bluuebunny/crossref_metadata_2025 huggingface dataset:
Activation of N-Acceptor in MOCVD-ZnSe by Excimer Laser Annealing
Authors: Padmapani Nallan , Neumark G. F. , Taskar N. , Dorman D.
Published: March 2011

The recent success in obtaining blue-green diode lasers using ZnSe-based heterostructures has been mainly due to the successful p-doping of ZnSe using a N plasma source in an MBE system. P-type ZnSe can also be grown by MOCVD, using NH3 as the dopant source. Dopant concentrations of up to 1018 cm−3 have been obtained but net acceptor concentrations are in the range of only about 1015 cm−3 Activation of the remaining N has been achieved to some extent (NA -ND∼3*1016cm−3 ) by rapid thermal annealing. However, this has had limited success. We have used fast surface annealing by an excimer laser to activate the N. We have observed an increase in the ratio of Acceptor Bound Exciton peak intensity to Free Exciton peak intensity on annealing and this effect increases as we increase the laser power density from 10 to 30 MW/cm2. Electrical measurements ( C-V ) give a net acceptor concentration of ∼2*1016 cm−3 and thus confirm the increase in carrier concentration after annealing.
Characterization of nGaAs-Au Schottky Diodes as Grating Coupled Photodetectors
Authors: Krishnaswami Kannan , Karakashian A. S. , Wong C.
Published: March 2011

Using holography and wet chemical etching, a grating of period 450nm and depth of 15nm was fabricated on a n-type GaAs substrate having a doping of 1016 cm−3. A 30 nm layer of Au was deposited on the substrate forming a Schottky contact. The ohmic back contact is an alloy of Ni, Au and Ge. These devices were optically and electrically characterized.

Optical characterization was done using a polarized 632.8 nm HeNe laser. Reflectivity measurements for complete angular scans with output currents were determined. It was observed that as reflectivity dropped to a minimum, at a specific incident angle, the output current peaked. This was attributed to excitation of surface plasma oscillations in the grating, allowing greater photon absorption in the depletion region. This was observed only when the incident electric field was p-polarized and normal to the orientation of the grating, thus satisfying the surface plasma resonance conditions.

Under the above conditions, it was observed that in a grating coupled photodetector a higher quantum efficiency can be achieved.
Plasma Generation
Authors: Pfender E.
Published: March 2011

In general, a plasma consists of a mixture of electrons, ions,and neutral species. Although there are free electric charges in a plasma, negative and positive charges compensate each other, i.e. overall a plasma is electrically neutral, a property which is known as quasi-neutrality. In contrast to an ordinary gas, the free electric charges in a plasma give rise to high electrical conductivities which may even surpass those of metals. A hydrogen plasma, for example, at atmospheric pressure heated to temperatures of 106 K, has the same electrical conductivity as copper at room temperature. As the plasma temperature increases, the electrical conductivity increases beyond that of copper. Plasma temperatures of the order of 106 K and above are typical for thermonuclear fusion experiments.
Method For Producing Prealloyed Chromium Carbide/Nickel/Chromium Powders and Properties of Coatings Created Therefrom
Authors: Houck David L. , Cheney Richard F.
Published: March 2011

A unique process for producing powder whose individual particles contain both chromium carbide and nickel/chromium is discussed. This process involves agglomeration of fine chromium carbide with nickel/ chromium-bearing materials using a proprietary binder system. The agglomerates are subsequently sintered, melted in a plasma flame, and sized. This powder does not exhibit the segregation and inhomogeneity problems associated with conventional mechanical blends of chromium carbide and Nichrome powders. Jet Kote* coatings created from the prealloyed powders have uniform microstructures, high hardnesses, and wear characteristics superior to those of plasma-sprayed coatings from the conventional blends.
Diagnostics Under Thermal Plasma Conditions
Authors: Fauchais P. , Coudert J.F. , Vardelle A. , Vardelle M. , Lesinski J.
Published: March 2011

A number of diagnostics problems in the low temperature plasma generators have been analysed with special attention to the plasma spraying process, and a general approach to these problems has been proposed. The advantages, difficulties and limitations of optical nonintrusive methods have been discussed. Examples based on authors experience during last few years, are given.
Excitation of the 4F-4F Emission of Donor-Type Rare-Earth Centers Through Donor-Acceptor Pair States (ZNS:TM)
Authors: LÖbe K. , Boyn R. , Zimmermann H.
Published: March 2011

Energy transfer from donor-acceptor pair states is known to be an efficient excitation channel for 4f-4f emission, especially if the rare-earth centers themselves are the relevant donors. Information on this type of mechanism can be obtained in the case when it is possible to observe, parallel to the 4f-4f emission, luminescence arising from radiative deexcitation of the pairs.

We have found these two kinds of emission, under electron-beam excitation, in ZnS:Tm crystals which, according to earlier site-selective studies performed by us, contain predominantly donor-type rare-earth centers. Characteristic differences between the two kinds of emission are found in the dependence of intensities on pumping rate; these arise from partial blocking of the energy transfer due to depopulation of the 4f ground levels. By quantitative studies of the correlation between those intensities we demonstrate that the same types of initial states are involved in the energy transfer and the pair transitions.
Sub-Nanometer Microscopy the Easy Way: An Underutilzed Tool for Reliability Assurance
Authors: Hamilton Doug , Colvard C.
Published: March 2011

Scanning electron microscopy (SEM) is a frequently used tool for establishing reliability where potential causes of failure are related to structural aspects that show up on a submicron scale. Conventional SEMs, however, even those equipped with field emission sources, can provide high-quality photomicrographs only up to a magnification of about 100,000×. For many purposes greater resolution (several nanometers or below) is required, in which case the usual alternative is to turn to transmission electron microscopy (TEM), in spite of the laborious sample preparation required and limited plan-view images obtained. We describe here an underutilized alternative to TEM for many applications. The in-lens field emission SEM (ILFESEM) can provide pictures above 500,000× magnification with sub-nanometer resolution, with the simple sample preparation and surface viewing advantages of the SEM. Magnification in this range is necessary to verify modern day tolerances on surface morphology and roughness, oxide and thin film structure, thickness, and step coverage, and pore sizes in adhesion layers or diffusion membranes.
Incorporation of Nitrogen into Oxynitride Dielectric Through Thermal Nitridation of Silicon
Authors: Maiti Bikas , Hao Ming-Yin , Lee Jack C.
Published: March 2011

A novel oxynitride processing scheme has been developed to provide improved performance over thermal oxides. These dielectrics were formed by nitridation of bare silicon wafers followed by deposition of low pressure chemical vapor deposited (LPCVD) oxides at 450°C and reoxidation at 900°C. This novel process provides a good control of dielectric thickness and the amount of nitrogen incorporated at the silicon/silicon dioxide interface. It also reduces the incorporation of the hydrogen-related electron traps in the bulk of the dielectric. Excessive electron trapping is a potential problem of the nitrided oxides. These oxynitride dielectrics referred to as “LPCVD Oxynitride” or “Reoxidized CVD Oxide on Nitrided Silicon” also exhibit relatively large charge-to-breakdown (QBD), considerable reduction in electron trapping and interface state (Dit) generation. The dielectric integrity of these LPCVD Oxynitride was also compared to other oxynitrides which were formed by oxidation of nitrided silicon (“Oxidized-Nitrided Silicon Dielectric”). It was found that the electrical characteristics of the oxidized nitrided silicon dielectrics are inferior compared to the LPCVD oxynitrides (e.g., QBD is substantially lower). Furthermore, for the case of LPCVD oxynitrides, higher nitridation temperatures leads to larger QBD. These results might be explained by the model in which microdefects are incorporated into the oxide when the silicon is consumed as in the cases of oxidized-nitrided silicon dielectrics.
Effect of Laminates and Alloy Additions on Electromigration in AI Interconnects
Authors: Atakov E. M. , Shepela A. , Miner B.
Published: March 2011

The effect of solutes and refractory-metal laminates on the electromigration resistance of Al films is consistent with the effect of those variables on Al grain growth during deposition and/or post-patterning anneal.
Effect of Post-Annealing on Electrical Properties of Ta2O5 Thin Film Deposited by Pecvd Using TaCl5 and N2O
Authors: Park Jong-Wan , Han S.W. , Moon H.S. , Lee J.S.
Published: March 2011

The effect of high temperature annealing, in the temperature range of 600∼900°C on the electrical properties and microstructure of tantalum pentoxide (Ta2O5) film deposited by PECVD was studied. The leakage current of the Ta2O5 film annealed at 600°C showed a minimum value in this study. However, it was found that the leakage current in the polycrystalline Ta2O5 film annealed above 800°C was decreased by increasing the annealing temperature. The dielectric constant of the annealed Ta2O5 film was 26 at 600°C, and decreased with the same tendency as leakage current characteristics. TEM and XRD analysis indicated that the microstructure of the Ta2O5 film annealed above 800°C was of ε-Ta2O5 with hexagonal crystal structure. Furthermore, TEM and AES observations revealed that Ta-O-Si transition layers were formed between annealed Ta2O5 layer and Si substrate. The electrical properties of the Ta2O5 films were discussed in terms of interface modification and film densification due to post-annealing
Group III Metal Clusters on (001) III-V Compound Semiconductors
Authors: Puddephatt S. , Lowes T.D.
Published: March 2011

The interaction of group III Metal clusters with the underlying III-V compound semiconductor substrate is examined. Specifically, both In and Ga on InP and GaAs (001) are discussed. Two Methods of obtaining an excess concentration of the group III Metal are treated: thermal decomposition in UHV where preferential group V dissociation and vaporization leaves a supersaturation of metal and Knudsen cell deposition in an MBE system. It is shown that the resulting morphologies for all cases are attributable to significant cluster/substrate interactions.
Pulsed Laser Deposition of Epitaxial (110) Tin Films on (100) Gaas - Processing, Characterization and Modeling
Authors: Zheleva Tsvetanka , Jagannadham K. , Biunno N. , Narayan J.
Published: March 2011

Epitaxial (110) titanium nitride films have been grown on (100) GaAs by pulsed laser deposition technique. The film quality has been found to be a strong function of the processing parameters. The films have been characterized using four point probe resistivity technique, Raman spectroscopy, X-ray diffraction analysis, and transmission electron Microscopy. Single crystal films were obtained at the deposition temperature 450° C and the room temperature resistivity was found to be 49.7 ΜΩ-cm. The epitaxial orientation relationship of the TiN films with the substrate is given by [001]TiN//[110] GaAs and [īlO]TiN// [līO]GaAs. Modeling studies have been performed to characterize the domain epitaxial growth in these large mismatch systems.
Energy Minimization During Epitaxial Grain Growth: Strain VS. Interfacial Energy
Authors: Floro J. A. , Carel R. , Thompson C. V.
Published: March 2011

We have investigated Epitaxial Grain Growth (EGG) in polycrystalline Ag films on Ni (001) substrates. EGG is driven by minimization of crystallographically anisotropie free energies such as the film/substrate interfacial energy and the film strain. Under some conditions EGG results in the preferred growth of the (111) epitaxial orientations that are predicted to minimize the interfacial energy. However, when Ag films are deposited on Ni (001) at low temperature, EGG experiments consistently find that (111) oriented grains are consumed by grains with (001) orientations predicted to have much higher interface and surface energy. The large elastic anisotropy of Ag can account for this discrepancy. The film thickness and the deposition temperature (relative to the grain growth temperature) determine whether strain energy or interface energy minimization dominates orientation evolution during grain growth.
Structural Transitions in Titanium-Aluminum Thin Film Multilayers
Authors: Ahuja Rajiv , Fraser Hamish L.
Published: March 2011

This paper presents the results of a detailed study of titanium - aluminum thin film multilayers fabricated using UHV Magnetron sputtering. Transmission electron Microscopy (TEM) techniques have been used to characterize the structure of these multilayers and to study the various structural transitions as a function of the composition modulation wavelength (CMW). Evidence is presented which indicates the existence of a titanium based fcc structure in these films, below a critical CMW. At even smaller values of CMW, both the Ti and Al layers adopt the hep structure and are coherent with each other. The evolution of thin film microstructure has been studied using high resolution TEM (HRTEM) and an attempt is made to rationalize the stability of different phases based on the energetics of atomic stacking.
AB Initio Study of the Ge Adsorption and Diffusion on Si (100) Surface
Authors: Milman V. , Pennycook S.J. , Jesson D.E. , Payne M.C. , Stich I.
Published: March 2011

We identify the binding sites for adsorption of a single Ge atom on the Si (100) surface using ab initio total energy calculations. The calculated diffusion barriers are in excellent agreement with experimental estimates. Using a large supercell we resolve the controversy regarding the binding geometry and migration path for the adatom, and investigate the influence of the adatom on the buckling of Si dimers. The adatom induces a buckling defect that is frequently observed using scanning tunneling Microscopy (STM); therefore the study of single adatoms may be experimentally accessible.
Nucleation of Dislocations in SIGe Layers
Authors: Mooney P.M. , Legoues F.K. , Chu J.O.
Published: March 2011

We present an x-ray diffraction study of the variation of the tilt angle between a relaxed Si1−xGex epitaxial layer and the Si (001) substrate. Such measurements provide the basis for a new method to determine the nucleation activation energy of misfit dislocations. We show that the nucleation activation energy for 60° dislocations in the case of the multiplication mechanism observed in graded SiGe layers grown by UHV-CVD at low temperature is 4 eV.
Computer Simulation of Creation of Dislocations in Copper Small Crystals
Authors: Tanaka H. , Doyama Masao
Published: March 2011

Dislocations were created near the center of the surface (101) of copper small crystals whose surfaces are (111), (111), (101), (101), (121), and (121) by use of n-body atom potentials and molecular dynamics. At first, a Heidenreich-Shockley partial dislocation was created., As the partial dislocation proceeds, the partial dislocation and the surface was connected with a stacking fault until the next Heidenreich-Shockley partial dislocation was created at the surface.Just before the creation of a partial dislocation the stress was the highest.
Second Phases and Impurity Segregations in MgO- and NiO-CO-Doped Alumina
Authors: Park K. , Sung C. , Vasilos T.
Published: March 2011

The microstructural and chemical characteristics of the segregated particles, Ni-(Mg)-Al spinel phases, and K-ß’’’ alumina precipitates in fine-grained alumina co-doped with 0.15 wt % of MgO and 0.10 wt % of NiO were studied using analytical transmission electron microscopy. The segregated Ni particles and second phases were generally found at triple junctions or on grain boundaries. The K-ß’’’ alumina precipitates were found to contain occasionally a high density of stacking faults. These microstructural observations point out the location of the dopants and impurities during the sintering process.
Non-Invasive Determination of Waste Drum Pressurization by Acoustic Resonance Spectroscopy
Authors: Sinha Dipen N. , Kosiewicz Stanley T.
Published: March 2011

Preliminary work suggests that Acoustic Resonance Spectroscopy (ARS) can non-invasively determine gas pressurization of waste drums. This is done by exciting the various mechanical vibrational modes of the test drum and analyzing the characteristics of the resulting resonance frequencies and their higher harmonics. If the contained waste is a liquid, the liquid level and also some properties of the liquid including density can be determined. Additional work is needed to exploit this novel acoustic technique for noninvasive characterization of waste storage drums.
Basic Radiation Damage Processes in Ionic Solids: The Role of Collisional Electron Capture
Authors: Fine J. , Szymonski M. , Kolodziej J. , Yoshitake M. , Franzreb K.
Published: March 2011

A new class of inelastic collisional processes accounts for the electron spectra of ion-bombarded sodium halide surfaces. These spectra indicate that the deexcitation process consists of a sequence of lattice-ion collisions in which localized electron transfer occurs. Such collisional processes demonstrate how collisions can initiate electronic change in molecular compounds and that electron-transfer processes must play an essential role in chemistry activated by energetic collisions.
Cement Minerals at Elevated Temperature: Thermodynamic and Structural Characteristics
Authors: Bruton Carol J. , Phillips Brian L. , Meike Annemarie , Martin Sue , Viani Brian E.
Published: March 2011

An experimental and modeling program has been designed to elucidate the structural and thermodynamic response of cement minerals to elevated temperature. The components of the program include: a) synthesis of hydrated Ca-silicates; b) structural analysis of cement phases during heating and dehydration/rehydration; c) mechanistic and thermodynamic descriptions of the hydration/dehydration behavior of hydrated Ca-silicates as a function of temperature, pressure and relative humidity; d) study of naturally occurring hydrated Ca-silicates; and e) measurements of thermodynamic data for hydrated Ca-silicates.
Retention Capability of Cement Barriers Applied in Nuclear Field
Authors: Ghattas N.K. , Ghorab H.Y. , Eskander S.B. , Bayoumi T.A.
Published: March 2011

The fraction released of radioactive cesium from waste forms (obtained by incorporating a given amount of simulated labelled waste materials into cement) was greater than that released when introducing the same amount of waste into a preformed cement container. Moreover, improving cement containers using chemical treatment or additives (organic or inorganic) lowers the fraction released. The effect of waste materials on cement hydration and on the properties of the obtained products has been studied. To improve repository performance it is therefore preferable to ameliorate the confinement properties of preformed cement containers rather than radioactive waste forms. In improving waste forms we are dealing with a complicated system resulting from the interaction of waste materials with cement besides allowing extra doses to workers and finally increasing the final total coasts.
Nuclear Waste Analytical Round Robins 1-6 Summary Report
Authors: Smith Gary L. , Marschman Steven C.
Published: March 2011

The Materials Characterization Center (MCC) at Pacific Northwest Laboratory(a) conducts Nuclear Waste Analytical Round Robins on simulated waste glasses with and without radionuclides. The analytical round robins are used to provide analytical laboratories with a forum for improving the accuracy and precision of analytical techniques that will be used for characterizing nuclear waste glasses. Chemical analysis data on glass waste forms produced by the nuclear waste community may need to withstand legal challenges for waste material storage qualification and for licensing repositories. Determining the quality of analytical data is important for meeting these challenges, making process operation decisions, and predicting long-term waste behavior.

The MCC has conducted six round robins for the waste management, research, and development community from 1987 to the present time. The laboratories that have participated regularly are Ames, Argonne, Catholic University, Lawrence Livermore, Pacific Northwest Laboratory, Savannah River, and West Valley Nuclear. The glass types analyzed in these round robins all have been simulated nuclear waste compositions expected from the vitrification of high-level nuclear waste. A wide range of analytical procedures have been used by the participating laboratories, including Atomic Absorption spectroscopy, inductively coupled plasma-atomic emission spectro-scopy, direct current plasma-emission spectroscopy, and inductively coupled plasma-mass spectroscopy techniques. The consensus average relative error for Round Robins 1 through 6 is 5.4%, with values ranging from 9.4 to 1.1%. The trend on the average improved with each round robin. When the laboratories analyzed samples over longer periods of time, the intralaboratory variability increased. Lab-to-lab variation accounts for most of the total variability found in all the round robins. To date, participation in the radiochemistry portion has been minimal and the analytical results poor when compared to the nonradiochemistry portion of the round robins. Additional radiochemical work is needed in future round robins.
Dissolution Mechanism of Soda-Lime Silicate Glass and of PNL 76-68 in the Presence of Dissolved Mg
Authors: Sang Jing C. , Guo Yan , Barkatt Alisa , Adel-Hadadi M.A. , Marbury Gwendolyn S. , Barkatt Aaron
Published: March 2011

Leaching studies were performed on powdered PNL 76-68 glass in de-ionized water in the presence of Mg solute. The results showed that the presence of Mg in the leachant greatly reduced the rate of glass dissolution. The equation Q=krα was used to express the experimental data. In the absence of Mg, α was about 1, i.e., the amount of glass dissolved was linear with time. In the presence of Mg, α was close to 0.5, i.e. the extracted amount was proportional to the square root of time. Therefore, the reduction of the dissolution rate of PNL 76-68 glass in the presence of Mg solute could be explained as a result of a change in the glass dissolution mechanism.

Comparative leaching studies on bulk soda-lime silicate glass in a sodium borate buffered system (pH 8.1) showed the same results. The presence of Mg in the leachant reduced the rate of glass dissolution. In the absence of Mg, α was about 1, while in the presence of Mg, α was 0.5. This change in α was not caused by changes in pH, and it represents a real change in the glass dissolution mechanism.
The Inpluence of Borehole Flushing on the Concentration of Microbes in Granitic Groundwaters.
Authors: Stroes-Gascoyne S. , Gascoyne M. , Hamon C.J. , Jain D. , Vilks P.
Published: March 2011

A number of groundvater parameters have been studied at AECL’s Underground Research Laboratory (URL) in support of the Canadian Nuclear Fuel Waste Management Program. The concentration of microbes in groundvater is of interest as they may modify the transport of dissolved radionuclides. Preliminary results from an earlier study suggested that the microbe concentrations may be affected by the extent of borehole flushing prior to sampling. A study was therefore carried out in which packer-isolated intervals of two boreholes intersecting a fracture zone at 250-m depth in the URL were flushed and sampled on two occasions at various flow rates. High initial microbial concentrations (most likely due to leaching of nutrients from sample tubes) decreased rapidly as flushing progressed, suggesting enhanced microbial growth near the top of the borehole zone. Also, a tenfold increase in flow rate during flushing caused an increase in microbial concentrations in the groundwater of one of the boreholes, concurrent with an increase in total particle count. This suggests that particulate and biofilm material may be flushed out of the fracture zone at this particular location.
Determination of the Composition and Thickness of Thin Potassium Polyphosphide Films
Authors: Kiss Klara , Figura Paul M.
Published: March 2011

An energy dispersive X-ray microprobe (EDX) analysis was developed to determine simultaneously the lateral uniformity of the thickness and the composition of thin potassium polyphosphide(KPx) films. The EDX analysis was based on theoretical calibration curves generated by the Monte Carlo simulation approach developed by Kyser and Murata and extended by Miller and Koffman. Simultaneous determination of both composition and thickness was possible for this binary-element thin film due to the concentration independence of the theoretical intensity ratio of

The EDX results were compared to macro techniques applied routinely in the characterization of thin films, i.e., piezoelectric thickness measurement and compositional analysis via X-ray fluorescence spectroscopy (XRF). A special XRF technique was developed to determine the weight ratios from fluorescent intensity measurements “directly” using “bulk” standards instead of thin film standards. The accuracy of this technique was demonstrated for an indium phosphide standard film since no certified KPx standard films are available.

The comparison was carried out on films of widely different thicknesses (0.26–2.0 um) and compositions (KP5–KP83). A Student's t test demonstrated that the compared techniques were identical at the 95% confidence level for the determinations of both thickness and composition. Thus, EDX analysis can be used to complement the macro techniques when the lateral uniformity of the thin films is to be determined at the micron scale.
Electron Energy Loss Fine Structure of Carbides and Nitrides
Authors: Disko Mark M.
Published: March 2011

Transition metal carbides and nitrides are important in a wide range of materials problems which include precipitates in high strength alloys and ceramic wear coatings. Electron energy loss spectroscopy (EELS) is a high spatial resolution (probe sizes < 100nm) analytical technique which is sensitive to variations in carbon or nitrogen stoichiometry. This sensitivity to light elements depends on the ability to relate the measured EELS spectrum to a material's electronic structure. The unique capabilities of EELS for the characterization of carbonitrides with high spatial resolution are discussed along with some of the experimental and analytical methods used to relate measured spectra to electronic structure. Data are presented for several members of the systems Ti-N-C and Cr-Fe-C.
Quality and Reliability Assurance of Semiconductor Devices through Transmission Electron Microscopy
Authors: Pinizzotto R. F. , Clark F. Y. , Jarvis M. L.
Published: March 2011

Modern methods of sample preparation have made it possible to analyze complete, packaged integrated circuits by transmission electron microscopy. TEM has two unique capabilities that cannot be matched by other characterization methods: 1) it is a direct crystallographic probe and 2) it has excellent spatial resolution, 0.2 nm. Small personal computers can be used to translate the micrographic data into statistical information that can be analyzed by non-TEM trained engineers. The data can also be stored in a MICROSTRUCTURAL DATABANK. The experimental data is automatically compared by the computer with previously established criteria. This methodology generates additional information that is used for quality and reliability assurance testing of integrated circuits. The method is applicable to devices that are removed from electronic systems after field operation, as well as to devices that have been lifetime tested. Two examples are described and discussed: aluminum grain size distribution analysis and silicide layer thickness measurement.
Compositional Profiling of Rapidly Solidified Cellular Structures
Authors: Mackey Terrence M. , Kelly Thomas F.
Published: March 2011

Solute partitioning during rapid solidification is being studied in cellular growth structures produced via pulsed-laser melting of binary alloys. This rapid solidification process can generate significant departures from local equilibrium at the liquid-solid interface which directly affects the resultant microsegregation patterns. Calculated compositional profiles are obtained from a solidification model incorporating the effects of both solute trapping and solute buildup with a suitable tip stability criterion. These are compared to experimentally determined campositional profiles generated across the steady-state cellular regrowth region of the melt pool using STEM x-ray microanalysis.
Center for Nondestructive Evaluation
Authors: Green Robert E.
Published: March 2011

The Johns Hopkins University Center for Nondestructive Evaluation (CNDE) has recently been established as an interdisciplinary center for research and instruction which draws on the resources and talent of the School of Engineering, the Applied Physics Laboratory, and the School of Medicine. The nondestructive evaluation techniques developed and employed are especially useful to control and improve product quality in manufacturing processes and to assure the highest level of reliability for materials, parts, and products. The center is dedicated to research which will lead to more sophisticated and accurate methods for the nondestructive evaluation of materials and systems and to the education of talented students who will enter the NDE field. The CNDE is a cooperative venture between the University, Industrial Affiliates, and Government Agencies. The present paper will describe the CNDE and the current and planned educational program in materials education.
Measurement of Particle Densities and Sizes: Application to Silane/Argon Plasmas
Authors: Spears Kenneth G. , Robinson Timothy J.
Published: March 2011

We discuss new methods for measuring particle number densities, masses and size distributions by laser techniques.These methods do not require assumptions of particle optical properties or instrumental calibration by known particles.We summarize the theoretical basis of these techniques and discuss the light scattering fluctuation analysis, which can yield number density and size information.Experimental data for rf discharges of silane/argon mixtures are briefly presented to illustrate some of the theoretical predictions.
Kinetic Modeling and Measurement of Active Species Distributions During Dry Etching
Authors: Uhm K. S. , Kump M. R. , Mcvittie J. P. , Dutton R. W.
Published: March 2011

A simple kinetic dry etching model accounting for generation, loss, and transport of the reactive and by-product species is developed.To demonstrate and evaluate the model, the etching of silicon using SF6+O2+Ar in the plasma etch mode is investigated.
In Situ Etching Rate Measurement of Si with XeF2
Authors: Padmanabhan K. R. , Bhowmick S. , Shaver R. , Hua Zhang Zu , Buchholz J. C.
Published: March 2011

Ion backscattering and channeling techniques have been employed to measure the etching rate of amorphous and single crystal Si by XeF2 under similar conditions.Both (100) Si on sapphire and (111) Si on spinel showed higher etching rates compared to amorphous Si.However, measurements of the etching rate using a Si cell aligned to the axis and along the planes under similar conditions did not show appreciable difference in the etching rate compared to the etching rate with random orientation of the cell.Presence of the analyzing 4He+ beam during etching enhances the etching rate to twice the value when compared to post etching analysis with the same beam.The enhancement of the etching rate due to ion induced decomposition of XeF2 have been considered in the explanation of the experimental results.
Performance Optimization of Woven Fabric Composites for Printed Circuit Boards
Authors: Chou Tsu-Wei , Yang Jenn-Ming
Published: March 2011

Woven fabric composites have been used extensively as substrate materials for multilayer printed circuit boards. This paper presents a brief overview of the recent accomplishments in the modeling and characterization of woven fabric composites. Three analytical models have been developed to predict the thermo-mechanical properties of fabric composites with various weaving geometries. A three-dimensional finite element analysis has also been adopted to determine the properties of plain-weave fabric composites.

Parametric studies are performed for both hybrid and non-hybrid woven fabric composites to generate data for materials selection and design. These data are presented in the form of “structure-performance maps” where the unique characteristics and relative effectiveness of various woven fabric composites can be easily assessed. The potential of tailoring a low thermal expansion coefficient substrate material through suitable materials selection, geometrical design, and fiber hybridization is also discussed.
Interdiffusion in Polyimide Thin Films
Authors: Kramer E. J. , Volksen W. , Russell T. P.
Published: March 2011

The interdiffusion in thin films of polyimide has been investigated using the forward recoil spectrometry (FRES) technique. Films 5–10 μm in thickness of polyamic acid spin coated onto a silicon substrate were imidized at a temperature TI. A second film, ∼300Å in thickness of perdeuterated polyamic acid was spin-coated onto the first layer and heated to a temperature TD to allow interdiffusion of the two films and imidization of the second coating. Depth profiling of the deuterated polymer by FRES showed that no interdiffusion occurred if TI>TD and TI>200°C. Substantial interdiffusion occurred if TD>TI and TI<400° C. Time averaged tracer diffusion coefficients were found to vary with the TD and TI, as well as the length of time allowed for interdiffusion. Since conversion of the deuterated polyamic acid to polyimide occurs at the diffusion temperature, the results are consistent with a relatively large diffusion coefficient for the polyamic acid (D>2.5× 10−14 cm2/sec) which decreases to a negligible value as the molecule is fully converted to the corresponding polyimide.
Stem Observations of the Microstructures Present in Polymer Blend Thin Films.
Authors: Sickafus K. E. , Berger S. D. , Donald A. M.
Published: March 2011

This paper examines the effectiveness of scanning transmission electron microscopy (STEM) as an analytical tool for determining composition in multi-phase polymer blend microstructures. The polymer blend polystyrene (PS) - polyether sulphone (PES) thin film used in this study exhibited a two-phase microstructure consisting of PES-rich inclusions, ranging from 0.2μm to 1.2μm in diameter, in a PS-rich matrix. Emphasis in this presentation is placed on the use of annular dark-field (ADF) STEM image contrast to infer information concerning the local composition of adjacent microstructural features.
Impact of Isotope Effects on the SANS Analysis of Amorphous Polymers
Authors: Bates F. S. , Koehler W. C. , Wignall G. D. , Fetters L. J.
Published: March 2011

Binary mixtures of the perdeuterated and protonated isotopes of four amorphous polymerspolystyrenes, 1,4-polybutadienes, 1,2-polybutadienes, and 1,2-polybutenes – have been examined by small-angle neutron scattering (SANS). In each case, evaluation of the SANS results based on the RPA theory of de Gennes indicates non-ideal mixing characterized by a Flory-Huggins interaction parameter 10-4 < χ 10-3. All four χ parameters can be closely predicted based on the measured change in the carbon-hydrogen bond polarizability with deuterium substitution. These findings are discussed in the context of past SANS studies of amorphous polymers.
A Reduced Variable Approach to Relating Creep and Creep Rupture in PMMA
Authors: McKenna G. B. , Crissman J. M.
Published: March 2011

Creep and creep rupture of PMMA at high stresses have been characterized and found to be relatable by use of reduced variables, it is shown that when the creep compliances can be correlated by a superposition principle for which the vertical shift is the ratio of the applied stress to a reference stress and when strain at failure is a constant, a commonly used failure criterion (that the product of the strain rate at failure and the time to failure is constant) becomes valid. The reduced variables approach is found to apply to two greatly different thermal histories. Consistent with the concept of physical aging, the response of a quenched sample is simply shifted along the log time axis to shorter times relative to the response of the aged sample.
Viscoelastic Relaxation in Glassy Polymers
Authors: Chow T. S.
Published: March 2011

The nonequilibrium mechanism controlling the viscoelastic response in the glassy state is analyzed in accordance with our multiple hole energy model. The change in the nonequilibrium glassy state defines the Struik physical aging exponent and determines the motion of the relaxation time spectrum, the transition of the global shift factor and the slow decay of the stress relaxation modulus especially at longer times in the glassy state where the Kohlrausch-Williams-Watts function fails. Although the distribution of relaxation times has its time scales shifted with the aging time, the shape of the spectrum remains very much the same which supports the notion of thermo-aging-rheological simplicity in the glassy and transition states.
Deformation Induced Dilatations and New Observations on Fracture In Compression in Metallic Glasses at Low Temperatures
Authors: Megusar Janez , Argon Ali S. , Grant Nicholas J.
Published: March 2011

Deformation induced dilatations were measured on a Pd-Cu-Si glass by a differential dilatometric method during crystallization. At large pre-strains, these dilatations are large and of the order of 20%. Fracture surfaces of specimens in compression show either the characteristic features of tensile separation or evidence for repeated nucleation of fracture. Rubbing was observed only in a small fraction of a fracture surface.
Rapidly Solidified Long Range Ordered Alloys
Authors: Lee E. H. , Koch C. C. , Liu C. T.
Published: March 2011

The influence of rapid solidification processing on the microstructure of long-range-ordered alloys in the (Fe,Co,Ni)3 V system has been studied by transmission electron microscopy. The main microstructural feature of the asquenched alloys was a fine cell structure (∼300 nm diameter) decorated with carbide particles. This structure was maintained after annealing treatments which develop the ordered crystal structure. Other features of the microstructures both before and after annealing are presented and discussed.
Critical Factors in Laser and Electron Beam Glazing of Materials.
Authors: Strutt P. R. , Lewis B. G. , Kear B. H.
Published: March 2011

The major effects of laser and electron beam glazing on solidification microstructure and melt zone geometry are described. It is shown that under comparable processing conditions, i.e. absorbed power density and interaction time, the glazed microstructures are similar. Some variations in microstructure of laser and electron beam glazed M2 steel have been noted, which seem to be related to fluid flow effects in the melt zone and possible interactions with the environment.
Development of Morphological Instability and Cells During Rapid Solidification of Laser Annealed Silicon Alloys
Authors: Narayan J. , White C. W.
Published: March 2011

The details of morphological instability occurring during rapid solidification have been studied in In+, Ga+, Sb+, Bi+, Ge+, Fe+ and Cr+ implanted silicon specimens after pulsed laser annealing. The average cell sizes were determined at the onset of instability and in the region of well-developed instability using x-section and plan-view electron microscopy. The total and substitutional solute concentration profiles were determined using Rutherford backscattering and channeling techniques. The formation of cells and the critical solute concentrations associated with instability were studied as a function of velocity of solidification, which was varied by controlling the substrate temperature or the laser parameters. The results on the cell formation and the critical solute concentrations were compared with the predictions of the perturbation theory which took into account the dependence of distribution coefficients on the velocity of solidification. A good agreement between the calculations and the experimental results was obtained. We also examined theoretically the effect of reduction in surface tension due to segregation of impurities on cell sizes and critical solute concentrations associated with instability.
Prospects for Monolithic GaAs/Si Integration
Authors: Choi H. K. , Turner G. W. , Tsaur B-Y.
Published: March 2011

The status of monolithic GaAs/Si (MGS) integration is reviewed and its future prospects are discussed. The MGS material now available is satisfactory for majority-carrier devices, but improvement in quality is needed for minority-carrier devices. By using a suitable sequence of processing steps, fabrication of GaAs MESFETs and Si MOSFETs on the same wafer and monolithic integration of GaAs/AlGaAs double-heterostructure LEDs and Si MOSFETs have been achieved. The GaAs and Si FETs show characteristics comparable to those for devices fabricated on separate GaAs and Si substrates. The LEDs have been modulated up to 27 Mb/s by applying a pattern of voltage pulses to the MOSFET gate. Two promising applications of MGS integration are optical interconnects between Si VLSI chips and monolithic microwave integrated circuits. Much better performance should be obtained by operating MGS ICs at liquid nitrogen temperature.
Admittance Measurements at Epitaxial and Nonepitaxial Silicide Schottky Contacts
Authors: Werner J. , Tung R. T. , Levi A. F. J. , Anzlowar M.
Published: March 2011

We report results of an extensive study examining the usefulness of low frequency capacitance measurements for the characterization of interface states at intimate Schottky contacts. Our measurements on epitaxial as well as on nonepitaxial silicides reveal that the imaginary component of the low frequency ac-admittance is usually inductive. This inductance is caused by minority carriers that are injected by the Schottky contact and modulate the conductivity of the series resistance of the bulk silicon. The frequently reported excess capacitances (instead of inductances) that were ascribed to interface states are only reproducible when we use imperfect back-contacts to the bulk Si that add a contact resistance to the equivalent dc-circuit of the Schottky diode. Excess low frequency capacitances at intimate Schottky contacts are therefore not related to interface states but rather to the contact resistance of the back-contact.
Effect of Dy Additions on Microstructure and Magnetic Properties of Fe-Nd-B Magnets
Authors: Ramesh R. , Thomas G. , Ma B. M.
Published: March 2011

This paper addresses the effect of Dy addition upon the magnetic properties, microstructure and microcomposition of Fe-Nd-B magnets. It is shown that increasing additions of Dy causes the remanence, Br to decrease linearly. The intrinsic coercivity, iHc, increases sharply for small additions of Dy, but the increase is not proportional for higher Dy contents. The iHc increases almost linearly with the effective anisotropy field of the RE2Fe14B phase until the Dy content is about 10% of the total rare earth content. Above this concentration, there is a strong deviation from linearity. Various types of possible concentration profiles of the substituted rare earth are suggested. It is also argued that preferential segregation of Dy to the interfaces could be beneficial in increasing the nucleation field. Morphologically there is no apparent effect of Dy on the microstructure. However, in the 5 atomic % Dy sample, Dy rich oxides were observed. It is shown through Energy Dispersive Xray Spectroscopy (EDXS) line profiling that Dy partitions preferentially into the RE2Fe14B phase in all the cases. No segregation of Dy to the interphase interfaces has been detected.
Thin Film Fabrication of R2Fe14B Compounds
Authors: Zasadzinski J. F. , Segre C. U. , Rippert E. D. , Chrzas J. , Radusewicz P.
Published: March 2011

Thin Films (≃4000 A) of R2Fe14B compounds have been synthesized by d.c. triode sputtering for R=Nd,Sm and Er. Deposition onto single-crystal substrates heated to 600”C and with rates of 1.3 A/s results in nearly epitaxial film growth such that the c-axis of the tetragonal structure is perpendicular to the film plane. As a consequence, intrinsic anisotropy effects are observed in the magnetic properties of the as-made films. Although sapphire and quartz substrates give the best results, similar directed growth is observed on recrystallized Nb foils. Magneto-optical measurements on the Nd-based compounds give a remnant polar Kerr angle θ=0.22° and coercive field Hc=5.5 k0e. The easy axis is in the film plane for R=Sm and Er and a remnant magnetization greater than 80% of saturation is observed for H applied parallel to the film plane. Electrical resistivity measurements on Nd2Fe14B films indicate that spin-disorder scattering from the rare earth site is important and features from both the Curie and spin reorientation temperatures are observed.
Low-Field Microwave Absorption in High-TC Superconducting Oxides
Authors: Ramakrishna B. L. , Ong E. W. , Iqbal Z.
Published: March 2011

Low-field non-resonant microwave absorption in an EPR spectrometer has been observed in the superconducting state of different samples of the new high-T oxides, YBa2Cu3O7-δ and La1.8Sr0.2CuO4. It has been attributed to flux slippage occurring at the Josephson junctions existing in the granular composite material. The dependence on particle size, temperature, microwave power, DC modulation amplitude and magnetic field has been studied.
Theoretical Studies of Oxygen Vacancies in YBa2Cu3O7-y
Authors: Richert Brent A. , Allen Roland E.
Published: March 2011

We have performed semiempirical tight-binding calculations of the electronic structure of YBa2Cu3O7, with dand s orbitals included for all the metal atoms and p and sorbitals for oxygen. Here we report studies of oxygen vacancies on the O(1) chain sites in YBa2Cu3O7-y. The modification of the density of states ρ(E) and the shift of the Fermi energy Ep were calculated for 0 < y ≤ 1.0. The Fermi energy is found to increase monotonically with y, confirming the expectation that oxygen vacancies act as donors. Also, ρ(EF)is found to decrease with y.
3d-Metal Doping (Fe,Co,Ni,Zn) Of The High Tc Perovskite YBa2Cu3O7-y
Authors: Tarascon J. M. , Barboux P. , Greene L. H. , Hull G. W. , Bagley B. G.
Published: March 2011

The structural, magnetic and superconducting properties of the mixed compounds YBa2Cu3−xMxO7-y (M = Ni,Zn,Fe and Co) are reported. Values of y, determined by titration, are found to be dependent on the nature and amount of the doping. The range of solubility is greater for the Fe and Co compounds (x = 1) than for those with Ni or Zn (x = 0.3). The undoped material is orthorhombic and remains orthorhombic after substitution for Cu by Ni or Zn, whereas a tetragonal phase is observed when Fe, Co are substituted for Cu. DC resistance and AC susceptibility measurements show that Tc is depressed from 90K (x = 0) to 45K (x = 0.2) for both the Ni and Zn doped compounds and Tc is destroyed in the Fe and Co doped compounds when x reaches 0.4. We suggest that a valence of 2 be assigned to the Ni and Zn and 3 to the Fe and Co ions.