Tin whisker growth has been observed since the 1950s and has become of more interest in the past 15 to 20 years due to the desire to use lead-free solders, pure tin being a good lead-free candidate. In the same time period, failure of satellites and other devices using pure tin solders has been blamed on tin whisker growth. The accepted driving force for whisker growth is compressive stresses in films. This article reports a microstructure-control method of limiting whisker growth through the introduction of pores that permit an alternate means of stress relief.

Since in instrumented indentation the contact area is indirectly measured from the contact depth, the natural and unavoidable roughness of real surfaces can induce some errors in determining the contact area and thus in calculating hardness and Young's modulus. To alleviate these possible errors and evaluate mechanical properties more precisely, here a simple contact model that takes into account the surface roughness is proposed. A series of instrumented indentations were made on W and Ni samples whose surface roughness is intentionally controlled, and the results are discussed in terms of the proposed model.

This paper provides an introduction for non-experts to first-principles electronic structure methods that are widely used in condensed-matter physics. Particular emphasis is placed on giving the appropriate background information needed to better appreciate the use of these methods to study actinide and other materials. Specifically, the underlying theory is described in sufficient detail to enable an understanding of the relative strengths and weaknesses of the methods. In addition, the meaning of commonly used terminology is explained, including density functional theory (DFT), local density approximation (LDA), and generalized gradient approximation (GGA), as well as linear muffin-tin orbital (LMTO), linear augmented plane wave (LAPW), and pseudopotential methods. Methodologies that extend the basic theory to address specific limitations are also briefly discussed. Finally, a few illustrative applications are presented, including quantum molecular dynamics (QMD) simulations and studies of surfaces, impurities, and defects. The paper concludes by addressing the current controversy regarding magnetic calculations for actinide materials.

The effect of Cu added eutectic Sn–9Zn solder reacting with the Ag substrate has been investigated in this study. Three Ag–Zn intermetallic compounds (IMCs), ∈–AgZn3, γ–Ag5Zn8, and ζ–AgZn, were formed on the Sn–9Zn/Ag interface at 260 °C. While Cu was gradually added to the Sn–9Zn alloy, microstructures of intermetallic compounds changed dramatically. The intermetallic compound microstructures became loose and Sn and Cu atoms in the Ag-Zn intermetallic compounds increased. If more than 3 wt% of Cu was added to the Sn-9Zn alloy, Ag-Sn intermetallic compounds were formed on the Ag surface and massive spalling of Ag–Zn IMC layers from the Ag surface occurred in a short reaction time.

A new approach is proposed to extract the elastic and viscoelastic properties of a polymeric film on a hard substrate using a sharp indentation relaxation test. In the theoretic formulation, a sharp indentation relaxation test on a film/substrate system was interpreted by its equivalent flat-ended punch indentation relaxation test. The radius of the equivalent flat-ended punch was determined by the residual depth of the sharp indentation. A semi-analytical solution for a flat-ended punch relaxation test was derived. Sharp indentation relaxation tests on a polymethyl methacrylate film and a polycarbonate film on a glass substrate were performed. The semi-analytical solution and the experimental results were used to extract the elastic-viscoelastic parameters of the films. The extracted elastic-viscoelastic parameters of both films were found to be in a good agreement with data sheets of the films. The proposed approach provides a simple and yet feasible way to extract “film-only” elastic and viscoelastic properties.

Titanium dioxide (TiO2) was synthesized in the water-in-oil (w/o) microemulsion system of n-heptane/water/sodium bis (2-ethylhexyl) sulfosuccinate (AOT) surfactant. This study reports the effect of microstructure of the synthesized TiO2 nanoparticles on the photocatalysis degradation of phenol in an aqueous solution, as compared to commercial TiO2 (P25) and TiO2 synthesized by bulk precipitation. The results indicated that the rate of phenol decomposition catalyzed by the synthesized TiO2 from microemulsion techniques is faster than those of TiO2 synthesized by bulk precipitation and commercial P25. This is due to the small crystal size of TiO2 prepared by the microemulsion technique. The exposed titanium sites on the surface controlled by the morphology of synthesized TiO2 are critical for photocatalytic activity.

Experimental studies of fibrous eutectic growth in succinonitrile–camphor reveal that models of the stable range of interfibrous spacings must incorporate the dynamic effects and the instability of the growth front of the fibrous phase, which determines the fineness and regularity of the microstructures. An analytical mathematical model for fibrous eutectic growth has been developed and compared with the experimental results. The selected wavelength scales obey , where d0, ls, lt are the capillary, diffusion, and thermal lengths, respectively. While only at a relatively high growth rate or steep temperature gradient, the scaling law λ2V = constant is fulfilled. It is found that the selected band of interfibrous spacings is very narrow. This means that the interfibrous spacing is almost unique at a given growth rate and a fixed temperature gradient. The effects of convection on the interfibrous spacing selection and fibrous phase instability of short wavelength perturbations have also been investigated. These studies reveal that the controlled solidification of a fibrous eutectic produces a very fine and regular microstructure.

Nickel mono-silicide has been considered a promising silicide candidate for sub-90 nm nodes of integrated circuits manufacturing. To form high-quality nickel mono-silicide as source/drain contact electrodes, a two-step low temperature rapid thermal process has been proposed, in which the as-deposited Ni will react with silicon during a low temperature (<310 °C) first anneal. Due to the lower annealing temperature Ni2Si will form after the first anneal. To better control the silicidation process the growth kinetics of Ni2Si thin film fabricated by solid-state reaction of sputtered Ni thin film on n+/p junction at low temperature is investigated in this paper. It is demonstrated that between 260 and 280 °C the thickness of Ni2Si thin film has a linear rather than parabolic dependence on annealing time. The corresponding activation energy for this linear growth is found to be ∼1.35 eV.

The changes in optical properties and damage mechanism of ZnO/silicone white paint caused by <200 keV protons in space were investigated in terms of ground-based simulation testing. The energies of protons were chosen as 50, 90, and 110 keV. The results show that the change in solar absorptance Δαs increases with increasing irradiation fluence as well as the proton energy. On the basis of photoluminescence spectroscopy, it is revealed that with increasing proton fluence, the 660-nm emission band related to the interstitial Zn-ions changes little, the 405-nm emission band related to the Zn vacancies decreases and tends to disappear, the 460-nm emission band related to the double ionized oxygen vacancies decreases, and the emission band related to the singly ionized oxygen vacancies increases. SRIM simulation analysis indicates that the damage effect of ZnO/silicone white paint caused by proton exposure would be aggravated due to the organic silicone binder. The proton irradiation leads to ionization of Zn atoms, formation of free oxygen and oxygen vacancies, and degradation of the organic silicone binder. It is believed that the optical degradation of ZnO/silicone white paint, induced by <200 keV protons, can be attributed to the combined effect of these three processes.

Accurate mechanical characterization of viscoelastoplastic materials in small volumes is required for the development of polymeric thin film, nanocomposite, and biomedical applications. Instrumented indentation-based approaches are increasingly implemented to quantify the resistance to permanent deformation of such systems via time-independent analyses. Here, we quantify the significant post-indentation recovery of several bulk polymers via time-lapsed scanning-probe microscopy under ambient conditions, indicating up to 80% recovery of both indentation depth and volume within 48 h. This viscoelastic response demonstrates that indentation hardness values for these polymers are accurate within 10% for less than 5 min to 3.5 days post-indentation, neglecting any other analytical or experimental errors. Further, although the extent and rates of volumetric recovery depend strongly on loading history and polymer structure/physical properties, deformation resistance inferred from indentation hardness does not quantitatively or qualitatively predict recoverable work or residual deformation of polymer surfaces.

Carbon in its various forms, specifically nanocrystalline diamond, may become a key material for the manufacturing of micro- and nano-electromechanical (M/NEMS) devices in the twenty-first century. To utilize effectively these materials for M/NEMS applications, understanding of their microscopic structure and physical properties (mechanical properties, in particular) become indispensable. The microcrystalline and nanocrystalline diamond films were grown using hot-filament and microwave chemical vapor deposition techniques involving novel CH4/[TMB for boron doping and H2S for sulfur incorporation] in high hydrogen dilution chemistry. To investigate residual stress distribution and intermolecular forces at nanoscale, the films were characterized using Raman spectroscopy and atomic force microscopy in terms of topography, force curves, and force volume imaging. Traditional force curve measures the force felt by the tip as it approaches and retracts from a point on the sample surface, whereas force volume is an array of force curves over an extended range of sample area. Moreover, detailed microscale structural studies are able to demonstrate that the carbon bonding configuration (sp2 versus sp3 hybridization) and surface chemical termination in both the un-doped and doped diamond have a strong effect on nanoscale intermolecular forces. The preliminary information in the force volume measurement was decoupled from topographic data to offer new insights into the materials’ surface and mechanical properties of diamond films. These measurements are also complemented with scanning electron microscopy and x-ray diffraction to reveal their morphology and structure and frictional properties, albeit qualitative using lateral force microscopy mode. We present these comparative results and discuss their potential impact for electronic and electromechanical applications.

The oxidation in air of NiAl(110) was investigated in the temperature range from 870 °C–1200 °C by in situ x-ray diffraction and transmission electron microscopy. Oxidation at 870 °C and 1 bar oxygen leads to the formation of an epitaxial layer of γ-alumina showing an R30° orientation relationship with respect to the underlying substrate. At oxidation temperatures between 950 °C and 1025 °C, we observed a coexistence of epitaxial γ- and polycrystalline δ-Al2O3. The α-Al2O3 starts to form at 1025 °C and the complete transformation of metastable phases to the stable α-alumina phase takes place at 1100 °C. The fcc-hcp martensitic-like transformation of the initial γ-Al2O3 to epitaxial α-Al2O3 was observed. X-ray diffraction and cross-section transmission electron microscopy proved the existence of a continuous epitaxial α-Al2O3 layer between the substrate and the polycrystalline oxide scale, having a thickness of about 150 nm. The relative orientation relationship between the epitaxial alumina and the underlying substrate was found to be NiAl(110) || α-Al2O3 (0001) and [110] NiAl || [1120].

The modified arc-discharge technique was used for the growth of boron-doped multiwalled carbon nanotubes. A variety of weight percentages of boron and sulfur were mixed (0.5–15 wt%) with graphite powder and packed in the consumable anode. Transmission electron microscopy, Raman spectroscopy, thermogravimetric analysis (TGA), and electron energy loss spectroscopy (EELS) were used to characterize the samples. EELS indicated a small percentage of boron present (<1 at.%) in the nanotubes. Sulfur was used primarily to enhance boron incorporation; however, Raman and TGA measurements indicated fewer defects and/or amorphous material present when sulfur was added.

The electromigration effect upon the γ-InSn4/Cu interfacial reactions have been studied by examining the γ-InSn4/Cu/γ-InSn4 couples annealed at 160 °C with and without current stressing. Scallop-type η-Cu6(Sn,In)5 phase layers are formed in the couples without current stressing and at the γ-InSn4/Cu interface where electrons are flowing from the γ-InSn4 to the Cu. The reaction path is Cu/η-Cu6(Sn,In)5/γ-InSn4. However, very large η-Cu6(Sn,In)5 compounds are found at the Cu/γ-InSn4 interface where electrons are from Cu to the γ-InSn4. Although the melting points of both γ-InSn4 and Cu are higher than 160 °C, the liquid phase is formed at 160 °C in the electrified couple at the downstream γ-InSn4 phase near the Cu/γ-InSn4 interface. The reaction path is Cu/η-Cu6(Sn,In)5/liquid/γ-InSn4. The liquid phase propagates along the grain boundaries of the γ-InSn4 matrix. The very large η-Cu6(Sn,In)5 compounds are the coupling results of the liquid phase penetration and the Cu transport enhancement due to electromigration.

Measurements of vibrational spectra of atomic force microscopy (AFM) microprobes in contact with a sample allow a good correlation between resonance frequencies shifts and the effective elastic modulus of the tip-sample system. In this work we use finite element methods for modeling the AFM microprobe vibration considering actual features of the cantilever geometry. This allowed us to predict the behavior of the cantilevers in contact with any sample for a wide range of effective tip-sample stiffness. Experimental spectra for glass and chromium were well reproduced for the numerical model, and stiffness values were obtained. We present a method to correlate the experimental resonance spectrum to the effective stiffness using realistic geometry of the cantilever to numerically model the vibration of the cantilever in contact with a sample surface. Thus, supported in a reliable finite element method (FEM) model, atomic force acoustic microscopy can be a quantitative technique for elastic-modulus measurements. Considering the possibility of tip-apex wear during atomic force acoustic microscopy measurements, it is necessary to perform a calibration procedure to obtain the tip-sample contact areas before and after each measurement.

Well-structured and monodisperse nanocomposite spheres with a magnetic core/mesoporous silica shell structure (MCMS) were obtained. The effects on the structure and morphology of the MCMS spheres were investigated under various synthesis conditions, including reaction time, quantity of silicate sources of tetraethoxysilane (TEOS) and n-octadecyltrimethoxysilane (C18TMS), ratio of TEOS/C18TMS, and ratio of H2O/EtOH in the starting solution. The particle size of the MCMS spheres and pore diameter are tunable in a certain range with 100% yield. A synthesis mechanism of the mesoporous silica shell was proposed that proceeds via three main stages. The silica shell proved to be effective on protecting the cores from leaching out in acidic conditions.

A hydroxyapatite-gelatin nanocomposite system has been developed to resemble the composition and ultrastructure of natural bone for the application of tissue engineering. In the current study, variations in composition—content of gelatin and glutaraldehyde crosslinker—were examined in the context of mechanical properties and material biocompatibility. It was found that increasing the gelatin concentration resulted in a decreased hydroxyapatite crystal length and was associated with a slight increase in elastic modulus. Increases in gelatin and glutaraldehyde content were associated with increased material fracture toughness. Cellular biocompatibility tests, including cellular attachment and proliferation assays, were also used to assist in the process of optimizing gelatin and glutaraldehyde content. Optimized biomimetic nanocomposite materials for in vivo applications will likely be a compromise between the improved mechanical properties and decreased cytocompatibility associated with increased glutaraldehyde contents.

The local deformation surrounding an indented area of Ensis siliqua mollusk shell is characterized using a Raman spectroscopic technique, the findings of which are related to the material’s mechanical function. Microhardness indentation of four directional planes is used to show the marked anisotropy of the structure, where the outer and inner layers of the shell are found to have a significantly higher microhardness value of 4.82 ± 0.02 GPa, compared with transverse and longitudinal cross-sectional values of 3.00 ± 0.07 GPa. This difference is related to the crossed lamellar microstructure of the shell, which is oriented to provide the maximum resistance to external attack from predators. Nanoindentation of the material shows no such anisotropy, giving mean hardness and modulus values for the four directional planes of 3.86 ± 0.10 GPa and 82.4 ± 2.7 GPa respectively, thereby clarifying the prominent role of microstructure in such materials. Scanning electron microscopy of indented samples shows that plastic deformation and delamination occur to different extents, depending on the orientation of the structure and local microstructural features such as prismatic layers. A Raman spectroscopic technique has been used to map relative deformation in the vicinity of the indents, showing that the amount of plastic or permanent deformation can be quantified, and that material delamination can be distinguished from other forms of deformation such as local cracking. These experimental methods are repeated using samples of non-biogenic aragonite, which act as an analogous material for comparison with the shell. It is proposed that the analysis of microhardness indents using Raman spectroscopy could be applied to other biomaterials exhibiting anisotropy.

Influence of low and medium energy electron beam (E-beam) irradiation on the single-walled (SW) and multiwalled (MW) carbon nanotube films grown by microwave chemical vapor deposition are investigated. These films were subjected to electron beam energy of 50 keV from scanning electron microscope for 2.5, 5.5, 8.0, and 15 h and 100, 200, and 300 keV from transmission electron microscope electron gun for a few minutes to approximately 2 h continuously. To assess the surface modifications/structural degradation, the films were analyzed prior to and post-irradiation using x-ray diffraction and micro-Raman spectroscopy in addition to in situ monitoring by scanning and high-resolution transmission electron microscopy. A minimal increase in intertube or interplanar spacing (i.e., d002) for MW nanotubes ranging from 3.25–3.29 Å (∼3%) can be analogized to change in c-axis of graphite lattice due to thermal effects measured using x-ray diffraction. Resonance Raman spectroscopy revealed that irradiation generated defects in the lattice evaluated through variation of: the intensity of radial breathing mode (RBM), intensity ratio of D to G band (ID/IG), position of D and G bands and their harmonics (D* and G*). The increase in the defect-induced D band intensity, quenching of RBM intensity, and only a slight increase in G band intensity are some of the implications. The MW nanotubes tend to reach a state of saturation for prolonged exposures, while SW transforming semiconducting to quasi-metallic character. Softening of the q = 0 selection rule is suggested as a possible way to explain these results. It is also suggestive that knock-on collision may not be the primary cause of structural degradation, rather a local gradual reorganization, i.e., sp2+δ ⇔ sp2+δ, sp2 C seems quite possible. Experiments showed that with extended exposures, both kinds of nanotubes displayed various local structural instabilities including pinching, graphitization/amorphization, and forming intra-molecular junction (IMJ) within the area of electron beam focus possibly through amorphous carbon aggregates. They also displayed curling and closure forming nano-ring and helix-like structures while mending their dangling bonds. High-resolution transmission electron microscopy electrons corroborated these conclusions. Manufacturing of nanoscale structures “nano-engineering” of carbon-based systems is tentatively ascribed to irradiation-induced solid-state phase transformation, in contrast to conventional nanotube synthesis from the gas phase.

We have investigated the effect that the Ta content has on the ferroelectric properties of strontium bismuth tantalate (SBT) thin films synthesized using metalorganic decomposition (MOD) and spin coating techniques. The physical properties of these SBT samples were strongly dependent upon the Ta ratio. Polarization measurements revealed that Ta-deficient SBT exhibited a relatively low coercive field (2Ec ∼ 87 kV/cm) and a high remanent polarization (2Pr ∼ 15 μC/cm2). The value of 2Pr decreased as the Ta ratio in SBT increased. The improved ferroelectric properties of the Ta-deficient SBT samples may have resulted from the uniformly well-grown bismuth-layered-structured (BLS) phases of the films and their highly preferential orientation along the a and b axes. We suggest that the incorporation of Ta vacancies plays an important role in enhancing the crystallinities and microstructures of Ta-deficient SBT films.