Quantum confinement in amorphous silicon quantum dots embedded in silicon nitride

Amorphous silicon quantum dots (a-Si QDs) were grown in a silicon nitride film by plasma enhanced chemical vapor deposition. Transmission electron micrographs clearly demonstrated that a-Si QDs were formed in the silicon nitride. Photoluminescence and optical absorption energy measurement of a-Si QDs with various sizes revealed that tuning of the photoluminescence emission from 2.0 to 2.76 eV is possible by controlling the size of the a-Si QD. Analysis also showed that the photoluminescence peak energy E was related to the size of the a-Si QD, a (nm) by E(eV) = 1.56+2.40/a(2), which is a clear evidence for the quantum confinement effect in a-Si QDs.     

Waveform preservation of the backscattered stimulated Brillouin scattering wave by using a prepulse injection

We have found that it is possible to preserve the temporal waveform of the reflected wave generated from stimulated Brillouin scattering (SBS) by using a prepulse technique. The waveform of the SBS wave usually shows a steep rising edge in the ordinary SBS process. It has been found that the waveform of the reflected wave depends on both the prepulse energy and the time delay between the main pulse and the prepulses. A prepulse energy of 5 mJ and a time delay of 5 ns have been measured to be the optimum values under the experimental conditions. This prepulse method is useful in developing a multistage system employing several SBS cells in series for high-power laser applications.     

Conformationally resolved structures of jet-cooled acetaminophen by UV-UV hole-burning spectroscopy

The conformational structures of jet-cooled acetaminophen were investigated in the gas phase by resonant 2-photon ionization and UV-UV hole-burning spectroscopy. In contrast to the results from a previous study, two nearly isoenergetic conformers were distinctly found in a supersonic molecular beam expansion and positively identified as the cis and trans isomers of acetaminophen by UV-UV hole-burning spectroscopy. The 0-0 bands of the cis and trans isomers were found at 33518.7 and 33485.6 cm(-1), respectively. The vibronic bands of the two isomers are close-lying and/or partially overlapping due to the small energy difference (33 cm(-1)) between the two 0-0 bands. As a consequence, the recorded resonant 2-photon ionization spectrum is highly congested in the low excitation energy region, which develops continuously into a featureless, broadened spectrum in the high energy region.     

Determining spin through quantum azimuthal-angle correlations

Determining the spin of new particles is critical in identifying the true theory among various extensions of the Standard Model at the next generation of colliders. Quantum interference between different helicity amplitudes was shown to be effective when the final state is fully reconstructible. However, many interesting new physics processes allow only for partial reconstruction. In this Letter, we show how the interference effect can be unambiguously extracted even in processes that have two-fold ambiguity, by considering the correlation between two decay planes in e⁺e⁻$e^{+}{e}^{-}$ collisions.     

High magnetic field solid‐state NMR analyses by combining MAS,MQ‐MAS,homo‐nuclear and hetero‐nuclear correlation experiments

A general strategy of structural analysis of alumina silicate by combining various solid‐state NMR measurements such as single pulse, multi‐quantum magic angle spinning, double‐quantum homo‐nuclear correlation under magic angle spinning (DQ‐MAS), and cross‐polarization hetero‐nuclear correlation (CP‐HETCOR) was evaluated with the aid of high magnetic field NMR (800 MHz for ¹H Larmor frequency) by using anorthite as a model material. The high magnetic field greatly enhanced resolution of ²⁷Al in single pulse, DQ‐MAS, and even in triple‐quantum magic angle spinning NMR spectra. The spatial proximities through dipolar couplings were probed by the DQ‐MAS methods for homo‐nuclear correlations between both ²⁷Al–²⁷Al and ²⁹Si–²⁹Si and by CP‐HETCOR for hetero‐nuclear correlations between ²⁷Al–²⁹Si in the anorthite framework. By combining various NMR methodologies, we elucidated detailed spatial correlations among various aluminum and silicon species in anorthite that was hard to be determined using conventional analytical methods at low magnetic field. Moreover, the presented approach is applicable to analyze other alumina‐silicate minerals. Copyright © 2012 John Wiley & Sons, Ltd.     

Formation of nanostructured polymer filaments in nanochannels

We describe the use of hard etching methods to create nanodimensional channels and their use as templates for the formation of polymer filament arrays with precise dimensional and orientational control in a single integrated step. The procedure is general as illustrated by the radical, coordination, and photochemical polymerizations that were performed in these nanochannels. The nanochannel templates (20 nm high, 20-200 nm wide, and 100 mum long) were fabricated by the combined use of electron-beam lithography and a sacrificial metal line etching technique. Radical polymerization of acrylates, metal-catalyzed polymerization of norbornene, and photochemical polymerization of 1,4-diiodothiophene were carried out in these nanochannels. The polymers grown follow the dimensions and orientation of the channels, and the polymer filaments can be released without breaking. The approach opens up the possibility of just-in-place manufacturing and processing of patterns and devices from nanostructured polymers using well-established polymer chemistry.     

Carbonyl­[di­hydro­bis­(pyrazol‐1‐yl‐κN2)­borato]­hydrido­bis­(tri‐p‐tolyl­phosphine‐κP)­ruthenium(II)

The title compound, [RuH(C₆H₈BN₄)(C₂₁H₂₁P)₂(CO)], possesses two trans‐disposed tri‐p‐tolyl­phosphines in axial positions and the remaining ligands in equatorial positions. The overall geometry of the Ru^II ion is a distorted octahedral structure. The P—Ru—P axis deviates from linearity by about 13°. This distortion arises mainly from the steric congestion between the bulky phosphine moieties and the tetrahedral di­hydro­bis­(pyrazol‐1‐yl)­borate ligands.     

Water vapor permeability of shape memory polyurethane with amorphous reversible phase

Shape memory thermoplastic polyurethanes (TPUs), based on amorphous soft segment from the reaction of hexamethylene diisocyanate and 1,2‐butane diol, and the crystalline hard segment from 4,4′‐methylenediphenyl diisocyanate and 1,6‐hexanediol, were modified by hydrophilic segments, diol‐terminated poly(ethylene oxide) or dimethylol propionic acid (DMPA). Differential scanning calorimetry, dynamic mechanical testing, tensile testing, and the measurement of shape memory effect, water swell, and water vapor permeability were carried out to examine these TPUs. The hydrophilic segment increased the hysterisis in shape memory effect by reducing the crystallinity of the hard segment. The neutralized DMPA unit enhanced the sensitivity of the thermoresponsive water vapor permeability (WVP) by amplifying the increase of WVP at the temperature range above the glass transition temperature. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3009–3017, 2000