On exfoliated graphene, with e-beam lithography and thermal evaporation. Measurements providing: -Position of the Fermi level -Carrier density -Carrier mobility -Band gap -Corrections to standard conductivity model at low temperature 0 2 4 6 8 10 12 14 16 18 20 -10 0 10 20 30 40 50 60 x (μm) Optical contrast (%) 0.0 0.5 1.0 G-band intensity (arb. units) [email protected] CONTACT : CONTACT : Miguel RUBIO-ROY [email protected] Coordinator: Pascale Maldivi [email protected] Miguel RUBIO-ROY [email protected] Coordinator: Pascale Maldivi [email protected] B. Kumar, 1 G. Lapertot, 1 F. Duclairoir, 1 L. Dubois, 1 G. Bidan, 1 P. Maldivi, 1 J.-L. Thomassin, 1 F. Lefloch, 1 D. Rouchon, 2 D. Mariolles, 2 M. Mikolasek, 3 J.-L. Bantignies, 3 M. Paillet, 3 J.-R. Huntzinger, 3 A. Tiberj, 3 J.-L. Sauvajol, 3 M. Rubio-Roy, 4 O. Couturaud, 4 E. Dujardin 4 1) INAC, CEA Grenoble, 17 rue des Martyrs, 38054 Grenoble cedex 09, 2) CEA/LETI, CEA Grenoble, 17 rue des Martyrs, 38054 Grenoble cedex 09, 3) L2C, Université Montpellier II , Pl. Eugène Bataillon , 34095 Montpellier, 4) CEMES, 29 rue Jeanne Marvig, BP 94347, 31055 Toulouse Cedex 4 GRAFONICS : Graphène Fonctionnalisé pour l'électronique C-MOS hybride P2N 2010 Journées Nationales en Nanosciences et Nanotechnologies 2012 semi-metallic graphene semi-conducting graphene chemical grafting Context Results presented on Task 3: SiC graphene growth Task 5: bulk graphene functionalization Task 3: suspended graphene Vacuum pump Coil Graphite susceptor Gas inlets Quartz tube Furnace (induction heating) key aspects: vacuum/inert gas and Ar/H 2 line available SiC graphene growth The objectives: of the project are to: optimize graphene fabrication test the functionalization as a tool to tune the graphene band gap Graphene is a material that has attracted a lot of scientific attention over the past few years as it seems to be compatible with a lot of applications. It can be obtained by various techniques and each technique will provide a graphene with properties better suited for one application rather than another. Regarding the microelectronics field, graphene is an interesting material as it shows ballistic transport and very high mobility; however it is not yet compatible with CMOS-like applications as it lacks a band gap. 330nm deep Technological steps: Starting substrate: SiO 2 (290nm) / Si (100) UV projection lithography Metal marks: double resist for undercut + thermal evaporation Pools: normal resist + CF 4 ICP RIE Lift-off The line scanned corresponds to the position of the laser spot on the background picture. In yellow, optical contrast. In cyan, G band integrated intensity. Experiments Calculations • Normalization with HOPG • True numerical apertures to be measured probably close to 0.7 • Normalization with graphene freely suspended in air • Numerical apertures: 0.9 G band intensity as a function of etched depth and laser wavelength 0 50 100 150 200 250 300 350 0.0 0.2 0.4 0.6 0.8 1.0 457 nm 476.5 nm 488 nm 514 nm 532 nm 561 nm 633 nm IG over trench /IG HOPG d etch (nm) Raman of CoPc 0.0 0.2 0.4 0.6 0.8 1.0 770 780 790 800 810 Binding Energy (eV) Co2p3 AFM topography Selective grafting on monolayer Graphene model: bilayer more electron donating than monolayer?: HOMO LUMO -2.87 eV -4.83 eV n Cy (n c ) 19 (54) -4.38 eV -2.76 eV Eint =44 meV/C 3.31Å Standard protocol: surface preparation = organic desorption + graphitization Optimized protocol: surface preparation = idem + H 2 annealing Ar/H2, 1600ºC (30 min) Stage 4 1100ºC (30 min) RT Ar/H2 Ar/H2 Ar/H2 switched off Stage 5 Stage 3 810ºC (4 h) 470ºC (1 h) Stage 2 RT Stage 6 1600ºC (30 min) Study of different growth parameters: With or without annealing and under Ar or vacuum G(Vac) G(Ar/H2-Vac) G(Ar/H2-Ar) G(Ar) 1500 2000 2500 Raman shift (cm-1) G 2D Sample P(2D) FWHM P(G) FWHM G(Vac) 2730.2 62.2 1588.9 24.2 G(Ar) 2743.1 56.4 1605 18.3 G(Ar/H2-Vac) 2737.9 46.3 1598.8 16.9 G(Ar/H2-Ar) 2718.3 31.8 1588.4 16.3 With anneal No anneal Under vacuum Under Ar Each growth cycle is decomposed into a preparation step and a sublimation/graphene growth step 12-14 layers thick, 2D band shape compatible with Bernal stacking Phase image AFM Height Optical microscopy 1/3 – bilayer or more 2/3 - monolayer mono-layer, relaxed, Good crystalline quality 2 layers, not perfect Bernal stacking, non homogeneous strain rough samples, small graphene domains 500 400 300 200 100 1500 2000 2500 Wavenumber (cm-1) G 2D Best graphene sample obtained after H 2 annealing and growth under Ar Large monolayer domains Suspended mechanically exfoliated graphene Graphene Functionalization Suspended graphene should not show interactions with the substrate. Such type of structure would prevent various parasitic phenomena occurring upon deposition of graphene flakes on SiO 2 (strain, local doping…) Substrate preparation 5x1 μm 2 pools: Depths of 160nm, 210nm, 260nm, 340nm already measured (400nm, 480nm, 615nm upcoming) Efficient model to simulate the G band intensity variation with pool depth and laser wavelength Modification of SiC graphene with CoPc Samples obtained after immersion of the sample in a CoPc solution in CHCl 3 (1’ dipping time – concentrations targeted ~10 -4 M) After selective molecule deposition monolayer domains appear brighter even on optical microscopy image Other studies in progress Theoretical calculations Raman G band Raman of Graphene (G band) Device fabrication Reflectivity / Transmission