Amorphous Metal Oxide Research Articles

Improving the photoswitching performance of a transistor with amorphous metal oxide semiconductor thin film by a gradient annealing approach

Metal oxides are attracting attention as electronic mate rials in research and industry. Thin films of amorphous indium gallium zinc oxide (a-IGZO) exhibit low absorbance in the visible spectrum, making them ideal components in transparent electronics. To widen the scope of use for thin film transistor (TFT) devices based on a-IGZO in on-chip sensing applications, photoresponsive behavior has been achieved by proper engineering of the active layers by either introducing a photosensitive top layer or using a method to generate localized states inside the band gap. In this paper, we propose a bilayer structured with the use of thermal annealing of a-IGZO film at different temperatures. Thermal annealing has been shown to improve the electrical performance of the TFT devices because of the improved film quality but negatively affects the photoresponsivity by removing tarp sites that play an important role in both charge generation and photomultiplication via the photogating effect. Therefore, here we propose an a-IGZO film with a high temperature-annealed bottom layer and pristine top layer. The bottom layer plays a vital role in the charge transport behavior, resulting in a low threshold voltage and subthreshold swing similar to the device with a fully annealed film, while the photoresponse of the device is driven by the higher density of gap states in the pristine top layer. This proposed method is advantageous to previously published procedures due to the simplicity of using no additional materials and complex steps to introduce trap sites into the photoactive layer, but only differential annealing temperature.

Noncontact Perception of Thin-Film Transistors by the Synergy of Both Capacitive and Electrostatic Induction Mechanisms.

In recent years, the rapid expansion of research and application of the Internet of Things and wearable electronics has prompted the development of a variety of sensors to perceive physical or chemical information from both the human body and the environment, among which the proximity sensor is a kind of noncontact sensor used to detect the approach of a target and thus exhibits promising applications in human-machine interactions. Thin-film transistors are one type of key components in modern electronics and have been further developed as electrostatic-induction-type proximity sensors to perceive the approach of electrically charged objects. However, they are immune to the approach of a zero-potential object. Capacitive-induction-type proximity sensors are capable of detecting the approach of conductive targets while being less sensitive to insulated ones. Integration of both electrostatic and capacitive induction mechanisms into one proximity sensor is highly expected to broaden its perception to a variety of targets. Here, an interdigital electrode was introduced as an extended gate into an amorphous metal oxide thin-film transistor to construct proximity sensors that combine both electrostatic and capacitive induction mechanisms and therefore can sensitively perceive the approach of a variety of objects that were electrically charged, grounded, or floated. Besides proximity sensing, remote velocity measurement and positioning of an invasive object were also realized, which further extended its functions as a kind of interdigital-electrode gate transistor.

Hierarchical design of self-standing FeNi-based metallic glass by in-situ surface amorphous oxide construction for durable and efficient oxygen evolution

As the driving force to accelerate water electrolysis in commercialization, electrocatalysts concurrently satisfying electrocatalytic activity, mechanical flexibility and low cost are essential in the design to lower the kinetic barriers of oxygen evolution reaction (OER). Herein, we present a strategy to in situ construct amorphous metal oxide nanolayers on different compositions of self-standing non-precious FexNiyP20 (at.%) metallic glasses (AMO-MG). With the mechanical flexibility, the processed FexNiyP20 MGs, particularly at Fe30Ni50P20, reaches low OER overpotentials of 238 at a current density of 10 mA cm−2 and a Tafel slope of 33 mV dec−1 in 1.0 M KOH solution while preserving a long-term durability exceeding 60 h. Further studies indicate these robust OER activities appear to be directly linked with the unique surface patterns of the in situ formed AMO nanolayer providing abundant active sites, low charge transfer resistance and superior structural-integration. Modelling analysis further shows that both Fe and Ni sites in the AMO nanolayer act as active sites leading to a strong charge transfer for effective H2O adsorption and an optimization of rate-determining step of OER process. Such in situ AMO-MG hierarchical structure therefore provides a novel structure-integration strategy and win–win situation to design and commercialize high-performance alloy catalysts for OER.

Rapidly reversible superwettability on textured metallic surfaces

Reversible superwettability on non-coated metallic surfaces has a broad range of engineering applications, yet achieving a rapid reverse of superwettability is still technically challenging on different metals. Here we show that rapid transition between superhydrophobicity (SHB) /hydrophobicity (HB) and superhydrophilicity (SHL) within tens of minutes can be achieved on femtosecond laser-treated Al surfaces with the assistance of ultraviolet (UV) irradiation and direct-current (DC) sputtering, overcoming traditional challenges posed by Al₂O3 in wettability conversion. The extremely high wettability conversion rate on Al surfaces was found to be related to the formation of textured amorphous metal oxides, whose relative content of oxygen vacancies (OVs) can be more easily changed. In the process of wettability change, there is a linear correlation between the metal surface potential and the cosine value of the contact angle. Our findings provide a versatile approach for designing metal surfaces with rapidly reversible superwettability, enabling various applications such as oil–water separations and the controlled release of hydrophilic drugs.

Enhancement of alkaline water-oxidation activity for amorphous CoOx by the underlying remote-region atom seeding

Scaling up hydrogen production via large-current-density water electrolysis requires durable electrocatalysts of oxygen evolution reaction (OER) to reduce energy consumption. While amorphous metal oxides are promising OER catalysts, the surface-sites-electronic-orbital chance from the underlying remote-region atom seeding remains elusive. Herein, vanadium atom was controllable seated in the underlying remote region of the bulk materials as a typical coupling mode of amorphous-CoVOx-supported amorphous CoOx (CoVOx@CoOx), to study long-distance atoms correlation. XPS characterization for CoVOx@CoOx can't reveal the V signal due to the limited test depth of 5 nm, suggesting that V is existent in the internal region where it can be detected by EDS with 1 μm test depth. For surface-etched CoVOx@CoOx, V XPS signal appeared due to the exposure of CoVOx counterpart. The bionic flower structured, amorphous CoVOx@CoOx presents low overpotential of 338.5 mV at an extremely high current density of 1000 mA cm−2 in 1 M KOH and reserves 90.4% of the initial catalytical current after 24 h operation, significantly outperforming single amorphous CoOx. Density functional theory calculations evidence that the charge transfer from V atoms of CoVOx to surface active Co sites of CoOx part leads to the d-band center of Co-3d orbital shifted towards the Fermi level, which enhanced O adsorption effect thus promoting the OER activity. This research not only provides an ultrahigh-current-tolerance OER catalyst but also throws in-depth insight into the long-distance atoms charge interaction towards knowledge-guide catalyst construction for practical utilization.

Tailoring the Ni-O Microenvironment in Amorphous-Dominated Highly Active and Stable Zn/NiO for Hydrogen Sulfide Detection.

Amorphous metal oxide semiconductor (MOS) materials are endowed with great promise to modulate electronic structures for gas-sensing performance improvement. However, the elevated-temperature requirement of gas sensors severely impedes the application of amorphous materials due to their low thermal stability. Here, a cationic-assisted strategy to tailor the Ni-O microenvironment in an amorphous-dominated Zn/NiO heterogeneous structure with high thermal stability was developed. It was found that 6 mol % Zn incorporation into amorphous NiO can effectively preserve the amorphous-dominated NiO phase even at high temperature. After calcination, the amorphous oxide can only be converted to crystals partly thus leading to the formation of amorphous/crystalline compounds, and the content of the amorphous phase can be adjusted by changing the calcination temperature. This amorphous/crystalline configuration can induce more electron transfer from Ni to Zn species, leading to the formation of active Niδ+ (δ>2) centers. Ex situ XPS and in situ Raman spectroscopy studies proved that the generated Niδ+ species pronouncedly promote the electron transfer during the H2S adsorption process. The amorphous/crystalline-6 mol % Zn/NiO sensor exhibits exceptional hydrogen sulfide response (2 ppm, 3.23), outstanding repeatability (as long as 5 weeks), and low limit of detection (as low as 50 ppb), surpassing most reported nickel-based gas sensors such as the crystal nickel oxide prepared in this work. The response and detection limit of the latter is only (2 ppm, 1.89) and (0.05 ppm) respectively. Our work thus opens up more opportunities for fundamental understanding and modulating of highly active amorphous sensing materials.

Thermal Stability of Amorphous Metal Oxides: The Interplay of Secondary Cations, Degree of Substitution, and Local Structure

Thermal Stability of Amorphous Metal Oxides: The Interplay of Secondary Cations, Degree of Substitution, and Local Structure

Thin-film memristor using an amorphous metal–oxide semiconductor with a gradient composition of conducting components

A thin-film memristor using an amorphous metal–oxide semiconductor (AOS) with a gradient composition of conducting components has been developed, which is another way to achieve memristive properties. The advantages are that conductivity distribution is already obtained as fabricated without forming operation, and an analog characteristic is obtained by optimizing the component composition in AOS. As the binary characteristic, the set operation induces the transition from a low conductance state to a high conductance state, whereas the reset operation does vice-versa. The switching ratio (SR) is high, 448. As the analog characteristic, the SR becomes greater rapidly as the V set increases, namely, the dynamic range is outstanding.

Amorphous mixed transition metal oxides: A novel catalyst for boosting dehydrogenation of MgH2

Magnesium hydride (MgH2) has been recognized as a promising hydrogen storage material. However, the sluggish hydrogen desorption kinetics is one of the main factors hindering its practical applications. To enhance the dehydrogenation kinetics of MgH2, an amorphous mixed TiO2-ZrO2-V2O5 catalyst is synthesized in this work. After adding the as-synthesized catalyst into MgH2 by ball milling, the dehydrogenation activation energy can be decreased to 65.7 kJ mol−1. Meanwhile, the catalyzed MgH2 shows excellent cycling stability after fifty hydrogen absorption-desorption cycles. The significant improvement of hydrogen desorption kinetics is attributed to the synergistic effect of abundant oxygen vacancies and in situ formed multivalent species in the catalyst. This highlights the importance of designing and synthesizing efficient catalysts for dehydrogenation of MgH2.

Highly efficient anion exchange membrane water electrolyzers via chromium-doped amorphous electrocatalysts

In-depth comprehension and modulation of the electronic structure of the active metal sites is crucial to enhance their intrinsic activity of electrocatalytic oxygen evolution reaction (OER) toward anion exchange membrane water electrolyzers (AEMWEs). Here, we elaborate a series of amorphous metal oxide catalysts (FeCrOx, CoCrOx and NiCrOx) with high performance AEMWEs by high-valent chromium dopant. We discover that the positive effect of the transition from low to high valence of the Co site on the adsorption energy of the intermediate and the lower oxidation barrier is the key factor for its increased activity by synchrotron radiation in-situ techniques. Particularly, the CoCrOx anode catalyst achieves the high current density of 1.5 A cm−2 at 2.1 V and maintains for over 120 h with attenuation less than 4.9 mV h−1 in AEMWE testing. Such exceptional performance demonstrates a promising prospect for industrial application and providing general guidelines for the design of high-efficiency AEMWEs systems.

Do we really need machine learning interatomic potentials for modeling amorphous metal oxides? Case study on amorphous alumina by recycling an existing ab initio database

In this study, we critically evaluate the performance of various interatomic potentials/force fields against a benchmark ab initio database for bulk amorphous alumina. The interatomic potentials tested in this work include all major fixed charge and variable charge models developed to date for alumina. Additionally, we introduce a novel machine learning interatomic potential constructed using the NequIP framework based on graph neural networks. Our findings reveal that the fixed-charge potential developed by Matsui and coworkers offers the most optimal balance between computational efficiency and agreement with ab initio data for stoichiometric alumina. Such balance cannot be provided by machine learning potentials when comparing performance with Matsui potential on the same computing infrastructure using a single Graphical Processing Unit. For non-stoichiometric alumina, the variable charge potentials, in particular ReaxFF, exhibit an impressive concordance with density functional theory calculations. However, our NequIP potentials trained on a small fraction of the ab initio database easily surpass ReaxFF in terms of both accuracy and computational performance. This is achieved without large overhead in terms of potential fitting and fine-tuning, often associated with the classical potential development process as well as training of standard deep neural network potentials, thus advocating for the use of data-efficient machine learning potentials like NequIP for complex cases of non-stoichiometric amorphous oxides.

Selenium-alloyed tellurium oxide for amorphous p-channel transistors.

Compared to polycrystalline semiconductors, amorphous semiconductors offer inherent cost-effective, simple and uniform manufacturing. Traditional amorphous hydrogenated Si falls short in electrical properties, necessitating the exploration of new materials. The creation of high-mobility amorphous n-type metal oxides, such as a-InGaZnO (ref. 1), and their integration into thin-film transistors (TFTs) have propelled advancements in modern large-area electronics and new-generation displays2-8. However, finding comparable p-type counterparts poses notable challenges, impeding the progress of complementary metal-oxide-semiconductor technology and integrated circuits9-11. Here we introduce a pioneering design strategy for amorphous p-type semiconductors, incorporating high-mobility tellurium within an amorphous tellurium suboxide matrix, and demonstrate its use in high-performance, stable p-channel TFTs and complementary circuits. Theoretical analysis unveils a delocalized valence band from tellurium 5p bands with shallow acceptor states, enabling excess hole doping and transport. Selenium alloying suppresses hole concentrations and facilitates the p-orbital connectivity, realizing high-performance p-channel TFTs with an average field-effect hole mobility of around 15 cm2 V-1 s-1 and on/off current ratios of 106-107, along with wafer-scale uniformity and long-term stabilities under bias stress and ambient ageing. This study represents a crucial stride towards establishing commercially viable amorphous p-channel TFT technology and complementary electronics in a low-cost and industry-compatible manner.

Improving hydrogen isotope permeation resistance of (TiVAlCrZr)O multi-component metal oxide coating by O+ Ion implantation

Oxygen vacancy can greatly affect the performance of metal oxide to hydrogen isotope permeation resistance. In this work, we report a new strategy to improve the permeation resistance by oxygen ion implantation. A (TiVAlCrZr)O multi-component metal oxide film was prepared as a tritium permeation barrier on a 316 L substrate by RF magnetron sputtering deposition, and then implanted by oxygen ions to fill the oxygen vacancies inside. The grazing incidence X-rays (GIXRD) analysis showed that the pristine and the oxygen-implanted coatings were in an amorphous phase. The deuterium permeation resistance of the four coatings was tested by a gas-driven device. The result showed that the pristine coating had a permeation reduction factor (PRF) of 5,610 at 500 °C, while there was a 13.6 times of increase in PRF with an oxygen concentration of 11.4 at.% with the best-reported value of 76,500, and more oxygen ions implanted, the better the deuterium permeation resistance of the coating. The GIXRD showed that after the test the pristine coating remained amorphous, while some crystals were formed in the oxygen-implanted coating with an oxygen concentration of 11.4 at.%. Oxygen ion implantation enhanced the deuterium permeation resistance by filling the oxygen vacancies and forming of more stable state of amorphous multi-component metal oxide, which is expected to be a new type of deuterium permeation barrier.

Colloidal Atomic Layer Deposition on Nanocrystals Using Ligand-Modified Precursors.

Atomic layer deposition (ALD) is a method to grow thin metal oxide layers on a variety of materials for applications spanning from electronics to catalysis. Extending ALD to colloidally stable nanocrystals promises to combine the benefits of thin metal oxide coatings with the solution processability of the nanocrystals. However, challenges persist in applying this method, which relate to finding precursors that promote the growth of the metal oxide while preserving colloidal stability throughout the process. Herein, we introduce a colloidal ALD method to coat nanocrystals with amorphous metal oxide shells using metal and oxygen precursors that act as colloidal stabilizing ligands. Our scheme involves metal-amide precursors modified with solubilizing groups and oleic acid as the oxygen source. The growth of the oxide is self-limiting and proceeds in a layer-by-layer fashion. Our protocol is generalizable and intrinsically scalable. Potential applications in display, light detection, and catalysis are envisioned.

Highly efficient catalytic oxidation of toluene by amorphous/microcrystalline mixed-phase MnO2

Amorphous transition metal oxides exhibit considerable potential in the catalytic oxidation of volatile organic compounds (VOCs) owing to their distinctive surface properties. In this study, we achieved the modulation of the crystalline structure of manganese oxides by employing various C3 alcohols (alcohols with three carbons) with distinct hydroxyl types during the reduction process with potassium permanganate. Subsequently, a series of characterization techniques were employed to assess the catalytic performance of the prepared MnO2 in the oxidation of toluene. Notably, the MnO2-G obtained from glycerol presented excellent catalytic activity (T90 = 219 °C), stability, and water resistance. The unique amorphous/microcrystalline state of MnO2-G exposed more phase boundaries, and the unsaturated coordination structure facilitated the generation of additional defective sites, favoring the adsorption and activation of oxygen. Furthermore, the mixed-crystalline state induced the elevated Mn3+ content on the surface of MnO2-G, leading to elongation of the Mn-O bond due to the pronounced Jahn-Teller effect of Mn3+. Consequently, the synergistic effects of the mixed crystalline state contributed to the efficient catalytic oxidation of toluene at relatively low temperatures. Additionally, the conversion pathway of toluene on MnO2-G was further revealed by in situ DRIFTS.

A Unique Amorphous Porous BiSbOx Nanotube with Abundant Unsaturated Sb‐Stabilized BiO8−x Sites for Efficient CO2 Electroreduction in a Wide Potential Window

AbstractThe CO2 electroreduction reaction using sustainable electricity emerges as a viable strategy to produce high‐value‐added and profitable chemicals. The achievement of superior activity at a lower overpotential and higher selectivity in a wide potential window is vitally important for large‐scale industrial applications. Herein, a carbon‐composite amorphous porous BiSbOx nanotube with abundant unsaturated sites is reported to boost the conversion of CO2 to formate, exhibiting a formate selectivity of >90% in an extremely broad range of potentials from −0.5 to −1.4 V versus reversible hydrogen electrode (RHE) and a maximal energy conversion efficiency of 77.1%. Importantly, pure formic acid solution is directly obtained in a solid‐electrolyte cell for industrial‐scale applications. The porous tubular structure can expose more catalytic active sites, accelerate the mass transfer, and show fast surface charge transfer. Moreover, the unique coordination‐unsaturated Sb‐stabilized BiO8−x site can not only enhance the adsorption and activation of CO2 but also reasonably balance the stabilization and hydrogenation of *OCHO intermediate, thus leading to its obviously higher catalytic performance. As a result, a novel amorphous porous BiSbOx nanotube is successfully designed for efficient CO2 electroreduction, which may shed new light on developing many more amorphous composite metal oxide catalysts for conversion of inert small molecules.

Universal Synthesis of Amorphous Metal Oxide Nanomeshes.

Constructing the pore structures in amorphous metal oxide nanosheets can enhance their electrocatalytic performance by efficiently increasing specific surface areas and facilitating mass transport in electrocatalysis. However, the accurate synthesis for porous amorphous metal oxide nanosheets remains a challenge. Herein,a facile nitrate-assisted oxidation strategy is reported for synthesizing amorphous mesoporous iridium oxide nanomeshes (a-m IrOx NMs) with a pore size of ∼4nm. X-ray absorption characterizations indicate that a-m IrOx NMs possess stretched Ir─O bonds and weaker Ir-O interaction compared with commercial IrO2. Combining thermogravimetric-fourier transform infrared spectroscopy with differential scanning calorimetry measurements, it is demonstrated that sodium nitrate, acting as an oxidizing agent, is conducive to the formation of amorphous nanosheets, while the NO2 produced by the in situ decomposition of nitrates facilitates the generation of pores within the nanomeshes. As an anode electrocatalyst in proton exchange membrane water electrolyzer, a-m IrOx NMs exhibit superior performance, maintaining a cell voltage of 1.67V at 1Acm-2 for 120h without obvious decay with a low loading (0.4mgcatalyst cm-2). Furthermore, the nitrate-assisted method is demonstrated to be a general approach to prepare various amorphous metal oxide nanomeshes, including amorphous RhOx, TiOx, ZrOx, AlOx, and HfOx nanomeshes.

Crystalline and amorphous Fe2O3 nanocubes grown on electrospun carbon nanofibers for lithium-ion batteries and lithium-sulfur batteries: A comparative study

Amorphous transition metal oxides have recently received particular research interests in electrochemical energy storage. However, there is still a lack of direct comparisons between amorphous materials and their crystalline counterparts. Here, we demonstrate the rational synthesis of crystalline and amorphous Fe2O3 nanocubes uniformly grown on carbon nanofibers (denoted as CNFs@C-Fe2O3 and CNFs@A-Fe2O3, respectively) for lithium-ion batteries (LIBs) and lithium-sulfur batteries (LSBs). In such a structure, the Fe2O3 nanocubes possess strong interfacial bonding with CNFs, which can ensure rapid electron transportation. Besides, these Fe2O3 nanocubes are highly porous, which can effectively alleviate the volume change, enlarge the surface area, increase active sites and facilitate ion diffusion. When employed as freestanding anode for LIBs, the CNFs@C-Fe2O3 electrode delivers much improved lithium ion storage performance compared to that of CNFs@A-Fe2O3. When evaluated as interlayers for LSBs, instead, the batteries with CNFs@A-Fe2O3 exhibit better rate performance cycling stability than that of with CNFs@C-Fe2O3. Moreover, theoretical calculations elucidate the amorphous Fe2O3 has stronger adsorption ability toward the soluble lithium polysulfides. This work would provide new insights into the reasonably development of crystalline and amorphous transition metal oxides toward electrochemical energy storage.

Thermal Evolution of NiFe-NO3 LDH and Its Application in Energy Storage Systems

In this work, the performances of nickel iron layered double hydroxides (LDH) with the nitrate anion at the interlayer (NiFe-NO3) for the manufacture of anodes for lithium-ion batteries have been tested before and after its sintering at different temperatures. After synthesis, the material was thermally analyzed in a range 30–1250 °C, showing a mass loss occurring in three different consecutive steps leading to a total mass decrease of ~30 mass%. Following thermogravimetric analysis (TGA), four samples were prepared by annealing at four different temperatures: one of the four did not undergo a thermal treatment (NiFe-0), while the remaining three were annealed at 250 °C, 360 °C, and 560 °C for 6 h (NiFe-250, NiFe-360, and NiFe-560). All materials where completely characterized via FE-SEM, PXRD, and FT-IR. The pristine LDH material showed some structural and compositional changes for growing temperatures, starting from the typical turbostratic hexagonal structure through a mixture of amorphous metal oxides and finally to the stoichiometric oxides FeNi2O4 and NiO. The as-obtained materials were mixed with carbon black (C65) and sodium alginate and tested as electrodes in Swagelok half cells in LP30 vs. metallic Li to perform CV and GCPL analysis. The electrochemical tests showed that the performances of NiFe-0, both in terms of stability and specific capacity, are not so different from the one of the NiFe-560, even if the Ni mass% in the former is lower than in the NiFe-560. This phenomenon could be explained by assuming a combined mechanism of reaction involving both intercalation and conversion.

Effects of Heat-Treatment on the Population of Intrinsic Defects in and the Stability of an Amorphous Metal-Oxide Thin-Film Transistor

Effects of Heat-Treatment on the Population of Intrinsic Defects in and the Stability of an Amorphous Metal-Oxide Thin-Film Transistor