g. palasantzas, w. broer, b. j. kooi, j. knoester zernike institute for advanced materials,...
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G. Palasantzas, W. Broer, B. J. Kooi, J. KnoesterZernike Institute for Advanced Materials, University of Groningen, The Netherlands
V. B. SvetovoyMESA+ Institute for Nanotechnology, University of Twente, The Netherlands
M. WuttigI. Physikalisches Institut (IA) and JARA-FIT, RWTH Aachen University, Germany
PASI Frontiers of Casimir Physics 2012, Ushuaia, Argentina
Casimir force control between real materials
for MEMS applications
Stanford researchers with the Stickybot
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…
Nature inspires…humans copy …!
…..glue .with .vdW . forces …..!
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/
Geim et al., Nature Materials 2003
Kwak et al, Advanced Materials 2011
Device / engines concepts……..
Stiction & Levitation
Quantum engine cycle between two Casimir force states – tap energy from vacuum (F. Pinto PRB 1999)
Engines
MEM Switches
Studies aimed to tame the Casimir force …with optical properties manipulation……
• Switchable mirrors (2003)• Si –carrier enhancement (2007)• PCM systems (2010--)• ITO / UV-ITO (2011---)
Quantum Engines
Control Optical properties: Phase change materials (PCM): Amorphous crystalline phase transitions / 2010-now…….
…more than a “billion switches per year”….
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)
Phase change materials Amorphous (A) crystalline (C) phase transitions
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
PCM candidates
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
Resonant bondingFree carriers /Drude relevant for optical data storage: photon energies between 1.5 eV (compact discs) - 3 eV (blu-ray disk) are employed /)( eV, 9.8
)/()( eV, 07.0
3
2
A
iC p
Phys. Rev. A 2010, New Scientist July 2, 2010 (interview with Eugene Reich)
Force measurement in UHV (Dynamic AFM)
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 ?
/)( eV, 9.8
)/()( eV, 07.0
3
2
A
iC p
Extrapolation
1600 |/ :Au toCompare
17 |/ :ITO toCompare
eV 07.0for 6.10|/
ITO
2
2
2
Au
AIST
p
p
p
Crystalline PCM: free carriers in many cases (1020/cm3)
But have very small mean free paths, even below 3 nm
How to achieve high force contrast in PCM ?
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
No electrostatic force (V=0)
: Bifurcation parameter
in certain situations typically two equilibria occur: • a stable center around which periodic solutions exist,• unstable saddle point
=0
(z)=(1-z/Lo)(FL(Lo)/FCas(z)
[(z)/ cas-1]Fcas(z)=0(z)/= cas
…..Conclusions……
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
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
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