Novel Functional Materials - An Optical Perspective

点击翻译按钮获取中文摘要

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.