M.G. Norton

Electron microscopy study of tin whisker growth

The growth of tin whiskers formed on sputtered tin layers deposited on brass was studied using electron microscopy. The occurrence of whiskers appeared to be largely independent of the macroscopic stress state in the film; rather it was microscopic compressive stresses arising from the formation of an intermetallic phase that appeared to be the necessary precursor. Whisker morphology was a result of whether nucleation had occurred on single grains or on multiple grains. In the latter case, the whiskers had a fluted or striated surface. The formation of whiskers on electron transparent samples was demonstrated. These samples showed the whiskers were monocrystalline and defect free, and that the growth direction could be determined.

Structural and mechanical characteristics of anodic oxide films on titanium

Abstract Oxide films were grown electrochemically on polycrystalline titanium in 0.1 M sulfuric acid (H2SO4) from open-circuit potential to a final potential of 9.4 V (vs silver-silver chloride [Ag...

Pulsed-laser deposition of polytetrafluoroethylene

Thin films of polytetrafluoroethylene have been deposited on amorphous substrates by the pulsed-laser deposition technique. By transmission electron microscopy, the polymer films were shown to consist of both amorphous and crystalline components. The data for the crystalline component are consistent with it being highly ordered with the long helical molecular chains aligned parallel to the film-substrate interface plane. The fraction of crystalline material in the films was found to be related to the substrate temperature during deposition with the maximum amount of crystalline material occurring when the substrate temperature was close to the melting temperature of the polymer.

Evidence for unzipping reactions in the laser ablation of polytetrafluoroethylene (PTFE)

Abstract We have characterized the neutral and charged species emitted by pulsed-laser irradiation of polytetrafluoroethylene (PTFE) in vacuum at 248 nm in fluence regimes appropriate for the pulsed-laser deposition of PTFE thin films. The time-of-flight behavior of the major neutral species is consistent with thermal emission at temperatures where PTFE is known to decompose thermally. The laser fluence dependence of the intensity of the most intense neutral component (the C 2 F 4 monomer) is analyzed in terms of a thermally activated decomposition process. Under isothermal conditions, thermal decomposition is believed to be rate limited by radical formation, with an activation energy of a few eV. In contrast, the fluence dependence of the monomer intensity indicates an activation energy of about 0.9 eV — appropriate to an unzipping reaction rate limited by radical transport along the polymer chain.

Strength enhancement of single crystal laser components

The effect of chemical etching on the surface roughness and fracture strength of Nd:yttrium-aluminum-garnet single crystals was investigated. Etching the laser host material in a 1:1 mixture of concentrated sulfuric and phosphoric acid at elevated temperatures enabled material removal from the surface of laser rods cored from single-crystal boules. The roughness on the rod surface increased from the as-drilled condition after etching, but after 17 μm of material was removed, the roughness remained approximately constant. The modulus of rupture increased from 133-530 MPa when 87 μm of material was removed by the chemical etching procedure.

Effect of thermal treatment on failure modes in tungsten wire

The modes of failure, from microvoid coalescence to transgranular cleavage, are documented in tungsten wire as a function of thermal history. The failure is primarily ductile at room temperature due to an initial highly elongated fine grain structure. When heat treated at temperatures of approximately 1350 K, strong evidence of transverse grain boundary formation is evident on the primarily intergranular failure surfaces. However, when subjected to heat treatments at 1630 K for 5 min, transgranular cleavage dominates both at temperature and after cooling to room temperature. It is suggested that this change is indicative of strengthening grain boundaries at the higher temperature heat treatments. In all of the cases examined, the fractography of tungsten wire allows the thermal history of the specimen to be determined.

Effect of ion fluence on the surface morphology of single crystal magnesium oxide implanted with xenon

The surface morphology of (001)-oriented single crystal magnesium oxide (MgO) implanted with xenon ions has been examined using atomic force microscopy. It was found that at the lowest fluence used in this study (1.0{times}10{sup 14}/cm{sup 2}), slight roughening of the (001) surface occurred. The magnitude of this roughening remained fairly constant with increases in fluence in the range 1.0{times}10{sup 14}/cm{sup 2} to 3.0{times}10{sup 16}/cm{sup 2}. Implantation at fluences of {ge}1.0{times}10{sup 17}/cm{sup 2} caused significant surface roughening with the concomitant formation of micro-sized blisters. The appearance of some of these blisters resembles the rosette pattern which is also observed when the cleaved surfaces of MgO crystals are etched following indentation using a spherical indenter. This observation suggests that these blisters are formed by the growth of xenon inclusions, during implantation, by a dislocation loop punching mechanism. {copyright} 1995 {ital Materials} {ital Research} {ital Society}.

Incorporating Diverse Majors and Backgrounds in Materials Science Research Experience for Undergraduates (REU) Sites

A summer Research Experience for Undergraduate (REU) site program has been operating at Washington State University for the past five summers. Over this time we have experimented with several modes of organized summer research methods, including students working in individual projects as well as students working in teams. We have balanced the academic standing of the students (freshmen to seniors), as well providing a diverse demographic background. The results of these past five summers will be presented, as well as recommendations for which methods have been the most successful in terms of generating publications and presentations from the students as well as the likelihood of students entering graduate school.

An Upper Division General Education Course on Materials for Non-Engineering Students

We present the structure of a new course which is designed to expose junior and senior level undergraduates in non-engineering fields to materials. Washington State University has a “General Education” requirement, which requires students to take a variety of courses including the area of sciences, humanities, and technology. We have developed this course to satisfy the requirement for technology for upper division students. The results of the enrollment over the past 3 years are presented: each semester more majors are taking the course, suggesting it is reaching an multidisciplinary audience. Comments from the students and plans for the future are discussed.

Relationships between Film Chemistry, Structure, and Mechanical Properties in Titanium Oxide

Titanium oxides were grown anodically to selected final potentials on grade II polycrystalline titanium under different anodization rates. XPS and RBS results show that the oxide consists of primarily TiO2 with a non-stoichiometric oxide/metal interface, with the slower growth rate associated with a thicker layer at the interface. Characterization using TEM reveals that the structure of the oxide evolves from a primarily amorphous phase to islands of crystallites in an amorphous matrix, to an entirely crystalline phase by increasing the polarization potential. Slower growth rates tend to remain crystalline at higher potentials. The mechanical strength of oxide films extracted from load-depth data by nanoindentation varies dramatically for oxide films grown by different rates at 9.4 V, and to a lesser extent at lower potentials. The variation of film strength is associated with both compositional and structural characteristics.