本文選題：尺寸效應(yīng) + 熱力學(xué)　； 參考：《太原理工大學(xué)》2017年碩士論文

【摘要】：當(dāng)材料尺度進(jìn)入到納米量級(jí),就會(huì)表現(xiàn)出與塊體材料不同的性能。例如半導(dǎo)體納米粒子就具有特殊的光學(xué)、電學(xué)、磁學(xué)、熱力學(xué)等不同于塊體結(jié)構(gòu)的性能,這類材料對(duì)光電轉(zhuǎn)換、存儲(chǔ)設(shè)備、傳感器、顯示技術(shù)等領(lǐng)域有著極其重要的影響。因此半導(dǎo)體納米材料引起了廣泛的關(guān)注和大量的研究。關(guān)于半導(dǎo)體光學(xué)性能的研究大多數(shù)集中在實(shí)驗(yàn)和計(jì)算模擬。在理論方面,目前有量子限制理論和鍵序-鍵長(zhǎng)-鍵強(qiáng)(BOLS)理論較為著名。但是這些理論模型中都存在有較多的自由變量,從而限制了這些理論模型的應(yīng)用。因此建立一個(gè)可變參數(shù)少,且在全尺寸范圍內(nèi)都適用的理論模型有必要的。在本論文中,引入鍵數(shù)作為唯一變量來(lái)描述半導(dǎo)體納米粒子的能隙和拉曼頻率的尺度依賴。在納米尺寸范圍內(nèi),由于高表面能的影響,為了獲得較穩(wěn)定的結(jié)構(gòu),原子會(huì)聚集在一起形成新的結(jié)構(gòu)來(lái)減小表面能。目前有很多關(guān)于納米粒子形狀的結(jié)構(gòu)模型,例如切角八面體結(jié)構(gòu)(TO)、二十面體(IH)、十面體(TH)等。因此用鍵數(shù)來(lái)描述納米粒子的物理性能,不僅要考慮尺寸的影響,還要考慮到納米粒子形狀帶來(lái)的影響。研究發(fā)現(xiàn),一種特殊的切角八面體(Cubo)結(jié)構(gòu)因在納米尺寸具有較穩(wěn)定的結(jié)構(gòu)得到廣泛的應(yīng)用,尤其是有效的描述了結(jié)合能和熔點(diǎn)的尺度依賴的問(wèn)題。因此本文采用Cubo結(jié)構(gòu)來(lái)描述所研究的半導(dǎo)體納米粒子的形狀。本論文以IV族半導(dǎo)體Si、II-VI族半導(dǎo)體(Cd S、Cd Se、Zn S、Zn Se、Cd Te)、氧化物半導(dǎo)體(Sn O2、Ce O2)、III-V族半導(dǎo)體(In P)等納米粒子為研究對(duì)象,采用熱力學(xué)理論分別解析了能隙和拉曼頻率隨尺度的變化規(guī)律:1.建立了半導(dǎo)體納米粒子能隙的尺度依賴模型,其中鍵數(shù)是所需要確定的唯一的變量。模型預(yù)測(cè)結(jié)果顯示,隨著尺度的降低能隙逐漸增大,并且當(dāng)粒子尺度D5 nm時(shí)出現(xiàn)明顯的增長(zhǎng)趨勢(shì)。該模型的預(yù)測(cè)結(jié)果與相應(yīng)的實(shí)驗(yàn)結(jié)果和第一原理計(jì)算結(jié)果相吻合。在該模型中,納米材料能隙Eg(D)的變化范圍為Eg(?)≤Eg(D)2Eg(?),其中Eg(?)為塊體材料的能隙。該模型解釋了能隙隨尺寸變化的原因在于原子鍵數(shù)逐漸減小,直接導(dǎo)致系統(tǒng)結(jié)合能的減弱,從而致使能隙增大。與同樣是從能量角度出發(fā)的Yang等人的模型相比,發(fā)現(xiàn)當(dāng)粒子尺度相同時(shí),該模型預(yù)測(cè)的能隙值略小于Yang的模型,其原因在于在建立Cubo結(jié)構(gòu)時(shí),并未考慮納米粒子表面空位和內(nèi)部缺陷,然而本文所建立的能隙模型卻相對(duì)其他理論模型更為簡(jiǎn)便、有效。2.通過(guò)解析配位數(shù)與原子熱振幅隨尺度的變化規(guī)律,建立了半導(dǎo)體納米粒子拉曼頻率的尺度依賴?yán)碚撃Ｐ汀Ｔ诒灸Ｐ椭?鍵數(shù)仍然是唯一需要確定的變量。理論模型預(yù)測(cè)結(jié)果與一系列的半導(dǎo)體單質(zhì)、化合物,以及半導(dǎo)體合金納米粒子的實(shí)驗(yàn)和計(jì)算模擬結(jié)果能夠很好的符合。研究發(fā)現(xiàn),隨著納米粒子直徑的減小,拉曼頻率逐漸減小,并且在尺寸下限出現(xiàn)較快的下降趨勢(shì)。半導(dǎo)體納米粒子的紅移現(xiàn)象,其原因在于隨著尺寸降低,表面原子缺鍵所占的比例不斷的增大,導(dǎo)致體系結(jié)合能降低,原子束縛能力降低,從而導(dǎo)致熱振幅增大,振動(dòng)頻率減小,拉曼光譜出現(xiàn)紅移。模型預(yù)測(cè)結(jié)果的合理性,也說(shuō)明我們所建立的模型可以同時(shí)預(yù)測(cè)不同的半導(dǎo)體納米粒子。因?yàn)殒I數(shù)是唯一變量,原則上我們所建立的理論模型也可擴(kuò)展到其他維度的半導(dǎo)體納米材料光電性能的預(yù)測(cè)。
[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.

【學(xué)位授予單位】：太原理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TB383.1

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