半导体纳米粒子能隙与拉曼频率尺度效应的研究

发布时间：2018-05-15 12:31

本文选题：尺寸效应 + 热力学　；参考：《太原理工大学》2017年硕士论文

【摘要】：当材料尺度进入到纳米量级,就会表现出与块体材料不同的性能。例如半导体纳米粒子就具有特殊的光学、电学、磁学、热力学等不同于块体结构的性能,这类材料对光电转换、存储设备、传感器、显示技术等领域有着极其重要的影响。因此半导体纳米材料引起了广泛的关注和大量的研究。关于半导体光学性能的研究大多数集中在实验和计算模拟。在理论方面,目前有量子限制理论和键序-键长-键强(BOLS)理论较为著名。但是这些理论模型中都存在有较多的自由变量,从而限制了这些理论模型的应用。因此建立一个可变参数少,且在全尺寸范围内都适用的理论模型有必要的。在本论文中,引入键数作为唯一变量来描述半导体纳米粒子的能隙和拉曼频率的尺度依赖。在纳米尺寸范围内,由于高表面能的影响,为了获得较稳定的结构,原子会聚集在一起形成新的结构来减小表面能。目前有很多关于纳米粒子形状的结构模型,例如切角八面体结构(TO)、二十面体(IH)、十面体(TH)等。因此用键数来描述纳米粒子的物理性能,不仅要考虑尺寸的影响,还要考虑到纳米粒子形状带来的影响。研究发现,一种特殊的切角八面体(Cubo)结构因在纳米尺寸具有较稳定的结构得到广泛的应用,尤其是有效的描述了结合能和熔点的尺度依赖的问题。因此本文采用Cubo结构来描述所研究的半导体纳米粒子的形状。本论文以IV族半导体Si、II-VI族半导体(Cd S、Cd Se、Zn S、Zn Se、Cd Te)、氧化物半导体(Sn O2、Ce O2)、III-V族半导体(In P)等纳米粒子为研究对象,采用热力学理论分别解析了能隙和拉曼频率随尺度的变化规律:1.建立了半导体纳米粒子能隙的尺度依赖模型,其中键数是所需要确定的唯一的变量。模型预测结果显示,随着尺度的降低能隙逐渐增大,并且当粒子尺度D5 nm时出现明显的增长趋势。该模型的预测结果与相应的实验结果和第一原理计算结果相吻合。在该模型中,纳米材料能隙Eg(D)的变化范围为Eg(?)≤Eg(D)2Eg(?),其中Eg(?)为块体材料的能隙。该模型解释了能隙随尺寸变化的原因在于原子键数逐渐减小,直接导致系统结合能的减弱,从而致使能隙增大。与同样是从能量角度出发的Yang等人的模型相比,发现当粒子尺度相同时,该模型预测的能隙值略小于Yang的模型,其原因在于在建立Cubo结构时,并未考虑纳米粒子表面空位和内部缺陷,然而本文所建立的能隙模型却相对其他理论模型更为简便、有效。2.通过解析配位数与原子热振幅随尺度的变化规律,建立了半导体纳米粒子拉曼频率的尺度依赖理论模型。在本模型中,键数仍然是唯一需要确定的变量。理论模型预测结果与一系列的半导体单质、化合物,以及半导体合金纳米粒子的实验和计算模拟结果能够很好的符合。研究发现,随着纳米粒子直径的减小,拉曼频率逐渐减小,并且在尺寸下限出现较快的下降趋势。半导体纳米粒子的红移现象,其原因在于随着尺寸降低,表面原子缺键所占的比例不断的增大,导致体系结合能降低,原子束缚能力降低,从而导致热振幅增大,振动频率减小,拉曼光谱出现红移。模型预测结果的合理性,也说明我们所建立的模型可以同时预测不同的半导体纳米粒子。因为键数是唯一变量,原则上我们所建立的理论模型也可扩展到其他维度的半导体纳米材料光电性能的预测。
[Abstract]:When the scale of the material enters the nanometer scale, it will show a different performance from the bulk material. For example, the semiconductor nanoparticles have special optical, electrical, magnetic, thermodynamic and other properties different from the block structure. This kind of material has an extremely important influence on the fields of photoelectric conversion, storage equipment, sensor, display technology and so on. Semiconductor nanomaterials have attracted wide attention and a lot of research. Most of the studies on optical properties of semiconductors are focused on experiments and computational simulations. In theory, the theory of quantum confinement and the bond order bond strength (BOLS) theory are more famous. However, there are many free variables in these theoretical models, so that there are many free variables in these theoretical models. The application of these theoretical models is limited. Therefore, it is necessary to establish a theoretical model with less variable parameters and a full size range. In this paper, the number of bond numbers is introduced as the only variable to describe the scale dependence of the energy gap and Raman frequency of semiconductor nanoparticles. In the nanoscale range, due to the shadow of the high surface energy In order to obtain a more stable structure, atoms gather together to form a new structure to reduce the surface energy. There are many structural models about the shape of the nanoparticles, such as the tangent eight - hedral structure (TO), twenty - hedron (IH), and ten - hedron (TH). Therefore, the physical properties of nanoparticles are described by the number of bonds, not only considering the effect of size. It is also necessary to take into account the effect of nanoparticle shape. It is found that a special structure of the tangent eight - hedron (Cubo) is widely used because of its relatively stable structure in nanoscale size, especially the scale dependence of binding energy and melting point. Therefore, the Cubo structure is used to describe the semiconductor. In this paper, IV semiconductors Si, II-VI semiconductors (Cd S, Cd Se, Zn S, Zn Se, Cd), oxide semiconductors, semiconductors and other nanoparticles are the research objects, and the energy gap and the Raman frequency variation with the scale are analyzed by thermodynamics theory: 1. the semiconductor nanoparticles are established. The size dependence model of the energy gap is the only variable which is required to determine the number of bonds. The model prediction results show that the gap gradually increases with the reduction of the scale, and there is an obvious growth trend when the particle size D5 nm. The prediction results of the model are in agreement with the corresponding experimental results and the first principle calculation results. The variation range of the energy gap Eg (D) of nanomaterials is Eg (?) < Eg (D) 2Eg (?), in which Eg (?) is the energy gap of the bulk material. The model explains that the reason for the gap with the size is that the number of atomic bonds decreases gradually, which directly leads to the weakening of the system binding energy, resulting in the increase of the energy gap. The model phase of Yang et al., which is also from the energy angle. It is found that when the particle size is the same, the predicted energy gap of the model is slightly less than that of the Yang model. The reason is that the surface vacancy and internal defects of the nanoparticles are not considered when the Cubo structure is established. However, the energy gap model established in this paper is more convenient than the other theoretical models, and the effective.2. is effective by analyzing the coordination number and the atomic thermal amplitude. In this model, the number of bonds is still the only variable which needs to be determined in this model. The results of the theoretical model prediction can be very good with the experimental and computational results of a series of semiconductors, compounds, and semiconductor nanoscale particles. It is found that with the decrease of the diameter of the nanoparticles, the Raman frequency decreases gradually and the lower limit of the size decreases. The reason for the red shift of semiconductor nanoparticles is that the proportion of the surface atoms is increasing with the decrease of the size, which leads to the reduction of the system binding and the reduction of the atomic binding capacity. It leads to the increase of the heat amplitude, the decrease of the vibration frequency and the red shift of the Raman spectrum. The model prediction results are reasonable. It also indicates that the model we have established can predict the different semiconductor nanoparticles at the same time. The number of keys is the only variable. In principle, the theoretical model we have established can also be extended to other dimensions of semiconductor Nana. Prediction of photoelectric properties of rice materials.

【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB383.1

【参考文献】