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.

Ballistic electron emission microscopy is utilized to investigate the hot-electron scattering properties of Cu through Cu/Si(001) Schottky diodes. A Schottky barrier height of 0.64±0.02 eV and a hot-electron attenuation length of 33.4±2.9 nm are measured at a tip bias of 1.0 eV and a temperature of 80 K. The dependence of the attenuation length with tip bias is fit to a Fermi liquid model that allows extraction of the inelastic and elastic scattering components. This modeling indicates that elastic scattering due to defects, grain boundaries, and interfaces is the dominant scattering mechanism in this energy range.

Articles you may be interested inSchottky barrier height measurements of Cu/Si(001), Ag/Si(001), and Au/Si(001) interfaces utilizing ballistic electron emission microscopy and ballistic hole emission microscopy AIP Advances 3, 112110 (2013); 10.1063/1.4831756 Hot-electron transport studies of the Ag/Si(001) interface using ballistic electron emission microscopy J. Vac. Sci. Technol. A 28, 643 (2010); 10.1116/1.3397795 Ambipolar ballistic electron emission microscopy studies of gate-field modified Schottky barriers Appl. Phys. Lett. 96, 242106 (2010); 10.1063/1.3453866Ion-bombardment effects on PtSi /n -Si Schottky contacts studied by ballistic electron emission microscopy

The hot electron attenuation length of Ag is measured utilizing ballistic electron emission microscopy on nanoscale Schottky diodes for Si(001) and Si(111) substrates. Marked differences in the attenuation length are observed at biases near the Schottky barrier depending upon the substrate orientation, increasing by an order of magnitude only for Si(001). These results provide clear evidence that the crystallographic orientation of the semiconductor substrate and parallel momentum conservation affect the charge transport across these interfaces. A theoretical model reproduces the effect that combines a free-electron description within the metal with an ab-initio description of the electronic structure of the semiconductor.

Scanning tunnelling microscopy and X-ray reflectivity are used to characterize adlayers of perylenetetracarboxylic diimide (PTCDI) deposited on epitaxial graphene (EG) on SiC(0001). PTCDI adopts a herringbone structural phase on EG/SiC that can accommodate sub-5 nm voids with molecularly defined boundaries and isolated molecular vacancies at room temperature. The PTCDI monolayer remains intact up to substrate temperatures of ~260 °C, thus demonstrating enhanced thermal stability compared to previously studied perylene derivatives on EG/SiC.