Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
J Chem Phys. 2010 Jan 14;132(2):021102. doi: 10.1063/1.3284740.
The understanding and control of the magnetic properties of carbon-based materials is of fundamental relevance in applications in nano- and biosciences. Ring currents do play a basic role in those systems. In particular the inner cavities of nanotubes offer an ideal environment to investigate the magnetism of synthetic materials at the nanoscale. Here, by means of (13)C high resolution NMR of encapsulated molecules in peapod hybrid materials, we report the largest diamagnetic shifts (down to -68.3 ppm) ever observed in carbon allotropes, which is connected to the enhancement of the aromaticity of the nanotube envelope upon doping. This diamagnetic shift can be externally controlled by in situ modifications such as doping or electrostatic charging. Moreover, defects such as C-vacancies, pentagons, and chemical functionalization of the outer nanotube quench this diamagnetic effect and restore NMR signatures to slightly paramagnetic shifts compared to nonencapsulated molecules. The magnetic interactions reported here are robust phenomena independent of temperature and proportional to the applied magnetic field. The magnitude, tunability, and stability of the magnetic effects make the peapod nanomaterials potentially valuable for nanomagnetic shielding in nanoelectronics and nanobiomedical engineering.
理解和控制基于碳的材料的磁性在纳米科学和生物科学中的应用中具有根本的相关性。环形电流在这些系统中起着基本的作用。特别是纳米管的内腔为在纳米尺度上研究合成材料的磁性提供了理想的环境。在这里，通过封装在豆荚混合材料中的分子的 (13)C 高分辨率 NMR，我们报告了在碳同素异形体中观察到的最大的抗磁性位移（低至-68.3 ppm），这与掺杂后纳米管包层芳香度的增强有关。这种抗磁性位移可以通过原位修饰（如掺杂或静电充电）来进行外部控制。此外，缺陷（如 C 空位、五边形和外纳米管的化学官能化）会使这种抗磁性效应消失，并使 NMR 特征与未封装分子相比略微呈现出顺磁性位移。这里报道的磁相互作用是与温度无关且与施加的磁场成正比的稳健现象。磁效应的大小、可调性和稳定性使得豆荚纳米材料在纳米电子学和纳米生物医学工程中的纳米磁屏蔽方面具有潜在的价值。
