Friction and wear on the nanoscale: A new research line in Jena
Enrico Gnecco
Otto Schott Institute of Materials Research, Friedrich Schiller University Jena, Germany
Thüringer Werkstofftag 2016
Ilmenau, April 6th 2016
MfM Group at FSU Jena
Jana Hennig
www.mfm.uni-jena.de
Felix Trillitzsch
Enrico Gnecco
Introduction
• Traditional lubricants are unefficient
• Surface vs body forces:
L
Fsurface
Fvolume
L2
L3
?
1
L
• Friction: Serious issue in MEMS
NO
Our goals:
1) Understanding and
2) Controlling
friction on the nanoscale
Introduction
• Friction: A multiscale problem
by I. Szlufarska
• Single asperity  ATOMIC FORCE MICROSCOPY  Friction can be mapped down to the atomic scale:
A simple model for atomic-scale friction
• The “tip” is pulled elastically until equilibrium is broken… and a transverse jump occurs:
k
STICK
SLIP
Ludwig Prandtl
x (nm)
LATERAL FORCE
Friction force microscopy on organic crystals
• 4,4'-dibutoxy-distyrylthiophene-based
system (TDDCS):
• Image contrast compatible with terminal
methyl groups
• Resolution depends on the scan
direction
• Friction maps were acquired in water
C. Pimentel et al., J. Phys.: Condens. Matt. 28 (2016) 134002
Friction force microscopy in water
• Graphene on Cu(111):
Vacuum:
Water:
• No capillary condensation  Lateral resolution is
better in water than in air
G. Vilhena et al., ACS Nano (2016) accepted
• Alternatively: The tip can be used to push (or pull) a nano-object:
What about friction here?
Modeling AFM-based manipulation
• Influence of scan path on nanomanipulation:
?
• The trajectories are precisely related to the scan path
• Friction increases the trajectory fluctuations but not the average direction of motion
A. Rao et al., Nanotechnology 20 (2009) 115706; A. Rao et al. Phys. Rev. B 80 (2009) 193405
Manipulation of asymmetric islands
• Sb islands on MoS2 in ambient conditions
(preparation in UHV)
• The islands translate and rotate at the same time
• In this case, friction can be related to the “angular speed” of the particles:
P. Nita, S. Casado, D. Dietzel, A. Schirmeisen & E. Gnecco, Nanotechnology 24 (2013) 325302
Manipulation on wavy substrates
• Glass surfaces can be made wavy by ion beam
sputtering:
• Stick-slip of gold nanospheres along / across
the “ripples”::
E. Gnecco, P. Nita, S. Casado, C. Pimentel, K. Mougin, M. Giordano, D. Repetto, and F. Buatier,
Nanotechnology 25 (2014) 485302
Stem cells on rippled glasses
• Ripples also influence adhesion properties of stem cells:
20 µm
• Filopodia are trapped II or
to ripples  the cell cannot spread out
P. Pedraz, S. Casado, V. Rodriguez, M.C: Giordano, F. Buatier de Mongeot, A. Ayuso-Sacido, and E. Gnecco,
Nanotechnology 27 (2016) 125301
Surface ripples on the macroscale
• Sand dunes (wind  global perturbation):
• Patterns of unpaved roads, ski slopes etc
(vehicle, skier  local perturbations):
Surface rippling in AFM lithography
• Polymer surfaces are good candidates for this kind of studies:
T
E. Gnecco, E. Riedo, W. P. King, S. R. Marder & R. Szoszkiewicz, Phys. Rev. B 79 (2009) 235421
Surface rippling in AFM lithography
• A better playground: Solvent-enriched polymer surfaces
 Very ordered ripples can be produced at room temperature!
- Example: Toluene-enriched PET
High load
- Wavelength increases with load
High load
- Ripple rotate with load
- Remarkable boundary effects are seen
• Q: How to model these effects?
S. Napolitano, M. D’Acunto, P. Baschieri, E. Gnecco & P. Pingue, Nanotechnology 23 (2012) 475301
PT model applied to surface rippling
• PT model with surface profile evolving in time:
• Time evolution suggested by indentation
measurements:
2σ
NN
• Four control parameters:
- Scan velocity (v)
- Lateral spring constant (k)
- Tip width ( )
- Indentation rate (N)
Influence of contact vibrations
• On the atomic scale: Stick-slip can be suppressed by normal (or lateral) vibrations:
• It works very well at contact resonance:
No excitation
Excitation ON
A. Socoliuc et al., Science 313 (2006) 207
EG, A. Socoliuc, S. Maier, J. Gessler, Th. Glatzel, A. Baratoff & E. Meyer, Nanotechnology 20 (2009) 025501
Influence of contact vibrations
• Ripples can be also suppressed by ultrasonic vibrations at the contact resonance frequency:
Compare with atomicscale stick-slip:
TOPOGRAPHY
FRICTION
No excitation
Excitation ON
P. Pedraz, R. Wannemacher & E. Gnecco, ACS Nano 9 (2015) 8859
Conclusions
• Molecular resolution can be easily achieved in AFM lateral force maps in water
• AFM can be used to study the motion of nano-objects…
… and also the initial stages of abrasive wear on compliant surfaces (e.g. polymers)
• One can also study ways to reduce friction and wear are reduced using AFM
Acknowledgments
IMDEA Nanociencia, Madrid
Universität Giessen
Angel Ayuso
Patricia Pedraz
Pawel Nita
Santiago Casado
Reinhold Wannemacher
Andre Schirmeisen
Dirk Dietzel
Università di Genova
Francesco Buatier de Mongeot
Marina Giordano
SNS & CNR, Pisa
Simone Napolitano
Franco Dinelli
Pasqualantonio Pingue
Universität Basel
Ernst Meyer (& coworkers)