Vanadium Dioxide Nanostructures Research Articles

Electrical and Optical Switching in Vanadium Dioxide Nanostructures Decorated with Gold Nanoparticles

The electrical parameters of the semiconductor-metal phase transition in vanadium dioxide nanostructures synthesized by chemical vapor deposition on a silicon substrate (100) and decorated with gold nanoparticles with a surface concentration from 3∙109 to 3∙1010 cm–2 are studied. X-ray phase analysis revealed that the synthesized nanostructures of vanadium dioxide contain a monoclinic M1 phase undergoing a phase transition at a temperature of about 68 °C. The morphology of the surface of vanadium dioxide nanostructures coated with gold nanoparticles was studied using a scanning electron microscope and an atomic force microscope. The characteristics of the temperature phase transition of the initial nanostructures and nanostructures decorated with gold nanoparticles are determined. The temperature dependence of the resistance near the phase transition point of the initial nanostructures showed that the resistance jump is about four orders of magnitude, which confirms their high quality. It is shown that an increase in the surface concentration of gold particles to a value of 3∙1010 cm–2 increases the conductivity of vanadium dioxide at room temperature by about two times, and shifts the phase transition temperature by 5 °C: from 68 °C to 63 °C. Optical switching in vanadium dioxide with an array of gold particles with a size of 9 nm is considered by numerical modeling methods. It is established that the response of the electromagnetic wave from the VO2 material during the phase transition is enhanced due to the excitation of localized plasmon resonance in gold nanoparticles and reaches a local maximum in the region of 600 nm. Additionally, this effect is enhanced at angles of incidence near the pseudo-Brewster angle for vanadium dioxide. The considered hybrid VO2–Au nanostructures are promising as basic nanoelements for next-generation computers, as well as for ultrafast and highly sensitive sensors.

Analytical electron microscopy analysis of insulating and metallic phases in nanostructured vanadium dioxide

We utilize analytical electron microscopy with in situ heating to observe the insulator–metal transition in vanadium dioxide and to identify additional vanadium oxides across the sample exhibiting nanoscopic pores and cracks.

A universal chemical approach to the growth of self-assembled vanadium dioxide nanostructures

Vanadium dioxide (VO2) nanocrystalline materials are of great interest as for modern electronics and photonics as well as for energy saving technologies. Nevertheless, there still remains a challenge to realize their controllable synthesis, as evidenced by the low rate of implantation of existing technologies into mass production. Here, a hydrothermal reaction in a water-ethylene glycol (EG) solution has been coupled with the post-deposition annealing, yielding a range of phase-pure vanadium dioxide nanostructures on single-crystal r-sapphire substrate. A directed change in the viscosity of the precursor solution by using a change in the EG : H2O ratio makes it possible to control the nucleation rate and thus form VO2 isolated nanocrystals, as well as their ordered ensembles with regular distribution and uniform films on the substrate. The obtained nanostructures were extensively characterized by Raman spectroscopy, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy combined with energy-dispersive X-ray spectroscopy. Continuous VO2 nanostructures demonstrated a metal-insulator transition (MIT) with a jump in resistivity of about 103–104, as well as a giant terahertz (THz) modulation depth up to 86 % (in the range from 0.3 to 2.0 THz), which confirms their high-quality and the possibility of their use in the creation of functional electronic and THz optical devices.

Chemical Modulation of Metal-Insulator Transition toward Multifunctional Applications in Vanadium Dioxide Nanostructures.

The metal-insulator transition (MIT) of vanadium dioxide (VO2 ) has been of great interest in materials science for both fundamental understanding of strongly correlated physics and a wide range of applications in optics, thermotics, spintronics, and electronics. Due to the merits of chemical interaction with accessibility, versatility, and tunability, chemical modification provides a new perspective to regulate the MIT of VO2 , endowing VO2 with exciting properties and improved functionalities. In the past few years, plenty of efforts have been devoted to exploring innovative chemical approaches for the synthesis and MIT modulation of VO2 nanostructures, greatly contributing to the understanding of electronic correlations and development of MIT-driven functionalities. Here, this comprehensive review summarizes the recent achievements in chemical synthesis of VO2 and its MIT modulation involving hydrogen incorporation, composition engineering, surface modification, and electrochemical gating. The newly appearing phenomena, mechanism of electronic correlation, and structural instability are discussed. Furthermore, progresses related to MIT-driven applications are presented, such as the smart window, optoelectronic detector, thermal microactuator, thermal radiation coating, spintronic device, memristive, and neuromorphic device. Finally, the challenges and prospects in future research of chemical modulation and functional applications of VO2 MIT are also provided.

Recent Progress on Vanadium Dioxide Nanostructures and Devices: Fabrication, Properties, Applications and Perspectives.

Vanadium dioxide (VO2) is a typical metal-insulator transition (MIT) material, which changes from room-temperature monoclinic insulating phase to high-temperature rutile metallic phase. The phase transition of VO2 is accompanied by sudden changes in conductance and optical transmittance. Due to the excellent phase transition characteristics of VO2, it has been widely studied in the applications of electric and optical devices, smart windows, sensors, actuators, etc. In this review, we provide a summary about several phases of VO2 and their corresponding structural features, the typical fabrication methods of VO2 nanostructures (e.g., thin film and low-dimensional structures (LDSs)) and the properties and related applications of VO2. In addition, the challenges and opportunities for VO2 in future studies and applications are also discussed.

Vanadium dioxide nanostructures with remarkable surface-enhanced Raman scattering activity.

Structure and size control are always considered to be effective routes to enhance the sensitivity of materials. Herein, rough VO2 (D) nanostars and nanospheres with highly dense and rough surfaces were synthesized. Accompanied by the properties inherited from the rough VO2 nanospheres, i.e., high adsorption and strong plasma resonance, these VO2 (D) nanospheres exhibit highly sensitive activity as a surface enhanced Raman spectrum substrate. The detection limit of Rhodamine 6G on this semiconductor SERS substrate is as low as 10-9 M.

Vanadium dioxide nanoparticles as a promising sorbent for controlled removal of waterborne fluoroquinolone ciprofloxacin

As recognized by international agencies, the uncontrolled release of antibiotics into global water resources have raised serious water security concerns. Herein, the uptake of a known persistent fluoroquinolone agent (ciprofloxacin; CIP) was studied by characterization of the adsorption properties of a novel metal oxide in aqueous media. Belt-like nanostructured vanadium dioxide (VO2) with specific surface area of 27.6 m2/g was prepared via an hydrothermal process that revealed exceptional chemical and physical properties related to its use as an adsorbent for CIP. The efficiency of the adsorption process was established using the Box–Behnken design (BBD) to determine optimal operational parameters: pH (4–10), contact time (5–60 min), CIP level (25–100 mg/L), and VO2 dosage (0.1–0.5 g/L). The BBD model enabled determination of the optimum CIP removal efficiency by considering different variables such as the adsorbent dosage, mixing time, pH, and CIP concentration. According to the BBD model, the optimized parameters for the highest uptake of CIP (theoretically 100%) are listed: pH 7, mixing time ~ 58.3 min, CIP concentration (27.6 mg/L), and VO2 dosage (0.49 g/L). The maximum adsorption capacity of CIP was calculated as 102.2 mg/g by the Langmuir isotherm model. The pseudo-second order kinetic model revealed that chemisorption was a rate-limiting step for the kinetic uptake process, in agreement with an ion-exchange mechanism based on the role of ionic charge on the adsorbate and adsorbent at the optimized conditions. The separation factor (0.01–0.09) values revealed that the process of CIP removal by VO2 is favorable. Regeneration of the VO2 adsorbent was demonstrated by use of a diluted HCl solution, where a slight decrease (ca. 10%) in the adsorption performance was evidenced over several cycles of adsorption-desorption.

Thermal tracing of a highly reconfigurable and wideband infrared heat sensor based on vanadium dioxide

In this paper, we investigate the thermodynamic properties of a highly reconfigurable and broadband perfect metamaterial absorber in the near-infrared region. Our model is a periodic nanostructure composed of an array of L-shaped hybrid gold and vanadium dioxide nanostructures on gold and glass substrates. The reconfigurability of the nanostructure is based on the metal–insulator transition of vanadium dioxide. The degree of reconfigurability depends on the temperature of the vanadium dioxide nanostructure. In order to study the photo-thermal effect on the reconfigurability of the nanostructure, we irradiate it with a time-dependent Gaussian pulse laser with a 1.5 ns pulse width. Our main purpose is twofold. On the one hand, we aim to investigate how the laser increases the temperature of the nanostructure, and on the other hand, we intend to explore whether the temperature modifies the absorption and reflection of the array. Our results reveal that the VO2 fully transitions to its metallic phase when the fluence of the incident laser is adjusted to 17.8 mJ/cm2.

Suppression of Photoinduced Surface Oxidation of Vanadium Dioxide Nanostructures by Blocking Oxygen Adsorption.

Controlling the surface is necessary to adjust the essential properties and desired functions of nanomaterials and devices. For nanostructured multivalent vanadium oxides, unwanted surface oxidation occurs at ambient atmosphere generally and needs to be suppressed or avoided. We describe the suppressed surface oxidation of VO2 nanostructures through blocking oxygen adsorption. During an enhanced photoinduced surface oxidation process, the increased oxidation states of vanadium in VO2 nanostructures are suppressed by the use of an inert atmosphere or coating. Intermediate oxidation states are observed, and an ALD-TiO2 coating has a good antioxidant capacity for preventing the formation of oxygen-enriched components. Such oxidation suppression is beneficial to improving the stability of VO2 nanostructures. Controllable surface oxidation helps us to understand the physical essentials of surface chemical reactions and achieve better control of surface functions and performances on correlated vanadium oxide nanostructures.

Optical, Magnetic, and Electronic Properties of Nanostructured VO2 Thin Films Grown by Spray Pyrolysis: DFT First Principle Study

In this work, we have grown nanostructured vanadium dioxide (VO2) thin films by a spray pyrolysis coating method on glass pre-heated substrates at 450 °C and studied their optical and electronic properties. As-prepared film structure and morphology, with a thickness of ~ 400 nm, were examined by X-ray diffraction, Raman spectra, and atomic force microscopy (AFM), thus revealing a polycrystalline monoclinic M1 phase. On the other hand, the electrical resistance was measured as a function of the temperature in the range of 25 to 100 °C where a clear transition from the M1 phase at T = 25 °C to the metallic one (conductive phase) at ~ 60 °C was observed. This also confirms the stability of the M1 phase for T < 60 °C. The electronic properties and band structure were additionally investigated by the local density approximation (LDA) using the first principle of the Korringa-Kohn-Rostroker (KKR). As a result, our material showed a magnetic property, specifically an antiferromagnetic stabilization of the M1 phase.

Growth of vanadium dioxide nanostructures on graphene nanosheets

The metal oxide/graphene hybrid nanomaterials have been known as promising functional materials for advanced applications such as high capacitive electrode material of secondary batteries, and high sensitive material of high performance gas sensors. Here, morphology controlled vanadium dioxide (VO2) nanostructures were grown on Si wafer and exfoliated graphene by the vapor transport method using a horizontal furnace system. One-dimensional VO2 nanowires were grown on SiO2(300 nm)/Si substrate under 0.4 kPa condition. On the other hand, thick polycrystalline of VO2 platelets were grown on exfoliated graphene nanosheets under 0.4 kPa condition. In addition, polycrystalline VO2 platelets were only grown on exfoliated graphene nanosheets under 101 kPa (atmospheric pressure) condition. The growth of polycrystalline VO2 platelets on graphene nanosheets in atmospheric pressure condition is attributed to preferential growth on functional group of graphene surface such as carbonyl. The functional group is served as nucleation site of VO2 nanostructures.

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.

A Study on the Effect of Graphene Substrate for Growth of Vanadium Dioxide Nanostructures

A Study on the Effect of Graphene Substrate for Growth of Vanadium Dioxide Nanostructures

Interdependence of Structure, Morphology, and Phase Transitions in CVD Grown VO2 and V2O3 Nanostructures

Phase selective chemical vapor deposition of nanostructured vanadium dioxide (VO2) and sesquioxide (V2O3) was achieved by deploying [V(OR)4]n (R = tBu, n = 1 (1), R = Et, n = 3 (2), R = Me, n = 4 (3)). Use of [V(OtBu)4] (1) produced thin films of monoclinic VO2 (M1) at 700 and 800 °C consisting of anisotropic nanostructures with high crystallinity and small hysteresis in the metal-to-semiconductor transition (MST). Film morphologies manifested strong dependence on growth temperatures and exhibited pronounced texturing effects at high temperatures (>700 °C). The microstructure of the films was found to significantly affect the MST behavior of VO2 films. DTA measurements of VO2 films showed MST at 63 °C (700 °C) and 65 °C (800 °C), much lower than the transition temperature observed in single crystal material (68 °C). Precursors were characterized in the solid state (XRD) and solution state (temperature dependent EPR, NMR) to reveal an association–dissociation equilibrium in solution (complexes 2 and 3), in...

Direct growth of VO2 nanoplatelets on glass and silicon by pulsed laser deposition through substrate temperature control

In this contribution, we explore the influence of substrate temperature on the phase evolution, morphology and transition properties of vanadium dioxide nanostructured thin films grown by pulsed laser deposition technique on glass and silicon substrates. The main objective is to grow directly on the top of substrates surface vanadium dioxide nanostructures with high density and high aspect ratio. Structural analysis using X-ray diffraction method showed highly oriented (011) VO2 films in the temperature range of 500–700°C. Successfully, catalyst free and dense VO2 nanoplatelets were obtained at 600 and 700°C. While the aspect ratio was limited for the nanoplatelets grown on silicon substrate, those grown on glass showed an aspect ratio of around 5. The study of the metal-insulator phase transition using a four probe technique evidenced the effect of the growth temperature on the transition properties through its influence on the stoichiometry, grain size and shape. Mechanisms behind the growth of elongated VO2 nanoplatelets on glass substrate are evidenced throughout substrate nature influence. The amorphous nature of glass which acts as a free standing environment at high temperature is suggested to be the key factor to grow elongated nanoplatelets in an open structure of particular morphology. As summary, using pulsed laser deposition, we have established a one-step growth protocol of dense VO2 nanoplatelets with a high surface-to-volume ratio which can find a potential application in gas sensing devices.

Phase-selective vanadium dioxide (VO2) nanostructured thin films by pulsed laser deposition

Thin films of monoclinic nanostructured vanadium dioxide are notoriously difficult to produce in a selective manner. To date, post-annealing, after pulsed laser deposition (PLD), has been used to revert the crystal phase or to remove impurities, and non-glass substrates have been employed, thus reducing the efficacy of the transparency switching. Here, we overcome these limitations in PLD by optimizing a laser-ablation and deposition process through optical imaging of the laser-induced plasma. We report high quality monoclinic rutile-type vanadium dioxide (VO2) (M1) nanoparticles without post-annealing, and on a glass substrate. Our samples demonstrate a reversible metal-to-insulator transition at ∼43 °C, without any doping, paving the way to switchable transparency in optical materials at room temperature.

Super-resolution in label-free photomodulated reflectivity.

We demonstrate a new, label-free, far-field super-resolution method based on an ultrafast pump-probe scheme oriented toward nanomaterial imaging. A focused pump laser excites a diffraction-limited spatial temperature profile, and the nonlinear changes in reflectance are probed. Enhanced spatial resolution is demonstrated with nanofabricated silicon and vanadium dioxide nanostructures. Using an air objective, resolution of 105 nm was achieved, well beyond the diffraction limit for the pump and probe beams and offering a novel kind of dedicated nanoscopy for materials.

Photoinduced active terahertz metamaterials with nanostructured vanadium dioxide film deposited by sol-gel method.

Applying the photoexcitation characteristics of vanadium dioxide (VO(2)), a dynamic resonant terahertz (THz) functional device with the combination of VO(2) film and dual-resonance metamaterial was suggested to realize the ultrafast external spatial THz wave active manipulation. The designed metamaterial realizes a pass band at 0.28-0.36 THz between the dual-resonant frequencies, and the VO(2) film is applied to control the transmittance of the spatial THz wave. More than an 80% modulation depth has been observed in the statics experiment, and the dynamic experimental results illustrate that this active metamaterial realizes up to a 1 MHz amplitude modulation signal loaded on a 0.34 THz carrier wave without any low noise amplified devices. The electromagnetic properties and photoinduced dynamic characteristics of this structure may have many potential applications in THz functional components, including modulators, intelligent switches, and sensors.

Ultrafast Phase Transition via Catastrophic Phonon Collapse Driven by Plasmonic Hot-Electron Injection

Ultrafast photoinduced phase transitions could revolutionize data-storage and telecommunications technologies by modulating signals in integrated nanocircuits at terahertz speeds. In quantum phase-changing materials (PCMs), microscopic charge, lattice, and orbital degrees of freedom interact cooperatively to modify macroscopic electrical and optical properties. Although these interactions are well documented for bulk single crystals and thin films, little is known about the ultrafast dynamics of nanostructured PCMs when interfaced to another class of materials as in this case to active plasmonic elements. Here, we demonstrate how a mesh of gold nanoparticles, acting as a plasmonic photocathode, induces an ultrafast phase transition in nanostructured vanadium dioxide (VO2) when illuminated by a spectrally resonant femtosecond laser pulse. Hot electrons created by optical excitation of the surface-plasmon resonance in the gold nanomesh are injected ballistically across the Au/VO2 interface to induce a subpicosecond phase transformation in VO2. Density functional calculations show that a critical density of injected electrons leads to a catastrophic collapse of the 6 THz phonon mode, which has been linked in different experiments to VO2 phase transition. The demonstration of subpicosecond phase transformations that are triggered by optically induced electron injection opens the possibility of designing hybrid nanostructures with unique nonequilibrium properties as a critical step for all-optical nanophotonic devices with optimizable switching thresholds.

Competitive growth texture of pulsed laser deposited vanadium dioxide nanostructures on a glass substrate

We report on the crystal structure and morphology of vanadium dioxide (VO2) nanostructures synthesized by pulsed laser deposition on soda-lime glass substrates. The VO2 nanostructures exhibit sharp a-axis diffraction peaks, characteristic of the VO2 monoclinic phase, which implies that highly a-axis textured VO2 was formed. A detailed description of the growth mechanisms and the substrate–film interaction is given, and the characteristics of the electronic transition and hysteresis of the phase transition are described in terms of the morphology and grain boundary structure. The sharpness of the transition and the hysteresis upon heating and cooling are found to be strong functions of the crystal structure and microstructure (grain size and shape).