Plasma Processing of Sapphire Nanostructures for Low-Loss Multilayer Composites
Abstract
The proposed research aims to investigate the plasma processing of sapphire and create surface nanostructures with well-defined geometry and order. Sapphire and other aluminum oxide materials have high optical transmission, high mechanical hardness, strength, and toughness, and are attractive for armor material, nanophotonics, and optoelectronics. However, they are also chemically inert and can be difficult to micromachining, especially for high density features. This research will examine the formation and physical/chemical etching dynamics of sapphire nanostructures. We will develop novel lithographic and plasma processes to enable precise control of geometry and order. Furthermore, we will use the sapphire nanostructures as a basic building block to suppress reflection losses, iridescence, and scattering to enhance transmission of multilayer composites. The broadband and wide-angle optical transmission of such sapphire-polymer composite will be characterized and compared with theoretical models. This work can lead to lightweight transparent armor with enhanced toughness and broadband optical transmission, and contribute towards the ArmyÕs mission in blast/projectile mitigation. The core scientific motivation of this work is to investigate the plasma processing of sapphire nanostructures with well-defined order and nanoscale features. Sapphire has many inherent advantages in physical properties owing to its chemical and thermal stability. However, these properties also result in sapphire being difficult to etch, making the fabrication of sapphire nanostructures challenging. Sapphire also has high refractive index, therefore losses due to Fresnel reflection and total internal reflection can be problematic. Our scientific hypothesis is that the plasma etching of sapphire nanostructures can be controlled by examining the chemical and physical etch mechanisms at the nanoscale. This effort will enable precise control on the order, feature, and profile of the sapphire nanostructures, which can be used to better mitigate optical losses and iridescent effects in a nanostructured gradient-index sapphire-polymer composite. This work will enable the creation of high-fidelity sapphire nanostructures, which enables effective manipulation of local light propagation and can lead to multifunctional nanostructured composites with better optical and mechanical properties. There are key technological advantages of the proposed methodology: (1) The plasma processing of sapphire and understanding in etch mechanisms can be potentially translated to other alumina-based armor materials such as AlON and spinel. (2) The geometry of the sapphire nanostructure can be defined with high precision and periodic order. This enables effective mitigation of light reflection and scattering to reduce optical haze and increase transmission. (3) The proposed fabrication technique is parallel process and suitable for mechanical testing. As oppose to other lithography methods, the proposed technique can fabricate structure over large enough area for macroscale characterization. These advantages can enable complex nanostructures that are difficult for biological organisms to synthesize naturally, and lead to materials with bio-improved properties in multiple physical domains. The result of this work will allow better understand of plasma processing of sapphire nanostructures and their optical properties. The modeling, design, and experimental tools developed in this research will enable the engineering of hierarchical multilayer composite with bio-improved performances in multiple physical domains. This work will support and contribute to the ArmyÕs mission in lightweight transparent armors with broadband and wide-angle optical clarity.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Sep 11, 2018
- Source ID
- W911NF1710591
Entities
People
- Chih-Hao Chang
Organizations
- Army Contracting Command
- North Carolina State University
- United States Army