Transition In Vanadium Dioxide Research Articles

Design of switchable, narrowband thermal absorption peaks in metal-vanadium-dioxide gratings

We design structures with switchable, narrowband thermal absorption peaks, based on metallic gratings incorporating phase-change materials. An insulator-to-metal phase transition in vanadium dioxide is used to turn the coupling between a surface plasmon mode and a normally incident electromagnetic wave on and off. We analyze the limits on absorptive switching within the framework of coupled-mode theory, in order to evaluate the optimality of specific designs.

Controllable phase-transition temperature upon strain release in VO2/MgF2 epitaxial films

Metal-to-insulator transition (MIT) behaviors accompanied by a rapidly reversible phase transition in vanadium dioxide (VO2) have gained much attention from researchers. In this research, lattice-mismatched epitaxial films of VO2 (210) on MgF2 (111) substrates exhibited different phase-transition temperatures and developed a phase regulation of misfit dislocations. It reveals an “effective phase-transition regulation” for VO2 films with different thicknesses in certain substrates—MgF2. It is speculated that the dislocation density could progressively increase with the increasing thickness of the film, and the dislocation spacing distribution tends to become narrower. When the thickness of the film is close to a certain thickness, the misfit dislocation density is close to saturation for full relaxation. The misfit dislocation arrangement produces hysteresis loops of different widths upon resistance and transmittance: when the width of the transmittance hysteresis loop is narrow at 3.9 °C, and the resistance hysteresis loop can reach the largest width at 14.0 °C. Further research about the hysteresis with other substrates and the thickness-dependent transition temperature showed that the variance of hysteresis properties during the phase transition can be ascribed to the different strain states along the V–V chains and the change of the hybrid t2g-orbital occupancy. In addition, critical thickness along the growth direction is also discussed, which could be identified by the experimental results. This research provides a comprehensive understanding of the strain effect on phase-transition behaviors and also could be a guidance for some potential applications in optoelectronic devices.

Electro-Thermal Simulation of Vertical VO2 Thermal-Electronic Circuit Elements

Advancement of classical silicon-based circuit technology is approaching maturity and saturation. The worldwide research is now focusing wide range of potential technologies for the “More than Moore” era. One of these technologies is thermal-electronic logic circuits based on the semiconductor-to-metal phase transition of vanadium dioxide, a possible future logic circuits to replace the conventional circuits. In thermal-electronic circuits, information flows in a combination of thermal and electronic signals. Design of these circuits will be possible once appropriate device models become available. Characteristics of vanadium dioxide are under research by preparing structures in laboratory and their validation by simulation models. Modeling and simulation of these devices is challenging due to several nonlinearities, discussed in this article. Introduction of custom finite volumes method simulator has however improved handling of special properties of vanadium dioxide. This paper presents modeling and electro-thermal simulation of vertically structured devices of different dimensions, 10 nm to 300 nm layer thicknesses and 200 nm to 30 μm radii. Results of this research will facilitate determination of sample sizes in the next phase of device modeling.

Role of the lattice in the light-induced insulator-to-metal transition in vanadium dioxide

VO$_{2}$ is a model material system which exhibits a metal to insulator transition at 67$^\circ$C. This holds potential for future ultrafast switching in memory devices, but typically requires a purely electronic process to avoid the slow lattice response. The role of lattice vibrations is thus important, but it is not well understood and it has been a long-standing source of controversy. We use a combination of ultrafast spectroscopy and ab initio quantum calculations to unveil the mechanism responsible for the transition. We identify an atypical Peierls vibrational mode which acts as a trigger for the transition. This rules out the long standing paradigm of a purely electronic Mott transition in VO$_{2}$; however, we found a new electron-phonon pathway for a purely reversible electronic transition in a true bi-stable fashion under specific conditions. This transition is very atypical, as it involves purely charge-like excitations and requires only small nuclear displacement. Our findings will prompt the design of future ultrafast electro-resistive non-volatile memory devices.

Vanadium Dioxide for Reconfigurable Antennas and Microwave Devices: Enabling RF Reconfigurability Through Smart Materials

We present a comprehensive study of a new method to reconfigure, tune, and/or program antennas and radio-frequency (RF) devices. The method consists of using electrical signals to induce the solid-tosolid phase transition in vanadium dioxide (VO2) thin-film patterned structures that connect the device metallization layer with extensions, thus effectively changing the geometry of the device. Applied voltage pulses to a resistive heater electrically isolated from the antenna metallization layers increase the temperature of the VO2 strip across the phase transition. Hence, the VO2-biasing mechanism and the antenna are electrically decoupled, which enables an additional degree of freedom for antenna and microwave device engineers as the reconfiguration is no longer restricted by any biasing network limitations. Radiation patterns are also maintained unaffected. This decoupling adds into the design spectrum, applications that require wideband tuning, low-loss structures (e.g., arrays and reflectarrays), and even reconfigurable cloaks. The VO2 switch is arguably the smallest ever used to reconfigure an antenna, which requires further circuit element considerations. The presented method is validated through a series of antenna prototypes that demonstrate VO2 applicability on wire and aperture antennas. Details and challenges of the monolithic integration of VO2 thin films and resistive heaters for reconfigurable antennas, along with the measurement setup, are presented. Results unveil this new reconfiguration technique and suggest further applications, as the VO2 may also be activated optically.

Impact of ion irradiation, elemental doping and coating cycles on structural characteristic parameters of nanocrystalline VO 2 thin films

The origin of the structural phase transition in vanadium dioxide (VO 2 ) has been the subject of immense disagreement in spite of decades of research carried out to comprehend this intriguing phenomenon. Diverse models have been developed to elucidate the obscure theory in order to corroborate assorted experimental results. Herein, the influence of swift heavy ion irradiation, elemental doping and coating cycles on the structural properties of thin films synthesised by sol-gel technique and deposited by spin coater on alumina and glass substrates is investigated. The thin films were characterised by X-ray diffractometry and the XRD spectra obtained at 1E11, 5E11, 1E12 ion beam fluances of 200 MeV Ag 9+ -ion irradiation; at 1, 3, 5% of Mo 6+ -ion doping and at different spin coating cycles were analysed to probe the influence of these effects on the structural characteristic parameters of nanocrystallites in VO 2 thin films. This aspect of VO 2 thin films has not been investigated to its full capacity and consequently, not reported in the scientific literature.

In-plane orientation-dependent metal-insulator transition in vanadium dioxide induced by sublattice strain engineering

Selectively modulating the sublattices in 3D transition metal oxides via strains could tailor the electronic configurations with emerging anomalous properties, which provides new platforms for fundamental researches as well as designs of devices. Here, we report tailoring the oxygen octahedral sublattices in vanadium dioxide (VO2) thin films by anisotropic in-plane strains, and the observation of in-plane orientation-dependent metal–insulator transition. Through multimodal characterizations based on high-resolution X-ray diffraction, electrical transport measurements, and polarization-dependent X-ray absorption spectroscopy at different temperatures, we demonstrate that nonequal strains were successfully induced along A and B oxygen octahedral chains in VO2 films via a special design of epitaxial growth on vicinal substrates. The V 3d1 orbital configurations are modulated in the two oxygen octahedral chains, resulting in in-plane orientation-dependent metal–insulator transition behaviors such as reduced hysteresis width and anisotropic phase transition temperature. This work provides new fundamental insights on metal–insulator transitions, and more importantly, opens up new opportunities for material and device developments

Metal Insulator Transition in Vanadium Dioxide Hydrated by Means of the Plasma-Immersion Ion Implantation Method

In the work, we explore the modification of the structure of vanadium dioxide films, as well as the metal-semiconductor phase transition in them, when hydrated by the method of plasma-immersion ion implantation. Based on a detailed X-ray analysis and the Raman spectra of the initial and hydrated films, it is shown that the plasma-ion modification of the transition and the metallization of vanadium dioxide (at a hydrogen concentration above 10at. %) are most likely associated with electron-correlation effects amplified by hydrogen implantation and an increase in the free charge carrier density in the material.

Tunable Optical Antennas Using Vanadium Dioxide Metal-Insulator Phase Transitions

Here, we investigate the possibility of exploiting the insulator-to-metal transition in vanadium dioxide (VO2) to tune and optically control the resonances of dipole nanoantennas in the visible near-infrared region. We compare the results obtained in the case of antennas completely made by VO2 with those of previous works and highlight the key role of the substrate to perform dynamical tuning. We also present a highly efficient configuration composed of dipole gold antenna loaded with VO2 and give some general guidelines to optimally exploit phase transitions to tune nanodevices.

Dynamic-Metasurface-Based Cavity Structures for Enhanced Absorption and Phase Modulation

Metasurface-based optical cavity structures consist of a metallic metasurface realized on top of a dielectric slab backed with a metal plane. Such structures have been employed in the design of optical devices such as flat lenses, wave plates, and holograms at frequencies from microwave to mid-infrared. Recently, such structures with dynamically reconfigurable optical characteristics have been explored for electrically tunable optical absorption and reflection phase modulation. To date, absorption modulation and phase modulation have been realized with large insertion loss. In this work, we employ an analytical approach based on transmission line theory where the metasurface is represented by a surface admittance. We extend the above approach for the design and analysis of under- and overcoupled resonance regimes in the metasurface cavity structure. This enables a mutual design of cavity thickness and individual metasurface for large amplitude or phase modulation. A dynamic-metasurface-based optical cavity is experimentally demonstrated at terahertz frequencies where the dynamic metasurface consists of metallic resonators embedded with thin-film vanadium dioxide patches. By driving an insulator to metal transition in vanadium dioxide, the terahertz optical response of the metasurface-based cavity structure is modulated. The fabricated device exhibits perfect absorption modulation and reflection phase modulation up to 180°. The reported results demonstrate the potential of such structures for realizing novel devices such as tunable holograms, high-efficiency modulators, and frequency-tunable filters at terahertz. The analytical approach presented here can be applied to the analysis and design of metasurface cavity structures based on other material systems at frequencies ranging from terahertz to mid-infrared.

Effect of photo-irradiation on metal insulator transition in vanadium dioxide

We report a large transition temperature (TC) decrease in a VO2 thin film device under photo-irradiation. With the increasing photo-irradiation intensity (PIntensity) with a wavelength of 405 nm, the TC of the VO2 device decreased at a rate of ∼3.2×10−2°CW/cm2 and reached as low as 40.0 °C at a PIntensity of 8.4×102 W/cm2. While the change in TC is primarily due to the photothermal effect when the PIntensity is below 3.6×102 W/cm2, both the photothermal and photo-induced carrier density effects contribute to the change in TC when the PIntensity is above 6.4×102 W/cm2.

Snapshots of a phase transition

Physics![Figure][1] Depiction of the insulator-to-metal transition of vanadium dioxide CREDIT: GREG STEWART/SLAC NATIONAL ACCELERATOR LABORATORY Time-resolved x-ray scattering can be used to investigate the dynamics of materials during the switch from one structural phase to another. So far, methods provide an ensemble average and may miss crucial aspects of the detailed mechanisms at play. Wall et al. used a total-scattering technique to probe the dynamics of the ultrafast insulator-to-metal transition of vanadium dioxide (VO2) (see the Perspective by Cavalleri). Femtosecond x-ray pulses provide access to the time- and momentum-resolved dynamics of the structural transition. Their results show that the photoinduced transition is of the order-disorder type, driven by an ultrafast change in the lattice potential that suddenly unlocks the vanadium atoms and yields large-amplitude uncorrelated motions, rather than occurring through a coherent displacive mechanism. Science , this issue p. [572][2]; see also p. [525][3] [1]: pending:yes [2]: /lookup/doi/10.1126/science.aau3873 [3]: /lookup/doi/10.1126/science.aav2019

Enhancement of thermal conductivity across the metal-insulator transition in vanadium dioxide

Metal-to-insulator transition (MIT) in vanadium dioxide (VO2) was investigated by electrical and thermal transport measurements. We report an order-of-magnitude enhancement of thermal conductivity across the MIT region in the VO2 single crystal. The magnetic field dependent measurement reveals that the thermal conductivity peak does not show an obvious dependence on the magnetic field, which indicates that the enhancement of thermal conductivity could come from neutral heat carriers such as phonons. Our experiment provides a direction of achieving thermal management in phase-change materials.

Vanadium dioxide based frequency tunable metasurface filters for realizing reconfigurable terahertz optical phase and polarization control.

Metasurfaces are two dimensional arrays of artificial subwavelength resonators, which can manipulate the amplitude and phase profile of incident electromagnetic fields. To date, limited progress has been achieved in realizing reconfigurable phase control of incident waves using metasurfaces. Here, an active metasurface is presented, whose resonance frequency can be tuned by employing insulator to metal transition in vanadium dioxide. By virtue of the phase jump accompanied by the resonance frequency tuning, the proposed metasurface acts as a phase shifter at THz frequency. It is further demonstrated that by appropriately tailoring the anisotropy of the metasurface, the observed phase shift can be used to switch the transmitted polarization from circular to approximately linear. This work thus shows potential for reconfigurable phase and polarization control at THz frequencies using vanadium dioxide based frequency tunable metasurfaces.

Switching Channel Development Dynamics in Planar Structures on the Basis of Vanadium Dioxide

The results of the experimental studies and numerical simulation of the switching channel development dynamics in planar structures on the basis of vanadium dioxide are reported. The obtained data on the variation of the temperature in the channel with time and of the current arisen after the pulsed load, and on the times of transition from the high-resistance to the low-resistance state and back are analyzed in order to determine the switching mechanism and to predict the functional characteristics of the switchable vanadium- oxide structures as promising materials for the creation of relaxation generators that can serve as prototypes of neural oscillators. It is shown that the switching behavior is associated with the metal–semiconductor phase transition in vanadium dioxide, which is stimulated by the emission of Joule heat.

Vanadium Dioxide Integrated Metasurfaces with Switchable Functionalities at Terahertz Frequencies

AbstractIntegration of switchable and diversified functionalities into a single metasurface has become an emerging research area that requires dealing with formidable challenges, especially for terahertz (THz) frequencies. Here, polarization‐insensitive and switchable THz metasurfaces are proposed with diversified functionalities that exploit insulator‐to‐metal transition in vanadium dioxide (VO2). The simulations demonstrate that the designed metasurface can be switched from a broadband absorber to a reflecting broadband halfwave plate (HWP). At room temperature, the metasurface efficiently absorbs normally incident waves ranging from 0.562 to 1.232 THz with the total absorption exceeding 90%. Once the temperature is high enough and VO2 is in its fully metallic state, the metasurface becomes a broadband HWP reflecting over 60% of the incident power with the linear polarization conversion efficiency exceeding 95% within the bandwidth of 0.49 THz. Moreover, the broadband performance is sustained over a wide range of incident angles. To extend the functionalities, metasurface supercell made of several VO2 antennas is integrated, consequently achieving directional polarization conversion when VO2 is in its fully metallic state while maintaining broadband absorption at insulating state. The proposed switchable metasurfaces are expected to enable advanced research and smart applications related to other tunable and diverse functionalities at THz frequencies.

Erratum: Computation of the Correlated Metal-Insulator Transition in Vanadium Dioxide from First Principles [Phys. Rev. Lett. 114, 176401 (2015)

This corrects the article DOI: 10.1103/PhysRevLett.114.176401.

Динамика развития канала переключения в планарных структурах на основе диоксида ванадия

AbstractThe results of the experimental studies and numerical simulation of the switching channel development dynamics in planar structures on the basis of vanadium dioxide are reported. The obtained data on the variation of the temperature in the channel with time and of the current arisen after the pulsed load, and on the times of transition from the high-resistance to the low-resistance state and back are analyzed in order to determine the switching mechanism and to predict the functional characteristics of the switchable vanadium- oxide structures as promising materials for the creation of relaxation generators that can serve as prototypes of neural oscillators. It is shown that the switching behavior is associated with the metal–semiconductor phase transition in vanadium dioxide, which is stimulated by the emission of Joule heat.

Phase transformation induced modulation of the resonance frequency of VO2/TiO2 coated microcantilevers

AbstractHere we present an investigation into the phase change mechanism and detection methods of the metal-insulator transition of vanadium dioxide (VO2). We are able to detect the onset of the phase transition, and track it to completion using both the mechanical and electrical response by depositing VO2/TiO2 layers onto microcantilever devices by pulsed laser deposition. The resonance frequency of v-shaped cantilevers was shown to increase by up to 41 % upon deposition of VO2 as detected by laser Doppler vibrometry. Such a large increase in resonance frequency is ascribed to high tensile stress imparted onto the cantilever during the deposition process. The insulator-metal transition manifested as a 5 % increase in the resonance frequency as a result of lattice compression, resulting in additional tensile stress in the more ordered metallic phase. Electrically, the transition was confirmed by over three orders magnitude decrease in resistance upon heating past the transition. The metal-insulator transition was measured with an accuracy of a few °C when comparing the two methods, however, the transition was much sharper in the mechanical response.

Stage-by-stage modeling of the mechanism of semiconductor–metal phase transition in vanadium dioxide

The algorithm of stage-by-stage qualitative modeling of the mechanism of a semiconductor–metal phase transition in vanadium dioxide has been proposed. The basis for the model is a statement that the transition is complex in character and consists of the anhysteretic, purely electronic Моtt transition occurring over a wide temperature range, and the temperature-abrupt structural Peierls transition having a thermal hysteresis. The initial stage of the model is based on the solution of a quantum-mechanical problem of an electronic spectrum of a linear vanadium-ion's chain. The model is completed by consideration of correlation effects and a martensitic character of the structural transition through taking consecutively account of results obtained by X-ray, spectroscopic, impedansmetric and magnetic resonance methods.