MANIPULATION OF NANOSCALE WRINKLES ON TRANSPARNET AND FLEXILBE FILMS FOR MULTI-MODAL STRUCTURL COLORATION

Department of Mechanical EngineeringMost materials and devices with structurally switchable color features responsive to external stimuli can actively and flexibly display various colors. However, realizing covert???overt transformation behavior, especially switching between transparent and colored states, is more challenging. Current stimulus-response pattern hiding and displaying technology responds to numerous external stimuli (temperature, light, mechanical stimulation, etc.) and causes a change in dye properties and in the spacing of nanostructures. In this phase change method, it is difficult to completely hide information because patterns are easily expressed due to limited viewing angles or irregular external conditions. Therefore, there is a need for a method of controlling a transparent nanoscale surface that can completely hide information. Thus, we introduce a method of forming traditional buckling-type corrugations using bilayer-like or trilayer film. In addition, the photonic structure is fabricated using an inkjet printing method and completely laminated into the film. Moreover, in this dissertation , we study the principle of structural color in which living organisms have color by a nanostructure without pigment and the characteristics of the nanostructured photonic crystal hidden in it and design a color-changing nanostructure for single and complex structural colors. Nanoscale wrinkles are generated on the ductile top surface of various multilayered substrates by external stimuli, and their geometrical and optical features are determined by the material and structural properties of the laminated films. First, we develop a bilayer-like laminated film with a rigid SiO2-nanoparticle (NP)-encapsulated poly(dimethylsiloxane) (PDMS) composite structure surrounded by soft PDMS as a multidimensional structural color platform. Owing to the similarity in the optical properties of PDMS and SiO2 NPs, this device is fully transparent in the normal state. However, as their mechanical strengths differ considerably, upon compressive loading, buckling-type instability arises on the surface of the laminate, leading to the generation of 1D or 2D wrinkled patterns in the form of gratings. As a result, we demonstrate an application of the device in which quick response codes are displayed or hidden as covert???overt convertible-colored patterns for optical encryption/decryption, showing their remarkable potential for anti-counterfeiting applications. Second, we describe a thin trilayer film that can generate various wrinkles on transparent and flexible films in the presence of external mechanical bending. In particular, the wrinkle wavelength can be controlled on a tens of nanometer scale by modulating the material properties of each layer. This active modulation plays a critical role in determining resulting structural color spectra. In other words, the wrinkles function as a diffraction grating so that the film displays bright structural colors under bending conditions. After the bending stress is released, the wrinkles disappear and the film becomes transparent again. Lastly, we demonstrate that the material and structural patterning technique shows remarkable potential for structural coloration applications such as multimodal displays and novel barcode-based anti-counterfeiting techniques.ope

Controlled open-cell two-dimensional liquid foam generation for micro- and nanoscale patterning of materials

Liquid foam consists of liquid film networks. The films can be thinned to the nanoscale via evaporation and have potential in bottom-up material structuring applications. However, their use has been limited due to their dynamic fluidity, complex topological changes, and physical characteristics of the closed system. Here, we present a simple and versatile microfluidic approach for controlling two-dimensional liquid foam, designing not only evaporative microholes for directed drainage to generate desired film networks without topological changes for the first time, but also microposts to pin the generated films at set positions. Patterning materials in liquid is achievable using the thin films as nanoscale molds, which has additional potential through repeatable patterning on a substrate and combination with a lithographic technique. By enabling direct-writable multi-integrated patterning of various heterogeneous materials in two-dimensional or three-dimensional networked nanostructures, this technique provides novel means of nanofabrication superior to both lithographic and bottom-up state-of-the-art techniques

Time-resolved photoluminescence of the size-controlled ZnO nanorods

Size dependence of the time-resolved photoluminescence (TRPL) has been investigated for the ZnO nanorods fabricated by catalyst-free metalorganic chemical vapor deposition. The nanorods have a diameter of 35 nm and lengths in the range of 150 nm to 1.1 mum. The TRPL decay rate decreases monotonically as the length of the nanorods increases in the range of 150 to 600 nm. Decrease of the radiative decay rate of the exciton-polariton has been invoked to account for the results

Excitonic emissions observed in ZnO single crystal nanorods

We report on the photoluminescent characteristics of ZnO single crystal nanorods grown by catalyst-free metalorganic vapor phase epitaxy. From photoluminescence (PL) spectra of the nanorods at 10 K, several PL peaks were observed at 3.376, 3.364, 3.360, and 3.359 eV. The PL peak at 3.376 eV is attributed to a free exciton peak while the other peaks are ascribed to neutral donor bound exciton peaks. The observation of the free exciton peak at 10 K indicates that ZnO nanorods prepared by the catalyst-free method are of high optical quality. (C) 2003 American Institute of Physics

Case of Small Bowel Perforation due to Enteropathy-Type T-Cell Lymphoma

Enteropathy-type T-cell lymphoma (ETTL) is a rare disease with a poor prognosis. According to the World Health Organization (WHO) classification, it is a subtype of the peripheral T-cell lymphomas. This disease is associated with gluten-sensitive enteropathy, has a high risk of intestinal perforation and obstruction, and is refractory to chemotherapeutic treatment. We report the case of a 73-year-old woman who was diagnosed with enteropathy-type T-cell lymphoma of the small intestine, which was positive for the markers of cytotoxic T cells, CD3, CD8, and CD56, on immunohistochemical staining after resection of the perforated terminal ileum