bluuebunny/crossref_metadata_2025 huggingface dataset:
Complexation of Transuranic Ions by Humic Substances: Application of Laboratory Results to the Natural System
Authors: Czerwinski Ken , Kim Jae-Il
Published: September 2012

Environmental investigations show transuranic ions sorb to humic substances. The resulting species are often mobile and are expected to be important vectors in the migration of transuranic ions in natural systems. However, theses environmental studies yield no quantitative data useful for modeling. Laboratory complexation experiments with transuranic ions and humic substances generate mermodynamic data required for complexation modeling. The data presented in this work are based on the metal ion charge neutralization model, which is briefly described. When a consistent complexation model is used, similar results are obtained from different experimental conditions, techniques, and laboratories. Trivalent transuranic ions (CM(III), AM(III)) have been extensively studied with respect to pH, ionic strength, origin of humic acid, and mixed species formation. The complexation of Np(V) has been examined over a large pH and metal ion concentration range with different humic acids. Some data does exist on the complexation of plutonium with humic acid, however further work is needed. Calculations on the Gorleben aquifer system using the thermodynamic data are presented. Critical information lacking from the mermodynamic database is identified.
The Effect of Specific Surface Area on Radionuclide Sorption on
Crushed Crystalline Rock
Authors: Hölttä P. , Siitari-Kauppi M. , Huihuri P. , Lindberg A. , Hautojärvt A.
Published: September 2012

The sorption of sodium (22Na), calcium (45Ca) and
strontium (85Sr) was studied on mica gneiss, unaltered,
moderately altered and strongly altered tonalite samples taken from hole
SY-KR7 drilled in the Syyry area in Sievi, Western Finland. The crushed rock
samples were sieved into six fractions from 71 μm to 1250 μm. A proportional
mineral composition for the different fractions were estimated by X-ray
diffraction. The specific fraction surface areas were determined by the BET
nitrogen adsorption method. The fractal method was applied to characterize
rocks and to describe quantitatively surface irregularity. The mass
distribution ratio values for each fraction were determined using the static
batch method. The sorption of tracers onto different minerals was observed
using rock thin sections. Kd-values calculated from thin section
Ka-values and Kd revalues obtained from batch
experiments were in good agreement. Mass distribution ratios for different
size fractions are given, and the effect of the specific surface area is
discussed. Owing to larger specific surface areas considerably higher
sorption on smaller fractions was found for altered tonalites.
The Effect of Temperature on the Sorption of Technetium, Uranium, Neptunium and Curium on Bentonite, Tuff and Granodiorite
Authors: Baston G M N , Berry J A , Brownsword M , Heath T G , Blett D J , Tweed C J , Yui M
Published: September 2012

A study of the sorption of the radioelements: technetium; uranium; neptunium; and curium onto geological materials has been carried out as part of the PNC programme to increase confidence in the performance assessment for a high-level radioactive waste repository in Japan. Batch sorption experiments have been performed in order to study the sorption of the radioelements onto bentonite, tuff and granodiorite from equilibrated de-ionised water under strongly-reducing conditions at both room temperature and at 60°C.

Mathematical modelling using the geochemical speciation program HARPHRQ in conjunction with the HATCHES database has been undertaken in order to interpret the experimental results.
Characterization of Electroactive Cs Ion-Exchange Materials
using XAS
Authors: Hess N. J. , Sukamto J. H. , Rassat S. D. , Hallen R. T. , Orth R. J. , Lilga M. A. , Lawrence W. E.
Published: September 2012

Various ion exchange materials have been proposed for the removal of Cs from
high level waste streams produced during the reprocessing of fuel rods. Cs
can be released from loaded traditional exchange resins by elution and then
the resin can be reused. However large quantities of secondary wastes are
generated. Another class of “single use” exchangers is directly incorporated
in the loaded state into a solid waste form (e.g. borosilicate glass logs).
A third alternative is electroactive ion-exchange materials, where the
uptake and elution of Cs are controlled by an applied potential. This
approach has several advantages over traditional reusable ion-exchange
resins including much reduced secondary waste, higher Cs selectivity, and
higher durability.

XAS experiments were conducted at the Fe K-edge and Cs Lm-edge on
a series of electrochemically produced nickel ferrocyanide films to
determine the effects of deposition conditions and subsequent alkali
exchange on structural and chemical aspects of the films. The deposition
conditions include methods described in the literature and PNNL proprietary
procedures. Although the performance and the durability of the films do vary
with processing conditions, Fe K-edge EXAFS results indicate that all
deposition conditions result in the. formation of the cubic phase. Initial
results from Cs Lm-edge EXAFS analysis suggest that the Cs ion is
present as a hydrated species.
Groundwater Colloid Properties and their Potential Influence on
Radionuclide Transport
Authors: Degueldre C.
Published: September 2012

Colloid facilitated transport is still an issue in radioactive waste
management. Sophisticated phenomenological transport models are available,
but progress is required to fully understand mechanisms and parameters. This
study lead in this direction. Investigation of the marl groundwater colloids
in steady-state conditions at Wellenberg, shows that their concentration is
independent of the water flow rate. Their generation is caused by the
re-suspension of the rock clay fraction only. The re-suspension process is
presently being studied under flow transient conditions. Extension of our
measurements to other safety relevant systems as well as a literature survey
show that the colloid concentration under steady-state conditions is
correlated to the concentration of alkali elements and earth alkali
elements. The higher their respective concentration, the fewer colloids are
occurring. Considerations on colloid contamination models are also included.
The paper emphasises various colloid transport mechanisms including colloid
generation from the irreversibly contaminated aquifer.
Investigation of Rock Samples Using X-Ray-Microcomputer-Tomography Before and After Mercury Intrusion Porosimetry
Authors: Klobes P. , Riesemeier H. , Meyer K. , Goebbels J. , Siitari-Kauppi M. , Hellmuth K-H.
Published: September 2012

A new method for the physical characterization of rock matrices for use in site investigations of nuclear waste repositories has been developed. The method can provide information needed in the assessment of the performance of the geosphere working as a natural barrier retarding the migration of radionuclides by diffusion into the rock matrix. Most conventional methods for the physical characterization of rocks give only bulk information. The combination of mercury po-rosimetry and computer tomography can give 3-D data on mineral-specific porosity distributions with additional pore size information. Additionally, limits for mineral-specific internal surface areas can be estimated, which is essential for the assessment of water-rock interaction and reactive interaction with radionuclides (sorption). Results of measurements on granitic rock (granodiorite) from the Baltic shield are discussed and integrated with results by complementary methods.
Matrix Diffusion of Some Alkali- and Alkaline Earth-Metals in
Granitic Rock
Authors: Johansson H. , Byegård J. , Skarnemark G. , Skålberg M.
Published: September 2012

Static through-diffusion experiments were performed to study the diffusion
of alkali- and alkaline earth-metals in fine-grained granite and
medium-grained Äspö-diorite. Tritiated water was used as an inert reference
tracer. Radionuclides of the alkali- and alkaline earth-metals (mono- and
divalent elements which are not influenced by hydrolysis in the pH-range
studied) were used as tracers, i.e.
22Na+, 45Ca2+ and Sr The
effective diffusivity and the rock capacity factor were calculated by
fitting the breakthrough curve to the one-dimensional solution of the
diffusion equation. Sorption coefficients, Kd, that were derived
from the rock capacity factor (diffusion experiments) were compared with
Kd determined in batch experiments using crushed material of
different size fractions.

The results show that the tracers were retarded in the same order as was
expected from the measured batch Kd. Furthermore, the largest
size fraction was the most representative when comparing batch Kd
with Kd evaluated from the diffusion experiments. The observed effective
diffusivities tended to decrease with increasing cell lengths, indicating
that the “transport” porosity decreases with increasing sample lengths used
in the diffusion experiments.
Behaviour of Plutonium Interacting with Bentonite and Sulfate-Reducing Anaerobic Bacteria
Authors: Kudo A. , Zheng J. , Cayer I. , Fujikawa Y. , Asano H. , Arai K. , Yoshikawa H. , Ito M.
Published: September 2012

The interactions between sulfate reducing anaerobic bacteria and plutonium, with or without bentonite present, were investigated using distribution coefficients {Kd (ml/g)} as an index of the radionuclide behaviour. Plutonium Kds for living bacteria varied within a large range, from 1,804 to 112,952, depending on the pH, while the Kds ranged from 1,180 to 5,931 for dead bacteria. In general, living bacteria had higher plutonium Kds than dead bacteria. Furthermore, the higher Kd values of 39,677 to 106,915 for living bacteria were obtained for a pH range between 6.83 and 8.25, while no visible pH effect was observed for dead bacteria. These Kd values were obtained using tracers for both236Pu and239Pu, which can check the experimental procedures and mass balance.

Another comparison was conducted for plutonium Kd values of mixtures of living bacteria with bentonite and sterilized bacteria with bentonite. The range of Kd values for the non-sterilized bacteria with bentonite were 1,194 to 83,648 while Kd values for the sterilized bacteria with bentonite were from 624 to 17,236. Again, the Kd values for the living bacteria with bentonite were higher than those of sterilized bacteria with bentonite. In other words, the presence of living anaerobic bacteria with bentonite increased, by roughly 50 times, the Kd values of239Pu when compared to the mixture of dead bacteria with bentonite. The plutonium Kd values for bentonite alone, both non-sterilized and sterilized, were within a constant range of around 10,000 even though some of the data are not yet available.

The bentonite used for this experiment was a product of Japan and the sulfate reducing anaerobic bacteria was previously used for the treatment of a pulp and paper wastewater. The results indicate that the effects of anaerobic bacteria within the engineered barrier system (in this case bentonite) will play a significant role in the behaviour of plutonium in geologic repositories.
Effect of Dry Density on Activation Energy for Diffusion of
Strontium in Compacted Sodium Montmorillonite
Authors: Kozaki Tamotsu , Sato Hiroki , Fujishima Atsushi , Saito Nobuhiko , Sato Seichi , Ohashi Hiroshi
Published: September 2012

For performance assessments of geological disposal of high-level radioactive
waste, activation energies for the diffusion of strontium ions and the basal
spacings of compacted sodium montmorillonite in the water-saturated state
were determined.

Basal spacings determined by XRD indicated changes in the interlamellar
space from a three-water layer hydrate state to a two-water layer hydrate
state as the dry density of the montmorillonite increased from 1.0 to 1.8 Mg
m-3. Activation energies from 17.3 to 30.8 kJ mol-1
for the apparent diffusion coefficients of strontium ions were obtained. The
lower activation energies than for diffusion of strontium ions in free water
were determined for montmorillonite specimens of lower dry density (1.2 Mg
m-3 and below), while the higher activation energies were at
higher dry densities (1.4 Mg m-3 and above).

These findings cannot be explained by changes in only the geometric
parameters, which the pore water diffusion model is based upon. Possible
explanations for the dry density dependence of the activation energy are the
changes of the temperature dependence of the distribution coefficients
and/or of the diffusion process with increasing dry density
Estimation of the Radionuclide Transport by Applying the Mean,
the Standard Deviation and the Skewness of Permeability
Authors: Niibori Y. , Tochiyama O. , Chida T.
Published: September 2012

A new method for estimating the mass transport by using the stochastic
values (the arithmetic mean, the standard deviation and the skewness) of
permeability is presented. Generally, detail of permeability distribution
cannot be obtained except for moments of the distribution. Also, measurement
results of permeability for the rock matrix including cracks or fast
flowpaths do not always follow the log-normal distribution frequently
applied. In such a situation, we must evaluate the characteristic
permeabilities for the whole or some regions of the disposal site including
the accessible environment.

The authors have investigated the characteristic permeability on the basis
of some probability density functions of permeability, applying the Monte
Carlo method and FEM. It was found that its value does not depend on type of
probability density function of permeability, but on the arithmetic mean,
the standard deviation and the skewness of permeability [1].

This paper describes the use of the stochastic values of permeability for
estimating the rate of radioactivity release to the accessible environment,
applying the advection-dispersion model to two-dimensional, heterogeneous
media. When a discrete probability density function (referred to as ‘the
Bernoulli trials’) and the lognormal distribution have common values for the
arithmetic mean, the standard deviation and the skewness of permeability,
the calculated transport rates (described as the pseudo impulse responses)
show good agreements for Peclet number around 10 and the
dimensionless standard deviation around 1. Further, it is
found that the transport rates apparently depends not only on the arithmetic
mean and the standard deviation, but also on the skewness of permeability.
When the value of skewness dose not follow the lognormal distribution which
has only two independent parameters (the mean and the standard deviation),
we can replicate the three moments estimated from an observed distribution
of permeability, by using the Bernoulli trials having three independent
parameters.
Near-Field Chemical Composition of Porewaters in a Near-Surface
Low-Level Radioactive Waste Vault
Authors: Caron F. , Haas M. K. , Manni G. , Torok J.
Published: September 2012

A long-term waste degradation experiment has been performed with actual
low-level radioactive wastes (LLRW) at the Chalk River Laboratories (CRL),
to support the licensing and modelling efforts for near-surface disposal.
The wastes consist of paper, mop heads, paper towels, used clothing, etc.
The wastes were compacted into bales and sealed into separate steel
containers, which were connected to leachate collection systems for
sampling. The leachates collected had a composition typical of landfill
leachates. The major inorganic ions were Na, Ca, Cl, and Fe, and the ionic
strength was ∼0.05 M. The relative distribution of inorganic ions in the
leachates was remarkably similar between bales. Volatile fatty acids (VFA)
were the major species of dissolved organic carbon (DOC, total DOC up to
7000 mg/L). A typical composition of leachates is proposed, which can be
used in geochemical and source term modelling.
Direct Characterization of Transport Parameters in Near-Field
and Engineered Backfill/Invert Materials
Authors: Conca J. L. , Robinson B. A. , Triay I. R. , Bussod G. Y.
Published: September 2012

Performance assessment of a potential repository at Yucca Mountain includes
flow and transport modeling of the unsaturated zone as the critical
predictive component, and involves a series of model calculations that
provide predictions of the migration of important radionuclides in the
inventory to the water table. The modeling requires the relevant properties
of both the natural environment and the engineered systems. The Unsaturated
Flow Apparatus, UFA, was used to directly measure the unsaturated and
saturated transport properties of whole rock tuff cores and candidate
barrier materials to provide real input parameters to the models. These
properties included hydraulic conductivity, matric potential, air
permeability, and diffusion coefficient, all of which are strong functions
of the volumetric water content. Results show that for all recharges above
0.1 mm/yr, fractures will be partially saturated and conducting at that
recharge rate. Whenever the thermal conditions relax enough to allow
rewetting of the host rock, there will be dripping from the drift ceiling.
Unsaturated transport of colloids through fractured cores of Topopah Spring
and Prow Pass tuffs was also investigated and found to depend primarily upon
colloid charge, and not size, for the rock cores investigated.
Experimental Study of Colloid Filtration by Compacted
Bentonite
Authors: Kurosawa Susumu , Yui Mikazu , Yoshikawa Hideki
Published: September 2012

In this study, the transport behavior of colloids through compacted
bentonite and sand-bentonite mixtures was investigated. Colloidal gold was
used to simulate mobile colloids because it was well characterized and its
dispersivity was controlled. The bentonite used was a sodium bentonite. The
sand-bentonite mixtures were prepared by mixing up to 50wt.% silica sand
with the bentonite. The bentonite and the sand-bentonite mixtures were
compacted to dry densities of 1000 and 1800 kg/m3 and then
saturated with distilled water. The sand-bentonite mixture was also
saturated with synthetic sea-water. Column experiments were performed to
investigate colloidal transport. Further, colloidal particles stabilities in
high ionic strength water such as bentonite porewater or saline groundwater
were interpreted based on the repulsion potential from the double layer
force and the attraction potential from the van der Waals force.

The results indicated that the colloidal particles were effectively filtered
by both the compacted bentonite and the sand-bentonite mixtures. This study
indicated that the effect of colloids on radionuclide transport in compacted
bentonite is negligible for the safety assessment of high level radioactive
waste (HLW) disposal.
Experimental Study on Self-Healing of Bentonite / Sand Mixtures
and its Impact on Hydraulic Permeability
Authors: Hokari Toshiyuki , Okihara Mitsunobu , Ishii Takashi , Kojima Keiji
Published: September 2012

The effects of gas permeation on the hydraulic permeability of
bentonite/sand mixtures were studied experimentally by conducting
permeability tests with various fluids and by microscopic observations. In
these tests, hydraulic permeabilities were measured before and after helium
gas was applied to permeate the mixtures.

Although gas formed preferential migration paths through the mixtures, the
imperviousness of the bentonite/sand mixtures to the tested fluids never
deteriorated because the paths became filled by swelling bentonite on
re-saturation.
Comparative Tests for Evaluating Permeability Changes of a
Compacted Bentonite/Sand Mixture During Shear
Authors: Esaki T. , Zhang M. , Mitani Y.
Published: September 2012

A compacted mixture of Kunigeru VI bentonite and D-sand is being considered
for use as an engineered barrier in low-level radioactive waste disposal
facilities in Japan. An important issue is the maintenance of the
retardation property of the mixture during shear that might be induced in
such barriers by earthquakes and/or gradual tectonic deformations occurring
over the design life of the facility. To investigate this issue, comparative
tests on a bentonite-sand mixture and kaolin-sand mixture were conducted by
means of a recently-developed coupled shear and permeability testing
apparatus under temperature controlled condition. In addition to
permeability, the specific storage of bentonite-sand specimen during shear
is also systematically evaluated with the new analytical theory for the
constant flow permeability test. The present study reveals that 1)
temperature control is preferred for measuring the permeability of
extremely-low permeability materials with the constant-flow pump method; 2)
both the permeability and specific storage of the mixture of Kunigeru VI
bentonite and D-sand (bentonite to sand weight ratio = 15: 85) were not
significantly influenced by shear strains up to 3% whereas the permeability
of the kaolin-sand mixture increased almost linearly with the increment of
shear strain; 3) the swelling of bentonite in the mixture under low
confining stress decreases both the permeability and specific storage of
bentonite-sand mixture. This feature of bentonite helps maintain the
long-term retardation property of the mixture; and 4) the constant flow
permeability test method, with the newly derived theoretical analysis,
promises to become a very effective means of investigating, rapidly and
systematically, the permeability and specific storage of extremely-low
permeability materials with relatively-low (i.e. close to in situ) hydraulic
gradients. This is necessary for the design and long-term performance
assessment of engineered barriers.
Experimental Study of Gas Permeabilities and Breakthrough
Pressures in Clays
Authors: Tanai K. , Kanno T. , Gallé C.
Published: September 2012

In this study, gas migration experiments in unsaturated and saturated states
were carried out to clarify the fundamental gas migration characteristics in
compacted bentonite to be used for the geological disposal of high-level
radioactive waste. In unsaturated experiments, the gas permeability for
Japanese bentonite (Kunigel VI) as a function of degree of saturation was
measured to examine the applicability of conventional two-phase flow models
to compacted bentonite. The intrinsic permeability obtained in this study
was about five orders of magnitude larger than that obtained in water
permeation tests with the same density. The difference seems to originate
from the change of pore structure due to the swelling phenomenon of the
bentonite. Since these effects have not been evaluated quantitatively yet,
various relative gas permeability functions of conventional two-phase flow
models were applied as a first approximation.

Saturated experiments designed to simulate the gas migration phenomenon in a
repository for the waste were carried out to obtain relationship between
breakthrough and swelling pressures using Kunigel VI and French Fo-Ca clay
in saturation state. The reproducibility of the breakthrough pressure was
also examined for Kunigel VI bentonite. The breakthrough pressure was almost
the same as swelling pressure irrespective of the type of clay. As to the
reproducibility of breakthrough pressure, it was observed that first and
second breakthrough pressures were almost the same for Kunigel VI specimens
with the dry densities of 1.7 and 1.8 g/cm3.
Photoinduced intermolecular Charge-Transfer Systems for Optical Limiting
Authors: Wu X.-L. , Heikal A. A. , Lee I.-Y. S. , Bohorquez M. , Perry J. W.
Published: September 2012

Photoinduced intermolecular charge transfer (PICT) in donor/acceptor systems has been investigated as an approach to the design of new optical limiting (OL) materials. Solution of cyanines or porphyrins (as sensitizers) and viologen derivatives (as electron acceptors) were used in these studies. Picosecond time-resolved fluorescence measurements were carried out to estimate the charge-transfer rate in these donor/acceptor systems. The radical-ion absorption bands were identified using spectroelectrochemistry. Nonlinear transmission measurements with picosecond and nanosecond laser pulses were utilized to determine the effective photo-induced to ground-state absorption cross-section ratio of the sensitizers alone and the sensitizer/acceptor systems. Our studies are consistent with optical limiting by PICT in solution and indicate a substantial radical-ion yield in the systems examined.
Spectroscopy and Nonlinear Absorption of α, ω-dithienyi Polyenes
Authors: Natarajan L. V. , Sowards Laura A. , Spangler C. W. , Tang N. , Fleitz P. A. , Sutherland R. L. , Cooper T. M.
Published: September 2012

The photophysics and nonlinear absorption behaviour of a series of α, ω-dithienyl polyenes were studied in chloroform and n-octane solutions. Steady state fluorescence, fluorescence lifetime and quantum yield measurements were made. The fluorescence quantum yields were significantly lower than those of the corresponding ax,o-diphenyl polyenes. Among the dithienyl polyenes, 3,3′-substituted polyenes exhibited stronger fluorescence than those of the 2,2′-substituted. Nonlinear optical absorption experiments showed evidence of two photon absorption.
Photorefractive Effect in CdSSe:V Crystals
Authors: Morgan Steven H. , Davis Michelle , Pan Zhengda , Chen Kuo-Tong , Chen Henry , Davis Swanson L. , Burger Arnold
Published: September 2012

We present two-wave mixing results obtained with CdSSe:V crystals. A large photorefractive gain of 0.24 cm-1 was observed at 633 nm with an optical intensity of 60 mW/cm2 and a grating period of 1.6 μrm. At this wavelength, we measured the photorefractive gain as a function of the grating period and incident optical intensity. To our knowledge, this is the first observation of the photorefractive effect in vanadium doped CdSSe crystals. The CdSSe crystals were grown by physical vapor transport (PVT) and doped with 150 ppm (nominal) vanadium for creating trap centers. The grown crystal has a large crystal size, good optical quality and a medium resistivity of 10-5 - 108 Ω-cm. Room temperature absorption and low temperature photoluminescence spectroscopy measurements are also discussed. With a significant photorefractive effect, the CdSSe:V crystals are promising for many device applications based on photorefractive effect, including optical limiting devices in the visible region.
Infrared Liquid Crystal Tunable Filters
Authors: Wu Shin-Tson , Wu Chiung-Sheng
Published: September 2012

Computer simulations on Fabry-Perot liquid crystal tunable filters are performed in the 3–5 and 8–12 μm bands and some discrete laser lines. Effects of transmittance, contrast ratio and response time on liquid crystal birefringence, layer thickness, absorption coefficient and reflectivity of mirrors are analyzed. Absorption spectra and responsible mechanisms of liquid crystals in the 2.5–20 μm region are studied. The fluorinated tolane and diphenyl-diacetylenes and dialkyl diphenyldiacetylenes are found to possess low absorption in the mid-IR range. Mixtures of these compounds will find useful applications for the proposed IR tunable filters.
Liquid Crystals for Fast Infrared Laser Switching and Optical Limiting Application
Authors: Khoo I. C. , Wood M. V. , Guenther Brett D.
Published: September 2012

The nonlinear optical effects of chlorophyll ‘a’ have been determined using an array of measurement techniques. Regions of spectral interest exhibiting induced excited state absorption were identified with transient absorption spectroscopy measurements. At specific wavelengths within these regions, the dye was characterised using the Z-scan technique. Additional measurements were made to complement the latter results including a focused aperture experiment in which thermal defocusing and scattering mechanisms were identified.
Optical Limiting in Phthalocyanine Solutions and in Pure Liquid Phthalocyanines
Authors: Flom Steven R. , Pong Richard G. S. , Shirk James S. , Bartoli F. J. , Cozzens R. F. , Boyle Michael E. , Snow Arthur W.
Published: September 2012

Optical limiting, degenerate four-wave mixing and transient absorption experiments have been performed on a neat liquid lead substituted phthalocyanine. The photophysical mechanisms responsible for the good optical limiting observed in other phthalocyanine solutions are maintained in this pure liquid despite its different peripheral substitution pattern. The liquid is shown to have excited state absorption cross sections that exceed those of the ground state through much of the visible spectrum. Hybrid absorptive/refractive nonlinear response is demonstrated to contribute to both the four-wave mixing and optical limiting response. The mechanism and states responsible are discussed.
Nonlinear Optical Fiber Core Materials For Optical Limiting Application
Authors: Khoo I. C. , Wood M. V. , Guenther Brett. D.
Published: September 2012

Several liquid phase liquid crystals and liquids are found to possess broadband nonlinear absorption characteristics suitable for optical limiting applications. Using these liquids as fiber waveguiding cores, we have developed fiber arrays that provide excellent limiting performance characteristics against frequency agile visible laser pulses in the nanosecond - picosecond time scale. These fiber arrays are compact, low cost/weight, and are capable of transmitting high quality images throughout the entire visible spectrum.
Shadowgraphic Imaging of Dilute Carbon and Mo2Ag4S8,[PPh3]4 Suspensions
Authors: Goedert Robert , Becker Roger , Clements Andrew , Whittaker Thomas
Published: September 2012

Time-resolved imagery is presented showing the changes that occur in the focal volume of dilute liquid/particle suspensions following the arrival of single, Q-switched, frequency-doubled, Nd:YAG laser pulses. Limiting data and corresponding imagery at 21, 84, 244, 790, and 2900 nanoseconds following the laser pulse are presented for a carbon particle suspension consisting of used (carbonized) 1OW-15 motor oil and for a suspension of the inorganic metallic cluster molecule Mo2Ag4S8 [PPh3]4. The images in conjunction with the accompanying limiting data show that the reduction in transmission, observed as the input pulse energy is increased, results from scattering from bubbles augmented by plasma absorption. Keywords: laser induced breakdown, plasma, suspension, bubble, nonlinear materials, shadowgraph, imagery
Non-Linear Optical Characteristics of Novel Porphyrin Dye Media
Authors: McEwan K. J. , Robertson J. M. , Wylie A. P. , Anderson H. L.
Published: September 2012

Measurements of sensitive RSA phenonema in new porphyrin dyes are presented. Both the linear and non-linear optical properties are shown to depend strongly on the molecular structure. A detailed analysis of two of the porphyrins reveals that inter-systems crossing rate and the excited state absorption profile are strongly influenced by substitution of a heavy atom into the central atom position. It is shown that by appropriate choice of wavelength values in excess of 30 can be achieved for the material parameter σex / σgr. This value compares well with previously reported results and is achieved in conjunction with excited state lifetimes on the order of 300 ns.
Nonlinear Mechanisms in Carbon-Black Suspension in a Limiting Geometry
Authors: Fougeanet Francois , Fabre Jean-Claude
Published: September 2012

Although Carbon-Black suspensions (CBS) have been studied extensively for optical limiting applications, the microscopic mechanisms responsible for their limiting behavior still remain unclear. To study the mechanisms leading to the nonlinearity, we have performed a pump-probe experiment coupled with plasma emission measurements. Time resolved probe transmission have permitted to differentiate bubbles from plasma effects in the case of Carbon-Black in CS2. Other effects are discussed in terms of limiting performance.
Reverse Saturable Absorption and Induced Thermal Effects in Chlorophyll ‘A’
Authors: Robertson J. M. , Bourhill G.
Published: September 2012

The nonlinear optical effects of chlorophyll ‘a’ have been determined using an array of measurement techniques. Regions of spectral interest exhibiting induced excited state absorption were identified with transient absorption spectroscopy measurements. At specific wavelengths within these regions, the dye was characterised using the Z-scan technique. Additional measurements were made to complement the latter results including a focused aperture experiment in which thermal defocusing and scattering mechanisms were identified.
DFT Study of Alkynyl Porphyrin Dimers and Brominated Tetraphenyl Porphyrins
Authors: Wang Zhiqiang , Day Paul , Pachter Ruth , McLean Daniel G.
Published: September 2012

Geometry optimizations and electronic structure calculations using Density Functional Theory (DFT) are reported for tetra-acetylene porphyrins (TAP), their dimers, and octabromotetraphenyl porphyrins (OBP). The acetylene group contributes to the π-electron conjugation along the porphyrin ring for the HOMO and LUMO, and reduces significantly the HOMO-LUMO gap. The gap is further reduced in dimers. The planar geometry of the TAP dimer has a lower energy than the non-planar one. The geometry of H2OBP is found to be non-planar, and the distortion of porphyrin ring is shown to be closely related to the HOMO-LUMO gap.
Nonlinear optical Properties of Pentaazadentate Expanded Porphyrins and Application in Optical Limiting
Authors: Wang Duoyuan , Sun Wenfang , Dong Shiming , Si Jinhai , Li Chunfei
Published: September 2012

Nonlinear optical properties of asymmetric pentaazadentate expanded porphyrin metal complexes are investigated. The transmittance dependence of the target compounds on the incident laser intensity generates different nonlinear optical effects in the excited states. The reverse saturable absorption at 532 nm in the ns pulses and the saturable absorption for the pspulses at high fluences are observed in solutions. The nonlinear refractive indices n2 aremeasured by the Z-scan technique. The optical limiting based on the RSA and transverse refraction are demonstrated for ns and continuous laser. An optical limiter based on the RSA and self-refraction is performed, in which the limitating threshold and amplitude of output energy are reduced.
The design of Optical Limiters Based on the Formation of Bipolaron-Like Dications
Authors: Spangler Charles W. , He Mingqian
Published: September 2012

During the past decade, there has been considerable effort in the design of new materials with greatly enhanced nonlinear absorption characteristics. In recent years, it has been shown that incorporation of bipolaronic charges in the pi-electron sequence in conjugated polymers or copolymers leads to enhanced third-order nonlinear optical properties. In this current study a design strategy for the synthesis of optical power limiting copolymers is presented whose properties are based on the photogeneration of stable bipolaron-like dications.
Optical Limiting in Fullerene Materials
Authors: Tang B. Z. , Peng H. , Leung S. M. , Yu N.-T. , Hiraoka H. , Fok W.
Published: September 2012

Fullerene chemistry is booming, but how the chemical reactions affect fullerene's materials properties has seldom been studied. We have investigated optical limiting behavior of a series of fullerene derivatives, polymers, and glasses and have observed the following structure-property relationships for optical limiting in the fullerene materials: (i) The fullerene polymers with aromatic and chlorine moieties, i.e., C60-containing polycarbonate (C60-PC), polystyrene (C60- PS), and poly(vinyl chloride) (C60-PVC), limit the 8-ns pulses of 532-nm laser light more effectively than does the parent C60; (ii) the fullerene polymers with carbonyl groups, i.e., C60- containing CR-39 (C60-CR-39) and poly(methyl methacrylate), (C60-PMMA), do not enhance C60's limiting power; and (iii) the aminated fullerene derivatives, i.e., HxC60 (NHR)x [R = -(CH2CH2O)2H (1), x = 11; -(CH2)6OH (2), x = 7; -cyclo-C6H11 (3), x = 11; -(CH2)3Si(OC2H5)3 (4), x = 4], and their sol-gel glasses, i.e., 1–3/SiO2 (physical blending) and 4-SiO2 (chemical bonding), show complex limiting responses, with 4(-SiO2) performing consistently better than 1-3(/SiO2). The fullerene glasses are optically stable and their optical limiting properties remainunchanged after being subjected to continuous attack by the strong laser pulses for ca. 1 h.
Non-Linear Effects in Thin Film Fullerene Structures
Authors: Lewis Keith , Blacker Richard S , Bourhill Grant , Robertson John M
Published: September 2012

The fullerene materials are well known for their non-linear behaviour arising from excited state absorption processes. In solution, the processes can set in at low irradiance levels, although evidence is building that the magnitude of the effects is dependent on the solvent used in the experiments and the role of charge transfer processes. In evaporated films of C60, the solvent is absent and reduced non-linearities are seen as irradiances approach the laser damage threshold of the films. When the chromophor is incorporated into polymer films, non-linear processes are found at the same levels as the solution case provided that some residual solvent remains in the composite. Excited state absorption spectra suggest that some ionisation of the C60 may be occuring.
Polymer Materials Design for Optical Limiting
Authors: Cumpston B. H. , Mansour K. , Heikal A. A. , Perry J. W.
Published: September 2012

Phthalocyanines (PC's) containing heavy metal central atoms have recently been recognized as leading candidates for reverse saturable absorption and optical limiting (OL) applications in the visible spectrum. Strong triplet excited state absorption brought about by a large intersystem crossing rate is responsible for the excellent limiting performance of these molecules. Moreover, devices which maximize the excited state population along the light path will demonstrate maximum limiting efficiency. A non-homogeneous distribution of indium tetra(tert-butyl) phthalocyanine chloride (InC1PC) has been shown to be very effective in attenuating 532 nm nanosecond laser pulses. This was accomplished by approximating a hyperbolic distribution of chromophores using discrete elements of fixed dye concentration. Greater OL should be achieved by fabricating materials containing a continuous concentration gradient of chromophore. This paper focuses on issues concerning the preparation of solid polymeric materials that contain such a chromophore gradient. This design is achieved by diffusing chromophore-containing solutions into partially polymerized poly(methyl methacrylate) (PMMA).
Two-Photon Absorbing Organic Chromophores for Optical Limiting
Authors: Ehrlich J. E. , Wu X. L. , Lee I.-Y. S. , Heikal A. A. , Hu Z.-Y. , Röckel H. , Marder S. R. , Perry J. W.
Published: September 2012

Strong optical limiting and large two-photon absorptivities are reported for a class of bisdonor diphenylpolyene derivatives with varying polyene bridge lengths. These molecules exhibit strong optical limiting using nanosecond pulses over a broad spectral range. Bis(diphenylamino)stilbene exhibits a 90 nm red shift of its optical limiting band, and only a minimal shift of about 13 nm of its lowest one-photon electronic absorption band relative to bis(di-n-butylamino)stilbene. This suggests a potential for broadband optical limiting with high transparency using mixtures of such compounds. Pulse width dependent nonlinear transmission measurements suggest that two-photon pumped excited-state absorption contributes significantly to the limiting of nanosecond pulses.
Reverse saturable Absorption in Organically Doped Xerogels
Authors: Brunel M. , Chaput F. , Vinogradov S. A. , Campagne B. , Canva M. , Boilot J-P. , Brun A.
Published: September 2012

Pd and Zn - tetraphenyltetrabenzoporphyrins (PdTPTBP and ZnTPTBP), hexacyanin 3 (HITCI), and substituted phthalocyanines were incorporated in solid-state matrices (xerogels) using a sol-gel process. Nonlinear reverse saturable absorption was observed with those materials when they were illuminated with nanosecond laser pulses at 532 nm, or other wavelengths in the visible spectrum (between 450 nm and 630 nm). PdTPTBP doped xerogels exhibit a nonlinear activation threshold of about 10 mJ/cm , which is much lower than the value of 80 mJ/cm2 obtained under similar conditions with classical Al phthalocyanine chloride, or HITCI molecules. Solid state “red active” reverse saturable absorbers can be obtained with substituted phthalocyanines doped xerogels. The different experimental results are discussed using classical 4- energy level diagrams.
Sructural evolution of GaN during initial stage MOCVD growth
Authors: Kim Chong Cook , Je Jung Ho , Yi Min-Su , Noh Do Young
Published: September 2012

The structural evolution of GaN films during the initial growth process of metalorganic chemical vapor deposition (MOCVD) - low temperature nucleation layer growth, annealing, and high temperature epitaxial growth - was investigated in a synchrotron x-ray scattering experiment. The nucleation layer grown at 560°C that was predominantly cubic GaN consisted of tensile-strained aligned domains and relaxed misaligned domains. The hexagonal GaN, transformed from the cubic GaN during annealing to 1100°C, showed disordered stacking. The atomic layer spacing decreased as the fraction of the hexagonal domains increased. Subsequent growth of epitaxial GaN at 1100°C resulted in the formation of ordered hexagonal GaN domains with rather broad mosaicity.
High-Quality AlxGa1−xN Using Low Temperature-Interlayer and its Application to UV Detector
Authors: Iwaya M. , Terao S. , Hayashi N. , Kashima T. , Detchprohm T. , Amano H. , Akasaki I. , Hirano A. , Pernot C.
Published: September 2012

Low-temperature (LT-) AlN interlayer reduces tensile stress during growth of AlxGa1−xN, while simultaneously acts as the dislocation filter, especially for dislocations of which Burger's vector contains [0001] components. UV photodetectors using thus-grown high quality AlxGa1−xN layers were fabricated. The dark current bellow 50 fA at 10 V bias for 10 [.mu]m strip allowing a photocurrent to dark current ratio greater than one even at 40 nW/cm2 have been achieved.
Improved Characteristics of InGaN Multi-Quantum-Well Laser Diodes Grown on Laterally Epitaxially Overgrown GaN on Sapphire
Authors: Hansen Monica , Fini Paul , Zhao Lijie , Abare Amber , Coldren Larry A. , Speck James S. , DenBaars Steven P.
Published: September 2012

InGaN multi-quantum-well laser diodes have been fabricated on fully-coalesced laterally epitaxially overgrown (LEO) GaN on sapphire. The laterally overgrown ‘wing’ regions as well as the coalescence fronts contained few or no threading dislocations. Laser diodes fabricated on the low-dislocation-density wing regions showed a reduction in threshold current density from 8 kA/cm2 to 3.7 kA/cm2 compared the those on the high-dislocation ‘window’ regions. Laser diodes also showed a twofold reduction in threshold current density when comparing those on the wing regions to those fabricated on conventional planar GaN on sapphire. The internal quantum efficiency also improved from 3% for laser diodes on conventional GaN on sapphire to 22% for laser diodes on LEO GaN on sapphire.
Spatially Resolved Electroluminescence of InGaN-MQW-LEDs
Authors: Schwegler Veit , Seyboth Matthias , Kirchner Christoph , Scherer Marcus , Kamp Markus , Fischer Peter , Christen Jürgen , Zacharias Margit
Published: September 2012

Electroluminescence (EL) is the most significant measure for light-emitting diodes since it probes the most relevant properties of the fully processed device during operation. In addition to the information gained by conventional spectrally resolved EL, scanning micro-EL provides spatially resolved information. The devices under investigation are InGaN/GaN-LEDs with single peak band-band emission at about 400 nm grown by MOVPE on sapphire substrates.

The μ-EL-characterization is performed as a function of injection current densities and the emission is investigated from the epitaxial layer as well as from substrate side. Spatially resolved wavelength images reveal emission peaks between 406 nm and 417 nm, corresponding either to In fluctuations of 1%–1.5% or local fluctuations of piezo electric fields. Beside the information on the emission wavelength fluctuations ν-EL is used to determine the temperature distribution in the LEDs and to investigate transparent contacts.
High Reflectance III-Nitride Bragg Reflectors Grown by Molecular Beam Epitaxy
Authors: Ng H. M. , Moustakas T. D.
Published: September 2012

Distributed Bragg reflector (DBR) structures based on AlN/GaN have been grown on (0001) sapphire by electron-cyclotron-resonance plasma-assisted molecular-beam epitaxy (ECR-MBE). The design of the structures was predetermined by simulations using the transmission matrix method. A number of structures have been grown with 20.5 – 25.5 periods showing peak reflectance ranging from the near-UV to the green wavelength regions. For the best sample, peak reflectance up to 99% was observed centered at 467 nm with a bandwidth of 45 nm. The experimental reflectance data were compared with the simulations and show excellent agreement with respect to peak reflectance, bandwidth of high reflectance and the locations of the sidelobes.
Properties and Effects of Hydrogen in GaN
Authors: Pearton S.J. , Cho H. , Ren F. , Chyi J.-I. , Han J. , Wilson R.G.
Published: September 2012

The status of understanding of the behavior of hydrogen in GaN and related materials is reviewed. In particular, we discuss the amount of residual hydrogen in MOCVD-grown device structures such as heterojunction bipolar transistors, thyristors and p-i-n diodes intended for high power, high temperature applications. In these structures, the residual hydrogen originating from the growth precursors decorates Mgdoped layers and AlGaN/GaN interfaces. There is a significant difference in the diffusion characteristics and thermal stability of implanted hydrogen between n- and p-GaN, due to the stronger affinity of hydrogen to pair with acceptor dopants and possibly to the difference in H2 formation probability.
A Comparative Study Of GaN Diodes Grown by MBE on Sapphire and HVPE-GaN /Sapphire Substrates
Authors: Sampath Anand V. , Misra Mira , Seth Kshitij , Fedyunin Yuri. , Ng Hock M. , Iliopoulos Eleftherios , Feit Zeev , Moustakas Theodore.D.
Published: September 2012

In this paper we report on the fabrication and characterization of GaN diodes (Schottky and p-n junctions) grown by plasma assisted MBE. We observed that Schottky diodes improve both in reverse as well as forward bias when deposited on 5 μm thick HVPE n+-GaN/sapphire instead of bare sapphire substrates. These improvements are attributed to the reduction of disloctions in the MBE homoepitaxially grown GaN. Similar benefits are observed in the reverse bias of the p-n junctions which according to EBIC measurements are attributed to the reduction of etch pits in the MBE grown p-GaN.
Full Band Monte Carlo Comparison of Wurtzite and Zincblende Phase GaN MESFETs
Authors: Farahmand Maziar , Brennan Kevin F.
Published: September 2012

The output characteristics, cutoff frequency, breakdown voltage and the transconductance of wurtzite and zincblende phase GaN MESFETs have been calculated using a self-consistent, full band Monte Carlo simulation. It is found that the calculated breakdown voltage for the wurtzite device is considerably higher than that calculated for a comparable GaN zincblende phase device. The zincblende device is calculated to have a higher transconductance and cutoff frequency than the wurtzite device. The higher breakdown voltage of the wurtzite phase device is attributed to the higher density of electronic states for this phase compared to the zincblende phase. The higher cutoff frequency and transconductance of the zincblende phase GaN device is attributed to more appreciable electron velocity overshoot for this phase compared to that for the wurtzite phase. The maximum cutoff frequency and transconductance of a 0.1 μm gate-length zincblende GaN MESFET are calculated to be 220GHz and 210 mS/mm, respectively. The corresponding quantities for the wurtzite GaN device are calculated to be 160GHz and 158 mS/mm.