Search

As the library of potential materials with plasmonic behavior in the infrared (IR) grows, we must carefully assess their suitability for nanophotonic applications. This assessment relies on knowledge of the materials’ optical constants, best determined via spectroscopic ellipsometry (SE). Transparent conductive oxides are great candidates for IR plasmonics due to their low carrier concentration (compared to noble metals) and the ability to tailor their carrier concentration by manipulating the defect composition. When the carrier concentration becomes low enough, phonon and defect states become the dominant mechanisms of absorption in the IR spectral range, leading to near-IR (NIR) tailing effects. These NIR tailing effects can be misinterpreted for free carrier absorption, rendering NIR-visible-ultraviolet-SE (NIR-VIS-UV-SE) incapable of reliably extracting the carrier transport properties. In this work, we report the limitations of NIR-VIS-UV and IR-SE (in terms of carrier concentration) by investigating the transport mechanisms of indium tin oxide, aluminum-doped zinc oxide and gallium-doped zinc oxide. We find regions of carrier concentration where NIR-VIS-UV-SE cannot reliably determine the transport properties and we designate material-dependent and application-specific confidence factors for this case. For IR-SE, the story is more complex, and so we investigate the multifaceted influences on the limitations, such as phonon behavior, grain size, presence of a substrate, film thickness, and measurement noise. Finally, we demonstrate the importance of identifying the IR optical constants directly via IR-SE (rather than by extrapolation from NIR-VIS-UV-SE) by means of comparing specific figures of merits (Faraday and Joule numbers), deemed useful indicators for plasmonic performance.

Gaining external control over self-organization is of vital importance for future smart materials. Surfactants are extremely valuable for the synthesis of diverse nanomaterials. Their self-assembly is dictated by microphase separation, the hydrophobic effect, and head-group repulsion. It is desirable to supplement surfactants with an added mode of long-range and directional interaction. Magnetic forces are ideal, as they are not shielded in water. We report on surfactants with heads containing tightly bound transition-metal centers. The magnetic moment of the head was varied systematically while keeping shape and charge constant. Changes in the magnetic moment of the head led to notable differences in surface tension, aggregate size, and contact angle, which could also be altered by an external magnetic field. The most astonishing result was that the use of magnetic surfactants as structure-directing agents enabled the formation of porous solids with 12-fold rotational symmetry. published

For the past several years we have been carrying out a long term experimental study of 3He in ErT2 (erbium di-tritide). This study has attempted to answer questions regarding the evolution of helium bubbles in ErT 2 - x He x . ErT2 samples have been studied periodically over four years using Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), and Nano-Indentation (NI). In ErT 2 - x He x , helium bubbles are plate-like and grow along {1 1 1} planes. The bubbles grow in three distinct phases. First, they nucleate and grow as “Griffith-cracks” until an age of ∼0.15 He:M. Second, around 0.15 He:M the diameter stops increasing and instead the bubbles grow in thickness by punching dislocation dipoles. Third, the bubbles grow in size until ∼0.3 He:M at which point the bubbles begin to link.

The high-temperature capabilities of multi-phase composites based on Mo5Si3Bx are examined after solid-state processing and pulsed laser deposition (PLD) coating fabrication approaches. These composites are prepared by mechanical alloying of elemental powders and densified by vacuum hot pressing, which is a scalable processing approach. Chemical analyses of the hot-pressed compacts reveal a consistent 15–22 percent loss of boron, which is primarily due to the high-temperature hot-pressing step. Composites possessing sufficient amounts of boron are evaluated by thermogravimetric studies in temperatures up to 1650 °C in air. One composition demonstrates oxidative stability after long-term (100 h) isothermal conditions, as well as thermal cycling to simulate solar-thermal operation. Hot-pressed samples of composites consisting of Mo5Si3Bx + MoSi2 + MoB are also employed as deposition targets for PLD trials. X-ray diffraction analysis of the resulting films indicates the absence of long-range crystallographic order.

Precession microscopy is applied to determine the morphology of pulsed laser deposited and unannealed Ni films. The nanostructure of these films, nominally 50 nm in thickness, is heterogeneous and comprised predominantly of face-centered cubic (fcc)-Ni phase with regions of 〈1 0 1〉fcc, 〈1 1 2〉fcc and 〈0 0 1〉fcc fiber texture. Metastable hexagonal close-packed (hcp)-Ni phase grains approximately 8.5 nm in size are also present, and there is compelling evidence that local texture of the predominant fcc-Ni phase facilitates the formation and resulting texture of the metastable counterpart.

Grain boundary migration associated with abnormal grain growth in pulsed-laser deposited Ni was studied in real time by annealing electron transparent films in situ in the transmission electron microscope. The resulting texture evolution and grain boundary types produced were evaluated by ex situ electron backscatter diffraction of interrupted anneals. The combination of these two techniques allowed for the investigation of grain growth rates, grain morphologies, and the evolution of the orientation and grain boundary distributions. Grain boundaries were found to progress in a sporadic, start/stop fashion with no evidence of a characteristic grain growth rate. The orientations of the abnormally growing grains were found to be predominately 〈1 1 1〉//ND throughout the annealing process. A high fraction of twin boundaries developed during the annealing process. The intermittent growth from different locations of the grain boundary is discussed in terms of a vacancy diffusion model for grain growth.

A novel palladium-promoted zeolite material with a significant ethylene adsorption capacity at room temperature is described. It was characterised by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and transmission electron microscopy (TEM) to show palladium particles dispersed over the support. Initial measurements of the ethylene adsorption capacity were conducted with a synthetic gas stream at a higher ethylene concentration than would normally be encountered in fruit/vegetable storage, in order to obtain an accelerated testing protocol. Further laboratory-based trials on fruit samples show that the palladiumpromoted zeolite material can be effective as an ethylene scavenger to prolong the shelf-life of fresh fruits.

The thermal stability of nanograined pulsed-laser deposited nickel was studied by annealing free-standing thin films in situ in a transmission electron microscope. The observed grain growth was sporadic and catastrophic, as expected for abnormal grain growth. The large grains contained a variety of defects that included twins, dislocation lines, small dislocation loops and stacking-fault tetrahedra. This microstructure was developed at annealing temperatures as low as 498 K and was stable at the annealing temperature. The proposed source of the defects and especially the stacking-fault tetrahedra is the grain boundaries, which have excess free volume. This defect source provides insight to the structure of the deposited grain boundaries, which has important consequences for the macroscopic mechanical properties of nanograined pulsed-laser deposited nickel.

Thin-film mechanical properties can be measured using nanoindentation combined with detailed finite element modeling. This technique was used for a study of very fine grained Ni films, formed using pulsed-laser deposition on fused silica, sapphire, and Ni substrates. The grain sizes in the films were characterized by electron microscopy, and the mechanical properties were determined by ultra-low load indentation, analyzed using finite element modeling to separate the mechanical properties of the thin layers from those of the substrates. Some Ni films were deposited at high temperature or annealed after deposition to enlarge the grain sizes. The observed hardnesses and grain sizes in these thin Ni films are consistent with the empirical Hall–Petch relationship for grain sizes ranging from a few micrometers to as small as 10 nm, suggesting that deformation occurs preferentially by dislocation movement even in such nanometer-size grains.

We used nanoindentation coupled with finite element modeling to determine the mechanical properties of amorphous Si layers formed by self-ion implantation of crystalline Si at approximately 100 K. When the effects of the harder substrate on the response of the layers to indentation were accounted for, the amorphous phase was found to have a Young’s modulus of 136 ± 9 GPa and a hardness of 10.9 ± 0.9 GPa, which were 19% and 10% lower than the corresponding values for crystalline Si. The hardness agrees well with the pressure known to induce a phase transition in amorphous Si to the denser β–Sn-type structure of Si. This transition controls the yielding of amorphous Si under compressive stress during indentation, just as it does in crystalline Si. After annealing 1 h at 500 °C to relax the amorphous structure, the corresponding values increase slightly to 146 ± 9 GPa and 11.6 ± 1.0 GPa. Because hardness and elastic modulus are only moderately reduced with respect to crystalline Si, amorphous Si may be a useful alternative material for components in Si-based microelectromechanical systems if other improved properties are needed, such as increased fracture toughness.

We have measured the yield strengths of Ni samples having high densities of nanometer-size precipitates. Surface layers containing NiO or γ-Al2O3 precipitates were formed in Ni specimens by ion implanting O alone or O and Al, with subsequent annealing. The yield strengths of the layers were obtained through nanoindentation in conjunction with finite-element simulations. The yield strengths of the Ni alloys were combined with earlier data for O-implanted Al and compared to predictions of a recent treatment of the Orowan mechanism, in which dislocations loop around precipitates and by-pass them. The strengths vary with changes in precipitate microstructure, as predicted, and conform to the theory in absolute magnitude to within a factor of 1.5. This agreement extends over broad microstructural ranges: precipitate sizes from ∼1 to 20 nm, volume fractions from 0.05 to 0.30, densities from 4×1016/cm3 to as high as ∼1020/cm3, edge-to-edge spacings as small as 1.4 nm, two precipitated phases, and two metal matrices with shear moduli differing by a factor of 3. Ion implantation increases near-surface yield strengths to as high as 5 GPa, suggesting that this treatment may be useful for hardening the surfaces of Ni components in micro-electromechanical systems.

Two nanocrystalline Ni thin films, one prepared via DC Magnetron Sputtering and the other prepared via Pulsed Laser Deposition, were strained in-situ in the Transmission Electron Microscope. Although the grain sizes were similar, the two films behaved quite differently in tension. The sputtered material was found to behave in a brittle manner, with failure occurring via rapid coalescence of intergranular cracks. Conversely, the laser deposited film behaved in a ductile manner, with failure occurring by slow ductile crack growth. The difference in failure mechanism was attributed to the presence of grain boundary porosity in the sputtered thin film. Both films exhibited pervasive dislocation motion before failure, and showed no conclusive evidence of a change in deformation mode.

Final chip passivation layers are shown to have a major impact on the total dose hardness of bipolar linear technologies. It is found that devices fabricated without passivation layers do not exhibit enhanced low-dose-rate sensitivity (ELDRS) or pre-irradiation elevated-temperature stress (PETS) sensitivity, whereas devices from the same production lot fabricated with either oxide/nitride or doped-glass passivation layers are ELDRS and PETS sensitive. In addition, removing the passivation layers after fabrication can mitigate ELDRS and PETS effects. ELDRS and PETS effects do not appear to be inherently related to circuit design or layout, but are related to mechanical stress effects, hydrogen in the device, or a combination of the two. These results suggest that proper engineering of the final chip passivation layer might eliminate ELDRS and PETS effects in bipolar integrated circuits.

One of the most important issues facing the continued development and application of microelectromechanical systems (MEMS) is that of adhesion and friction between microstructures intended to transfer force. In this work, we develop modeling approaches for studying adhesion (i.e., stiction) using the observed shape of microcantilevers under electrostatic loading. Analytical models for an idealized configuration are presented first. The solutions reveal the regimes over which the cantilever deflections are sensitive to adhesion versus applied loading. Also, the energy release rate and hence the cantilever adhesion value is shown to be independent of the curvature of the initially freestanding beam. Second, with a finite-element modeling approach, we quantify the slight sensitivity of the cantilever deflections to the surface force law assumed and show that with Angstrom scale resolution of beam deflections, cohesive zone law information can in principle be deduced. We also use this approach to model the nonuniform electrostatic loading force used in our experiments and the effect of support post compliance. We then demonstrate how adhesion values are obtained along the length of a microcantilever.

Rare earth tritide films evolve as tritium decays into 3He, which forms bubbles that influence long-term film stability in applications such as neutron generators. We followed the properties of model ErT2 films as they aged using ERD analysis to monitor T and 3He profiles, nanoindentation testing for mechanical properties and transmission electron microscopy to characterize bubble growth. The profiles of T and 3He are separately measured in ERD using a ΔE − E detector, taking advantage of the differences in energy loss within the ΔE detector. The composition measured by ERD followed the expected build-up of 3He up to near critical release, where 3He begins to escape from the film as bubbles overlap. These measurements complement observations of the changing mechanical properties of these films, where the observed behavior divided into two regimes: a substantial increase in layer hardness but elasticity little changed over ∼18 months, followed by a decrease in elastic stiffness and a modest decrease in hardness over the final 24 months. The evolution of properties has been explained by a combination of dislocation pinning by the bubbles, elastic softening as the bubbles occupy an increasing fraction of the material, and details of bubble growth modes. The ERD measurements confirm that the changes in properties are due to changes in bubble morphology and not to changes in 3He or T content.

We have developed a new experimental approach for measuring hysteresis in the adhesion between a free standing thin film and a substrate. By accurately measuring and modeling the deformations in micromachined cantilever beams that are subject to combined interfacial adhesive and applied electrostatic forces, we determine adhesion energies for advancing and receding contacts. We examined adhesion hysteresis for silane coated cantilevers and found no hysteresis at low relative humidity (RH) conditions. The dominant contribution to interfacial energy at low RH is van der Waals attraction between portions of the surfaces that are separated by nanometer asperities. In contrast, significant hysteresis was observed for surfaces that were exposed to high RH conditions. Atomic force microscopy studies of these surfaces showed spontaneous formation of silane mounds that have irreversibly transformed from initially uniform hydrophobic surface layers. Contact mechanics considerations show that the compliance of the mounds can reasonably allow microcapillaries in surrounding hydrophilic areas to bridge at high RH as the surfaces are forced into contact by an externally applied load, leading to the adhesion hysteresis.

This paper examines the correlation between mechanical properties and the density, phase and hydrogen content of deposited alumina layers, and compares them to those of sapphire and amorphous alumina synthesized through ion-beam irradiation of sapphire. Alumina films were deposited using electron beam evaporation of aluminum and co-bombardment with O 2 + ions (30–230 eV) from an electron–cyclotron resonance (ECR) plasma. The H content and phase were controlled by varying the deposition temperature and the ion energy. Sapphire was amorphized at 84 K by irradiation with Al and O ions (in stoichiometric ratio) to a defect level of 4 dpa in order to form an amorphous layer 370 nm thick. Nanoindentation was performed to determine the elastic modulus, yield strength and hardness of all materials. Sapphire and amorphized sapphire have a higher density and exhibit superior mechanical properties in comparison to the deposited alumina films. Density was determined to be the primary factor affecting the mechanical properties, which showed only a weak correlation to the hydrogen content.

Precipitation strengthening of nickel was investigated using ion-implantation alloying and nanoindentation testing for particle separations in the nanometer range and volume fractions extending above 10O/O. Ion implantation of either oxygen alone or oxygen plus aluminum at room temperature was shown to produce substantial strengthening in the ion-treated layer, with yield strengths near 5 GPa in both cases. After annealing to 550"C the oxygen-alone layer loses much of the benefit, with its yield strength reduced to 1.2 GP~ but the dual ion-implanted layer retains a substantially enhanced yield strength of over 4 GPa. Examination by transmission electron f microscopy showed very fine dispersions of 1-5 nm diameter NiO and y-A1203 precipitates in the implanted layers before annealing. The heat treatment at 550"C induced ripening of the NiO particles to sizes ranging from 7 to 20 nm, whereas the more stable ~-A1203 precipitates were little changed. The extreme strengthening we observe is in semiquantitative agreement with predictions based on the application of dispersion-hardening theory to these microstructure.

Procedures have been developed based on finite-element modeling of nanoindentation data to obtain the mechanical properties of thin films and ion-beam-modified layers independently of the properties of the underlying substrates. These procedures accurately deduce the yield strength, Young’s elastic modulus, and layer hardness from indentations as deep as 50% of the layer thickness or more. We have used these procedures to evaluate materials ranging from ion implanted metals to deposited, diamond-like carbon layers. The technique increases the applicability of indentation testing to very thin layers, composite layers, and modulated compositions. This article presents an overview of the procedures involved and illustrates them with selected examples.

We have developed procedures based on finite-element modeling of nanoindentation data to extract mechanical properties from thin, hard films and ion-beam-modified layers on softer substrates. The method accurately deduces the yield stress, Young's modulus, and hardness from indentations as deep as 50% of the layer thickness. We use these procedures to evaluate two hard layers potentially useful for reducing friction and wear of components in micro-electromechanical systems (MEMS): Ni implanted with Ti and C, and diamond-like carbon layers. We show that the modeling works well even for materials whose hardness approaches that of diamond, a case where commonly used analytical methods for deducing the modulus fail.

The microstructure of high-purity Ni implanted with overlapping concentration profiles of Ti and C was examined with transmission electron microscopy. An amorphous phase forms at concentrations of 15-18 at.% Ti and 22 at.% C. while a two-phase alloy (amorphous + f.c.c. Ni) forms for

Dual ion implantation of titanium and carbon was shown to produce an amorphous layer of exceptional strength within annealed bulk Ni and also within electroformed Ni and Ni 80 Fe 20 materials used in micro-electromechanical systems. The intrinsic elastic and plastic mechanical properties of the implanted region were quantified using nanoindentation testing in conjunction with finite-element modeling, and the results were interpreted in the light of microstructures observed by transmission electron microscopy. The implantation treatment was found to produce substantial reductions in unlubricated friction and wear.

Heavy Ion Backscattering Spectrometry (HIBS) is a new IBA tool for measuring extremely low levels of surface contamination on very pure substrates, such as Si wafers used in the manufacture of integrated circuits. HIBS derives its high sensitivity through the use of moderately low energy (∼100 keV) heavy ions (e.g. C12) to boost the RBS cross-section to levels approaching 1000 b, and by using specially designed time-of-flight (TOF) detectors which have been optimized to provide a large scattering solid angle with minimal kinematic broadening. A HIBS User Facility has been created which provides US industry, national laboratories, and universities with a place for conducting ultra-trace level surface contamination studies. A review of the HIBS technique is given and examples of using the facility to calibrate Total-Reflection X-ray Fluorescence Spectroscopy (TXRF) instruments and develop wafer cleaning processes are discussed.

Dual ion implantation of titanium and carbon into nickel was shown to produce an amorphous layer with exceptionally high strength and hardness and substantially improved tribological properties. Indentation testing at submicrometer penetrations combined with finite-element modeling permitted quantification of the intrinsic elastic and plastic properties of the amorphous layer, which was found to have a yield strength near 5 GPa. During unlubricated sliding contact with a steel pin, the implantation treatment reduced friction, suppressed adhesion-and-fracture wear, and reduced wear depth. These tribological effects may enhance the performance and lifetime of microelectromechanical systems constructed from nickel.

Significant ion irradiation is needed during growth to synthesize cubic boron nitride (cBN) films. This results in large film stresses, which have limited cBN film thicknesses to only a few hundred nm and represents a significant barrier in the development of cBN film technology. Using a new hybrid deposition technique, we have synthesized cubic BN films up to 700 nm (0.7 μm) thick. A compositional and structural analysis of the films using several standard characterization techniques confirms that relatively thick polycrystalline films with a high cBN content were synthesized. Thicker cBN films enable hardness measurements to be undertaken without major substrate effects. Nanoindentation measurements yield hardness values for the cubic BN films up to 60–70 GPa, which are greater than values measured for bulk cBN. The measured elastic modulus was observed to be lower than the bulk, and this can be accounted for by an elastic deformation of the silicon substrate. The mechanical properties of the cubic BN f...

The mechanical properties of implanted layers and thin films on dissimilar substrates are difficult to accurately determine. Nanoindentation of the layer provides information, but detailed numerical modeling is required in order to separate the properties of the layer from those of the substrate. We describe here the procedures we have developed to accomplish this modeling with the commercially available finite-element code ABAQUS. Using these techniques, we are able to extract from nanoindentation testing the yield stress, Young`s modulus, and hardness of the layer material, with an absolute accuracy of at least 20%. The procedure is applicable to layers as thin as 50 nm on essentially any substrate, hard or soft. We have used it for materials ranging from ion-implanted layers to thin films of metals and dielectrics formed using plasma-deposition methods. An example is given of 0-implanted Al, a thin, hard layer on a soft substrate.

We have investigated the behavior of low levels of transition metal atoms on silicon surfaces subject to nitrogen bombardment. Submonolayer coverages of gold, iron, copper, molybdenum and tungsten were deposited on 〈100〉 silicon surfaces. Samples were analyzed using 270 keV He + time-of-flight backscattering before and after irradiation with 6 mC of 270 keV N + at current levels in the hundreds of nanoamps. The yield of sputtered metallic atoms ranged from 1.0 × 10 −3 per incident nitrogen ion to 3.3 × 10 −3 per incident ion. Lower yields were correlated with migration of the metallic species into the silicon. The implications for ultra-high sensitivity measurement of contamination on silicon wafers by time-of-flight heavy-ion backscattering spectrometry are discussed.

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.

Interfaces are a critical determinant of the full range of materials properties, especially at the nanoscale. Computational and experimental methods developed a comprehensive understanding of nanograin evolution based on a fundamental understanding of internal interfaces in nanocrystalline nickel. It has recently been shown that nanocrystals with a bi-modal grain-size distribution possess a unique combination of high-strength, ductility and wear-resistance. We performed a combined experimental and theoretical investigation of the structure and motion of internal interfaces in nanograined metal and the resulting grain evolution. The properties of grain boundaries are computed for an unprecedented range of boundaries. The presence of roughening transitions in grain boundaries is explored and related to dramatic changes in boundary mobility. Experimental observations show that abnormal grain growth in nanograined materials is unlike conventional scale material in both the level of defects and the formation of unfavored phases. Molecular dynamics simulations address the origins of some of these phenomena.

The amorphous phase formed by implanting C into Fe alloyed with Cr, which is a prototype for the amorphous phase formed by implanting C into stainless steels, is compared to that formed by implanting C and Ti into Fe and steels. The composition range of the phase has been examined; higher Cr and C concentrations are required than needed with Ti and C. The friction and wear benefits obtained by implanting stainless steels with C only do not persist for the long durations and high wear loads found with Ti and C. However, the amorphous FeCrC alloys exhibit good aqueous corrosion resistance.

In situ tensile straining transmission electron microscopy tests have been carried out on nanocrystalline Ni. Grain agglomerates (GAs) were found to form very frequently and rapidly ahead of an advancing crack with sizes much larger than the initial average grain size. High-resolution electron microscopy indicated that the GAs most probably consist of nanograins separated by low-angle grain boundaries. Furthermore, both inter- and intra-GA fractures were observed. The observations suggest that these newly formed GAs may play an important role in the formation of the dimpled fracture surfaces of nanocrystalline materials.

Radiation effects microscopy (REM) for the next generation integrated circuits (ICs) will require GeV ions both to provide high ionization and to penetrate the thick overlayers in present day ICs. These ion beams can be provided by only a few cyclotrons in the world. Since it is extremely hard to focus these higher-energy ions, we have proposed the ion photon emission microscope (IPEM) that allows the determination of the ion hits by focusing the emitted photons to a position sensitive detector. The IPEM needs a thin luminescent foil that has high brightness, good spatial resolution and does not change the incident ion’s energy and direction significantly. Available organic-phosphor foils require a large thickness to produce enough photons, which results in poor spatial resolution. To solve this problem, we have developed thin, lightly doped n-type GaN films that are extremely bright. We have grown high quality GaN films on sapphire using metal organic chemical vapor deposition (MOCVD), detached the films from the substrate using laser ablation, and made them self-supporting. The smallest foils have 1 mm2 area and 1 μm thickness. The optical properties, such as light yield, spectrum and decay times were measured and compared to those of conventional phosphors, by using both alpha particles from a radioactive source and 250 keV ions from an implanter. We found that the GaN performance strongly depends on composition and doping levels. The conclusion is that 1–2 μm GaN film of a 1 mm2 area may become an ideal ion position detector.

Electrochemical cells constructed with a thin Pd or Ti foil electrode mounted at one wall of the cell have been used both to test for the existence of “cold fusion” and to measure directly D∶Pd loading ratios in an operating cell. The first type of experiment used a surface-barrier particle detector positioned a few millimeters from the foil to provide a very sensitive monitor for possible fusion-generated protons at 3.02 MeV. The detection limit for this arrangement is estimated to be 10−24 fusions/deuterium/s, assuming a bulk fusion effect. These experiments included cells with 5- and 25-μm-thick Pd foils, 10-μm Ti foils, parallel experiments with 0.1M LiOD (heavy water) in one cell and LiOH (light water) in another, current densities up to 0.5 A/cm2, and run times as long as 22 days. No evidence for fusion products was seen. The second type of experiment using these cells, both as an adjunct to the fusion tests and to provide new information, was the use of external beam nuclear reaction analysis to monitor directly the loading and unloading of deuterium in the foil of an operating cell. Using a 1.5-MeV3He ion beam in air, the deuterium in the outer 2 μm of the exposed Pd foil was measured for the first time using the D(3He,p) nuclear reaction. The maximum D∶Pd ratios observed using this technique were 0.8–0.9.

Under circumstances in Zone-Melt-Recrystallization (ZMR) of Si-on-Insulator (SOI) structures where radiative heat loss is significant, the ∼50% decrease in emissivity when Si melts destabilizes the Si molten zone. We have demonstrated this both experimentally using a slowly scanned e-beam line source and numerically with a finite-element computational simulation. The resulting instability narrows the process window and tightens requirements on beam control and background heating uniformity, both for e-beam ZMR systems and optically-coupled systems such as a graphite strip heater.

Porous silicon and its oxide can be converted into porous silicon oxynitrides by ammonia heat treatment. For example, ammonia treatment at 1000 °C for 1 h following 850 °C, 30‐min steam oxidation of porous silicon can result in up to 40 at. % nitrogen in the porous oxynitrides. These porous silicon oxynitrides are compositionally more uniform than ammonia‐nitrided thermal oxides which exhibit nitrogen buildup at the oxide layer interfaces. However, the order of the oxidation and nitridation treatment matters: nitrided oxidized porous silicon exhibits higher electrical breakdown strength than nitrided porous silicon or oxidized nitrided porous silicon.

It is believed that the dynamics of dislocation processes during the deformation of nanocrystalline materials can only be visualized by computational simulations. Here we demonstrate that observations of dislocation processes during the deformation of nanocrystalline Ni with grain sizes as small as 10 nm can be achieved by using a combination of in situ tensile straining and high-resolution transmission electron microscopy. Trapped unit lattice dislocations are observed in strained grains as small as 5 nm, but subsequent relaxation leads to dislocation recombination.

We have developed a process for making thick, stress-free, amorphous-tetrahedrally bonded carbon (a-tC) films with hardness and stiffness near that of diamond. Using pulsed-laser deposition, thin a-tC films (0.1–0.2 μm) were deposited at room temperature. The intrinsic stress in these films (6–8 GPa) was relieved by a short (2 min) anneal at 600 °C. Raman and electron energy-loss spectra from single-layer annealed specimens show only subtle changes from as-grown films. Subsequent deposition and annealing steps were used to build up thick layers. Films up to 1.2 μm thick have been grown that are adherent to the substrate and have low residual compressive stress (

Interfacial adhesion and friction are important factors in determining the performance and reliability of microelectro- mechanical systems. We demonstrate that the adhesion of micromachined surfaces is in a regime not considered by standard rough surface adhesion models. At small roughness values, our experiments and models show unambiguously that the adhesion is mainly due to van der Waals dispersion forces acting across extensive non-contacting areas and that it is related to 1/Dave2, where Dave is the average surface separation. These contributions must be considered because of the close proximity of the surfaces, which is a result of the planar deposition technology. At large roughness values, van der Waals forces at contacting asperities become the dominating contributor to the adhesion. In this regime our model calculations converge with standard models in which the real contact area determines the adhesion. We further suggest that topographic correlations between the upper and lower surfaces must be considered to understand adhesion completely.

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.

The paper studies the metastable control of cooling slow- and fast-growth crystalline compounds, which have: low solubility at 25°C, high solubility parameters and a detectable metastable zone. Nyvlt's and alternative methods are applied to measure the metastable limits. An optimal control problem is developed in GAMS and solved for the optimal cooling temperature set points. Various cooling and seeding strategies are implemented in a laboratory-scale crystalliser to compare the yields and Crystal Size Distributions (CSD). For both compounds, slow cooling with initial fine seeds is the optimal crystallisation strategy in batches, which can achieve the highest yield and the narrowest range of particle size. The successful laboratory-scale results will lead to further pilot- and industrial-scale investigations.

Detailed finite-element modeling of nanoindentation data is used to obtain accurate mechanical properties of very thin films or surface-modified layers independently of the properties of the underlying substrates. These procedures accurately deduce the yield strength, elastic modulus, and layer hardness, and greatly increase the usefulness of indentation testing with very thin surface layers. Moreover, extraction of the effective Young’s modulus in the near surface region should enable mechanical damage studies on a small scale. This paper presents a brief overview of the procedures involved and illustrates them with He-implanted Ni.Copyright © 2002 by ASME

Detailed finite-element modeling of nanoindentation data is used to obtain the micromechanical properties of Ni implanted with ∼5 at.% He to a depth of 600–700 nm. Properties of He-containing metals have implications for studies of radiation damage and for fundamental issues of dislocation pinning. Cross-section TEM shows the implantation produces a highly damaged layer containing a fine dispersion of He bubbles with diameters of ∼1 nm or smaller, with some evidence for interconnection between bubbles. Nanoindentation of the Ni(He) layers gave a fairly hard, stiff response to depths of 100–120 nm, beyond which the layer failed. By modeling the layer as an isotropic, elastic-plastic solid with the Mises yield criterion, the Ni(He) is shown to have a hardness nearly 7 times that of untreated Ni. However, unlike other treatments that we have used to produce very hard Ni-based layers, the Ni(He) layer fails at relatively modest shear stress levels.

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

Ion implantation of O and Al were used to form nanometer-size precipitates of NiO or Al{sub 2}O{sub 3} in the near-surface of Ni. The yield strengths of the treated layers were determined by nanoindentation testing in conjunction with finite-element modeling. The strengths range up to {approximately}5 GPa, substantially above values for hard bearing steels. These results agree quantitatively with predictions of dispersion-hardening theory based on the precipitate microstructures observed by transmission electron microscopy. Such surface hardening by ion implantation may be beneficial for Ni components in micro-electromechanical systems.

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

Due to extreme surface to volume ratios, adhesion and friction are critical properties for reliability of Microelectromechanical Systems (MEMS), but are not well understood. In this LDRD the authors established test structures, metrology and numerical modeling to conduct studies on adhesion and friction in MEMS. They then concentrated on measuring the effect of environment on MEMS adhesion. Polycrystalline silicon (polysilicon) is the primary material of interest in MEMS because of its integrated circuit process compatibility, low stress, high strength and conformal deposition nature. A plethora of useful micromachined device concepts have been demonstrated using Sandia National Laboratories' sophisticated in-house capabilities. One drawback to polysilicon is that in air the surface oxidizes, is high energy and is hydrophilic (i.e., it wets easily). This can lead to catastrophic failure because surface forces can cause MEMS parts that are brought into contact to adhere rather than perform their intended function. A fundamental concern is how environmental constituents such as water will affect adhesion energies in MEMS. The authors first demonstrated an accurate method to measure adhesion as reported in Chapter 1. In Chapter 2 through 5, they then studied the effect of water on adhesion depending on the surface condition (hydrophilic or hydrophobic). As described in Chapter 2, they find that adhesion energy of hydrophilic MEMS surfaces is high and increases exponentially with relative humidity (RH). Surface roughness is the controlling mechanism for this relationship. Adhesion can be reduced by several orders of magnitude by silane coupling agents applied via solution processing. They decrease the surface energy and render the surface hydrophobic (i.e. does not wet easily). However, only a molecular monolayer coats the surface. In Chapters 3-5 the authors map out the extent to which the monolayer reduces adhesion versus RH. They find that adhesion is independent of RH up to a threshold value, depending on the coating chemistry. The mechanism for the adhesion increase beyond this threshold value is that the coupling agent reconfigures from a surface to a bulk phase (Chapter 3). To investigate the details of how the adhesion increase occurs, the authors developed the mechanics for adhesion hysteresis measurements. These revealed that near-crack tip compression is the underlying cause of the adhesion increase (Chapter 4). A vacuum deposition chamber for silane coupling agent deposition was constructed. Results indicate that vapor deposited coatings are less susceptible to degradation at high RH (Chapter 5). To address issues relating to surfaces in relative motion, a new test structure to measure friction was developed. In contrast to other surface micromachined friction test structures, uniform apparent pressure is applied in the frictional contact zone (Chapter 6). The test structure will enable friction studies over a large pressure and dynamic range. In this LDRD project, the authors established an infrastructure for MEMS adhesion and friction metrology. They then characterized in detail the performance of hydrophilic and hydrophobic films under humid conditions, and determined mechanisms which limit this performance. These studies contribute to a fundamental understanding for MEMS reliability design rules. They also provide valuable data for MEMS packaging requirements.