Novel Functional Materials - An Optical Perspective

材料科学建立在发现和操纵具有能量转换和存储、电荷-自旋耦合和多铁性等功能特征的新材料的基础上。这些特性可用于光伏、光电子学和自旋电子器件。石墨烯的发现及其因其高机械强度、优异的导热和导电性以及光学透明度而产生的特殊多功能重新点燃了人们对其他二维材料的兴趣，如层状氧化物、硫化物和范德华偶合化合物。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。我们选择关注几种新材料，其中包括：(1)2D层状硫属化合物(I)β-As2Te3，其结构与拓扑绝缘体Bi2Te3相同，以及(Ii)失配(PbSe)-(-NbSe2)，其中层之间的不可公度性可能导致独特的应用，(2)具有多铁性的DyCrO_3薄膜，以及(3)2D层状卤化物双钙钛矿(BA)2CsAgBiBr7(BA=正丁基铵)，其3D变体Cs2AgBiBr6具有光伏功能和几个未知的相变。我们的策略是通过掺杂和插层来操纵它们的性质，以便表征和研究它们的演变，最终适合于应用。我们的主要重点将是它们对光的响应，以及为表征目的而评估的其他性质。硫化物家族中的材料通常具有带隙的基态，如超导或电荷密度波。对这些态的光学性质的研究是严格的，因为它必须在挑战低温和能量的实验中进行。我们的光学设备是专门为处理这一问题而设置的。我们打算进一步扩展我们的系统在磁场存在的情况下进行测量的能力，因为我们打算研究DyCrO_3的磁光性质，并在我们正在研究的2D层状材料中引入磁性掺杂。我们还计划增加我们可以在非常低的温度下测量的光谱波长范围，方法是使用我们通过电化学腐蚀硅使其多孔而创建的滤光片。滤光片的工作原理是散射波长小于孔径的光。通过改变硅掺杂、取向和刻蚀工艺参数，我们可以改变孔的大小，从而改变滤光片的截止波长。通过随时间变化电流，我们可以制造多孔硅多层器件，如布拉格反射器和微腔，应用于检测溶剂、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.