Novel Functional Materials - An Optical Perspective

材料科学是建立在发现和操纵新材料的功能特性，如能量转换和存储，电荷-自旋耦合，和多铁性。这些性质可以在光伏、光电和自旋电子器件中利用。石墨烯的发现及其由其高机械强度、优异的导热性和导电性以及光学透明性引起的特殊的多功能性重新点燃了对其他二维材料如层状氧化物、硫属化物和货车范德华耦合化合物的兴趣。作为研究量子材料光学性质的研究计划的一部分，我们建议合成和研究低维功能材料的结构，热，电，磁和光学性质。我们选择专注于几种新型材料，包括：（1）2D层状硫属化物（i）β-As 2 Te 3，其结构上与拓扑绝缘体Bi 2 Te 3相同，和（ii）失配（PbSe）-（-NbSe 2），其中层之间的不相容性可导致独特的应用，（2）具有多铁性行为的DyCrO 3薄膜，和（3）2D-层状卤化物双钙钛矿（BA）2CsAgBiBr 7（BA=正丁基铵），其3D变体Cs2 AgBiBr 6具有光伏功能并表现出几种尚未理解的相变。我们的策略是通过掺杂和插层来操纵性能，以表征和研究它们的演变，最终适应应用。我们的主要重点将是对他们的响应与其他性能的表征目的进行评估。硫族化物家族中的材料通常具有带隙基态，例如超导性或电荷密度波。在这些状态下的光学性质的调查是严格的，因为它必须在实验上具有挑战性的低温和低能量进行。我们的光学仪器是专门用来处理这个问题的。我们打算进一步扩展我们的系统在磁场存在下进行测量的能力，因为我们打算研究DyCrO 3的磁光特性，并在我们正在研究的2D层状材料中引入磁性掺杂。我们还计划增加光谱波长范围，我们可以在非常低的温度下测量，通过使用我们通过电化学蚀刻硅使其多孔而创建的过滤器。过滤器通过散射波长短于孔隙尺寸的光来工作。通过改变硅掺杂、取向和蚀刻工艺的参数，我们可以改变孔的尺寸，从而改变滤波器的截止波长。通过改变电流作为时间的函数，我们可以生产多孔硅多层器件，如布拉格反射器和微腔，用于检测溶剂，农药和生物材料的传感器。

Materials science is built on the discovery and manipulation of novel materials with functional characteristics such as energy conversion and storage, charge--spin coupling, and  multi-ferroicity. These properties can be exploited in photovoltaic, optoelectronic and spintronic devices. The discovery of graphene and its exceptional multi-functionality arising from its high mechanical strength, excellent heat and electrical conductivity, and optical transparency has re--ignited interest in other two dimensional materials such as layered oxides, chalcogenides, and van der Waals coupled compounds. As part of a research program established to study the optical properties of quantum materials we propose to synthesize and investigate the structural, thermal, electrical, magnetic, and optical properties of low dimensional functional materials. We have chosen to focus on several novel materials which include: (1) 2D layered chalcogenides (i) beta--As2Te3, which is structurally identical to topological insulator Bi2Te3, and (ii) misfit (PbSe)-(-NbSe2),  where incommensurability between layers could lead to unique applications, (2) thin films of DyCrO3 with multiferroic behaviour,  and (3) 2D-layered Halide double perovskite (BA)2CsAgBiBr7 (BA=n-butylammonium), whose 3D variant Cs2AgBiBr6  has photovoltaic functionality and exhibits several as yet not understood phase transitions. Our strategy is to manipulate the properties via doping and intercalation in order to characterize and study their evolution towards eventual tailoring to applications. Our main emphasis will be on their response to light with other properties evaluated for characterization purposes. Materials within the chalcogenide family typically have gapped ground states such as superconductivity or a charge density wave. The investigation of the optical properties in these states is exacting because it must be conducted at experimentally challenging low temperatures and energies. Our optical apparatus is uniquely set up to handle this. We intend to further extend the capabilities of our system to perform measurements in the presence of a magnetic field since we intend to investigate the magneto--optical properties of DyCrO3 and to introduce magnetic doping in the 2D layered materials we are investigating. We also plan to increase the spectral wavelength range that we can measure at very low temperature by using filters that we create by electro-chemically etching silicon to make it porous. The filters work by scattering light of wavelengths shorter than the pore dimension. By varying the silicon doping, orientation and parameters of the etching process we can change the size of the pores which changes the cutoff wavelength of the filter. By varying current as a function of time we can produce porous silicon multi-layer devices such as  Bragg reflectors and micro-cavities with applications in sensors to detect solvents, pesticides, and biological material.