The STM Study of Bi Adsorption on the InAs(111)B Surface

Abstract

Semiconductors composed of group III and group V elements have a variety of promising applications, such as topological insulators and quantum computers. Among this category of semiconductors, bismuth (Bi)-containing III-V compounds are able to make these applications possible. However, the difficulty was found to alloy Bi atoms into the host lattice.

To solve the problem of material fabrication, we need to understand how Bi atoms affect the structure of the host material. In this thesis, we chose to study the Bi adsorption on the indium arsenide (InAs) (111)B surface. Bi atoms were evaporated from a solid source, and deposited on the InAs(111)B surface. Scanning tunneling microscopy (STM) was used to investigate the surface morphology, as well as distinguish the difference between different deposition durations and the effect of annealing. From STM images, we found that deposited Bi atoms tend to scatter around as single atoms, and then aggregate into small islands. The growth of Bi films were prohibited due to the short diffusion length on the substrate, since the deposition was done at room temperature. In addition, we also found Bi-induced substrate reconstruction after the deposition. From deposition tests, we noticed that the Bi morphology is sensitive to experimental parameters, such as the Bi source temperature. Thus, the key to improve the reproducibility of the results is the precise control over the source temperature. After annealing the Bi-deposited substrate, the number of Bi clusters decreases significantly, meanwhile, some holes were left on the surface.

Our study is just the rst step of understanding the Bi adsorption behavior. The next step will be combining the STM results with other techniques to obtain quantitative and structural information of the surface. Also, the adsorption on nanowires (NWs) is of
high interests, since the large surface-to-volume ratio of NWs may exhibit highly different properties from the surface of a bulk.

Popular Abstract

How Atoms Behave--Investigate the Surface with STM!

Semiconductors play a crucial role in daily electronics, such as computers, mobile phones, and solar cells. Nowadays, people cannot live without these electronics, especially computers. With the increasing demand for high-speed computers, quantum computers are proposed as the computers of the next generation. However, the making of the suitable material becomes a problem.

Semiconductors composed of group III and group V elements (III-V compound) are considered to have adjustable and diverse properties. Thanks to researches done by scientists, it is found that bismuth (Bi)-containing III-V compounds are potential materials for quantum computers. Nevertheless, since Bi is the largest atom among group V elements, it is difficult for Bi to incorporate in to the host III-V material. Thus, fabricating high quality III-V-Bi materials becomes the field that needs more studies and efforts.

Taking seats on the surface

To take part in this research field, we studied the Bi adsorption behavior. We chose indium arsenide (InAs) as the host material, and deposited Bi atoms on the InAs(111)B surface. With different amount of deposition, we expected to see distinct Bi arrangements on the surface. Just imaging that there are many available seats on the InAs(111)B surface, with some of them more favored by Bi. If there are bunches of incoming Bi atoms, some of them inevitably sit on the sites that are less preferred. To further observe the Bi behavior on the InAs(111)B surface, we heated the sample after the deposition. By raising the temperature, Bi atoms can possess enough energy to diffuse around, find their comfortable seats, or even leave the surface.

See tiny blocks of all the matters

The most important part of the experiment is to see Bi atoms on the surface. Atoms are blocks that build up all the matters in the universe, yet they are so small that they cannot be easily seen. For example, stacking one million atoms in a row has the same thickness as a sheet of paper. Scanning tunneling microscopy (STM) is a powerful imaging technique that is able to visualize these tiny blocks on the surface. A STM image is mapped based on the tunneling current, which is an effect that only occurs in microscopic scale. The tunneling current is very weak but surface-sensitive. Even a tiny bump of an atom can be detected by STM.

• author: Liu, Jung-Ching
• supervisor: Anders Mikkelsen; Sandra Benter
• organization: Synchrotron Radiation Research; Department of Physics
• course: FYSM30 20191
• year: 2019
• type: H2 - Master's Degree (Two Years)
• subject: Physics and Astronomy
• keywords: bismuth, indium arsenide (111)B, adsorption, surface, scanning tunneling microscopy
• language: English
• id: 8980734
• date added to LUP: 2019-06-17 08:15:54
• date last changed: 2019-06-17 08:15:54