Frustrated interactions can lead to short-range ordering arising from incompatible interactions of fundamental physical quantities with the underlying lattice. The simplest example is the triangular lattice of spins with antiferromagnetic interactions, where the nearest-neighbor spin-spin interactions cannot simultaneously be energy minimized. Here we show that engineering frustrated interactions is a possible route for controlling structural and electronic phenomena in semiconductor alloys. Using aberration-corrected scanning transmission electron microscopy in conjunction with density functional theory calculations, we demonstrate atomic ordering in a two-dimensional semiconductor alloy as a result of the competition between geometrical constraints and nearest-neighbor interactions. Statistical analyses uncover the presence of short-range

The development of room-temperature sensing devices for detecting small concentrations of molecular species is imperative for a wide range of low-power sensor applications. We demonstrate a room-temperature, highly sensitive, selective, and reversible chemical sensor based on a monolayer of the transition metal dichalcogenide Re0.5Nb0.5S2. The sensing device exhibits thickness dependent carrier type, and upon exposure to NO2 molecules, its electrical resistance considerably increases or decreases depending on the layer number. The sensor is selective to NO2 with only minimal response to other gases such as NH3, CH2O, and CO2. In the presence of humidity, not only are the sensing properties not deteriorated, but also the monolayer sensor shows complete reversibility with fast recovery at room temperature. We present a theoretical analysis of the sensing platform and identify the atomically-sensitive transduction mechanism.

Alloying two-dimensional (2D) semiconductors provides a powerful method to tune their physical properties, especially those relevant to optoelectronic applications. However, as the crystal structure becomes more complex, it becomes increasingly difficult to accurately correlate response characteristics to detailed atomic structure. We investigate, via annular dark-field scanning transmission electron microscopy, electron energy loss spectroscopy, and second harmonic generation, the layered III−VI alloy GaSe 0.5 Te 0.5 as a function of layer number. The local atomic structure and stacking sequence for different layers is explicitly determined. We complement the measurements with first-principles calculations of the total energy and electronic band structure of GaSe 0.5 Te 0.5 for different crystal structures and layer number. The electronic band gap as well as the π and π + σ plasmons are found to be sensitive to layer number.

Radio-frequency (RF) magnetron sputtering method was used to fabricate ferroelectric films of hafnium oxide doped with 6 mol. % silicon. The effect of polarization of the Si doped HfO2 layer on photovoltaic properties of this ferroelectric-semiconductor system was investigated. Piezoresponse force microscopy method provided clear evidence for ferroelectric properties of HfO2 films with 10 nm thickness. Kelvin probe force microscopy showed that change in the surface potential of the negatively poled sample due to illumination is opposite to the response from unpoled and positively poled samples. Transport measurements also revealed a significant difference between photo-responses of the ferroelectric films that were polarized in opposite directions.

Stress dependence and effect of plastic deformation on magnetic hysteresis and anhysteretic magnetization of FeNi32% filmsThin films of Fe-Ni with graded composition have been deposited on a Si (001) substrate at room temperature by co-sputtering of Fe and Ni with variable rates of the constituting elements. The composition of the films was changing linearly across the thickness from Fe 80 Ni 20 to Fe 6 Ni 94 . Five samples were studied with the thickness of 30, 50, 100, 150, and 200 nm. The hysteresis loops measured with the field applied in the film plane had square shape and the coercivity was varying from 11 to 22 Oe. However, the loops for the field perpendicular to the film plane displayed unusual shapes consisting of a double-step hysteresis loop at low fields and unhysteretic part at higher fields. The size of the steps varied with the thickness of the film. The most likely source of the double step hysteretic curves was identified as magnetostrictive stresses at the film/substrate interface. This was evidenced by the disappearance of the second hysteresis step after annealing at 200 C for 1 h and significant changes of the hysteresis loops when the same structure was deposited starting from Fe-rich or Ni-rich compositions at the substrate.

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Microscopic origami figures can be created from thin film patterns using surface tension of liquids or residual stresses in thin films. The curvature of the structures, direction of bending, twisting, and folding of the patterns can be controlled by their shape, thickness, and elastic properties and by the strength of the residual stresses. Magnetic materials used for micro-and nano-origami structures play an essential role in many applications. Magnetic force due to applied magnetic field can be used for remote actuation of microrobots. It can also be used in targeted drug delivery to direct cages loaded with drugs or microswimmers to transport drugs to specific organs. Magnetoelastic properties of free-standing micro-origami patterns can serve for stress or magnetic field sensing. Also, the stress-induced anisotropy and magnetic shape anisotropy provide a convenient method of tuning magnetic properties by designing a shape of the microorigami figures instead of varying the composition of the films. Micro-origami figures can also serve as building blocks for two-and three-dimensional meta-materials with unique properties such as negative index of refraction. Micro-origami techniques provide a powerful method of self-assembly of magnetic circuits and integrating them with microelectro-mechanical systems or other functional devices.

We study the effect of micro-scale electric fields on voltage-gated ion channels in mammalian cell membranes. Such micro-and nano-scale electric fields mimic the effects of multiferroic nanoparticles that were recently proposed [1] as a novel way of controlling the function of voltage-sensing biomolecules such as ion channels. This article describes experimental procedures and initial results that reveal the effect of the electric field, in close proximity of cells, on the ion transport through voltage-gated ion channels. We present two configurations of the whole-cell patch-clamping apparatus that were used to detect the effect of external stimulation on ionic currents and discuss preliminary results that indicate modulation of the ionic currents consistent with the applied stimulus.