| Summary: | 碩士 === 國立臺灣大學 === 化學研究所 === 103 === Forming stable MMM (Metal-Molecule-Metal) junctions is a fundamental method for studying electric properties of a tailored single molecule. Low successful rates (< 10%) of fabricating three-electrode single-molecular transistor (SMT) by electromigration provokes us to propose a new molecular electronic platform: Synthesize “m-SWNT−Molecule−m-SWNT” (metallic single-walled carbon nanotube) configurations first, and then deposit metal film electrodes by FIBD or FEBID (focused ion/electron beam-induced deposition). So far, Pt−m-SWNT−Pt devices have been fabricated and measured. Unexpected results are attributed to deposition mechanism of FIBD or FEBID. FIBD Part: Electrodes deposited by FIBD are always surrounded by “halo” structure. While the distance of two electrodes is less than 500 nm, leakage current arising from overlap of nearby platinum halo of two electrodes would be measured. Temperature-variable I−V result shows that conductance of Pt−m-SWNT−Pt device decreases with temperature, which is not consistent with m-SWNT characteristic. Besides, IETS (inelastic electron tunneling spectroscopy) peaks corresponding to vibrational modes of m-SWNT such as radial breathing mode (100~350 cm‒1) and carbon-carbon bond stretching of graphite-like material, G band (~1600 cm‒1) are nearly undetectable. FEBID Part: Platinum halo less extend in FEBID. IETS signals of m-SWNT are detected. However, the amount of “remaining carbon residue” in the platinum electrodes is so significant that it result in lower conductance of device (~0.025 G0), which is much less than quantum conductance of m-SWNT (2 G0). It is also presumed that discrepancy of temperature-variable I−V result also comes from less quantity of “platinum”. In summary, owing to deposition mechanism of FIBD and FEBID, some features of m-SWNT are not observed in Pt−m-SWNT−Pt devices. Adjusting fabrication parameters or introducing other lithography may improve device performance.
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