Molecular Length, Monolayer Density, and Charge Transport: Lessons from Al–AlOx/Alkyl–Phosphonate/Hg Junctions

Abstract

A combined electronic transport-structure characterization of self-assembled monolayers (MLs) of alkyl-phosphonate (AP) chains on Al-AlOx substrates indicates a strong molecular structural effect on charge transport. On the basis of X-ray reflectivity, XPS, and FTIR data, we conclude that "long" APs (C14 and C16) form much denser MLs than do "short" APs (C8, C10, C12). While current through all junctions showed a tunneling-like exponential length-attenuation, junctions with sparsely packed "short" AP MLs attenuate the current relatively more efficiently than those with densely packed, "long" ones. Furthermore, "long" AP ML junctions showed strong bias variation of the length decay coefficient, β, while for "short" AP ML junctions β is nearly independent of bias. Therefore, even for these simple molecular systems made up of what are considered to be inert molecules, the tunneling distance cannot be varied independently of other electrical properties, as is commonly assumed.

Organic Monolayers from 1-Alkynes Covalently Attached to Chromium Nitride: Alkyl and Fluoroalkyl Termination

“…This allows us to derive information regarding the short-range order and packing density, the overall molecular orientation (tilt angle), and the presence of functional groups within the monolayers. 49 In Figure 4, the C−H stretching vibration peaks for short-chain C6YNE ( Figure 4A) and long-chain C18YNE ( Figure 4B) are depicted. For comparison purposes, with relevant modes assigned, the exact IR peak positions are shown in Figure 4C.…”

High-yield metal transfer printing on alkyl bis-phosphonate monolayers

“…3. A very hydrophilic, bare AlOx substrate surface (CA: <10°) became rather hydrophobic (CA: >105°) after SAM modification with C8mono and C12mono, which is expected for a microscopically uniform methyl-terminated surface [12], [13]. Deposition of C8bis SAM gave a moderately hydrophilic (CA: ~55°) surface.…”

N‐Type Self‐Assembled Monolayer Field‐Effect Transistors and Complementary Inverters

“…[ 18 ] In comparison to thiols, which form relatively weak bonds to gold, phosphonic acids bind more strongly to aluminum oxide. [ 19 ] After immersion for 24 h under ambient atmosphere and room temperature, the devices were dipped into tetrahydrofuran and annealed at 120 ° C under N 2 atmosphere for 20 min. Subsequently the SAMFETs were analyzed and measured.…”