Mechanical properties of microwave hydrothermally synthesized titanate nanowires

In this investigation titanate nanowires were synthesized by a microwave hydrothermal process and their nanomechanical characterization was carried out by a compression experiment via buckling instability using a nanomanipulator inside a scanning electron microscope. Nanowires of diameters 120-150?nm and length tens of microns can be synthesized by keeping a commercial nanoparticle inside a microwave oven at 350?W and 210?°C for 5?h. The nanowire was clamped between two cantilevered AFM tips attached to two opposing stages of the manipulator for nanomechanical characterization. The elasticity coefficients of the titanate nanowires were measured by applying a continuously increasing load and observing the buckling instability of the nanowires. The buckling behavior of a nanowire was analyzed from the series of SEM images of displacement of the cantilever attached to the nanowire due to application of load. The critical loads for different sized titanate nanowires were determined and their corresponding Young's modulus was computed with the Euler pinned-fixed end model. The Young's modulus of these microwave hydrothermal process synthesized titanate nanowires were determined to be approximately in the range 14-17?GPa. This investigation confirms the capability of the nanomanipulator via the buckling technique as a constructive device for measuring the mechanical properties of nanoscale materials.     

Study of dispersion compensation in femtosecond lasers

Abstract

We present a formal analysis of dispersion compensation in femtosecond lasers and provide a detailed examination of the relevant features in Ti: sapphire and Cr: LiSAF lasers. It is shown that the essential of dispersion compensation up to the fourth order consists of searching for the solutions of a group of three linear equations. With the use of a prism pair, complete compensation of both the second- and the third-order dispersion corresponds to solving two of the three equations with the prism separation and the intraprism beam path length as variables. Owing to the limitations on the practically achievable prism separation and the intraprism path length in a laser set-up, only some of these solutions are physically meaningful; hence both zero second- and third-order cavity dispersion may be realized merely within a certain specific spectral range. The fourth-order dispersion, however, cannot be completely compensated for in this case unless a third control variable is introduced. It is also shown that the dominant parameter in determining the spectral region where dispersion is minimized is the difference between the ratio of the third-order dispersion to the second-order dispersion of the laser rod and that of the selected prism pair material. This also explains the major differences between Ti: sapphire and Cr: LiSAF lasers in terms of dispersion compensation.     

Compact, stable 1 GHz femtosecond Er-doped fiber lasers

We demonstrate a high-repetition-rate soliton fiber laser that is based on highly doped anomalously dispersive erbium-doped fiber. By splicing an 11 mm single-mode fiber to the erbium-doped fiber, the thermal damage of the butt-coupled saturable Bragg reflector (SBR) is overcome. The laser generates 187 fs pulses at a repetition rate of 967 MHz with a measured long-term stability of more than 60 h.     

Influence of Fe catalytic doping on the properties of TiO2 nanoparticles synthesized by microwave method

The present work focus on the development of an effective process for undoped and Fe doped TiO₂ powders production by microwave technique. The influence of Fe doping on the structure, phase, vibrational bands and optical properties of TiO₂ were discussed. The X-ray diffraction patterns of nanoparticles revealed a preferentially oriented (101) anatase phase for TiO₂ and transforms to rutile TiO₂ with Fe doping. Fourier transform infrared spectra analysis confirmed the phase transformation from anatase to rutile TiO₂ with Fe doping. The UV–visible spectra showed the increase in absorption band with Fe doping when compared with undoped TiO₂ nano particles, and optical band gap decreased slightly with Fe doping. SEM micrographs revealed spherical shaped grains of TiO₂ with high homogeneity, with a subsequent reduction in the agglomeration of particles with Fe doping suggesting its potential application for better photo catalytic activity.     

High resolution material ablation and deposition with femtosecond lasers and applications to photomask repair

Abstract

We describe experiments using 100 femtosecond pulses of 266 nm light to ablate Cr defects from photomasks with resolution below 100 nm. In addition to the ablative removal of Cr, experiments were carried out to deposit Cr metal onto fused silica substrates using 100 fs, 400 nm light at atmospheric pressure. Multiphoton dissociation of Cr(CO)₆ adsorbed on fused silica substrates initiates Cr deposition. The mechanisms for deposition on both transparent (fused silica) and absorbing (Cr metal) substrates are discussed. Finally we describe initial experiments to ablate Cr metal at wavelengths below 200 nm using light generated by frequency mixing of ultrashort, 30 fs pulses in an Ar filled capillary.     

Effect of Sn doping on microstructural and optical properties of ZnO nanoparticles synthesized by microwave irradiation method

Pure and Sn-doped ZnO nanostructures have been synthesized by the microwave irradiation method. The influence of Sn loading on the morphology and microstructure was evaluated by using field emission scanning electron microscopy, transmission electron microscopy (TEM), energy-dispersive spectrum analysis techniques, X-ray diffraction, and Fourier transform infrared spectroscopy. A change in the growth pattern, from needle-like particles for pure ZnO to agglomerated spherical crystallites for Sn-doped ZnO, has been observed. TEM observations indicated that the average particle size of the pure ZnO nano needles is in the range of 40–60 nm, whereas on addition of Sn spherical nanoassemblies size lies in the range of 10–21 nm. The pure ZnO and Sn-doped ZnO nanostructures were further characterized for their optical properties by UV–Vis reflectance spectra (DRS) and photoluminescence (PL) spectroscopy.     

Characteristics of microwave plasma induced by lasers and sparks

Characteristics of the plasma light source of microwave (MW) plus laser-induced breakdown spectroscopy (LIBS) or spark-induced breakdown spectroscopy (SIBS) were studied. The plasma was initially generated by laser- or spark-induced breakdown as a plasma seed. A plasma volume was then grown and sustained by MWs in air. This MW plasma had a long lifetime, large volume, strong emission intensity, and high stability with time. These characteristics are suitable for applications in the molecular analysis of gases such as OH or N(2). Because the plasma properties did not depend on laser or spark plasma seeds, the resulting plasma was easily controllable by the input power and duration of the MWs. Therefore, a significant improvement was achieved in the spectral intensity and signal-to-noise ratio. For example, the peak intensity of the Pb spectra of LIBS increased 15 times, and that of SIBS increased 880 times without increases in their background noise. A MW-enhanced plasma light source could be used to make the total system smaller and cheaper than a conventional LIBS system, which would be useful for real-time and in situ analysis of gas molecules in, for example, food processing, medical applications, chemical exposure, and gas turbine or automobile air-to-fuel ratio and exhaust gas measurement.     

Noise parameter measurement of microwave transistors at cryogenictemperature

A major drawback of active two-port microwave noise parameter measurement, by means of the multiple impedance technique at cryogenic temperature, lies in that a nonnegligible part of a lossy transmission line featuring a nonuniform temperature must be inserted between the automatic tuner (operated at room temperature) and the device input. Since the temperature distribution over that line is not precisely known, the contributed noise cannot be directly corrected. To overcome this, the use of a noise de-embedding technique is proposed, based on the measurement of a suitable noise standard made of a cooled mismatched two-port. By way of example, noise parameters of a GaAlAs/GaAs HEMT measured between 14 and 18 GHz at 77 K are reported. Finally, the accuracy of this technique is discussed     

Active synchronization and carrier phase locking of two separate mode-locked femtosecond lasers

Two independent mode-locked femtosecond lasers are synchronized to an unprecedented precision. The rms timing jitter between the lasers is 4.3 fs observed within a 160 Hz bandwidth over tens of seconds, or 26 fs within a 50 kHz bandwidth. Novel multi-stage phase-locked loops help to preserve this ultrahigh timing resolution while setting on arbitrary delay between the two pulse trains (0–5 ns). Under such synchronization, phase locking between the carrier frequencies of the two femtosecond lasers has been achieved. It is also demonstrated that the same level of synchronization can be achieved with two lasers at different repetition frequencies.     

Polarization properties of fiber lasers with twist-induced circular birefringence

We have experimentally observed and theoretically analyzed the polarization properties of fiber lasers with twist-induced birefringence. Twisting a fiber induces the circular birefringence of a fiber laser cavity, and this birefringence reduces the effects of intrinsic linear birefringence on the polarization properties of fiber lasers. The frequencies of their polarization eigenmodes coincide with each other gradually as the twist rate increases, and the directions of polarization eigenmodes deviate from the birefringence axis at a much larger twist rate than the magnitude of intrinsic linear birefringence. We describe the successful experimental results for Nd and Er fiber lasers.     

Comparison of the properties of BN films synthesized by inductively coupled r.f. and microwave plasmas

Thin films of boron nitride are synthesized by two plasma-enhanced chemical vapour deposition techniques: inductively coupled r.f. plasma (13.56 MHz) and microwave plasma (2.45 GHz). We study the composition (impurity level, B/N ratio), the proportion of c-BN phase in the films and other properties of those films as a function of various process parameters. Two boron and two nitrogen precursors are compared: trimethyl borazine and diborane, dini trogen and ammonia, respectively. The advantages and disadvantages of each combinations are presented. The deposition process is followed by optical emission spectroscopy. Adhesion is one of the main problems encountered for films containing c-BN.     

Noise properties of inductive transducer with field feedback

Translated from Izmeritel'naya Tekhnika, No. 4, pp. 31–32, April, 1991.     

CuO urchin-nanostructures synthesized from a domestic hydrothermal microwave method

This letter reports the synthesis of CuO urchin-nanostructures by a simple and novel hydrothermal microwave method. The formation and growth of urchin-nanostructures is mainly affected by the addition of polyethylene glycol (PEG). The hierarchical malachite particles are uniform spheres with a diameter of 0.7-1.9 μm. CuO urchin-nanostructures were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FEG-SEM) and nitrogen adsorption (BET). The specific surface area of the CuO nanostructured microspheres was about 170.5 m²/g. A possible mechanism for the formation of such CuO urchin-nanostructures is proposed.     

CuNi/Al hydrotalcites synthesized in presence of microwave irradiation

To enhance the electronic properties of nanoparticles, functional clusters are usually supported on metal oxides as alumina. Copper and nickel clusters supported on magnesia or alumina are promising materials to catalyze the decomposition of methane to produce hydrogen. A mixed support of alumina and magnesia can be proposed in the form of a hydrotalcite. In this work, the synthesis of hydrotalcites containing Cu, Ni, Mg and Al in the presence of microwave irradiation is studied. Cu/Al hydrotalcite which is hardly synthesized through conventional methods was easily prepared in the presence of microwaves.     

Improve the binding force of PEEK coating with Mg surface by femtosecond lasers induced micro/nanostructures

Journal of Materials Science - A polymer coating is an effective approach to increase the surface wear and corrosion resistance of magnesium alloys, but the low bonding strength limits its further...     

Two-color femtosecond experiments by use of two independently tunable Ti:sapphire lasers with a sample-and-hold switch

We performed femtosecond two-color experiments (four-wave mixing and pump probe) using two independently tunable, partially synchronized femtosecond lasers. Despite the fact that the jitter is of the order of 5-10 ps, the time resolution is limited only by the pulse width when a homemade sample-and-hold switch is used.