VO2 Nanostructures Research Articles

Influence of Al doping on structural, luminescence and electrochemical properties of V2O5 nanostructures synthesized via non-hydrolytic sol-gel technique

Phase pure and Al3+ doped vanadium pentoxide nanostructure materials (AlxV(2-x)O5(x = 0, 0.01, 0.03 and 0.05)) have been synthesized by surfactant-free non-hydrolytic sol-gel route. The effect of dopant concentration on structural, morphological, elemental, luminescence and electrochemical properties was studied for the prepared samples. XRD analysis shows that all the samples possess orthorhombic structure in nature. HRSEM and HRTEM images of Al3+ doped V2O5 nanostructures revealed the morphology of self-assembled nanorods. The presence of elements, V, Al and O with their oxidation states was ensured by FTIR, EDXS and XPS analyses. The DRS-UV–vis and PLE spectral analyses exhibit that the optical band gap of Al:V2O5 nanostructure materials increases with increase in dopant concentration. The CV results reveal that the product has a better cyclic performance and might act as a primary cathode material for high energy density secondary lithium ion batteries.

Light-Enhanced Vanadium Pentoxide (V2O5) Thin Films for Gas Sensor Applications

Generally, semiconductors such as SnO2, ZnO, and Fe2O3 are mostly used for gas detection. However, low sensitivity and high operating temperature limit their optoelectronic application, hence the need for viable alternative semiconductors. Vanadium pentoxide (V2O5) was selected for this study because of its layered structure and different valence states. V2O5 nanostructures were deposited on preheated glass substrates using the spray pyrolysis technique. Structural and morphological properties of the V2O5 nanoparticles were studied using x-ray diffraction (XRD) analysis and field-emission scanning electron microscopy (FESEM). The results reveal an orthorhombic structure with preferred orientation along (001) plane and average grain size of 27.179 nm. A V2O5/SiO2/Si gas sensor device was fabricated by depositing the V2O5 nanostructures on oxidized p-type silicon substrate. The current–voltage (I–V) characteristic and response of the sensor to different concentrations of ethanol and acetone gases at different operating temperatures were investigated. The light-enhanced sensor response was also studied under illumination from a green laser source. The sensing mechanism for the V2O5 nanostructures with and without illumination was also determined. The sensitivity of the V2O5/SiO2/Si gas sensor to ethanol and acetone was higher at low operating temperatures (40°C to 50°C). The gas sensor was more sensitive to ethanol than acetone at room temperature under both dark and illumination conditions. The results also indicated higher sensitivity under light illumination compared with dark conditions. In addition, the fabricated sensor exhibited faster response/recovery time for ethanol (43.493 μs/195.42 μs) than acetone (43.2001 μs/214.17 μs) at exposure duration of 10 min. Therefore, the application of V2O5 nanostructures is promising for detection of both acetone and (particularly) ethanol at low operating temperatures.

Selected‐Area Chemical Nanoengineering of Vanadium Dioxide Nanostructures Through Nonlithographic Direct Writing

AbstractNanoscale selected‐area chemical engineering is challenging but critical to manipulate carrier transport and realize multifunctional characteristics in advanced devices. Undesired chemical contaminants might occur in conventional lithographic processes and would degrade the characteristics of chemical‐sensitive vanadium oxide nanostructures. Here, a facile strategy is introduced to chemically engineer VO2 nanostructures using a nonlithographic direct‐writing process without chemical reagents and sacrificial layers. Nanoscale selected‐area photooxidation promotes the formation of VO2+x patterns in VO2 nanostructures. Selected‐area chemical nanoengineering allows direct designing and engineering of correlated vanadium oxides for controllable Mott field‐effect transistors and memory devices.

Photocatalytic degradation performance of Nd3+ doped V2O5 nanostructures

Bougainvillea flower extract was used as a fuel in solution combustion synthesis of pure and Nd3+ (1–9 mol %) doped vanadium pentoxides (V2O5) nanostructure. Powder x-ray Diffractogram, Scanning electron microscopy and Transmission electron microscopy images revealed the orthorhombic phase in Nd3+ doped V2O5 nanostructure. The additional peaks in Fourier Transform Infrared spectra and in Raman spectra were due to lattice distortion and mixed valence oxide in VO4 led to structural and morphological changes. The synthesized Nd3+ doped V2O5 nanostructure exhibited good photocatalytic activity for the degradation of Methylene blue dye due to decrease in its work function as well as decrease in electron-hole recombination.

Dynamic Photoinduced Controlling of the Large Phase Shift of Terahertz Waves via Vanadium Dioxide Coupling Nanostructures

Utilizing terahertz (THz) waves to transmit data for communication and imaging places high demands on phase modulation. However, until now, it is difficult to realize a more than 100° phase shift in the transmission mode with one-layer structure. In this paper, a ring-dumbbell composite resonator nested with VO2 nanostructures is proposed to achieve the large phase shift. It is found that in this structure a hybrid mode with an enhanced resonant intensity, which is coupled by the L-C resonance and dipole resonance has been observed. Applying the photoinduced phase transition characteristics of VO2, the resonant intensity of the mode can be dynamically controlled, which leads to a large phase shift in the incident THz wave. The dynamic experimental results show that controlling the power of the external laser can achieve a phase shift of up to 138° near 0.6 THz using this one-layer VO2 nested composite structure. Moreover, within a 55 GHz (575–630 GHz) bandwidth, the phase shift exceeds 130°. This attracti...

Growth of <i>a</i>-axis Textured Pulsed Laser Deposited VO<SUB>2</SUB> Nanostructures on Glass Substrate

Vanadium dioxide thin film nanostructures were synthesized by pulsed laser deposition on soda lime glass at a substrate temperature of 600°C and an oxygen ambient pressure of 15 mTorr. The effect of cooling pressure on the crystalline orientation of VO2 nanostructures was investigated. As the cooling oxygen pressure is increased, the VO2 nanostructures exhibit sharp a-axis diffraction peaks, showing the growth of (1 0 0) oriented VO2 on glass, which is characteristic of the VO2 monoclinic phase and implies that pure highly a-axis textured VO2 was formed. We found that the growth mechanism and substrate–film interaction play important roles in the development of these well-textured films via the formation of an interlayer of SiO2.

Epitaxial Growth of Well-Aligned Single-Crystalline VO2 Micro/Nanowires Assisted by Substrate Facet Confinement

Vanadium dioxide (VO2) nanowires/microbeams have attracted great interest recently because of their pronounced single-domain metal–insulator phase transition (MIT) behavior, which is promising for various device applications and deeper mechanism investigation. It is known that monoclinic VO2 nanostructures can be effectively prepared by a simple thermal evaporation method, while the growth of dense and ordered VO2 micro/nanowires with controlled cross sections is still a challenge. In the current study, we have selected different crystal facets as the growth template and achieved controllable growth of well-aligned VO2 micro/nanowire arrays. Combined with the crystal growth simulations, it is clarified that the epitaxial growth of VO2 micro/nanowires on TiO2 substrates is mainly dominated by both the initial crystallization mechanism and confinement of the crystal facets. The current studies not only show the potentials of fabricating VO2 micro/nanowire array-based devices but also demonstrate a facile st...

Superhierarchical Nickel–Vanadia Nanocomposites for Lithium Storage

New materials are critically needed for advanced energy storage devices due to the limited performance of currently used electrodes. We report an alternative approach to fabricate a novel class of nanostructured cathodes with a three-dimensional configuration that shows superior performance. A superhierarchical Ni/porous-Ni/V2O5 nanocomposite is designed and synthesized using a simple electrodeposition process followed by a hydrothermal treatment. Hierarchical V2O5 nanostructures are deposited directly on a Ni microchanneled current collector. Morphological characterization shows that two-dimensional V2O5 nanosheets are uniformly distributed on the porous Ni substrate. A peony-like V2O5 microstructure arises having a diameter of ∼4 μm. The superhierarchical Ni/porous-Ni/V2O5 nanocomposite exhibits superior electrochemical performance as a binder-free cathode. Its maximum reversible discharge capacity reaches 165.6 mAh g–1 at 0.2 C, which is higher than the theoretical capacity of bulk V2O5 cathodes. The c...

A Novel and One‐pot Green Synthesis of Vanadium Oxide Nanorods Using a Phytomolecule Isolated from Phyllanthus amarus

AbstractThe nanorods of vanadium oxide (V2O5) is synthesized by environmentally benign synthetic approach using a phytomolecule, 4‐(3‐(3,4‐dimethoxybenzyl)‐4‐methoxy‐2‐(methoxymethyl)butyl)‐3,6‐dimethoxybenzene‐1,2‐diol, isolated from Phyllanthus amarus. The rod shaped V2O5 nanostructures with the widths about 10–60 nm and the lengths reaching up to 1.5 μm was evident from scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. The orthorhombic structure of V2O5 is apparent from X‐ray diffraction (XRD) results. Furthermore, the crystalline nature of V2O5 nanorods was supported by the results of high‐resolution TEM (HRTEM) and selected area electron diffraction (SAED) analysis, which showed that the interplanar distance between two lattice fringes is 0.33 nm corresponding to (001) reflection plane. The X‐ray photoelectron spectroscopic (XPS) studies revealed that the peak at 533.6 eV indicates the presence of metal oxide and also confirms that the oxidation state of vanadium in as‐prepared V2O5 is V5+. The scission of supercoiled plasmid DNA was observed from 2D gel‐image, which clearly indicated that the propensity of plasmid cleavage increases with increase in concentration of V2O5 nanorods. Interestingly, high degree of cell viability with relatively less cytotoxicity was observed for V2O5 nanorods than phytomolecule in comparison with standard drug, Methotrexate against breast cancer cell line MDA MB 231 and MCF 12 A human cell line, respectively.

Structural, optical and electrical properties of pure and Fe doped V2O5 nanoparticles for junction diode fabrications

Structural, optical and electrical studies of V2O5 and FexV2O5 (x = 5%) nanostructures synthesized by a wet chemical method have been reported. The synthesized nanostructures were characterized by XRD, SEM–EDX, HRTEM, XPS, UV(DRS), FT-IR, PL, TG–DTA, AC and DC conductivity study’s. The anorthic phase was observed in the XRD patterns of undoped and Fe doped samples which are prepared at low temperature. This anorthic phase was reduced with the heat treatment and gradually transformed into orthorhombic phase in the samples annealed at 600 °C for 1 h. The change in the surface morphology in the present samples from micro-rod to nanorods network seems to be dependent on the substitution of Fe. As observed from the PL analysis that the ultraviolet (UV) emission intensity was found to be decreased and exhibited a blue shift with the increase of Fe concentration. The analysis of AC and DC conductivity measurements recorded at room temperature in the temperature range of 303–403 K, revealed that the activation energy is high for Fe doped V2O5 compared to undoped V2O5. The junction diodes of n-V2O5/p-Si and V2O5:Fe/p-Si was successfully prepared by the nebulizer spray pyrolysis method. The (I–V) characteristics of nonlinear and asymmetric nature revealed the Schottky diode based behavior for pure and doped samples.

Shape control VO2 nanorods prepared by soft chemistry and electrochemical method

“Bottom up” approach is of primary interest for chemistry and materials science because the fundamental building blocks are atoms. Thus colloidal chemical synthetic methods can be utilized to prepare uniform nanocrystals with controlled particle size. In the following work of study, thermochromic VO2 nanostructures were prepared by hydrothermal technique soft chemistry. We concentrate on solution phase synthetic methods that enable a proper shape and size control of metal oxide nanocrystals. Their structural properties were studied by Scanning Electron Microscopy (SEM), Fourier Transform IR (FTIR) and Differential Scanning Calorimetry (DSC). It is demonstrated that the surfactant assistance (NaOH) has great influence on the morphology-control of the material. Electrochemical properties of the nanospheres show good stability after 20 cycles and the surface diffusion coefficient was calculated to be 5 × 10−6 cm2 s−1.

Spectroscopic study of native defects in the semiconductor to metal phase transition in V2O5 nanostructure

Vanadium is a transition metal with multiple oxidation states and V2O5 is the most stable form among them. Besides catalysis, chemical sensing, and photo-chromatic applications, V2O5 is also reported to exhibit a semiconductor to metal transition (SMT) at a temperature range of 530–560 K. Even though there are debates in using the term “SMT” for V2O5, the metallic behavior above the transition temperature and its origin are of great interest in the scientific community. In this study, V2O5 nanostructures were deposited on a SiO2/Si substrate by the vapour transport method using Au as a catalyst. Temperature dependent electrical measurement confirms the SMT in V2O5 without any structural change. Temperature dependent photoluminescence analysis proves the appearance of oxygen vacancy related peaks due to reduction of V2O5 above the transition temperature, as also inferred from temperature dependent Raman spectroscopic studies. The newly evolved defect levels in the V2O5 electronic structure with increasing temperature are also understood from the downward shift of the bottom most split-off conduction bands due to breakdown of pdπ bonds leading to metallic behavior in V2O5 above the transition temperature.

First-Principles Analysis of Li Intercalation in VO2(B)

Bronze-phase vanadium dioxide VO2(B) is notable as a promising cathode material for high-capacity Li ion batteries. While various forms of VO2(B) nanostructures have been experimentally investigated, a comprehensive theoretical understanding of the lithium storage mechanism is still lacking. In this research, we examine the redox mechanism, structural evolution, electronic characteristics, and the kinetics of Li ion diffusion in VO2(B) by first-principles calculations. The impact of the surface environment on the Li ion insertion properties is also investigated. Our study demonstrates that, although VO2(B) is capable of incorporating one Li per formula unit from a thermodynamic perspective, its actual capacity can be much less due to kinetic factors. Energy barrier calculations reveal a pronounced compositional dependence of Li diffusion in bulk VO2(B): the b axis tunnels, which account for the excellent Li diffusivity at low Li content, become blocked when Li concentration goes up. The equilibrium surfac...

Size- and Interface-Modulated Metal-Insulator Transition in Solution-Synthesized Nanoscale VO2 -TiO2 -VO2 Heterostructures.

The M1 form of vanadium dioxide, which exhibits a reversible insulator-metal transition above room temperature, has been incorporated into nanoscale heterostructures through solution-phase epitaxial growth on the tips of rutile TiO2 nanorods. Four distinct classes of VO2 -TiO2 -VO2 nanorod heterostructures are accessible by modulating the growth conditions. Each type of VO2 -TiO2 -VO2 nanostructure has a different insulator-metal transition temperature that depends on the VO2 domain sizes and the TiO2 -VO2 interfacial strain characteristics.

Design and development of graphene intercalated V2O5 nanosheets based electrochemical sensors for effective determination of potentially hazardous 3,5–Dichlorophenol

In the present work, we present the facial synthesis of reduced graphene oxide (Gr) intercalated–vanadium pentoxide (Gr–V2O5) nanosheets with varying wt % of graphene oxide (GO) (1 wt% – 5 wt%) into V2O5 layers. Physio–chemical properties of as prepared V2O5 and Gr–V2O5 nanosheets were characterized by XRD, XPS, Raman, FTIR, FESEM and HRTEM techniques. Results reveals that the Gr was effectively intercalated into V2O5 nanostructures and morphology of V2O5 was tuned from nanorods to nanosheets. Further, the Gr–V2O5 nanosheets on modified glassy carbon electrode (Gr–V2O5/GCE) was fabricated and utilized for electrochemical characterization. Under the optimized conditions, the modified electrodes is a simple and versatile tool for electrochemical detection of potentially hazardous 3,5–Dichlorophenol (DCp) with the wide concentration range between 1.9 × 10−8 M to 2.2 × 10−4 M. The modified electrode possesses highly selective and it can able to detect DCp at nanomolar concentration (5 nM) with a high sensitivity of 0.3577 μAμM−1. The modified electrode exhibits good reproducibility, high stability and also has promising electrochemical oxidation behavior of DCp in environmental samples even in presence of common interfering electroactive species. In view of analytical application, our proposed sensor could be directly employed for the electrochemical detection of DCp in industrial wastes, river water and sediment soil dispersion, without any pre–treatment.

High Capacity Carbon-Coated Honeycomb Ni-Mn-Co-O Inverse Opal Anode for Li-Ion Batteries

In recent years Li-ion batteries have been the subject of an extensive research effort aimed at improving their performance for ever more demanding energy storage applications. (1, 2) The demands from consumer devices such as smartphones as well as electric vehicles have necessitated studies into the development of active materials with higher specific capacities and enhanced cycle-lives. With regards to anode materials three distinct classes of materials are being investigated namely, intercalation mode, alloying mode and conversion mode materials.(3-5) Conversion mode materials store charge via the transformation of a transition metal oxide (e.g. Co3O4, MnO etc.) to its parent metal and LiO2 during charging, with the metal being oxidised during discharge (for anodes).(6) Higher specific capacity values can be facilitated from these reactions than typically seen for intercalation materials and consequently, there has been an increase in the interest in the development of conversion mode materials. In this work, we present the formation of a carbon-coated honeycomb ternary Ni-Mn-Co-O inverse opal (IO) as a conversion mode anode material for Li-ion battery applications. Ni-Mn-Co-O (IO) samples are systemically structurally characterised via a combination of analytical techniques, including X-ray diffraction, X-ray photoelectron spectroscopy, electron microscopy, electron diffraction, Raman spectroscopy and Energy-dispersive X-ray spectroscopy. This Ni-Mn-Co-O oxide material is unlike the classic lithiated NMC cathode material (LiNi0.33Mn0.33Co0.33O2) and functions as a conversion mode anode material. The electrochemical performance of the Ni-Mn-Co-O material is evaluated through analysis of results obtained from cyclic voltammetry, rate capability testing and galvanostatic charging and discharging. The effect of ordering is investigated by comparing the performance of highly ordered, porous Ni-Mn-Co-O IO samples with disordered Ni-Mn-Co-O nanoparticles. We demonstrate that ordering and electrolyte additives have a profound influence of the specific capacity values and the capacity retention observed for our Ni-Mn-Co-O anode materials. In order to investigate the practical potential of C-coated Ni-Mn-Co-O IO anodes, they were tested in a full cell arrangement against a V2O5 IO cathode. Similar to our previous work, the Ni-Mn-Co-O IO anode was electrochemically pre-charged by a single charge against a Li metal counter electrode before being paired with a V2O5 IO cathode.(7) We demonstrate that the capacity values obtained the V2O5 IO/Ni-Mn-Co-O IO full cells are greater than previously reported values for V2O5 nanostructures cycled against Li in a half cell configuration.(8) Acknowledgements This work was also supported by Science Foundation Ireland (SFI) through an SFI Technology Innovation and Development Award under contract no. 13/TIDA/E2761. This research has received funding from the Seventh Framework Programme FP7/2007-2013 (Project STABLE) under grant agreement no. 314508. This publication has also emanated from research supported in part by a research grant from SFI under Grant Number 14/IA/2581.

Phase transition study in strongly correlated VO2 based sensing systems

Intermediate phase monoclinic M2 was observed by inducing in situ X-ray thermo diffraction on VO2 (M) nanoplatelets. The solid-solid phase transition occurs at around 65°C assisted with the percolative transition metal-insulator. The existence of an intermediate crystalline phase with room temperature insulator phase and high temperature metallic phase across MIT in VO2 could be of relevance to understand structural contributions to the phase transition dynamics. In addition, pellet of VO2 nanostructures have shown to present good sensing properties to various alcohols vapors at room temperature and good selectivity of methanol with 5.54% sensitivity and limit detection below 5ppm, compared to isopropanol 3.2% and acetone 2.4% respectively.

Polycrystalline V2O5/Na0.33V2O5 electrode material for Li+ ion redox supercapacitor

This work essentially offers a new kind of V2O5/Na0.33V2O5 as electrochemical active material for the development of Li+ ion redox supercapacitors. Here, polycrystalline mixed phase of V2O5/Na0.33V2O5 (V/Na) nanostructures are synthesized via simple co-precipitation technique. The various molar ratio of precipitator (NaOH) in the synthesis process displays different nanostructures of V/Na. The structural and morphological properties of V/Na samples are studied using physico-chemical analysis methods. The electrochemical properties of V/Na nanostructured samples are performed using cyclic voltammetry, galvanostatic charge/discharge test and electrochemical impedance spectroscopy techniques in 1M LiClO4 aqueous electrolyte. The sample V/Na synthesized using equimolar ratio of vanadium salt and precipitator displayed nanopellet morphology, which exhibited the highest capacitance value of 334Fg−1 at 1 Ag−1 discharge current density. Moreover, these polycrystalline V/Na nanostructured electrodes show excellent electrochemical properties with comparable stability after 1000 charge/discharge cycles.

Enhanced electrochemical performance of orientated VO2(B) raft-like nanobelt arrays through direct lithiation for lithium ion batteries

Lithiation modification of VO2(B) has been carried out by a facile hydrothermal process, and the compact and locally ordered VO2(B) raft-like nanobelt arrays have been prepared. The synthesis route provides a new approach to elaborate a VO2(B) nanostructure under a mild environment condition. It is found that the growth mechanism of VO2(B) raft-like nanobelt arrays is different from the traditional nucleation-growth process. A novel chemical lithiating–exfoliating–splitting model is proposed. Compared with the bulk counterpart, the lithiated VO2(B) raft-like nanobelt arrays as cathodes exhibit a higher discharge capacity and an enhanced high-rate performance owing to their increased structural anisotropy and decreased polarization. This work indicates that VO2(B) raft-like nanobelt arrays have great potential applications as cathode materials for lithium ion batteries.

Phase evolution and infrared transmittance in monophasic VO2 synthesized by a rapid non-equilibrium process

VO2 displays a semiconducting to metallic (SMT) transition accessible near room temperature. This makes it one of the most sought after materials for electrical and optical switching. But this can be utilized only when the synthesis process yields phase pure VO2 without other oxides of vanadium. Across the SMT, VO2 exhibits difference crystal structures with a rich phase behavior of insulating monoclinic M1, M2 and T phases. The objective of this study is to synthesize phase pure VO2 and to investigate its structural evolution and infrared switching during the transition. In this work, a rapid non-equilibrium process namely Solution Combustion Synthesis (SCS) was employed. The structural phase transition (SPT) of VO2 nanostructures synthesized by SCS was investigated by in-situ temperature controlled XRD across the SMT. Gaussian curve fittings for measured XRD patterns revealed that competing phases of M1 and R significantly contribute to the observed pattern at every increase in temperature. The powders were further characterized by FTIR, DSC and DC electrical conductivity. These studies show that a sharp SMT was observed at 68–70 °C. Infrared transmittance experiments pinpointed the transition. Carrier density and mobility of VO2 were calculated. This suggests that this VO2 thus synthesized displays excellent phase transition behavior and can be utilized in optical and electrical switching.