Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA and Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
Phys Rev Lett. 2013 Sep 20;111(12):126101. doi: 10.1103/PhysRevLett.111.126101. Epub 2013 Sep 16.
We have developed a new scanning-tunneling-microscopy-based spectroscopy technique to characterize infrared (IR) absorption of submonolayers of molecules on conducting crystals. The technique employs a scanning tunneling microscope as a precise detector to measure the expansion of a molecule-decorated crystal that is irradiated by IR light from a tunable laser source. Using this technique, we obtain the IR absorption spectra of [121]tetramantane and [123]tetramantane on Au(111). Significant differences between the IR spectra for these two isomers show the power of this new technique to differentiate chemical structures even when single-molecule-resolved scanning tunneling microscopy (STM) images look quite similar. Furthermore, the new technique was found to yield significantly better spectral resolution than STM-based inelastic electron tunneling spectroscopy, and to allow determination of optical absorption cross sections. Compared to IR spectroscopy of bulk tetramantane powders, infrared scanning tunneling microscopy (IRSTM) spectra reveal narrower and blueshifted vibrational peaks for an ordered tetramantane adlayer. Differences between bulk and surface tetramantane vibrational spectra are explained via molecule-molecule interactions.
我们开发了一种新的基于扫描隧道显微镜的光谱技术，用于表征导电晶体上亚单层分子的红外（IR）吸收。该技术采用扫描隧道显微镜作为精密探测器，测量由可调谐激光源照射的分子修饰晶体的膨胀。使用该技术，我们获得了[121]四甲基烷和[123]四甲基烷在 Au(111)上的 IR 吸收光谱。这两种异构体的 IR 光谱之间存在显著差异，表明即使单分子分辨扫描隧道显微镜（STM）图像看起来非常相似，这种新技术也具有区分化学结构的能力。此外，该新技术被发现具有比基于 STM 的非弹性电子隧道光谱更高的光谱分辨率，并允许确定光吸收截面。与大块四甲基烷粉末的 IR 光谱相比，有序四甲基烷吸附层的红外扫描隧道显微镜（IRSTM）光谱显示出更窄和蓝移的振动峰。通过分子-分子相互作用解释了大块和表面四甲基烷振动光谱之间的差异。
