New Developments in Surface Science Complex 2D Systems (Graphene and beyond…) Biosurfaces - PowerPoint PPT Presentation

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New Developments in Surface Science Complex 2D Systems (Graphene and beyond…) Biosurfaces

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  1. New Developments in Surface Science • Complex 2D Systems (Graphene and beyond…) • Biosurfaces • Magnetic systems (new sort of…)

  2. Development of Surface Science Techniques   Materials Binnig, Rohr (STM) Fert, Grunberg (GMR) Bader (MOKE) ~1985 Goodman Haber Bell, Somorjai, Ertl Nanocatalysts and particles Catalysis Complex catalysts Biomaterials Langmuir Electronic Materials Micro/nano electronics 2D systems, new materials Bardeen, Sigbahn, Bell Labs, IBM Research Seitz, etc…. Spintronics LEED (1927) TPD AES XPS ~1900 STM, AFM Spin-polarized PES MOKE, SFG Spin-polarized LEED, STM 1960-1980’s

  3. 2-D Systems Beyond Graphene: • BN, MoSe2, MoS2…. • Stacks combining the above with graphene • Spintronics and Graphene, BN, etc.

  4. Boron nitride, isostructural and isoelectronic with graphene, but different Weck, et al. Phys. Chem. Chem. Phys., 2008, 10, 5184-5187

  5. Watanabe, et al. p. 404

  6. Britnell, et al., Science 335 (2012) 947 Multilayer BN tunneling barrier Application of gate voltage induces increase in carrier densities in cond. Bands of both graphene layers (weak screening). Note, graphene low DOS yields much greater increase in EF for given Vg Application of VBinduces tunneling between graphene layers

  7. Note, relatively small increase in I with Vg. (interf. Charge screening? MoS2 give higher on/off ratios Britnell, et al., Science 335 (2012) 947

  8. Tunneling transit time ~ femtoseconds, better than electron transit time in modern planar FETs Conclusion: Graphene/BN And Graphene/MoS2 (MoSe2) stacks have exciting photonic/nanoelectronic applications.

  9. Alternative proposed design for a graphene tunneling transistor (BN could be used as the base…) Graphene has band gap in vertical direction: monolayer thickness favors ballistic transport with applied bias High on/off ratios (> 105) and THZ switching predicted in simulations

  10. Issues: • Orbital overlap/hybridization—band gap formation • Growth • Multilayer BN, precise thickness control?? • Graphene on BN (or MoS2) and vice versa • 3. Interfacial Effects, Charge transfer, mass transfer, etc.

  11. WHY A BAND GAP? LEED is C3V: A site/B sites different electron densities Degeneracy of HOMO,LUMO at Dirac Point due to chemical equivalency of A and B lattice sites = +1 = -1/2 A , B equivalent (C6v) no band gap k B B A A A ≠ B (C3V) band gap HOMO and LUMO Orbitals in Graphene at Dirac point (adopted from Cox: The Electronic Structure and Chemistry of Solids (1991) k

  12. Giovanneti, et al., DFT calcns on graphene/BN interface Lowest energy interfacial structure:

  13. Band gap of 0.05 eV predicted. How does this compare to RT? Prediction, O.1 eV band gap for graphene on Cu, but huge charge transfer.

  14. Isolated Graphene Sheet Graphene/BN—band gap, with Fermi level in middle of gap E EF EF k Eg Giovanetti, et al; DFT results Graphene on Cu: charge transfer masks the gap, moves Fermi level well above the gap EF Eg

  15. Evidence of orbital mixing, Fermi level broadening

  16. Cu 3d/BN π mixing: weaker than in Ni (Cu d’s more localized)

  17. Why don’t we see a band gap for BN/Ru???

  18. Can we grow BN multilayers? Yes! Atomic layer deposition (see Ferguson, et al. Thin Sol. Films 413 (2002) 16 BCl2 BCl3 + (surface)  BCl2(ads) BCl2(ads) + NH3  B-N-H(ads) + 2HCl(desorbed) BNH(ads) + BCl3  B-N-B-Cl2 + HCl(desorbed) BNBCl2 + NH3  BNBN BNH

  19. BN/Si(111): ALD Growth Characteristics BN films are stoichiometric (1:1) for thin films (<5 ML) and become slightly B-rich (?) as film thickness increases AMC 2012

  20. h-BN(0001): ALD/BCl3+NH3 vs CVD/Borazine ALD: Epitaxial Multilayers CVD/Borazine: Flat or puckered monolayers Ru(0001) Ni(111) We need multilayers for applications, and not just on Ru! AMC 2012

  21. Lattice Overlay: Graphene (BN) on CoSi2(111) BN/graph 3x3~ CoSi2(2x2) C Co Si AMC 2012

  22. BN bilayer on CoSi2(111) 4 BCl3/NH3 cycles at 550 K, anneal to 850 K in UHV AMC 2012

  23. Anneal of BN/CoSi2 at 1000K: LEED analysis: BN implant lattice constant =2.5(±0.1)Å CoSi2 implant lattice constant=3.8(±0.1)Å Expected values E=78ev 243 187

  24. Interesting results, but: • Anneal to 1000 K to induce order, but CoSi2 is slightly unstable at this temp. (slow Co diffusion) • Can we go to lower temperatures, other silicides? • Carbon buildup is worrisome. • Clean up our act? • Heteroepitaxy (BN 3x3 vs. silicide 2x2) demonstrated. • What about BN/transition metals vs. silicides? • Spintronics? {Spin filtering predicted in MTJs} AMC 2012