Scanned Probe Microscopy using Single-Electron Device Arrays

该项目将使用连接到扫描针的超灵敏电荷探测器，类似于原子力显微镜，以制作固体或软材料表面电势的纳米分辨率地图。基于最灵敏的电荷探测器-单电子晶体管(SET)的高速版本的新型传感器将被使用。该传感器使用多组阵列和射频反射仪来提供有关快速充电过程的信息，发生在微秒的时间框架内。这项技术的能力使无法使用传统的表面电位测量进行的实验成为可能。例如，在现有的测量中，扫描探头会干扰被测量的表面，这使得测量电荷变得困难，例如电子，这些电荷只被微弱地限制在表面的一个区域。相比之下，该项目中进行的测量对表面的干扰将小得多，从而有可能观察到电子的维格纳局域化等现象。该项目还包括一个外展计划，通过教师和研究生参与的课堂活动以及实地考察将学生带到巴黎圣母院的实验室，以南本德学校的中学生为目标。这些活动每年将接触50-100名学生。初中年龄的儿童是一个很好的外展群体，因为他们已经足够先进，能够理解科学，但仍然在自己的兴趣领域做出选择。南本德公立学校有一个多样化的学生群体，有大量的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头系统相结合来绘制材料表面的电位图。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)。开尔文探头是更受欢迎的技术，因为它可以定量测量接触电势差(CPD)，而EFM只能测量接触电势差的质变。本项目设计并制作了扫描单电子晶体管探头(S组)，并用它们来表征半导体表面的表面电荷和电位。S SET探测器将使用射频反射术，以实现高电荷和潜在灵敏度以及高空间和时间分辨率的CPD测量。SET阵列将用于提高对随机背景电荷波动的免疫力，并提供与RF电路的改进匹配，从而消除对复杂谐振网络的需要。此外，使用射频装置将使开尔文力测量成为可能，文献中尚未报道，这将比传统的KPFM进行的侵入性更小。有了扫描探头系统，就有可能表征包括半导体和绝缘体在内的各种表面。特别是，该系统将用于研究半导体量子点中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.