bluuebunny/crossref_metadata_2025 huggingface dataset:
Is the Available Alkalitest A Good Durability Predictor for Fly Ash Concrete Incorporating Reactive Aggregate?
Authors: Smith Robert L.
Published: March 2011

The available alkali test has been used for years as a method for preventing the use of a high-alkali fly ash in concrete containing reactive aggregate. This report presents data on fifteen good-quality Western ashes, both Class C and Class F, that are currently used in readymixed concrete. All fifteen ashes were effective in reducing the expansion due to the alkaliaggregate reaction. The reduction in mortar bar expansion (ASTM C 441) varied from 16% to 81%. Correlation of the percent reduction was made with available alkalies as Na2O, silica content, lime content, sulfur content, and the sum of silica, alumina and iron oxide. Surprisingly, the best correlation to percent reduction was with sulfur and the least was with available alkalies. This data indicates that most, if not all, fly ashes are effective in reducing the alkali aggregate reaction and that the available alkali test is not the best method for predicting the effectiveness of a fly ash in controlling this reaction.
The Effect of Blast Furnace Slag on the Microstructure of the Cement Paste/Steel Interface
Authors: Onabolu O. A. , Pratt P. L.
Published: March 2011

The microstructures of steel reinforced ordinary Portland cement mortar samples, and those containing 40% and 70% slag as cement replacement, have been studied by electron optical techniques, after exposure to stagnant sea-water at 23°C for 320 days. Fracture surfaces along the interface with steel were examined using secondary electron imaging in the SEM. This revealed differences between the OPC and slag specimens as regards the morphology of the phases and the amounts of calcium hydroxide present. The microstructure at the interface with steel was studied by means of back scattered electron imaging combined with quantitative image analysis. Chloride concentrations at sections around the interface were determined by means of an EDXA facility linked to the SEM. Even after 320 days immersion in sea-water, there was some calcium hydroxide present in the interfacial zone.
Sample Preparation Technique for Examination of SiC Whisker Cross-Sections
Authors: Bradley S. A. , Dietz N. L. , Karakek K. R.
Published: March 2011

An ultramicrotomy technique for preparing SiC whisker cross-sections is described. With this method a large number of axially oriented whiskers can be examined.
Novel Methods of Preparing Polymers for High Resolution Transmission Electron Microscopy
Authors: Howell Barbara F. , Reneker Darrell H.
Published: March 2011

This work was undertaken to guide the development of methods for preparing very thin polymer samples on an atomically flat, conducting surface so that the molecules could be examined with a scanning tunneling microscope. Polymer molecules with segments in an extended configuration were sought so that details of polymer structure such as branching, distances between branches, and other structural features of the molecules could be examined. Three different methods, (mechanical deformation, solution entrapment, and solution spreading) used for preparing the samples resulted in the “self-assembly” of the polymer molecules into a variety of structures which are described below.
Sample Preparation of Aluminum Bridge Test Vehicles for Tem In-Situ Crystallographic Studies of Electromigration
Authors: Rhoden W. E. , Maskowitz J. V. , Kitchen D. R. , Omlor R. E. , Lloyd P. F.
Published: March 2011

Introduction

Electromigration in aluminum films has been identified as an increasing concern for integrated circuit reliability. Electromigration is the mass transport of atoms in a conductor under a current stress. Electromigration occurs in conductors experiencing current densities greater than 105 A/cm2 and is accelerated by high temperature. The damage to aluminum films manifests itself in the formation of voids, hillocks and whiskers along the conductor. This paper presents a test vehicle preparation procedure which can be used to investigate electromigration.
A Grinding/Polishing Tool for TEM Sample Preparation
Authors: Klepeis S. J. , Benedict J. P. , Anderson R. M.
Published: March 2011

A grinding/polishing tool has been developed for preparing TEM samples. The hand-held tool is 2.50″ in diameter and 3.0″ high. Rough-cut samples, 300 to 600 microns thick, are routinely polished to 5 microns thick in four to six hours using this tool. As these 5 micron samples are so thin and uniform, a separate dimpling operation can be eliminated. Likewise, the time required to ion-mill the sample can be reduced to 0.5 to 2.0 hours – greatly reducing ion-milling artifacts and significantly increasing the area viewable by TEM. The process is equally effective for all classes of samples: Silicon devices, ceramics or metals – in either cross-section or planar views.
Preparation of Multilayer Optical Coatings for Tem Cross-Sectional Microanalysis by Ultramicrotomy
Authors: Swab P. , Klinger R. E.
Published: March 2011

Ultramicrotomy is a technique for cutting cross-sections of material which was originally used by biologists for soft tissue analysis. With only a few changes to accommodate the hard dielectric coatings and substrates, the technique may be used to prepare specimens of optical multilayer devices for cross-sectional transmission electron microscopy (XTEM).

The ultramicrotome, mounted on a vibration damped table, is capable of cutting uniform 40 nm thick cross-sections of materials with a diamond knife. An epoxy embedded sample is cycled past the knife at a controlled rate and advanced by a precise, preset distance on each pass. As each section is cut, it comes off the knife edge to a reservoir of water where, while floating, it can be picked up on a TEM grid.

Artifacts generated by this mechanical technique for preparing thin cross-sections are readily apparent yet easy to disregard. TEM analysis of these cross-sections provides direct imaging of real samples for accurate feature and thickness measurement and direct chemical and crystalline structure analysis.
Xtem of Silicon Vlsic Device Structures
Authors: Knoell Robert V.
Published: March 2011

The use of XTEM (cross-sectional TEM) as a diagnostic tool for quality control of device processing has experienced a surge of popularity recently due to the need for better feature resolution and the improvement in equipment and techniques for preparing such samples. As device features shrink below one micrometer, interface morphology and the detection of microstructural defects make TEM a most effective imaging tool. The demand for XTEM is tempered by problems in sample preparation, which impose restraints on turnaround time and image quality, especially for devices utilizing multilevel metallizations. A reliable technique for preparing these devices for XTEM observations, along with helpful hints to integrate into a sample preparation routine, will be presented. This technique reduces turnaround time to about a day and a half per group of samples. The rate of success is high if care is exercised, and all parts of the sample, metallized or not, are electron transparent to produce a clear image with minimized brightness contrast between layers. Finally, micrographs will be presented to illustrate what can be achieved with this technique and what features of interest can be observed for failure analysis determination.
Specimen Preparation for Transmission Electron Microscopy of Metals
Authors: Goodhew Peter J.
Published: March 2011

The aim of thin foil preparation is to produce a specimen for microscopy which is representative of a larger volume of material, and in which the detail can be seen and interpreted. It is in general necessary to undertake some initial preparation before the final thinning process. Both stages are described. The final preparation methods described in this paper include electropolishing, ion beam thinning, ultramicrotomy and replication. A guide to the choice of technique is presented.
Cross-Sectional TEM Sample Preparation for Multilayer Electronic Materials
Authors: Chang Peng-Heng , Coviello M. D. , Scott A. F.
Published: March 2011

The preparation of cross-sectional TEM samples from multilayer materials commonly encountered in electronic industry is difficult in general due to the large variation in chemical and physical etching rate. We have developed a technique consisting of a median incidence angle ion sputtering to perforation followed by a short time (<2 hours) low incidence angle sputtering with the glue line direction shielded from the ion beams. This technique takes advantage of the fast sputtering rate associated with the median incidence angle sputtering initially. The near normal (relative to the glue line direction) low angle sputtering in the second step smooths out any non-uniformity in thickness due to the strong dependence of sputtering rate on the sputtering angle. High quality TEM samples prepared from many different types of multilayer structures using this technique are demonstrated.
ArF Excimer Laser-Induced Epitaxial Growth of GaAs Films on Si
Authors: Chu Shirley S. , Cpu T. L. , Chang C. L.
Published: March 2011

Epitaxial gallium arsenide films have been deposited on single crystalline GaAs substrates of {100} orientation and Si substrates of 3° off the {100} orientation by ArF excimer laser-induced metalorganic chemical vapor deposition. The important process parameters include the cleanliness of the substrate surface, substrate temperature, the composition, flow rate, and pressure of the reaction mixture, and the pulse energy and pulse rate of the laser. Particular attention was directed to the in-situ cleaning of the substrate surface prior to the deposition process. Homoepitaxial gallium arsenide films of good structural perfection have been deposited at 425°- 500 ° C and their single crystallinity has been confirmed by transmission electron microscopy. The carrier concentration decreases with increasing AsH3/(CH3)3 Ga molar ratio and with decreasing substrate temperature. Lower growth rate during the initial stage of deposition is necessary to obtain heteroepitaxial gallium arsenide films on Si with good structural perfection. The TEM examination of GaAs films of 0.15–0.2 µm thickness deposited on Si substrates at 500 °C has shown that stacking faults were present in the GaAs films; however, there is no apparent threading dislocations in the surface region of the thin GaAs film.
Heterogeneous Strain Relaxation in GaAs on Si (100)
Authors: Freundlich A. , Neu G. , Leycuras A. , Carles R. , Verie C.
Published: March 2011

Residual stress in MOVPE grown GaAs on (100)Si substrates is investigated using Haman spectroscopy, X-ray diffraction, low temperature photoluminescence and photoluminescence excitation spectroscopy experiments. At room temperature, 2 µm-thick GaAs/Si is found to be under biaxial (100) tensile stress of X = 1.8 ± 0.3 kbar, near the epilayer surface. The stress magnitude decreases as the distance from interface decreases. PL and PLE studies on post-growth thermally annealed GaAs/Si reveal coexistence of unstrained and strained GaAs.
CaP/Si Heteroepitaxial Layers with Reduced Defect Density
Authors: Blakeslee A.E. , Al—jassim M.M. , Olson J.M. , Jones K.M. , Vernon S.M.
Published: March 2011

It is shown that GaP layers grown upon Si at a single temperature of 900ºC can have a crystalline quality superior to that exhibited by previous two—step and one—step growth methods. The layers are characterized by a planar network of misfit dislocations confined to the interface plane an a reduced density of threading dislocations (low 106 cm-2; previously >108). Very few threading defects were observed in areas devoid of amorphous oxide contamination, as shown by HREM examination of cross—sectional samples. A low growth rate during nucleation enhances crystalline perfection, since it decreases the tendency toward three—dimensional islanding.
Initial Stages of GaAs Epitaxy on Si
Authors: Biegelsen O. K. , Ponce F. A. , Krusor B. S. , Tramontana J. C. , Yingling R. D. , Bringans R. D. , Fenner D. B.
Published: March 2011

The initial stages of heteroepitaxial growth of GaAs on Si have been observed using a technique of graded-thickness sample deposition. We find that an initial uniform passivating layer is grown, followed by three-dimensional nucleation determined by Ga diffusion and clustering, followed in turn by an interfacial reaction limited island growth mechanism. Results for various substrate temperatures and substrate orientations are consistent with the simple models of nucleation and growth.
An Investigation of the Heteroepitaxial Growth of Beta—silicon Carbide Thin Filmson Silicon Substrates
Authors: Glass J. T. , Wang Y. C. , Kong H. S. , Davis R. F.
Published: March 2011

High purity β—SiC films have been epitaxially grown on Si (100) and off-axis Si (100) substrates. Conventional chemical vapor deposition at 1633K and 1 atm using SiH4 and C2H4 reactants in an H2 carrier gas was employed for this growth. Large differences in lattice parameter and thermal coefficients of expansion between the film and the substrate were partially compensated for by growing aninitial “conversion layer.” Plan view and cross—sectional transmission electron microscopy were utilized to study the conversion layer and the defects present in the films. A high density of stacking faults and dislocations were present in allthe films grown on Si, however, antiphase boundaries were eliminated when certain off—axis Si (100) substrates were employed. The effects of misorientation angle and substrate preannealing were investigated. The electrical properties of the β-SiC films were also studied using differential capacitance—voltage and Hall effect measurements as well as the I—V characteristics of Au—β—SiC Schottky diodes. It was found that the elimination of antiphase boundaries reduced leakage current but did not significantly effect carrier concentration or Hall electron mobility. Finally, the I—V characteristics of a Metal—Semiconductor—Field—Effect—Transistor (MESFET) have been evaluated for a β—SiC filmon an on—axis Si (100) substrate.
Schottky Diode Characteristics of CVD—Grown β —SiC Epitaxial Films on (n11) Silicon Substrates ( n= 1,3,4,5,6 ).
Authors: Fujii Yoshihisa , Ogura Atsuko , Furukawa Katsuki , Shigeta Mitsuhiro , Suzuki Akira , Nakajima Shigeo
Published: March 2011

Schottky barrier contacts have been made on CVD—grown β - SiC on Si substrates, and their C—V and I—V characteristics are measured. Dependence of the Schottky characteristics on Si substrate orientation ((n11),(n=1,3,4,5,6), and (100)) is examined. The Schottky diodes of the β-SiC films on Si (611), Si(411), and Si (111) show excellent characteristics compared with the conventional Schottky diodes using Si(100) substrates. That is, reverse leakage currents are small, ideality factors are close to unity, and barrier heights are larger.
Improvement in Surface Morphology and Crystal Epitaxial CaF2 on Si (100) Through two Mbe Growth Stages
Authors: Morimoto Yoshihiro , Matsumoto Shoichiro , Sudo Shoji , Yoneda Kiyoshi
Published: March 2011

We report the first study on improvement in surface morphology and crystal quality of as—grown epitaxial CaF2 film on a (100) Si substrate grown through two MBE growth stages without any post-growth treatment. The degree of improvement in surfacemorphology and crystal quality depends not only on the thickness of an initial thin CaF2 film grown at the early growth stage of 550ºC but also on both the subsrate temperature and thickness of a sequential grown CaF2 film used for thesecond growth stage. Under optimum conditions, the CaF2 films exhibited high quality with an RBS/channeling minimum yield of 4%, together with a very smooth surface morphology without any other nuclel or cracks.
Epitaxial BaF2-CaF2 Stacks on Si(111) and Si(100)
Authors: Blunier S. , Zogg H. , Weibel H.
Published: March 2011

Stacks of non lattice matched epitaxial CaF2, SrF2 and BaF2 layers have been grown by MBE onto Si(lll), and, for the first time, onto Si(l00). On CaF2 covered Si(lll) surfaces, BaF2 grows in a 2—d way after formation of the first monolayers despite a lattice mismatch of 14%. On Si(l00), BaF2 grows with the same (100)—lattice orientation as the underlying substrateif at least a thin (=100 Å) intermediate CaF2 layer is deposited first. Growth is 3—d on (100)—surfaces because of the large (100)—surface free energy of the group IIa—fluorides. By applying in situ short anneal cyclesat the first stages of growth, the crystallographic quality increases for (111)— as well as for (100)—orientation.
Localized Epitaxial Growth of IrSi3, ReSi2, and Rh3Si4 on (111) and (00l)Si
Authors: Chu J.J. , Chen L.J. , Tu K.N.
Published: March 2011

IrSi3, ReSi2, and Rh3Si4 have been grown epitaxially on (111) and (001) Si. Transmission electron microscopy has been applied to characterize the epitaxial films. The orientation relationships between epitaxial sulicides and substrate silicon were determined from electron diffraction analysis. The average size, areal fraction of surface coverage, and fraction of epitaxy were measured. The silicide/silicon interface structures were analyzed.

The best epitaxy in the three metal/Si systems was found to be epitaxial IrSi3 in Ir/(111)Si samples annealed at 1000 °C. Epitaxial regions, as large as 40 μm in size, were observed. Three major modes of IrSi3 epitaxy on (111)Si were identified.
Technological Prospects for Germanium Silicide Epitaxy
Authors: Bean John C.
Published: March 2011

This paper describes preliminary device work on GexSil−x based devices and examines progress towards the realization of a silicon based heterostructure technology. Target areas for further work are identified including: An enhanced understanding of metastable-growth processes; The need for defect confinement in discommensurate epitaxy; Elimination of manufacturing barriers caused by particulate induced defects in MBE and low growth rates in low temperature CVD.

Over the last five years, studies of GexSi1−x have yielded an understanding of crystal growth mechanisms and information on electrical and optical properties such as bandstructure and heterojunction band alignment. These in turn lead to a number of preliminary device applications including optical detectors, modulation doped transistors and heterojunction bipolar transistors. In this paper, I will try to answer the question posed by the symposium organizers: In the germanium silicide system, has our understanding and experience reached the point that we have the basis for a technology, and if not, where must further work be done?
Structural Effects in Al(111)/Si(111) Heteroepitaxy by Partially Ionized Beam Deposition α
Authors: Yapsir A. S. , Choi C.-H. , Yang S. N. , Lu T.-M. , Madden M. , Tracy B.
Published: March 2011

Single crystal Al(111) films were grown on Si(111) surface at room temperature under a conventional vacuum condition using the partially ionized beam (PIB) deposition technique. The Al films were deposited with an ion to atom ratio of about 0.3% and an acceleration voltage of 1 kV. Transmission electron microscopy (TEM) analysis showed that the as-deposited films were single crystal with certain density of dislocation networks. These dislocations disappeared following a heat treatment at 450°C for 30 min. From X-ray diffraction and TEM patterns, it was observed that the Al(111) was aligned to the substrate with Al<1l0>//Si<1l0>. Possible mechanisms of the PIB epitaxial growth and a novel structural defect that is unique to this large lattice mismatch system are discussed.
Metastability in SiGe/Si Strained-Layer Structures
Authors: Dodson Brian W.
Published: March 2011

The physics governing growth and stability properties in SiGe/Si strainedlayer structures is reviewed. The role of metastability in crystal growth is outlined. Experimental data on stability limits and rates of strain relaxation are examined. We conclude that essentially all observations on relaxation of semiconductor strained-layer structures can be explained by standard models of plastic deformation adapted to the special conditions controlling dislocation dynamics in these structures.
Growth Studies of Heteroepitaxial Ge Films ON Si
Authors: Heim D.J. , Holesinger T.G. , Lakin K.M. , Shanks H.R.
Published: March 2011

One of the approaches to the growth of GaAs on Si substrates involves the use of a heteroepitaxial buffer layer such as Ge to reduce lattice mismatch. Recently, we have had success in growing heteroepitaxial Ge films on low temperature (∼275-500°C) Si substrates by the ionized cluster beam (ICB) technique. The design of a computer-controlled phase modulated ellipsometer for rapid monitoring of the initial stages of nucleation will be described. Ellipsometric data for single crystalline, polycrystalline and amorphous morphologies are reported.
Heteroepitaxy on (001) Silicon: Growth Mechanisms and Defect Formation.
Authors: Pirouz P. , Ernst F. , Cheng T. T.
Published: March 2011

In the growth of thin films of compound semiconductors on (001) silicon substrates by vapor deposition techniques, it is usual to employ a two-step process. In this method, an initial (buffer) layer is first grown at a relatively low temperature; once a continuous film has formed on the substrate, its temperature is raised for the subsequent bulk growth. Carrying out the growth in a one-step process by heating the substrate to the final temperature before allowing the gases into the CVD reactor usually results in a polycrystalline aggregate. In this paper, classical nucleation and growth mechanisms are used to explain-the reasons for the different morphology of the one-step and two-step growth films.

The heteroepitaxial films on (001) silicon often contain a high density of stacking faults and twins. The occurrence of these planar defects is usually attributed to stresses that arise from lattice mismatch and/or thermal mismatch (differences in coefficients of thermal expansion) between the substrate and the epilayer. It is argued that, in fact, mismatch stresses play a minor role in the generation of planar defects. Instead, an alternative mechanism for their formation is proposed which is based on the facetted shape of nuclei and errors in stacking of {111} planes which occur during deposition on the facets.

Conventional and high resolution transmission electron microscopy have been used to investigate three systems grown by CVD or MOCVD: SiC/Si, GaAs/Si and GaP/Si. These systems have different lattice and thermal mismatches, and the results support the proposed model for the formation of defects.
Multiphoton Excitation Techniques in Combustion Diagnostics
Authors: Goldsmith J. E. M.
Published: March 2011

Multiphoton excitation provides spectroscopic access to several species that are very important in flame studies, but that cannot be detected in combustion environments using conventional optical techniques. This paper describes applications of multiphoton excitation techniques for detecting such species in combustion environments, with an emphasis placed on measurements of atomic hydrogen in flames.
Space Potential and Ion Energies in a Low Pressure Discharge Containing at least Two Negative Species
Authors: Ingram S G , Braithwaite N St J
Published: March 2011

A Tonks-Langmuir type model for a one-dimensional low pressure (collisionless) plasma containing at least two species of Maxwellian negative charge carriers is examined. The solutions of this model yield the positive ion energy distribution at the sheath edge without needing to specify the ionization process. This distribution has a width consistent with the potential drop across the plasma, and is shown to satisfy the generalised Bohm criterion for sheath formation. However by assuming a form for the ionization rate in the plasma, the potential profile across the discharge has been calculated. It has been found that for a range of plasma parameters the solution for the potential at which quasineutrality fails becomes triple valued; the physical solution in this regime is identified.

Many plasmas used for materials processing contain negative ions. It is important to understand how these ions influence the positive ion energy distribution at the substrate where the processing occurs.

This work is also of relevance to the behaviour of Langmuir probes in electronegative plasmas.
Interferometry Techniques on Fusion Plasmas
Authors: Peebles W. A.
Published: March 2011

Optical interferometry techniques allow phase changes in a medium to be accurately determined. Since plasmas introduce a phase modification proportional to electron density, interferometry has been used routinely to determine the time development of electron density profiles in magnetic confinement fusion plasmas. The present paper describes the basic principles of interferometry of plasmas and establishes criteria regarding wavelength selection, vibrational phase noise, phase averaging etc. In addition, recent advances at UCLA in interferometry of fusion plasmas will be described. For example, high spatial sampling has allowed the detailed study of MHD phenomena such as sawteeth and Mimov oscillations, and 2-D imaging interferometry has permitted tomographic reconstruction of electron density contours. Difficulties associated with interferometry on future fusion devices, such as CIT, will also be discussed together with possible solutions.
A Microwave Interferometer for Density Measurement and Stabilization in Process Plasmas
Authors: Pearson David I. C. , Campbell G. A. , Domier C. W. , Efthimion P. C.
Published: March 2011

A low-cost heterodyne microwave interferometer system capable of measuring and/or controlling the plasma density over a dynamic range covering two orders of magnitude is demonstrated. The microwave frequency is chosen to match the size and density of plasma to be monitored. Large amplitude, high frequency fluctuations can be quantitatively followed and the longer-time-scale density can be held constant over hours of operation, for example during an inline production process to maintain uniformity and stoichiometry of films. A linear relationship is shown between plasma density and discharge current in a specific plasma device. This simple relationship makes control of the plasma straightforward using the interferometer as a density monitor. Other plasma processes could equally well benefit from such density control capability. By combining the interferometer measurement with diagnostics such as probes or optical spectroscopy, the total density profile and the constituent proportions of the various species in the plasma could be determined.
Mass Spectrometric Studies of Ions Produced in Halofluorocarbon Plasma Etching of Silicon and Silicon Dioxide
Authors: Occhiello E. , Garbassi F. , Coburn J. W.
Published: March 2011

The distribution of ions present in halofluorocarbon (CF4, CF3Cl, CF3Br, CF2Cl2 ) plasmas has been studied by mass analysis of the ions extracted from the discharge. Silicon and silicon dioxide targets have been used to study the discharge chemistry in Reactive Ion Etching (RIE) conditions. In the case of silicon, both fluorine and chlorine participate in the etching; therefore, the discharge is enriched in halocarbon oligomers and etch products containing fluorine, chlorine and bromine. The higher reactivity of fluorine induces the formation of chlorine or bromine-enriched molecules and ions. Chlorine and bromine molecules are formed but their concentration in the discharge is not high due to consumption by etching. The situation is different with the silicon dioxide target. In this case, etching consumes both fluorine and fluorocarbon radicals, leading to the formation of silicon tetrafluoride and carbon oxides. The target, in this case, is “neutral”; the discharge is not enriched in oligomers as for silicon. The tendency to form chlorine and bromine-enriched species is still present and considerable amounts of molecular chlorine and bromine are present in the discharge because they do not participate efficiently in etching.
The Adhesion of Growing Oxides to Metallic Substrates
Authors: Stringer John , Wood Graham C.
Published: March 2011

There are several possible descriptions of the nature of the adhesion between an oxide and a metal substrate, some of which are formally equivalent. These include electrostatic interactions connected with the development of space charge regions, chemical bonding across the interface, van der Waals forces, and mechanical interactions associated with a nonplanar interface. However, the detailed mechanism must also be consistent with the growth process and the associated evolution of the interface for an oxide growing on a metal substrate. The problem is further complicated by the nature of the failure at or near the interface which leads to a phenomenological definition of adhesion which is not necessarily identical to the formal definition, and involves other parameters such as the growth stresses in the oxide, the plasticity of the oxide or the surface metal, and the effect of thermal cycling when the coefficients of thermal expansion of the two phases differ. In this paper, an attempt is made to describe these different aspects of the problem, and to refer to some of the more important ways of modifying the adhesion of an oxide, including the reactive element effect and the segregation of impurities to the interface and the modification of the morphology of the interface.
Plasma Treatment of Polymers for Improved Adhesion
Authors: Kelber Jeffry A.
Published: March 2011

A variety of plasma treatments of polymer surfaces for improved adhesion are reviewed: noble and reactive gas treatment of fluoropolymers; noble and reactive treatment of polyolefins, and plasmainduced amination of polymer fibers. The plasma induced surface chemical and morphological changes are discussed, as are the mechanisms of adhesion to polymeric adhesives, particularly epoxy. Noble gas plasma etching of fluoropolymers produces a partially defluorinated, textured surface. The mechanical interlocking of this textured surface is the primary cause of improved adhesion to epoxy. Reactive gas plasmas also induce defluorination, but oxygen containing gases cause continual ablation of the fluoropolymer surface. Noble and reactive gas (except for hydrogen) etching of polyolefins results in surface oxidation and improved adhesion via hydrogen bonding of these oxygen containing groups across the interface. The introduction of amine groups to a polymer surface by ammonia or amine plasma treatment generally results in improved adhesion to epoxy. However, amine-epoxy ring interactions can be severely effected by steric factors due to chemical groups surrounding the amine.
Photolithography of Polytetrafluoroethylene for Tailored Adhesion
Authors: Rye R. R. , Martinez R. J.
Published: March 2011

Irradiation of polytetrafluoroethylene (PTFE) with Mg(Ka) X-rays is shown to protect the surface against the chemical etching steps used to prepare PTFE for adhesion. Pre-irradiated etched samples of PTFE have adhesion strengths of less than 3% of that for non-irradiated etched samples. The major portion of this decrease in adhesion strength occurs for X-ray exposures of less than 10 min (∼4.8×103 mrads) and failure in every case occurs in PTFE and not in the bonded transition region. XPS measurements (20 Å sampling depth) show little difference in F content between irradiated and non-irradiated samples, but thermal desorption shows increasing fluorocarbon desorption with irradiation time. These results are consistent with the known radiation chemistry of PTFE. Irradiation produced free radicals lead to branching and/or cross-linking, and a surface rich in low molecular weight fluorocarbons. The more rigid cross-linked surface is resistant to deep (10,000 Å) chemical attack and the bond formed is with a surface rich in short chain fluorocarbons. Both a thin boundary region and bonding to short chain species is expected to lead to weak adhesive bonding. Electron irradiation is shown to lead to protection against chemical etching comparable to that obtained with X-rays. With electrons one has the capability of rastering the electron beam and drawing low adhesion strength patterns with resolution limited by the beam diameter.
Oxygen Reactive Ion Beam Etching on Polyimide to Enhance Copper Film Adhesion
Authors: Paik Kyung W. , Ruoff Arthur L.
Published: March 2011

Polyimide(PI) films were modified by O2 reactive ion beam etching(RIBE) to make special surface features which enhance the adhesion of copper films. The top plane and the cross-sectional plane of PI films were changed to a grass-like structure and a plate-like structure, respectively. The reason for these surface morphological changes is presumably due to the structural inhomogeniety of PI. XPS studies show that the O2 RIBE oxygenates the PI, resulting in an increase in oxygen and a decrease in carbon and nitrogen. The adhesion of evaporated copper on the O2 RIBE modified PI was substantially increased. In this study, the maximum peel strength of modified PI, 70 grams/mm, is more than 25 times larger than that of the unmodified PI, 2.5 grams/mm. Two types of failure mechanisms were observed with various ion doses:adhesive failure at the Cu/PI interface and at very large doses cohesive failure at the roots of the thin and long grass blades of PI.
The Elastic Behavior of Partially-Sintered Materials
Authors: Green David. J. , Brezny Rasto , Nader Chris
Published: March 2011

A simple model is presented for the elastic behavior of a powder compact that has undergone small amounts of sintering. The analysis shows that the elastic constants are sensitive to small changes in the interparticle contact areas. The elastic constants are also shown to be dependent on factors relating to the structure of the powder compact, such as the particle coordination number. It is concluded that such elastic constant measurements are a valuable tool in studying adhesion within compacts, the mechanisms involved in the initial stages of sintering and the characterization of powders.
Density Functional Theory for Thin Film Adhesion
Authors: Senbetu L. , Pronko J. G. , Bardin T. T.
Published: March 2011

A theoretical formalism to describe interface adhesion phenomena between materials has been developed. In this model electron densities, potentials, and adhesion energies of thin metal films at metal–semiconductor and metal–insulator interfaces are derived through a partially self–consistent calculation. The theory is based on a density–functional formalism applied to a simple model of the system in which the metal is replaced by a uniform positive background and the semiconductor by a continuum with a static dielectric constant. Numerical results of the metal electron density distribution and effective potential of Au–vacuum and Au–GaAs system, and the adhesion energy at Au–GaAs interface are presented. The interface energies are then used to estimate the adhesion strength and compare with experiment.
Direct Observation of Friction at the Atomic Scale
Authors: McClelland Gary M. , Mate C. Mathew , Erlandsson Ragnar , Chiang Shirley
Published: March 2011

An atomic force microscope has been used to measure the frictional force on a tungsten tip sliding across the basal plane of graphite at low loads < 10-4 N. The frictional force displays the 2.5 Å periodicity of the graphite surface.
Liquid Mediated Adhesion of Ultra-Flat Solid Surfaces
Authors: Matthewson M. J. , Mamin H. J.
Published: March 2011

The presence of a liquid film between contacting ultra-flat surfaces can produce high levels of adhesion. The liquid film may be a pre-existing film of lubricant or may be a capillary condensate. This paper considers the meniscus and viscous components to the adhesion. Different regimes are identified which are distinguished by differing quantities of liquid in the gap between the surfaces. The role of surface roughness is also evaluated. The force required to separate the surfaces in the tangential direction is considered. The magnitude of this force is dependent not only on the adhesion but also on the separation rate and loading conditions.
Growth and Thermal Stability of γ/γ'-α Eutectic Composite
Authors: Nakagawa Y. G. , Nemoto M.
Published: March 2011

The paper summarizes the results of a series of investigations carried out for a γ/γ'-α(Ni-Al-Mo) eutectic. The subjects include a thermal analysis of the composite growth in a high temperature gradient provided by a fluidized bed cooling, a study of defect formation such as the banding structure at unstable thermal conditions, Tem observation and phase identification for micro-phases existed in an as-growth state as well as phases produced after various quench and aging treatments, and an evaluation of the composite thermal stability in terms of the microstructures and the high temperature strength. The fluidized bed placed beneath a melting furnace was proved to establish a temperature gradient equivalent to the liquid metal cooling, and to promote a stable steady growth of the composites without bandings. Quenching the eutectic above a peritectoid temperature diminished the blocky γ'. The subsequent aging treatments induced small Mo platelets above 830°C and blow the temperature a metastable Ni2Mo particle precipitation in the γ phase causing appreciable composite hardening. The creep rupture strength, however, was reduced by the heat treatment due to δ-NiMo phases precipitated during the test in consumption of the Mo fibers.
Development of The γ-γ'-Cr3C2 In-Situ Composite
Authors: Mclean M. , Quested P.N. , Henderson P.J. , Menzies K.
Published: March 2011

The effects of various alloy additions to the microstructures and properties of the γ-γ'-Cr3C2 in-situ composite have been investigated. Combinations of platinum and Yttrium prevent the formation of an additional phase that occurs when Yttrium alone is added; the phase morphology is unaffected by rhenium and ruthenium dopants.

Combined quenching studies and differential thermal analysis show that phase alignment at high growth rates in this alloy is not due to plane front solidification but to highly branched carbide growth ahead of the melt/ matrix interface. This mechanism allows good phase alignment to be achieved over a wide composition range. Tests on six alloy casts to commercial specifications indicate retention of, and often improvement to, the microstructures and properties obtained with laboratory control.
In Situ Composites Prepared By Solidification And Mechanical Techniques
Authors: Verhoeven J. D.
Published: March 2011

An alternate in situ technique is presented for preparation of aligned microstructures which has been successfully applied to the preparation of copper alloys. In this technique, a two phase alloy is first prepared by conventional casting techniques to produce a random array of dendrites of phase 1 in a matrix of phase 2. The casting is then reduced to wire size by mechanical reductions. It is demonstrated that the alignment of the dendritic phase produced by the mechanical reduction is surprisingly good, and that one can achieve a wide range of microstructural control over the filament size and morphology by utilization of controlled coarsening anneals followed by additional wire drawing. Examples are presented of Cu-Nb alloys which are converted to Nb3 Sn-Cu superconducting wires possessing excellent critical current values, and of Fe-Cu alloys which produce wires having quite high strength to resistivity ratios.
The High Temperature Degradation of Cd-Zn and Pb-Cd Eutectic Alloys
Authors: van de Merwe R. H. , Smith R. W.
Published: March 2011

Various thermal treatments have been applied to Cd-Zn and Pb-Cd eutectic alloys in an attempt to better understand the thermal stability of eutectics close to their melting temperatures. Specimens of each system were grown at 40, 400 and 4000 mm/hr to obtain microstructures which were either lamellar, lamellar/cellular, or cellular. These specimens were thermally treated by either: (1) isothermal annealing at 0.95 Tm (up to 192 hrs), (2) thermal cycling between room temperature and 0.95 Tm (up to 64 cycles), (3) exposing to thermal gradients parallel to the growth direction and maintaining one end of the specimen at 0.95 Tm and the opposite end at room temperature (up to 48 hrs). It was found in all cases that some microstructural changes occurred but that the two alloy systems displayed marked differences in degradation sequence. An explanation and interpretation of these decay sequences is attempted. The mechanical properties of the variouslytreated alloy specimens were determined and are correlated with the observed microstructural features. The Cd-Zn specimens coarsened more rapidly than equivalent Pb-Cd specimens, as might be expected since the interphase boundary energies have been reported as 86 and 67 erg/cm2respectively.
The Response of Mnsb-Sb Composites to Isothermal Aging
Authors: Marinis T. F. , Sekerka R. F.
Published: March 2011

An eutectic alloy of antimony and manganese was directionally solidified to produce a composite of cylindrical fibers of MnSb aligned in a Sb matrix. The fibers were about 3 microns in diameter by 1 millimeter long and occupied 30% of the composite volume. Isothermal aging caused the fibers to develop undulations that had an average wavelength of 1.74 + 0.45 times the fiber circumference. The Nichols' and Mullins' model of fiber spheroidization predicts an undulation wavelength of √2 times the fiber circumference, for interface diffusion control. The Coine model, for volume diffusion control, predicts a wavelength that approaches infinity for this fiber volume fraction. Our modeling efforts have shown that the predicted wavelength is quite sensitive to the assumed spatial correlation between nodes on adjacent fibers. We also found that the undulation growth rate achieves a broad maximum as a function of wavelength, which may account for the large standard deviation associated with our measurements.
The Elevated Temperature Response of Silicon Carbide and Boron Reinforced Aluminum and Titanium Metal Matrix Composites
Authors: Madhukar M. S. , Fareed A. , Awerbuch J. , Koczak M. J.
Published: March 2011

The elevated temperature modulus and strength of aluminum, titanium, and hybrid aluminum/titanium metal matrix composites were investigated. Aluminum (6061-F) and titanium (Ti-6AI-4V) metal matrix composites reinforced with AVCO silicon carbide or boron fibers were vacuum hot pressed and their tensile properties evaluated to temperatures in excess of 300°C. Microstructure, fracture modes and mechanical properties were characterized to assess the effect of fibers and matrix on composite strength and modulus as a function of temperature. Finally, a comparison of specific strength and modulus is provided as a function of temperature. In general, the metal matrix composites exhibited low density (<2.8 g/cm3), high modulus (200 GPa), and strengths equivalent to 1250 MPa at 250–300°C. The effect of fiber orientation on axial stiffness was investigated using boron fiber reinforced aluminum (6061-F).
Enhanced Plasticity of Mechanically Alloyed Aluminum IN90211
Authors: Bieler T. R. , Nieh T. G. , Wadsworth J. , Mukherjee A. K.
Published: March 2011

The tensile behavior of IN90211 was characterized at strain rates between 0.0001/sec and 340/sec at temperatures between 425 and 475 °C. At strain rates below 0.1/sec, the strain rate sensitivity m is about 0.027, with corresponding low elongation (<100%). At strain rates above 0.1/sec, the strain rate sensitivity increases to 0.26. A maximum elongation of 500% was obtained at 475 °C at a strain rate of 2.5/sec. Grain boundary sliding and rotation was observed on the highly elongated specimens and fracture surfaces exhibited intergranular fracture. Experimental data in the high strain rate regime (superplastic) revealed the existence of a temperature dependent threshold stress that seemed unrelated to the low stress deformation regime. This result is consistent with stress relaxation experiments. These threshold stresses are generally lower than those typically observed in other oxide dispersion strengthened (ODS) alloys. This observation is not expected from conventional superplastic creep theory.
Glass and Ceramic Matrix Composites Present and Future
Authors: Prewo Karl M.
Published: March 2011

During the past 25 years materials scientists have been able to make a major change in the way materials are considered for application. In the past designers have worked with data representing the properties of homogeneous, isotropic materials and designed their components to fit written accepted ranges of “design allowables”. More recently, however, the concept of composite materials has permitted almost limitless tailoring of composites to create entirely new designs never previously possible. By choice of types of material constituents, their relative percentages and their orientation the designer can now work closely with the materials scientist to optimize system performance. This philosophy has firmly taken hold in the family of fiber reinforced polymer matrix composites and more recently has made metal matrix composites an industrial reality.
Microstructural characterization of a SiC Whisker-Reinforced HIPped Reaction-Bonded Si3N4
Authors: Farmer S. C. , Pirouz P. , Heuer A. H.
Published: March 2011

A SiC whisker reinforced HIPped RBSN material fabricated with a Y2O3 sintering aid was characterized using TEM. The matrix is > 90% β-Si3 N4 with a Y-Si-O-N glassy phase at the Si3 N4 grain boundaries and about the SiC whiskers. The SiC whisiers are heavily faulted and have a well defined core. Si3 N4 precipitates are observed in the core region after composite fabrication. A preliminary mechanism for the growth of the SiC whisker, based on the VLS mechanism is proposed.
The Frictional Resistance to Sliding of a SiC Fiber in a Brittle Matix
Authors: Weihs T. P. , Dick C. M. , Nix W. D.
Published: March 2011

The frictional resistance to sliding of a SiC fiber in a brittle, ceramic matrix has been measured with two different experimental techniques. Both techniques utilize a load-controlled indentation instrument. In the first technique, the ends of individual fibers are displaced down into the matrix. The frictional resistance to sliding, τ, was calculated using the elastic model of Marshall and Oliver and the load-displacement data. Alternatively, fibers have been displaced along their complete lengths through thin sections of the matrix. The critical force for complete slip and the sample geometry determined τ for a given fiber. For this technique slip over the complete length of a fiber was verified by the protrusion of that fiber from the bottom of the sample. By inverting the sample and loading the protruding fiber, the frictional resistance to reverse sliding was also measured. The results obtained from the two complementary techniques are in general agreement.
Creep Behavior of an Al2O3-Sic Composite
Authors: Lipetzky P. , Nutt S. R. , Becher P. F.
Published: March 2011

The addition of SiC whiskers to Al2O3 causes significant improvement in mechanical properties, including fracture toughness, thermal shock resistance, and creep resistance. The creep response of a whisker-reinforced alumina composite has been measured using four-point flexural loading at temperatures of 1200 and 1300C. Composites were fabricated by hot-pressing a blend of alumina powder with 33 volume percent SiC whiskers. The creep data showed a stress-dependent stress exponent equal to 1 at low stress levels and ranging from 4–6 at higher stresses. The applied stress at which the transition occurred was temperature dependent and ranged from 50–125 MPa. Mechanisms of creep deformation were determined from TEM observations of specimens prepared from interrupted creep tests. Voids were observed at grain boundary-interface junctions in tensile regions and whiskers within the composite were sometimes oxidized where voids had formed. TEM observations from specific stages of steady state creep reached under different applied loads are presented, and the relative contributions of different deformation mechanisms are discussed.