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Multimedia : Watch Introduction to AFM by Asylum Research, Inc. (Quicktime Movie) for Lectures 4-5 posted on Stellar. HIGH RESOLUTION FORCE SPECTROSCOPY (HRFS) EXPERIMENT : FORCE-DISTANCE CURVESATOMIC FORCE MICROSCOPY : GENERAL COMPONENTS AND FUNCTIONSATOMIC FORCE MICROSCOPY : DEFLECTION VS HEIGHT IMAGES -Processed data from z-piezo, less clear compared to deflection image, maximize your feedback system, can quantify the height of structural features, in 2D image corresponds to brightness1.5 m z-scale bar ATOMIC FORCE MICROSCOPY : 3D PLOTS AND 2D SECTION PROFILES ATOMIC FORCE MICROSCOPY IMAGING : NORMAL MODES OF OPERATION ATOMIC FORCE MICROSCOPY IMAGING : OTHER MODES OF OPERATION ATOMIC FORCE MICROSCOPY IMAGING : FACTORS AFFECTING RESOLUTION ATOMIC FORCE MICROSCOPY IMAGING : TIP DECONVOLUTION ATOMIC FORCE MICROSCOPY IMAGING OF CELLS ATOMIC FORCE MICROSCOPY IMAGING OF DNA3.052 Nanomechanics of Materials and Biomaterials Thursday 02/22/07 Prof. C. Ortiz, MIT-DMSE I LECTURE 5: AFM IMAGING Outline : LAST TIME : HRFS AND FORCE-DISTANCE CURVES .......................................................................... 2 ATOMIC FORCE MICROSCOPY : GENERAL COMPONENTS AND FUNCTIONS................................. 3 Deflection vs. Height Images ................................................................................................... 4 3D Plots and 2D Section Profiles ............................................................................................ 5 Normal Modes of Operation..................................................................................................... 6 Other Modes of Operation........................................................................................................ 7 Factors Affecting Resolution .................................................................................................... 8 Tip Deconvolution .................................................................................................................... 9 Imaging of Cells ..................................................................................................................... 10 Imaging of DNA...................................................................................................................... 11 HRFS COMBINED WITH AFM : SPATIALLY SPECIFIC SURFACE INTERACTIONS........................... 12 Objectives: To review the basic principles, capabilities, and current state of the art uses of the atomic force microscopy Readings: Course Reader Document 12-15. Multimedia : Watch Introduction to AFM by Asylum Research, Inc. (Quicktime Movie) for Lectures 4-5 posted on Stellar. 13.052 Nanomechanics of Materials and Biomaterials Thursday 02/22/07 Prof. C. Ortiz, MIT-DMSE HIGH RESOLUTION FORCE SPECTROSCOPY (HRFS) EXPERIMENT : FORCE-DISTANCE CURVES approachingretractingA.tip and sampleout of contactB.attractiveinteraction pulls tip down towards surfaceδ1=0δ2<0δ3<0δ4>0C.tip jumpsto surfaceD.tip and sample/ z-piezomove in unisonE.attractive force keeps tip incontact with surfaceF.tip releasesfrom surfaceG.tip and sampleout of contact(δ=cantilever deflection)D.tip and sample/ z-piezomove in unison-Normal vs. Lateral Force Microscopy Tip-Sample Separation Distance, D (nm)Force, F (nN)repulsiveregimeattractive regime0kc - Conversion of raw data; sensor output, s (Volts) vs. z-piezo displacement/deflection, δ (nm) to Force, F, versus tip-sample separation distance, D : δ=s/m m= slope in constant compliance regime =Δs/Δδ (V/nm) F=kδ D= z±δ -zeroing the baseline 23.052 Nanomechanics of Materials and Biomaterials Thursday 02/22/07 Prof. C. Ortiz, MIT-DMSE ATOMIC FORCE MICROSCOPY : GENERAL COMPONENTS AND FUNCTIONS samplesensor output, δ, Flaser diodefeedback loop• controls z-sample positionposition sensitive photodetector• measures deflection of cantilevermirrorABCDERROR = actual signal - set pointδcantileverwhich deflects as≈10°-15°• spring probe tip scans sample surfacecomputer • controls systemxyz• performs data acquisition,display, and analysispiezoelectric scannerpositions sampprobe tip• senses surface • le (x, y, z) with Åaccuracyproperties and causescantilever to deflect Advantages : 1) Unlike electron microscopes, samples do not need to be coated or stained, minimal damage, 2) Unlike electron microscopes, samples can be imaged in fluid environments (near-physiological conditions), 3) Unlike STM samples do not need to be conductive, 4) Sub-nm resolutions have been achieved on biological samples (detailed information on the molecular conformation, spatial arrangement, structural dimensions, rate dependent processes, etc.) -Piezo rasters or scans in the x-y direction across the sample surface ↓ -Cantilever deflects (δ) in response to an a topographical feature (hill or valley) ↓ Feedback loop -System continuously changes in response to an experimental output (δ= cantilever deflection which is the feedback parameter) -Computer adjusts the piezo z-displacement to keep δ constant = "setpoint" ↓ Error signal (actual signal-set point) used to produce a topographical (height) map in the z-direction of the surface 33.052 Nanomechanics of Materials and Biomaterials Thursday 02/22/07 Prof. C. Ortiz, MIT-DMSE ATOMIC FORCE MICROSCOPY : DEFLECTION VS HEIGHT IMAGES Deflection Image: -Raw data output of cantilever deflection from photodiode, very clear, the less feedback the clearer, One can identify and measure high resolution (x/y) spatial dimensions of structural features Height Image: -Processed data from z-piezo, less clear compared to deflection image, maximize your feedback system, can quantify the height of structural features, in 2D image corresponds to brightness 1.5 μm 0.00 nm z-scale bar (e.g. images are a large residual nanoindent of bone using an instrumented indenter and Berkovich diamond probe showing plastic deformation of mineralite nanogranular structure, K. Tai and C. Ortiz Nano Letters, 2006) 43.052 Nanomechanics of Materials and Biomaterials Thursday 02/22/07 Prof. C. Ortiz, MIT-DMSE ATOMIC FORCE MICROSCOPY : 3D PLOTS AND 2D SECTION PROFILES 765432107 3D Height image 1.4µm 2D Height image 6543210X[µm]Z[Å] 2D Section Profile -Select linear region of plot


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MIT 3 052 - Lecture Notes

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