Raman Spectroscopy of Individual Suspended Carbon Nanotubes under Immense Strains

 

論文發表人：張家旗 (南加州大學物理所博士班)

http://www.aps.org/meetings/march/

本文中用化學氣相沉積法生長超長奈米碳管並使其懸空橫跨一百奈米寬之可分離基板. 由於碳管與基板間的摩擦力,我們可以增加基板距離而不使碳管滑落. 此時碳管處於伸張狀態. 我們使用拉曼光譜來研究碳管的應力性質, 因為碳管特徵拉曼光譜G band 具有很明顯之應力反應. 當碳鍵長度增加G band頻率產生明顯紅位移(下降). 數據顯示, 碳管可伸張達13.6%而沒有滑動或斷裂. 同時, 我們發現G band頻率變化率具有很強之對稱性相關, 其取決於碳管之對掌性. 變化範圍從 -6.2 ~-23.6 cm-1/% strain. 儘管G band頻率變化率在不同碳管間有很大差異. 但我們觀察到G band 半高寬(FWHM)在相同的頻率下降值 (75 cm-1) 時突然增加. 另外, 我們觀察到G band頻率下降達157cm-1 (1592到1435 cm -1), 意指碳管確實可承受相當大的彈性伸張而不產生缺陷.

Suspended carbon nanotubes with long nanotube-substrate contacts grown by chemical vapor deposition enable us to explore carbon nanotubes up to strains of 13.6%. Here, Raman spectroscopy is utilized to observe strain-induced changes in the G band vibrational modes, which have a linear and pronounced response to the extension of the C-C bonds under various degrees of strain. The G band is found to downshift at rates ranging from -6.2 to -23.6cm-1/% strain among the different nanotubes measured in this study.  Despite this wide range of downshift coefficient, we observe broadening of the G band linewidth (FWHM) at a universal threshold downshift of DwG > 75cm-1. The G band is observed to downshift by up to 157cm-1 (from 1592 to 1435cm-1) under immense strains without any noticeable D band. Our measurements show that carbon nanotubes remain intact up to 13.6% strain with no slippage, breakage, or defect formation.