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Understanding the physical changes during electroformation and switching processes in transition-metal-oxide-based non-volatile memory devices is important for advancing this technology. Relatively few characteristics of these devices have been assessed in operando. In this work, we present scanning thermal microscopy measurements in vacuum on TaO x -based memory devices electroformed in both positive and negative polarities and high- and low-resistance states. The observed surface temperature footprints of the filament showed higher peak temperatures and narrower temperature distributions when the top electrode served as the anode in the electroformation process. This is consistent with a model in which a hot spot is created by a gap in the conducting filament that forms closest to the anode. A similar behavior was seen on comparing the high-resistance state to the low-resistance state, with the low-resistance footprint showing a lower peak and a larger width, consistent with the gap disappearing when the device is switched from high resistance to low resistance., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

The original version of this Article contained an error in Eq. 1. The arrows between the symbols "T" and "B", and "B" and "T", were written "↔" but should have been "→", and incorrectly read: I EBIC =I EBAC +I SEE +I (e↔h)+ I EBIC T↔B +I ESEE B↔T The correct from of the Eq. 1 is as follows:I EBIC =I EBAC +I SEE +I (e↔h)+ I EBIC T→B +I ESEE B→T This has now been corrected in both the PDF and HTML versions of the article.

Static domain structures and polarization dynamics of silicon doped HfO2 are explored. The evolution of ferroelectricity as a function of Si-doping level driving the transition from paraelectricity via ferroelectricity to antiferroelectricity is investigated. Ferroelectric and antiferroelectric properties can be observed locally on the pristine, poled and electroded surfaces, providing conclusive evidence to intrinsic ferroic behavior., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Mapping surface potential with time-resolved Kelvin probe force microscopy (tr-KPFM) in LiNbO3 periodically poled single crystals reveals activation of the surface ionic subsystem. Electric fields of certain strength induce injection of charge, formation of an active region in its vicinity and uneven distribution of screening charge on the opposite ferroelectric domains. Tr-KPFM technique allows investigating these phenomena in details., (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The novel phenomena induced by symmetry breaking at homointerfaces between ferroic variants in ferroelectric and ferroelastic materials have attracted recently much attention. Using variable temperature scanning microwave microscopy, we demonstrate the mesoscopic strain-induced metal-insulator phase transitions in the vicinity of ferroelastic domain walls in the semiconductive VO(2) that nucleated at temperatures as much as 10-12 degrees C below bulk transition, resulting in the formation of conductive channels in the material. Density functional theory is used to rationalize the process low activation energy. This behavior, linked to the strain inhomogeneity inherent in ferroelastic materials, can strongly affect interpretation of phase-transition studies in VO(2) and similar materials with symmetry-lowering transitions, and can also be used to enable new generations of electronic devices though strain engineering of conductive and semiconductive regions.

Formation of ferroelastic twin domains in vanadium dioxide (VO(2)) nanosystems can strongly affect local strain distributions, and hence couple to the strain-controlled metal-insulator transition. Here we report polarized-light optical and scanning microwave microscopy studies of interrelated ferroelastic and metal-insulator transitions in single-crystalline VO(2) quasi-two-dimensional (quasi-2D) nanoplatelets (NPls). In contrast to quasi-1D single-crystalline nanobeams, the 2D geometric frustration results in emergence of several possible families of ferroelastic domains in NPls, thus allowing systematic studies of strain-controlled transitions in the presence of geometrical frustration. We demonstrate the possibility of controlling the ferroelastic domain population by the strength of the NPl-substrate interaction, mechanical stress, and by the NPl lateral size. Ferroelastic domain species and domain walls are identified based on standard group-theoretical considerations. Using variable temperature microscopy, we imaged the development of domains of metallic and semiconducting phases during the metal-insulator phase transition and nontrivial strain-driven reentrant domain formation. A long-range reconstruction of ferroelastic structures accommodating metal-insulator domain formation has been observed. These studies illustrate that a complete picture of the phase transitions in single-crystalline and disordered VO(2) structures can be drawn only if both ferroelastic and metal-insulator strain effects are taken into consideration and understood.

Using temperature driven sharp metal-insulator phase transition in single crystal VO(2) nanowires, the realization of a novel gas sensing concept has been tested. Varying the temperature of the nanowire close to the transition edge, the conductance of the nanowire becomes extremely responsive to the tiny changes in molecular composition, pressure, and temperature of the ambient gas environment. This gas sensing analog of the transition edge sensor radiometry used in astrophysics opens new opportunities in gas sensorics.

The effect of Joule self-heating of the semiconducting metal oxide nanowire (here (and below unless specified), due to the generality of the effect, we use the term 'nanowire' without specification as to whether the nanobelt or other class of quasi-1D nanostructure is considered) conductometric gas sensor on its surface reactivity and kinetics is demonstrated. Due to small thermal capacitance and hampered thermal losses from the nanowire to its surroundings, the sensor was able to operate without a heater, consuming only a few microwatts of power. These results demonstrate the importance of the self-heating effect in nanowire electronics and its potential use in chemical and bio-sensing, where the ultra-small size of the active element and minimal power consumption are crucial.