bluuebunny/crossref_metadata_2025 huggingface dataset:
Low Loss Transmission Electron Spectroscopic Studies in Donor Doped BaTiO3
Authors: Katti Kalpana S. , Qian Maoxu , Sarikaya Mehmet
Published: April 2011

We used the Kramers-Kronig transformation to investigate the local dielectric function of barium titanate, BaTiO3 from regions of sub-micrometer scale. Further the effect of dopants, in this case, Nb, on the dielectric function was investigated to assess the level of its local partitioning in the BaTiO3 lattice. The transmission electron energy loss spectroscopy technique was used to obtain dielectric function by placing a small electron probe in isolated regions of the electron transparent BaTiO3 samples. We observed an anomalous, but consistent, shift in the volume plasmon in all regions of the doped sample (compared to the pure one) indicating a uniform incorporation of the dopant within the lattice.
In-Plane Permittivity of Spin-Cast Polymer Films
Authors: Weinberg Shari A. , Bidstrup-Allen Sue Ann
Published: April 2011

Polymeric materials such as polyimides are used in a multitude of microelectronic applications including interlevel dielectrics for insulation. Polyimide films have shown a difference between the through-plane and in-plane refractive index measurements.(1,2,3) This anisotropy in optical properties has been attributed to in-plane orientation of polymer chains and implies anisotropy in electrical properties. Thus, it is necessary to measure the electrical properties in both the in-plane and through-plane directions to accurately design three-dimensional electronic packages. The purpose of this research is to develop an in-situ technique to measure the in-plane permittivity of these spin-coated polymer films. Using capacitance measurements obtained from interdigitated electrodes, through-plane permittivity measurements, and ANSYS finite element analysis software, the in-plane permittivity of a given material can be determined. Several polyimide systems including Du Pont PI-2611 (BPDA-PPD), Du Pont PI-2540 (PMDA-ODA), and Probimide 293 (BTDA-DAPI) from OCG Microelectronics, as well as Cyclotene 3022 (BCB) from Dow Chemical were investigated. Anisotropy in the permittivity was observed in the three polyimide films, but not in the BCB film. Results were compared with predictions using refractive index measurements and a modified form of Maxwell's equation.
Correlations Between Medium Frequency Blocking Parameters and Microstructure in Low Conductivity Materials
Authors: Kleitz M. , Dessemond L. , Steil M. C. , Thevenot F.
Published: April 2011

Observations have been made by impedance spectroscopy of various microstructure-induced blocking effects in cubic zirconias and composites. Correlations have been established between shape parameters of the microstructure defects and specific parameters of the electric response, such as the blocking factor and frequency factor, in the medium frequency range.

Appropriate diagrams show the continuity and changes in the regimes of the microstructure evolutions.
Tunnelling in and The Microstructure of Granular Superconductors
Authors: McLachlan D. S. , Rosenbaum R.
Published: April 2011

The microstructure of granular superconductors are discussed and the difference between granular and random composites is noted. The model where a granular (and a random) superconductor, close to the percolation threshold, is considered to be made up of large granular clusters, linked by tunnelling junctions or weak links, is introduced. This model is illustrated using recent experimental measurements on nanostructured granular Aℓ–Ge. The measurements clearly show that the coupling junctions between clusters can,depending on the volume fraction of superconductor, be of either a Josephson or quasi–particle nature, or a combination of both. The differences between a granular and adirty superconductor and the upper critical field of granular superconductors is then discussed and it is shown that the diameter of the grains can be estimated from the upper critical field. Random Aℓ–Ge, which has a rather different microstructure, is also discussed.
Correlation of Electrical, Dielectric And Mechanical Properties of Polymer Composites
Authors: Strümpler Ralf , Glatz-Reichenbach Joachim , Greuter Felix
Published: April 2011

The electrical and dielectric response upon thermal expansion and contraction of polymer composites have been studied for thermoset polymers containing ceramic or metallic fillers. Before curing, the resistivity p of epoxy containing a metallic filler is in the range of 106 to 107 Ωcm. During curing a sudden reduction of p by eight orders of magnitude is observed. The shrinkage of the polymer during cross-linking and the build-up of internal stresses results in a lower interparticle contact resistance. The contraction can be reversed by heating. Around curing temperature, the resistivity increases by six to eight orders of magnitude due to the expansion of the material. The resistivity increases progressively until the percolation network of the conducting particles is interrupted and the composite reaches a high-ohmic state. Surprisingly, the critical temperature is related to the curing temperature and not to the glass transition temperature, as would be generally expected. Changes of the interparticle gap size can also be observed in the dielectric constant ε. For conducting fillers covered by a thin oxide layer, ε decreases by several orders of magnitude after a certain expansion has been achieved. However, for poorly conducting or insulating fillers dielectric response becomes insensitive to the gap distance. Hence, the electrical or dielectric response of polymers containing metallic fillers can be used as a sensitive probe for the internal stress state and the corresponding micro-structure of the composite.
Dielectric Spectroscopy of Nematic Liquid Crystal Confined in Random Porous Matrices
Authors: Aliev F. M. , Sinha G. P.
Published: April 2011

We performed dielectric spectroscopy measurements to study dynamics of dielectrically active modes of nematic liquid crystals (LC) 5CB with polar molecules confined in silica porous glasses with average pore sizes of 1000 Å (volume fraction of pores 40%) and 100 Å (27%). In the nematic phase of bulk 5CB there is only one mechanism of dielectric relaxation: rotation of polar molecules around short molecular axis with relaxation time τ ∼10−8s. The spatial confinement and the existence of a highly developed interphase have a strong influence on dielectric properties of LC. We found that at temperatures about 30°C below the bulk melting point in both porous matrices the dielectric behavior of confined liquid crystal is very different from the behavior expected for solid state. The dielectric modes were not frozen in both porous matrices and we observed four well defined relaxational processes with relaxation times τ1 ∼ 10−1s, τ2 ∼10−5s, τ3 ∼10−8s (bulk like) and τ3 ∼10−9s. These four processes do not vanish even at temperatures corresponding to deep bulk isotropic phase. The relaxation time of the first process (slow) shows glass-like behavior in a wide temperature range below bulk melting point.
Phosphate-Sulfate Interaction in Simulated Low-level Radioactive Waste Glasses
Authors: Li H. , Darab J. G. , Matson D. W. , Smith P. A. , Hrma P. , Chen Y. , Liu J.
Published: April 2011

Using simulated low-level radioactive waste glasses, interaction between phosphate and sulfate in the glass network was systematically studied using Raman spectroscopy. Phosphate and sulfate interaction was shown to depend on the extent of saturation of both species in the glass. At elevated concentration level of phosphate and sulfate in combination, yet below the solubility limits, phosphate and sulfate both separated from the glass. In the 7-day product consistency test (PCT), the phase separated glasses were found to have higher normalized releases of sodium, phosphorous, sulfur, boron, and silicon than those of their baseline glasses without phase separation.
Dissolution of Basaltic Glass: Effects of pH and Organic Ligands
Authors: Teng Hui , Grandstaff D. E.
Published: April 2011

Dissolution of powdered glass from Kilauea volcano, Hawaii (ca 51% SiO2) was studied in a fluidized-bed, flow-through reactor at room temperature in both dilute HCI and organic ligand-bearing solutions (citrate and oxalate) to determine the effects of pH and organic acids on the dissolution rate. Dissolution was non-stoichiometric in both HCI and organic solutions; however, the relative release rates of various ions and the composition of leached layers or secondary phases are fimctions of pH and organic ligand concentration and type. In HCl solutions, the minimum glass dissolution rate, as assessed from the Na leaching rate, was 7.4 × 10−12 gm cm−2 sec−1, comparable with previous results, and was virtually independent of pH. Addition of citrate and oxalate increased the non-stoichiometry of dissolution. At pH 7, the overall rate of glass dissolution decreased (by as much as 5 times) at low ligand concentrations (< 1 mM), but increased by as much as five times at higher concentration (3 mM). High ligand concentrations do increase the release rate of some elements, especially multivalent cations, such as Fe3+ which form strong organic complexes, by as much as 100 times.
Immobilization of Separated Tc and Cs/Sr in Synroc
Authors: Hart K. P. , Vance E. R. , Day R. A. , Begg B. D. , Angel P. J. , Jostsons A.
Published: April 2011

In some radwaste applications, such as immobilization of U.S. Tank wastes using vitrification, Tc and Cs/Sr are likely to be separated out from HLW supernates. Simplified Synroc preparations can be devised for the immobilization of separated Tc and Cs/Sr, either together or individually. Under suitably reducing processing conditions, Tc can be immobilized, as metal or Tc4+. The volatility of Tc and Cs/Sr in Synroc processing is very restricted.

In Synroc-C, designed for Purex high-level reprocessing wastes, Tc exists as a metal alloy. In air-saturated water, normalized MCC-1 type total differential leach rates at 90°C decreased with leaching time and after 90 days were <10-4 g/m2/d, decreasing by a factor of ∼100 in anoxic conditions. The corresponding results in a pH=6.1 buffer solution were fairly similar to those in deionised water, but in anoxic conditions, the leach rates were higher in the buffer solution than in the deionised water.

A single perovskite phase was loaded with ∼40 wt% of TcO2 to form CaTc0.5Ti0.5O3 by a combination of graphite-die hot-pressing and heating in argon. Rutile, intended to be doped with ∼35wt% TcO2, was fabricated by bellows hot-pressing at 1200°C; aproximately 75% of the Tc formed a solid solution with rutile, but some metallic Tc was also present due to imperfect redox control. Results of both MCC-1 and PCT-type leach tests are presented on a preparation containing 70 wt% hollandite + 20 wt% perovskite + 10 wt% rutile containing about 5 wt% of Cs and Sr respectively. Phase distributions resulting from incorporating Cs and Sr in Synroc-B precursor were studied.
Hot Isostatic Press (Hip) Vitrification of Radwaste Concretes
Authors: Siemer Darryl D. , Scheetz Barry E. , Gougar Mary Lou
Published: April 2011

Properly prepared cementitious waste forms can be hot-isostatically-pressed into materials that exhibit performance equivalent to typical radwaste-type glasses. The HIPing conditions (temperature/pressure) required to “vitrify” these concretes are quite mild and therefore consistent with both safety and good productivity. This paper describes both the process and its products with reference to potential application to Idaho Chemical Processing Plant (ICPP) reprocessing wastes.
The Necessity for Scale Up in R&D: Approach for Waste Immobilisation in Cement by BNFL
Authors: Fairhall Graham A , Miller Eric W
Published: April 2011

The full scale processing of nuclear wastes immobilised in cement utilises a wide range of chemical and physical parameters. The success of this work however, involves many factors and material properties which are affected by the actual scaling up processes. The paper outlines the approach and experience gained by BNFL to recognise and evaluate the major factors involved in order to successfully produce large scale stable products acceptable to the appropriate regulatory bodies and suitable for long term disposal.
Migration of Solutes in Unsaturated, Fractured Rock at Yucca Mountain: Measurements, Mechanisms, and Models
Authors: Wolfsberg A. V. , Robinson B. A. , Fabryka-Martin J. T.
Published: April 2011

Characterization and performance assessment (PA) studies for the potential high-level nuclear waste repository at Yucca Mountain require an understanding of migration mechanisms and pathways of radioactive solutes. Measurements of 36C1 in samples extracted from boreholes at the site are being used in conjunction with recent infiltration estimates to calibrate a site-scale flow and solute transport model. This exercise using the flow and solute transport model, FEHM, involves testing different model formulations and two different hypotheses to explain the occurrence of elevated 36Cl in the Calico Hills unit (CHn) which indicates younger water than in the overlying Topopah Spring unit (TSw). One hypothesis suggests fast vertical transport from the surface via fractures in the TSw to the CHn. An alternative hypothesis is that the elevated 36C1 concentrations reflect rapid horizontal flow in the CHn or at the interface between the CHn and the TSw with the source being vertical percolation under spatially isolated regions of high infiltration or at outcrops of those units. Arguments in favor of and against the hypotheses are described in conjunction with the site-scale transport studies.
The Release of Cesium and the Actinides from Spent Fuel Under Unsaturated Conditions
Authors: Finn P. A. , Hoh J. C. , Wolf S. F. , Slater S. A. , Bates J. K.
Published: April 2011

Tests designed to be similar to the unsaturated and oxidizing conditions expected in the candidate repository at Yucca Mountain are in progress with spent fuel at 90°C. The similarities and the differences in release behavior for 137Cs during the first 2.6 years and the actinides during the first 1.6 years of testing are presented for tests done with (1) water dripped on the fuel at a rate of 0.075 and 0.75 mL every 3.5 days and (2) in a saturated water vapor environment.
A Natural Analogue Study of Uranium Migration in the Tono Mine
Authors: Clark K. J. , Takase H. , Impey M. D. , Humm J. P. , Maekawa K. , Ogata N. , Yanaegizawa K.
Published: April 2011

The Tono uranium mine in Japan, consists of a granite basin infilled with layered marine sedimentary rocks, within which uranium is heterogeneously distributed. This site is being used as a natural analogue to study the migration of uranium. The irregular observed uranium distribution had not satisfactorily been explained by local geochemical properties. This paper examines the hypothesis that the distribution of uranium could be dominated by the accessibility of locations to the migrating uranium, i.e. by the heterogeneous hydrology of the site.

High resolution heterogenous transmissivity fields were generated, conditioned on data from four boreholes through the mine. Steady state Darcy flow calculations and particle tracking simulations of uranium migration have been carried out. The time dependent relative intensity of a set of sources on the boundary of the modelled region were used as parameters to fit the modelled uranium distribution to the observed.

The relative intensities so obtained could be interpreted in a physically reasonable way. Good qualitative agreement was achieved between the observed heterogenous irregular uranium distribution and that fitted. We conclude that this supports the hypothesis, and that detailed knowledge of channelling flows can provide a better understanding of possible radionuclide dispersal.
Ion Exchange and Dehydration Effects on Potassium and Argon Contents of Clinoptilolite
Authors: Woldegabriel G. , Levy S.
Published: April 2011

Zeolite-rich Miocene tuffs are an important part of the principal hydrochemical barrier to water-borne radionuclide transport from a potential high-level nuclear waste repository at Yucca Mountain, Nevada. The timing of zeolitization is an issue that relates to paleohydrology, permeability, zeolite stability, and unsaturated-zone geochemical processes. Exploratory K/Ar dating of clinoptilolite, the most abundant and widespread zeolite, shows a striking and consistent pattern of increasing apparent ages (2–13 Ma) with depth. Only the isotopic ages from the saturated zone are compatible with geologic evidence suggesting an age >10 Ma for most of the zeolites.

Factors that may be responsible for the young apparent ages in the unsaturated zone were investigated. Cation exchange with recharge water and Ar diffusion under unsaturated conditions (processes that may be characteristic of the unsaturated zone) were evaluated experimentally for their effects on K/Ar systematics. Cation exchanging a natural clinoptilolite with Ca-, Cs-, K-, and Na-chloride solutions showed minimal effects on radiogenic Ar content. However, clinoptilolite heated at 2007deg;C for 16 hours in air lost a significant amount of its radiogenic Ar compared with minimal losses from clinoptilolite heated in water at 100°C for over 5 months. The preliminary results indicate that Ar loss from incompletely hydrated clinoptilolite may be a major factor contributing to the young apparent ages of clinoptilolite in the unsaturated zone at Yucca Mountain.
Applications of Electro-optic Polymers in Photonics
Authors: Steier William H. , Kalluri Srinath , Chen Antao , Garner Sean , Chuyanov Vadim , Ziari Mehrdad , Shi Yongqiang , Fetterman Harold , Jalali Bahram , Wang Wenshen , Chen Datong , Dalton Larry R.
Published: April 2011

This review gives a summary of our research in the applications of EO polymers for very broad band infrared modulators, in solving some of the initial problems one faces in integrating semiconductor electronics and EO polymers, and in the fabrication of low loss infrared waveguides.
Nlo Polymer Material Systems for Electro-Optic Devices
Authors: Kenney J. T. , Nurse J. C. , Chon J. C. , Binidey E. S. , Stiller M. , Ball D. W. , Jen A. K-Y.
Published: April 2011

Non linear optical (NLO) polymers have great potential to be fabricated into integrated electro-optic (E/O) devices for use as high speed electro-optic (E/O) switches, modulators and interconnects in computer and communication systems [1,2]. The fabrication of practical integrated E/O devices requires a material system that meets the final device requirements and can be processed using standard fabrication technologies [3]. Applications of polymer E/O devices in electronic systems have been limited by the relatively low thermal stability and poor processability of non linear optical (NLO) polymers. This paper describes a thermally stable electro-optic material system and the fabrication process to make compact integrated E/O devices for application in electronic systems. This material system consists of high thermal stability polyimide core and cladding materials. The active NLO material is a side chain polyimide that uses a new high activity and high thermal stability chromophore.
Multiphasic Nanostructured Composites for Photonics
Authors: Prasad P. N. , Gvishi R. , He G. S. , Bhawalkar J. D. , Kumar N. D. , Ruland G. , Zhao C. F. , Reinhardt B. A.
Published: April 2011

The realization of photonics technology rests on the development of multifunctional materials, which simultaneously satisfy many functional requirements. Towards this goal, we present here, the preparation of novel multifunctional nanostructured composites using the sol-gel process. Two specific applications: optical limiting, and two-photon pumped lasing in these composite materials will be discussed.

We have been able to dope two optical limiting materials in a single bulk and retain the optical limiting effects at each of their characteristic wavelengths. The materials selected for this purpose were C60 which shows optical limiting behavior at a wavelength of 532 nm and bisbenzothiazole 3,4-didecyloxy thiophene (BBTDOT) which exhibits a strong two-photon absorption induced optical limiting at 800 nm. The resulting glass acts as a multi-wavelength optical limiter.

In addition, we present results of two-photon pumped upconverted lasing at 600 nm in a nanostructured composite glass doped with a new dye, trans-4-[P-(N-ethyl-Nhydroxylethylamino) styryl]-N-methylpyridinium tetraphenylborate (ASPT). The pump source was a Q-switched Nd:YAG laser producing 1064 nm pulses of ˜ 10 ns duration.
Polyamic Acid Langmuir-Blodgett (LB) Films Containing A Stable Second-Order NLO Chromophore
Authors: Cheong D. W. , Chen J. -I , Kumar J. , Tripathy S. K.
Published: April 2011

Nonlinear optical (NLO) LB films of polyamic acid containing a stable NLO dye were prepared and imidized either chemically or thermally. The optical properties and molecular orientation of these LB films were studied. From the absorption spectra, we infer that the derivative of the pnitroazobenzene chromophore covalently attatched to polyamic acid did not show significant aggregation. Quadratic dependence of SHG on the number of layers in polyamic acid films indicated the noncentrosymmetric organization of polar NLO chromophores. A second-order nonlinear coefficient (d33) of 23.4 pm/V was observed at 1064 nm after absorption correction. In polyimide films, SH intensity was dramatically reduced due to the collapse of the layered structure upon imidization process. In-plane isotropy of the LB films of polyamic acid and polyimide were lost upon irradiation of polarized light.
Surface Enhanced Raman Spectroscopy Of AgTCNQ Formed From Ag Micellar And Inverse Micellar Colloidal Systems
Authors: Ong Ivan W. , Cowan Dwaine O. , Poehler Theodore O.
Published: April 2011

Silver Tetracyanoquinodimethane (AgTCNQ) is an organometallic semiconductingcompound with potential for use as an optical memory storage media due to its ability to exist intwo states. A laser Raman system has been proposed for this application as the two states havedistinct Raman vibrational peaks. However, the Raman spectra of bulk AgTCNQ films is veryweak and requires special measures to prevent laser-induced degradation and to ensure adequatesignal to noise ratios. In this paper, we report a synthesis AgTCNQ consisting of AgTCNQnanolayers grown around silver colloidal particles in both water and heptane with the use of theamphiphilic surfactants, AOT and SDS. The Raman scattering of such AgTCNQ systems hasbeen found to be strongly enhanced and far superior to that obtained on bulk AgTCNQ films.We believe that such a system represents a novel and advantageous way of detecting theswitching behavior of AgTCNQ (and other metal-TCNQ compounds) by laser, as Ramanresearch on metal-TCNQ systems has been stymied in the past by poor Raman signals andsusceptibility to laser-induced degradation.
A Study On The Thermal Decomposition of Ba(tmhd)2 and Sr(tmhd)2
Authors: Ryu Hyun-Kyu , Han Jae Hyun , Moon Sang Heup
Published: April 2011

Decomposition of Sr(tmhd)2 and Ba(tmhd)2 was investigated by thermogravimetric analysis, in-situ FTIR, and mass spectrometry. Both compounds decomposed following 3 steps: 1) decomposition of the ligands, 2) simultaneous vaporization and partial decomposition of metal-organics, and 3) decomposition of the vaporized metal-organics which existed as the oligomeric species.

The Sr source decomposed at lower temperatures and in a narrower temperature range than the Ba source. Also, the gaseous oligomeric species from the Sr source decomposed relatively quickly while the corresponding species from the Ba source decomposed slowly over a long period. Such a difference between the two compounds is due to different bond energies between the metal atom and the ligands, as indicated by our FTIR results.
MOCVD of the Blue Electro-luminescent Phosphor CaGa2 S4:Ce from a Liquid Reagent Delivery System
Authors: Moss T.S. , Dye R.C. , Smith D.C. , Samuels J.A. , DelaRosa M.J. , Schaus C.F.
Published: April 2011

The deposition of CaS, Ga2S3, and CaGa2S4:Ce has been accomplished by MOCVD using Ca(tmhd)2, Ga(tmhd)3, and Ce(tmhd)4, with bubblers and with a liquid delivery system to control the flows. Samples were primarily characterized using x-ray fluorescence and electroluminescence measurements of the color and brightness. Deposition using the bubblers showed a definitive relationship between the Ga(tmhd)3 bubbler temperature and the Ga XRF counts. The Ca conversion shows a tenuous relationship with the Ca(tmhd)2 bubbler temperature, but the scatter of the data makes determining a correlation impractical. Use of the liquid delivery system is preferred to the bubblers because it delivered a reliable reagent flow without the same problems of degradation of the reagent over time. Analysis shows the CaS deposition is mass transport limited, while the Ga2S3 is limited by the deposition kinetics. However, application of these mechanisms to the CaGa2S4:Ce deposition system reveals that the CaGa2S4:Ce is independent of its components. Further, the deposition of CaGa2S4:Ce is found to be Ca rich under conditions which leads to low Ga/Ca ratios in the deposited film. This indicates that the conversion of Ca from Ca(tmhd)2 was catalyzed by the slight presence of Ga in the form of CaGa2S4:Ce or Ga2S3 on the surface. The Ca is thought to be deposited as CaS:Ce since there is a shift in the EL color towards green under low Ga/Ca ratios. The Ca conversion is also found to approach values predicted by the CaS deposition mechanism under conditions which lead to high Ga/Ca ratios, implying that excess Ga2S3 is needed for the deposition of CaGa2S4:Ce without any CaS:Ce inclusions.
Room Temperature Deposition of High Dielectric Constant, High Density Ceramic Thin Films
Authors: Chen K. , Nielsen M. , Soss S. , Liu S. , Rymaszewski E.J. , Lu T.-M.
Published: April 2011

Future high-performance integrated circuits and electronic packaging technology require the integration of many passive components, including high storage capacitors, on the systems. Because of the low melting temperature metal lines and polymer dielectrics in these electronic systems, one cannot employ most of the existing high temperature deposition techniques to grow thin film components. In this paper, we will report our recent work on the room temperature deposition of amorphous ceramic thin films, including BaxTi 2−xOy and SiOx, using the newly developed partially ionized beam technique. This technique utilizes a small percent (<3%) of selfions derived from the depositing materials to bombard the surface growth front during deposition. It is shown that a dramatic control of the density (and therefore the leakage current) and uniformity of the film can be achieved using this deposition technique without post annealing. Al or Cu was used as the electrodes in our multilayer MIM (metal-insulator-metal) test structure. As deposited thin film capacitors with a capacitance ranging from 25 to 100 nF/cm 2 have been fabricated with tan δ <0.01, leakage current of <l.μA/cm2 at 0.5 MV/cm, and breakdown field strength of several MV/cm. These ceramic capacitors do not show any dispersion up to 1 GHz.
Diamond Heat Sinks For High Temperature Electronics: Simuilation, And Thermal Analysis
Authors: Strifas Nickolaos , Christou Aris
Published: April 2011

performance that can be achieved by utilizing a diamond heat - sink design which minimizes junction - to - case thermal resistance. Effects of the thermal conductivity of the substrate material, the thermal conductivity of the die attach material, the substrate thickness, and the die attach thickness onl Ihe thermal resistance are addressed. The results indicate that the temperature increase could be 3 to 4 times less with diamond heat-sinks when compared to other materials.
Luminescence Characterization and Application of Diamond
Authors: Zaitsev A. M. , Melnikov A. A. , Denisenko A. V. , Varichenko V. S. , Job R. , Fahrner W. R.
Published: April 2011

The main advantages of stationary luminescence as a characterization technique of diamond are its relatively simple technical realization and a wide information gained on the impuritydefect structure of crystal. The physical reasons of capability of luminescence come from a very high Debye temperature of the diamond crystal, a strong interatomic bonding, and a relatively weak electron-phonon coupling in optical centers. As a result, a majority of optical centers in diamond possess the luminescence spectra with well resolved zero-phonon lines assisted by vibration-related replica, many of them retaining this spectral structure to room temperature and even above. As zero-phonon line spectrum is normally very sensitive to any external forces applied to the crystal (temperature, mechanical stress, magnetic and electrical fields), the optical centers can serve as sensitive markers, providing much information on the state of the didmond lattice surrounding them.

The value of the luminescence increases when diamond is characterized as a material for electronic and, particularly, optoelectronic applications. In this area luminescence really proves to be a unique characterization tool giving a direct information on optical and electronic properties (for instance, impurity and defect content, lifetime of charge carriers, efficiency of radiative recombination etc.), to be used in the devices.

In this review the basic parameters of the luminescence centers of diamond are considered and discussed from the view-point of the information they provide. Cathodoluminescence of diamond films and ion implanted layers is given as an example of luminescent characterization of diamond. The semiconducting structures with insulating active zones are discussed as a promising application of diamond for light emitting devices operating at high temperatures.
Negative Electron Affinity Effects And Schottky Barrier Height Measurements Of Metals On Diamond (100) Surfaces
Authors: Baumann P. K. , Nemanich R. J.
Published: April 2011

In this study copper and cobalt films have been deposited on natural type IIb single crystal semiconducting diamond (100) surfaces in ultra-high vacuum (UHV). Prior to metal deposition the diamond crystals have been cleaned by a 1150°C anneal in UHV. This treatment resulted in positive electron affinity surfaces. Upon deposition of 2Å of Cu or Co a negative electron affinity (NEA) was observed. Schottky barrier heights of 0.70 eV and 0.35 eV were found for Cu and Co respectively. In-situ Auger electron spectroscopy (AES) was employed to confirm the presence of a metal layer.
Diamond Film CVD Synthesis on Titanium: Experimental Evidence of the Intermediate Phases at the Film/Substrate Interface
Authors: Rossi M. , Terranova M. L. , Sessa V. , Vitali G.
Published: April 2011

The present findings concern the CVD deposition of diamond films on Ti substrates and the presence of a stratification of other various phases (Titanium Carbide, Titanium Hydride and Graphite) through the thickness of the CVD coatings.

The reflection high energy electron diffraction (RHEED) technique is mainly used to gain insight into the structure of the various phases generated at the diamond/substrate interface.

The experimental results seem to indicate that the structure of the transition layers present at the substrate/film interface play a fundamental role for the control of the heterogeneous nucleation process of the diamond.
Diamond Needles And Tips As Engineered Growth Shapes
Authors: Cherian K. A. , Litster J. , Rudolph V. , White E. T.
Published: April 2011

Diamond nucleation and growth by CFD were investigated to examine the possibility of engineering diamond growth shapes for practical applications. The results obtained include the following:

a) Evidence supporting certain factors influencing nucleation - useful in controlling nucleation sites and nucleation density.

b) Evidence for a double spiral growth mechanism operating on (111) faces under specific conditions - indicates the possibility of a new mechanism operating for diamond growth from the vapour phase, and the possibility of larger growth rates.

c) Evidence for the enhanced growth in <100= crystallographic direction on a cubooctahedral crystal and its control by varying the process parameters – thus showing the possibility of obtaining diamond needles and tips as engineered growth shapes, for specific applications.
Temperature Sensor On Boron Ion Implanted Diamond
Authors: Job R. , Denisenko A. V. , Zaitsev A. M. , Werner M. , Melnikov A. A. , Fahrner W. R.
Published: April 2011

p-type semiconducting boron doped layers have been fabricated on diamond substrates by ion implantation and subsequent annealing. A number of the related published experimental data and theoretical models on electrical properties of boron doped diamond are analyzed with regard to the temperature coefficient of resistance (TCR) of temperature sensors. The dependencies of the conductivity and activation energy on three parameters: (i) boron doping level NA, (ii) electrical compensation ratio ND/NA- C and (iii) duration of the postimplantation annealing time ta are studied. By variation of NA, C and t, an optimized technological regime for the temperature sensor fabrication can be obtained. One can summarize that: 1) the TCR value is not remarkably reduced with the boron concentration up to NA -1019 cm-3, 2) an increase of the electrical compensation decreases the activation energy and consequently the TCR coefficient,3) 1 h annealing at 1500°C is sufficient to remove the compensating radiation defects, 4) the variation of the ta from 1 min to 1 h changes the TCR value by 20% to 30%. Technological steps of the fabrication of a micro temperature sensor are given.
Microstructures of Amorphic Diamond™ Films Deposited by Laser-Ablation
Authors: Sohn Hyunchul , Krishnan Kannan , Fink Richard
Published: April 2011

Microstructures of Amorphic Diamond™ films deposited by laser ablation method were investigated using transmission electron microscopy. The AD films matrix was homogeneous with a sp3-type bonding fraction of 40%∼45% confirmed by electron energy-loss spectroscopy. The sp3 bonding fraction decreased monotonically with increasing annealing temperature. The main inhomogeneity in Amorphic Diamond™ was observed to be particulates of high density (>105/cm2) distributed through the depth of the film. Particulate size ranged from ∼10nm to a few μm and most of them were identified to be graphite. Large particles (>0.5μm) were agglomerates of smaller graphite crystallites. Possible mechanisms for cold field emission are discussed based on the microstructures observed in these AD films.
Studies of Pyrolysis Products of Explosives in Soils using Infrared Tunable Diode Laser Detection
Authors: Wormhoudt J. , Shorter J. H. , Kolb C. E.
Published: April 2011

We report on laboratory studies of the thermal decomposition of TNT under a variety of conditions. Our goal is a better understanding of the soil contamination detection technique used in site characterization using cone penetrometers, in which hot filament pyrolysis results in small gaseous molecules, such as NO, which can be detected by a variety of methods to indicate the presence of explosives in the soil. Our laboratory studies use a long-path sampling cell and tunable infrared diode laser absorption, which provide sensitive, specific, time-resolved detection of several of the key decomposition products. In this paper, we present both the initial results of laboratory experiments on mixtures of soil and TNT, designed to simulate the operation of a cone penetrometer probe, and also results of a series of heated tube experiments which serve to relate the first type of experiment to previously reported TNT decomposition studies.
The Design of Stable High Nitrogen Systems
Authors: Tartakovsky V. A.
Published: April 2011

A general strategy for the design of high nitrogen systems with an adequate degree of stability has been elaborated. The design of nitro compounds in which terminal nitro groups are bonded to the chain of several heteroatoms is a specific case within the strategy. In the process of working out the strategy a number of new high nitrogen systems ( dinitrazenic acid or dinitroamide HN3O4 and it salts, nitrodiazene oxides RN3O3 and tetrazine dioxides ) were discovered.

A number of new types of nitro compounds (bicyclo nitro-bis-hydroxylamine, nitrohydrazine, nitrohydroxylamine, sulfo-N-nitroimide and bis-N-nitroimide were synthesized.

This study opens new prospects in the field of the synthesis of high energy materials.
New Energetic Epoxy Binders
Authors: Jain S. R. , Amanulla S.
Published: April 2011

A new class of epoxy resins having N-N bonds in the backbone has been synthesized with a view to explore their properties as energetic binders. The N-epoxidation of bis-dicarbonylhydrazones of adipic, azelaic and sebacic dihydrazides results in the formation of viscous resins having epoxide end groups. The resins have been characterized by the elemental and end group analyses, IR and NMR spectra. Relevant properties for their use as binders in solid propellants, such as thermal stability, heat of combustion, burn rate and performance parameters of AP-based propellant systems, have been evaluated. A significant increase in the burn rate of AP-based propellants noticed, is perhaps related to the exothermicity of the binder decomposition and the reactivity of N-N bonds with perchloric acid formed during the combustion of AP.
Polynitroalkanes, Nitroazoles and Oximes in Electroorganic Synthesis
Authors: Niyazymbetov Murat
Published: April 2011

Electrochemical oxidation of anions of polynitroalkanes (PNA) proceeds via one-electron transfer and results in the formation of unstable radicals. The radicals undergo fragmentation, abstraction of a hydrogen atom from the solvent, and reaction with aromatic compounds to form aryl-PNA. The yield of aryl-PNA depends on the structure of the radicals and on the electron donating properties of the aromatic substrates. Due to their electrophilic properties, PNA-radicals also react with compounds containing heteroatoms with unshared electron pairs resulting in formation of dinitromethylides. Under anodic electrolysis conditions dinitromethylides which have a carbanionic structure can effectively transfer the dinitromethyl group to other organic substrates. Electrochemical oxidation of anions of nitroazoles also proceeds via one-electron transfer to generate nitroazolyl radicals. Their principal reaction is abstraction of hydrogen from the solvent. However, electrolysis of nitroazoles in the presence of aromatic compounds results in formation of N-aryl derivatives in good yield. It has been shown that electrooxidation of mono oximes leads to formation of unstable nitroso dimers, while electrooxidation of vicinal dioximes results in formation of furoxans in high yield.
Research on New Energetic Materials
Authors: Miller R. S.
Published: April 2011

The goal in this paper is to review progress in two emerging topics in energetic materials science. These emerging two areas are fluorine and oxygen rich energetic crystals and polymers and environmentally friendly energetic material classes.
Time Resolved Optical Spectroscopy to Examine Chemical Decomposition of Energetic Materials Under Static High Pressure and Pulsed Heating Conditions
Authors: Russell Thomas P. , Allen Theresa M. , Gupta Y. M.
Published: April 2011

The study of the deflagration or detonation reactions of energetic materials is challenging due to the high pressure, high temperature, and time domain under which the reactions occur. Experimental measurements, are presented that demonstrate the ability to continuously monitor the global reaction times and reaction sequences associated with chemical reactions under these conditions. Time resolved absorption spectroscopy is used in conjunction with a high pressure gem anvil cell to probe the real-time chemical processes during pulsed-heating. Samples are initiated by a rapid thermal jump induced by absorption of a single laser pulse. Time resolved absorption spectroscopy of 3,6 trinitroethylamine tetrazine reaction is demonstrated by the real time measurement of the decrease in the ϕ-ϕ* absorption at 110 ns temporal resolution during laser heating at pressures up to 3.5 Gpa
A Reactive Flow Model with Coupled Reaction Kinetics for Detonation and Combustion in Non-Ideal Explosives
Authors: Miller Philip J.
Published: April 2011

A new reactive flow model for highly non-ideal explosives and propellants is presented. These compostions, which contain large amounts of metal, upon explosion have reaction kinetics that are characteristic of both fast detonation and slow metal combustion chemistry. A reaction model for these systems was incorporated into the two-dimensional, finite element, Lagrangian hydrodynamic code, DYNA2D. A description of how to determine the model parameters is given.
Anta and its Oxidation Products
Authors: Lee Kien-Yin , Gilardi Richard , Hiskey Michael A. , Stine James R.
Published: April 2011

5-Amino-3-nitro-lH-1,2,4-triazole (ANTA) is a molecule with high stability. Aside from being an insensitive high explosive (IHE), it is also used as a synthon for other potential new IHEs. The crystal structure of ANTA was resolved by X-ray crystallography. However, when ANTA was recrystallized from 2-butanone, crystals with molecular packing characterized by extended planar sheets were obtained (ß-ANTA). The crystal density of ß-ANTA is 1.73 g/cm3, which is less dense than α-ANTA (p = 1.82g/cm3).

The high-nitrogen molecule, 5,5'-dinitro-3,3'-azo-1,2,4-triazole (DNAT) was calculated to have a high density and a positive heat of formation (AHf). In an attempt to prepare DNAT, we have studied the oxidation of ANTA with different oxidizers. It was found that DNAT is the reaction product when the potassium salt of ANTA was oxidized with potassium permanganate. However, when ANTA was oxidized with ammonium persulfate in aqueous medium, one of the reaction products obtained was the azoxy moleclue of DNAT (DNAzT). We are unable to determine the crystal densities of either DNAT and DNAzT because the crystals obtained were solvated with the crystallization solvents.
Fast Color Detection with Two-Terminal P-I-I-N Devices
Authors: Neidlinger T. , Schubert M. B. , Schmid G. , Brummack H.
Published: April 2011

In order to overcome the intrinsic speed limitation of amorphous silicon nipin color sensors we present an alternative way of achieving bias-controlled spectral sensitivity of two-terminal thin film devices, piin structures with appropriate band gap and thickness of their single layers can be used as photodetectors that are able to sequentially extract different color signals. Color separation is achieved by controlling the absorption and electric field profile across these piin devices, and thanks to the differences in electron and hole transport properties. Because in contrast to nipin devices there is no need for reverting readout voltages for color separation, this type of sensors can be operated at much higher readout frequencies. Spectral response and bias voltage transients have been analysed up to 20kHz, and preliminiary data are presented on the optimization of speed, dynamic range and color separation by varying bandgap and thickness of p- and i-layers. Furthermore a three-color sensor has been realized by introducing an additional intrinsic layer.
Capacitance Characterization of Amorphous Silicon/Amorphous Silicon Germanium Heterostructures
Authors: Palsule C. , Paschen U. , Cohen J. D. , Yang J. , Guha S.
Published: April 2011

We have performed voltage-pulse stimulated capacitance transient measurements along with other junction capacitance measurements on a-Si:H/ a-Si,Ge:H heterostructures deposited on p-type crystalline silicon using the glow discharge technique. For a filling pulse that puts the c-Si/a-Si:H junction in forward bias, the capacitance transients consist of two components- a fast component corresponding to electron emission and a slow component corresponding to hole emission. For a fixed starting reverse bias, we have found that the density of trapped holes is proportional to the product of the filling pulse voltage and the filling pulse width and reaches a saturation value at a certain value of the product. These hole traps appear to reside at or very close to the a-Si:H/a-Si,Ge:H interface. The estimated trap concentration is around 1011/cm2 and is independent of temperature and applied bias, ruling out the creation of the traps during the filling pulse. We also report results on samples in which a-Si:H/ a-Si,Ge:H interface has been modified during growth to alter the concentration of the hole traps.
Admittance of a-Si:H/c-Si Schottky Diodes
Authors: Gall S. , Hirschauer R. , Kolter M. , Bräunig D.
Published: April 2011

We have measured the admittance (conductance and capacitance) of a-Si:H/c-Si heterostructure Schottky diodes as a function of frequency, temperature and voltage in the dark and under spectral illumination (in the wavelength range between λ=500nm and λ=1200nm). Thus, it is possible to observe the activation/deactivation of trapping-detrapping effects within the a-Si:H layer (near the a-Si:H/c-Si interface). We have determined the conduction band offset of the a-Si:H/c-Si heterostructure. The spectral behaviour of the admittance is dominated by the absorption of light in the c-Si and the valence band offset of the heterojunction. We have also developed an equivalent circuit of the a-Si:H/c-Si heterostructure Schottky diode in the dark, which is capable of describing the measured behaviour.
Physics of Below Threshold Current Distribution in a-Si:H TFTs
Authors: Slade H. C. , Shur M. S. , Deane S. C. , Hack M.
Published: April 2011

We have examined the material properties and operation of bottom-gate amorphous silicon thin film transistors (TFTs) using temperature measurements of the subthreshold current. From the derivative of current activation energy with respect to gate bias, we have deduced information about the density of states for several different transistor types. We have demonstrated that, in TFTs with thin active layers and top nitride passivation, the current conduction channel moves from the gate insulator interface to the passivation insulator interface as the transistor switches off. Our 2D simulations clarify these experimental results. We have examined the effect of bias stress on the transistors and analyzed the resulting reduction in the subthreshold slope. Based on these results, we have extended our analytic amorphous silicon TFT SPICE model to include the effect of bias stress.
Material Basis of Highly Stable a-Si:H Solar Cells
Authors: Rech B. , Wieder S. , Siebke F. , Beneking C. , Wagner H.
Published: April 2011

We achieved a stabilized efficiency of 9.2 % after only 8 % relative degradation for an a-Si:H/a-Si:H stacked cell with the top-cell i-layer prepared at 140 °C using a high hydrogen dilution of the silane process gas. From a comprehensive characterization of p-i-n cells and the corresponding i-layer material prepared at 140 °C and 190 °C substrate temperature with different hydrogen dilutions, we conclude that the performance of these pin cells strongly correlates with the material properties of the corresponding i-layers. High fill factors after light soaking are reflected in a good microstructure, high photo-conductivity, and relatively low defect density. Whereas the initial Voc is limited by interface recombination, volume recombination dominates the forward-dark current after light soaking. The stabilized Voc as well as the short-circuit current densities correlate with the optical bandgap of the i-layer.