bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural Approach to Improve the Response Characteristics of Copper Phthalocyanine Thin Film-Based NO2Gas Sensor
Authors: Nagasawa Tadashi , Murakami Kenji , Watanabe Kenzo 
Published: April 2011

AbstractIn order to realize a high-sensitivity, low temperature operable NO2gas sensor, thin films of at-form copper phthalocyanine (α-CuPc) have been deposited by vacuum sublimation. In this study, we have attempted to improve the gas-sensing characteristics through a modification of the film microstructure. Firstly, the gas sensitivity is remarkably increased by an insertion of higher-sensitive layer (vanadyl Pc film) between the α-CuPc film and the glass substrate in the low gas concentration range. Secondly, a reversibility in cycles of gas doping and dedoping is improved by film deposition on hydrofluoric acid-treated substrate. It is found from atomic force microscope analyses that this phenomenon may be closely related to a modification of the film microstructure.
Novel Liquid Crystal Displays Based on Highly Polarized Photoluminescent Polymer Films
Authors: Sarwa Christian , Montali Andrea , Bastiaansen Cees , Weder Christoph , Smith Paul 
Published: April 2011

AbstractSince the early 90's, much research has focused on the photoluminescence (PL) and electroluminescence (EL) properties of conjugated polymers, because of their potential application as emitting layer in EL devices. The introduction of uniaxial molecular orientation into films of luminescent polymers was naturally found to yield structures that emit polarized light. Rather surprisingly, the photoluminescence properties of oriented, conjugated polymers have attracted substantially less attention, especially from an application point of view. In this paper we report the fabrication of highly-polarized photoluminescent polymer films based on poly(2,5- dialkoxy-p-phenyleneethynylene)s (PPE), and their use in a new family of liquid crystal displays (LCDs). As one relevant example, a back-lit twisted-nematic configuration of an LCD was built, in which one of the absorbing polarizers was replaced by a polarized PL film, characterized by a dichroic ratio in excess of 70. Such devices can exhibit a substantial improvement in brightness, contrast and viewing angle, since the polarized photoluminescent films can combine two separate features, i.e. the functions of a polarizer and an efficient color filter.
Toward Electrically Pumped Organic Diode Lasers: Electroluminescence of Proton Transfer Polymers
Authors: Zhang Xuejun , Tarkka Richard M. , Jenekhe Samson A. , Schlenoff Joseph B. 
Published: April 2011

AbstractElectroluminescence from a series of polymers and copolymers which exhibit photoinduced excited-state intramolecular proton transfer (ESIPT) is reported. Among these polymers containing ESIPT moieties in the main chain or side chain are poly(1,4-(2-hydroxy)phenylene benzobisthiazole-co-decamethylene benzobisthiazole), poly(styrene-co-3-hydroxy-4′-ethenylflavone) and poly(2,5-benzoxazolediyl(2,2,2,-trifluoro-1-(trifluoromethyl) ethylidene)-5,2-benzoxazolediyl-4-hydroxy-1,3-phenylene). The electroluminescence spectra of these polymers are identical to their photoluminescence spectra, indicating that electroluminecence originates from electrically-generated intramolecular proton transfer (EGIPT). Because electroluminescence from EGIPT implies electrically-induced population inversion, these results demonstrate the possibility of electrically-pumped organic solid-state laser diodes.
Ionic Complexes Of Conjugated Oligoquinolines
Authors: Shetty Ashok S. , Jenekhe Samson A. 
Published: April 2011

AbstractSingle crystal X-ray structures of salt complexes of oligoquinoline, 2,2'-bis(4- phenylquinoline)-1,4-phenylene (4), with p-toluenesulfonic acid, trifluoromethanesulfonic acid and a laser dye, Sulforhodamine 101 hydrate have been determined and used to study the effects of molecular packing on physical and photophysical properties of conjugated oligomer and polymers. UV-vis and emission spectra of thin films of the oligoquinoline-p-toluenesulfonate complex were also performed. These results indicate that they form an intermolecular charge-transfer complex. These complexes serve as models of quarternized polyquinolines such as the self-assembled bilayer films of polyquinoline and polystyrenesulfonic acid.
Preparation of Chromophoric Dipolar Dendrons as Second-Order Nonlinear Optical Material
Authors: Yokoyama S. , Mashiko S. 
Published: April 2011

AbstractDendritic macromolecules, called “dendrons,” having a branching structure modified with an electron donor/acceptor functionalized azobenzene chromophore have been synthesized. The structurally different dendrons possess different numbers, 1, 3, 7, and 15, of chromophore units. The second harmonic generation (SHG) of dendrons was measured in the molecular oriented thin films prepared by the Langmuir-Blodgett film transfer technique. In such structurally organized thin films, individual chromophores coherently contribute to the increase in the molecular hyperpolarizability of dendrons. The SHG activity became large as the numbers of branching units of dendrons increased. The highest molecular hyperpolarizability was found to be <8000×10−30 esu for dendron containing 15 chromophoric units. The SHG results suggest that the structure of dendrons synthesized is uniaxially dipolar, and that there is a particular merit in this structure for the generation of SHG.
Magnetic Supramolecular Grid Structures: Intramolecular Coupling of Four Separate Spins
Authors: Waldmann O. , Hassmann J , Koch R. , Müller P. , Hanan G. S. , Volkmer D. , Schubert U. S. , Lehn J.-M. 
Published: April 2011

AbstractThe magnetization of novel tetranuclear supramolecular grid structures and their mononuclear analogues was measured. In the tetranuclear complexes with Co2+ or Ni2+ ions an intramolecular antiferromagnetic coupling of the four metal centers is observed. The isotropic coupling strength was determined to be J = -8 K for the Ni2+ grids, and J = -2 K for the Co2+ grids.
Physical Characterization and Electrical Transport in End-Group Functionalized Self-Assembled Monolayers
Authors: Collet J. , Vuillaume D. , Bonnier M. , Bouloussa O. , Rondelez F. , Gay J. M. , Kham K. , Chevrot C. 
Published: April 2011

AbstractWe have previously demonstrated that a self-assembled monolayer (SAM) of alkyltrichlorosilane molecules, covalently bonded to the native oxide of a silicon substrate, allows the fabrication of MIS (Metal-Insulator-Semiconductor) devices with excellent electrical properties [1]. Here we demonstrate that we can functionalize, with π-electron moieties, the end-groups of the molecules, once grafted to the substrate, without disturbing the low conductivity through the SAM (σ⊥), while strongly increasing the in-plane conductivity (σ//). The functionalization of the monolayer is monitored by FTIR, ellipsometry and X ray reflectivity. Conductivity, photoconductivity and capacitance measurements are carried out to study the effect of these chemical functionalizations on the electrical properties of the monolayers. We demonstrate that the low perpendicular conductivity (σ⊥≈10−15 S/cm) is not altered by the end-group functionalities while high anisotropic conductivities (σ///σ⊥ ≈ 107-108) are obtained at a monolayer level. Interfacial (Si/SAM and SAM/metal) energy barriers are investigated as a function of the end-group functionalities. We also show that conducting monomers substituted by alkyl chains (3,6- dibromocarbazole-N-octyltrimethoxysilane), directly grafted to the substrate, exhibit similar behavior.
Investigation of ETCH Profiles in Etching of PZT and Pt Thin Films
Authors: Chung Chee Won , Song Inyong , Lee Jong Sig 
Published: April 2011

ABSTRACTReactive ion etching of PbZrxTi1−xO3 (PZT) and Pt thin films was studied by using chlorine and fluorine gas chemistry in an Inductively Coupled Plasma (ICP). PZT films were etched by varying the etching parameters including coil RF power, dc-bias voltage to substrate, and gas pressure. Etching characteristics of PZT films were investigated in terms of etch rate, etch selectivity, etch profile. Etch profile along with etch anisotropy was observed as a function of etching parameter by field emission scanning electron microscopy (FESEM). For the understanding of etching mechanism, X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma (ICP) analysis for the film composition were utilized. Platinum thin films have been etched by using Cl2/Ar in an ICP for the development offence-free etching. The redeposited materials formed on the pattern sidewall by using Cl2/Ar gas combination were analyzed by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). We found that the redeposited material was mainly PtCh compound. Based on this result, SiCl4/Cl2/Ar gas chemistry has been proposed as a new etching gas and demonstrated good etching profile of Pt films without unwanted redeposition.
Synthesis of Photodefinable RuO2 Precursors For Electrode Contacts
Authors: Law K. J. , Spooner Y. H. 
Published: April 2011

ABSTRACTA wet-chemical process for depositing and patterning RuO2 contacts for use in ferroelectric thin film capacitive devices is described. Three new ruthenium compounds containing photocrosslinkable organic groups have been synthesized which polymerize upon UV exposure. Preliminary pattern forming ability of the new precursors has been tested with the use of a simple straight line contact mask. The exposed portions of the precursor films are resistant to ethanol, acetone, and light abrasion. The formation of crystalline RuO2 upon organic pyrolysis was confirmed by x-ray diffraction. Synthesized ruthenium complexes were compared to commercially available ruthenium acetylacetonate. The synthesized organo-ruthenium complexes showed improvement in pattern resolution and clarity.
Stoichiometric Effects of Sputtered Barium Strontium Titanate Films
Authors: Baumert B. A. , Tsai T.-L. , Chang L.-H. , Remmel T. P. , Kottke M. L. , Fejes P. L. , Chen W. , Ehlert E. P. , Sullivan D. F. , Tracy C. J. , Melnick B. M. 
Published: April 2011

ABSTRACTBarium Strontium Titanate films have been deposited by rf magnetron sputtering and have been studied with respect to Ba/Sr ratio. Physical and electrical characterization has been done as a function of temperature, thickness, and composition, and results show that dielectric constant increases with increasing temperature, thickness (up to ∼80 nm), and Ba/Sr ratio for the compositions studied. The lattice parameters for the sputtered films are larger than those expected for powder samples and also increase with increasing Ba/Sr ratio.
(1-x)SrBi2Ta2O9-xBi3Ti(TayNb1-y)O9 Layered Structure Solid Solutions for Ferroelectric Random Access Memory Devices
Authors: Joshi P. C. , Ryu S. O. , Tirumala S. , Desu S. B. 
Published: April 2011

ABSTRACTThin films of layered-structure solid-solution material, (1−x)SrBi2Ta2O9−xBi3Ti(TayNb1−y)O9, have shown much improved ferroelectric properties compared to SrBi2Ta2O9, a leading candidate material for ferroelectric random access memory applications. The higher Pr, higher Tc, and lower crystallization temperature of the thin films of solid solution material promise to solve many problems with the present materials of interest. The films were fabricated by metalorganic solution deposition technique using room temperature processed alkoxide-carboxylate precursor solution and characterized in terms of structural, dielectric, and ferroelectric properties. It was possible to obtain a pyrochlore free crystalline phase at an annealing temperature of 600 °C. The effects of annealing temperature and excess Bi content on the film microstructure and properties were analyzed. The electrical measurements were conducted on metal-ferroelectric-metal (MFM) capacitors using Pt as the top and bottom electrode. It was possible to obtain good ferroelectric properties on films annealed at 650 °C. For example, thin films with 0.7SrBi2Ta2O9-0.3Bi3TiTaO9 composition, which were annealed at 650 °C, exhibited typical 2Pr and Ec values of 12.4 μC/cm2 and 80 kV/cm, respectively. The films exhibited low leakage current density, good fatigue characteristics under bipolar stressing at least up to 1010 switching cycles, and good memory retention characteristics after about 106 s of memory retention indicating a favorable behavior for memory applications.
Electronic Structure and Surface Properties of SrBi2Ta2O9 and Related Oxides
Authors: Robertson J , Chen C W 
Published: April 2011

ABSTRACTThe electronic structure of SrBi2Ta2O9 and related oxides such as SrBi2Nb2O9, Bi2WO6 and Bi3Ti4O12 have been calculated by the tight-binding method. In each case, the band gap is about 4.1 eV and the band edge states occur on the Bi-O layers and consist of mixed O p/Bi s states at the top of the valence band and Bi p states at the bottom of the conduction band. The main difference between the compounds is that Nb 5d and Ti 4d states in the Nb and Ti compounds lie lower than the Ta 6d states in the conduction band. The surface pinning levels are found to pin Schottky barriers 0.8 eV below the conduction band edge.
Laser-Assisted Low Temperature Processing of PZT Thin Films
Authors: Zhu Yongfei , Zhu Jinsong , Song Y. J. , Desu S. B. 
Published: April 2011

ABSTRACTA novel method for lowering processing temperature of ferroelectric Pb(Zr1−xTix)O3 (PZT) thin films was developed utilizing a laser-assisted two-step process. In the first step, perovskite phase was initiated in the PZT films by subjecting the films to a fornace anneal at low temperatures in the range of 470 °C to 550 °C depending on the Zr/Ti ratio. Later, the films were laser-annealed (using krF excimer laser) at room temperature to grow the perovskite phase, and to improve microstructure and ferroelectric properties. It was found that this two-step process was very effective in producing excellent quality ferroelectric PZT films at low temperatures. It should be noted that although laser annealing of amorphous and/or pyrochlore films directly (one-step process) produces perovskite phase, the ferroelectric properties of these films, irrespective of the composition, were rather unattractive. Some possible reasons for the ineffectiveness of the one-step process were discussed.
Crystallization of Amorphous Thin BST/MgO(001) Films Grown by R.F. Magnetron Sputtering
Authors: Noh D. Y. , Lee H. H. , Je J. H. , Kim H. K. 
Published: April 2011

ABSTRACTThe crystallization of amorphous BST thin films was studied in a synchrotron x-ray scattering experiment. At around 600°C, an intermediate phase, which was suspected to be a metastable pyrochlore phase, was formed. The x-ray reflectivity curves showed that the film-substrate interface became rough as the pyrochlore-like phase was formed. This suggests that the pyrochlore phase was nucleated near the interface area. Upon further annealing to higher temperatures, the film transformed to the crystalline perovskite phase. The crystallization was sensitive to the film thickness. In the thin 550Å thick film, the crystallization occurred at 750 °C with the <001> preferred orientation. On the other hand, the 5500Å thick film became crystalline even at 500°C with random crystalline orientation. The observed thickness dependence of the crystallization suggests that the crystalline perovskite phase was nucleated in the bulk of the film, rather than the near interface area.
Measurement of Effective Longitudinal Piezoelectric Coefficient of thin Films by Direct Piezoelectric Effect
Authors: Xu F. , Chu F. , Shepard J. F. , Trolier-McKinstry S. 
Published: April 2011

ABSTRACTThis paper presents a new method for the measurement of the longitudinal piezoelectric coefficient of piezoelectric thin films using the direct piezoelectric effect. A uniform uniaxial stress was applied to the piezoelectric thin film by high-pressure gas and the induced charge was collected and measured by a charge integrator. The effective longitudinal piezoelectric coefficient of lead zirconate titanate (PZT) 52/48 thin films made by sol-gel processing was measured by this method. Undoped films typically have d33 values of ∼ 5 pC/N, while poled films have values up to 220 pC/N.
PZT/PVDF Composite for Actuator/Sensor Application
Authors: Kowbel W. , Xia X. , Withers J. C. , Crocker M. J. , Wada B. K. 
Published: April 2011

ABSTRACTCurrently, smart structures utilize both polymeric sensor and PZT-based actuators. The benefit of self-sensing calls for the development of integrated actuator/sensor composites. This paper addresses the development of this new class of smart materials. Porous PZT ceramics were fabricated by several techniques. PVDF was subsequently infiltrated within the controlled porosity PZT. In addition, PVDF or its blends and PZT powders were in-situ processed to generate controlled piezo and mechanical property composites. Both actuating and sensing of this new class of composite materials were studied. The paper presents the processes-structure-property relationship of this new class of piezocomposites.
Strontium Bismuth Tantalate Based Ferroelectric Gate Field Effect Transistor with Yttrium Oxide as the Buffer Layer
Authors: Lim Myoung-Ho , Kalkur T. S. , Kim Yong-Tae 
Published: April 2011

ABSTRACTWe report the first demonstration of an enhancement mode n-channel metal -ferroelectric-semiconductor field effect transistor (MFISFET) realized directly on silicon with yttrium oxide as the buffer layer. The capacitance-voltage (C-V) characteristics of Metal Ferroelectric Insulator Silicon (MFIS) structures show hysteresis and the direction of hysteresis corresponds to ferroelectric polarization. The memory window in the C-V characteristics was 2V for an applied voltage of ± 10V. The memory window did not show significant change due to decrease in rate of change of sweep voltage and temperature. The transmission electron microscopy (TEM) analysis confirms the formation of an amorphous oxide layer between silicon and yttrium oxide buffer layer.
A Multi-Technique Analysis of MOCVD- Grown Lead Lanthanum Titanate (Pb1−xLax)TiO3Thin Films on Quartz Substrates
Authors: Chen H. Y. , Lin J. , Tan K. L. , Feng Z. C. , Kwak B. S. , Erbil A. 
Published: April 2011

AbstractA series of Lead lanthanum titanate (Pb1−xLax)TiO3thin films with different compositions of x = 0 − 0.33 have been grown on fused quartz substrates by metalorganic chemical vapor deposition (MOCVD) and analyzed by a variety of techniques including X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman scattering spectroscopy (RSS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) techniques. XPS results confirmed the film composition of (Pb1−xLax)TiO3and lanthanum enrichment in top surface layers. XRD indicates a preferred (100) orientation for the films with x values of 0.05–0.17, while the films with x values above 0.32 have randomly distributed orientations. A gradual change in the crystal structure from tetragonal to cubic arrangement with increasing La composition is noted. XPS data also show the variation of Ti-O, Pb-0 and La-0 bonding with the change in the La composition. The stretching vibrations corresponding to these oxygen related bonding are observed by DRIFT at 667, 826, 936 and 529 cm−1respectively. This combined investigation on epitaxial PLT films may enhance our understanding of the ferroelectric PLT materials.
The Impact of Domains on the Dielectric and Electromechanical Properties of Ferroelectric Thin Films
Authors: Trolier-McKinstry S. , Aungkavattana P. , Chu F. , Lacey J. , Maria J-P. , Shepard J. F. , Su T. , Xu F. 
Published: April 2011

ABSTRACTIn ferroelectric thin films for capacitive and piezoelectric applications, it is important to understand which mechanisms contribute to the observed dielectric constant and piezoelectricity. In soft PZT (PbZr1−xTixO3) ceramics, over half the room temperature response is associated with domain wall contributions to the properties. However, recent studies on bulk ceramics have demonstrated that the number of domain variants within grains, and the mobility of the twin walls depend on the grain size. This leads to a degradation in the dielectric and piezoelectric properties for grain sizes below a micron. This has significant consequences for thin films since a lateral grain size of 1 μm is often the upper limit on the observed grain size. In addition, since the pertinent domain walls are ferroelastic, the stress imposed on the film by the substrate could also clamp the piezoelectric response. To investigate these factors, controlled stress levels were imposed on PZT films of different thickness while the dielectric and electromechanical properties were measured. It was found that for undoped sol-gel PZT 40/60, 52/48, and 60/40 thin films under a micron in thickness, the extrinsic contributions to the dielectric and electromechanical properties make very modest contributions to the film response. No significant enhancement in the properties was observed even when the film was brought through the zero global stress condition. Comparable results were obtained from laser ablated films grown from hard and soft PZT targets. Finally, little twin wall mobility was observed in AFM experiments. The consequences of this in terms of the achievable properties in PZT films will be presented. Work on circumventing these limitations via utilization of antiferroelectric phase switching films and relaxor ferroelectric single crystal films will also be discussed.
An Important Failure Mechanism in MOCVD (Ba,Sr)TiO3 thin Films: Resistance Degradation
Authors: Basceri C. , Lash S. E. , Parker C. B. , Streiffer S. K. , Kingon A. I. , Grossmann M. , Hoffmann S. , Schumacher M. , Waser R. , Bilodeau S. , Carlt R. , Van Buskirk P. C. , Summerfelt S. R. 
Published: April 2011

ABSTRACTWe have investigated the intrinsic resistance degradation behavior of fiber-textured MOCVD (Ba,Sr)TiO3 thin films appropriate for use in advanced DRAMs and integrated decoupling capacitors, as a function of applied voltage polarity, thickness, temperature, and dc bias/field. The results suggest that there is a significant stoichiometry effect on the measured resistance degradation lifetimes. The measured degradation lifetime increases as the Ti content is increased from 51.0 to 52.0 at%Ti, and then decreases with higher at%Ti. Predicted resistance degradation lifetimes obtained from both temperature and voltage extrapolations to DRAM operating conditions of 85°C and 1.6 V exceed the current benchmark of 10 years for all of the films studied.
New Magnesium Precursors for Doping Semiconductor Films
Authors: Winter Charles H. , Sebestl Jennifer L. , Heeg Mary Jane 
Published: April 2011

ABSTRACTMagnesium-doped semiconductors have existing and anticipated applications in the fabrication of blue and green light-emitting diodes, blue and green laser diodes, and in microelectronics devices. At present, the area is limited by the precursor characteristics of bis(cyclopentadienyl)magnesium and substituted derivatives. We will describe our efforts to identify new magnesium source compounds that are potentially superior to magnesocenes and can be used in chemical vapor deposition processes. Monomeric three- and four-coordinate amides have been synthesized and totally characterized. These complexes are low-melting solids and are significantly more volatile than magnesocene derivatives. We will also describe the synthesis and characterization of several other classes of volatile magnesium compounds that might be useful in chemical vapor deposition processes.