KEYWORDS: Data storage, Databases, Data modeling, Copper, Information science, Prototyping, Semiconductors, Semiconductor materials, Temperature metrology, Systems modeling
Informatics-based identification of candidate semiconducting radiation detection materials depends upon the
development of a robust knowledge base of materials properties. However, the accuracy and integrity of the
knowledge base are often affected by information loss due to incomplete entry and loss of context. We describe our
methods for materials property data storage and retrieval, in support of semiconductor development for gamma
radiation detection materials informatics applications. Analysis-ready data representations vary with each materials
design problem, and are often inconsistent with accurate generic property storage. The proposed approach provides
simple, strongly-typed generic storage for as-measured properties, with tools for assessing as-measured properties
and converting them to analysis-ready representations. This process simplifies property data stewardship, and allows
fine control over the assumptions of data fusion, system characterization, and property representation employed in
property-estimation models.
KEYWORDS: Semiconductors, Dielectrics, Semiconductor materials, Information science, Sensors, Crystals, Physics, Phonons, Chemical species, Data analysis
Materials properties important to the design and performance of semiconducting gamma detectors, such as band gap,
density, mobility, and crystal cell anisotropy, can depend on similar underlying physics. The resulting property
correlations limit the number of design variable and the place effective bounds on the range of physical properties
available to gamma-detection materials However, trend correlations can also limit the dependence of error in
structure-property relationships and information gaps when considering new candidate materials. Trend analysis
complements property estimation via data regression techniques, increasing the generality and certainty of
information-based conclusions.
KEYWORDS: Crystals, Chemistry, Principal component analysis, Data modeling, Information science, Nonlinear crystals, Crystallography, Complex systems, Systems modeling, Statistical analysis
Information-based materials discovery offers a structured method to evolve materials signatures based upon their physical properties, and to direct searches using performance-based criteria. In this current paper, we focus on the crystal structure aspects of an optical material and construct an information-based model to determine the proclivity of a particular AB composition to exhibit multiple crystal system behavior. Exploratory data methods used both supervised (support-vector machines) and unsupervised (disorder-reduction and principal-component) classification methods for structural signature development; revealing complementary valid signatures. Examination of the relative contributions of the materials chemistry descriptors within these signatures indicates a strong role for Mendeleev number chemistry which must be balanced against the cationic/anionic radius ratio and electronegativity differences of constituents within the unit cell.
The nonlinear optical response for index-matched, non-absorbing immiscible phases (liquid-solid, liquid-liquid, solid-solid) has been determined by means of open aperture z-scan measurements. In mixtures where one constituent shows a relatively high optical nonlinearity, rapid and reversible transformation to a light-scattering state is observed under conditions where a critical incident light fluence is exceeded. This passive broadband response is induced by a transient change in the dispersive part of the refractive index, and is based upon the Christiansen-Shelyubskii filter that at one time was used as a means to monitor the
temperature of glass melts. Modeling studies are used to simulate scattering intensities in such textured composites as a function of composition, microstructure, and constituent optical properties. Results provide a rational approach to the selection of materials for use in these limiters. Challenges to preparing dispersed phase mixtures and their response to 532 nm nanosecond pulsed laser irradiation are described.
Mixtures of two non-absorbing and index-matched materials with contrasting nonlinear optical response have been shown to optically limit above a critical fluence of pulsed nanosecond laser light. Under these conditions, index mismatch is induced between the disparate phases leading to strong Tyndall scattering. The effect has been demonstrated previously by the authors in both solid-liquid mixtures (hexadecane and calcium fluoride), and surfactant-stabilized liquid-liquid emulsions consisting of dichloroethane as the organic phase and a concentrated aqueous phase of sodium thiocyanate (NaSCN). Materials used in these studies exhibit low absorption coefficients over extended wavelength regions allowing for a broadband response of the limiter. Recently, limiting has been observed at 532 nm in a polymer composite consisting of barium fluoride and poly-(n-butyl acrylate). A modified open-aperture z-scan method was used to quantify optical limiter performance in this system. Modeling studies provide the basis for designing optical limiters based upon this light scattering mechanism and show the importance of size resonance and constituent optical properties on limiter performance.
Nonionic surfactants are used to stabilize a dispersed droplet phase in a continuous liquid phase when two immiscible liquids are mixed. As both liquid phases approach the index-matched condition, interfacial scattering is suppressed, and the mixture takes on the characteristics of a Christiansen-Shelyubskii filter. If, in addition, one of the liquids exhibits a substantial nonlinear optical response, then interfacial light scattering can be reversibly turned on when a laser beam incident upon the filter exceeds a critical fluence. To demonstrate this effect, an organic phase (dichloroethane) was dispersed in an aqueous phase containing sodium thiocyanate (NaSCN) using an alkyl end-capped polyethylene glycol ether. Optical limiting was observed through this transparent medium under conditions where the focused second-harmonic output of a Q-Switched Nd:YAG laser was on the order of about 50 mJ/cm2. An open-aperture z-scan technique was used to quantify the limiting behavior. Since the thiocyanate anion is both isostructural and isoelectronic with carbon disulfide which exhibits a large optical nonlinearity, the mechanism of optical limiting is proposed to be associated with a nonlinear shift in the aqueous fluid index of refraction, resulting in an index mismatch between the disparate phases at high laser fluence. Index mismatch between the two phases leads to multiple reflections, loss of coherence, and a significant transmission decrease due to Tyndall scattering. Fundamental studies of such systems are used to verify theoretical predictions of the limiting effect, and aid in the design and development of improved sub nanosecond limiters based upon this optical deflection approach.
Methods for predicting the refractive indices of materials are evaluated with respect to the design criteria for composite optical limiters. The efficiency of a nonlinear Christiansen optical limiter is dependent upon refractive index of the individual phases of the composite device and their comparative response characteristics. The overall performance of the structure-property relationships for the linear refractive indices is generally excellent within the training sets; however, the accuracy of an individual case sample is challenged by the low energy case requirements. Outside the general class of materials for which these methods were designed, significant degradation occurs as a result in incomplete parameterizations or compounding errors of imprecise predictions. Accurate predictions of linear and nonlinear refractive indices by TDHF methods are more problematic, yet these techniques demonstrate sensitivity to chemical bonding environments.
A densely packed bed of alkaline earth fluoride particles percolated by a fluid medium has been investigated as potential index-matched optical limiter in the spirit of a Christiansen-Shelyubskii filter. Marked optical limiting was observed through this transparent medium under conditions where the focused second-harmonic output of a Q-Switched Nd:YAG laser was on the order of about 1 J/cm2. An open- aperture Z-scan technique was used to quantify the limiting behavior. In this case, the mechanism of optical limiting is thought to be a nonlinear shift in the fluid index of refraction, resulting in an index mismatch between the disparate phases at high laser fluence. This induced mismatch appears to be promoted by localized electric field enhancement present near the sharp edges at the crystallite/fluid boundaries. Index mismatch between the two phases leads to multiple reflections, loss of coherence, and a significant transmission decrease due to Mie scattering. The presence of many boundaries significantly amplifies the effect. The role of thermally induced changes in refractive index for this system appears to be relatively small in pulsed-laser experiments. However, cw-laser blocking was achieved by a thermal mechanism when an absorber (iodine) was dissolved in the liquid phase. Fundamental studies of such systems are used to verify theoretical predictions of the limiting effect, and aid in the design and development of improved limiters based upon this optical deflection approach.
Using the LOCALF method, we have examined electric field distributions for high and low dielectric susceptibility cases through systematic variations of defect concentration and orientation. The addition of nonlinear susceptibility terms to the conventional linear contributions in the dielectric formalism incrementally perturbs both the electric field intensities and predicted dielectric constants, having a greater influence on low dielectric materials. These effects are modulate by the relative ratios of the linear and nonlinear susceptibility terms for a material due to polarization-derived changes. Nonlinear effects can have a strong influence on the magnitude of these changes; potentially obscuring predicted changes in dielectric response due to microstructural detail.
While many studies have focused on the computation of static properties of small organic molecules, dynamic fluctuations can introduce important perturbations to the electronic structure and subsequent optical properties. In this paper, we present results from combined molecular dynamics/quantum mechanical calculations on the linear and nonlinear optical properties of 5-alkyl-cyanobiphenyl molecule. As opposed to the static structure commonly used in computations of optical properties, the dynamic picture requires a number of configurations with unique optical properties. As an example, the torsion angle between the phenyl rings in the optimal static picture is 40.1 degrees, but is better described as a probability distribution in the time dependent problem. Simulations of the nematic phase using periodic boundary conditions further emphasize the importance of these fluctuations on the electronic structure of this system.
The microstructure of dielectric films is an inherent characteristic of the fabrication process, and imposes distinctive behavior on the electric field distributions in these inhomogeneous media. In this paper, we examine the size dependent problem for cubic defects for an Al2O3 dielectric material. Using the LOCALF method to analyze the electric field response, we have developed models for Al2O3 dielectric films of varying microstructure size and volume fraction, and compare these results with conventional effective medium methods. Besides the dielectric susceptibility and volume fraction dependencies, the physical size of the heterogeneities creates localized regions of high field intensity.
KEYWORDS: Dielectrics, Composites, Dielectric polarization, 3D modeling, Chemical elements, Systems modeling, Finite element methods, Polarizability, Optical components, Coating
In modeling the dielectric properties of inhomogeneous materials, the treatment of the electric field interaction s differentiate the usual modeling formalism and their accuracy. In this paper, we show that the performance of effective medium methods is dependent upon a number of variables - defect concentration, alignment, and the dielectric constant of the material itself. Using our previously developed finite element model of an inhomogeneous dielectric, we have developed models for a number of dielectric films of varying dielectric constant and microstructures. Alignment to of defects parallel to the applied field and the larger defect aspect ratios increase the overall dielectric constant. The extent of these effects is dependent on the dielectric constant of the bulk component.
The surface and bulk microstructures inherent to the fabrication process of dielectric films, affects both the distribution of the local electric field intensities and its associated dielectric properties. In this paper, we have used a finite element electric field model to examine the effects of a low dielectric surface layer, alignment of a low dielectric component within the dielectric film, and the interaction of these two influences on the local electric fields and dielectric constants. Columnar microstructure and alignment of dielectric components perpendicular to the surface norm are shown to enhance electric intensities and dielectric constants. Predicted dielectric constants are compared against conventional effective medium approximation results.
The microstructure of dielectric films provides a significant influence on the electric field distribution in these materials. In this paper, we focus on the relationship between the electric field distribution and organization of film constituents. Using our self- consistent determination of the local electric field in inhomogeneous media, we have shown that enhanced fields can result from columnar microstructures such as typically generated by CVD-type fabrication processes, and low dielectric components in optical coatings. In addition to the microstructural enhancement, a surface specific enhancement due to presence of low dielectric components is observed.
The complex microstructure of dielectric films alters the local electric fields affecting both the strength by which different sites within a film interact, and the spatial extent. Using our self- consistent lattice element model, we determined the site by site interaction of the local electric fields within a defect ridden dielectric film to determine the effects of microstructure on the interaction of defects sites on its surroundings. Local dielectric properties are compared to currently accepted models of dielectric film properties (such as effective medium methods) determine the local field and polarization.
Using a finite element representation of a dielectric film, we have examined the effects of surface defects on the local electric field and its intensity. Surface defects possess the potential to affect the local electric fields in a dielectric film in a manner similar to those introduced in the bulk solid. Both raised and removed regions tend to focus the electric field vector about the defect, and the interaction of two defects can lead to an enhanced local electric field intensity. In these cases, effective medium methods would approximate the film by an idealized defect-free structure, and thus would not note the sensitivity of the electric field to surface structure.
Inorganic polymers are characterized by both in-plane it''and out-of-plane it bonding interactions in contrast to organic materials where iteffects dominate the optical properties. Involvement of the it'' bonding system results in higher electronic transition energies with the first transition being a it'' ic process. Second hyperpolarizabiities are affected by both it bonding systems and are reduced by higher transition energies and lower transition probabilities. In this paper we present electronic structure calculations of the static hyperpolarizabilities of a series of model compounds for inorganic polymers to illustrate the relationship between their electronic structure and nonlinear optical properties. 1. 0
Different film deposition techniques have been found to generate distinct grain morphologies
and defect distributions, which can result in a wide distribution of local field intensities. We
have developed a lattice element model of an inhomogeneous medium, which we use to selfconsistently
determine the local internal electric field and polarization. We use this method to
show the sensitivity of the polarization to defect shape. The results of this method predict the
local field to have a large range of values within the film and have been used to identify regions
where the local field is a maximum.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.