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The evolutions of localized states, dielectric functions, and electronic band structure for nitrogen (N) incorporated GeTe (NGT) as functions of temperature (210-660 K) and N concentration (0%-18%) have been investigated with the aid of temperature dependent spectroscopic ellipsometry experiments. The increased Urbach absorption energy, caused by band-tail localized states, can be attributed to the increment of structure defects with N concentration, which is generated from the N atoms bonding with Ge. Besides, the details of the dynamic crystallization process and the role of nitrogen in NGT films have been elucidated by the abnormal behavior of interband transition energy and the evolutions of surface morphology, namely, the nitrides separation before crystallization and the inhibition on GT crystallization. The dynamic crystallization process and the nitrogen behavior in NGT are of great significance for further study on the reliability and endurance of the NGT-based data storage devices. [ABSTRACT FROM AUTHOR]

Sandwiched fluoroethylene propylene films with charged, parallel-tunnel voids between the layers, which exhibit high d31 piezoelectric activity, were designed. Stripes of such piezoelectrets were exposed to mechanical stress in length direction by a seismic mass excited to vibrations. Due to the piezoelectricity of the films, a current in a terminating resistor is generated. The harvested power across the resistor amounts to about 0.2mW for a seismic mass of 2 g and an acceleration of 1 g. In comparison with other piezoelectret or with poly(vinylidene fluoride) harvesters, the generated power referred to equal acceleration and force, is significantly larger. [ABSTRACT FROM AUTHOR]

Tungsten (W) doping effects on Ge2Sb2Te5 (GSTW) phase change films with different concentrations (3.2, 7.1, and 10.8%) have been investigated by variable-temperature spectroscopic ellipsometry. The dielectric functions from 210 K to 660 K have been evaluated with the aid of Tauc-Lorentz and Drude dispersion models. The analysis of Tauc gap energy (Eg) and partial spectral weight integral reveal the correlation between optical properties and local structural change. The order degree increment and chemical bond change from covalent to resonant should be responsible for band gap narrowing and electronic transition enhancement during the phase change process. It is found that the elevated crystalline temperature for GSTW can be related to improved disorder degree. Furthermore, the shrinkage of Eg for GSTW should be attributed to the enhanced metallicity compared with undoped GST. [ABSTRACT FROM AUTHOR]

Solid-state nucleation of Si nanocrystals in a SiO2 bilayered matrix was observed at temperatures as low as 450 °C. This was achieved by aberration corrected high-resolution transmission electron microscopy (HRTEM) with real-time in-situ heating up to 600 °C. This technique is a valuable characterization tool especially with the recent interest in Si nanostructures for light emitting devices, non-volatile memories, and third-generation photovoltaics which all typically require a heating step in their fabrication. The control of size, shape, and distribution of the Si nanocrystals are critical for these applications. This experimental study involves in-situ observation of the nucleation of Si nanocrystals in a SiO2 bilayered matrix fabricated through radio frequency co-sputtering. The results show that the shapes of Si nanocrystals in amorphous SiO2 bilayered matrices are irregular and not spherical, in contrast to many claims in the literature. Furthermore, the Si nanocrystals are well confined within their layers by the amorphous SiO2. This study demonstrates the potential of in-situ HRTEM as a tool to observe the real time nucleation of Si nanocrystals in a SiO2 bilayered matrix. Furthermore, ideas for improvements on this in-situ heating HRTEM technique are discussed. [ABSTRACT FROM AUTHOR]

High-resolution 3-Dimensional Reciprocal Space Mapping (3D-RSM) has been performed on mixed-phase BiFeO3 (BFO) epitaxial films on (001)-oriented LaAlO3 substrates. Our results demonstrate that 3D-RSM is an effective way to present a structural overview of the different BFO polymorphs, domain variants, and even the interfacial regions between coexisting triclinic phases. The dislocation-free boundaries between the triclinic phases revealed by these 3D-RSMs are believed to be responsible for the large electromechanical response found in mixed-phase BFO films. This study demonstrates the unique merits of the 3D-RSM technique for the structural characterization of ferroic films with complicated domain structures. [ABSTRACT FROM AUTHOR]

In this paper, the thermal stability of TiN metal gate with various composition prepared by different preparation technology [(e.g., atomic layer deposition (ALD) or physical vapor deposition (PVD)] on HfO2 high-K dielectric is investigated and compared by physical and electrical analysis. After annealing of the TiN/HfO2 stack at 1000 °C for 30 s, it is observed that: (1) Nitrogen tends to out-diffuse from TiN for all the samples; (2) Oxygen from the interfacial layer (IL) between HfO2 and Si tends to diffuse toward TiN. PVD Ti-rich TiN shows a wider oxygen distribution in the gate stack, and a thinner IL than the N-rich sample. Ti penetration into HfO2 is also observed in the Ti-rich sample, which can potentially lead to the dielectric break-down. Besides, the oxygen out-diffusion can be significantly suppressed for ALD TiN compared to the PVD TiN samples. [ABSTRACT FROM AUTHOR]

A lead-free ceramic with the composition (K0.55Na0.45)0.965Li0.035Nb0.80Ta0.20O3 was found having an outstanding piezoelectric performance. It possesses high piezoelectric properties of d33=262 pC/N, kp=0.53, k33=0.63, and k31=0.31 with [variant_greek_epsilon]′=1290 and tan δ=0.019 at room temperature. In spite of the orthorhombic-tetragonal polymorphic phase transition around 30 °C, temperature stability of the electromechanical coupling coefficients is very good over the common usage temperature interval between -40 and 85 °C. Furthermore, the piezoelectric properties remain almost unchanged in the severe thermal aging test down to -150 °C and up to about 300 °C. It is suggested that the outstanding piezoelectric performance of this ceramic can be largely ascribed to the phase coexistence in a wide temperature range and the Ta-rich composition. [ABSTRACT FROM AUTHOR]

The mechanisms have been identified for the hetero-epitaxial nucleation of YBa[sub 2]Cu[sub 3]O[sub ∼6.1] (YBCO) at the buried interface between a precursor film and SrTiO[sub 3] for the so-called BaF[sub 2] process which is a postdeposition reaction process for the synthesis of epitaxial YBCO films. It is shown that the preferential nucleation of YBCO at the interface is due to (1) the strong chemical affinity of the (Y, Ba)-oxy-fluoride, an intermediate phase, to SrTiO[sub 3] and (2) the epitaxial alignment of its (111) planes with the (001) surface of the SrTiO[sub 3] which reduces the activation barrier for the formation of YBCO. In thin films (<2–3 μm) the YBCO nuclei, whose c axes are perpendicular to the SrTiO[sub 3] surface, form directly from this aligned oxy-fluoride. In thick films (5 μm), however, this oxy-fluoride decomposes into a disordered transitory cubic phase which then orders to form YBCO nuclei with three orientational variants, one with its c axis perpendicular and two with their c axes parallel to the (001) plane of SrTiO[sub 3]. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A tunable coherent blue light source with a tuning range of 430–470 nm has been built. Tunable blue radiation was obtained by intracavity frequency doubling of a Ti:Al2O3 laser in KNbO3 crystals. The titanium sapphire laser was operated in a pulsed mode pumped by the second harmonic of a Q-switched Nd:YAG laser. An infrared to blue conversion of 45% and a total conversion efficiency (532 nm to tunable blue) of 2% were reached. [ABSTRACT FROM AUTHOR]

In this work, the dielectric loss tangent (tan δ) of a series of strain sensors, fabricated from an epoxy nanocomposite with multi-wall carbon nanotube (MWCNT) content varying at 1 wt. % - 5 wt. %, was characterized experimentally. The effects of four parameters including frequency, strain of nanocomposite, MWCNT content, and loading voltage were investigated extensively. Moreover, an alternative current gauge factor KAC was developed. The largest value of KAC was found to be 256 for the nanocomposite strain sensor with 1 wt. % MWCNT content at 0.6% tensile strain, which indicates the ultra-sensitivity of the present strain sensor. [ABSTRACT FROM AUTHOR]

The evolution of three-dimensional strain states and crystallographic domain structures of epitaxial colossal magnetoresistive La[sub 0.8]Ca[sub 0.2]MnO[sub 3] films have been studied as a function of film thickness and lattice mismatch with two types of (001) substrates, SrTiO[sub 3] and LaAlO[sub 3]. In-plane and out-of-plane lattice parameters and strain states of the films were measured directly using normal and grazing incidence x-ray diffraction techniques. The unit cell volume of the films is not conserved, and it exhibits a substrate-dependent variation with film thickness. Films grown on SrTiO[sub 3] substrates with thickness up to ∼250 Å are strained coherently with a pure (001)[sup T] orientation normal to the surface. In contrast, films as thin as 100 Å grown on LaAlO[sub 3] show partial relaxation with a (110)[sup T] texture. While thinner films have smoother surfaces and higher crystalline quality, strain relaxation in thicker films leads to mixed (001)[sup T] and (110)[sup T] textures, mosaic spread, and surface roughening. The magnetic and electrical transport properties, particularly Curie and peak resistivity temperatures, also show systematic variations with respect to film thickness. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]