1 (c) 2008 R.W. Carpick. Do not distribute without permission and attribution On the Scientific and Technological Importance of Nanotribology R.W. Carpick U. Pennsylvania, Dept. of Mechanical Engineering and Applied Mechanics A free resource for you - please join: http://www.nanoprobenetwork.org Copyrighted material (c) 2008 R.W. Carpick. Do not distribute without permission and attribution Outline • Some Nano(tribology) 101 • Examples of applications where nanotribology is critical • Some scientific challenges, in my view Shameless plug: Recent advances in single-asperity nanotribology Szlufarska, Chandross, & Carpick J. Phys. D.: Appl. Phys. 41 (2008) Copyrighted material
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ASME Paneltalk Carpick forMikefiles.asme.org/Divisions/Tribology/17451.pdf · 2009. 2. 13. · Scale effects: Surface-to-volume Attractive forces per 1 µm2 for two perfectly smooth
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(c) 2008 R.W. Carpick. Do not distribute without permission and attribution
On the Scientific andTechnological Importanceof Nanotribology
R.W. CarpickU. Pennsylvania, Dept. of MechanicalEngineering and Applied Mechanics
A free resource for you - please join:http://www.nanoprobenetwork.orgCopyrig
hted material
(c) 2008 R.W. Carpick. Do not distribute without permission and attribution
Outline• Some Nano(tribology) 101• Examples of applications where
nanotribology is critical• Some scientific challenges, in my
(c) 2008 R.W. Carpick. Do not distribute without permission and attribution
Problem, or opportunity?
Sandia National Labs
Micro-scale (not nano!): Water insideof this micro-compression cylinder isheated by electric current andvaporizes, pushing the piston out.Capillary forces then retract the pistononce current is removed.
Evidence for van der Waals adhesion in geckosetae, Autumn et al, PNAS, 2003
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Scanning ProbeMicroscopy (SPM)
Definition: Methods for imaging or measuringnanoscale features of surfaces by scanning a sensor(probe) over a surface and measuring a particulartype of interaction
• electric current (electrons)• force• light (photons)
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The atomicforcemicroscope(AFM) sensesforce in nano-contacts atthenanoNewtonlevel
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Read this
R.P. Feynman, “There’s Plenty of Room at theBottom”
The National Nanotechnology Initiative - StrategicPlan, Dec. 2007
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Some applications wherenanotribology is critical
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Scanning probe microscopy, and SPM-basedapplications: Nanolithography, nanomanufacturing,nanomechanical data storage
PacificNanotechnology
Prof. D. Bonnell, U. Penn
5 µm IBM Zürich
MacroscopicContact
MultipleAsperities
Ff=µL
SingleAsperityFf=???
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New technologies can be enabled byunderstanding how to apply “traditional” and“nano” mechanics approaches
– Data storage
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F. Himpsel, UW-MadisonCopyrighted material
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IBM’s “Millipede” project
Vettiger, IBM Research journal (1999)
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We have already achieved several keymicro- and nano-mechanicalcapabilities
• Working MEMS devices• Computer hard disks• AFM/scanning probes
– imaging of atomic structure, manipulation of individualatoms and molecules, measurement of molecularinteractions, high-resolution mechanical propertiesmeasurements
• Nanomanipulation
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Key point
Widespread commercial/societalsuccess of nanotechnology reliescritically on scientific and technologicaladvances in nanomechanics andnanotribology
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Some scientificchallenges
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C. M. Mate, G. M. McClelland, R. Erlandsson, andS. Chiang, “Atomic-Scale Friction of a Tungsten Tip on a
Graphite Surface,” Phys. Rev. Lett. 59, 1942 (1987)
History: First observation ofatomic-scale stick-slip behavior
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Atomic-scale stick-slip motion with a well-defined friction force is frequently observed
Muscovite mica7.5 x 7.5 nm2
slip
stic
k
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Tomlinson Model
Stable equilibrium: !U dx = 0, !2U !x
2> 0 .
Metastable equilibrium: !U dx = !2U !x
2= 0
Unstable equilibrium: !U dx = 0, !2U !x
2< 0 .
U =Uelastic
+Uinterface
= 1
2k x ! x
tip( )2
+U0sin kx( )
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Energy vs. lateraldisplacement
A
B
C
dAB d
AC
dslip
displacement
V,
tota
l e
ne
rgy
lateral
http://www.nano-world.org/frictionmodule/content/Copyrighted material
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“Superlubricity”
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What is happening at the interface?
fcc
hcp
fcc
hcp
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(c) 2008 R.W. Carpick. Do not distribute without permission and attribution from MD, at 12KCopyrig
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Single asperity contact results: Friction isproportional to the true contact area;continuum mechanics ‘works’ at nm scale
0
100
200
300
400
500
-200 -100 0 100 200 300
pull-
off
Load (nN)
Friction (
nN
)
JKR fit
Platinum-coated tip, Mica sample, in UHV
contact area
shear strength
friction
Ff = τ · A
Carpick et al., J. Vac. Sci. Technol. B 14 1289 (1996)Carpick et al., Langmuir 12 3334 (1996)
τ ~ GPa, approaches ideal strengthCopyrighted material
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RIGHT: Local pressure distributions for cylinders with differentatomic scale roughness. Pressure P is plotted as a function of lateraldistance x from the cylinder axis for bent incommensurate crystal(a), bent commensurate crystal (b), amorphous cylinder (c), andstepped crystal (d). Results for two loads, N/lRE* = 0.0019 (blacktriangles) and 0.0077 (black squares), are averaged along the lengthl of the cylinder axis and over bins of width σ along x. Solid linesshow continuum predictions for the two loads, which are the samefor all panels.
but... Robbins’model
sphere radius R=100σ=30nmσ3=volume per atomCopyrig
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Geometry and stress for spherical tips with and without adhesion. The top row shows the central regions(diameter 50σ) of bent, amorphous and stepped spherical tips, from left to right. The second and third rowsshow the pressure distributions for these tips with non-adhesive and adhesive interactions, respectively. In theadhesive case, the interaction potential between surfaces is about half as strong as interactions within thesubstrate (Supplementary Information). In all cases N/E*R2 = 0.0013 and R = 100σ. The pressure is plottedover a central square region of edge 42.9σ, with a constant vertical scale. Almost 107 atoms are included inthe substrate to include subsurface deformations.Copyrig
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Nanoscale mechanics theories arerapidly emerging
• First-principles (ab-initio) techniques– Every atom is treated quantum-mechanically
• Molecular dynamics (MD)– Classical/semi-classical trajectories of atoms are
calculated
• Hybrid atomistic-continuum approaches– e.g. finite element modeling+MD
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At small scales, disciplinary boundariesdisappear. Mechanics becomes integral to all ofnanotechnology.