Derick Engles

Augmenting Molecular Junctions with Different Transition Metal Contacts

In this research paper, the effect of the material of electrodes at the nanometer scale was elucidated towards measuring the electron transport properties of a single molecular junction comprising of anthracenedithiol molecule (ADT) stringed to two semi-infinite metallic electrodes using Extended Huckle Theory (EHT)-based semi-empirical modelling approach. The electron transport parameters i.e., I–V curves, Conductance-Voltage curves and transmission spectrum were investigated through ADT molecule by buffering it between different electrodes composed of rhodium, palladium, nickel and copper, all from transition metals series, under finite bias voltages within Keldyshs non equilibrium green function formulism (NEGF). The simulated results revealed that the copper electrodes showed maximum conduction whereas palladium showed least. The maximum conductance of 0.82 G0 and 43 μA current was exhibited by copper and thus affirmed to be the most effective electrode at nanometre scale when compared with other electrodes viz. nickel, rhodium and palladium.

Transport in fullerene device coupled to Cu, Ag and Au electrodes

ABSTRACT We present an ab initio approach of the electronic transport through a single molecular junction based on C20 fullerene. The electronic properties of a single molecular junction constrained within two semi-infinite metallic electrodes are largely affected by the choice of electrode material. The two-probe device formed by the mechanically control break technique has been modelled with three distinct electrode materials from group IB of the periodic table, namely copper, silver and gold. The quantum characteristics of these mechanically stable devices are obtained by utilising first-principle density functional theory together with non-equilibrium green function method. We evaluate the quantum characteristics, namely density of states, transmission spectrum, energy levels, current and conductance, which essentially determine the behaviour of a molecule linked to different electrodes. Our investigation concludes that copper, silver and gold electrode configuration in conjunction with C20 fullerene behaves as metallic, non-metallic and semi-metallic in nature, respectively.

Effect of gold electrode crystallographic orientations on charge transport through aromatic molecular junctions

ABSTRACT We examined the electrical conduction through single-molecular junctions comprising of anthracenedithiol molecule coupled to two gold electrodes having ⟨1,0,1⟩, ⟨1,1,0⟩ and ⟨1,1,1⟩ crystallographic orientations. Owing to this jellium model, we evaluated the values of current and conductance using non-equilibrium Greens functions combined with extended Huckel theory. This data was further interpreted in terms of transmission spectra, density of states and their molecular orbital analysis for zero bias. We evinced the oscillating conductance in all three cases, due to the oscillation of orbital energy relative to Fermi level. Our detailed analysis suggested that electrode orientation can tune the molecule–electrode coupling and hence conduction. Anthracene molecular junction with ⟨1,1,0⟩ orientation displayed favourable conduction, when compared to the other two orientations, thus can provide us an insight while designing futuristic molecular electronic devices.

To evince pure C24 as superconductoring mechanically controllable break junction configuration

In this paper, we expounded the superconductive nature for fullerenes, which are being explored for the molecular electronics applications. The fullerene we picked for our research work is the C24 which was then doped with popular dopants- Boron, Nitrogen and Phosphorus and the self-consistent calculations were performed in the configuration where molecule was bridged between the gold electrodes using MCBJ (Mechanically Controlled Break Junctions) technique at sub-zero temperature of 0.100K. The characteristics of these variants of doped C24were compared with that for pure C24 and the results clearly demonstrated the electrical superiority of the pure C24 over its doped counterparts for cryogenic applications of electronics. This paper would represent another mark in the field of molecular electronics that prefer carbon or organic materials as competing future in nanotechnology for military and defence applications.

Contemplating Transport Characteristics by Augmenting the Length of Molecule

In this paper, we contemplated the transport characteristics of a single molecular device junction by augmenting the length of the molecule in the scattering region. The molecules considered here belongs to class of alkanedithiols (CnH2n+2S2). Specifically, we used a tight binding semi-empirical model to compute the transport characteristics of butanedithiol, pentanedithiol, hexanedithiol and heptanedithiol connected to semi-infinite gold electrodes through thiol anchoring elements. The exploration of transport properties of considered alkanes was completed for different bias voltages within the sphere of Keldyshs Non Equilibrium Greens Function (NEGF) and Extended Huckel Theory (EHT), for studying the self-consistent steady-state solution, analyzing the out-of-equilibrium electron distribution, and the behavior of the self-consistent potential. We perceived that the current and conductance retrenches with aggravation with the increase in length of the molecule with exhibition of single electron tunneling. We observed that the coupling regime shifts from strong coupling to weak for higher order alkanedithiols and the transmission is function of evenness or oddness of the carbon atoms forming an alkane.

Proliferating miller indices of C20 fullerene device under DFT-NEGF regime

We present ab-initio scrutiny of electron transport through C20 fullerene cleaved with gold electrodes having unique set of miller orientations. The three families of miller indices {100}, {110} and {111} are considered with four exclusive device models for elucidating electronic transport under applied potential of - 2 to +2V. Thereafter, the quantum calculations employing DFT-NEGF are performed for envisaging density of states, transmission function, energy levels, molecular orbitals, charge transfer. These electronic transfer parameters lead to the study of its two electrical parameters: current and conductance. We conclude that in molecular-devices of constituted miller family {110}, HOMO-LUMO gap are inversely proportional to extent of charge carriers. While for miller devices {100} and {111}, the situation is fully contrasting with HOMO-LUMO gap being directly proportional to its charge carriers. Another important conclusion is that the gold electrodes having miller family {100} and {111} are providing equal opportunity to fullerene molecule to imply its behavior while electrodes of miller family {110} are over shadowing the performance of fullerene molecule.

First principle electron transport modeling of Be-doped organic molecular junctions

The transport properties of beryllium doped anthracene molecular junction are investigated using density functional non-equillibrium Greens function method. The equilibrium conductance of anthracene Metal-molecule-Metal (MmM) junction increases by approximately 77% by adding beryllium impurity to it. The electronic transport characteristics under both zero bias as well as finite bias are explored of such molecular junction. We observe novel attributes such as molecular rectification and NDR behavior for the molecular junction under consideration. It is found that the doping effect of Be- atom significantly changes the transport properties of aromatic molecular junction. Our findings shed light on the electron transport metrics that affect the conductance of MmM junctions within appreciable transmission limits. We firmly believe that the results deduced in this paper can be generalized for other aromatic molecular junctions as well.

MDS Algorithm for Encryption

Most of the encryption algorithms used today generates huge cipher messages as well as long encryption keys. These approaches require time and are computationally intensive .While sending data packets through the network a compression technique along with cryptography can be applied to reduce the data packet size for better bandwidth utilization and hence faster transmission of data. In this study we propose a new encryption technique which will encrypt data into reduced size cipher text while keeping the check on size of key. The algorithm was first introduced in an earlier paper. In this study we modified algorithm to preprocess text as well as numeric data.

AROMATIC MOLECULAR JUNCTIONS WITH INERT GASES AS ALLIGATOR CLIPS

In this research paper, we examined the effect of placing the elements of Group 0 as alligator clips with Anthracene molecule binding gold electrodes on the nanometer scale using Extended Huckle Theory (EHT) based semi-empirical model. The electron transport parameters i.e., I-V curves, Conductance-Voltage curves and transmission spectrum were investigated through Anthracene molecule by buffering it between two semi-infinite gold electrodes but via different alligator clips-Helium, Neon, Argon, Krypton, Xenon and Radon, all from Noble gas group or group-0 under finite bias voltages within Keldyshs nonequilibrium green function formalism (NEGF). The simulated results revealed that the Xenon and Radon showed maximum conduction whereas Krypton, Neon, Helium and Argon showed least. The maximum conductance of 0.62G0 and 70.4 μA current was exhibited by Xenon and thus affirmed to be the most optimal alligator clip amongst noble gases at nanometre scale.

Charge transport through a molecular wire for flexible electronics

In the present work we used a system consisting of a molecular wire of multiple thiophene rings bridged between gold electrodes to study the charge transport mechanism, the effect of the tilt angle, the temperature dependence, the atomic configuration of the gold electrodes, the molecule–electrode interaction and the effect of rotation of the molecular wire on the conductance of the studied system. We found that, for shorter molecular lengths, the charge transport can be explained by tunneling, but, as the molecular length increases, it changes to hopping, which is supported by modeling the conductance of the molecular wire with a change in the temperature of the system. The results show that shorter molecular wires exhibit temperature-invariant behavior, and longer molecular wires exhibit highly temperature-variant behavior. The geometrically optimized symmetries of thiophene molecules with even and odd orientation are different, which leads to a difference in the contact configurations between the molecule and the electrodes, and results in a larger coupling parameter for thiophene molecules with even thiophene rings than for thiophene molecules with odd thiophene rings.