Self-Assembled Two-Dimensional Heteromolecular Nanoporous Molecular Arrays on Epitaxial Graphene

The development of graphene functionalization strategies that simultaneously achieve two-dimensional (2D) spatial periodicity and substrate registry is of critical importance for graphene-based nanoelectronics and related technologies. Here, we demonstrate the generation of a hydrogen-bonded molecularly thin organic heteromolecular nanoporous network on epitaxial graphene on SiC(0001) using room-temperature ultrahigh vacuum scanning tunneling microscopy. In particular, perylenetetracarboxylic diimide (PTCDI) and melamine are intermixed to form a spatially periodic 2D nanoporous network architecture with hexagonal symmetry and a lattice parameter of 3.45 ± 0.10 nm. The resulting adlayer is in registry with the underlying graphene substrate and possesses a characteristic domain size of 40–50 nm. This molecularly defined nanoporous network holds promise as a template for 2D ordered chemical modification of graphene at lengths scales relevant for graphene band structure engineering

Coexistence of Two Electronic Nano-Phases on a CH₃NH₃PbI_3–<i>x</i>Cl_<i>x</i> Surface Observed in STM Measurements

Scanning tunneling microscopy is utilized to investigate the local density of states of a CH₃NH₃PbI_3–<i>x</i>Cl_<i>x</i> perovskite in cross-sectional geometry. Two electronic phases, 10–20 nm in size, with different electronic properties inside the CH₃NH₃PbI_3–<i>x</i>Cl_<i>x</i> perovskite layer are observed by the d<i>I/</i>d<i>V</i> mapping and point spectra. A power law dependence of the d<i>I/</i>d<i>V</i> point spectra is revealed. In addition, the distinct electronic phases are found to have preferential orientations close to the normal direction of the film surface. Density functional theory calculations indicate that the observed electronic phases are associated with local deviation of I/Cl ratio, rather than different orientations of the electric dipole moments in the ferroelectric phases. By comparing the calculated results with experimental data we conclude that phase A (lower contrast in d<i>I/</i>d<i>V</i> mapping at −2.0 V bias) contains a lower I/Cl ratio than that in phase B (higher contrast in d<i>I/</i>d<i>V</i>)

Templating Sub-10 nm Atomic Layer Deposited Oxide Nanostructures on Graphene via One-Dimensional Organic Self-Assembled Monolayers

Molecular-scale control over the integration of disparate materials on graphene is a critical step in the development of graphene-based electronics and sensors. Here, we report that self-assembled monolayers of 10,12-pentacosadiynoic acid (PCDA) on epitaxial graphene can be used to template the reaction and directed growth of atomic layer deposited (ALD) oxide nanostructures with sub-10 nm lateral resolution. PCDA spontaneously assembles into well-ordered domains consisting of one-dimensional molecular chains that coat the entire graphene surface in a manner consistent with the symmetry of the underlying graphene lattice. Subsequently, zinc oxide and alumina ALD precursors are shown to preferentially react with the functional moieties of PCDA, resulting in templated oxide nanostructures. The retention of the original one-dimensional molecular ordering following ALD is dependent on the chemical reaction pathway and the stability of the monolayer, which can be enhanced via ultraviolet-induced molecular cross-linking