MRI: Acquisition of an Ultra-High Vacuum Scanning Tunneling Microscope for Study of Local Electronic Inhomogeneity and Disorder in Aluminum Oxide

点击翻译按钮获取中文摘要

Technical AbstractThis proposal is for an ultra-high-vacuum combination scanning tunneling microscope/atomic force microscope (UHV STM/AFM). The instrument comes as a complete pre-engineered and pre-assembled system including vacuum chamber, manipulators, pumps, and control electronics. In addition, sample preparation capabilities include sputtering, heating and in situ gas dosing. The instrument will be used to study the atomic scale properties of insulating tunnel-junction materials used in conventional and quantum computation. The prevalence of aluminum oxide (AlOx) in tunnel-junction devices along with preliminary STM and AFM studies of AlOx demonstrating significant atomic-scale variation in the local density of states (LDOS) both motivate choosing this material for initial study. A spectral survey consisting of a closely spaced grid of spectra (dI/dV vs. V) with simultaneously acquired topography is the primary dataset. Here we propose to grow AlOx on a clean Al single crystal substrate and obtain a spectral survey after each monolayer deposition. Anticipated analysis will provide a series of maps at different oxide thicknesses showing the local insulating gap spatially correlated with local disorder such as the location of impurity atoms and topographic defects. Theory suggests that disorder affects the gap and conductance of an oxide, and the objective here is to study this interplay on an atomic length scale for AlOx. The instrument will be located at Colorado College (CC), a primarily undergraduate institution with a strong focus on education in research. It will allow many undergraduates to engage in a significant and timely research project on their campus, which significantly improves the PI's ability to attract a diverse group of students. In addition, the instrument will be used by senior physics majors in projects presented at their required senior seminars. Finally, the 6 materials scientists in the physics department at the University of Colorado, Colorado Springs comprise an eager pool of auxiliary users and collaborators. The department has significant materials science facilities, which will be accessible to the PI, but lacks any scanned probe capability so the fit with the PI is a natural one.Lay AbstractAs computers become smaller, so must the tiny electronic devices inside of them. In the next decade these devices will become so small that a single atom out of place could significantly affect their performance. We will study a particular common device which is shaped like a tiny sandwich with metal as its "bread" and an insulator as its "meat". While both the metal and insulator are important, the atom sized properties of the insulator are particularly crucial to making the devices work. In this project we propose to study the atom sized properties of the insulating "meat" using an instrument called a scanning tunneling microscope (STM for short). An STM can take pictures of the surface of the insulator in which the position of each individual atom can be seen. In addition to pictures of the atoms, we will be able to use the STM to measure whether the region around a certain atom is electrically conducting (like a metal) or insulating (like plastic). By studying the relationship between the atom pictures and the electrical information we will better understand how all the atoms work together to give the material its overall properties, and we can learn how to make more perfect insulating "meat" and hence better electronic devices. The microscope will be located at a college and used by many undergraduate students in their first research experience. These students will greatly benefit by being involved in a project that is very current but nonetheless accessible - the proposed instrument is relatively user friendly and the required background science is learned in the first two years of the physics curriculum. In addition, the instrument will be used by senior physics majors in projects presented at their required senior seminars. Finally, 6 scientists in the physics department at the nearby University of Colorado, Colorado Springs comprise an eager pool of auxiliary users and collaborators.