Tin Oxide Nanowires Research Articles

Flexible transparent memory cell: bipolar resistive switching via indium–tin oxide nanowire networks on a poly(dimethylsiloxane) substrate

This report describes the fabrication and resistive switching (RS) characteristics of a novel flexible transparent (FT) resistive random access memory (ReRAM) device with a Ag/indium–tin oxide (ITO) nanowire network/ITO capacitor deposited on a PDMS substrate. The transmittance of the device is ∼70% in the visible region, and it exhibits a stable high-resistance state (HRS) to low-resistance state (LRS) ratio (HRS/LRS ratio) in different bending states. The RS characteristics are attributed to the congregate state of oxygen vacancies at different voltages, and the difference between positive and negative bending is mainly contributed by the effect of stress on the conductive layer. The FT-ReRAM can be used as nonvolatile memory element in future flexible transparent devices.

(Invited) Bottom-up Growth of Fully Transparent Indium Tin Oxide Nanowire Layers for Enhanced Light Output for Light Emitting Devices

The development of optically transparent and mechanically flexible electronic circuitry is an essential step in the effort to develop next-generation display technologies which will undoubtedly have to address so-called ‘see-through’ and conformable products. In view of the inherent limitations of silicon-based electronic circuits and the demand for portable display and communication products, the development of high performance transparent devices is the focus of much activity. With the addition of branched and cross-wired structures to assemblies of nanorods and nanowires, the potential for synthesizing materials with interesting electrical, optical, and mechanical properties is even greater. As the most important transparent conducting oxide, tin-doped indium oxide has found a wide range of applications in photovoltaics, smart windows, organic light-emitting diodes, and flat-panel displays. The ability to realize fully transparent and conductive arrays of indium tin oxide nanowires grown as dedicated, uniform contact layers is demonstrated here to exhibit such dual functionality. The growth method mimics that of standard epitaxial growth regimes for known device architectures, allowing a one-step bottom-up method of both device and epitaxial nanowire layer fabrication. Large area nanowire arrays of various morphologies, self-catalysed and seeded during molecular beam epitaxy (MBE) are shown. We detail this new molecular beam epitaxial growth method; control of the nucleation, crystal growth direction, nanowire shape, density, conductivity and transparency is possible without necessitating neither a heterogeneous metal catalyst nor predefined placement of nanowire seeding. The electronic and photonic properties of branched nanostructured arrays are optimized for application as fully transparent contacts in the visible to near-infra red region for silicon-based light emitting devices (LEDs). References C. M. Eliason and M. D. Shawkey, Optics Express, 22 A642 (2014).C. O’Dwyer, M. Szachowicz, G. Visimberga, V. Lavayen, S. B. Newcomb and C. M. S. Torres, Nat. Nanotech., 4, 239 (2009).C. O'Dwyer and C. M. S. Torres, Front. Physics, 1, 18 (2013).M. Osiak, W. Khunsin, E. Armstrong, T. Kennedy, C. M. S. Torres, K. M. Ryan and C. O’Dwyer, Nanotechnology, 24, 065401 (2013).M. Osiak, E. Armstrong, T. Kennedy, C. M. S. Torres, K. M. Ryan and C. O’Dwyer, ACS Appl. Mater. Interfaces, 5, 8195 (2013).P. D. C. King, T. D. Veal, J. Phys. 23, 334214 (2011).J. Q. Xi, M. F. Schubert, J. K. Kim, E. F. Schubert, M. Chen, S. Y. Lin, W. Liu and J. A. Smart, Nature Photonics, 1, 176 (2007).M.L. Kuo, Y.S. Kim, Mei-Li Hsieh and Shawn-Yu Lin, Nano Lett. 11, 476 (2011).

An Assessment of Chemical Vapor Deposition Synthesis of SnO<sub>2</sub> Nanowires by Statistical Design

This paper studies the chemical vapor deposition (CVD) synthesis conditions for tin oxide (SnO2) nanowires (NWs) by using statistical design of experiment (DOE). The influences of synthesis parameters (growth temperature, deposition time and flow rate of argon) on SnO2 NWs diameter were studied. From perturbation analysis with DOE, it was found that temperature gave the most significant effect to the diameter of SnO2 NWs via CVD method followed by flowrate of argon and deposition time. Furthermore, based on the cube graph, the smallest SnO2 NWs (~18 nm) can be obtained at temperature of 850 °C with argon flow rate of 100 sccm using a deposition time of 60 min. On the other hand, the largest SnO2 NWs (~248 nm) can be produced at 900 °C.

Gibbs–Thomson Effect in Planar Nanowires: Orientation and Doping Modulated Growth

Epitaxy-enabled bottom-up synthesis of self-assembled planar nanowires via the vapor-liquid-solid mechanism is an emerging and promising approach toward large-scale direct integration of nanowire-based devices without postgrowth alignment. Here, by examining large assemblies of indium tin oxide nanowires on yttria-stabilized zirconia substrate, we demonstrate for the first time that the growth dynamics of planar nanowires follows a modified version of the Gibbs-Thomson mechanism, which has been known for the past decades to govern the correlations between thermodynamic supersaturation, growth speed, and nanowire morphology. Furthermore, the substrate orientation strongly influences the growth characteristics of epitaxial planar nanowires as opposed to impact at only the initial nucleation stage in the growth of vertical nanowires. The rich nanowire morphology can be described by a surface-energy-dependent growth model within the Gibbs-Thomson framework, which is further modulated by the tin doping concentration. Our experiments also reveal that the cutoff nanowire diameter depends on the substrate orientation and decreases with increasing tin doping concentration. These results enable a deeper understanding and control over the growth of planar nanowires, and the insights will help advance the fabrication of self-assembled nanowire devices.

High Photosensitivity and Fast Response Ultraviolet PD Based on Large-Scale Individual Tin Oxide (SnO2) Nanowire

High Photosensitivity and Fast Response Ultraviolet PD Based on Large-Scale Individual Tin Oxide (SnO₂) Nanowire

Fabrication of flexible ultraviolet photodetectors using an all-spray-coating process

We report on a flexible ultraviolet (UV) photodetector fabricated using an all-spray-coating process. Two spray coating units were utilized to deposit semiconducting tin oxide nanowires as an active channel layer and metallic silver nanowires as an electrode layer. The device was mounted on the back of a human hand, and the UV intensities in sunlight were monitored over time. The fabricated flexible UV photodetector showed highly sensitive, stable, and reproducible detection properties. The main advantage of the proposed fabrication method is the extension of the integration environment by allowing direct application on various substrates, such as clothes and human skin, with varying device size and shape.

Scalable solvo-plasma production of porous tin oxide nanowires

This paper reports a fast, scalable method for synthesizing tin oxide nanowire powder using cheap starting material of commercial tin oxide particles and an atmospheric microwave plasma reactor. Specifically, the synthesis concept involves plasma oxidation of tin oxide powder combined with potassium hydroxide for few seconds to a minute which is orders of magnitude lower than that using hydrothermal or vapor–liquid–solid (VLS) techniques. Even at lab scale, large-scale production of tin oxide nanowire powder as high as 10g per hour has been produced. Systematic studies reveal nucleation and growth of K2SnO3 nanowires from molten alloy involving KOH and tin oxide. A simple annealing step is used to convert K2SnO3 intermediate nanowires into pure tin oxide nanowires. The extremely short reaction time of 20s is three orders of magnitude faster than that of traditional hydrothermal method. It was shown that our tin oxide nanowire powder shows a high reversible capacity of 848mAhg−1 after 55 cycles at a current density of 100mAg−1. The scalable production technique presented here and the applicability of resulting tin oxide nanowire powders makes it as suitable for practical implementation into lithium-ion battery applications.

Bipolar resistive switching behaviors of ITO nanowire networks

We have fabricated indium tin oxide (ITO) nanowire (NW) networks on aluminum electrodes using electron beam evaporation. The Ag/ITO-NW networks/Al capacitor exhibits bipolar resistive switching behavior. The resistive switching characteristics of ITO-NW networks are related to the morphology of NWs. The x-ray photoelectron spectroscopy was used to obtain the chemical nature from the NWs surface, investigating the oxygen vacancy state. A stable switching voltages and a clear memory window were observed in needle-shaped NWs. The ITO-NW networks can be used as a new two-dimensional metal oxide material for the fabrication of high-density memory devices.

Zn2GeO4와 Zn2SnO4 나노선의 리튬 및 소듐 이온전지 성능 비교 연구

High-yield zinc germanium oxide () and zinc tin oxide () nanowires were synthesized using a hydrothermal method. We investigated the electrochemical properties of these and nanowires as anode materials of lithium ion battery and sodium ion battery. The and nanowires showed excellent cycling performance of the lithium ion battery, with a maximum capacity of 1021 mAh/g and 692 mAh/g after 50 cycles, respectively, with a high Coulomb efficiency of 98 %. For the first time, we examined the cycling performance of and nanowires for sodium ion batteries. The maximum capacity is 168 mAh/g and 200 mAh/g after 50 cycles, respectively, with a high Coulomb efficiency of 97%. These nanowires are expected as promising electrode materials for the development of high-performance lithium ion batteries as well as sodium ion batteries.

Improvement of Gas Sensing Characteristics by Adding Pt Nanoparticles on ZnO-Branched SnO2 Nanowires.

We coated zinc-oxide (ZnO)-branched tin oxide (SnO2) nanowires with a Pt shell layer via a sputtering method and subsequently annealed the composite to generate Pt nanoparticles. The spillover effect of Pt nanoparticles was expected to play a significant role in enhancing the response. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy revealed that the nanoparticles were comprised of a cubic Pt phase. A sensing test with NO2 gas revealed that the sensor response to NO2 gas was significantly increased, being related to the spillover effect of the Pt nanoparticles. As a result of the Pt-functionalization, the sensor response time and recovery time were decreased and increased, respectively. The high sensor response and fast response time make Pt-functionalized ZnO branched nanowires a promising candidate for gas sensors. The present work will be useful in exploring new areas of multiple-component nanosystems.

Synthesis, characterization and field emission properties of tin oxide nanowires

Tin oxide (SnO2) nanowires are synthesized by Au catalyzed chemical vapor deposition of Sn and C mixture at 900 °C by employing a continuous flow of Ar: O2 (10:1) for an hour. X-ray diffraction and Raman spectroscopy studies indicate that the as-grown SnO2 nanowires are crystalline in nature with tetragonal rutile phase. Electron microscopy studies reveal towards high aspect ratio of nanowires. The field emission studies show that SnO2 nanowires grown on Si substrate exhibit low turn-on field of 1.75 V/μm (at 0.1 μA/cm2) and long-term emission stability over a period of more than 50 h with a current density of 4 μA/cm2 at a constant electric field of 2.25 V/μm. Hardly any considerable degradation in the emission current is noticed even after 50 h which may be attributed to the high crystallinity of SnO2 nanowires.

Performance Enhancements for Chemiresistive Electronic Noses Based upon Materials, Temperature Modulation and Signal Processing

Chemical sensors capable of detecting, identifying and quantifying trace chemical species in the air would be beneficial for a broad range of application areas from the laboratory, to workplace safety, to medical diagnostics, to homeland security and environmental monitoring, and even extending to planetary exploration. Our recent research has focused on studying the analytical capabilities of electronic nose-type sensors that utilize arrays of chemiresistive microsensor elements. In particular, we have explored the utility of microsensor arrays populated with varied sensing materials and employing temperature modulation to further enhance the analytical content of the measured signal streams. It is important that these aspects work together to improve the performance of the electronic nose, and we will illustrate that with several examples. One scenario demonstrates the discrimination of several volatile organic compounds at varied concentrations using a temperature-modulated electronic nose. We have studied both inorganic and polymer-based sensing materials in the past, which were integrated with the microsensor array using a variety of approaches [1]. Here, the materials that we employed in the arrays are based upon metal oxide semiconductors with varied morphologies (including: tin oxide nanowire clusters, copper oxide films, and porous indium oxide films) deposited using semi-automated microcapillary pipetting. While each material is cross-selective to the targeted analytes, their ensemble performance with temperature modulation shows enhancements for analyte and concentration discrimination when evaluated using Linear Discriminant Analysis. Concentrations for the analytes (acetone, toluene and chlorobenzene) range from 1 µmol/mol to 80 µmol/mol, and these chemicals are presented to the microsensor array in air backgrounds either alone or in mixtures with varied levels of humidity. A second example demonstrates different temperature-modulation approaches to improve the performance characteristics of the microsensors. We have expanded our use of a relatively simple bi-level program to enhance the speed of the sensor responses [2], testing the approach for use with different materials and different types of analyte molecules. The utility of the approach for attaining faster responses is shown in Figure 1. Here the raw data collected from a microsensor element based upon a porous indium oxide film are shown for two operating conditions: fast temperature modulation and isothermal. As seen, the response time for the modulated operation is ≈ 2× faster (t 90 = (2.0 ± 0.2) s vs. (4.1 ± 0.2) s) than for the isothermal operation when responding to 40 µmol/mol of chlorobenzene in dry air. Finally, we conclude by touching on several examples of using more complex ramp/base temperature programs that cover a broader range of temperature-induced sensor-analyte interactions. Here, we examine the potential of the different temperatures in the modulation program for yielding sensor responses that show resilience versus confounding chemicals (e.g., humidity, other analytes) or aging and drift, or those temperatures that maximize the overall response magnitude for particular analytes. This work emphasizes our collaborative research efforts, which have examined a variety of approaches, including those inspired by biological olfaction, to enhance the analytical capabilities of the chemiresistive electronic noses. Ultimately, for the flexibility needed to impact different applications, as well as for obtaining optimized performance, it is important the materials selections, operational mode and data analysis work together synergistically.

Decoration of Co nanoparticles on ZnO-branched SnO2 nanowires to enhance gas sensing

We sputtered zinc-oxide (ZnO)-branched tin oxide (SnO2) nanowires with a Co shell layer with subsequent annealing to produce cobalt (Co) nanoparticles on the ZnO branches. X-ray diffraction, selected area electron diffraction, and lattice-resolve TEM images showed that the nanoparticles corresponded to a hexagonal Co phase. We further studied the NO2 sensing performance of Co-decorated ZnO branched structures in the range of 2–10ppm at 250°C. Sensor characteristics were examined in terms of sensitivity (i.e., sensor response), response time, and recovery time; we further proposed the possible mechanisms of enhancement of sensing behavior by the attachment of Co nanoparticles. Co-functionalization enhanced the sensor response and significantly decreased the recovery times. The Co-decorated ZnO branched structures showed promising sensing performance toward NO2 gas at concentrations as low as 2ppm.

Pt-Decorated Fluorine-Doped Tin Oxide Nanowire Arrays As Highly Sensitive H2O2 sensor Electrodes

Fluorine-doped tin oxide (FTO) nanowre aways were grown on top of commercial FTO glass through a vapor-liquid-solid process, by using Au nanocrystals as the anisotropic growth catalyst, tin powders as the precursor, and NH4F as the fluorine source. This extended 3-D FTO nanostructure was then decorated with Pt nanocrystals, with a polyol method, to serve as a sensing electrode for H2O2. These FTO nanowires not only offer greatly enlarged sensing area and fast charge transport channels, but also significantly enhance the hydrophilicity of the electrode, all beneficial for electrochemical sensing of aqueous samples. A two-order of magnitude improvement in sensitivity toward H2O2 over the plain commercial FTO glass was achieved, reaching a high sensitivity value of 272 mA/M.

Sputtered gold-coated ITO nanowires by alternating depositions from Indium and ITO targets for application in surface-enhanced Raman scattering

Indium Tin oxide (ITO) nanowires were deposited by RF sputtering over oxidized silicon using ITO and Indium targets. The nanowires grew on the substrate with a catalyst layer of Indium by the vapor–liquid–solid (VLS) mechanism. Modifications in the deposition conditions affected the morphology and dimensions of the nanowires. The samples, after being covered with gold, were evaluated as surface-enhanced Raman scattering (SERS) substrates for detection of dye solutions and very good intensifications of the Raman signal were obtained. The SERS performance of the samples was also compared to that of a commercial SERS substrate and the results achieved were similar. To the best of our knowledge, this is the first time ITO nanowires were grown by the sputtering technique using oxide and metal targets.

Indium tin oxide nanowires as hyperbolic metamaterials for near-field radiative heat transfer

We investigate near-field radiative heat transfer between Indium Tin Oxide (ITO) nanowire arrays which behave as type 1 and 2 hyperbolic metamaterials. Using spatial dispersion dependent effective medium theory to model the dielectric function of the nanowires, the impact of filling fraction on the heat transfer is analyzed. Depending on the filling fraction, it is possible to achieve both types of hyperbolic modes. At 150 nm vacuum gap, the heat transfer between the nanowires with 0.5 filling fraction can be 11 times higher than that between two bulk ITOs. For vacuum gaps less than 150 nm the heat transfer increases as the filling fraction decreases. Results obtained from this study will facilitate applications of ITO nanowires as hyperbolic metamaterials for energy systems.

Phototransistor Properties of Indium Tin Oxide Nanowires Grown by RF Sputtering Mechanism and Annealing Process

Photoconducting properties of indium tin oxide (ITO) nanowires grown by RF sputtering associated with annealing process were studied. ITO nanowires have been grown without the use of catalysts or oblique deposition. The cubic cross-sectional nanowires length was of the order of several microns, while their diameter was ~150–250 nm. The photoluminescence (PL) analysis on nanowires proved their excellent photoemission characteristics. Devices based on ITO nanowires showed a substantial increase in conductance of up to three orders of magnitude upon exposure to UV light and showing reproducible UV photoresponse and remaining relatively stable. The rising speed is slightly reduced, while the decay time is prolonged. Such devices also exhibited short response times and significant shifts in the threshold gate voltage. It was found that the dynamic response of the ITO nanowires phototransistor was stable with an on/off current contrast ratio of around 101. It is thus found that the change in the carrier concentrations in constant gate voltage was enhanced by 1.12 × 1017 cm-3 for the 350 nm UV light, corresponding to threshold-voltage shifts of before to after UV-light exposition. The photoconductive gain corresponding to responsivity measured at 350 nm was 0.11 × 105.

Occurrence of non-equilibrium orthorhombic SnO2 phase and its effect in preferentially grown SnO2 nanowires for CO detection

Tin oxide nanowires (NWs) were deposited successfully on silicon substrate. Depending on the distance between the source and substrate, NWs exhibit either a single phase structure or a mixed phase structure, the latter exhibits enhanced sensitivity to CO detection.

Indium Tin Oxide Conductive Nanowires Formed by Magnetron Sputtering

ABSTRACTIndium tin oxide (ITO) nanowires (NWs) were grown on glass substrates by using ITO sputtering sources (targets) with SnO2 contents in the range of approximately 5.0 to 30.0 wt%. NW growth became apparent at temperatures above 125 °C, and the In, Sn and O contents of the resulting ITO NWs were similar to those of the ITO source. NWs grown from ITO sources containing 5.0 to 12.0 wt% SnO2 had circular or elliptical cross-sections, while those obtained from sources with 12.0 to 30.0 wt% SnO2 exhibited square cross-sections. ITO NWs approximately 2 μm in length were obtained as single crystals with a cubic crystal structure. The resistivity of an ITO NW was measured using four nanoprobes in conjunction with a field emission scanning electron microscope and was found to range from 0.13 to 0.6 μΩ-m, values that were approximately one order of magnitude lower than those of transparent ITO films.

Effect of synthesis temperature and N2/O2 flow on morphology and field emission property of SnO2 nanowires

A large amount of tin oxide (SnO2) nanowire arrays were synthesized on the flexible conductive carbon fiber substrate by thermal evaporation of tin powders in a tube furnace. The temperature, as well as the flow rate of the carrier N2 gas and the reaction O2 gas, plays an important role in defining the morphology of the SnO2 nanowires. Morphology and structure of the as-grown SnO2 samples are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). Results show that all the samples possess a typical rutile structure, and no other impurity phases are observed. The morphology changes from rod to wire with the increase of reaction temperature. Ratio of length to diameter of the nanowires increases first and then decreases with the flow ratio of N2/O2 gas. The optimum synthesis conditions of SnO2 nanowire are: reaction temperature 780 ℃, N2 and O2 flow rates being 300 sccm and 3 sccm respectively. In our growth process, the nanowire grows mainly due to the vapor-liquid-solid (VLS) growth process, but both the VLS process and surface diffusion combined with a preferential growth mechanism play the important role in morphology evolution of the SnO2.Field emission measurements for Samples 1-6 are carried out in a vacuum chamber and a diode plate configuration is used. Relationship between the growth orientation, aspect ratio, density and uniformity of the arrays and field emission performances will be investigated first. Results reveal that the field emission performance of SnO2 nanostructures depends on their morphologies and array density. The turn-on electric field (at the current density of 10 upA/cm2) decreases and the emission site density increases with tin oxide array density, and the turn-on electric field of Sample 5 (synthesized at 780 ℃, nitrogen and oxygen flow rates being 300 sccm and 3 sccm respectively) is about 1.03 V/m at a working distance of 500 m. By comparison, for the turn-on electric fields of the not well-aligned SnO2 nanowire arrays we have 1.58, 2.13, 2.42, 1.82, and 1.97 V/m at 500 m. These behaviors indicate that such an ultralow turn-on field emission and marked enhancement in (～ 4670) can be attributed to the better orientation, the good electric contact with the conducting fiber substrate where they grow, and the weaker field-screening effect. Our results demonstrate that well-aligned nanowire arrays, with excellent field-emission performance, grown on fiber substrate can provide the possibility of application in flexible vacuum electron sources.