Fundamental Characterization for Nanotechnology

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Problem Sheet 5 – Assessed Problem Sheet for Module 3

(You need to answer all 5 questions. The maximum word limit is 1,500 excl. references.)

Question 1 (Diffraction)

Using the Bragg equation for X-ray diffraction, determine the angles at which the (111), (200) and (220) planes of a nickel crystal will diffract X-rays of wavelength 0.154 nm. Nickel is FCC with a = 0.352 nm (edge length of the conventional unit cell).

Question 2 (TEM)

The very latest generation of TEM instruments incorporates aberration correction. This may be within the optics of the beam incident upon the specimen, or sometimes also in the optics that forms the image. Explain the following:

1. What aspect of the conventional TEM beam(s) are being corrected?

• How is the correction being done in practice?

• What is the extent of improvement of performance (you may wish to consult the JEOL website for example) and consider the effect on point-to-point resolution?

Question 3 (EDS / WDS)

Chemical microanalysis in electron beam instruments may be carried out using both energy-dispersive and wavelength-dispersive X-ray spectrometers.

• Briefly describe the principle of operation of each of these types of spectrometer. Which types of instrument would you expect to be equipped with such spectrometers?
• What are the main problems associated with the use of energy-dispersive spectrometers for:
  • light-element analysis?
  • quantitative analysis?

Explain why these problems are reduced by the use of wavelength-dispersive spectrometers for chemical microanalysis of bulk specimens.

What other advantages do wavelength-dispersive spectrometers have? What disadvantages do they have?

Question 4 (SPM)

A multi-walled nanotube with a diameter of 5 nm is lying flat on an atomically flat substrate. The tube is being imaged in the contact mode by a tip that is terminated at the apex by a spherical section of 2.5 nm radius of curvature. Describe the resultant image, and determine the apparent width of the nanotube at half-height (that is, 2.5 nm above the substrate).

Question 5 (Spectroscopy)

Compare and contrast the following for Imaging XPS and AES/SAM: (You are addressing in particular the choice of technique for particular analytical requirements and types of specimens.)

• Elemental sensitivity
  • Surface specificity
  • Lateral resolution and information volume
  • Availability of ‘chemical’ information (information about the electronic environment of particular atoms in the specimen)
  • Analysis of insulating materials.

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