Institute of Mineral Engineering, Division of Materials Science and Engineering, Faculty of Georesources and Materials Engineering, RWTH Aachen University, 52064 Aachen, Germany.
Nanotechnology. 2016 Jul 1;27(26):265706. doi: 10.1088/0957-4484/27/26/265706. Epub 2016 May 20.
Silica is one of the most abundant materials in the Earth's crust and is a remarkably versatile and important engineering material in various modern science and technology. Recently, freestanding and well-ordered two-dimensional (2D) silica monolayers with octahedral (O-silica) building blocks were found to be theoretically stable by (Wang G et al 2015 J. Phys. Chem. C 119 15654-60). In this paper, by performing first-principles calculations, we systematically investigated the electronic and thermal transport properties of 2D O-silica and also studied how these properties can be tuned by simple mechanical stretching. Unstrained 2D O-silica is an insulator with an indirect band gap of 6.536 eV. The band gap decreases considerably with bilateral strain up to 29%, at which point a semiconductor-metal transition occurs. More importantly, the in-plane thermal conductivity of freestanding 2D O-silica is found to be unusually high, which is around 40 to 50 times higher than that of bulk α-quartz and more than two orders of magnitude higher than that of amorphous silica. The thermal conductivity of O-silica decreases by almost two orders of magnitude when the bilateral stretching strain reaches 10%. By analyzing the mode-dependent phonon properties and phonon-scattering channel, the phonon lifetime is found to be the dominant factor that leads to the dramatic decrease of the lattice thermal conductivity under strain. The very sensitive response of both band gap and phonon transport properties to the external mechanical strain will enable 2D O-silica to easily adapt to the different environment of realistic applications. Our study is expected to stimulate experimental exploration of further physical and chemical properties of 2D silica systems, and offers perspectives on modulating the electronic and thermal properties of related low-dimensional structures for applications such as thermoelectric, photovoltaic, and optoelectronic devices.
二氧化硅是地壳中最丰富的物质之一，是各种现代科学技术中非常通用和重要的工程材料。最近，通过（Wang G 等人，2015 年 J. Phys. Chem. C 119 15654-60）的计算发现，具有八面体（O-二氧化硅）构筑块的独立有序二维（2D）二氧化硅单层在理论上是稳定的。在本文中，通过执行第一性原理计算，我们系统地研究了 2D O-二氧化硅的电子和热输运性质，并研究了这些性质如何通过简单的机械拉伸进行调节。未拉伸的 2D O-二氧化硅是一种具有 6.536 eV 间接带隙的绝缘体。在双边应变高达 29%时，带隙会显著减小，此时会发生半导体-金属转变。更重要的是，发现独立的 2D O-二氧化硅的面内热导率异常高，约为体相α-石英的 40 到 50 倍，比非晶态二氧化硅高两个数量级以上。当双边拉伸应变达到 10%时，O-二氧化硅的热导率下降近两个数量级。通过分析模态相关的声子性质和声子散射通道，发现声子寿命是导致应变下晶格热导率急剧下降的主要因素。带隙和声子输运性质对外界机械应变的敏感响应将使 2D O-二氧化硅能够轻松适应实际应用的不同环境。我们的研究有望激发对二维硅系统进一步物理和化学性质的实验探索，并为相关低维结构的电子和热性能的调节提供了思路，以应用于热电、光伏和光电等器件。
