The spontaneous whisker growth phenomenon was investigated by exposing Sn3Nd intermetallic compound (IMC) to different environments. In a humid environment, tin whiskers grew rapidly; the incubation time for whisker formation was only 0.75 h. However, no whiskers were formed when Sn3Nd IMC was exposed to dry argon for 33 days or dry oxygen (DO) for 7 days. In situ observation of whisker growth during room ambient (RA) exposure gave an average whisker growth rate of the Sn3Nd IMC of about 11 Å/s, which are 2–3 orders of magnitude faster than that previously reported for tin plating. Following whisker growth, a new hydroxide compound, Nd(OH)3, was found to have formed on the Sn3Nd. The results show that the presence of humidity in the exposure environment is necessary for whisker growth from Sn3Nd. Finally, the driving force for whisker growth is also discussed.

A cosolvent spray pyrolysis process was used for the generation of micrometer-sized pure copper particles. Ethylene glycol (EG) and ethanol (ET) were selected as cosolvents, and their effects on particle morphology and composition were systematically investigated. Experimental results showed that oxide-free copper particles could be generated at temperatures greater than 400 °C with either cosolvent. Hollow particles with cracks were generated with ET at temperatures from 400 to 1000 °C, whereas EG promoted the formation of porous particles at temperatures up to 600 °C and hollow shell particles with smooth surfaces at 875 and 1000 °C. Results from short residence time experiments indicated that, during the generation process, lamellar and fragment-like copper hydroxy nitrate [Cu2(OH)3NO3] precipitated when EG and ET were used respectively. Cu2(OH)3NO3 then decomposed to cupric oxide (CuO) and cuprous oxide (Cu2O). Finally the oxides were reduced to copper (Cu) in the reducing atmosphere created by EG and ET.

Nanostructured tungsten trioxide films were prepared by reactive dc magnetron sputtering at different working pressures Ptot = 1–4 Pa. The films were characterized by scanning electron microscopy, x-ray diffraction, Rutherford backscattering spectroscopy, Raman spectroscopy, and ultraviolet–visible spectrophotometry. The films were found to exhibit predominantly monoclinic structures and have similar band gap, Eg ≈ 2.8 eV, with a pronounced Urbach tail extending down to 2.5 eV. At low Ptot, strained film structures formed, which were slightly reduced and showed polaron absorption in the near-infrared region. The photodegradation rate of stearic acid was found to correlate with the stoichiometry and polaron absorption. This is explained by a recombination mechanism, whereby photoexcited electron–hole pairs recombine with polaron states in the band gap. The quantum yield decreased by 50% for photon energies close to Eg due to photoexcitations to band gap states lying below the O2affinity level.

Hybrid ultrahigh molecular weight polyethylene–nylon 6–single-wall carbon nanotube fibers were processed using solution spinning method. Elastic properties and normalized velocity ($\root 3 \of \Omega $) of the hybrid fibers were measured before and after strain hardening through repeated loading–unloading cycles. Phenomenal improvement in the properties was found: strength, modulus, and normalizing velocity increased by almost one order of magnitude after strain hardening. Neat and reinforced filaments were characterized through differential scanning calorimetry, Raman spectroscopy, and scanning electron microscope before and after strain hardening. It has been revealed that nylon 6 contributed to the deformation ability of the composite fiber, while carbon nanotubes contributed to the sharing of load as they aligned during extrusion and strain hardening processes. Important morphological features determining the fiber properties were the change in crystallinity and rate of crystallization, formation of microdroplets, interfacial sliding, polymer coating of nanotubes, alignment of polymer fibrils and nanotubes.

This article presents a novel microscratch technique for the determination of the fracture toughness of materials from scratch data. While acoustic emission and optical imaging devices provide quantitative evidence of fracture processes during scratch tests, the technique proposed here provides a quantitative means to assess the fracture toughness from the recorded forces and depth of penetration. We apply the proposed method to a large range of materials, from soft (polymers) to hard (metal), spanning fracture toughness values over more than two orders of magnitude. The fracture toughness values so obtained are in excellent agreement with toughness values obtained for the same materials by conventional fracture tests. The fact that the proposed microscratch technique is highly reproducible, almost nondestructive, and requires only small material volumes makes this technique a powerful tool for the assessment of fracture properties for microscale materials science and engineering applications.

TiN–indium composite films were deposited by simultaneous sputtering of titanium and indium in a mixed Argon/Nitrogen atmosphere and characterized for tribological applications. Film compositions showed a nonlinear behavior as a function of sputter gun power. For films deposited at −50 V bias, and containing less than 29 relative percent indium, the films had a face centered cubic structure, but at higher indium contents (63–82%) the structure was not consistent with either TiN or indium. At −150 V bias, the films had either the TiN structure, In-type structure, or a mixture of the two. Atomic force microscopy images showed the formation of semispherical drops on the surface of the samples deposited at −50 V bias voltage, whereas at −150 V bias voltage the samples exhibited a smooth coating surface with occasional ellipsoidal blisters. Nanoindentation test of the films shows low hardness (5–12 GPa), but tribological testing showed that frictional behavior can be improved by moderate heating before testing, suggesting indium segregation to the surface.

Microcompression tests were performed on the Al/Nb multilayers of incoherent interfaces with the layer thicknesses of 5 nm Al/5 nm Nb and 50 nm Al/50 nm Nb. The Al-Nb multilayers showed increase in strength as the layer thickness was reduced; the average flow stresses at 5% plastic strain from the 5 nm Al/5 nm Nb and 50 nm Al/50 nm Nb layer thickness specimens were determined to be 2.1 GPa and 1.4 GPa respectively. The results from this Al-Nb microcompression study were compared with those of the previous report on Cu-Nb multilayer microcompression results that indicated that the flow stresses of the Al-Nb multilayer are lower than those of Cu-Nb with the same bilayer spacing. The observed difference in strength was attributed to a potential difference in the interfacial strength of the two incoherent multilayer systems.

The compilation of measured effective rate constants for oxygen surface exchange on mixed conducting perovskites, which covers a great variety of compositions ranging from (La,Sr)MnO3−δ to (La,Sr)(Co,Fe)O3−δ and (Ba,Sr)(Co,Fe)O3−δ, demonstrates the importance of ionic conductivity—i.e., high oxygen vacancy concentration as well as vacancy mobility—as a key factor for the surface oxygen exchange rate. This interpretation is corroborated by ab initio calculations, which indicate that the approach of an oxygen vacancy to oxygen intermediates adsorbed on the surface is the rate determining step for a number of perovskites.

Uniform PbS nanostructures with varied morphology have been synthesized by a surfactant-assisted reflux route. ZnS and CdS layers were successfully coated onto PbS nanocrystals by encapsulation or epitaxial growth. The nanocrystals were characterized by x-ray diffraction, (high-resolution) transmission electron microscopy, selected area electron diffraction, and scanning electron microscopy. The truncated cubic nanostructures displayed a symmetric emission band at about 860 nm. Diffuse reflectance infrared (IR) spectroscopy was measured to estimate the band gap. High temperature and high frequency measurements of impedance and permittivity taught that the samples were stable and showed collateral evidence of the existence of epitaxial layers. Measurements illustrate that the luminescent properties of semiconductor PbS nanostructures are closely related to their surface nature, and encapsulation can affect their electrical properties and photoluminescence performance greatly. The study may prove useful in developing high frequency IR sensors and light signal amplification devices.

Ag nanoparticles dispersed SiO2 composite films were successfully prepared by a sol–gel method. The structural transition, formation, and optical property along with relevant band gap of Ag/SiO2 thin films during the annealing process were studied by Fourier transform infrared spectroscopy, thermogravimetry–differential thermal analysis, x-ray diffraction, and ultraviolet–visible spectroscopy, while the microstructure of thin films was revealed by transmission electron microscopy. The results indicate that the Ag spherical particles with the diameter of 10–20 nm were formed by breaking Si–O–Ag bonds above 200 °C and dispersed in the SiO2 matrix. The optical absorption property of Ag/SiO2 nanofilm in the visible range is enhanced, and the band gap (Eg) is widened with raising annealing temperatures, which is promising for the potential applications in nonlinear optical and related fields.

Transparent conducting oxide films are usually several 100-nm thick to achieve the required low sheet resistance. In this study, we show that the filtered cathodic arc technique produces high-quality low-cost ZnO:Al material for comparably smaller thicknesses than achieved by magnetron sputtering, making arc deposition a promising choice for applications requiring films less than 100-nm thick. A mean surface roughness less than 1 nm is observed for ZnO:Al films less than 100-nm thick, and 35-nm-thick ZnO:Al films exhibit Hall mobility of 28 cm2/Vs and a low resistivity of 6.5 × 10−4 Ωcm. Resistivity as low as 5.2 × 10−4 Ωcm and mobility as high as 43.5 cm2/Vs are obtained for 135-nm films.

Thin films of Ni-49 at.%Ti were deposited by DC magnetron sputtering on silicon substrates at 300 °C. The as-deposited amorphous films were annealed at a vacuum of 10−6 mbar at various temperatures between 300 and 650 °C to study the effect of annealing on microstructure and mechanical properties. The as-deposited films showed partial crystallization on annealing at 500 °C. At 500 °C, a distinct oxidation layer, rich in titanium but depleted in Ni, was seen on the film surface. A gradual increase in thickness and number of layers of various oxide stoichiometries as well as growth of triangular shaped reaction zones were seen with increase in annealing temperature up to 650 °C. Nanoindentation studies showed that the film hardness values increase with increase in annealing temperature up to 600 °C and subsequently decrease at 650 °C. The results were explained on the basis of the change in microstructure as a result of oxidation on annealing.

Single-walled carbon nanotube (SWNT) radical anions will react with tetrahydrofuran and generate ethylene, enolates, and a partially hydrogenated nanotube backbone. The experimental evidence suggests that there are sp3 C–H binding interactions. The total gravimetric content of hydrogen on a sample averages from 3.5% to 3.9% w/w, about four times the total amount observed for nanotubes hydrogenated via traditional Birch reduction reactions. Furthermore, the hydrogen desorbs at temperatures up to 400 °C less than those observed for the hydrogenated SWNTs formed after the Birch reduction. Finally, the first room temperature electron spin resonance spectrum of a nanotube radical ion is also reported.

In this article, the binary-phased PbTe–Sb2Te3 nanopowders were synthesized via a hydro/solvo-thermal route to improve the thermoelectric properties of PbTe matrix material. The single-phased PbTe powders exhibit pure nanoparticles, but the binary-phased PbTe–Sb2Te3 powders have a mixed morphology composed of nanospheres and nanoribbons. Our results suggest that the thermal conductivity of the binary-phased PbTe–Sb2Te3 bulks can be reduced significantly and the Seebeck coefficient can be increased obviously, although the electrical conductivity can also be decreased sharply. Consequently, a large figure of merit 0.85 at 623 K can be achieved for 0.7PbTe–0.3Sb2Te3 bulk, which is enhanced by about one time as compared to that of the single-phased PbTe bulk. This large enhancement could be attributed to the lowered carrier concentration and the increased interface scattering in the binary-phased PbTe–Sb2Te3 materials with a mixed morphology.

Indentation load–displacement curves for Mo (100) single crystals reveal clear displacement bursts from spherical indenters with various radii from ∼0.1 to ∼130 μm. There are two different size-dependent mechanisms for dislocation evolution involved during the displacement bursts. It has been postulated that these bursts are triggered by the nucleation of dislocations for a small indenter radius and the activation of preexisting dislocations for a large indenter radius. We present a simple model with which the displacement bursts from a larger indenter radius can be rationalized. This model relates the load and the excursion length during the first displacement burst. The correspondence between the model and experimental data indicates that the displacement bursts are initiated by the activation of preexisting dislocations and the model can accurately describe the mechanism for the displacement bursts from large indenters.

Dynamic tensile strength of polyurea is measured at an ultrahigh strain rate of 1.67 × 107 s−1 by generating spall failures inside thick polyurea coatings bonded to steel plates using laser-generated stress waves of several nanoseconds in duration. Specifically, thick polyurea films were cast on a steel plate whose backside was provided with water glass–covered Al film. The Al film was melted by focusing a high-energy Nd:YAG laser pulse over 3-mm-diameter area. Exfoliation of the Al generated a compressive stress wave toward the polyurea coating, which turned tensile upon reflection from the free surface. At a threshold laser energy, the amplitude of the returning tensile stress wave exceeded the dynamic tensile strength of polyurea. The stress wave profile inside the steel plate was interferometrically recorded at the threshold laser fluence and was used in a wave mechanics simulation to calculate the peak tensile stress. The polyurea was modeled as a viscoelastic solid.

Boron-doped, single (∼54 nm) or double (∼21 + 54 nm) Si1−xGex layers were epitaxially grown on 300-mm-diameter p−-Si(100) device wafers with 20 nm technology node design features, by ultrahigh vacuum chemical vapor deposition. The Si1−xGex/Si wafers were annealed in the temperature range of 950–1050 °C for 60 s to investigate the effect of annealing on possible changes of Ge content and Si stress near the Si1−xGex/Si interface. High spectral resolution, micro-Raman spectroscopy was used as a nondestructive characterization technique with five excitation wavelengths of 363.8, 441.6, 457.9, 488.0, and 514.5 nm. Ge diffusion and generation of compressive stress at the Si1−xGex/Si interface were measured on all annealed wafers. Ge diffusion and the accumulation of compressive Si stress after annealing showed significantly different behaviors between single- and double-layer Si1−xGex/Si wafers. Raman characterization results were compared with secondary ion mass spectroscopy and high-resolution x-ray diffraction results.

The long afterglow phosphor, CaWO4: Eu3+, is synthesized and the intensity and duration of its afterglow can be enhanced by the Ti4+ and Mg2+ incorporation. The x-ray diffraction patterns depict pure tetragonal CaWO4 of all samples. The emission spectra show the Eu3+ emission and the charge transfer (CT) emission of WO42−. The intensity of CT increases with the Mg2+ incorporation. The excitation spectra monitoring 616 nm exhibit the strongest CT band with Ti4+ incorporation. These results indicate that Mg2+ enhances the efficiency of CT emission of WO42− while the Ti4+ enhances the energy transfer rate from CT to Eu3+. Since the thermoluminescence (TL) curves do not imply a new trap, the enhancement of the afterglow results from the coreinforcement of CT efficiency and energy transfer rate.

A new technique based on the detection of the amplitude of the second harmonic was described in a previous paper. To compute the elastic modulus and the hardness of materials, the technique uses only the derivative of the contact radius with respect to the indentation depth. For this reason, this method is applicable only to homogeneous materials. In this paper, the method is extended to any materials with constant Young modulus. The indentation depth value is not needed at all, thus eliminating uncertainties related to the displacement measurement, which are very influent at small penetration depths. Furthermore, we also explain how to compute the indentation depth from the detection of the amplitude of the second harmonic. This new measurement technique was tested on three samples: fused silica, Poly(methyl methacrylate) (PMMA), and calcite, which is expected to exhibit indentation size effect. The obtained results show that mechanical properties and the indentation depth can be determined with good accuracy for penetration depths between 25 and 100 nm using this method.