Investigation of non-equilibrium phonon populations in biased metallic single-walled carbon nanotubes (SWCNTs)

我们将对偏置金属单壁碳纳米管中所谓的热声子的产生进行实验研究。电子-声子耦合对金属单壁碳纳米管电阻的影响与互连等大电流应用有关。在高偏压下，金属纳米管中加速的电子在高能声子的发射下松弛。如果这些声子的产生速率超过它们的驰豫速率，它们就会在纳米管中积累起来。在这些条件下，可以通过拉曼光谱检测到布居的增加，其中光谱将显示高能区特定模式的强度增加。利用玻色-爱因斯坦统计，我们可以计算出这些声子的声子温度。热声子产生的一个重要问题是声子沿单壁碳纳米管的空间分布。在这个项目中，我们试图回答以下问题：(I)非平衡声子的产生是局域效应吗？(Ii)必须将管子悬浮以达到几千开尔文的预测声子温度，以及(Iii)光谱的高能部分的信号(反斯托克斯信号)是来自自由悬挂的管段还是来自整个管子长度？对于实验，我们建议使用近场拉曼光谱和远场拉曼显微镜操作在狭缝限制孔径模式，提供所需的空间分辨率低于50纳米，并结合纳米管特定的电子传输测量装置。

The generation of so called hot-phonons in biased metallic single-walled carbon nanotubes will be experimentally explored. The influence of electron-phonon coupling on the resistance of metallic single-walled carbon nanotubes is relevant to high-current applications such as interconnectors. In the regime of high-bias, accelerated electrons in metallic nanotubes relax under the emission of high-energy phonons. These phonons will accumulate in the nanotube if their generation rate exceeds their relaxation rate. Under these conditions, the increase in population can be detected by Raman spectroscopy where the spectrum will show an increase in the intensity of a particular mode in the high energy region. Using Bose-Einstein statistics one can then calculate the phonontemperature of these phonons. An unresolved and important issue of hot-phonons generation concerns the spatial distribution of the phonons along the single-walled carbon nanotube. In this project we attempt to answer the following questions: (i) Is the generation of the non-equilibrium phonons a local effect? (ii) Must the tube be suspended to reach the predicted phonon-temperature of a few thousand Kelvin and (iii) Does the signal in the high-energy part of the spectrum (anti-Stokes signal) arise from freely suspended tube-segments or from the entire tube length?For the experiment we propose to use Near-field Raman spectroscopy and far-field Raman microscopy operating in a slit-limited-aperture mode, which provide the required spatial resolution of less than 50 nm, in combination with a nanotube specific electron transport measurement setup.