Growth Of Urtrathin Pb Films On Bi₂Te₃（111） Surface And The Reactivity Of Bi₂Te₃（111） Surface Towards Water

In recent 10 years, three-dimensional topological insulators have attracted tremendous attention of physicists and become frontier of condensed matter physics. Topological insulators are a new class of materials that behave as insulators in the bulk but exist gapless metallic surface states due to spin-orbit coupling and time-reversal symmetry. Topological insulators have a lot of unique physical properties need to be researched, in addition, there are many novel physical phenomena at the interface between topological insulators and superconductor. Those phenomena may provide new way to solve some basic physics problem. For example, some physicists try to find magnetic monopole near a magnetic layer at a Tl surface and there is some prediction that Majorana fermions may emerge at a topological insulators/superconductor interface. What is more, the discovery and study of topological insulators not only have theoretical significance but also have exciting prospect of application due to the low-energy-consumption of surface electron transport.In this article, we try to grow Pb film on Bi2Te3/Si(111) substrate by low temperature deposition and post annealing. We obtained ultrathin Pb films with thickness of～1 monolayer (ML) and we characterize the film by using low-temperature scanning tunneling microscopy in combination with x-ray photoemission spectroscopy. We adjusted the annealing temperature several times and record the change of surface topography by STM image. X-ray photoemission spectroscopy determines the valence state of Pb films, indicating that the Pb films are not reacted with Bi2Te3. There is great potential for this topological insulators/superconductor system and our method of deposition or choice of annealing temperature can help subsequent researchers.There are still many problems to be solved if we want to use topological insulators in practical devices. For example, we used to study topological insulators in ultra-high vacuum, but it is difficult to avoid the topological insulators contact with atmosphere in actual application. Whether the surface reacts with water or not is meaningful because the nature of topological insulator is determined by the surface. Surface reactivity is important in modifying the physical and chemical properties of topological insulators. In this article, we employ scanning tunneling microscopy to directly probe the surface reaction of Bi2Te3 towards H2O. We increase the depositing amount of water gradually and we take STM image/STS spectrum for each dosage. It is found that only the top quintuple layer is reactive to H2O. Combining STM images and STS spectrums, we proposed that Bi2Te3 react with water, resulting in a hydrated Bi bilayer as well as some Bi islands. Another product hhTe may desorbed from the surface at room temperature. We performed low temperature STM measurement during H2O adsorption and we found deposited structure which was not observed at room temperature. Those deposited structure was considered as H2Te. We directly characterized the reaction of water at Bi2Te3(111) surface and we gave an reasonable explanation for our experiment.