Scanned Probe Microscopy using Single-Electron Device Arrays

这个项目将使用超灵敏的电荷探测器连接到一个扫描针上，类似于原子力显微镜，来制作固体或软材料表面的纳米级分辨率的电势图。将使用一种新型传感器，基于最灵敏的电荷探测器的高速版本，单电子晶体管（SET）。该传感器采用set阵列和射频反射计来提供在微秒时间内发生的快速充电过程的信息。这种技术的能力使得使用传统的表面电位测量无法进行实验。例如，在现有的测量中，扫描探针会干扰被测量的表面，使得测量电荷（如电子）变得困难，因为电子只被微弱地限制在表面的一个区域内。相比之下，在这个项目中进行的测量对表面的破坏要小得多，这使得观察电子的维格纳定位等现象成为可能。该项目还包括一项外展计划，将通过教师和研究生参与的课堂活动，以及将学生带到圣母大学实验室的实地考察，针对南本德学校的中学生。这些活动每年将接触50 - 100名学生。中学年龄的孩子是一个很好的推广群体，因为他们已经足够了解科学，但仍在对自己感兴趣的领域做出选择。南本德公立学校的学生群体多样化，其中大量学生来自科学和技术领域代表性不足的群体。该项目将使用超灵敏静电计与扫描探针系统耦合来绘制材料表面的电位。在表面电位测量中，主要有两种方法：开尔文探针力显微镜（KPFM）和静电力显微镜（EFM）。开尔文探针是比较流行的技术，因为它可以定量测量接触电位差（CPD），而EFM只能测量CPD的质变。本项目设计和制造扫描单电子晶体管探针（s - set），并使用它们来表征半导体表面的表面电荷和电位。S-SET探头将使用射频反射仪来测量CPD，具有高电荷和电位灵敏度，以及高空间和时间分辨率。set阵列将用于提高对随机背景电荷波动的免疫力，并提供改进的射频电路匹配，消除了对复杂谐振网络的需要。此外，使用RF SET将实现开尔文力测量，这在文献中尚未报道，这将比传统KPFM的侵入性更小。通过扫描探针系统，可以表征各种表面，包括半导体和绝缘体。特别是，该系统将用于研究半导体量子点内电子的维格纳局域化。

This project will use ultra-sensitive charge detectors coupled to a scanning needle, similar to an Atomic Force Microscope, to make nanoscale-resolution maps of the electrical potential of a surface of solid or soft materials. A novel sensor, based on high-speed version of the most sensitive charge detector, single-electron transistor (SET), will be used. This sensor employs arrays of SETs and radio-frequency reflectometry to give information on fast charging processes, occurring in a microsecond time frame. The capabilities of this technique enable experiments that cannot be performed using traditional measurements of surface potentials. For instance, in existing measurements the scanning probe disturbs the surface that is being measured, making it difficult to measure charges, such as electrons, that are only weakly confined to an area of the surface. In contrast, the measurements made in this project will be much less disruptive to the surface, making it possible to observe phenomena such as Wigner localization of electrons. The project also involves an outreach program that will target middle school students in South Bend Schools through classroom activities involving faculty and graduate students, and field trips to bring students to the Notre Dame labs. These activities will contact 50 - 100 students per year. Middle school aged children are an excellent group for outreach since they are advanced enough to understand science, but are still making choices about their areas of interests. South Bend public schools have a diverse student population with a large number of students from groups underrepresented in the areas of science and technology.This project will use ultra-sensitive electrometers coupled to a scanned probe system to map the potential of material surfaces. In surface potential measurements, two methods dominate: Kelvin Probe Force Microscopy (KPFM) and Electrostatic Force Microscopy (EFM). Kelvin probe is the more popular technique because it produces a quantitative measurement of the contact potential difference (CPD) while EFM can measure only qualitative changes in CPD. This project design and fabricate scanning single-electron transistor probes (S-SETs) and use them to characterize the surface charge and potential of semiconductor surfaces. The S-SET probes will use radio-frequency reflectometry to enable measurements of the CPD with high charge and potential sensitivity, as well as high spatial and temporal resolution. Arrays of SETs will be used to provide improved immunity to random background charge fluctuations, and to provide improved matching to the RF circuit, eliminating the need for a complicated resonant network. In addition, the use of an RF SET will enable a Kelvin force measurement, not yet reported in the literature, that will be less invasive than those made by conventional KPFM. With the scanned probe system it will be possible to characterize a variety of surfaces including semiconductors and insulators. In particular, the system will be used to investigate Wigner localization of electrons within semiconductor quantum dots.