Metal Oxide Films Research Articles

Enhanced high-energy proton radiation hardness of ZnO thin-film transistors with a passivation layer

Metal-oxide thin-film semiconductors have been highlighted as next-generation space semiconductors owing to their excellent radiation hardness based on their dimensional advantages of very low thickness and insensitivity to crystal structure. However, thin-film transistors (TFTs) do not exhibit intrinsic radiation hardness owing to the chemical reactions at the interface exposed to ambient air. In this study, significantly enhanced radiation hardness of Al2O3-passivated ZnO TFTs against high-energy protons with energies of up to 100 MeV is obtained owing to the passivation layer blocking interactions with external reactants, thereby maintaining the chemical stability of the thin-film semiconductor. These results highlight the potential of passivated metal-oxide thin films for developing reliable radiation-hardened semiconductor devices that can be used in harsh space environments. In addition, the relationship between low-frequency noise and defects due to oxygen vacancies was revealed, which can be utilized to improve device reliability.

Atomic Layer Deposition + Parylene Conformal Nanocoatings for Robust Corrosion Protection of Electronics

The use of flexible and miniaturized electronic devices is continuously growing with the advancement of interconnect, microvia and microBGA technologies. While these advancements have offered many benefits to high speed and complex electronics applications, they also have some design and reliability challenges, including corrosion protection. The drive for ultra-thin conformal coatings that can provide long-term robust and reliable protection for electronics and their components in harsh environments is continuing. While advancement of conformal coatings, including plasma polymerized coatings, nano liquid coatings and ultra-thin vapor phase coatings, have been able to meet the requirements up to a certain extent, the need to have an ultra-thin, lightweight conformal coating option that can provide the moisture barrier and corrosion resistance to a hermetic level is still unmet. The Atomic Layer Deposition (or ALD) technique, which was introduced in late 1990’s, has been advancing in many applications as it deposits ultra-thin films (a few nanometers) of metal and metal oxides with a precise thickness and conformality. However, its use in general electronics has been limited due to its high temperature processing conditions. This paper introduces an advanced ALD conformal coating - both alone and in combination with Parylenes - that is applied at room temperature, making it suitable for printed circuit boards and other components to provide robust and reliable protection from corrosion and other harsh environments. To understand the effectiveness of this coating on electronics against corrosion resistance, the mixed flow gas (MFG) testing was performed using Chlorine (Cl2), Hydrogen sulfide (H2S), Nitrogen dioxide (NO2) and Sulfur dioxide (SO2) for the period of 21 days. A long-term evaluation results demonstrates a robust and reliable protection against severe corrosive environments. In addition to these beneficial properties, experiments demonstrate excellent corrosion resistance, adhesion to the substrate, electrical insulation and a significant (sixty-three times) improvement on Parylene C’s water vapor transmission rate when combined with ALD.

Isoelectric Point of Metal Oxide Films Formed by Anodization.

The surface charge of metal oxides is an important property that significantly contributes to a wide range of phenomena, including adsorption, catalysis, and material science. The surface charge can be predicted by determining the isoelectric point (IEP) of a material and the pH of a solution. Although there have been several studies of the IEP of metal oxide (nano)particles, only a few have reported the IEP of metal oxide films. The IEP of various compact metal oxide films such as TiO2, Nb2O5, WO3, ZrO2, NiO, and Al2O3 formed via electrochemical anodization was determined using the streaming potential technique. Nanostructured TiO2 and NiO were additionally produced using a single-step anodization technique, and their IEP was compared with the compact ones. The surface morphology and wettability of the oxides were studied by scanning electron microscopy and contact angle measurements, respectively. X-ray powder diffraction and X-ray photoelectron spectroscopy measurements were carried out to assess the phase and elemental composition, respectively. The IEP of compact anodic oxides deviates from that of their nanoparticle and atomic layer-deposited counterparts. The comparative results indicate that the IEP of metal oxides is influenced by factors such as the chemical composition, degree of hydroxylation, and crystallographic phases of the oxide.

Graphene-Based, Flexible, Wearable Piezoresistive Sensors with High Sensitivity for Tiny Pressure Detection.

Flexible, wearable, piezoresistive sensors have significant potential for applications in wearable electronics and electronic skin fields due to their simple structure and durability. Highly sensitive, flexible, piezoresistive sensors with the ability to monitor laryngeal articulatory vibration supply a new, more comfortable and versatile way to aid communication for people with speech disorders. Here, we present a piezoresistive sensor with a novel microstructure that combines insulating and conductive properties. The microstructure has insulating polystyrene (PS) microspheres sandwiched between a graphene oxide (GO) film and a metallic nanocopper-graphene oxide (n-Cu/GO) film. The piezoresistive performance of the sensor can be modulated by controlling the size of the PS microspheres and doping degree of the copper nanoparticles. The sensor demonstrates a high sensitivity of 232.5 kPa-1 in a low-pressure range of 0 to 0.2 kPa, with a fast response of 45 ms and a recovery time of 36 ms, while also exhibiting excellent stability. The piezoresistive performance converts subtle laryngeal articulatory vibration into a stable, regular electrical signal; in addition, there is excellent real-time monitoring capability of human joint movements. This work provides a new idea for the development of wearable electronic devices, healthcare, and other fields.

A Review of Semiconductor Metal Oxides for Hydrogen Sulfide and Methane Gas Detection

This review contains comprehensive study of semiconductor metal oxide films gas sensors. SMO are smaller in size, simple fabrication technique, sensitivity and selectivity is good. Review study paper offers understanding about the dopants impurity made the deviations in the SMO materials used to fabrication of gas sensor. Reviews study shows SnO₂-WO₃, ZnO, Au composites good for H2S and methane (CH4) gases it has sensitivity in the range 75 % to 90% at operating temperature between 200 0C to 350 0C. Composites of ZnO-Au, SnO₂, TiO₂ shows decent sensitivity in the range between 72 % to 95% at operating temperature between 200 0C to 350 0C towards H2S and methane (CH4) gases. Pure and composite of different SMO films prepared using Sol-Gel, Sputtering, CVD and Screen printing method result shows Screen printing technique is most preferred and it shows increase in sensitivity at lower operating temperature. This review provides summary of the advance and performance of pure and composites of ZnO and SnO2 based films sensors for H₂S and CH₄ detection, focusing on key parameters such as response time, operating temperature, sensitivity and fabrication technologies. It provides detail analysis of the pure and composite of SnO2 &ZnO towards H₂S and CH₄ and shows future perspective towards increase in sensitivity, lower operating temperature, response time and stability of gas sensor.

Laser writing of metal-oxide doped graphene films for tunable sensor applications.

Flexible and wearable devices play a pivotal role in the realm of smart portable electronics due to their diverse applications in healthcare monitoring, soft robotics, human-machine interfaces, and artificial intelligence. Nonetheless, the extensive integration of intelligent wearable sensors into mass production faces challenges within a resource-limited environment, necessitating low-cost manufacturing, high reliability, stability, and multi-functionality. In this study, a cost-effective fiber laser direct writing method (fLDW) was illustrated to create highly responsive and robust flexible sensors. These sensors integrate laser-induced graphene (LiG) with mixed metal oxides on a flexible polyimide film. fLDW simplifies the synthesis of graphene, functionalization of carbon structures into graphene oxides and reduced graphene oxides, and deposition of metal-oxide nanoparticles within a single experimental laser writing setup. The preparation and surface modification of dense oxygenated graphene networks and semiconducting metal oxide nanoparticles (CuO x , ZnO x , FeO x ) enables rapid fabrication of LiG/MO x composite sensors with the ability to detect and differentiate various stimuli, including visible light, UV light, temperature, humidity, and magnetic fluxes. Further, this in situ customizability of fLDW-produced sensors allows for tunable sensitivity, response time, recovery time, and selectivity. The normalized current gain of resistive LiG/MO x sensors can be controlled between -2.7 to 3.5, with response times ranging from 0.02 to 15 s, and recovery times from 0.04 to 6 s. Furthermore, the programmable properties showed great endurance after 200 days in air and extended bend cycles. Collectively, these LiG/MO x sensors stand as a testament to the effectiveness of fLDW in economically mass-producing flexible and wearable electronic devices to meet the explicit demands of the Internet of Things.

Characterizing the stability of ultra-thin metal oxide catalyst films in non-thermal plasma CO2 reduction reactions.

The use of metal oxide catalysts to enhance plasma CO2 reduction has seen significant recent development towards processes to reduce greenhouse gas emissions and produce renewable chemical feedstocks. While plasma reactors are effective at producing the intended chemical transformations, the conditions can result in catalyst degradation. Atomic layer deposition (ALD) can be used to synthesize complex, hierarchically structured metal oxide plasma catalysts that, while active for plasma CO2 reduction, are potentially vulnerable to degradation due to their high surface area and nanoscopic thickness. In this work, we characterized the effects of extended non-thermal, glow discharge plasma exposure on ALD synthesized, ultra-thin film (<30 nm) TiO2 and ZnO catalysts. We used X-ray diffraction, reflectivity, and spectroscopy to compare films exposed to a CO2 plasma to ones exposed to an Ar plasma and to ones annealed in air. We found that the CO2 plasma exposure generated some surface reduction in TiO2 and increased surface roughening by a small amount, but did not initiate any phase changes or crystallite growth. The results suggest that ALD-deposited metal oxide films are robust to low pressure CO2 plasma exposure and are suitable as catalysts or catalyst supports in extended reactions.

Non-uniform Al2O3 back reflector for performance enhancement of thin rear passivated silicon solar cells

Abstract Low material usage, physical flexibility, portability, and lightweight applications are some of the major advantages that have claimed serious research attention towards ultrathin crystalline wafer-based solar cells. This work seeks to address a major challenge for such cells namely poor light absorption in thin absorbers. A novel inclined back reflector layer (BRL) of aluminium oxide for both planar and textured surfaced silicon devices with a thickness of 20 μm was investigated, combined with the passivation properties of the metal oxide film. A study of symmetric, asymmetric, and textured conformal BRL revealed an optical gain of ∼32% for the optimized BRL as compared to the structure without BRL. The combined effect of passivation and back reflection of the proposed BRL improved the power conversion efficiency by 60%. The optical and efficiency gain of 17% was observed for the structures with inclined BRL, as compared to that of a planar BRL. A remarkable omnidirectional response was also observed for textured BRL structures.

A Nitrogen-Doped CuWO4 Photoanode with Oriented Crystal Growth for Efficient Visible-Light-Driven Water Oxidation

A photoanode capable of efficiently promoting water oxidation is a key essence for realizing a photoelectrochemical (PEC) water splitting system for hydrogen production. Copper tungsten oxide, CuWO4 is a superior photoanode material with a narrower band gap (2.2- 2.4 eV) than BiVO4 (~ 2.4 eV) and WO3 (~ 2.7 eV) studied extensively as photoanodes for water oxidation. In the last decade, many efforts have been devoted to developing efficient CuWO4-based photoanodes by elements doping and surface treatments. However, there has been no report on nitrogen doping CuWO4 for improving its PEC performance. Recently, we have reported a unique preparation technique (a mixed metal-imidazole casting; MiMIC) to form rigidly adhering metal oxides films on electrode substrates by casting precursor methanol solutions (or suspensions) of the corresponding metal ions in the presence of imidazole derivatives followed by annealing.1) Imidazole derivatives were reported to act as a binder for metal oxide nanoparticles to be well-interconnected and nitrogen source for N-doping for synthesis of N-doped BiVO4.2) Herein we report effects of N-doping into a CuWO4 photoanode on its electronic property and PEC performance for efficient water oxidation CuWO4.The N-doped CuWO4 photoanode was prepared using a MiMIC method. The top view SEM images of the CuWO4 films with different fraction (Fim = 0 ~ 50%) of imidazole derivatives in precursor solutions showed that the particle size decreased from 1 to 0.1 μm with secondary particle decay. PEC properties were measured using a single-chamber cell in the three-electrode configuration under solar simulated irradiation. The photocurrent density (0.21 mA cm-2 at 1.23 V vs. RHE) for the N-doped CuWO4 photoanode with Fim of 33% is higher than that (0.04 mA cm-2) for a CuWO4 photoanode (Fim = 0%). An onset wavelength of an IPCE action spectrum for the CuWO4 photoanode (Fim = 33%) was longer than the CuWO4 photoanode (Fim = 0%) due to nitrogen doping.1) Z. N. Zahran, T. Katsuki, M. Yagi, et al., ACS Appl Energy Mater, 2022, 5, 2, 1894.2) T. Eo, T. Katsuki, Z. N. Zahran, M. Yagi, et al., ACS Appl Energy Mater, 2021, 4, 4, 2983.

Amorphous Doped Indium Tin Oxide Thin‐Films by Atomic Layer Deposition.Insights into Their Structural, Electronic and Device Reliability

AbstractThin semiconducting films of magnesium doped indium‐ and tin oxide are prepared by thermal atomic layer deposition (ALD). The metal oxide films are deposited at 200 °C from the precursors trimethylindium, tetrakis(dimethylamido)tin, bis(ethylcyclopentadienyl)magnesium and water as oxidant. These thin‐films are observed to be amorphous by electron microscopy and X‐ray diffraction. However, they exhibited a near‐range atomic order with correlation lengths of up to 10 Å, as demonstrated by high energy total scattering at grazing incidence employing synchrotron radiation. Even minor alterations in composition reveal a significant impact on the thin‐film transistor (TFT) device parameters, due to magnesium's high oxygen binding capability and its ability to inhibit the formation of oxygen vacancies, resulting in a decrease of free charge carriers in the material. Stability tests indicate a device degradation after storage in ambient conditions due to water adsorption on the surface, which could be reversed by an additional annealing step which qualify the films as robust. This studie demonstrate the possibility of employing minor amounts of high band gap oxides such as MgO to manipulate and control the electric behavior of the active channel layer performance in inorganic TFT devices.

Study of molecular layer deposition of zinc-based hybrid film as photoresist

Molecular layer deposition (MLD) of metal oxide and organic hybrid thin films has great potential to be utilized in extreme ultraviolet photoresist, thanks to its excellent uniformity on the nanometer scale thickness control. Zn has large photoelectron effect cross-section, resulting in lots of secondary electrons, which can break the organic bonds, causing changes in solubility upon the ultraviolet (UV) light exposure. In this work, Zn-based MLD thin films have been demonstrated for their potential to be used as photoresist for extreme ultraviolet (EUV) application. UV light exposure mechanisms have been proposed based on X-ray photoelectron spectroscopy (XPS) analysis.

A Free-Standing Boron-Doped Diamond Grid Electrode for Fundamental Spectroelectrochemistry.

Spectroelectrochemistry (SEC) is a powerful technique that enables a variety of redox properties to be studied, including formal potential (Eo), thermodynamic values (ΔG, ΔH, ΔS), diffusion coefficient (D), electron transfer stoichiometry (n), and others. SEC requires an electrode which light can pass through while maintaining sufficient electrical conductivity. This has been traditionally composed of metal or metal oxide films atop transparent substrates like glass, quartz, or metallic mesh. Robust electrode materials like boron-doped diamond (BDD) could help expand the environments in which SEC can be performed, but most designs are limited to thin films (∼100-200 nm) on transparent substrates less resilient than free-standing BDD. This work presents a free-standing BDD grid electrode (G-BDD) for fundamental SEC measurements, using the well-characterized Fe(CN)63-/4- redox couple as proof-of-concept. With a combination of cyclic voltammetry (CV), thin-layer SEC, and chronoabsorptometry, several of the redox properties mentioned above were calculated and compared. For Eo', n, and D, similar results were obtained when comparing the CV [Eo' = +0.279 (±0.002) V vs Ag/AgCl; n = 0.97; D = 4.1 × 10-6 cm2·s-1] and SEC [Eo' = +0.278 (±0.001) V vs Ag/AgCl; n = 0.91; D = 5.2 × 10-6 cm2·s-1] techniques. Both values align with what has been previously reported. To calculate D from the SEC data, modification of the classical equation used in chronoabsorptometry was required to accommodate the G-BDD electrode geometry. Overall, this work expands on the applicability of SEC techniques and BDD as a versatile electrode material.

Nanostructure of TiO\(_{2}\) and WO\(_{3}\) multilayer films deposited on ITO glass for electrochromic enhanced photocatalytic activity

The photocatalytic activity (PA) by electrochromic (EC) enhancement of single and multilayer films of TiO2, WO3, TiO2/WO3, and WO3/TiO2 was investigated. All films were deposited from metal on an ITO glass substrate using direct current (DC) magnetron sputtering via an oblique angle deposition (OAD) technique at 85°. Subsequently, a thermal oxidation (TO) process at 500℃ was applied for the samples to form metal oxide films. The morphology, elemental composition, crystal structure, and optical properties were studied by using field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffractometry (XRD), and UV-vis spectroscopy, respectively. The photocatalytic properties were investigated by showing the degradation rate of methylene blue (MB) solution as an organic pollutant that was examined under ultraviolet irradiation of 300 µW∙cm‒2. The film samples were investigated by comparing the pre-color and colored states that were achieved through the EC process. The EC properties of WO3 led to increased charge insertion on the film surface. This observation was further supported by cyclic voltammetry (CV) testing, which revealed a higher current density for the thin film samples. The photodegradation results showed that the samples in the colored state exhibited a significantly higher degradation rate of MB compared to the pre-color state.

Effects of Thermal Energy on the Formation of Lattice Strain in VO2 Thin Films Grown on TiO2(001).

Film thickness is a well-known experimental parameter for controlling lattice strain in oxide films. However, due to environmental and resource conservation considerations, films need to be as thin as possible, increasing the need to find alternative factors for strain management. Herein, we present the importance of thermal energy as a factor for the formation of lattice strain in the oxide films, specifically focusing on the effects of laser fluence during pulsed laser deposition (PLD) on the in-plane lattice strain of vanadium dioxide (VO2) thin films grown on titanium dioxide (TiO2) (001). VO2 thin films were deposited using a KrF excimer laser (λ = 248 nm) at laser fluences ranging from 0.88 to 1.70 J/cm2. The film thickness ranged from 10-15 nm, below the critical thickness. Films grown at higher laser fluences exhibited smooth surfaces and completely strained in-plane lattices. In contrast, films grown at lower laser fluences displayed numerous small islands and relaxed in-plane lattice strain. The metal-insulator transition (MIT) temperature was lower for films grown at higher laser fluencies compared to those grown at lower laser fluences. It was also revealed that Ti-V interdiffusion occurs, forming a solid solution (V1-xTixO2) near the interface. These observations suggest that the thermal energy of the particles, influenced by laser fluence, is a critical factor in the formation of lattice strain in metal oxide films and also that laser fluence in PLD is an effective experimental parameter for strain management in oxide films. Our findings enhance the understanding of lattice strain formation in metal oxides and offer insights for establishing effective methods for controlling lattice strain in metal oxide films.

Modification of High-Surface-Area Carbons Using Self-Limited Atomic Layer Deposition

This study explores the application of Atomic Layer Deposition (ALD) to functionalize high-surface-area carbon supports with metal and metal oxide films and particles for applications in catalysis and electrocatalysis. The work reported here demonstrates that, through careful choice of precursors and absorption and reaction conditions, self-limited ALD growth on a high-surface-area carbon support can be achieved. Specific examples presented include the growth of conformal films of ZrO2 and SnO2 and the deposition of Ga2O3 and Pt particles on a carbon black support with a surface area of 250 m2·g−1. A novel strategy for controlling the Pt weight loading and producing sub-nanometer Pt particles on a carbon support using a single ALD cycle is also presented.

Robust Metal Oxide Adhesion Layers for Cellulose Nanofiber-Based QCM Sensors.

Here, we demonstrate the significant role of robust metal oxide adhesion layers on the cellulose nanofiber (CNF)-based quartz crystal microbalance (QCM) humidity sensor characteristics including sensitivity and stability. In this study, we deposited various metal oxide films (NiO, TiO2, ZnO, and WO3) onto QCM Au electrodes as adhesion layers before drop-casting CNF dispersion water. These metal oxide adhesion layers significantly enhanced the stability of CNF films on QCM sensors even in a high-humidity environment where a conventional adhesion layer (polyethylenimine) for CNF could not maintain stable adhesion. There was a significant difference between different metal oxide layers in the QCM data for humidity sensing. We found a negative correlation between the QCM sensitivity and the water wettability of metal oxide surfaces. Morphology analysis of the deposited CNF films revealed that the center-concentrated CNF microstructures on the metal oxide adhesion layers rigorously explained the observed negative correlation between the sensitivity and the wettability of metal oxide surfaces. This trend was further confirmed by gradually changing the hydrophobicity of the NiO adhesion surfaces. Thus, the proposed strategy using robust metal oxide adhesion layers will be a foundation for further development of various CNF-based QCM gas sensors.

Evaluation of imidazole blocking layers for perovskite stability

The prevention of AgI formation is critical for ensuring long term stability of perovskite solar cells. While sputtered metal oxide films are known for uniform dense film formation, solution phase nanoparticle coatings of metal oxides are prone to pinholes through which free iodide can migrate leading to AgI formation at the back contact. Iodide migration can be prevented through the addition of passivator or blocking layers at the perovskite/charge transport or charge transport/Ag interfaces. In this paper we evaluated a series of imidazoles as interfacial layers to prevent iodide migration from the perovskite to the Ag back contact through solution phase deposited Y:SnO2. We identified structural features of the imidazoles that contribute to an effective blocking layer. Specifically, it was found that imidazoles with conjugated planer systems and hydrogen bonding heteroatoms were able to prevent ion migration while retaining device performance. Of the materials evaluated 4-(Imidazol-1-yl)phenol had the best performance with a 60 % increase in stability verse the control under illumination at short circuit conditions.

Dewetting-driven printing of thin metal oxide films

Dewetting-driven printing of thin metal oxide films

Inducing high-concentration Tb3+ with free oxygen via atomic layer deposition.

Precise preparation and control of trivalent states in rare earth metal oxide films are crucial for their optical and magnetic applications. In this study, compact and continuous terbium-doped nanofilms were deposited on silica substrates using atomic layer deposition (ALD). The average nanoparticle size varied from 17.9 to 78.5 nm with increasing growth cycles. X-ray photoelectron spectroscopy showed that the Tb3+/Tb4+ ratio increased from 0.98 to 1.42. A valence reduction mechanism involving free oxygen was introduced to analyze the reasons for the enhanced Tb3+ concentration in the nanofilms. The enhanced photoluminescence of Tb3+ (5D4→7F5) ions and the increased magnetization in terbium oxide nanofilms both reveal that free oxygen ions are the effective active sites responsible for the transition from the tetravalent to the trivalent state, in excellent agreement with theoretical analysis. Size control and free oxygen induction are promising strategies for enhancing the optical and magnetic properties of multivalent rare earth oxides.

An Optimized Ultrasonic Spray Pyrolysis Device for The Production of Metal Oxide Films and Their Morfology

In this work, we developed an optimized ultrasonic spray pyrolysis device for obtaining metal oxide films. The key benefit of this facility lies in its cost-effectiveness and its ability to consistently coat extensive surfaces without sacrificing the integrity of the semi-conductive films, thus streamlining the manufacturing process of semiconductor films. The resulting films exhibit the following attributes: the thickness of the deposited layer is approximately 400 nm, while the diameters of ZnO1-xSx nanocrystals range from 50 to 200 nm, oriented perpendicular to the crystallographic orientation (111). In the production of nanorods, the average height is estimated to be approximately 30-50 nm, with a density of 2.9×10¹¹ cm⁻² being indicated.