A scanning tunneling microscopy (STM) study, combined with density functional theory (DFT) calculations and thermal desorption spectroscopy (TDS) data, on the growth and structure of Zn on a Pd(111) surface is presented. The STM results demonstrate that PdZn(111) surface alloy bilayer islands with a p(2 × 1) structure already form during the room temperature deposition of submonolayer amounts of Zn on Pd(111). DFT calculations predict that the PdZn bilayers are energetically more stable than single PdZn layers and establish their structural parameters. The TDS data show that Zn desorbs below 600 K in a multiple-peak desorption structure with fractional order desorption kinetics of the individual components, which is due to multilayer Zn desorption. The experimentally derived adsorption energies of the low temperature desorption peaks are reproduced in the DFT calculations. At temperatures above 750 K, Zn desorbs from the PdZn alloy, and the desorption kinetics is a mixture of a first-order and a diffusion-limited desorption process.

Scalably grown and transferred graphene is a highly promising material for organic electronic applications, but controlled interfacing of graphene thereby remains a key challenge. Here, we study the growth characteristics of the important organic semiconductor molecule para-hexaphenyl (6P) on chemical vapor deposited graphene that has been transferred with polymethylmethacrylate (PMMA) onto oxidized Si wafer supports. A particular focus is on the influence of PMMA residual contamination, which we systematically reduce by H2 annealing prior to 6P deposition. We find that 6P grows in a flat-lying needle-type morphology, surprisingly independent of the level of PMMA residue and of graphene defects. Wrinkles in the graphene typically act as preferential nucleation centers. Residual PMMA does however limit the length of the resulting 6P needles by restricting molecular diffusion/attachment. We discuss the implications for organic device fabrication, with particular regard to contamination and defect tolerance.

Tapping mode atomic force microscopy (AFM) is employed for dynamic plowing lithography of exfoliated graphene on silicon dioxide substrates. The shape of the graphene sheet is determined by the movement of the vibrating AFM probe. There are two possibilities for lithography depending on the applied force. At moderate forces, the AFM tip only deforms the graphene and generates local strain of the order of 0.1%. For sufficiently large forces the AFM tip can hook graphene and then pull it, thus cutting the graphene along the direction of the tip motion. Electrical characterization by AFM based electric force microscopy, Kelvin probe force microscopy and conductive AFM allows us to distinguish between the truly separated islands and those still connected to the surrounding graphene.

We report on para-hexaphenyl (6P) ultrathin film growth on freshly prepared and air-passivated atomically flat rutile titanium dioxide single-crystal (110) surfaces. The surface morphology of the developed structures has been investigated in situ and ex situ by means of various scanning probe techniques and electron microscopy. In situ 6P deposition results in the formation of a wetting layer of lying molecules coexisting with bunches of tens of micrometers long needles oriented along the TiO 2 [11̅ 0] surface direction. The observed bunching of the 3−5 nm high needles is explained in terms of anisotropic diffusion paths along and perpendicular to the needles. Air exposure of the asprepared films induces the formation of small features at the cost of the 6P wetting layer, whereas the needles stay unchanged. In contrast, 6P deposition on already air-passivated TiO 2 (110) yields the formation of dendritic islands, composed of roughly upright-standing molecules. No 6P wetting layer forms on the air-passivated surface. In addition to air exposure, we have checked the impact of surface modification via ion beam bombardment. Growth of 6P on gradient ion-beam-modified titanium dioxide substrates kept at either room or elevated temperature reveals that a slight surface roughening is sufficient to switch the film from lying molecular orientation to upright-standing orientation. However, surface stoichiometry severely influences film properties like size, density, and shape of the 6P islands.

This study focuses on hexagonal boron nitride as an ultra-thin van der Waals dielectric substrate for the epitaxial growth of highly ordered crystalline networks of the organic semiconductor parahexaphenyl. Atomic force microscopy based morphology analysis combined with density functional theory simulations reveal their epitaxial relation. As a consequence, needle-like crystallites of parahexaphenyl grow with their long axes oriented five degrees off the hexagonal boron nitride zigzag directions. In addition, by tuning the deposition temperature and the thickness of hexagonal boron nitride, ordered networks of needle-like crystallites as long as several tens of micrometers can be obtained. A deeper understanding of the organic crystallites growth and ordering at ultra-thin van der Waals dielectric substrates will lead to grain boundary-free organic field effect devices, limited only by the intrinsic properties of the organic semiconductors.