Power spectral density imaging for polymeric films using ex-situ solid-state magnetic resonance with needlelike ferromagnet.

An ex-situ solid-state nuclear magnetic resonance (NMR) method employing localized magnetic field gradients generated by a needlelike ferromagnet is described. The depth profiling of a multilayer polymeric film using the proposed method and spin density imaging is successfully acquired. The imaging of the variable-frequency spinlattice relaxation rate in the depth direction reveals differences in the spectral density function for molecular dynamics between the surface and interior of the film.

Planar Nanoactuators Based on VO Phase Transition.

Actuation at micro- and nanoscale often requires large displacements and applied forces. The high work energy density that lies inside many phase transitions is an appealing feature for developing new actuating schemes, especially if the transition is reversible and scalable into small actuating domains. Here, we show the fabrication of a planar nanomechanical actuator having chevron-type geometry and based on the phase transition of VO.

Long-range propagation of protons in single-crystal VO involving structural transformation to HVO.

Vanadium dioxide (VO) is a strongly correlated electronic material with a metal-insulator transition (MIT) near room temperature. Ion-doping to VO dramatically alters its transport properties and the MIT temperature. Recently, insulating hydrogenated VO (HVO) accompanied by a crystal structure transformation from VO was experimentally observed.

Barrier Formation at the Contacts of Vanadium Dioxide and Transition-Metal Dichalcogenides.

Phase-transition field-effect transistors (FETs) are a class of steep-slope devices that show abrupt on/off switching owing to the metal-insulator transition (MIT) induced in the contacting materials. An important avenue to develop phase-transition FETs is to understand the charge injection mechanism at the junction of the contacting MIT materials and semiconductor channels. Here, toward the realization of high-performance phase-transition FETs, we investigate the contact properties of heterojunctions between semiconducting transition-metal dichalcogenides (TMDCs) and vanadium dioxide (VO) that undergoes a MIT at a critical temperature () of approximately 340 K.

Growth of vanadium dioxide thin films on hexagonal boron nitride flakes as transferrable substrates.

Vanadium dioxide (VO) is an archetypal metal-insulator transition (MIT) material, which has been known for decades to show an orders-of-magnitude change in resistivity across the critical temperature of approximately 340 K. In recent years, VO has attracted increasing interest for electronic and photonic applications, along with advancement in thin film growth techniques. Previously, thin films of VO were commonly grown on rigid substrates such as crystalline oxides and bulk semiconductors, but the use of transferrable materials as the growth substrates can provide versatility in applications, including transparent and flexible devices.

Gate-Tunable Thermal Metal-Insulator Transition in VO Monolithically Integrated into a WSe Field-Effect Transistor.

Vanadium dioxide (VO) shows promise as a building block of switching and sensing devices because it undergoes an abrupt metal-insulator transition (MIT) near room temperature, where the electrical resistivity changes by orders of magnitude. A challenge for versatile applications of VO is to control the MIT by gating in the field-effect device geometry. Here, we demonstrate a gate-tunable abrupt switching device based on a VO microwire that is monolithically integrated with a two-dimensional (2D) tungsten diselenide (WSe) semiconductor by van der Waals stacking.

Enhanced electronic-transport modulation in single-crystalline VO nanowire-based solid-state field-effect transistors.

Field-effect transistors using correlated electron materials with an electronic phase transition pave a new avenue to realize steep slope switching, to overcome device size limitations and to investigate fundamental science. Here, we present a new finding in gate-bias-induced electronic transport switching in a correlated electron material, i.e.

Selective High-Frequency Mechanical Actuation Driven by the VO Electronic Instability.

Relaxation oscillators consist of periodic variations of a physical quantity triggered by a static excitation. They are a typical consequence of nonlinear dynamics and can be observed in a variety of systems. VO is a correlated oxide with a solid-state phase transition above room temperature, where both electrical resistance and lattice parameters undergo a drastic change in a narrow temperature range.

Electrochemical gating-induced reversible and drastic resistance switching in VO2 nanowires.

Reversible and drastic modulation of the transport properties in vanadium dioxide (VO2) nanowires by electric field-induced hydrogenation at room temperature was demonstrated using the nanogaps separated by humid air in field-effect transistors with planer-type gates (PG-FET). These PG-FETs allowed us to investigate behavior of revealed hydrogen intercalation and diffusion aspects with time and spatial evolutions in nanowires. These results show that air nanogaps can operate as an electrochemical reaction field, even in a gaseous atmosphere, and offer new directions to explore emerging functions for electronic and energy devices in oxides.

Fractal Nature of Metallic and Insulating Domain Configurations in a VO2 Thin Film Revealed by Kelvin Probe Force Microscopy.

We investigated the surface work function (WS) and its spatial distribution for epitaxial VO2/TiO2 thin films using Kelvin probe force microscopy (KPFM). Nearly grain-boundary-free samples allowed observation of metallic and insulating domains with distinct WS values, throughout the metal-insulator transition. The metallic fraction, estimated from WS maps, describes the evolution of the resistance based on a two-dimensional percolation model.

Programmable mechanical resonances in MEMS by localized joule heating of phase change materials.

A programmable micromechanical resonator based on a VO2 thin film is reported. Multiple mechanical eigenfrequency states are programmed using Joule heating as local power source, gradually driving the phase transition of VO2 around its Metal-Insulator transition temperature. Phase coexistence of domains is used to tune the stiffness of the device via local control of internal stresses and mechanical properties.

Controlled fabrication of artificial ferromagnetic (Fe,Mn)3O4 nanowall-wires by a three-dimensional nanotemplate pulsed laser deposition method.

We have developed a new method to fabricate extremely small transition-metal oxide nanowires. Using a combination of nanoimprint template patterning and inclined substrate pulsed laser deposition, we successfully fabricated magnetic oxide Fe(2.5)Mn(0.

Position-controlled functional oxide lateral heterostructures consisting of artificially aligned (Fe,Zn)3O4 nanodots and BiFeO3 matrix.

We demonstrate an advanced fabrication method for perfectly position-controlled ferromagnetic semiconductor (Fe,Zn)(3)O(4) nanodot arrays down to several hundred nanometers in size surrounded by a ferroelectric BiFeO(3) matrix. By performing position-selective crystal growth of perovskite BiFeO(3) on the position-controlled epitaxial spinel (Fe,Zn)(3)O(4) nanodot-seeding template, which is prepared using a hollow molybdenum mask lift-off nanoimprint lithography process on a perovskite La-doped SrTiO(3)(001) substrate, we produce functional oxide three-dimensional lateral heterojunctions. The position-selectivity can be explained based on standard surface diffusion theory with a critical nucleation point.

Multistate memory devices based on free-standing VO2/TiO2 microstructures driven by Joule self-heating.

Two-terminal multistate memory elements based on VO(2)/TiO(2) thin film microcantilevers are reported. Volatile and non-volatile multiple resistance states are programmed by current pulses at temperatures within the hysteretic region of the metal-insulator transition of VO(2). The memory mechanism is based on current-induced creation of metallic clusters by self-heating of micrometric suspended regions and resistive reading via percolation.

Direct fabrication of integrated 3D epitaxial functional transition metal oxide nanostructures using extremely small hollow nanopillar nano-imprint metal masks.

A novel nanofabrication technique is developed for functional oxides. Combining nano-imprint lithography, sidewall-etching and sidewall-deposition processes enables us to prepare Mo hollow nanopillar masks with 100 and 60 nm window sizes, which is smaller than the original nano-imprint mold size of 250 nm. Using this Mo nanomask, extremely small epitaxial ferromagnetic oxide (Fe(2.

Enhancement of spin polarization in a transition metal oxide ferromagnetic nanodot diode.

Enhancement of spin polarization was observed in a transition metal oxide (Fe,Zn)(3)O(4)/Nb-SrTiO(3) ferromagnetic nanodot Schottky diode. The highly integrated oxide nanodot diodes were constructed using nanoimprint lithography based on a Mo lift-off method in combination with a pulsed laser deposition technique. The junction magnetoresistance of diodes increased as diode size increased.

Giant magnetoresistance observed in (Fe,Mn)3O4 artificial nanoconstrained structures at room temperature.

We fabricated ferromagnetic oxide (Fe,Mn)(3)O(4) (FMO) nanoconstrained structures using two different steps involving atomic force microscope lithography in combination with a pulsed laser deposition technique. The widths of three FMO nanoconstrained structures were 150, 100, and 50 nm. The I-V characteristic of the 50 nm width FMO nanoconstrained structure changed dramatically from linear to nonlinear after forming the nanoconstrained structure.

Direct fabrication of integrated 3D Au nanobox arrays by sidewall deposition with controllable heights and thicknesses.

This paper provides a unique strategy for controlling integrated hollow nanostructure arrays such as boxes or pillars at the nanometer scale. The key merit of this technique is that it can overcome resolution limits by sidewall deposition and deposit various materials using a sputtering method. The sputtering method can be replaced by other dry deposition techniques such as pulsed laser deposition (PLD) for complex functional materials.

Noise-driven attractor switching device.

Problems with artificial neural networks originate from their deterministic nature and inevitable prior learnings, resulting in inadequate adaptability against unpredictable, abrupt environmental change. Here we show that a stochastically excitable threshold unit can be utilized by these systems to partially overcome the environmental change. Using an excitable threshold system, attractors were created that represent quasiequilibrium states into which a system settles until disrupted by environmental change.

Ordered nano-lslands on (La,Ba)MnO3 thin film surface by self-organization.

Self-organized nanostructures composed of discrete coherent islands were found on La0.67Ba0.33 MnO3 (LBMO) film surfaces.