Microscopie à champs proche: et application

Transcription

1 Microscopie à champs proche: Théorie et application STM, effet tunnel et applications AFM, interactions et applications im2np, Giens 2010

2 Optical microscopy: resolution limit resolution limit: d min = λ 2* NA λ lentille avec ouverture numerique NA

3 Scanning probe microscopy: resolution limit resolution limit: atomic length scale problems: - mechanical stability - tip-sample interaction current (STM), force (AFM), - control tip sample distance to a few Å topography

4 Implementation PtIr wire for Scanning Tunneling Microscopy (STM) microfabricated silicon beam for Atomic Force Microscopy (AFM) Bohr-radius a 0 = 5,29 * m tip height: 10-5 m table tennis ball r ~ 5 * 10-2 m Mont Cervin height: 4477 m/m 10 9 length = 450 µm / width = 45 µm thickness = 1.5 µm E = N/m 2 tip height = 12 µm / radius: 10 nm

5 What is imaged in STM?

6 Scanning tunneling microscope (STM) typical values: current 10 pa...10 na voltage mv...several V distance 0.5 nm exponential dependence on distance s: x xyz piezo scanner y topography information z controller I exp(-αs), α 2 Å -1 tip U atomic resolution sample + desired value G. Binnig and H. Rohrer, Helv. Phys. Acta 55, 726 (1982) Nobel Prize 1986

7 Tunnelling barrier Le PASSE-MURAILLE Sculpture de Jean MARAIS Julian Chen: Introduction to STM, Oxford University Press

8 Tunnelling barrier Julian Chen: Introduction to STM, Oxford University Press

9 Tunnelling process IT deρt ( E + ev ) ρs ( E) T( E, ev ) E E F F ev ρ s, ρ t T LDOS of sample and tip barrier transmission

10 Tunnelling spectroscopy IT deρt ( E + ev ) ρs ( E) T( E, ev ) E E F F ev ρ s, ρ t T LDOS of sample and tip barrier transmission

11 STM imaging of a surface state M.F. Crommie et al., Nature 363, 524 (1993)

12 Nanostructuration: : STM M. Abel, D. Catalin, S. Clair, M. Koudia, O. Ourdjini, R. Pawlak, M. Mossoyan, and L. Porte

13 BDBA on KCl: : Motivation dehydration - nh 2 O STM results: BDBA on Ag(111) Zwaneveld N. et al., JACS 190, 6678 (2008)

14 BDBA on Ag (100) spontaneous polarization tip induced polymerization 4.0nm 12nm 6.0nm 12nm

15 organometallic π - conjugated network iron-phthalocyanines on Ag + Fer + Fer 12nm 6.0nm

16 Properties for molecular electronics S=1 on each iron atom 2.0nm spin-polarized conductivity molecular magnet

17 What is imaged in AFM? L. Gross et al., Science 325, 1110 (2009)

18 Beam Deflection L. Howald et al., Appl. Phys. Lett. 63, 117 (1993)

19 Experimental setup for noncontact AFM excitation amplitude controller frequency demodulation f 0 distance controller Lock-In amplifier Kelvin controller topography bias voltage see poster by Jérémy BOULOC, PLL up to 100 MHz more details: U. Zerweck, Ch. Loppacher et al. Phys. Rev. B 71, (2005)

20 Forces R Nano- Tip α d S d L Van der Waals forces: (F.O. Goodman und N. Garcia, Phys. Rev. B 43, 4728 (91)) electrostatic forces: (S. Hudlet et al., Euro. Phys. J. 25, (98)) chemical forces: attractive: binding and adhesion forces repulsive: Pauli and nuclear repulsion Literature: J. Israelachvili: Intermolecular and Surface Forces, Academic Press (1985) D. Tabor: Gases, liquids and solids, Cambridge University Press (1979)

21 Separation of interactions I force oscillation amplitude 3-30 nm distance U sample = -U CPD

22 Separation of interactions II f VdW = f0 ka 12d L HR 2d L A 0-10 f [Hz] U sample = -U CPD distance [nm] M. Guggisberg, Ch. Loppacher et al., Phys. Rev. B 61, (2000)

23 Calculation of forces f 0 U 0 d S ds f chem = exp( 2 ) 2 exp( ) ka πaλ λf λ F F 2U = 0 d S d S F exp( 2 ) exp( ) chem λf λf λf 0 f chem [Hz] ,0-0,2-0,4 F [nn] distance [nm] M. Guggisberg, Ch. Loppacher et al., Phys. Rev. B 61, (2000)

24 Single molecular switch Cu-tetra(3,5 di-t-butylphenyl)porphyrine 25 nm Calculations: H. Tang and C. Joachim, CEMES/CNRS, Toulouse, France (MM2) Ch. Loppacher et al., Phys. Rev. Lett. 90, (2003)

25 Single molecular switch Cu-tetra(3,5 di-t-butylphenyl)porphyrine E = 83zJ = 0.6eV 25 nm Calculations: H. Tang and C. Joachim, CEMES/CNRS, Toulouse, France (MM2) Ch. Loppacher et al., Phys. Rev. Lett. 90, (2003)

26 Atom recognition surface Si(111) 7x7 avec des atomes de plomb et étain Y. Sugimoto et al., Nature 446 (2007) 64

27 Electrostatic forces: Kelvin Force Microscopy topography (10µm) 2 topography (500nm) 2 F el U ext φ 2 U mod surface potential 800 U CPD ~ 900mV U DC Oscillating force C ( ) π z U DC φ e U mod cos( 2 f mod t ) 1 C + π z U 2 mod cos( 4 f mod t ) 4 vibration at f mod and 2f mod number of points U cpd [V] U. Zerweck, Ch. Loppacher et al., Phys. Rev. B. 71: (2005)

28 Nanostructuration: : AFM F. Bocquet, L. Nony, and Ch. Loppacher electronic properties of single molecules and interfaces single charge, molecular dipole KBr Ag(111) «tunable» insulating and wide-gap surfaces quantitative understanding

29 BDBA on KCl: : Experiments R. Pawlak et al., J. Phys. Chem. C, in press ad hoc model: Flat-lying configuration impossible, tilt around long axis necessary (steric hindrance) lattice constant: a = 5.2 Å; b = 10.0 Å

30 BDBA on KCl: : Calculations BDBA unit cell (SIESTA code, GGA functional, PBE type) y 4 H-bonds/mol: 1eV (0.25 ev/ H-bond/mol.) Theoretical lattice constant: a = 4.99 Å; b = Å calculations: V. Oison, M. Sassi, and J.-M. Debierre cf: Rodriguez-Cuamatzi P. et al., Acta Cryst. E60, o1315 (2004)

31 BDBA on KCl: : Calculations calculations: V. Oison, M. Sassi, and J.-M. Debierre cf: Rodriguez-Cuamatzi P. et al., Acta Cryst. E60, o1315 (2004)

32 BDBA on HOPG: Experiments (700x700)nm 2, f= -1Hz (25x25)nm 2, f=-12hz identical structure on HOPG (first ML) as on KCl

33 Measurement of local charges L. Gross et al., Science 324, 1428 (2009)

34 Measurement of local charges L. Gross et al., Science 324, 1428 (2009)

35 Imaging ionic surfaces: Model F. Bocquet et al., PRB 78, (2008)

36 Imaging ionic surfaces: Forces and simulations Forces L. Nony et al., PRB 74, (2006) KPFM simulation F. Bocquet et al., PRB 78, (2008)

37 Imaging ionic surfaces: Model II L. Nony et al., PRL 103, (2009) atomistic calculations by A. Foster, Tampere and Helsinki University, Finland

38 Imaging ionic surfaces: Model II topography LCPD LCPD, constant height L. Nony et al., PRL 103, (2009)

39 Influence of Molecular Organization on φ ZnPcCl8 on Ag(111) first phase: P1 intermediate : P2 end phase : P3 ZnPcCl8 Image 10 nm x 10 nm time or annealinig evolution with time: sequential formation of hydrogen bonds M. Koudia et al., J. Phys. Chem. B 110, (2006) M. Abel et al., ChemPhysChem 7, 82 (2006)

40 Influence of Molecular Organization on φ ZnPcCl 8 on Ag(111) P1 P2 Kelvin DFT electronic structure calculations using SIESTA P. Milde, Ch. Loppacher et al., Nanotechnology 19, (2008)

41 Influence of Molecular Orientation on φ 5,15-bis(2,6 -bis(3,3-dimethyl-1- butyloxy)phenyl)porphyrin M. Nikiforov, Ch. Loppacher et al., Nano Letters (2008)

42 Influence of Molecular Orientation on φ M. Nikiforov, Ch. Loppacher et al., Nano Letters (2008)

43 Optical properties of adsorbed molecules PTCDA on KCl < 1 monolayer > 1 monolayer sublimation > 1 monolayer optical properties change PTCDA/KCl R/R λ(nm) quadratic herringbone T. Dienel, Ch. Loppacher et al., Advanced Materials, 20, 959 (2008)

44 Optical properties of adsorbed molecules PTCDA on KCl < 1 monolayer > 1 monolayer dissipation [010] [100] PTCDA/KCl commensurate 2x2 overlayer! quadratic herringbone T. Dienel, Ch. Loppacher et al., Advanced Materials, 20, 959 (2008)

45 Conclusion what is imaged in STM? formation of covalent network separation and calculation of forces single charge manipulation image simulation

46 merci pour votre attention!