Scattering-type Scanning Near Field Optical Microscopy (s-SNOM) has been demonstrated as a valuable tool for revealing important properties of materials at nanoscale. Recent proof-of-concept experiments have shown that, among others, s-SNOM can provide quantitative information on the real and imaginary parts of the dielectric function, and hence of intrinsic optical properties of materials and biological samples. In this work we further explored these capabilities in several experiments dealing with microcapsules for drug delivery, ultra-thin optical coatings with tunable color properties, and two types of nanoparticles with important applications in energy storage and conversion, or biosensing and theranostics.
In nature, arthropods have a remarkably sophisticated class of imaging systems, with a hemispherical geometry, a wideangle field of view, low aberrations, high acuity to motion and an infinite depth of field. There are great interests in building systems with similar geometries and properties due to numerous potential applications. However, the established semiconductor sensor technologies and optics are essentially planar, which experience great challenges in building such systems with hemispherical, compound apposition layouts. With the recent advancement of stretchable optoelectronics, we have successfully developed strategies to build a fully functional artificial apposition compound eye camera by combining optics, materials and mechanics principles. The strategies start with fabricating stretchable arrays of thin silicon photodetectors and elastomeric optical elements in planar geometries, which are then precisely aligned and integrated, and elastically transformed to hemispherical shapes. This imaging device demonstrates nearly full hemispherical shape (about 160 degrees), with densely packed artificial ommatidia. The number of ommatidia (180) is comparable to those of the eyes of fire ants and bark beetles. We have illustrated key features of operation of compound eyes through experimental imaging results and quantitative ray-tracing-based simulations. The general strategies shown in this development could be applicable to other compound eye devices, such as those inspired by moths and lacewings (refracting superposition eyes), lobster and shrimp (reflecting superposition eyes), and houseflies (neural superposition eyes).
Compound eyes in arthropods demonstrate distinct imaging characteristics from human eyes, with wide angle field of view, low aberrations, high acuity to motion and infinite depth of field. Artificial imaging systems with similar geometries and properties are of great interest for many applications. However, the challenges in building such systems with hemispherical, compound apposition layouts cannot be met through established planar sensor technologies and conventional optics. We present our recent progress in combining optics, materials, mechanics and integration schemes to build fully functional artificial compound eye cameras. Nearly full hemispherical shapes (about 160 degrees) with densely packed artificial ommatidia were realized. The number of ommatidia (180) is comparable to those of the eyes of fire ants and bark beetles. The devices combine elastomeric compound optical elements with deformable arrays of thin silicon photodetectors, which were fabricated in the planar geometries and then integrated and elastically transformed to hemispherical shapes. Imaging results and quantitative ray-tracing-based simulations illustrate key features of operation. These general strategies seem to be applicable to other compound eye devices, such as those inspired by moths and lacewings (refracting superposition eyes), lobster and shrimp (reflecting superposition eyes), and houseflies (neural superposition eyes).
This study reports broadband antireflective subwavelength structures (SWS) on various semiconductor materials for
near-infrared detector applications. Two fabrication methods are proposed, i.e., a lenslike shape transfer and an overall
dry etch process of Ag nanoparticles. These methods provide relatively simple, fast, inexpensive process steps, which is
applicable for practical device applications. The fabricated SWS showed extremely lower reflectance spectra compared
to that of flat surface in the near-IR range, indicating good agreement with the simulation results. We also propose
amorphous silicon SWS on InGaAs photodetector to enhance the absorption efficiency.
We report the subwavelength antireflection structures in various semiconductor materials such as Si, ZnO, and GaP/light
emitting diode (LED) structure for LED and solar cell applications in the visible and near-infrared wavelength region,
together with the rigorous coupled wave analysis simulation. Subwavelength structures are fabricated by holographic
lithography and dry etching, effectively suppressing the surface reflection. To enhance the absorption efficiency over a
wide-angle broadband range of incident light, the thin-film crystalline Si solar cells with subwavelength structure, which
reduce the surface reflection, are studied. The improvement of light intensity is achieved for the fabricated LEDs with a
subwavelength structure compared to the conventional LEDs due to a strongly reduced internal reflection at the
We investigate the influence of oxide aperture size on the performance of intracavity contacted oxide-aperture vertical-cavity surface-emitting lasers with asymmetric current injection. Several counteracting mechanisms are shown to result in size dependent behavior, which limits the performance of very small cavities. Reducing the oxide aperture is shown to improve the threshold current and the 3dB bandwidth. However, significant increase of optical losses is observed that is attributed to increase the threshold current density and to decrease the maximum output power. From the far-field measurement, we have shown that the smaller aperture VCSELs have large FWHM. Also, we have achieved the small signal modulation bandwidth of 10.3GHz with 4.5μm oxide aperture diameter at 9mA bias current.