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The implementation of advanced multi-level modulation schemes such as quadrature phase-shift keying (QPSK) in contrast to the conventional on–off keying is crucial to further boost the terahertz (THz) communications speed. Thereby, carrier phase noise reduction in the THz range is one of the key goals that need to be urgently achieved. In this paper, the photonic-based THz sources and the phase noise problem are briefly summarized. Then, a low phase-noise photonic source based on the stimulated Brillouin scattering (SBS) optical fiber cavity is first applied for a 300-GHz-band QPSK wireless communication link. The highest data rate at forward-error-correction limited condition was 15 Gbaud utilizing the SBS-based photonic source with a small transmit power of ~ −36 dBm. Its transmission characteristics are evaluated and compared with the conventional optical frequency comb generator (OFCG)-based source at 5 Gbaud. The proposed SBS-based photonic source has been proven to offer better performances than the OFCG-based source with respect to the phase noise, optical carrier to noise ratio, and bit error rate in communications.
We report the formation and optical properties of site-controlled InAs/GaAs quantum dots (QDs) embedded in GaAs nanowires (NWs) by selective metalorganic chemical vapor deposition for application to single photon sources. InAs/GaAs QD-in-NWs with various InAs thicknesses are realized on patterned GaAs(111)B substrates in the form of InAs/GaAs heterostructures and identified by structural analyses using scanning transmission electron microscopy and photoluminescence characterization. Sharp excitonic emission peaks at 10 K from single QD-in-NWs with the narrowest exciton linewidth of 87 μeV are observed. Light emission from the single QD-in-NW shows photon antibunching which evidences single photon emission from high-quality QD-in-NWs.
“Stand-support sintering”, that is supporting the load of the sinter cake with bars or
plates attached to pallets, has been developed and applied practically to the sintering
machines in Kimitsu works, Nippon Steel. The stands start to support the load of the sinter
cake just after the top layer is melted and starts to solidify. Shrinkage is stopped
and the gas flow rate is increased when the stands start to support the load of the
sinter cake. It was found that sintering time was shortened and productivity was improved in
actual sintering machines.
Deformation behavior of the BN film was dynamically observed by high-resolution transmission electron microscopy. BN thin films were deposited on a narrow edge of Si flakes, using inductively coupled plasma-enhanced chemical vapor deposition. High-resolution observation of the sample revealed that the BN film was possibly deposited on the edge of the Si thinned to less than 10 nm in thickness, whose morphology varied depending on the thickness of the Si edge. Intriguing mechanical properties of the BN films, especially relating their dynamic behavior, were clearly verified by the high-resolution observation with piezo-ceramic tube for three-axis positioning of an indenter.
Cubic boron nitride (cBN) thin films were deposited on silicon wafers by low-pressure inductively coupled plasma-enhanced chemical vapor deposition (ICP-CVD). By using special substrate pre-treatment processes including positive biasing treatment in H2 plasma or 1200 K pre-heating in H2 atmosphere followed by an N2 plasma treatment, turbostratic BN (tBN) intermediate layer was revealed to directly grow on Si substrates without an initial amorphous layer. The thickness of the tBN transition layer can be reduced to less than 3 nm.
A conductivity difference in a PZT film in a Pt/PZT/Pt capacitor was found by novel charged-up SIMS analyses for the first time. The charged-up SIMS technique was useful for evaluating the conductivity profile in the PZT film. It was found that the conductive region existed in an as-prepared PZT film near the bottom Pt electrode. After hydrogen plasma treatment at 45°C, the conductive region increased in the PZT film near the top electrode. Electrical measurements showed that the leakage current of the capacitor increased after hydrogen treatment. The hydrogen was expected to reduce PZT both at grain boundaries and the electrode-PZT interfaces, and to form the conductive region, which induced an increase in leakage current.
Microstructure evolution was studied in silicon nitride ceramics by a novel characterization method, and its relevance to the strength was discussed. The characterization method involves an immersion liquid for making green and partially sintered bodies transparent, and a subsequent direct optical microscopic examination. Granules for compaction process were prepared with the spray-drying process and were found to contain pores or deep dimples. Green bodies formed by CIP with these granules contain regularly arrayed pores at the center of granules and also crack-like voids at the boundaries of granules. These pores were preserved in the sintering process and resulted in large pores in the sintered body. They behave as fracture origin in ceramics and reduce the fracture strength. The Weibull modulus was high due to the presence of uniformly distributed pores.
A novel characterization method is applied to study the evolution of microstructures during densification of silicon nitride ceramics. This characterization method involves an immersion liquid for making green and sintered bodies transparent, and a subsequent direct optical microscopic examination. Granules were prepared with the spray drying processand formed into green bodies by CIP. After sintering at various temperatures, the specimens were examined for microstructural evolution. Large pores were located at the center and boundary regions of granules left in the green bodies; they were not removed by densification and resulted in large pores in the sintered body, possibly forming fracture origin in ceramics.
Optical emission spectroscopy and laser Doppler velocimetry were done for an Rf inductively coupled plasma at atmospheric pressure in order to elucidate the super-rapid coofling of the thermal plasma during the growth of diamond thin film. Attention was given to the vicinity of the water-cooled substrate located 20 mm beneath the RF coil. It was found that at 1.5 mm above the substrate, the temperature of plasma was still high. At the temperature, high concentration of hydrogen atoms exist, which may take a important role in diamond growth.
X-ray fluorescence spectrometry has been used in a broad spectrum of applications. These include elemental analysis, both qualitative and quantitative, based on wavelength dispersive (WDXRF) or energy dispersive (EDXRF) methods. In these methods the detection limit of analyte elements is mainly in the one to ten ppm range in solid samples. Therefore, improvement of these limits is desirable for many useful applications. In this context it is essential to remember that the excitation efficiency for fluorescent X-rays is very low when compared with electron or proton excitation. In the case of WDXRF, the dominant factor is the low reflectivity from the analyzing crystal.
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