【作者】 周琳；

【导师】 柴常春； 张冰；

【作者基本信息】 西安电子科技大学 ， 工程硕士（专业学位）， 2022， 硕士

【摘要】 碳元素能形成无穷无尽、不同形式的同素异形体,这使得它在一众化学元素中显得尤为独特。自古以来,碳元素就以各种形式被广泛应用,在现代科学的加持下,人类更是有了能够随心所欲操纵晶格结构的能力,这更加拓宽了碳元素的应用场景。以金刚石为代表的超硬碳材料便是其中极具代表性的一类,所谓超硬材料,指的是维氏硬度大于40 GPa的材料,正如它们的名字所述,这些材料的共同特点就是硬度极高。这一特性使得该类材料在航空航天、军工、冶金等高压极端环境中展现出比其他材料更强的应用优势。随着整个集成电路产业的快速发展,寻找新的、具有更加优异性能的新型半导体材料已是大势所趋,超硬特性毫无疑问是人们所追求的优异性能之一。因此,本文在新型碳基超硬半导体材料的合成与应用方面做了一些基础性研究,主要完成的工作如下:(1)通过手动构造的方法,以sp~3杂化的方式,搭建起了一个具有32个碳原子的笼状结构,将该笼状结构在立体空间内堆叠排列从而设计出了一个具有Immm空间群的晶体型碳同素异形体,将其命名为o I20-carbon。经过了一系列第一性原理相关的仿真和计算,该晶体结构的热力学、力学和动力学稳定性得到了验证。该晶体结构在100 GPa的高压或1000 K的高温下都能够保持稳定。在力学特性方面,该各向异性的晶体结构具有46.62 GPa的维氏硬度,值得注意的是,在拥有超硬特性的前提下,它还具有与大多数超硬晶体相比更低的密度,仅为2.88 g/cm~3。在研究该晶体结构的电子特性时,采用HSE06方法的仿真计算结果显示它的能带宽度为4.55 e V,这意味着该晶体结构是具有超宽带隙的半导体材料。此外,也对该结构的电子有效质量进行了计算。以上种种优异的仿真和计算结果说明该结构能够经受得住高温、高压等极端环境,且相比于之前的同类半导体超硬碳材料更加轻便。(2)同时具有高硬度与低密度的半导体材料是十分罕见的,因此在完成第一项工作的基础上,再次通过手动构造的方法,设计出了一个更为复杂的具有Cmmm空间群的全sp~3杂化的晶体碳同素异形体,将其命名为o S44-carbon。该晶体结构由两种完全不同的笼状结构和一个六棱柱结构以特定的堆叠方式组成。同样对该晶体结构进行了第一性原理的相关计算与仿真,优化之后的晶体结构具有良好的热力学、力学和动力学稳定性,能够在60 GPa的高压以及1000 K的高温下保持稳定。计算得到的结果显示它的维氏硬度达到了55.93 GPa,而密度仅为2.77 g/cm~3,这些特性相较于第一种设计出的晶体结构相比有较大的提升。同时,采用HSE06方法的仿真计算结果显示它的能带宽度为4.81 e V,这远远超过了超宽禁带半导体的带隙要求。此外,对该晶体结构的电子有效质量在不同方向上进行了数值上的计算。最后,还在加压情况下观察查到了导带底位置的变化,这在之前的类似研究中也是十分少见的。这些新设计的半导体超硬碳材料能够在极端环境下保持稳定,且具有比同类更低的密度,两种晶体中的笼状结构中的空腔则可能能够在吸附氢等小分子上做出贡献。这些出色的特性使得这些晶体结构未来在航空航天、便携电子器件、高压、宽禁带半导体器件等方向有巨大的潜在应用价值。更多还原

【Abstract】 Carbon can form an ocean of different forms of allotropes,making it a unique one among all the chemical elements.Carbon has been widely used in various forms through the ages.With the development of modern science,humans could manipulate the lattice structure at will,which further broadens the application scenarios of carbon.The superhard carbon materials represented by diamond is one of the most representative ones.Superhard materials are those with a Vickers hardness of more than 40 GPa,and as their name suggests,the common feature of these materials is that they are extremely hard.This feature makes this type of material show better application advantages than other materials in extreme environments such as aerospace,military industry,metallurgy and other high-pressure scenarios.With the rapid development of the integrated circuit industry,it has become an irresistible trend to search for new semiconductor materials with better performance,and the superhard characteristics is undoubtedly one of the outstanding performances that people pursue.Therefore,this paper has done some basic research on the synthesis and application of new carbon-based superhard semiconductor materials.The main work is as follows:(1)A cage-like structure with 32 carbon atoms was built by manual method based on sp~3hybridization.The cage-like structure was stacked and arranged in the three-dimensional space to design a crystalline carbon allotrope processing Immm space group,named as o I20-carbon.The thermodynamic,mechanical and dynamic stability of o I20-carbon was verified by first-principle calculations and simulations.o I20-carbon can maintain stable at high pressure of 100 GPa or high temperature of 1000 K.In terms of mechanical properties,this anisotropic crystal structure has a Vickers hardness of 46.62 GPa,and it is worth noting that it also has a lower density than most superhard crystals under the premise of having superhard property,only 2.88 g/cm~3.When studying the electronic properties of the crystal structure,the simulation results using the HSE06 method show that the bandwidth of o I20-carbon is 4.55 e V,which means that o I20-carbon is a semiconductor material with ultra-wide bandwidth.In addition,the electronic effective mass of o I20-carbon was calculated in this paper.The above excellent simulation and calculation results show that o I20-carbon can withstand extreme environments such as high temperature and high pressure,and is lighter than the previous similar semiconductor superhard carbon materials.(2)Semiconductor materials with both high hardness and low density at the same time are very rare.Based on the first work,a more complex fully sp~3 hybrid crystalline carbon allotrope with Cmmm space group was designed by manual method,named as o S44-carbon.The crystal structure consists of two completely different cage-like structures and a hexagonal prismatic structure in a specific stacking pattern.The optimized crystal structure has good thermodynamic,mechanical and dynamic stability,and can be stable at high pressure of 60 GPa and high temperature of 1000 K.The calculated results show that its Vickers hardness reaches 55.93 GPa,and its density is only 2.77 g/cm~3,these indicators are greatly improved compared with the first designed crystal structure.While,the simulation results using HSE06 method show that its bandwidth is 4.81 e V,which reaches the bandwidth criterion of ultra-wide bandwidth semiconductors.In addition,the effective mass of the electron in the crystal structure is numerically calculated in different directions.Finally,the change of the position of the bottom of the conduction band under pressure was observed and described,which is very rare in previous similar studies.These newly designed semiconducting superhard carbon materials are stable in extreme environments and have lower densities than their counterparts,and the cavities in the cage-like structures in the two crystals may be able to be used to adsorb small molecules such as hydrogen.These excellent properties make these crystal structures have great potential applications in aerospace,portable electronic devices,high voltage and wide bandwidth semiconductor devices and other directions in the future.更多还原