A. Di Bartolomeo

Field emission from single and few-layer graphene flakes

We report the observation and characterization of field emission current from individual single- and few-layer graphene flakes laid on a flat SiO2/Si substrate. Measurements were performed in a scanning electron microscope chamber equipped with nanoprobes which allowed local measurement of the field emission current. We achieved field emission currents up to 1 μA from the flat part of graphene flakes at applied fields of few hundred volt per micrometer. We found that the emission process is stable over a period of several hours and that it is well described by a Fowler–Nordheim model for currents over five orders of magnitude.

Multiwalled carbon nanotube films as small-sized temperature sensors

We present the fabrication of thick and dense carbon nanotube networks in the form of freestanding films (CNTFs) and the study of their electric resistance as a function of the temperature, from 4 to 420 K. A nonmetallic behavior with a monotonic R(T) and a temperature coefficient of resistance around −7×10−4 K−1 is generally observed. A behavioral accordance of the CNTF conductance with the temperature measured by a solid-state thermistor (ZnNO, Si, or Pt) is demonstrated, suggesting the possibility of using CNTFs as temperature small-sized (freely scalable) sensors, besides being confirmed by a wide range of sensitivity, fast response, and good stability and durability. Concerning electric behavior, we also underline that a transition from nonmetal to metal slightly below 273 K has been rarely observed. A model involving regions of highly anisotropic metallic conduction separated by tunneling barrier regions can explain the nonmetallic to metallic crossover based on the competing mechanisms of the metal...

Automatic analysis of digitized TV-images by a computer-driven optical microscope

Abstract New methods of image analysis and three-dimensional pattern recognition were developed in order to perform the automatic scan of nuclear emulsion pellicles. An optical microscope, with a motorized stage, was equipped with a CCD camera and an image digitizer, and interfaced to a personal computer. Selected software routines inspired the design of a dedicated hardware processor. Fast operation, high efficiency and accuracy were achieved. First applications to high-energy physics experiments are reported. Further improvements are in progress, based on a high-resolution fast CCD camera and on programmable digital signal processors. Applications to other research fields are envisaged.

A study of the multigap RPC at the gamma irradiation facility at CERN

Abstract The selected device for the ALICE Time-of-Flight array is the Multigap Resistive Plate Chamber (MRPC). We have tested this device at the Gamma Irradiation Facility at CERN to evaluate the rate dependence. We find that the rate capability of the MRPC easily exceeds the 50 Hz/cm 2 maximum expected rate at the ALICE experiment. In addition, we have measured the power dissipated for an equivalent flux of 1.6 kHz/cm 2 of through-going muons to be 650 mW/m 2 .

Leakage and field emission in side-gate graphene field effect transistors

We fabricate planar graphene field-effect transistors with self-aligned side-gate at 100 nm from the 500 nm wide graphene conductive channel, using a single lithographic step. We demonstrate side-gating below 1 V with conductance modulation of 35% and transconductance up to 0.5 mS/mm at 10 mV drain bias. We measure the planar leakage along the SiO2/vacuum gate dielectric over a wide voltage range, reporting rapidly growing current above 15 V. We unveil the microscopic mechanisms driving the leakage, as Frenkel-Poole transport through SiO2 up to the activation of Fowler-Nordheim tunneling in vacuum, which becomes dominant at higher voltages. We report a field-emission current density as high as 1 μA/μm between graphene flakes. These findings are important for the miniaturization of atomically thin devices.We fabricate planar all-graphene field-effect transistors with self-aligned side-gates at 100 nm from the main graphene conductive channel, using a single lithographic step. We demonstrate side-gating below 1V with conductance modulation of 35% and transconductance up to 0.5 mS/mm at 10 mV drain bias. We measure the planar leakage along the SiO2/vacuum gate dielectric over a wide voltage range, reporting rapidly growing current above 15 V. We unveil the microscopic mechanisms driving the leakage, as Frenkel-Poole transport through SiO2 up to the activation of Fowler-Nordheim tunneling in vacuum, which becomes dominant at high voltages. We report a field-emission current density as high as 1μA/μm between graphene flakes. These findings are essential for the miniaturization of atomically thin devices. * Tel: +39.089.969189. E-mail: dibant@sa.infn.it (Antonio Di Bartolomeo)

Record Endurance for Single-Walled Carbon Nanotube-Based Memory Cell.

We study memory devices consisting of single-walled carbon nanotube transistors with charge storage at the SiO2/nanotube interface. We show that this type of memory device is robust, withstanding over 105 operating cycles, with a current drive capability up to 10−6 A at 20 mV drain bias, thus competing with state-of-the-art Si-devices. We find that the device performance depends on temperature and pressure, while both endurance and data retention are improved in vacuum.

Transfer characteristics and contact resistance in Ni- and Ti-contacted graphene-based field-effect transistors

We produced graphene-based field-effect transistors by contacting mono- and bi-layer graphene by sputtering Ni or Ti as metal electrodes. We performed electrical characterization of the devices by measuring their transfer and output characteristics. We clearly observed the presence of a double-dip feature in the conductance curve for Ni-contacted transistors, and we explain it in terms of charge transfer and graphene doping under the metal contacts. We also studied the contact resistance between the graphene and the metal electrodes with larger values of ~30 kΩμm(2) recorded for Ti contacts. Importantly, we prove that the contact resistance is modulated by the back-gate voltage.

A modified Schottky model for graphene-semiconductor (3D/2D) contact: A combined theoretical and experimental study

In this paper we carry out a theoretical and experimental study of the nature of graphene/semiconductor Schottky contact. We present a simple and parameter-free carrier transport model of graphene/semiconductor Schottky contact derived from quantum statistical theory, which is validated by the quantum Landauer theory and first-principle calculations. The proposed model can well explain experimental results for samples of different types of graphene/semiconductor Schottky contact.

Structural, electrical and magnetic characterization of artificial ferromagnetic/superconducting (La0.7Ca0.3MnO3/YBa2Cu3O7−x) heterostructures

The fabrication and characterization of superconducting and ferromagnetic heterostructures is an open field due to the fundamental interest in the physics of the coexistence of these two competing orders and their possible applications in the spintronics industry. In this paper we present structural, electrical and magnetic characterization for the single La(0.7)Ca(0.3)MnO(3) (LCMO) thin layer, La(0.7)Ca(0.3)MnO(3)/YBa(2)Cu(3)O(7-x) (LCMO/YBCO) bilayers and the LCMO/YBCO/LCMO trilayers. In particular, we show a detailed magnetic characterization of the LCMO thin films by means of low temperature magnetic force microscopy. We discuss the different dynamics of the magnetic domains observed, depending on the substrate induced strain and on the film thickness.

Graphene enhanced field emission from InP nanocrystals

We report the observation of field emission (FE) from InP nanocrystals (NCs) epitaxially grown on an array of p-Si nanotips. We prove that FE can be enhanced by covering the InP NCs with graphene. The measurements are performed inside a scanning electron microscope chamber with a nano-controlled W-thread used as an anode. We analyze the FE by Fowler-Nordheim theory and find that the field enhancement factor increases monotonically with the spacing between the anode and the cathode. We also show that InP/p-Si junction has a rectifying behavior, while graphene on InP creates an ohmic contact. Understanding the fundamentals of such nanojunctions is key for applications in nanoelectronics.