arXiv subjects

Saverio Russo

Publications and source records attributed to Saverio Russo.

29 records · Page 2Linked to original sources

arXiv2016

Side-gate leakage and field emission in all-graphene field effect transistors on SiO2/Si substrate

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 1uA/um between graphene flakes. These findings are essential for the miniaturization of atomically thin devices.

cond-mat.mes-hall↗

arXiv2015

Contact doping, Klein tunneling, and asymmetry of shot noise in suspended graphene

The inherent asymmetry of the electric transport in graphene is attributed to Klein tunneling across barriers defined by $\textit{pn}$-interfaces between positively and negatively charged regions. By combining conductance and shot noise experiments we determine the main characteristics of the tunneling barrier (height and slope) in a high-quality suspended sample with Au/Cr/Au contacts. We observe an asymmetric resistance $R_{\textrm{odd}}=100-70$ $Ω$ across the Dirac point of the suspended graphene at carrier density $|n_{\rm G}|=0.3-4 \cdot 10^{11}$ cm$^{-2}$, while the Fano factor displays a non-monotonic asymmetry in the range $F_{\textrm{odd}} \sim 0.03 - 0.1$. Our findings agree with analytical calculations based on the Dirac equation with a trapezoidal barrier. Comparison between the model and the data yields the barrier height for tunneling, an estimate of the thickness of the $\textit{pn}$-interface $d < 20$ nm, and the contact region doping corresponding to a Fermi level offset of $\sim - 18$ meV. The strength of pinning of the Fermi level under the metallic contact is characterized in terms of the contact capacitance $C_c=19 \times 10^{-6}$ F/cm$^2$. Additionally, we show that the gate voltage corresponding to the Dirac point is given by the work function difference between the backgate material and graphene.

cond-mat.mes-hall↗

arXiv2015

High quality monolayer graphene synthesized by resistive heating cold wall chemical vapour deposition

Emerging flexible and wearable technologies such as healthcare electronics and energy-harvest devices could be transformed by the unique properties of graphene. The vision for a graphene-driven industrial revolution is motivating intensive research on the synthesis of (1) high quality and (2) low cost graphene. Hot-wall chemical vapour deposition (CVD) is one of the most competitive growth methods, but its long processing times are incompatible with production lines. Here we demonstrate the growth of high quality monolayer graphene using a technique that is 100 times faster than standard hot-wall CVD, resulting in 99% reduction in production costs. A thorough complementary study of Raman spectroscopy, atomic force microscopy, scanning electron microscopy and electrical magneto-transport measurements shows that our cold wall CVD-grown graphene is of comparable quality to that of natural graphene. Finally, we demonstrate the first transparent and flexible graphene capacitive touch-sensor that could enable the development of artificial skin for robots.

cond-mat.mtrl-sci↗

arXiv2015

Electron transport of WS$_2$ transistors in a hexagonal boron nitride dielectric environment

We present the first study of the intrinsic electrical properties of WS$_2$ transistors fabricated with two different dielectric environments WS$_2$ on SiO$_2$ and WS$_2$ on h-BN/SiO$_2$, respectively. A comparative analysis of the electrical characteristics of multiple transistors fabricated from natural and synthetic WS$_2$ with various thicknesses from single- up to four-layers and over a wide temperature range from 300K down to 4.2 K shows that disorder intrinsic to WS$_2$ is currently the limiting factor of the electrical properties of this material. These results shed light on the role played by extrinsic factors such as charge traps in the oxide dielectric thought to be the cause for the commonly observed small values of charge carrier mobility in transition metal dichalcogenides.

cond-mat.mes-hall↗

arXiv2014

Molybdenum-Rhenium superconducting suspended nanostructures

Suspended superconducting nanostructures of MoRe $50\%/50\%$ by weight are fabricated employing commonly used fabrication steps in micro- and nano-meter scale devices followed by wet-etching with Hydro-fluoric acid of a SiO$_2$ sacrificial layer. Suspended superconducting channels as narrow as $50\,\rm{nm}$ and length $3\,\rm{μm}$ have a critical temperature of $\approx 6.5\,\rm{K}$, which can increase by $0.5\rm{K}$ upon annealing at $400\,^{\circ}\mathrm{C}$. A detailed study of the dependence of the superconducting critical current and critical temperature upon annealing and in devices with different channel width reveals that desorption of contaminants is responsible for the improved superconducting properties. These findings pave the way for the development of superconducting electromechanical devices using standard fabrication techniques.

cond-mat.supr-con↗

arXiv2013

Single- and multi-mode Fabry-Pérot interference in suspended graphene

Phase coherence of charge carriers leads to electron-wave interference in ballistic mesoscopic conductors. In graphene, such Fabry-Pérot-like interference has been observed, but a detailed analysis has been complicated by the two-dimensional nature of conduction, which allows for complex interference patterns. In this work, we have achieved high-quality Fabry-Pérot interference in a suspended graphene device, both in conductance and in shot noise, and analyzed their structure using Fourier transform techniques. The Fourier analysis reveals two sets of overlapping, coexisting interferences, with the ratios of the diamonds being equal to the width to length ratio of the device. We attribute these sets to a unique coexistence of longitudinal and transverse resonances, with the longitudinal resonances originating from the bunching of modes with low transverse momentum. Furthermore, our results give insight into the renormalization of the Fermi velocity in suspended graphene samples, caused by unscreened many-body interactions.

cond-mat.mes-hall↗

arXiv2012

Novel highly conductive and transparent graphene based conductors

Future wearable electronics, displays and photovoltaic devices rely on highly conductive, transparent and yet mechanically flexible materials. Nowadays indium tin oxide (ITO) is the most wide spread transparent conductor in optoelectronic applications, however the mechanical rigidity of this material limits its use for future flexible devices. Here we report novel transparent conductors based on few layer graphene (FLG) intercalated with ferric chloride (FeCl3) with an outstandingly high electrical conductivity and optical transparency. We show that upon intercalation a record low sheet resistance of 8.8 Ohm/square is attained together with an optical transmittance higher than 84% in the visible range. These parameters outperform the best values of ITO and of other carbon-based materials, making these novel transparent conductors the best candidates for future flexible optoelectronics.

cond-mat.mtrl-sci↗

arXiv2012

Gate tunable non-linear currents in bilayer graphene diodes

Electric transport of double gated bilayer graphene devices is studied as a function of charge density and bandgap. A top gate electrode can be used to control locally the Fermi level to create a pn junction between the double-gated and single-gated region. These bilayer graphene pn diodes are characterized by non-linear currents and directional current rectification, and we show the rectified direction of the source-drain voltage can be controlled by using gate voltages. A systematic study of the pn junction characteristics allows to extract a gate-dependent bandgap value which ranges from 0 meV to 130 meV.

cond-mat.mes-hall↗

arXiv2011

Electrical transport in suspended and double gated trilayer graphene

We present a fabrication process for high quality suspended and double gated trilayer graphene devices. The electrical transport measurements in these transistors reveal a high charge carrier mobility (higher than 20000 cm^2/Vs) and ballistic electric transport on a scale larger than 200nm. We report a particularly large on/off ratio of the current in ABC-stacked trilayers, up to 250 for an average electric displacement of -0.08 V/nm, compatible with an electric field induced energy gap. The high quality of these devices is also demonstrated by the appearance of quantum Hall plateaus at magnetic fields as low as 500mT.

cond-mat.mes-hall↗

arXiv2007

Aharonov-Bohm effect in graphene

We investigate experimentally transport through ring-shaped devices etched in graphene and observe clear Aharonov-Bohm conductance oscillations. The temperature dependence of the oscillation amplitude indicates that below 1 K the phase coherence length is comparable to or larger than the size of the ring. An increase in the amplitude is observed at high magnetic field, when the cyclotron diameter becomes comparable to the width of the arms of the ring. By measuring the dependence on gate voltage, we also observe an unexpected linear dependence of the oscillation amplitude on the ring conductance, which had not been reported earlier in rings made using conventional metals or semiconducting heterostructures.

cond-mat.mes-hall↗

arXiv2005

Reproducible Low Contact Resistance in Rubrene Single-Crystal Field-Effect Transistors with Nickel Source and Drain Electrodes

We have investigated the contact resistance of rubrene single-crystal field-effect transistors (FETs) with Nickel electrodes by performing scaling experiments on devices with channel length ranging from 200 nm up to 300 $μ$m. We find that the contact resistance can be as low as 100 $Ω$cm with narrowly spread fluctuations. For comparison, we have also performed scaling experiments on similar Gold-contacted devices, and found that the reproducibility of FETs with Nickel electrodes is largely superior. These results indicate that Nickel is a very promising electrode material for the reproducible fabrication of low resistance contacts in organic FETs.

cond-mat.other↗