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Measurements of Forces at the Nanoscale some ideas for measurements at LEPES in 2005 J. Chevrier

Measurements of Forces at the Nanoscale some ideas for measurements at LEPES in 2005 J. Chevrier 18 November 2004. we consider three different forces: - Casimir: hc [J.m] - Electrostatic: e 2 /4 pe 0 [J.m] -Gravity: Gm 2 [J.m].

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Measurements of Forces at the Nanoscale some ideas for measurements at LEPES in 2005 J. Chevrier

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  1. Measurements of Forces at the Nanoscale some ideas for measurements at LEPES in 2005 J. Chevrier 18 November 2004

  2. we consider three different forces: - Casimir: hc [J.m] - Electrostatic: e2/4pe0 [J.m] -Gravity: Gm2[J.m]

  3. -electrostatic: Charles A. Coulomb 1736-1806 - strong force - long range today “Easily” measured -gravity: Henry Cavendish Nice 1731 - Londres 1810 - weaker force: (e2/4pe0) / Gm2 1040 - long range a bit more difficult…but still a student training

  4. - Casimir/van der Waals versus electrostatic: Sphere diameter 50 mm sphere/surface: 10nm -1 mm hc / (e2/4pe0)  137 fine structure constant However unless at very short distances (< 1nm) (if static charges present …not neutral) electrostatic >> Casimir Casimir… short range characteristic distance at the nanoscale Nanosciences

  5. origin of van der waals/casimir interaction between two neutral systems in their fundamental state: electron-photon coupling by dipolar interaction -d.E Fundamental state Fundamental state Electronic excitations e(q,w) -d.E -d.E temps -d.E -d.E Fundamental state Fundamental state

  6. Characteristic length for two metallic surfaces (jellium model) defined by electronic excitations coupled to photons: surface plasmons characteristic length: l p= 2p c/ w p Aluminium h w p= 14eV l p  100nm

  7. Surface plasmons Surface plasmons E E z x +++ --- +++ --- +++ --- Hy e metal ( <0) 1

  8. +++ --- +++ --- +++ --- E E z x Hy e e metal ( metal ( <0) <0) +++ --- +++ --- +++ --- 2 1 Coupling of Surface plasmons Surface plasmons d<< l p

  9. F>0 attractif F<0 répulsif Al Plasmon polariton SiC Phonon polariton d=10nm Plasmon polariton d<< l p

  10. Surface plasmons Surface plasmons Changing coupling of plasmons with extended photon modes ??? E E z x +++ --- +++ --- +++ --- Hy e metal ( <0) 1

  11. w = ck x p 2 D = Î k n , n Z x a p 2 w = ck q + = = ± ± k sin n k , n 0, 1, 2,... x ph sp a w e e = 1 2 k sp e + e c 1 2 The way the plasmon-photon coupling is changed w q k 1 e ph 1 2 k e x 2 k sp a w 1 k x p /a

  12. Experiment: Force measurement at distances close to 10nm below the plasma length to be sensitive to surface electronic excitations Using a resonating oscillator perturbed by the van der Waals/Casimir interaction. k, w Interaction F sample

  13. sample

  14. 1000 100 Frequency shift Hz 10 1 0,1 10 100 1000 Distance (nm) Electrostatic calibration Dispersion force in the non retarded régime

  15. Home made force machine built within the X tip european project at the ESRF in 2004 Pour le LEPES en 2005: extension to measurement at short distances d<< l p under vacuum and at low T (4K) …...

  16. Very very large roughness... hope we shall avoid such a hard collision next time good point however: parallel surfaces well prepared….

  17. Experimental objective: Combination of sphere on cantilever or on tuning fork + measurement of frequency shift with resolution close to 1mHz

  18. Gauthier Torricelli Thèse LEPES/ESRF Mario Rodriguez stage de Master 2 ESRF Guillaume Jourdan Thèse LEPES/Lab. Kastler Brossel Direction: J. Chevrier/ A. Lambrecht

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