Tuning electronic properties of epitaxial multilayer-graphene/4H–SiC(0001) by Joule heating decomposition in hydrogen

Abstract(#br)On the semi-insulating 4H–SiC (0001) surface, hydrogenated multilayers graphene (MLG) were epitaxially prepared by the method of Joule heating decomposition in the hydrogen atmosphere. The structural and chemical characteristics of multilayers graphene have been elaborately analyzed by the X-ray photoelectron and Raman spectroscopies, showing the level of hydrogenation being promoted with the increase of hydrogen pressure. Then, diodes with MLG/4H–SiC contact were fabricated and studied, proving that the Schottky barrier height (SBH) of MLG/4H–SiC junction was enhanced by the hydrogenation. By studying the typical current-voltage characteristics, the SBH was observed to be heightened from 0.84 eV to 1.0 eV along with the hydrogen pressure increasing from 10 −2 mbar to 10 2 mbar. Finally, graphene-semiconductor-graphene photodetectors were fabricated, showing peak responsivity as high as~ 0.9 A/W and external quantum efficiency of 345%, under the 324 nm illumination and biased at 3V

Stable Temperature Characteristics of InAs/GaAs Quantum Dots at Long Wavelength Emission

The time-resolved photoluminescence and steady photoluminescence (TRPL and PL) spectra on self-assembled InAs/GaAs quantum dots (QDs) are investigated. By depositing GaAs/InAs short period superlattices (SLs), 1. 48 μtm emission is obtained at room temperature. Temperature dependent PL measurements show that the PL intensity of the emission is very steady. It decays only to half as the temperature increases from 15 K to room temperature, while at the same time, the intensity of the other emission decreases by a factor of 5 orders of magnitude. These two emissions are attributed to large-size QDs and short period superlattices (SLs), respectively. Large-size QDs are easier to capture and confine carriers,which benefits the lifetime of PL, and therefore makes the emission intensity insensitive to the temperature

High-performance 4H-SiC-based ultraviolet p-i-n photodetector

A high-performance 4H-SiC p-i-n photodetector for visible-blind ultraviolet (UV) applications has been designed and fabricated. The electrical and optical characteristics were measured at room temperature. The photodetector suffered from significant dark current of 2.5 pA/mm(2) at reverse bias of 5 V, and the UV light photocurrent was larger than four orders of magnitude higher than the dark current. The built-in potential and the unintentional i-layer doping concentration were obtained from capacitance-voltage (C-V) measurements. The spectral peak responsivity of the detector reached 0.13 A/W at a wavelength of 270 nm, corresponding to a maximum external quantum efficiency of similar to 61%. And the ratio of responsivity at 270 nm to that at 380 nm was > 10(3). The characteristics imply that the photodetector has a great improved ultraviolet-visible rejection ratio which is needed for ultraviolet signal detection

4H-SiC ultraviolet avalanche photodetectors with low breakdown voltage and high gain

Xiamen Science and Technology Plan Foundation of Fujian Province [350Z20031076]The separate absorption and multiplication (SAM) 4H-SiC ultraviolet (UV) avalanche photodetectors (APDs) have been designed, fabricated and characterized. A gain higher than 1.8 x 10(4) was achieved at 90% breakdown voltage of similar to 55 V. At 0 V, the peak absolute responsivity was estimated to be larger than 0.078 A/W at 270 nm, corresponding to a peak external quantum efficiency of over 35.8%. The long-wavelength cutoff was about 380 nm. In addition, the UV-to-visible rejection ratio of around three orders of magnitude was extracted from the spectra response. When the reverse bias was larger than 35 V, the spectral responsivity enhanced distinctly. At the reverse bias of 42 V, the peak responsivity increased to 0.203 A/W at 270 nm, corresponding to a maximum external quantum efficiency of similar to 93%, which showed a distinct avalanche behavior. Furthermore, the ideality factor around 1.65 and the spectral detectivity about 3.1 X 10(13) cm Hz(1/2) W(-1) were estimated. in conclusion, the 4H-SiC APD have excellent performance for UV detection. (C) 2008 Elsevier Ltd. All rights reserved

NLRP3 Inflammasome and Its Central Role in the Cardiovascular Diseases

Background/Aims. NLRP3 inflammasome, an inflammasome which consists of nucleotide-binding oligomerization domain- (Nod-) like receptor3 (NLRP3) scaffold, apoptosis-associated speck-like protein (ASC) containing a CARD adaptor, and pro-caspase-1, is assembled after the cytoplasmic leucine-rich repeats (LRRs) of NLRP3 sense pathogens or danger signals. In recent years, the role of inflammasome in cardiovascular diseases has attracted mounting attention, and the in-depth study of its mechanism is gradually clear. Materials. The NLRP3 inflammasome controls the activation of the proteolytic enzyme caspase-1. Caspase-1 in turn regulates the maturation of the proinflammasome cytokines IL-1β and IL-18, which leads to an inflammatory response. We made a mini-review on the association of regulatory mechanisms of NLRP3 inflammasome with the development of cardiovascular diseases systematically based on the recent research studies. Discussion. The inflammasome plays an indispensable role in the development of atherosclerosis, coronary heart diseases (CHD), and heart ischemia-reperfusion (I/R) injury, and NLRP3 inflammasome may become a new target for the prevention and treatment of cardiovascular diseases. Effective regulation of NLRP3 may help prevent or even treat cardiovascular diseases. Conclusion. This mini-review focuses on the association of regulatory mechanisms of NLRP3 inflammasome with the development of cardiovascular diseases, which may supply some important clues for future therapies and novel drug targets for cardiovascular diseases

Low-dark-current TiO2 MSM UV photodetectors with Pt schottky contacts

10.1109/LED.2011.2104354IEEE Electron Device Letters324530-532EDLE

No-tillage did not increase organic carbon storage but stimulated N₂O emissions in an intensively cultivated sandy loam soil: A negative climate effect

Although numerous studies have been conducted on the effects of no-tillage on carbon (C) sequestration in agricultural systems, there is still no consensus on the balance between the potential of C sequestration and nitrous oxide (N₂O) or nitric oxide (NO) emissions. A no-tillage field experiment in the North China Plain was established in 2006 and the influence of no-tillage on N₂O and NO emissions was monitored under an annual wheat-maize cropping system. The study included four treatments: no-tillage (NT) and conventional tillage (CT) soils amended with N fertilizer at a rate of 225 kg N ha ⁻¹for wheat and 195 kg N ha⁻¹ for maize (NTN and CTN) and without N fertilizer (NT0 and CT0). Three years of no-tillage significantly (p < 0.05) increased soil organic C (SOC) content by 12.2% in the 0–5 cm soil layer, possibly due to the surface aggregation of organic C derived from crop roots and exudates, but did not alter SOC pool in the 0–30 cm profile. Annual N₂O emissions in the NT0 and CT0 treatments were 0.53 and 0.57 kg N₂O-N ha⁻¹, respectively, and were significantly (p < 0.05) increased to 0.96 kg N₂O-N ha⁻¹ in CTN and to 1.23 kg N₂O-N ha⁻¹ in NTN. Remarkable differences in N₂O emissions between CTN and NTN were observed during the maize growing season. In contrast, NO emissions were not affected by the tillage regimes regardless of N fertilization. The mean ratios of NO/N₂O fluxes in N-unfertilized plots were 0.26–0.29 and 1.79–2.11 for the maize and wheat season, respectively, indicating that both NO and N₂O were primarily derived from denitrification during the maize growing season and from nitrification under wheat cultivation. Under N-fertilized plots, the ratios increased to 1.44–2.02 and 5.00–6.03 for the maize and wheat season, respectively, with significantly (p < 0.05) lower values in NTN plots than in CTN plots. The N₂O emission factors for N applied in the wheat-maize rotation system were 0.16% and 0.09% for NTN and CTN, respectively, which was far lower than the IPCC Tier 1 default value (1.0%), primarily due to the absence of irrigation after fertilization in maize season and low temperature in wheat season. The results suggest that the 3-year no-tillage regime with residue removal did not substantially increase C storage in the 0–30 cm profile, but stimulated N₂O emissions primarily by increasing denitrification

Determinants of Health Care-Seeking Delay among Tuberculosis Patients in Rural Area of Central China

Background The prevalence of tuberculosis (TB) in low and middle-income countries is a significant public health and social concern. TB is a common infectious disease caused by the Mycobacterium tuberculosis infection, which has a widespread infection rate. Health care-seeking delay maybe one of the most important neglected risk factors for the spread of TB. Objectives The aim of this study was to understand the situation of health care-seeking delay among rural tuberculosis patients in Hubei Province, and explore its risk factors. Methods A total of 1408 rural tuberculosis patients were surveyed using a standard structured questionnaire in three cities of Hubei Province during the past two years. Results For the 1408cases of pulmonary tuberculosis, 39.70% of them were health care-seeking delayed. Logistic regressions indicate that the Han nationality, farming careers, the over 45 min walk to the township&rsquo;s hospital, and awareness of the national TB free treatment policy, were significantly associated with higher odds of a delay in care seeking. Conclusions The prevalence of health care-seeking delay among tuberculosis patients was high in rural areas. It is essential to take comprehensive targeted interventions to reduce care-seeking delay

High-performance 4H-SiC-based p-i-n ultraviolet photodiode and investigation of its capacitance characteristics

We report on high-performance 4H-SiC-based p-i-n ultraviolet (UV) photodiodes and investigation of the capacitance characteristics. The fabricated p-i-n photodiode exhibits a large UV-to-visible rejection ratio (R266 nm/R380 nm) while displaying a low dark current and a high responsivity at room temperature. Interestingly, even at 450 k, the photodiode presents a high responsivity of 0.15 A/W and high UV-to-visible rejection ratio more than 200. Capacitance-voltage measurements reveal that the 4H-SiC p-i-n photodiode presents strong frequency-, temperature-, and wavelength-dependent capacitance properties. These results indicate that the advances on the 4H-SiC material and the p-i-n junction offer exciting opportunities for important UV detection in a variety of commercial and military fields. ? 2014 Elsevier B.V. All rights reserved