- Restrictions on Access:
- Open Access.
- This thesis performs theoretical calculations and designs a vibration absorber for a Scanning Tunneling Microscope(STM). Since its invention more than thirty years ago by Binnig and Rohrer, the STM has become the primary instrument to study surfaces at the atomic scale. Not only does an STM routinely achieve sub-Angstrom level resolution, making it the most powerful microscope ever built, it is also used to study local variations in the electronic state density on the sample surface . The energy resolution of the local density of states (LDOS) is smudged by the scale of thermal fluctuations in the system, and so it is a common practice to cool the STM to low temperatures (<5 K) by using cryogenic liquid Helium. Unfortunately, Helium prices have increased alarmingly in the past decade, calling for an urgent need for more economic use of this rare resource. The Hudson Group at Penn State University are building a new STM system, in which the liquid Helium kept in a dewar will be recondensed in situ by a Pulse Tube Cryocooler (PTC). The PTC recycles Helium in a closed loop, and pumps on it to produce the low temperature (~2.8K) required for the recondensing. Thus, by preventing the Helium from evaporating, the system could be significantly more economical than the conventional method of just replacing the escaped Helium. However, incorporating a PTC with an STM is a challenging task, as the pumping motion of the PTC introduces significant vibrations between the STM tip and the sample being studied.In this thesis, we design a vibration absorber that would eliminate these vibrations in the tip sample junction. We begin the analysis by developing a spring-mass-damper model of the system. Next, system identification is performed to obtain system parameters that match with experimentally measured hammer impact testing input-output data. The vibration absorber parameters are then finally optimized using MATLAB routines.
- Dissertation Note:
- B.S. Pennsylvania State University, 2017.
- Technical Details:
- The full text of the dissertation is available as an Adobe Acrobat .pdf file ; Adobe Acrobat Reader required to view the file.
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