Yu He

Electric field manipulation of magnetization at room temperature in multiferroic CoFe2O4/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 heterostructures

Multiferroic heterostructures were fabricated by growing ferrimagnetic CoFe2O4 films on ferroelectric Pb(Mg1/3Nb2/3)0.7Ti0.3O3 substrates using pulsed laser deposition. Upon applying an electric field, the in-plane magnetization of the heterostructures increases and the out-of-plane magnetization decreases. Sharp and reversible changes in magnetization under electric field were also observed for the poled sample. The relative change in magnetization-electric field hysteresis loops were obtained for both the in-plane and out-of-plane magnetizations. Analysis of the results suggests that the electric field induced change in magnetic anisotropy via strain plays an important role in the magnetoelectric coupling in the heterostructures.

Modeling and simulation of uniaxial strain effects in armchair graphene nanoribbon tunneling field effect transistors

In this paper, we perform a modeling and simulation study on strained armchair graphene nanoribbon (AGNR). Two uniaxial strain models based on a tight binding method are compared with results from first-principles calculation. Tunneling field effect transistors (TFETs) with channels made of strained AGNR of different widths are modeled and simulated by a ballistic quantum transport model based on nonequilibrium Green’s function and nonparabolic effective mass approximation. Compared with TFETs with narrow AGNR, those with strained wide AGNR can achieve better device performance.

Enhancement in ordering of FePt films by magnetic field annealing

Effect of magnetic field annealing on chemical ordering of FePt films has been investigated. It is found that the ordering rate in FePt films is enhanced by applying a magnetic field during postdeposition annealing. Measurements of the structure and magnetic properties of FePt films reveal that the disorder–order transformation starts at or below 450°C when the film is annealed in a magnetic field of 40kOe. The possible reason for the enhancement in the ordering of FePt films by magnetic field annealing is discussed.

Coating geometries of metals on single-walled carbon nanotubes

This paper studies the coating geometries of metals on single-walled carbon nanotubes (SWNTs) on the basis of the nucleation theory and wetting theory. The metal surface energy, cohesion energy, diffusion barrier, and metal-SWNT interfacial energy are calculated using first-principles calculation. Metals including Fe, Al, Au, Pd, Ni, and Ti are considered. For Ti, Ni, and Pd, low metal-SWNT interfacial energies and high diffusion barriers are responsible for forming continuous or quasicontinuous layers on the SWNT surface. In contrast, Al and Au have small diffusion barriers and poor SWNT surface wetting, thus they tend to aggregate and form large clusters. Although the binding energy between Fe and SWNTs is large, due to the large cohesion energy and poor wetting, Fe may form isolated clusters. All results are in good agreement with experimental observations.

Schottky barrier formation at metal electrodes and semiconducting carbon nanotubes

Schottky barrier (SB) formation at the contact interface between metal and semiconducting carbon nanotubes (CNTs) is of great importance in determining the transport characteristics of a CNT field effect transistor. In this paper, we studied the SB height (SBH) between different metals and CNT contacts using first-principles calculation. A method to calculate SBH is proposed based on the interface dipole effect, which will induce an electrical potential variation at the metal and CNT interface. The SBH of a metal and CNT contact could then be determined by the work function difference between the metal and CNT and the electrical potential variation. We extensively investigated different contacts between Sc, Al, Pd, (8,0) CNT, and (11,0) CNT. The calculated SBHs for these contacts are all in good agreement with experimental results.

Molecular Dynamics Study of the Switching Mechanism of Carbon-Based Resistive Memory

An electric molecular dynamics (MD) method is proposed, where an electroheat solver is introduced into a traditional MD simulation to perform a coupled calculation. The switching mechanism of carbon-based resistive random access memory is studied through this method, and the heat generation and propagation driven by an electric current pulse are simulated during the switching process. Graphitic filament breakage and growth are responsible for resistance switching. The simulation shows that a short and strong voltage pulse induces graphitic filament breakage, resulting in a high-resistance state, whereas a moderate but much longer pulse is required to enable filament growth, resulting in a low-resistance state. Key factors such as the bias condition and the power supply for such switching process are also studied. The results are quantitatively consistent with experimental measurements.

Gas bubble phenomenon in nanoscale liquid film under external electric field

The effects of an external electric field on liquid films confined within a nanogap between a smooth plate and a highly polished steel ball have been investigated. It was found that some gas microbubbles emerged around the edge of the Hertz central region and then moved off the central region. Experimental results indicated that the emergence of the bubbles was largely dependent on the liquid polarity and the external voltage. It is thought that the emergence of the bubbles is due to the liquid surface vibration.

Nickel-induced enhancement of photoluminescence from Si-rich silica films

The effect of Ni on the near-infrared luminescence emitting from silicon nanocrystals embedded in SiO2 matrix has been investigated. According to the thermodynamics calculation, nickel can give additional driving force to the phase separation process. The photoluminescence intensity increases with the increasing annealing temperature because of the crystallization of amorphous silicon in SiOx films. The intensity of near-infrared emission of SiO1.56∕Ni∕Si is stronger by a factor of 5 than that of regular specimen after annealing at 1000 or 1100°C due to the increase of the density of Si nanocrystals.

Dynamic Modeling and Atomistic Simulations of SET and RESET Operations in

In this letter, atomistic-level models and simulations of unipolar TiO₂ RRAM are addressed. A dynamic model of SET/RESET is developed based on recent experimental findings, which attributes SET to oxygen vacancy (V_O) drift and Ti₄O₇ conductive filament (CF) growth, while RESET is explained by the melting of Ti₄O₇ CF and subsequent (V_O) diffusion and recombination. Based on the model, electro-thermal and molecular dynamics simulations are carried out to reproduce the complete switching cycle at an atomistic level.

\hbox{TiO}_{2}

Multiferroic p-n junctions were fabricated by growing La0.1Bi0.9MnO3 films on Nb–SrTiO3 using pulsed laser deposition. The current-voltage curves of the junction show good rectifying property. Both the ferroelectric transition and ferromagnetic transition of La0.1Bi0.9MnO3 have remarkable influence on the transport properties of the junction. A large positive magnetocapacitance was also observed in this junction. Analysis suggests that the property of La0.1Bi0.9MnO3∕Nb–SrTiO3 is dominated by the property of La0.1Bi0.9MnO3. This work demonstrates that multiferroic p-n junctions possess some interesting properties that may be useful for future applications.