Nanoscale Probing of Dynamics in Local Molecular Environments

被引:20
作者
Atkin, Joanna M. [1 ,2 ,4 ]
Sass, Paul M. [1 ,2 ,5 ]
Teichen, Paul E. [3 ]
Eaves, Joel D. [3 ]
Raschke, Markus B. [1 ,2 ]
机构
[1] Univ Colorado, Dept Phys, Dept Chem, Boulder, CO 80309 USA
[2] Univ Colorado, JILA, Boulder, CO 80309 USA
[3] Univ Colorado, Dept Chem, Boulder, CO 80309 USA
[4] Univ N Carolina, Dept Chem, Chapel Hill, NC 27599 USA
[5] Pacific NW Natl Lab, Environm & Mol Sci Lab, Richland, WA 99354 USA
来源
JOURNAL OF PHYSICAL CHEMISTRY LETTERS | 2015年 / 6卷 / 22期
基金
美国国家科学基金会;
关键词
VIBRATIONAL DYNAMICS; RAMAN-SCATTERING; ECHO EXPERIMENTS; PHOTON-ECHO; REAL-TIME; SPECTROSCOPY; ULTRAFAST; POLYTETRAFLUOROETHYLENE; LIQUIDS; POLY(TETRAFLUOROETHYLENE);
D O I
10.1021/acs.jpclett.5b02093
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Vibrational spectroscopy can provide information about structure, coupling, and dynamics underlying the properties of complex molecular systems. While measurements of spectral line broadening can probe local chemical environments, the spatial averaging in conventional spectroscopies limits insight into underlying heterogeneity, in particular in disordered molecular solids. Here, using femto-second infrared scattering scanning near-field optical microscopy (IR s-SNOM), we resolve in vibrational free-induction decay (FID) measurements a high degree of spatial heterogeneity in polytetrafluoroethylene (PTFE) as a dense molecular model system. In nanoscopic probe volumes as small as 10(3) vibrational oscillators, we approach the homogeneous response limit, with extended vibrational dephasing times of several picoseconds, that is, up to 10 times the inhomogeneous lifetime, and spatial average converging to the bulk ensemble response. We simulate the dynamics of relaxation with a finite set of local vibrational transitions subject to random modulations in frequency. The combined results suggest that the observed heterogeneity arises due to static and dynamic variations in the local molecular environment. This approach thus provides real-space and real-time visualization of the subensemble dynamics that define the properties of many functional materials.
引用
收藏
页码:4616 / 4621
页数:6
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