Effects of Different Self-Assembled Monolayers on Thin-Film Morphology: A Combined DFT/MD Simulation Protocol

Abstract

Organic thin film transistors (OTFTs) are multilayer field-effect transistors that employ an organic conjugated material as semiconductor. Several experimental groups have recently demonstrated that the insertion of an organic self-assembled monolayer (SAM) between the dielectric and the semiconductive layer is responsible for a sensible improvement of the OTFT performances in terms of an increased charge carrier mobility caused by a higher degree of order in the organic semiconductor layer. Here, we describe a combined periodic density functional theory (DFT) and classical molecular dynamics (MD) protocol applied to four different SAMs and a pentacene monolayer deposited onto their surfaces. In particular, we investigate the morphology and the surface of the four SAMs and the translational, orientational, and nematic order of the monolayer through the calculation of several distribution functions and order parameters pointing out the differences among the systems and relating them to known experimental results. Our calculations also suggest that small differences in the SAM molecular design will produce remarkable differences in the SAM surface and monolayer order. In particular, our simulations explain how a SAM with a bulky terminal group results in an irregular and rough surface that determines the deposition of a disordered semiconductive monolayer. On the contrary, SAMs with a small terminal group generate smooth surfaces with uninterrupted periodicity, thus favoring the formation of an ordered pentacene monolayer that increases the mobility of charge carriers and improves the overall performances of the OTFT devices. Our results clearly point out that the in silico procedure presented here might be of help in tuning the design of SAMs in order to improve the quality of OTFT devices.

Single-molecule detection with a millimetre-sized transistor

“…In order to model a realistic SAM surface, a computational protocol inspired by Ref. 49 , herein described, was adopted. All the periodic density functional theory (DFT) calculations were performed using the CP2K/Quickstep package 50 .…”

The supramolecular structure and van der Waals interactions affect the electronic structure of ferrocenyl-alkanethiolate SAMs on gold and silver electrodes

“…7 This is mainly because SAMs provide a convenient strategy to control the physical, chemical, and electronic properties of surfaces of metals and inorganic semiconductors. 7 For applications in electronics, SAMs have been used to lower charge injection barriers, 8 to improve packing of polymers and small molecules in organic thin lm transistors, 9,10 and as the active component in SAM-based molecular electronics. 7,[11][12][13][14][15][16] One of the advantages of SAMs in these applications is that they can be chemically tailored, allowing for atomic scale control over the electronic structure of the molecule-electrode interfaces, which, in turn, determines the performance of the SAM-based devices.…”

Surface Modification of Pseudoboehmite-Coated Aluminum Plates with Squaramic Acid Amphiphiles

“…The (010) surface was selected because previous studies have already shown that it is the most stable, 50 and, moreover, it has been successfully used to analyze the insertion of phosphonic acids. 51 The proposed mechanism involves the protonation of one of the OH groups of the supercell by the squaramic acid (or carboxylic acid) and a subsequent replacement of water by the squaramate (or a carboxylate) anion though a coordination bond to two Al-atoms. For the theoretical studies, we have used squaramic acid 4 and butyric acid as models.…”