Two-Dimensional Molecular Crystals of Phosphonic Acids on Graphene

Abstract

The synthesis and characterization of two-dimensional (2D) molecular crystals composed of long and linear phosphonic acids atop graphene is reported. Using scanning probe microscopy in combination with first-principles calculations, we show that these true 2D crystals are oriented along the graphene armchair direction only, thereby enabling an easy determination of graphene flake orientation. We have also compared the doping level of graphene flakes via Raman spectroscopy. The presence of the molecular crystal atop graphene induces a well-defined shift in the Fermi level, corresponding to hole doping, which is in agreement with our ab initio calculations.

Electro-optical interfacial effects on a graphene/π-conjugated organic semiconductor hybrid system

“…2 – side view). Comparing the total energy involved in both tail–tail and tail–head configurations, the former was found to be the most stable by 0.5 eV, indicating that hydrogen bond formation minimizes the system energy [16]. This result corroborates the experimental results in Fig.…”

“…The RA multilayer (bulk-like film) was produced by spread coating method [59–61]. Thin film samples were prepared by spin-coating (2200 rpm) from 0.2 mM and 2 mM tetrahydrofuran solution on a given substrate (monolayer graphene up to graphite microplates prepared via mechanical exfoliation of graphite flakes) [16]. According to recent literature, the expression “graphite microplate” is the accurate term to describe a flake with tens of microns in lateral size and tens, or hundreds, of graphene layers in thickness [62–63], which is exactly the substrate we used for SPM and PL measurements.…”

“…In this context, it is important to control the ordering of π-conjugated organic molecules to make their use on optoelectronic devices possible. In another front, self-assembled monolayers (SAMs) on low-dimensional systems, such as a graphene (an archetypical 2D material), have attracted significant attention due to the myriad of applications in nanoelectronic devices [14–16]. Aiming at the improvement of graphene-based devices, SAM surface functionalization is employed for both doping level control and work function tuning [14–16].…”

“…In another front, self-assembled monolayers (SAMs) on low-dimensional systems, such as a graphene (an archetypical 2D material), have attracted significant attention due to the myriad of applications in nanoelectronic devices [14–16]. Aiming at the improvement of graphene-based devices, SAM surface functionalization is employed for both doping level control and work function tuning [14–16]. The present work brings these two fronts together by investigating a graphene/retinoic acid (RA) – a π-conjugated organic semiconductor – hybrid system and its interfacial effects.…”

Supramolecular Approaches to Graphene: From Self‐Assembly to Molecule‐Assisted Liquid‐Phase Exfoliation

“…In 2010 Neves and co-workers showed that p-type doping of graphene can be achieved under ambient conditions through non-covalent functionalization of graphene with octadecylphosphonic acid (OPA, Figure 2) molecules. [151] AFM images demonstrated that OPA molecules, which comprise phosphonic acid headgroups on linear alkyl chains (Figure 5a), self-assemble into ordered 2D crystals by drop-casting onto SLG surface (prepared by mechanical exfoliation), supported on SiO 2 . Raman spectroscopy analysis of OPA-functionalized graphene revealed that the position of graphene G peak shifts to higher wavelengths.…”