Study of a charge transition-driven resistive switching mechanism in TiO-based random access memory density functional theory.

The nature of the conducting filament (CF) with a high concentration of oxygen vacancies (Vs) in oxide thin film-based resistive random access memory (RRAM) remains unclear. The Vs in the CF have been assumed to be positively charged (V) to explain the field-driven switching of RRAM, but V clusters in high concentration encounter Coulomb repulsion, rendering the CF unstable. Therefore, this study examined the oxidation state of Vs in the CF and their effects on the switching behavior density functional theory calculations using a Pt/TiO/Ti model system.

ænet-PyTorch: A GPU-supported implementation for machine learning atomic potentials training.

In this work, we present ænet-PyTorch, a PyTorch-based implementation for training artificial neural network-based machine learning interatomic potentials. Developed as an extension of the atomic energy network (ænet), ænet-PyTorch provides access to all the tools included in ænet for the application and usage of the potentials. The package has been designed as an alternative to the internal training capabilities of ænet, leveraging the power of graphic processing units to facilitate direct training on forces in addition to energies.

An ab initio approach on the asymmetric stacking of GaAs 〈111〉 nanowires grown by a vapor-solid method.

This study provides an ab initio thermodynamics approach to take a step forward in the theoretical modeling on the growth of GaAs nanowires. In order to understand the effects of growth conditions on the involvement of stacking faults and polytypism, we investigated the vapor-phase growth kinetics under arbitrary temperature-pressure conditions by combining the atomic-scale calculation with the thermodynamic treatment of a vapor-solid system. Considering entropy contribution and electronic energy, the chemical potential and surface energies of various reconstructions were calculated as a function of temperature and pressure, leading to the prediction of the change in Gibbs free energy at each stage of nucleation and growth.

Ferroelectric switching in bilayer 3R MoS via interlayer shear mode driven by nonlinear phononics.

We theoretically investigate the mechanism of ferroelectric switching via interlayer shear in 3R MoS using first principles and lattice dynamics calculations. First principle calculations show the prominent anharmonic coupling of the infrared inactive interlayer shear and the infrared active phonons. The nonlinear coupling terms generates an effective anharmonic force which drives the interlayer shear mode and lowers the ferroelectric switching barrier depending on the amplitude and polarization of infrared mode.

Optical control of the layer degree of freedom through Wannier-Stark states in polar 3R MoS.

Electrons in two-dimensional layered crystals gain a discrete positional degree of freedom over layers. We propose the two-dimensional transition metal dichalcogenide homostructure with polar symmetry as a prototypical platform where the degrees of freedom for the layers and valleys can be independently controlled through an optical method. In 3R MoS, a model system, the presence of the spontaneous polarization and built-in electric field along the stacking axis is theoretically proven by the density functional theory.

Equilibrium crystal shape of GaAs and InAs considering surface vibration and new (111)B reconstruction: ab-initio thermodynamics.

This work reports on the theoretical equilibrium crystal shapes of GaAs and InAs as a function of temperature and pressure, taking into account the contribution of the surface vibration, using ab-initio thermodynamic calculations. For this purpose, new (111)B reconstructions, which are energetically stable at a high temperature, are suggested. It was found that there was a feasible correspondence between the calculated equilibrium shapes and the experimental shapes, which implied that the previous experimental growth was performed under conditions that were close to equilibrium.

Surface reconstruction of InAs (001) depending on the pressure and temperature examined by density functional thermodynamics.

A detailed understanding of the atomic configuration of the compound semiconductor surface, especially after reconstruction, is very important for the device fabrication and performance. While there have been numerous experimental studies using the scanning probe techniques, further theoretical studies on surface reconstruction are necessary to promote the clear understanding of the origins and development of such subtle surface structures. In this work, therefore, a pressure-temperature surface reconstruction diagram was constructed for the model case of the InAs (001) surface considering both the vibrational entropy and configurational entropy based on the density functional theory.

Resistance switching behavior of atomic layer deposited SrTiO3 film through possible formation of Sr2Ti6O13 or Sr1Ti11O20 phases.

Identification of microstructural evolution of nanoscale conducting phase, such as conducting filament (CF), in many resistance switching (RS) devices is a crucial factor to unambiguously understand the electrical behaviours of the RS-based electronic devices. Among the diverse RS material systems, oxide-based redox system comprises the major category of these intriguing electronic devices, where the local, along both lateral and vertical directions of thin films, changes in oxygen chemistry has been suggested to be the main RS mechanism. However, there are systems which involve distinctive crystallographic phases as CF; the Magnéli phase in TiO2 is one of the very well-known examples.