Absorption spectra of a number of shellfish extracts have been obtained, and reveal prominent absorptions in all samples at 210 and 260 nm, and at 325 nm in some of them. These absorptions preclude the use of chromophores with similar absorptions in testing of shellfish samples for paralytic shellfish toxins. Two crown ether chemosensors featuring a boron azadipyrrin chromophore have been synthesized; both have absorption maxima at 650 nm, where all the shellfish extracts are transparent. The synthetic sensors feature either 18-or 27-membered crown-ether rings, and have been evaluated as visible sensors for the paralytic shellfish toxin saxitoxin. The binding constant for one of them is in the range of 3 -9 × 10 5 M -1 , and exhibits a fluoresence enhancement of over 100% at 680 nm, in the presence of 40 μM saxitoxin.Contamination of shellfish by paralytic shellfish toxins or poisons (PSTs, PSPs) continues to be a near-worldwide health risk. 1,2 Monitoring of shellfish beds for the presence of PSTs continues to use the mouse bioassay as the most common means of detection, 3,4 although recent advances in HPLC methods have been made and approved for use by monitoring agencies. 5 The mouse bioassay has obvious economic and ethical drawbacks, 6 and alternatives are being actively sought in a number of laboratories. 4,7-9Our work in this area has focussed on optical methods, and we have developed and explored a number of chemosensor systems that are based on the concept of photoinduced electron transfer, or PET. In PET-based chemosensors, a host for a given analyte is designed in which a chromophore is separated from the host by a spacer (see Figure 1). 10-12 In our case, the host component of the sensor is a crown ether that is separated from the fluorophore by a methylene spacer. In the absence of a guest such as saxitoxin, PET from the crown to the fluorophore quenches the excited state after photon absorption, and fluorescence is turned off (or more accurately, is minimized). When the host is complexed to the toxin, the relative energies of the molecular orbitals are perturbed so that PET is no longer favorable, and fluorescence is "turned on". 13,14 The sensitivity of a PET-based chemosensor is influenced by a number of factors, including the quantum yield of the fluorophore and the equilibrium, or binding constant, K b , between the chemosensor and the fluorescent complex.In past studies, we have evaluated anthracene, 13,14 coumarin, 15,16 and acridine 17 fluorophores in our chemosensors, all of which have absorption maxima in the ultraviolet. This class of chemosensors is selective for detection of saxitoxin over tetrodotoxin, 17 metal ions such as sodium and potassium, 15 and several other analytes. 13 They can also be incorporated into self-assembled monolayers for sensing on a surface. 16,18,19 Recently, we reported that incorporation of larger crown ether rings can significantly increase the binding constant. 14 We now report the synthesis and evaluation of boron azadipyrrins 1 and 2, having absorp...

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steel substrates via closed field unbalanced magnetron sputtering technology. These were investigated using XRD, SEM, XPS, UV-Vis, FTIR and nanoindentation techniques. Analysis of the optical properties showed the solar absorptance, in the visible range, of the Ti x M 1ÀxÀy N y films improved significantly from 51% to 81% with AlSi-doping and an increase of solar absorptance of up to 66% was recorded from films doped with Al. Moreover, the Al doping can reduce the thermal emittance in the infrared range from 6.06% to 5.11%, whereas doping with AlSi reduces the emittance to ca. 3.58%. The highest solar selectivity of 22.63 was achieved with TiAlSiN films. Mechanical studies showed enhanced hardness by $32%; enhanced yield strength by $16% and enhanced plastic deformation by $110% of Al and AlSi doped TiN matrix. IntroductionA spectrally selective surface is, generally, used to improve the photothermal conversion performance and, as such, it possesses two characteristics: high absorptance, a in the visible region of solar spectrum (0.3 to 2.5 mm) and low emittance, 3, (i.e., high reection) in the infra-red (IR) region ($2.5 mm) at operating temperatures. An excellent selective surface maximises the absorption of incoming photons in the visible region and minimises photon emission through thermal radiation in the IR energy region. Such a surface can be designed by an absorber-reector assembly. In such an approach, the reector is coated with a highly absorbing layer over the visible solar spectrum, while the infrared region is made transparent. Various types of metal nitrides based selective solar surfaces such as TiN, ZrN, HfN, TiAlN, TiAlON, NbAlN, NbAlON, MoAlN, and WAlN have been investigated by numerous groups.1-11 Over the past few years, transition metal nitride based thin lms have attracted signicant research interest as selective solar surfaces in solar thermal conversion devices. Generally, the energy conversion performance of a selective solar surface depends on the lm materials, lm design and fabrication technique used. A multi-layer lm stack with mixture of metal nitride, metal oxide and metal oxynitride lms e.g., TiAlN/AlON, and TiAl/ TiAlN/TiAlON/TiAlO has been explored for the potential commercial development of selective solar surfaces.3,12 TiAlN/ TiAlON/Si 3 N 4 selective absorbers have been produced on various substrates such as copper, nickel, stainless steel, glass and nimonic alloys.13 However, these materials are yet to be commercialized for solar energy conversion applications. View Article OnlineView Journal | View Issue solar selective surface applications, transition metal oxides based thin lms also received signicant research interests. 15-19Various synthesis methods such as evaporation, electrodeposition, chemical conversion, chemical vapour deposition and magnetron sputtering have been employed in manufacturing selective solar surfaces. Owing to its advantages in large area deposition, dry, clean and environment friendly, magnetron sputtering technique is widely used for syn...

The presence of undesirable hydrogen-related impurities and the resulting stress instability in chemical vapor deposited silicon dioxide films are important issues. In this work, the bonding nature and stress behavior of relatively low-temperature deposited silicon dioxide films deposited at high rates were investigated. Films were deposited at 1000 Å/min and at a substrate temperature in the 250–350 °C range. A considerable change in stress was observed in these films upon annealing in the 250–400 °C temperature range. Both as-deposited and annealed films were then stored in a cleanroom environment for long periods of time, and their stress was monitored intermittently. In parallel, Fourier transform infrared studies were performed on an identical set of as-deposited and annealed films to investigate changes in the bonding nature of the films during aging. Thus, film stress and their bonding nature were studied concurrently over an extended period of time. Si–H and silanol (Si–OH) were identified as impurities responsible for the observed stress instability of the deposited films. Initial concentrations of these impurities have been observed to vary depending on the deposition conditions. Also, depending on the concentrations of these impurities, both reversible and irreversible bond reconstruction were observed in the films upon annealing. Concomittantly, reversible and irreversible changes in stress were observed in annealed films, the amount of change depending on the impurity type and content. Impurities responsible for reversible and irreversible bond reconstruction were identified. Good correlation between film stress and bonding was observed.

Articles you may be interested inExcimer laser crystallization and doping of source and drain regions in high quality amorphous silicon thin film transistors Appl.Effects of high temperature rapid thermal annealing using a flat gas flame on the electrical properties of phosphorusdoped polycrystalline silicon films A comparative study of the lightinduced defects in intrinsic amorphous and microcrystalline silicon deposited by remote plasma enhanced chemical vapor deposition AIP Conf.Aluminum metal-induced crystallization and doping of hydrogenated amorphous silicon ͑a-Si:H͒ have been investigated. Aluminum was evaporated onto device quality a-Si:H films deposited in an ultrahigh vacuum plasma-enhanced chemical vapor deposition system. These Al/a-Si:H structures were annealed in the 100-300°C range. Electrical, surface morphological, and chemical characterizations of the material were performed. The transmission line model technique was used for electrical characterization. Raman spectroscopy showed that crystallization of the interacted a-Si:H film underneath Al pads initiates at temperatures as low as 180°C. X-ray diffraction analysis showed very good polycrystallinity of the interacted film. Electrical measurement, Hall measurement and x-ray photoelectron spectroscopy analysis results revealed that a-Si:H film in contact with Al becomes heavily doped by Al during crystallization as a result of annealing at relatively low temperatures.

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