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Static Force Curve Activity in Nanofluidic Channels How various treatments effect the behavior of nanofluidic devices
Jon Zickermann University of Wisconsin-Platteville
Agenda
Background
AFM basics
Surface Topography
Force Measurement
Procedure
Goals of Project
Results
Surface Roughness
Force Curves
Analysis and Discussion
Conclusions
Background
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
Background
Project Members
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 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
Dr. Yan Wu
Jon Zickermann
Shaurya Prakash
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
Atomic Force Microscopy Basics
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, Reviews of Modern Physics, Vol. 71, No. 2, 1999http://www.tut.fi/en/units/departments/physics/research/computational-
physics/surfaces-and-interfaces-at-the-nanoscale/research/
How it works
“AFM and Combined Optical Techniques” Nicholas Geisse, Asylum Research
Basic Contact vs. Tapping Mode
“Advanced AFM,” Dr. Yan Wu, 2011
Basic Contact vs. Tapping Mode
“Fiber optic atomic force microscope,” http://physics-animations.com/Physics/English/afm_txt.htm
Detailed Contact vs. TappingCONTACT MODE TAPPING MODE
The probe (cantilever and tip) is scanned over the surface (or the sample is scanned under the probe) in an x-y raster pattern. The feedback loop maintains a constant cantilever deflection, and consequently a substantial, constant force on the sample
The probe moves with a small vertical (z) oscillation (modulation) which is significantly faster than the raster scan rate.
This means the force on the sample is modulated such that the average force on the sample is equal to that in contact mode.
When the tip is in contact with a 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
Interacting Forces
Summary of Interacting Forces
Force Calculation
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
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 allows auto tuning of the 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.
iDrive cantilever holder (left) and schematic diagram of the cantilever which shows the
Lorentz Force exerted onto the cantilever (right).
Equipment - iDrive
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.
Lever Shape Triangular
Lever Thickness 0.4µm
Lever Width 13.4µm
Lever Length 100µm
Spring constant (N/m) 0.09
Resonant freq. (kHz) 32
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
Equipment – Tips for Force Curve
SiNi Triangle Tip Spherical Tip
0.05N/m Cantilever
5µm SiO2 Glass
Au surface
Nanofludics
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 (Mukhopadhyay2006)
Applies to fluids inside nanoscale channels, porous alumina and nanoscale conduits
“As long as a hollow structure has a dimension on the nanoscale and can handle fluids, it qualifies for nanofluidics”
http://www.nano.org.uk/news/914/
Nanofluidics Applications
Primary applications: separation and analysis of DNA strands
Other uses:
Diodes
Field effect transistors
Lab-on-a-chip for nanoscale
Critical dimensionless parameters as specified in Oosterbroek (1999)
Bhushan, Wang (2010)
Nanofluidics
Nanofluidic Dynamics
Nanofluidic Dynamics
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
Nanofluidics Advantages and Disadvantages
ADVANTAGES DISADVANTAGES
Offers the possibility to confine molecules to very small spaces and subject them to controlled forces.
Potential for precise control of liquid flow and molecular behavior at the nanoscale
Harder to fabricate
Higher tendency for channels to get clogged
Lower signal quality when trying to send voltages
Relatively unexplored area of nanotechnology
Procedure
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
Results
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
250nm: 3.912nm, 5.318nm
450nm: 3.422nm
Fluoride Treated Sample from AFM
Force Curve Analysis
SiNi Tip
Calculated Results – Force Curves - SiNi
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
Calibration
Calculated Results – Force Curves: SiNi Tip
Plain Glass Sample:
Adhesion Data:
µ = 6.30nN
σ = 0.078nN
Bromine Sample:
Adhesion Data:
µ = 21.97nN
σ = 0.405nN
Fluorine Sample:
Adhesion Data:
µ = 1.06nN
σ = 0.144nN
iDrive Cantilever Tip from Asylum Research’s website
In Water
Calculated Results – Force Curves
PLAIN GLASS FORCE CURVE
Calculated Results – Force Curves
BROMINE FORCE CURVE
Calculated Results – Force Curves
FLORO FORCE CURVE
Force Curve Results
Spherical Tip
Calculated Results – Force Curves: Spherical
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
Calibration
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
Calculated Results – Force Curves
PLAIN FORCE CURVE
Calculated Results – Force Curves
BROMINE FORCE CURVE
Calculated Results – Force Curves
FLORO FORCE CURVE
Charge Density
Charge Density – Plain GlassCharge Distribution Charge Values
Charge Density – Br TreatedCharge Distribution Charge Values
Charge Density – Fluorine TreatedCharge Distribution Charge Values
Charge Density – Gold SurfaceCharge Distribution Charge Values
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
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
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
Thank You!Any Questions?