SnO2 Nanowires Research Articles

Quantitative in situ fracture testing of tin oxide nanowires for lithium ion battery applications

SnO2 is considered as a promising anode material in lithium-ion batteries (LIBs). However, limited work has been focused on tensile mechanical properties and fracture mechanisms of lithiated and delithiated SnO2-based nanomaterials, which is of critical importance for the reliability of LIBs. In this study, in-situ tensile test performed in scanning electron microscope is employed to quantitatively study the tensile fracture of these electrochemically modified SnO2 nanowires (NWs). It is found that the lithiation-delithiation processes can cause a phase transition from crystalline to composite structure, leading to an obvious increase in fracture strain accompanied by plastic deformation, as compared to pristine SnO2 NWs. Meanwhile, the fracture strength and Young's modulus of SnO2 NWs were dramatically reduced. Interestingly, mechanical properties of delithiated SnO2 NWs are generally higher than those of lithiated ones. A finite element model was established based on a linear elastic-to-plastic hardening law to predict the tensile mechanical behaviors of lithiated and delithiated SnO2 NWs. The fitting results are in good agreement with experimental data. This work provides a basic understanding of mechanical characteristics of SnO2-based nanomaterials for LIBs applications.

Selective NO2 sensor based on Bi2O3 branched SnO2 nanowires

We present a highly sensitive and selective NO2 sensor based on Bi2O3 branched SnO2 nanowires (NWs). SnO2 NWs were first synthesized by a vapor-liquid-solid method, were coated with an Au layer, and Bi2O3 branches were grown on their stems by the same procedure used for pure Bi powders. The fabricated sensor showed a high response (Rg/Ra) of 56.92 to 2 ppm of NO2 gas at an optimal temperature. Furthermore, its response to other interfering gases such as ethanol, acetone, toluene, and benzene, was less than 1.55, which demonstrated excellent selectivity of the sensor towards NO2 gas. For comparison and to better understand the sensing mechanism, a pristine SnO2 NWs sensor was also tested. The superior sensing properties of the branched NW sensor relative to the pristine sensor were mainly attributed to the high surface area of the sensor resulting from Bi2O3 branching, as well as the formation of homo-and heterojunctions (Bi2O3-SnO2). In addition, several factors including the presence of Au contributed to the excellent selectivity to NO2 gas. Based on the results obtained in this work, we believe that the present sensor with an easy fabrication method, along with its high sensitivity and selectivity towards NO2, can be used for the detection of NO2 gas in real applications.

Synthesis of SnO2 nanowires forCO, CH4 and CH3OH gases sensing

Synthesis of one-dimensional nanostructures, such as nanowires, is of vigorous significance for achieving the desired properties and fabricating functional devices. In this work, we report the synthesis of tin oxide (SnO2) nanowires on gold-catalyzed silicon substrate by carbothermal reduction process. SnO2 nanowires were synthesized with SnO2 and graphite powders as the source materials at atmospheric pressure and temperature of 900°C in the ambience of nitrogen (N2) gas. First, the effect of source material ratio SnO2:C on growth of SnO2 nanowires was studied. The structural, morphological and compositional properties of the samples were investigated by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. The scanning electron microscopy investigation reveals that uniform dense nanowires of SnO2 (diameter ~127 nm and length ~40 µm) were synthesized with vapour–liquid–solid mechanism. Ultraviolet–visible spectra estimate that the optical band gap of the synthesized SnO2 nanowires was 3.72 eV. Second, the gas sensing performance of synthesized SnO2 nanowires was investigated by testing with carbon monoxide (CO), Methane (CH4) and methanol (CH3OH) gases at different operating temperatures and concentrations. Results indicate that the synthesized SnO2 nanowires are highly promising for gas sensing applications.

In Situ Transmission Electron Microscopy to Uncover Electrochemical Reactions

This talk gives an overview of the PI’s research program on the opportunities and challenges of in situ transmission electron microscopy (TEM) to study novel two dimensional materials and metal oxides for Li-ion and Na-ion battery applications. Various anode materials including SnO2, ZnSb, MnO2 , phosphorene were subjected to lithiation process and the transport of Li ions was visualized within their atomic structure. For SnO2 nanowires, it was observed that the Li ion transport results in local strain development preferably along (200) or (020) plans and [001] crystallographic directions. Extremely fast ionic transport was also observed along [100] directions of phosphorene and in ZnSb crystalline materials indicating that atomic structure engineering of electrode materials can provide an efficient path for the movement of larger ions such as sodium ions overcoming their sluggish kinetics. In one-dimensional materials the structural engineering of tunnels and the tunnel stabilizers can be very effective in allowing the ions to be transported at fast rates. Overall a summary will be given on new science obtained from the in situ TEM studies and how this new information can help to further grow the opportunities in materials designed for electrochemistry.

Low temperature detection of ammonia vapor based on Al-doped SnO2 nanowires prepared by thermal evaporation technique

ABSTRACTWith the growth of nanotechnology during the last few decades, development of novel materials, devices, or other structures possessing at least one dimension in nanoscale has found immense attractions for functional applications. The present work reports the in situ synthesis and ammonia-sensing behavior of pure and Al-doped SnO2 nanowires (NWs) to study the effect of Al3+ incorporation on host SnO2 lattice. The Al-doped SnO2 NWs are deposited by a catalyst-free simple evaporation–condensation method. The average diameter of the NWs ranges within 160–250 nm. We investigated sensitivity, repeatability, and response/recovery time of the as-deposited doped sensor. Responses at five different concentrations (10, 25, 50, 100, and 200 ppm) were investigated by varying the temperature (150–300°C range). The minimum and maximum sensitivity for Al-SnO2 NWs was found to be 35% (10 ppm and 150°C) and the maximum as 73% (200 ppm and 300°C), which is considerably higher than the pristine SnO2 nanostructures. The resistance transients were very sharp and prominent, taking less than 6 s for 90% response. The sensitivity of Al-SnO2 NWs to NH3 vapor witnessed a substantial increase due to the creation of additional oxygen vacancies at the surface of SnO2.

SnO2 Nanowires on Carbon Nanotube Film as a High Performance Anode Material for Flexible Li-ion Batteries

Today, Li-ion batteries (LIBs) are the most common rechargeable batteries used in electronic devices. SnO2 with theoretical specific capacity of 782 mAh/g is among the best anode materials for LIBs. In this report, Three-dimensional SnO2 nanowires (NWs) on carbon nanotube (CNT) thin film (SnO2 / CNT) is fabricated using a combination of vacuum filtration and thermal evaporation techniques. The resulting 3D heterostructure SnO2/CNT was characterized by X-ray diffraction, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). This fabricated SnO2/CNT electrode has been tested as a flexible and binder-free anode for LIB, which exhibits high initial discharge/charge capacity of 4.8/2.25 mAh/cm2 at a current density of 0.25 A/g, much larger than discharge/charge capacity of bare CNT film (2.2/0.3 mAh/cm2). Relatively high areal capacity of 1.23 mAh/cm2 has been achieved for the fabricated LIB with SnO2/CNT electrode after 20 cycles, proposing this material as a high performance flexible LIB anode material.

Enhancing the NO sensing properties of the SnO2 nanowires sensors by Ar–O2 plasma modification

SnO2 nanowires were prepared in an Au-catalyzed VLS growth process by thermal evaporation. The NO sensing properties of the resistive gas sensor based on the SnO2 nanowires was found to be improved obviously after the SnO2 nanowires were treated by Ar–O2 plasma. The responses of the gas sensors to 10, 20, 30, 40, 50 ppm NO gas increased from 8.4, 10.6, 12.6, 14.2, 16.1% to 44.2, 91.9, 108.0, 118.1, 157.4% at 100 °C, respectively. The selectivity of the gas sensors to NO gas against NO2, NH3, CH4, H2 and O2 was also enhanced greatly. The characterization by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy revealed that the enhanced gas sensing properties can be attributed to the rough surfaces, the resultant dangling bond and free lattice sites, and the Sn3O4 grains appearing on the surface of the Ar–O2 plasma treated SnO2 nanowires.

Twin Crystal Induced near Zero Thermal Expansion in SnO2 Nanowires.

Knowledge of controllable thermal expansion is a fundamental issue in the field of materials science and engineering. Direct blocking of the thermal expansions in positive thermal expansion materials is a challenging but fascinating task. Here we report a near zero thermal expansion (ZTE) of SnO2 achieved from twin crystal nanowires, which is highly correlated to the twin boundaries. Local structural evolutions followed by pair distribution function revealed a remarkable thermal local distortion along the twin boundary. Lattice dynamics investigated by Raman scattering evidenced the hardening of phonon frequency induced by the twin crystal compressing, giving rise to the ZTE of SnO2 nanowires. Further DFT calculation of Grüneisen parameters confirms the key role of compressive stress on ZTE. Our results provide an insight into the thermal expansion behavior regarding to twin crystal boundaries, which could be beneficial to the applications.

Microwave-assistant hydrothermal synthesis of SnO2@ZnO hierarchical nanostructures enhanced photocatalytic performance under visible light irradiation

In this paper, for the first time, SnO2@ZnO hierarchical nanostructures (HNSs) were synthesized by a simple two-step microwave-assistant hydrothermal method. Systematical characterization of the SnO2@ZnO HNSs revealed that the rutile SnO2 nanowires (NWs) were uniformly and tightly grown on the entire surface of each ZnO nanoflowers (NFs). The photocatalytic performance of the SnO2@ZnO HNSs showed a remarkably enhanced photocatalytic performance under visible light irradiation (400 nm≤λ ≤ 800 nm). The photoluminescence (PL) spectrum results indicated that the defect related energy level is the main mechanism of the photocatalytic performance under the visible light irradiation. The unique morphology and heterojunction structures in SnO2@ZnO HNSs were the core enhanced mechanism in photodegradation process. The advantage endowed with the microwave-assistant hydrothermal method can result in the efficient spatial charge separation between ZnO nanorods (NRs) and SnO2 NWs and reduce the charge recombination along the heterojunction, which makes SnO2@ZnO HNSs a highly promising for photocatalytic applications.

Effect of Sn/Zn ratio on structure and photoluminescence properties of SnO2@ZnO composites

ABSTRACTThe SnO2@ZnO composites, with Sn/Zn molar ratio (Sn/Zn–ratio) from 4:1 to 8:1, were successfully prepared via two–step hydrothermal method. The microstructure and morphology of the as–prepared Sn/Zn–ratio–dependence SnO2@ZnO composites were investigated. Furthermore, a reasonable growth mechanism of SnO2@ZnO composites was proposed and the results indicated that the dispersity of SnO2 nanowires on the ZnO nanorods surface was obviously influenced by the Sn/Zn–ratio. The photoluminescence (PL) properties of the Sn/Zn–ratio–dependence SnO2@ZnO composites were investigated. The results showed the opposite intensity change of ultraviolet (UV) and visible emission while the Sn/Zn–ratio increased. In addition, the possible emission mechanisms were also discussed that the UV emission is attributed to free–exciton recombination at the near–band edge and the potential difference between SnO2 and ZnO result in the visible emission.

Self-Assembly of Transition Metal Oxide Nanostructures on MXene Nanosheets for Fast and Stable Lithium Storage.

Recently, a new class of 2D materials, i.e., transition metal carbides, nitrides, and carbonitrides known as MXenes, is unveiled with more than 20 types reported one after another. Since they are flexible and conductive, MXenes are expected to compete with graphene and other 2D materials in many applications. Here, a general route is reported to simple self-assembly of transition metal oxide (TMO) nanostructures, including TiO2 nanorods and SnO2 nanowires, on MXene (Ti3 C2 ) nanosheets through van der Waals interactions. The MXene nanosheets, acting as the underlying substrate, not only enable reversible electron and ion transport at the interface but also prevent the TMO nanostructures from aggregation during lithiation/delithiation. The TMO nanostructures, in turn, serve as the spacer to prevent the MXene nanosheets from restacking, thus preserving the active areas from being lost. More importantly, they can contribute extraordinary electrochemical properties, offering short lithium diffusion pathways and additional active sites. The resulting TiO2 /MXene and SnO2 /MXene heterostructures exhibit superior high-rate performance, making them promising high-power and high-energy anode materials for lithium-ion batteries.

Investigation of the Nano-Heterojuntion Electrochemistry Effect By Using in-Situ Spectrum and Electrical Measurement System

In this research, the broadband light (from 365-940 nm) and room temperature gas (NO, CO) sensing can be achieved by using nano-heterojunction (Ge and SnO2 nanowire) device; the detail analysis can be measured by in-situ spectrum and electrical measurement system. The in-situ spectrum and electrical measurement can provide the response immediately to investigate the interface defect, band bending and Joule-heating effect through the response of the devices. For broadband light detection experiment, the visible light (532 nm) beam was illuminated at different parts of the nano-heterjunction device (p-type semiconductor, n-type semiconductor, and interface). The broadband light responses only happen at interface part, not at both nanowires. For gas detection experiment, the Raman spectrum and electrical signal can be used for studying gas molecule and nano-heterjunction dynamics. Base on the abovementioned experiment, we can find the parameters to create and design new nano-device in smart way.

Ultrasensitive NO2 gas sensors using hybrid heterojunctions of multi-walled carbon nanotubes and on-chip grown SnO2 nanowires

Hybrid heterojunction devices are designed for ultrahigh response to NO2 toxic gas. The devices were constructed by assembling multi-walled carbon nanotubes (MWCNTs) on a microelectrode chip bridged bare Pt-electrode and a Pt-electrode with pre-grown SnO2 nanowires (NWs). All heterojunction devices were realized using different types of MWCNTs, which exhibit ultrahigh response to sub-ppm NO2 gas at 50 °C operated in the reverse bias mode. The response to 1 ppm NO2 gas reaches 11300, which is about 100 times higher than that of a back-to-back heterojunction device fabricated from SnO2 NWs and MWCNTs. In addition, the present device exhibits an ultralow detection limit of about 0.68 ppt. The modulation of trap-assisted tunneling current under reverse bias is the main gas-sensing mechanism. This principle device presents a concept for developing gas sensors made of a hybrid between semiconductor metal oxide NWs and CNTs.

Effect of inhomogeneous Schottky barrier height of SnO2 nanowires device

The current–voltage (I–V) characteristics of metal–semiconductor junction (Au–Ni/SnO2/Au–Ni) Schottky barrier in SnO2 nanowires were investigated over a wide temperature range. By using the Schottky–Mott model, the zero bias barrier height ΦB was estimated from I–V characteristics, and it was found to increase with increasing temperature; on the other hand the ideality factor (n) was found to decrease with increasing temperature. The variation in the Schottky barrier and n was attributed to the spatial inhomogeneity of the Schottky barrier height. The experimental I–V characteristics exhibited a Gaussian distribution having mean barrier heights of 0.30 eV and standard deviation σs of 60 meV. Additionally, the Richardson modified constant was obtained to be 70 A cm−2 K−2, leading to an effective mass of 0.58m0. Consequently, the temperature dependence of I–V characteristics of the SnO2 nanowire devices can be successfully explained on the Schottky–Mott theory framework taking into account a Gaussian distribution of barrier heights.

EFFECT OF ANNEALED TEMPERATURE ON NO2 GAS-SENSING PERFORMANCES OF SnO2 NANOWIRE SENSORS

NO2 gas is a highly toxic gas and emitted from vehicles such as motocycles and internal engine transportations. It is one of the major reasons which cause air pollution in recent years, especially in big cities. Therefore, the development of NO2 gas sensor for environmental monitoring has been gained research attention in the global. In this work, we report a simple and effective method to prepare SnO2 nanowire gas sensors. The SnO2 nanowires were directly grown on the unplosihed Al2O3 substrate equipped with a pair of Pt-electrodes. The morphology and microstructure of as-grown nanowires have been investigated via X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and transimission electron microscopy (TEM). The results indicated that the diameters and lengths of nanowires are about 60 – 100 nm and tens of μm, respectively. The gas-sensing performance of the SnO2 nanowires sensors annealed at different temperatures have also investigated. The results revealed that the annealed temperatures of 400 C and 500 oC do not affected on gas-sensing performance of SnO2 nanowires sensors, while the annealed temperature of 600oC results in strong decrease in NO2 gas response as compared with as-grown SnO2 nanowires sensor.

Thermal chemical vapor deposition of tin oxide nanowires in a hydrogen reduction atmosphere

We fabricated tin oxide nanowires (NWs) on Au/Si3N4/Si(001) substrates using thermal chemical vapor deposition (CVD) in a hydrogen reduction atmosphere. Unlike typical thermal CVD conditions, a mixture of H2 and Ar gas was used as the carrier gas, and a catalyst powder such as graphite was not used. The hydrogen gas maintained the reducing atmosphere and easily vaporized the SnO2 powder without a catalyst, to supply vapors of Sn and O. This process enables vapor-liquid-solid (VLS) growth of SnO2 NWs at temperatures below 600 °C. The formation of a eutectic AuSn alloy that acts as a liquid seed during the VLS process contributes to lowering the growth temperature. X-ray diffraction and transmission electron microscopy analysis show that SnO2 NWs and SnO NWs coexist in the as-prepared sample. The oxygen-deficient atmosphere results in nucleation and growth of SnO NWs.

Ethylene Gas Sensing Properties of Tin Oxide Nanowires Synthesized via CVD Method

This paper studies ethylene gas sensing performance of tin oxide (SnO2) nanowires (NWs) as sensing material synthesized using chemical vapor deposition (CVD) technique. The effect of NWs diameter on ethylene gas sensing characteristics were investigated. SnO2 NWs with diameter of ∼40 and ∼240 nm were deposited onto the alumina substrate with printed gold electrodes and tested for sensing characteristic toward ethylene gas. From the finding, the smallest diameter of NWs (42 nm) exhibit fast response and recovery time and higher sensitivity compared to largest diameter of NWs (∼240 nm). Both sensor show good reversibility features for ethylene gas sensor.

Site-Specific Growth and in Situ Integration of Different Nanowire Material Networks on a Single Chip: Toward a Nanowire-Based Electronic Nose for Gas Detection.

A new method for the site-selective synthesis of nanowires has been developed to enable material growth with defined morphology and, at the same time, different composition on the same chip surface. The chemical vapor deposition approach for the growth of these nanowire-based resistive devices using micromembranes can be easily modified and represents a simple, adjustable fabrication process for the direct integration of nanowire meshes in multifunctional devices. This proof-of-concept study includes the deposition of SnO2, WO3, and Ge nanowires on the same chip. The individual resistors exhibit adequate gas sensing responses toward changing gas concentrations of CO, NO2, and humidity diluted in synthetic air. The data have been processed by principal component analysis with cluster responses that can be easily separated, and thus, the devices described herein are in principle suitable for environmental monitoring.

1/2D SnO2 nanowires on MnO2 nanosheets hybrid architecture for reducing fire hazards of epoxy nanocomposites

SnO2 nanowires decorated MnO2 nanosheets hybrids, were prepared and incorporated into epoxy resins to improve the flame retardancy and inhibite the smoke in combustion. SnO2-MnO2 hybrids shows significant improve in flame retardancy, fire toxicity and thermal properties of epoxy nanocomposites, compared to neat epoxy and nanocomposites with a single SnO2 or MnO2. The char residues and glass transition temperature of the epoxy/2 wt% SnO2-MnO2 nanocomposite were remarkably increased. The peak heat release rate of EP/2 wt% SnO2-MnO2 was significantly decreased by 62.9% than that of pure epoxy. TG-FTIR results that the concentration of organic volatiles of epoxy was significantly reduced and the toxic CO was suppressed after incorporating SnO2-MnO2. The physical barrier for SnO2-MnO2 hybrids and the synergism between the catalysis effect of SnO2 and MnO2 can improve the flame retardancy of epoxy resin.

Sb doping of VLS synthesized SnO2 nanowires probed by Raman and XPS spectroscopy

We here report the growth and structural characterization of Sb-doped SnO2 nanowires synthesized by Vapor-Liquid-Solid technique using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray Photoelectron Spectroscopy (XPS) and Raman spectroscopy. Both X-ray diffraction and Raman spectroscopy exhibited typical features of the rutile phase of SnO2 nanowires for all samples. The analysis of XPS confirmed the Sb doping effectiveness. In addition, Raman spectra revealed inactive modes (242 and 284 cm−1) attributed to local structural disorder caused by the incorporation of the dopant into the SnO2 lattice and leading to the breakdown of the Raman selection rules.