1 Preparation of nGLs 3 G Raman Imaging of nGLs 2D+G 2D HOPG n=5 n=2 n=8 n=1 n nGL substrate n=19 SiO2: Si G ~ 1/n (side view) (top view) Graphene Electronics Micro-Mechanical cleaving process to make nGLs n-Graphene Layer = nGL ; n is integer 2 A. Guptaa, X. Honga, P. Joshib, a a Y. Tang , H. Romero , P. Lammerta, N. Durateb, G. H. Huanga, C. Cheng-Inga , S. Tadigadapab, J. Zhua, a,c V. H. Crespi and P. C. Eklunda,c Visualization of nGLs Optical Image Raman scattering is found to be sensitive to the number of layers in nGLs. 4 Splitting of electronic bands is captured in the shape of 2D band. 1GL shows a single 2D peaks while nGLs (small n) show 4 peaks which evolve in 2 peaks for higher n. 5 Graphene Publications Introduce 10% NH3 Contrast in optical image strongly depends on the thickness of oxide as well as the wavelength of illuminating light. Graphene shows high contrast in white light illumination for ~ 100 nm thick SiO2 Transport in FET geometry for nGLs shows Dirac peak with finite resistance. Graphene (1GL) FETs patterned into Hall bar and van der Pauw geometries show half-integer quantum Hall sequence 4(n+1/2) at low temperature. After Magneto-resistance (Rxx) and Hall (Rxy) measurements of nGL (n>1) devices at low temperature. S AFM height measurements for nGLs. Extra thickness of graphene (0.7 nm) may reflect inherent difference in attractive AFM tip force between SiO2 and graphene 6 Theoretical Calculations 1. A. Gupta, Y. Tang, V. H. Crespi and P. C. Eklund, “Raman Scattering form Incommensurately Stacked Bi-Layer Graphene” Submitted to Phys. Rev. Lett.) 2. C. Nisoli, P. E. Lammert, E. Mockensturm and V. H. Crespi, "Carbon Nanostructures as an Electromechanical Bicontinuum," Phys. Rev. Lett. 99, 045501 (2007). 5. P. Joshi, A. Gupta, P. C. Eklund and S. A. Tadigadapa,"On the Possibility of a Graphene Based Chemical Sensor," Solid-State Sensors, Actuators and Microsystems Conference, 2007. TRANSDUCERS 2007. International , pp.2325-2328 (2007) 6. P. Joshi, A. Gupta, P. C. Eklund, and S. A. Tadigadapa, “Electrical Properties of Back-Gated n-Layer Graphene Films”, Proc. SPIE Int. Soc. Opt. Eng. 6464, 646409 (2007) 7. A. Gupta, G. Chen, P. Joshi, S. Tadigadapa and P. C. Eklund, “ Raman Scattering from High-Frequency phonons in Supported nGraphene Layer Films” Nano Lett. 6 (12), 2667-2673 (2006) 200-400 nm PZT Non-volatile memory device based on nGL-FET using ferroelectric film Pb(Zr Ti)O3 (PZT) as gate oxide. The large remnant polarization field of PZT ( ~ 40 µC/cm2) can potentially induce enormous 2D carrier doping (~3x1014/cm2) and lead to non-volatile memory effect. Pronounced hysteresis in carrier density and resistivity as a function of Vg with long retention time is observed in our nGL-FET. D + - + - + - + - + - + - Nb doped SrTiO3 Incommensurately Stacked Bi-Layer Graphene 2D peak dispersion Optical Image and Schematics of incommensurate bilayer (IBL) Graphene phonon dispersion curves calculated from the bicontinuum theory (solid lines), compared to EELS data. The bi-continuum theory of graphene provides a unified treatment of a wide range of electromechanical couplings well beyond that accessible to a traditional singlecontinuum (i.e. elastic) model. Chemisorption of hydrogen can generate well-defined graphenic bi- ribbons which access a new regime of electronic coupling wherein characteristic phonon energies exceed the characteristic electronic energy scales for band dispersion and inter-ribbon coupling. The Dirac peak of a graphene device before exposure to 10% NH3, during exposure to 10% NH3 and after annealing the NH3-doped device in vacuum (top). The Dirac peak recovery during vacuum annealing of a different graphene device exposed to Cl2(bottom) nGL 7 3. D. Stojkovic, P. E. Lammert and V. H. Crespi, "Electronic Bisection of a Single-Wall Carbon Nanotube by Controlled Chemisorption," Phys. Rev. Lett. 99, 026802 (2007) 4. J. Charlier, P. C. Eklund, J. Zhu and A. C. Ferrari,``Electron and phonon properties of graphene: their relationship with carbon nanotubes,'' in Carbon nanotubes: Advanced topics in the synthesis, structure, properties and applications, ed. M. S. Dresselhaus, G. Dresselhaus and A. Jorio (Springer Verlag, 2007) in press nGL Sensors Before Departments of Physicsa, Electrical Engineeringb and Material Science and Engineeringc NSF ECS0609243 Raman spectrum can count n in nGLs nGL Electronics AFM The Pennsylvania State University, University Park, PA, USA M-K, 2D, 2D’ and 2D+G peaks found to be dispersive with laser excitation with ~-21, ~100, ~18 and ~100 cm-1/eV ,respectively, for 1GL. Dispersion of different Raman peaks can be used to map the electronic and phonon band dispersion in nGLs Band splitting for IBL ~ 6 meV (Vienna Ab-initio Simulation Package calculation) Incommensurate stacking of two graphene layers produces a pair of almost decoupled graphene layers 2 peaks ~1350 cm-1 and 1384 cm-1 (I1 and I2) are seen in IBL and compared with defect induced D band peaks (1 peak for mono graphene layer and 4 peaks for commensurate bi layer) at the edges of nGLs. I1 and I2 are activated by a superimposed potential stemming from the I stacking. Peak at ~1350 cm-1 found to be dispersive with excitation energy while 1384 cm-1 is non dispersive. Peak strength and dispersive behavior is understood (right) by perturbing potential from one layer on another by calculating the matrix element between suitable electronic states Dispersion of 2D peak for 1GL, IBL and 2GL.