Scanning Tunneling Microscopy History General Overview The Tip Quantum Tunneling
Smith, Leo, Features Editor has reference to this Academic Journal, PHwiki organized this Journal Scanning Tunneling Microscopy By Lucas Carlson Reed College March 2004 Image from an STM Iron atoms on the surface of Cu(111) The STM is an electron microscope that uses a single atom tip to attain atomic resolution. The Scanning Tunneling Microscope (STM)
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History The scanning tunneling microscope was developed at IBM Zürich in 1981 by Gerd Binning in addition to Heinrich Rohrer who shared the Nobel Prize as long as physics in 1986 because of the microscope. Gerd Binning Heinrich Rohrer General Overview An extremely fine conducting probe is held about an atoms diameter from the sample. Electrons tunnel between the surface in addition to the tip, producing an electrical signal. While it slowly scans across the surface, the tip is raised in addition to lowered in order to keep the signal constant in addition to maintain the distance. This enables it to follow even the smallest details of the surface it is scanning. The Tip As we will see later, is very important that the tip of the probe be a single atom. Tungsten is commonly used because you can use Electro-chemical etching techniques to create very sharp tips like the one above. 150x Magnification
Quantum Tunneling Classically, when an object hits a potential that it doesnt have enough energy to pass, it will never go though that potential wall, it always bounces back. In English, if you throw a ball at a wall, it will bounce back at you. Classical Wave Function For Finite Square Well Potential Where E
How to Process a Trace The trace (1) can be interpreted as a grid which can be shown as a grayscale picture (2). 1 2 3 4 The grayscale picture can be interpreted as a contour map (3) which can then be averaged out to make smooth (4) in addition to finally colored (below). Uses of STM Measuring high precision optical components in addition to disk drive surface roughness of machined or ground surfaces is a common use as long as STM. Below is a trace of an individual turn mark on a diamond-turned aluminum substrate to be used as long as subsequent magnetic film deposition as long as a high capacity hard disc drive. 1 micron Uses of STM By measuring variations in current, voltage, tip/surface separation, in addition to their derivatives, the electronic properties of different materials can be studied. One such element studied was the bucky ball (C60). When you press down on a bucky ball by 1/10th nm, it lowers the resistance of the bucky ball by 100 times. C. Joachim J. K. Gimzewski, “An electromechanical amplifier using a single molecule, Chemical Physics Letters, Vol. 265, Nos. 3-5, page 353, February 7, 1997.
Different STM Ideas You could decide not to use piezoelectricity to keep the distance between the tip in addition to the surface equal at all times, in addition to instead use the current measurements to determine the surface of a sample. Pros: You can scan much faster Cons: The surface must not have cavities more than a few Angstroms deep (an atom or two) because of tunneling Different STM Ideas Imagine increasing the tunneling current when you are on top of an atom by lowering the tip a little. The attractive as long as ce between the tip in addition to the atom would then increase, allowing you to drag atoms around. IBM imagined this. Iron atoms were first physisorbed (stuck together using intermolecular as long as ces, aka Van Der Waals foces) on a Cu surface. The iron atoms show up as bumps below. Different STM Ideas The iron atoms were then dragged along the surface of to as long as m a circle.
Different STM Ideas Iron atoms on the surface of Cu(111) Different STM Ideas References G. Binnig in addition to H. Rohrer. “Scanning Tunneling Microscopy”, IBM J Res. Develop., 30:355, 1986. G. Binnig, H. Rohrer, Scanning Tunneling Microscopy – From Birth to Adolescence, Nobel lecture, December 8, 1986. Tit-Wah Hui, Scanning Tunneling Microscopy – A Tutorial, http://www.chembio.uoguelph.ca/educmat/chm729/STMpage/stmtutor.htm Wikipedia, Scanning Tunneling Microscope, http://en.wikipedia.org/wiki/Scanning-tunneling-microscope Nobel e-Museum, The Scanning Tunneling Microscope, http://www.nobel.se/physics/educational/microscopes/scanning/index.html Pictures from http://www.almaden.ibm.com/vis/stm/blue.html Carbon Monoxide on Platinum (111) Carbon Monoxide Man
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