Direct observation of optically forbidden energy transfer between CuCl quantum cubes via near-field optical spectroscopy

We report, for the first time, evidence of near-field energy transfer among CuCl quantum cubes using an ultrahigh-resolution near-field optical microscopy and spectroscopy in the near UV region at 15 K. The sample was high-density CuCl quantum cubes embedded in a NaCl matrix. Measured spatial distributions of the luminescence intensities from 4.6-nm and 6.3-nm quantum cubes clearly established anticorrelation features. This is thought to be a manifestation of the energy transfer from the lowest state of exciton in 4.6-nm quantum cubes to the first dipole-forbidden excited state of exciton in 6.3-nm quantum cubes, which is attributed to the resonant optical near-field interaction.     

Frequency stabilization in semiconductor lasers

Three promising methods of improving temporal coherence in semiconductor lasers are reviewed. They are the development of novel laser devices, a technique of optical feedback and a technique of electrical feedback. The main discussion in this paper is focused on the technique of electrical feedback. The theoretical limit of frequency stability and recent experimental results are presented with respect to the following five subjects which are indispensable in the realization of highly coherent lasers: (a) frequency stabilization; (b) improvements in frequency reproducibility; (c) linewidth reduction; (d) frequency tracking; and (e) stable, accurate and wideband frequency sweep.     

An Organic Mixed‐Valence Ligand for Multistate Redox‐Active Coordination Networks

The multistate redox‐active/multi‐interactive ligand 5,5′,8,8′‐tetra(4‐pyridyl)‐2,2′‐(1,4‐phenylene)bis‐1H‐perimidine (H₂TPP) was designed and synthesized. H₂TPP undergoes four one‐electron oxidation steps, and was used for the preparation of a multistate redox‐active coordination network in a solid–liquid interface reaction using molten Cd²⁺ salts. The multiple redox states of H₂TPP were confirmed spectroscopically by stepwise four‐electron oxidation. Spectroscopic analysis indicated that the mixed‐valence states of the ligand are class II on the UV/Vis/NIR timescale and borderline class II/class III on the ESR timescale.     

Characterization of imidazolate-bridged dinuclear and mononuclear hydroperoxo complexes

Dinucleating ligands having two metal-binding sites bridged by an imidazolate moiety, Hbdpi, HMe(2)bdpi, and HMe(4)bdpi (Hbdpi = 4,5-bis(di(2-pyridylmethyl)aminomethyl)imidazole, HMe(2)bdpi = 4,5-bis((6-methyl-2-pyridylmethyl)(2-pyridylmethyl)aminomethyl)imidazole, HMe(4)bdpi = 4,5-bis(di(6-methyl-2-pyridylmethyl)aminomethyl)imidazole), have been designed and synthesized as model ligands for copper-zinc superoxide dismutase (Cu,Zn-SOD). The corresponding mononucleating ligands, MeIm(Py)(2), MeIm(Me)(1), and MeIm(Me)(2) (MeIm(Py)(2) = (1-methyl-4-imidazolylmethyl)bis(2-pyridylmethyl)amine, MeIm(Me)(1) = (1-methyl-4-imidazolylmethyl)(6-methyl-2-pyridylmethyl)(2-pyridylmethyl)amine, MeIm(Me)(2) = (1-methyl-4-imidazolyl-methyl)bis(6-methyl-2-pyridylmethyl)amine), have also been synthesized for comparison. The imidazolate-bridged Cu(II)-Cu(II) homodinuclear complexes represented as [Cu(2)(bdpi)(CH(3)CN)(2)](ClO(4))(3).CH(3)CN.3H(2)O (1), [Cu(2)(Me(2)bdpi)(CH(3)CN)(2)](ClO(4))(3) (2), [Cu(2)(Me(4)bdpi)(H(2)O)(2)](ClO(4))(3).4H(2)O (3), a Cu(II)-Zn(II) heterodinuclear complex of the type of [CuZn(bdpi)(CH(3)CN)(2)](ClO(4))(3).2CH(3)CN (4), Cu(II) mononuclear complexes of [Cu(MeIm(Py)(2))(CH(3)CN)](ClO(4))(2).CH(3)CN (5), [Cu(MeIm(Me)(1))(CH(3)CN)](ClO(4))(2)( )()(6), and [Cu(MeIm(Me)(2))(CH(3)CN)](ClO(4))(2)( )()(7) have been synthesized and the structures of complexes 5-7 determined by X-ray crystallography. The complexes 1-7 have a pentacoordinate structure at each metal ion with the imidazolate or 1-methylimidazole nitrogen, two pyridine nitrogens, the tertiary amine nitrogen, and a solvent (CH(3)CN or H(2)O) which can be readily replaced by a substrate. The reactions between complexes 1-7 and hydrogen peroxide (H(2)O(2)) in the presence of a base at -80 degrees C yield green solutions which exhibit intense bands at 360-380 nm, consistent with the generation of hydroperoxo Cu(II) species in all cases. The resonance Raman spectra of all hydroperoxo intermediates at -80 degrees C exhibit a strong resonance-enhanced Raman band at 834-851 cm(-1), which shifts to 788-803 cm(-1) (Deltanu = 46 cm(-1)) when (18)O-labeled H(2)O(2) was used, which are assigned to the O-O stretching frequency of a hydroperoxo ion. The resonance Raman spectra of hydroperoxo adducts of complexes 2 and 6 show two Raman bands at 848 (802) and 834 (788), 851 (805), and 835 (789) cm(-1) (in the case of H(2)(18)O(2), Deltanu = 46 cm(-1)), respectively. The ESR spectra of all hydroperoxo complexes are quite close to those of the parent Cu(II) complexes except 6. The spectrum of 6 exhibits a mixture signal of trigonal-bipyramid and square-pyramid which is consistent with the results of resonance Raman spectrum.     

Short-term frequency stabilization of diode-laser-pumped Nd:YAG lasers using double-pendulum suspended cavities

We describe the improvement of short-term frequency stability of diode-laser-pumped Nd:YAG lasers. To improve the vibrational isolation of reference cavities, the reference cavities were suspended by a double pendulum with magnetic damping. The frequency noise was reduced to lower than 1 Hz/Hz at Fourier frequencies higher than 5 Hz and the minimum noise of 7 × 10^–3 Hz/Hz was recorded. The minimum root Allan variance was about 10^–14 for the sampling time of 0.01 s. Heating of the reference cavity by absorbed laser power caused the thermal drift of cavity resonance frequencies. It resulted in the laser linewidth in the range of 30–50 Hz.     

Stereoregular and Bernoullian copolymerization of styrene and ethylene by bridged metallocene catalysts

A stereoregular and Bernoullian copolymer of styrene and ethylene was produced by the catalyst system of rac-[isopropylidenebis(1-indenyl)]zirconium dichloride and MAO. This catalyst system yields a high molecular weight copolymer with good activity at 50°C. The copolymer consists of Et-Et, St-Et, and head to tail St-St sequences and has a highly isotactic Et-St alternating sequence. This copolymer shows a melting point (80 – 110°C), due to the isotactic alternating sequence.     

XPS spectra of chromium monosilicides and disilicides obtained by in situ fractured clean surfaces

X-ray photoelectron spectroscopy spectra of chromium monosilicide (CrSi) and disilicide (CrSi₂) were collected from a clean surface prepared by fracturing the bulk silicide compound in a spectrometer under ultrahigh vacuum; the analytical procedure for the phase identification of the Cr–Si system was examined. A negligible binding energy shift was observed in the Cr 2p_3/2 level between elemental Cr and CrSi₂, whereas the energy of CrSi was 0.2 eV lower than that of Cr and CrSi₂. The satellite peak in the Cr 2p spectra originating from the plasmon-loss phenomena was found only for CrSi and CrSi₂. The binding energy of Si 2p shifted, reflecting the silicide phases; the energy of CrSi₂ and CrSi was 0.3 eV higher and lower, respectively, than that of elemental Si. Although a slight difference in the spectral shape was observed in the valence band region, the phase identification was considered unreliable. However, the energy shifts of Si 2p and the presence of the plasmon-loss peak in the Cr 2p spectra provide important insights into the phase identification of the Cr–Si system.     

An optical and electrical relaxation oscillator using a Si homojunction structured light emitting diode

We propose an optical and electrical relaxation oscillator making use of an S-shaped negative resistance characteristic of a recently developed light-emitting diode using a bulk silicon crystal homojunction. From simulations, we found that the voltage and optical power oscillated synchronously, and their oscillation frequency increased with increasing injection current. The synchronous oscillation was also confirmed by experimental measurements. The amplitude of the voltage was 50?V_p-p, the amplitude of the optical power was 3?mW_p-p, and the maximum oscillation frequency was 34?kHz. The measured value of the spontaneous emission lifetime of a Si wafer was 900?ps, which was as short as that of direct transition-type semiconductors.     

Selective photocurrent generation in the transparent wavelength range of a semiconductor photovoltaic device using a phonon-assisted optical near-field process

In this paper, we propose a novel photovoltaic device using P3HT and ZnO as test materials for the p-type and n-type semiconductors, respectively. To fabricate an electrode of this device, Ag was deposited on a P3HT film by RF-sputtering under light illumination (wavelength λ ₀=660 nm) while reversely biasing the P3HT/ZnO pn-junction. As a result, a unique granular Ag film was formed, which originated from a phonon-assisted process induced by an optical near-field in a self-organized manner. The fabricated device generated a photocurrent even though the incident light wavelength was as long as 670 nm, which is longer than the long-wavelength cutoff λ _c (=570 nm) of the P3HT. The photocurrent was generated in a wavelength-selective manner, showing a maximum at the incident light wavelength of 620 nm, which was shorter than λ ₀ because of the Stark effect brought about by the reverse bias DC electric field applied during the Ag deposition.     

Observation of ring–shaped pulsed DC discharge plasma source using single pole magnet setups for material processing

ABSTRACT

A pulsed direct current (DC) discharge ring–shaped plasma source has been proposed using single pole magnet arrangements, including a center magnet, with magnets in the setups (a): one circle, (b): two circles, and (c): three circles. The three-dimensional (3D) magnetic flux lines profiles, gyro–radii and Hall parameters of the electrons and ions, the electrical discharge characteristics, the temporal evolutions of the ion saturation currents were investigated to characterize the proposed plasma source. The calculated electron gyro–radii, r_e were 0.17, 1.64, 5.82?mm for setups (a), (b), and (c), respectively. The strong ring–shaped plasma discharges was observed for all setups. The typical discharge voltages were 1.0, 0.6, and 0.6?kV for setups (a), (b), and (c), respectively. The ion saturation currents, I_isat were 1.44, 2.88, and 2.2?mA for setups (a), (b), and (c), respectively at r?=?45?mm and t?=?+10?μs. The I_isat of setup (b) is less fluctuating, whereas I_isat of setup (a) and (c) is highly variable in all positions, so that setup (b) has the best profile among the setups.