Band gap engineering of MoS2_2 upon compression

Molybdenum disulfide (MoS$_2$) is a promising candidate for 2D nanoelectronic devices, that shows a direct band-gap for monolayer structure. In this work we study the electronic structure of MoS$_2$ upon both compressive and tensile strains with first-principles density-functional calculations for different number of layers. The results show that the band-gap can be engineered for experimentally attainable strains (i.e. $\pm 0.15$). However compressive strain can result in bucking that can prevent the use of large compressive strain. We then studied the stability of the compression, calculating the critical strain that results in the on-set of buckling for free-standing nanoribbons of different lengths. The results demonstrate that short structures, or few-layer MoS$_2$, show semi-conductor to metal transition upon compressive strain without bucking

Fast MoS 2_2 2 thickness identification by transmission imaging

AbstractDetermining the thickness of a few-layer 2D material is a tough task that often involves complex and time consuming measurements. Here we discuss a rapid method for determining the number of layers of molybdenum disulfide, MoS$$_2$$ 2 , flakes based on microscopic transmission imaging. By analyzing the contrast of the red, blue and green channels of the flake image against the background, we show that it is possible to unequivocally determine the number of layers. The presented method is based on the light absorption properties of MoS$$_2$$ 2 and its validity is confirmed by micro-Raman measurements. The main advantage of this method against traditional methods is to quickly determine the thickness of the material in the early stages of the experimental process with low cost apparatus

Heterogeneous Integration of Autonomous Systems in Package for Wireless Sensor Networks

AbstractThe concept of Energy Harvester in Package (EHiP) is focused on the vertical heterogeneous integration of a MEMS die, dedicated to scavenge energy, with another auxiliary chip which includes the control and power management circuitry, sensors and RF capabilities. Based on this concept, we have developed and characterized several approaches for piezoelectric and electrostatic transductions to extract energy from the harmonic motion generated by a permanent magnet attached to the EHiP and placed in the surroundings of a cable of the power grid, i.e. an alternate electromagnetic field, in addition to the ambient mechanical vibrations

Multiscale Modelling of Resistive Switching in Gold Nanogranular Films*

Metallic nanogranular films display a complex dynamical response to a constant bias, typically showing up as a resistive switching mechanism which, in turn, could be used to create electrical components for neuromorphic applications. To model such a phenomenon we use a multiscale computational approach blending together (i) an ab initio treatment of the electric current at the nanoscale, (ii) a molecular dynamics approach dictating structural rearrangements, and (iii) a finite-element solution of the heat equation for heat propagation in the sample. We also consider structural changes due to electromigration which are modelled on the basis of experimental observations on similar systems. Within such an approach, we manage to describe some distinctive features of the resistive switching occurring in a nanogranular film and provide a physical interpretation at the microscopic level

Piezoelectric monolayers as nonlinear energy harvesters

We study the dynamics of h-BN monolayers by first performing ab-initio calculations of the deformation potential energy and then solving numerically a Langevine-type equation to explore their use in nonlinear vibration energy harvesting devices. An applied compressive strain is used to drive the system into a nonlinear bistable regime, where quasi-harmonic vibrations are combined with low-frequency swings between the minima of a double-well potential. Due to its intrinsic piezoelectric response, the nonlinear mechanical harvester naturally provides an electrical power that is readily available or can be stored by simply contacting the monolayer at its ends. Engineering the induced nonlinearity, a 20 nm device is predicted to harvest an electrical power of up to 0.18 pW for a noisy vibration of 5 pN

Inducing bistability with local electret technology in a microcantilever based non-linear vibration energy harvester

A micro-electro-mechanical system based vibration energy harvester is studied exploring the benefits of bistable non linear dynamics in terms of energy conversion. An electrostatic based approach to achieve bistability, which consists in the repulsive interaction between two electrets locally charged in both tip free ends of an atomic force microscope cantilever and a counter electrode, is experimentally demonstrated. A simple model allows the prediction of the measured dynamics of the system, which shows an optimal distance between the cantilever and the counter electrode in terms of the root mean square vibration response to a colored Gaussian excitation noise