Manipulating Light at Micro- and Nano-Scale: Enable Photonic Structures Toward Real-World Applications

Recent advances in fabrication and processing methods have spurred many breakthroughs in the field of nano- and micro-structures that provide novel ways of manipulating light interaction in a well controllable manner, thereby enabling various innovative applications. In this dissertation, new photonic design concepts and materials featuring high performance and long-term stability are investigated for bridging the gap between the research and the real-world applications. Firstly, angle-insensitive and high-purity structural color filters based on one-dimensional layered structures that are suitable for mass-production are studied. Various scenarios including reducing the layer number and depositing the whole device via an all-solution process have been proposed to simplify the fabrication, thereby lowering the manufacturing cost. The proposed structures offer significant advantages over existing colorant-based filters in terms of high efficiency, slim dimension, and being free from photobleaching. They have been successfully adapted into practical applications including decorative paints, visibly-opaque but near-infrared-transmitting camouflage coatings, and highly-efficient colored photovoltaics. As a special color, ‘black’ has been studied separately based on ultrabroadband absorbers that are achieved by simultaneously exciting multiple absorption resonances. It can significantly enhance the efficiency of energy harvesting and conversion in various applications. In addition, optical designs are incorporated into vehicle interiors, opening up a new path to the extensive use of optics in automobiles: Anti-glare colored dashboard with the potential for high-resolution dashboard displays are demonstrated with micro-scale lenticular lenses; Invisible vehicle pillars for safe driving are realized with compact optical cloaks using different optical components, including polarizers and mirrors. The next part is the research into a cost-effective and easy-to-fabricate method for flexible transparent electrodes employing ultrathin (thickness < 10 nm), ultra-smooth (roughness < 1 nm), and low-loss copper-doped silver. This novel silver alloy requires only room-temperature deposition and presents outstanding optical and electrical properties, mechanical flexibility, and environmental stability, which are greatly desired in potential high-performance flexible optoelectronic devices. Lastly, other optical structures inspired by methods employed in above researches that have impactful applications, including retro-reflective particles that can be embedded in transparent glasses for light detection and ranging and omnidirectional planar solar concentrators based on curved micro-reflectors, are briefly discussed. All the strategies and methodologies proposed here could bring optical researches out of the labs and open up more opportunities for further advancement.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/149791/1/jichg_1.pd

Enhancing the Purity of Reflective Structural Colors with Ultrathin Bilayer Media as Effective Ideal Absorbers

Structural colors of high purity and brightness are desired in various applications. This study presents a general strategy of selecting the appropriate material and thickness of each layer to create high‐purity reflective colors in a classic asymmetric Fabry–Pérot cavity structure based on a dielectric–absorber–dielectric–metal multilayered configuration. Guided by the derived complex refractive index of the ideal absorber layer, an effective absorbing bilayer medium consisting of two ultrathin lossy films is used to improve the color purity of reflective colors by suppressing the reflection of its complementary colors with the enhanced optical absorption. Highly pure red, green, and blue reflective colors are designed and experimentally demonstrated employing different effective bilayer absorbers. Due to the high refractive index of the dielectric material, the colored structures exhibit great angle‐robust appearance (blue and red colors are up to ±60°, and green color is up to ±45°). The generalized design principles and the proposed method of using effective bilayer absorbers open up new avenues for realizing high‐purity thin‐film structural colors with more materials selections.A general strategy for the material and layer thickness selection to produce high‐purity reflective colors in a dielectric–absorber–dielectric–metal multilayered structure is presented. The color purity of red, green and blue reflective colors can be significantly improved by designing different effective absorbing bilayer media to enhance the optical absorption over a broad wavelength range of nontargeted colors.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151998/1/adom201900739-sup-0001-S1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151998/2/adom201900739.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151998/3/adom201900739_am.pd

High‐Purity Hybrid Structural Colors by Enhancing Optical Absorption of Organic Dyes in Resonant Cavity

This work presents a novel approach of incorporating an ultrathin dye film into a classic dielectric‐absorber‐dielectric‐metal resonator configuration for generating high‐purity reflective structural colors. Utilizing a thin film of organic dye having the same color as the targeted reflection color as a part of the cavity layer in the structure, its absorption at complementary color wavelengths is significantly enhanced due to the strong cavity resonances, hence reflection at the unwanted wavelengths strongly suppressed, leading to the improved purity of the desired reflective color. This design principle can be applied to create essentially all colors, and is demonstrated by experiment to produce high‐purity blue and red colors. In addition, the fabricated device exhibits outstanding stability under UV exposure without additional protections compared to traditional organic pigments. The proposed method in this work largely simplifies the design process of high‐purity structural colors, which paves the way for more potential applications in various fields.A simple approach that incorporates an ultrathin dye film into a classic dielectric‐absorber‐dielectric‐metal multilayered structure is presented to produce high‐purity reflective colors. The enhanced optical absorptions of the colored dye layer as a result of the strong cavity resonances can effectively suppress the reflection within the unwanted wavelength range, thus significantly improving the purity of the desired reflective colors.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155972/1/adom202000317.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155972/2/adom202000317_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155972/3/adom202000317-sup-0001-SuppMat.pd

Angular‐ and polarization‐independent structural colors based on 1D photonic crystals

Wide‐angle, polarization‐independent structural reflective colors from both directions based on a one‐dimensional photonic crystal are demonstrated. Our device produces a distinct and saturated color with high angular tolerant performance up to ±70° for any polarization state of an incident light wave, which is highly desirable for a broad range of research areas. Moreover, the purity of the color and luminous intensity of the proposed device are improved as compared to conventional colorant‐based color filters and colloidal glasses. The present approach may have the potential to replace existing color filters and pigments and pave the way for various applications, including color displays and image sensor technologies.A 1D photonic crystal‐based structural reflective color with angle‐invariant, polarization‐independent, and high‐purity characteristics is presented. Our proposed device is capable of creating a distinctive color that is insensitive with respect to the angle of incidence up to ±70° regardless of the polarization state of incident light. The presented approach can open the door to numerous applications, such as colored display technologies and imaging sensors.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111776/1/lpor201500029.pd

Angleâ Insensitive and CMOSâ Compatible Subwavelength Color Printing

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134900/1/adom201600287_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134900/2/adom201600287.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134900/3/adom201600287-sup-0001-S1.pd

Transparent Perfect Microwave Absorber Employing Asymmetric Resonance Cavity

The demand for high‐performance absorbers in the microwave frequencies, which can reduce undesirable radiation that interferes with electronic system operation, has attracted increasing interest in recent years. However, most devices implemented so far are opaque, limiting their use in optical applications that require high visible transparency. Here, a scheme is demonstrated for microwave absorbers featuring high transparency in the visible range, near‐unity absorption (≈99.5% absorption at 13.75 GHz with 3.6 GHz effective bandwidth) in the Ku‐band, and hence excellent electromagnetic interference shielding performance (≈26 dB). The device is based on an asymmetric Fabry–Pérot cavity, which incorporates a monolayer graphene and a transparent ultrathin (8 nm) doped silver layer as absorber and reflector, and fused silica as the middle dielectric layer. Guided by derived formulism, this asymmetric cavity is demonstrated with microwaves near‐perfectly and exclusively absorbs in the ultrathin graphene film. The peak absorption frequency of the cavity can be readily tuned by simply changing the thickness of the dielectric spacer. The approach provides a viable solution for a new type of microwave absorber with high visible transmittance, paving the way towards applications in the area of optics.A general strategy is presented to design a new type of microwave absorber based on an asymmetric Fabry–Pérot resonant cavity by employing monolayer graphene, transparent spacer, and ultrathin doped Ag film. This asymmetric cavity is demonstrated with microwaves near‐perfectly and exclusively absorbs in the ultrathin graphene layer at resonances and maintains high visible transmittance.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151816/1/advs1299-sup-0001-S1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151816/2/advs1299.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151816/3/advs1299_am.pd

Enhanced Light Utilization in Semitransparent Organic Photovoltaics Using an Optical Outcoupling Architecture

Buildingâ integrated photovoltaics employing transparent photovoltaic cells on window panes provide an opportunity to convert solar energy to electricity rather than generating waste heat. Semitransparent organic photovoltaic cells (STâ OPVs) that utilize a nonfullerene acceptorâ based nearâ infrared (NIR) absorbing ternary cell combined with a thin, semitransparent, high conductivity Cuâ Ag alloy electrode are demonstrated. A combination of optical outcoupling and antireflection coatings leads to enhanced visible transmission, while reflecting the NIR back into the cell where it is absorbed. This combination of coatings results in doubling of the light utilization efficiency (LUE), which is equal to the product of the power conversion efficiency (PCE) and the average photopic transparency, compared with a conventional semitransparent cell lacking these coatings. A maximum LUE = 3.56 ± 0.11% is achieved for an STâ OPV with a PCE = 8.0 ± 0.2% at 1 sun, reference AM1.5G spectrum. Moreover, neutral colored STâ OPVs are also demonstrated, with LUE = 2.56 ± 0.2%, along with Commission Internationale d’Eclairage chromaticity coordinates of CIE = (0.337, 0.349) and a color rendering index of CRI = 87.An efficient and neutral colored semitransparent organic photovoltaic cell (STâ OPV) is realized by utilizing a nearâ infrared (NIR) absorbing ternary cell combined with a thin, semitransparent, highâ conductivity Cuâ Ag alloy electrode. A combination of optical outcoupling and antireflection coatings leads to enhanced visible transmission, while reflecting the NIR back into the cell where it is absorbed.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151812/1/adma201903173.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151812/2/adma201903173_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151812/3/adma201903173-sup-0001-S1.pd

High‐Performance Doped Silver Films: Overcoming Fundamental Material Limits for Nanophotonic Applications

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137336/1/adma201605177-sup-0001-S1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137336/2/adma201605177_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137336/3/adma201605177.pd

Epidemiological investigation and analysis of Clostridium perfringens food poisoning caused by food delivery

Objective To find out the suspicious food, pathogenic factors and risk factors of a foodborne disease outbreak in a factory, and to discuss the problems exposed in the investigation of the incident, so as to provide reference for the prevention, control and investigation of similar incidents in the future. Methods A case was defined as the onset of abdominal pain or diarrhea (≥3 times/24 hours) or vomiting in a person who worked in M factory from March 3 to March 4 in 2019. Case interviews and retrospective research was carried out using descriptive and analytical epidemics pathological method. Stool specimens of the cases, leftover food and related environmental samples were gathered for pathogen isolation and toxin gene detection using polymerase chain reaction (PCR). Results 106 cases were identified with a attack rate of 73.6% (106/144). The symptoms were diarrhea (78.3%, 83/106), abdominal cramps (78.3%, 83/106), abdominal gas pains (9.4%, 10/106), and no fever. The epidemic curve showed a point source exposure pattern. The median incubation time was 10 hours (range: 2-22 h). Illness were associated with three food items of the lunch on March 3 in 2019 by univariate analysis and Logistic regression analysis: braised fish pieces [relative risk (RR)=1.55, 95% confidence interval (95%CI): 1.29-1.85], pork stir-fried with garlic sprouts (RR=1.26, 95%CI: 1.01-1.57) and duck blood stir-fried with pickles (RR=1.47, 95%CI: 1.16-1.87). Alpha toxin and enterotoxin CPE genes were positive and beta toxin genes was negative in the Clostridium perfringens strain isolated in anal swabs of three patients, three environmental samples and two leftover food samples. There were possible bacterial contamination and reproduction in the processing and preparation of enterprise D, which delivered food. Conclusion This incident was caused by the food poisoning of Clostridium perfringens caused by the consumption of a meal provided by a catering company. After the meal was delivered, it should be cooled quickly and stored at low temperature. If it cannot be eaten immediately, it should be heated sufficiently before eating