bluuebunny/crossref_metadata_2025_split huggingface dataset:
Growth Stress of Thin Ti-, Al- and TiAlx-Films Deposited Under UHV-conditions and its Dependence on Substrate Temperature
Authors: Lackner St. , Abermann R. 
Published: April 2011

AbstractThe growth stress of metal films was measured continuously both during as well as after their deposition under UHV-conditions with a cantilever beam technique. The metal films were deposited onto 10 rim thick alumina substrate films prepared by reactive evaporation of Al in an oxygen atmosphere. The substrate temperature for the metal deposition was varied from -20°C to 500°C.The growth stress of both titanium and aluminum films deposited at room temperature and above is characteristic of island growth and the formation of a polycrystalline film. The film stress built up in these films decreases with increasing substrate temperature. Below RT the growth stress of titanium films indicates a transition from island growth to layer by layer growth due to a reduced adatom mobility. The temperature range in which this transition in the growth mode occurs is strongly affected by impurities in the Ti-evaporation source material and gas ambient.In the last part of this paper we present results of experiments in which the above metals were evaporated simultaneously from separate sources to form alloy films with TiAl3-stoichiometry. Sudden changes in the incremental film stress are tentatively attributed to segregation and phase formation phenomena.
Modeling of Non-Random Nucleation Protocols
Authors: Pineda Eloi , Pradell Trinitat , Crespo Daniel 
Published: April 2011

AbstractNon random nucleation processes are a subject of much interest in the study of first order phase transformations. However, the theory available to obtain the time evolution of the transformation for a nucleation and growth process, the well known Kolmogorov, Johnson-Mehl and Avrami kinetic equation (KJMA), is not accomplished if the nucleation process is nonrandom. Therefore, KJMA does not give an adequate description of the transformation kinetics.In the present paper, a non-random nucleation protocol resulting from a reduced nucleation rate due to the nearby presence of other growing grains is considered. Monte-Carlo simulations of such processes are performed, and the deviations from the Avrami kinetics observed are analyzed in detail.
Phase Evolution and Transformations During Long-Term Creep of Two-Phase Titanium Aluminides
Authors: Appel F. , Oehring M. , Ennis P.J. 
Published: April 2011

AbstractTitanium aluminide alloys based on the intermetallic γ (TiAl) and α2 (Ti3Al) phases are being considered as light-weight materials for high-temperature applications in advanced energy conversion systems. However, for such applications the material suffers from insufficient creep resistance at the intended service temperature of 700°C. The paper reports an electron microscope study of diffusion controlled mechanisms which apparently cause the degradation of the strength properties. The processes lead to significant structural changes involving the formation of extended ledges and recrystallization. The driving forces of these mechanisms probably arise from non-equilibrium phase compositions and significant coherency stresses occurring at the interfaces.
Evolution of Stress; Phase Formation and Microstructure in TiCux-Alloy Films
Authors: Bertel S. , Abermann R. 
Published: April 2011

AbstractThe internal stress of TiCux-alloy films on alumina substrates was measured in situ under UHV-conditions as a function of substrate temperature and stoichiometry using a cantilever beam technique.The stress vs. thickness curves of alloy films with TiCu0.5, TiCu, TiCu2 and TiCu3 stoichiometry indicate that the film growth is amorphous at 130°C and polycrystalline at 350°C substrate temperature, which was confirmed by TEM-investigations. Furthermore TED-results of alloys deposited at 350°C imply that the TiCux-alloy-phases formed at that temperature are Ti2Cu, γ-TiCu, TiCu3 and TiCu4.The influence of substrate temperature on the growth of TiCux-alloy films (x = 1) was investigated in more detail. At substrate temperatures below 300°C the stress vs. thickness curves indicate the formation of amorphous alloy films, again confirmed by TEM- and TED-analysis. At substrate temperatures around 300°C a strong tensile stress contribution above a mean thickness of about 20 nm indicates a change in the growth mode and thus microstructure of the alloy film. The corresponding TEM- and TED-micrographs show quasi single-crystalline films. Finally at 350°C substrate temperature the stress vs. thickness curves indicate once again a change in the film growth mode, the film structure is polycrystalline and the formation of γ-TiCu is deduced fore TED-results.
Stress Formation in Boron Nitride Films Prepared by Ion Beam Assisted Deposition
Authors: Rauschenbach B. , Sienz S. 
Published: April 2011

AbstractThe stress formation during N/Ar ion assisted deposition of boron nitride films on Si(001) substrates was measured in-situ by a very sensitive capacity technique in dependence on the ion energy, temperature during deposition and the ion to atom arrival rate.The stress evolution in dependence on the layer thickness is characterized by a high tensile stress in the initial stage of the film growth, followed by a transition from the tensile to the compressive stress state, a strong increase of the compressive stress with the film thickness. A simultaneous UV-light irradiation during the deposition process leads to a reduction of the compressive stress.
An Electron Microscope Study of Diffusion Assisted Dislocation Processes in Intermetallic Gamma TiAl
Authors: Appel F. , Lorenz U. , Oehring M. 
Published: April 2011

AbstractThe paper reports an electron microscope study of diffusion controlled deformation mechanisms in two-phase titanium aluminides which apparently cause the degradation of the strength properties at elevated temperatures. Climb velocities were analyzed in terms the critical vacancy supersaturation necessary for the operation of diffusion assisted dislocation sources. Particular emphasis was paid on structural changes occurring during long-term creep, which are apparently associated with dislocation climb.
Site Occupancy Determination by ALCHEMI of Nb and Cr in γ-TiAl and Their Effects on the a to γ Massive Phase Transformation
Authors: Miller T.M. , Wang L. , Hofmeister W.H. , Wittig J.E. , Anderson I.M. 
Published: April 2011

AbstractAtom location by channeling enhanced microanalysis (ALCHEMI) has been used to characterize the site distributions of Nb and Cr alloying additions in the L10-ordered γ phase of ternary titanium aluminides. Two alloys, Ti50Al48Cr2and Ti50A148Nb2, were processed by furnace cooling from 1300°C (within the α-γ two phase field) as well as by rapid solidification using twin-anvil splat quenching of electromagnetically levitated and undercooled samples. ALCHEMI studies of furnace cooled samples yield results generally consistent with those in the published literature. Nb alloying additions are found to partition exclusively to the ‘Ti’ sublattice, while Cr alloying additions exhibit an ‘Al‘ sublattice preference. However, a higher degree of disorder can be achieved with rapid solidification and high solid state cooling rates (105-106K/s). Significant distribution of the ternary elements between the ‘Ti’ and ‘Al‘ sublattices has been measured in the splat quenched samples, with up to 12% of the Nb atoms occupying the ‘Al‘ sublattice and the fraction of Cr atoms on the ‘Ti’ sublattice doubling to ∼30%. Rapid solidification of TiAl produces an equiaxed hexagonal α phase solidification structure that transforms in a massive fashion to the tetragonal γ phase. Although the amount of massively transformed γ is dependent upon the solid state cooling rate, ternary alloying additions can more strongly influence the transformation kinetics. The Nb-modified alloy exhibits significant amounts of the massively tranformed γ, similar to the Ti52Al48binary alloy, whereas little massively transformed γ is observed in the Cr-modified alloy. These results can be correlated with the relative atomic size, lattice distortion, and sublattice site occupancy of Nb and Cr in the L10unit cell.
Atomic-Scale Imaging of Dopant Atom Distributions Within Silicon δ-Doped Layers
Authors: Vanfleet R. , Muller D.A. , Gossmann H.J. , Citrin P.H. , Silcox J. 
Published: April 2011

AbstractWe report measurements of the distribution of Sb atoms in σ-doped Si, over a wide 2-D concentration range. Both annular dark-field imaging and electron energy loss spectroscopy proved sufficiently sensitive to locate Sb atoms at the atomic scale. Improvements in both detector sensitivities and specimen preparation were necessary to achieve these results, which offer a surprising explanation for the dramatic difference in electrical activity between 2-D and 3-D dopant distributions at the same effective volume concentrations. The prospects for the general identification of individual dopant atoms will be discussed.
Imaging Heterophase Molecular Materials in the Environmental SEM
Authors: Thiel B.L. , Donald A.M. , Stokes D.J. , Bache I.C. , Stelmashenko N. 
Published: April 2011

AbstractThe Environmental Scanning Electron Microscope allows imaging of hydrated specimens, as well as fluid-containing or even fully fluid microstructures. This is possible so long as all of the phases can be thermodynamically stabilized. Experimental operating parameters include specimen temperature and chamber gas chemistry and pressure. However, it is also possible to alter the thermodynamic properties of phases by various chemical and physical means. These approaches have been used in ESEM studies on soft condensed matter such as emulsions, complex fluids and gels. By deliberately moving away from stabilizing conditions, it is also possible to perform dynamic experiments. A number of applications are illustrated.
High Spatial Resolution X-ray Microanalysis of Radiation-Induced Segregation in Proton-Irradiated Stainless Steels
Authors: Kenik E.A. , Busby J.T. , Was G.S. 
Published: April 2011

AbstractThe spatial redistribution of alloying elements and impurities near grain boundaries in several stainless steel alloys arising from non-equilibrium processes have been measured by analytical electron microscopy (AEM) in a field emission scanning transmission electron microscope. Radiation-induced segregation (RIS) has been shown to result in significant compositional changes at point defects sinks, such as grain boundaries. The influence of irradiation dose and temperature, alloy composition, prior heat treatment, and post-irradiation annealing on the grain boundary composition profiles have been investigated. Understanding the importance of these microchemical changes relative to the radiation-induced microstructural change in irradiation-assisted stress corrosion cracking (IASCC) of the irradiated materials is the primary goal of this study.
Formation of AlN Films on Ti/TiN Arc-Layer Interface With AL-0.5%Cu Interconnects Evaluated by XPS and Energy-Filtered-TEM
Authors: Gazda J. , Zhao J. , Smith P. , White R. A. 
Published: April 2011

AbstractTitanium/titanium nitride anti-reflective coatings (ARC) are widely used in the semiconductor industry during photolithography of aluminum metal interconnect lines. The quality and effectiveness of these coatings, however, depend strongly on the ability to control reaction products formed at film interfaces during processing. In the present study, formation of an Al-N compound at the interface between Ti/TiN ARC/BARC and Al-(0.5 wt. %)Cu interconnect was investigated. The effects of deposition temperatures for individual films and ensuing thermal cycling of the whole metal stack on formation of intermetallics were evaluated. The composition and chemical bonding state of an aluminum nitride interfacial layer was evaluated by x-ray photoelectron spectroscopy (XPS) of blanket wafers. These results were combined with measurements made by energy filtered transmission electron microscopy (EFTEM) of thickness and continuity of the film in specimens prepared by focused ion beam milling (FIB). Formation of AIN depends on the thermal cycling history of the metal stacks
Alkali-Metal Containing Amorphous Carbon: Reactivity and Electronic Structure
Authors: Töwe M. , Reinke P. , Oelhafen P. 
Published: April 2011

ABSTRACTAmorphous hydrogen-free carbon films (sp2-dominated a-C) were deposited under ultrahigh vacuum conditions between room temperature and 800°C. These films served as matrices for the in-situ incorporation of alkali-metal atoms (Li, Na). In-situ sample characterization was performed by photoelectron spectroscopy with both x-ray and ultraviolet excitation (XPS, UPS). While the clean metal-containing samples were prepared with metal contents of about 10 at%, a strong oxidation driven accumulation of metal atoms on the film surface exceeding 50 at% was observed upon exposure to molecular oxygen. Work-function measurements by UPS reflected the changes within the electronic structure of the material. Metal incorporation considerably decreased the work-function, but only after oxidation we observed work-functions below the values given for pure alkali metals.
Study of Carbon Nanotubes Under High Pressure
Authors: Tang J. , Qin L.C. , Matsushita A. , Kikegawa T. , Yudasaka M. , Bandow S. , Iijima S. 
Published: April 2011

ABSTRACTThe elastic behavior and structural changes of single-walled carbon nanotubes under hydrostatic pressure produced by a gasketed diamond anvil cell has been studied using in situ synchrotron x-ray diffraction. The compaction of the raft-like bundles of single-walled carbon nanotube showed a linear behavior up to 1.5 GPa pressure and the volume compressibility deduced from the experimental data is 0.024 GPa−1. The elastic deformation is attributed to the combination of a reduction in the inter-tubular distance and the polygonization of the otherwise circular nanotube sections.
Study of Chromium-Doped Diamond-Like Carbon by Z-Contrast Imaging and Electron Energy Loss Spectroscopy
Authors: Fan X. , Dickey E. C. , Pennycook S. J. 
Published: April 2011

ABSTRACTMetal-doped diamond-like carbon films were produced for the purpose of an electrochemical nano-electrode. In this study we use Z-contrast scanning transmission electron microscopy to directly observe metal cluster formation and distributions within the chromium-doped carbon films. At low doping (∼6at%Cr), Cr is uniformly distributed; at high doping (∼12at%Cr), Cr-rich clusters are formed. Using electron energy loss spectroscopy, we find that the Cr clusters tend to be metallic-like at low doping levels and carbide-like at high doping levels according to the Cr L2.3 white line ratios. The carbon is more diamond-like at low doping and more graphite/carbide like at high doping according to the sp2/sp3 electron percentage measurements.
Electrical Behavior of Pure and Cu Doped Diamondlike Carbon Prepared by Pulsed Laser Deposition
Authors: Wei Q. , Sharma A. K. , Yamolenko S. , Sankar J. , Narayan J. 
Published: April 2011

ABSTRACTWe have prepared pure diamondlike carbon films and Cu doped diamondlike carbon films through pulsed laser deposition. The Cu concentration does not exceed 3.0 atomic percent. Electrical conduction studies were carried out on the films to understand the electrical transport mechanism. It was found that both pure DLC and Cu doped DLC are of p-type conduction. Incorporation of Cu into the DLC films decreases the resistivity significantly. Transmission electron microscopy and radial distribution function analyses showed that the DLC films are typical tetrahedral amorphous carbon. The conductivity of Cu doped DLC films exhibited T1/2 temperature dependence, rather than the T1/4 dependence (Mott-Davis law). This dependence was observed within a wide temperature range (from below liquid nitrogen temperature to near room temperature). The T1/2 dependence was explained on the basis of the Efros-Shklovskii model which considers the long range Coulomb interaction between localized states
Diamond-Like Carbon Coatings for Rhenium Wire and Foils
Authors: Evans Edward A. , Hafeli U , Wusinka Ram , Morrison Philip W. 
Published: April 2011

ABSTRACTDiamond like carbon has been deposited as a protective layer for coronary stenting applications. Taking advantage of DLC's resistance to chemical attack, its flexibility, and other properties. our current technical objective is to develop DLC as a coating for radioactive rhenium stents. Radioactive rhenium stents are being investigated to limit smooth muscle cell growth following coronary surgery. The DLC coating is being investigated to reduce the release of radioactive rhenium (released activity) into the blood following the stenting procedure. An inductively coupled RF plasma system was used to deposit the DLC onto rhenium substrates. Foils, wires, and coils were coated and tested for adhesion, cytotoxicity, and release of radioactive rhenium. Our initial results indicate up to a three-fold decrease in released activity relative to uncoated rhenium
Altering Resistivity in Diamond Films Without Impurity Addition
Authors: Baker Colin C. , McNamara Karen M. 
Published: April 2011

ABSTRACTCVD Diamond films with resistivites comparable to that measured in natural type IIA diamond can be fabricated using a microwave-plasma assisted growth environment. Modification of the resistivity of these films is typically accomplished through the introduction of impurities, or dopants such as boron. Some applications, however, require that the purity of the carbon lattice be maintained, while still altering the resistivity of the film. This is the case for many applications of diamond in space. Here, varying the resistivity of CVD diamond is investigated by controlling the introduction of sp2coordinated bonds, yet maintaining the overall diamond structure and carbon purity. Experimental results will be presented, and the use of these materials in NASA's Genesis Discovery Mission will be discussed
Molecular Dynamics Simulation of Impurities in Nanocrystalline Diamond Grain Boundaries
Authors: Sternberg Michael , Zapoll Peter , Frauenheim Thomas , Gruen Dieter M. , Curtiss Larry A. 
Published: April 2011

ABSTRACTNanocrystalline diamond films grown on Si substrates at 800°C from hydrogen-poorplasmas have a number of highly desirable mechanical and electronic properties. Impurities were found by SIMS measurements to be uniformly distributed throughout the thickness of the films at a level of 1017–1018 cm−3. It is likely that the impurities are located at the grain boundaries, which play a crucial role in controlling important characteristics of the films, such as electrical conductivity and electron emission. Density-functional based tight-binding (DFTB) molecular dynamics simulations were performed for diamond high-energy high-angle (100) twist grain boundaries with impurities such as N, Si and H
Nanocrystalline Silicon Carbide Film Growth Using Hot Filament CVD
Authors: Yu M.B. , S.F. Rusli , J. Yoon , Chew Cui K. , Ahn J. , Zhang Q. 
Published: April 2011

ABSTRACTNanocrystalline cubic silicon carbide (nc-SiC) films embedded in an amorphous SiC matrix was fabricated by the hot filament chemical vapor deposition (HFCVD) technique using methane and silane as reactance gases. The presence of nanocrystalline grains was confirmed by the high resolution transmission electron microscope (HRTEM). x-ray photoelectron spectroscopy (XPS) measurements showed that the atomic percentages of Si and C are nearly 50%. X-ray diffraction spectrum of the sample revealed a diffraction peak of 3C-SiC (111) at 2ϕ=35.6°. Infrared absorption of the film had a strong peak at 800 cm−1 which is related to the transverse optical phonons of Si-C bonds in 3C-SiC. Raman spectrum of the sample showed that there are two peaks at 790 cm−l and 970 cm−1 which correspond to longitudinal and transverse optical phonons of SiC respectively. Room temperature photoluminescence (PL) study of these nc-SiC samples revealed a visible peak at 2.2 eV, which has not been observed so far for 3C-SiC.
Film Formation Behavior of the Endohedral Metallofullerene DY@C82
Authors: Huang Houjin , Yang Shihe 
Published: April 2011

ABSTRACTThe Langmuir-Blodgett (LB) film formation behavior of the endohedral metallofullerene Dy@C82 was studied at the air/water and Ar/water interfaces. The LB film constructed at the Ar/water interface (2-4 layers) was found to be thinner and more uniform than at the air/water interface (4-6 layers). Particulate aggregates were observed in the LB films, which contrasts the extended wire networks formed by direct evaporation of the metallofullerene solution on a quartz plate. The UV-Vis absorption peaks are blue-shifted for the LB film deposited in air, which is attributed to the partial oxidation of the metallofullerene balls. They are red-shifted, however, for the LB film at the Ar/water interface presumably due to the interaction between the pristine metallofullerenes.
Synthesis and Characterization of Cluster-Assembled Carbon Films
Authors: Milani P. , Piseri P. , Barborini E. , Podestà A. 
Published: April 2011

ABSTRACTNanostructured carbon films have been grown by deposition of supersonic cluster beams. A novel pulsed microplasma cluster source allows to obtain cluster beams of high intensity and stability. Cluster growth and beam formation have been charaterized. Separation effects typical of supersonic expansions cause inhomogeneities of cluster distribution in the beam, depending on their masses. This effect, observed for the first time, has been carefully characterized. The deposited films have a low density porous structure based on nanometer-size grains. The coordination is essentially three-fold with a large number of defects. Film density, morphology and surface roughness can be controlled by varying the precursor cluster mass distribution. Applications of cluster-assembled carbon films will be presented.
Creep Behavior of a Superplastic Y-TZP/Al2O3 Composite: An Examination of the Possibility for Diffusion Creep
Authors: Sosa Siari S. , Langdon Terence G. 
Published: April 2011

AbstractThe creep characteristics of a high purity superplastic Y-TZP/Al2O3 composite were studied. The test samples had a uniform initial grain size of essentially equiaxed grains and the phase distribution was also uniform. Creep tests were conducted at elevated temperatures in tension and measurements were taken after testing to determine the average size and shape of the grains. The creep curves showed the existence of a primary stage of creep and then a transition into a steady-state region where the strain rate remained reasonably constant. Observations by scanning electron microscopy revealed an elongation of the alumina grains with the grain strain essentially matching the overall strain within the sample. There was some grain growth after testing at the lower stresses. Preliminary observations using an atomic force microscope revealed direct evidence for the occurrence of some grain boundary sliding within the samples. The results are compared with earlier data reported for Y-TZP/Al2O3 composites and they are analyzed using the interface reaction-controlled diffusion creep model.