Effect of carboxylic acid on sintering of inkjet-printed copper nanoparticulate films

The reduction effect of various carboxylic acids on inkjet-printed copper film was investigated. Carboxylic acids were exposed to the film by nitrogen gas that was bubbled through the liquid acids during the annealing process. It was observed that in the case of saturated monocarboxylic acid (formic, acetic, propionic, butyric), the acids with shorter hydrocarbon chains perform better in reducing the surface copper oxides in the printed copper conductive film. The printed films exposed to formic acid vapor exhibited the lowest resistivity (3.10 and 2.30 μΩ cm when annealed at 200 and 250 °C, respectively). In addition, the oxalic acid more effectively reduces copper oxide than formic acid and its usage can shorten the annealing time for highly conductive printed copper film. This reductive annealing process allows fabrication of copper patterns with low resistivity, (3.82 μΩ cm annealed at 250 °C) comparable to the resistivity of bulk copper.     

Size effects on the mechanical behavior of gold thin films

The Membrane Deflection Experiment was used to test the mechanical response of freestanding thin film gold specimens. We present stress-strain curves obtained on films 0.3, 0.5, and 0.1 m thick. Elastic modulus was consistently measured in the range of 53–55 GPa. Several size effects on the mechanical properties were observed including yield stress variations with membrane width and film thickness. It was observed that a width of 2.5 m and a thickness of 0.5 m correspond to major transitions in the material deformation behavior.     

The effects of surface layers on the conductivity of gold films

An experimental investigation has been made of the effects of added, vacuum-deposited, gold layers upon the conductivity of specially prepared gold films in which the conduction electrons are specularly scattered at the film boundaries. The “specular” films were prepared by vacuum depositing gold upon bismuth oxide nucleating layers and then annealing in air at 350 °C. The experimental results have been related to a theoretical analysis based on the Fuchs-Sondheimer formalism.It was observed that the deposition of an added layer of gold upon the surface of a “specular” film caused an initial increase of resistance, which rose to a maximum, and then decreased with increasing thickness. The initial increase of resistance was attributed to a change from specular to diffuse scattering of the conduction electrons at the surface.     

Environmental effects on thermally induced multistability in unsymmetric composite laminates

The principles involved in the generation of thermal induced multistability in carbon fibre epoxy laminates have received much interest in the published literature. This work examines the effects of moisture absorption on the mechanical properties of these plates focussing on geometry and ‘snap-through’ loadings. Samples were monitored from a dry state until moisture equilibrium was achieved. It was observed that substantial changes in geometry and snap-through performance occurred as moisture content increased. As part of this work, a first order strain energy analysis was modified to incorporate a hygrothermal strain term to enable prediction of the laminate shape due to moisture content.     

Biological effects of nanoparticulate materials

A range of morphologically nanoparticulate materials including Ag, NiO, TiO₂, multiwall carbon nanotubes, and chrysotile asbestos have been characterized by transmission electron microscopy. All but the TiO₂ (anatase and rutile) were observed to exhibit some cytotoxicity at concentrations of 5 μg/ml for a murine macrophage cell line as a respiratory response model. Silver exhibits interesting systemic differences for animal and human toxicity, especially in light of its nanoparticulate materials, and should be avoided even if there is no detectable in vitro cytotoxic response, as a prudent approach to their technological applications.     

Atmospheric effects on the photosensitive response of poly(methylphenylsilane) thin films

Agile ready-when-needed patterning of refractive index structures in photosensitive materials requires an understanding of the impact of local application environment on mechanisms contributing to the desired photoinduced index change. The present work examines the impact of atmosphere on the photosensitive response of poly(methylphenylsilane) (PMPS) thin films whose high photoinduced index change under low incident optical fluence make them attractive candidates for such applications. Changes in optical absorption and refractive index are investigated after exposure to ultraviolet (UV) light resonant with the lowest energy transition exhibited by the Si–Si backbone structure in the material. A comparison between photoinduced absorption changes for thin films exposed in an air atmosphere versus those observed for samples subjected to a nitrogen environment during photoexposure is made for the first time. The study reveals that the anaerobic conditions of the nitrogen atmosphere significantly reduce the photosensitive response of the material to light. These results are discussed in terms of photooxidation processes within the polysilane structure and in the context of the need for predictable photosensitive refractive index change in varied photoimprinting environments.     

Spectroscopic measurements of stress relaxation during thermally induced crystallization of amorphous titania films

Amorphous TiO₂ optical films transform irreversibly to a crystalline phase when subjected to temperatures in excess of 573 K. The transformation is accompanied by film densification and a marked change in the intrinsic film stress. Work reported here involves the application of real-time Raman spectroscopy to follow the transformation dynamics and to evaluate transient stresses which evolve during thermally induced crystallization of amorphous sol-gel deposited films. Relative changes in vibrational mode intensities characteristic of the crystalline phase correlate with the degree of crystallinity in the film while mode frequency shifts also acquired in real time are used to estimate the film temperature and the magnitude of internal stress. A contour analysis method is presented whereby knowledge of two vibrational mode frequencies is sufficient to determine these quantities uniquely. Results suggest that both deposition temperature and crystallization temperature affect the intrinsic film stress. Advantages and limitations of this method for the evaluation of stress in dielectric films are discussed.     

Misfit and thermally induced strain in epitaxial IV–VI semiconductor films

Epitaxially grown single-crystal PbTe films on BaF₂ are subjected to a considerable strain due to the mismatch of the lattice constants and the thermal expansion coefficients. By the magneto-optical and X-ray experiments reported in this paper it was possible to investigate separately the contributions of the compressive misfit strain and the thermally induced tensile strain. As a consequence of the opposite directions of the two effects, the system PbTe/BaF₂ is suited to grow single-crystal PbTe films exhibiting low strain below room temperature.     

Temperature effects on the electrical conductivity of thiol encapsulated gold nanoparticle thin films

Presented in this paper are results demonstrating the irreversibility in conductivity changes seen for thin, Langmuir–Schaeffer deposited thiol encapsulated gold nanoparticle films raised to a high temperature. The conductivity changes from low values that rapidly increase at higher temperature, to values that remain high and are almost linear with temperature. Comparisons are made to the expected behavior predicted by the conventional model of electron hopping in metal nanoparticle films.     

Observations of thermally induced transformations in amorphous chalcogenide films using transmission electron microscopy

Thermally induced phase transformations in chalcogenide thin films evaporated from the alloy As 36-Te 53-Ge 11 (wt.%) onto glass substrates kept at room temperature were investigated using transmission electron microscopy. Although the as-deposited films showed an amorphous structure, a sudden and very fast transformation to a crystalline phase took place dendritically on electron-beam heating in the microscope. Annealing of thin films outside the microscope in the temperature range 100–170 °C was also found to cause and assist dendritic recrystallization. This formation of dendrites is discussed in terms of the properties of the material.     

A reinterpretation of the effects of impurities on the thermoelectric power of thin gold films

Previously published data are re-examined in the light of a grain-boundary model for monocrystalline films. New interpretations are proposed which show that the thermoelectric power due to thickness-dependent scattering attains a constant value.     

A new approach to the fabrication of ZnO ultrathin films from annealing ZnS nanoparticulate films

The ZnO ultrathin films were fabricated from annealing the ZnS nanoparticulate films. By the layer by layer self-assembly technique, we constructed the ZnS nanoparticulate films from alternating layers of ZnS nanoparticles and polydiallyldimethylammonium chloride (PDDA). The result of the emission spectra indicated that PDDA played a role of passivator. Annealing the ZnS/PDDA films at different temperatures led to the changes in absorption. The SEM images showed that the preannealed film was composed of the uniformly distributing domains, while on the annealed film, there exist some holes formed by the burning of the organic components. The EDS confirmed that ZnS could be converted to ZnO at 500 °C.     

Effect of sintering on thermally sprayed carbon nanotube reinforced aluminum nanocomposite

Reconsolidation of thermally spray formed (plasma and high velocity oxyfuel spraying) hypereutectic Al–Si nanocomposites with multiwalled carbon nanotube (MWCNT) reinforcement was carried out by inert atmosphere sintering for prolonged time periods. The sintering treatment resulted in the removal of porosity and residual stress, and increase in size and volume fraction of primary Si particles in the Al–Si matrix. The morphology of multiwalled carbon nanotubes in sintered nanocomposites remained unchanged after sintering. The interfacial ultrathin product layer of silicon carbide between MWCNT reinforcement and Al–Si matrix was unaltered. Microhardness and elastic modulus of the sintered nanocomposites were influenced by combined effect of multiple factors, i.e. reduction in porosity, residual stress removal and MWCNT distribution. Overall improvement of microhardness and elastic modulus of the sintered nanocomposites was observed. The experimentally measured elastic modulus values were compared with theoretically estimated values using micromechanics models.     

Chemisorption and chemical reaction effects on the resistivity of ultrathin gold films at the liquid-solid interface

Ultrathin gold films, with thicknesses between the onset of conductivity (d ～ 5 nm) and the electron mean free path (d ～ 80 nm), display surface-sensitive resistivities, which have been exploited to follow the adsorption and desorption of molecular monolayers at the metal-solution interface with high precision. For nominal Au film thicknesses (d ～ 40 nm), strongly chemisorbed thiolate monolayers increase the resistivity of the thin Au films by ～4%, but weakly adsorbed species, such as pyridine or phenolate at open circuit, induce no observable change in the Au film resistance. Resistivity measurements implemented with a high-stability current source and high-precision digital voltmeter sampling at 1 Hz resulted in 3σ uncertainties in alkanethiolate coverage of 1.4 × 10(-)(4) monolayer. Surface plasmon resonance measurements, performed simultaneously with resistivity measurements, indicate that changes in resistivity vary monotonically with coverage with three distinct regions: a low-coverage region of heightened adsorbate mobility, an intermediate-coverage region with generally linear behavior, and a chain length-dependent saturation region at high coverages. Resistivity measurements were also capable of reproducibly following the chemical state of the Au surface through a complex set of redox manipulations, demonstrating the versatility of this simple measurement.     

Interfacial energy induced microstructure of thin magnetic iron/gold multilayer films

Magnetron sputtered iron/gold multilayers are investigated by cross-sectional transmission electron microscopy. Thermodynamic considerations can explain the different observed microstructures near the substrate and near the top of the multilayers.     

Gamma-ray irradiation induced structural and optical constants changes of thermally evaporated neutral red thin films

Neutral red (NR) is polycrystalline in powder form, it transforms to nanocrystallite phase upon thermal deposition. Gamma-ray irradiation with doses 1.25–6 KGy induced partial transformation of nanocrystallite phase to amorphous structure. The changes of optical constants with γ-ray doses were calculated using spectrophotometer measurements of transmittance and reflectance at normal incidence of light over spectral range 200–2500 nm. The complex refractive index of NR film is highly influenced by exposure to γ-ray irradiation, the onset and optical energy gaps decrease with increasing γ-ray doses, and Urbach tail increases linearly with increasing irradiation dose. The type of electronic transition, oscillator, and electric dipole strengths and dispersion parameters were determined before and after irradiation. The spectral behavior of dielectric constant with γ-ray doses was also estimated.     

Structural design optimization on thermally induced vibration

The numerical method of design optimization for structural thermally induced vibration is originally studied in this paper and implemented in the software JIFEX. The direct and adjoint methods of sensitivity analysis for thermal‐induced vibration coupled with both linear and non‐linear transient heat conduction is firstly proposed. Based on the finite element method, the linear structural dynamics is treated simultaneously with linear and non‐linear transient heat conduction. In the heat conduction, the non‐linear factors include the radiation and temperature‐dependent materials. The sensitivity analysis of transient linear and non‐linear heat conduction is performed with the precise time integration method; and then, the sensitivity analysis of structural transient responses is performed by the Newmark method. Both the direct method and the adjoint method are employed to derive the sensitivity equations of thermal vibration. In the adjoint method, two adjoint vectors of structure and of heat conduction are used to derive the adjoint equations. The coupling effect of heat conduction on thermal vibration in the sensitivity analysis is particularly investigated. With the coupling sensitivity analysis, the optimization model is constructed and solved by the sequential linear programming or sequential quadratic programming algorithm. Numerical examples are given to validate the proposed methods and to demonstrate the importance of the coupled design optimization. Copyright © 2003 John Wiley & Sons, Ltd.     

Some thermally and optically induced changes of optical properties of amorphous As38S62 films

The exposure (in air) of As₃₈S₆₂ amorphous film was found to be accompanied (i) by significant structural changes in the film matrix (an increase of As-S bond density as indicated by IR spectroscopy), and (ii) by darkening of the film. No indications of photo-oxidation have been found. Exposure and subsequent annealing of the well-annealed film are accompanied by reversible changes of the As-S bond density, as indicated by the results of differential infrared spectroscopy. The dispersion of the refractive index of the virgin, annealed and exposed films can be described using the Wemple-DiDomenico (W-D) single-oscillator formula. Annealing- and exposure-induced changes of the parameters of the W-D formula follow the changes of both the optical gap and the As-S bond density.