Growing interest in nanomaterials has raised many questions regarding the operating mechanisms active during the deformation and failure of nanoscale materials. To address this, a simple, effective in situ TEM straining technique was developed that provides direct detailed observations of the active deformation mechanisms at a length scale relevant to most nanomaterials. The capabilities of this new straining structure are highlighted with initial results in pulsed laser deposited (PLD) Al-Al2O3 thin films of uniform thickness. The Al-Al2O3 system was chosen for investigation, as the grain size can be tailored via deposition and annealing conditions and the active mechanisms in the binary system can be compared to previous studies in PLD Ni and evaporated Al films. PLD Al-Al2O3 free-standing films of various oxide concentrations and different thermal histories were produced and characterized in terms of average grain and particle sizes. Preliminary in situ TEM straining experiments show intergranular failure for films with 5 vol% Al2O3. Further work is in progress to explore and understand the active deformation and failure mechanisms, as well as the dependence of mechanisms on processing routes.

In situ transmission electron microscopy was used to show that nanocrystalline nickel produced by pulsed-laser deposition undergoes abnormal grain growth at moderate temperatures (225-400°C). The growth rate was found to increase with thickness for the three film thicknesses examined, 50, 80 and 150 nm. The abnormal growth proceeded in an irregular manner: initiation sites and growth direction were unpredictable, and the grains exhibited no preferred orientation. Some abnormal grains show internal boundaries such as twins, while others exhibited lattice misalignments across the grain body. The grains contain many defects, including dislocations, stacking faults and surprisingly, stacking fault tetrahedra. The stacking fault tetrahedra are not a result of quenching nor of electron irradiation-induced lattice displacements; they instead are thought to form from vacancies trapped in the growing grain as it incorporates lower-density material at the high-angle grain boundaries in the nanocrystalline matrix.

Ion implantation was used to form high densities (~1019 /cm3) of small oxide precipitates in Ni in order to investigate the strength mechanism produced by such highly refined structures. Nanometer-size precipitates of Al2O3 and NiO are found to block dislocation motion in the Ni matrix, producing yield strengths up to 4.6 GPa, more than twice that of hardened bearing steel. Dispersion strengthening theory, developed for micrometer-size precipitates and spacings, was found to account quantitatively for the yield strengths produced by nanometer-size oxides as well. Nanoindentation plus finite-element modeling was used to quantify the mechanical properties of implanted metal layers, and was extended to examination of amorphous Si layers formed by self-ion implantation. The amorphous phase was found to have a yield strength of 4.45 ± 0.20 GPa, Young's modulus of 144 ± 7 GPa, and hardness of 10.3 ± 0.4 GPa. The modulus and hardness are reduced by 10% and 15%, respectively, from those of crystalline Si.

Stiction and friction are of concern for the reliable, long-term application of Ni-alloy micromachines. We have found that the application of a 30 - 70 nm hard carbon coating produces a significant reduction in the friction coefficient and wear rate of electroformed Ni substrates in reciprocating sliding contact under simulated MEMS operating conditions. To evaluate the performance of coated components, a series of 70-μm-thick microgears ranging in diameter from 0.2 to 2.2 mm were fabricated from electroformed Ni via standard LIGA processes and fixtured on posts in preparation for the coating procedure. A pulsed vacuumarc deposition process was used to deposit a carbon coating on the gears with the plasma incident at a shallow angle to the gears' top surface. A sample bias of −2 keV was used in order to produce a coating with relatively low stress and good adhesion while maintaining high hardness. This coating process is known to be somewhat comformal to the component surfaces. The coating uniformity, particularly in the high-aspect-ratio areas between the gear teeth, was evaluated with micro-Raman spectroscopy. It is shown that the coating can be applied uniformly on the top gear surface. Between the gear teeth the coating was the same thickness as on top of the gear down to a point 50 μm below the top surface. Below that point (i.e. between 50 and 70 μm), the coating thickness is somewhat thinner, but is still present. These results demonstrate that it is possible to a deposit hard carbon coating on microgears to reduce friction and wear in micromachines.

The microstructures of In0.5Ga0.5P alloys grown on (100) GaAs by MOVPE have been characterized with cross-section TEM and their optical emission examined with photoluminescence at low temperatures. All the alloys exhibit spinodal-like decomposition with compositional modulations along directions in the growth plane. Alloys grown at 775 °C have the highest emission energy, 2.0 eV; growth at 675°C gave the lowest, 1.89 eV, due to strong CuPt-type ordering of In and Ga. The ordered domains are platelets 20 to 200 nm wide and 10-20 nm thick, with antiphase boundaries 1-2 nm apart. We have also formed "unicompositional" quantum wells of thin (1.3-20 nm) ordered layers grown at 675°C between disordered barriers grown at 750°C. Ordering is found only in the active layer, with domains similar to those of thick layers. The emission energy increases by 90 meV as the well thickness is decreased from 10 to 1.3 nm, thus demonstrating quantum size effects solely through disorder-order phenomena.

The microstructures of Si ion-implanted with Cu have been characterized by TEM after annealing. For 1.2 at.%, the Cu is trapped at planar defects, but for 10 at.%, η-Cu3Si forms, allowing Cu to diffuse at its equilibrium solubility. These observations allow proper evaluation of the binding energies of Cu to previously formed internal cavities (2.2 eV) and η-Cu3Si (1.7 eV). The η-Cu3Si in the 10 at.% layer catalyzes oxidation of the Si. The microstructures also indicate that Si implanted with ~2 at.% Cu reforms epitaxially with embedded defects after 8 hr. at 700°C, but for ~10 at.% Cu, epitaxy is not recovered after 6 hours at 600ºC.

We describe the acquisition of Raman and photoluminescence (PL) spectra on porous silicon (PS) samples that emit visible light. Spectra were acquired in both ex situ experiments (after exposure to air) and in situ experiments (with the PS covered either with the hydrofluoric acid electrolyte used in the formation process or water). Our results generally show a correlation of blue-shifted PL with increased oxidation. In one set of ex situ experiments, however, we observed an inconsistency in the shift of the wavelengthof maximum luminescence intensity for PS samples that exhibit oxygenated character in the Raman spectra. A higher anodization current density produced a red shift in the PL spectra in one experiment, while chemical dissolution of the PS by hydrofluoric acid produced the well-known blue shift in the other case. In two in situ experiments, we observed very weak and red-shifted PL for a PS sample immersed in HF (compared to the same sample measured later in air) while in another we immersed air-exposed PS in water and observed a 15-fold increase in PL intensity along with a blue shift in the luminescence maximum.

We have discovered that the β and γ brasses of Cu-Zn exhibit clearly resolved increases in reflectance upon melting with a 30 ns ruby laser, which allow their melt durations to be readily measured. This system thus offers potential for obtaining quantitative information about the solidification kinetics of metals. We have also found that a heteroepitaxial layer of β' brass is formed on the surface of (ordered) γ brass with 63 wt.% Zn following pulsed laser-induced melting. The β' layer is interpreted to mean that the metastable β phase (bcc) formed on the liquid-solid interface as the γ substrate attempted to regrow, and that β ordered to β' (B2) during cooling. The β formation implies that undercoolings > 16 K were attained during the attempted regrowth of the γ phase.

The microstructuTe and mechanical properties of high purity aluminum implanted with 20 at.% oxygen to a depth of roughly 500 nm and subjected to various thermal histories have been examined. Transmission electron microscopy and Rutherford-backscattering spectrometry were used to characterize the depth and nature of the implanted zone. As implanted, the material appears to contain a homogeneous distribution of disordered precipitates with sizes of 1.5-3.5 nm. Annealing at 450 or 550ΰC for 1 hour, induces ordering of the precipitates but only causes slight coarsening. Ultra-low load indentation hardness testing was used to probe the mechanical response of the surface-modified material. The data from the hardness tests were interpreted through the use of a finite-element model; the results indicate the flow stresses of an implanted and annealed layer are as high as 1600 MPa. The as-implanted material is much harder, approaching 3300 MPa. The degree of strengthening expected for the as-implanted and post-annealed material on the basis of the observed microstructure was estimated using several micromechanical models, and the results conform to the findings from indentation testing.

The dual ion implantation of Ti and C into 304 stainless steel has been found to reduce friction and wear in ultrahigh vacuum (UHV). The implantation treatment producing this result, 4.6 × 1017 Ti/cm2 (180 keV) followed by 2.0 × 1017 C/cm2 (50 keV), produced TiC precipitates dispersed in an amorphous surface layer. Friction and wear track compositions were measured in situ with a scanning Auger microprobe without removing the pin from the track. This treatment decreased the friction coefficient from 1.2 to 0.6–0.8 and the wear track width from 342 μm to 225 pm after 1000 cycles. Relative to unimplanted 304, wear tracks formed in UHV and air on implanted ‘304 had more N and less C. Oxygen and the metallic elements were similar in concentration, except for the presence of implanted Ti. Friction coefficients measured in air were less than those in UHV; track composition suggests that oxides or adsorbed moisture helped lower the friction in air.