Undoped and Ga- and Al- doped ZnO films were synthesized using sol-gel and spin coating methods and characterized by X-ray diffraction, high-resolution scanning electron microscopy (SEM), optical spectroscopy and Hall-effect measurements. SEM measurements reveal an average grain size of 20 nm and distinct individual layer structure. Measurable conductivity was not detected in the unprocessed films; however, annealing in hydrogen or zinc environment induced significant conductivity $(\sim {10}^{-2}\mathrm{\Omega }.\text{cm})$ in most films. Positron annihilation spectroscopy measurements provided strong evidence that the significant enhancement in conductivity was due to hydrogen passivation of Zn vacancy related defects or elimination of Zn vacancies by Zn interstitials which suppress their role as deep acceptors. Hydrogen passivation of cation vacancies is shown to play an important role in tuning the electrical conductivity of ZnO, similar to its role in passivation of defects at the Si/SiO2 interface that has been essential for the successful development of complementary metal–oxide–semiconductor (CMOS) devices. By comparison with hydrogen effect on other oxides, we suggest that hydrogen may play a universal role in oxides passivating cation vacancies and modifying their electronic properties.

Assessing levels of neuropeptide Y (NPY) in the human body has many medical uses. Accordingly, we report the quantitative detection of NPY biomarkers applying guided-mode resonance (GMR) biosensor methodology. The label-free sensor operates in the near-infrared spectral region exhibiting distinctive resonance signatures. The interaction of NPY with bioselective molecules on the sensor surface causes spectral shifts that directly identify the binding event without additional processing. In the experiments described here, NPY antibodies are attached to the sensor surface to impart specificity during operation. For the low concentrations of NPY of interest, we apply a sandwich NPY assay in which the sensor-linked anti-NPY molecule binds with NPY that subsequently binds with anti-NPY to close the sandwich. The sandwich assay achieves a detection limit of ~0.1 pM NPY. The photonic sensor methodology applied here enables expeditious high-throughput data acquisition with high sensitivity and specificity. The entire bioreaction is recorded as a function of time, in contrast to label-based methods with single-point detection. The convenient methodology and results reported are significant, as the NPY detection range of 0.1–10 pM demonstrated is useful in important medical circumstances.

This research addresses fuel biocontaminant sensing using resonant photonic gratings. The fundamental photonic resonance physics enables compact, economic sensors that provide a rapid, quantitative, and effective modality for detecting and monitoring biochemical bindings. Thus, we present resonant sensors and attendant surface chemistry targeting yeast cells as representative biofouling agents. We apply biorecognition elements (BREs) to functionalize the dielectric grating surface (TiO2) to produce a sensitive, quantitative wavelength shift-based assay for detecting Yarrowia yeast cells. Concanavalin A (Con A) is used as a BRE consisting of carbohydrate-binding proteins binding to ligands on the yeast cell surface. Corresponding resonance wavelength shifts are measured relative to concentration expressed in log10[C] where C represents the concentration of cells in solution. The assay is shown to be highly specific for detecting Yarrowia cells in various concentrations. The experimental limit of detection (LOD) of the assay is 1.92 for yeast cells in culture media and 1.22 for cells in phosphate buffer saline (PBS). The comparisons of the various functionalization methods show that (3-aminopropyl)triethoxysilane (APTES) with glutardialdehyde (GA) and Con A protocol provides optimal detection of cells in PBS.

We propose a hybrid silicon-nitride ( $Si_{3}N_{4}$ or SiN for short) / nonlinear polymer waveguide to achieve second-harmonic generation of an input 1550-nm signal by modal phase-matching between zero-order spatial mode at 1550 nm and second-order mode at 775 nm. We explore and optimize two cases, single channel waveguide and slot waveguide, by varying the waveguide dimensions. For TE polarized light, the optimum slot waveguide exhibits an effective interaction area $A_{\rm eff}$ of about $16 \mu m^2$ , which is an order-of-magnitude improvement over the single channel waveguide and can translate to a high value of effective nonlinearity. We also show that the optimum slot waveguide geometry is robust with respect to fabrication uncertainties and bending effects.

We demonstrate a room-temperature semiconductor-based photodetector where readout is achieved using a resonant radio-frequency (RF) circuit consisting of a microstrip split-ring resonator coupled to a microstrip busline, fabricated on a semiconductor substrate. The RF resonant circuits are characterized at RF frequencies as function of resonator geometry, as well as for their response to incident IR radiation. The detectors are modeled analytically and using commercial simulation software, with good agreement to our experimental results. Though the detector sensitivity is weak, the detector architecture offers the potential for multiplexing arrays of detectors on a single read-out line, in addition to high speed response for either direct coupling of optical signals to RF circuitry, or alternatively, carrier dynamics characterization of semiconductor, or other, material systems.

We report the design, fabrication, and characterization of a silicon-nitride (SiN) microring-resonator-based label-free biosensor for the purpose of neuropeptide Y (NPY) protein detection. NPY is commonly associated with stress in human body. The device uses evanescent field sensing, its geometry is optimized for 1550-nm signal, and it is fabricated by following standard CMOS processes. Top surface of the device is designed to function in aqueous environment and appropriately functionalized to ensure the biomaterial-specific attachment. The time-dependent spectral response to the biomaterial attachment is observed by scanning a tunable laser source around 1550 nm and measuring the resonance shift in the transmission spectrum. We experimentally achieve the detection into nanomolar concentration level in a regular assay system with 0.1 nm/( μg/mL) of sensitivity and ~ 30 mins of analysis time. This sensitivity is further amplified by a factor of three with a sandwiched assay technique, with which ~ 58 nM ( 0.25 μg/mL) concentration of NPY is successfully detected.