G. Palasantzas - Physics @ IUPUI

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)
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,  ( )  C
  8.9 eV,
Resonant bonding  relevant for optical data storage:
 i ( 2p
 ( )  A /  3
/  )
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
• Or both and how much they contribute ?
  0.07 eV,  ( )  C  i ( 2p /  )
  8.9 eV,
 p2 /  |
 ( )  A / 
 10.6 for   0.07 eV
Compare to ITO :  p2 /  | ITO  17
Compare to Au :  p2 /  | Au  1600
 Crystalline PCM: free carriers
in many cases (1020/cm3)
 But have very small mean free
paths, even below 3 nm
We substracted form the
crystalline phase the Drude
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
…plethora of issues to
be resolved to make a
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 : F Cas ( z )  F el ( z )
No electrostatic force (V=0)
in certain situations typically two equilibria occur:
• a stable center around which periodic solutions exist,
• unstable saddle point
[(z)/  cas-1]Fcas(z)=0
: Bifurcation
(z)/= cas
electrostatic force absent (V=0 V)
Lo=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

similar documents