Scanned Probe Microscopy using Single-Electron Device Arrays

该项目将使用与扫描针耦合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级分辨率地图。 一种新型的传感器，最敏感的电荷检测器，单电子晶体管（SET）的高速版本的基础上，将被使用。该传感器采用SET阵列和射频反射仪，以提供在微秒时间范围内发生的快速充电过程的信息。 这种技术的能力使实验，不能使用传统的表面电位测量进行。 例如，在现有的测量中，扫描探针干扰正被测量的表面，使得难以测量仅被弱地限制到表面的区域的电荷，诸如电子。 相比之下，在这个项目中进行的测量对表面的破坏性要小得多，这使得观察电子的维格纳局域化等现象成为可能。 该项目还涉及一个外展计划，将通过涉及教师和研究生的课堂活动，以及实地考察，将学生带到圣母院实验室，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。中学生是一个很好的推广群体，因为他们已经足够先进，可以理解科学，但仍然在选择他们感兴趣的领域。南本德公立学校的学生群体多元化，其中大量学生来自科学技术领域代表性不足的群体。该项目将使用与扫描探针系统耦合的超灵敏静电计来绘制材料表面的电位。 在表面电位测量中，两种方法占主导地位：开尔文探针力显微镜（KPFM）和静电力显微镜（EFM）。Kelvin探针是比较流行的技术，因为它产生的接触电位差（CPD）的定量测量，而EFM只能测量CPD的定性变化。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，以高电荷和电位灵敏度以及高空间和时间分辨率测量CPD。SET阵列将用于提供对随机背景电荷波动的改进的抗扰性，并提供与RF电路的改进的匹配，从而消除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，尚未在文献中报道，这将比传统KPFM的侵入性更小。 使用扫描探针系统，可以表征各种表面，包括半导体和绝缘体。 特别是，该系统将被用来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.