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STM-TunnelingSTM-Tunneling

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STM-TunnelingSTM-Tunneling

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Why STM ? l The electronic microscopes gives volume images (penetration depth) l In STM-no use of external particles l Principle-Electrons tunneling between an atomically sharp tip and a surface (animation-program files/netscape/communicator/program/stmanimation) STM-IntroductionSTM-Introduction

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The STM combines three main concepts: l Scanning l Tunneling l Tip-point probing l Uniqueness: STM-IntroductionSTM-Introduction

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l In March 1981, Gerd Binning, H. Rohrer, Ch. Gerber and E. Weibel observed electrons tunneling in vacuum between W tip and Pt; this in combination with scanning marked the birth of STM. l The breakthrough-atomic imaging in real space l The development of STM paved the way for a new family of techniques called : scanning probe microscopy. l 1986-Nobel prize to G. Binnig and H. Rohrer. STM-HistorySTM-History

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Comparison of Characterization Techniques

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Constant height vs constant current imaging STM Instrumentation

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Constant Current Imaging (CCI)

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Si (111) Surface STM: Si(7x7)

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STM Images1. GaSb/InAs Only every-other lattice plane is exposed on the (110) surface, where only the Sb (reddish) and As (blueish) atoms can This color-enhanced 3-D rendered STM image shows the atomic-scale structure of the interfaces between GaSb and InAs in cross-section. A superlattice of alternating GaSb (12 monolayers) and InAs (14 monolayers) was grown by molecular beam epitaxy. A piece of the wafer was cleaved in vacuum to expose the (110) surface, and then the tip was positioned over the superlattice about 1 m from the edge. Due to the structure of the crystal, only every-other lattice plane is exposed on the (110) surface, where only the Sb (reddish) and As (blueish) atoms can be seen. The atoms are 4.3 apart along the rows, with a corrugation of