Localized Detection of Inelastic Electron Tunneling Using a Scanning Tunneling Microscopy

这项来自实验物理化学项目的资助分别支持了加州理工学院J. Baldeschwieler和W.Kaiser以及喷气推进实验室的研究。该奖项资助旨在检测表面单个分子内部原子运动的研究。为了证明扫描隧道显微镜（STM）在局部非弹性电子隧道探测中的适用性。我们将研究涉及吸附物非弹性电子隧穿光谱基本物理的简单系统。它们被精心选择为稳定的，易于制备的，并且易于同位素取代，从而通过激发吸附质振动模式来促进光谱特征对非弹性隧道的明确分配。将建造一台专门为本研究设计的液氦浸入式扫描隧道显微镜；它将是加州理工学院喷气推进实验室用于超导体声子光谱的STM设计的改进版，这是迄今为止发表的最灵敏的低温光谱测量。最初的努力将是在氢化和氘化简并硅表面上检测Si-H和Si-D振动拉伸模式。对金和硅表面化学吸附的富含氢（或氘）的小分子也计划进行类似的测量。这些简单的系统可用于优化STM非弹性隧道光谱的实验和仪器参数。该项目将建立非弹性电子隧穿可探测性的下限，并可能证明STM在检测由吸附质振动模式激发的非弹性电子隧穿方面的适用性。提出的研究是实现单个吸附分子的空间分辨振动光谱及其结合环境的三维成像的一步。这是STM的一个潜在应用，将具有深远的科学和技术重要性。

This grant from the Experimental Physical Chemistry Program supports research of J. Baldeschwieler and W.Kaiser of California Institute of Technology and the Jet Propulsion Laboratories respectively. The award funds research aimed toward the realization of examining the atomic motions inside individual molecules on surfaces. It is proposed to demonstrate the applicability of the scanning tunneling microscope (STM) to the detection of localized inelastic electron tunneling. Simple systems which entail the essential physics for inelastic electron tunneling spectroscopy of adsorbates will be studied. They are carefully chosen to be stable, easily prepared, and amenable to isotopic substitution to facilitate unambiguous assignment of spectral features to inelastic tunneling via excitation of adsorbate vibrational modes. A liquid-helium immersed scanning tunneling microscope designed specifically for the proposed work will be constructed; it will be a modification of the STM design used at the Jet Propulsion Laboratory of the California Institute of Technology for superconductor phonon spectroscopy, the most sensitive low-temperature spectroscopy measurement published to date. Initial efforts will be directed toward detecting Si-H and Si-D vibrational stretching modes on hydrogenated and deuterated degenerate silicon surfaces. Similar measurements are planned for hydrogen (or deuterium) rich small molecules chemisorbed to gold and silicon surfaces. These simple systems can be used to optimize experimental and instrumental parameters for inelastic tunneling spectroscopy with the STM. The project will establish lower limits for the detectability of inelastic electron tunneling and may demonstrate the applicability of the STM to the detection of inelastic electron tunneling due to excitation of adsorbate vibrational modes. The proposed investigation constitutes a step toward the realization of spatially resolved vibrational spectroscopy of individual adsorbed molecules together with three dimensional imaging of their binding environments. This is a potential application of the STM which would be of profound scientific and technological importance.