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Erin E. Flater, Ph.D. |
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Research [TOP] CURRENT
RESEARCH A multi-scale approach to understanding
and prediction of friction and wear on the microscale In collaboration with Maarten
de Boer, Alex Corwin, and others at Sandia
National Labs We seek to better
understand the fundamental mechanisms of friction for the improvement of MicroElectroMechanical Systems (MEMS). We
approach this problem in several ways. (1) We have studied
the surface topography of polycrystalline silicon MEMS surfaces with a range
of surface roughening treatments. We find that the atomic force microscope
(AFM) resolves critical roughness features from nanometer to micrometer
scales. Controlled roughness of the lowest polysilicon layer is significantly
transferred to subsequent layers. We derive surface roughness parameters from
the AFM data and use a simple analytic model to estimate general contact
properties of the MEMS interfaces. We find that the roughening procedure
leads to smaller contact areas, but also higher contact pressures that may
approach yield values. This suggests that surface topographic design in MEMS
should integrate surface imaging at the nanometer scale and contact asperity
modeling in order to predict optimal surface preparations that minimize adhesion,
friction and wear. These results are also evaluated for their validity by
comparing the surface parameters from the model to those determined directly
from the AFM data. (2) Wear tests have
also been performed on MEMS devices specifically tailored for controlled
loading conditions. The Nanotractor (3) Investigations are
also underway on self-assembled monolayer-coated silicon surfaces using the
AFM. While calibrated information about the frictional response of a silicon
tip sliding on the monolayer coatings has been made possible by recent
instrument modifications and calibration procedures, more investigation needs
to be made on these specific surfaces for a better understanding of the role
of these monolayers in MEMS devices. A tribopair more closely mimicking the
interface in actual MEMS devices can be created by coating both AFM tips and
silicon flats simultaneously. Publications: E.E.Flater, A.D.Corwin, M.P.de Boer, R.W.Carpick, “In-situ
wear studies of surface micromachined interfaces subject to controlled
loading”, Wear 260, 6 (2006) p.580-593. D.S.Grierson, E.E.Flater,
R.W.Carpick, “The JKR-DMT transition as applied to Atomic Force
Microscopy measurements”, Journal of Adhesion Science and Technology
19, 3–5 (2005) p. 291–311. C.K.Bora,
E.E.Flater, M.D.Street,
J.M.Redmond, M.J.Starr, R.W.Carpick, M.E.Plesha, “Multiscale
Roughness and Modeling of MEMS Interfaces”, Tribology Letters 19, 1 (2005) p.37-48. E.D.Reedy,
Jr., M.J.Starr, R.E.Jones, E.E.Flater,
R.W.Carpick. “Contact Modeling of Sam-Coated Polysilicon
Asperities”, in 28th Annual
Meeting of The Adhesion Society. M.J.Starr, H.Sumali,
J.M.Redmond, E.E.Flater, and R.W.Carpick, “Analysis of Contact Forces
Using AFM Data of Polycrystalline Silicon Surfaces”, Proceedings: Society for
Experimental Mechanics Annual Conference, R.W.Carpick, E.E.Flater, J.R.VanLangendon, M.P.de Boer,
“Friction in MEMS: From Single to Multiple Asperity Contact”, Proceedings:
Society for Experimental Mechanics Annual Conference, PREVIOUS
RESEARCH Investigating the origins of friction
with diamond-like carbon (DLC) In collaboration with Kumar
Sridharan of the Plasma
Source Ion Implantation facility at UW-Madison Diamond-like carbon is
a unique material that exhibits very low friction. If friction can be
understood in more fundamental ways, this would significantly help those who
currently make micromachines. At the micro-scale friction becomes significant
since the surface to volume ratio of the material is quite large. This
research involves the characterization of DLC films created using plasma
source ion implantation (PSII). The tribological properties of DLC will be
studied using atomic force microscopy (AFM) using both silicon nitride and
DLC-coated AFM tips. Investigations on
how frictional properties change with humidity have shown that the while the
frictional response of a SiN tip on DLC surface increases with humidity, the
adhesion force at this interface is unchanged by the presence of water vapor.
Preliminary investigations also show that DLC coatings for AFM tips are
robust and can withstand the forces during AFM scanning. Publications: R.W.Carpick, E.E.Flater, K.Sridharan, D.F.Ogletree, M.Salmeron,
“Atomic scale friction and its connections to fracture
mechanics”, JoM 56,10 (2004) p.48-52. R.W.Carpick, E.E.Flater, K.Sridharan, “The effect
of surface chemistry and structure on nano-scale adhesion and
friction”, Polymeric Materials:
Science & Engineering 90
(2004) p.197-198. E.E.Flater, J.R.VanLangendon, E.H.Wilson, K.Sridharan.
R.W.Carpick, “Frictional and adhesive properties of Diamond-like Carbon/Silicon
Nitride Nanocontacts”, Proceedings: Society for Experimental
Mechanics Annual Conference, The mechanics of turbulent water flow
with air bubbles in tubes In describing laminar
flow of fluids through pipes, Poiseuille's law gives useful information about
how flow rate will vary depending on pressure differences, viscosity, and
pipe diameter. Since this relationship does not apply to turbulent flows,
describing and quantifying turbulent flow is a long-standing and non-trivial
problem. Understanding of turbulent flows has direct applications, such as
the engineering of the rivets on a submarine's hull to reduce drag. Moreover,
this investigation was motivated the simple beauty of physical phenomena
draws one to investigate and understand the reasons behind it. Turbulent
water flows through vertical, circular tubing were studied. Several different
patterns in the flow were observed, including a metastable helical water flow
around an air bubble. Visualization of flow patterns was accomplished through
introducing a stream of dye into the flow Factors related to turbulent
behavior in these tubes, such as pressure, tube diameter, and Reynolds
numbers for varying flow patterns, were also measured and related to
mechanics of the flow configuration. Characterizing the mechanical properties
of hydrogel components Advancements in
biomedical engineering have paved the way for the creation of microfluidic
devices: self regulated systems that work on the microscale. The major
components of these systems are hydrogels, unique cross-linked polymers that
change volume in response to particular environmental conditions, such as pH.
The forces generated by the volume change can be used to create mechanical
action. The purpose of this research was to set critical design parameters
for the optimal use of these materials in microfluidic systems. The hydrogel
samples were tested on a micromechanical testing machine highly sensitive to
both load and displacement. Links [TOP] Academic/research affiliations: ·
Department
of Engineering Physics at the University
of Wisconsin - Madison ·
Luther
College Physics Dept. ·
Sandia
National Laboratories ·
NSF Graduate Research Fellowship Higher education
resources: ·
American
Society for Engineering Education (ASEE) ·
The
Chronicle of Higher Education AFM links: ·
A Practical Guide to Scanning Probe Microscopy ·
AFM Cantilevers
- Calibration ·
LEGO SPM Physics links: Math links: |
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