bluuebunny/crossref_metadata_2025 huggingface dataset:
Elastic Constants and Coefficients of Thermal Expansion of Laves Phase Cr2X (X=Hf, Nb, Ta, Zr) Alloys
Authors: Hong Suklyun , Fu C. L.
Published: April 2011

To examine the effect of thermal expansion mismatch on cracking in two-phase Cr-Cr2X (X=Hf, Nb, Ta, Zr) alloys, we calculate the elastic constants and associated elastic anharmonicity by the local-density-functional approach from which the coefficients of thermal expansion (CTEs) of Cr and Cr2X are determined. The calculation shows that the CTE of Cr at high temperatures is notably larger than those of Cr2X. If the difference in CTE between Cr and Cr 2X is a primary source of crack initiation, our results fail to explain the experimental observation that, among Cr-Cr2X alloy systems, the ingot cracking occurs mainly in Cr-Cr2Nb. We suggest that for the cracking to occur, thermal mismatch stresses are retained by a hard and supersaturated Cr matrix (e.g., due to the relatively high solubility of Nb in Cr in the case of Cr-Cr2Nb). On the other hand, a soft Cr matrix can accommodate the thermal misfit dislocations plastically even when the CTE difference between Cr and Cr2X is large (e.g., in the case of Cr-Cr2Zr).
Microstructural Stability Of a NiAI-Mo Eutectic Alloy
Authors: Kush M. T. , Holmes J. W. , Gibala R.
Published: April 2011

The microstructural stability of a directionally-solidified NiA1–9 at.% Mo quasi-binary alloy was investigated under conditions of thermal cycling between the temperatures 973 K and 1473 K utilizing time-temperature heating and cooling profiles which approximate potential engine applications. Two different microstructures were examined: a cellular microstructure in which the faceted secondphase Mo rods in the NiAl matrix formed misaligned cell boundaries which separated aligned cells approximately 0.4 mm in width and 5–25 mm in length, and a nearly fault-free fully columnar microstructure well aligned along the [001] direction. Both microstructures resisted coarsening under thermal cycling, but plastic deformation induced by thermal stresses introduced significant specimen shape changes. Surprisingly, the cellular microstructure, for which the cell boundary region apparently acts as a deformation buffer, exhibited better resistance to thermal fatigue than the more fault-free and better aligned columnar microstructure.
Structural Studies Of Al55 Si7Cu25.5 Fe12.5 1/1-Cubic Approximant By Means Of X-Ray Rietveld, Method And Haadf-Stem
Authors: Yamada H. , Takeuchi T. , Mizutani U. , Tanaka N.
Published: April 2011

By combining the powdered x-ray Rietveld analysis and the High Angle Annular Dark Field Scanning Transmission Electron Microscopy (HAADF-STEM), we have made the detailed structural analysis for the Mackay-type Al55Si7Cu25.5Fe12.5, 1/1-cubic approximant. Electron diffraction measurements revealed its space group to be Pni3. Both position and occupancy in every atomic site are refined by means of the Rietveld analysis. The factors Rwp and Riwhich are taken as measures for the precision of the Rietveld analysis, are reduced to 2.57 and 3.89 %, respectively. The refined structure of this approximant is a simple cubic with the lattice constant of 12.31916(2) Å. Two different icosahedral clusters consisting of triply stacked atomic shells exist at the vertex and body centered positions in the CsCl-type unit cell. In addition, we propose that there exists most likely a “structural disorder” in the first shell of the cluster in one of the sublattices. The HAADF images taken along [100] and [111] directions agree with the projection images calculated from the Rietveld-refined structure, lending a strong support to the validity of the present atomic structure model deduced from the Rietveld analysis.
Interfaces In Quasicrystalline Systems
Authors: Divakar R , Sundararaman D , Ranganathan S
Published: April 2011

Structural relations between quasicrystalline and related crystalline rational approximant phases have been of interest for some time now. Such relations are now being used to understand interface structures. Interfaces between structural motif - wise related, but dissimilarly periodic phases are expected to show a degree of lattice match in certain directions. Our earlier studies in the Al-Cu-Fe system using the HREM technique has shown this to be true. The structural difference leads to well defined structural ledges in the interface between the icosahedral Al-Cu-Fe phase and the monoclinic Al13Fe4 type phase. In the present paper we report our results on the HREM study of interfaces in Al-Cu-Fe and Al-Pd-Mn systems. The emphasis will be on heterophase interfaces between quasiperiodic and periodic phases, where the two are structurally related. An attempt will be made to correlate the results with calculated lattice projections of the two structures on the grain boundary plane.
Surface Characteristics Of Quasicrystalline Materials: An Overview Of Work Conducted At Ames Laboratory
Authors: Jenks C. J.
Published: April 2011

Over the last few years, work in our laboratories in Ames has focussed on elucidating the surface characteristics of Al-based quasicrystalline materials, namely icosahedral (i-) Al-Cu-Fe and i-Al-Pd-Mn. Our work involves the study of the clean surfaces of these materials under ultrahigh vacuum conditions. We find that surfaces cleaned by Ar+ sputtering are depleted in Al relative to the bulk composition. Single grains, after sputtering, undergo a two-stage regrowth process as they are annealed. After heating to about 600 K, a crystalline overlayer is formed. This is rather abruptly replaced at about 750 K by a surface that appears quasicrystalline within the resolution of the experimental techniques used. Calculations based on low-energy electron diffraction (LEED) measurements of this higher temperature state indicate that the Al-rich layers in the bulk model of these materials are the favored surface terminations. Results of low-energy ion scattering (LEIS) corroborate this finding. Consistent with this, we find that the oxidation behavior and general reactivity of these materials are analogous to pure Al.
Metal-Insulator Transitionlike Behavior In Several Icosahedral Phases
Authors: Poon S. J. , Zavaliche F. , Beeli C.
Published: April 2011

The highly non-metallic electron transport properties in icosahedral Al70.5Pd21(Re,Mn)8.5 phases and their dependence on alloy composition and sample preparation are reviewed and fuirther studied. The study has led to the highest resistivity ratios ρ(4.2K)/ρ(295K)˜280 reported so far on i-AIPdRe alloys. Similar investigation has also resulted in enhanced resistivity ratios in i-AlCuOs. Evidences for the metal-insulator transition in these i-alloys are documented and discussed in light of the new results. Electron diffraction studies (article by Beeli, Poon, Guo, and Haussler in this Conference Proceedings) have provided evidence for electron localization induced by phason disorder. These findings may provide the basis for understanding the nature of electronic states and effects of disorder on electron localization in quasiperiodic systems.
Dielectric Relaxation in Filled Nematic Liquid Crystals
Authors: Sinha G.P. , Kreuzer M. , Aliev F.M.
Published: April 2011

Nematic liquid crystals filled with Aerosil particles are new heterogeneous materials important for different optoelectronic applications. These materials are suspensions of small silica particles, about 10-17 nm in diameter, dispersed in nematic liquid crystals. The particles are known to form a network structure dividing liquid crystal into domains with linear size approximately 250 nm. We used both hydrophilic and hydrophobic particles, filling them with the nematic liquid crystal-5CB.

Broad band dielectric spectroscopy (1 mHz - 1.5 GHz) was applied for the investigation of these materials. Two bulk-like modes due to the rotation of molecules around the short axis and the tumbling motion were observed in filled 5CB. Additionally, a low frequency relaxation process and the dispersion of dielectric permittivity due to conductivity were also observed. The modification of the surface of the particles has stronger influence on the slow process and is less important for the molecular modes. The contribution of the slow process for the hydrophilic sample to the total polarization is greater than for the hydrophobic sample. In addition, the corresponding characteristic frequencies are lower for the case of hydrophilic samples. These facts suggest that the low frequency relaxation is an Aerosil particle-liquid crystal interface related phenomena and the origin of this process maybe explained on the basis of surface induced polarization.
Interface Governed Magnetostriction in Ultra Thin CoFe and Fe Films
Authors: Mattheis R. , Langer J. , Senz S. , Berg H. A. M van den
Published: April 2011

Two different types of polycrystalline films, films with low (Fe) and films with high (Co50Fe50) saturation magnetostriction λs, were sandwiched between Cu to study the thickness dependence of λs in Cu/X/Cu systems. We utilised a new method (ROTMOKE) for a high accurate Hk determination. The values for X, were determined by analysing the change of Hk during application of compressive and tensile stress by cylindrical bending of the substrate joint with the film. For both systems, a remarkable contribution of the interface to the λs, was found. The sign of the interface contribution is opposed to the sign of bulk λs, leading to a zero transition of λs., For Fe this transition occurs at a thickness of 5 nm whereas for the CoFe film with a strong λs, value of the bulk of around 80 · 10−6 a transition was extrapolated at a thickness around 1 nm.
An In-Situ Study of the Segregation and the Strain Relaxation During Growth of Gold and Nickel Ultrathin Films
Authors: Labat S. , Gergaud P. , Thomas O. , Gilles B. , Marty A.
Published: April 2011

We report on in-situ real time measurement of both stress and strain during growth of ultrathin layers, with submonolayer sensitivity. The in-plane parameter is measured by Reflection High Energy Electron Diffraction (RHEED) and the stress is determined via the measurement of the curvature. The system studied is Au/Ni (i.e. Au on Ni and Ni on Au). We have evidenced a large asymmetry in the two different growths: Au (on Ni) shows a progressive elastic strain relaxation whereas Ni (on Au) exhibits a strong interplay between the stress and the interfacial mixing.
Effect of ultra-thin Cu underlayer on the magnetic properties of Ni80Fe50 / Fe50Mn50 films
Authors: Liu C. , Shen L. , Jiang H. , Yang D. , Wu G. , Alexander C. , Mankey G. J.
Published: April 2011

The Ni80Fe20/Fe50Mn50,thin film system exhibits exchange bias behavior. Here a systematic study of the effect of atomic-scale thin film roughness on coercivity and exchange bias is presented. Cu (t) / Ta (100 Å) / Ni80Fe20 (100 Å) / Fe50Mno50 (200 Å) / Ta (200 Å) with variable thickness, t, of the Cu underlayer were DC sputtered on Si (100) substrates. The Cu underlayer defines the initial roughness that is transferred to the film material since the film grows conformal to the initial morphology. Atomic Force Microscopy and X-ray diffraction were used to study the morphology and texture of the films. Morphological characterization is then correlated with magnetometer measurements. Atomic Force Microscopy shows that the root mean square value of the film roughness exhibits a maximum of 2.5 Å at t = 2.4 Å. X-ray diffraction spectra show the films are polycrystalline with fcc (111) texture and the Fe50Mn50 (111) peak intensity decreases monotonically with increasing Cu thickness, t. Without a Cu underlayer, the values of the coercivity and loop shift are, Hc = 12 Oe and Hp = 56 Oe, respectively. Both the coercivity and loop shift change with Cu underlayer thickness. The coercivity reaches a maximum value of Hc= 36 Oe at t = 4 Å. The loop shift exhibits an initial increase with t, reaches a maximum value of HP = 107 Oe at t = 2.4 Å, followed by a decrease with greater Cu thickness. These results show that a tiny increase in the film roughness has a huge effect on the exchange bias magnitude.
Surfactant Based Alumina Slurries for Copper CMP
Authors: Babel Ashok K , Mackay Raymond A.
Published: April 2011

The polishing of copper and examination of the polished surfaces were carried out with surfactant based alumina slurries to yield interesting results. Contrary to our expectation and previously reported research, some of the surfactant based alumina slurries resulted in higher copper polish rates when compared to the control. Of the nonionic surfactants, BrijR 35 was overall the most effective in both acidic and basic media. Ionics were effective at the pH for the appropriate charge type. For the range of surfactants studied, polish rates correlated with the HLB of the nonionic surfactants. The Hydrophile-Lipophile Balance (HLB) is related to the solubility of the surfactant, with higher number corresponding to increased water dispersibility. The surfactant BrijR 35, with the nonionic composition polyoxyethylene(23) lauryl ether, resulted in a dramatic improvement in the average surface uniformity when compared with the control at pH 2, and Sodium Dodecyl Sulfate produced even greater uniformity. Additionally, the effect of BrijR 35 surfactant was maintained with change in abrasive size, pad and polishing tool. In order to insure that surfactants are compatible with the chemical reagents contained in the commercial slurries, two chemistries (ferric nitrate and hydrogen peroxide) were employed to test the efficiency of the selected surfactants in their presence. The results showed that the effect of surfactant on stability and removal rate is not influenced by the presence of the chemicals. Preliminary results indicate that surfactants can have a beneficial effect on both defects and post polish clean.
Post-CMP Megasonic Cleaning Using Dilute SCI Solution
Authors: Busnaina A. A. , Moumen N. , Piboontum J. , Guarrera M.
Published: April 2011

Non contact cleaning or wet-cleaning processes, were the megasonic play a key role in the separation of the particles from the wafer is a commonly used technique in semiconductor manufacturing. CMP process can be very damaging to the production yield if not followed by an effective post clean process. McQueen identified the effect of the acoustic boundary layer and its role in the removal of small particles at high frequency. Busnaina et alt studied ultrasonic and megasonic particle removal and the effect of acoustic streaming. They showed that the cleaning efficiency increased with power until a certain range and then decrease slightly. Busnaina et al result indicted that SCI removes more particles than DI water particularly at lower megasonic powers specially in the case were the slurry particles are deposited onto the wafer surface by dipping experiments. But they also demonstrated that it was possible to achieve 100 % removal in DI water when using the optimum conditions. This paper presents the latest results of the post-CMP megasonic cleaning process, this study is focused on the cleaning of thermal oxide silicone wafer polished using silica based slurry and cleaned using diluted SC1 (H20/H202/NH4OH: 40/2/1).
Capturing Properties of Two-Fold Coordinated Nitrogen Atom in Silicon Oxynitride
Authors: Novikov YU.N. , Morokov YU.N. , Gritsenko V.A. , Xu J.B.
Published: April 2011

Electronic structure of two-fold coordinated nitrogen atom ≡Si2N• in Si3N4 and SiOxNy is studied in different charged states by the semiempirical quantum-chemical method MINDO/3 taking into account an atomic relaxation. It is shown theoretically that the neutral paramagnetic defect ≡Si2N• captures an electron, therefore it is an electron trap in Si3N4 and SiOxNy. The calculations show that the capturing of hole by the ≡Si2N• defect can be energetically favorable only for large oxygen concentration in oxynitride. It is predicted that the electron localization by the ≡Si2N• defect will result in the ESR signal disappearance.
Enhanced Degradation in P+-Poly PMOSFETs With Oxynitride Gate Dielectrics Under Hot-Hole Injection
Authors: Chen Y. Y. , Gardner M. , Fulford J. , Wristers D. , Joshi A. B. , Kwong D. L.
Published: April 2011

In this paper, a significant degradation under hot hole injection is observed in P+ -poly PMOSFETs with oxynitride gate dielectrics. In our study, both oxynitrides formed by gate oxide grown on Nitrogen Implanted Si Substrates (NISS) and NO-annealed SiO2 oxynitride gate dielectrics are used and compared to control SiO2 gate dielectrics of identical thicknesses. A physical model responsible for such enhanced degradation in PMOSFETs with oxynitride gate dielectric is proposed. It is shown that the hole injection barrier lowering as a result of the nitrogen-rich layer at the SiO2/Si interface in oxynitride is responsible for such enhanced degradation.
Ultra Thin High Quality Ta2O5 Gate Dielectrics Prepared by In-situ Rapid Thermal Processing
Authors: Luan H. F. , Lee S. J. , Lee C. H. , Mao A. Y. , Vrtis R. , Roberts D. , Kwong D. L.
Published: April 2011

In this paper, ultra thin CVD Ta2O5 stacked gate dielectrics (Teq∼14Å-22Å) was fabricated by in-situ RTP processing. The leakage current of Ta2O5 devices is 103× lower leakage current compared to SiO2 of identical thickness for devices with Teq between 18Å-22Å. While Teq<18Å, the leakage current follows same train and J∼10−3A/cm2 for Ta2O5 stacked gate dielectrics with Teq=14Å. Superior interface properties and reliability have been obtained.
The Influence of Fluorine on Various Mos Devices
Authors: Innertsberger G. , Jurk R. , Felsner J. , Kakoschke R. , Yuwono B. , Schlösser T. , Krautschneider W. , Gschwandtner A.
Published: April 2011

The influence of Vapor Phase Precleans leads to a different controllable fluorine content within the subsequently grown dielectric. The influence of the clean is discussed for non-volatile memory devices, advanced MOS transistors and ultra thin gate dielectrics. On the one hand, the Qbd values for in situ cleaned samples are lower than for wet cleaned samples. Performing cycle stress on the EEPROM devices, the tunnel oxide (7.5nm) degrades the quicker with the increase in fluorine concentration within the oxide. On the other hand, MOS transistor characteristics show a significant improvement on the negative bias temperature instability (NBTI) in the PMOS threshold voltage. MOS transistors with ultra thin gate dielectrics (1.5nm) show the expected significant increase of the saturation current compared with 0.35µm technology (tox = 7.5nm). Excellent times until soft breakdown for ultra thin dielectrics are found when the in situ cleaning is used.
High Quality Ultra Thin CVD Si3N4Gate Dielectrics Fabricated By Rapid Thermal Process
Authors: Song S. C. , Luan H. F. , Gardner M. , Fulford J. , Allen M. , Kwong D. L.
Published: April 2011

In this paper, we report performance and reliability of CMOS devices with ultra thin (<20Å) Si3N4gate dielectric fabricated by in-situ rapid thermal CVD (RTCVD) process, and compare with control SiO2devices of identical equivalent oxide thickness (Tox,eq). Ultra thin CVD Si3N4 devices show significantly lower gate leakage current, complete suppression of boron penetration, improved MOSFET performance, and enhanced reliability against electrical stress.
Interface Interstitial Recombination Rate and the Reverse Short Channel Effect
Authors: Rubin M.E. , Saha S. , Lutze J. , Nouri F. , Scott G. , Pramanik D.
Published: April 2011

Experiment shows that the reverse short channel effect (RSCE) in nMOS devices is critically impacted by the inclusion of nitrogen in the gate oxide. A higher concentration of nitrogen results in a lessened RSCE, i.e. more threshold voltage rolloff for smaller gate lengths. We propose that the additional nitrogen reduces the interstitial recombination rate at the interface, resulting in a smaller interstitial flux and therefore less transient enhanced diffusion (TED) of boron to that interface. To test this hypothesis, we simulate boron redistribution in one and two dimensional MOS capacitor structures, as well as full nMOS devices. We then present simulations calibrated to a 0.2 pim technology currently in production.
Mechanical Stress Characterization of Shallow Trench Isolation by Kelvin Probe Force Microscopy
Authors: Rueda Hernan , Slinkman James , Chidambarrao Dureseti , Moszkowicz Leon , Kaszuba Phil , Law Mark
Published: April 2011

method for characterizing the mechanical stress induced in silicon technology is described. Analysis by scanning Kelvin probe force microscopy (SKPM) coupled with finite-element (FE) mechanical strain simulations is performed. The SKPM technique detects variations in the semiconductor work function due to strain influences on the band gap. This technique is then used to analyze the strain induced by shallow trench isolation processes for electrical isolation. The SKPM measurements agree with the FE simulations qualitatively.
Estimation of the Number of Injected Interstitial Atoms during Nitrous Oxidation of Silicon
Authors: Skarlatos D. , Giles L.F. , Tsamis C. , Claverie A. , Tsoukalas D.
Published: April 2011

In this work we use dislocation loops to monitor the interstitial injection during the oxynitridation (oxidation in 100% N2O ambient) of silicon at low temperatures (850–950 °C). The interstitials captured by the loops are measured using Transmission Electron Microscopy. The number of Si atoms released after oxynitridation was calculated from the difference in the total amount of atoms stored in the loops between oxidizing and inert ambient. We obtained that this number is larger compared with the respective under the same dry oxidation (in 100% O2 ambient) conditions.
Onset of Extended Defect Formation and Enhanced Diffusion for Ultra-Low Energy Boron Implants
Authors: Liu Jinning , Jones Kevin S. , Downey Daniel F. , Mehta Sandeep
Published: April 2011

To meet the challenge of achieving ultra shallow p+/n source/drain extension junctions for 0.1 Oim node devices, ultra low energy boron implant and advanced annealing techniques have been explored. In this paper, we report the extended defect and boron diffusion behavior with various implant and annealing conditions. Boron implants were performed at energies from 0.25keV to lkeV and doses of 5 × 1014 cm−2 and 1 × 1015cm−2. Subsequent anneals were carried out in nitrogen ambient. The effect of energy, dose and oxide capping on extended defect formation and enhanced dopant diffusion was examined. It was observed that a thin screen oxide layer (35Å), grown prior to implantation, reduces the concentration of dopant in the Si by a significant amount as expected. This oxide also reduces the dislocation loops in the lattice and lowers diffusion enhancement of the dopant during annealing. The final junction depth can be optimized by using a low thermal budget spike anneal in a controlled oxygen ambient.
In-situ real time studies of nickel silicide formation
Authors: Tinani M. , Irene E.A. , Hu Y.Z. , Tay S.P.
Published: April 2011

NiSi, with its low resistivity and wide processing window (350 - 750°C), is an attractive candidate for use as a gate contact material. In order to follow the interface reaction that leads to the formation of NiSi in real time, ellipsometry and atomic force microscopy (AFM) were used to study changes on the surface resulting from the reaction between Ni and Si for various times and temperatures, and Rutherford Backscattering spectrometry (RBS) to determine compositional changes in the forming silicides. We report that ellipsometry can be used to monitor the various Ni-Si phases forming in real time, and we have observed agglomeration of the silicide, which has been reported to occur at 1000°C, at temperatures, as low as 550°C for long time anneals.
Remote True Temperature Pyrometry of Si Wafers: Theoretical and Practical Considerations
Authors: Glazman E. , Glazman A. , Thon A.
Published: April 2011

The problems of real thermodynamic temperature measurement in semiconductor processing can be divided into fundamental and environmental. The first type arises from a-priori unknown and in process changing optical properties (emissivity) of the target wafer. Others have to do with the need to eliminate direct and indirect stray heat flux from entering into the sensor. We describe the advantages and pitfalls of various (passive and active) remote measurement methods. Experimental results of a novel emissivity independent technique for real time measurement in the range of 450–850°C with accuracy better than 1% for wafer emissivity in the range of 0.2 to 0.95 are given.
An Appreciation of Dave Turnbull
Authors: Cohen Morrel H.
Published: April 2011

Dave, Carol, Mr. Chairman and assembled colleagues and friends, we are here at this symposium to honor Dave Turnbull in his 70th year for his qualities as a human being and his achievements and contributions as a scientist and as a teacher.
Ordering Kinetics and Diffusion in Some L12Alloys
Authors: Cahn Robert W.
Published: April 2011

A comparison is made of, ordering kinetics for Cu3Au, (Tc= 388 ° C), Ni3Mn (Tc= 500° C) Ni3Fe (Tc= 517°C) and Ni3Al (Tc= 1450 ° C), which all form the L12superlattice, and these kinetics are correlated with diffusion data for the same alloys. Comparing different alloys, it is shown that for a fixed relaxation time for the establishment of order, the lower is the self-diffusivity, Ds, of the slowest-diffusing species, the higher the critical temperature, Tc, for the first appearance of order. Ni3A1, in particular, has an estimated Dsof about 5 orders of magnitude lower, on average, than the three other alloys. The implications of this inverse relation between Tcand Dsare discussed in relation to published models for diffusion in ordered alloys and ordering kinetics.
Neutron-Induced Vaporization of Superheated Liquids: Theory and Experiment
Authors: Apfel Robert E.
Published: April 2011

My interest in neutron-induced nucleation began with a simple and elegant demonstration in one of David Turnbull's classes in which a drop of water was superheated to about 250°C as it rose in a column of heated oil. As David Glaser, the inventor of the bubble chamber, so ably demonstrated, such superheated liquids are radiation sensitive. Our test system is a simple one. Halocarbon and hydrQcarbon drops are introduced into an aqueous holding gel under pressure at room temperature. As the pressure is released, the drops become superheated. Neutrons of sufficient energy will trigger vaporization of these moderately superheated drop detectors (SSDs), but gammas and x-rays will not unless the homogeneous nucleation limit is approached. We have performed measurements on the neutron energy threshold to produce nucleation in a number of different superheated materials at different temperatures. We have also developed a theory which indicates that of the energy deposited in a critical radius, only about 5% is effective in producing bubble formation. Both theory and experiment are discussed.
A Comparison of the Photophysical Properties of Thiolate-Capped CdS Quantum Dots with Thiolate-Capped CdS Molecular Clusters
Authors: Yeung Lee K. , Sooklal Kelly , Mahtab Rahina , Zhang Bin , Adams Richard D. , Murphy Catherine J.
Published: April 2011

In the last several years, great advances have been made in the ability to synthesize semiconductor quantum dots with very narrow size distributions. Here, we report the synthesis of a series of thiolate-capped CdS quantum dots having reasonably narrow size distributions and make optical property comparisons to the crystallographically defined CdS molecular clusters having essentially “zero” size distribution. These clusters contain a “Cd10S4” core and thiolate/halide capping ligands. The luminescence of the molecular clusters, like the nanoparticles, is greatly influenced by the nature of the capping ligands. Additionally, the luminescence of the molecular clusters can be quite similar to that observed for their larger quantum dot counterparts.
Optical Properties of Cds Quantum Dots: The Key Role of the Spin-Orbit and Coulomb Interactions
Authors: Chamarro M. , Voliotis V. , Dib M. , Gacoin T. , Delerue C. , Allan G. , Lannoo M.
Published: April 2011

We study theoretically and experimentally the effects of the Coulomb and the spin-orbit coupling on the electronic structure of small quantum dots. A tight-binding calculation with restricted configuration interaction is developed in a typical case: very small cubic quantum dots for which the electron-hole exchange interaction is of the order of magnitude of the spinorbit interaction. Experimentally, resonant photoluminescence and photoluminescence excitation are used to obtain information on a single size of CdS quantum dot obtained by a chemical growth method.
Absorption and Photoluminescence Study of Cds Quantum Dots: The Role of Host Matrix and Nanocrystal Size and Density
Authors: Rakovich Yu.P. , Rolo A.G. , Stepikhova M.V. , Vasilevskiy M.I. , Gomes M.J.M. , Artemyev M.V. , Jantsch W. , Heiss W. , Prechtl G.
Published: April 2011

In this paper we present results of the absorption and photoluminescence (PL) of CdSdoped Si02 films fabricated by RF co-sputtering (semiconductor volume fraction f=1–15%, nano-crystallite's mean size 5–7nm) and matrix-free films of close-packed CdS nanocrystallites (f∼30%, size 2–5nm) produced by an original chemical method. The absorption spectra have been modelled using the modified Maxwell-Garnett model. This gives the e-h pair state energies and evidence of a strong absorption in the glass matrix containing CdS. The temperature dependence of the spectral position and broadening of the PL peak is analysed. It is concluded that a photo-generated hole is captured on an acceptor-type trap before the radiative recombination with a confined electron. The excitation of this ‘band-edge’ PL occurs through some states in the matrix and directly in the CdS crystallites for the two kinds of samples, respectively. The temperature coefficients of the optical transition energies for the nearly matrix-free films are similar to those of bulk CdS, while for the CdS/glass films they are smaller. This may be because of the different boundary conditions for the thermal expansion of CdS crystallites.
Stress and Deformation of Pzt Thin Film on Silicon Wafer Due to Thermal Expansion
Authors: Zang Ming , Polla Dennis L. , Zurn Shayne M. , Cui Tianhong
Published: April 2011

Stress and deformation of PZT thin films deposited on silicon wafers due to thermal expansion during the annealing process are modeled using a 3-D shell element of ANSYS. Two different designs of PZT thin films on the wafer are modeled. The first design is a PZT/Pt/Ti/silicon dioxide/silicon wafer, which is used for making acoustic emission sensors. The second design is a PZT/Pt/Ti/silicon dioxide/silicon nitride/silicon dioxide/silicon wafer, commonly used in fabrication of cantilever beams. For the design without the silicon nitride layer, the thermal stress of the PZT film is 298MPa, Pt 1280MPa, Ti 647MPa, the silicon dioxide layer is 228MPa, and the silicon wafer is 0.41–1.67MPa. For the design with silicon nitride, the thermal stresses are: PZT 301MPa, Pt 1280MPa, Ti 651MPa, silicon dioxide 226MPa, silicon nitride 416MPa, silicon dioxide 226MPa, and silicon wafer 1.05–4.23MPa. The residual stress of the PZT film is measured at 200–25OMPa for the design without silicon nitride, and 336MPa for the design with silicon nitride. Comparisons of the thermal stress with the tensile or proof stress of material for each layer indicate that thermal stress of the PZT film is slightly greater than its bulk tensile stress, that of Pt film is five times greater than its bulk tensile stress, and that of Ti film is approximately equal to its bulk tensile stress. The thermal stresses of silicon dioxide, silicon nitride, and silicon wafer layers are far smaller than their proof stresses.
Growth of (Ni,Zn)Fe2O4 Thin Films by Liquid Delivery Metal-Organic Chemical Vapor Deposition
Authors: Gangaware D. , Woolcott R. , Kingon A. I. , Roeder J. F. , Baum T. H.
Published: April 2011

Ni,Zn-ferrite (NZF) thin films are of interest for high frequency applications because of their high saturation magnetization compared to garnet films and their low eddy current losses compared to metal alloy films. Therefore there is an increasing need for methods to deposit single crystal ferrite thin films for incorporation into next generation microwave devices.

Epitaxial thin films of NZF have been deposited by liquid delivery metal-organic chemical vapor deposition onto (100) oriented MgO substrates. The morphology, orientation and magnetic properties of the as-deposited films were investigated as a function of deposition temperature and pressure. X-ray diffraction (XRD) reveals highly oriented films with a film strain of 1.01% compared to bulk lattice parameters. Films with well saturated magnetic hysteresis were obtained under a number of conditions with values of saturation magnetization up to 270 emu/cc (3400 gauss) with relatively low coercive fields ~100 Oe. The influence of metal cation ratio on magnetic properties is discussed.
Compositional Design of Faraday Rotator Materials
Authors: Fratello V. J. , Licht S. J. , Brandle C. D.
Published: April 2011

Bismuth-doped rare-earth iron garnet thick films have become the material of choice for a wide variety of magnetooptic applications including optical isolators and circulators. Garnet compositional design and liquid phase epitaxial growth have been adapted to the requirements of these devices. Properties such as optical absorption, specific Faraday rotation, temperature dependence of Faraday rotation, saturation magnetization and temperature dependence of saturation magnetization can be controlled to a high degree. Introduction of nucleation induced coercivity has even allowed the elimination of a permanent bias magnet. However, in optimizing device performance and film growth, there are often tradeoffs among these properties. Material design is therefore a compromise based on the requirements of device designers.
Uniformity of Misfit Strain in Heteroepitaxial (Ba, Sr)Tio3 Films on SrRuO3/SrTiO3
Authors: Abe K. , Yanase N. , Sano K. , Fukushima N. , Kawakubo T.
Published: April 2011

Uniformity of lattice misfit strain was quantitatively evaluated in heteroepitaxial (Ba, Sr)TiO3 films which were deposited by radio-frequency magnetron sputtering on SrRuO3/SrTiO3 substrates. Due to lattice misfit strain, the (Ba, Sr)TiO3 films had a 3% longer c-axis than the inherent bulk of (Ba0.75Sr0.25)TiO3. As analyzed by Hall's theory, the uniformity of the strain was 0.3% of the c-axis (0.413 nm) and 9% of the elongation of the c-axis (0.015 nm). It was suggested by the comparative study of two specimens that there is a strong correlation between the quality of the ferroelectric hysteresis loop and the uniformity of the misfit strain in heteroepitaxial (Ba,Sr)TiO3 films.
Strain Inhomogeneity in Epitaxial Colossal Magnetoresistive La1-xCaxMnO3 Thin Films
Authors: Rao R. A. , Nath T. K. , Lavric D. , Eom C. B. , Tsui F.
Published: April 2011

The strain inhomogeneity and crystallographic domain structures and their influence on the electrical transport and magnetic properties of epitaxial colossal magnetoresistive La1-xCaxMnO3 (x = 0.2, 0.33) films have been studied as a function of film thickness and two types of (001) substrates, SrTiO3 and LaAlO3. Out-of-plane and in-plane lattice parameters were determined using normal and grazing incidence x-ray diffraction (GID), and least-squares fits of off-axis x-ray reflections. The lattice strain near the film surface as determined by GID appears to relax faster than that at the film interior as determined by the least-squares fit, indicating the presence of strain inhomogeneity in the films. The observed strain inhomogeneity appears to influence the magnetic and electrical transport properties. In particular the measured temperature dependent magnetization exhibits multiple transitions indicating a variation of Curie temperatures within the same sample. While the very thin films exhibit single out-of-plane domains, accompanied by a high crystalline coherence and smooth surfaces, strain relaxation in thicker films leads to mixed ( 001)T and (110)T textures, and increased mosaic spread and surface roughness. The films also exhibit electrically insulating “dead” layers about 100 – 200Å thick.
Computation of Optical Properties for Quantized Electronic Systems
Authors: Jacobs V. L.
Published: April 2011

A density-matrix description has been developed to treat relaxation (decoherence) phenomena during resonant and non-resonant radiative transitions of quantized electronic systems, including many-electron atoms and quantum-confinement systems (e. g., semiconductor microstructures). Radiative and collisional relaxation phenomena have been treated using Liouville-space proj ecti on-operator techniques. Both time-independent (resolvent-operator) and time-dependent (equation-of-motion) formulations have been developed. The self-energy operators that occur in these formulations can provide the fundamental basis for a self-consistent determination of the non-equilibrium and coherent electronic-state kinetics together with the homogeneous spectral-line shapes. This density-matrix description can be adapted for the computer simulation of electromagnetic processes. From first-principles electronic-structure calculations or from semi-empirical approaches, the parameters describing the elementary collisional and radiative interactions can be evaluated and organized into the basic data set for the application of the density-matrix description. The final product is a theoretical prediction for the linear or non-linear optical absorption or emission spectrum corresponding to a given set of values for the appropriate physical variables, such as temperatures, densities, and electric or magnetic field strengths.
Theoretical and Experimental Analysis of the Low Dielectric Constant of Fluorinated Silica
Authors: Demkov A. , Liu R. , Zollner S. , Werho D. , Kottke M. , Gregory R.B. , Angyal M. , Filipiak S. , Mcintyre L.C. , Ashbaugh M.D.
Published: April 2011

Fluorinated silica has a dielectric constant E in the range of 3—3.5, lower than that of F-free SiO2 (ω=4). The reasons behind this reduction are controversial. It is not known whether the electronic or ionic contributions to the overall screening are being diminished upon F doping. To shed more light on this phenomenon we have studied F-doped SiO2 with ab-initio modeling and various characterization techniques. FTIR transmission and spectroscopic ellipsometry give us information about the ionic and electronic contributions to ω Nuclear reaction analysis and Auger spectrometry measure F composition. XPS and FTIR provide information on the atomic structure and stability of the film. We use a large cell of cristobalite to model fluorinated silica theoretically. The ground state geometry is obtained via energy minimization. We calculate the vibrational density of states and find a localized mode (Si-F stretch), in good agreement with FTIR transmission. We analyze the effects of F incorporation on the dielectric properties.
Fiber Bragg Grating Growth Simulation Using an Inverse Scattering Matrix Approach
Authors: Manca A. , Anedda A.
Published: April 2011

Fiber Bragg gratings are playing an important role in the field of optical telecommunications and sensors. We have simulated the growth of gratings, longitudinally written in the core of germanosilicate optical fibers by an Ar+ laser. Following a Kramer-Kronig model, absorption in the Germanium Oxygen deficient centers band (∼240 nm) is considered to be responsible for the fiber photosensitivity and a two photon absorption process models the dynamics of the refractive index variation.

The spatial propagation of light along the grating is described by the coupled wave theory and is calculated by using an inverse scattering matrix technique. The predicted physical properties of the gratings, reflectivity and temporal dispersion of propagating light as a function of wavelength and input power, show that a sustained growth is possible. A good agreement with previous simulations and experiments is found.
Excitons in Low-Dimensional Systems: Conjugated Polymers and Semiconductor Surfaces
Authors: Rohlfing Michael
Published: April 2011

We investigate the formation of excitons in low-dimensional semiconducting systems. To this end a recently developed ab initio approach is employed to determine the excitation energies and optical transition matrix elements of bound and unbound excitonic states. From these results the optical spectrum can be evaluated. We discuss two classes of low- dimensional prototype materials: conjugated polymers and a semiconductor surface. Due to the reduced dimensionality, the excitonic binding energies are much larger than in con- ventional semiconductors.
Crystallization of TiO2 in Sol-Gel Derived SiO2-TiO2 System: Formation of TiO2(B) Nanocrystallites
Authors: Kogure T. , Umezawa T. , Kotani Y. , Matsuda A. , Tatsumisago M. , Minami T.
Published: April 2011

The crystallization of TiO2 in monolithic SiO2-TiO2 (SiO2>TiO2) gels by annealing has been investigated. The temperatures of the crystallization of TiO2 to anatase and anatase-to-rutile phase transition were considerably raised with the addition of SiO2. It is supposed that the anatase-torutile phase transition is primarily controlled by the grain size of the crystals. TiO2(B), one of the TiO2 polymorphs, was formed as one of the first crystalline phase in SiO2-TiO2 gels at 800-900°C. Transmission electron microscope observations revealed that TiO2(B) nanocrystallites with a size of 5-10 nm were dispersed in amorphous SiO2 matrix. TiO2(B) nanocrystallites did not grow larger but transformed to anatase at higher temperatures. It is supposed that the nucleation and stability of TiO2(B) are enhanced with the presence of surrounding SiO2, presumably by a low interfacial energy.
Nucleation Behavior and Solid-Liquid Interfacial Energy of Polytetrahedral Phases
Authors: Holland-Moritz Dirk
Published: April 2011

According to classical nucleation theory the nucleation- and phase-selection behavior of undercooled meltallic melts is strongly dependent on the solid-liquid interfacial energy.

A structural approach to the modelling of the interfacial energy for simple melt-crystal interfaces (fcc, hcp, bcc) was developed a number of years ago [1-4]. This approach is extended to polytetrahedral phases using numerical simulation. Results of these calculations are presented for different polytetrahedral structures: the tetragonal σ-phase in Ni-V, the monoclinic phase λ-Al13Fe4, the orthorhombic phase μ-Al5Fe2 and the icosahedral quasicrystalline I-phase in Al-Pd-Mn. The numerically estimated values for the solid-liquid interfacial energy are compared with results from experiments on the undercooling- and phase-selection behavior.
Sputtering of Au Induced by Single Xe Ion Impacts
Authors: Birtcher R. C. , Donnelly S. E.
Published: April 2011

Sputtering of Au thin films has been determined for Xe ions with energies between 50 and 600 keV. In-situ transmission electron microscopy was used to observe sputtered Au during deposition on a carbon foil near the specimen. Total reflection and transmission sputtering yields for a 62 nm thick Au thin film were determined by ex-situ measurement of the total amount of Au on the carbon foils. In situ observations show that individual Xe ions eject Au nanopanicles as large as 7 nm in diameter with an average diameter of approximately 3 nm. Particle emission correlates with crater formation due to single ion impacts. Nanoparticle emission contributes significantly to the total sputtering yield for Xe ions in this energy range in either reflection or transmission geometry.
X-Ray Standing Wave Assisted Layer Deposition and Crystal Growth (Xswdg)
Authors: Meyer D. C. , Paufler P.
Published: April 2011

We propose to combine layer deposition or crystal growth with an X-ray standing wave field to influence the structure of growth products in-situ on an atomic scale. By placing the periodic local density distribution of energy of these wave fields properly, photo-fragmentation of precursor gases and other relevant processes can be supported at definite atomic sites at the surface of substrates. In certain cases also a local variation of the probability of desorption can be favorable to remove atoms from unwanted adsorption sites. A large number of growth processes is conceivable, which can be affected intentionally that way. The general physical principle behind this proposal is the availability of non-thermal energy contributions on a sub-nanometer scale. The fundamentals of production and application of these wave fields are communicated as well as results of theoretical estimations.
Synthesis of SiC on Si by Seeded Supersonic Beams of Fullerenes
Authors: Ciullo G. , Biasioli F. , Podestá A. , Milani P. , Toccoli T. , Iannotta S.
Published: April 2011

A well characterized C60 supersonic seeded beam has been used to synthesize SiC films on Si (111) 7×7. The control of beam parameters such as energy and flux distributions is shown to be important to improve quality of films in terms of morphology, defect density and structure. We demonstrate that a kinetic energy of a few eV of the C60 precursor is enough to induce carbidization at moderate substrate temperature. Kinetic energy activated SiC formation at 750°C is achieved with a strong reduction of the dimensions and density of defects. The films show a reduced roughness of about 2.5 nm (root mean square).
Relationship Between Structure and Luminescent Properties of Epitaxial Grown Y2O3:Eu Thin Films on LaAlO3 Substrates
Authors: Gao H-J. , Duscher G. , Fan X.D. , Pennycook S.J. , Kumar D. , Cho K.G. , Holloway P.H. , Singh R.K.
Published: April 2011

Cathodoluminescence images of individual pores have been obtained at nanometer resolution in europium-activated yttrium oxide (Y2O3:Eu) (001) thin films, epitaxially grown on LaA1O3 (001) substrates. Comparison with Z-contrast images, obtained simultaneously, directly show the “dead layer” to be about 5 nm thick. This “dead layer” is the origin of the reduced emission efficiency with increasing pore size. Pore sizes were varied by using different substrate temperatures and laser pulse repetition rates during film growth. These films are epitaxially aligned with the substrate, which is always Al terminated.
Structure Refinement of S-Phase Precipitates in Al-Cu-Mg Alloys by Quantitative HRTEM
Authors: Kilaas R. , Radmilovic V. , Dahmen U.
Published: April 2011

The crystal structure of the Al2CuMg S-phase precipitate in an Al matrix has been determined by quantitative high resolution electron microscopy. This work combines techniques of image processing and quantitative comparison between experimental and simulated images with automatic refinement of imaging and structural parameters.
Interfacial Interaction Between Cr Thin Films and Oxide Glasses
Authors: Jiang N. , Silcox J.
Published: April 2011

The interfacial interaction between Cr thin films and multi-component oxide glasses has been observed by means of high spatial resolution electron energy loss spectroscopy. Besides a partially oxidized Cr thin layer, a ∼5nm wide Cr diffusion layer is seen. Chromium oxidation at the interface results from the difference between the heats of oxide formation. Ion exchange between Cr2+ and alkaline earth ions then causes the formation of the diffusion layer. The electronic states of the Cr in this diffusion layer are different from that in the oxidized layer. Strong interaction between Cr and O in the diffusion layer suggests that such a layer could be responsible for the formation of a strong Cr/glass interface