Atomic Force Microscopy Long Phan Nanotechnology Summer Series May 15, 2013 1
World s Smallest Movie 2
Outline What is AFM? How does AFM Work? 3 Modes: Contact mode Non contact mode Tapping mode Imaging Advantages of AFM hnp://www.graphene info.com/files/graphene/images/atomic force microscope on graphene.jpg 3
History The first Atomic Force Microscope (AFM) was developed by G. Binnig, Ch. Gerber, and C. Quate in 1985 Glued a [ny shard of diamond onto one end of a [ny strip of gold foil Small hook at end of the [p pressed against sample surface hnps://en.wikipedia.org/wiki/file:atomic_force_microscope_science_museum_london.jpg hnp://img.direc[ndustry.com/images_di/photo g/atomic force microscope afm 34990 2834889.jpg 4
What Can We Look At? AFM is currently the most widely used scanning probe microscopy technique Materials inves[gated: thin and thick film coa[ngs, ceramics, composites, glasses, synthe[c and biological membranes, metals, polymers, and semiconductors hnp://butler.cc.tut.fi/~foster/images/afmman.png hnp://www.enm.bris.ac.uk/teaching/projects/2005_06/eb3990/pics/bluedna.jpg 5
Applica[ons To produce a topographical image of a surface with atomic resolu[on Determine roughness of a sample s surface Measure trenches to determine film thickness Image non conduc[ng surfaces Study the dynamic behavior of living and fixed cells hnp://phys.org/news/2012 09 world atomic microscope chemical bonds.html hnp://www.azonano.com/work/d47sb44y9c5twcr9edku_files/image005.jpg 6
AFM Essen[al Elements 1. Laser deflected off can[lever 2. Mirror reflects laser beam to photodetector 3. Photodetector dual element photodiode that measures differences in light intensity and converts to voltage 4. Amplifier 5. Register 6. Sample 7. Probe [p that scans sample made of Si 8. Can:lever moves as scanned over sample and deflects laser beam hnp://stm2.nrl.navy.mil/how afm/how afm.html#imaging%20modes hnp://www.nanoscience.com/store/pc/catalog/03_oem probe series_tn_624_detail.jpg 7
AFM Principles Leonard Jones Poten[al Separa[on distance hnp://engr.iupui.edu/bme/bbml/figures/vdwpecurve.jpg 8
AFM Principles During scan, features affect laser deflec[on off can[lever Laser detector reads deflec[on and either: Translates deflec[on into topography map Moves stage to maintain zero laser deflec[on and translates stage movement to topography. hnp://www.weizmann.ac.il/chemical_research_support/surflab/peter/afmworks/ 9
3 Modes of AFM Contact Mode High resolu[on Damage to sample Non Contact Mode Lower resolu[on No damage to sample Tapping/IntermiNent Mode Intermediate resolu[on Minimal damage to sample 10
Contact Mode Measures repulsion between [p and sample Commonly, force of [p against sample remains constant Feedback regula[on keeps can[lever deflec[on at zero Voltage required indicates height of sample Problems: Will damage soqer surfaces 11
Non Contact Mode Tip doesn t touch sample Measures Van der Waals forces between [p and sample to acquire topography data Doesn t degrade or interfere with sample bener for soq samples Problems: Can t use with samples in fluid 12
Tapping/IntermiNent Mode Tip ver[cally oscillates between contac[ng sample surface and liqing off at 50 500kHz. Oscilla[on amplitude reduced as probe nears surface Advantages: overcomes problems associated with fric[on, adhesion, electrosta[c forces hnp://cdn.intechopen.com/pdfs/30111/intech Tapping_mode_afm_imaging_for_func[onalized_surfaces.pdf 13
Genera[ng an Image Scanning Tip Raster Mo[on The [p rasters back and forth in a straight line across the sample (think old typewriter or CRT) In the typical imaging mode, the [p sample force is held constant by adjus[ng the ver[cal posi[on of the [p (feedback). A topographic image is built up by the computer by recording the ver[cal posi[on as the [p is rastered across the sample. www.nanodevices.com www.fz borstel.de/biophysik/ de/methods/afm.html 14
Effect of Tip Resolu[on Radius of [p limits the accuracy of analysis/ resolu[on Wider probe radii lead to feature inaccuracies and rounding of steps www.pacificnanotech.com hnp://jnm.snmjournals.org/content/48/7/1039/f1.large.jpg 15
Effect of Tip Resolu[on hnp://www.nilt.com/default.asp?ac[on=details&item=513 16
Imaging Materials 17
Imaging Materials Thakurdesai, M.; et. al. Vacuum 2008, 82, 639 644 hnp://ej.iop.org/images/0960 1317/22/4/045012/Full/jmm399735f1_online.jpg 18
Imaging Materials Biro, L.; Lambin, P. New J. Phys., 2013, 15, 035024. 19
Imaging Biological Samples Single stranded G4 DNA hnp://www.parkafm.com/afm_guide/true_non_contact_mode_4.php 20
Other Capabili[es Electrosta[c Force Microscopy (EFM) Dis[nguishing differences in sample composi[on (crystal orienta[on, chemical composi[on) Measuring conduc[vity (CAFM) Micro/nanoindenta[on Piezoresponse Force Microscopy (PFM) Magne[c Force Microscopy (MFM) 21
Electrosta[c Force Microscopy (EFM) Non contact mode Constant height or constant deflec[on Track changes in [p oscilla[ons due to electrosta[c force gradients between [p and sample (at large separa[on). hnp://www.nanowerk.com/nanobusiness/showroom/park_systems/downloads/electrosta[c_force_microscopy.pdf 22
23 hnp://www.nanoandmore.com/uploads/gallery/veeco Electrosta[c Force Microscopy EFM test sample 20120828090801.png
hnp://www.nanoandmore.com/uploads/gallery/veeco Electrosta[c Force Microscopy EFM test sample 20120828090801.png 24 hnp://www.sciencedaily.com/releases/2011/05/110524094507.htm
hnp://www.nanoandmore.com/uploads/gallery/veeco Electrosta[c Force Microscopy EFM test sample 20120828090801.png 25 hnp://www.sciencedaily.com/releases/2011/05/110524094507.htm
More EFM Images Carbon Nanotube Ferrite (bright) and Austenite (dark) hnp://www.asylumresearch.com/gallery/materials/materials.shtml#conduc[ve 26
AFM Phase Mapping In Tapping / IntermiNent mode, changes in material lead to changes in phase angle of [p oscilla[on hnp://www.intechopen.com/source/html/16843/media/image12.png 27
Phase Images hnp://www.surfacesciencewestern.com/research/publica[ons/ 28
Conduc[ve AFM Operates in Contact mode to map varia[on in electrical conduc[vity of sample Also able to collect current voltage (IV) spectra at specific points on sample hnp://www.azom.com/ar[cle.aspx?ar[cleid=3285 29
CAFM Images GaAs Quantum Dots DVD Recording hnp://www.asylumresearch.com/gallery/materials/materials.shtml#conduc[ve 30
Micro / Nanoindenta[on Test mechanical proper[es of materials: Hardness (max load divided by indent area) Young s Modulus (elas[city) hnp://www.engineering.unl.edu/research/bm3/graphics/nanoindenter_cube_corner_[p_01.jpg hnp://www.asylumresearch.com/gallery/materials/materials.shtml#conduc[ve 31
Load Displacement Young s Modulus 32
Piezoresponse Force Microscopy Measures the mechanical response when an electrical voltage is applied to the sample surface with a conduc[ve [p hnp://www.asylumresearch.com/applica[ons/pfmappnote/pfmappnote.shtml 33
PFM Images 34
Magne[c Force Microscopy (MFM) As the [p moves over an magne[c field gradient, it is either pulled toward or repulsed away from the sample. 35
MFM Images 36
Advantages of AFM AFM vs. STM (scanning tunneling microscope): Images both conductors and insulators AFM vs. SEM (scanning electron microscope): Greater topographic contrast AFM vs. TEM (transmission electron microscope): No expensive and [me intensive sample prep 37
Summary AFM images surface topography 3 Modes Contact IntermiNent / Tapping Non Contact Many different imaging abili[es! EFM, Phase, CAFM, Indenta[on, PFM, MFM 38