Metallic Diluted Dimerization in VO₂ Tweeds

Abstract

The observation of electronic phase separation textures in vanadium dioxide, a prototypical electron‐correlated oxide, has recently added new perspectives on the long standing debate about its metal–insulator transition and its applications. Yet, the lack of atomically resolved information on phases accompanying such complex patterns still hinders a comprehensive understanding of the transition and its implementation in practical devices. In this work, atomic resolution imaging and spectroscopy unveils the existence of ferroelastic tweed structures on ≈5 nm length scales, well below the resolution limit of currently used spectroscopic imaging techniques. Moreover, density functional theory calculations show that this pretransitional fine‐scale tweed, which on average looks and behaves like the standard metallic rutile phase, is in fact weaved by semi‐dimerized chains of vanadium in a new monoclinic phase that represents a structural bridge to the monoclinic insulating ground state. These observations provide a multiscale perspective for the interpretation of existing data, whereby phase coexistence and structural intermixing can occur all the way down to the atomic scale.

Basic aspects of the metal–insulator transition in vanadium dioxide VO2: a critical review

“…Note also that a surface study of thin films of VO 2 grown on (110)-oriented substrates of rutile TiO 2 around T MI and atmospheric pressure reports decoupled structural and electronic transitions and reveal the presence of an additional monoclinic-like metallic phase in between the M 1 and R phases [103]. Very recently, atomic resolution imaging and spectroscopy reveal the existence of fine-scale tweed structures on nm length scale in VO 2 /TiO 2 (001) films [104]. Such textures, which behave like the standard metallic rutile phase, is in fact weaved by semi-dimerized chains of vanadium in a new monoclinic phase that appear to be a structural bridge between the different monoclinic insulating ground states of VO 2 .…”

Picoampere Dark Current and Electro‐Opto‐Coupled Sub‐to‐Super‐linear Response from Mott‐Transition Enabled Infrared Photodetector for Near‐Sensor Vision Processing

“…It is interesting to note that the measured work function with light illumination is closer to the work function of vanadium metal thin film (i.e., 5.3 eV), as shown in Figure 1k. [ 19,21,22 ] This change in the work function indicates that the light illumination is inducing the metallic nature of the VO 2 , and thus, the effective turn‐on voltage is reduced (see Figure 1g). The possible cause behind the IR photo illumination‐induced change in the metallic nature could be due to photo‐induced heating, and thus, as a confirmation, we used the thermometer mapping of the sample under dark and with IR illumination.…”

“…As a potential approach, electric-field triggered insulator-to-metal transition (IMT) in quantum Mott materials, such as vanadium oxide (VO 2 ), with a sharp threshold voltage (V T ) value and its effective modulation with photon illumination could potentially provide a unique way not only to reduce the dark current but also to obtain a superlinear photoresponse. [17][18][19][20][21] Indeed, dark current across the Mott materialbased devices remains negligible in the insulating phase (i.e., below V T ); nevertheless, current increases rapidly at or above V T because the current is primarily driven by the metallic phase in this voltage region. [19,20] As a result, by integrating Mott material with commercially used photosensing material (such as silicon, Si), ultralow dark current and even superlinear photoresponse can be achieved.…”

“…[17][18][19][20][21] Indeed, dark current across the Mott materialbased devices remains negligible in the insulating phase (i.e., below V T ); nevertheless, current increases rapidly at or above V T because the current is primarily driven by the metallic phase in this voltage region. [19,20] As a result, by integrating Mott material with commercially used photosensing material (such as silicon, Si), ultralow dark current and even superlinear photoresponse can be achieved. Specifically, achieving a superlinear photoresponse is critical for the development of near-sensor vision processing and pattern classification since they can function as an intensity selector and separate the noise from the input pattern even with a small variation in the intensity.…”

Suppression of Strain Relaxation in VO2/TiO2 Multilayered Films

“…This higher local resistance disturbs the current flow homogeneity and eventually results in an uncontrolled IMT behavior as well as deterioration of stability. These behaviors limit practical optoelectronic applications of VO 2 . − For example, in the case of smart window applications, a thicker VO 2 layer is required to maintain a significant transmittance change; however, due to the crack effects, this is incompatible with the stable phase transition behavior with room temperature T c .…”