ICTP Conference Graphene Week 2008

Transcription

1 ICTP Conference Graphene Week August 2008 Current-induced cleaning of graphene J. Moser CIN2 Barcelona, Campus UAB, Bellaterra, Spain A. Barreiro CIN2 Barcelona, Campus UAB, Bellaterra, Spain A. Bachtold CIN2 Barcelona, Campus UAB, Bellaterra, Spain

2 Current-induced cleaning of graphene J. Moser, A. Barreiro, and A. Bachtold CIN2 Barcelona, Campus UAB, E Bellaterra, Spain

3 Motivation Conductivity conductivity (S) G (S) Typical mobilities: ~20,000 cm 2 V -1 s -1 on SiO 2 ~200,000 cm 2 V -1 s -1 suspended V gate (V) gate bias (V) K. I. Bolotin, K. J. Sikes, Z. Jiang, G. Fudenberg, J. Hone, P. Kim, and H. L. Stormer, Solid State Communications 146, (2008). X. Du, I. Skachko, A. Barker, E. Y. Andrei, arxiv:

4 Motivation Conductivity conductivity (S) G (S) Typical mobilities: ~20,000 cm 2 V -1 s -1 on SiO 2 ~200,000 cm 2 V -1 s -1 suspended Mobility μ was shown to be limited by charge disorder V gate (V) gate bias (V) J. H. Chen, C. Jang, M. S. Fuhrer, E. D. Williams, and M. Ishigami Nature Physics 4, 377 (2008).

5 Motivation Conductivity conductivity (S) G (S) Typical mobilities: ~20,000 cm 2 V -1 s -1 on SiO 2 ~200,000 cm 2 V -1 s -1 suspended F. Schedin, A. K. Geim, S. V. Morozov, E. W. Hill, P. Blake, M. I. Katsnelson, and D. K. S. Novoselov, Nature Material 6, 652 (2007) V gate (V) gate bias (V) Shaffique Adam, E. H. Hwang, Victor Galitski, S. Das Sarma, Proc. Natl. Acad. Sci. USA 104, (2007)

6 Outline: 1) Characterizing contaminants by Electrostatic Force Microscopy (EFM) 2) Current-induced cleaning (annealing) of graphene

7 z -V dc + V ac sinωt Difference between surface potentials on the plates

8 z -V dc + V ac sinωt

9 V dc + V ac sinωt 10 μm

10 step flowing N 2 varying V dc, measuring F ω 0 movie

11 step graphene annealed at 150 deg C for 1 hour in flowing N 2 varying V dc, measuring F ω movie

12 flowing, moist N 2 step 3 varying V dc, measuring F ω

13 step 1 step 2 Dry N 2 and moist N 2 yield similar results Annealed sample in dry N 2 stands out step 3

14 (e.g., for graphene)

15 tip above SiO 2 : Varies by a few 100mV

16 A. Verdaguer, C. Weis, G. Oncins, G. Ketteler, H. Bluhm, and M. Salmeron, Langmuir 23, 9699 (2007)

17 tip above graphene:

18 What s in?

19 difference in comes from influence of water on no water water

20 δ+ + δ+ H H O - δ+ + δ+ H H 2δ- O 2δ- - graphene - Electric field vanishes rapidly far from dipole layer - Inhomogeneous charge distribution at the Dirac point

21 E graphene no water water

22 E graphene no water water

23 E graphene no water water

24 More about water on graphene: Tuning the effective fine structure constant in graphene: opposing effects of dielectric screening on short- and long-range potential scattering C. Jang, S. Adam, J.-H. Chen, E. D. Williams, S. Das Sarma, and M. S. Fuhrer arxiv: Detection of individual gas molecules adsorbed on graphene F. Schedin, A. K. Geim, S. V. Morozov, E. W. Hill, P. Blake, M. I. Katsnelson, and D. K. S. Novoselov Nature Material 6, 652 (2007) Electrostatic interactions between graphene layers and their environment J. Sabio, C. Seoánez, S. Fratini, F. Guinea, A. H. Castro Neto, and F. Sols Phys. Rev. B 77, (2008)

25 Other possible contaminant: adhesive residues

26 Unavoidable contaminants: nanofabrication residues M. Ishigami, J. H. Chen, W. G. Cullen, M. S. Fuhrer, and E. D. Williams Nano Lett. 7, 1643 (2007). E. Stolyarova, K. T. Rim, S. Ryu, J. Maultzsch, P. Kim, L. E. Brus, T. F. Heinz, M. S. Hybertsen, and G. W. Flynn PNAS 104, 9209 (2007).

27 Outline: 1) Characterizing contaminants by Electrostatic Force Microscopy (EFM) 2) Current-induced cleaning (annealing) of graphene

28 Graphene can sustain very high current densities Saturates at J ~ 10 9 A/cm 2 (like in metallic SWCNT)

29 Graphene can sustain very high current densities Saturates at J ~ 10 9 A/cm 2 (like in metallic SWCNT) width that is J ~ μa/nm

30 High heat melts CdSe particles away before after

31 Current-induced cleaning technique PMMA residues melt away Stop increasing V SD Current vs Time I (ma) V SD (V) I (ma) time (sec)

32 Current-induced cleaning technique Another possible cleaning mechanism: electro-migration I (ma) I (ma) V SD (V) time (sec)

33 Current-induced cleaning technique Another possible cleaning mechanism: electro-migration I (ma) I (ma) V SD (V) time (sec)

34 Current-induced cleaning technique Another possible cleaning mechanism: electro-migration I (ma) I (ma) V SD (V) time (sec)

35 Current-induced cleaning technique Another possible cleaning mechanism: electro-migration I (ma) I (ma) V SD (V) time (sec)

36 Influence on doping and mobility μ = 25,000 cm 2 V -1 s σ xx (S) No annealing μ = 7000 cm 2 V -1 s V gate (V)

37 Influence on doping and mobility μ = 25,000 cm 2 V -1 s -1 current cleaning σ xx (S) μ = 7000 cm 2 V -1 s -1 oven annealing at 400 C in Ar/H V gate (V) A. Barreiro, et al., work in progress

38 cleaned with current 8 1 σ xy (4e 2 /h) ρ xx (kω) annealed in Ar/H 2 T=4K B=9T V gate (V) ν=0 plateau: high quality samples V gate (V) - Y. Zhang, Z. Jiang, J. P. Small, M. S. Purewal, Y.-W. Tan, M. Fazlollahi, J. D. Chudow, J. A. Jaszczak, H. L. Stormer, and P. Kim, PRL 96, (2006). - D. A. Abanin, K. S. Novoselov, U. Zeitler, P. A. Lee, A. K. Geim, and L. S. Levitov, PRL 98, (2007). - Z. Jiang, Y. Zhang, H. L. Stormer, and P. Kim, PRL 99, (2007).

39 Conclusion 1) Electrostatic Force Microscopy: water sticks to graphene J. Moser, A. Verdaguer, D. Jiménez, A. Barreiro, and A. Bachtold Appl. Phys. Lett. 92, (2008) 2) Current-induced cleaning technique: lowers extrinsic doping, improves mobility even for samples in contact with substrate J. Moser, A. Barreiro, and A. Bachtold Appl. Phys. Lett. 91, (2007)

40 1 nm layer 4.6 x Capacitance (F) ε=80 ε=20 ε= z (nm)

41 Solving Poisson s equation x (10-17 F/nm) First C-derivative [F/nm] ε=80 ε=20 ε= z (nm) height (nm)

42 height (nm) EFM signal distance EFM signal distance distance

43 EFM signal height (nm) FGL SGL 0 distance EFM signal V dc 1 V dc 1 V dc 2 V dc EFM signal distance V dc 2 distance