Quantum transport in alkane molecular wires: Effects of binding modes and anchoring groups

Abstract

Effects of binding modes and anchoring groups on nonequilibrium electronic transport properties of alkane molecular wires are investigated from atomic first-principles based on density functional theory and nonequilibrium Green's function formalism. Four typical binding modes, top, bridge, hcp-hollow, and fcc-hollow, are considered at one of the two contacts. For wires with three different anchoring groups, dithiol, diamine, or dicarboxylic acid, the low bias conductances resulting from the four binding modes are all found to have either a high or a low value, well consistent with recent experimental observations. The trend can be rationalized by the behavior of electrode-induced gap states at small bias. When bias increases to higher values, states from the anchoring groups enter into the bias window and contribute significantly to the tunneling process so that transport properties become more complicated for the four binding modes. Other low bias behaviors including the values of the inverse length scale for tunneling characteristic, contact resistance, and the ratios of the high/low conductance values are also calculated and compared to experimental results. The conducting capabilities of the three anchoring groups are found to decrease from dithiol, diamine to dicarboxylic-acid, largely owing to a decrease in binding strength to the electrodes. Our results give a clear microscopic picture to the transport physics and provide reasonable qualitative explanations for the corresponding experimental data.

Towards quantitative accuracy in first-principles transport calculations: The GW method applied to alkane/gold junctions

“…Our DFT results are in reasonable agreement with previous DFT studies showing decay factors in the range 0.83–1.01 and conductance resistances in the range (0.09–0.28) G 0 [8–10]. While the β values obtained with GW are rather close to the DFT calculated ones, the contact conductance is reduced by a factor of 3–5, depending on the coverage.…”

“…Although previous studies based on DFT yielded β values within the experimental range, the contact conductance, G c , is typically overestimated by around an order of magnitude [3–10]. A study based on the many-body configuration interaction method has shown similar β values, but slightly reduced G c values, as compared to DFT [52].…”

Altering regularities on resistances of doped Au–alkanedithiol–Au junctions

“…Such a device is becoming even more interesting because different laboratories reported transport data that were quantitatively consistent with each other [19][20][21]. In addition, theoretical researchers also do their utmost to explore the effects of length, end groups, bonding sites, and interface states on the transport properties of alkane molecular junction [22][23][24]. The same conclusion was obtained from the above experimental and theoretical works: the resistance of alkane molecule is enormous.…”

Impact of Anchoring Groups on Ballistic Transport: Single Molecule vs Monolayer Junctions

“… 16 − 18 Thus, alternative anchoring groups have been studied extensively both theoretically and experimentally. These include, for example, pyridines 10 , 19 − 21 , isocyanides (−NC), 7 , 22 , 23 cyanides (−CN), 5 , 10 , 22 the above-mentioned selenolates (−Se), 24 , 25 amines (−NH 2 ), 10 , 26 − 28 carboxyl-acids (−COOH), 26 , 29 and fullerenes (C 60 ). 30 − 32 These investigations showed that, depending on their donor and acceptor character, anchoring groups can have a profound impact on the level alignment, 9 i.e., the relative energetic position of the HOMO (highest occupied molecular orbital) and the LUMO (lowest unoccupied molecular orbital) with respect to the metal Fermi level.…”