This paper presents a fabrication technology of enhancement-mode AlGaN/GaN high electron mobility transistors (HEMTs) using standard fluorine ion implantation. An 80 nm silicon nitride layer was deposited on the AlGaN as an energy-absorbing layer that slows down the high energy (similar to 25 keV) fluorine ions so that majority of the fluorine ions are incorporated in the AlGaN barrier. The threshold voltage was successfully shifted from -1.9 to +1.8 V, converting depletion mode HEMTs to enhancement-mode ones. The fluorine ion distribution profile was confirmed by Secondary Ion Mass Spectrometry (SIMS). (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3562273] All rights reserved.
A more accurate emission inventory of Black Carbon (BC) from China in 2000 was established based on county-level statistical data and recently published emission factors (EFs) from local measurements, which were further gridded at 0.5° × 0.5°. A comprehensive database for BC emission factors was compiled for main anthropogenic sources. BC emissions from China in 2000 were estimated to be 1228.52 Gg under normal operating conditions, and would increase to 2136.53 Gg if failures in control devices and combustion were considered. Spatial distribution of national BC emissions and emissions from different sources were determined; districts with extraordinarily high emissions cover 18.0% of China’s territory but generated 69.14% of the total emissions. Separate EFs were developed for each vehicle type fueled with gasoline or diesel; both the absolute value and relative share of BC emissions from vehicles in this work were higher than those in previous reports, suggesting that previous studies which did not differentiate vehicle types may have underestimated vehicle emissions.
This study discusses the evolution of particle number size distribution during episodes of heavy pollution and new particle formation in the urban atmosphere of Beijing to quantify the effects of dynamic processes (coagulation and condensation) on the particle number size distribution. During a heavy-pollution event, an extremely low number concentration of 3-10 nm particles (on average 46 cm(-3)) was observed. This is because nucleation-mode particles were easily removed by strong coagulational scavenging of larger particles under this condition. In addition, a large condensation sink (on average 0.13 s(-1)) restrained nucleation, which is one of the major sources of nucleation-mode particles. Conversely, during a new-particle formation event, the small condensation sink (0.01 s(-1)) of precursor facilitated nucleation. At the same time, preexisting particles had little ability to scavenge newly formed particles (around 1 nm) and allowed them to grow to a detectable size (larger than 3 nm currently). We suggest that the effects of dynamic processes (coagulation and condensation) on particle size distribution should be stressed under some extreme conditions of the relatively polluted urban atmosphere in addition to traffic and meteorological factors.
