bluuebunny/crossref_metadata_2025 huggingface dataset:
Stress and Stability of Sputter Deposited A-15 and BCC Crystal Structure Tungsten Thin Films
Authors: O'keefe M. J. , Stutz C. E.
Published: April 2011

Magnetron sputter deposition was used to fabricate body centered cubic (bec) and A-15 crystal structure W thin films. Previous work demonstrated that the as-deposited crystal structure of the films was dependent on the deposition parameters and that the formation of a metastable A-15 structure was favored over the thermodynamically stable bec phase when the films contained a few atomic percent oxygen. However, the A-15 phase was shown to irreversibly transform into the bec phase between 500°C and 650°C and that a significant decrease in the resistivity of the metallic films was measured after the transformation. The current investigation of 150 nm thick, sputter deposited A-15 and bec tungsten thin films on silicon wafers consisted of a series of experiments in which the stress, resistivity and crystal structure of the films was measured as a function of temperature cycles in a Flexus 2900 thin film stress measurement system. The as-deposited film stress was found to be a function of the sputtering pressure and presputter time; under conditions in which the as-deposited stress of the film was ∼ 1.5 GPa compressive delamination of the W film from the substrate was observed. Data from the thermal studies indicated that bec film stress was not affected by annealing but transformation of the A-15 structure resulted in a large tensile increase in the stress of the film, regardless of the as-deposited stress of the film. In several instances, complete transformation of the A-15 structure into the bec phase resulted in ≥ 1 GPa tensile increase in film stress.
An X-ray Photoelectron Spectroscopie Study of B-N-Ti system
Authors: Seal Sudipta , Barr Tery L. , Sobczak Natalie , Benko Ewa , Morgiel J.
Published: April 2011

Composite nitrides (such as BN, TiN) are widely used in various industrial applications because of their extreme wear and corrosion resistance, thermal and electrical properties. In order to obtain composite materials with mese optimal properties, it is important to elucidate whether any chemical reactions occur at nitride/metal interfaces, e.g., those involving BN-Ti/TiN. Materials of interest include the deposition by PVD of Ti and TiN on BN substrates. Some of these systems were then subjected to varying degrees of physical and thermal alteration. Detailed X-ray photoelectron spectroscopy (XPS) has merefore been rendered of these interfaces using cross-sectional display and sputter etching. Resulting structural and morphological features have been investigated with transmission electron microscopy (TEM) and X-ray diffraction (XRD). Diffusion of the nitridation, oxynitride formation and interfacial growth are of general interest.
Microstructural Observations of LPCVD Double Layer Polysilicon Thin Film Tensile Specimens
Authors: Legros M. , Kumar M. , Jayaraman S. , Hemker K. J. , Sharpe W. N.
Published: April 2011

The vast majority of micro electro-mechanical systems fabricated today depend on polycrystalline silicon thin films for structural support. Studies involving the mechanical performance of these thin films have progressed to the point where the elastic properties and tensile strength of the films can routinely be measured using a specially designed microsample tensile testing machine. However, a fundamental understanding to predict the mechanical behavior of the polycrystalline silicon films requires that these experimental measurements be complemented with detailed observations of the underlying thin film microstructure. This paper describes some of the plan view and cross-section transmission electron microscope observations that have been performed on different deposition runs of double layer polycrystalline films obtained from the Microelectronics Center of North Carolina. The emphasis has been placed on determining the flatness and dimensions of the polycrystalline films, grain morphology and distribution, texture, and dislocation substructure and microtwinning in the undeformed films.
Automated Crystal Orientation Mapping (ACOM) of Thin Metallization Layers and Interconnects
Authors: Schwarzer R.A.
Published: April 2011

A system for acquisition and interpretation of Kikuchi patterns with computer-controlled electron microscopes is presented. It enables interactive as well as fully automated determination of individual grain orientations. Special features for automated crystal orientation mapping (ACOM) with the scanning electron microscope (SEM) are digital beam scan, autocalibration and dynamic focus controlled by the computer. With the present setup about three orientations per second can be measured unattendedly. In the transmission electron microscope (TEM) the on-line determination of Burgers vectors and identification of deformation systems are based on crystal orientation measurement. The characterization of dislocations is facilitated by the simulation of diffraction patterns on the computer as a function of specimen tilt.

Crystal orientation maps are obtained by assigning to the raster points in the image a color specific for the grain orientation, the misorientation or character of the grain boundary. The dala set of grain orientations is used to calculate the Schmid factors grain by grain, the orientation distribution function (ODF) and the correlated as well as the uncorrelated misorientation distribution functions (MODF) which characterize crystallographic texture in a statistical sense.

Applications of individual grain orientation measurement are:

. Thermomechanical hillocks in aluminum metallization layers on silicon substrates

. Stress-induced grain growth in aluminum metallization layers on silicon substrates

. Electromigration voids and hillocks in aluminum interconnects

A working hypothesis for electromigration failure, based on experimental findings, is discussed
Highly Conductive and Optically Transparent Polycrystalline Iridium Oxide Thin Films Grown by Reactive Pulsed Laser Deposition
Authors: El Khakani M.A. , Chaker M.
Published: April 2011

Reactive pulsed laser deposition has been used to deposit IrO2 thin films on both SiO2 and fused quartz substrates, by ablating a metal iridium target in oxygen atmosphere. At a KrF laser intensity of about 1.7 × 109 W/cm2, IrO2 films were deposited at substrate deposition temperatures ranging from room-temperature to 700 °C under an optimum oxygen ambient pressure of 200 mTorr. The structure, morphology, electrical resistivity and optical transmission of the deposited films were characterized as a function of their deposition temperature (Td). High quality IrO2 films are obtained in the 400–600 °C deposition temperature range. They are polycrystalline with preferred orientations, depending on the substrate, and show a dense granular morphology. At a Td as low as 400 °C, highly conductive IrO2 films with room-temperature resistivities as low as (42±6) μΩ cm are obtained. Over the 300–600 °C Td range, the IrO2 films were found to exhibit a maximum optical transmission at 450 °C (∼ 45 % at 500 nm for 80 nm-thick films).
Free-Energy Barrier to Crystallite Nucleation in Solid-Phase Crystallized Poly-Silicon Thin Films
Authors: Kumomi Hideya , Shi Frank G.
Published: April 2011

We introduce a non-Arrhenius method for measuring free-energy barrier to nucleation, W*, directly from size distribution of crystallites. W* is determined independent of any model for the nucleation barrier and independent of energy barrier to growth. The method is applicable to three-dimensionally growing crystallites, planar crystallites in thin films, and both compact and fractal crystallites. We apply the method to dendritic crystallites obtained by solid-phase crystallization of amorphous Si thin films into which Si+ ions are implanted at various conditions prior to the isothermal annealing. The ion implantation suppresses the nucleation of the crystallites and enhances the crystallite size of the resulting polycrystalline films. The directly measured W* increases as the accelerating energy or the dose of the Si+ ions increases. This result suggests that the observed suppression of the nucleation could not be accounted for simply by the amor-phization of the preexisting crystallites by the ion bombardment.
Hot Water Etching of Silicon Surfaces: New Insights of
Mechanistic understanding and Implications to Device
Fabrication
Authors: Rosamilia J. M. , Boone T. , Sapjeta J. , Raghavachari K. , Higashi G. S. , Liu Q.
Published: April 2011

Over the recent years, many new approaches in wafer cleaning have utilized
hot water rinsing. Benefits of hot water rinsing are (1) it aids the removal
of residual chemicals and (2) it improves the performance of the dry, e.g.
TREBOR hydrodry. However, there have been a number of significant
disadvantages documented with regard to device performance. Earlier work
done at this laboratory showed that the use of DI rinse water at elevated
temperatures can cause etching of the Si surface producing unwanted surface
topography and microroughness. The surface erosion created under these
conditions had a negative device impact which led to product yield loss. In
this paper, we provide a fundamental understanding of the mechanism by which
Si is etched during hot water rinsing. To this end, we have explored the
interaction of dissolved oxygen concentration, water temperature, and rinse
time as it relates to the attack/dissolution of H-terminated silicon.
Contact angle measurements, surface roughness measurements, and etch rate
data from TEM measurements as a function of water temperature, rinse time,
and dissolved oxygen concentration have been made. The etch rate data
strongly correlates with the rinse water temperature, however little
dependence was observed with dissolved oxygen concentration. A mechanism to
explain the etching will be discussed.
Influence of BHF Treatments on Hydrogen-Terminated Si(100)
Surfaces
Authors: Osada T. , Kawazawa Y. , Miyazaki S. , Hirose M.
Published: April 2011

The hydrogen bonding features of Si(100) surfaces treated with BHF
(NH4F/HF/H2O) have been studied by Fourier
transform infrared attenuated total reflection spectroscopy (FT-IR-ATR). The
amount of residual silicon-fluorine bonds on Si(100) surfaces has been
evaluated by X-ray photoelectron spectroscopy (XPS). It is found that
Si-H3 bonds appears to be preferentially removed by OH ions so
as to increase the surface SiH2 and SiH bonds. On the other hand,
it is likely that fluorine-containing ionic species such as HF2
might attack the backbonds of surface hydrides to produce Si-H3
and Si-F bonds. ATR spectra have shown that a BHF treated Si(100) surface in
5∼10% NH4F with molar ratios of HF/NH4F=0.37∼0.56
(pH=3.7∼4.0) at a treatment time of 5 minutes is atomically flatter than
that treated in BHF containing 15∼20% NH4F. This is because the
amount of residual Si-F bonds on Si(100) increases with HF2
concentration in BHF and these Si-F bonds enhance attacking of silicon
backbonds of Si-F bond by OH− and HF2− ions.
The Effect of contamination solutions and substrate conditions
on Copper Particle Growth Behavior
Authors: Choi Geun-Min , Sekijne Katsuyuki , Morita Hiroshi , Ohmi Tadahiro
Published: April 2011

Cu particle growth behavior on two silicon substrates, amorphous and single
crystal silicon, has been investigated using two contamination solutions.
This study reveals that the growth behavior of Cu particle depends on
substrate conditions and copper contamination solutions. Contamination level
is independent of split conditions. From the SEM images of an amorphous
silicon shows a big difference in the number of particles depending on
copper contamination solution. The amorphous silicon has similar native
oxide thickness in ultrapure water spiked with CuF2 and
CuCl2, whereas the single crystal silicon is different from
the native oxide thickness depending on copper contamination solution. When
1 ppm of Cu in ultrapure water was spiked as a function of time, the amount
of Cu impurity on amorphous silicon in the early dipping stage was measured
10 times higher than that on single crystal silicon for both of copper
contamination solutions.
The Adsorption-Desorption of Cations at the Silica-Water its
Implication in Wafer-Cleaning Efficacy
Authors: Lee W. , Torek K. J. , Palsulich D. A. , Weston L.
Published: April 2011

The adsorption-desorption of various cations at the silica-water interface
is discussed in terms of electrical double layer and surface complexation
models. Some experimentally determined surface equilibria constants from the
literature are tabulated for Fe, Cu, and Mg. The adsorption phenomena of
those cations onto silica gel is described using the stability calculation
(STABCAL) computer program based on the suggested models.

A chemical oxide (silica) is grown on the silicon surface during the SC1
and/or SC2 processes. Adsorption of Fe, Cu, and Mg onto this chemical oxide
is studied as a function of pH and compared to the modeling results. In
general, there is a qualitative correlation between the experimental and
modeling data, which can be used as a basis to develop a quantitative model
for cation adsorption-desorption on the wafer surface.
Transport Properties of Partially-Filled CeyCo4Sb12
Authors: Uher C. , Chen B. , Hu S. , Morelli D.T. , Meisner G.P.
Published: April 2011

We have investigated the magnetic and transport properties of CeyCo4Sb12 filled skutterudites with the filling fraction y ≤ 0.1. These compounds are n-type materials that develop a magnetic moment upon the presence of trivalent cerium. Cerium has a strong influence on all transport properties and even in small amounts it drastically reduces the lattice thermal conductivity. The resulting figures of merit are comparable to the values established previously for the p-type filled skutterudites.
Studies of Bulk Materials for Thermoelectric Cooling
Authors: Sharp Jeff W. , Nolas George S. , Volckmann Edward H.
Published: April 2011

We discuss ongoing work in three areas of thermoelectric materials research: 1) broad band semiconductors featuring anion networks, 2) filled skutterudites, and 3) polycrystalline Bi-Sb alloys. Key results include: a preliminary evaluation of a previously untested ternary semiconductor, KSnSb; the first reported data in which Sn is used as a charge compensator in filled antimonide skutterudites; the finding that Sn doping does not effect polycrystalline Bi1−xSbx as it does single crystal samples.
Progress on GaInAsSb And InAsSbP Photodetectors for MiD-Infrared Wavelengths
Authors: Shellenbarger Z. A. , Mauk M. G. , Sims P. E. , Cox J. A. , Lesko J. D. , Bower J. R. , South J. D. , Dinetta L. C.
Published: April 2011

Progress on mid-infrared photodetectors fabricated by the liquid phase epitaxial growth of GaInAsSb, InAsSbP, and AlGaAsSb on GaSb and InAs substrates is reported. GaInAsSb p/n and p-i-n detectors, InAsSbP p/n detectors and AlGaAsSb/GaInAsSb avalanche photodiode (APD) structures were fabricated. Preliminary results indicate that these devices can have higher detectivity with lower cooling requirements than commercially available detectors in the same wavelength range. Infrared p/n junction detectors made from GaInAsSb and InAsSbP showed cut-off wavelengths of 2.3.μm and 2.8. μm respectively. Room temperature background noiselimited detectivity (D*BLIP) of 4 × 1010 cmHz1/2/W for GaInAsSb detectors and 4 × 108 cmHz1/2/W for InAsSbP was measured. Room-temperature avalanche multiplication gain of 20 was measured on AlGaAsSb/GaInAsSb avalanche photodiodes.
Free Carrier Absorption in P-Type Epitaxial Si and GaAs Films for far-Infrared Detection
Authors: Perera A. O. U. , Shen W. Z. , Tanner M. O. , Wang K. L. , Schaff W.
Published: April 2011

We report the investigation of free-carrier absorption characteristics for epitaxially grown p-type thin films in the far-infrared region (50 ∼ 200 μm), where homojunction interfacial workfunction internal photoemission (HIWIP) detectors are employed. Five Si and three GaAs thin films were grown by MBE over a range of carrier concentrations, and the experimental absorption data were compared with calculated results. The freehole absorption is found to be almost independent of the wavelength. A linear regression relationship between the absorption coefficient and the carrier concentration, in agreement with theory, has been obtained and employed to calculate the photon absorption probability in HIWIP detectors. The detector responsivity follows the quantum efficiency predicted by concentration dependence of the free carrier absorption coefficient.
Fabrication of Cdznte Strip Detectors for Large Area Arrays
Authors: Stahle C. M. , Shi Z. Q. , Hu K. , Barthelmy S. D. , Snodgrass S. J. , Lehtonen S. J. , Mach K. J. , Barbier L. , Gehrels N. , Krizmanic J. F. , Palmer D. , Parsons A. M. , Shu P.
Published: April 2011

A CdZnTe strip detector large area array (∼ 60 cm2 with 36 detectors) with capabilities for high resolution imaging and spectroscopy has been built as a prototype for a space flight gamma ray burst instrument. The detector array also has applications in nuclear medical imaging. Two dimensional orthogonal strip detectors with 100 gm pitch have been fabricated and tested. Details for the array design, fabrication and evaluation of the detectors will be presented.
Tem Investigation of Al0.5Ga0.5As1-y Sby Buffer Layer Systems
Authors: Chen E. , Ahearn J. S. , Nichols K. , Uppal P. , Paine D. C.
Published: April 2011

We report on a TEM study of Sb-adjusted quaternary Al0.5Ga0.5As1-y Sby buffer-layers grown on <001> GaAs substrates. A series of structures were grown by MBE at 470°C that utilize a multilayer grading scheme in which the Sb content of Al0.5Ga0.5As1-ySby is successively increased in a series of eight 125 nm thick layers. Post growth analysis using conventional bright field and weak beam dark field imaging of these buffer layers in cross-section reveals that the interface misfit dislocations are primarily of the 60° type and are distributed through out the interfaces of the buffer layer. Plan view studies show that the threading dislocation density in the active regions of the structure (approximately 2 μm from the GaAs substrate) is 105–6/cm2 which is comparable to equivalent InxGa1−x As buffers. Weak Sb-As compositional modulations with a period of 1.8 nm were observed that provide a marker for establishing the planarity of the growth process. These features reveal that the growth surface remains planar through out the buffer layer growth sequence.
Control of Defects and Impurities in Production of CdZnTe Crystals by the Bridgman Method
Authors: Glass H. L. , Socha A. J. , Bakken D. W. , Speziale V. M. , Flint J. P.
Published: April 2011

Cadmium zinc telluride crystals were grown by vertical Bridgman processes using in situ compdunding from high purity elements into pyrolytic boron nitride crucibles within sealed fused quartz ampoules containing cadmium vapor at a pressure of roughly one atmosphere. These conditions produce material having the low etch pit density, low precipitate density, high infrared transmission and high purity required for use as substrates for infrared focal plane detector arrays fabricated in epitaxial mercury cadmium telluride. Similar processes should be satisfactory for producing cadmium zinc telluride for gamma ray detectors.
Photoresponse Studies of The Polarization Dependence of the CdGeAs2 Band Edge
Authors: Brown G. J. , Ohmer M. C. , Schunemann P. G.
Published: April 2011

Mid-infrared photoresponse studies were performed on an oriented p-type cadmium germanium arsenide uniaxial crystal. The effects of optical polarization alignment, parallel and perpendicular to the c-axis of the crystal, were studied, as well as the effects of the transport electric-field direction. The measured optical band edge was 0.578 eV at 10 K for all polarization and bias configurations. This band gap energy is in good agreement with absorption and photoluminescence results for this sample. However, the photoresponse spectrum measured with unpolarized light at 10 K showed a much lower onset at 0.50 eV. This difference in the low temperature activation energy of the photoresponse is attributed to deep native defect levels near the band edge. These deep levels at times obscure the true band edge and can cause under estimates of the band gap energy. These results can explain the wide disparity in the reported CdGeAs2 band gap in the literature. In addition, the intensity of the photoresponse was found to be only slightly dependent on the optical polarization direction, but strongly dependent on the bias electric-field direction. The largest photoreponse was observed when the optical polarization was parallel to the c-axis and the bias electric field was perpendicular to the c-axis. The bias electric-field direction also had a significant effect upon the temperature dependence of the peak photoresponse intensity. The temperature dependence of the CdGeAs2 energy band gap was determined by empirical fitting.
Influence of Quantum Confinement on the Photoemission From Nonlinear Optical Materials
Authors: Ghatak Amakhya P. , Bose P. K. , Majumder Gautam
Published: April 2011

wells (QWs), quantum well wires (QWWs) and quantum dots (QDs) of nonlinear optical materials, respectively on the basis of a newly derived electron dispersion law considering all types of anisotropies within the framework of k.p. formalism. It is found, taking CdGeAs2, GaAs and InAs, as exmaples, that the photoemission increase with increasing photon energy in a ladder like manner and also exhibits oscillatory dependences with changing electron concentration with film thickness respectively for all types of quantum confinement. The photoemission current density is greatest in QDs and least in QWWs. In addition, the theoretical results are in agreement with the experimental observation as reported elsewhere.
Theoretical Performance Of Mid-Infrared Broken-Gap Multilayer Superlattice Lasers
Authors: Flatté Michael E. , Olesberg J. T. , Grein C. H.
Published: April 2011

We present calculations of the intersubband absorption and Auger recombination rate of superlattices based on the InAs/GaInSb material system involving more than two layers in the repeating unit cell and strain balanced to match the GaSb substrate. We demonstrate theoretically the presence of final-state optimization in a 4.0 μm strain-balanced brokengap superlattice. This system's band structure is optimized not only at the band edge, where the valence density of states has been reduced, but also at resonance energies, where reside final states for Auger and intersubband processes. The spectral structure of the intersubband absorption, which for some wavelengths near the lasing wavelength can exceed 500 cm−1 at lasing threshold, has been considered when designing this active region. Fortunately, final-state optimized designs which minimize Auger recombination tend to minimize intersubband absorption as well. The effectiveness of final-state optimization is evaluated by considering band structures with identical band edge structure, but different final-state structure.
Evaluation of Indium Diffused M-i-n CdZnTe Detectors
Authors: Gagliardi M-A. , Nenonen S. , Gagliardi T. , Aleksejeva L. , Ivanov V. , Bavdaz M.
Published: April 2011

One of the main electronic noise sources of a room temperature spectroscopy system is the leakage current of a detector. It can be reduced with a pn-junction type detector structure such as a M-i-n configuration, and with cooling. In this work eight CdZnTe detectors with a M-i-n structure were fabricated by indium diffusion. The junction was characterized by a currentvoltage technique. Detector electrical, charge collection and spectroscopic properties were compared to the ones received with the traditional electroless Au contacts, before the junction formation. As a result of the indium diffusion an improved detector leakage current performance was achieved. However, a corresponding improvement in the detector energy resolution was not always observed due to the CdZnTe charge collection properties and process variables.
Spectroscopic Response Versus Interelectrodic Charge Formation Position in CdTe Detectors
Authors: Auricchio N. , Caroli E. , Cesare G. De , Dusi W. , Grassi D. , Hage-Ali M. , Perillo E. , Siffert P. , Spadaccini G.
Published: April 2011

The electron-hole pair production energy (∼ 4.43 eV) in cadmium telluride semiconductor based detector would allow, in principle, to achieve spectroscopic performance close to germanium. In fact the material impurities, crystal lattice defects and low charge mobility, mainly for holes, can severely degrade the spectroscopic properties through charge trapping/detrapping and recombination phenomena, limiting the usable distance between the electrodes. The charge collection efficiency depends, following the Hecht relation, on the distance between the charge production location and the collecting cathode; we have studied the dependence of some CdTe spectroscopic parameters (energy resolution, photo-peak gain and efficiency) from this distance. A set of experimental tests were performed using a well collimated photon beam. The beam spot, obtained from a 57Co radioactive source through a thick (20 mm) tungsten collimator having a 0.2×2 mm window, was positioned between the two electrodes of a CdTe crystal of size 3×5×2 mm3, with the electrodes deposited on the 3×5 mm2 sides.

The detector was irradiated on the face having the area of 2×3 mm2, in the arrangement with the collecting field orthogonal to the incoming radiation (PTF configuration), and the largest side of the spot parallel to the electrode plane. Using a micro-positioning system a fine scanning of the interelectrodic region was performed.

In order to evaluate the detector behavior in a wider energy range, further tests using energies between 14 keV to 662 keV have been performed.

The results of these measurements are presented and discussed in order to emphasize a method to improve CdTe detector spectroscopic capabilities and to understand the detection behavior
Raman And Photo-Luminescence Studies On Intrinsic And Cr-Doped Znse Single Crystals
Authors: Rai Brajesh K. , Bhaskar S. , Bist H. D. , Katiyar R. S. , Chen K.-T. , Burger A.
Published: April 2011

Single crystals of ZnSe, with varying amounts of Cr doping have been studied using Raman and photoluminescence(PL) spectroscopy. The Cr-doped samples show the existence of a coupling mechanism of longitudinal optical(LO) phonons of ZnSe with hole-plasmons. The dependence of intensity ratio of LO and transverse optical(TO) mode on temperature and excitation wavelength, has been attributed to the interaction of the field of LO phonons with the surface electric field in the depletion layer. The interaction of discreet phonons with the electronic continuum of conduction band in ZnSe is responsible for the shift of Raman peaks. The large electron capture cross-section of deep-level Cr2+ and Cr1+ impurities is inhibitive for the observation of band-to-band PL transition at ˜2.7eV in ZnSe:Cr.
Dielectric Spectroscopy Study Of Znse Grown By Physical Vapor Transport
Authors: Kokan Julie , Gerhardt Rosario , Su Ching-Hua
Published: April 2011

ZnSe, although generally thought of as a wide band gap semiconductor, is insulating in the as-grown state. It is only after heat treatment in a zinc rich atmosphere that semiconducting properties are observed Therefore, dielectric spectroscopy is an appropriate tool to study the electrical properties of as grown ZnSe. The dielectric properties of large-grained samples of ZnSe grown by physical vapor transport were measured as a function of frequency. Differences can be seen in the dielectric properties of samples grown under different conditions (such as the effect of a seed and the orientation of the gravity field during growth). The spectra of heat treated samples were also acquired and were found to exhibit significant deviations from those of the as grown crystals.
Polymer Layer Ordering of Polyaniline Derivatives in Pled Devices: Surface Adsorption and Characterization
Authors: Advincula R. C. , Knoll W. , Frank C. W. , Roitman D. , Moon R. , Sheats J.
Published: April 2011

The fabrication and characterization of polyaniline (PANI) derivatives deposited on ITO coated glass is investigated as possible hole injection layers for MEH-PPV based polymer light emitting diode (PLED) devices. This involved multilayer ordering by the alternate polyelectrolyte adsorption of polyaniline and sulfonated poyaniline with an oppositely charged polyelectrolyte from solution. A combination of spectroscopic and microscopic techniques was utilized to determine the layer ordering, film structure, morphology, and homogeneity. The deposition process generally showed a linear behavior for all pairs as shown by ellipsometry and UV-vis spectroscopy. However, surface plasmon spectroscopy (SPS) and AFM revealed that thicker films are accompanied by increased surface roughness regardless of concentration. Comparison in performance was made between bare ITO and PANI or SPANI coated devices. Initial investigations of PLED performance showed significant improvements in lifetime and efficiency compared to bare ITO.
Photofabrication of Surface Relief Gratings using Post Functionalized Azo Polymers
Authors: Tripathy Sukant K. , Kumar Jayant , Kim Dong-Yu , Jiang Xinli , Wang Xiaogong , Li Lian , Sukwattanasinitt Mongkol , Sandman Daniel J.
Published: April 2011

A series of azobenzene functionalized polymers has been synthesized by post polymerization azo coupling reaction. Photo-fabrication of surface relief gratings were studied on the polymer films. Epoxy based azo polymers were prepared by post azo coupling reaction to form polymers containing donor-acceptor type azo chromophores. The azo chromophores were designed to contain ionizable groups to impart self-assembling and photoprocessing capabilities to the polymers. The polymers containing 4-(4-(carboxylic acid)phenylazo)aniline chromophores can be directly photofabricated to form surface relief gratings with large surface modulations. Charge interactions had a strong influence on the details of the writing process. A new soluble polydiacetylene, post-functionalized with azobenzene groups was also prepared. Large amplitude surface gratings could be fabricated on this polydiacetylene film as well.
Molecular Second-Order Optical Nonlinearity of Push-Pull Bisdithiolene Nickel Complexes
Authors: Chen Chin-Ti , Liao Sish-Yuan , Lin Kuan-Jiuh , Lai Long-Li
Published: April 2011

The synthesis and characterization of donor-acceptor substituted unsymmetrical bisdithiolene nickel complexes are described for the first time. X-ray single crystal data indicate that the complexes exist with two types of bonding structures, namely, the π-localized and π-delocalized structures. The relation between bonding structures and the molecular second-order nonlinear optical properties, i.e., solvatochromism, dipole moment, and molecular first hyperpolarizability is discussed.
New Photopolymers Based on Two-Photon Absorbing Chromophores and Application to Three-Dimensional Microfabrication and Optical Storage
Authors: Cumpston B. H. , Ehrlich J. E. , Erskin L. L. , Heikalt A. A. , Hu Z.-Y. , Leet I.-Y. S. , Levin M. D. , Marder S. R. , McCord D. J. , Perry J. W. , Röckel H. , Rumi M. , Wu X.-L.
Published: April 2011

Molecules exhibiting strong two-photon absorption hold great potential for a wide range of applications including two-photon fluorescence imaging, three-dimensional (3D) optical data storage, and 3D microfabrication. We have observed two-photon absorptivities as high as 1500×10− 50 cm4 s/photon in bis-donor diphenylpolyene derivatives that are correlated to simultaneous charge transfer from the end groups to the polyene bridge in the molecule. Many of these molecules are also excellent photoexcitable electron donors that can initiate charge-transfer reactions with acrylate monomers. Marcus theory is used to describe the efficiency of these charge-transfer reactions. Polymerization rates have also been measured and we show that these twophoton chromophores display increased sensitivity and recording speed over conventional UV photo-initiators. The fabrication of complex, three-dimensional structures by twophoton polymerization is demonstrated and discussed in the context of advanced photonic applications.
Design and Synthesis of New Conjugated Porphyrin Copolymers for Optical-Electronic Applications
Authors: Jiang Biwang , Yang Szu-Wei , Lam Phuong T. , Jones Wayne E.
Published: April 2011

New linear conjugated porphyrin polymers were synthesized by a palladium-catalyzed cross-coupling reaction of [5,15-bis(ethynyl)-10,20-bis (mesityl)porphyrin]zinc and diiodobenzene derivatives. Enhanced solubility of the conjugated porphyrin polymers was achieved by attachment of long alkyl ether or dialkyl amide groups to the aryl moiety, resulting in unambiguous characterization by 1H NMRLR, GPC, UV-Vis and fluorescence spectroscopies. The introduction of alkyl ether (electron donor) or dialkyl amide (electron acceptor) results in significant modulation of the electronic properties of the conjugated porphyrin polymers due to strong electronic coupling. The spectroscopic and electronic characterization of these materials provides for comparison to earlier preparations of ethynyl bridged conjugated copolymers in which electronic coupling was substantially weaker.
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

In 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

Since 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

Electroluminescence 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

Single 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

Dendritic 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

The 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

We 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

Reactive 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

A 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

Barium 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

Thin 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

The 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

A 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.