50,000,000x Magnification

The speaker introduces the audience to the microscopy suite in the materials department at UCSB, where a Scanning Transmission Electron Microscope (STEM) is located. The STEM is a complex instrument used to visualize atoms, and the speaker plans to demonstrate its operation by searching for a specific defect in a crystalline material called tin selenide. The video aims to showcase real research in action, with the speaker acknowledging the possibility of not finding the defect but emphasizing the learning experience. The importance of having a very thin sample for electron transmission is discussed, and the process of creating such a sample using a focused ion beam is mentioned. The speaker also introduces the vacuum tweezers used for handling the tiny samples and shares an anecdote about dropping the sample during filming, but assures that the sample was not damaged.

The speaker explains the fundamentals of transmission electron microscopy, likening it to casting shadows with a beam of electrons through a material. The analogy of using a flashlight and pinhole is used to illustrate how images are formed. The limitations of using light are discussed, such as the inability to create a true point source for imaging at the atomic scale. The speaker then introduces the concept of using lenses to project a sharp image, even with an imperfect light source. The process is compared to using an electron gun and electromagnets instead of a flashlight and glass lenses, highlighting the advanced technology involved in electron microscopy. The speaker also discusses the challenges of aligning the beam and sample, especially when dealing with crystalline materials, and introduces the concept of using diffraction patterns to assist in alignment.

The speaker transitions the discussion from traditional Transmission Electron Microscopy (TEM) to Scanning Transmission Electron Microscopy (STEM). Using the analogy of a laser mounted on a gimbal, the speaker explains that STEM involves scanning an image by rastering the electron beam across the sample, pixel by pixel. This is a significant shift from the parallel beam approach used in TEM. The speaker emphasizes the need for a focused, sub-atomic sized beam for high-resolution imaging in STEM. The process of scanning is likened to a computer rastering a grid, with the electron beam acting as a tiny 'laser' that probes the sample. The speaker also discusses the importance of achieving the highest possible resolution by focusing the beam to the smallest possible point.

The speaker describes the process of examining multi-layered crystalline structures using the STEM. The sample consists of layers of gallium arsenide, lead selenide, and tin selenide. The speaker explains the process of zooming in to observe individual atoms, specifically gallium and arsenic, and how they form a crystalline pattern. The speaker also discusses the challenges of focusing on a 'bendy film' sample and the iterative process of adjusting the focus and tilt to achieve a clear image. The search for specific defects within the tin selenide layers is highlighted, with the speaker expressing excitement upon finding a gap, which is a particular type of defect in the layered structure.

The speaker narrates the successful identification of a specific defect in the tin selenide structure. This defect is described as a 'hiccup' in the layered structure, where one layer is shifted by half its height, creating a unique 'zipper' structure at the boundary. The speaker shares the frustration and tedium of searching for this defect, acknowledging the luck and persistence required to find and photograph it. The discovery is celebrated as it confirms the existence of this defect in tin selenide, marking a scientific achievement that can be documented and reported. The speaker reflects on the challenges of working with an old, warped sample and the satisfaction of overcoming these obstacles to achieve the research goal.