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Chien-Chang Chen (Nai-Chang Yehs group)

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IMAGE FROM AN STM Iron atoms on the surface of Cu(111) Image from an STM

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STM schematic "ScanningTunnelingMicroscop e schematic" by Michael Schmid - Michael Schmid, TU Wien; adapted from the IAP/TU Wien STM Gallery. Licensed under Creative Commons Attribution-Share Alike 2.0-at via Wikimedia Commons - http://commons.wikimedia.or g/wiki/File:ScanningTunneling Microscope_schematic.png#m ediaviewer/File:ScanningTunn elingMicroscope_schematic.pn g

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Theory of STM: tunneling effect

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Tunneling current

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VIDEO: TUNNELING EFFECT VIDEO: TUNNELING EFFECT thanks to http://www.toutestquantique.frhttp://www.toutestquantique.fr

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Tunneling current with bias

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A little more approximation

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What STM can really detect STM detect the electronic state, not the atom itself. STM detect the electronic state, not the atom itself. We can detect different electronic state or even bonding by applying different voltage We can detect different electronic state or even bonding by applying different voltage

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The operation of STM Constant current mode Constant current mode use the feedback to maintain the tip at constant density of state position. If the material is the same, this can be seen as constant distance from the sample. Thus we can get the topography image of the sample surface Constant height mode Constant height mode disable the feedback and let tip move in the constant height. The scan in this mode can be much faster, but can only be done in the flat surface to avoid the crash of the tip

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Positioning The STM tip position was controlled by several piezoelectrical component The STM tip position was controlled by several piezoelectrical component For the ease of use, it usually includes coarse positioner and fine positioner (tube scanner with tip) For the ease of use, it usually includes coarse positioner and fine positioner (tube scanner with tip)

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Conclusion STM and (AFM) make seeing atom and manipulate the atom not a dream at all. STM and (AFM) make seeing atom and manipulate the atom not a dream at all. We can control and play the single atom. Someone even draw a movie by atoms We can control and play the single atom. Someone even draw a movie by atoms STM gives us the direct and extremely localized information about electronic density of state for the materials. Even the spin can be measured by the spin- polarized STM. STM gives us the direct and extremely localized information about electronic density of state for the materials. Even the spin can be measured by the spin- polarized STM. STM is suitable to study the material with non-empty density of state, that is metal, semiconductor STM is suitable to study the material with non-empty density of state, that is metal, semiconductor With AFM, even the insulator can be studied directly With AFM, even the insulator can be studied directly