STM / AFMImages Explanations from www.iap.tuwien.ac.at/www/surface/STM_Gallery/stm_schematic.html www.almaden.ibm.com/vis/stm/lobby.html www.nanoscience.com/education/STM.html
Scanning Tunneling Microscopy • In 1981, the Scanning Tunneling microscope was developed by Gerd Binnig and Heinrich Rohrer – IBM Zurich Research Laboratories in Switzerland (Nobel prize in physics in 1986). • This instrument works by scanning a very sharp metal wire tip over a sample very close to the surface. By applying an electric current to the tip or sample, we can image the surface at an extremely small scale – down to resolving individual atoms.
Tunneling Quantum mechanics tells us that electrons have both wave and particle like properties. Tunneling is an effect of the wavelike nature. The top image shows us that when an electron (the wave) hits a barrier, the wave doesn't abruptly end, but tapers off very quickly. For a thick barrier, the wave doesn't get past. The bottom image shows the scenario if the barrier is quite thin (about a nanometer). Part of the wave does get through, and therefore some electrons may appear on the other side of the barrier.
The number of electrons that will actually tunnel is very dependent upon the thickness of the barrier. The actual current through the barrier drops off exponentially with the barrier thickness. • To extend this description to the STM: The barrier is the gap (air, vacuum, liquid) between the sample and the tip. By monitoring the current through the gap, we have very good control of the tip-sample distance.
Computer software is used to add color and analyze the captured data.
SCAN IMAGEDEMONSTRATE ANALYSISUse images from Science Express laptop. Actual Demonstration...
Purdue UniversityPhysics Department http://www.physics.purdue.edu/nanophys/stm.html Visit Purdue and other image alleries online !
Atomic Force Microscopy • In principle, the AFM works like the stylus on an old record player. • There is actual contact between the probe tip and the sample. The following explanation taken from www.chembio.uoguelph.ca/educmat/chm729/afm/general.htm
Atomic Force Microscopy 1. Laser 2. Mirror 3. Photodetector 4. Amplifier 5. Register 6. Sample 7. Probe 8. Cantilever
Atomic Force Microscopy www.wikipedia.com
AFM IMAGES http://jpk.com/spm/gallery1.htm JPK INSTRUMENTS GERMANY
DIC (Differential Interference Contrast) image of human lymphocyte metaphase chromosomes on microscopy slidedimensions 83 µm * 83 µm
height image (left, 3D plot) and corresponding optical microscope image (above, bright field) of a moth wing scaleintermittent contact mode scan field 10 µm * 10 µmz-range 0 - 1.7 µm
Height image (left, 3D plot) and corresponding optical microscope image (above, phase contrast) of a moth's eye - region of three adjacent facets. intermittent contact mode scan field 10 µm * 10 µmz-range 0 - 6.0 µm
Atomic force microscope topographical scan of a glass surface. The micro and nano-scale features of the glass can be observed, portraying the roughness of the material. Constructed at the Nanorobotics Laboratory at Carnegie Mellon University (http://nanolab.me.cmu.edu).
…science has helped us see in fine detail… What does the future hold?