In-situ grown CuO and ZnO nanowire (NW) arrays were evaluated for their gas sensing performance. The metal structures were fabricated by standard e-beam lithography, thermal evaporation and lift-off process onto a silicon substrate with gold electrodes. After integration onto a test structure with resistive heater and thermocouple for temperature control, the samples were thermally oxidized at 400°C. During thermal oxidation, nanowires were grown between the oxidized metal structures. The gas sensing performance of the NW array was tested for carbon monoxide, - and a hydrocarbon-mixture (acetylene, ethane, ethene, and propene) at three relative humidity levels.

Titanium dioxide (TiO2) loaded with gold (Au) as noble metal, acts as an efficient photocatalyst that has been extensively investigated for water splitting processes. In this paper, we report on the microstructure of atomic layer deposited titanium dioxide and the crystallinity modification of the material using energetic electron beam irradiation. A rapid high-energy electron beam induced crystallization of the nanostructures has been observed in-situ inside a High-Resolution Transmission Electron Microscope (HRTEM). The systematic crystallization of the nanomaterial occurring under the electron beam irradiation (300 KV) indicates the transformation of the near amorphous material into a mixture of two nuances of TiO2 polymorphs, namely rutile and anatase. We believe that this transformation will enhance the efficiency of water splitting process, as the mixed phases of rutile and anatase are known to possess better optical properties than the individual polymorphs of TiO2. This finding may be of particular interest in developing appropriate heat treatment methods for these nanostructures dedicated to water splitting to increase their efficiency.

We recently demonstrated a sub-bandgap photoresponse with our wafer-scale Au/TiO2 metallic-semiconductor photonic crystals (MSPhC). The sub-bandgap energy with 590 nm peak could be absorbed in the form of hot electron and injected to TiO2, which provides 5.28 times more energy for photolysis than that of energy absorbed to flat TiO2. If the solar energy already absorbed above 700 nm could be injected to the catalyst, higher than 10 times improvement will be achieved, and above 20% solar to fuel efficiency will be feasible with the robust but inefficient TiO2 catalyst. In order to achieve photocurrent near and above 700 nm spectrum, we deposited gold nanorods on the surface of MSPhC to incur localized surface plasmon (LSP) modes absorption and subsequent injection to the TiO2 catalyst. We used electrophoretic deposition (EPD) method to deposit nanorods on the top, sidewall and bottom well surface of the photonic nanocavities. The deposition of nanorods was achieved reasonably uniform and sparse not to block the optical cavities of MSPhC. Flat gold surfaces were tested at 4 different suspension densities to get the optimum gold nanorods density. Under 10V applied electric field, positively charged gold nanorods at the concentration of 6.52×1013 #/mL could deposit MSPhC surface with the density of 230 #/µm2, which was reasonably uniform and sparse. Preliminary tests show an absorbance increase near 700 nm on flat device coated with gold nanorods. Photocurrent measurement is under way to demonstrate the enhanced hot electron transfer over full visible light and near-infrared solar spectrum.

Improved solar spectrum optical absorption in multilayered nanostructures consisting of metal, semiconductor and dielectric layers increase their potential for efficient photon to electron conversion. In this work, we analyze the influence of different nanostructure shapes and dimensions on the optical absorption in the vacuum wavelength range of 400 nm to 1500 nm based on Finite Domain Time Difference (FDTD) method. A periodic metallic photonic crystal composed of nanorods of gold, titanium oxide, and alumina is proposed by optimizing thickness of Au and TiO2, aspect ratio, sidewall angle, and geometry of the elemental shape. A high aspect ratio structure consisting of elliptical nose cone elements with optimized dimensions is seen to absorb more than 90% of the solar spectrum in the range considered.

Glucose sensor based on ITO/ZnO NRs/GOx/nafion is fabricated and tested under different glucose concentrations. Hydrothermal growth method along with sol-gel technique is used to grow high quality ZnO nanorods that have well-alignment and high density with an acceptable aspect ratio. The as-grown of ZnO nanorods are used to fabricate a working electrode that can be used for glucose detection in blood after a modification process with GOx and nafion membrane. Annealing at 110 °C helped in improves the crystallinity of the seed layer and as a result, a high density and well alignment as-grown ZnO nanorods were obtained. High sensitivity and short response time were obtained from the fabricated device with an acceptable lower limit of detection.

The paper describes a novel electrochemical method of metal nanowire synthesis via coherent cocrystallization of metal with metal salt. Using the method described, iron, copper, and tin nanowires as well as lead nanowalls in the matrix of ferrous chloride FeCl2 salt were synthesized. Influence of electrolyte composition and electrolysis regime on the deposit structure is revealed. Morphology, chemical composition, and structure of the NW@salt nanocomposite is studied and discussed.

An electrochemical glucose sensor based on zinc oxide (ZnO) nanorods is fabricated, characterized and tested. The ZnO nanorods are synthesized on indium titanium oxide (ITO) coated glass substrate, using the hydrothermal sol-gel technique. The working principle of the sensor under investigation is based on the electrochemical reaction taking place between cathode and anode, in the presence of an electrolyte. A platinum plate, used as the cathode and Nafion/Glucose Oxidase/ZnO nanorods/ITO-coated glass substrate used as anode, is immersed in pH 7.0 phosphate buffer solution electrolyte to test for the presence of glucose. Several amperometric tests are performed on the fabricated sensor to determine the response time, sensitivity and limit of detection of the sensor. A fast response time less than 3 s with a high sensitivity of 1.151 mA cm-2mM-1 and low limit of detection of 0.089 mM is reported. The glucose sensor is characterized using the cyclic voltammetry method in the range from -0.8 – 0.8 V with a voltage scan rate of 100 mV/s.

Two segments of horizontally grown crystalline ZnO nanorods (NRs) connected with an amorphous layer have been successfully and reproducibly synthesized using one-step hydrothermal technique by controlling the growth rate. The confocal photoluminescence (PL) imaging and spectroscopy of twin ZnO NRs at different temperatures shows intense red emission with comparably week UV emission. The strong red emission from the twin NRs is a consequence of structural imperfections. Both UV and red bands showed signatures of strong temperature dependent exciton-phonon scattering. Using the intensity ratio of the UV and red emissions, we show that the individual ZnO NRs can be used as highly sensitive cryogenic temperature sensors below ∼175 K.

We present here a reactive ion etching recipe to fabricate germanium nanowires. We used a combination of Cl2, N2 and O2 and studied the influence of both the gas pressure and the O2 mass flow on the morphology of the nanowires. 5 µm long nanowires with an aspect ratio of 20 are demonstrated with smooth surfaces and a tapering below 20 nm/µm. We also show that both gold and aluminum can be used as hard mask; the latter achieving a selectivity with germanium above 100.