超强静电场下氙原子能级结构的强外场效应

Atomic structure under extreme conditions (e.g. strong external field) is one of the classic and most important subjects in physics. Conventional static electric field is not strong enough, while in the case of ultra-short pulse laser, it produces an ultra strong ac electromagntic field. If we want to obtain the structural information of an atom, ultra-short wavelength light source is one of the must. How to apply an ultra-strong field, and how to obtain the stuctural information which is equivlent by using the ultra-short wavelength light souce? These are the important issues for atomic physics. As a possible solution, we propose to use ultra-high vacuum low temperature scanning tunneling microscope (STM) as a tool to investigate the subject addressed above. (1)The STM tip and the substrate,i.e.the tunneling juction, form an ultra-strong static electric field. (2)Scanning tunneling spectrascopy (STS) is utilized to obtain the electronic structure of a physically adsorbed xenon atom in the energy range of -10eV to +10eV. To avoid charge transfer between the adsorbed xenon atom and the metal substrate, a substrate of an ultra-thin layer of KCl covered single-crystal metallic platium will be used. Under ultra-low temerature (less than 1 Kelvin) with very small Brownian thermal noise, we use lock-in apmlifying method with a very small modulating signal (the amplitude of the signal is less than 0.3mV) to get atomic spectra with a resolution better than 0.5meV. (3)Quantum thereotical calculation with quantun defects counted will be performed to further understand the observed results of xenon atomic structure under such ultra-high electric static field. The thereotical work will also be helpful to understand the change of STM images of xenon with deferent bias or with different tunneling currents.

极端条件下（如强外场中）的原子结构是原子物理学经典而重要的研究课题之一。超短强激光脉冲能形成超强的瞬态交变电磁场，原子与其作用时有丰富的动力学行为。而在室验条件下由于电场极板间距的限制，形成的静电场强度远远小于一个原子单位，原子的强外静场效应尚不清楚。本项目基于实验室现有的极低温超高真空扫描隧道显微镜，利用STM探针与衬底构造一个超强的静电场，由于探针与衬底之间的距离达到纳米量级，电场强度可以达到10^8V/m量级；处于探针和衬底之间的单个氙原子在强场下能态结构发生急剧改变，其强场效应在0-10eV能量范围内由采用精密锁相放大技术的扫描隧道谱记录下来；在极低温条件下（<1K）获得分辨率优于0.2meV的原子结构。为避免氙原子与金属表面的电荷转移，采用金属上覆盖可隧穿的超薄氯化钾绝缘层的衬底。本申请利用STM探针独特的强电场环境测量单个氙原子扫描隧道谱将首次直接揭示原子的强静电场效应。

本项目利用超高真空-极低温扫描隧道显微镜研究了.Xe原子在表面上的吸附及电子性质。通过纳米级间距的扫描探针与表面之间施加电压构筑108V/m量级的静电场，研究了在该静电场中的原子能级结构。发现在液氦温度下，Xe原子会在Cu(100)表面上排列成晶格常数为0.39nm的六角密堆积结构；通过研究Xe原子STS谱，我们发现在Cu(100)表面会由于有库伦阻塞效应而导致的费米能级附近的峰，而在Ag(111)表面则没有。