A tracking system is provided for a roof-mounted solar array. The system includes a sensor mechanism for sensing an orientation of the sun relative to the solar array, and a controller connected to the sensor mechanism that generates a... more
A tracking system is provided for a roof-mounted solar array. The system includes a sensor mechanism for sensing an orientation of the sun relative to the solar array, and a controller connected to the sensor mechanism that generates a signal that represents an optimal tilt angle of the solar array relative to the orientation of the sun. An actuator connected to the controller receives the signal from the controller and adjusts the tilt angle of the solar array in response to the received signal.
Abstract A static IV measurement method for ferroelectric thin films is developed to distinguish the leakage current from the switching current. The initial polarization state and the exponential decay behavior of the switching current... more
Abstract A static IV measurement method for ferroelectric thin films is developed to distinguish the leakage current from the switching current. The initial polarization state and the exponential decay behavior of the switching current are considered in this method. The feasibility of this IV measurement method is investigated by examining fatigue effects on sol-gel derived PZT thin films. Changes in polarization due to fatigue are correlated with the changes in the switching current and the leakage current.
Recent studies to improve the crystallization of PZT on silicon by using a very thin intermediate barrier layer are presented. Barrier layer compositions which displayed beneficial effects included: SrTiO3, BaTiO3, BaZrO3, LaAlO3 and... more
Recent studies to improve the crystallization of PZT on silicon by using a very thin intermediate barrier layer are presented. Barrier layer compositions which displayed beneficial effects included: SrTiO3, BaTiO3, BaZrO3, LaAlO3 and NdAlO3. X-ray diffraction was performed to monitor the phase transformation using barrier layers. High Resolution Transmission Electron Microscopy (HRTEM) was used to characterize the sample with the SrTiO3 inter-layer.
Careful analysis of the grain interaction effects during nucleation and growth have been performed. The blocking and transformation characteristics for a one dimensional process involving anisotropic particles have been considered.... more
Careful analysis of the grain interaction effects during nucleation and growth have been performed. The blocking and transformation characteristics for a one dimensional process involving anisotropic particles have been considered. Structures which transform via randomly oriented anisotropic particles will also exhibit a texture which is based is biased in favor of the fastest growth direction.
ABSTRACT A series of sol-gel derived PZT films with various Zr/Ti ratios-namely PT, 0/100-20/80, 35/65, 53/47, 65,/35, 80/20, 94/6 and PZ, 100/0-were prepared on platinized Si wafers. Excess PbO was added to the precursor chemistries to... more
ABSTRACT A series of sol-gel derived PZT films with various Zr/Ti ratios-namely PT, 0/100-20/80, 35/65, 53/47, 65,/35, 80/20, 94/6 and PZ, 100/0-were prepared on platinized Si wafers. Excess PbO was added to the precursor chemistries to compensate for eventual PbO loss and also to aid in obtaining the desired perovskite phase.
A series of solgel derived lead lanthanum titanate films were prepared on Corning 7059 glass substrates. Waveguiding properties of these films were studied as a function of La content and film thickness. 0.5 M precursor solutions based on... more
A series of solgel derived lead lanthanum titanate films were prepared on Corning 7059 glass substrates. Waveguiding properties of these films were studied as a function of La content and film thickness. 0.5 M precursor solutions based on lead acetate, La nitrate and Ti Zr alkoxides were refluxed for 1 hour and later spincoated at various speeds on the substrates under clean room condition. Films were fired to 400C for 1 hr to burn off the organics and to consolidate the coatings.
Abstract A series of sol-gel-derived PZT (lead zirconate titanate) films with Zr: Ti ratios of 100: 0, 94: 6, 80: 20, 65: 35, 53: 47, 35: 65, 20: 80, and 0: 100 was prepared on platinized Si wafers. The precursor chemistries were based on... more
Abstract A series of sol-gel-derived PZT (lead zirconate titanate) films with Zr: Ti ratios of 100: 0, 94: 6, 80: 20, 65: 35, 53: 47, 35: 65, 20: 80, and 0: 100 was prepared on platinized Si wafers. The precursor chemistries were based on lead acetate and Zr/Ti alkoxides containing the appropriate amounts of cations in the required stoichiometries. Excess PbO was incorporated to compensate for PbO loss during processing.
Abstract The field-dependent polarization model is a commonly proposed model to describe the hysteresis loop of a ferroelectric material. The electric field in the model refers to the local field which varies with position within the... more
Abstract The field-dependent polarization model is a commonly proposed model to describe the hysteresis loop of a ferroelectric material. The electric field in the model refers to the local field which varies with position within the ferroelectric film. However, the parameters in the field-dependent polarization are usually extracted based on the macroscopic experimentally averaged field, ie, applied voltage divided by film thickness.
Simulations were conducted of transformations involving anisotropic particles growing into a matrix of simultaneously growing isotropic particles. The ultimate shape development of the anisotropic particles, present in dilute... more
Simulations were conducted of transformations involving anisotropic particles growing into a matrix of simultaneously growing isotropic particles. The ultimate shape development of the anisotropic particles, present in dilute concentration, was determined. The faster growing directions are found to impinge neighboring grains earlier in the transformation, thus creating a final particle morphology that is less eccentric than the shape would be if grown in isolation.
Gradient crystallization methods have been proposed and studied for creating microstructures which exhibit crystal orientation. For many of these processes it is possible for spurious heterogeneous nucleation and growth to occur from the... more
Gradient crystallization methods have been proposed and studied for creating microstructures which exhibit crystal orientation. For many of these processes it is possible for spurious heterogeneous nucleation and growth to occur from the sample sides and compete with desired oriented growth. We analyze this growth interference effect for two methods of crystallizing in a temperature gradient: either moving up a temperature gradient, or crystallizing in a stationary temperature gradient.
Abstract: A solar power collector optimization design project has been developed for use in undergraduate classrooms and/or laboratories. The design optimization depends on understanding the current-voltage characteristics of the starting... more
Abstract: A solar power collector optimization design project has been developed for use in undergraduate classrooms and/or laboratories. The design optimization depends on understanding the current-voltage characteristics of the starting photovoltaic cells as well as how the cell's electrical response changes with increased light illumination. Students were given the assignment of building a small reflective concentrator to match with a single solar cell--and to maximize the total power output from the system.
Description/Abstract Even by todays standards, the Eddystone I power plant of the Philadelphia Electric Company, commissioned in 1959, represents ambitious steam conditions. It is a 325-MW, double-reheat unit designed for 5,000 psig,... more
Description/Abstract Even by todays standards, the Eddystone I power plant of the Philadelphia Electric Company, commissioned in 1959, represents ambitious steam conditions. It is a 325-MW, double-reheat unit designed for 5,000 psig, 1200/1050/1050/degree/F (34.5 MPa, 649/566/566/degree/C) turbine pressure and temperature.
Abstract Sol-gel derived lead zirconate titanate (PZT) films were deposited and crystallized on platinized Si/SiO 2 and Al 2 O 3 wafer substrates in the film thickness range of 500-7000 Å. Electrical testing was conducted to evaluate the... more
Abstract Sol-gel derived lead zirconate titanate (PZT) films were deposited and crystallized on platinized Si/SiO 2 and Al 2 O 3 wafer substrates in the film thickness range of 500-7000 Å. Electrical testing was conducted to evaluate the effect of PZT film thickness on capacitor performance. Optical microscopy and AFM data were used to identify factors which might cause shorting in crystallized PZT films. Thin films of Ti or TiO x were used for Pt bottom and top electrode adhesion in the substrate/Pt/PZT/Pt structured device.
The effect of liquid content on the creep behaviour of dense polycrystalline materials is examined. Two very important variables are included in the analysis, (1) the dihedral angle that the liquid makes with the boundary between two... more
The effect of liquid content on the creep behaviour of dense polycrystalline materials is examined. Two very important variables are included in the analysis, (1) the dihedral angle that the liquid makes with the boundary between two solid grains and (2) the total volume fraction of liquid. Nabarro-Herring creep (bulk diffusion limited) and Coble creep (grain boundary diffusion limited) are examined. In both cases, the presence of liquid enhances the creep rate.
Abstract The conduction behavior in a realistic three-dimensional two-phase microstructure is examined. Specifically, the case of a nonconducting, partially wetting second phase is examined. An electrical circuit analogue is used to... more
Abstract The conduction behavior in a realistic three-dimensional two-phase microstructure is examined. Specifically, the case of a nonconducting, partially wetting second phase is examined. An electrical circuit analogue is used to quantitatively measure the effect. The dihedral angle that the second phase makes at grain boundaries is found to significantly influence the conductivity. As the second phase penetrates deeper into the grain boundary region, the conduction pathways are restricted to a greater degree.
Polymer films containing non-centrosymmetric crystals have been prepared and characterized by second harmonic generation. Combinations of watersoluble polymers and KDP or ADP produced good films. Efforts were made to extend this method to... more
Polymer films containing non-centrosymmetric crystals have been prepared and characterized by second harmonic generation. Combinations of watersoluble polymers and KDP or ADP produced good films. Efforts were made to extend this method to lead titanate, lead zirconate titanate and potassium titanyl phosphate. These materials were successfully produced as crystalline thin films via sol-gel chemistry with a high temperature annealing step.
Solvent evaporation induced by the airflow above the spinning substrate can be the cause of defects in films formed by spin coating. A solvent concentration gradient is formed in the film as a consequence. Surface tension effects arising... more
Solvent evaporation induced by the airflow above the spinning substrate can be the cause of defects in films formed by spin coating. A solvent concentration gradient is formed in the film as a consequence. Surface tension effects arising from solvent evaporation can cause radial striation defects in films. This can be alleviated by using mixed solvents, with the more volatile having a relatively high specific surface tension.
The kinetic processes relevant to up-gradient crystallization are analyzed in detail. Crystallization occurs upon moving an amorphous sample up through a temperature gradient which is the reverse of traditional crystallization from the... more
The kinetic processes relevant to up-gradient crystallization are analyzed in detail. Crystallization occurs upon moving an amorphous sample up through a temperature gradient which is the reverse of traditional crystallization from the melt. Both nucleation and growth processes are important to the present technique. To obtain a highly oriented microstructure, bulk nucleation must be prevented. Generally, a liquid with small nucleation rate and large crystal growth rate is favorable for the present route.
Spin coating is a common method for depositing very thin uniform films across a planar surface in a short period of time. An abundance of fluid is dispensed across a substrate that is then quickly accelerated to a predetermined spin... more
Spin coating is a common method for depositing very thin uniform films across a planar surface in a short period of time. An abundance of fluid is dispensed across a substrate that is then quickly accelerated to a predetermined spin speed. The fluid spreads rapidly due to centrifugal effects. Thinning occurs due to the combined effects of centrifugal spin-off and evaporation.
Abstract Phase separation is found for the first time in quenched samples of amorphous Bi 2 Sr 2 Ca 1 Cu 2 O x (often called “2212” composition). Clear evidemce for metastable phase separation is found using X-ray diffraction (XRD),... more
Abstract Phase separation is found for the first time in quenched samples of amorphous Bi 2 Sr 2 Ca 1 Cu 2 O x (often called “2212” composition). Clear evidemce for metastable phase separation is found using X-ray diffraction (XRD), transmission electron microscopy (TEM), and differential thermal analysis (DTA). This has serious implications for possible fabrication of high current density devices from these compositions, especially via glass-ceramic processing routes.
Half-micron-thick tungsten oxide films were deposited by the sol-gel method onto indium tin oxide (ITO) coated soda lime silicate substrates. Following a 100° C prebake, the samples were fired with a carbon dioxide laser at a variety of... more
Half-micron-thick tungsten oxide films were deposited by the sol-gel method onto indium tin oxide (ITO) coated soda lime silicate substrates. Following a 100° C prebake, the samples were fired with a carbon dioxide laser at a variety of power densities and translation speeds. The laser-fired tungsten oxide films were characterized by spectrophotometry, electrochemistry, multiangle ellipsometry, and transmission electron microscopy and compared to similar furnace-fired films.
Abstract In this paper, the extraction of doping profiles in ferroelectric thin-film capacitors using ferroelectric capacitance–voltage (CV) measurements is studied. For a ferroelectric field-dependent permittivity model, the doping... more
Abstract In this paper, the extraction of doping profiles in ferroelectric thin-film capacitors using ferroelectric capacitance–voltage (CV) measurements is studied. For a ferroelectric field-dependent permittivity model, the doping profile relation to measured CV curves for ferroelectric thin-film capacitors is found to be analogous to the well-known result of metal–semiconductor Schottky junctions with an easily determined effective dielectric constant.
Abstract A domain model consistent with the measured capacitance–voltage (CV) characteristics of lead zirconate titanate (PZT) capacitors is proposed. Two variants of this model are presented and compared with experimentally measured CV... more
Abstract A domain model consistent with the measured capacitance–voltage (CV) characteristics of lead zirconate titanate (PZT) capacitors is proposed. Two variants of this model are presented and compared with experimentally measured CV data. The basic model is developed adopting a macroscopic electric field that is spatially uniform through the depth of the film.
Abstract The electric‐field distribution in a ferroelectric capacitor often is treated as a uniform effective field for circuit‐level modeling. By solving Poisson's equation and treating the ferroelectric capacitor as a back‐to‐back... more
Abstract The electric‐field distribution in a ferroelectric capacitor often is treated as a uniform effective field for circuit‐level modeling. By solving Poisson's equation and treating the ferroelectric capacitor as a back‐to‐back Schottky‐barrier system, the nonuniform electric‐field distribution is calculated inside a ferroelectric thin film, assuming that the thin‐film capacitor is completely depleted and has a constant doping concentration.
Abstract Sol-gel derived PZT (lead zirconate-titanate) thin films were irradiated to a total-dose of 1 Mrad (Si) or 86 krad (PZT) under open-circuit bias. An asymmetric distortion in the hysteresis curves was observed. The distortion... more
Abstract Sol-gel derived PZT (lead zirconate-titanate) thin films were irradiated to a total-dose of 1 Mrad (Si) or 86 krad (PZT) under open-circuit bias. An asymmetric distortion in the hysteresis curves was observed. The distortion depends on the polarization state of the capacitor before irradiation. Postirradiation electrical cycling makes the hysteresis loops symmetric initially, but results in fatigue effects.
The evolution of a temperature gradient at the free surface of a coating solution during the spin coating process is examined. Solvent evaporation causes localized cooling at the top that can result in thermocapillary instability within... more
The evolution of a temperature gradient at the free surface of a coating solution during the spin coating process is examined. Solvent evaporation causes localized cooling at the top that can result in thermocapillary instability within the coating solution, and thereby driving convective flows that may result in non-uniform coatings.
Abstract Ferroelectric thin film capacitors (FTFCs) are the basic storage element in ferroelectric memory cells. In this paper, the effects of varying film thickness and niobium doping level on electrical properties for memory... more
Abstract Ferroelectric thin film capacitors (FTFCs) are the basic storage element in ferroelectric memory cells. In this paper, the effects of varying film thickness and niobium doping level on electrical properties for memory applications in FTFCs are examined. Reliability issues such as leakage current and fatigue are studied while the niobium doping level is varied.
Abstract Several copper vanadium oxide melts were tested for possible application as the active medium in phase-change optical data storage devices. These materials were melted in the bulk and then quenched. Their phase development was... more
Abstract Several copper vanadium oxide melts were tested for possible application as the active medium in phase-change optical data storage devices. These materials were melted in the bulk and then quenched. Their phase development was characterized to help determine their applicability to optical data storage. It was found that they satisfy many of the criteria necessary for successful phase-change data storage; further studies of their behavior in thin film geometry would be warranted.
1. ABSTRACT Optical interference filters were fabricated using multilayers derived from sol-gel Si02 and Si02-Ti02 thin films. Laser processing was then used to modify the spectral properties of local regions of these stacks. The... more
1. ABSTRACT Optical interference filters were fabricated using multilayers derived from sol-gel Si02 and Si02-Ti02 thin films. Laser processing was then used to modify the spectral properties of local regions of these stacks. The feasibility of using laser processing for selectively changing the optical properties of thin film devices was thus demonstrated. Design considerations and some basic limitations of this technique for tuning interference filter colors are then discussed.
Abstract: Polymer films containing non-centrosymmetric crystals have been prepared and characterized by second harmonic generation. Combinations of water-soluble polymers and KDP or ADP produced good films. Efforts were made to extend... more
Abstract: Polymer films containing non-centrosymmetric crystals have been prepared and characterized by second harmonic generation. Combinations of water-soluble polymers and KDP or ADP produced good films. Efforts were made to extend this method to lead titanate, lead zirconate titanate and potassium titanyl phosphate. These materials were successfully produced as crystalline thin films via sol-gel chemistry with a high temperature annealing step.
Abstract: Polymer films containing non-centrosymmetric crystals have been prepared and characterized by second harmonic generation. Combinations of water-soluble polymers and KDP or ADP produced good films. Efforts were made to extend... more
Abstract: Polymer films containing non-centrosymmetric crystals have been prepared and characterized by second harmonic generation. Combinations of water-soluble polymers and KDP or ADP produced good films. Efforts were made to extend this method to lead titanate, lead zirconate titanate and potassium titanyl phosphate. These materials were successfully produced as crystalline thin films via sol-gel chemistry with a high temperature annealing step.
ABSTRACT Developed technologies in vitrification, cement, and polymeric materials manufactured using flammable organic solvents have been used to encapsulate solid wastes, including low-level radioactive materials, but are impractical for... more
ABSTRACT Developed technologies in vitrification, cement, and polymeric materials manufactured using flammable organic solvents have been used to encapsulate solid wastes, including low-level radioactive materials, but are impractical for high salt-content waste streams (Maio, 1998). In this work, we investigate an emulsification process for producing an aqueous-based polymeric waste form as a preliminary step towards fabricating hybrid organic/inorganic polyceram matrices. The material developed incorporates epoxy resin and polystyrene-butadiene (PSB) latex to produce a waste form that is non-flammable, light weight, of relatively low cost, and that can be loaded to a relatively high weight content of waste materials. Sodium nitrate was used as a model for the salt waste. Small-scale samples were manufactured and analyzed using leach tests designed to measure the diffusion coefficient and leachability index for the fastest diffusing species in the waste form, the salt ions. The microstructure and composition of the samples were probed using SEM/EDS techniques. The results show that some portion of the salt migrates towards the exterior surfaces of the waste forms during the curing process. A portion of the salt in the interior of the sample is contained in polymer corpuscles or sacs. These sacs are embedded in a polymer matrix phase that contains fine, well-dispersed salt crystals. The diffusion behavior observed in sections of the waste forms indicates that samples prepared using this emulsion process meet or exceed the leachability criteria suggested for low level radioactivity waste forms.
Research Interests: Electron Microscopy, Water quality, Arsenic, Water Purification, Wastewater Treatment, and 15 moreWater Reuse, Environmental Risk, Undergraduate, Solid waste, Iron, Diffusion Coefficient, Waste Water, Microstructures, Water Quality, Arsenic Contamination, Ion Exchange, Water Content, Diffusion Model, Heavy Metal Removal, and Radioactive waste
We have used direct and inverse photoemission to measure the occupied and unoccupied electronic states, and their alignment with the band edges of the substrate, of N3 dye adsorbed on the rutile TiO$_{2}$(110) surface and on anatase... more
We have used direct and inverse photoemission to measure the occupied and unoccupied electronic states, and their alignment with the band edges of the substrate, of N3 dye adsorbed on the rutile TiO$_{2}$(110) surface and on anatase TiO$_{2}$ nanoparticle thin films. In dye-sensitized solar cell applications, the HOMO-LUMO gap determines the useful portion of the solar spectrum, and charge transfer of photoexcited electrons to the substrate depends on the alignment of the LUMO to the TiO$_{2}$ conduction band edge. Samples were prepared and passivated with a ...
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The destructive influence of internally nucleated growing crystallites upon the growth of an oriented crystal front is examined. In particular, a simple two-dimensional model system is used to study the interaction of an oriented, planar... more
The destructive influence of internally nucleated growing crystallites upon the growth of an oriented crystal front is examined. In particular, a simple two-dimensional model system is used to study the interaction of an oriented, planar growth front with a particle, initially of negligible size, which grows by circular growth. The locus of the intersection points of the fronts is obtained and used to derive an expression for the misoriented (ruined) area fraction produced by the presence of the growing particle. It is demonstrated that the reduced ...
Research Interests:
Research Interests:
Research Interests:
Abstract Proton exchange rate data from the literature are examined with particular emphasis on finding information about the composition dependence of the interdiffusion rate. In general, these data show that the proton exchange process... more
Abstract Proton exchange rate data from the literature are examined with particular emphasis on finding information about the composition dependence of the interdiffusion rate. In general, these data show that the proton exchange process yields a surface layer which is predominantly depleted of lithium and has protons replacing them on a one-for-one basis. Also, the composition profiles are generally very flat near the free surface, but the concentration changes quite abruptly in the interior of the lithium niobate crystal. These ...