Papers by Author: Emanuele Rimini

Abstract: The electrical properties of epitaxial graphene (EG) grown on 8° off-axis 4H-SiC (0001) by annealing at 1600 °C in inert gas ambient (Ar) were studied. The sheet resistance of the EG layers (R_sh=740±50Ω/sq) and the specific contact resistance of Ni contacts to EG (ρ_c≈6x10^-5 Ωcm²) were evaluated on micrometer scale by measurements on transmission line model (TLM) structures. Si₃N₄ was evaluated as a gate dielectric, showing excellent coverage to EG and a limited effect on its conductivity. The high n-type doping (~10¹³ cm^-2) of EG, as well as the field effect mobility (μ) dependence on n were determined using top gated field effect transistors (FETs) with Si₃N₄ gate dielectric. Electron mean free path (l_loc) and mobility (μ_loc) were also locally determined, on submicrometer scale, by scanning probe microscopy, showing a broad distribution of μ_loc values, with the most probable value very similar to macroscopic carrier mobility μ.

Abstract: We present a nanoscale morphological and structural characterization of few layers of graphene grown by thermal decomposition of off-axis 4H-SiC (0001). A comparison between transmission electron microscopy (TEM) in cross-section and in plan view allows to fully exploit the potentialities of TEM. Such a comparison was used to get information on the number of graphene layers as well as on the rotational order between the layers and with respect to the substrate. Some peculiar structures observed by TEM (wrinkles) could only be systematically measured by atomic force microscopy (AFM). In particular, the density and the height of the wrinkles in the few layers of graphene was investigated.

Abstract: Graphene films were grown on thin polycrystalline Ni using a buried amorphous carbon (a-C) layer as C source. Rapid thermal processes (RTP) at temperatures from 600 to 800°C were used to promote C diffusion into Ni and its subsequent segregation on Ni surface, during the sample cool down. RTP at 800°C was the optimal condition for graphene film formation. Micro-Raman spectroscopy showed that the grown film is mostly composed by multilayers of graphene. Atomic force microscopy showed that the film presents peculiar corrugations (wrinkles), isotropically oriented and with heights ranging from from ~1 to ~15 nm. Selected area diffraction by transmission electron microscopy on the MLG membranes shows a rotational disorder between the stacked graphene layers.

Abstract: In this study we examined the structural evolution of graphene grown on 8° off-axis 4H-SiC(0001) substrates at temperatures from 1600°C to 1700°C in Ar ambient. Morphological transformation of SiC substrate after annealing was examined by Tapping Mode Atomic Force Microscopy. Moreover, by etching-out graphene layers from graphitized SiC substrates in selective trenches we determined the number of graphene layers. Numbers of graphene layers were then independently confirmed by Transmission Electron Microscopy imaging.

Abstract: Irradiation with high energy (500 keV) C+ ions at fluences from 11013 to 11014 cm-2 was used to introduce controlled amounts of defects in single layers of graphene deposited on a SiO2(100 nm)/n+Si substrate. Scanning Capacitance Spectroscopy (SCS) was used as non-destructive characterization technique to probe the effect of irradiation on the electrical properties of graphene. In particular, a comparative study between the local capacitance of pristine graphene and irradiated graphene is presented, showing that lateral variations in irradiated graphene are distinctly higher. The local quantum capacitance per unit area C’q of graphene was extracted from raw data. While a narrow distribution of C’q values was obtained in pristine graphene, two distinct distributions were obtained in irradiated monolayers, associated to locally damaged and not damaged regions, respectively.

Abstract: Optical interferometric sensors represent the most advanced measurement tools in terms of precision and sensitivity for position detection. Micro-mechanical and micro-optical active and passive devices can be realized with present technologies on integrable substrates such as silicon wafers. We are working on the fabrication and characterization of micromirrors realized with micromachining technique. Our goal is to realize structures with a mechanical resonance frequency in ranges 1 kHz – 100 kHz and 1 MHz – 100 MHz. In these ranges we can think of different applications above all in the detection of gravitational waves and in quantum computation.