bluuebunny/crossref_metadata_2025 huggingface dataset:
Open Applicator Analysis For Material Joining And Dielectric Measurements
Authors: Chen S. P. , Tinga W. R. , Vermeulen F. E.
Published: April 2011

Resonant internal and radiated external electromagnetic fields of an open coaxial structure are analyzed using FDTD. These fields are characterized for two structures, with and without a quarter-wave choke. Techniques utilized to obtain a steady state solution are discussed. Good agreement with field measurements is obtained. This moveable open applicator is convenient for creating intense hot zones as required in ceramic joining. It is also suitable for the measurement of surface dielectric properties of planar materials at room or elevated temperatures.
Scale-Up of the Nitridation and Sintering of Silicon Preforms Using Microwave Heating
Authors: Kiggans J. O. , Tiegs T. N. , Davisson C. C. , Morrow M. S. , Garvey G. J.
Published: April 2011

Scale-up studies were performed in which microwave heating was used to fabricate reactionbonded silicon nitride and sintered reaction-bonded silicon nitride (SRBSN). Tests were performed in both a 2.45 GHz, 500 liter and a 2.45 GHz, 4000 liter multimode cavities. A variety of sizes, shapes, and compositions of silicon preforms were processed in the studies, including bucket tappets and clevis pins for diesel engines. Up to 230 samples were processed in a single microwave furnace run. Data were collected which included weight gains for nitridation experiments, and final densities for nitridation and sintering experiments. For comparison, nitridation and sintering studies were performed using a conventional resistance-heated furnace.
Development Of A Multi-Grid Fdtd Code For Three-Dimensional Simulation Of Large Microwave Sintering Experiments
Authors: White Mikel J , Iskander Magdy F. , Kimrey Hal D.
Published: April 2011

The Finite-Difference Time-Domain (FDTD) code available at the University of Utah has been used to simulate sintering of ceramics in single and multimode cavities, and many useful results have been reported in literature [1–4]. More detailed and accurate results, specifically around and including the ceramic sample, are often desired to help evaluate the adequacy of the heating procedure. In electrically large multimode cavities, however, computer memory requirements limit the number of the mathematical cells, and the desired resolution is impractical to achieve due to limited computer resources. Therefore, an FDTD algorithm which incorporates multiple-grid regions with variable-grid sizes is required to adequately perform the desired simulations. In this paper we describe the development of a three-dimensional multi-grid FDTD code to help focus a large number of cells around the desired region. Test geometries were solved using a uniform-grid and the developed multi-grid code to help validate the results from the developed code. Results from these comparisons, as well as the results of comparisons between the developed FDTD code and other available variable-grid codes are presented. In addition, results from the simulation of realistic microwave sintering experiments showed improved resolution in critical sites inside the three-dimensional sintering cavity. With the validation of the FDTD code, simulations were performed for electrically large, multimode, microwave sintering cavities to fully demonstrate the advantages of the developed multi-grid FDTD code.
Numerical Simulation and Experimental Validation of RF Drying
Authors: Bringhurst S. , White M. J , Iskander M. F.
Published: April 2011

The Finite-Difference Time-Domain (FDTD) method has been used by our group to simulate a wide variety of Radio Frequency (RF) and induction-drying processes and realistic, microwave-sintering experiments. Many results were presented and some guidelines towards the effective use of the microwave and RF heating technologies of ceramic ware were developed.

In this paper we describe an experimental effort which was used to validate the FDTD simulation results. Specifically an experimental RF dryer, Thermax Model No. T3GB operating at 25 MHz, was used to dry ceramic ware of various materials, sizes, and shapes and the temperature distribution pattern was monitored using six fiber-optic temperature probes. The measured heating patterns were then compared with the FDTD simulation results. Many of the guidelines developed using the numerical simulations were confirmed experimentally.

Results from various comparisons between simulation and experimental data will be presented. Additional results from the simulation efforts illustrating possible procedures for improving the efficiency and the uniformity of RF drying will also be described
Application of the 50 Ω Radio Frequency Technology in the Automotive Industry: Fast Bonding of Composite Materials: Rear Doors of the Citroen Zx and Citroen Xantia Cars
Authors: Bernard J. P. , Sabran Mr. , Collet L.
Published: April 2011

In the field of plastic and composite materials the radio frequency dielectric heating is more and more used. Compared to traditional techniques such as conduction and convection heating, the radio frequency technology is interesting, because it allows fast heating of thick materials and heat insulation materials.

As bonding techniques are more and more integrated in production lines, the polymerization of glues must be realized in a very short time. The 50 use of the Ω radio frequency technology makes this heating process possible.

The authors describe the industrial application of this technology to the CITROEN ZX and CITROEN XANTIA cars. Steps involved in implementing this industrial process (laboratory - pilot -industrial equipment) are presented and analysis the technical and economic results of this application.
Spread Spectrum Microwave Power Generation for Improving Efficiency
Authors: Van Loock W. M.
Published: April 2011

Microwave power for heating applications is normally generated in the designated ISM frequency bands which occupy a band of 4%. Actual microwave generators, such as are used in domestic ovens utilise only a small fraction of this bandwidth. It is being demonstrated that spreading the power uniformly over the full ISM band by controlled frequency modulation dramatically reduces all levels of potential electromagnetic interference. With such controlled modulation telecommunication channels can operate within the ISM bands without serious problems because the leakage levels are reduced by 20 to 30 dB with no additional shielding costs. One simple (though not optimum) modulating waveform is a large ripple voltage on the magnetron power supply. Frequency modulation that spreads the energy over the full ISM band also improves the overall energy efficiency in multimode heating applications.
Microwave Process Control Through A Traveling Wave Tube Source
Authors: Vogt G. J. , Regan A. , Rohlev A. , Curtin M.
Published: April 2011

A rapid feedback control system was designed to operate with a traveling wave tube amplifier for regulating the sintering temperature of tows and tubes in a single mode microwave cavity. The control system regulated the microwave frequency and power absorbed by the sample in order to maintain the sample temperature. Testing with NICALON tows and mullite tubes demonstrated that the control scheme worked well for stationary and slowly moving (<10mi/min) samples, but failed for fast moving samples. Difficulty with measuring sample temperatures was resolved by using a light sensor to measure the emitted light intensity and to gauge the relative degree of heating. This work was supported by the Department of Energy, Office of Industrial Technologies, Advanced Industrial Materials Program.
Control of Microwave Process for Polymer Curing by Dielectric Property Measurements in a Broad Frequency Range, 1 MHz-10 GHz
Authors: Meyer O. , Belhadj-Tahar N. , Fourrier-Lamer A.
Published: April 2011

Let us present a new automatic system which couples a high power circuit (2.45 GHz) for heating with a low power one, for broad frequency band measurements of dielectric permittivity (1 MHz-10 GHz). The sample under microwave curing consists in an epoxy resin + hardener complex (DGEBA+DDS). The broad band spectra shows the existence of a dielectric relaxation. This absorption is used as a marker to describe the evolution of the reaction in relation with time and temperature, in terms of conversion ratio, kinetic velocity and quality. The phenomenum of microwave activation and interactions between permanent molecular dipoles and electromagnetic waves form the subject of this study. We also try to establish the specificity of microwave curing from a microscopic point of view. This work emphasizes new concepts which concern microwave chemistry.
Use of Microwaves for Nondestructive Material Inspection
Authors: Hokkanen B. R. , Lindsey J. F.
Published: April 2011

Wideband S-parameter measurements have been used to investigate the properties of electrically non-conductive materials using a vector network analyzer. Using S21 scattering parameters, amplitude and phase shift measurements were taken for a variety of both homogeneous and heterogeneous materials. With these initial S-parameter measurements as a reference, surface defects were modeled on the test samples and the S-parameter measurements were reevaluated. The effect of varying levels of moisture absorption in certain materials was also investigated. The results of this study indicate that there is indeed potential for the use of a vector network analyzer as a nondestructive testing tool to evaluate the structural integrity and/or moisture content of electrically non-conductive materials through the transmission of microwave energy.
Mask-Edge Distributions Produced by 80 KeV As+ Ion Implantation Into Si
Authors: Danailov D. , Karpuzov D. , Almazouzi A. , Almeida P.De , Victoria M.
Published: April 2011

The 2D-dopant and defect distributions resulting from 80 keV ion implantation of As+ ions into Si through a high-edge mask are presented. The distributions are obtained by means of an efficient computer procedure using the results of Monte Carlo simulation. Two versions of the computer code TRIM are used. The 2D-target atom redistribution is obtained as a result of cascade collisions. The simulation reveals the effect of near-mask-edge target atom depletion. This effect is related to the recoil phenomena and can be explained on the basis of simple model.
Dose Rate Effects During Damage Accumulation in Silicon
Authors: Caturla M. -J. , Rubia T. Diaz de la
Published: April 2011

We combine molecular dynamics and Monte Carlo simulations to study damage accumulation and dose rate effects during irradiation of Silicon. We obtain the initial stage of the damage produced by heavy and light ions using classical molecular dynamics simulations. While heavy ions like As or Pt induce amorphization by single ion impact, light ions like B only produce point defects or small clusters of defects. The amorphous pockets generated by heavy ions are stable below room temperature and recrystallize at temperatures below the threshold for recrystallization of a planar amorphous-crystalline interface. The damage accumulation during light ion irradiation is simulated using a Monte Carlo model for defect diffusion. In this approach, we study the damage in the lattice as a function of dose and dose rate. A strong reduction in the total number of defects left in the lattice is observed for lower dose rates.
Annealing Properties of Defects in Bf2+ Implanted Silicon
Authors: Kitano T. , Watanabe M. , Yaoita A. , Oguro S. , Uedono A. , Moriya T. , Tanigawa S. , Kawano T. , Suzuki R. , Ohdaira T. , Mikado T.
Published: April 2011

The annealing properties of defects in BF2+ implanted silicon were investigated using positron annihilation, TEM and SIMS techniques. For the as-implanted specimens, the major species of defects was identified to be divacancies. After thermal annealing, vacancy-fluorine complexes were formed. The size of open volume in the vacancy-fluorine complexes became larger with increasing annealing temperature. Even after 1100 °C, the vacancy-fluorine complexes were still stable with the size of open volume close to V5. The depth profile of vacancy-fluorine complexes was not largely changed after re-crystallization. In this way, the fluorine atoms played an important role in forming the defects with a large size of open volume. After 1100°C annealing, the fluorine atoms piled up at two regions; the projected range of fluorine and the original amorphous/crystalline interface, where bubbles were observed by TEM. The vacancy-fluorine complexes detected by positron annihilation might be precursors of the bubbles observed by TEM.
Competition Between Gettering by Implantation-Induced Cavities in Silicon and Internal Gettering Associated with SiO2 Precipitation
Authors: McHugo S. A. , Weber E. R. , Myers S. M. , Petersen G. A.
Published: April 2011

The gettering behavior of Cu and Fe was investigated in CZ silicon containing both internal-gettering sites in the bulk due to SiO2 precipitation and a device-side layer of cavities formed by He ion implantation and annealing. The objective was to quantify the effectiveness of impurity gettering at cavities relative to the widely used internal-gettering process. Both rapid thermal anneals and furnace anneals were used during the gettering sequences to reveal transient effects as well as the final, thermodynamically-equilibrated condition. For temperatures of 700, 800 and 850°C, the cavity gettering was observed to dominate the internal gettering as indicated both by the number of gettered atoms in the cavities and the residual solution concentration in the device region. The results are interpreted in detail by numerically solving the diffusion equation with sink-related source terms based on earlier, fundamental studies of the underlying mechanisms of internal and cavity gettering.
Secondary Defect Formation And Gettering in Mev Self-Implanted Silicon
Authors: Brown R. A. , Kononchuk O. , Radzimski Z. , Rozgonyi G. A. , Gonzalez F.
Published: April 2011

Secondary defect and impurity distributions in MeV self-implanted Czochralski (Cz) and float-zone (FZ) silicon have been investigated by transmission electron microscopy, optical microscopy with preferential chemical etching, and secondary ion mass spectroscopy. We found that the ion fluence and the oxygen content of the implanted wafers affect the number and depth distribution of extended defects remaining after annealing. Intrinsic oxygen also redistributes during annealing of Cz wafers, producing two regions of relatively high oxygen concentration: one at extended defects near the ion projected range, and another, shallower region, which correlates with the distribution of vacancy-type defects. Both of these regions are also able to getter metallic impurities, depending on the implantation and annealing conditions. These defect issues may adversely affect the quality of the near surface device region, and must be controlled for successful gettering by ion implantation.
Ion Beam Synthesis of SiC/Si Heterostructures by Mevva Implantation
Authors: Wong S. P. , Ho L. C. , Cihen Djhu , Guo W. S. , Yan H. , Kwok R. W. M.
Published: April 2011

Ion beam synthesis of SiC/Si heterostructures was performed by MIEVVA (metal vapor vacuum arc) implantation under various implantation and annealing conditions. The implanted SiC/Si heterostructures were characterized by various techniques. Carbon redistribution in overstoichiometrically implanted samples during annealing to form a stoichiometric SiC layer has been observed for the first time. The FTIR spectra were found to be composed of two components, one attributed to amorphous SiC and the other to ß-SiC. It was also found that there are critical dose and critical energy at which the crystalline fraction increases abruptly. Other results on electrical and optical characterization are also presented and discussed.
SiC Precipitate Formation During High Dose Carbon Implantation Into Silicon
Authors: Lindner J. K. N. , Volz K. , Stritzker B.
Published: April 2011

The formation of SiC precipitates during the high-dose implantation of carbon ions into Si(100) is studied by means of TEM for implantation conditions, which are suitable for the ion beam synthesis of buried SiC layers in silicon. It is observed that in crystalline silicon nm-sized epitaxially oriented 3C-SiC precipitates are formed which are almost identical in size, nearly independent of the depth and dose (4 – 9 ×1017 C+/cm2). With increasing dose, it is mainly the density of precipitates which increases. Amorphization of the silicon host lattice leads to depth intervals with a strongly decreased density of oriented crystalline SiC precipitates. The irradiation induced formation of larger randomly oriented SiC crystallites is observed to occur in amorphized regions after prolonged implantation. Both the irradiation induced destruction and formation of SiC precipitates contribute to the generation of a nearly box-shaped precipitate density distribution at doses near the stoichiometry dose.
Formation and Characteristics of CoSi2 Layers Synthesized by Mevva Implantation
Authors: Wong S. P. , Peng Qicai , Cheung W. Y. , Guo W. S. , Xu J. B. , Wilson I. H. , Hark S. K. , Morton R. , Lau S. S.
Published: April 2011

Ion beam synthesis of CoSi2 layers in Si by NIEVVA (Metal Vapor Vacuum Arc) implantation has been performed under various conditions. The formation and characteristics of these CoSi2 layers have been studied by XTEM, RBS, AFM, X-ray diffraction, ellipsometry, electrical and Hall effect measurements. It was found that a higher substrate temperature during implantation results in an as-implanted Co distribution closer to the surface and hence the formation of a shallower CoSi2 layer after annealing. Buried CoSi2 layers of good crystal quality and low resistivity CoSi2 can be formed by MEVVA implantation and annealing under appropriate conditions. A strong temperature dependence of the Hall coefficient showing a large peak at around 100K was observed for the CoSi2 layers formed in p-type Si substrates but not in n-type substrates. The properties and their dependence on the processing conditions, in particular, the substrate temperature during implantation, are presented and discussed.
On the Determination of Loop Nature in the Tem
Authors: Jenkins M. L. , Fukushima H. , Kirk M. A.
Published: April 2011

We have carried out systematic experiments to explore the range of applicability of the two direct methods which are available for the determination of the nature of small clusters. Experiments in heavy-ion irradiated silver and copper, including direct comparisons with the results of Black-White contrast analysis (B-W), forced us to the conclusion that use of the 21/2D technique for the analysis of faulted loops is effectively impossible because of reciprocal-lattice spike and other effects. We used B-W analysis to investigate the nature of the clusters produced by room-temperature heavy-ion irradiation of copper. In-situ irradiations were performed in the Argonne HVEM-Tandem Facility using 40keV and 80keV Kr+ ions. Nearly all of the analysable first-layer loops were found to be vacancy in nature. Some deeper clusters were also certainly vacancy. There is no unequivocal evidence for interstitial loops under these conditions. The near impossibility of establishing that interstitial loops are not present is shown by the fact that a large fraction of loops - over 50% - could not be analysed either because they did not display clear B-W contrast under any condition or sufficiently consistent B-W contrast under several different operating conditions.
Microstructure of V-4Cr-4Ti Following Low Temperature Neutron Irradiation
Authors: Rice P. M. , Snead L. L. , Alexander D. J. , Zinkle S. J.
Published: April 2011

The V-4Cr-4Ti alloy displays excellent mechanical properties, including a ductile-to-brittle transition temperature (DBTT) below -200°C in the unirradiated condition. Specimens of this alloy were fission neutron-irradiated in the High Flux Beam Reactor (HFBR) at Brookhaven National Laboratory (BNL) to a dose of 0.4 dpa at temperatures from 100 to 275°C. Mechanical testing showed significant irradiation hardening in the alloy which increased with increasing irradiation temperature. Charpy impact testing also showed a dramatic increase in the DBTT on the order of 200 to 350°c. The mechanical property changes are correlated with preliminary results from the transmission electron microscopy (TEM) analysis of the defect microstructure resulting from the low-dose neutron irradiations. The TEM analysis of the irradiated material showed a nearly constant defect density of ∼1.6 × 1023 m−3, with an average defect diameter of slightly greater than 3 nm.
Modeling of Dislocation Loop Growth and Transient Enhanced Diffusion in Silicon for Amorphizing Implants
Authors: Gencer Alp H. , Dunham Scott T.
Published: April 2011

It has been observed that dislocation loops form and grow during annealing of silicon wafers implanted at doses above the amorphization threshold. Dislocation loops can act to store interstitials for prolonged periods of anneals, sustaining an interstitial super-saturation and thus causing substantial transient enhanced diffusion (TED). We have developed a comprehensive model which, in combination with a model and parameters for {311} defects from previous work, accounts for the formation and evolution of dislocation loops during ion implant annealing, as well as giving the correct TED behavior.
Nitrogen Vacancy Complexes in Nitrogen Irradiated Metals
Authors: Veen A.Van , Westerduin K. T. , Schut H. , Melker E. J. E. , Thijsse B. J. , Nielsen B. , Kumar P. Asoka , Ghosh V. J. , Lynn K. G.
Published: April 2011

Gas desorption and positron annihilation techniques have been employed to study the evolution of nitrogen associated defects in nitrogen irradiated metals: Fe, Ni, Mo and W. Nitrogen in these metals has a rather high affinity to vacancy type defects. The results obtained for low irradiation dose show that substitutional nitrogen (NV; with V=vacancy) is formed. The nitrogen vacancy complex dissociates at temperatures ranging from 350 K for Ni to 900K for Mo and 1100 K for W. At high doses defects are formed which can be characterized as nitrogen saturated vacancy clusters. These defects, as observed by helium probing, disappear during annealing for nickel at 800K, and for Mo at 1100 K. The direct observation of the desorbing nitrogen for nickel and molybdenum reveals a very fast desorption transient at the dissociation temperature of the clusters. This is the characteristic desorption transient of a small nitride cluster, e.g., by shrinkage with constant rate. For iron the nitrogen desorption is complicated because of a general background that continuously rises with temperature. With the positron beam technique depth information was obtained for defects in iron and the defect character could be established with the help of the information provided on annihilation with conduction and core electrons of the defect trapped positrons.
Irradiation-Induced Changes in the Mechanical Properties and Microstructures of Solution Annealed Austenitic Stainless Steel at Low to Intermediate Temperatures
Authors: Lucas G. E.
Published: April 2011

The evolution of the microstructure of solution annealed austenitic stainless steels irradiated by neutrons at temperatures less than 300°C is dominated by black spots and Frank loops. This leads to hardening and a degradation of ductility and work hardening accompanied by a loss of fracture toughness. Microscopic flow localization is attributed to the annihilation of loops by their interaction with moving dislocations. The resulting loss of work hardening can lead to flow localization on a macroscopic scale as well in the vicinity of notches, holes and cracks. The combination of macro and microscopic flow localization may have important implications to the failure modes available to structures and to irradiation-assisted stress corrosion cracking.
On the Composition and Structure of Nanoprecipitates in Irradiated Pressure Vessel Steels
Authors: Odette G. R. , Liu C. L. , Wirth B. D.
Published: April 2011

Nanoscale Cu rich precipitates (CRPs) are widely believed to be the dominant hardening feature resulting in severe embrittlement in irradiated reactor pressure vessel (RPV) steels. However, this view has recently been challenged by interpretations of atom probe field ion microscopy (APFIM) measurements that describe the dominant nanofeatures as dilute solute atmospheres (DSAs). The practical impact of these differing views is very significant. This work compares and contrasts the CRP versus DSA descriptions to a wide variety of pertinent data. Mechanical property trends as well as small angle neutron scattering (SANS) and field emission scanning transmission electron microscopy (FEGSTEM) measurements support the presence of CRPs. CRPs are also consistent with the fundamental thermodynamic and kinetic laws. However, standard theory cannot provide the atomic level resolution needed to fully understand the nanofeatures. Therefore, a new Lattice Monte Carlo (LMC) atomistic method is used to simulate the complex chemical structures of the CRPs. The LMC method unifies the SANS/FEGSTEM and APFIM data within a well founded physical framework.
Small Angle Neutron Scattering Modeling of Copper-Rich Precipitates in Steel
Authors: Spooner Stephen
Published: April 2011

The magnetic-to-nuclear scattering intensity ratio observed in the scattering from copper-rich precipitates in irradiated pressure vessel steels is much smaller than the value of 11.4 expected for a pure copper precipitate in iron. A model for precipitates in pressure vessel steels which matches the observed scattering typically incorporates manganese, nickel, silicon and other elements and it is assumed that the precipitate is non-magnetic. In the present work consideration is given to the effect of composition gradients and ferromagnetic penetration into the precipitate on the small angle scattering cross section for copper-rich clusters as distinquished from conventional precipitates. The calculation is an extension of a scattering model for micelles which consist of shells of varying scattering density. A discrepancy between recent SANS scattering experiments on pressure vessel stells was found to be related to applied magnetic field strength. The assumption of cluster structure and its relation to atom probe FIM findings as well as the effects of insufficient field for magnetic saturation is discussed.
Comparative Study on Intergranular Segregation of Sulfur and Phosphorus Induced During Neutron Irradiation And Thermal Ageing in Vanadium-20 WT.% Titanium Alloys
Authors: Bloomer T. E. , Lyu D. Y. , Kameda J.
Published: April 2011

Intergranular impurity segregation induced during neutron irradiation (9.8 × 1024 n/mr at 438 °C) and thermal ageing has been studied in V-20 wt.% Ti alloys undoped, P doped and S doped all containing residual C and O. Neutron irradiation induced intergranular segregation and desegregation of S in undoped and S doped alloys, respectively. Thermal ageing resulted in a large increase in the S segregation in the undoped and S doped alloys. However, all unirradiated, aged and irradiated P doped alloys showed negligible S segregation. The vanadium alloys had smaller P segregation, compared to the S segregation in the undoped and S doped alloys. The irradiation and ageing enhanced the P segregation in a different fashion depending on the alloys. The grain boundary enrichment of C, O and Ti was reduced during the irradiation but promoted by the thermal ageing. The underlying mechanisms controlling intergranular impurity segregation caused by irradiation or thermal ageing are discussed in light of the impurity solubility change and dynamic interaction of defect and impurity fluxes.
Radiation-Induced Minor Element Segregation at Austenitic Stainless Steel Grain Boundaries
Authors: Simonen E. P. , Bruemmer S. M.
Published: April 2011

Measurement of minor element compositions at irradiated grain boundaries in austenitic stainless steels indicates that Si is the only element that significantly responds to radiation-induced segregation. Other minor elements, such as P or S, do not exhibit elevated grain boundary concentrations after irradiation. A rate theory evaluation of segregation is in accord with ioninduced Si enrichment, but reveals complexities in the interpretation of extrapolating behavior from ion-irradiation to neutron-irradiation behavior. The model calibrated to measured high-rate, ioninduced segregation greatly overestimates measured low-rate, neutron-irradiation segregation of Si.
Radiation-Induced Segregation of Metals At Moving SiO2-Amorphous Si Interfaces
Authors: Williams J. S. , Petravic M. , Conway M. , Short K. T.
Published: April 2011

Secondary ion mass spectrometry and Rutherford backscattering/channeling analysis have been used to study the segregation of Au at moving Si-SiO2 interfaces during bombardment of Si with 15 keV O- ions. Essentially 100% of the Au is found to segregate at a bombardment temperature of 250°C, whereas only partial segregation occurs for room temperature bombardment. Up to 10 monolayers of Au can be segregated in disordered Si behind an SiO2 layer at 250°C. These results are discussed in terms of ion-assisted migration of Au in disordered Si and extremely low solubilities of Au in SiO2.
Threshold Irradiation Dose for Amorphization of Silicon Carbide
Authors: Snead L. L. , Zinkle S. J.
Published: April 2011

The amorphization of silicon carbide due to ion and electron irradiation is reviewed with emphasis on the temperature dependent critical dose for amorphization. The effect of ion mass and energy on the threshold dose for amorphization is summarized showing only a weak dependence near room temperature. Results are presented for 0.56 MeV silicon ions implanted into single crystal 6H-SiC as a function of temperature and ion dose. From this, the critical dose for amorphization is found as a function of temperature at depths well separated from the implanted ion region. Results are compared with published data generated using electron and xenon irradiating species. High resolution TEM analysis is presented for the Si ion series showing the evolution of elongated amorphous islands oriented such that their major axis is parallel to the free surface. This suggests that surface or strain effects may be influencing the apparent amorphization threshold. Finally, a model for the temperature threshold for amorphization is described using the Si ion irradiation flux and the fitted interstitial migration energy which was found to be ∼0.56 eV. This model successfully explains the difference in the temperature-dependent amorphization behavior of SiC irradiated with 0.56 MeV silicon ions at 1×10-3 dpa/s and with fission neutrons irradiated at 1×10-6 dpa/s irradiated to 1 5 dpa in the temperature range of ∼340 ±10K.
Hrtem of Extended Defects in Tl-2212 Thin Films
Authors: Newcomer P. P. , Venturini E. L. , Schöne H. , Doyle B. L. , Myers K. E.
Published: April 2011

Many applications of high temperature superconductors, HTS, require the presence of lattice defects in the material structure to suppress the motion of magnetic vortices and enhance the critical current density, Jc. The microstructure of Tl2Ba2CaCu2O8-δ (T1–2212) thin films which have extended defects induced by high energy Au and Cu ion irradiation is studied using high resolution transmission electron microscopy, HRTEM, with slow scan digital imaging. In order to optimize the HTS properties and better analyze the consequent microstructural modification, the fluence is varied. At moderate fluences, resulting in ∼4% reduction of the superconducting transition, large enhancements of Jc, and vortex pinning potential are observed. The density and microstructure of isolated defects and surrounding structure will be discussed and compared to damage profiles calculated using the TRIM code. Correlation will be made between the HRTEM results and the changes in HTS properties.
Effects of Interstitial Clustering on Transient Enhanced Diffusion of Boron in Silicon
Authors: Solmi S. , Valmorri S.
Published: April 2011

A simulation model for Boron diffusion which takes into account the aggregation of the excess interstitials in clusters, and subsequently, the dissolution of these defects, is proposed. The interstitial supersaturation and generation rate are determined according to the classical theory of nucleation and growth of particles, in analogy with the precipitation of a new phase in heavily doped silicon. The clusters are considered as precipitates formed by interstitial Si atoms. The B diffusion is modelled on the basis of the dopant-interstitial pair diffusion mechanism. The clusters dissolution during annealing maintains nearly constant, for a long period, the interstitial supersaturation and the related enhancement of the boron diffusion. This gives a good account of the diffusion results over a large range of experimental conditions. Furthermore, this approach describes most of the behavior of the transient enhanced diffusion (TED), like the temperature dependence of the level of the B diffusion enhancement, the dependence of the duration of the phenomenon on implanted dose, and the scarce dependence on the damage distribution in depth. The results of the simulations are compared with experimental data on the kinetics of interstitial cluster dissolution and of B TED.
Particle - Induced and Photo - Conductivities in Amorphous Si:H Under Proton Irradiation
Authors: Kishimoto N. , Amekura H. , Kono K. , Saito T.
Published: April 2011

Radiation damage of amorphous Si (a- Si) under 17 MeV- proton bombardment has been studied, measuring particle- induced conductivity(PIC) and photoconductivity(PC). The in- situ measurements have been conducted to focus on the structural flexibility and the metastable nature, inherent in the amorphous structure. While the PC (with weak illumination) has a fast response and reversible nature, the PIC has a long time- constant ∼60 s, followed by a persistent conductivity for more than ∼103 s. Both the PIC and the PC remain fairly stable against further irradiation, comparing to crystalline Si (c-Si), but they decay in the higher fluence region. A large part of the decayed PC recovers after annealing at 450 K. The results of a- Si are compared with those of c- Si. It is suggested that, in the lower fluence region, a-Si is more resistant against proton irradiation than c- Si, relaxing the atomic displacements, and the excited conductivities gradually decay with accumulation of the dangling bonds.
1.8 MeV Electron Bombardment Induced Structural Changes on Graphite Surfaces Observed by Scanning Tunnelling Microscopy
Authors: Chen Y. J. , Wilson I. H. , Libin Lin , Xu J. B.
Published: April 2011

Highly oriented pyrolitic graphite (HOPG) was irradiated with 1.8 MeV electrons at 45° and near grazing (86°) angles of incidence. For doses up to 1016 cm−2 the surface for the case of 45° incidence, observed by scanning tunnelling microscopy (STM), remained the same as the original sample showing only the usual periodic atomic corrugation. For near grazing incidence, at a dose of 5×10−2 cm−2, nm-hillocks are observed, some elongated along the direction of the beam incidence. These are attributed to the effects of single electron-carbon interactions in the top surface layers. At a dose of 5×1014 cm−2 (near grazing incidence) STM observations show an anomalously large (period 2.5 to 17 nm) superperiodicity superimposed on the normal 0.246 nm atomic spacing of graphite. This Moiré-like pattern suggests that the corrugations are electronic as well as topographic in origin. We propose that near grazing incidence electron irradiation causes a break-up of the surface layers into fragments, largely retaining the six-fold atomic rings, that rotate by a small angle resulting in the observed pattern by interaction with the deeper bulkstructure layers.
Ion Beam Injected Point Defects in Crystalline Silicon: Migration, Interaction and Trapping Phenomena
Authors: Priolo F. , Privitera V. , Coffa S. , Libertino S.
Published: April 2011

Our recent work on the room temperature migration and trapping phenomena of ion beam generated point defects in crystalline Si is reviewed. It is shown that a small fraction (˜10−6) of the defects generated at the surface by a shallow implant is injected into the bulk. These defects undergo a long range trap-limited diffusion and interact with both impurities, dopants and preexisting defects along their path. In particular, these interactions result in dopant deactivation and/or partial annihilation of pre-existing vacancy-type defect markers. It is found that in highly pure, epitaxial Si layers, these effects extend to several microns from the surface, demonstrating a long range migration of point defects at room temperature. By a detailed analysis of the experimental evidences we have identified the Si self-interstitials as the major responsible for the observed phenomena. This allowed us to give a lower limit of 6 × 10−11 cm2/s for the room temperature diffusion coefficient of the Si self-interstitials. Room temperature trap-limited migration of vacancies is also detected as a broadening in the divacancy profile of as implanted samples. In this case the room temperature diffusion coefficient of vacancies has been found to be ≥3 × 10−12 cm2/s. These data are presented and their implications discussed.
A New Single-Crystal Adsorption Calorimeter for Determining Metal Adsorption and Adhesion Energies
Authors: Stuckless J. T. , Starr D. , Bald D. , Campbell Charles T.
Published: April 2011

A microcalorimeter for measuring adsorption heats on clean single-crystal surfaces is described. The principle is similar to that pioneered by David King's group: A pulse of gas from a molecular beam adsorbs on an ultrathin single crystal's surface, causing a measurable transient heat input and temperature rise. Our novel heat detector is a 9 μm pyroelectric polymer ribbon, which is mechanically driven to make a gentle mechanical/thermal contact to the back of the singlecrystal sample during measurements. Advantages include use of thicker samples (>3 microns), sample preparation at very high temperatures, and measurements at 100 K. We have applied this to study the heats of adsorption of metals on clean, well-defined and single-crystalline oxide surfaces as a detailed function of coverage, from which we also extract the metal/oxide adhesion energy. We obtain pulse-to-pulse standard deviations of >2% for pulses containing >0.03 ML of Cu, and absolute accuracy within a few percent.
Micromechanical Deformation of Single-Crystal Alumina Surfaces
Authors: Zagrebelny Andrey V. , Nelson John C. , Carter C. Barry
Published: April 2011

In the present study, the micromechanical properties of single-crystal A12O3 have been tested using a micromechanical depth-sensing testing device. A series of microscratches are produced on the annealed {0001}, {1120} sapphire specimens of special geometry. The scratches were positioned in pre-selected crystallographic directions, determined with the backreflection Laue method X-ray diffraction method.

The microscratch tracks were examined with transmission electron microscopy (TEM). The main emphasis in the analysis of deformation structure of sapphire has been placed on the correlation of irregularities observed on load-displacement curves to the extent of elastically deformed regions, nucleation of the dislocations on the surface, unique nature of the crack-dislocation networks associated the sapphire anisotropic deformation behavior.
Relating Polymer Indentation Behavior to Elastic Modulus Using Atomic Force Microscopy
Authors: Vanlandingham M. R. , Mcknight S. H. , Palmese G. R. , Eduljee R. F. , Gillespie J. W. , Mccullough R. L.
Published: April 2011

The atomic force microscope (AFM) has become a popular tool for characterizing surfaces of many different types of materials. In this paper, an AFM is used to probe the mechanical properties of polymer samples through examination of force curves produced during tip-sample contact and indentation. Three types of cantilever probes with spring constants estimated to be 1–5 N/m, 20–100 N/m, and 400–500 N/m respectively, were used to study different polymer samples with known modulus values ranging from 20 MPa to 3 GPa. A technique is developed that relates the measured sample response to elastic modulus, and illuminates the importance of the relative stiffnesses of the cantilever probe and the sample to the material response.
Deformation of Polymer Films by Bending Forces
Authors: Heermann D.W. , Linke A. , Pätzold G. , Hapke T.
Published: April 2011

We study the deformation of nano-scale polymer films which are subject to external bending forces by means of computer simulation. The polymer is represented by a generalized bead-spring-model, intended to reproduce characteristic features of n-alkanes. The film is loaded by the action of a prismatic blade which is pressed into the polymer bulk from above and a pair of columns which support the film from below. The interaction between blade and support columns and the polymer is modeled by the repulsive part of a Lennard-Jones potential. For different system sizes as well as for different chain lengths, this nano-scale experiment is simulated by molecular dynamics methods. Our results allow us to give a characterization of deformed states for such films. We resolve the kinetic and the dynamic stage of the deformation process in time and access the length scale between discrete particle and continuum mechanics behavior. For the chain lengths considered here, we find that the deformation process is dominated by shear.
Surface Morphology of Ingap in the Ai-Free Pump Ld
Authors: Choo Ahn Goo , Kim Seong Heon , Kim Nam Heon , Laboutine Oleg , Yu Joon Sang , Kim Tae Il
Published: April 2011

We have studied the effects of growth parameters and substrate orientations on InGaP quality using Normarski microscopy, photoluminescence (PL) spectrum and atomic force microscopy (AFM). The full width at half maximum (FWHNM) and peak position of PL spectrum were closely related with the surface morphology. The InGaP layers of narrower FWHM and shorter peak wavelength had smoother surface morphology. The InGaP layers grown on (100) substrates at the moderately low reactor pressure showed rougher surface than those on the tilted substrates. But the surface morphology was noticeably improved to be mirror-like at the lower reactor pressure. The surface morphology was inverted between the exact and tilted substrates in this reactor pressure. Furthermore, the samples grown on the tilted substrate exhibited rougher surface than the samples grown on the exact substrate. (111)B-misoriented growth surfaces had smoother than (111)A-misoriented surfaces.
Structural and Electrical Properties of Ni/Co Superlattices Using Pb as a Surfactant
Authors: Iwanami M. , Furukawa R. , Matsumoto T. , Kamiko M. , Yamamoto R.
Published: April 2011

To obtain informations about the correlation between structure and electrical property in metallic multilayers, we have fabricated Ni/Co superlattices with and without Pb as a surfactant by molecular beam epitaxy. From the observations of RHEED and x-ray diffraction patterns, we confirmed that the surfaces of Ni/Co superlattices with Pb are flatter and the interfaces are sharper than one without Pb, which means that Pb operates as an effective surfactant.We have investigated the electrical properties of superlattices by measuring magnetoresistance. The initial change of resistance with magnetic field from 0 to 1 kOe was larger for the superlattices with a surfactant, while once magnetic field was applied, the effect of a surfactant to resistivity change was not observed. This suggests that Pb also changes the initial magenetic domain structure and the magnetotransport property of Ni/Co superlattice is not sensitive to interface structure.
Skewed Height Distributions of Kinetically Roughened Films
Authors: Kleban P. , Krim J. , Ruffing C.
Published: April 2011

We examine height distribution functions (height histograms) of kinetically roughened metal films, making use of STM data for vapor-deposited Ag on quartz. The height distribution of the raw data is Gaussian to quite high accuracy. However, if one averages each height over a region of length scale L, the resulting distributions deviate increasingly from Gaussian behavior, becoming skewed as L increases. We quantified this behavior by means of moments of the distribution; with increasing L a non-negligible third moment appears. The responsible morphology is minima that tend to form steep valleys or deep pits while the corresponding (at the same height above the average) maxima tend to form rounded hilltops. Skewed height distributions have been predicted on the basis of model calculations, but not previously observed to our knowledge.
Evolution of Interfacial Roughness Correlations of Fe Au Films Grown on Mgo(001) Substrates
Authors: Chow P. C. , Paniago R. , Forrest R. , Moss S. C. , Parkin S. S. P. , Cookson D.
Published: April 2011

The growth by sputtering of a series of thin films of Fe/Au on MgO(001) substrates was analyzed using Bragg and diffuse X-ray scattering. The Fe (bcc) layer grows rotated by 45° with respect to the MgO – Au(fcc) (001) epitaxial orientation, resulting in an almost perfect match between the two metallic structures. By collecting the X-ray diffuse scattering under grazing incidence using a 2-dimensional image plate detector, we mapped the reciprocal space of these films. We characterized the correlated interface roughness starting with a buffer of Fe in which only three interfaces are present. The propagation of the roughness was subsequently characterized for Fe/Au multilayers with 40 and 100 bilayers. We observe an enlargement of the surface features as a function of time, evidenced by the longer lateral cutoff length measured for thicker films.
Autocorrelation Function and Roughness Spectrum of a Growing Film Surface
Authors: Trofimov V. I.
Published: April 2011

Recently we developed a method that allows to derive a height-height autocorrelation function (ACF) for a randomly rough surface of a thin – film growing by the 3D island mechanism. In this paper, the ACF and roughness spectrum for several versions of the island growth model deduced by this method are presented and discussed. In the model dimension d=1+1 the ACFs are deduced in exact analytical form, and for d=2+1 the ACF' s are calculated numerically. In both model dimensions for the rms roughness the universal analytical expression connecting its with physical deposition parameters is derived. The impact of the growth hillock shape and the hillock space distribution are studied. It is shown that the ACF form is determined by the hillock space distribution and in the cases of an ideally random Poisson distribution and slightly ordered distribution the ACF is nearly gaussian although the surface profile height distribution is non-gaussian. The rms roughness is strongly dependent on the hillock shape while the autocorrelation length is determined by the hillock number density. The theoretical predictions are compared with published TEM and STM-data and the scaling behaviour of the rms roughness is analysed.