Search

A self-supporting thin film is useful as a target material for laser-driven ion acceleration experiments. In this study, 100-nm-thick sputtered gold (Au) thin films were released from substrates using water-soluble sacrificial layers, and the released films were subsequently scooped up on perforated substrates. Au thin films were deposited by DC plasma sputtering on the sacrificial layers. In the releasing test, sodium chloride (NaCl) was shown to be most suitable as a sacrificial layer for Au thin films. In addition, sputtered Au thin films with thicknesses of 50 and 150 nm were deposited onto NaCl sacrificial layers, released on water, and scooped up on perforated substrates. Self-supporting Au thin films were obtained for all film thicknesses, but wrinkles and cracks appeared in the 50 nm film.

In this research, ambipolar behavior, which is one of graphene's unique characteristics, is studied for the epitaxial graphene formed on 3C-SiC grown on a Si substrate. The graphene channel is believed to be unintentionally p-type-doped at Dirac-point voltages of approximately +0.11 to +0.12 V. However, as drain voltage negatively increases, Dirac point voltage shifts. The drain current in the p-channel mode of operation saturates at a lower level than that in the n-channel mode of operation. These behaviors are caused by asymmetric carrier transport throughout channel-substrate heterojunctions (i.e., graphene, thin n-type SiC layer, and p-type Si substrate) and source/drain Schottky metal contacts. The interface between the p-type Si substrate and n-type SiC has a significant effect on transport in graphene channels. The results may be helpful for understanding transport in the device and for suppressing ambipolar operation, leading to a unipolar FET operation.

We have fabricated and characterized field-effect transistors (FETs) with an epitaxial graphene channel on a SiC layer grown on a Si substrate. Epitaxial graphene can be formed on SiC substrates by thermal decomposition of its surface under an ultrahigh-vacuum (UHV) condition. To incorporate the thermal decomposition of SiC on Si substrates, we used an approach of growing a thin 3C-SiC(111) layer on Si substrates and subsequently annealing them in UHV to form graphene on the surface of the 3C-SiC layer. Backgate-field-effect transistors using the SiC layer as a gate insulator were characterized. Although a large amount of gate-leakage current is observed, the drain current modulation by backgate voltage is confirmed by extracting the channel current from the total drain current. The extracted channel current characteristics also suggest that the extracted effective mobility exceeds the universal mobility of bulk silicon under similar circumstances.

Few-layers graphene is epitaxially grown on silicon substrates via SiC thin films inserted in between. We have conducted a detailed structural characterization of this graphene-on-silicon (GOS) material by Raman spectroscopy and transmission-electron microscopy, to obtain insights into the impacts of process parameters on defect formation. Results suggest that defects in graphene preferentially dwell at steps. Future flattening of the SiC surface, prior to graphene growth, is thus expected to contribute to the improvement of GOS quality.