.4 at 5 ppm), rapid response time (4.7 s at 5 ppm), ultra-low detection limit of 10 ppb, and remarkable cross-selectivity. These outstanding features result from their high surface area, gas permeability within porous hollow structures, and well-dispersed Pt NPs, which catalytically activate the sensor. Our study provides great promise for advancing surface catalytic reactions due to their exceptional surface area and gas permeability, paving the way for future applications.

High‐Performance Self‐Powered Deep Ultraviolet Photodetector Based on NiO/β‐Ga2O3 Heterojunction with High Responsivity and Selectivity

A high‐performance self‐powered deep ultraviolet (DUV) photodetector based on the NiO/β‐Ga2O3 heterojunction is fabricated and analyzed. The NiO/β‐Ga2O3 heterojunction photodetectors are fabricated both with and without a post‐annealing process following NiO film deposition. Each photodetector structure is investigated through technology computer‐aided design simulations, including energy band diagram, trap density, and carrier concentration. The pristine self‐powered NiO/β‐Ga2O3 photodetector, lacking a post‐annealing process, exhibits partial Schottky contact formation between metal and NiO film, leading to performance degradation, including reduced responsivity, detectivity, and response time. On the other hand, the post‐annealed self‐powered NiO/β‐Ga2O3 photodetector demonstrates high performance such as a responsivity of 592.0 mA W−1, a detectivity of 4.30 × 1012 Jones, and response times of 30.93 ms and 72.32 ms, respectively. Therefore, the fabricated NiO/β‐Ga2O3 photodetector shows a promising potential for various applications requiring DUV detection without an external voltage bias.

Diagnostics of phase composition of lithium niobate films on sapphire by principal component analysis using Raman spectra

Thin films of lithium niobate were deposited by RF diode sputtering of a LiNbO3 single-crystal target on a heated sapphire substrate (R-cut, 650 °C). Radial distributions of the phase composition of the films along the substrate were obtained by principal component analysis (PCA) using Raman spectra. It was found that at small target-substrate distances (12 mm is the distance between the target and the substrate, 76 mm is the diameters of the target and the substrate holder, 30 mm is the size of the film deposition area in axial geometry), the effects of resputtering of the deposited film do not lead to a considerable decrease in the lithium content: no phases other than LiNbO3 are formed in the extended central part of the film, the edge of the film contains no more than 2 % of the undesirable LiNb3O8 phase, and the difference in the measured values of deviation of LiNbO3 phase composition from stoichiometry in the film compared to the target is 0.7 mol% Li2O. These results indicate that the technology for depositing of lithium niobate films can be improved since there is no need to produce a target additionally enriched with Li2O.

Targeting Manganese Amidinate and ß-Ketoiminate Complexes as Precursors for Mn-Based Thin Film Deposition.

With a focus on Mn based organometallic compounds with suitable physico-chemical properties to serve as precursors for chemical vapor deposition (CVD) and atomic layer deposition (ALD) of Mn-containing materials, systematic synthetic approaches with ligand variation, detailed characterization, and theoretical input from density functional theory (DFT) studies are presented. A series of new homoleptic all-nitrogen and mixed oxygen/nitrogen-coordinated Mn(II) complexes bearing the acetamidinate, formamidinate, guanidinate and ß-ketoiminate ligands have been successfully synthesized for the first time. The specific choice of these ligand classes with changes in structure and coordination sphere and side chain variations result in significant structural differences whereby mononuclear and dinuclear complexes are formed. This was supported by density functional theory (DFT) studies. The compounds were thoroughly characterized by single crystal X-ray diffraction, magnetic measurements, mass spectrometry and elemental analysis. To evaluate their suitability as precursors for deposition of Mn-based materials, the thermal properties were investigated in detail. Mn(II) complexes possessing the most promising thermal properties, namely Bis(N,N'-ditertbutylformamidinato)manganese(II) (IV) and Bis(4-(isopropylamino)pent-3-en-2-onato)manganese(II) (ßIII) were used in reactivity studies with DFT to explore their interaction with oxidizing co-reactants such as oxygen and water which will guide future CVD and ALD process development.

Vacuum‐ultraviolet‐photoionization chamber for the investigation of ion‐based surface treatment and thin film deposition at atmospheric pressure

AbstractThe vacuum‐ultraviolet‐photoionization chamber was constructed to allow controlled ion generation and well‐defined surface treatment with these ions at atmospheric pressure. It utilizes atmospheric helium plasma as a photon source and separates the ion generation from the plasma by an aerodynamic window. The ions are guided to the grounded substrate by a weak electric field, while the diffusive transport of neutrals is reduced by a helium gas flow along the substrate. Ionic species and the absolute ion flux were determined in the substrate region. Ion‐based thin film deposition using a precursor was investigated as a model process. The proposed system enables future investigation of e.g. the isolated interaction of ions with biological substrates.

Recent Progress in Heat and Mass Transfer Modeling for Chemical Vapor Deposition Processes

Chemical vapor deposition (CVD) is a vital process for deposit of thin films of various materials with precise control over the thickness, composition, and properties. Understanding the mechanisms of heat and mass transfer during CVD is essential for optimizing process parameters and ensuring high-quality film deposition. This review provides an overview of recent advancements in heat and mass transfer modeling for chemical vapor deposition processes. It explores innovative modeling techniques, recent research findings, emerging applications, and challenges in the field. Additionally, it discusses future directions and potential areas for further advancement in CVD modeling.

Deposition of hydrogenated amorphous carbon films by CH4/Ar capacitively coupled plasma using tailored voltage waveform discharges

We investigated the effects of tailored voltage waveform (TVW) discharges on the deposition of hydrogenated amorphous carbon (a-C:H) films in CH4/Ar capacitively coupled plasma. TVW discharges employ two driving radio frequencies (13.56 MHz and 27.12 MHz) and control their phase shifts to independently regulate ion bombardment energy (IBE) and ion flux. In this study, a-C:H films were deposited by changing DC-self bias with phase shift and constant applied voltage peak-to-peak. Additionally, we investigated phase-resolved optical emission spectroscopy (PROES) for plasma characterization. As a result, plasma-enhanced CVD (PECVD) for a-C:H films using TVW discharges realize control of film properties such as mass density, sp3 fraction, and H content, while keeping the deposition rate constant. Thus, it is suggested that TVW discharges realize the independent control of IBE and ion flux with high accuracy, highlighting its utility in a-C:H film depositions.

From nano to giant grains: Optimizing Pt thermistors for microbolometers

Pt is a suitable thermistor for use in microbolometers due to its high melting point, chemical inertness, and low 1/f noise. This work explores mechanisms of grain growth to fabricate Pt thin film thermistors for maximizing the temperature coefficient of resistance (TCR). The interplay between the microstructure and TCR is examined by varying Pt film deposition parameters, AlOX interlayer deposition technique, patterning technique, and annealing parameters. A smooth thin film morphology having giant grains of several hundreds of micrometers is achieved by abnormal grain growth, which is not attainable through normal grain growth. The fabrication of thermistor meanders is demonstrated through a combination of processes including Pt film deposition in O2/Ar environment, annealing at 1000 °C in Ar, and ion beam etching. Pt thermistors with a TCR (0 °C – 100 °C) of 0.371 ± 0.001 %/ °C are compatible with microbolometers utilizing carbon nanotube absorbers.

Pulsed laser deposition and structural analysis of Ba2Ti6O13 epitaxial thin film on the (210) surface of SrTiO3 single crystal

A single crystalline thin film of Ba2Ti6O13 was grown on the (210) surface of a SrTiO3 single-crystal substrate by pulsed laser deposition. Scanning transmission electron microscopy shows that the Ba2Ti6O13 thin film grew epitaxially with the a-plane, and the b-/c-axes of Ba2Ti6O13 parallel to the (210) plane and the [00 1¯ ]/[ 1¯ 20] directions of SrTiO3, respectively. The electrical conductance of the Ba2Ti6O13 film was approximately one order larger than that of the reduced SrTiO3−δ single crystal with oxygen deficiency of roughly δ = 0.05. Electronic structure calculations predict that Ba2Ti6O13 is an n-type degenerate semiconductor with spin-split states primarily of Ti 3d orbital.

The effect of gadolinium-doped ceria interlayer on the oxygen reduction reaction in a LSCF cathode-ScSZ electrolyte supported IT-SOFCs

Solid oxide fuel cells (SOFCs) are rapidly emerging as a technology, offering the potential for carbon neutral or carbon negative generation of electricity and heat (combined heat and power) using synthetic carbohydrate fuels and hydrogen. A significant challenge associated with SOFCs is the high polarization resistance experienced at the cathode during the oxygen reduction reaction (ORR), which diminishes the cell efficiency. The kinetics of the ORR are influenced by factors such as the cathode material type, its microstructure, and the quality of the interface between the cathode and electrolyte. In our research, we have addressed this issue by modifying the interface between the state-of-the-art cathode material, Lanthanum Strontium Cobalt Ferrite—La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF), and the Scandia stabilized Zirconia (ScSZ) electrolyte. This modification involved the deposition of a micron-sized film of ion-conducting gadolinium-doped ceria (Gd0.1Ce0.9O2-δ) – (GDC) as an interface layer. Our analysis involved systematic studies, including variations in cell operating temperatures and applied potentials, as well as measurements of cell performance over an extended period. We observed a significant enhancement in cell performance with the introduction of the GDC interfacial layer between the LSCF cathode and ScSZ electrolyte. Specifically, we recorded a cathode polarization resistance as low as 0.40 Ωcm2 for the modified interface, which is substantially lower compared to bare LSCF cathodes (3.04 Ωcm2) at 600 °C. This reduction in cathode resistance can primarily be attributed to the improved conditions for the oxygen reduction reaction (ORR), resulting from enhanced interfacial contact between the electrode and the electrolyte and mitigation of any zirconium interdiffusion as seen from detailed scanning electron microscopic studies.

Heteroepitaxial growth of Ga2O3 thin films on Al2O3(0001) by ion beam sputter deposition

Deposition of epitaxial oxide semiconductor films using physical vapor deposition methods requires a detailed understanding of the role of energetic particles to control and optimize the film properties. In the present study, Ga2O3 thin films are heteroepitaxially grown on Al2O3(0001) substrates using oxygen ion beam sputter deposition. The influence of the following relevant process parameters on the properties of the thin films is investigated: substrate temperature, oxygen background pressure, energy of primary ions, ion beam current, and sputtering geometry. The kinetic energy distributions of ions in the film-forming flux are measured using an energy-selective mass spectrometer, and the resulting films are characterized regarding crystalline structure, microstructure, surface roughness, mass density, and growth rate. The energetic impact of film-forming particles on the thin film structure is analyzed, and a noticeable decrease in crystalline quality is observed above the average energy of film-forming Ga+ ions around 40 eV for the films grown at a substrate temperature of 725 °C.

Advancing Hydrogen Sensing for Sustainable Aviation: A Metal Hydride Coated TFBG Optical Fibre Hydrogen Sensor

The aviation industry is undergoing a significant shift toward sustainability, with hydrogen emerging as a promising green fuel to reduce carbon emissions due to its high gravimetric energy density and clean combustion exhaust compared to traditional aviation fuels. However, realizing hydrogen's aviation potential requires advanced sensors to ensure safety and efficiency in challenging environments, particularly for monitoring hydrogen near high-temperature engines and cryogenic storage tanks. Fibre optic sensors offer an exceptional advantage in these demanding conditions due to their capacity to operate in harsh environments, their small size, immunity to electromagnetic interference, spark-free operation, and remote sensing capabilities. Metal hydrides are prominent sensing materials studied for hydrogen sensing, especially palladium (Pd). Nonetheless, existing literature pertaining to Pd-coated fiber optic sensors for hydrogen detection has brought to light concerns regarding response hysteresis, stability, and linearity of Pd hydrogen sensors, calling for innovative solutions. In response to these challenges, our research introduces an innovative fibre optic hydrogen sensor, introducing tantalum (Ta) based metal hydrides as the sensing material. The sensor's construction involved the deposition of a nanometer-thick Ta thin film onto the surface of a tilted fibre Bragg grating (TFBG) using a magnetron sputtering technique. The sensing mechanism relies on the modulation of optical constants of the Ta thin film in response to even minute hydrogen concentrations, culminating in spectral changes in the transmission spectrum of the TFBG. In this proof of concept work, changes in both amplitude and the centre wavelength of cladding resonances of the TFBG transmission spectrum were observed in the hydrogen concentration range from 0.01% to 4% at room temperature. These initial findings underscore the substantial potential of our approach in developing highly sensitive and robust fibre-optic hydrogen sensors tailored specifically for hydrogen-powered aviation.

Characterization of polyamide thin films by atomic force microscopy

This study directly compares the mechanical behavior of novel molecular layer deposition (MLD) and analogous interfacial polymerization (IP) polyamide thin films in environments relevant to reverse osmosis (RO) membrane operation. The elastic modulus of the films was determined using atomic force microscopy (AFM) in dry, hydrated, and chlorinated states. Surface roughness characteristics were also obtained given their potential influence on AFM modulus measurements. The much smoother MLD films demonstrated a statistically higher modulus in all states as compared to their IP counterparts. The MLD films maintained a modulus ∼3X and ∼5X greater than that of IP films after hydration and chlorination, respectively. Such differences in behavior may be due to the higher density and correspondingly lower void content of the MLD films. Results from this study provide a rationale for future development of MLD for fabrication of polyamide films for incorporation in RO membranes.