Laura Riester

Young's modulus of nanocrystalline Fe measured by nanoindentation

Abstract Nanoindentation techniques were used to measure Youngs modulus for nanocrystalline Fe samples produced by inert-gas condensation and warm consolidation. The samples had grain sizes of 4–20 nm and residual porosity of 2–30% calculated relative to conventional Fe. Values of Youngs modulus for the nanocrystalline Fe are reduced relative to that of conventional, fully dense Fe. A review of Youngs modulus for other nanocrystalline materials showed similar trends. Published results for porous conventional Fe showed similar reductions in Youngs modulus for samples with comparable porosity levels. The observed reductions in Youngs modulus for both the nanocrystalline and the conventional porous Fe can be described adequately by several theories utilizing spheroidal porosity.

Buckling instabilities in multiwalled carbon nanotubes under uniaxial compression

We report experimental observations of shell buckling instabilities in freestanding, vertically aligned multiwalled carbon nanotubes subjected to uniaxial compression. Highly ordered and uniform arrays of carbon nanotubes embedded in an alumina matrix were fabricated and subjected to uniaxial compression using a nanoindenter. The buckling load was found to be on the order of 2μN for nanotubes with 25nm outer radius, 13nm inner radius, and heights of 50 and 100nm. Good agreement was found between the experimental observations and the predictions of linear elastic shell buckling theory.

Porous Methylsilsesquioxane for Low-k Dielectric Applications

A commercially available spin-on glass ~methylsilsesquioxane, MSQ! was modified by the introduction of porosity. The porosity reduced the effective dielectric constant of the MSQ by the incorporation of air. The pores were created by adding a sacrificial polymer ~substituted norbornene polymer! to the silsesquioxane matrix. The sacrificial material was thermally decomposed to form nanosize voids within the films. The physical and electrical properties of the porous films were studied as a function of the reactivity of the sacrificial polymer with the glass, and the loading and molecular weight of the sacrificial polymer. Transmission electron microscopy was used to evaluate the porous microstructure. Cross-sectional images show pores of nearly spherical geometry with 5-20 nm diam. The dielectric constant and the index of refraction of the porous MSQ were lower after the decomposition of the sacrificial material. The dielectric constant decreased from 2.7 for a nonporous MSQ film to ;2.2 for a film with 30 wt % loading of the sacrificial polymer. In a similar way, the index of refraction was reduced from 1.42 to 1.29 for the porous MSQ film. The mechanical properties were evaluated using nanoindentation techniques. This paper focuses on the significant improvements observed upon introduction of porosity to the films. The fracture toughness, or the resistance to crack propagation, increased dramatically with porosity, as compared with the nonporous MSQ films. As a result, thicker MSQ films can be fabricated without spontaneous cracking. The elastic modulus and the hardness of the porous films were measured and showed a reduction in both properties with increasing porosity in the film.

A study of microstructure and hardness of bulk copper sample obtained by consolidating nanocrystalline powders using plasma pressure compaction

Bulk copper samples were prepared by consolidating ultrafine-grained copper powders using the technique of Plasma Pressure Compaction. The microstructure and hardness are compared with a sample made from consolidating micron-sized powders using identical processing conditions. Samples made by consolidating nanometer powders revealed evidence of grain coarsening and a higher density than the sample made from consolidating micron-sized powders. Both nanohardness and microhardness measurements revealed an increase in hardness of the bulk sample obtained by consolidating the smaller sized powders. Influence of powder particle size and processing variables on microstructure, to include the presence and distribution of artifacts, density, and microhardness are discussed.

Nanoindentation measurements of combustion CVD Al2O3 and YSZ films

Abstract Combustion chemical vapor deposition (combustion CVD) was used to deposit thin films of yttria stabilized zirconia (YSZ) and alumina (Al 2 O 3 ). Nanoindentation analysis for hardness, modulus and fracture toughness of the films as well as several bulk materials, including single crystal Al 2 O 3 , MgO, SiO 2 , YSZ and polycrystalline Al 2 O 3 was conducted. YSZ films that were produced with a total cation molarity of 0.005 M possessed significant surface roughness that was not conducive to nanoindentation measurements. The lower concentration investigated, 0.002 M provided a repeatable deposition condition that produced thin films with consistent hardness and modulus values. Load-displacement measurements at very low loads (up to total displacements of 200 nm) showed that the Al 2 O 3 films tended to plastically deform, whereas the YSZ films showed less of a tendency to do so. For Al 2 O 3 films that were 0.38±0.09 μm thick, the modulus, hardness and fracture toughness values were 28.6±1.6 GPa, 479±15 GPa and 2.22±0.31 MPa m 0.5 , respectively; for YSZ films that were 0.65±0.05 μm thick, the values were 16.1±4.6 GPa, 388±89 GPa and 1.67±0.46 MPa m 0.5 , respectively. These values were found to be consistent with the values measured via nanoindentation in this work for bulk samples of Al 2 O 3 and YSZ, as well as to those reported in the literature.

Characterization of sputtered amorphous platinum dioxide films

Amorphous platinum dioxide, a-PtO2, films are formed commonly during reactive sputtering of platinum at relatively high power density levels and high oxygen partial pressures. The structure of a-PtO2 is intermediate between the crystalline alpha and beta phases of this compound and either phase may form upon annealing or by lowering the power density during sputtering. Amorphous platinum dioxide is a semiconductor, and its resistivity depends on deposition parameters. Films of a-PtO2 are dense, chemically resistant, smooth, reflective, and have a hardness similar to titanium nitride. The films may be reduced in hydrogen at room temperature or in carbon monoxide at 200 °C to produce metallic platinum with crystallite sizes in the range of 5–10 nm. Any of these properties may be exploited to produce films that could be used in the development of sensors, optical materials, and in microelectronics.

Nanoindentation characterization of surface layers of electrical discharge machined WC/Co

Abstract This study applies nanoindentation and other analysis techniques to investigate the influence of wire electrical discharge machining (EDM) process on the structure and properties of machined surface layers of WC–Co composites. Multiple indents were conducted on the cross-section of the surface recast layer, sub-surface heat-affected zone, and bulk material. The energy disperse X-ray spectrometry and X-ray diffraction were used to analyze the material compositions in the heat-affected zone and recast layer and to study the electrical spark eroded surface. The indents were inspected by scanning electron microscopy to distinguish between regular and irregular indents in these three regions. Irregular indents were caused by the porosity, soft matrix material, separation of grain boundaries, and thermal cracks caused by EDM process. The hardness and modulus of elasticity obtained from regular indents in bulk material and heat-affected zone were comparable to those of WC. It was found that the recast layer had lower hardness and modulus of elasticity than the bulk material and heat-affected zone.

Mechanical properties of carbon—carbon composite components determined using nanoindentation

Abstract The near-surface mechanical properties of the individual components (fiber, resin char, and CVD carbon) within several carbon—carbon composites are reported from the analysis of nanoindentation data. These near-surface properties (elastic modulus, stiffness, and hardness) are important parameters in thermal and mechanical models of friction processes occurring in carbon—carbon composite brakes.

Antimicrobial properties of diamond-like carbon-silver-platinum nanocomposite thin films

Silver and platinum were incorporated within diamond-like carbon (DLC) thin films using a multicomponent target pulsed laser deposition process. Transmission electron microscopy of the DLC-silver and DLC-platinum composite films reveals that these films self-assemble into particulate nanocomposite structures that possess a high fraction of sp3-hybridized carbon atoms. Nanoindentation testing of DLC-silver nanocomposite films demonstrates that these films possess hardness and Young’s modulus values of approximately 35 and 350 GPa, respectively. DLC-silver-platinum films demonstrated exceptional antimicrobial properties against Staphylococcus and Pseudomonas aeruginosa bacteria.

Chemically Bonded Porogens in Methylsilsesquioxane II. Electrical, Optical, and Mechanical Properties

The electrical, optical, and mechanical properties of porous methylsilsesquioxane (MSQ) films created using two different sacrificial polymers: trimethoxysilyl norbornene (TMSNB), and triethoxysilyl norbornene (TESNB) were evaluated in this study. The introduction of porosity lowered the dielectric constant, the index of refraction, and the elastic modulus and hardness of the films as compared to the nonporous MSQ films. The dielectric constant was lowered from 2.7 for a pure MSQ film to 2.35 for a film with 30 wt % initial concentration of TMSNB. Similarly, the index of refraction was lowered from 1.42 to 1.30 for a 30:70 wt %. TMSNB:MSQ film. The TMSNB:MSQ films showed a transition from closed-to-open cell porosity in the range from 20 to 30 wt % loading of sacrificial polymer as determined from positron annihilation spectroscopy. Improvements in the fracture toughness were observed for the TESNB:MSQ films as compared to the pure MSQ or TMSNB:MSQ films.