bluuebunny/crossref_metadata_2025 huggingface dataset:
Valence Band Discontinuity at and Near The
SiO2/Si(111) Interface
Authors: Nohira Hiroshi , Hattori Takeo
Published: April 2011

The changes in X-ray excited valence band of silicon oxide during
progressive oxidation of Si(111) surface in 1 Torr dry oxygen at 600–850°C
were studied. Following results are obtained: 1) energy level of top of
valence band within 0.9 nm from the SiO2/Si interface is
different from that of bulk silicon oxide by about 0.2 eV, 2) valence band
discontinuity at the interface changes periodically with the interface
structures.
A Model for the Etching of Ti and Tin in SC-1
Solutions
Authors: Verhaverbeke Steven , Parker Jennifer W.
Published: April 2011

The Standard Clean 1 (SC-1), developed by W. Kern and D. Puotinen in 1965
and disclosed in 1970 [1], consists of a mixture of ammonium-hydroxide,
hydrogen-peroxide, and water. (SC-1 is also called the Airfmonium-Hydroxide
Peroxide Mixture or APM). Originally, this chemical mixture was developed
for cleaning silicon wafers and it has proven to be the most efficient
particle removing agent found to date. SC-1 can, however, also be used for
etching. SC-1 will etch the following materials: SiO2,
Si3N4, Si, Ti and TiN. On top of this, SC-1 will
grow an oxide on several materials (i.e., bare silicon).

In this paper, a quantitative model for the SC-1 solution is presented. The
etching of Ti and TiN is shown to be fundamentally different from the
etching of SiO2. The mixture of Ammonium-hydroxide and Hydrogen
Peroxide must be optimized differently for Ti and TiN etching than for the
particle removal from Silicon wafers.
The Enhancement of Thermoelectric Power and Scattering of Carriers in Bi2−xSnxTe3 Single Crystals
Authors: Kulbachinskii V.A. , Negishi H. , Sasaki M. , Giman Y. , Inoue M.
Published: April 2011

Thermoelectric power, electrical resistivity, and Hall effect of p-type Bi2−xSnxTe3 (0<x<0.03) singlecrystals have been measured in the temperature range 4.2–300K. By doping of Sn atoms into the host Bi2Te3 lattice, the enhancement in the thermoelectric power is observed in the intermediate temperature range 30–150 K for x≤0,0075. The activation type behaviour of Hall coefficient and resistivity are found which corresponds to the Sn-induced impurity band located above the second lower valence band.
Thermoelectric Properties of ZnSb Films Grown by MOCVD
Authors: Venkatasubramanian R. , Watko E. , Colpitts T.
Published: April 2011

The thermoelectric properties of ZnSb films grown by metallorganic chemical vapor deposition (MOCVD) are reported. The growth conditions necessary to obtain stoichiometric ZnSb films and the effects of various growth parameters on the electrical conductivity and Seebeck coefficients of the films are described. The as-grown ZnSb films are p-type. It was observed that the thicker ZnSb films offer improved carrier mobilities and lower free-carrier concentration levels. The Seebeck coefficient of ZnSb films was found to rise rapidly at approximately 160°C. The thicker films, due to the lower doping levels, indicate higher Seebeck coefficients between 25 to 200°C. A short annealing of the ZnSb film at temperatures of ˜ 200°C results in reduced free-carrier level. Thermal conductivity measurements of ZnSb films using the 3-ω method are also presented.
Synthesis of New Thermoelectrics Using Modulated Elemental Reactants
Authors: Hornbostel Marc D. , Sellinschegg Heike , Johnson David C.
Published: April 2011

A series of new, metastable ternary crystalline compounds with the skutterudite crystal structure have been synthesized using modulated elemental reactants. The initial reactants are made up of multiple repeats of a ˜25Å thick unit containing elemental layers of the desired ternary metal, iron and antimony. Low temperature annealing (150°C) results in interdiffusion of the elemental layers to form amorphous reaction intermediates. Annealing these intermediates at temperatures between 200°C and 250°C results in exothermic crystallization of the desired skutterudite crystal structure. Most of the new compounds prepared are only kinetically stable, decomposing exothermically to form thermodynamically more stable mixtures of binary compounds and elements. Low angle x-ray diffraction studies show that the resulting films are exceedingly smooth. These films have an ideal geometry for measuring properties of importance for thermoelectric devices—the Seebeck coefficient and the electrical conductivity. Thermal conductivity can be measured using a modification of the 3ω technique of Cahill. Samples can be produced rapidly, allowing for systematic screening and subsequent optimization as a function of composition and doping levels.
Measurement of the Thermoelectric Properties of Quasicrystalline AlPdRe and AlCuFe Alloys.
Authors: Wilson M.L. , Legault S. , Stroud R.M. , Tritt T.M.
Published: April 2011

We report the measurement of the thermal conductivity, electrical resistivity, and thermoelectric power on two quasicrystalline compounds, A170Pd20Re10 and A162.5Cu25Fe12.5. These materials are found to posses a thermal conductivity of order 1 W/m K, while retaining their semimetallic conductivity. These features coupled with moderately large thermopowers, up to 55 μV/K, imply that the general class of quasicrystalline compounds warrants careful investigation for their potential as new thermoelectric materials.
Electrical Properties and Figures of Merit for New Chalcogenide-Based Thermoelectric Materials
Authors: Schindler Jon L. , Hogan Tim P. , Brazis Paul W. , Kannewurf Carl R. , Chung Duck-Young , Kanatzidis Mercouri G.
Published: April 2011

New Bi-based chalcogenide compounds have been prepared using the polychalcogenide flux technique for crystal growth. These materials exhibit characteristics of good thermoelectric materials. Single crystals of the compound CsBi4Te6 have shown conductivity as high as 2440 S/cm with a p-type thermoelectric power of ≈ +110 μV/K at room temperature. A second compound, β-K2Bi8Se13 shows lower conductivity ≈ 240 S/cm, but a larger n-type thermopower ≈ −200 μV/K. Thermal transport measurements have been performed on hot-pressed pellets of these materials and the results show comparable or lower thermal conductivities than Bi2Te3. This improvement may reflect the reduced lattice symmetry of the new chalcogenide thermoelectrics. The thermoelectric figure of merit for CsBi4Te6 reaches ZT ≈ 0.32 at 260 K and for β-K2Bi8Se13 ZT ≈ 0.32 at room temperature, indicating that these compounds are viable candidates for thermoelectric refrigeration applications.
Design Concepts for Improved Thermoelectric Materials
Authors: Slack Glen A.
Published: April 2011

Some new guidelines are given that should be useful in the search for thermoelectric materials that are better than those currently available. In particular, clathrate and crypto-clathrate compounds with filler atoms in their cages offer the ability to substantially lower the lattice thermal conductivity.
Non-Destructive and Whole Wafer Characterization of III-V Infrared Epitaxial Materials Prepared by Turbo Disk Metalorganic Chemical Vapor Deposition
Authors: Feng Z. C. , Pelczynski M. , Beckham C. , Cooke P. , Ferguson I. , Stall R. A.
Published: April 2011

Multiple wafer growth of infrared III-V semiconductor materials of InSb and InGaAsP have been produced by metalorganic chemical vapor deposition technology employing a vertical reactor growth configuration with a high speed rotating disk. Three measurement techniques of sheet resistivity, Fourier transform infrared (FTIR) reflectance and photoluminescence have been used to characterize epitaxial films on wafers up to 4″ diameter. Mapping distributions of the film thickness, sheet resistivity, surface morphology, and PL peak wavelength with uniformities better than 1% are illustrated. Data from our 2900 runs are produced. Variations of the characteristic features of the film with the growth conditions are discussed. These whole wafer and non-destructive material characterization techniques tightly coupled with the epitaxial processes are necessary to realize the high quality and high uniformity growth of state-of-art materials in a production environment.
High Temperature Infrared Photon Detector Performance
Authors: Grein C. H. , Ehrenreich H.
Published: April 2011

The combined effects of suppressing Auger recombination by band structure engineering strained-layer superlattices (SL), suppressing radiative recombination by photon recycling, and suppressing both Auger and radiative recombination with carrier depletion are calculated quantitatively for long-wavelength and mid-wavelength InAs/ InxGa1-xSb SL-based infrared detectors operating at temperatures between 200 and 300K. The results are compared to their HgCdTe counterparts. The SL performance is better in all cases. However, the carrier concentrations required for typical background limited performance (300K, 2π field of view), ranging between about 1 × 1013 and 4 × 1013 cm−3 at 300K in long-wavelength to mid-wavelength SLs, are seen to be impractically low. The carrier concentration in a 11 μm photon detector yielding equivalent performance to an ideal 300K thermal detector is about 1014 cm−3. Large performance enhancement using carrier depletion therefore appears impractical even in optimized SLs.
New Type of ir Photodectors Based on Lead Telluride and Related Alloys
Authors: Khokhlov D. R.
Published: April 2011

Doping of the lead telluride and related alloys with the group III impurities results in an appearance of the unique physical features of a material, such as such as persistent photoresponse, enhanced responsive quantum efficiency (up to 100 photoelectrons/incident photon), radiation hardness and many others. We review the physical principles of operation of the photodetecting devices based on the group ifi-doped IV-VI including the possibilities of a fast quenching of the persistent photoresponse, construction of the focal-plane array, new readout technique, and others. The advantages of infrared photodetecting systems based on the group IIIdoped IV-VI in comparison with the modem photodetectors are summarized.
Active Anti-Guide Vertical Cavity Surface Emitting Lasers with Diffused Quantum Wells Structure
Authors: Yu S. F. , Li E. Herbert , Man W. M.
Published: April 2011

The enhancement of single transverse mode operation in vertical cavity surface emitting lasers by using interdiffused quantum wells is proposed and analyzed. It is observed that the influence of self-focusing (arising from carrier spatial hole burning and thermal lensing) on the profile of transverse modes can be minimized by introducing a step diffused quantum wells structure inside the core region of quantum-well active layer. Stable single-mode operation in vertical cavity surface emitting lasers can also be maintained.
Second-Harmonic and Sum-Freqency Generation in CdGeAs2
Authors: Tanaka Eiko , Kato Kiyoshi
Published: April 2011

CdGeAs2 has been found to be phase-matchable for type-2 SHG down to 2.833 μ m and type-2(b) SFG between the fundamental and second harmonic of a CO2 laser down to 10.4406 μ m at 20.0°C. The Sellmeier's equations and the thermo-optic dispersion formula which reproduce well the phasematching properties of SHG and direct FHG of the CO2 lasers at 77K are presented together with the absolute value of the nonlinear optical constant.
Laser Damage Studies of Silver Gallium Sulfide Single Crystals
Authors: Ruderman Warren , Maffetone John , Zelman David E. , Poirier Derrick M.
Published: April 2011

Although AgGaS2 single crystals have desirable optical and nonlinear properties, the low laser damage threshold has limited their application for tunable infrared laser sources. Crystals have been studied by ESCA and Auger techniques and the surface of polished crystals has been found to be silver deficient, while the bulk composition is closer to stoichiometry.
Electron-Nuclear Double Resonance Study of the Zinc Vacancy in Zinc GERMANIUM PHOSPHIDE (ZnGeP2)
Authors: Stevens K. T. , Setzler S. D. , Halliburton L. E. , Fernelius N. C. , Schunemann P. G. , Pollak T. M.
Published: April 2011

As-grown crystals of ZnGeP2 are highly compensated and contain significant concentrations of donors and acceptors. The dominant acceptor in ZnGeP2 is believed to be the zinc vacancy. This center is paramagnetic in its normal singly ionized state, and gives rise to an electron paramagnetic resonance (EPR) signal characterized by a resolved primary hyperfine interaction with two equivalent phosphorus nuclei adjacent to the vacancy. The present investigation has focused on electron-nuclear double resonance (ENDOR) measurements of additional hyperfine interactions which are not resolved in the regular EPR spectra. Principal values and principal axes directions for four additional phosphorus nuclei are determined from the ENDOR angular dependence. These parameters support the zinc-vacancy assignment for the acceptor and they provide an experimental check of wave functions generated in future computational modeling efforts.
Frequency Doubling of CW And Pulsed CO2 Lasers Using Diffusionbonded, Quasi-Phase-Matched Gaas Stacks
Authors: Ohmer Melvin C. , Guha Shekhar , Perrin Ronald E. , Rea Laura S. , Yu Phil Won , Fathimulla Ayub
Published: April 2011

We describe the fabrication, characterization and frequency doubling properties of first order stacks of diffusion bonded 2″ diameter GaAs wafers. Near IR imaging through the stacks indicated that excellent bonding was obtained over 40%–70% of the central area of the wafers. A power spectrum analysis of the spectral noise (due to interface reflections) appearing in the transmission data is shown to be a quantitative diagnostic tool useful for determining interface quality and for accurately estimating the thickness of the bonded layers in a stack. The conversion efficiency for a four layer stack at 10.6 microns was found to be 0.03% or 3 mJ for a 10 mJ pulse with a 100 nanosecond pulse length. The corresponding efficiency for cw SHG was found to be 0.0002%.
The Burstein-Moss Shift in Quantum Dots of III-V, II-VI and IV-VI Semiconductors Under Parallel Magnetic Field
Authors: Ghatak Kamakhya P. , Bose P. K. , Majumder Gautam
Published: April 2011

In this paper, we have investigated the Burstein-Moss shift(BMS) in QDs of III-V, II-VI and IV-VI semiconductors in the presence of a parallel magnetic field on the basis of newly formulated carrier disperson laws. It is found, taking QDs of InSb, Cds and CdTe as examples that the BMS increases with increasing doping and decreasing film thickness in ladder like manners. The numerical values of the BMS in QDs are much greater than that of their corresponding values for bulk specimens. The theoretical results as presented here are in agreement with the experimental observations as reported in literature.
CdTe and CdZnTe Room-Temperature X-Ray and Gamma Ray Detectors and Imaging Systems
Authors: Eisen Y. , Shor A.
Published: April 2011

CdTe and CdZnTe X-ray and gamma ray detectors in the form of single elements or as monolithic segmented arrays have been shown to be useful in imaging systems utilized in medical, research or industrial applications. These detectors possess inherently better energy resolution than scintillators coupled to either photodiodes or photomultipliers, and they may lead to compact imaging systems or to imaging systems of enhanced spatial resolution and better contrast resolution. Photopeak efficiencies of these detectors is greatly affected by relatively low hole mobility-lifetime product and therefore continuing efforts are still underway to improve the characteristics of both CdTe and CdZnTe materials in order to achieve reproducible detectors with higher photopeak efficiencies for either low or high energy gamma rays.

The following paper is divided into three parts: The first part compares the characteristics of planar CdTe and CdZnTe single elements nuclear detectors containing metal contacts. Characteristics include: Charge collection efficiencies for both electrons and holes indicated by the mobility-lifetime product, energy resolutions, leakage currents and robustness in field use. The second part describes excellent spectroscopic results using a lcm thick CdZnTe monolithic segmented pad detector array. This part also compares spectra for various gamma energies obtained by this segmented detector to that of a 1 cm 3 detector acting as a single element planar detector. The third part discusses the characteristics of a new generation nuclear gamma camera for medical diagnostics based on room-temperature CdTe and CdZnTe spectrometers and its advantages over an Anger type scintillating nuclear camera.
Prototype Imaging CD-ZN-TE Array Detector
Authors: Bloser P. F. , Narita T. , Grindlay J. E. , Shah K.
Published: April 2011

We describe initial results of our program to develop and test Cd-Zn-Te (CZT) detectors with a pixellated array readout. Our primary interest is in the development of relatively thick CZT detectors for use in astrophysical coded aperture telescopes with response extending over the energy range ∼ 10 – 600 keV. The coded aperture imaging configuration requires only relatively large area pixels (1–3 mm), whereas the desired high energy response requires detector thicknesses of at least 3–5 mm. We have developed a prototype detector employing a 10 × 10 × 5 mm CZT substrate and 4 × 4 pixel (1.5 mm each) readout with gold metal contacts for the pixels and continuous gold contact for the bias on the opposite detector face. This MSM contact configuration was fabricated by RMD and tested at Harvard for uniformity, efficiency and spatial as well as spectral resolution. We have developed an ASIC readout (IDE-VA-1) and analysis system and report results, including ∼ 4% (FWHM) energy resolution at 60 keV. A prototype design for a full imaging detector array is discussed.
Elementary Analysis Of Line Shapes And Energy Resolution In Semiconductor Radiation Detectors
Authors: Toney J. E. , Schlesinger T. E. , Brunett B. A. , James R. B.
Published: April 2011

We have used an elementary statistical technique to derive a closed-form expression for the hole-tailing line shape produced by photoelectric absorption of monoenergetic radiation in a semiconductor X-ray/γ-ray detector. In the case of compound semiconductors, where the drift length for electrons is much greater than that for holes, the line shape is given by a type of power law, except for a small region very near the photopeak. This analytical result agrees well with Monte Carlo simulations and is used to extract approximate μτ products from a 57Co pulse height spectrum. We also present an expression for the maximum obtainable energy resolution of a semiconductor detector in the presence of leakage current noise and intrinsic statistical fluctuations as a function of material parameters, along with a chart of the optimal band gap as a function of temperature and photon energy. Based on these considerations, the optimal band gap for room-temperature operation is approximately 2.0 eV.
Performance of P-I-N CdZnTe Radiation Detectors and Their Unique Advantages
Authors: Sudharsanan R. , Stenstrom C. C. , Bennett P. , Vakerlis G. D.
Published: April 2011

We present the performance characteristics of CdZnTe radiation detectors with a new P-I-N design and their unique advantages over metal-semiconductor-metal (M-S-M) devices. In M-S-M CdZnTe detectors the bulk resistivity of the substrate largely determines the leakage current. High leakage current is a dominant noise factor for CdZnTe detector arrays, coplanar detectors, and detectors used for low X-ray energy applications. P-I-N devices provide low leakage currents. Early CdZnTe detectors exhibited polarization, were limited to small detection volumes, and some required high deposition temperatures. We have developed a new heterojunction design which can be deposited at low temperatures so that even high-pressure Bridgman CdZnTe can be used. Using the P-I-N design, CdZnTe detectors with high detection volumes (>200 mm3) were fabricated and exhibited low leakage current, good energy resolution, and no polarization. These detectors have significant advantages over M-S-M detectors in three specific areas. First, X-ray fluorescence studies require detectors with low leakage currents to provide less spectral broadening due to electronic noise. Second, less expensive vertical Bridgman CdZnTe material can be used for imaging applications since it normally possesses too low of a bulk resistivity to be useful as a M-S-M detector. Third, leakage currents across the anode grid in large volume coplanar detectors can be significantly reduced
Use of a Monte-Carlo Code to Determine in High Z Semi-Conductor CdTe and CZT, Both Carriers Lifetimes and Mobilities
Authors: Muller E. , Jung M. , Fougfères P. , Hage-Ali M. , Siffert P.
Published: April 2011

This paper deals with a comparison between experimental gamma-ray spectra recorded with CdTe and CdZnTe detectors and a Monte Carlo code simulating the spectrum, in order to extract realistic values of the transport properties of both electrons and holes in these materials. In a second section, these values are compared to that obtained by others using other methods, in order to evaluate the accuracy of the various experimental procedures.
ZnxCd1−xTe Epitaxial Growth by Remote Plasma Enhanced MOCVD Method
Authors: Noda Daiji , Aoki Torn , Nakanishi Yoichiro , Hatanaka Yoshinori
Published: April 2011

For epitaxial growth of compound Zn1−xCd1−XTe by metal organic chemical vapor deposition (MOCVD), it is difficult to obtain a high composition ratio x. In this study, we have adopted a remote plasma enhanced (RPE) MOCVD method for the epitaxial growth. Cd1−xZnxTe with the composition ratio x in the range of 0 to 1 has been obtained while varying the ratio of dimethylcadmium (DMCd) to diethylzinc (DEZn) from 0 to 20%. The crystallinity of the epitaxial films was about 400 to 700 arcsec FWHM defined by X ray diffiraction measurements.
Synchrotron x-Ray Topographic Study Of Dislocations In Gaas Detector Crystals Grown By Vertical Gradient Freeze Technique
Authors: Tuomi T. , Juvonen M. , Rantamäki R. , Hjelt K. , Bavdaz M. , Nenonen S. , Gagliardi M -A. , Mcnally P. J. , Danilewsky A. N. , Prieur E. , Taskinen M. , Tuominen M.
Published: April 2011

Large area transmission and section topographs of semi-insulating gallium arsenide wafers grown by the gradient freeze technique are made with synchrotron radiation at HASYLAB in Hamburg and at ESRF in Grenoble. Several high-resolution images including stereo pairs are obtained on the same film at a time. A typical dislocation line is an arc of a circle which starts from one surface and ends at the same surface. From the disappearance of the dislocation image and using the g · b = 0 criterion it is concluded that the Burgers vector b of the most common dislocations is parallel to 〈110〉. Rather large volumes of the wafer are dislocation-free. Section topographs of epitaxial wafers show defects and strain fields at the interface between an n-type substrate and the epitaxial layers grown by chemical vapor deposition. The results are compared with those obtained from detector performance measurements.
Semi-Insulating InP Particle Detectors For X- And γ-Ray Detection
Authors: Pelfer P. G. , Dubecký F. , Fomari R. , Pikna M. , Krempaský M. , Gombia E. , Darmo J. , Mosca R. , Sekácová M.
Published: April 2011

A study of electrical properties and detection performances of the semi-insulating (SI) InP based detectors is presented. Detectors with a top P+ layer and a Schottky back contact give the charge collection efficiency about 90 % and an energy resolution 3.7% (FWHM) for 5.48MeV α-particles at 250 K. Detection of X-rays (122 keV and 60 keV) photons in temperature region 220–250 K is demonstrated. Multiple peaking observed during detection of photons is discussed.
Pl And Epr Spectroscopy Of Point Defects In Detector-Grade Cd1−xZnxTe
Authors: Rablau C. I. , Setzler S. D. , Halliburton L. E. , Doty F. P. , Giles N. C.
Published: April 2011

Cadmium zinc telluride (CdZnTe) is an emerging material for room-temperature x-ray and gamma ray detectors. The identification and control of point defects and charge compensators are currently important issues. Low-temperature photoluminescence (PL) and electron paramagnetic resonance (EPR) spectroscopies have been used to characterize point defects in CdZnTe crystals grown by the high-pressure Bridgman technique. Luminescence due to shallow donors, shallow acceptors, and deeper acceptors was monitored for a series of samples. An isotropic EPR signal attributed to shallow hydrogenic donors is observed in all samples, and the concentration of shallow donors has been determined. The nature of the defect centers (impurities, vacancies, vacancy-impurity complexes), and the correlation between defect concentration and device performance is discussed.
A Study Of The Composition Uniformity, Electrical And Spectroscopic Properties Of CdZnTe Detectors
Authors: Gagliardi M-A. , Nenonen S. , Gagliardi T. , Hjelt K. T. , Juvonen M. , Tuomi T. , Bavdaz M.
Published: April 2011

The electrical and charge collection properties of a semiconductor detector play an important role in a spectrometer's final performance. However, the studies of these properties often concentrate on only a few samples. In this work over 100 CdZnTe detectors from 12 different growth boules were characterized with one of the following test methods. The composition uniformity was evaluated with low temperature photoluminescence (PL) measurements. From the current-voltage characteristics the differences in CdZnTe detector resistivities were investigated. Charge collection properties, μτ-products, and energy resolutions were characterized with spectroscopic methods using an alpha and isotopic sources. A wide selection of test results are presented indicating the variety of CdZnTe material.
Recent Progress of Electro-optic Polymers for Device Applications
Authors: Jen Alex K-Y. , Yang Qing , Marder Seth R. , Dalton Larry R. , Shu Ching-Fong
Published: April 2011

Electro-optic (E-O) polymers have drawn great interest in recent years because of their potential applications in photonics devices such as high speed modulators and switches, optical data storage and information processing1–2. In order to have suitable materials for device fabrication, it is essential to design and develop polymeric material systems (active and passive polymers) with matched refractive indices, large E-O coefficients, good temporal and photochemical stability3–8 The E-O response of an active polymer commonly arises from the electric field induced alignment of its second-order nonlinear optical (NLO) chromophore, either doped as a guest/host system or covalently bonded as a side-chain. Because of the strong interaction among the electric dipoles, the poled structure is in a meta-stable state; the poled NLO chromophores which possess large dipole moment will tend to relax back to the randomly oriented state. As a result, the stability of the poled structure strongly depends on the rigidity of the overall material system. As it might be expected, the continuous increases of the rigidity and Tg of poled polymers imposes constraints on the selection of suitable chromophores that can survive the hightemperature poling and processing conditions. To circumvent this problem, we have developed a series of chromophores that possess conformation-locked geometry and perfluoro-dicyanovinylsubstituted electron-accepting group which demonstrate both good thermal stabilty and nonlinearity. This paper provides a brief review of these highly efficient and thermally stable chromophores and polymers for device applications.
Study on the Relations of Structure and the Ultrafast Optical Kerr Effect of Polynitriles
Authors: Wang Q. , Li Y. Y. , Pei W. W. , He Y. K. , Luo C. Q. , Chen H. Y. , Lin L. , Wang C. F. , Zou Y. H.
Published: April 2011

A series of polybenzonitrile derivatives, prepared by plasma glow discharge processes or chemical polymerization, were characterized by FT-IR, UV-Vis, GPC and VPO etc. The secondorder nonlinear optical hyperpolarizability γ of various benzonitrile monomers and their, polymers were measured by the femtosecond time-resolved optical Kerr effect technique, and the structureproperty relationships were discussed. The power law dependence of γ on the averagepolymerization- degree of several polybenzonitrile derivatives were also reported.
Radiative Decay of Excitons in Model Aggregates of π-Conjugated Oligomers
Authors: Manas Eric S. , Spano Frank C.
Published: April 2011

Spontaneous emission from exciton states in an aggregate of π-conjugated oligomers is studied theoretically. Each oligomer is taken as a ring of N carbon atoms and is treated using a PPP Hamiltonian. Coulombic interactions between rings are treated to first order. The radiative decay rate γ from an exciton state in an aggregate of M aligned oligomers is superradiant, being M times faster than the decay rate of an isolated oligomer exciton. Inter-oligomer interactions have little effect on the exciton size and energy when the oligomer size N is large compared to the interoligomer spacing. However, when N is small, both the exciton size and energy are strongly affected by these interactions, leading to a markedly different N dependence for γ.
An Emulsion Polymerization Process for Soluble and Electrically Conductive Polyaniline
Authors: Kinlen P. J. , Ding Y. , Graham C. R. , Liu J. , Remsen E. E.
Published: April 2011

A new emulsion process has been developed for the direct synthesis of the emeraldine salt of polyaniline (PANI) that is soluble in organic solvents. The process entails forming an emulsion composed of water, a water soluble organic solvent (e.g., 2-butoxyethanol), a water insoluble organic acid (e.g., dinonylnaphthalene sulfonic acid) and aniline. Aniline is protonated by the organic acid to form a salt which partitions into the organic phase. As oxidant (ammonium peroxydisulfate) is added, PANI salt forms in the organic phase and remains soluble. As the reaction proceeds, the reaction mixture changes from an emulsion to a two phase system, the soluble PANI remaining in the organic phase. With dinonylnaphthalene sulfonic acid (DNNSA) as the organic acid, the resulting product is truly soluble in organic solvents such as xylene and toluene(not a dispersion), of high molecular weight (Mw >22,000), film forming and miscible with many polymers such as polyurethanes, epoxies and phenoxy resins. As cast, the polyaniline film is only moderately conductive, (10−5 S/cm), however treatment of the film with surfactants such as benzyltriethylammonium chloride (BTEAC) or low molecular weight alcohols and ketones such as methanol and acetone increases the conductivity 2–3 orders of magnitude.
Electrical Rectification by a Molecule of Hexadecylquinolinium Tricyanoquinodimethanide
Authors: Metzger R. M. , Chen B. , Vuillaume D. , Höpfner U. , Baldwin J. W. , Kawai T. , Tachibana H. , Sakurai H. , Lakshmikantham M. V. , Cava M. P.
Published: April 2011

The asymmetrical forward versus reverse - bias DC electrical conductivity (macroscopic and also nanoscopic) through Langmuir-Blodgett multilayers and monolayers of γ-(nhexadecyl) quinolinum tricyanoquinodimethanide, C16H33Q-3CNQ (1) is attributable to rectification of electrical current by a single molecule.
A Scanning Force Microscopy Study of Block Copolymers Containing a Conjugated Segment
Authors: Leclère Ph. , Lazzaroni R. , Parente V. , François B. , Brédas J. L.
Published: April 2011

Atomic Force Microscopy (AFM) and related techniques are used to investigate the morphology of diblock copolymers. We focus on compounds containing a conjugated segment, polyparaphenylene, associated to a polymethylmethacrylate or a polystyrene block. The influence of the presence of the conjugated segment on the microdomain morphology is analyzed as a function of chain composition. Separate microdomains are observed on the surface of thin films by means of phase-detection imaging tapping-mode AFM. Their shape and size are interpreted in terms of molecular aggregation, with the help of molecular dynamics calculations.
Double-strand Polyaniline as a Molecular Quasi-Memory to Chemical Stimuli
Authors: Kota Gowri P. , Sun Linfeng , Liu Huaibing , Yang Sze C.
Published: April 2011

We report the apparent hysteresis cycles in the protonation/deprotonation induced conductor-insulator transition for a water-soluble double-strand polyaniline. Experimental evidences show that the polymeric complexes of polyaniline and poly(styrene sulfonic acid) are soluble in water as non-aggregated single molecules. Although the hysteresis loop becomes narrower within 40 hours and the bistability is not permanent, the rate of collapse of the hysteresis loop is extremely slow for a solvated polymer in water. The water soluble polyaniline was compared with solid state samples of PAN:HCl. It was found that, under thermodynamically identical conditions, the memory effect is stronger for the water-soluble polyaniline than the water-insoluble solid of PAN:HCI.
Synthesis and Photophysical Properties of Some Conjugated Polymers Functionalized with Ruthenium Polypyridine Complexes
Authors: Ng Po King , Ng Wai Yue , Gong Xiong , Chan Wai Kin
Published: April 2011

A series of conjugated polymers functionalized with different ruthenium polypyridine metal complexes were synthesized by the palladium catalyzed reaction. Two conjugated polymer systems have been studied: 1. poly(phenylenevinylene) with bis(2,2':6',2”-terpyridine) ruthenium (II) on the mainchain and 2. quinoxaline based polymers with tris(2,2'-bipyridine) ruthenium (II). The ruthenium polypyridine complexes exhibit a long-lived metal to ligand charge transfer excited state which can enhance the photosensitivity of the resulting polymers. Different physical properties such as the photoconductivity and charge mobility in these polymers are also studied.
Electrochemically Based Light Emitting Devices from Sequentially Adsorbed Multilayers of a Polymeric Ruthenium (II) Complex and Poly(Acrylic Acid)
Authors: Wu Aiping , Lee Jin-Kyu , Rubner Michael F.
Published: April 2011

We have investigated a new light emitting material, Ru(bpy)3 2+ polyester for fabricating electrochemically based solid state light emitting devices using the layer-by-layer sequential adsorption processing technique. By controlling the deposition conditions such as the pH of the Ru(bpy)32+ polyester and poly(acrylic acid) (PAA) solutions, we systematically altered the layer thickness and bilayer composition to obtain multilayers that contain different amounts of Ru(bpy)32+ polyester (from 46% to 70%). Differences in the Ru(bpy)32+ polyester composition, in turn, influence the device performance dramatically.
Synthesis, Characterization and Properties of Conjugated Poly(1-Alkyl-2,5-Pyrrylene Vinylene)
Authors: Kim In Tae , Elsenbaumer Ronald L.
Published: April 2011

A series of poly(N-alkylpyrrylene vinylenes)( alkyl = methyl(l), hexyl(2), dodecyl(3)) have been synthesized from the monomer, N-alkyl-2,5-bis(thiophenylmethylene)pyrrole, by base induced elimination and polymerization. The resulting deep purple conjugated polymers (2,3) were soluble in a variety organic solvents. The electrical conductivities of the polymers lie in the range, 10−2to 2.5 S/cm. The highest yield was obtained when the polymers were synthesized in refluxing THF with a monomer/ base mole ratio of 1/4. The optical band gap of the undoped polymers were 1.89 eV(1), 1.69 eV(2) and 1.65 eV(3). Characterization of the polymers includes IR, CV,1H and13C NMR, UV-vis spectroscopy, TGA and molecular weight studies.
Conjugated Polymers Containing Pendant Terpyridine Complexes as Photoactive Sensors
Authors: Jiang Biwang , Sahay Shailesh , Jones Wayne E.
Published: April 2011

We have synthesized a novel conjugated polymer containing terpyridine receptors. This conjugated, polymer-based fluorescent chemosensory system exhibits unusually high sensitivity toward transition metal ions (∼-10−9 M). The fluorescence quenching response of the terpyridine containing conjugated polymer to transition metal ions is related to a facile energy migration in which energy from absorption of a photon, can migrate through the conjugated polymer system and be quenched by trapping sites. Terpyridine receptors can readily bind to transition metal ions and create a low lying Metal to Ligand Charge Transfer (MLCT) state which can act as an excitation trap.
Self-Assembling Functionalizable Polydiacetylenes and their Optical Properties
Authors: Sukwattanasinitt M. , Wang X. , Lee D-C. , Li L. , Kumar J. , Tripathy S. K. , Sandman D. J.
Published: April 2011

The alkoxycarbonylmethylurethanes of 9-(N-methyl-N-phenylamino)-5,7-nonadiyn-l-ol were synthesized and polymerized by 60Co gamma radiation. The resulting polydiacetylenes (PDA) are soluble, processable, and self-assemble into an acentric array. These PDAs are susceptible to postpolymerization functionalization via its dialkylaniline and ester groups, and hence comprise the most versatile PDA system for systematic chemical modification reported to date. Dialkylaniline functionalization via tetracyanoethylene and diazonium salt coupling led, respectively, to materials with interesting second order nonlinear optical properties and that exhibit directly photofabricated regular surface relief gratings. The latter materials provide the first example of a rigid rod polymer (lacking a detectable glass transition) to exhibit such phenomena. Moreover, these PDAs can form self-assembled multilayer structure in water by ester hydrolysis.
Investigation of Organic-Organic Interfaces by Time-Resolved Photocurrent, Electrochemical, And Photoemission Techniques
Authors: Lin Liang-Bih , Mason M. Gary , Young Ralph H. , Schildkraut Deniz E. , Borsenberger Paul M. , Jenekhe Samson A.
Published: April 2011

Hole transporting properties and energy barriers at organic-organic interfaces relevant to electrophotographic and organic electroluminescent (EL) devices are described. Three wellknown hole transporting molecules, 1,1-bis(di-4-tolylaminophenyl)cyclohexane (TAPC), N,N′- diphenyl-N,N′-bis(1 -naphthyl)-(1,1 ′-biphenyl)-4,4′-diamine (NPB), and N,N,N′,N′-tetrakis(4- tolyl)-(1,1 ′-biphenyl)-4,4′-diamine (TTB) are used in this study. The ionization potentials (IP) and oxidation potentials (Eox) of these materials are determined by photoemission spectroscopy and electrochemical measurements, from which a conversion formula is obtained (IP ∼ 4.5 eV + eEox). Hole transport across organic-organic interfaces is investigated by time-of-flight transient photocurrent techniques. The efficiencies of hole injection are consistent with the energy barriers, when present, at these interfaces.
Polymeric Complexes of Polyaniline as Anticorrosion Coatings
Authors: Racicot R. J. , Yang S. C. , Brown R.
Published: April 2011

During the past few years there has been a strong interest in developing conducting polymers as an alternative to the traditional anticorrosion coatings. One of the driving forces for this research comes from the need for an environmentally friendly chromate-free anticorrosion coating for highstrength light weight aluminum alloys. The possibilities for a new scratch-tolerant paint for steel prompted the development of conductive polymer anticorrosion paints. By molecular engineering, we have synthesized a double-strand polymeric complex of polyaniline that is suitable as an anticorrosion paint on metals in low pH environments. In this article, we will discuss (1) the molecular design for solubility and adhesion, (2) the effectiveness of the electroactive coating under electrochemical impedance tests, and (3) a mechanistic study of the anticorrosion mechanism by examining the polymer/metal interfacial interactions.
Very Large Second Order Non-Linear Optical Activity Shown by Heterocycle-Based Dicyanomethanide Zwitterions
Authors: Abbotto A. , Bradamante S. , Facchetti A. , Pagani G. A. , Ledoux I. , Zyss J.
Published: April 2011

The new series of recently synthesized chromophores 2 - 6 in which a positively charged N-alkylpyridinium acceptor and a negatively charged dicyanomethanide donor are spaced by thiophene-based and/or ethylenic bridging units show dramatically enhanced first molecular hyperpolarizabilities (μβ as high as 27000 × 10−48esu), in comparison with some of the best recently reported neutral systems 7 and 8.
Ab Initio Calculations on Porphyrins in the Condensed Phase
Authors: Day P.N. , Wang Z. , Pachter R.
Published: April 2011

Porphyrins are a promising class of materials for optical limiting applications, and in the condensed phase solvent effects have been shown to be significant. We report results with a method designed to simulate the effects of discrete solvent molecules, namely the effective fragment potential (EFP) approach which has been implemented for use in ab initio calculations. Further, a simulated annealing (SA) method has been implemented with the EFP solvation model in an attempt to solve the problem of multiple minima in clusters of molecules. The results with this method indicate some success on models of aqueous formamide and aqueous glutamic acid. Ab initio calculations can now be carried out on porphyrins, and the solvation methods are being updated for their use on these systems.
Morphology Dependence of the Optical Properties of Dalm Related Materials
Authors: Wagner-Brown K. B. , Ferris K. F. , Kiel J. L. , Albanese R. A.
Published: April 2011

Diazoluminomelanin (DALM) is an electroluminescent polymer which has shown significant optical activity in response to perturbing fields. The current model for this process features optical excitation of a polymer backbone containing conducting conjugation, with subsequent energy transfer to a luminescent group. In this paper we have performed electronic structure calculations using the AM1 Hamiltonian with configuration interaction to estimate the electronic properties of two potential models for the DALM backbone. Contrary to the conventional picture of conjugation, the phenyl groups in the DALM backbone show significant twist angles (42° –55°) depending on substitutional group, resulting in localized electronic excitations.
Infrared Studies on C60 Polymers
Authors: Kamarás K. , Forró L. , Iwasa Y.
Published: April 2011

We present infrared spectra of linear and planar polymeric structures consisting of C60 balls. The splittings of infrared lines can be explained fairly well on the basis of symmetry reduction, indicating that the structures are ordered. Increasing the temperature results in breaking of intermolecular bonds. This process is reversible in the alkali salts but irreversible in the neutral rh-C60 polymer; we conclude that charged C60 balls are more stable in polymer form than as monomers, while for neutral C60 the situation is reversed.
Formation of Ultra Smooth Bi-Based Ferroelectric Films and their size effect on Dielectric Constant
Authors: Tabata H. , Yanagita T. , Hamada M. , Kawai T.
Published: April 2011

ABSTACT

We have formed Bi-based ferroelectric films, such as Bi2WO6, Bi2VO5.5(n=1), Bi2SrTa2O9, Bi3TiNbO9(n=2) and Bi4Ti3O12(n=3) using a pulsed laser deposition technique. Especially, the Bi2VO5.5 film shows an atomically smooth surface with a flat 2000-3000Å wide terrace and steps of 8 Å and 16Å which correspond to a half and one unit cell, respectively. The dielectric constant, remanent polarization and coercive field of the Bi2VO5.5 thin films formed on Nb-SrTiO3(100) are 8, 3.0 μ C/cm2 and 16.0 kV/cm, respectively. The Bi2VO5.5 film formed on SiO2/Si(100) shows memory windows of 0.35V against a±2V gate bias during C-V measurements‥
MOCVD of SrBi2Ta2O9 for Integrated Ferroelectric Capacitors
Authors: Hendrix Bryan C. , Hintermaier Frank , Desrocherst Debra A. , Roedert Jeffrey F. , Bhandarit Gautam , Chappuist Maggie , Baumt Thomas H. , Van Buskirkt Peter C. , Dehm Christine , Fritsch Elke , Nagel Nikolas , Honlein Wolfgang , Mazure Carlos
Published: April 2011

SrBi2Ta2O9 (SBT) is a promising material for ferroelectric random access memories (FERAM's) because it has high resistance to fatigue and imprint combined with low coercive field. Metalorganic chemical vapor deposition (MOCVD) offers the ability to produce high quality, conformai SBT films for both high and low density memory applications. An MOCVD process based on liquid delivery and flash vaporization has been developed which allows precise delivery of low vapor pressure precursors to the process. Precursor decomposition has been examined over a wide temperature range and the effects of process pressure have been examined. It is shown that Bi(thdb is superior to Bi(Ph)3 as a source of Bi, offering a wide decomposition window with compatible Sr and Ta precursors so that a simple, well-controlled, and repeatable process is achieved at low temperatures. Films with 90% conformallity have been grown on 0.6 μm structures with a 1:1 aspect ratio. The MOCVD process yields the fluorite phase, which is transformed to the ferroelectric layered perovskite phase upon annealing in oxygen. Dielectric constants (ε) of 200 and remanent polarization (2Pr)up to 16 μC/cm2 have been achieved on 150 mm wafers.
Reversible and Irreversible Contributions to the Polarization in SrBi2Ta2O9 Ferroelectric Capacitors
Authors: Lohse O. , Bolten D. , Grossmann M. , Waser R. , Hartner W. , Schindler G.
Published: April 2011

This work presents a survey of the mechanisms of the polarization in ferroelectric thin films which are relevant for application in non-volatile ferroelectric memories (FeRAM). Since the integration of these materials in new memory generations requires small structures and therefore a maximum utilization of the switchable polarization, the distinction between the several polarization mechanisms is of specific interest. Standard characterization methods, such as hysteresis loops, C-V measurements and fast pulse switching tests are evaluated and used to distinguish between the reversible and irreversible contributions to the total polarization. The respective contributions are described qualitatively and demonstrated at spin-coated SrBiTa2O9 thin films and compared with Pb(Zr,Ti)O3 films. Additionally, a method is described to obtain the static hysteresis curve, a precise characterization of the polarization which does not depend on the measuring frequency. These data are compared with C-V measurements. It is shown that the standard dynamic hysteresis curve reveals misleading statements about the remanent polarization and the coercive voltage.
Thickness Dependence of the Electrical Properties of Sol-Gel Derived Lead Zirconate Titanate Thin Films with (111) and (100) Texture
Authors: Chu F. , Xu F. , Shepard J. , Trolier-McKinstry S.
Published: April 2011

Crack-free (111) and (100)-textured Pb(Zr0.52Ti0.48)O3 films with thicknesses ranging from 0.25 to 2.5 μm were prepared using a methoxyethanol-based precursor solution, multiple spin-coating and multiple crystallization steps. The thickness dependence of the dielectric, ferroelectric and piezoelectric properties were investigated on both (111) and (100) oriented PZT films. In both cases, the degree of preferred orientation did not change with thickness. It is found that the dielectric constant, remanent polarization and piezoelectric coefficients (d33 and d31) increase with increasing film thickness. The (100)-textured film showed higher dielectric constant but lower remanent polarization relative to (111) textured film. 1 μm was identified to be a critical thickness that marks the change of dielectric, ferroelectric and piezoelectric behaviors as a function of thickness.
Sol-Gel Derived Pb(Zn1/3Nb2/3)O3-PbTiO3 Thin Films
Authors: Teowee G. , McCarthy K. C. , McCarthy F. S. , Davis D. G. , Dawley J. T. , Zelinski B.J.J. , Uhlmann D. R.
Published: April 2011

A series of sol-gel derived PB(Zn1/3Nb2/3)O3-PbTiO3 (PZN-PT) films, with various PbTiO3 contents, have been prepared on platinized Si wafers. The (l-x)PZN - xPT films fired to 700C became single phase perovskite for x > 0.7. In the PZN-0.1PT films, the films still contain pyrochlore phase at a firing temperature of 850C; the perovskite phase appeared at a firing temperature of 800C. The dielectric constant increased with increasing PT content, with a peak in dielectric constant at x = 0.8. PZN-PT films with x = 0.8 exhibited dielectric constant, dissipation factor, remanent polarization and coercive field values of 600, 0.10, 6 and 45 kV/cm respectively.