An abrupt first-order metal-insulator transition (MIT) as a current jump has been observed by applying a dc electric field to Mott insulator VO2-based two-terminal devices. The size of the jumps was measured to be asymmetrical depending on the direction of the applied voltage due to heating effects. The structure of VO2 is investigated by micro-Raman scattering experiments. An analysis of the Raman-active Ag modes at 195 and 222cm−1, explained by pairing and tilting of V cations, and 622cm−1, shows that the modes below a low compliance (restricted) current do not change when the MIT occurs, whereas a structural phase transition above the low compliance current is found to occur secondarily, due to heating effects in the device induced by the MIT. The MIT has applications in the development of high-speed and high-gain switching devices.
Graphene leading to high surface-to-volume ratio and outstanding conductivity is applied for gas molecule sensing with fully utilizing its unique transparent and flexible functionalities which cannot be expected from solid-state gas sensors. In order to attain a fast response and rapid recovering time, the flexible sensors also require integrated flexible and transparent heaters. Here, large-scale flexible and transparent gas molecule sensor devices, integrated with a graphene sensing channel and a graphene transparent heater for fast recovering operation, are demonstrated. This combined all-graphene device structure enables an overall device optical transmittance that exceeds 90% and reliable sensing performance with a bending strain of less than 1.4%. In particular, it is possible to classify the fast (≈14 s) and slow (≈95 s) response due to sp(2) -carbon bonding and disorders on graphene and the self-integrated graphene heater leads to the rapid recovery (≈11 s) of a 2 cm × 2 cm sized sensor with reproducible sensing cycles, including full recovery steps without significant signal degradation under exposure to NO2 gas.
An abrupt metal-insulator transition (MIT) was observed in VO2 thin films during the application of a switching voltage pulse to two-terminal devices. Any switching pulse over a threshold voltage for the MIT of 7.1 V enabled the device material to transform efficiently from an insulator to a metal. The characteristics of the transformation were analyzed by considering both the delay time and rise time of the measured current response. The extrapolated switching time of the MIT decreased down to 9 ns as the external load resistance decreased to zero. Observation of the intrinsic switching time of the MIT in the correlated oxide films is impossible because of the inhomogeneity of the material; both the metallic state and an insulating state co-exist in the measurement volume. This indicates that the intrinsic switching time is in the order of less than a nanosecond. The high switching speed might arise from a strong correlation effect (Coulomb repulsion) between the electrons in the material.Vanadium dioxide, VO 2 , possesses a first-order metalinsulator transition (MIT) making it an attractive material for switching devices.1-3 The MIT occurs near 68 • C and is accompanied by a structural phase transition. Various transition properties have been studied such as crystal structure and other physical quantities. In particular, aspects of the transition have been examined during thermal and optical inducements.3-7 It is also known that a negative differential resistance (NDR) is observed when the current-voltage characteristic of this material is controlled by a static current. 8,9 Such an experiment allows the measurement of the MIT with respect to temperature. The current-controlled NDR has been widely investigated for the various compounds of vanadium oxide. 8-10The resistance of the systems abruptly changes at the transition point in contrast to the NDR properties of a conventional semiconductor system. The MIT behavior controlled by a static current is extremely stable and reversible.9,10 Up until now, controversy over the mechanism of this transition has existed. It is not known whether the transition is due to thermal or electronic effects.Recent research favors the electronic model. Observations of the sample stability and the current injected to initiate the MIT support this view.9,10 We have reported a stable MIT induced by a constant applied electric field in highly oriented VO 2 films and revealed the mechanism of the MIT to be based upon electron-electron correlation using a Raman study of the planar devices.11 The transition speed of the MIT in VO 2 films has been reported to be below a picosecond through the use of ultrafast optical techniques.12 If the field-induced MIT occurs quickly enough to apply to high speed devices and shows a reproducible behavior, there are various applications for VO 2 in switching devices such as electrical switches, modulators, and electro-optical devices. Therefore, it is very important to observe the time dependence of the fieldinduced MIT and also to study the transient...
An ambipolar dual-channel field-effect transistor (FET) with a WSe /MoS heterostructure formed by separately controlled individual channel layers is demonstrated. The FET shows a switchable ambipolar behavior with independent carrier transport of electrons and holes in the individual layers of MoS and WSe , respectively. Moreover, the photoresponse is studied at the heterointerface of the WSe /MoS dual-channel FET.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.