Effect of substrates and underlayer on CNT synthesis by plasma enhanced CVD

Due to their unique thermal, electronic and mechanical properties, carbon nanotubes （CNTs） have aroused various attentions of many researchers. Among all the techniques to fabricate CNTs, plasma enhanced chemical vapor deposition （PECVD） has been extensively developed as one growth technique to produce verticallyaligned car bon nanotubes （VACNTs）. Though CNTs show a trend to be integrated into nanoelectromechanical system （NEMS）, CNT growth still remains a mysterious technology. This paper attempts to reveal the effects of substrates and un derlayers to CNT synthesis. We tried five different substrates by substituting intrinsic Si with high resistivity ones and byincreasing the thickness of SiO2 insulativity layer. And also, we demonstrated an innovative way of adjusting CNT den sity by changing the thickness of Cu underlayer.

Plasma-assisted molecular beam epitaxy of ZnO on in-situ grown GaN/4H-SiC buffer layers

Plasma-assisted molecular beam epitaxy （MBE） was used to grow ZnO （0001） layers on GaN（0001）/4H-SiC buffer layers deposited in the same growth chamber equipped with both N- and O-plasma sources. The GaN buffer layers were grown immediately before initiating the growth of ZnO. Using a substrate temperature of 440℃- 445℃ and an 02 flow rate of 2.0-2.5 sccm, we obtained ZnO layers with smooth surfaces having a root-mean-square roughness of 0.3 nm and a peak-to-valley distance of 3 nm shown by AFM. The FWHM for X-ray rocking curves recorded across the ZnO（0002） and ZnO（1015） reflections were 200 and 950 arcsec, respectively. These values showed that the mosaicity （tilt and twist） of the ZnO film was comparable to corresponding values of the underlying GaN buffer. It was found that a substrate temperature 〉 450℃ and a high Zn-flux always resulted in a rough ZnO surface morphology. Reciprocal space maps showed that the in-plane relaxation of the GaN and ZnO layers was 82.3% and 73.0%, respectively and the relaxation occurred abruptly during the growth. Room-temperature Hall-effect measurements showed that the layers were intrinsically n-type with an electron concentration of 10^19 cm-3 and a Hall mobility of 50 cm2.V-1 .s-1.

One photon-per-bit receiver using near-noiseless phase-sensitive amplification

Space communication for deep-space missions,inter-satellite data transfer and Earth monitoring requires high-speed data connectivity.The reach is fundamentally dictated by the available transmission power,the aperture size,and the receiver sensitivity.A transition from radio-frequency links to optical links is now seriously being considered,as this greatly reduces the channel loss caused by diffraction.A widely studied approach uses power-efficient formats along with nanowire-based photon-counting receivers cooled to a few Kelvins operating at speeds below 1 Gb/s.However,to achieve the multi-Gb/s data rates that will be required in the future,systems relying on pre-amplified receivers together with advanced signal generation and processing techniques from fibre communications are also considered.The sensitivity of such systems is largely determined by the noise figure(NF)of the pre-amplifier,which is theoretically 3 dB for almost all amplifiers.Phase-sensitive optical amplifiers(PSAs)with their uniquely low NF of 0 dB promise to provide the best possible sensitivity for Gb/s-rate long-haul free-space links.Here,we demonstrate a novel approach using a PSA-based receiver in a free-space transmission experiment with an unprecedented bit-error-free,black-box sensitivity of 1 photon-per-information-bit(PPB)at an information rate of 10.5 Gb/s.The system adopts a simple modulation format(quadrature-phase-shift keying,QPSK),standard digital signal processing for signal recovery and forward-error correction and is straightforwardly scalable to higher data rates.