Origin of ion beam mixing effects on morphological features in solid-phase titanium silicide formation

The origin of the ion beam mixing effect, which causes the formation of smooth silicide films, is investigated for the Ti/Si solid-phase silicidation reaction. Ge ion beam mixing of a conventional Ti/c-Si structure with an oxide-contaminated interface shows an obvious effect when the implant conditions are such that the Ti/Si interface is amorphized. On the other hand, silicidation without ion mixing for Ti/a-Si and Ti/c-Si structures with oxide-free interfaces, prepared by sequential deposition in UHV, results in smooth and rough film surfaces, respectively. This strongly suggests that the ion beam mixing effect primarily comes from the amorphization of the Si substrate surface rather than the destruction of the interfacial oxide film.     

Nonlinear processes in UV optical materials at 248 nm

Nonlinear processes in UV optical materials were investigated by using 280-fs, 248-nm pulses. Nonlinear absorption in CaF₂ was confirmed to be a two-photon process by using the luminescence of self-trapped excitons, which was also used for the single shot pulse width measurement. The absorption bands due to F centers were identified in CaF₂, MgF₂, and LiF after several hundred shots at 100 GW/cm². Absorption at 248 nm was considerable especially in MgF₂ and LiF. Self-focusing and self-phase modulation were observed in CaF₂.     

Dynamical study of femtosecond-laser-ablated liquid-aluminum nanoparticles using spatiotemporally resolved x-ray-absorption fine-structure spectroscopy

We study the temperature evolution of aluminum nanoparticles generated by femtosecond laser ablation with spatiotemporally resolved x-ray-absorption fine-structure spectroscopy. We successfully identify the nanoparticles based on the L-edge absorption fine structure of the ablation plume in combination with the dependence of the edge structure on the irradiation intensity and the expansion velocity of the plume. In particular, we show that the lattice temperature of the nanoparticles is estimated from the L-edge slope, and that its spatial dependence reflects the cooling of the nanoparticles during plume expansion. The results reveal that the emitted nanoparticles travel in a vacuum as a condensed liquid phase with a lattice temperature of about 2500 to 4200 K in the early stage of plume expansion.     

Pressure loading of detonation waves through 90-degree bend in high pressure H2–O2–N2 mixtures

Detonation experiments are conducted to investigate the detonation wave behavior in steam pipelines of boiling water reactors. Accumulated gases in BWRs are stoichiometric hydrogen/oxygen mixtures diluted with steam at 7 MPa. In the experiment, flammable gas mixture diluted with nitrogen at room temperature and up to 5 MPa is used to achieve equivalent detonation condition. Two test pieces are used, one is straight tube and the other is 90-degree bend. No initial pressure dependency in detonation wave behavior is observed in the experiments. However, in the straight tube tests, detonation velocities higher than theoretical values are measured when the initial pressures are greater than 2.3 MPa. This result is considered as attribution of real gas effect. In the 90-degree bend experiments, pressure time histories reveal pressure loads greater than the straight tube portion at two locations. One is a high pressure peak at the extrados of the bend and the other is a double pressure peak just downstream of the bend outlet. Second pressure peak just downstream of the bend outlet is due to transverse wave propagation. Additionally, the largest impulse is observed not at the extrados of the bend but at the intrados of bend outlet. These results show the importance of more investigations on transverse wave behaviors in failure potential evaluation.     

Surface-sensitive NMR in optically pumped semiconductors

We present a scheme of surface-sensitive nuclear magnetic resonance in optically pumped semiconductors, where an NMR signal from a part of the surface of a bulk compound semiconductor is detected apart from the bulk signal. It utilizes optically oriented nuclei with a long spin-lattice relaxation time as a polarization reservoir for the second (target) nuclei to be detected. It provides a basis for the nuclear spin polarizer [IEEE Trans. Appl. Supercond. 14:1635, 2004], which is a polarization reservoir at the surface of the optically pumped semiconductor that polarizes nuclear spins in a target material in contact through the nanostructured interfaces.     

Effects on spontaneous emission on dynamic characteristics of semiconductor lasers

Dynamic characteristics of semiconductor lasers are calculated with single-mode rate equations, taking into account spontaneous emission factor β and bias current     

Synthesis and radical ring-opening polymerization behavior of vinylcyclopropane bearing six-membered cyclic acetal moiety

Synthesis and radical ring-opening polymerization of vinylcyclopropane bearing six-membered cyclic acetal moiety, 1-vinyl-4,8-dioxaspiro[2.5]octane (1), were carried out. 1 was prepared by the reaction of 1,1-dichloro-2-vinylcyclopropane and 1,3-propanediol in DMF in the presence of a base. Radical polymerization of 1 was carried out in the presence of an appropriate initiator (3 mol % vs. 1) at 60 and 120°C in degassed sealed ampoules for 20 h. A colorless transparent viscous polymer was obtained by the isolation with preparative HPLC. The structure of poly(1) was determined to consist of two 1,5-ring-opened units and a unit bearing no olefinic moiety. The difference of the activation energies for the ring-opening reaction of the cyclopropane ring calculated by the molecular orbital method could explain the selectivity in the direction of the cleavage of the cyclopropane ring. Acid hydrolysis of poly(1) afforded the corresponding polyketone in quantitative conversion. © 1996 John Wiley & Sons, Inc.     

Effective Application of Microwave Resonant Cavity System to Flow Chemistry

By applying advanced telecommunication solid state devices to microwave (MW) resonant cavity system for flow chemistry, it becomes possible to heat up low polarity solvents higher than 250 C, that are considered impossible to heat up by MW until now. The resonant cavity system is opening new process windows to production processes of specialty chemicals which require low cost, high yield and high productivity.     

Reaction dynamics of excited 2-(3-benzoylphenyl)propionic acid (ketoprofen) with histidine

Photoreaction dynamics of 2-(3-benzoylphenyl)propionic acid (ketoprofen, KP), one of nonsteroidal anti-inflammatory drugs, with histidine in a phosphate buffer solution (pH 7.4) was investigated with the laser flash photolysis. The deprotonated form of KP (KP(-)) was decarboxylated via UV laser excitation to form a carbanion. It was found that histidine accelerates the protonation reaction of the carbanion to 3-ethylbenzophenone ketyl biradical (3-EBPH) for the first time. The experimental results of the photoreaction of KP with alanine as well as the photoreaction of KP with 4-methylimidazole (a part of the side chain of histidine) in methanol, clearly showed that the protonated form of histidine is a key species for the protonation reaction of the carbanion. These series of the initial reactions should result in the occurrence of photosensitization in vivo. The reaction mechanism was discussed in detail.