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报告题目：Scanning Probe Microscopy with qPlus sensors
报告时间：2024-07-22 10:00
报告人： Professor Franz J. Giessibl
Experimental and Applied Physics, University of Regensburg
报告地点：翔安校区能源材料大楼3号楼会议室2
转播地点：化四112教室
报告摘要：
The scanning tunneling microscope (STM) has enabled us to “see” and move single atoms. STM relies on vacuum tunneling with an exponential increase of a tunneling current between two biased conductive electrodes at a factor of ten per Å (100 pm). If a tip has one atom that sticks out one Å more than all the others, this front atom carries ten times more current than the other atoms. The monotonic decrease of current with distance facilitates distance feedback and allows to scan the tip across a sample with atomic precision. In 1986, Binnig, Gerber and Quate introduced atomic force microscopy (AFM), a method that also images insulators by relying on forces. Unlike the current, the force between tip and sample is non-monotonic and includes long- and short range components. AFM has been inferior in resolution to STM for a long time. Today, AFM exceeds STM in spatial resolution by utilizing Pauli repulsion forces that change even stronger with distance than the tunneling current. That progress was enabled by advances in measuring small forces and by the isolation of chemical bonding forces from strong background forces. The special challenges of AFM are met by the qPlus sensor,1 a quartz force sensor that measures force gradients by frequency changes and was initially based on tuning forks used in Swatch wristwatches. Using the outstanding precision of frequency measurements, we can today measure the forces that act in atomic manipulation, measure exchange interactions with sub-pN sensitivity, image metal clusters (see figure) and molecules with atomic resolution and single adatoms with subatomic resolution. Highest precision measurements require vacuum and low temperatures, and measuring the deflection of a force sensor usually introduces heat. Nevertheless, we could show that the tip of a qPlus sensor remains superconductive during its operation.3 Tips that are electrically conductive allow to measure the tunneling current (moving electrons with energies close to the Fermi level) and the forces (electrons at rest, ranging from van-der-Waals attraction to bond formation and Pauli repulsion), including spin dependent forces4 and a direct measurement on the influence of tip-sample forces on the eigenfrequencies of molecules that are detected by inelastic electron tunneling spectroscopy.5 An exciting possibilities of AFM with qPlus sensors is its capability to obtain subatomic resolution, i.e. the measurement of the angular dependence of chemical bonding forces shown in Fig. C. The quantum corral, introduced by Crommie, Lutz and Eigler in 1993, was revisited by AFM in 2021, showing that the 102 electrons that the corral contains can be viewed as the shell of a two-dimensional atom with similar bonding properties to AFM tips as a natural atom.7 More recently, electrochemical applications of qPlus emerged. 8
报告人简介：
Franz J. Giessibl教授于 1982 年至 1987 年在慕尼黑工业大学和苏黎世联邦理工学院学习物理学。1988年，他在Gerhard Abstreiter教授的指导下获得实验物理学学士学位，并在慕尼黑IBM 物理小组跟随诺贝尔奖获得者Gerd Binnig攻读物理学博士学位，研究原子力显微镜。1991 年底博士毕业，他继续在慕尼黑IBM物理小组担任了6个月的博士后研究员。1992 年中至 1994 年底，他加入帕克科学仪器公司担任高级科学家，后来又担任真空产品总监。1995 年至 1996 年，他加入著名管理咨询公司麦肯锡，担任高级经理。在此期间，他发明了用于原子力显微镜的新型探针qPlus传感器，并在奥格斯堡大学Jochen Mannhart 教授的课题组继续从事原子力显微镜的实验和理论研究工作，并于2001年获得habilitation。2005年，他受聘德国雷根斯堡大学的讲席教授，并开始与不同单位合作建立超低温扫描隧道显微镜和原子力显微镜组合。
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