纳米材料学英文教学PPT.ppt

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Co/Cu(111) H.C. Monoharan, C.P. Lutz, D.M. Eigler Nature 403 (2000) 512
• Association: the bias was raised to 500 mV for 10 s
• It is not possible to break the C-H and C-C bonds with a single electron process at this voltage, especially as their bond energies are about 2 and 3 times higher than the C-I bond.
Pried them apart into iodine and phenyl (C6H5) by injecting electrons from the STM tip (a).
Used the tip to pull the iodine away (b and c) and draw the phenyl molecules closer together (d).
MIX-AND-MATCH molecule: Atomic engineers eventually hope to create molecules from scratch, adding atoms exactly as needed to perform specific functions. This molecule, with 18 cesium and 18 iodine atoms, was built--one atom at a time--with a STM
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Atomic Scale Bond Breaking & Nanochemistry
(a e) C6H5I C6H5 + I, (f) 2C6H5 C12H10
S.-W. Hla, L. Bartels, G. Meyer, & Karl-Heinz Rieder, PRL 85(2000)2777
20. 表面纳米化学 - 局部化学反应
The application of a bias voltage between the tip of a scanning probe microscope and a semiconductor surface modifies the bandstructure locally. At a certain bias threshold the redoxpotential of an electrochemical reaction is reached and thus a local surface reaction may get possible.
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纳米科技是传统学科在纳米尺度上的交差与深入
micrometer
Solid State Physics
Device miniaturization
Length Scale
Biology
Self assembly of complex functional units
Nanoscience & Technology
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The shortest achievable distance between the centers of two phenyls is 3.9 6 Å, as determined from the STM images.
STM induced H desorption from Si(100)
Atomic Engineering
Scientific American: December 1999
A carbon nanotube has been transformed into a writing implement. Using an atomic force microscope with a nanotube tip, researchers at Stanford University removed hydrogen atoms from the top of a silicon base. The exposed silicon oxidized, leaving behind a visible tracing.
Introduction to the Nanoworld
Nanochemistry
Lecture Outline
Nanochemistry on Surfaces Surface Chemistry with the STM Atomic Scale Chemical Analysis Pathways to molecular engineering NanoChemistry in Catalysis Computing with Molecules
• Nanochemistry is the use of synthetic chemistry to make nanoscale building blocks of desired shape, size, composition and surface structure, charge and functionality with an optional target to control self-assembly of these building blocks at various scale-lengths.
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Nanochemistry on Surfaces
Demonstration of the nanostructuring capabilities
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Surface Chemistry with the STM
Adsorbed several C6H5I molecules resting on a terraced Cu (111) substrate at 20 K.
Bonding the two by adding another shot of electrons (e).
To prove that the phenyls were chemically joined, they pulled one, and the other followed (f).
“Nature’s Way”
nanometer
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Chemistry
Assembly, macromolecules
What is nanochemistry?
• Nanochemistry is the science of tools, technologies, and methodologies for chemical synthesis, analysis, and biochemical diagnostics, performed in nanolitre to femtolitre domains.
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Towards Single Molecule Engineering
• Positioning the STM tip right above the molecule at fixed height and switching the sample bias to 1.5 V for several seconds. Thereby electrons of up to 1.5 eV are injected into the molecule.
The Ultimate Ullman Reaction
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Physical Review Letters 85 (2000) 2777
Experiments
The experiments were performed with a homebuilt UHV-STM operated at 20 K using electrochemically etched W tips. The Cu(111) surface was cleaned by cycles of sputtering with Ne ions and annealing up to 800 K. The iodobenzene (Aldrich 98%) was first purified by several freeze-pump-thaw cycles with liquid nitrogen and then small amounts were dosed onto a cooled Cu(111) sample through an aperture in the radiation shield of the STM. The energy transfer from a single electron causes the breaking of the C-I bond. It is not possible to break the C-H and C-C bonds with a single electron process at this voltage
This idea is demonstrated on metaldichalcogenides (e.g. WSe2) under ambient conditions. At a tip material dependent bias threshold, the surface is etched locally. It is thought that this is a consequence of a water splitting reaction in an adsorbed water film, where nascent oxygen and hydrogen ions are formed. The oxygen modifies the surface towards soluble oxides. Thus nanostructuring can be achieved by applying potential to the tip of scanning probe microscopes. Due to the sharp threshold the bias voltage controls the modification of the surface and allows such switching between surface modification and surface mapping.