bluuebunny/crossref_metadata_2025 huggingface dataset:
Sequential Growth of High Quality Diamond Films from Hydrocarbon and Hydrogen Gases
Authors: Olson Darin S. , Kelly Michael A. , Kapoor Sanjiv , Hagstrom Stig B.
Published: March 2011

We have constructed a novel, sequential DC glow and hot filament CVD reactor, to study the influence of single parameters on the deposition of diamond thin films. This reactor is capable of growing diamond films, with independent excitation of hydrogen and methane. This is achieved by the sequential exposure of the substrate to spatially separated, chemically independent, plasma regions of hydrogen, and methane in helium. The substrate is mounted on a rotating plate above the gas sources at a variable distance, typically 0.5 – 2 mm. The plate is radiantly heated from behind to a desired temperature up to 1300 K. Using the sequential deposition chamber we have been able to deposit good quality diamond up to 8% methane in helium, without the presence of oxygen, by separating a source of atomic hydrogen and a source of methane. These experiments show that methane and atomic hydrogen do not need to be present simultaneously to grow diamond. Our results further indicate that the primary critical parameter for both quality and growth rate, in hot filament deposition of diamond, is the concentration of atomic hydrogen in the system.
Mombe Growth of GaP and its Efficient Photoeniiancement at Low Temperatures
Authors: Yoshimoto Masahiro , Tsuji Tsuzumi , Kajimoto Atsushi , Matsunami Hiroyuki
Published: March 2011

GaP epllayers grown at temperatures ranging from 420 to 500°C had smooth surfaces and streaky RHEED patterns. The decomposition of group-III sources of TEGa limits the growth rates of GaP at lower substrate temperatures(<390 °C ). The growth rate of GaP epitaxial layers was efficiently enhanced by N2∼laser irradiation at lower substrate temperatures.
The Origin of Polytypes in SiC and ZnS
Authors: Heine Volker , Cheng C. , Engel C. E. , Needs R. J.
Published: March 2011

Both SiC and ZnS exist in the cubic diamond-like (zinc blende) structure. A polytype is derived from the cubic stacking of atomic double layers by having a regularly repeated pattern of stacking faults. Dozens of such polytypes are known for SiC and ZnS.

A study with several co-workers has been completed into the origin of this phenomenon. Are the polytypes genuine stable phases frozen in from some higher equilibrium temperature? Or are they inherently metastable structures born of some growth mechanism?

Quantum mechanical calculations have shown that SiC polytypes formed from bands of 2 and 3 cubically stacked layers have a lower energy than other structures, in particular lower than the cubic or wurtzite structures. That already suggests that the polytypes can be stable phases. Further calculations of the phonon free energy and relaxation of the bond lengths rounds out the phase diagram. In this connection it is somewhat surprising that the material normally grows initially in the metastable cubic modification, transforming subsequently to a mixture of polytypes, but the calculations also suggest why this is so.

The answers for ZnS turn out to be different from those for SiC.
Effect of Carbonization Gas Precursor on the Heteroepitaxial Growth of Sic-on-Si by Rtcvd
Authors: Steckl A. J. , Li J. P.
Published: March 2011

A comparison of several simple hydrocarbon gases, with H:C ratios ranging from 1 to 4, as precursors for the carbonization of Si is presented. The growth experiments were performed by RTCVD at reactor pressures of 760 and 5 Torr. For AP-RTCVD, we have found that C3H8, C2H4 and C2H2 have very similar dependence of growth rate on hydrocarbon partial pressure in the chamber. At 1300°C, this involved a maximum in film thickness being obtained at a hydrocarbon flow rate of 8–10 seem, representing a transition hydrocarbon fraction (in H2) of ∼ 5×10-4. CH4 carbonization produces a peak growth rate at a significantly higher fraction, ∼ 4×10-3. For LP-CVD at 5 Torr, the transition carbonization fraction increases by approximately an order of magnitude. The AP-RTCVD carbonization activation energy for C3H8, C2H4 and C2H2 at higher temperatures (∼1200–1300°C) has a common value of ∼ 0.8 eV, while for lower temperatures it depends on the hydrocarbon.
Characterization of Silicon Carbide thin Films Deposited by Laser Ablation on [001] and [111] Silicon Wafers
Authors: Rimai L. , Agar R. , Logothetis E. M. , Weber W. H. , Hangas J.
Published: March 2011

Stoichiometric films of 3C SiC, 50 to 1000 nm thick were deposited on Si wafers by laser ablation of ceramic stoichiometric SiC targets. Films grown at substrate temperatures above 1000° C on [001] and above 900° C on [111] show orientation epitaxial to the Si substrate along the film normal. Depending on the deposition conditions, the oriented crystallite dimension along this direction ranges from 20 nm to over 100 nm. The crystallite dimensions in the film plane range from 20 to 70 nm. Raman spectra show the expected TO and LO lines from SiC but indicate that the films sometimes contain other material, for example (30 to 50 Å) graphitic inclusions or small amounts of polycrystalline silicon.
High Temperature Ohmie Contacts for N-Tvpe Β-Sic Sensors
Authors: Sho J. S. , Weber R. A. , Provost L. G. , Goldstein D. , Kurtz A. D.
Published: March 2011

In order to fabricate high temperature sensors and other devices, it is necessary to develop ohmic contact metallizations that can withstand elevated temperatures. A variety of ohmic contact metallizations were investigated with contact resistivity measured as a function of anneal time in air. The metallizations were based on Ti and W ohmic contacts, which have contact resistivities as low as 10-4 Ω-cm2. Several of the contact metallizations were stable after 10 hrs. at 650°C, while one system, based on a Ti ohmic contact, was able to withstand > 20 hrs. at 650°C with only a 30–40% increase in contact resistivity.
Characterization of Boron Carbide Films Formed by PECVD
Authors: Mazurowski John , Lee Sunwoo , Ramseyer G. , Dowben P. A.
Published: March 2011

Boron carbide films have been fabricated from pentaborane (B5H9) and methane using plasma enhanced chemical vapor deposition (PECVD). Availability of high quality specimens has facilitated analysis of electronic and optical properties. We have undertaken measurements of photoluminescence spectra and infra-red band-edge absorption. Results show that the bandgap is strongly influenced by the ratio of boron to carbon. There is evidence for the existence of shallow trapping levels.
Amorphous and Microcrystalline SiC as New Synthetic Wide Gap Semiconductors
Authors: Hamakawa Y. , Okamoto H.
Published: March 2011

A review is given on recent progress in amorphous and microcrystalline silicon-carbide (a-SiC, nc-SiC) semiconductors and their technological applications to optoelectronic functional devices. Firstly, some significant properties in this alloy as a new synthetic material are pointed out with recent advances of thin film technologies, such as plasma CVD, ECR-CVD and ion-beam CVD etc. There exists an energy gap controllability from 1.7eV to 3.6 eV with retaining the valency electron control from n-type through i- to p-type semiconductors. While its conductivity can also be controlled more than ten order of magnitudes, e.g., from 10-9to 102 Scm-1 by controlling the impurity doping and preparation conditions.

Secondly, a series of technical data on the electronic and optoelectronic properties of a-Si, C1−x C1−x and μ-SiC are demonstrated from recent achievements. In the final part of the paper, current state of the art in the field of optoelectronic applications from live technologies on amorphous silicon solar cells. a-SiC visible light LED and EL devices are reviewed. A technological evolution from “microelectronics” to “macroelectronlcs” will be discussed.
Structure, Characteristics, and the Application of Phosphorus Doped Hydrogenated Microcrystalline Silicon
Authors: Jeng S. J. , Kotecki D. E. , Kanicki J. , Parks C. C. , Tien J.
Published: March 2011

The microstructure, electrical, and optical properties of in situ phosphorus doped hydrogenated macrocrystalline silicon (μc-Si:H:P) films are strongly affected by deposition parameters and subsequent thermal processes. μc-Si:H:P films with thickness ranging Trom 200 to lOOOÅ have been deposited on Si and SiO2 substrates. The μc-Si:H:P film is best deposited at 200°C in terms of structure, and H and P content. In this film, microcrystallites arc embedded in an amorphous matrix and have a volume fraction of ≃85%. The band-gap of the film is 1.8 eV. In this paper, the materials and processing issues of μc-Si:H:P deposited in a parallel plate RF plasma and in a downstream RF plasma chemical deposition reactor have been studied using HRTEM, SIMS, electrical, and optical measurements.
Lattice-Matched Heteroepitaxy of Wide Gap Ternary Compound Semiconductors
Authors: Bachmann Klaus J.
Published: March 2011

A variety of applications are identified for heteroepitaxial structures of wide gap I-III-VI2and II-IV-V2semiconductors, and are assessed in comparison with ternary III-V alloys and other wide gap materials. Non-linear optical applications of the I-III-VI2and II-IV-V2compound heterostructures are discussed, which require the growth of thick epitaxial layers imposing stringent requirements on the conditions of heteroepitaxy. In particular, recent results concerning the MOCVD growth of ZnSixGe1-xP2alloys lattice-matching Si or GaP substrates are reviewed. Also, heterostructures of CuzAg1-zGaS2alloys that lattice-match Si, Ge, GaP or GaAs substrates are considered in the context of optoelectronic devices operating in the blue wavelength regime. Since under the conditions of MOCVD, metastable alloys of the II-IV-V2compounds and group IV elements are realized, II-IV-V2alloys may also serve as interlayers in the integration of silicon and germanium with exactly lattice-matched tetrahedrally coordinated compound semiconductors, e.g. ZnSixGe1-xP2.
Chemical Vapor Deposition of Highly Transparent and Conductive Boron Doped Zinc Oxide Thin Films
Authors: Hu Jianhua , Gordon Roy G.
Published: March 2011

Boron doped zinc oxide films have been successfully deposited from a gas mixture of 0.05% diethyl zinc, 2.3% ethanol and various diborane concentrations in the temperature range 300°C to 430°C in an atmospheric pressure chemical vapor deposition reactor. The dopant diborane was found to decrease the film growth rate. The crystallite sizes of doped films were smaller than those of undoped films. Hall coefficient and resistance measurements at room temperatures gave conductivities between 250 and 1700 Ω-1, electron densities between 1.4×1020 and 6.7×1020 cm-3, and mobilities between 7 and 23 cm2/V-s. Optical measurements showed that a film with a sheet resistance of 8.8 Ω/square has an average visible absorption of about 8% and maximum infrared reflectance close to 85%. The ratio of conductivity to absorption coefficient is between 0.05 Ω-1 and 0.55 Ω-1. The band gap of doped film was widened and followed the Burstein-Moss relation.
Influence of Geometrical Parameters on the Electrical Properties of Ferroelectric Thin Films
Authors: Faure S.P. , Gaucher P. , Ganne J.P.
Published: March 2011

Ferroelectric thin films of PbZr0.5Ti0.5O3 were prepared by sol-gel process. Top electrodes of different sizes were deposited on thin films in order to study their influence on electrical properties. Histograms of the measured electrical characteristics are related to the electrode sizes. By reducing the electrode size, it is possible to improve the electrical properties of the film. Various properties, such as remanent polarization Pr and coercive voltage Vc, were measured statistically in order to show the evolution of their mean value and of their variance with the electrode size.
Polarization Dependent Conductivity in Thin Film Pzt Capacitors
Authors: Bernacki Stephen E.
Published: March 2011

Polarization dependent conductivity is a dependence of the low field non switching steady state conduction current through a metal ferroelectric metal (MFM) thin film capacitor on the remanent polarization state of the capacitor. This paper proposes a simple theoretical model based on Schottky barrier formation due to PZT-platinum work function differences and barrier height modulation due to remanent polarization. The model predicts a conduction current dependence on both remanent polarization state and electrode material. Finally, we present experimental data in qualitative agreement with the model.
Optical Spectroscopic Profiling of Off-Axis Rf Sputtering
Authors: Klein J. D. , Yen A.
Published: March 2011

The optical emission spectra resulting from if magnetron sputtering a BaTiO3 target were observed to survey substrate position implications. A collimated optical fiber bundle parallel to the plane of the sputter target was translated vertically and horizontally to spectroscopically profile the sputter process. The resulting Ar, O, Ba, and Ti emission intensity contours and the O/Ba and Ba/Ti intensity ratio contours suggest substrate positions that should provide uniform undistorted films. Films deposited on sapphire substrates were found to differ in orientation, lattice parameter, and index of refraction. The optimum offaxis deposition position shifted as the chamber pressure was varied.
Physicochemical Properties of Rf Magnetron Sputtered Lead Zirconate Titanate Thin Films
Authors: Catitan E. , Agius B. , Achard H. , Joly J.P. , Cheang Wong J.C. , Ortega C. , Siejka J.
Published: March 2011

Lead zirconate titanate thin films have been grown by rf magnetron sputtering an oxide target of nominal composition [Pb(Zr0.55,Ti0.45)O3 or PZT] in argon. The kinetics of the sputtering process and the effect of sputtering parameters on film composition have been studied and related to the continuously monitored optical emission of the plasma. The relative and absolute cation and oxygen compositions of the thin films were determined by a new method based on the simultaneous use of Rutherford backscattering spectroscopy (RBS) and nuclear reaction analysis (NRA) induced by a deuteron beam. The conditions for the deposition at room temperature of stoichiometric PZT films were established.
Characterizat Ion of thin Pzt Films on Platinlm Films
Authors: Kugimiya Koichi , Ueda Ichiro , Iizima Kenji
Published: March 2011

Anomalous layers 20-40nm thick were found at the interfaces of lead zirconate-titanate films and Pt electrode films. Detailed study has shown evidence that absorption of PbO by Pt during sputtering resulted in a Pb deficiency in the PZT films and the formation of PbTi3O7 phase. The anomaly was also partly due to island formation at the initial PZT film deposition which allowed PbO to react with Pt films. The Pb controlled PZT films 50nm thick exhibited excellent ferroelectric properties comparable to thicker ones.
Electrical Characterization of Sol-Gel Derived PZT Films
Authors: Teowee G. , Boulton J.M. , Lee S.C. , Uhlmann D.R.
Published: March 2011

Sol-gel derived PZT films were successfully prepared from precursor solutions based on lead acetate and Zr/Ti alkoxides. A pyrochlore phase was observed in films fired at low temperatures, while single-phase perovskite films were obtained at temperatures above 725C. The dielectric constant increased to above 1000 when there was a higher proportion of perovskite than pyrochlore. The films were essentially fatigue-free up to 108 cycles and exhibited a low aging rate of 5.7% / decade-sec.
Transmission Electron Microscopy Study of Mod Plzt and Pnzt Thin Films
Authors: Chang Jhing–Fang , Kwok Chi Kong , Desu Seshu B.
Published: March 2011

Both La and Nd–doped PZT, i.e., PLZT and PNZT, ferroelectric thin films were prepared by the metalorganic deposition (MOD) process. The precursor solutions used were derived from lead acetate, lanthanum acetylacetonate, neodymium acetate, zirconium n–propoxide, and titanium iso–propoxide. The dopant concentration of the films analyzed by electron microprobe indicated a one–to–one correspondence between film composition and the composition of the precursor from which the film was made. In this study, the effects of Nd and La dopants in PZT films on Curie temperature was determined by in–situ hot–stage TEM and compared with those of bulk materials. Lattice parameter and phase transformation were determined by both X–ray and electron diffraction. Our observations were: (1) Curie temperature decreases with increasing dopant concentration for both thin foils and bulk ceramics, (2) for a given dopant concentration, Curie temperature and crystal tetragonality of PNZT thin foils is lower than those of PLZT samples, (3) Curie temperature of thin foils was found to be less than those of the corresponding bulk materials, and (4) ferroelectric domains is easily observed in both PLZT and PNZT TEM specimens prepared by the spin–coating method.
Photovoltaic Effect in Thin Ferroelectric Films
Authors: Brody Philip S. , Rod B. J. , Cook L. P. , Schenck P. K.
Published: March 2011

Polarization-dependent photovoltaic currents are observed in continuously illuminated ferroelectric thin films under conditions of polarization reversal. Following reversal, an initial current rapidly decays to an essentially steady current, which then decays slowly with the current decreasing in proportion to the logarithm of elapsed time. These polarization-dependent currents are attributed to the action of internal fields on photocarriers where the fields result from the incomplete screening of the polarization field.
SrTiO3 and (Ba,Sr)TiO3 Thin Films Preparation by Ion Beam Sputtering and Their Dielectric Properties
Authors: Yamamichi Shintaro , Sakuma Toshiyuki , Hase Takashi , Miyasaka Yoichi
Published: March 2011

SrTiO3 and (Ba,Sr)TiO3 thin films have been prepared by ion beam sputtering on Pd coated sapphire substrates. Film compositions were almost the same as target compositions when powder targets were used. Capacitance-voltage characteristics depended on Sr/Ti ratio of the SrTiO3 films. Only small changes of capacitance value were observed in the range from -3V to 3V when the Sr/Ti ratio was 1.0. Compared with rf-magnetron sputtered film, ion beam sputtered SrTiO3 film indicated lower leakage current density in 50nm thickness. In (Bax,Sr1-x)TiO3 thin films, dielectric constant changed with Ba content (x) and showed a maximum at x=0.5. It also changed with the firing temperature of target powder. The highest value was obtained by using the target powder fired at 900°C. A 100nm thick (Ba0.5,Sr0.5)TiO3 thin film indicated a dielectric constant value of 320.
Electron Microscopic Study of Domains in Relaxor Ferroelectrics
Authors: de Graef Marc , Speck J.S. , Clarke D.R. , Dimos D.
Published: March 2011

The ferroelectric and antiferroelectric displacements in perovskite-based ceramics give rise to a wide range of domain structures. This paper reports on transmission electron microscopy observations as a function of temperature of such structures in PLZT and PLSnZT. In the PLZT system superposition of the diffraction patterns from modulated domains of low symmetry give rise to patterns with an apparent high symmetry. The ½(hkl)-type reflections become more intense with decreasing temperature and split into diffuse rods at high temperature. In the PLSnZT system a hierarchy of domain structures is observed with length scales ranging from unit cell dimensions to the full grain size. A temperature dependent long-period modulation along the < 110 > directions is observed.
Influence of Grain-Growth Inhibiting Dopants on the Electrophysical Properties of Rhombohedral Pyroelectric Lead Zirconate-Titanate Ceramics
Authors: Hahn Jean-Paul , Kostorz Gernot
Published: March 2011

The aim of this work was to develop a ceramic material exhibiting a large pyroelectric coefficient p = -dP/dT (P = polarization, T = temperature) and a low dielectric constant ∈ in order to obtain a high figure of merit F = p/∈pCp for applications in infrared temperature sensing (p denotes the sintered density of the ceramic, cp the specific heat). The influence of the dopants is paramount, and it was only possible to investigate a few promising ones. Best results were obtained for PZT 60/40 (Zr:Ti=60:40) doped with 2 mol% MnO2. The effects of various dopants and some aging results for PZT 60/40 with MnO2 are presented.
Investigation of Structure Development in Mod Pb(ZrxTi1-x)O3 Films by an Optical Method
Authors: Peng Chien H. , Desu Seshu B.
Published: March 2011

For i roving the metalorganic decomposition (MOD) process, such that perovskite Pb(ZrxTi1-x)O3 thin films can be fabricated at low temperatures, understanding of structure development is required. Here we report a nondestructive optical method for investigating the structure development in MOD PZT films. Using this method we have identified the temperatures at which the formation of both pyrochlore and perovskite was completed as a function of Zr/Ti ratio. Also for PZT solid solutions, we have identified the temperatures at which the initial presence of both pyrochlore and perovskite was observed. These temperatures compare very well with those obtained from the X-ray diffraction studies. In contrast to X-ray methods, the proposed technique can also be effectively utilized for studying the pyrochlore formation from the amorphous phase. Furthermore, it was also shown that the optical method can be used for characterizing the phase transformation kinetics in PZT films.
The Role of the Lead Zirconate Titanate (PZT)-Pt Interface in the Anomalous Phase Transformation Kinetics in Sputtered Pzt Thin Film Capacitors at Sub-2000 Å Thicknesses
Authors: Chikarmane Vinay , Kim Jiyoung , Sudhama C. , Lee Jack , Tasch Al , Novak Steve
Published: March 2011

The Pt-Lead Zirconate Titanate (PZT) thin film interface plays a key role in determining the electrical properties and phase transformation kinetics of Pt-PZT-Pt thin film capacitor structures. The results of the electrical and material properties of PZT (65/35) films that vary in thickness between 500 Å to 4000 Å deposited by DC-magnetron sputtering under identical deposition conditions, and subjected to the same post-deposition thermal processing conditions shows that the Pt-PZT interface dominates thin film properties at low thicknesses (≦ 2000 Å). The charge storage density (Qc') and maximum polarization (Pmax) shows an anomalous variation with thickness, showing an initial increase followed by a drastic decrease as the film thickness is scaled down to 500Å. Significant interdiffusion at the PZT film-Pt electrode retards the pyrochlore-to-perovskite phase transformation nucleation and growth rate in PZT films of thickness 2000Å and lower. Gate polarity dependence of the time-tobreakdown and the degradation field is observed for all PZT film thicknesses (including 4000Å). This indicates that the ferroelectric film-electrode interface has an important role to play in determining the electrical reliability properties even in the 4000Å thick PZT film, although Qc' and Pmax are not adversely affected at these thicknesses.
Preparation and Characterization of PbTiO3 and PbZrO3 Films from Oxide Multilayers
Authors: Li Chen C. , Desu Seshu B.
Published: March 2011

PbTiO3 and PbZrO3 thin films were successfully fabricated from oxide multilayers by employing ion-assisted deposition process (IAD). Excellent control of the film thickness and composition were achieved by using the multilayer deposition technique. A (001)-oriented phase was found in the PbTiO3 films at 550°C with 300 and 600eV Ar+ ion bombardment. Very fine equiaxial grain size of 0.2μm was seen in the IAD deposited PbTiO3 films, which is independent of the Ar+ ion beam energy. The optical properties of the PbTiO3 films were studied for different energies of Ar+ ion beam and for various post-deposition annealing temperatures. PbTiO3 films with packing density of near unity (≅0.99) were obtained at temperatures as low as 600°C.
Properties of Electro-Optic Bi12SiO20 Thin Films Grown by Electron Cyclotron Resonance Plasma Sputtering
Authors: Nomura Koji , Ogawa Hisahito
Published: March 2011

Bi12SiO20 thin films have been prepared on glass and (0001) sapphire substrates by ECR plasma sputtering with a Bi and Si multitarget system. Polycrystalline thin films of δ-phase Bi12SiO20 have been obtained without any substrate heating. These films can be transformed into γ-phase Bi12SiO20 by heat treatment above 400°C in air and show a large photoconductivity in the range of 380–460 nm. Epitaxial thin films of γ-phase Bi12SiO20 have been obtained on (0001) sapphire substrates at the substrate temperature of 600δ during the sputtering process. Excellent quadratic electrooptic effects for these epitaxial thin films are successfully observed for the first time, and a spatial light modulator using this γ-phase Bi12SiO20 thin film has also been demonstrated. The details of the preparation, structure and some electrical and electrooptic properties of the Bi12SiO20 thin films are described.
Microstructural Evolution of Sol-Gel Derived PZT Thin Films
Authors: Hsueh Cheng-Chen , Mecartney Martha L.
Published: March 2011

Transmission electron microscopy (TEM) was used to investigate the microstructural evolution of sol-gel derived ferroelectric PZT films. Aggregates of perovskite crystals nucleated and grew out of a pyrochlore matrix at 550°C. A dense, single-phase perovskite PZT film was obtained by fast firing the film at 650°C for 30 minutes. The grain size of this film was approximately 0.2-0.4 μm. Hot-stage TEM observed disappearance of ferroelectric domains as the temperature approaching 325°C.
Substrate Effects in In-Situ Growth of Perovskites by Pulsed Laser Deposition
Authors: Etzold K. F. , Roy R. A. , Saenger K. L.
Published: March 2011

In this study we report on in-situ growth of lead zirconate titanate (PbZr1-xTixO3, PZT) and strontium titanate (SrTiO3, STO) films by pulsed laser deposition at 248 nm. Films were deposited in an oxygen background at elevated temperatures on a variety of substrates including MgO(l00), Pt(100)/MgO(100), Pt(111)/MgO(111), Pt(110)/MgO(110), Pt(111)/SiO2/Si, and Pt(111)/glass.Deposited films were characterized by Rutherford Backscattering Spectroscopy (RBS), x-ray diffraction (XRD), and electrical (dielectric constant and leakage) measurements. A strong substrate dependence was found for both the fraction of pyrochlore (Pb2Zr2-xTixO7) phase in the PZT films, and the STO film dielectric constants. The origin of the substrate dependence is discussed with regard to nucleation and interface layer cffects, and the chemistry of the relevant materials.
Dielectric Constant and Hysteresis Loop Remanent Polarization from 100 Hz to 2 MHz for Thin Ferroelectric Films
Authors: Bennett K. W. , Brody P. S. , Rod B. J. , Cook L. P. , Schenck P. K. , Dey S.
Published: March 2011

A modification of the standard Sawyer-Tower circuit method of displaying ferroelectric hysteresis allowed the technique to be extended to sinusoidal switching frequencies of 2 MHz. Using this method, probe station measurements of switched remanent polarization were made for two films: excimer-laser-deposited lead zirconate titanate (PZT) and sol-gel PZT. Switched remanent polarization and dielectric constant were measured as a function of frequency between 100 Hz and 2 MHz and as a function of elapsed switching cycles at the 1-MHz rate. Both films showed decreasing switched remanent polarization and dielectric constant with increasing frequencies. This effect is attributed to limitations in domain wall velocity.
Optical Characterization of Potassium Niobate Thin Film Planar Waveguides
Authors: Graettinger Thomas M. , Kingon A. I.
Published: March 2011

Initial results of the waveguiding properties of KNbO3 thin films are presented. The refractive indices of epitaxial films deposited on single crystal magnesium oxide substrates have been measured. Additionally, these films have been used as the basis for modelling a potassium niobate thin film phase modulator. Results of the model are compared with existing technology.
IR Transmission Chalcogenide Glass Fibers
Authors: Yamagishi T. , Inagawa I. , Nishii J.
Published: March 2011

Several chalcogenide glass fibers with Teflon cladding and glass cladding were prepared for infrared optical application. A minimum transmission loss, at C02 laser wavelength, of 0.9 dB/m was attained in SeTel glass fiber. The CO and CO2 laser power transmission characteristics of fibers were investigated. Selenide and telluride glass fibers yielded damage thresholds lower than sulfide glass fiber because of their large temperature dependence of refractive index and transmission loss. Deliveries of 80 W of CO laser light in AsS glass fiber, and 10 W of CO2 laser light in GeSeTe glass fiber, were attained. An AsS fiber bundle of 8400 cores was prepared, which could deliver a clear thermal image below 100 °C. Prepared fibers were also found useful for low temperature monitoring and gas sensing in narrow or restricted spaces.
Plasma-Enhanced Chemical Vapor Deposition of ZrF4-Based Fluoride Glass Film and Oxygen Doping Effects on Glass Forming Ability
Authors: Fujiura K. , Nishida Y. , Kobayashi K. , Takahashi S.
Published: March 2011

ZrF4-based binary glass film is synthesized for the first time by plasma-enhanced chemical vapor deposition (PCVD). The optical transmission spectrum is measured and the effects of oxygen doping on the glass forming ability are clarified. No absorption band caused by OH or other impurities is observed in the near IR region. Weak absorption bands attributed to defect centers are observed in the UV to visible region. The glass forming region in the ZrF4-BaF2 system is significantly improved by oxygen doping. Oxygen ions are distributed homogeneously in the fluoride glass film by PCVD and improve its stability against crystallization.
Optical Properties of ZrF4 Thin Film Formed by Vapour Phase Deposition
Authors: Kono Takao , Morita Shinzo , Goto Toshio , Nishiwaki Akira
Published: March 2011

Zirconium fluoride (ZrF4 ) thin films were formed by plasma CVD and evaporation for thin-film optical wave guide. In the case of plasma CVD, ZrF4 compound was actually observed to be synthesized from the vapour of Zr and CF4 gas according to. ESCA measurement, even if the film contained impurities. As for evaporation, transparent and amorphous film was obtained and optical transmission loss was measured by scattering detection method, and the loss was calculated to be 9.5 dB/cm. But when only ZrF4 was deposited, thin film was tarnished to be white because of adsorption of moisture. Therefore, simultaneous evaporation of ZrF4 and BaF2 was performed and the charastaristic was stabilized.
Hydroxyl Formation in Silica Tubes and Layers due to Oxy–Hydrogen Flames
Authors: Kirchhof J. , Braun G.
Published: March 2011

A novel kind of hydroxyl formation during the processing of quartz glass tubes with oxy-hydrogen burners was found and studied in detail by high-resolution laser spectroscopy. The formation mechanism involving hydrogen penetration from the flame and following reactions is discussed.
Concentration and Hydroxyl Impurity Quenching of the 4I13/2–4I15/2 Luminescence in Er3+ Doped Sodium Silicate Glasses
Authors: Bruce Allan J. , Reed W. A. , Neeves A. E. , Copeland L. R. , Grodkiewicz W. H. , Lidgard A.
Published: March 2011

Lifetimes for the 4I13/2–4I15/2 transition of excited Er3+ ions in sodium di-silicate glasses have been measured as a function of Er3+ concentration and glass melting conditions. Lifetimes in excess of 20 ms have been measured for Er3+ levels up to 1021 ions/cm3. For Er3+ levels above 5 × 1020 ions/cm3 high lifetimes are only observed in glasses with low −OH impurity levels. The results are consistent with a quenching mechanism incorporating energy transfer between Er3+ ions followed by non-radiative decay via Er3+ ions coupled to the −OH impurity phonons.
Excited-State-Absorption Cross Sections and Amplifier Modeling in the 1300-nm Region for Nd-Doped Glasses
Authors: Zemon S. , Pedersen B. , Lambert G. , Miniscalco W. J. , Hall B. T. , Folweiler R. C. , Thompson B. A. , Andrews L. J.
Published: March 2011

The performance of Nd3+-doped fiber amplifiers is limited by strong excited state absorption (ESA) of the signal, even for fluorozirconate glasses where ESA prevents the important region below 1320 nm from being used. To quantify this and explore alternative host materials, ESA and stimulated-emission cross sections have been measured for a representative group of glass compositions. These parameters have been used in an accurate, fiber-amplifier model to provide the first quantitative comparisons of performance for Nd3+-doped glasses in the 1300-nm band as a function of host. A high-fluorine fluorophosphate is predicted to extend the short-wavelength boundary of the gain spectrum to 1295 nm but only at reduced gain levels and at the cost of having lower gains at longer wavelengths than fluorozirconates. A substantial increase in small-signal gain is predicted if the amplified spontaneous emission for the 1050-nm band is suppressed.
Luminescent Properties of Rare Earth Doped AlF3-Based Glasses
Authors: Copeland L. R. , Reed W. A. , Shahriari M. R. , Iqbal T. , Hajcak P. , Sigel G. H.
Published: March 2011

Rare earth ions can easily be incorporated into fluoride glasses in moderate to large concentrations and, due to their low phonon energy, these glasses appear to have many advantages over oxide glasses as hosts for rare earth ions used in optical amplifiers and lasers. We have therefore investigated the optical properties of Pr3+, Pr3+/Yb3+ and Pr3+/Yb3+/Lu3+ doped bulk AIF3-based glass samples as a function of rare earth ion concentration. We find that the addition of 2 wt% of Yb increases the fluorescence of Pr3+ at 1.32 μm by a factor of 35 when excited with 488 nm radiation. The fluorescence intensity and excited state lifetimes are found to be comparable to those measured for Pr in a ZBLAN host. Since it has also been demonstrated that optical fibers drawn from AIF3-based glasses exhibit relatively low loss (< 0.05 dB/m) and posses superior chemical durability compared to other fluotide glasses, it is possible that AIF3 glasses may become the fluoride glass of choice for practical fiber laser and amplifier applications.
Efficient Erbium-Doped Fiber Amplifiers Pumped in the 800-nm Band
Authors: Pedersen B. , Zemon S. , Miniscalco W. J.
Published: March 2011

A comprehensive theoretical investigation of the 800-nm pump band for erbium-doped fiber amplifiers is presented. Both a silica and a fluorophosphate host are examined. To obtain the same amplification, the fluorophosphate requires 2–3 dB less pump power.
Optical Properties of Soot Remelted Silica Irradiated with Excimer Lasers
Authors: Matsumoto Yasutaka , Kuzuu Nobu , Murahara Masataka
Published: March 2011

Characteristics of ArF laser induced luminescence, and absorption bands in soot remelted silica, before and after annealing in various atmospheres, were investigated. A soot remelted silica containing no OH has an absorption band at 5.1 eV which can be annealed out with H2, but an absorption band at 5.8 eV is induced by subsequent the ArF laser irradiation. In a soot remelted silica containing 50 ppm of OH, an emission band at 1.9 eV was induced by the ArF laser irradiation. The 1.9 eV band can be annealed out with He and H2, but, by annealing in H2, the 5.8 eV absorption band was induced by the ArF laser irradiation as in the case of the silica containing no OH.
Sol-Gel and RF Sputtering Thin Film Coatings for Fiber Optic Sensor Applications
Authors: Shahriari M. R. , Ding J. Y. , Wang C. M. , Lin C. H. , Sigel G. H.
Published: March 2011

Thin film coating techniques appear to have many advantages over other techniques for immobilization and incorporation of chemical indicators to optical waveguides in developing dye based fiber optic chemical sensors. We have fabricated thin films of composites by using sol-gel and RF sputtering techniques. Different organic and inorganic indicators were immobilized in these films and incorporated into optical waveguides for sensor applications. A fiber optic pH sensor has been developed by introducing pH indicators into a silica matrix and coated as a thin film onto a porous glass fiber by a sol-gel technique. Also, a hydrogen gas fiber optic sensor has been developed by using a RF sputtered WO3/Pd coated porous optical fiber.
Active Waveguides in LiNbO3
Authors: Micheli M. P. De
Published: March 2011

In Integrated Optics (10), LiNbO3 is a well known material, widely used to realize very efficient electro-optic integrated devices for telecommunications such as phase modulators, intensity modulators and directional couplers. But, with the availability of good quality rare earth doped material and the perfecting of a new waveguide fabrication technique, Proton Exchange (PE), a completely different set of active devices are now possible. The common factor of these devices is that they take advantage of the high optical power resistance of the PE waveguides, of the amplification due to the rare earths, and, of the electro-optic/nonlinear properties of the crystal. In this paper we shall present such devices we have demonstrated in collaboration with the Central Research Laboratory of Thomson CSF and the Ecole Nationale Supérieure de Physique de Marseille.:

-an optically pumped CW amplifier in Nd:MgO:LiNbO3 offering up to 8 dB small signal gain at δ = 1.085μm

-an optically pumped CW laser in Nd:MgO:LiNbO3 emitting 14 mW at X = 1.085μm with a slope efficiency of 34% and a threshold of 2.7 mW

-an FM Mode-locked waveguide laser in Nd:MgO:LiNbO3 realized by electro-optically driving the laser at the cavity round-trip frequency emitting 8 ps pulses of 250 mW peak power with a 6.2 GHz repetition rate

-a self doubled waveguide laser in Nd:MgO:LiNbO3 emitting some hundreds of μW in the blue (SHG of the pump and mixing the pump with the laser frequency) and the green (SHG of the laser wavelength).
Radiation-Hardened Optical Fibers for High Dosage Space Applications
Authors: Miller A. E. , Yan M. F. , Watson H. A. , Nelson K. T.
Published: March 2011

Hydrogen doping of optical fibers has been examined as an approach to increase the radiation hardness of optical fibers for high dosage (107 rad) space applications. A systematic study has been performed on 4 types of optical fibers designed to operate at 1.31 and 1.55 μm and doped with up to 8200 ppm H2. For low dosages, the most significant reductions m radiation-induced losses were obtained with low H2 concentrations (<10 ppm). Spectral loss measurements for hydrogen-doped fibers containing GeO2 show a radiation-induced loss peak at 1.45 μm and a broad absorption band around 0.6–0.8 μm. These bands are not observed in the pure silica-core fibers.

Fibers were fabricated to permanently trap 2.7 ppm H2 and the radiation-induced losses in these fibers are 35 to 85% that of the untreated fibers. Experimental data are used to delineate the γ-T-α operating limits which define the maximum gamma radiation (γ) dosages at different temperatures (T) while still meeting a requirement of α<150 dB/km. Among the four fiber types, hydrogen-doped silicacore fibers show the widest operating range and smallest radiation-induced loss for space applications. However, hydrogen-doped fibers with moderately high GeO2-doped core offer the best tradeoff between the bending and radiation-induced losses.
Dopants in LiNbO3: Lattice Site Location, Ion Implantation and Epitaxial Regrowth
Authors: Rebouta L. , Soares J. C. , Silva M. F. Da , Sanz-Garcia J. A. , Dieguez E. , Agullo-Lopez F.
Published: March 2011

Ion-beam/channeling data for the lattice location of Ti, Hf, Er and Nd in LiNbO3 and LiNbO3: Mg are presented. These impurities are relevant in relation to waveguide and integrated optics devices. It is shown that co-doping with Mg markedly influences the lattice location observed in LiNbO3. The amorphization and recrystalization process following Hf implantation and annealing are also discussed.
Excimer Laser Induced 5.8 eV Absorption and 1.9 eV Emission Bands in Fused Silicas
Authors: Kuzuu Nobu , Matsumoto Yasutaka , Murahara Masataka
Published: March 2011

Characteristics of ArF excimer laser induced 1.9 eV emission and 5.8 eV absorption bands in type III and soot remelted silicas were investigated. In a type III silica synthesized in a reducing condition, an absorption band at 5.8 eV band is induced. The creation of this band can be prevented by annealing in an atmosphere of He. In the soot remelted silicas with and without OH, the creation of the 5.8 eV band is strongly promoted by annealing in H2. An emission band at 1.9 eV is induced in a type III fused silica synthesized in an oxydizing condition and soot remelted silica containing OH. When annealing in He, creation of the 1.9 eV band is strongly promoted in the former but suppressed in the latter sample. This difference is derived from the difference of higher order structures between the type III and the soot remelted silicas.
Realization of SiO2-B2O3-TiO2 Waveguides and Reflectors on Si Substrates
Authors: Schneider Hartmut W.
Published: March 2011

TiO2-B2O3 doped silica single-mode waveguide arrays on silicon substrates were fabricated by flame hydrolysis soot deposition, glass consolidation and etching. CHF3 reactive ion etching is suitable for more than 15 μm deep vertical gap and reflector preparation. Minimum waveguide propagation loss values of (0.21±0.01) dB/cm were measured on 50 mm single-mode samples. Spectral measurements proved the absence OH absorption in the 850 to 1600 nm range and indicate scattering as the most important loss effect.
Photolithographic Imaging of Planar Optical Waveguides and Integrated Optic Devices onto Porous Silicate Glasses and Silica Sol-Gels
Authors: Mendoza Edgar A. , Gafney Harry D.
Published: March 2011

The success of photonic switching depends on the development of materials capable of processing light signals without the interweaving conversion to electronic signals. The photodeposition of metal oxides onto porous Vycor glass and silica glass sol-gels produce changes in the index of refraction of the glass of the order of 0.1 to 0.001. Nonlinearities in transmission and refractive index allow the deposition of 1.0-10.0 μm width planar waveguides with attenuations of 0.6 dB/cm. This technique is being evaluated for the optical performance of couplers, dividers, and interferometers. Also 3-dimmensional interactive planar waveguide structures are being fabricated in silica sol-gel thin-films.
Photoinduced Second Harmonic Generation in Optical Fibers: Materials and Mechanisms
Authors: Krol D. M. , Simpson J. R. , DiGiovanni D. J. , Atkins R. M. , Lemaire P. J. , Nelson K. T.
Published: March 2011

Permanent X(2) gratings can be written in doped silica fibers by coherent irradiation with light at ω and 2ω. The X(2) gratings give rise to phase-matched second harmonic generation (SHG), i.e. subsequent irradiation of the prepared fiber with light at ω results in an output at 2ω. The efficiency with which the gratings can be written depends on the nature and concentration of defect states induced by dopants in the, glass. We present results for fibers doped with Ge and rare earth ions and discuss the implications of our results for the various mechanisms that have been proposed to explain photoinduced SHG in fibers.
Chemical Kinetics Applied to the Fatigue of Silica Fibers in Sodium Hydroxide Solutions
Authors: Inniss Daryl , Brownlow Darryl L. , Kurkjian Charles R. , Borges Lourdes R.
Published: March 2011

Chemical kinetics is applied to the fatigue (stress assisted corrosion) of silica fibers in NaOH solutions. The thermodynamic parameters are determined and compared to measurements in water; the zero stress activation energy is the same for the two systems (∼25kcal/mol), but the activation volume in aqueous NaOH solutions is smaller (∼11cm3/mol) than that in water (∼27cm3/mol). The accelerated fatigue rate is dominated by a three decade decrease in the pre-exponential factor; it is shown that this decrease can be attributed to an increase in the entropy of the system.
Microstructural Properties of Fly Ashes from Oklahoma and Wyoming Coals and their Blends
Authors: Laguros Joakim G. , Gollahali S. R.
Published: March 2011

Blending of different types of coals is an economical method of utilizing locally available lower quality coals. Four blends of Wyoming/Oklahoma coal were prepared (100:0, 90:10, 75:25, 0:100) and burned in a laboratory furnace in a diffusion flame of a mixture of propane and nitrogen in air. Flame temperatures ranged from 1419 K for Oklahoma to 1626 K for Wyoming coal. The higher temperatures indicate better boiler utility, more oxidation, less free carbon, more and better quality fly ash. These observations conform well with the SEM evaluations which indicated that as the amount of Wyoming coal increased, the matrix contained densely populated glassy spherical particles. The SEM data on cured paste samples indicated that the Wyoming fly ash showed a better tendency to crystal (presumably ettringite) formation, followed by the blends of 90% Wyoming-10% Oklahoma and 75% Wyoming-25% Oklahoma. The least amount of crystal formation was observed in the fly ash of 100% Oklahoma coal. These effects are extremely pronounced in the early curing stages.
Polyphosphate Chain Stability in Magnesia-Polyphosphate Cements
Authors: Dimotakis E. D. , Klemperer W. G. , Young J. F.
Published: March 2011

Polyphosphates of the general formula NanH2PnO3n+1·H2O, n = 6, 15, 70, where n is the average degree of polymerization, have been synthesized and characterized by 31P NMR and HPLC. Aqueous solutions of these polyphosphates react at room temperature with magnesia to form cement pastes that harden to amorphous materials. The compressive strengths and porosities obtained are similar to those of MgO-(NH4)H2P3O10-H2O cements. Although polyphosphate chain length does not have a significant effect on the strength of the cement, 31P MAS-NMR spectroscopy showed that the degree of polyphosphate chain degradation decreases as the average degree of polymerization, n, increases.
DSP with Rutile Substituting for Microsilica
Authors: Aldridge Laurence. P. , Campbell Ross J. , Cassidy David J.
Published: March 2011

DSP is made from heavily superplasticized cement combined with microsilica and relatively small amounts of water. In this paper it is shown that substitution of fine-grained rutile for microsilica results in a workable DSP mix.

A comparison of the TGAs, XRDs, SEMs, mercury intrusion porosimetry, and compressive strengths between the two DSP preparations is reported. The results indicate that the DSP made with rutile has very similar properties to DSP made with microsilica.
Microwave Characterization of Cement Hydration
Authors: Moukwa M. , Brodwin M. , Christo S. , Chang J. , Shah S.P.
Published: March 2011

Conductivity and permittivity of cements were measured during the first 24 h hydration period at 10.0 GHz using front surface reflection methods. Data trends closely followed the hypothesis that the microwave results responded to the transition from free to bound water as hydration proceeded. The results were also compared to measured hydration curves and changes in the slope of the data versus time correlated well with characteristics regions of the hydration curve. The results establish the usefulness of microwave characterization for the study of chemistry and structure during the hydration period and may lead to a non destructive test method for cementitious materials during the early curing period.
Hot Pressed DSP Cement Paste
Authors: Lu Ping , Young J. Francis
Published: March 2011

DSP cement paste is prepared by hot-pressing technique in this study in order to improve its particle packing and chemical composition, and to investigate the relationship between its solid phase microstructure and mechanical strength at the porosity close to zero. The addition of silica fume improves strength development, although capillary porosities are not changed significantly. Results obtained indicate that the highest compressive strength reached are 800 MPa after 28 days hydration and oven drying at 200°C. The strength has better relation with degree of hydration or the physical density of C-S-H. the silicate anion polymerization closes not appear to influence strength.