Single wall carbon nanotubes (SWNT)-nafion bilayer composites have a significant mechanical response (photoactuation) upon exposure to near infrared or visible light. The composites are formed as cantilevers of a thick nafion film (tens to hundreds of microns) coated with a thin SWNT film (one to ten microns). This configuration leads to a bending response upon light exposure. The wavelength dependence of the magnitude of the photoactuation corresponds to the absorption spectrum of semiconducting SWNTs. The thickness of each film in the bilayer affects both the magnitude of the bending and the rate of the response. The mechanism of the photoresponse is proposed to be a result of the photocarriers migrating to the interface, attracting hydrated hydrogen ions from the nafion acid groups, which then induces swelling of the nafion substrate.
Solar cells based on organic and inorganic materials are an emerging technology for a new generation of photovoltaics (PV). Hybrid solar cells, which use both organic and inorganic components, have advantages such as cost-effective processing and the ability to fabricate devices on flexible substrates. The combination of organic materials with semiconductor nanostructures allows enhancement of the conversion efficiency due to the fast electron transport in semiconductors and a high interface area between organic and inorganic components. In our work, anodized porous Si (PSi) was chosen as a host matrix filled with Copper Phthalocyanine (CuPC) molecules. The resulting nanocomposite can yield high performance novel materials for solar cells.
The fabrication of PSi was completed using electrochemical etching of Si in diluted hydrofluoric acid (HF). Also, this process, with some modifications, can be applied to produce free-standing PSi films of desired thickness. PSi layer was filled with CuPC dissolved in concentrated sulfuric acid. The top contact was made by sputtering of Au or ITO. A power conversion efficiency (PCE) of 3% (33 mW/cm2) was obtained for 12 um thick n-type pSi layer with pore sizes of approximately 15 nm filled with CuPC. The electrochemical etching of Si under different conditions was carried out to optimize the photovoltaic parameters. A detailed investigation of the solar cell performance depending on porous layer thicknesses and pore sizes is presented. The use of free-standing films of PSi can lead to the fabrication of novel PV solar cells on flexible substrates with high conversion efficiency.
An optical strain gage, employing a hollow polyimide-coated glass capillary tube, is currently under development. The capillary tube serves as a waveguide, in which an optical signal is attenuated in an amount proportional to applied bending strain. The capillary is incorporated into an optical fiber link which acts as both the source of signal and as the return path to a photodiode detector. The inherent compatibility of this optical strain sensor with fiber optic telecommunication systems makes it amenable for incorporation into intelligent systems for the continuous monitoring and damage assessment of bridges, highways, piers, airframes, and buildings. By applying various thin films to the interior and/or exterior surfaces of the waveguide, the strain gage can be optimized for specific strain ranges. This optical strain sensor exhibits advantages in comparison to commercially available metal foil (resistance) strain gages, including gage factors 100 times larger and temperature insensitivity for operating temperatures ranging from -25 degrees Celsius to +51 degrees Celsius.
A strain gage is being developed, based on optical modulation that is capable of gage factors on the order of 500 for stains in excess of 2000 (mu) (epsilon) . The strain sensing element is a coated, hollow, glass waveguide of dimensions 0.5 mm ID X 1mm X OD X 100mm long. Since the geometry is compatible with standard telecommunication optical fiber such gages it can be readily incorporated into smart system arrays for damage assessment in structure such as buildings, roads and bridges. Optical fibers bring the excitation light signal to and the response signal for the sensing element. The small diameter glass tubes act as the substrate for a multiple thin film layers which can be optimized to provide the maximum dynamic range for a predetermined strain excursion. The sensor respond to bending strain by attenuation the optical intensity of the excitation signal. The gage elements exhibit little or no hysteresis and are insensitive to temperature. Also, they are environmentally stable and are not affected by factors such as corrosion or electromagnetic fields. The preliminary experimental result will be presented for this type of strain gage system operating to 2000 (mu) (epsilon) . Also, the model for the physical process will be discussed.
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