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Micro-Mechanical cleaving process to make nGLs Publications Publications 3 3 Befor e Raman Imaging of Raman Imaging of n n GLs GLs n n GL Electronics GL Electronics Visualization of Visualization of n n GLs GLs Preparation of Preparation of n n GLs GLs Graphene Electronics A.Gupta a , X. Hong a , P. Joshi b , Y. Tang a , H. Romero a , P. Lammert a , N. Durate b , G. H. Huang a , C. Cheng- Ing a , S. Tadigadapa b , J. Zhu a , V. H. Crespi a,c and P. C. Eklund a,c Departments of Physics a , Electrical Engineering b and Material Science and Engineering c The Pennsylvania State University, University Park, PA, USA NSF ECS0609243 1 1 2 2 4 4 n nGL substrate n nGL SiO 2 : Si n= 2 n=1 n= 8 n=1 9 n= 5 HOPG (top view) (side view) Optical Image Graphene 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 SiO 2 AFM AFM height measurements for nGLs. Extra thickness of graphene (0.7 nm) may reflect inherent difference in attractive AFM tip force between SiO 2 and graphene 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. Magneto- resistance (R xx ) and Hall (R xy ) measurements of nGL (n>1) devices at low temperature. n n GL Sensors GL Sensors 5 5 Introduce 10% NH 3 After The Dirac peak of a graphene device before exposure to 10% NH 3 , during exposure to 10% NH 3 and after annealing the NH 3 -doped device in vacuum (top). The Dirac peak recovery during vacuum annealing of a different graphene device exposed to Cl 2 (bottom) Incommensurately Stacked Bi-Layer Graphene 7 7 Optical Image and Schematics of incommensurat e bilayer (IBL) Incommensurate stacking of two graphene layers produces a pair of almost decoupled graphene layers Band splitting for IBL ~ 6 meV (Vienna Ab-initio Simulation Package calculation) Theoretical Theoretical Calculations Calculations 6 6 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 single- continuum (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 200-400 nm PZT 2 peaks ~1350 cm -1 and 1384 cm -1 (I 1 and I 2 ) are seen in IBL and compared with defect induced D band peaks (1 peak for mono graphene layer and 4 peaks for commensurate bi I 1 and I 2 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 Dispersion of 2D peak for 1GL, IBL and 2GL. 2D peak dispersion - - - + + + - - - + + + S D Nb doped SrTiO 3 nGL Non-volatile memory device based on nGL-FET using ferroelectric film Pb(Zr Ti)O 3 (PZT) as gate oxide. The large remnant polarization field of PZT ( ~ 40 µC/cm 2 ) can potentially induce enormous 2D carrier doping (~3x10 14 /cm 2 ) and lead to non-volatile memory effect. Pronounced hysteresis in carrier density and resistivity as a function of V g with long retention time is observed in our nGL-FET. Raman scattering is found to be sensitive to the number of layers in nGLs. 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. 2D G 2D+G G ~ 1/n Raman spectrum can count n in nGLs 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 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). 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 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) n-Graphene Layer = nGL ; n is integer
