3.052 Nanomechanics of Materials and Biomaterials Thursday 02/15/07
Prof. C. Ortiz, MIT-DMSE
I
LECTURE 4: FORCE-DISTANCE CURVES
Outline :
LAST TIME : ADDITIONAL NANOMECHANICS INSTRUMENTATION COMPONENTS ......................... 2
PIEZOS TUBES : X/Y SCANNING ............................................................................................................ 3
GENERAL COMPONENTS OF A NANOMECHANICAL DEVICE............................................................. 4
HIGH RESOLUTION FORCE SPECTROSCOPY (HRFS) ....................................................................5-9
Force-Distance Raw Data ....................................................................................................... 5
Force-Distance Data Conversion ............................................................................................ 6
Chemical Force Microscopy (CFM).......................................................................................... 7
Macromolecular Adhesion : Cartilage Aggrecan ...................................................................... 8
Lateral Force Microscopy (LFM) .............................................................................................. 9
Objectives: To understand high resolution force spectroscopy data; i.e. how it is converted from
raw data, interpretation of different regions, and different types (i.e. normal, lateral, & chemically specific)
Readings: Course Reader Document 10-11.
Multimedia : Watch movie Introduction to AFM by Asylum Research, Inc., and the Force curve
animation from NCState.
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3.052 Nanomechanics of Materials and Biomaterials Thursday 02/15/07
Prof. C. Ortiz, MIT-DMSE
LAST TIME : ADDITIONAL NANOMECHANICS INSTRUMENTATION
COMPONENTS
High resolution displacement detection : Optical
Lever (Beam) Deflection Technique
Lateral Force V -V
A+C
B+D
Microscopy
(LFM)
VA+ B-VC+D
High resolution displacement control :
"piezoelectric materials" : material which exhibits a
change in dimensions in response to an applied
voltage due to dipole alignment
mirror
A B
C D
Normal Force
Microscopy
4-quadrant
(NFM) position sensitive
laser beam
photodiode
cantilever
ε is linearly proportional to electric field strength :
ε j = dij Εi
sample
probe tip
ΔL
= strain (m/m = unitless)
Lo
dij = strain coefficients or sensitivity (m/Volt)
εj =
D+ΔD
Ei = electric field strength (Volt/m)
d
+Z D
i = direction of applied field, j = direction of strain
1,2,3 = normal axes ; 4, 5, 6 = shear
+ Poisson's ratio
ΔL =
Lo d 31U 3
where d = wall thickness,U = operating voltage
d
~
-Z
electrodes
Lo
Lo+ΔL
voltage
applied
-X
+Y
electrodes
+X
z (1)
y (3)
x (2)
connecting
wires
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3.052 Nanomechanics of Materials and Biomaterials Thursday 02/15/07
Prof. C. Ortiz, MIT-DMSE
PIEZO TUBES X/Y SCANNING
x/y (bottom) scanner (side view) :
single axis positioner
apply
voltages to different sides of tube
side view of monolithic tube z- piezo (top)
left x-segment
right x-segment
U=0
z
outer
electrode
-
y
inner
electrode
+
ysegment
front
z
-
+
+
-
+
-
-tube contracts radially (small amount) tube expands radially tube contracts radially
-expands much more in z-direction due to
lowers height
height increases
high aspect ratio
tube tilts
- reverse voltage- scan in opposite direction
- same for y-axis positioning
-Coupling - if you tell the piezo tube to move in x-direction, it will also
move a bit in y and z, x is coupled to y and z
Figure by MIT OCW.
-Another approach : individual "piezo stacks" with flexures in a "nested design" (Introduction to AFM by
Asylum Research, Inc. (Quicktime Movie)- Pset 2
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3.052 Nanomechanics of Materials and Biomaterials Thursday 02/15/07
Prof. C. Ortiz, MIT-DMSE
GENERAL COMPONENTS OF A NANOMECHANICS DEVICE
I.
high-resolution
force transducer
III.
displacement
detection
system
δ
sample
II.
high-resolution
displacement
control
z
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3.052 Nanomechanics of Materials and Biomaterials Thursday 02/15/07
Prof. C. Ortiz, MIT-DMSE
approaching
A.
tip and sample
out of contact
B.
attractive
interaction
pulls tip down
towards surface
C.
tip jumps
to surface
D.
tip and sample
/ z-piezo
move in unison
(δ=cantilever deflection)
δ1=0
δ2<0
δ3<0
δ4>0
G.
tip and sample
out of contact
F.
tip releases
from surface
E.
attractive force
keeps tip in
contact with
surface
D.
tip and sample
/ z-piezo
move in unison
Photodiode
Sensor Output, s (V)
HIGH RESOLUTION FORCE SPECTROSCOPY EXPERIMENT (HRFS): RAW DATA
no
interaction
repulsive
regime
jump-to-contact
0
adhesion
attractive
regime
0
z-Piezo Deflection, z (nm)
- Measure sensor output (Volts) vs. z-piezo
displacement/deflection
- See animation on the MIT Server (Force curve animation
from NC State).
retracting
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3.052 Nanomechanics of Materials and Biomaterials Thursday 02/15/07
Prof. C. Ortiz, MIT-DMSE
HIGH RESOLUTION FORCE SPECTROSCOPY EXPERIMENT: CONVERTED F-D DATA
repulsive
regime
Δδ
Δz
D
kc
attractive
regime
sample
piezo
Force, F (nN)
x-axis conversion
0
D= Δz-Δδ
Tip-Sample Separation
Distance, D (nm)
Contact vs. Noncontact region
Zero x-axis position chosen (x=0) : by baseline far away from sample
Zero y-axis position chosen (D=0) : as region of apparent infinite slope (artifact of soft spring, stiff
sample)
Jump to contact region : region of mechanical instability, cantilever moving too fast to collect data, lose
all data in this region
Adhesion force : maximum force needed to separate two bodies, determined by surfaces force/
intermolecular interactions; sources; hydration capillary forces in air, noncovalent interactions, polymer
interactions, etc.
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3.052 Nanomechanics of Materials and Biomaterials Thursday 02/15/07
Prof. C. Ortiz, MIT-DMSE
CHEMICAL FORCE MICROSCOPY (CFM)
Vezenov DV, Noy A, Rosznyai LF, Lieber CM. 1997. J. Am. Chem. Soc.
www.polymercentre.org.uk
Image removed due
to copyright restrictions.
See Vezenov DV, Noy A, Rosznyai LF,
Lieber CM. 1997. J. Am. Chem. Soc.
Courtesy of The University of Sheffield Polymer Centre. Used with permission.
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3.052 Nanomechanics of Materials and Biomaterials Thursday 02/15/07
Prof. C. Ortiz, MIT-DMSE
MEASURING MACROMOLECULAR ADHESION : CARTILAGE AGGRECAN
Cartilage aggrecan is a very
unique "bottle-brush"
macromolecule that is largely
responsible for the mechanical
properties and health of
cartilage tissue in our joints.
(*podcasts later on in the
semester on this topic,
unpublished data by L. Han)
Tip Motion
H
9
Approach
Retract
7
Force (nN)
Image removed due
to copyright restrictions.
Diagram of cartilage aggrecan.
5
3
1
-1
-3
-5
0
200
400
600
Distance (nm)
800
1000
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3.052 Nanomechanics of Materials and Biomaterials Thursday 02/15/07
Prof. C. Ortiz, MIT-DMSE
LATERAL FORCE MICROSCOPY (LFM)
shear of
aggrecan
“slip”
HIGH NORMAL LOAD (F~20nN)
“stick” “slip” “stick” “slip”
Lateral Force (nN)
“stick”
12
0.001M NaCl
μΙ = 0.10±0.01
8 μII = 0.44±0.03
(II)
(I)
4
0
10
20
Normal Force (nN)
30
-Measure shear / friction coefficient→nanotribology - study of friction and wear.
-Linear dependence of lateral force on normal force between OH-SAM and aggrecan changed upon the
point of full penetration of aggrecan layer by the nanosized probe tip.
-At the same height, larger lateral forces were observed at lower IS, due to stronger shear resistance
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