Abstract
Scanning tunneling microscopy (STM) is one of the most prominent techniques to resolve atomic structures of flat surfaces and thin films. With the scope to answer fundamental questions in physics and chemistry, it was used to elucidate numerous sample systems at the atomic scale. However, dynamic sample systems are difficult to resolve with STM due to the long acquisition times of typically more than 100 s per image. Slow electronic feedback loops, slow data acquisition, and the conventional raster scan limit the scan speed. Raster scans introduce mechanical noise to the image and acquire data discontinuously. Due to the backward and upward scan or the flyback movement of the tip, image acquisition times are doubled or even quadrupled. By applying the quasi-constant height mode and by using a combination of high-speed electronics for data acquisition and innovative spiral scan patterns, we could increase the frame rate in STM significantly. In the present study, we illustrate the implementation of spiral scan geometries and focus on the scanner input signal and the image visualization. Constant linear and constant angular velocity spirals were tested on the Ru(0001) surface to resolve chemisorbed atomic oxygen. The spatial resolution of the spiral scans is comparable to slow raster scans, while the imaging time was reduced from ∼100 s to ∼8 ms. Within 8 ms, oxygen diffusion processes were atomically resolved.
Highlights
A significant increase in the frame rate opens new possibilities to study dynamic systems.[1,2] Faster Scanning tunneling microscopy (STM) would lead to higher prominence in academia and industry across different disciplines, such as life- and materials science.[3,4] Limiting factors and challenges for videorate and high-speed STMs are discussed in the literature.[3,5] The image rate is mainly limited by three factors: (1) The electronic feedback to control the tunneling current is slow. (2) The data acquisition is too slow in conventional hardware and software. (3) The conventional raster scan geometry is inefficient and introduces mechanical noise to the scanner
Dynamic sample systems are difficult to resolve with STM due to the long acquisition times of typically more than 100 s per image
While unconventional scan geometries have already been explored in other scanning microscopy techniques, such as atomic force microscopy (AFM) and scanning transmission electron microscopy (STEM), STM still sticks to the conventional raster scan
Summary
A significant increase in the frame rate opens new possibilities to study dynamic systems.[1,2] Faster STMs would lead to higher prominence in academia and industry across different disciplines, such as life- and materials science.[3,4] Limiting factors and challenges for videorate and high-speed STMs are discussed in the literature.[3,5] The image rate is mainly limited by three factors: (1) The electronic feedback to control the tunneling current is slow. (2) The data acquisition is too slow in conventional hardware and software. (3) The conventional raster scan geometry is inefficient and introduces mechanical noise to the scanner. By applying the quasi-constant height mode and by using a combination of highspeed electronics for data acquisition and innovative spiral scan patterns, we could increase the frame rate in STM significantly. We illustrate the implementation of spiral scan geometries and focus on the scanner input signal and the image visualization.
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