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Design and Construction of Tunneling Spectroscope to Study Reaction of Gas with Porous Silicon Surface

Seify, Omid | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 44676 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Iraji zad, Azam
  7. Abstract:
  8. Studying the interactions between gas molecules and surface is one of the important issues in the field of sensing. In nanometer scales, it can play a key role in fabricating novel nanosensors. Tunneling spectroscopy, on the other hand, is a powerful method for studying the local electrical properties of surface. Our purpose in this project is to design and construct a local tunneling spectroscope, which is able to probe the effects of adsorption of gas molecules on local density of state (LDOS) in sub-nanometer scales. The designed and constructed local tunneling spectroscope system includes a small chamber, which is isolated from any vibrations by means of a set of dampers. In the main part, a sharp tip is brought close to the surface, by around one nanometer, in two stages: rough approaching first, and then approaching to 1 nm above the surface by a piezoelectric. In this case, potential difference between the tip and the sample (bias) is probed in a specific voltage interval. The tunneling current will then be sent to a computer to be recorded using an amplifier and a data acquisition system. Although there was a significant noise in the system (about ±1 Volt), we tried to reduce the ratio of noise to signal as much as possible by simulating an equivalent circuit, changing its parameters, and designing different amplifiers. Finally, an amplifier with 10-8 A/V expected gain was constructed, for which results show that ratio of noise to signal has been significantly reduced.
    In the next step, the effect of gas molecules adsorption on the surface density state of a porous silicon sample and the changes in surface LDOS are measured by Veeco atomic force microscope (model: Autoprobe CP) and the constructed system. The collected results are largely in agreement with the reported results from other methods, and explain that the adsorption of acetone molecules increases empty states in conduction levels in the porous silicon surface.
    As a future work, using the constructed machine, more experiments have to be conducted with the other samples, and the results should be compared with those of the commercial instruments
  9. Keywords:
  10. Tunneling Spectroscope ; Porous Silicon ; Nanosensor ; Piezoelectric

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