Charge transport across metal/molecular (alkyl) monolayer-Si junctions is dominated by the LUMO level

Abstract

We compare the charge transport characteristics of heavy doped p ++ -and n ++ -Si-alkyl chain/Hg junctions. Photoelectron spectroscopy (UPS, IPES and XPS) results for the molecule-Si band alignment at equilibrium show the Fermi level to LUMO energy difference to be much smaller than the corresponding Fermi level to HOMO one. This result supports the conclusion we reach, based on negative differential resistance in an analogous semiconductor-inorganic insulator/metal junction, that for both p ++ -and n ++ -type junctions the energy difference between the Fermi level and LUMO, i.e., electron tunneling, controls charge transport. The Fermi level-LUMO energy difference, experimentally determined by IPES, agrees with the non-resonant tunneling barrier height deduced from the exponential length-attenuation of the current.

Electron transport in all-carbon molecular electronic devices

“…However, if the two phases interact electronically, particularly by charge transfer across the interface, the classical literature used the terms "strong electronic coupling", also the "Bardeen limit". Such electronic interactions have been described extensively for interfaces between two semiconductors, a metal and semiconductor, or a metal and organic layer, and can result in apparent changes in work function and alterations in orbital energies of the system 43,[49][50][51][52][53] . Bonding an aromatic molecule to the surface of PPF creates a conjugated, covalent bond between two aromatic systems, which are likely to interact electronically.…”

“…If d is small enough, there is finite overlap between the electron density from the carbon surface and the Cu contact, thus permitting electron transport across the molecular layer in response to an applied bias. Electron tunnelling with its exponential distance dependence has been reported for a wide range of systems5,22,[35][36][37][38][39][40][41][42][43][44][45] , including single molecule as well as "ensemble" MJs, and it is reassuring that a β of 8-9 nm -1 is often reported for aliphatic molecules in homogeneous, electrochemical, and solid state electron transport.Off-resonant tunnelling mechanisms always involve an energy barrier, with higher or thicker barriers decreasing the probability of a tunnelling event. The often assumed barriers for a MJ are shown infigure 5C, with Φ e indicating the electron tunnelling barrier, assumed to equal the difference in energy between the Fermi level of the contacts and the lowest unoccupied molecular orbital (LUMO).…”

Monolayers of Biphenyl-3,4′,5-tricarboxylic Acid Formed on Cu and Ag from Solution

“…[81][82] It is noted that the molecular orbitals are based on calculations of the isolated neutral BPTCA molecule, i.e., no bonding to the substrate is taken into account. The rationale behind this is that for upright standing molecules the MOs of the molecule should not be fundamentally affected by the comparably weak BPTCA-Ag coupling.…”

Fluorinated alkyne-derived monolayers on oxide-free silicon nanowires via one-step hydrosilylation

“…In this regard, the use of fluorinated alkynes would provide an easily accessible additional tool, namely the stepwise variation of the work function of the underlying Si NWs surface. [32][33][34] In this study, we investigated the formation of five different 1-hexadecyne-derived monolayers with a varying number of fluorine atoms (HCC-(CH 2 ) 6 C 8 H 17-x F x ; x = 0, 1, 3, 9, 17) onto oxidefree hydrogen-terminated Si NWs by a one-step hydrosilylation using 1-alkynes F0 to F17 (Scheme 1). These monolayers were characterized in detail by X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR), static contact angle measurements, scanning electron microscopy (SEM) and transmission electron microscopy (TEM …”