measurements of forces at the nanoscale some ideas for measurements at lepes in 2005 j. chevrier 18...
DESCRIPTION
-electrostatic: Charles A. Coulomb strong force - long range today “Easily” measured -gravity: Henry Cavendish Nice Londres weaker force: (e 2 /4 0 ) / Gm 2 long range a bit more difficult…but still a student trainingTRANSCRIPT
Measurements of Forces at the Nanoscalesome ideas for measurements at LEPES in 2005
J. Chevrier
18 November 2004
we consider three different forces:
- Casimir: hc [J.m]
- Electrostatic: e2/40 [J.m]
-Gravity: Gm2 [J.m]
-electrostatic: Charles A. Coulomb 1736-1806 - strong force- long range
today “Easily” measured
-gravity: Henry CavendishNice 1731 - Londres 1810
- weaker force: (e2/40) / Gm2 1040
- long range
a bit more difficult…but still a student training
- Casimir/van der Waals versus electrostatic:
hc / (e2/40) 137
fine structure constant
However unless at very short distances (< 1nm)(if static charges present …not neutral)
electrostatic >> Casimir
Casimir… short rangecharacteristic distance at the nanoscale
Nanosciences
Sphere diameter 50 msphere/surface: 10nm -1 m
origin of van der waals/casimir interaction between two neutral systems in their fundamental state:
electron-photon coupling by dipolar interaction -d.E
-d.E
-d.E
-d.E
Fundamental state
Fundamental state
Fundamental state
Fundamental state
temps
-d.E
Electronic excitations(q,)
Characteristic length for two metallic surfaces(jellium model)
defined by electronic excitations coupled to photons:
surface plasmons
characteristic length:
p= 2 c/ p
Aluminium h p= 14eV
p 100nm
Surface Surface plasmonsplasmons
metal (1<0)
Hy
ExEz
+++ --- +++ --- +++ ---
Surface Surface plasmonsplasmons
x
Hy
EEz+++ --- +++ --- +++ ---
metal (1<0)+++ --- +++ --- +++ --- metal (2<0)
d<< p
Coupling ofCoupling of
F<0 répulsif
F>0 attractif
d=10nm
Al
SiCPlasmon polariton
Phononpolariton
Plasmon polaritond<< p
Surface Surface plasmonsplasmons
metal (1<0)
Hy
ExEz
+++ --- +++ --- +++ ---
Changing coupling of plasmons with extended photon modes ???
kph
a
ksp
1
2 kx
xck
12
Zn ,2 a
nkx
21
21spk
2,...1,0,n ,2sin
c
ka
nk spph
kx
xck
/a
1
The way the plasmon-photon coupling is changed
Experiment:Force measurement at distances
close to 10nm below the plasma lengthto be sensitive to surface electronic excitations
Using a resonating oscillatorperturbed by the van der Waals/Casimir interaction.
kFdf res
2
sample
Interaction F
k,
sample
10 100 10000,1
1
10
100
1000
Freq
uenc
y sh
ift H
z
Distance (nm)
Electrostatic calibration
Dispersion forcein the non retarded régime
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<< punder vacuum and at low T (4K)
…...
hope we shall avoid such a hard collision next timehope we shall avoid such a hard collision next time
good point however: good point however: parallelparallel surfaces well prepared…. surfaces well prepared….
Very very large roughness...
Experimental objective:
Combination of sphere on cantilever or on tuning fork
+
measurement of frequency shift with resolution close to 1mHz
Mario Rodriguezstage de Master 2ESRF
Gauthier TorricelliThèse LEPES/ESRF
Guillaume JourdanThèse LEPES/Lab. Kastler BrosselDirection: J. Chevrier/ A. Lambrecht