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

技术摘要：本设计为一种超高真空扫描隧道显微镜/原子力显微镜（UHV STM/AFM）组合装置。该仪器是一个完整的预设计和预组装系统，包括真空室，机械手，泵和控制电子设备。此外，样品制备能力包括溅射，加热和原位气体加药。该仪器将用于研究用于常规和量子计算的绝缘隧道结材料的原子尺度性质。氧化铝（AlOx）在隧道结器件中的普遍存在，以及对AlOx的初步STM和AFM研究表明，局域态密度（LDOS）在原子尺度上存在显著变化，这都促使我们选择这种材料进行初步研究。由紧密间隔的光谱网格（dI/dV vs. V）和同时获得的地形组成的光谱调查是主要数据集。在这里，我们建议在干净的Al单晶衬底上生长AlOx，并在每次单层沉积后获得光谱测量。预期的分析将提供一系列不同氧化物厚度的图，显示局部绝缘间隙在空间上与局部无序（如杂质原子的位置和地形缺陷）相关。理论表明，无序会影响氧化物的间隙和电导率，这里的目标是在原子长度尺度上研究这种相互作用。该仪器将位于科罗拉多学院（CC），这是一所主要侧重于研究教育的本科院校。它将允许许多本科生在他们的校园参与一个重要的和及时的研究项目，这大大提高了PI吸引不同学生群体的能力。此外，该仪器将用于高年级物理专业学生在他们要求的高年级研讨会上提出的项目。最后，科罗拉多大学物理系的6位材料科学家组成了一个热心的辅助用户和合作者池。该部门拥有重要的材料科学设施，PI将可以使用，但缺乏任何扫描探针能力，因此与PI的配合是自然的。随着计算机变得越来越小，其内部的微型电子设备也必须变得越来越小。在接下来的十年里，这些设备将变得非常小，以至于一个原子的错位可能会严重影响它们的性能。我们将研究一种特殊的普通装置，它的形状像一个小三明治，金属是它的“面包”，绝缘体是它的“肉”。虽然金属和绝缘体都很重要，但绝缘体的原子大小的特性对于使设备工作尤为关键。在这个项目中，我们建议使用一种称为扫描隧道显微镜（简称STM）的仪器来研究绝缘“肉”的原子大小性质。STM可以拍摄绝缘体表面的照片，其中可以看到每个原子的位置。除了原子的图片，我们将能够使用STM来测量某个原子周围的区域是导电的（像金属）还是绝缘的（像塑料）。通过研究原子图像和电子信息之间的关系，我们将更好地理解所有的原子是如何一起工作来赋予材料整体特性的，我们可以学习如何制造更完美的绝缘“肉”，从而更好地制造电子设备。这种显微镜将被放置在一所大学，供许多本科生在他们的第一次研究经验中使用。这些学生将通过参与一个非常最新但仍然可以获得的项目而受益匪浅-拟议的仪器相对容易使用，所需的背景科学在物理课程的前两年学习。此外，该仪器将用于高年级物理专业学生在他们要求的高年级研讨会上提出的项目。最后，附近科罗拉多大学斯普林斯分校物理系的6位科学家组成了一个热心的辅助用户和合作者群体。

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.