Design and Construction of Low-Temperature Scanning Tunnelling Microscope for Spectroscopy

University dissertation from Joakim Lindahl, Örnvägen 78:123, S-22731 Lund, Sweden

Abstract: This thesis discusses some of the fundamental requirements needed to be fulfilled when constructing a low temperature scanning tunnelling microscope (STM). Three different designs, two non-vacuum and one ultra-high vacuum (UHV), based on either inertial-mass or novel stepper motor principles are presented. The selection rules that forms the basis for designs are discussed in terms of thermophysical properties (such as thermal expansion and conductivity) and mechanical properties (such as stiffness and structural damping), and are exemplified by experimental results both known from literature and as found during the thesis work. Furthermore, the application of STM as a local probe for investigation of optical properties of low-dimensional III-V semiconductors at low-temperatures is discussed. Photon emission as a result from local injection of carriers using an STM tip, scanning tunnelling luminescence (STL), has been studied for three different low-dimensional systems: quantum wells (QW), quantum wires (QWR), and quantum dots (QD). It is demonstrated that it is possible to excite an individual low-dimensional structure, using the spatial resolution of the STM. Employed tips have been made of both wide bandgap semiconductors and metalls.

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