First Principles Study Of Two Dimensional Germanium Materials Grown On Aluminum Surfaces

In this thesis,using the first-principles method within the framework of the density functional theory,we have studied in detail the growth mechanism of two-dimensional germanium material grown Al(111)Metallic substrate?Firstly,since the growth of two-dimensional germanium materials on Al(111)metal substrate has been successfully prepared experimentally,our aim is to find out its growth mechanism and structure.Considering the possibility of forming a cluster of germanium atoms in the experiment,we first explored the structure and energy of the germanium clusters in the vacuum,and then observed the structure and energy of the clusters on the surface of the Al(111)metal substrate.So,we finally found that germanium clusters are not dominant on the surface of Al(111)metal substrate compared with two-dimensional germanium,moreover,the germanium atoms evaporated experimentally at a very slow speed,then we denced the possibility of the growth of germanium clusters on the surface of Al(111)metal substrate from the theoretical calculation.Secondly,We explored the growth mechanism and the final growth structure of germanium atoms on Al(111)metal substrate.We adopted the method of single atom growth on the surface of metal substrate and summarized three growth modes.The three growth modes are grown into three two-dimensional germanium materials respectively.The first two kinds of growth patterns is two-dimensional germanium material,which is a pure plane without folds,while the two-dimensional germanium material produced by the third growth modes has folds.Moreover,the growth of germanene in this mode is consistent with the experimental results observed by STM,and also consistent with the experimental simulation results.But a serious problem is that in the process of growth,the third modes are not the lowest energy one,and there is no one size that is dominant in the growth process relative to the other two growth modes,which means that the experiment is not inclined to form this structure,and the experimental and theoretical simulation calculations are inconsistent.There inconsistents are needed to be solved.Finally,in order to solve the optimal structure of Al(111)metal substrate and the STM bright spot observed in the experiment,we solved by constructing the near-surface alloy of Al(111)metal substrate.We first simulated the growth process of the formation of germanium atoms on the surface of Al(111)metal substrate,forming a near-surface alloy and beginning to grow with a single atom of germanium.We have explored three growth patterns in which the first growth pattern has a two-dimensional structure with folds.Most of structure of this growth pattern are ground states in the growth process,that is,a very large number of structures are the lowest energy structures.This growth pattern is the most capacitive in the experiment.The image obtained by the STM image simulation of the first growth pattern is the same as that observed by the experimental STM,and the distance error between the bright spots is about 4%,which is within the range of error,and the growth mode is very easy to form in the experiment.The other two kinds of structures are pure planes,and the two structures are the most easily formed on the surface of Al(111)metal substrate,but it is not easy to form on the germanium and Al(111)metal substrate near-surface alloy.Compared with the first structure,the energy difference between them is large,and the probability of developing the latter two structures is small.We explored the growth pattern of germanium on the surface of Al(111)metal substrate,solved the unreasonable interpretation of the structure in the experiment,gave a more reasonable and accurate structural prediction,which will offer theoretical guidances for the experimental scientists.