bluuebunny/crossref_metadata_2025 huggingface dataset:
Formation of Silicon-on-Insulator Films from Powders
Authors: Gadepally Kamesh V. , Hawk Roger M. , Brown William D.
Published: March 2011

Silicon powders have been successfully deposited by a corona discharge assisted electrostatic process on insulating, semiconducting, and conducting substrates. Subsequently, the deposits were heat treated and films have been formed. We present data pertatining to silicon films on insulators. The insulating surfaces used were sapphire, SiO2 on Si, and Si3N4 on Si. The electrical, chemical, and physical characteristics of these films are presented along with the time and temperature effects on the film formation. The impact of the above method with emphasis to the microelectronics industry will be discussed.
The Research and Development of Silicon-Germanium Thermoelements for Power Generation
Authors: Rosi Fred D.
Published: March 2011

On the 25th of August 1989, radio signals from the unmanned Voyager II spacecraft produced high resolution radio displays of the planet Neptune and its moon, Triton, on the monitors of Caltech's Jet Propulsion Laboratory. Thus ended the 12-year NASA Voyager I and II missions to the giant outer planets of our solar systems. Somewhat overlooked in the excitement over the impressive scientific findings from Voyager's epic planetary encounters was the power system aboard the spacecraft for data collection and signal transmission. This was the multi-hundred watt, radioisotope fueled thermoelectric generator using thermocouple modules made of Si-Ge alloys. The first section of this paper presents a historical review of the research program at the RCA Laboratories in Princeton, N.J. during the 4-year period required for the conception and development of Si-Ge thermoelements for power generation. This includes RCA's strategy in thermoelectric materials research from the viewpoint of device principles and requirements, scientific issues relating to the growth and thermoelectric characterization of Si-Ce alloys, and device feasibility studies. The performance of Si-Ge thermoelements in the power source of several space missions is also discussed. Finally, a perspective is presented on the research management of this remarkably successful program. The second section of the paper describes the results of more recent research on the thermoelectric properties of hot-pressed, sintered Si-Ge alloys and, in particular, the effects of grain size and additions of GaP. In the final section, consideration is given to future areas of research based, in part, on the results of the earlier studies of Si-Ge technology for thermoelectric power generation.
Composite Thermoelectrics - Exact Results and Calculational Methods
Authors: Bergman David J. , Levy Ohad
Published: March 2011

A theoretical study of composite thermoelectric media has resulted in the development of a number of simple approximations, as well as some exact results. The latter include exact upper and lower bounds on the bulk effective thermoelectric transport coefficients of the composite and upper bounds on the bulk effective thermoelectric quality factor Ze. In particular, as a result of some exact theorems and computer simulations we conclude that Ze can never be greater than the largest value of Z in the different components that make up the composite.
Finite Element Modeling of Thermo-Electric Materials
Authors: Duyn D. C. van , Vries P. de
Published: March 2011

This paper deals with the modeling of materials in which electric, thermal and cross effects between these are important. Also the effect of a magnetic field is included. A basic model and its FEM implementation are discussed. Some numerical test result are given.
On the Thermoelectric Power in Ultrathin Films of A3IIB2V Semiconductors Under Magnetic Quantization
Authors: Ghatak Kamakhya P. , De Badal
Published: March 2011

An attempt is made to study the thermoelectric power in ultrathin films of semiconductors under magnetic quantization by including all types of aniso tropies in the energy spectrum within the domain of theory, and taking n-Cd3As2 as an example. It is found that, the magne to-thermopower decreases with increasing surface electron concentration and also changes in an oscillatory manner with film thickness respectively. The theoretical results are in agreement with the experimental observations as reported elsewhere.
Uv-Curable Epoxy Based Second Order Nonlinear Optical Material
Authors: Jeng Ru Jong , Chen Yong Ming , Mandal Braja K. , Kumar Jayant , Tripathy Sukant K.
Published: March 2011

Epoxy based material incorporating 4-(4'-nitrophenylazo) phenylamine has been synthesized and subsequently functionalized with cinnamoyl groups. These materials can be easily solution-processed into thin films by spin-coating. The uncrosslinked polymer has excellent thermal and linear optical properties. Glass transition temperature of 115°C and degradation temperature (air) of 278°C were recorded.

This material exhibits large second order nonlinear optical (NLO) effects subsequent to poling. In a poled film sample, second harmonic generation coefficient, d33, of 34 pm/V was observed at 1.06 μm. Crosslinking is brought about by exposure to UV radiation at 254 nm wavelength. In a poled and crosslinked film sample, a d33 of 22 pm/V was observed. This d33 value is less than the d33 value of the poled and uncrosslinked film sample due to photo-induced cis-trans isomerization and partial degradation of the NLO chromophores. Nevertheless, the poled and crosslinked film shows a much more stable second order response at ambient conditions compared to the poled film which has not been crosslinked.
Lattice Bending in Poly(Diacetylene) Droplets Near Surfaces
Authors: Wilson Patricia M. , Martin David C.
Published: March 2011

Droplets of l, 6-di(N-carbazolyl)-2, 4 hexadiyne (DCHD) diacetylene were prepared by room temperature evaporation of dilute (0.01 wt %) solution of the monomer in chloroform on amorphous carbon-coated mica substrates. HREM and SAED examination revealed small crystallographically textured droplets (∼1 μm diameter) with cracks parallel to the [001] chain direction. The droplet geometry allowed us to investigate the structure of the polymer near edges both parallel and perpendicular to the chain axis. It was found that the curvature of the droplet edge caused a local bending of the polymer crystal lattice. The direct imaging of the molecular organization near the droplet surface allowed an investigation of the mechanisms of lattice bending via the formation of edge dislocations. An understanding of these defects is important in determining how they relate to the optical properties of poly(diacetylenes).
Nonlinear Optical Material Fabrication via Sol-Gel Processing
Authors: Kim Jongsung , Plawsky Joel L.
Published: March 2011

Nonlinear optical materials which are highly transparent and show large second harmonic generation coefficients were fabricated via the sol-gel process. Nonlinear chromophores were directly incorporated into the silica network by polymerizing chromophore containing organo silanes such as N-[3-(Triethoxysilyl)propyl]-2, 4-dinitrophenylamine (TDP) and 3-(4-Formyl phenoxy)propyl trimethoxy silane (FPT).
Epitaxial Growth of Organic Nonlinear Optical Materials
Authors: Hattori Y. , Mizoguchi A. , Ogaki Y. , Nishimtjra A.
Published: March 2011

As an orientation control technique for organic materials, epitaxial growth on crystal substrates was studied for DBNA, a derivative of p-nitroani1 ine, and polydiacetylene(PDA)-3BCMU using Vacuum Deposition and Molecular Beam Epitaxy(MBE).

The thin film of DBNA was epitaxially grown on a KCl(001) surface by Vacuum Deposition. Molecular orientation to the substrate (parallel or normal) was controlled by MBE. PDA-3BCMTJ thin films were prepared by UV light irradiation of DA-3BCMU(monomer) thin films which were epitaxially grown on a KCl(001) surface, x(3) values of this oriented thin film were larger than those of unoriented spin-casted thin film.
Electrical and Optical Properties of Thermid Polyimide
Authors: Jobe Patrick G. , Puglisi Christine , Zhu Z. X. , Fang K. J. , Liu D. , Patel N. , Niver E. , Grebel H. , Qin G. M. , Moller K. D. , Zhao S. N. , Feng G. , Ravindra N. M. , Chin K. K.
Published: March 2011

THERMID, made of acetylene-terminated polyimide oligomers, was developed by National Starch & Chemical Co. It is capable of forming thicker deposits than conventional polyimides. It is a candidate for a broad array of electronic and optoelectronic applications, including passivation coating, alpha-particle barrier, interlayer dielectric, encapsulation of discrete devices and IC, optical waveguide, and multilayer dielectric for thin hybrids. The study and evaluation of electrical and optical properties of THERMID polyimide give more support to their application in the semiconductor industry.
Cubic Nonlinear Optical Properties of Thin Films of a Series of Aromatic Schiff Base Polymers
Authors: Yang Chen-Jen , Jenekhe Samson A. , Vanherzeele Herman , Meth Jeffrey S.
Published: March 2011

The third-order nonlinear optical properties of a series of homopolymers and a random copolymer of conjugated aromatic Schiff base polymers have been investigated by picosecond third harmonic generation spectroscopy in the wavelength range 0.9–2.4 um. The off-resonant χ(3)(-3ω;ω, ω, ω) value at 2.4 μm was found to be 1.6×10−12esu for the parent polymer (PPI). 2, 5-Dimethoxy and 2, 5-dihydroxy substitutions or random colpolymerization was found to enhance the nonresonant optical nonlinearity of PPI by a factor of 1.5–4.5. 2-Methyl substitution lowered the χ(3) value. The three-photon resonance enhanced χ(3) of the polymers was in the range l.l×10−11 to 5.2×l0−11 esu. A three-level essential states model was found to describe the observed χ(3) spectra and the resulting fitting parameters were used to explain the observed trends in structure - χ(3) relationships.
Benzthiazole and Thiophene Capped Polyenes for Nonlinear Optical Applications: Single Crystal, Semi-empirical and A b Initio Results
Authors: Yeates A. T. , Dudis D. S. , Resch T. , Fratini A. V.
Published: March 2011

The molecule 2-(2-benzthiazolyl)-1-(2-thienyl)ethene has been studied by x-ray crystallography and has been found to be in the planar conformation with the double bonds in the trans configuration (from the N=C of the benzthiazole to the first double bond in the thiophene). Semi-empirical calculations show this configuration to be the least stable one by 1.5 Kcal/mole. To determine whether this discrepancy is due to crystal packing forces or a deficiency in the semi-empirical methodologies employed, ab initio Hartree-Fock calculations at the RHF/6–31G* level were performed on the four possible planar conformations. A comparison of the AM1 and the Hartree-Fock calculations indicates that while AM1 reproduces the trend in the energy components well, the trend in the total energy is not reproduced well. Comparisons with the experimental structure are also made. Analysis of the second hyperpolarizability indicates an enhancement of the NLO properties of this molecule over that of the uncapped polyenes.
Mechanisms of the Nonlinear Optical Response in Tetraras(Cumylphenoxy)Phthalocyanines
Authors: Flom Steven R. , Shirk James S. , Lindle J. R. , Bartoli F. J. , Kafafi Zakya H. , Pong R. G. S. , Snow Arthur W.
Published: March 2011

The third order nonlinear optical (NLO) response of metal free tetrakis(cumylphenoxy)-phthalocyanine, (H2Pc(CP)4) was investigated at 597 nm, near resonance with the strong Q band. The second hyperpolarizability, γ, and the figure of merit, χ(3)/α, measured with a 1.2 ps pulse. was approximately independent of concentration between a 4.6×10−4 M solution and a neat thin film. The decay of the nonlinear response, however, depended substantially on the concentration and physical state of the material.
Third- and Fifth-Order Optical Properties of Transition Metal Complexes of Benzenedithiol at 1.064 μm
Authors: Lindle J. R. , Weisbecker C. S. , Bartoli F. J. , Pong R. G. S. , Kafafi Z. H.
Published: March 2011

Time-resolved degenerate four-wave-mixing studies have been conducted on solutions of transition-metal complexes of benzenedithiol using a 35 ps Nd:YAG laser operating at 1.064 μm. The nonlinear optical properties of the first-row Co(d7), Ni(d8), and Cu(d9) and the d8 group Ni and P t transition metal complexes are discussed.
Excited State Enhancement Mechanism for Nonresonant Nonlinear Optical Processes
Authors: Heflem J. R. , Zhou Q. L. , Rodenberger D. C. , Cai Y. M. , Garito A. F.
Published: March 2011

A general enhancement mechanism is discussed for nonlinear optical processes originating from real population of electronic excited states. Enhancement of greater than two orders of magnitude of nonresonant third harmonic generation from an optically pumped s1 electronic excited state is experimentally observed in a conjugated disc-like metallophthalocyanine.
C60 with Metalloporphyrins
Authors: Penicaud Alain , Hsu John , Reed Christopher
Published: March 2011

CrII(OEP) (OEP: Dianion of octaethylporphyrin) quantitatively reacts with C60 in a THF-toluene (THF: tetrahydrofurane) mixture to give purple-black crystals of formula Cr(OEP)(C60)(THF)x. ESR and SQUID measurements show this compound to be a salt better described as [Cr(OEP)(THF)2+][(C60)−].THF(x-2). ESR spectra in frozen 2-Me-THF show an anisotropie signal centered at g = 1.998.
Superconductive Properties of CsxRbyC60 (33K) - Isotope Effect -
Authors: Ebbesen T. W. , Tanigaki K. , Saito S. , Mizuki J. , Tsai J. S. , Kubo Y. , Kuroshima S.
Published: March 2011

The surprisingly high Tc for the superconductivity of alkali doped C60 has spurred wide interest in understanding its mechanism [1–7]. We first report the superconductive properties of CsxRbyC60 which has a Tc as high as 33 K when x=2 and y=1 in the feed [4, 5]. SQUID measurements show that in this material the coherence length is 45 A and the penetration depth about 1, 800 A [5]. It has now been proven that the observed increase in the Tc with the size of the alkali dopant is due to the increase in the lattice constant [6]. This is most likely due to the changes in the density of states at the Fermi level. The other important parameter according to BSC theory is the phonon which mediates the electron-electron coupling. In the second part of this paper we present recent results which show that the Tc is indeed strongly influenced by this parameter [7]. The isotope effect is unexpectedly strong on the Tc.
ESR Studies of the Anion Radicals of the Fullerene: C60n- (n = 1, 2, and 3).
Authors: Dubois Dominique , Thomas Jones M. , Kadish Karl M.
Published: March 2011

The results of ESR studies on several anion radicals of the fullerene C60, C60n-(n = 1, 2, and 3), in the solvents benzonitrile, dichloromethane, pyridine and tetrahydrofuran containing 0.1 M TBAClO4 are reported and discussed. The samples are prepared by electrochemical reduction techniques which allow the preparation of samples which contain, quantitatively, the desired anionie species. The results of ESR spectral studies on the anions in frozen solutions as a function of temperature are presented. The ESR lineshapes and linewidths are dependent upon the solvent and the temperature. The g-values are weakly dependent upon temperature. The results obtained from this study are presented and discussed in terms of the unique physical structure and properties of C60.
Optical Properties of C60 and M6C60 (M=K, Rb, Cs) films
Authors: Ren S. L. , Wang Ying , Holden M. , Rao A. M. , Ni F. , Lee W. , Hager G. T. , Eklund P. C.
Published: March 2011

We report the optical properties of C60 determined from the variable angle ellipsometry and near normal incidence reflection / transmission (R.T) experiments, and of M6C60 from the R, T experiments. The measurements were performed on thin films (d∼1000 Å) of C60 and M6C60 deposited on both Si(100) and suprasil substrates. The onset for strong absorption across the HOMO-LUMO gap in CgQ is measured to be -2.3 eV, slightly larger than the gap values obtained from the x-ray photoelectron spectroscopy (XPS) and electron-energy-loss spectroscopy (EELS) experiments. The observed peak positions in ε2(ω) for M6C60 and C60 compares well with the recent band structure calculations and suggests that the M6C60 compounds exhibit only a weak hybridization between the C60 and M states.
Electronic Effects of Adducts on C60: A Molecular Orbital Analysis
Authors: Fann Y. C. , Singh D. , Jansen S. A.
Published: March 2011

Buckmisterfullerene, C60, has attracted great interest because of its carbon-cage structure and potential applications in the field of superconductivity when doped with alkali metals. The icosahedral framework of C60 has been confirmed by X-ray analysis of an osmylated C60, called ‘Bunnyball’. Little theoretical work has been done to understand the electronic mechanism of C60 and substituted C60. This work has focused on electronic properties of C60 and the bunnyball with hypothetical analogs metal substitutions to understand the electronic effects of adducts on the bunnyball. In this analysis, the osmylated C60and hypothetical analogs were studied by extended Hückel methods. Molecular orbital(MO) interaction diagrams constructed from Density of States (DOS) analysis of the bunnyballs are presented. The results suggest electronic effects induced by substitution /adduct strongly affect electronic population in the C60 unit.
Nonlinear Optical Properties of Buckminsterfullerene, C60, in the Near-Infrared
Authors: Kafafi Z. H. , Lindle J. R. , Pong R. G. S. , Bartoli F. J. , Lingg L. J. , Milliken J.
Published: March 2011

Time-resolved degenerate four-wave mixing experiments were conducted on films of pure Qo using a 35 ps Nd:YAG laser. The measurements wavelength 1.064 μm was far off resonance with any one-photon absorption bands. A small linear absorption coefficient α=6 cm−1 was measured at this wavelength. The third-order optical susceptibility χxxxx(3) of C60, derived from its phase conjugate signal, is 7 × 10−12 esu. The nonlinear optical temporal response was largely laser-pulse limited. Evidence for a fifth-order contribution to the nonlinear optical response was observed at high laser intensities.
Magnetic Properties in Charge-Transfer Complexes of High-Symmetry Organic Acceptors
Authors: Sugimoto Toyonari , Murahashi Eiji , Ikeda Kaoru , Yoshida Zen-Ichi , Nakatsuji Hiroshi , Yamauchi Jun , Kai Yasushi , Kasai Nobutami
Published: March 2011

Tris(l, 2-benzodithio)- and tris(l, 2-ethylenedithio)-trimethylenemethane dication salts were synthesized for the purpose of using as an acceptor in the formation of charge-transfer (CT) complexes with some dianionic donors. In the CT complexes of these dications with hexacyanotrimethylenecyclopropane and tetrafluorotetracyanoquinodimethane dianions, in which the CT degree is albeit small, the spin-spin interaction between the cation radical and the anion radical was antiferro magnetic in the temperature range of 60–293 K, but changed to a ferromagnetic one in the lower temperature range till 15 K, the lowest temperature used in this experiment. This provides the first demonstration of ferromagnetic spin-spin interaction in purely organic/molecular CT complexes. It is conceivable that the ferromagnetic spin-spin interaction is caused by a“spin polarization”mechanism rather than a“CT configurational mixing”mechanism.
Finding of Bulk Ferromagnetism in Stable Organic Radical Crystal
Authors: Kinoshita Minoru
Published: March 2011

Transition to a ferromagnetic long range ordered state was found at 0.60 K in the orthorhombic β-phase crystal of p-nitrophenyl nitronyl nitroxide (or 2-(4′-nitrophenyl)-4, 4, 5, 5-tetramethyl-4, 5-dihydro-lH-imidazol-1-oxyl-3-N-oxide in the IUPAC nomenclature). This finding provides the first example of an organic bulk ferromagnet consisting of light elements and having a definite molecular and crystal structure.
Characterization of Glassy State Relaxations in Styrene and Methacrylate Based Nonlinear Optical Materials
Authors: Schen Michael A. , Mopsik Fred I.
Published: March 2011

Sub-Ts relaxations in polymethylmethacrylate (PMMA) and in narrow molecular weight polystyrene (PS) thin films with and without second order nonlinear optical dyes have been examined using time domain dielectric spectrometry. Dyes used include 4-[N, N-dimethylamino]-4’-nitrostilbene (DANS) and 4-[N-ethyl, N-hydroxyethylaminoJ-4’-nitroazobenzene (DR1) at a level of 0.19 mole percent. In dye/PS blends, dye relaxations are seen to occur at frequencies similar to the frequencies of the β-relaxation of pure PS below the glass transition temperature. Analysis of the glassy phase dispersion leads us to conclude that, at near room temperature, appreciable dye reorientation occurs on a time scale of a few seconds. This dye reorientation is coupled to the dynamic motions of the localized polystyrene subunits. Experiments using dye in PMMA did not conclusively reveal dye motions because of the intrinsically large dispersion of PMMA itself. The β-relaxation frequency range is higher in the PMMA dye/polymer blend than in dye-containing PS implying dye reorientation would likewise occur more rapidly than in PS. Our results indicate that the randomization of dye orientation observed in a dye/polymer system depends on the rapid, local chain motions which continue at temperatures well below the glass transition temperature, as well as on the long range, slow relaxations associated with the glass-to-rubber transition.
Synthesis of New Stable Functionalized Organic Radicals for the Study of their Magnetic Properties
Authors: Chiang Long Y. , Upasani Ravi. B. , Swirczewski John. W.
Published: March 2011

Several phenoxy radicals were chemically modified in order to probe the intermolecular spin interactions between these radicals. Based on the ketenimine chemistry, we demonstrated an efficient synthetic sequence for the preparation of new dicyano substituted hindered phenols. A series of new polar group substituted nitroxide-nitroxyl radicals were also synthesized. These radicals with polar functionalities include 3, 5-dinitro-phenyl, 3, 5-dimethoxyphenyl, 3, 5-dihydroxyphenyl, 4-hydroxyphenyl, 4-cyanophenyl, 3, 5-dicyano-phenyl, and 3, 5-di-i-butyl-4-hydroxyphenyl derivatives of 4, 4, 5, 5-tetramethylimidazolidine-3-oxide-1-oxyl. They are intended for the study of functional substitution effects on the nature of spin exchanges in solid state.
Interelectronic Exchange Interactions between Organic Radicals in the Solid State
Authors: Rossitto Frank C. , Lahti Paul M.
Published: March 2011

The poly(4'-vinylphenoxy) nonconjugated polyradical was generated by photolysis of an oxalate-functionalized poly(4-hydroxystyrene). Spin-counting experiments in the electron spin resonance spectrum (ESR) showed efficient production of radicals with g = 2.0041, consistent with the expected pendant phenoxyl radicals. The thermal behavior of the ESR signal intensity indicated through-space antiferromagnetic coupling of the pendant radicals. The similarity of the behavior of this nonconjugated system to that of nominally conjugated polyradical systems synthesized by others suggests that geometric effects leading to deconjugation may be a major consideration in the synthesis of organic ferromagnetically exchange coupled polyradicals.
Poled Polyimides for Thermally Stable Electro-Optic Materials
Authors: Wu J. W. , Valley J. F. , Stiller M. , Ermer S. , Binkley E. S. , Kenney J. T. , Lipscomb G. F. , Lytel R.
Published: March 2011

Using polyimide as host in a guest-host electro-optic (EO) thin film a thermally stable poled electro-optic response is demonstrated at temperatures at 150 °C and 300 °C. Electric field poling during curing process including imidization (170 -230 °C) and densification (340 -380 °C) accounts for the highly thermally stable EO response. As a room temperature curing process, chemical imidization is employed as a novel curing process. Dehydration occurring through imidization of the polyamic acid is completed chemically after poling rather than thermally during poling. After thermal aging at 155 °C (above the poling temperature) chemically imidized samples retain over 30% of their original poling induced EO signal while similarly poled samples, which have not been chemically imidized, produce a null EO response. For a class of polyimides possessing aliphatic structure, the thermoplastic behavior of cured guest-host polyimide system allowed the electric field poling at temperatures above the glass transition temperature (Tg). One example of polyimide doped with 10% nonlinear optical molecules exhibits Tg near 200 °C, leading to an excellent thermal stability of the poled EO response with a depoling knee-temperature of 150°C.
Synthesis of a Novel Donor, BTFE-DMB, and Electrical Properties of its Iodine Salt
Authors: Mizutani Makoto , Tanaka Keiji , Ikeda Kiyoshi , Kawabata Kazushige
Published: March 2011

1, 4-Bis [2-(tetrathiafulvalen-2-yl)ethenyl] -2, 5-dimethylbenzene (BTFE-DMB) is synthesized and its structure is found to be planar. The single crystal of its iodine salts undergoes a metal-insulator transition about 180K. The compaction pellets of the iodine salts show the current dependent resistive anomaly under high pressure.
Chemical Properties of Porphyrin Thin Films Deposited by ICB
Authors: Usui Hiroaki , Yamada Atsushi , Murayama Kouji
Published: March 2011

Porphyrin thin films were deposited by ionized cluster beam from a source material of tetraphenylporphyrin iron(III) chloride. It was found that the chlorine atoms are mostly removed from the original molecules during the film formation process, resulting in a film of tetraphenylporphyrin iron(II) complex. The film is chemically active and showed reversible reaction with O2 and CO gases at an elevated temperature. The formation of μ-oxo dimera, which hinders the chemical activity, was not observed. Electrical conductivity of the film was also measured under various atmosphere.
Structural Aspects of the Polyaniline Family of Electronic Polymers
Authors: Pouget J. P. , Laridjani M. , Jozefowicz M. E. , Epstein A. J. , Scherr E. M. , MacDiarmid A. C.
Published: March 2011

Recent structural studies of the polyaniline family of electronic polymers in the base and salt forms are reviewed. We describe the crystalline and amorphous structures of the two classes of emeraldine. The structural evolution with HC1 doping and ring substitutions are also discussed in relationship with the electronic properties of these materials. Implications for charge transport phenomena are also considered.
Heteroaromatics: Exceptional Materials for Second Order Nonlinear Optical Applications
Authors: Jen Alex K-Y. , Wong K. Y. , Pushkara Rao V. , Drost K. , Mininni R. M.
Published: March 2011

New classes of nonlinear optical molecules were synthesized and characterized. It is shown experimentally that molecules with heteroaromatic π-electron systems exhibit exceptional second order nonlinear optical response and good solubility. Measurement of the nonlinear optical properties of molecules containing heteroaromatic moieties with different length scale reveals a power law dependence of Bμ on the number of π-electrons. Also, the effects of two nitro groups as electron acceptors on the aromatic ring are discussed.
The Polymerization of Heterocycles on Clay Templates
Authors: Mahe Loic , Laszlo Pierre , Dubois Jean-Claude
Published: March 2011

The oxidizing power of clays is put to use for the polymerization of heterocycles (pyrrole- and thiophene- types) in the 2D-interfoliar space and on the external surface of the clay particles. A mechanism is proposed for the oxidative polymerization.
An Overview of Conjugated Polymers in their Insulating Forms
Authors: Sandman Daniel J.
Published: March 2011

A brief overview is presented of the electrical and linear optical properties of conjugated polymers in their electrically insulating forms. Topics discussed include electronic structure and optical spectroscopy, thermochromism, and device applications, particularly electroluminescence. Structure-property relationships are stressed. Particular emphasis is placed on the properties of polydiacetylenes as they are available as macroscopic single crystals and, hence, are the best defined class of conjugated polymers.
Polyarenemethylidenes, A new Class of low GAP Polymers
Authors: Hanack M. , Hieber G. , Mangold K. -M. , Ritter H. , Röhrig U.
Published: March 2011

Based on theoretical calculations Polyarenemethylidenes (PAM) 1 have been predicted to be low gap polymers with good semiconducting and photoelectrical properties. The preparation of such a polymer with a well defined structure affords the synthesis of suitable precursors. We have been able to synthesize and characterize a variety of monomers in which the inner quinonoid system is present. Also more extended systems containing one or two additional benzene rings at the quinonoid system have been prepared. The chemical and electrochemical polymerization of the precursors is reported, leading to polymers 1 in a great structural variety.
Light-Emitting Diodes Based on Conjugated Polymers: Control of Colour and Efficiency
Authors: Burn Paul L. , Holmes A. B. , Kraft A. , Brown A. R. , Bradley D. D. C. , Friend R. H.
Published: March 2011

Studies of the effect of different electrode combinations on the device characteristics of simple three layer light-emitting diodes (LEDs) prepared with poly(ρ-phenylenevinylene) (PPV) as the emissive layer sandwiched between two metal contacts have shown that it is generally more difficult to inject electrons than holes. In order to improve the efficiency of such devices it is, therefore, necessary to develop methods to enhance the injection of electrons and we illustrate here one example where we have successfully achieved this by the introduction of a further, electron transport, layer. The result is an eight fold increase in efficiency over our best three layer PPV devices. The efficiency is also dependent on the details of the polymer electronic structure and using a family of copolymers we have been able to produce enhancements in efficiency to values of up to 30 times that of the corresponding PPV devices. Variations in the polymer electronic structure also affect the colour of emission and the same family of copolymers allow control of emission colour from blue/green to orange/red. Supramolecular control of the copolymer electronic structure can be achieved by lithographic patterning and we show that it is possible to produce regions within a single polymer film that possess different π-π* energy gaps.
Optical Spectroscopy and Photochemistry of Thin Films of Propylmethylpolyazine
Authors: Sherman Bradford C. , Euler William B.
Published: March 2011

Propylmethylpolyazine, [N=C(R1)-C(R2)=N]X (R1=CH3, R2=CH2CH2CH3), is an organic-soluble linear conjugated polymer. The ultraviolet spectrum of thin films of this material shows two peaks at about 280 nm and 320 nm. These absorptions are ascribed to transitions from different filled valence bands to the same empty conduction band. Oxidative doping of this polymer with iodine gives spectra that are consistent with the generation of bipolarons. Irradiation of pristine thin films with 300 nm light causes a two step photoprocess to occur. The first step happens during the first hour of irradiation and if the film is left in the dark is completely reversible. The second step takes considerably longer to complete (more than 12 hr of irradiation) and is irreversible. The UV spectrum and FTIR spectrum of the step one photoproduct suggest that the imine bond is undergoing an E to Z isomerization photochem-ically which reverses in the dark. The step two product is probably due to a cycloaddition reaction.
A Three-Level Model Useful for Exploring Structure/Property Relationships for Molecular Third Order Optical Polarizabilit1Es
Authors: Dirk C. W. , Cheng L-T. , Kuzyk M. G.
Published: March 2011

Approximations are applied to the three-level perturbation theory expressions for the third order optical polarizability. We conclude there will be three competing dominant terms, γ ≈ γc + γn + γtp each of which can be optimized at different molecular electronic structures. The two-photon term, γtp, has been commonly ascribed as the most dominant one for γ. However, the other two terms, which optimize at different structures, potentially offer equivalent or larger overall γ. The term, γn, will be optimized at structures with large second order polarizability β, while the term, γC, optimizes at certain centrosymmetric free electron structures with large first order polarization, α Optimization by γc is the preferred route, since this leads to elimination of the canceling terms which limit optimization by γtp or γn. Recent EFISH results have confirmed our earlier speculations that the free electron squarylium dye structures are particularly good for optimization by way of γc. Strategies are presented to selectively optimize to either of the three structure types and to obtain molecules with even larger γ.
Effects of Humidity and Heat on the Conductivity of Poly(3-Alkylthiophenes)
Authors: Punkka E. , Isotalo H. , Ahlskog M. , Stubb H.
Published: March 2011

The stability of the conductivity of poly(3-alkylthiophenes) has been studied in controlled environmental conditions. High humidity levels at elevated temperatures have been found to strongly influence the dedoping process. Highly FeCl3-doped samples lose their conductivity faster than lightly doped or undoped polymers. The conductivity of undoped poly(3-octylthiophene), however, initially increased by nearly two orders of magnitude as the relative humidity level was raised from 50% to 95% at 70 °C. The largest conductivity decay induced by humidity and heat was observed in thin samples. Measurements of the field-effect mobility reveal that the humidity-induced drop of the conductivity is caused by a decreasing number of active dopants, whereas heating the sample additionally results in a deterioration of the charge carrier mobility.
Layer-by-Layer Molecular Assembly Approaches to the Construction of Thin Films Having High Second-Order Optical Nonlinearities
Authors: Allan David S. , Kubota Fuyuhiko , Kakkar Ashok K. , Marks Tobin J. , Zhang Tongguang , Lin Weiping , Shih Mingchih , Wong George K. , Dutta Pulak
Published: March 2011

Chromophoric multilayer thin films exhibiting efficient second harmonic generation have been constructed on inorganic substrates via a stepwise layer-by-layer process using molecular self-assembly techniques. In each step, chemical species bearing appropriate functional groups form covalent bonds with functional groups deposited in the previous step. Bulk acentricity is achieved by the orientation of chromophore-containing layers outward from the substrate surface. A new chromophore having comparable hyperpolarizability but different steric and transparency characteristics than the stilbazolium chromophore used previously has been incorporated into self-assembled films. The large effects of octachlorotrisiloxane capping on the structure of these films have been investigated by second harmonic generation and X-ray reflectivity measurements. Novel in situ measurements of second harmonic generation efficiency as a function of chromophore layer growth are described and provide information useful for optimizing deposition conditions and understanding the film growth process.
A Two-Legged Spacer Molecule for Alternate Layer LB Film Deposition with Optically Nonlinear Dyes
Authors: Ash Well G. J. , Crossland W. A. , Martin P. J. , Thompson P. A. , Hewson A. T. , Marsden S. D.
Published: March 2011

Second harmonic generation from Langmuir-Blodgett films of E-N-octadecyl-4-(2-(4-dimethylaminophenyl)ethenyl)pyridinium iodide (a hemicyanine) interleaved with 4, 4'-dioctadecyl-3, 5, 3', 5'-tetramethyldipyrrylmethene hydrobromide (spacer) increases quadratically with the number of active layers, the second-order nonlinear optical susceptibility of film structures comprising from 1 to 150 bilayers being 70 pm/V. The synthesis and nonlinear optical properties are reported.
Thin Film Crystalline Organic Semiconductors: A New Class of Engineered Materials for Optoelectronics
Authors: Haskal E. I. , So F. F. , Zang D. Y. , Forrest S. R.
Published: March 2011

We have demonstrated that a class of stable aromatic compounds based on perviene and naphthalene can be deposited in extensive single crystalline thin films using the ultrahigh vacuum process of organic molecular beam deposition (OMBD). Furthermore, highly ordered “quasi-epitaxial” structures consisting of alternating, ultra-thin (to 10A) layers of two or more crystalline organic compounds have also been grown using this novel process, thus opening the door to a wide range of artificially “engineered” structures analogous to conventional semiconductor multiple quantum wells (MQWs). Unlike the case of inorganic semiconductors, however, organic materials bonded by the flexibly van der Waals forces are free of the need to choose layer compositions from materials whose crystal structures are matched. In this paper we summarize many of the unusual growth and materials characteristics of quasi-epitaxial organic thin films grown by OMBD.
Nanoscopic Molecular Engineering: Organic MBE and STM
Authors: Hara Masahiko , Garito Anthony F. , Sasabe Hiroyuki
Published: March 2011

Application of molecular beam epitaxy (MBE) and scanning tunneling microscopy (STM), especially for organic molecular systems, has been drawing our attention as a new approach to realizing novel material structures with low dimensionality, which are expected to exhibit important electronic and photonic properties. The following is an outline of our work in progress, including an overview of “nanoscopic” molecular engineering. Future possibilities of fabrication, modification and characterization for organic low-dimensional materials are reviewed with the new concept embraced by “nanoscopic” science and technology.
Quantum Well Formation in One-Dimensional Polymer Films by Molecular Layer Deposition and Chemical Vapor Deposition
Authors: Yoshimura Tetsuzo , Tatsuura Satoshi , Sotoyama Wataru
Published: March 2011

Quantum wires and dots were fabricated in one-dimensional conjugated polymer films by chemical vapor deposition. In the wires, a sharp exciton absorption peak, and in the dots, a blue shift in the absorption band due to electron confinement were observed. We showed that acceptors could be substituted into the conjugated polymer chain. We also demonstrated that molecular layer deposition (MLD), in which molecules are stacked on substrates one by one in order of preference in a vacuum, is feasible in fabricating one-dimensional conjugated polymers.
Mechanisms of Photo Currents in Phthalocyanine Thin Film Solar Cells
Authors: Siebentritt Susanne , Gunster Stefan , Meissner Dieter
Published: March 2011

Photocurrents in phthalocyanine ohmic samples and in phthalocyanine/perylene solar cells are shown. In principle current spectra follow the absorption spectra of the materials. Deviations from this behaviour can be accounted for by filtering effects. The influence of intensity, bias light and applied voltage is discussed.
Novel Langmuir-Blodgett Films of Electrically Conducting Polyion Complexes and Diblock Copolymers
Authors: Timothy Royappa A. , Saunders Randall S. , Cohen Robert E. , Rubner Michael F.
Published: March 2011

The Langmuir-Blodgett (LB) technique has been used to form two different types of multilayer films with novel molecular organizations. In the first case, a new method of fabricating superlattices of conducting polymers has been devised and studied. This method involves forming polyion complexes of acid derivatized conducting polymers with stearylamine (StNH2) and subsequently manipulating them into AB type superlattices by the LB technique. To date, superlattices consisting of isolated alternating monolayers of poly(thiophene acetic acid) (PTAA) and sulfonated polyaniline (PAn) have been studied. The layered structure of these films was found to be very similar to that of their respective homopolymer LB films, as evidenced by X-ray diffraction patterns. The conductivity of these superlattices was in the range of 10−1 S/cm, which is approximately one order of magnitude higher than that obtained with the homopolymer LB films (about 10−2 S/cm). In the second case, LB films of a novel diblock copolymer have been made, where one of the blocks is a water-insoluble polyacetylene precursor and the other block a non-conjugated, water-soluble poly(norbornene) derivative. The precursor block of the LB films could be converted to trans-polyacetylene by heating, and doped to a conductivity of 10−3 S/cm, which was significantly higher than that of cast (10−7 S/cm) or spin-coated (10−5 S/cm) films of the same material. Thus, in both cases, the unique molecular organization created by the LB technique has resulted in films with higher conductivities than those obtained by traditional casting techniques.
Application of Positron Annihilation Methods for Investigation and Testing of Polymer
Authors: Tishin S. A. , Tishin V. A. , Kestelman V. N.
Published: March 2011

The principal directions of application of positron annihilation methods (MAP) for investigation of polymer and polymer composition with attraction the original dates are analyzed. The results obtained allow to make the conclusion about efficiency of MAP at analyses microvoids and microdefects in disordered polymer (5…20 Å) which are inaccessible or difficult for the other analytical methods. The correlation of the probability of positronium formation and its annihilation characteristics with microstructure properties is discussed.
Intermolecular Effects on Third Order Nonlinear Optical Properties
Authors: Dudis D. S. , Yeates A. T. , Kurtz H. A.
Published: March 2011

Hartree-Fock ab initio calculations have been used to examine the magnitude of non-polar intermolecular interactions on polarizabilities and second hyperpolarizabilities. In the present case two ethylene molecules were examined in a cofacial interaction. Basis set requirements and correlation effects were considered in deriving the intermolecular potential. Two basis sets were considered for the intermolecular interactions at the Hartree-Fock level, while one set of calculations was performed with corrections for correlation. It is found that intermolecular contacts at the van der Waals distance has little effect on the molecular second hyperpolarizability, but it is not clear what the effect would be for longer oligomers.
Large Nonlinear Refractive Indices of Nickel Dithiolene Doped Polymethylmethacrylate
Authors: Winter Christopher S. , Oliver S. N. , Hill C A. S.
Published: March 2011

The nonlinear refractive index, linear and nonlinear absorption coefficients of a number of nickel dithiolene-doped PMMA polymers have been measured. Nonlinear refractive indices up to about 10−8 cm−2/KW were observed, with figures of merit defined by δnsat/αλ and Reχ(3) / Im χ(3) within acceptable device limits.
Interactive use of Electron Microscopy and Light Scattering as Diagnostics for Pyrogenic Aggregates
Authors: Dobbins Richard A.
Published: March 2011

Both electron microscopy and light scattering have played an important role in elucidating the processes of inception, growth, and oxidation of carbonaceous particles in flames. The techniques developed have application to the various pyrogenic materials including the metallic oxides, carbides, etc. Thermophoretic sampling has been developed to afford efficient extraction of particle samples from hot reaction zones. The sampling procedure preserves the particle morphology for subsequent analysis by transmission electron microscopy (TEM). Studies using this technique have shown aggregate structures with fractal dimensions of 1.6 to 1.8, a result that is consistent with the computer simulations of the cluster-cluster aggregation process. Diverse morphologies, including microparticles found in the particle inception zone, reveal the evolution of these aggregates. The optical cross sections for polydisperse aggregates which are used to interpret the laser scattering/extinction tests (LSE) are described. Population averaged properties - volume fraction, volume mean diameter, monomer and aggregate number concentrations, mean-square radius of gyration - are derived. The interactive use TEM and LSE data leads to a global description of the aggregate dynamic processes which are found to be regionally partitioned within the laminar hydrocarbon diffusion flame.
Axial Concentration Profile of H2 Produced in the CVD of Si3N4.
Authors: Hay Stephen O. , Roman Ward C.
Published: March 2011

Silicon nitride (Si3N4) has been demonstrated to be an effective high temperature anti-oxidant when deposited in its α-crystalline form. The Materials Technology Laboratory at UTRC has developed a pilot-scale chemical vapor deposition (CVD) reactor capable of depositing α-Si3N4 from ammonia (NH3) and silicon tetrafluoride (SiF4) at 1.8 torr and 1440 C. Coherent anti-Stokes Raman spectroscopy (CARS) has been applied to measure H2 produced in this reactor. Axial concentration measurements have been performed both in the presence and absence of SiF4. Previous CARS measurements demonstrated the importance of surface (Si3N4) catalyzed decomposition of NH3:

as a competing reaction to:

in the CVD reactor under deposition conditions. The observed hydrogen concentration profiles confirm these measurements and allow quantitative comparison between the competing reactions. NH3 decomposition is suppressed 20% by the addition of SiF 4 in a 6:1 (NH3:SiF4) molar ratio. No decomposition is observed in the absence of Si3N4.
CVD of Silicon Nitride Plate from HsiCl3-NH3-H2 Mixtures
Authors: Lennartz J. W. , Dowell M. B.
Published: March 2011

Preferred conditions for deposition of thick α-Si3 N4 plate from HSiCl3 -NH3-H2 on the vertical surfaces of a lowpressure, hot-wall CVD reactor were identified by means of a designed experiment. The design included the range of temperatures 1300°C-1500°C, pressures 0.5–2.0 Torr, and residence times 0.01–1.0 sec. The vertical deposition surfaces received a viscous, laminar flow of well mixed, thermally equilibrated reactants. Plates 0.05–0.5 mm thick were produced on multiple vertical substrates 350 cm2 in area at deposition rates 5–70 μm/hr. Plates 0.5–4.0 mm thick were produced on horizontal substrates at deposition rates of 60–120 μm/hr. When NH3 flows in stoichiometric excess, deposition rates on vertical surfaces increase approximately linearly with the flow rate of HSiCl3 but depend little on temperature, as would be expected if the reaction proceeds under mass transport control with product depletion. Multiple correlation analyses show that thickness variations in the deposit are reduced by increasing the temperature and decreasing the gas residence time. CVD silicon nitride plate produced under the optimized conditions exhibits theoretical density and is free of pores and cracks. It exhibits a columnar morphology in which the <222> and <101> crystallographic directions are oriented preferentially normal to a surface, which consists of well-defined trigonal facets 10–50 μm across. Crystallite sizes determined by Xray line broadening range from 0.06–1.0 μm. This CVD plate is gray and contains approximately 0.5 w/o C and 0.5 w/o 0 as principal impurities.
Chemical Vapor Deposition of Multiphase Boron-Carbon-Silicon Ceramics
Authors: Golda E. Michael , Gallois B.
Published: March 2011

Specific compositions of boron-carbon-silicon ceramics exhibit improved abrasive wear and good thermal shock resistance, but require bulk sintering at temperatures in excess of 2100K. The formation of such phases by chemical vapor deposition was investigated in the temperature range of 1073K–1573K. Methyltrichlorosilane (CH3SiCl3), boron trichloride, and methane were chosen as reactant gases, with hydrogen as a carrier gas and diluent. The coatings were deposited in a computer-controlled, hot-wall reactor at a pressure of 33 MPa (200 Torr).

Below 1473K the coatings were amorphous. At higher temperatures non-equilibrium reactions controlled the deposition process. The most common coating consisted of a silicon carbide matrix and a silicon boride, SiB6, dispersed phase. Multiphase coatings of B+B4C+SiB6 and SiC+SiB6+SiB14 were also deposited by controlling the partial pressure of methane and boron trichloride. Non-equilibrium thermodynamic analysis qualitatively predicted the experimentally deposited multiphase coatings.