Oxide Nanowires Research Articles

Defect Location in Laterally Aligned Tin Oxide Nanowires: The Role of Growth Direction, Interface Dimensionality, and Catalyst

Laterally aligned SnO2 nanowires, which exhibit planar growth along crystallographically defined directions of a sapphire substrate surface, are superior for bio- and gas-sensing applications. Little is known about their cross-sectional geometry and the defect distribution within the nanowire cross section, although this substantially determines the electronic properties of the nanowires. In this study, SnO2 nanowires were grown on r-plane sapphire substrates. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) reveal the highly oriented growth of the SnO2 nanowires toward the substrate edges. High-resolution transmission electron microscopy (HRTEM) of the NW cross section and strain mapping allowed for analyzing the crystallographic alignment of the SnO2 NW to the sapphire substrate and the defect distribution within the SnO2 nanowire cross section. These techniques revealed a defect-free SnO2–Al2O3 interface and a high alignment of the SnO2 NW lattice toward the sapphire substrate along the NW width. The determined high defect density close to the nanowire surface will be discussed in comparison to freestanding SnO2 nanowires and SnO2 thin films on sapphire substrates considering the differences in the growth direction and the interface dimensionality.

Scaling-Up Seeded Hydrothermal Nanowire Synthesis on Non-planar Surfaces Using a Flow Reactor

While many nanomaterial synthesis processes have been demonstrated at the laboratory scale, grand challenges remain at the nanomanufacturing frontier, where it is necessary to maintain tunable material structure and properties at large length scales using high-throughput, low-cost, and sustainable processes. Seeded hydrothermal synthesis is widely used to generate tunable nanostructures with controlled geometric parameters. In this study, we used atomic layer deposition to deposit precise and conformal seed layers which were subsequently processed using a customized hydrothermal flow reactor. The reactor design allows for control of the solution temperature profile in space and time, as well as the solution flow profile. Recirculation of the hydrothermal growth solution enables reduction of the chemical waste by 77–92% compared to a single pass flow reactor. This “surface-directed assembly” process allows for the growth of vertically aligned zinc oxide (ZnO) nanowires (NWs) directly onto macroscopic (cm-scale) non-planar surfaces. We quantify the uniformity of the NW morphology using scanning electron microscopy and UV absorption measurements. The NWs were further functionalized to form superhydrophobic and optically transparent surface coatings along a curved glass dome substrate. The surface coatings were shown to significantly reduce the rate of biofouling from marine algae by ∼75%. This demonstrates a pathway for the scale-up of hydrothermal synthesis processes with a variety of applications in the biological and environmental fields, including medical devices and optical and oceanographic sensors.

Out-of-Plane Electronics on Flexible Substrates Using Inorganic Nanowires Grown on High-Aspect-Ratio Printed Gold Micropillars.

Out-of-plane or3Delectronics on flexible substrates are an interesting direction that can enable novel solutions such as efficient bioelectricity generation and artificial retina. However, the development of devices with such architectures is limited by the lack of suitable fabrication techniques. Additive manufacturing (AM) can but often fail to provide high-resolution, sub-micrometer 3D architectures. Herein, the optimization of a drop-on-demand (DoD), high-resolution electrohydrodynamic (EHD)-based jet printing method for generating 3D gold (Au) micropillars is reported. Libraries of Au micropillar electrode arrays (MEAs) reaching a maximum height of 196µm and a maximum aspect ratio of 52 are printed. Further, by combining AM with the hydrothermal growth method, a seedless synthesis of zinc oxide (ZnO) nanowires (NWs) on the printed Au MEAs is demonstrated. The developed hybrid approach leads to hierarchical light-sensitive NW-connected networks exhibiting favorable ultraviolet (UV) sensing as demonstrated via fabricating flexible photodetectors (PDs). The 3D PDs exhibit an excellent omnidirectional light-absorption ability and thus, maintain high photocurrents over wide light incidence angles (±90°). Lastly, the PDs are tested under both concave and convex bending at 40mm, showing excellent mechanical flexibility.

Dielectric and mechanical properties of TiO2/polyimide composites with low dielectric constant

AbstractWith the advent of 5G era, the high millimeter‐wave frequency band, poor signal penetration and large loss make 5G communication more dependent on low dielectric constant materials. Therefore, the research and development of low dielectric polymer materials has become a hot spot in recent years. With its good chemical corrosion resistance, thermal stability, high dispersion and high mobility, titanium dioxide (TiO2) as a high function fine inorganic material is doped in polymer systems to improve the electrical properties of polymer composites. In recent years, a large number of studies have used spherical TiO2 nanoparticles doped on the polymer matrix, however, there is almost no research on doping nanolinear TiO2 nanoparticles on the polymer matrix. Here, TiO2 nanowires were prepared by hydrothermal method, and the prepared TiO2 nanowires were added to polyimide (PI). TiO2/PI monolayer and three‐layer composite films with good dielectric and mechanical properties were prepared by in‐situ polymerization. Fourier transform infrared spectoscopy, scanning electron microscopy and X‐ray diffraction were used to characterize the structure and test the properties of the composites. During the initiation process, the thermal initiation reaction of the composite membrane was completed. The composite film with good mechanical properties and excellent dielectric properties were obtained by adding titanium oxide nanowires, which can meet the requirements of its use in the field of microelectronic devices.

A first principles study on spin dependent electronic characteristics of zinc oxide nanowires linked to nickel electrodes

The spin resolved electronic transport behavior of ZnO nanowires (ZnONWs) linked to electrodes is investigated using first principles calculations within Density Functional Theory incorporating the Hubbard (U) term. A defect (resulting from Zn vacancy) in ZnO, as well as the use of Ni electrodes, have a significant influence on the electronic structure properties. They improve the magnetic moment of the system and generate a spin-asymmetric spectra. The ZnONWs linked to the Ni electrodes are probed for spin resolved differential conductance and current. Although the spin down differential conductance curves have a similar trend, the variations in spin up conductance are dissimilar. ZnONW-based devices appear promising for prospective spintronic applications due to their nearly half-metallic behavior around the Fermi energy and acceptable spin polarization in current.

All-in-one supercapacitors with high performance enabled by Mn/Cu doped ZnO and MXene

Here, we report the development of high-performance supercapacitor devices using manganese-doped zinc oxide nanowires (Mn-doped ZnO NWs) and copper-doped zinc oxide nanoparticles (Cu-doped ZnO NPs) as a positive electrode with MXene as a negative electrode. Both transition metal (TM)-based electrodes were used separately with MXene, and the performance was tested. When used in combination with MXene as a second electrode, TM-ZnO samples displayed a major increase in the supercapacitors’ performance. The highest-performance supercapacitor recorded values of 151 F/g specific capacitance along with 84 Wh/kg energy density and a power density of 75 kW/kg. Electron paramagnetic resonance and photoluminescence spectroscopy of Mn/Cu-doped ZnO reveals intrinsic and extrinsic defect signals, which were discussed and attributed to the enhancement of the capacitive performance. The presence of the aforementioned defects optimizes the intrinsic properties and boosts the reaction kinetics, thus providing increased electrochemical activity and superior supercapacitor device performance.

Self-Limiting Growth of Monolayer Tungsten Disulfide Nanoribbons on Tungsten Oxide Nanowires

Transition metal dichalcogenides (TMDCs) are promising two-dimensional (2D) materials for next-generation optoelectronic devices; they can also provide opportunities for further advances in physics. Structuring 2D TMDC sheets as nanoribbons has tremendous potential for electronic state modification. However, a bottom-up synthesis of long TMDC nanoribbons with high monolayer selectivity on a large scale has not yet been reported yet. In this study, we successfully synthesized long WxOy nanowires and grew monolayer WS2 nanoribbons on their surface. The supply of source atoms from a vapor-solid bilayer and chemical reaction at the atomic-scale interface promoted a self-limiting growth process. The developed method exhibited a high monolayer selection yield on a large scale and enabled the growth of long (∼100 μm) WS2 nanoribbons with electronic properties characterized by optical spectroscopy and electrical transport measurements. The produced nanoribbons were isolated from WxOy nanowires by mechanical exfoliation and used as channels for field-effect transistors. The findings of this study can be used in future optoelectronic device applications and advanced physics research.

One-dimensional γ-Al2O3 growth from the oxidation of NiAl

We report an oxide nanowire growth phenomenon that morphologically resembles the vapor-liquid-solid process but with a fundamentally different mechanism. This is demonstrated with the high-temperature NiAl oxidation that results in the unidirectional γ-Al2O3 growth with a NiO nanoparticle at the nanowire tip. The NiO nanoparticle surface serves as the active site for dissociative O2 adsorption that produces an inward flux of atomic oxygen toward the γ-Al2O3/NiAl interface for γ-Al2O3 growth by reacting with bottom-up diffusing Al3+ cations. The nanowire lengthening follows the parabolic kinetics with the upward lattice diffusion of Al3+ cations in the γ-Al2O3 nanowires as the rate-limiting factor.

Nanoporous Mo-Doped NiFe Oxide Nanowires from Eutectic Dealloying as an Active Electrocatalyst for the Alkaline Oxygen Evolution Reaction

Nanoporous Mo-Doped NiFe Oxide Nanowires from Eutectic Dealloying as an Active Electrocatalyst for the Alkaline Oxygen Evolution Reaction

Impact of Magnetite Nanowires on In Vitro Hippocampal Neural Networks.

Nanomaterials design, synthesis, and characterization are ever-expanding approaches toward developing biodevices or neural interfaces to treat neurological diseases. The ability of nanomaterials features to tune neuronal networks' morphology or functionality is still under study. In this work, we unveil how interfacing mammalian brain cultured neurons and iron oxide nanowires' (NWs) orientation affect neuronal and glial densities and network activity. Iron oxide NWs were synthesized by electrodeposition, fixing the diameter to 100 nm and the length to 1 µm. Scanning electron microscopy, Raman, and contact angle measurements were performed to characterize the NWs' morphology, chemical composition, and hydrophilicity. Hippocampal cultures were seeded on NWs devices, and after 14 days, the cell morphology was studied by immunocytochemistry and confocal microscopy. Live calcium imaging was performed to study neuronal activity. Using random nanowires (R-NWs), higher neuronal and glial cell densities were obtained compared with the control and vertical nanowires (V-NWs), while using V-NWs, more stellate glial cells were found. R-NWs produced a reduction in neuronal activity, while V-NWs increased the neuronal network activity, possibly due to a higher neuronal maturity and a lower number of GABAergic neurons, respectively. These results highlight the potential of NWs manipulations to design ad hoc regenerative interfaces.

The beneficial effect of reducing agent on the synthesis of manganese oxide nanowires as electrode materials for supercapacitors

We examine the effects of precursor concentration and changes in the volume of reducing agent on the physico-chemical properties and electrochemical performance of the manganese oxide materials. Despite the fact that studies have been published on the usage of ethylene glycol as a reducing agent in the preparation of manganese oxide, there is no report on the investigation of the change in concentration of the precursor and volume of the reducing agent and how it impacts the physical, chemical, and electrochemical properties of the end products. Hence, the present work attempts to attain knowledge of the found research gap. Three different concentrations of precursor, viz. 0.1, 0.25, and 0.5 M, and four different volumes of reducing agent, viz. 0.5, 1, 3, and 5 ml, are studied. Crystallinity, morphology, chemical state, and surface area characteristics of the prepared samples are thoroughly studied using a variety of techniques. There is an increment in crystallinity and a significant change in morphology observed from nanowires to agglomerated nanostructures when the volume of reducing agent linearly increases. Interestingly, the results indicate that a lower volume of reducing agent can facilitate the development of an end product with optimum electrochemical properties for supercapacitor applications. The samples prepared with a minimum volume of reducing agent achieve a high specific surface area of 241 m2/g with a noteworthy specific capacitance of 179 F/g and also show an acceptable capacitance retention of 74.2% even after 5000 consecutive cycles. These findings might develop a favorable impact and understanding on the ratio of reactants that can be utilized in various material preparations.

One-step cladding metal oxide nanowires with a carbon-dots-embedded ZnO amorphous layer toward boosted photoelectrochemical water oxidation

An effective method was proposed for constructing carbon dots (CDs)-sensitized multijunction composite photoelectrodes via one-step cladding a CDs-embedded ZnO amorphous overlayer on vertically aligned metal oxide nanowires. This strategy involved the double role of hexamethylenetetramine (HMTA) in the ethylene glycol (EG) solvent mixed with a controllable trace amount of water. In the water-deficient synthetic system, a limited portion of HMTA served as the pH buffer and hydroxyl source to force the hydrolytic process of zinc ions for the production of ZnO. The precipitated ZnO clusters were instantly capped by EG molecules through the activated alkoxidation reaction, and further crosslinked into an amorphous network surrounding the individual nanowires. Meanwhile, the excess HMTA was simultaneously depleted as the precursor for producing CDs in the EG solution through thermal condensation, which were packed in the gradually formed aggregates. We revealed that a CDs-embedded amorphous ZnO overlayer with an appropriate proportion of ingredient could be tailored through an optimal tradeoff between hydrolysis and condensation of HMTA. Benefiting from the synergy of the amorphous ZnO layer and the embedded CDs, the multijunction composite photoanodes exhibited significantly improved PEC performance and stability for water oxidation.

Voidless metal lines sintered with intense pulsed light and their applications as transparent metal-mesh electrodes

An optimal metal ink that can be sintered without void generation by intense pulsed light (IPL) was systematically formulated. This ink is a hybrid ink in which silver (Ag) nanoparticle ink and copper (Cu) precursor ink are mixed in an optimal weight ratio, and the reduced Cu fills the space between Ag nanoparticles during the sintering process. The optimization process of the ink encompasses the shape and size of nanoparticles, the type of solvent, and the mixing ratio of the Cu precursor ink. This optimized ink was filled in the engraved trenches and IPL-sintered to fabricate flexible transparent metal-mesh electrodes. If there are voids in the metal lines after IPL sintering, the metal lines may shrink under condition of high temperature and high humidity for a long time, which may deteriorate the stability of the metal electrode. It was confirmed that the hybrid ink optimized in this study hardly shrinks due to no voids inside the metal lines after IPL sintering and has excellent environmental and mechanical stability. The metal-mesh electrode produced using this ink showed superior properties compared to other competing transparent electrodes such as indium-tin oxide or Ag nanowires when used for transparent heaters and electromagnetic shielding applications.

Mutation detection of urinary cell-free DNA via catch-and-release isolation on nanowires for liquid biopsy

Cell-free DNA (cfDNA) and extracellular vesicles (EVs) are molecular biomarkers in liquid biopsies that can be applied for cancer detection, which are known to carry information on the necessary conditions for oncogenesis and cancer cell-specific activities after oncogenesis, respectively. Analyses for both cfDNA and EVs from the same body fluid can provide insights into screening and identifying the molecular subtypes of cancer; however, a major bottleneck is the lack of efficient and standardized techniques for the isolation of cfDNA and EVs from clinical specimens. Here, we achieved catch-and-release isolation by hydrogen bond-mediated binding of cfDNA in urine to zinc oxide (ZnO) nanowires, which also capture EVs by surface charge, and subsequently we identified genetic mutations in urinary cfDNA. The binding strength of hydrogen bonds between single-crystal ZnO nanowires and DNA was found to be equal to or larger than that of conventional hydrophobic interactions, suggesting the possibility of isolating trace amounts of cfDNA. Our results demonstrated that nanowire-based cancer screening assay can screen cancer and can identify the molecular subtypes of cancer in urine from brain tumor patients through EV analysis and cfDNA mutation analysis. We anticipate our method to be a starting point for more sophisticated diagnostic models of cancer screening and identification.

In-situ composition development of Zn/In-doped Ga2O3 nanowire with ultrahigh responsivity and long-term stability for deep-UV photodetector

High-performance deep ultraviolet photodetectors (UV PDs) based on Ga2O3 have been applied widely in civil and military exploration. The incident photon-to-electron conversion efficiency of Ga2O3-based UV PDs could be improved by doping metal or non-metal elements in the lattice. Herein, multi-metallic oxide of InZn co-doped Ga2O3 (InZn-Ga2O3) nanowires is synthesized via the in-situ chemical vapor deposition (CVD) method. The favorable 25%InZn-Ga2O3 exhibits a maximum responsivity of 440.42 A W−1 and a peak external quantum efficiency (EQE) of 2.15 × 105% under 254 nm light illumination at 10 V, which are 1.19 × 104 times higher than that for pure Ga2O3, indicating its enhanced detection ability for deep-UV light and high conversion efficiency from photons to electrons. A high UV/visible rejection ratio of 7.3 × 105 is also obtained, implying a high sensitivity for UV light. Moreover, the responsivity of the InZn-Ga2O3 UV PD remains unchanged after a long period of 8000 s testing. The superior performances of InZn-Ga2O3 UV PD are attributed to the improved crystal quality with decreased oxygen vacancies and elevated conductivity, which facilitate the separation and transfer of photoinduced electron-hole carriers. The DFT calculation and UV–vis spectra results reveal that the InZn-Ga2O3 possesses a narrowed band gap with enhanced light absorption and a decreased work function for the fast escape of electrons. In addition, the ohmic contact between InZn-Ga2O3 and Ag electrode accelerates the transfer and diffusion of photogenerated electrons. The achievements in our work present a multi-metallic oxide nanowire with high performance and an innovative mechanism analysis method for the applications of optoelectronic devices.

Exploiting the complete efficacy of 3D-nitrogen-doped ZnO nanowires photoanode via type-II ZnS core-shell formation toward highly stable photoelectrochemical water splitting

The hierarchical 3D-zinc oxide (ZnO) nanowires (NWs) photoanode promises high cost-to-efficiency ratios toward photoelectrochemical (PEC) water splitting owing to their enthralling characteristics. However, minimal visible light harvesting, and sluggish surface oxidation kinetics severely hinder the water-splitting efficiencies along with the resistance to photo-corrosion. We report a unique strategy of constructing type-II heterostructure of N-doped ZnO NWs with ultrathin zinc sulfide (ZnS) layer to form a core-shell structure that provides dual benefits of accelerating the charge transfer process and significantly enhancing the resistance to photo-corrosion of N-doped ZnO NWs. The PEC water splitting analyses showed that the optimal ZnS/N:ZnO core-shell NWs photoanode exhibited a photocurrent density of 0.85 mA cm−2 at 1.23 Vs RHE which was 3-fold higher than N:ZnO NWs photoanode. The ZnS shell encapsulation effectively protects the N:ZnO NWs core over a period of ∼16 h from detrimental photo-corrosion with 76% photocurrent density retention. Additionally, the integration of multilateral tactics of staggered heterojunction and core-shell formation provided higher photoconversion efficiencies over N:ZnO NWs. The reported approach may provide an alternative to address the sluggish surface kinetics that bothers the chemical stability, prolong the charge lifetime, and thus open up wide opportunities in the construction of efficient and highly stable PEC water-splitting devices.

Disulfonated polyarylene ether sulfone membrane for graphitic carbon nitride/zinc oxide based photo-supercapacitors

Photo-supercapacitors (PSCs) are environmentally friendly devices that directly convert and store solar energy into electricity and have a high potential to eliminate the need for grid electricity for a sustainable future. In this study, lithiated (Li+) biphenol-based disulfonated poly (arylene ether sulfone) random copolymer (BPS) membrane has been successfully integrated into graphitic carbon nitride/zinc oxide nanowire composite-based PSC to increase the efficiency and to offer simpler and more cost-effective designs. It has been observed that after UV illumination specific capacitance (Cp) and energy density (Ed) increased 2.8 and 2.7-fold, respectively, indicating that the PSC with BPS-Li+performs approximately 3 times better under illumination than dark conditions. Furthermore, at elevated temperatures and 100% relative humidity Cp and Ed of the PSC increased to 23.61 Fg−1 and 47.22 Whkg−1 at 85 °C, respectively. This enhancement can be linked to the temperature-boosted ionic conductivity of the membrane.

An in-depth analysis on the switching response and impedance curves of n-si/In2O3 NW/Ag NPs/In based devices by a double-step glancing angle deposition technique

Silver (Ag) nanoparticles (NPs) were coated upon indium oxide (In2O3) nanowires (NW) by a double-step glancing angle deposition (GLAD) technique. The study focuses on the experimental analysis of current (I) versus voltage (V), current (I) versus time (t), as well as impedance (Zexp) versus voltage (V) curves for n-Si/In2O3 NW/Ag NPs/In based devices with a sweeping voltage of ±10 V at room temperature in different frequency responses varying from 100 Hz to 2 MHz. The n-Si/In2O3 NW/Ag NPs/In based device showed faster rise and fall time of 0.13 s and 0.12 s than the other devices due to oxygen-related defect states. The presence of Ag NPs also improved oxygen related defect states, resulting in high impedance value for n-Si/In2O3 NW/Ag NPs/In based device. The series circuit model (SCM) was used to derive the theoretical investigations of impedances, indicating the n-Si/In2O3 NW/Ag NPs/In based device can be used in nanoelectronics applications.

Sequential coating of Sb-doped SnO2 nanowire for photoelectrochemical cells of panchromatic light absorption and low thermalization loss

A photoelectrochemical (PEC) cell is a device of enormous potential in producing hydrogen via water splitting using solar energy. However, the low charge collection efficiency and thermalization loss of a photoelectrode limit the performance of the PEC cell. In this study, these problems are addressed by sequentially coating CdS and CdSe along the longitudinal direction of antimony-doped tin oxide and tin oxide nanowire (NW) arrays. Because of the vertical alignment of CdS and CdSe, larger band gap material (CdS) and smaller band gap material (CdSe) absorb blue and red light, respectively. Such selective absorption reduces the thermalization loss and increases the photocurrent density. In addition, antimony-doped tin oxide NWs increase the collection efficiency of photogenerated carriers and decrease the onset voltage by increasing the electric conductivity and decreasing the mismatch in the Fermi energy level. The photocurrent of the vertically aligned CdS and CdSe on antimony-doped tin oxide NWs is 17.6 mA cm−2, which is 50% higher than that of the traditional cascade-type CdSe/CdS photoelectrode.

WOx nanowire supported ultra-fine Ir-IrOx nanocatalyst with compelling OER activity and durability

Ultra-fine iridium (Ir) nanocatalyst is successfully dispersed and stabilized on sub-stoichiometric tungsten oxide nanowires (WOxNW) forming an active and stable OER catalyst. With its abundant amount of exposed active surfaces, the WOxNW supported Ir catalyst shows a high mass activity of 812 A/gIr at 1.55 V vs RHE. This value is three times higher than Ir-black and 30 times higher than Ir supported on antimony-doped tin oxide. The Ir@WOxNW possesses much satisfactory stability, showing a loss of only 40 % compared with the nearly 100 % loss of Ir-black after 1,000 accelerated durability testing cycles. Non-destructive depth profile by synchrotron-based XPS and density functional calculations unambiguously reveal the strong catalyst-support interaction between the WOxNW and the supported Ir catalyst. Due to the inhibited oxidation, the OER active core–shell-like structure of the Ir-IrO2 is well-maintained on the WOxNW supports under OER testing conditions. The developed catalyst shows high potential to significantly reduce Ir usage for practical water electrolysis.