Metal-insulator Transition In Vanadium Dioxide Research Articles

Nanoelectrical monitoring the nonvolatile behavior of VO2 under multi-field stimulate by conductive atomic force microscopy

The ability to control the metal–insulator phase transition is crucial for future neuromorphic and memristive technologies. The key goal of this implementation is to understand and control the nanoscale mechanisms that support these two fundamental switching modalities (volatile and non-volatile states). Here, by adjusting the temperature (60 °C) close to the metal–insulator transition temperature, external application of low voltage (1 V) and laser excitation (18.6 mw · cm−2) can complete the metal–insulator transition of vanadium dioxide (VO2). The nonvolatile behavior of the VO2 devices was nanoelectrically monitored using conductive atomic force microscopy (C-AFM). Using this technique, we were able to reversibly transform the local switching response from volatile to nonvolatile, providing a unique approach for nanoelectrical monitoring in phase transition materials.

The Role of Local DFT+U Minima in the First-Principles Modeling of the Metal-Insulator Transition in Vanadium Dioxide.

The DFT+U method is frequently employed to improve the first-principles description of strongly correlated materials. However, it is prone to deliver metastable electronic minima. While these local minima of the DFT+U method are often considered to be computational artifacts, their physical meaning and relationship to true excited states remains unclear. In this work, the possibility of theoretically modeling transformations in the solid state that require thermal or optical excitations of electrons is explored, taking into account the metastable states of the computationally undemanding DFT+U formalism. For this purpose, we choose to examine the example of the VO2 metal-insulator transition. Metastable states that are located on different electronic potential energy surfaces are found to correspond to experimentally observed VO2 phases. The identified metastable electronic states can be used to model the collapse of the VO2 band gap at elevated temperatures and upon photoexcitation as well as other monoclinic-monoclinic phase transformations. The results suggest that local DFT+U minima can indeed carry physical meaning, while they remain under-reported in theoretical literature on transition metal oxides like VO2.

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

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.

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.

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.

Effect of process parameters on phase stability and metal-insulator transition of vanadium dioxide (VO2) thin films by pulsed laser deposition

Owing to remarkable thermochromic, electrochromic, and photochromic properties which arise from a first-order phase transition from insulator to metal at 68 °C, vanadium dioxide (VO2) has an enormous range of potential applications. However, due to such narrow thermodynamic stability, there is a major challenge surrounding selective phase deposition of vanadium dioxide thin films. Here, we present a report that establishes precise conditions for the deposition of three major polymorphs of VO2 by pulsed laser deposition. By a systematic study of the synergistic effects of the deposition conditions using a robust design of experiment (Taguchi design), we are able to deposit the VO2 (M1), VO2 (T), and VO2 (A) phases onto thermal oxide (Si/SiO2) substrates with remarkable precision. By electrically probing the temperature induced phase transformation from insulator to metal of each of these polymorphs, we find not only a strong dependence on the phase, but that the nature of the deposition conditions influences the magnitude and hysteresis width of the temperature cycle.

Imaging metal-like monoclinic phase stabilized by surface coordination effect in vanadium dioxide nanobeam

In correlated systems, intermediate states usually appear transiently across phase transitions even at the femtosecond scale. It therefore remains an open question how to determine these intermediate states—a critical issue for understanding the origin of their correlated behaviour. Here we report a surface coordination route to successfully stabilize and directly image an intermediate state in the metal-insulator transition of vanadium dioxide. As a prototype metal-insulator transition material, we capture an unusual metal-like monoclinic phase at room temperature that has long been predicted. Coordinate bonding of L-ascorbic acid molecules with vanadium dioxide nanobeams induces charge-carrier density reorganization and stabilizes metallic monoclinic vanadium dioxide, unravelling orbital-selective Mott correlation for gap opening of the vanadium dioxide metal–insulator transition. Our study contributes to completing phase-evolution pathways in the metal-insulator transition process, and we anticipate that coordination chemistry may be a powerful tool for engineering properties of low-dimensional correlated solids.

A Steep-Slope Transistor Combining Phase-Change and Band-to-Band-Tunneling to Achieve a sub-Unity Body Factor

Steep-slope transistors allow to scale down the supply voltage and the energy per computed bit of information as compared to conventional field-effect transistors (FETs), due to their sub-60 mV/decade subthreshold swing at room temperature. Currently pursued approaches to achieve such a subthermionic subthreshold swing consist in alternative carrier injection mechanisms, like quantum mechanical band-to-band tunneling (BTBT) in Tunnel FETs or abrupt phase-change in metal-insulator transition (MIT) devices. The strengths of the BTBT and MIT have been combined in a hybrid device architecture called phase-change tunnel FET (PC-TFET), in which the abrupt MIT in vanadium dioxide (VO2) lowers the subthreshold swing of strained-silicon nanowire TFETs. In this work, we demonstrate that the principle underlying the low swing in the PC-TFET relates to a sub-unity body factor achieved by an internal differential gate voltage amplification. We study the effect of temperature on the switching ratio and the swing of the PC-TFET, reporting values as low as 4.0 mV/decade at 25 °C, 7.8 mV/decade at 45 °C. We discuss how the unique characteristics of the PC-TFET open new perspectives, beyond FETs and other steep-slope transistors, for low power electronics, analog circuits and neuromorphic computing.

Correlating the Energetics and Atomic Motions of the Metal-Insulator Transition of M1 Vanadium Dioxide

Materials that undergo reversible metal-insulator transitions are obvious candidates for new generations of devices. For such potential to be realised, the underlying microscopic mechanisms of such transitions must be fully determined. In this work we probe the correlation between the energy landscape and electronic structure of the metal-insulator transition of vanadium dioxide and the atomic motions occurring using first principles calculations and high resolution X-ray diffraction. Calculations find an energy barrier between the high and low temperature phases corresponding to contraction followed by expansion of the distances between vanadium atoms on neighbouring sub-lattices. X-ray diffraction reveals anisotropic strain broadening in the low temperature structure’s crystal planes, however only for those with spacings affected by this compression/expansion. GW calculations reveal that traversing this barrier destabilises the bonding/anti-bonding splitting of the low temperature phase. This precise atomic description of the origin of the energy barrier separating the two structures will facilitate more precise control over the transition characteristics for new applications and devices.

Investigation on onset voltage and conduction channel temperature in voltage-induced metal-insulator transition of vanadium dioxide

The characteristics of onset voltages and conduction channel temperatures in the metal-insulator transition (MIT) of vanadium dioxide (VO2) devices are investigated as a function of dimensions and ambient temperature. The MIT onset voltage varies from 18 V to 199 V as the device length increases from 5 to 80 μm at a fixed width of 100 μm. The estimated temperature at local conduction channel increases from 110 to 370 °C, which is higher than the MIT temperature (67 °C) of VO2. A simple Joule-heating model is employed to explain voltage-induced MIT as well as to estimate temperatures of conduction channel appearing after MIT in various-sized devices. Our findings on VO2 can be applied to micro- to nano-size tunable heating devices, e.g., microscale scanning thermal cantilevers and gas sensors.

Dynamically Babinet-invertible metasurface: a capacitive-inductive reconfigurable filter for terahertz waves using vanadium-dioxide metal-insulator transition

This paper proposes a reconfigurable planar metamaterial that can be switched between capacitive and inductive responses using local changes in the electrical conductivity of its constituent material. The proposed device is based on Babinet's principle and exploits the singular electromagnetic responses of metallic checkerboard structures, which are dependent on the local electrical conductivity. Utilizing the heating-induced metal-insulator transition of vanadium dioxide (VO2), the proposed meta-material is designed to compensate for the effect of the substrate and is experimentally characterized in the terahertz regime. This reconfigurable metamaterial can be utilized as a switchable filter and as a switchable phase shifter for terahertz waves.

Multilevel radiative thermal memory realized by the hysteretic metal-insulator transition of vanadium dioxide

Thermal information processing is attracting much interest as an analog of electronic computing. We experimentally demonstrated a radiative thermal memory utilizing a phase change material. The hysteretic metal-insulator transition of vanadium dioxide (VO2) allows us to obtain a multilevel memory. We developed a Preisach model to explain the hysteretic radiative heat transfer between a VO2 film and a fused quartz substrate. The transient response of our memory predicted by the Preisach model agrees well with the measured response. Our multilevel thermal memory paves the way for thermal information processing as well as contactless thermal management.

Random Field Driven Spatial Complexity at the Mott Transition in VO(2).

We report the first application of critical cluster techniques to the Mott metal-insulator transition in vanadium dioxide. We show that the geometric universal properties of the metallic and insulating puddles observed by scanning near-field infrared microscopy are consistent with the system passing near criticality of the random field Ising model as temperature is varied. The resulting large barriers to equilibrium may be the source of the unusually robust hysteresis phenomena associated with the metal-insulator transition in this system.

Computation of the correlated metal-insulator transition in vanadium dioxide from first principles.

Vanadium dioxide (VO2) is a paradigmatic example of a strongly correlated system that undergoes a metal-insulator transition at a structural phase transition. To date, this transition has necessitated significant post hoc adjustments to theory in order to be described properly. Here we report standard state-of-the-art first principles quantum Monte Carlo (QMC) calculations of the structural dependence of the properties of VO2. Using this technique, we simulate the interactions between electrons explicitly, which allows for the metal-insulator transition to naturally emerge, importantly without ad hoc adjustments. The QMC calculations show that the structural transition directly causes the metal-insulator transition and a change in the coupling of vanadium spins. This change in the spin coupling results in a prediction of a momentum-independent magnetic excitation in the insulating state. While two-body correlations are important to set the stage for this transition, they do not change significantly when VO2 becomes an insulator. These results show that it is now possible to account for electron correlations in a quantitatively accurate way that is also specific to materials.

Vanadium dioxide nanowire-based microthermometer for quantitative evaluation of electron beam heating.

Temperature measurement is critical for many technological applications and scientific experiments, and different types of thermometers have been developed to detect temperature at macroscopic length scales. However, quantitative measurement of the temperature of nanostructures remains a challenge. Here, we show a new type of microthermometer based on a vanadium dioxide nanowire. Its mechanism is derived from the metal-insulator transition of vanadium dioxide at 68 °C. As our results demonstrate, this microthermometer can serve as a thermal flow meter to investigate sample heating from the incident electron beam using a transmission electron microscope. Owing to its small size the vanadium dioxide nanowire-based microthermometer has a large measurement range and high sensitivity, making it a good candidate to explore the temperature environment of small spaces or to monitor the temperature of tiny, nanoscale objects.

Thermally driven analog of the Barkhausen effect at the metal-insulator transition in vanadium dioxide

The physics of the metal-insulator transition (MIT) in vanadium dioxide remains a subject of intense interest. Because of the complicating effects of elastic strain on the phase transition, there is interest in comparatively strain-free means of examining VO2 material properties. We report contact-free, low-strain studies of the MIT through an inductive bridge approach sensitive to the magnetic response of VO2 powder. Rather than observing the expected step-like change in susceptibility at the transition, we argue that the measured response is dominated by an analog of the Barkhausen effect, due to the extremely sharp jump in the magnetic response of each grain as a function of time as the material is cycled across the phase boundary. This effect suggests that future measurements could access the dynamics of this and similar phase transitions.

Nonlinear Phenomena and Deterministic Chaos in Systems With Vanadium Dioxide

 Abstract— The switching effect with current-controlled negative resistance (S-shaped voltage-current characteristics) associated with the metal-insulator transition in vanadium dioxide is studied. The experiment shows that the switching devices exhibit complex nonlinear behaviors, including 1/f-type electronic noise, the effect of burst noise, stochastic resonance, period-adding sequences with intermittent chaos. In addition, deterministic chaos in the region of negative differential resistance is observed and, near the threshold point, the intrinsic dimension of the attractor is d = 2.3. Mechanisms of these phenomena are discussed. The analysis allows concluding that the noise and chaotic effects should obviously be taken into account in applications of VO2 in electronic devices, particularly in thermal sensors and bolometeric detectors.

Voltage-Triggered Ultrafast Phase Transition in Vanadium Dioxide Switches

Electrically driven metal-insulator transition in vanadium dioxide (VO2) is of interest in emerging memory devices, neural computation, and high speed electronics. We report on the fabrication of out-of-plane VO2 metal-insulator-metal (MIM) structures and reproducible high-speed switching measurements in these two-terminal devices. We have observed a clear correlation between electrically-driven ON/OFF current ratio and thermally-induced resistance change during metal-insulator transition. It is also found that sharp metal-insulator transition could be triggered by external voltage pulses within 2 ns at room temperature and the achieved ON/OFF ratio is greater than two orders of magnitude with good endurance.

Metal–insulator transition in vanadium dioxide

Metal-insulator transition in vanadium dioxide Metal-insulator transition in vanadium dioxide