TWe have observed that inhomogeneity can affect the refringence and emission significantly. We are investigating refractive index and the absorption coefficients of multi-functional sensor materials to understand the defect driven changes using birefringence interferometry. In order to simplify and faster data collection, we are exploring low-cost reflectance probe fiber optics designed in-house. In this presentation we will compare the data obtained by using this new system with available literature data. In this paper we will report results of doped ZnSe crystals grown by physical vapor transport method.
It was demonstrated by Rai et al. in 2014 that artifacts can cause big problems in sensor materials and devices which have smaller than TEM lamella thickness. These artifacts are generated due to incongruency, eutectics and peritectic. In high power, high frequency and high sensitivity optical and electronic devices and systems, binary and ternary materials can be designed with superior properties. For example, halides, selenides and tellurides have wide transparency, high mobility and low absorption and wide transparency. It is extremely difficult to achieve to good quality materials due to multicomponent without knowledge of phase diagram, vapor pressure and other thermodynamic parameters. We will present excess thermodynamic functions of several binary and ternary industrially important materials such as ZnSe, GaSe, Tl3AsSe3 and Tl4HgI6 showing the stability of these materials. These parameters are indications of congruency and stability of melts near the growth temperature.
A variety of sensors utilize nanoengineered titanium oxide TiO2 since it changes oxidation states due to high energy exposure. It has been proven to be a good sensor material for radiation sensors. It also provides changes in hydrophobicity on crystalline or glassy surfaces since it affects the contact angles when embodied matrix is treated on the surface. In addition, TiO2 forms very thin film on most substrates and avoids surface corrosion. To increase the sensitivity of sensors one must avoid high contact angle when using materials such as TiO2. In this paper, we propose to discuss the effect of matrix and processing on the interaction by measuring hydrophobic properties of the composites. Accordingly, polystyrene and poly methyl methacrylate filled with TiO2 nanoparticles composites were used. The effect of water, cyclohexane, toluene, and tetrahydrofuron (THF) solvent were studied. It was observed that the mixing of copper oxide significantly alters the sensing capability since it affects the contact angle on the surface and, hence sensitivity.
The accidental release of industrial and agricultural chemicals can pose a serious threat to life and the environment. Therefore, researchers have been exploring detection methods of commonly transported chemicals in order to minimize potential harm or destruction in response to an accidental release. One method is to use a network of commercial sensors to track a chemical spill but with each sensor costing upwards of $600, this type of network can become prohibitively expensive and may not be practical for real world use. Specifically, we aimed to develop a network of custom electrical conductivity sensors with each sensor made from an inexpensive Arduino board showing comparable detection results while costing an order of magnitude less. In our experiments, the network of sensors covered 83 in2 in a container filled with different types of water (e.g. deionized, melted snow, sea, river, and tap). The network of custom sensors showed high ammonia concentrations near the release point of an initial laboratory scale ammonia release with low ammonia concentrations away from the release point. As equilibrium was reached, the sensors showed the same ammonia reading. Additionally, a 2-D map was made to track the simulated ammonia spill overtime. Overall, this works shows that this network of custom Arduino sensors can be used to map the detection of accidental ammonia release as an inexpensive replacement for the commercial sensors, which will promote accessibility of future testing for the broader community.
During the past several decades physical vapor transport (PVT) method has been extensively used for developing laser and electronic and optical sensor materials especially for incongruent and high vapor materials. Extensive careful studies of the NASA Marshall Space Flight Center on ZnSe growth by PVT has demonstrated that both thermal and solutal convection play very important roles on the quality of crystals and can be controlled by microgravity experiments. In case, the growth is performed by sputtering or systems such as DENTON, it is very difficult to control fluid flow and both thermal and solutal convective flows. We have demonstrated that by controlling the transport path, temperature of substrate and source and using purified source micron size thick ness can be achieved. We will present the experimental results of pure and doped lead selenide (PbSe) which demonstrated various morphologies and bandgap based on size of particles based on growth condition.
The performance of optical and electronic detectors and sensors are affected by surface and bulk impurities. In some cases, nanoscale thin films are used as detectors and their life cycle is significantly decreased. In the case of conformal shapes, surfaces with different polishing, decoration and geometries exhibit unusual wetting and nucleation characteristics for impurities and this requires continuous attention for cleaning. The situation for space borne components and vehicles surfaces exposed to wetting liquids requires remote cleaning. In the present paper, we report the effect of surface topographies of substrates with nanoengineered titanium oxide and copper oxide nanoparticles embodied in polystyrene and study the effect of the composites to create different hydrophobic characteristics with great potential for detectors and sensors operating in ultra-violet and infrared regions.
Heavy metal selenides have shown very good properties including wavelength conversion in MWIR and LWIR regions, acousto-optic and great potential for radiation detection. We have extensively studied thallium-based compounds for variety of applications. Studies were performed for crystal growth, fabricability and radiation detection characteristics of ternary congruent compounds of thallium mercury iodide system from the melt by Bridgman method. The congruency and phase transition was studied by DTA. Material melts congruently between 300-400 0C and do not show any other phases between room temperature and melting point. Crystal slabs were fabricated as bulk detector to demonstrate good characteristics for detectivity of X-ray and gamma-rays. Effect of impurities on performance were evaluated by using source materials of different purity for synthesis. Crystals with high purity source materials and mixed by vibrating method were determined for resistivity in range of 1012ohm-cm.
A great deal of research has been performed on refractive index n and extinction coefficient k due to varieties of applications in optical industries. The dispersion equation is described for the photons of varying energies and their interactions with materials since there is a strong correlation of n and k with wavelength. Measurements based on reflectance can be expensive and are very difficult due to compositional variations. We present a low-cost reflectance probe fiber optics designed in-house to determine the absorption coefficients and refractive index of solids. The solutions using a modified Beer-Lamberts Law and merging the concentration and extinction coefficient terms into an absorption coefficient, α, can be given by the equation I = I0 exp (-α* d) where I is the transmitted intensity, I0 is incident intensity and d is the thickness. We have experimented with several semiconductor compounds for this study.
Polarity is very important in developing materials with colossal dielectric. To meet the demands for the tunable devices and high dielectric parallel plate capacitors, several perovskites such as CaCu3Ti4O12 (CCTO), La2/3Cu3Ti4O12 (LCTO) Pr2/3Cu3Ti4 O12 (PCTO) and several other materials of this class have been studied all over the world. Detailed studies showed that results vary a lot based on processing methods, such as powder vs. multi crystals and single crystals. In spite of great progress in processing, low resistivity and process driven variables in properties remain a big hurdle for its applications as a dielectric capacitor. We observed that dielectric values are significantly changed when these materials are exposed to chemicals and biological agents. We used parallel plate capacitor design for making chemical and biological sensors from CCTO member of this group. The data indicated huge difference in the dielectric and resistivity of the exposed samples.
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