bluuebunny/crossref_metadata_2025 huggingface dataset:
SiC Thin Films by Chemical Conversion of Single Crystal Si
Authors: Chiu Chien C. , Kwok Chi Kong , Desu Seshu B.
Published: March 2011

The reaction of (100)Si with C2H2 in a hot wall CVD reactor has been studied using a X-ray photolectron spectroscopy, and a scanning electron microscopy. The growth of the SiC films was observed through the behavior of Si2p peaks and their plasmons. Smooth surface morphology with a monolayer of SiC was obtained at 950°C for 7 minutes and defects were observed for longer reaction times at this temperature. For higher reaction temperatures (e.g. 1000°C), defects were observed for reaction times as short as 10 seconds. The formation of defects was correlated to the out-diffusion of Si in the carborization process.
Low-Temperature PACVD Silicon Carbide Coatings
Authors: Halverson W. , Vakerlis G. D. , Garg D. , Dyer P. N.
Published: March 2011

Plasma-assisted chemical vapor deposition (PACVD) is used extensively to coat planar (2-dimensional) substrates. In principle, the technique can be used to deposit coatings on 3-dinensional objects. However, extending PACVD to coat 3-dimensional objects uniformly requires careful control of the plasma, substrate temperature, and reactant concentrations over a large volume. A novel low-temperature radio frequency PACVD reactor design was developed to deposit coatings uniformly and reproducibly on 3-dimensional metallic substrates. The design features a temperature-controlled reaction chamber fitted with one or more rf-driven electrodes to generate uniform, large-volume plasma. The reactor was used to develop a series of silicon carbide coatings, which were deposited at or below 500°C. The coatings contain SiC and varying amounts of free silicon and/or amorphous carbon (diamond-like carbon), depending on reagent gas composition and reactor operating parameters. The coatings significantly reduced wear on stainless steel samples in ball-on-disk and abrasive wear tests and provided oxidation protection to molybdenum and titanium alloy.
X-Ray Tomographic Microscopy of Nicalon Preforms and Chemical Vapor Infiltrated Nicalon/Silicon Carbide Composites
Authors: Butts M. D. , Stock S. R. , Kinney J. H. , Starr T. L. , Nichols M. C. , Lundgren C. A. , Breunig T. M. , Guvenilir A.
Published: March 2011

Following the evolving microstructure of composites through all stages of chemical vapor infiltration (CVI) is a key to improved understanding and control of the process. X-ray Tomographic Microscopy (XTM), i.e., very high resolution computed tomography, allows the microstructure of macroscopic volumes of a composite to be imaged nondestructively with resolution approaching one micrometer. Results obtained with XTM on dense SiC/SiC composites and on woven SiC fiber preforms illustrate how details of the densification process can be followed using this technique during interruptions in processing. Ways in which the three-dimensional microstructural information may be used to improve modeling are also indicated.
Effect of Bn Interfacial Coating on the Strength of a Silicon Carbide/Silicon Nitride Composite
Authors: Norton Kirk P. , Streckert Holger H.
Published: March 2011

Boron nitride has been identified as a good fiber/matrix interface coating for SiC fibers in a Si3N4 matrix. Boron nitride thin films prepared from BCl3 and NH3 at 1000°C and from B2 H6 and NH3 at 550°C were deposited on SiC (Nicalon®) cloth in a low pressure chemical vapor deposition reactor. The coating thickness was varied from 0.1 μm up to 4 μm. Six layers of cloth for each coating thickness were incorporated into a chemical vapor infiltrated matrix of amorphous Si3N4.

Flexural strength data and composite toughness were obtained from three-point bend tests. Scanning electron microscopy and metallographic analysis of fracture surface morphology were used to determine the failure mode.
Microwave Assisted Chemical Vapor Infiltration
Authors: Devlin D. J. , Currier R. P. , Barbero R. S. , Espinoza B. F. , Elliott N.
Published: March 2011

A microwave assisted process for production of continuous fiber reinforced ceramic matrix composites is described. A simple apparatus combining a chemical vapor infiltration reactor with a conventional 700 W multimode oven is described. Microwave induced inverted thermal gradients are exploited with the ultimate goal of reducing processing times on complex shapes. Thermal gradients in stacks of SiC (Nicalon) cloths have been measured using optical thermometry. Initial results on the “inside out” deposition of SiC via decomposition of methyltrichlorosilane in hydrogen are presented. Several key processing issues are identified and discussed.
CVD Coating of Ceramic Monofilaments
Authors: Guth Jason R.
Published: March 2011

In many composite systems it has become apparent that coatings on the reinforcements are necessary to achieve high toughness materials. In order to examine materials which may be used as coatings on ceramic monofilaments and remain stable in high temperature, oxidizing environments, the deposition of a number of refractory metals has been attempted. The results of coating experiments using silicon carbide fibers as substrates as well as general observations concerning the prospects of continuously coating long lengths of fibers will be discussed. The materials studied include carbon, cobalt, zirconium, molybdenum, tantalum, tungsten, and iridium. Carbon has been deposited from methane and propylene onto both SiC and sapphire fibers. Deposition of the metals has been achieved by direct chlorination of the metals followed by hydrogen reduction at the fiber. Iridium(III)2,4-pentanedionate has been used to deposit iridium metal. All metals were deposited at low pressure in a hot wall reactor with fibers continuously spooled through the reactor.
Facility for Continuous CVD Coating of Ceramic Fibers
Authors: Moore Arthur W.
Published: March 2011

The development of new and improved ceramic fibers has spurred the development and application of ceramic composites with improved strength, strength/weight ratio, toughness, and durability at increasingly high temperatures. For many systems, the ceramic fibers can be used without modification because their properties are adequate for the chosen application. However, in order to take maximum advantage of the fiber properties, it is often necessary to coat the ceramic fibers with materials of different composition and properties. Examples include (1) boron nitride coatings on a ceramic fiber, such as Nicalon silicon carbide, to prevent reaction with the ceramic matrix during fabrication and to enhance fiber pullout and increase toughness when the ceramic composite is subjected to stress[l]; (2) boron nitride coatings on ceramic yarns, such as Nicalon for use as thermal insulation panels in an aerodynamic environment, to reduce abrasion of the Nicalon and to inhibit the oxidation of free carbon contained within the Nicalon[2]; and (3) ceramic coatings on carbon yarns and carbon-carbon composites to permit use of these high-strength, high-temperature materials in oxidizing environments at very high temperatures[3,4].
CVD of SiC and AlN Using Cyclic Organometallic Precursors
Authors: Interrante L. V. , Larkin D. J. , Amato C.
Published: March 2011

The use of cyclic organometallic molecules as single-source MOCVD precursors is illustrated by means of examples taken from our recent work on SiC and AlN deposition, with particular focus on SiC. Molecules containing (SiC)2 and (AlN)3 rings as the “core structure” were employed as the source materials for these studies. The organoaluminum amide, [Me2AlNH2]3, was used as the AlN source and has been studied in a molecular beam sampling apparatus in order to determine the gas phase species present in a hot-wall CVD reactor environment. In the case of SiC CVD, a series of disilacyclobutanes, [Si(XX′)CH2]2 (with X and X′ - H, CH3 , and CH2 SiH2CH3), were examined in a cold-wall, hot-stage CVD reactor in order to compare their relative reactivities and prospective utility as single-source CVD precursors. The parent compound, disilacyclobutane, [SiH2 CH2]2, was found to exhibit the lowest deposition temperature (ca. 670 °C) and to yield the highest purity SiC films. This precursor gave a highly textured, polycrystalline film on the Si(100) substrates (70% with a SiC orientation).
The Chemical Vapor Deposoitin of Pure Nickel and Nickel Boride Thin Films from Borane Cluster Compounds
Authors: Kher Shreyas , Spencer James T.
Published: March 2011

Several borane cluster compounds, such as pentaborane(9) and their corresponding metal complexes have been investigated in our laboratory for their utility as unique source materials for synthesizing metal/metal boride thin films by MOCVD. In this paper we report the preparation of thin films of nickel boride from the thermal decomposition of nido- pentaborane( 9) in the presence of anhydrous nickel chloride [NiCl2] in the vapor phase. Crystalline nickel boride thin films of controlled composition ranging from 0.1 to several microns have been readily prepared by controlling the temperature and the flow rate of the pentaborane(9) into the reaction chamber. The nickel boride films on GaAs were thermally annealed to form the Ni7B3 phase as hexagonal crystals in a Ni3B matrix. These films have been characterized by AA, AES, EDXA, SEM, XRD and electron diffraction. The phases were determined primarily by X-ray and electron diffraction experiments.
Routes to Diamond Heteroepiitaxy
Authors: Badzian Andrzej , Badzian Teresa
Published: March 2011

This paper reviews the status of diamond heteroepitaxy approached by chemical vapor deposition and by physical methods. Reported are experiments with cubic boron nitride and nickel conducted with the help of microwave plasma chemical vapor deposition. X-ray diffraction data confirm diamond heteroepitaxy on the (111) faces of cubic boron nitride crystals. Heteroepitaxy on nickel was not demonstrated yet nevertheless suppression of graphite nucleation was achieved by formation of nickel hydride.
Kinetic Modelling of the Deposition of SiC from Methyltrichlorosilane
Authors: Sotirchos Stratis V. , Papasouliotis George D.
Published: March 2011

A kinetic model is presented for the deposition of silicon carbide through decomposition of methyltrichlorosilane (MTS). The developed model includes gas phase (homogeneous) reactions that lead to formation of deposition precursors and surface (heterogeneous) reactions that lead or can lead to deposition of silicon carbide, silicon, and carbon. The kinetic model is incorporated in a transport and reaction model for a tubular hot-wall reactor, and the overall reactor model is used to obtain some preliminary results on the effects of pressure and distance in the reactor on the rate of deposition and the composition of the deposit. The results show that the model can reproduce most of the experimental observations of the literature.
Growth and Characterization of PECVD Diamond Films
Authors: Mucha J. A. , Seibles L.
Published: March 2011

Polycrystalline diamond films have been deposited on (100) silicon wafers by plasma enhanced chemical vapor deposition (PECVD) using a 1.5 kW microwave source to dissociate dilute gas mixtures of CH4 and O2 in H2. Films as thick as 20μm covering a 2″ diameter area were deposited at 925 °C, 40 Torr total pressure, and 500 sccm total flow. These have been characterized as a function of CH4 [0.2–4%] and Os [0–3%] concentrations by measurements of deposition rate, stress, surface roughness, morphology, and impurity levels (C-H and amorphous-graphitic carbon). Addition of oxygen to the discharge tends to reduce impurity levels in the diamond films; however, this is accompanied by a reduction in deposition rate. When an effective CH4 concentration [= %CH4 - %O2] is used as a metric for O2 -containing feed compositions, deposition rates as well as film properties are found to agree well with those obtained in the absence of O2. Thus, 1% CH4 in hydrogen is nearly equivalent to 4% CH4, 3% O2 in hydrogen as feed compositions for depositing diamond.
Correlation of Raman Spectra and Bonding in DLC Films Deposited by Laser Ablation and Laser-Plasma Ablation Techniques
Authors: Rengan A. , Narayan J. , Park J. L.
Published: March 2011

We have deposited diamondlike carbon (DLC) films on a variety of substrates from 250° C and higher. The effects of deposition temperature on the properties of DLC films deposited by a conventional laser ablation technique are compared with that of a unique laser-plasma deposition scheme. The calculated values of neff, the effective number of valence electrons, suggest that, with the increase in the deposition temperature, the diamondlike component (sp3 bonds) remains invariant for the laser deposited samples, and increases for the laser-plasma deposited films. Raman measurements show that the Raman allowed ‘G’ band upshifts to ˜1600 cm−1 for both deposition schemes. However, the disorder induced 'D' band remains invariant at ˜1370 cm−2 for the laser ablated samples, and downshifts to ˜1350 cm−1 for the laser-plasma deposited samples. These results suggest a correlation between the diamondlike content (sp3 bonds) and the Raman shift of the ‘D’ band.
Kinetics of Chemical Vapor Deposition of Sic Between 750 and 850°C at 1 Bar Total Pressure
Authors: Neuschütz Dieter , Salehomoum Farzin
Published: March 2011

The deposition rate from mixtures of methyltrichlorosilane (MTS), hydrogen and methane was measured thermogravimetrically using a hot wall vertical reactor and planar SiC substrates. Below 850 °C and at sufficiently high gas velocities, the rate of the phase boundary reaction could be determined. In the absence of CH4 and at H2 :MTS=55, Si was deposited together with SiC. Addition of CH4 lowered the Si content, pure SiC being deposited at CH4 :MTS above 10. The deposition rate j in the range 750 to 850 °C follows the equation with E(Si) = 160 and E(SiC) = 300 kJ/mol. Reaction mechanisms are presented to account for the observed reaction orders with respect to MTS. Between 900 and 970 °C, the reaction rate decreased with temperature indicating a change in the deposition mechanism.
Rapid Growth of Ceramic Films by Particle-Vapor Codeposition
Authors: Hurt Robert H. , Allendorf Mark D.
Published: March 2011

Particle-enhanced chemical vapor deposition (PECVD) is capable of producing ceramic films at high deposition rates. A mathematical model of the particle-vapor codeposition process has been developed and has been applied to PECVD processes to predict deposition rate enhancements and deposit properties.
Determination of the Roughness of CVD Surfaces by Laser Scattering
Authors: Klein Max , Gallois Bernard
Published: March 2011

A laser scattering apparatus was developed for the determination of surface roughness and other surface statistical parameters of chemically vapor-deposited coatings. Visual examination of HeNe laser scattering patterns reflected from polished sapphire and CVD titanium nitride surfaces showed a sensitivity to roughness differences of tens of nanometers. The scattering apparatus was integrated with a cold-wall CVD reactor. The root mean square roughness of silicon carbide deposits on silicon in the early stages of growth was determined from the intensity of the specularly reflected beam. Changes in roughness and the spatial arrangement of depositing crystallites were monitored in situ by angular resolution of the scattered light spectra. Both ex situ and in situ results were in good agreement with profilometric examinations of the rough surfaces.
Effects of Lamp Pulses on the Oxygen - Precipitation - Gettering of Cr in Czochralski Grown Si
Authors: Chabane-Sari N-E. , Krieger-Kaddour S. , Vinante C. , Barbier D.
Published: March 2011

Experiments on the intrinsic gettering of Cr in p-type Czochralski-grown Si including lamp pulse annealings have been carried out. Transmission Electron Microscopy observations of both oxide and metallic precipitates on cross-sectional specimens, as well as quantitative results about the electrically active metal depth-profiles, using Deep Level Transient Spectroscopy measurements, are presented. We have observed that a lamp pulse (1200 °C/5 s) applied prior to a three-step gettering cycle produced a strong retardation of the oxygen precipitation, and consequently an inhibition of the Cr bulk precipitation during the nucleation step. Besides, it was observed that the Cr-precipitates formed in the bulk during the oxygen nucleation step were highly unstable upon a post-gettering 2–4 s lamp pulse at 1000 °C, whereas the same lamp pulse did not produce a significant re-dissolution of Cr-precipitates formed during the oxide precipitate growth step. The reversibility of the intrinsic gettering of Cr upon a post-gettering lamp pulse thus critically depends on the oxide precipitate growth rate during the gettering process.
Damage to Crystalline Silicon Following Implantation by Low Energy Silicon Ions
Authors: Levine Y. , Herbots N. , Dunham S.
Published: March 2011

A new approach to investigate low energy defect formation and annealing in a crystal is developed, based on experimental observations of the total number of interstitials. The model is applied to damage in crystalline silicon caused by low energy implantation of Si-atoms during 40eV implants at 300°Kand 685°K. The model has two versions, analytical and computational, and includes two kinds of diffusing species, self-interstitials and vacancies, their interaction, surface motion of the growing crystal, and a constant source of defects. The source was calculated using a modified TRIM code (TRJMCSR). The focal point of the analysis is the number of interstitials per ion dose surviving at the end of the deposition time (damage to dose ratio or DDR, which is found to be an informative quantity and can be calculated for more sophisticated models including precipitation.
Passivation of Ion-Beam-Induced Defects at and Around the Si-SiO2 Interface by Ion Beam Hydrogenation
Authors: Kar S. , Srikanth K. , Ashok S.
Published: March 2011

Electronic defects were introduced at and around the Si-SiO2 interface by exposing thermally-oxidized silicon samples to a 16 keV Si ion beam in an ion implanter. The oxide thickness was 350 Å. Following Si self-implantation, hydrogenation was carried out at room temperature by a 400 eV hydrogen ion beam from a Kaufman source. Experimental results obtained from the admittance-voltage-frequency measurements of the metal-oxide-silicon structures indicated significant passivation of the ion-beam-induced defects.
B+, P+, AS+ and Si+ Ion Implantation Induced Defects in Silicon Studied by a Variable-Energy Positron Beam
Authors: Sugiura Jun , Ogasavara Makoto , Uedono Akira , Vei Long , Tanigava Shoichiro
Published: March 2011

Vacancy type defects introduced by As+, P+, Si+ and B+ ion implantations into Si (100) single crystals were studied by a variable-energy positron beam. Depth distributions of the defects were obtained from measurements of Doppler broadening profiles of the positron annihilation as a function of incident positron energy. The results showed that this technique is sensitive not only to a vacancy type defect but to formation of amorphous regions. The defects introduced by lower doses were identified as vacancy clusters from isochronal annealing experiments. By higher doses such as 5×1014 /cm2, amorphous layers were formed for 150KeV As+, 150KeV P+, and 200KeV Si+ ions, and it was not formed for 80KeV B+ by the dose of 5×1015 /cm2. These results are consistent with the calculated critical doses. In the case of B+, pre-amorphous formation was observed with higher ion beam current over 5mA and a dose of 5×1015 /cm2.
Noncontact Characterization for Ultraviolet Light Irradiation Effect on Si-SiO2 Interface
Authors: Katayama K. , Shimura F.
Published: March 2011

The effect of ultraviolet (UV) irradiation on the minority-carrier surface recombination lifetime (τs) in silicon wafers with native or thermal oxide was studied with a noncontact laser/microwave photoconductance (LM-PC) technique. The τs greatly increases in samples with native oxide after the irradiation. The dominant factor for the τs change can be negative charges created by photo-injected electrons in the surface area. On the other hand, the irradiation decreases τs in silicon with thermal oxide. The τs decrease is due to the generation of carrier recombination centers with an energy level around 0.2eV at the Si-SiO2 interface.
Dry Etching of Indium Phosphide
Authors: Bond P. , Sengupta P. , Orrman-Rossiter Kevin G. , Reeves G. K. , Paterson P. J. K.
Published: March 2011

Indium Phosphide (InP) based multilayer structures are becoming increasingly important in the semiconductor industry with optoelectronic applications being the main growth area. Mesa type structures with finely controlled width and etch angle, often form the building blocks for many of these photonic devices. Traditional wet etching techniques have often proved to be inadequate for the required anisotropie removal of material. This paper presents the results of etching semi-insulating InP (100) using a combination of an Argon ion beam and a reactive gas, CCl2F2 (Freon 12). It was found that the etch rate was enhanced by increasing the ion energy and by the addition of CCl2F2. Auger electron spectroscopy revealed that the increased etch rate was accompanied by an increase in the surface indium concentration and at low ion beam energies carbon build-up retarded the etch rate. The optimum etch angle to fabricate 3μm waveguides was found to be 22° to the surface normal, however Schottky contacts to these structures were unsuccessful.
Simultaneous Implant Activation and Isolation Formation in GaAs in a Single High-Temperature Anneal
Authors: Ko Kei-Yu , Chen S. , Braunstein G. , Zheng L.-R. , Lee S.-T.
Published: March 2011

Using void-related compensation in Al-implanted GaAs, high-resistivity isolation regions that are thermally stable to high temperatures (> 700 °C) are demonstrated. The high-temperature thermal stability of the isolation regions allows the simplification of device processing in which a single high-temperature anneal (e.g., at 900 °C) can be used to activate the implant dopants in the device-active regions, and simultaneously to convert the Al-implanted regions highly resistive for electrical isolation. Other advantages of using void-related isolation will also be discussed.
Electronic Levels and Properties of the Selfinterstitials in Irradiated Silicon
Authors: Abdullin Kh. A. , Mukashev B. N. , Tamendarov M. F. , Tashenov T. B.
Published: March 2011

DLTS studies of electronic states and properties of the selfinterstitial in α-irradiated p-Si and n-Si are performed. The injection-enhanced annealing is observed for two traps E2 (Ec -0.39 eV) and El (Ec -0.26 eV) in p-Si. The annealing of E2 and E1 are simultaneous with the growth of hole traps connected with vacancy (V), Ci and Ali. It is concluded that the observed electronic levels belonq to different charge states of silicon selfinterstitial. The conclusion is confirmed by the differences of cross sections of the formation of Ali and Ci, by the influence of the zero and reverse bias conditions on the introduction rate and optical annealing of the E2 state in p-Si as well as by DLTS spectra of n-Si.
The Growth of Effective Potential Barrier Height in Au/ (100) n-GaP Contact Induced by Phosphorous Ion Implantation
Authors: Ivashchenko Anatol I. , Kopanskaya F.Ya. , Solomonov A. I. , Tarchenko V. P.
Published: March 2011

The effect of phosphorous ion implantation and/or rapid thermal treatment on the behaviour of Schottky barrier elect-rophysical characteristics formed on the plane (100) of n-GaP epitaxial layer is discussed. Even though the implantation and post implantation rapid annealing lead to the generation of deep recombination centers in the bulk, the dominant mechanism of current transport across the barrier structure becomes thermo-ionic - like in initial samples. The analysis of the behaviour of forward current-voltage characteristics, steady state capacitance-voltage characteristics and DLTS data allow to conclude that the obtained reduction of forward current after ion im- plactation can be attributed to an increase of effective potenia! barrier height.
Vacancy-Type Defects in Proton-Bombarded InP
Authors: Ascheron C. , Krause R. , Polity A. , Sobotta H. , Riede V.
Published: March 2011

In proton-bombarded InP single crystals the fluence-dependent production of vacancy-type radiation defects and their annealing behaviour are studied. The results are interpreted using measurements of the total defect concentration, the carrier concentration and the infrared absorption.
Processing of Refractory Ores in a Microwave Induced “Cold” Plasma
Authors: Bullard D.E. , Lynch D.C.
Published: March 2011

A Microwave Induced Plasma has been used to investigate the processing of metallurgically significant refractory oxides in a non-equilibrium or “cold” plasma. The main emphasis of this work has centered on the reduction of TiO2 in a hydrogen plasma. The plasma was maintained using microwave energy (2.45 GHz) in a single mode resonant cavity. The reaction was monitored for volatile species with a quadrupole mass spectrometer, while the extent of reaction was determined by an external standard X-Ray diffraction technique. The effect of process variables (absorbed power by the plasma, chamber pressure, and time) on the extent of reaction was investigated. Hydrogen reduction in a plasma has produced up to 60% conversion of TiO2 to Ti2O3 in 11 minutes with the sample on a grounded support rod, while only an 8% conversion is observed for a sample on an insulated support rod. Sample temperatures were below 735 K for most plasma conditions, based upon thermodynamic considerations.
Characterization of an ECR Microwave Plasma Etching System
Authors: Jin Ming , Kao Kwan C.
Published: March 2011

An ECR microwave plasma etching system and an alternating bias voltage source with variable frequencies ( 10kHz to 10 MHz ) have been built for the study of the effects of the substrate bias on the submicron feature etching. A quadrupole mass spectrometer was used for the end-point monitoring and the plasma chemistry analysis. A Langmuir probe was used to characterize the etching plasma. The system can generate plasmas with densities ranging from 1×1015m−3 to 5×1016m−3 corresponding to gas pressures from 1×10−4 torr to 6×10−3torr at a fairly low microwave power. This condition results in a stable electron temperature. The magnetic field profile can be adjusted to obtain a constant plasma density of 2.8×1016m−3 and an electron temperature in kTe of 4 eV to 5 eV. The plasma beam is of 75mm in diameter with the ion current intensity fluctuation of about ±5% at the etching position for the gas pressures ranging from 4×10−4 torr to 3×10−3 torr at an absorbed power of 70Watts. The plasma density, the electron temperature, the breakdown power, and the sustaining power have been studied as functions of gas pressure in order to optimize the etching performance.
The Effect of Particle Size on Microwave Heated Carbon and the Subsequent Crystallite Growth
Authors: Lorenson Claude P. , Patterson Mark C.L. , Risto Gail , Kimber Robert
Published: March 2011

The dielectric properties of carbon imply that heating with microwave energy should not be significant at elevated temperatures. It has been demonstrated, however, that temperatures in excess of 1900°C can be achieved with low powers. The effect of particle size on the heating rate will be presented and a heat absorption mechanism is postulated to explain the high temperatures observed.

Under controlled conditions, conventional and microwave heating has been used to observe growth of the carbon crystallite size up to a temperature of 1400°C. Under these conditions, no enhanced crystal growth was observed for microwave heating.
Theory of Sublinear Power Dependence of Microwave Heating in Some Ceramic Materials
Authors: Kenkre V. M. , Kus M. , Katz J. D.
Published: March 2011

A sublinear dependence of the microwave heating rate on the incident microwave power implying a saturation effect appears to have been observed recently. We present simple model calculations to address this observation on the basis of an idea of spatial confinement of the absorbing charges in grain boundary regions. Two natural lengths exist in this model: the spatial extent of the confining region, and the maximum distance an absorbing charge travels under the combined action of damping and of the oscillating microwave field. We suggest that a mismatch of these lengths results in the observed saturation, more generally, in the observed decrease in absorption efficiency.
Microwave Absorption by Lossy Ceramic Materials
Authors: Campisi Isidoro E. , Summers Lynda K. , Finger Keith E. , Johnson Anne M.
Published: March 2011

Microwave energy generated by the electron beam in the superconducting cavities of the Continuous Electron Beam Accelerator Facility (CEBAF) is absorbed by special loads fabricated with a novel lossy ceramic material (AIN-glassy carbon) developed especially for this application. Strict environmental constraints (ultra-high vacuum compatibility, operation at 2 K, brazeability, etc.) are imposed on the materials which can be used. Several other ceramics were sintered with AIN and various minority conductive powders to obtain the desired electrical properties according to the ‘artificial dielectric’ model. Dielectric permittivity data and results of low temperature measurements are reported.
Pulsed Microwave Processing of High-TC Superconducting Films
Authors: James R. B. , Alvarez R. A. , Stamper A. K. , Bao X. J. , Schlesinger T. E. , Ginley D. S. , McCarty K. F. , Friedmann T. A. , Stulen R. H.
Published: March 2011

We have used 2.0-μsec microwave pulses at a frequency of 2.856 GHz to rapidly heat thin amorphous yttrium-barium-copper-oxide (YBCO) films deposited onto silicon substrates. The samples were irradiated inside a WR-284 waveguide by single-pass TE10 pulses in a traveling wave geometry. X-ray diffractometry studies show that an amorphous-to-crystalline phase transition occurs for incident pulse powers exceeding about 6 MW, in which case the amorphous YBCO layer is converted to Y2BaCuO5. Microscopy of the irradiated film reveals that the phase transition is brought about by melting of the YBCO precursor film and crystallization of the molten layer upon solidification. Time-resolved in situ experiments of the microwave reflectivity (R) and transmissivity (T) show that there is an abrupt change in R for microwave pulse powers exceeding the melt threshold, so that measurements of R and T can be used to monitor the onset of surface melting.
Metallorganic- and Microwave-Processing of Monolithic and Polyphasic Ceramics
Authors: Willert-Porada M.
Published: March 2011

A method for microstructural modelling of ceramic materials utilising precursor compounds and heating by microwave radiation to introduce a second phase as well as to control grain growth is described. The precursor compounds are introduced into the ceramic material by infiltration of a porous compact or by impregnating a classical powder with the precursor prior to compaction. Microwave radiation is used for decomposition of the precursor and for sintering. Decomposition rate controlled pyrolysis of the precursor is only possible by microwave heating. The resulting microwave processed ceramics display a finer and in some cases more bimodal microstructure as compared to conventionally processed samples with the same density.
Metallorganic and Microwave Processing of Cermets
Authors: Willert-Porada M. , Gerdes T. , Vodegel S.
Published: March 2011

Preliminary results are decribed on synthesis of ceramic-metal composites with a functional gradient material character utilizing infiltration of a porous metallic matrix with ceramic precursors and thermal processing by MW-heating. Infiltration of the metal matrix with a ceramic precursor facilitates bonding between metal and ceramic. By repeated infiltration and decomposition, complete filling of the pores with a ceramic phase is achieved.

Using SiC as MW absorbing material in a sandwich-like configuration, heating of the metal-ceramic composite in a strong MW field is possible. Temperatures of apr. 1000°C were achieved with this method.
Microwave Processing of Polymers - An Overview
Authors: Lewis David A.
Published: March 2011

This paper surveys some of the recent research into the microwave processing of polymers. The mechanism of coupling of the radiation with polymers is described and a historical perspective is presented on the development of this technology from the 1960's when the processing of rubber was first initiated, to current research in high performance materials and composites. The controversial area of microwave effects on processing is also discussed.
Reaction Sintering of Ceramic Materials by Microwave Heating
Authors: Boch Ph. , Lequeux N. , Piluso P.
Published: March 2011

Microwave heating was used to reaction sinter Al2O3 + SiO2 and Al2O3 + TiO2 powder mixtures to prepare mullite and aluminum titanate ceramics, respectively. In comparison with conventional heating, microwave heating leads to a decrease in the temperatures of treatment of 50 to 100°C.
Microwave Sintering of Multilayer Ceramic Capacitors
Authors: Lauf R. J. , Holcombe C. E. , Hamby C.
Published: March 2011

Multilayer ceramic capacitors of several compositions (both Z5U and NPO types) were sintered in air in both conventional and microwave furnaces. Several casketing and insulation techniques were used to improve temperature uniformity and minimize dopant losses. Zirconia and yttria are suitable packing materials as either powders or fibers. After sintering, the packing material remains friable and can be recycled. The presence of metallization layers did not interfere with the microwave process and no arcing was observed at surfaces where the internal electrodes emerged. In some runs, however, local thermal runaway was observed, which could severely decrease process yields and must be eliminated in a commercial process.
Thermal Runaway and its Control in Microwave Heated Ceramics
Authors: Kriegsmann Gregory A.
Published: March 2011

The heating of a ceramic slab under TEM illumination is modeled and analyzed in the small Biot number regime. The temperature distribution is almost spatially uniform in this limit and its evolution in time is governed by a first order nonlinear amplitude equation. This equation admits a time independent solution which is a multivalued function of the microwave power. The dynamics of the heating process are deduced, from the amplitude equation and the multivalued response, and are dependent upon the microwave power and initial conditions. The results of this analysis give a plausible explanation of certain difficulties arising in sintering experiments, such as thermal runaway. A simple control process is presented and analyzed which mitigates against these deleterious effects. Abbreviated parameter studies are performed showing trends in the controlled heating process.

A quasi-three-dimensional problem modeling the heating process of a thin cylindrical sample in a waveguide applicator is also presented. For certain excitations the physical phenomenon deduced from this model and the required control process are the same as those obtained for the slab. For other excitations there is a strong spatial structure along the axis of the sample. For a certain choice of parameters the middle portion of the sample is at an elevated temperature while the remaining portion is at a much lower temperature. This phenomenon may be useful in joining applications.
Automatic Control to Prevent Thermal Runaway During Microwave Joining of Ceramics
Authors: Beale Guy O. , Arteaga Francisco J.
Published: March 2011

A temperature control system is designed and simulated for microwave joining of ceramics. The objective is to develop a control system for reliable, high quality joints to be produced on a variety of ceramics. The described procedure permits the derivation of a closed-loop configuration for controlling temperature. The ceramics (alumina) heating model equation is linearized around an operating point and represented as a transfer function. Conditions for closed-loop stability with any linearized model are presented and mathematically proven. A computer simulation is implemented for the closed-loop control and numerical integration is used for solving the non-linear heating equations. Results are very good and show that the temperature can be regulated to a set point value and thermal runaway in the ceramics can be prevented.
Microwave Joining of Silicon Carbide Using Several Different Approaches
Authors: Ahmad Iftikhar , Silberglitt Richard , Black W. Murray , Sa'Adaldin Hussamaldin S. , Katz Joel D.
Published: March 2011

Microwave joining of sintered silicon carbide, both to itself and reaction bonded silicon carbide, has been accomplished in a single mode rectangular resonant cavity. Several approaches using different interlayer materials were employed to join sintered silicon carbide. Effective joining of reaction bonded silicon carbide to itself and sintered silicon carbide was accomplished without the use of any interlayer material in the single mode resonant cavity as well as in a multi-mode oven. Specimens cut from 0.95 cm diameter rods were joined in the single mode cavity, whereas a variety of arbitrary shapes and larger specimens (of reaction bonded silicon carbide) were joined in the multi-mode oven.
Batch Process for Microwave Sintering of Si3N4
Authors: Patterson M.C.L. , Apte P.S. , Kimber R.M. , Roy R.
Published: March 2011

A method for sintering silicon nitride using microwave energy at 2.45 GHz is described. Sintering takes place in air, in times of between 30 and 120 minutes and has been scaled up to give isothermal conditions over a batch size of 150 mm diameter by 200 mm in height and weighs approximately 1.0 kg. Additions of 5% alumina and 5% yttria result in a sintered product density of approximately 97% of theoretical, with a density variation better than:±0.5% throughout the batch.

It has been estimated that a load of 7.0 kg can be conventionally sintered using a 12 hour cycle and an energy consumption of 19.7 kWh/kg. In contrast with microwave energy, a batch of 540 g can be sintered in 120 minutes with an energy consumption of approximately 3.1 kWh/kg. This results in a possible energy savings of up to 78% for microwave heating.
Microwave Processing of Ceramics - An Overview
Authors: Sutton Willard H.
Published: March 2011

During the past decade, many exploratory studies and experiments have been performed on the microwave heating and processing of ceramics and composite materials. Much of this effort was stimulated by the unique and potential benefits that microwave energy can provide over conventional processing methods. While microwave processing of ceramics is still in an early developmental stage, there are many areas yet to be explored, challenges to be met, and economic and commercial payoffs to be substantiated.

Since the first MRS International Symposium on Microwave Processing in 1988, interest in this field has grown and many new developments have occurred. The purpose of this paper is to highlight some of the recent advances, to discuss the current state-of-the-art, and to suggest some future directions.
Microwave Sintering of ZnO Varistor Ceramics
Authors: Levinson Lionel M. , Comanzo Holly A. , Schultz William N.
Published: March 2011

ZnO varistors are electronic ceramics whose electrical behavior is dominated by grain boundary effects. A careful evaluation of the effect of microwave sintering compared to conventional sintering revealed no significant differences between varistor devices processed by these two methods. A slight apparent enhancement of grain growth was observed for microwave processing, but further evaluation of this effect leads us to believe that it arises from a small systematic shift in temperature derived from the different experimental configurations.
Densification kinetics of Alumina During Microwave Sintering
Authors: Cheng Jiping , Qiu Jinyu , Zhou Jian , Ye Neng
Published: March 2011

Some kinetics parameters of alumina during microwave sintering were studied and compared with that during conventional sintering. The results demonstrated that the sintering rates for microwave processing were much greater than that for conventional processing, and the grain growth of alumina was rapid with prolonged time at high temperature in a microwave field. It was indicated that the microwave sintering at higher temperatures for a shorter time was favorable for preparing high density and fine-grained alumina ceramics.
Microwave Processing in the UK
Authors: Binner JGP , Cross TE
Published: March 2011

A brief review of the current status of microwave processing in the UK is provided, focussing on ceramic and polymer processing, materials synthesis, catalyst preparation and dielectric property measurement. The central role of the Materials and Microwave Processing Group is also discussed.
Microwave Joining of Ceramics: A Study on Joining Alumina Both Directly and with Alumina Gel
Authors: Al-Assafi Salwan , Clark David E.
Published: March 2011

Alumina ceramics of different purities were joined using alumina gel as an interlayer and microwave energy as the heating source. Direct microwave joining of alumina was also accomplished. A comparison between the two joining methods was made. The effect of the gel on joining time and joining temperature was determined. Knoop microhardness was measured across the joint to show the change in the microhardness at the joint region. Joints of hardness as high as that of the bulk were produced when the joining parameters were properly selected. The dielectric properties of the aluminas used in this study were measured. X-ray maps and SEM micrographs were taken for different joints.
Microwave Curing and Drying of Cellular Concrete
Authors: van Loock Walter M.
Published: March 2011

Traditionally the heating and curing of cellular concrete takes place in an autoclave. This building material is a thermal insulator so the curing and drying processes are energy and time consuming. Volumetric heating is an attractive method for improving the throughputs.

A feasibility study leads to the conclusion that microwave processing is not likely to be applied in a large scale production process.
Use of the Inverse Temperature Profile in Microwave Processing of Advanced Ceramics
Authors: Binner J.G.P. , Al-Dawery I.A. , Aneziris C. , Cross T.E.
Published: March 2011

Attempts are being made to exploit the inverse temperature profile which can be developed with microwave heating with respect to the processing of certain advanced ceramics. This paper discusses the results obtained to date during the microwave sintering of YBCO high-Tc superconductors and the microwave reaction bonding of silicon nitride.
Computer Modeling of Two Dimensional Temperature Distributions in Microwave Heated Ceramics
Authors: Tian Y.L. , Feng J.H. , Sun L.C. , Tu C.J.
Published: March 2011

A two dimensional model for computer simulation of microwave heating of ceramics has been developed. The effects of microwave power, properties of ceramics, and thermal insulation on dynamic temperature distributions of ceramics under various processing conditions have been simulated. The practical solutions for eliminating thermal runaway and improving temperature homogeneity under microwave rapid heating can be approached using this computation technique.
Automation of Microwave Processing of Graphite / Epoxy Composite Materials using an Expert Systems Technique
Authors: Adegbite Valerie , Hawley Martin , Decker Dave , Sticklen Jon
Published: March 2011

Microwave curing of composite materials is a novel technology which can be an alternative to conventional thermal curing and has many advantages over thermal curing, i.e, fast and direct heating, selective heating, and controllability. Currently, the existing technology is more empirical and cannot be easily described by traditional process models. One key enabling step for realizing the advantages of the microwave curing technology is a capability for utilizing all the available existing knowledge in a concise manner. The major elements of a control system which utilizes traditional control techniques and (non-traditional) expert systems techniques in a real time microwave cure monitoring and control is discussed.
Modeling and Controlling During Microwave and Thermal Processing of Composites
Authors: Wei Jianghua , Sundaram Ananthapadmanaban , Hawley Martin C.
Published: March 2011

A process model was developed and coded in FORTRAN to simulate the temperature and the extent of cure profiles across the thickness of the composite during microwave and thermal processing. A simplified five-parameter microwave power absorption model was developed for microwave processing. The computer code was used to predict the behavior of Hercules AS4/3501-6 prepreg during thermal processing using various laminate thickness and boundary conditions. The simulation results show that 4.0 cm is the thickest composite that can be processed with the manufacture's cure cycle. The advantages of microwave processing over thermal processing are fully demonstrated.
Microwave Imaging Techniques for Non-Destructive Testing of Materials
Authors: Bolomey J.Ch. , Pichot Ch.
Published: March 2011

Recent technological advances for microwave multiport sensors lead us to look for efficient wavefront processing techniques in order to improve image quality, in terms of spatial resolution and contrast. This paper reviews some of these techniques which can be used for Non-Destructive Testing purposes. Mutual advantages and limitations are analysed.
Microwave Based and Microwave Aided non Destructive Test Methods
Authors: d'Ambrosio G. , Massa R. , Migliore M.D. , Ciliberto A. , Sabatino C.
Published: March 2011

The reflection coefficient of Fiberglass/Kevlar slabs, including a layer of a different material was calculated as a function of permittivities, thicknesses, defect depth, and microwave frequency. Experimental tests were done with a single-frequency, amplitude and phase sensitive circuit, and with a swept-frequency amplitude only sensitive set-up. In this latter case a suitable processing of data allowed effective and fast defect detection. First experiments on microwave heating for thermographic NDT were also performed.
The Electromagnetic Properties of Materials Program at Nist
Authors: Weil Claude M.
Published: March 2011

The Electromagnetic Properties of Materials (EPM) program at the National Institute of Standards and Technology (NIST) is described, including an outline of the current goals of the project as well as some details of measurement techniques being used at NIST for characterizing dielectric and magnetic materials at RF and microwave frequencies.
RF and Microwave Dielectric Measurements to 1400°C and Dielectric Loss Mechanisms
Authors: Hutcheon R.M. , Jong M.S. De , Adams F.P. , Lucuta P.G. , McGregor J.E. , Bahen L.
Published: March 2011

A system has been developed, based on the cavity perturbation technique, for measuring the complex scalar permittivity of materials at frequencies between 50 MHz and 3 CHz, and up to a temperature of 1400°C. Measurements have been made on several classes of materials, including metallic oxides, conventional and advanced ceramics, fabrics, earthenwares, geological and biological materials, foods, glasses, organics and ferrites. Some materials remain unchanged by thermal cycling, but many undergo irreversible changes; the latter are of interest in microwave processing. The system measures the complex dielectric constant of materials during conventional heating, curing or sintering. Correlating these microwave measurements with other diagnostic techniques will help in the understanding of these processes in several classes of materials.