VEDA - V irtual E nvironment for Dynamic Atomic Force Microscopy VEDA - V irtual E nvironment for Dynamic Atomic Force Microscopy D ynamic A tomic Force Microscopy D ynamic A tomic Force Microscopy John Melcher, Daniel Kiracofe, doctoral students Steven Johnson, undergraduate Shuiqing Hu, Veeco Arvind Raman, Associate Professor Mechanical Engineering Mechanical Engineering Birck Nanotechnology Center
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VEDA - Virtual Environment for Dynamic Atomic Force Microscopy
VEDA - Virtual Environment for Dynamic Atomic Force MicroscopyDynamic Atomic Force MicroscopyDynamic Atomic Force Microscopy
John Melcher, Daniel Kiracofe, doctoral studentsSteven Johnson, undergraduate
Shuiqing Hu, VeecoArvind Raman, Associate Professor
Mechanical EngineeringMechanical EngineeringBirck Nanotechnology Center
OutlineOutline
Introduction to dynamic AFM
VEDA - dynamic approach curves toolVEDA dynamic approach curves tool
VEDA lit d d l t d i t lVEDA - amplitude modulated scanning tool
VEDA- multi-mode (advanced) tool
Tapping mode AFMTapping mode AFMZ approach
Ainit
AA
A ~hScanning
AA
h
QuestionsHo to choose cantile er stiffness?How to choose cantilever stiffness?How to choose operating amplitude?What are the imaging forces?What does phase contrast mean?Influence of feedback on images?How to choose imaging controls?How to choose imaging controls?Do matl prop. influence images?
VEDA- Virtual Environment for Dynamic AFM
VEDA- Virtual Environment for Dynamic AFMDynamic AFMDynamic AFM
Three tools released on www.nanohub.org1: DynamicApproach Curves , Amplitude Modulated Scanning, Multi-modemodeAccurate numerical simulationsConvenient input parametersp pMeaning of phase contrastImaging forcesProbe instabilities, stable scanning
1 J. Melcher, S. Hu and A. Raman, http://www.nanohub.org, 2007
Why VEDA?Why VEDA?VEDA is free, sponsored by the NSFp yVEDA does not require you to download and maintain software (other simulators require simulink, matlab etc.)VEDA is cyber-enabled, run off the national teragrid, needs only a web-browserVEDA is extremely accurate, very few assumptions, f FORTRAN i f iff li ifast FORTRAN recipes for stiff, nonlinear equations VEDA is supplemented by a detailed user manual, t i id /I d l i d lstreaming video/Ipod learning modules
Extremely versatile, many high end applications, simulations in liquids bi modal higher harmonics allsimulations in liquids, bi-modal, higher harmonics all possible
Interaction forces in dynamic AFMInteraction forces in dynamic AFMLong-range electrostatic and magnetic forces (upto 100 nm)Capillary forces (few nm)N G bh p y ( )Van der Waals forces (few nm) that are fundamentally quantum mechanical (electrodynamic) in nature
Nanosensors Gmbh
( y )Short-range chemical forces (fraction of nm) Elastic contact forcesElastic contact forces Electrostastic double-layer forcesSolvation forcesN ti f (Dü i (2003))Nonconservative forces (Dürig (2003)) viscoelasticity and surface hysteresisincluded in VEDA
Tip-sample gap(d)
Tip-sample interaction Force (Fts)
RepulsiveTip sample gap(d)
Attractive Blue: included in VEDA
Microcantilever model in VEDAMicrocantilever model in VEDAk
ρc , Ec , Ic , Lc
ith mode of microcantilever d(t)≈Z+x(t) kc, i
mi
Z
( )x td(t) Fts(d(t))
i
ts( ( ))
F (d) F cos(τ)Ω Drive freq
Nonlinear micromechanical oscillator model captures commonly observed
2 ts drive,ττ ,τ
c c
F (d) F cos(τ)Ω Drive freqΩ x + x +x= + ,Q k k Re sonance freq
Ω =
p ydynamic AFM physicsAccurate non-smooth, nonlinear simulations using DDASKR FORTRAN routine with root finding algorithm Probe driven near resonance and brought closer to/scanned over to sampleMulti-mode tool allows simultaneous excitation of two modes
How to access VEDA and supporting information
How to access VEDA and supporting informationinformationinformation
Register on www.nanohub.orgLook under “simulate” tab, and click on “Tools for oo u de s u ate tab, a d c c o oo s oNEMS and nanofluidics” under which the VEDA tools appear. Click on any VEDA tool and click launchAfter launching the tool, click the tab “About” to access the comprehensive User manualLearning module (live streaming slide+audio) on VEDA also available. Under the “Teach and learn” t b li k “ ” d l t “R L itab click on “more” and select “Resources:Learning modules” scroll to find the Learning module for VEDA (I-Pod version also available)VEDA (I-Pod version also available)
OutlineOutline
Introduction to dynamic AFM
VEDA - dynamic approach curves toolVEDA dynamic approach curves tool
VEDA lit d d l t d i t lVEDA - amplitude modulated scanning tool
VEDA- multi-mode (advanced) tool
Example 1Example 1While imaging a polymer sample (E*=1GPa) with aWhile imaging a polymer sample (E =1GPa) with atapping mode cantilever in air k=20 N/m, freq=250kHz,Q=200), what initial amplitude and setpoint ratio toh t k th i i f 5 N ?choose to keep the imaging forces<5 nN ?
AnswerOnly meaningful way is to remain in the attractive regime ofoscillation so say at 15nm free amplitude if the setpointoscillation, so say at 15nm free amplitude, if the setpointratio is >90%
OutlineOutline
Introduction to dynamic AFM
VEDA - dynamic approach curves toolVEDA dynamic approach curves tool
VEDA lit d d l t d i t lVEDA - amplitude modulated scanning tool
VEDA- multi-mode (advanced) tool
Example 2Example 2While imaging a Silicon sample with trench with a tappingWhile imaging a Silicon sample with trench with a tappingmode cantilever in air k=20 N/m, freq=250kHz, Q=200,Ainit=30nm, 90% setpoint), how do the proportional andi t l i ff t i i ?integral gains effect imaging error?
AnswerAnswerPrimary effect is from proportional gain, too small meansinsensitivity to topography, too large and feedback loop cany g y gbecome unstable
OutlineOutline
Introduction to dynamic AFM
VEDA - dynamic approach curves toolVEDA dynamic approach curves tool
VEDA lit d d l t d i t lVEDA - amplitude modulated scanning tool
VEDA- multi-mode (advanced) tool
Example 3Example 3How does a magnetically excited cantilever (slowHow does a magnetically excited cantilever (slowstiffness) tap on a soft biological sample (0.1 GPa) inaqueous buffer? What are the interaction forces, contactti d h d th d d lit d t i t?times, and how do they depend on amplitude stpoint?
AnswerIn liquids the two-mode model must be used to understandthe cantilever response and the peak forces and contactthe cantilever response, and the peak forces and contacttimes behave quite differently when compared to operationin air
Possible additions to VEDAPossible additions to VEDA
Capability to enter user specific interaction lawsFrequency modulated AFMLonger term- magnetic, electrostatic force microscopyCoupling with molecular dynamics simulations of tip-sample interactionsOther ideas? Please email [email protected]
How to access VEDA and supporting information
How to access VEDA and supporting informationinformationinformation
Register on www.nanohub.orgLook under “simulate” tab, and click on “Tools for oo u de s u ate tab, a d c c o oo s oNEMS and nanofluidics” under which the VEDA tools appear. Click on any VEDA tool and click launchAfter launching the tool, click the tab “About” to access the comprehensive User manualLearning module (live streaming slide+audio) on VEDA also available. Under the “Teach and learn” t b li k “ ” d l t “R L itab click on “more” and select “Resources:Learning modules” scroll to find the Learning module for VEDA (I-Pod version also available)VEDA (I-Pod version also available)
Questions?Questions?
J. Melcher, S. Hu and A. Raman, Cover feature , Rev. Sci. Inst, 2008