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Atomic Manipulation & Single-Molecule Studies: Energy, STM, Quantum Dots & Transport, Slides of Computational Physics

Aligarh Muslim UniversityComputational Physics

Various aspects of atomic manipulation and single-molecule studies, including the use of scanning tunneling microscopy (stm), potential energy, quantum dots, self-assembly, and coherent transport. Topics covered include atomic manipulation with stm, single-molecule vibrations, scanning force microscopy (sfm), self-assembly, quantum corals, coulomb blockade, and conductance quantization.

Typology: Slides

2011/2012

Uploaded on 08/12/2012

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laniban 🇮🇳

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Simulations and Surfaces
More on numerical simulation techniques:
•Extracting information from Monte Carlo calculations (e.g. energy, heat capacity, free
energy)
•Comparison of molecular dynamics and Monte Carlo methods
•Interatomic interactions beyond the pair potential
Structure of (crystalline, clean) surfaces:
•Two-dimensional crystallography
•Low Energy Electron Diffraction (LEED)
• The silicon (001) surface as an example of a surface reconstruction driven by local
bonding changes
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Download Atomic Manipulation & Single-Molecule Studies: Energy, STM, Quantum Dots & Transport and more Slides Computational Physics in PDF only on Docsity!

Simulations and Surfaces

More on numerical simulation techniques:

  • Extracting information from Monte Carlo calculations (e.g. energy, heat capacity, free energy)
  • Comparison of molecular dynamics and Monte Carlo methods
  • Interatomic interactions beyond the pair potential

Structure of (crystalline, clean) surfaces:

  • Two-dimensional crystallography
  • Low Energy Electron Diffraction (LEED)
  • The silicon (001) surface as an example of a surface reconstruction driven by local bonding changes

Nanotechnology

  • A survey of possibilities for nanotechnology
  • Ways of making and characterising nano-scale structures
    • Lithography (conventional, electron-beam, ‘soft’)
    • Scanning probe microscopy
    • Self-assembly and directed assembly
  • Some electronic properties of nanoscale systems
    • Coulomb blockade
    • Conductance quantization

What is Nanotechnology?

  • A set of tools and ideas for the manipulation and

control of matter in the size range between 0.1nm

and 1m

  • Corresponds to the range of sizes between current

electronics and atomic/molecular dimensions

Possible applications in electronics

  • Current CMOS electronic technology may be approaching fundamental limits in hardware performance and cost
  • New types of electronic components (e.g. wires, transistors) operating at smaller length scales
  • Completely new ways of manipulating information (e.g. using re-orientable magnetisation of small magnetic particles)
  • New ways of coupling light to electronic processes (e.g. using patterns on the scale of the optical wavelength)

Richard Feynman’s 1959 Lecture

  • Richard Feynman at the 1959 annual meeting of the American Physical Society:

Another thing we will notice is that, if we go down far enough, all of our devices can be mass produced so that they are absolutely perfect copies of one another. We cannot build two large machines so that the dimensions are exactly the same. But if your machine is only 100 atoms high, you only have to get it correct to one-half of one percent to make sure the other machine is exactly the same size---namely, 100 atoms high!

Methods for producing structure on the nanoscale

  • How do we pattern matter on the nanometer length-

scale?

  • Using layer-by-layer growth
  • By interaction with a ‘beam’ of light or particles
  • By interaction with a scanning probe tip
  • By using contact with a ‘stamp’ or ‘mask’
  • By exploiting molecules’ natural tendency to order as a result of their mutual interactions

Electron beam lithography

  • Just as have higher spatial resolution in imaging with shorter- wavelength electron microscopes, have higher resolution in patterning too
  • Sensitive to electrons because can induce free radical formation (promoting resist removal) or cross-linking (preventing resist removal)

Electron beam lithography

  • Possible to produce feature sizes down to about 5nm using this technique
  • Figure shows 5nm metallic line on silicon surface (Welland et al. , Cambridge)

Soft lithography - nanoimprint lithography

  • Get a variety of structures e.g. holes and pillars

Soft lithography - lithographically induced self-assembly (LISA)

  • Apply a large electric field between a mask and a polymer film
  • Polymer film spontaneously grows up towards mask:
  • Pillars form when mask-polymer separation between 200nm and 800nm
  • Works because polymer attracted to high-field region

Mask

Polymer film

The scanning probe idea

  • Get very high spatial resolution by
    • Scattering very short-wavelength waves and detecting them a long way away (e.g. electron microscopy, neutron or X-ray diffraction)

Sample

The scanning probe idea

  • Get very high spatial resolution by
    • Scattering very short-wavelength waves and detcecting them a long way away (e.g. electron microscopy, neutron or X-ray diffraction)
    • Bringing a small detector up to the sample

Sample

The scanning probe idea

  • Get very high spatial resolution by
    • Scattering very short-wavelength waves and detcecting them a long way away (e.g. electron microscopy, neutron or X-ray diffraction)
    • Bringing a small detector up to the sample and arranging for a very localised interaction between them

Sample

Scan detector

across sample

The STM

(Scanning Tunnelling Microscope)

  • Electrons tunnel across small (few Å) vacuum gap between tip and sample.
  • Relies on sensitivity of tunnelling to tip-surface distance (hence localised interaction).
  • Normal mode of operation is ‘constant-current’: feedback loop keeps current constant as tip is scanned across surface.