Static force curve activity in nanofluidic channels


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Undergraduate Research Project for Microsystems and Nanotechnology Minor

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  • Image shown: Nanopump
  • AFM works by bringing an atomically sharp tip close to a surface. There is an attractive force between the tip and the surface and this force is kept the same throughout the experiment. As the probe tip scans back and forth over the surface, the tip will rise and fall with the different features on the surface. A laser is pointed at the tip and is reflected to a sensor. As the tip goes up and down the laser hits different parts of the sensor. With the information the sensor collects, an image of the surface can be recreated.
  • InVOLS= Inverse Optical Lever Sensitivity
  • Critical dimensions:
  • Static force curve activity in nanofluidic channels

    1. 1. Static Force Curve Activity in Nanofluidic Channels How various treatments effect the behavior of nanofluidic devicesJon Zickermann University of Wisconsin-Platteville
    2. 2. Agenda Background AFM basics  Surface Topography  Force Measurement Procedure Goals of Project Results  Surface Roughness  Force Curves Analysis and Discussion Conclusions
    3. 3. Background
    4. 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. 5. BackgroundProject 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. 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. 7. Atomic Force Microscopy Basics
    8. 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, Reviews of Modern Physics, Vol. 71, No. 2, 1999physics/surfaces-and-interfaces-at-the-nanoscale/research/
    9. 9. How it works “AFM and Combined Optical Techniques” Nicholas Geisse, Asylum Research
    10. 10. Basic Contact vs. Tapping Mode “Advanced AFM,” Dr. Yan Wu, 2011
    11. 11. Basic Contact vs. Tapping Mode “Fiber optic atomic force microscope,”
    12. 12. Detailed Contact vs. TappingCONTACT 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. 13. Interacting Forces
    14. 14. Summary of Interacting Forces
    15. 15. Force Calculation
    16. 16. Force Calculation Determining spring rate from F = ks:  Sader Method:where: *All equations and constants courtesy of Asylum Research
    17. 17. 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.
    18. 18. Equipment - iDrive
    19. 19. 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.
    20. 20. Equipment – Tips for Force CurveSiNi 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
    21. 21. Nanofludics
    22. 22. 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 nanoscale and can handle fluids, it qualifies for nanofluidics”
    23. 23. 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)
    24. 24. Nanofluidics
    25. 25. Nanofluidic Dynamics
    26. 26. Nanofluidic Dynamics
    27. 27. 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
    28. 28. Nanofluidics Advantages and DisadvantagesADVANTAGES 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
    29. 29. Procedure
    30. 30. 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
    31. 31. Results
    32. 32. 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
    33. 33. SiNi TipForce Curve Analysis
    34. 34. 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
    35. 35. 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
    36. 36. Calculated Results – Force Curves PLAIN GLASS FORCE CURVE
    37. 37. Calculated Results – Force Curves BROMINE FORCE CURVE
    38. 38. Calculated Results – Force Curves FLORO FORCE CURVE
    39. 39. Spherical TipForce Curve Results
    40. 40. 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
    41. 41. 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
    42. 42. Calculated Results – Force Curves PLAIN FORCE CURVE
    43. 43. Calculated Results – Force Curves BROMINE FORCE CURVE
    44. 44. Calculated Results – Force Curves FLORO FORCE CURVE
    45. 45. Charge Density
    46. 46. Charge Density – Plain Glass Charge Distribution Charge Values
    47. 47. Charge Density – Br Treated Charge Distribution Charge Values
    48. 48. Charge Density – Fluorine Treated Charge Distribution Charge Values
    49. 49. Charge Density – Gold Surface Charge Distribution Charge Values
    50. 50. 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
    51. 51. 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
    52. 52. 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
    53. 53. Any Questions?Thank You!