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Unformatted text preview: M SE 2020 3/10/2011 Page 1 of 2 I n C l ass P resenta t ion: Scan n i ng T u n ne l i ng M ic roscopy
• Binnig and Rohrer came up with i t in 1981 • Resolution limi ted by curvature of scanning tip • Conducting probe (very fine) held close to sample • Quantum tunneling creates a current
o Movement of tip recorded (due to tunneling current of electrons) o Electrons tunnel through the vacuum o Tunneling current moves t ip (creates a contour map of surface) • Use in vacuum but low contamination needed • 0.1 nm lateral and 0.01 nm depth considered good • 3D profile of surface • Atomic scale images • Rastered over sample • Important for semiconductors, microelectronics, catalysis, surface chemistry • Works best with conducting materials
o Can create quantum corrals to observe quantum properties • Need to have a very f lat surface • Uses current as a probe (current leaking from surface to t ip is cause of high
f ield) • Atomically sharp probe tip • Size of gap between tip and surface controls current • Or constant current mode – maintains constant gap • Non conducting samples must be thin M SE 2020 3/10/2011 Page 2 of 2 • May be able to see shape of d orbitals, but too blunt to measure nucleus • Tip made of gold, platinum (won’t oxidize readily)
o • Noble metals needed for this Stable surface, sharp t ips, very clean surface, no vibrations
(weaknesses/necessary conditions) Rev iew of Test
See attached scans of test ...
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- Spring '09