Graphene Nanoribbons: A Route to Atomically Precise Nanoelectronics Mike Crommie

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1 Graphene Nanoribbons: A Route to Atomically Precise Nanoelectronics Mike Crommie Dept. of Physics, UC Berkeley and Materials Science Division, LBNL Berkeley, CA

2 Outline 1) Graphene Graphene Nanoribbon (GNR) behavior 2) Potential applications for GNRs. 3) How do we make GNRs? 4) New developments in bottom-up fabrication Molecular bandgap engineering New bottom-up strategies Graphene Nanoribbon

3 Electronic Structure of Graphene K Energy Conduction band Valence band Dirac pt. zigzag direction k y k x M armchair direction Reciprocal Space k x K k y M

4 Graphene Nanoribbon Electronic Structure w Armchair Reciprocal Space Armchair E 0 No Edge State (ev) k 0 Zigzag Reciprocal Space Zigzag E 0 Edge State (ev) Spin-polarized k 0 M. Fujita, et al., J. Phys. Soc. Jpn 65, 1920 (1996); K. Nakada, et al., PRB 54, (1996); J. Heyd et al, J. Chem. Phys. 118, 8207 (2003); Y.-W. Son, et al, PRL 97, (2006)

5 Potential GNR Device Advantages Energy gap, capacitance Bandgap Engineering GNRs solve the nanotube metallicity problem V SD Big gap Small gap Width E V G I D V G for nanotubes k µ Energy Length off Smaller capacitance H. Park, et al., Nat. Nanotech. 7, 787 (2012) Faster on Uniquely Efficient Tunneling GNR GNR Fast onset tube tube Length

6 Potential GNR Device Advantages Energy gap, capacitance Bandgap Engineering GNRs solve the nanotube metallicity problem V SD Big gap Small gap Width E V G I D V G for nanotubes k µ Energy off Smaller capacitance H. Park, et al., Nat. Nanotech. 7, 787 (2012) Faster on Uniquely Efficient Tunneling GNR GNR Fast onset tube tube Length

7 High-current low-dissipation switching: HFET New proposed GNR implementation Requires GNR doping and bandgap/width variation Large gap Small gap Large gap S p n D J. Bokor

8 How Do We Make High Quality GNR Devices? Top-down Lithography M. Y. Han et al., PRL 98, (2007) Rough Edges are a Problem Graphene platelet on Si(100) Y. Kobayash et al., PRB 71, (2005) Ritter and Lyding, Nat. Mat. 8, 235 (2009)

9 Unzipping Nanotubes: A Better Edge Unzipped GNRs Smooth Edges (8, 1) GNR width = 20 nm 5.5 Å Jiao, et al, Nat. Nanotechnol 5, 321 (2010) Kosynkin, et al, Nature 458, 872 (2009) Au(111) 48 Å 48 Å 0.0 Å C. Tao, et al., Nat. Phys. 7, 616 (2011) Unzipped GNR FETs High Mobility Controlling width and chirality A problem X. Wang, et al, Nat. Nanotechnol 6, 563 (2011)

10 A New Idea Molecular precursor Bottom-up Fabrication: Final assembled GNR

11 A New Idea Molecular precursor Bottom-up Fabrication: Final assembled GNR Width Chirality Edge functionalization Bottom-up Heterostructures: p n p p-n junctions bandgap engineering

12 GNR Bottom-up Synthesis Breakthrough: n=7 AGNRs Precursor molecule Metallic surfaces. 200 C n = 7 AGNR. 200 C 400 C (7 atoms across) STM Image: AGNRs / Au(111) Width = 0.7 nm Fasel, Muellen, & co-workers J. Cai et al, Nature 466, 470 (2010)

13 STM Allows Measurement of Local Electronic Structure STM Spectroscopy tip sample V tip sample E F Ñwω E F LDOS(E) 0

14 Using STM to Measure GNR Energy Gap GNR Electronic Structure STM Bandedge Electrons Show Higher Density at GNR Edges GNR = 2.5 ev Au reference LUMO di/dv map M. Koch, et al., Nat. Nanotech. 7, 713 (2012) P. Ruffieux, et al., ACS Nano 6, 6930 (2012)

15 Can We Tune the Energy Gap? (ev) Armchair 4 N=7 Tune? 2? 0 N = 7 N > 7 Must synthesize new precursor molecules

16 A New Precursor Molecule to Tune GNR Bandgap: N=13 New Precursor 200 C. 200 C 400 C n = 13 Metallic surface. F. Fischer & Crommie STM image: Polymer stage Fully cyclized (after annealing) width = 1.4 nm Yen-Chia Chen, et al., ACS Nano 7, 6123 (2013)

17 STM Spectroscopy of N=13 AGNR GNR width width N = 13 = N = 7 2 Au N = 13 = N = di/dv maps HOMO LUMO Y.-C. Chen et al., ACS Nano 7, 6123 (2013)

18 Variable-Width Heterostructures + Molecular Bandgap Engineering (B.E.) Previous Mesoscale B.E. : New Molecule-scale B.E. : (theory, DFT) GaAs AlGaAs GaAs 5-9 Junction E E c E v x Sevinçli, et al, PRB 78, (2008)

19 Molecular Bandgap Engineering: 7-13 Junctions n=7 n= Junction

20 Molecular Bandgap Engineering: 7-13 Junctions n=7 n= Junction Fabricating 7-13 Molecular Junctions on Au(111) 3.8 nm 2 nm

21 STM Spectroscopy of 7-13 Junction Topograph N=7 N=13

22 STM Spectroscopy of 7-13 Junction: Interface States Topograph N=7 N=13 1 2

23 STM Spectroscopy of 7-13 Junction: Interface States Topograph N=7 N=13 1 2

24 Theoretically Modeling the 7-13 Molecular Junction Assume Periodic Structure: Perform DFT Calculation Unit Cell Theory: Ting Cao, Steven Louie

25 Electronic Structure of 7-13 Molecular Junction n=13 LUMO n = ev n = ev D.O.S Energy (ev) -1.0 Calculate LDOS distribution for these states, compare to experiment S. G. Louie, T. Cao

26 Topograph Comparing Theoretical Wave-function Maps to Experiment Experimental LDOS Theoretical LDOS

27 How Can Devices be Made From Bottom-up GNRs? A Must transfer GNRs to insulator: SiO 2 PMMA Au Mica GNRs Mica Device Layout for 7-AGNRs 26nm gap Fischer, Crommie, Bokor

28 Bottom-up GNR Device Results Bottom-up N=7 GNR FET Schottky barrier behavior: E k µ n-type Φ e E metal contact GNR metal contact x Challenges: Improve contacts Improve transfer to insulator New GNR heterostructures Grow directly on insulator? P. B. Bennett et al., APL 103, (2013)

29 New Chemistry: New Opportunities Currently requires metal substrate Au(111) SiO 2 Difficult Bergman Cyclization of Enediynes: Flexible coupling: + Alkyne coupling.. Radical step growth Polymerization:..Q. Sun, et al., JACS 135, 8448 (2013) A. Riss, et al., Nano Lett. 14, 2251 (2014)

30 Model System for Surface Chemistry Enediyne Fragment: Felix Fischer (UC Berkeley) Expected Reaction Path: But what really happens?

31 Imaging Enediyene Cyclization on Ag(100) STM Images heat

32 Imaging Enediyene Cyclization on Ag(100) STM Images heat F. J. Giessibl, Appl. Phys. Lett. 76, 1470 (2000) L. Gross, F. Mohn, N. Moll, P. Liljeroth, G. Meyer, Science 325, 1110 (2009) tip Qplus nc-afm G. Meyer & co-workers (2009)

33 Imaging Enediyene Cyclization on Ag(100) STM Images heat nc-afm Images D. Oteyza, et al., Science, /science (2013)

34 Modifying Enediyne Molecules to Induce Coupling Alkyne Coupling heat Enediynes on Ag(100)

35 Modifying Enediyne Molecules to Induce Coupling Radical Polymerization heat Enediynes on Au(111)

36 Energy Landscape and Reaction Pathway Theory: A. Rubio & co-workers D. de Oteyza, et al., Science 340, 1434 (2013)

37 Energy Landscape and Reaction Pathway Theory: A. Rubio & co-workers Improved Structural Control at the Nanoscale D. de Oteyza, et al., Science 340, 1434 (2013)

38 Conclusions 1) GNRs novel electronic properties. 2) Bottom-up synthesis molecular bandgap engineering. 3) New chemistries new nanostructures. Future 1) Incorporate bottom-up heterojunctions into devices. 2) New bottom-up GNR structures, improved control. 3) Grow GNRs directly on insulators.

39 Collaborators / Funding Nano-Bio Spect. Gp., ETSF Sci. Dev. Center, UPV, San Sebastian, Spain: Angel Rubio, Duncan J. Mowbray, Alejandro Perez UC Berkeley / LBL: M. F. Crommie (Physics) Dimas G.de Oteyza (now at Centro de Fisica, San Seb., Spain) Felix Fischer (Chemistry) Alexander Riss (now at Inst. of App. Phys., TU Wien) Steven Louie (Physics) Sebastian Wickenberg Jeff Bokor (EECS) Hsinzon Tsai Marvin Cohen (Physics) Patrick Bennett Alex Zettl (Physics) Miguel Moreno-Ugeda Zahra Pedramrazi Chen Chen Aaron Bradley Danny Haberer Grisha Etkin Patrick Gorman Liang Z. Tan Ivan Pechenezhskiy Yenchia Chen

40 THE END