Enhancement of the electron spin resonance of single-walled carbon nanotubes by oxygen removal.
Enhancement of the electron spin resonance of single-walled carbon nanotubes by oxygen removal.
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DOI：
10.1021/nn204094s
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发表时间：
2011-10
期刊：
影响因子：
17.1
通讯作者：
W. Rice;R. Weber;A. Leonard;J. Tour;P. Nikolaev;S. Arepalli;V. Berka;A. Tsai;J. Kono
中科院分区：
文献类型：
--
作者：
W. Rice;R. Weber;A. Leonard;J. Tour;P. Nikolaev;S. Arepalli;V. Berka;A. Tsai;J. Kono
我们已经观察到了近4倍的增加，在电子自旋共振（ESR）信号从合奏单壁碳纳米管（SWCNT）由于氧解吸。通过在热退火之前和之后进行随温度变化的ESR谱，我们发现单壁碳纳米管中的ESR可以通过样品中的分子氧含量可逆地改变。独立的吸附氧的存在下，居里定律（自旋磁化率<$1/T）被认为是从~4至300 K，表明探测自旋是有限水平的物种。对于退火前和退火后的样品条件下，ESR谱线宽度随着温度的增加而减小，我们将这种现象识别为运动变窄。从线宽的温度依赖性，我们提取了估计的管间跳跃能量;对于这两个样本条件下，我们发现这个跳跃能量为~1.2毫电子伏。由于自旋跳跃能量只有轻微的变化时，氧被解吸，我们得出结论，只有自旋磁化率，而不是自旋运输，是由物理吸附的分子氧的存在下，单壁碳纳米管合奏的影响。令人惊讶的是，当SWCNT样品中的氧量改变时，没有观察到线宽变化，这与其他碳质体系和某些1D导电聚合物相反。我们假设，物理吸附的分子氧作为受体（p型），补偿供体样（n型）的缺陷，负责在散装单壁碳纳米管的ESR信号。
We have observed a nearly 4-fold increase in the electron spin resonance (ESR) signal from an ensemble of single-walled carbon nanotubes (SWCNTs) due to oxygen desorption. By performing temperature-dependent ESR spectroscopy both before and after thermal annealing, we found that the ESR in SWCNTs can be reversibly altered via the molecular oxygen content in the samples. Independent of the presence of adsorbed oxygen, a Curie law (spin susceptibility ∝ 1/T) is seen from ~4 to 300 K, indicating that the probed spins are finite-level species. For both the pre-annealed and post-annealed sample conditions, the ESR line width decreased as the temperature was increased, a phenomenon we identify as motional narrowing. From the temperature dependence of the line width, we extracted an estimate of the intertube hopping energy; for both sample conditions, we found this hopping energy to be ~1.2 meV. Since the spin hopping energy changes only slightly when oxygen is desorbed, we conclude that only the spin susceptibility, not spin transport, is affected by the presence of physisorbed molecular oxygen in SWCNT ensembles. Surprisingly, no line width change is observed when the amount of oxygen in the SWCNT sample is altered, contrary to other carbonaceous systems and certain 1D conducting polymers. We hypothesize that physisorbed molecular oxygen acts as an acceptor (p-type), compensating the donor-like (n-type) defects that are responsible for the ESR signal in bulk SWCNTs.