Copper-vapor-assisted chemical vapor deposition for high-quality and metal-free single-layer graphene on amorphous SiO2 substrate.

We report that high-quality single-layer graphene (SLG) has been successfully synthesized directly on various dielectric substrates including amorphous SiO2/Si by a Cu-vapor-assisted chemical vapor deposition (CVD) process. The Cu vapors produced by the sublimation of Cu foil that is suspended above target substrates without physical contact catalyze the pyrolysis of methane gas and assist nucleation of graphene on the substrates. Raman spectra and mapping images reveal that the graphene formed on a SiO2/Si substrate is almost defect-free and homogeneous single layer. The overall quality of graphene grown by Cu-vapor-assisted CVD is comparable to that of the graphene grown by regular metal-catalyzed CVD on a Cu foil. While Cu vapor induces the nucleation and growth of SLG on an amorphous substrate, the resulting SLG is confirmed to be Cu-free by synchrotron X-ray photoelectron spectroscopy. The SLG grown by Cu-vapor-assisted CVD is fabricated into field effect transistor devices without transfer steps that are generally required when SLG is grown by regular CVD process on metal catalyst substrates. This method has overcome two important hurdles previously present when the catalyst-free CVD process is used for the growth of SLG on fused quartz and hexagonal boron nitride substrates, that is, high degree of structural defects and limited size of resulting graphene, respectively.

Fast benchtop visualization of graphene grain boundaries using adhesive properties of defects.

Highly adhesive properties of graphene grain boundaries to permanganate lead to a very quick, easy and convenient method to visualize the grain boundaries simply using an optical microscope, which would be vital to improve specific properties of graphene.

Breakdown of the interlayer coherence in twisted bilayer graphene.

Coherent motion of electrons in Bloch states is one of the fundamental concepts of charge conduction in solid-state physics. In layered materials, however, such a condition often breaks down for the interlayer conduction, when the interlayer coupling is significantly reduced by, e.g., a large interlayer separation. We report that complete suppression of coherent conduction is realized even in an atomic length scale of layer separation in twisted bilayer graphene. The interlayer resistivity of twisted bilayer graphene is much higher than the c-axis resistivity of Bernal-stacked graphite and exhibits strong dependence on temperature as well as on external electric fields. These results suggest that the graphene layers are significantly decoupled by rotation and incoherent conduction is a main transport channel between the layers of twisted bilayer graphene.

Crystal-plane-dependent photoluminescence of pentacene 1D†wire and 2D†disk crystals.

Down to the wire: Pentacene exhibits crystal-plane-dependent photoluminescence (PL) activity, as demonstrated in highly crystalline 1D wires and 2D disks, which were selectively synthesized using the vaporization-condensation-recrystallization (VCR) process. Although pentacene 1D wires and 2D disks have identical triclinic crystal structures, PL activity is observed only from pentacene 1D wires owing to the presence of "PL-active" (010) planes.

Large scale metal-free synthesis of graphene on sapphire and transfer-free device fabrication.

Metal catalyst-free growth of large scale single layer graphene film on a sapphire substrate by a chemical vapor deposition (CVD) process at 950 °C is demonstrated. A top-gated graphene field effect transistor (FET) device is successfully fabricated without any transfer process. The detailed growth process is investigated by the atomic force microscopy (AFM) studies.

Direct growth of graphene pad on exfoliated hexagonal boron nitride surface.

A direct and metal layer-free growth of flat graphene pads on exfoliated hexagonal boron nitride substrate (h-BN) are demonstrated by atmospheric chemical vapour deposition (CVD) process. Round shape with high flatness graphene pads are grown in high yield (∼95%) with a pad thickness of ∼0.5 nm and homogenous diameter.

Unique photoemission from single-layer graphene on a SiO2 layer by a substrate charging effect.

Single-layer graphene (SLG) shows an anomalously large surface charging effect during scanning photoelectron microscopy (SPEM), which is distinguished from bi-layer graphene (BLG). The different behaviour is believed due to a different screening effect for SLG and BLG.