Adsorption And Alloying Of Ga On Bi(111) Surface

Metals and their alloys are materials with a long history in basic research and industrial applications,whose properties and functions are closely related to size,shape,structure,and composition.As one of the key research directions in the field of alloy materials,low melting point alloys play a great role in die manufacturing,electronic and electrical automatic control and metal Mosaic due to their unique physical and chemical properties.The main materials of common low melting point alloys are bismuth,tin,chromium,etc.Gallium is a relatively valuable dispersed metal with high ductility,low melting point and high boiling point.Gallium is liquid at room temperature and can also be used as one of the main materials of low melting point alloys.The low melting point alloy made of gallium as the main material can be used as the heat exchange medium of nuclear reaction,and gallium indium alloy can also be used as a substitute for mercury,and its toxicity is far less than that of mercury.Gallium,gallium phosphide,gallium nitride and other materials prepared by gallium as dopant have high application value and potential in semiconductor industry,and have attracted the attention of many researchers.Based on the above research background,we studied the adsorption of gallium on semi-metal Bi(111)surface and the formation process of its alloy structure.In this study,the adsorption and alloying process of gallium atoms on Bi(111)surface was studied by ultra-high vacuum and low temperature tunneling microscopy.The atomic structure of two-dimensional gallium bismuth alloy was determined by the simulation calculation based on the first-principles method of density functional theory(DFT).Specific research contents include the following aspects:(1)Effect of substrate temperature on growth of Ga-bismuth alloy on Bi(111)surface.During sample preparation,Ga(gallium)was deposited several times by changing the substrate Bi(111)temperature,and the influence of different substrate temperatures on the alloy growth was observed.Ga was deposited at low temperature(200 K).Due to the low mobility of gallium atoms scattered on the substrate surface,gallium atoms clustered into small and dense atomic clusters on Bi(111)surface.As the substrate temperature increases,gallium atoms combine with bismuth atoms to form hexagonal alloy islands.When the substrate temperature is increased to about 270 K,gallium and bismuth alloys will appear in large quantities at the edge of the bismuth step while the hexagonal alloy island exists.As the substrate temperature continues to increase,the number of hexagonal Ga-bismuth alloy islands gradually decreases,and most of them are attached to the edge of the bismuth step,and the area of Ga-bismuth alloy gradually increases.When the substrate temperature rose to 330 K,the alloy area gradually decreased until the temperature reached 400 K,and no absorbed gallium atoms or gallium bismuth alloy appeared on Bi(111)surface.In addition,Ga atoms were deposited again at low temperature on the surface of the sample with Ga-bismuth alloy,and it was found that all the gallium atoms deposited twice were absorbed on the surface of Bi(111),and the surface of the alloy layer was extremely clean,which also indicated that the alloy layer formed on the surface of Bi(111)can only be single layer rather than multi-layer growth,with self-limited growth.(2)Effect of annealing temperature on gallium bismuth alloy.Ga was deposited at low temperature(200K),and the substrate was annealed for several times to observe the effect of annealing temperature on the growth of alloy.It is found that when the annealing temperature is lower than 200 K,gallium atomic clusters of different sizes can be observed on the substrate surface.When the annealing temperature is raised,the gallium clusters deposited on Bi(111)surface will gather to form a large hexagonal alloy island.When the annealing temperature is about 360 K,the hexagonal Ga-bismuth alloy island begins to dealloying,and the bismuth atoms in the alloy island re-form small bismuth islands,and the gallium atoms gather on the edge of the bismuth island to form small spherical droplets and gradually desorbed.When the annealing temperature reached about 400 K,Ga droplets at the edge of the bismuth island were completely desorbed from the surface of the sample.(3)Study on atomic structure of gallium bismuth alloy.Based on the first principles method of density functional theory(DFT),the growth of gallium atoms on Bi(111)surface is simulated theoretically.Combined with the STM diagram and the theoretical calculation results,the analysis shows that the gallium atoms deposited on the surface of Bi(111)will enter the Bi crystal to replace the second layer of bismuth atoms,forming A hexagonal densely packed single layer of gallium bismuth alloy,the thickness of which is 3.32 (?).