van der Waals Bonded Co/h-BN Contacts to Ultrathin Black Phosphorus Devices

Due to the chemical inertness of 2D hexagonal-Boron Nitride (h-BN), few atomic-layer h-BN is often used to encapsulate air-sensitive 2D crystals such as Black Phosphorus (BP). However, the effects of h-BN on Schottky barrier height, doping and contact resistance are not well known. Here, we investigate these effects by fabricating h-BN encapsulated BP transistors with cobalt (Co) contacts. In sharp contrast to directly Co contacted p-type BP devices, we observe strong n-type conduction upon insertion of the h-BN at the Co/BP interface. First principles calculations show that this difference arises from the much larger interface dipole at the Co/h-BN interface compared to the Co/BP interface, which reduces the work function of the Co/h-BN contact. The Co/h-BN contacts exhibit low contact resistances (~ 4.5 k-ohm), and are Schottky barrier free. This allows us to probe high electron mobilities (4,200 cm2/Vs) and observe insulator-metal transitions even under two-terminal measurement geometry

Computational Study of Ga NMR Shielding in Metallic Gallides

We present first-principles calculations of the isotropic NMR Ga shielding in metallic MGa2 with M = Ca, Sr, Ba and MGa4 with M = Na, Ca, Sr and Ba. We show that the experimentally observed trend of Ga NMR shifts is as expected driven mainly by the spin part of the response, but the orbital contribution must not be neglected. For all analyzed compounds the spin contact term constitute the major component of the response, except for BaGa2, where the spin-dipolar contribution is unusually large. This spin-dipolar contribution is related to the difference of the Ga-4pz and 4px,y partial density of states (PDOS) at the Fermi level, which is large only for BaGa2. It is related to the honeycomb-like Ga-lattice and the distances between Ga atoms. The spin-contact term is determined to a large extend by Ga-4s PDOS at the Fermi level, because the magnetic field leads to a small spin-splitting and a reoccupation of spin-up and spin-down states. This Ga-4s PDOS is related to the local atomic structure around the Ga atoms and results in fact from an overlap with the neighboring Ga-4p orbitals, therefore more symmetric local arrangements of atoms around Ga result in higher Ga-4s PDOS. However, we noticed that for very low Ga-4s PDOS the spin contact term does not tend to zero but changes sign and becomes diamagnetic. This can be explained by the energy dependence of the Ga-4s radial wave function near the nucleus, leading to a contraction/expansion of 4s densities, respectively. This effect is also present in all insulating materials; however, it has been neglected so far in literature

Chemical affinity can govern notch-tip brittle-to-ductile transition in metallic glasses

Chemical short-range order (CSRO) has emerged as an important index of material properties for multicomponent metallic alloys and glasses, but its role in transition between brittle and ductile fracture mechanisms is not understood. Here, using molecular dynamics simulations of fracture in notched samples of a nominally brittle metallic glass Fe80P20, we show that the fracture mode can be altered from crack propagation to shear banding by tuning CSRO. The underlying mechanism is identified as the agglomeration of metalloid (P) atoms as heterogeneous brittle zones with the formation of CSRO, leading to brittle fracture. By reducing the extent of CSRO, shear banding at the notch tip becomes the dominant failure mechanism. (c) 2022 Elsevier Ltd. All rights reserved.Peer reviewe

Length dependence of electron transport through molecular wires - a first principles perspective

PHYSICAL CHEMISTRY CHEMICAL PHYSICS17177-9

Origin of Contact Resistance at Ferromagnetic Metal-Graphene Interfaces

10.1021/acsnano.6b06286ACS NANO101211219-1122

Low Resistance Metal Contacts to MoS2 Devices with Nickel-Etched-Graphene Electrodes

ACS NANO91869-87