Browsing by Author "Tian, Zhipeng"

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    Fundamental mechanisms of focused ion beam guided anodization
    Tian, Zhipeng; Lu, Kathy; Chen, Bo (American Institute of Physics, 2010-11-01)
    This paper is focused on understanding the fundamental mechanisms of focused ion beam guided anodization and the unique capabilities of generating new patterns based on such an understanding. By designing proper interpore distance, pore arrangement, and pore shape during focused ion beam patterning, nonspherical pore shape and nonhexagonal patterns can be obtained by further anodization. The electrical field and the mechanical stress field around each focused ion beam patterned concave dictate the pore formation and growth. The oxide barrier layer thickness and shape around the focused ion beam guided pores affect new pore formation and the meshing of different size pores. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3500513]
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    Magnetoelectric quasi-(0-3) nanocomposite heterostructures
    Li, Yanxi; Wang, Zhongchang; Yao, Jianjun; Yang, Tiannan; Wang, Zhiguang; Hu, Jia-Mian; Chen, Chunlin; Sun, Rong; Tian, Zhipeng; Li, Jiefang; Chen, Long-Qing; Viehland, Dwight D. (Nature Publishing Group, 2015-12-01)
    Magnetoelectric composites of magnetic and ferroelectric components are promising for their use in applications such as information storage. Here, the authors find that magnetic quasiparticles embedded in a ferroelectric film matrix show promising properties compared to the usual thin-film architectures.
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    Nanopore/Nanotube Pattern Formation through Focused Ion Beam Guided Anodization
    Tian, Zhipeng (Virginia Tech, 2010-12-01)
    Anodization is a kind of method that can produce oxide layer in a large area and on flexible shaped metals. In some specific conditions, anodic oxide layers exhibit interesting nanopore/nanotube structures. In this work, focused ion beam patterning method is introduced to general anodization, aiming to make highly ordered anodic porous alumina and titania nanotubes. Focused ion beam guided porous anodic alumina is carried out by pre-designing hexagonal and square guiding patterns with different interpore distances on well electropolished Al foil before anodization. After anodization, the guiding interpore distance is found to affect the new pores' locations and shapes. Two important elements, electrical field and mechanical stress, are discussed for the development of the guiding pores and the generation of new pores. Based on the proposed pore growth mechanism, novel patterns, non-spherical pores, and large patterns across the grain boundaries are successfully produced. The research on focused ion beam guided anodic titania nanotubes begins with surface polishing. The influence of four polishing conditions, as-received, chemically polished, mechanically polished, and electropolished samples, are investigated. A polished smooth sample provides a desired surface for focused ion beam guided anodization. Hexagonal guiding patterns with different interpore distances are created on Ti surface. Ordered nanotube arrays are produced, and the structure of the anodized guiding pattern is identified.
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    Sapphire Fiber Optic Sensor for High Temperature Measurement
    Tian, Zhipeng (Virginia Tech, 2018-01-10)
    This dissertation focuses on developing new technologies for ultra-low-cost sapphire fiber-optic high-temperature sensors. The research is divided into three major parts, the souceless sensor, the simple Fabry-Perot (F-P) interrogator, and the sensor system. Chapter 1 briefly reviews the background of thermal radiation, fiber optic F-P sensors, and F-P signal demodulation. The research goal is highlighted. In Chapter 2, a temperature sensing system is introduced. The environmental thermal radiation was used as the broadband light source. A sapphire wafer F-P temperature sensor head was fabricated, with an alumina cap designed to generate a stable thermal radiation field. The radiation-induced optical interference pattern was observed. We demodulated the temperature sensor by white-light-interferometry (WLI). Temperature resolution better than 1°C was achieved. Chapter 3 discusses a novel approach to demodulate an optical F-P cavity at low-cost. A simple interrogator is demonstrated, which is based on the scanning-white-light-interferometry (S-WLI). The interrogator includes a piece of fused silica wafer, and a linear CCD array, to transform the F-P demodulation from the optical frequency domain to the spatial domain. By using the light divergence of an optical fiber, we projected a tunable reference F-P cavity onto an intensity distribution along a CCD array. A model for S-WLI demodulation was established. Performance of the new S-WLI interrogator was investigated. We got a good resolution similar to the well-known traditional WLI. At last, we were able to combine the above two technologies to a sapphire-wafer-based temperature sensor. The simple silica wafer F-P interrogator was optimized by focusing light to the image sensor. This approach improves the signal to noise ratio, hence allows the new integrator to work with the relatively weak thermal radiation field. We, therefore, proved in the experiment, the feasibility of the low-cost sourceless optical Fabry-Perot temperature sensor with a simple demodulation system.