First-principles nonequilibrium analysis of STM-induced molecular negative-differential resistance on Si(100)

Abstract

We report on theoretical investigations of scanning tunneling microscopy ͑STM͒induced molecular negative-differential resistance ͑NDR͒ on heavily p-type doped Si͑100͒. Calculations are performed using the density functional theory ͑DFT͒ local density approximation ͑LDA͒ within the Keldysh nonequilibrium Green's function ͑NEGF͒ formalism. The nonequilibrium Hamiltonian is determined self-consistently for molecules on a Si͑100͒ substrate and below a Pt͑100͒ STM tip. We investigate in detail the nonequilibrium conditions which are likely to produce electronic p-type resonant NDR. The discussion is divided into two parts. First, we discuss STM distance dependence and its relation to p-type resonant NDR. It is shown that under high bias conditions electron tunneling is dominated by tunneling near the top of the vacuum barrier thereby preventing resonant NDR at large STM imaging distances. Second, we discuss the self-consistent bias profile and its effect on p-type NDR. It is shown that molecular charging effects may prevent the highest occupied molecular orbital from passing the silicon electrochemical potential, though bistable effects beyond the self-consistent NEGF-LDA method cannot be ruled out.

First-principles calculation of current density in molecular devices

“…(4) and (5) and the nonlocal electron density according to Eqs. (10) and (16). Finally, the nonlocal current density J nl (r) can be computed by solving the Poisson equation 9, and the total current density J(r) can be obtained.…”

“…For instance, numerical investigation of current-voltage characteristics of molecular devices show negative differential resistance effect. [14][15][16] In addition, other dc transport properties such as shot noise, 17,18 thermoelectric properties, 19 spin-dependent electron transport, [20][21][22] and ac transport as well as transient transport [23][24][25][26][27] of nanodevices have also been studied. Quantitative agreement between theoretical prediction and experimental results has been reached.…”

Gold/Molecule/p$^+$ Si Devices: Variable Temperature Electronic Transport

“…Based on prior MMM modeling, the transmission through the molecule is related to the molecular DOS which is related to the isolated molecule orbital energies that are shifted and broadened due to contact coupling effects [15]. For the molecular modifiers on Si in this paper, the molecular transmission can be approximated by a Gaussian distribution with a half-width in the range of 0.5-1 eV [30]. As shown in Fig.…”

Electron transport in multiterminal molecular devices: A density functional theory study

“…[1][2][3][4][5][6][7][8] These results have substantially improved the general understanding of the I-V characteristic of nanojunctions. While it is still difficult to fully determine the atomic geometries of measured junctions and to establish a one-to-one correspondence between the observed and the calculated results, 9 there has been significant progress in both experimental and theoretical capabilities.…”

“…In fact, all of the existing ab initio approaches to electron transport that we are aware of have dealt only with two-terminal systems. 3,4,[17][18][19][20][21] It is however of general interest to develop robust computational schemes that can routinely and reliably account for the transport mechanism in multiterminal molecular junctions, as these are critically important in both fundamental studies and applications. Even in classical measurements of key electrical properties, four-terminal techniques are vastly more accurate and reliable than the two-terminal ones.…”