Measurements of Forces at the Nanoscale

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Measurements of Forces at the Nanoscale some
ideas for measurements at LEPES in 2005 J.
Chevrier 18 November 2004
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we consider three different forces - Casimir
hc J.m - Electrostatic e2/4pe0
J.m -Gravity Gm2 J.m
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-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 difficultbut still a student training
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- 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 (lt
1nm) (if static charges present not
neutral) electrostatic gtgt Casimir
Casimir short range characteristic distance
at the nanoscale Nanosciences
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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
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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
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Coupling of
Surface
plasmons
Surface
plasmons
dltlt l p
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Fgt0 attractif
Flt0 répulsif
Al
Plasmon polariton
SiC
Phonon polariton
d10nm
Plasmon polariton
dltlt l p
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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
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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
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sample
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Electrostatic calibration
Dispersion force in the non retarded régime
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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 dltlt l p under vacuum and at
low T (4K) ...
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Very very large roughness...
hope we shall avoid such a hard collision next
time good point however parallel surfaces well
prepared.
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Experimental objective Combination of sphere
on cantilever or on tuning fork measurement
of frequency shift with resolution close to 1mHz
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Gauthier Torricelli Thèse LEPES/ESRF
Mario Rodriguez stage de Master 2 ESRF
Guillaume Jourdan Thèse LEPES/Lab. Kastler
Brossel Direction J. Chevrier/ A. Lambrecht