Controllable Synthesis of Few-Layer Graphene on β-SiC(001)

Few-layer graphene exhibits exceptional properties that are of interest for fundamental research and technological applications. Nanostructured graphene with self-aligned domain boundaries and ripples is one of very promising materials because the boundaries can reflect electrons in a wide range of energies and host spin-polarized electronic states. In this chapter, we discuss the ultra-high vacuum synthesis of few-layer graphene on the technologically relevant semiconducting β-SiC/Si(001) wafers. Recent experimental results demonstrate the possibility of controlling the preferential domain boundary direction and the number of graphene layers in the few-layer graphene synthesized on the β-SiC/Si(001) substrates. Both these goals can be achieved utilizing vicinal silicon wafers with small miscuts from the (001) plane. This development may lead to fabricating new tunable electronic nanostructures made from graphene on β-SiC, opening up opportunities for new applications

2D/3D Metallic Nano-objects Self-Organized in an Organic Molecular Thin Film

We present the fabrication and investigation of the properties of nanocomposite structures consisting of two-dimensional (2D) and three-dimensional (3D) metallic nano-objects self-organized on the surface and inside of organic molecular thin-film copper tetrafluorophthalocyanine (CuPcF4). Metallic atoms, deposited under ultrahigh vacuum (UHV) conditions onto the organic ultrathin film, diffuse along the surface and self-assemble into a system of 2D metallic overlayers. At the same time, the majority of the metal atoms diffuse into the organic matrix and self-organize into 3D nanoparticles (NPs) in a well-defined manner. The evolution of the morphology and electronic properties of such structures as a function of nominal metal content is studied under UHV conditions using transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM), and photoelectron spectroscopy (PES) techniques. Using HR-TEM, we have observed the periodicity of atomic planes of individual silver NPs. The steady formation of agglomerates from individual single nanocrystallites with intercrystallite boundaries is observed as well. PES reveals generally weak chemical interactions between silver and the organic matrix and n-doping of CuPcF4 at the initial stages of silver deposition, which is associated with charge transfer from the 2D wetting layer on the basis of core-level spectra shift analysis. Copyright © 2020 American Chemical Society

A photochemical approach for a fast and self-limited covalent modification of surface supported graphene with photoactive dyes

Herein, we report a simple method for a covalent modification of surface supported graphene with photoactive dyes. Graphene was fabricated on cubic-SiC/Si(001) wafers due to their low cost and suitability for mass-production of continuous graphene fit for electronic applications on millimetre scale. Functionalisation of the graphene surface was carried out in solution via white light induced photochemical generation of phenazine radicals from phenazine diazonium salt. The resulting covalently bonded phenazine-graphene hybrid structure was characterised by scanning tunnelling microscopy (STM) and spectroscopy (STS), Raman spectroscopy and density functional theory (DFT) calculations. It was found that phenazine molecules form an overlayer, which exhibit a short range order with a rectangular unit cell on the graphene surface. DFT calculations based on STM results reveal that molecules are standing up in the overlayer with the maximum coverage of 0.25 molecules per graphene unit cell. Raman spectroscopy and STM results show that the growth is limited to one monolayer of standing molecules. STS reveals that the phenazine-graphene hybrid structure has a band gap of 0.8 eV

Large positive in-plane magnetoresistance induced by localized states at nanodomain boundaries in graphene

Graphene supports long spin lifetimes and long diffusion lengths at room temperature, making it highly promising for spintronics. However, making graphene magnetic remains a principal challenge despite the many proposed solutions. Among these, graphene with zig-zag edges and ripples are the most promising candidates, as zig-zag edges are predicted to host spin-polarized electronic states, and spin-orbit coupling can be induced by ripples. Here we investigate the magnetoresistance of graphene grown on technologically relevant SiC/Si(001) wafers, where inherent nanodomain boundaries sandwich zig-zag structures between adjacent ripples of large curvature. Localized states at the nanodomain boundaries result in an unprecedented positive in-plane magnetoresistance with a strong temperature dependence. Our work may offer a tantalizing way to add the spin degree of freedom to graphene

Hybrid organic-inorganic systems formed by self-assembled gold nanoparticles in CuPcF4 molecular crystal

In this work we have fabricated and studied hybrid organic-inorganic nanocomposite system formed by gold nanoparticles self-assembled in organic semiconductor thin film - copper tetrafluorophthalocyanine (CuPcF4). By means of Photoelectron Spectroscopy and Transmission Electron Microscopy (TEM) the evolution of the morphology and electronic structure of the system as a function of nominal gold content have been investigated. The gold atoms, deposited onto the CuPcF4 surface, diffuse into the organic matrix and self-assemble to nanoparticles in a well-defined manner with a narrow size distribution, which depends on the amount of deposited gold. Using High-Resolution TEM, we were able to observe the atomic planes of single gold nanoparticles and their coalescence processes. Photoelectron spectroscopy has not revealed any detectable chemical reaction between gold and organic. However, the strong upward band bending, induced by gold nanoparticles in the organic film, takes place

Fabrication of [001]-Oriented Tungsten Tips for High Resolution Scanning Tunneling Microscopy

The structure of the [001]-oriented single crystalline tungsten probes sharpened in ultra-high vacuum using electron beam heating and ion sputtering has been studied using scanning and transmission electron microscopy. The electron microscopy data prove reproducible fabrication of the single-apex tips with nanoscale pyramids grained by the {011} planes at the apexes. These sharp, [001]-oriented tungsten tips have been successfully utilized in high resolution scanning tunneling microscopy imaging of HOPG(0001), SiC(001) and graphene/SiC(001) surfaces. The electron microscopy characterization performed before and after the high resolution STM experiments provides direct correlation between the tip structure and picoscale spatial resolution achieved in the experiments

Graphene Synthesis on Cubic SiC/Si Wafers. Perspectives for Mass Production of Graphene-Based Electronic Devices

The outstanding properties of graphene, a single graphite layer, render it a top candidate for substituting silicon in future electronic devices, The so far exploited synthesis approaches, however, require conditions typically achieved in specialized laboratories and result in graphene sheets whose electronic properties are often altered by interactions with substrate materials. The development of graphene-based technologies requires an economical fabrication method compatible with mass production. Here we demonstrate for the fist Lime the feasibility of graphene synthesis on commercially available cubic SiC/Si substrates of >300 mm in diameter, which result in graphene flakes electronically decoupled from the substrate. After optimization of the preparation procedure, the proposed synthesis method can represent a further big step toward graphene-based electronic technologies

Transport Gap Opening and High On Off Current Ratio in Trilayer Graphene with Self Aligned Nanodomain Boundaries

Trilayer graphene exhibits exceptional electronic properties that are of interest both for fundamental science and for technological applications. The ability to achieve a high on off current ratio is the central question in this field. Here, we propose a simple method to achieve a current on off ratio of 104 by opening a transport gap in Bernal stacked trilayer graphene. We synthesized Bernal stacked trilayer graphene with self aligned periodic nanodomain boundaries NBs on the technologically relevant vicinal cubic SiC 001 substrate and performed electrical measurements. Our low temperature transport measurements clearly demonstrate that the self aligned periodic NBs can induce a charge transport gap greater than 1.3 eV. More remarkably, the transport gap of amp; 8764;0.4 eV persists even at 100 K. Our results show the feasibility of creating new electronic nanostructures with high on off current ratios using graphene on cubic Si