Double point contact single molecule absorption spectroscopy
Howard, John Brooks
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The generation of high-frequency current oscillations when a constant voltage is applied across an insulating tunnel gap separating two superconductors was one of the fundamental theoretical predictions made by Brian Josephson, which earned him a share of the 1973 Nobel Prize in physics. Our primary objective is to utilize superconducting transport through microscopic objects to both excite and analyze the vibrational degrees of freedom of various molecules of a biological nature. The technique stems from a Josephson junction's ability to generate radiation that falls in the terahertz gap ( 10THz) and consequently can be used to excite vibrational modes of simple and complex molecules. Analysis of the change in IV characteristics coupled with the differential conductance ( ) allows determination of both the absorption spectra and the vibrational modes of biological molecules. Presented here are both the theoretical foundations of superconductivity relevant to our experimental technique and the fabrication process of our samples. Comparisons between our technique and that of other absorption spectroscopy techniques are included as a means of providing a reference upon which to judge the merits of our novel procedure. This technique is meant to improve not only our understanding of the vibrational degrees of freedom of useful biological molecules, but also these molecule's structural, electronic and mechanical properties.