電極−碳管−電極之電性量測平台：聚焦離子和電子束誘導沉積製程及非彈性電子穿隧能譜

｢電極−分子−電極｣橋接系統(molecular junctions)為分子電性量測平台的基本架構。過去以電遷徙法(electromigration)製造的橋接系統，由於成功率極低(< 10%)且不足以維持數小時供非彈性電子穿隧能譜(inelastic electron tunneling spectroscopy, IETS)的訊號擷取，而有待改善。本實驗在掃描式電子顯微鏡(scanning electron microscope)監控下，以聚焦離子和電子束誘導沉積法(focused ion/electron beam- induced deposition, FIBD/FEBID)製作金屬導線電極，藉此固定碳管並與外界量測系統進行連結。目前本研究進展到量測｢鉑電極−金屬型奈米碳管−鉑電極,｣ (M−m-SWNT−M, M = Pt)系統的變溫I−V曲線與非彈性電子穿隧能譜。結果顯示Pt−m-SWNT−Pt系統導電值受限於聚焦離子和電子束誘導法的沉積機制，使得電性量測結果無法顯現金屬型單壁碳管的radial breathing mode (100~350 cm‒1)、石墨類物質(graphite-like)的C-C鍵振動譜峰(G band, ~1600 cm‒1)、理論導電值2 G0與導電值隨溫度下降而增加等特徵。本論文據此結果進行討論：(1)以離子束法(FIBD)沉積電鉑極，當兩鉑電極間距小於500 nm，電極外圍的鉑暈(platinum halo)會互相堆疊，於無碳管的空白橋接系統，仍可測得~1 G0的導電值，顯示鉑暈成為橋接電極間的漏電通路。因此，碳管的訊號會被鉑暈掩蓋而無法測得碳管的電性特徵。(2)若以電子束誘導法(FEBID)沉積鉑電極可有效減少鉑暈的現象，且非彈性電子穿隧能譜可測得金屬型單壁碳管的訊號。然而電子束誘導沉積法製作的鉑電極中，由於″碳″殘留和″鉑″含量比例過低等因素，使得Pt−m-SWNT−Pt系統導電值僅0.025 G0，仍不符合電極材料導電值遠大於單分子導電值的要求。綜觀聚焦離子束與電子束誘導沉積法結果，未來除了製作參數改良外，搭配其他製程方式，如電子束微影(e-beam lithography)將可預期有效改善M−m-SWNT−M電性表現。

關鍵字

單壁金屬型奈米碳管；聚焦離子束和電子束誘導沉積製程；非彈性電子穿隧能譜

並列摘要

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.

並列關鍵字

metallic single-walled carbon nanotube ； focused ion/electron beam-induced deposition ； inelastic electron tunneling spectroscopy

參考文獻

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電極−碳管−電極之電性量測平台：聚焦離子和電子束誘導沉積製程及非彈性電子穿隧能譜

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