Nanomechanical devices constitute an important and growing field, as they allow for new understanding of the mechanical properties at interfaces and surfaces. As an example, a newly developed nanoindentation device has been used to accomplish μN load indents into GaAs. First, it is shown that a plastic zone can be measured and is comparable to theory. Also, it is shown that the rate of indentation affects both the depth and upset zone of low load indents, implying a strain-rate sensitivity effect at room temperature. This is reinforced by observation of what appears to be a glide-based relaxation process.

This communication reports on the microstructure and interdiffusion observed in a new NbSn2/Nb metallization structure on SiO2, previously reported [H. S. Chen et al., Appl. Phys. Lett. 66, 2191 (1995)]. The as-deposited NbSn2 layer was found to be amorphous. After heating, the NbSn2 becomes polycrystalline and heavily diffused with Au from the Au-Sn solder. The Nb layer remains pure and intact after heating. The microstructure, compositions, and phases of the Au-Sn solder layer are also presented.

The ordering behavior of La-modified lead zirconate titanate relaxor (PLZT 9/65/35) was investigated by use of an x-ray diffractometer (XRD) and high-resolution transmission electron microscopy (HRTEM). It was shown that a {h + 1/2, k + 1/2, 0}-type superlattice exists both in the x-ray diffraction pattern and selected area electron diffraction (SAED) image. High-resolution electron micrographs further demonstrated the existence of the superlattice and exposed the ordered and disordered regions in the lattice level. A model referring to an A-site body-centered pseudo-cubic superstructure was proposed.

The structural, microwave absorption, and oxidation characteristics of diesel particulate matter (DPM) collected from a CAT 3304 diesel engine are reported. The x-ray diffraction of DPM yields the characteristic peaks of pregraphitic carbons (cokes and pitches), and its modeling yields d(002) ≍ 3.429 Å and a crystallite size of about 20 Å. The real and imaginary parts of the dielectric constant ∊ = ∊′ + i∊″ are measured at 8.7 GHz using the cavity perturbation technique. The measured values for the DPM are ∊′ = 8.6 ± 1.7 and ∊″ = 7.4 ± 1.5, compared to ∊′ ≍ 1.0 and ∊″ ≍ 6 × 10−5 for the ceramic trap material used for collecting DPM. The oxidation products of the DPM, analyzed by FTIR spectroscopy, are found to contain CO2 and CO with a peak yield occurring around 500 °C. Since microwave power absorption is proportional to ∊″, these results show that selective microwave heating of the DPM in the ceramic traps should be a very efficient process with CO2 and CO as the main oxidation products.

A nanocrystalline β–Sn film of 7 nm average grain size was prepared by inert gas condensation followed by ballistic consolidation, and was investigated by x-ray diffractometry at temperatures of 77 and 293 K. Although Sn normally undergoes a βα phase transformation at 286 K, this transformation was suppressed in the nanocrystalline film. Compared with large-grained β-Sn, a larger Debye–Waller factor and a lower Debye temperature were measured for nanocrystalline β-Sn; ΘD = 133 K for nanocrystalline material while ΘD = 161 K for large-grained material. The lower Debye temperature of the nanocrystalline β-Sn indicates that its vibrational entropy is increased by 0.6 kB/atom with respect to large-grained material.

Phase relationships in the system Si3N4−SiO2−Yb2O3 have been investigated at 1750 °C and compared with those in the system Si3N4−SiO2−Y2O3. Two types of ytterbium silicon oxynitride, Yb2Si3O3N4 (tetragonal) and Yb4Si2O7N2 (monoclinic), were confirmed to exist. The x-ray powder diffraction data of two compounds were indexed based on the space group and unit cells. Melting temperature of Yb4Si2O7N2 was determined as 1870 °C. Yb4Si2O7N2 is a better intergranular phase of silicon nitride ceramics for its high melting temperature.

Using ultrasonic-resonance spectroscopy (URS), we measured the elastic constant C and companion internal friction Q−1 of isotropic polycrystalline copper. The annealed material was 0.9999 pure with equiaxed heavily twinned grains averaging about 75 μm diameter. The URS method offers the principal advantage of point contact or loose coupling, thus there was no contribution from a transducer-specimen bond and only small contributions from transducers and fixture. A second advantage is one measurement for all elastic constants and all associated internal frictions. The C's agree with established values. The Q−1's are much lower than pulse-echo-method values. Comparison of measured Q−1 with the Koehler-Granato-Lücke model permits estimating an effective dislocation-loop length. Q−1 (shear) exceeds Q−1 (longitudinal) by a factor of about 1.5.

La:Mn = 1:1 mixtures of lanthanum oxide and manganese carbonate were heat-treated under various oxygen partial pressures at 1400 °C or 1300 °C. The Mn valence of the samples was measured by a chemical analysis, and the crystal structures were refined by the powder x-ray diffraction and the Rietveld analysis. A novel orthorhombic perovskite phase, belonging to the space group Pbnm and containing - Mn2+ ions, was formed by heat-treatment under low oxygen partial pressures. The structure was very close to a cubic symmetry. It is supposed that the micro Jahn-Teller effects of Mn2+ ions were nearly canceled by one another.

We propose an angular redistribution model to understand the negative ions resputtering effect in sputter depositing YBa2Cu3O7−x (YBCO) films. On the basis of this model, the negative oxygen ions resputtering effect has been greatly minimized by introducing a Cu mask between the substrate and the target to block energetic oxygen particles from directly bombarding the growing film. Thus, YBCO films with almost exact stoichiometric composition and zero resistance critical temperatures as high as 90 K are obtained under oxygen partial pressure as low as 3 mTorr in a temperature regime well beyond that proposed by R.H. Hammond and R. Bormann. Preliminary results of a modified masking and shiclding technique to eliminate the resputtering effect and fabricate large area (>1 in. × 1 in.) YBCO superconducting films with high uniformity are also presented.

Crystalline thin films of NdNiO3 have been epitaxially grown on the (100) face of single-crystal LaAlO3 substrates. These films exhibit the characteristic reversible change in electrical conductivity with temperature previously observed in bulk polycrystalline material. The temperature of the electrical transition in the epitaxial thin films was lower than reported for the bulk polycrystalline ceramics. This effect is attributed to lattice strains associated with the film processing and interfacial lattice matching constraints.

High-quality YBCO thin films have been grown by Inverted Cylindrical Magnetron Sputtering (ICMS) on LaAlO3(100), SrTiO3(100), SrTiO3(110), and MgO(100) substrates. Transition temperatures of c-axis films exceed 90 K, and transition widths are within 1 K. Critical currents range up to 5 × 106 A/cm2 at 77 K. Structural and morphological features analyzed by x-ray diffraction and scanning electron microscopy, respectively, are found to be strongly dependent on film orientation and deposition temperature. In order to understand such dependence, a simple interpretation is proposed in terms of Gibbs energies and growth dynamics of the nucleation process.

Polysulfones, such as poly(oxy-1,4-phenylenesulfonyl-1,4-phenyleneoxy-1,4-phenyleneisopropylid-ene-1,4-phenylene), poly(phenylene ether sulfone), poly(phenylene sulfone), and aliphatic polysulfone, poly(bicycloheptene sulfone), were employed as a host resin. N-ethyl-N-hydroxyethyl-4-(4'-nitrophenylazo)phenylamine (Disperse Red 1) acted as a guest molecule and was dispersed in those hosts with a concentration of 5 wt. % to 10 wt.%. Their second harmonic generation properties were characterized and compared. Xijk values obtained varied from 11 pm/V to 21 pm/V. The merits of polysulfones as a host material are good optical clarity, easy film forming, and fairly high glass transition Tg temperature (140 °C to 190 °C). Chemically, compared to polyimides they have good resistance to moisture, i.e., less vulnerable to hydrolysis. It is a good candidate for electro-optical materials.

Electron emission from chemical vapor deposited (CVD) diamond and amorphous carbon (a-C) films was observed with a simple field emission device (FED). Both diamond and a-C films were prepared with microwave plasma-enhanced CVD techniques. Electron emission in the ficld strength range + 10 to −10 MVm−1 was studied, and the field emission source was confirmed by a diode characteristic of the I-V curve, a straight line in the Fowler-Nordheim (F-N) plot, and direct observation of light emission from a fluorescent screen. The turn-on field strength was ∼5 MVm−1, which was similar for both kinds of carbon films. The highest current density for diamond films, observed at a field strength of 10 MVm−1, was ∼15 μA cm−2. Diamond films yielded a higher emission current than a-C films. The reasons for the observed field emission are discussed.

A two-dimensional model of oxygen-deficit layer of superconducting material YBa2Cu3O7 has been simulated by the molecular-dynamics technique in order to study the influence of the impurities in the site of copper on the low-temperature microstructure. The microstructure pattern arises as a result of quenching the system from a high-temperature tetragonal phase to the low-temperature orthorhombic one and subsequent annealing. The potential of the impurity is modified in such a way that it promotes occupation of opposite nearest-neighbor sites around impurity by an oxygen and vacancy simultaneously. The simulations of the annealing processes showed that the domain pattern becomes very tiny with increased concentration of randomly distributed impurities. Domains of larger sizes would appear if the impurities were able to diffuse to the domain walls. This is confirmed by annealing the sample containing linear chains of impurities. The tweed microstructure depends on the magnitude of the force constants of the elastic subsystem, and at too large coupling the randomly distributed impurities are not able to pin the stiff domain walls. The results resemble the electron-microscope photographs made for cobalt in YBa2(Cu1−xCox)3O7−δ.

A large magnetoresistance change (ΔR/RH) of −550% has been observed at 270 K in (La0.8Ca0.2)MnO3 thin films. The films were prepared in situ on LaAlO3 substrates by single-liquid-source metal-organic chemical vapor deposition. M(thd)n (M = La, Ca, and Mn, and n = 2, 3) were dissolved together in an organic solution and used as precursors for the deposition of (La0.8Ca0.2)MnO3 thin films. Deposition was conducted at an oxygen partial pressure of 1.2 Torr and a substrate temperature ranging from 600 °C to 700 °C. The mechanism for the large magnetoresistance change in this manganese oxide is briefly discussed.

The deposition of thin films and coatings frequently results in the generation of toxic waste, volatile organic compounds, or large amounts of waste water and sludge. Vapor deposition in vacuum offers a more environmentally benign alternative, but is not prevalent outside of the microelectronics industry due to economic reasons. However, vacuum coating could be more widely accepted, and could potentially replace nonvacuum deposition methods, if either the cycle time or costs associated with vacuum coating were reduced. In order to reduce the cycle time for vacuum deposition, a robust system for continuous air-to-vacuum-to-air (AVA) transportation of discreet substrates has been developed and constructed in this study. This technology allows the insertion of discrete components into vacuum at high rates, without the need for venting the deposition chamber. Substrates have been repeatedly transported from atmosphere to 10−5 Torr in under a second. The capability of the AVA technology was studied through the deposition and characterization of CdS and CdTe films and photovoltaic devices. With the AVA technology, the need for venting the vacuum chamber to insert the substrates and subsequent pumping of the system for deposition is eliminated. The AVA technology could be applied to the processing of silicon wafers, compact disks, optical components, solar cells, cutting tools, and fasteners.

Ni2+ ions in aqueous solutions were electrochemically deposited within pores of alumina compacts attached to carbon or Pt electrode at room temperature. The deposition behavior of Ni metal in the pores of alumina compacts was expressed by an empirical power law equation of W = ktn, where W is the weight of Ni deposited, k the deposition rate constant, t the deposition time, and n the experimental constant (0.52-0.56). The shape of Ni deposited was dependent on the geometry of positive electrode.

Condensed silica fume, a by-product from the production of silicon alloys, was sintered by (i) conventional heating in a dilatometric furnace, both at constant heating rate and isothermal heating, and (ii) by the microwave heating. The dense products with relative density up to 95% of theoretical can be obtained only by short runs at high heating rates, preferentially accomplished by the microwave treatment. Prolonged heating leads to the devitrification of the original glassy phase to cristobalite, accompanied by an arrest of densification.

α-hexathienyl (α–6T) is a highly promising material for application in thin film transistor devices. Recently, record high mobilities, together with record high current on/off ratios, have been reported.1 Thus far, structural information on this exciting material is sketchy. The crystal structures of several such hexamers have been investigated, but only with powder samples, since the crystal growth has proven exceedingly difficult.2-5 Powder Rietveld refinements on these materials are severely hampered by the large number of overlapping reflections, preferred orientation, ambiguities in symmetry, etc. Here, we present a crystal structure of the high-temperature polymorph of α–6T (α–6T/HT), as determined from a single-crystal structure analysis. In this polymorph, the hexamer crystallizes in the smallest unit cell so far reported for this material, but the molecule is flat. Extended Hückel theory (EHT) band structure calculations show that α–6T/HT is an indirect gap semiconductor, with the conduction band minimum at Y and the valence band maximum at Γ. The conduction and valence bands both show a remarkable degree of dispersion along X and Y for a molecular crystal. The electronic band structure of this material is strikingly similar to that of the two-dimensional organic superconductors based on bis(ethylenedithio)tetrathiafulvalene (ET), such as κ−(ET)2 Cu(NCS)2.

Defects in Bi2Sr2Can-1CunOy superconducting thin films annealed in an oxygen atmosphere are examined by high-resolution electron microscopy (HREM). In addition to the majority 2212 (n = 2) phase, subsequent slabs of other homologous phases with n values up to n = 10 are found intergrown in the films. Large-angle tilt grain boundaries and various secondary phases such as CuO, Sr-Cu-O oxides are formed in the films. The occurrence of these defects is attributed to an inhomogeneous Sr, Ca, and Cu distribution induced by the post-annealing. Superconducting transition temperature (Tc) is increased by the annealing under suitable conditions.