Metal Oxide Heterostructures Research Articles

Heterojunction Transistors Printed via Instantaneous Oxidation of Liquid Metals

Semiconducting transparent metal oxides are critical high mobility materials for flexible optoelectronic devices such as displays. We introduce the continuous liquid metal printing (CLMP) technique to enable rapid roll-to-roll compatible deposition of semiconducting two-dimensional (2D) metal oxide heterostructures. We leverage CLMP to deposit 10 cm2-scale nanosheets of InOx and GaOx in seconds at a low process temperature (T < 200 °C) in air, fabricating heterojunction thin film transistors with 100× greater Ion/Ioff, 4× steeper subthreshold slope, and a 50% increase in mobility over pure InOx channels. Detailed nanoscale characterization of the heterointerface by X-ray photoelectron spectroscopy, UV-vis, and Kelvin probe elucidates the origins of enhanced electronic transport in these 2D heterojunctions. This combination of CLMP with the electrostatic control induced by the heterostructure architecture leads to high performance (μlin up to 22.6 cm2/(V s)) while reducing the process time for metal oxide transistors by greater than 100× compared with sol-gels and vacuum deposition methods.

Crystal facets-controlled NiO/SnO2 p-n heterostructures with engineered surface and interface towards triethylamine sensing

Crystal facets engineering is an effective means to improve the gas sensing performance of metal oxides and has become a research hotspot recently. However, research on crystal facets engineering are mainly focused on single metal oxides semiconductor, there are still very limited report about the crystal facets engineering on the semiconductor p-n heterostructures. In the present study, NiO/SnO2 p-n heterostructures were constructed by wrapping SnO2 nanocrystals exposing different crystal facets with 2D porous NiO nanosheets networks. It was found that the heterostructures with coexisted SnO2 {221} and {110} crystal facets displayed a significantly improved triethylamine sensing performance with a high response value of 78.5 towards 100 ppm triethylamine, together with ultrafast response characteristics (< 3 s), excellent stability and selectivity. The related mechanism was described through theoretical calculation. On the one hand, {221} crystal facets had higher activity and provided more active sites for the surface adsorption of triethylamine. On the other hand, the strong electron interaction between {110} facets and NiO was favorable for efficient electron transfer in interface, which further enhanced the gas sensing activity of heterostructures. This study provides a new idea for improving the gas sensing performance of metal oxide heterostructures through collaborative optimization of surface and interface.

Coupling interface design of metal oxide heterostructures derived from MXene@MOFs hybrids for high-sensitivity acetone sensor

Acetone is used in a variety of fields for being highly volatile chemicals that may have detrimental effects on both industrial security and human health. With a view to testing the leak and concentration of acetone, we have successfully developed TiO2/Fe2O3-X (TF-X) sensors via a carboxyl group-shared coordination route. Here, Ti3C2Tx MXene and Fe salt provide chelation sites enabling coordination with carboxyl groups to fabricate two kinds of MOFs (MIL-125(Ti)/MIL-53(Fe)) followed by calcination. The tightly coupled heterogeneous interface between TiO2 and Fe2O3 promotes carrier transfer and elicits sharp resistance variation thereby raising the sensitivity towards acetone. Meantime, the porous TF-X heterostructures generate numerous oxygen vacancies and surface functional groups to be conducive to the gas flow and surface reaction. Accordingly, the optimal TF-400 heterostructure endows the extraordinary sensitivity (R = 446.8) to 100 ppm acetone at 268 ℃, much higher than that of the pristine TiO2 and Fe2O3. Rapid response (15 s) and recovery (7 s) time are implemented, as well as remarkable selectivity and stability. Moreover, the enhanced mechanism of TF-400 heterostructure is presented and studied. It is anticipated to open up a new avenue for the design and synthesis of high-sensitivity acetone sensors.

In situ synthesis of integrated dodecahedron NiO/NiCo2O4 coupled with N-doped porous hollow carbon capsule for high-performance supercapacitors

NiO and NiCo2O4 exhibit excellent synergistic effects and broad application prospects in electrochemical applications. However, the apparent interfacial instability between NiO and NiCo2O4 limits ion transport kinetics, charge/ion transfer, and electrochemical stability. In response, we developed and designed an integrated dodecahedron NiO/NiCo2O4 by a facile in-situ calcination method. Moreover, by utilizing the porous hollow structure of nitrogen-doped carbon capsules (N-Cc) as a conductive network, the N-Ccx@NiO/NiCo2O4 heterostructures with stable interface structure, excellent electrolyte adsorption, and electron transfer pathways were carefully designed. The N-Cc1.0@NiO/NiCo2O4 heterostructures are found to deliver an outstanding specific capacitance of 658.8 F g−1, and a high energy density of 101.40 Wh kg−1 at a power density of 775.03 W kg−1, along with capacitance retention of more than 93.5% after 8000 cycles. Based on the DFT calculations and electrochemical experimental results, this work provides an effective in situ route for the construction of high-performance metal oxide heterostructure electrode materials for new energy storage devices.

One-pot synthesis of MoS2–CNx–metal oxide hetero structures and their synergistic role towards efficient oxygen reduction reaction

One-pot synthesis of MoS2–CNx–metal oxide hetero structures and their synergistic role towards efficient oxygen reduction reaction

Prussian blue analogue-derived hollow metal oxide heterostructure for high-performance supercapacitors.

Supercapacitors (SCs) have been the subject of considerable interest because of their distinct advantages. The performance of SCs is directly affected by the electrode materials. Metal oxides derived from Prussian blue analogues (PBAs) are often used as electrode materials for SCs. Herein, we developed a multi-step strategy to fabricate ternary hollow metal oxide (CuO/NiO/Co3O4) heterostructures. The core-shell structured PBA (NiHCC@CuHCC) with Ni-based PBA (NiHCC) as the core and Cu-based PBA (CuHCC) as the shell was prepared by a crystal seed method. The ternary metal oxide (CuO/NiO/Co3O4) with a hollow structure was obtained by calcinating NiHCC@CuHCC. The prepared CuO/NiO/Co3O4 demonstrates an excellent specific capacitance of 262.5 F g-1 at 1 A g-1, which is 27.4% and 16.2% higher than those of CuO/Co3O4 and NiO/Co3O4, respectively. In addition, the material showed outstanding cycling stability with a capacitance retention of 107.9% after 3000 cycles. The two-electrode system constructed with CuO/NiO/Co3O4 and nitrogen-doped graphene hydrogel (NDGH) demonstrates a stable and high energy density of 27.1 W h kg-1 at a power density of 1037.5 W kg-1. The capacitance retention rate was 100.7% after 4000 cycles. The reason for the excellent electrochemical properties could be the synergistic effect of the introduced heterojunction of CuO/NiO, the hollow structure, and various metal oxides. This strategy can greatly inspire the construction of SC electrodes.

Solution Processed NiO/MoS2 Heterostructure Nanocomposite for Supercapacitor Electrode Application

Metal oxide and metal dichalcogenide heterostructure composites are promising candidates for electrochemical use. In this study, a hybrid heterostructure composite electrode material was made using a straightforward hydrothermal process using transition metal oxide (NiO) and metal dichalcogenide (MoS2). The surface of the flower-like structured MoS2 was grown with granular structured NiO, and this heterostructure composite exhibited considerably improved specific capacitance when compared to the pure NiO and MoS2 materials. The pseudocapacitive performance was effectively supported by the heterostructure combination of transition metal oxide (TMOs) and metal dichalcogenide (MDC), which greatly improved ion transport within the material and storage. At a current density of 1 A/g, the prepared heterostructure composite electrode material exhibited a specific capacitance of 289 F/g, and, after 2000 cycles, the capacitance retained 101% of its initial value. The symmetric device was constructed and put through tests using LED light. This finding opens up a new avenue for the quickly increasing the field of heterostructure materials.

Metal Oxide Heterostructures for Improving Gas Sensing Properties: A Review.

Metal oxide semiconductor gas sensors are widely used to detect toxic and inflammable gases in industrial production and daily life. The main research hotspot in this field is the synthesis of gas sensing materials. Previous studies have shown that incorporating two or more metal oxides to form a heterojunction interface can exhibit superior gas sensing performance in response and selectivity compared with single phase. This review focuses on mainly the synthesis methods and gas sensing mechanisms of metal oxide heterostructures. A significant number of heterostructures with different morphologies and shapes have been fabricated, which exhibit specific sensing performance toward a specific target gas. Among these synthesis methods, the hydrothermal method is noteworthy due to the fabrication of diverse structures, such as nanorod-like, nanoflower-like, and hollow sphere structures with enhanced sensing properties. In addition, it should be noted that the combination of different synthesis methods is also an efficient way to obtain metal oxide heterostructures with novel morphologies. Despite advanced methods in the metal oxide semiconductors and nanotechnology field, there are still some new issues which deserve further investigation, such as long-term chemical stability of sensing materials, reproducibility of the fabrication process, and selectivity toward homogeneous gases. Moreover, the gas sensing mechanism of metal oxide heterostructures is controversial. It should be clarified so as to further integrate laboratory theory research with practical exploitation.

Low-dimensional electronic state at the surface of a transparent conductive oxide

Materials that blend physical properties that are usually mutually exclusive could facilitate devices with novel functionalities. For example, the doped perovskite alkaline earth stannates BaSnO3 and SrSnO3 show the intriguing combination of high light transparency and high electrical conductivity. Understanding such emergent physics requires deep insight into the materials’ electronic structures. Moreover, the band structure at the surfaces of those materials can deviate significantly from their bulk counterparts, thereby unlocking novel physical phenomena. Employing angle-resolved photoemission spectroscopy and ab initio calculations, we reveal the existence of a 2-dimensional metallic state at the SnO2-terminated surface of 1% La-doped BaSnO3 thin films. The observed surface state is characterized by a distinct carrier density and a lower effective mass compared to the bulk conduction band, of about 0.12me. These particular surface state properties place BaSnO3 among the materials suitable for engineering highly conductive transition metal oxide heterostructures.

Polaronic Trions Induced by Strong Interfacial Coupling in Monolayer WSe2

AbstractThe weak dielectric screening in 2D semiconducting transition metal dichalcogenides give rise to strongly bound quasiparticles, which provides a platform to investigate the diverse excitonic phenomena and correlated physics. However, how to effectively control these quasiparticles is still a challenge for their applications in optoelectronic and valleytronic devices. Herein, by means of fabricating monolayer WSe2 and transition metal oxide (TMO) heterostructures, polaronic trion, that is a trion dressed with soft rotational optical (RO) phonons, is realized due to the strong interfacial coupling. This Fröhlich bound state of trion dramatically increases the trion binding energy (BE) from room temperature to 65 meV at 80 K in WSe2/LaAlO3 (LAO). However, the increase of the trion BE for WSe2/SrTiO3 (STO) occurs below the phase transition temperature. This work expands the possibilities of the TMDs/TMOs heterostructures and promotes the development of 2D van der Waals materials for quasiparticle‐based devices.

Low-power-consumption ultraviolet photodetector based on p-NiO/SiO2/n-ZnO

Ultraviolet (UV) photodetector has found extensive applications, ranging from optical communication to ozone sensing. Wide bandgap metal oxide heterostructures have gained significant interest in the development of UV photodetectors due to their excellent electronic and optical properties, as well as ease of fabrication. However, there are surface and interface issues at these heterostructures that have detrimental effects on device performance. In this work, UV photodetector consisting of p-NiO/SiO2/n-ZnO heterostructure was prepared by RF magnetron sputtering method. The device exhibited remarkable performances, such as having a rectification ratio of 57, responsivity (R) of 5.77 AW−1, external quantum efficiency (EQE) of 1.96 × 103% and rise time of 0.048 s at a low power consumption of −0.1 V under 365 nm UV irradiation. This work demonstrated a method for low-cost fabrication of photodetectors with rectification behavior and at low power consumption.

Development of novel antiviral nanofinishes for bioactive textiles.

Virus-caused public health outbreaks represent a serious threat to humans all over the world. The rampant new 2019 coronavirus (SARS-CoV-2) has wreaked havoc on China and the rest of the world since December 2019. Now focus is on effective reduction of corona and other viral and bacterial infections in hospitals, public and private sectors, households, schools, etc. Metal and metal oxide nanoparticles, carbon nanotubes, heterostructures, patterned surfaces, and graphene-based materials have shown up to 99.9998% efficacy against bacteria, mold, and viruses. The stability, long shelf life, and robustness of inorganic nanoparticles make them desirable for antimicrobial nanofinishes. These inorganic antimicrobial agents are more stable than organic antibacterial compounds at high temperature and pressure. The high specific surface area-to-volume ratios and unique physicochemical characteristics of nanoparticles are largely responsible for their antibacterial actions. But their immobilization is a huge challenge. To address this issue, NPs were modified with (glycidoxypropyl) trimethoxysilane (GPTS) and applied on cotton fabric. The silane part of GPTS reacted with the NPs under acidic conditions while epoxy reacted with cotton under alkaline conditions. Treated cotton fabric showed good antiviral and antibacterial activity even after severe industrial washing.Graphical abstract

Quasi‐Two‐Dimensional Ferromagnetic SrRuO3 Grown by Pulsed Laser Deposition with Layer‐by‐Layer Growth Fashion

AbstractOne of the keys to the construction of metal oxide heterostructures is the short characteristic length scale, which requires controlled growth and interface engineering on an atomic level. At present, the growth mode of SrRuO3 (SRO) thin films grown on TiO2‐terminated (001) SrTiO3 (STO) substrates usually transitions from 2D layer‐by‐layer to step‐flow at the first few growth periods, which is not conducive to the construction of superlattices or multilayer films. In this paper, persistent layer‐by‐layer growth of SRO thin films is demonstrated by regulating the growth conditions. As a result, the thickness can be precisely controlled down to a single unit cell (u.c.) and achieve precise regulation of superlattices. Interestingly, the physical properties are well comparable to that of traditional step‐flow mode and the critical thickness (tc) for the dead layer is only 3 u.c. Through constructing SRO/STO superlattices, the SRO layers become more conductive and a quasi‐2D ferromagnetic monolayer film is achieved. The results pave a path toward SRO heterostructure synthesis and properties control at an atomic scale.

Hierarchical Fe2O3 hexagonal nanoplatelets anchored on SnO2 nanofibers for high-performance asymmetric supercapacitor device

Metal oxide heterostructures have gained huge attention in the energy storage applications due to their outstanding properties compared to pristine metal oxides. Herein, magnetic Fe2O3@SnO2 heterostructures were synthesized by the sol–gel electrospinning method at calcination temperatures of 450 and 600 °C. XRD line profile analysis indicated that fraction of tetragonal tin oxide phase compared to rhombohedral hematite was enhanced by increasing calcination temperature. FESEM images revealed that hexagonal nanoplatelets of Fe2O3 were hierarchically anchored on SnO2 hollow nanofibers. Optical band gap of heterogeneous structures was increased from 2.06 to 2.40 eV by calcination process. Vibrating sample magnetometer analysis demonstrated that increasing calcination temperature of the samples reduces saturation magnetization from 2.32 to 0.92 emu g-1. The Fe2O3@SnO2-450 and Fe2O3@SnO2-600 nanofibers as active materials coated onto Ni foams (NF) and their electrochemical performance were evaluated in three and two-electrode configurations in 3 M KOH electrolyte solution. Fe2O3@SnO2-600/NF electrode exhibits a high specific capacitance of 562.3 F g-1 at a current density of 1 A g-1 and good cycling stability with 92.8% capacitance retention at a high current density of 10 A g-1 after 3000 cycles in three-electrode system. The assembled Fe2O3@SnO2-600//activated carbon asymmetric supercapacitor device delivers a maximum energy density of 50.2 Wh kg-1 at a power density of 650 W kg-1. The results display that the Fe2O3@SnO2-600 can be a promising electrode material in supercapacitor applications.

Defect-induced magnetism in homoepitaxial SrTiO3

Along with recent advancements in thin-film technologies, the engineering of complex transition metal oxide heterostructures offers the possibility of creating novel and tunable multifunctionalities. A representative complex oxide is the perovskite strontium titanate (STO), whose bulk form is nominally a centrosymmetric paraelectric band insulator. By tuning the electron doping, chemical stoichiometry, strain, and charge defects of STO, it is possible to control the electrical, magnetic, and thermal properties of such structures. Here, we demonstrate tunable magnetism in atomically engineered STO thin films grown on STO (001) substrates by controlling the atomic charge defects of titanium (VTi) and oxygen (VO) vacancies. Our results show that the magnetism can be tuned by altering the growth conditions. We provide deep insights into its association to the following defect types: (i) VTi, resulting in a charge rearrangement and local spin polarization, (ii) VO, leading to weak magnetization, and (iii) VTi–VO pairs, which lead to the appearance of a sizable magnetic signal. Our results suggest that controlling charged defects is critical for inducing a net magnetization in STO films. This work provides a crucial step for designing magnetic STO films via defect engineering for magnetic and spin-based electronic applications.

Construction of three‐dimensional marigold flower‐shaped Ni3V2O8 for efficient solid‐state supercapacitor applications

AbstractDevelopment of binary spinel‐type mixed metal oxide and fabrication various morphological heterostructure nanomaterials having two distinct metals paid a wide attention in emerging field. Here, we prepared three‐dimensional (3D) marigold flower‐like Ni3V2O8 structure via a simple and facile technique for electrochemical supercapacitor applications. 3D Ni3V2O8 with thick petals as cathode materials exhibits high specific capacitance of 263.12 F g−1 at a scan rate of 0.5 mA cm−2. The high energy density of 32.98 W h kg−1 at power density of 189.96 W kg−1 is obtained by the cathode formation of marigold flower‐shaped Ni3V2O8, indicating excellent ions accessibility and large charge storage ability of Ni3V2O8 structure. It is also observed that even after 5000 cycles charging‐discharging profile analysis, Ni3V2O8 cathode retains 32% of its initial capacitance along with 100% Coulombic efficiency. This higher capacitance retention strengthens its adoption as a potential candidate for supercapacitor application.

Heterogeneous ZnO@CF structures and their excellent microwave absorbing properties with thin thickness and low filling

• A simple preparation method to design carbon fiber and metal oxide heterostructures • ZnO@CF heterostructure is beneficial to electromagnetic wave absorption • The effective bandwidth of ZnO@CF heterostructure achieved 4.94 GHz at low filling content (20wt%) and ultra-thin thickness (1.5mm) • The effective bandwidth covered the whole 2-18 GHz band with the increase of thickness from 0.5 to 10 mm With the aim to obtain enhanced absorbing performance at small thickness and low filling, a robust strategy to fabricate zinc oxide (ZnO) modified carbon fiber (CF) structures have been successfully prepared by using low temperature hydrothermal method. Due to the multi-interface polarization caused by the high specific surface area of the complex heterostructures and the improvement of impedance matching, the composites show excellent electromagnetic wave absorption properties. Under the condition of low filling content (20 wt%) and ultra-thin thickness (1.5 mm), the excellent absorption performance of minimal reflection loss of −34.4 dB and an effective absorption bandwidth (RL ≤ −10 dB) of 4.94 GHz is achieved. In addition, the effective absorption bandwidth covers the whole 2-18 GHz band with the increase of thickness from 0.5 to 10 mm. This work provides an innovative method for designing the matching layer of carbon-based absorbing materials, and ZnO@CF heterostructure is expected to become a potential absorbing material.

In-situ construction of ternary metal oxide heterostructures Mn@LaZrO: A novel multi-functional nanocatalyst for detecting environmental hazardous 4-nitroaniline

The level of environmental pollutants is kept increasing as the continued sources of waste discharges into the ecosystem. The improper discharge of industrial waste products, widely used pesticides in agriculture, and pharmaceutical discharges are the major source of this uplift. Nitro aromatics are one among the major intermediates for producing dyes, pesticides, and fungicides. Monitoring and assessing these environmental pollutants is more important to reduce the consequences experienced by human and aquatic life. Thus, the dual-sensing platform was developed for analyzing the 4-nitroaniline (4-NA) derivative via electrochemical and UV–vis sensing analysis. Inspired by the unique properties of nanomaterials trimetallic oxides as manganese with lanthanum zirconium oxide (Mn@LaZrO) were synthesized. The physicochemical features were determined with different analytical techniques. The Mn@LaZrO was found with pure crystalline nature and nanospheres at nanoplates were identified. The fabricated electrode with Mn@LaZrO was exposed to both the sensing analysis (UV and electrochemical) with 0.049 µM −1443.78 µM and 0.49 µM-159.61 µM linear ranges of 4-NA addition. The higher surface area with more reactive active sites triggered the faster electron transfer rate in 4-NA sensing. The Mn@LaZrO/GCE showed lowered resistance with the Rct value of 117.75 Ω determining the higher electrocatalytic activity of the composite. The LOD was obtained to be 0.003 µM and 0.041 µM. The highly influential factors such as selectivity, repeatability, reproducibility, and stability parameters depicted excellent performances. Thus, the dual-functional Mn@LaZrO executes excellent performances with its unique features.

Heterostructure Silicon Solar Cells with Enhanced Power Conversion Efficiency Based on Si x /Ni3+ Self-Doped NiO x Passivating Contact.

Developing efficient crystalline silicon/wide-band gap metal-oxide thin-film heterostructure junction-based crystalline silicon (c-Si) solar cells has been an attractive alternative to the silicon thin film-based counterparts. Herein, nickel oxide thin films are introduced as the hole-selective layer for c-Si solar cells and prepared using the reactive sputtering technique with the target of metallic nickel. An optimal Ni3+ self-doped NiOx film is obtained by tuning the reactive oxygen atmosphere to construct the optimized c-Si/NiOx heterostructure band alignment. A thin SiOx interlayer was further introduced to reduce the defect of the c-Si/NiOx interface with the UV–ozone (UVO) treatment. The constructed p-type c-Si/SiOx/NiOx/Ag solar cell exhibits an increase in the open voltage from 586 to 611 mV and achieves a 19.2% conversion efficiency.

Manipulating the metal-to-insulator transition and magnetic properties in manganite thin films via epitaxial strain

Strain engineering of epitaxial transition metal oxide heterostructures offers an intriguing opportunity to control electronic structures by modifying the interplay between spin, charge, orbital, and lattice degrees of freedom. Here, we demonstrate that the electronic structure, magnetic and transport properties of ${\mathrm{La}}_{0.9}{\mathrm{Ba}}_{0.1}{\mathrm{MnO}}_{3}$ thin films can be effectively controlled by epitaxial strain. Spectroscopic studies and first-principles calculations reveal that the orbital occupancy in Mn ${e}_{g}$ orbitals can be switched from the ${d}_{3{z}^{2}\ensuremath{-}{r}^{2}}$ orbital to the ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ orbital by varying the strain from compressive to tensile. The change of orbital occupancy associated with Mn $3d$-O $2p$ hybridization leads to dramatic modulation of the magnetic and electronic properties of strained ${\mathrm{La}}_{0.9}{\mathrm{Ba}}_{0.1}{\mathrm{MnO}}_{3}$ thin films. Under moderate tensile strain, an emergent ferromagnetic insulating state with an enhanced ferromagnetic Curie temperature of 215 K is achieved. These findings not only deepen our understanding of electronic structures, magnetic and transport properties in the ${\mathrm{La}}_{0.9}{\mathrm{Ba}}_{0.1}{\mathrm{MnO}}_{3}$ system, but also demonstrate the use of epitaxial strain as an effective knob to tune the electronic structures and related physical properties for potential spintronic device applications.