Search

The barrier properties of graphene coating are highly correlated with its microstructure which is then determined by the chemical vapor deposition (CVD) growth history on metals. We demonstrate here an unrevealed selective area oxidation of copper under graphene, which is derived from the implicit-etching-controlled CVD growth mode of graphene. By charactering and analyzing the selective area patterns of Cu oxidation, an etched pattern trace with nano/microvoids during graphene growth has been proposed to account for this. Based on such selective oxidation of Cu, distributed galvanic corrosion will be triggered and proceed locally at the interface of graphene-Cu system to coalescence together under a continuous corrosion environment, eventually presenting a homogeneous oxidation of Cu and gradual decoupling of graphene-Cu system. This discovery will assist our understanding of the barrier properties of two-dimensional materials and can be extended to other applications related to quality monitoring of grown materials and defects-based chemical modifications.

Micro four-point probes (M4PP) provide rapid and automated lithography-free transport properties of planar surfaces including two-dimensional materials. We perform sheet conductance wafer maps of graphene directly grown on a 100 mm diameter SiC wafer using a multiplexed seven-point probe with minor additional measurement time compared to a four-point probe. Comparing the results of three subprobes we find that compared to a single-probe result, our measurement yield increases from 72%-84% to 97%. The additional data allows for correlation analysis between adjacent subprobes, that must measure the same values in case the sample is uniform on the scale of the electrode pitch. We observe that the relative difference in measured sheet conductance between two adjacent subprobes increase in the transition between large and low conductance regions. We mapped sheet conductance of graphene as it changed over several weeks. Terahertz time-domain spectroscopy conductivity maps both before and after M4PP mapping showed no significant change due to M4PP measurement, with both methods showing the same qualitative changes over time.

We observe the formation of thin films of fibre-like aggregates from the prototypical organic semiconductor molecule para-hexaphenylene (p-6P) on graphite thin flakes and on monolayer graphene. Using atomic force microscopy, scanning electron microscopy, x-ray diffraction, polarized fluorescence microscopy, and bireflectance microscopy, the molecular orientations on the surface are deduced and correlated to both the morphology as well as to the high-symmetry directions of the graphitic surface: the molecules align with their long axis at ±11° with respect to a high-symmetry direction. The results show that the graphene surface can be used as a growth substrate to direct the self-assembly of organic molecular thin films and nanofibres, both with and without lithographical processing.

Fabrication of ultra-high aspect ratio exchangeable and customizable tips for atomic force microscopy (AFM) using lateral focused ion beam (FIB) milling is presented. While on-axis FIB milling does allow high aspect ratio (HAR) AFM tips to be defined, lateral milling gives far better flexibility in terms of defining the shape and size of the tip. Due to beam-induced deformation, it has so far not been possible to define HAR structures using lateral FIB milling. In this work we obtain aspect ratios of up to 45, with tip diameters down to 9 nm, by a deformation-suppressing writing strategy. Several FIB milling strategies for obtaining sharper tips are discussed. Finally, assembly of the HAR tips on a custom-designed probe as well as the first AFM scanning is shown.

We present here a method for cleaning intermediate-size (up to 50 nm) contamination from highly oriented pyrolytic graphite and graphene. Electron-beam-induced deposition of carbonaceous material on graphene and graphite surfaces inside a scanning electron microscope, which is difficult to remove by conventional techniques, can be removed by direct mechanical wiping using a graphite nanoeraser, thus drastically reducing the amount of contamination. We discuss potential applications of this cleaning procedure.

We consider here the possibility of using III-V heterostructure nanowires as electrodes for molecular electronics instead of metal point contacts. Using ab initio electronic structure and transport calculations, we study the effect on electronic properties of placing a small molecule with thiol linking groups, benzene-di-thiol (BDT), within a nanosize gap in a III-V nanowire. Furthermore, it is investigated how surface states affect the transport through pristine III-V nanowires and through the BDT molecule situated within the nanogap. Using GaAs and GaP as III-V materials we find that the BDT molecule provides transport through the entire system comparable to the case of gold electrodes.

Microfabricated grippers could be useful for the manipulation of nanoscopic and microscopic samples. A survey is presented of the force requirements for a microgripper to complete pick-and-place nanomanipulation tasks. We then demonstrate in situ pick-and-place operations of nanowires inside a scanning electron microscope using microfabricated electrostatically actuated grippers, and compare the theoretically estimated force requirements with the results of experimental tests of picking up nanowires to evaluate how grippers and strategies for nanomanipulation can be optimized.