Optical coherence tomography (OCT) allows for imaging of fine structures below the surface of tissue based on inherent contrast from heterogeneity of optical refractive index. A contrast agent may be used when intrinsic contrast of a target in the sample is not enough. We synthesize magnetically-responsive nanorods whose reflectivity can be modulated by the orientation of a magnetic field and demonstrate their use in background-free OCT imaging. Because normal tissue does not respond to switching magnetic field, the signal from nanorods can be isolated from tissue.
Photonic nanostructures with widely, rapidly and reversibly tunable diffraction in the visible and near-infrared spectrum
can be created through a magnetic field assisted assembly strategy. We first describe the mechanism for the formation of
dynamic photonic chains and the tuning of the diffraction colors using an external magnetic field. Then we discuss the
fixation of photonic chains in a solid polymer matrix through combining instant magnetic assembly with a rapid UV
polymerization process which allows us to confirm the chaining structures. Finally, we demonstrate several applications of
magnetically tunable photonic nanostructures for security and sensing devices, high resolution patterning of multiple
We present a novel method to fabricate photonic crystal for visible light control and demonstrate high resolution
patterning of multiple structural colors using a single material. The material, termed as "M-Ink", whose color is
magnetically tunable and lithographically fixable, is developed. By combining novel material system and specially
designed instrument, we produce patterns with arbitrary spatial arrangements of colors with single material.
We present a new method for in-situ synthesis of multiple color and shape encoded particles in microfluidic channel
using single material. Material developed in this work is M-Ink whose color is magnetically tunable and lithographically
fixable. By combining novel material system and special instrumentation enables generation of limitless number of codes
and greatly simplify the manufacturing process of encoded particles.
We have demonstrated a variety of solution-phase approaches for the synthesis of dimensionally confined nanostructures of a wide range of materials. These materials include metals (Ag and Au) and semiconductors (Te, Se, and Ag2Se) with interesting properties such as high electric, thermal, and ionic conductivities, piezoelectricity, and photoconductivity. Direct and indirect routes for the solution-phase synthesis of 1-dimensional nanostructures are presented. Control over morphology, chemical purity, and crystallinity are well maintained. We show that by using solution-phase methods, it is possible to generate not only high yields of nanowires but also more complex structures such as tubes and co-axial nanocables. These nanostructures are ideal for the study of size-confinement effects on electrical and optical properties, and also as the future interconnects and active components in nanoscale electronic and electromechanical devices.
This paper describes the use of confined self-assembly in organizing monodispersed spherical colloids into face-center-cubic crystalline lattices for photonic crystals applications. Using this method, we were able to conveniently control the thickness, the density and structure of defects, and the orientation of a crystal. Inverse opals of polymers and ceramic materials were also synthesized by templating corresponding precursors against three-dimensional colloidal crystals. As an extension to this method, we also demonstrated the hierarchical self-assembly that involved building blocks with sizes on two different scales, and its application in forming inverse opals.
An approach to metallic photonic crystals is demonstrated by using gold-silica core-shell colloids as the building blocks. The formation of gold-silica core-shell nanoparticles involved a base-catalyzed hydrolysis of precursor TEOS and subsequent condensation of silica onto the surfaces of gold cores. The obtained core-shell colloids were monodispersed in size and their shell thickness could be controlled in the range of a few nanometers to about 500 nm. The core diameter could also be varied from ~5 nm to ~100 nm. The core-shell colloids were then employed as building blocks to self-assemble highly ordered three-dimensional photonic crystals using a non-lithographic method. The photonic band-gap properties were characterized by taking the transmittance and reflectance spectra.
Self-assembly of monodispersed spherical colloids has been demonstrated as an effective strategy to fabricate three-dimensional photonic bandgap crystals. The major challenge in this field is to control the order, thickness, domain size, crystal orientation, defects, and registry of colloidal crystals. In this paper we describe a Template-Assisted Self-Assembly (TASA) approach to control the orientation of the photonic crystals. The self-assembled crystalline lattice usually has a face-center-cubic (fcc) structure with its (111) planes parallel to the surface of the solid support. In TASA process, we used an array of pyramid-shaped pits etched in a Si (100) wafer as the templates. The pits were fabricated by photolithographic patterning and anisotropic etching. Owing to the 70.6° angular geometry of the pyramid-shaped pits, monodispersed colloids nucleated and grew in a vectorial fashion exclusively within the pits to forma pattern of fcc colloidal crystals with (100) layer planes parallel to the (100) face of the single crystalline Si wafer. The small crystals in silicon pits then served as seeds to define and direct the further growth of the crystal along the direction perpendicular to the substrate. A large, (100)-oriented single crystal of colloids with well-controlled thickness was obtained if the diameter of the colloids matched the separation between adjacent pits, and if the raised edge between adjacent pits was small enough.