G. Palasantzas, W. Broer, B. J. Kooi, J. Knoester
Zernike Institute for Advanced Materials, University of Groningen, The Netherlands
V. B. Svetovoy
MESA+ Institute for Nanotechnology, University of Twente, The Netherlands
M. Wuttig
I. Physikalisches Institut (IA) and JARA-FIT, RWTH Aachen University, Germany

60 groups
11 countries

Boesel et al., Advanced Materials 2010

If all 6.5 million setae of one gecko toes attached simultaneously  it lifts 30-40 kg
….am I a “”Drude”gecko or
.… a “plasma”….one…
Stanford researchers with the Stickybot

Geim et al., Nature Materials 2003
A photo showing a stainless steel adapter of 473 g hanging on a SiO2/Si-wafer supported vertically aligned SWCNT dry adhesive film (4mm x 4mm) http://www.nanowerk.com/spotlight/
Kwak et al, Advanced Materials 2011

Quantum engine cycle between two Casimir force states – tap energy from vacuum (F. Pinto PRB 1999)
Stiction & Levitation

Intersting idea but…..no clear force contrast !

Chen et al, Opt. Express 2007, PRB 2007

Chang et al., PRL 2011, PRB 2012

 A laser beam heats the PCM above the melting temperature & Rapid quenching  glass-like amorphous state
 heating the amorphous phase with moderate intensity laser beam: amorphous state  more stable crystalline phase
 This principle has already been successfully employed in three generations of rewriteable
(RW) optical data storage ( CD, DVD, BD )

Pandian et al.,
Adv. Materials 2007

Pandian et al.,Adv. Materials 2007

 Crystallization is accompanied by the formation of resonance bonds
 Change of bonding mechanism affects the optical properties in the visible & UV range
 So far no other materials have similar change of optical properties upon crystallization
 Crystallization generates of a large amount of free carriers affecting the IR range

The situation in which a single, half-filled p-band forms two bonds to the left and right more than allowed by the 8-N rule (N valence) was coined as resonant bonding by Pauling.
electron delocalization characterizing resonant bonding  increased electronic polarizability a fingerprint of resonance bonding

Free carriers /Drude



0 .
07 eV,

(

)

8 .
9 eV,

(

)

C

Resonant bonding
 i (
 2 p
A /
 3
/


)
 relevant for optical data storage : photon energies between

1.5 eV
(compact discs) - 3 eV (blu-ray disk) are employed

Phys. Rev. A 2010, New Scientist July 2, 2010 (interview with Eugene Reich)

Casimir force upon crystallization is due to the change of the dielectric function
• in the infrared regime (free carriers) ……?
• or in the visible-UV range (resonance bonding)….?
• Or both and how much they contribute ?

 
0 .
07 eV,

(

)

C
 i (
 2 p
/

 )
 
8 .
9 eV,

(

)

A /
 3
Extrapolation

2 p
/


|
AIST

10 .
6 for
 
0 .
07 eV
Compare to ITO :

2 p
/


|
ITO

17
Compare to Au :

2 p
/


|
Au

1600
 Crystalline PCM: free carriers in many cases (

10 20 /cm 3 )
 But have very small mean free paths, even below

3 nm

We substracted form the crystalline phase the Drude contribution…….

Two strategies to maximize the force contrast upon crystallization of phase change materials:
• employ materials with particularly strong resonant bonds (PCM with low iconicity and low hybridization of s- and p-states)
• small disorder and large carrier concentration to ensure a large Drude contribution

…plethora of issues to be resolved to make a device…..

Take roughness contributions for both Casimir and electrostatic forces……

Broer et al, EPL 2011, PRB 2012

Broer et al, EPL 2011, PRB 2012

Flat surface Pertubative term
Peak contribution

V eq Cas z

F el z

in certain situations typically two equilibria occur:
• a stable center around which periodic solutions exist,
• unstable saddle point
=0

(z)=(1-z/L o
)(F
L
(L o
)/F
Cas
(z)
[

(z)/
 cas-1]Fcas(z)=0
 (z)/=  cas
: Bifurcation parameter

L o
=100 nm Stable region

 PCMS are promissing for Casimir engines .....more research is needed to fabricate materials to have larger force contrast Two strategies to maximize force contrast of PCMs:
• employ materials with particularly strong resonant bonds (low ionicity and low s-p hybridization)
• small disorder and large carrier concentration to ensure a large
Drude contribution
 Surface roughness strongly influences actuation dynamics and proper roughening can benefit systems against stiction/pull-in instabilities (see poster W. Broer) .... ............take into account hydrodynamic forces for rough surfaces... Work in progress