Undergraduate Research Project for Microsystems and Nanotechnology Minor

1. Static Force Curve Activity in
Nanofluidic Channels
How various treatments effect the behavior of
nanofluidic devices
Jon Zickermann University of Wisconsin-Platteville

2. Agenda
 Background
 AFM basics
 Surface Topography
 Force Measurement
 Procedure
 Goals of Project
 Results
 Surface Roughness
 Force Curves
 Analysis and Discussion
 Conclusions

3. Background

4. Background
 Research a part of the Microsystems and
Nanotechnology Minor offered by UW-
Platteville
 GE4000 Research in Microsystems and
Nanotechnology
 The “capstone” for the minor
 Worked with Dr. Yan Wu
 Nanochannel samples were fabricated by
Shaurya Prakash at Ohio State
 Selected this project to do research on an
Atomic Force Microscope and interest in
micro/nanofluidics

5. Background
Project Members
 Dr. Yan Wu Dr. Yan Wu
 Ph.D., University of Illinois at Urbana-Champaign, M.S. The University
of Alabama, B.E., Tsinghua University, China
 Joined UW-Platteville staff in 2009
 Shaurya Prakash
 Assistant Professor, Mechanical & Aerospace Engineering at the Shaurya Prakash
Ohio State University
 Jon Zickermann
 B.S. Mechanical Engineering, Microsystems & Nanotechnology;
University of Wisconsin-Platteville (Expected)
 Transferred to UW-Platteville in Spring 2010 after receiving
Associate’s in Arts and Science at UW-Washington County Jon Zickermann

6. Project Goals
 Understand the operation principle of dynamic AFM imaging and static force
curve measurements
 Learn the impact of surface treatment of micro-nanofluidic channel wall on
slip flow and electrokinectic flow
 Perform surface topography measurements and surface roughness
measurements using AFM inside nanofluidic channels
 Calculate charge density distributions

7. Atomic Force Microscopy Basics

8. Surface Topography
 Atomic Force Microscopes (AFMs) can
allow imaging at the nanoscale – beyond
limits of optical imaging
 Analog to a finger feeling the surface
 Two basic modes: Contact Mode and
Tapping Mode
“In touch with atoms,” G. Binnig, and H. Rohrer,
http://www.tut.fi/en/units/departments/physics/research/computational- Reviews of Modern Physics, Vol. 71, No. 2, 1999
physics/surfaces-and-interfaces-at-the-nanoscale/research/

9. How it works
“AFM and Combined Optical Techniques” Nicholas Geisse, Asylum Research

10. Basic Contact vs. Tapping Mode
“Advanced AFM,” Dr. Yan Wu, 2011

11. Basic Contact vs. Tapping Mode
“Fiber optic atomic force microscope,” http://physics-animations.com/Physics/English/afm_txt.htm

12. Detailed Contact vs. Tapping
CONTACT MODE TAPPING MODE
 The probe (cantilever and tip) is  The probe moves with a small vertical
scanned over the surface (or the (z) oscillation (modulation) which is
significantly faster than the raster
sample is scanned under the scan rate.
probe) in an x-y raster pattern. The  This means the force on the sample is
feedback loop maintains a constant modulated such that the average force on
the sample is equal to that in contact
cantilever deflection, and mode.
consequently a substantial,  When the tip is in contact with a
constant force on the sample sample, the sample surface resists
the oscillation and the cantilever
bends
 The variation in cantilever deflection
amplitude at the frequency of
modulation is a measure of the
relative stiffness of the surface

13. Interacting Forces

14. Summary of Interacting Forces

16. Force Calculation

17. Force Calculation
 Determining spring rate from F = ks:
 Sader Method:
where:
*All equations and constants courtesy of
Asylum Research
http://www.asylumresearch.com/Applications/EquationCard.pdf

18. Equipment - iDrive
 The iDrive NbFeB magnet is fully
enclosed and sealed within the
cantilever holder which allows for
unobstructed bottom view of
samples and prevents sample
contamination. iDrive cantilever holder (left) and schematic
diagram of the cantilever which shows the
 iDrive allows auto tuning of the Lorentz Force exerted onto the cantilever (right).
cantilever in fluid.
 The cantilever tune with iDrive actuation
closely resembles the thermal tune.
 Clean cantilever tunes allow for the
implementation of Q-control and
other techniques in fluid.

19. Equipment - iDrive

20. Equipment - AFM
 Asylum Research MFP-3D-BIO AFM
 Specs:
 Most accurate and sensitive AFM available with inverted
optical microscope
 Inverted microscope allows for fluorescence microscopy
and many other types of optical investigation including
Raman, ANSOM, and most other optical microscopy
techniques (DIC, TIRF, etc.)
 90 x 90 µm maximum window (0.5 nm resolution)
 5 µm Z axis range (0.25 nm resolution)
 Fully-enclosed in an acoustic chamber and placed on top
of an active vibration-damping table
 Voltage noise <70μV in a bandwidth of 1Hz to 10kHz.

21. Equipment – Tips for Force Curve
SiNi Triangle Tip Spherical Tip
Lever Shape Triangular  0.05N/m Cantilever
Lever Thickness 0.4µm
Lever Width
Lever Length
13.4µm
100µm
 5µm SiO2 Glass
Spring constant (N/m) 0.09
Resonant freq. (kHz) 32  Au surface
Tip shape 4-sided pyramid
Tip height 3µm
Tip radius <40nm
Tip angle <35° front
<35° side
Coating 40nm Au on tip side
50nm Au on reflex side

22. Nanofludics

23. Nanofluidics Basics
 Definition: any liquid system where you have
the movement and control over liquids in or
around objects with one dimension at most
100 nm
 Dimensions can be typically 10-50nm (Mukhopadhyay
2006)
 Applies to fluids inside nanoscale channels, porous
alumina and nanoscale conduits
 “As long as a hollow structure has a dimension on the
http://www.nano.org.uk/news/914/
nanoscale and can handle fluids, it qualifies for
nanofluidics”

24. Nanofluidics Applications
 Primary applications: separation and
analysis of DNA strands
 Other uses:
 Diodes
 Field effect transistors
 Lab-on-a-chip for nanoscale
Bhushan, Wang (2010)
Critical dimensionless parameters as specified in Oosterbroek (1999)

25. Nanofluidics

26. Nanofluidic Dynamics

27. Nanofluidic Dynamics

28. Fabrication
 Top-down methods
 Photolithography methods on a substrate silicon wafer
 Can be integrated on a MEMS chip on one wafer
 Traditional top-down methods offer an economical method to nanofluidic device
fabrication
 Bottom-up methods
 Self-Assembled Monolayers can be used with biological materials to form a molecular
monolayer on the substrate
 Carbon Nanotubes offer a future option
 Bottom-up methods can precise shapes at the nanoscale

29. Nanofluidics Advantages and Disadvantages
ADVANTAGES DISADVANTAGES
 Offers the possibility to confine  Harder to fabricate
molecules to very small spaces and
 Higher tendency for channels to get
subject them to controlled forces.
clogged
 Potential for precise control of
 Lower signal quality when trying to
liquid flow and molecular behavior
send voltages
at the nanoscale
 Relatively unexplored area of
nanotechnology

30. Procedure

31. Procedure
 Surface topography of 3 samples using AC
mode
 Measured in the three segments
 Force curve analysis in air and water
 Using iDrive cantilever tips and
 Electrolyte solution creation
 Force curve analyses in electrolyte
solutions of various pH levels

32. Results

33. Results – Surface RMS
 Plain Glass
 80nm: 950pm
 250nm: 1.549nm, 1.421nm, 972pm
 450nm: 589pm, 1.113nm
 Bromine Treated
 80nm: 2.11nm, 1.103nm
 250nm: 1.549nm, 1.421nm
 450nm: 1.91nm
 Fluoride Treated
 80nm: 4.926nm Fluoride Treated Sample from AFM
 250nm: 3.912nm, 5.318nm
 450nm: 3.422nm

34. SiNi Tip
Force Curve Analysis

35. Calculated Results – Force Curves - SiNi
Calibration
 Plain Glass Sample:
 k = 83.32mN/m
 Q = 15.2
 freq = 31.267kHz
 Bromine Sample:
 k = 87.26mN/m
 Q = 15.2
 freq = 30.947kHz
 Fluorine Sample:
 k = 85.29 mN/m
 Q = 14.7
 freq = 30.733kHz

36. Calculated Results – Force Curves: SiNi Tip
In Water
 Plain Glass Sample:
Adhesion Data:
 µ = 6.30nN
 σ = 0.078nN
 Bromine Sample:
Adhesion Data:
 µ = 21.97nN
 σ = 0.405nN
 Fluorine Sample:
iDrive Cantilever Tip from Asylum Research’s website
Adhesion Data:
 µ = 1.06nN
 σ = 0.144nN

37. Calculated Results – Force Curves
PLAIN GLASS FORCE CURVE

38. Calculated Results – Force Curves
BROMINE FORCE CURVE

39. Calculated Results – Force Curves
FLORO FORCE CURVE

40. Spherical Tip
Force Curve Results

41. Calculated Results – Force Curves: Spherical
Calibration
 Plain Glass Sample:
 k = 87.34 mN/m
 Q = 25.0
 freq = 21.336kHz
 Bromine Sample:
 k = 84.82 mN/m
 Q = 25.1
 freq = 21.319kHz
 Fluorine Sample:
 k = 89.85 mN/m
 Q = 24.9
 freq = 21.568kHz

42. Calculated Results – Force Curves: Spherical
 Plain Glass Sample:
Adhesion Data:
 µ = 27.60nN
 σ = 0.024917nN
 Bromine Sample:
Adhesion Data:
 µ = 18.05nN
 σ = 0.001897nN
 Fluorine Sample:
Adhesion Data:
 µ = 15.33nN
 σ = 2.750`nN

43. Calculated Results – Force Curves
PLAIN FORCE CURVE

44. Calculated Results – Force Curves
BROMINE FORCE CURVE

45. Calculated Results – Force Curves
FLORO FORCE CURVE

46. Charge Density

47. Charge Density – Plain Glass
Charge Distribution Charge Values

48. Charge Density – Br Treated
Charge Distribution Charge Values

49. Charge Density – Fluorine Treated
Charge Distribution Charge Values

50. Charge Density – Gold Surface
Charge Distribution Charge Values

51. Analysis and Discussion
 Surface Roughness
 The untreated samples were the smoothest – around 1nm RMS – followed by the Bromine
and Fluorine samples
• Untreated nanochannels favors flow by pressure gradients
• Fluorine nanochannels favors flow by electric differentials
 Force Curves Data
 Bromine treatment produces a positive charge buildup that strongly attracts electrical charges,
whereas fluorine treatment produces a repulsive force that resisted the cantilever tip
 Stronger attraction forces from spherical tip compared to triangular tips

52. Analysis and Discussion
 The bromine treated surface reach far from the substrate surface as indicated
by the large Debye lengths
 Consistent to the force curves generated by the AFM software, where the cantilever probe
“jumped in” to the surface substrate at a faster rate than any other surface treatments
 Fluorine surface has a large concentration of charges near the surface, however, compared to
the plain and bromine treated surfaces, the charges are repelling them

53. Acknowledgements
 Dr. Yan Wu for working with me and helping me out
 Peers doing research in the cleanroom from helping me in the first
week
 You, the audience, for listening

54. Any Questions?
Thank You!