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  1. Atomic force microscope
  2. Atomic nanoscope
  3. Atom probe
  4. Ballistic conduction
  5. Bingel reaction
  6. Biomimetic
  7. Bio-nano generator
  8. Bionanotechnology
  9. Break junction
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  12. Cantilever
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  15. CeNTech
  16. Chemical Compound Microarray
  17. Cluster
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  20. Computronium
  21. Coulomb blockade
  22. Diamondoids
  23. Dielectrophoresis
  24. Dip Pen Nanolithography
  25. DNA machine
  26. Ecophagy
  27. Electrochemical scanning tunneling microscope
  28. Electron beam lithography
  29. Electrospinning
  30. Engines of Creation
  31. Exponential assembly
  32. Femtotechnology
  33. Fermi point
  34. Fluctuation dissipation theorem
  35. Fluorescence interference contrast microscopy
  36. Fullerene
  37. Fungimol
  38. Gas cluster ion beam
  39. Grey goo
  40. Hacking Matter
  41. History of nanotechnology
  42. Hydrogen microsensor
  43. Inorganic nanotube
  44. Ion-beam sculpting
  45. Kelvin probe force microscope
  46. Lab-on-a-chip
  47. Langmuir-Blodgett film
  48. LifeChips
  49. List of nanoengineering topics
  50. List of nanotechnology applications
  51. List of nanotechnology topics
  52. Lotus effect
  53. Magnetic force microscope
  54. Magnetic resonance force microscopy
  55. Mechanochemistry
  56. Mechanosynthesis
  57. MEMS thermal actuator
  58. Mesotechnology
  59. Micro Contact Printing
  60. Microelectromechanical systems
  61. Microfluidics
  62. Micromachinery
  63. Molecular assembler
  64. Molecular engineering
  65. Molecular logic gate
  66. Molecular manufacturing
  67. Molecular motors
  68. Molecular recognition
  69. Molecule
  70. Nano-abacus
  71. Nanoart
  72. Nanobiotechnology
  73. Nanocar
  74. Nanochemistry
  75. Nanocomputer
  76. Nanocrystal
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  78. Nanocrystal solar cell
  79. Nanoelectrochemistry
  80. Nanoelectrode
  81. Nanoelectromechanical systems
  82. Nanoelectronics
  83. Nano-emissive display
  84. Nanoengineering
  85. Nanoethics
  86. Nanofactory
  87. Nanoimprint lithography
  88. Nanoionics
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  90. Nanomanufacturing
  91. Nanomaterial based catalyst
  92. Nanomedicine
  93. Nanomorph
  94. Nanomotor
  95. Nano-optics
  96. Nanoparticle
  97. Nanoparticle tracking analysis
  98. Nanophotonics
  99. Nanopore
  100. Nanoprobe
  101. Nanoring
  102. Nanorobot
  103. Nanorod
  104. Nanoscale
  105. Nano-Science Center
  106. Nanosensor
  107. Nanoshell
  108. Nanosight
  109. Nanosocialism
  110. Nanostructure
  111. Nanotechnology
  112. Nanotechnology education
  113. Nanotechnology in fiction
  114. Nanotoxicity
  115. Nanotube
  116. Nanovid microscopy
  117. Nanowire
  118. National Nanotechnology Initiative
  119. Neowater
  120. Niemeyer-Dolan technique
  121. Ormosil
  122. Photolithography
  123. Picotechnology
  124. Programmable matter
  125. Quantum dot
  126. Quantum heterostructure
  127. Quantum point contact
  128. Quantum solvent
  129. Quantum well
  130. Quantum wire
  131. Richard Feynman
  132. Royal Society's nanotech report
  133. Scanning gate microscopy
  134. Scanning probe lithography
  135. Scanning probe microscopy
  136. Scanning tunneling microscope
  137. Scanning voltage microscopy
  138. Self-assembled monolayer
  139. Self-assembly
  140. Self reconfigurable
  141. Self-Reconfiguring Modular Robotics
  142. Self-replication
  143. Smart dust
  144. Smart material
  145. Soft lithography
  146. Spent nuclear fuel
  147. Spin polarized scanning tunneling microscopy
  148. Stone Wales defect
  149. Supramolecular assembly
  150. Supramolecular chemistry
  151. Supramolecular electronics
  152. Surface micromachining
  153. Surface plasmon resonance
  154. Synthetic molecular motors
  155. Synthetic setae
  156. Tapping AFM
  157. There's Plenty of Room at the Bottom
  158. Transfersome
  159. Utility fog

 



NANOTECHNOLOGY
This article is from:
http://en.wikipedia.org/wiki/Scanning_tunneling_microscope

All text is available under the terms of the GNU Free Documentation License: http://en.wikipedia.org/wiki/Wikipedia:Text_of_the_GNU_Free_Documentation_License 

Scanning tunneling microscope

From Wikipedia, the free encyclopedia

 
Image of substitutional Cr impurities (small bumps) in the Fe(001) surface.
Image of substitutional Cr impurities (small bumps) in the Fe(001) surface.

The scanning tunneling microscope (STM) is a non-optical microscope that scans an electrical probe over a surface to be imaged to detect a weak electric current flowing between the tip and the surface. The STM (not to be confused with the scanning electron microscope) was invented in 1981 by Gerd Binnig and Heinrich Rohrer of IBM's Zurich Lab in Zurich, Switzerland. Although initially greeted with some scepticism by materials scientists, the invention garnered the two a Nobel Prize in Physics (1986). The STM allows scientists to visualize regions of high electron density and hence infer the position of individual atoms and molecules on the surface of a lattice. Previous methods required arduous study of diffraction patterns and required interpretation to obtain spatial lattice structures. The STM is capable of higher resolution than its somewhat newer cousin, the atomic force microscope (AFM). Both the STM and the AFM fall under the class of scanning probe microscopes.

The STM can obtain images of conductive surfaces at an atomic scale 2 10−10 m or 0.2 nanometer, and also can be used to manipulate individual atoms, trigger chemical reactions, or reversibly produce ions by removing or adding individual electrons from atoms or molecules.

The acronym STM can mean either scanning tunneling microscope or scanning tunneling microscopy. This microscope has an extremely sharp stylus that scans the surface. The stylus is so sharp that its tip consists only of one atom. Strictly, as the tunnelling current is such a short ranged phenomenon (which is what gives STM its impressive resolution), tunnelling normally only occurs through the furthest extremity of the stylus - which might itself appear to be rather blunt on a larger scale.

Overview

Schematic view of an STM
Schematic view of an STM

The STM is a non-optical microscope which employs principles of quantum mechanics. An atomically sharp probe (the tip) is moved over the surface of the material under study, and a voltage is applied between probe and the surface. Depending on the voltage electrons will "tunnel" (this is a quantum-mechanical effect) or jump from the tip to the surface (or vice-versa depending on the polarity), resulting in a weak electric current. The size of this current is exponentially dependent on the distance between probe and the surface. For a current to occur the substance being scanned must be conductive (or semiconductive). Insulators cannot be scanned through the STM, as the electron has no available energy state to tunnel into or out of due to the band gap structure in insulators.

A servo loop (feedback loop) keeps the tunneling current constant by adjusting the distance between the tip and the surface (constant current mode). This adjustment is done by placing a voltage on the electrodes of a piezoelectric element. By scanning the tip over the surface and measuring the height (which is directly related to the voltage applied to the piezo element), one can thus reconstruct the surface structure of the material under study. High-quality STMs can reach sufficient resolution to show single atoms. The STM will get within a few nanometers of what it is observing. The scanning tunneling microscope (STM) is widely used in both industrial and fundamental research to obtain atomic-scale images of metal surfaces. It provides a three-dimensional profile of the surface which is very useful for characterizing surface roughness, observing surface defects, and determining the size and conformation of molecules and aggregates on the surface. Examples of advanced research using the STM are provided by current studies in the Electron Physics Group at NIST and at the IBM Laboratories. Several other recently developed scanning microscopies also use the scanning technology developed for the STM.

The electron cloud associated with metal atoms at a surface extends a very small distance above the surface. When a very sharp tip--in practice, a needle which has been treated chemically or mechanically so that a single atom projects from its end--is brought sufficiently close to such a surface, there is a strong interaction between the electron cloud on the surface and that of the tip atom, and an electric tunneling current flows when a small voltage is applied. At a separation of a few atomic diameters, the tunneling current rapidly increases as the distance between the tip and the surface decreases. This rapid change of tunneling current with distance results in atomic resolution if the tip is scanned over the surface to produce an image.

Russell D. Young, of the National Bureau of Standards (now NIST), was the first person to combine the detection of this tunneling current with a scanning device in order to obtain information about the nature of metal surfaces. The instrument which he developed between 1965 and 1971, the Topografiner, altered the separation between the tip and the surface (z) so that, at constant voltage, the tunneling current (or, at constant current, the tunneling voltage) remained constant as the tip was scanned over the surface. The x, y, and z coordinates of the tip were recorded. (For details of the design and operation of the Topografiner, see the references given in the Bibliography.) The same principle was later used in the scanning tunneling microscope. The remaining barrier to the development of that instrument was the need for more adequate vibration isolation, in order to permit stable positioning of the tip above the surface. This difficult problem in mechanical design was surmounted through the work of Gerd Binnig and Heinrich Rohrer, IBM Research Laboratory, Zurich, Switzerland, who in 1986 shared in the Nobel Prize in Physics for their discovery of atomic resolution in scanning tunneling microscopy. In their announcement of the award, the Royal Swedish Academy of Sciences recognized the pioneering studies of Russell Young.

See also

Wikibooks
Wikibooks has more about this subject:
The Opensource Handbook of Nanoscience and Nanotechnology
  • Microscopy
  • Scanning probe microscopy
  • Scanning tunneling spectroscopy
  • Electrochemical scanning tunneling microscope
  • Atomic force microscope
  • Electron microscope
  • Spin polarized scanning tunneling microscopy

External links

  • SPM - Scanning Probe Microscopy Website
  • STM Image Gallery at IBM Almaden Research Center
  • STM Gallery at Vienna University of technology
  • Teen-ager develops microchip printing technique in bedroom 17 year old built an STM for $50 out of legos, plasticine, gold jewelry, and bungee cords, computer interface controlled in QBasic, patented as new photolithography method (U.S. Patent 5,865,978 )
  • Build a simple STM with a cost of materials less than $100.00 excluding oscilloscope

Retrieved from "http://en.wikipedia.org/wiki/Scanning_tunneling_microscope"