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Register a new userHigh-Yield Production and Transfer of Graphene Flakes Obtained by Anodic Bonding
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We report large-yield production of graphene flakes on glass by anodic bonding. Under optimum conditions, we counted several tens of flakes with lateral size around 20-30 {mu}m and few tens of flakes with larger size. 60-70% of the flakes have negligible D peak. We show that it is possible to easily transfer the flakes by wedging technique. The transfer on silicon does not damage graphene and lowers the doping. The charge mobility of the transferred flakes on silicon is of the order of 6000 cm^2/V s (at carrier concentration of 10^12 cm^-2), which is typical for devices prepared on this substrate with exfoliated graphene.
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The recent observation of fractional quantum Hall effect in high mobility suspended graphene devices introduced a new direction in graphene physics, the field of electron-electron interaction dynamics. However, the technique used currently for the fabrication of such high mobility devices has several drawbacks. The most important is that the contact materials available for electronic devices are limited to only a few metals (Au, Pd, Pt, Cr and Nb) since only those are not attacked by the reactive acid (BHF) etching fabrication step. Here we show a new technique which leads to mechanically stable suspended high mobility graphene devices which is compatible with almost any type of contact material. The graphene devices prepared on a polydimethylglutarimide based organic resist show mobilities as high as 600.000 cm^2/Vs at an electron carrier density n = 5.0 10^9 cm^-2 at 77K. This technique paves the way towards complex suspended graphene based spintronic, superconducting and other types of devices.
We show that the manifestation of quantum interference in graphene is very different from that in conventional two-dimensional systems. Due to the chiral nature of charge carriers, it is sensitive not only to inelastic, phase-breaking scattering, but also to a number of elastic scattering processes. We study weak localization in different samples and at different carrier densities, including the Dirac region, and find the characteristic rates that determine it. We show how the shape and quality of graphene flakes affect the values of the elastic and inelastic rates and discuss their physical origin.
Electron paramagnetic resonance (EPR) study of air-physisorbed defective carbon nano-onions evidences in favor of microwave assisted formation of weakly-bound paramagnetic complexes comprising negatively-charged O2- ions and edge carbon atoms carrying pi-electronic spins. These complexes being located on the graphene edges are stable at low temperatures but irreversibly dissociate at temperatures above 50-60 K. These EPR findings are justified by density functional theory (DFT) calculations demonstrating transfer of an electron from the zigzag edge of graphene-like material to oxygen molecule physisorbed on the graphene sheet edge. This charge transfer causes changing the spin state of the adsorbed oxygen molecule from S = 1 to S = 1/2 one. DFT calculations show significant changes of adsorption energy of oxygen molecule and robustness of the charge transfer to variations of the graphene-like substrate morphology (flat and corrugated mono- and bi-layered graphene) as well as edges passivation. The presence of H- and COOH- terminated edge carbon sites with such corrugated substrate morphology allows formation of ZE-O2- paramagnetic complexes characterized by small (<50 meV) binding energies and also explains their irreversible dissociation as revealed by EPR.
Exploring the mechanism of interfacial thermal transport and reducing the interfacial thermal resistance is of great importance for thermal management and modulation. Herein, the interfacial thermal resistance between overlapped graphene nanoribbons is largely reduced by adding bonded carbon chains by performing molecular dynamics simulations. And the analytical model (cross-interface model, CIM) is utilized to analyze and explain the two-dimensional thermal transport mechanism at cross-interface. An order of magnitude reduction in interfacial thermal resistance is found as the graphene nanoribbons are bonded by just one carbon chain. Interestingly, the decreasing rate of interfacial thermal resistance slows down gradually with the increasing of the number of carbon chains, which can be explained by the proposed theoretical relationship based on CIM. Moreover, by the comparison of CIM and traditional simplified model, the accuracy of CIM is verified and demonstrated in overlapped graphene nanoribbons. This work provides a new way to improve the interfacial thermal transport and reveal the essential mechanism for low-dimensional materials applied in thermal management.
Here, the synthesis of Molybdenum Disulphide (MoS2) flakes by means of anodic atmospheric arc discharge is reported for the first time. The vertical electrode configuration consisted of a compound anode (hollow graphite anode filled with MoS2 powder) and a solid graphite cathode placed just above of the compound anode. Arc processes were operated in pulsed mode to preferentially evaporate the powder component from the anode and to minimize Carbon ablation. Pulsed anodic arc discharges were conducted at 2 Hz and 10% duty cycle in 300 Torr of Helium with a peak current of 250-300 A and peak voltage of 35 V. A probe made of Tungsten wire was placed in the vicinity of the arc column to collect the evaporated material. The measured thickness profile was correlated to the particle flux distribution and it was fitted by a simple model of plasma expansion. During pulse phase, electron density was estimated around 5E22 m-3 or higher, and ion current density was of the order of 10 A/mm2. Morphology, structure and composition of the samples were characterized by Raman spectroscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and x-ray diffraction (XRD). The study shows that pulsed arc discharge of the compound anode leads to moderate C deposition combined with MoS2 deposition in the form of fragmented nanocrystals and few atomic monolayers of MoS2. Such synthesis technique is promising to produce new 2D nanomaterials with tailored structure and functionality thanks to the flexibility of pulsed power.
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