| 1. |
- Phu, Vu Dinh, et al.
(författare)
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Burden of Hospital Acquired Infections and Antimicrobial Use in Vietnamese Adult Intensive Care Units
- 2016
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Ingår i: PLOS ONE. - : PUBLIC LIBRARY SCIENCE. - 1932-6203. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Background Vietnam is a lower middle-income country with no national surveillance system for hospital-acquired infections (HAIs). We assessed the prevalence of hospital-acquired infections and antimicrobial use in adult intensive care units (ICUs) across Vietnam. Methods Monthly repeated point prevalence surveys were systematically conducted to assess HAI prevalence and antimicrobial use in 15 adult ICUs across Vietnam. Adults admitted to participating ICUs before 08: 00 a.m. on the survey day were included. Results Among 3287 patients enrolled, the HAI prevalence was 29.5% (965/3266 patients, 21 missing). Pneumonia accounted for 79.4% (804/1012) of HAIs Most HAIs (84.5% [855/1012]) were acquired in the survey hospital with 42.5% (363/855) acquired prior to ICU admission and 57.5% (492/855) developed during ICU admission. In multivariate analysis, the strongest risk factors for HAI acquired in ICU were: intubation (OR 2.76), urinary catheter (OR 2.12), no involvement of a family member in patient care (OR 1.94), and surgery after admission (OR 1.66). 726 bacterial isolates were cultured from 622/1012 HAIs, most frequently Acinetobacter baumannii (177/726 [24.4%]), Pseudomonas aeruginosa (100/726 [13.8%]), and Klebsiella pneumoniae (84/726 [11.6%]), with carbapenem resistance rates of 89.2%, 55.7%, and 14.9% respectively. Antimicrobials were prescribed for 84.8% (2787/ 3287) patients, with 73.7% of patients receiving two or more. The most common antimicrobial groups were third generation cephalosporins, fluoroquinolones, and carbapenems (20.1%, 19.4%, and 14.1% of total antimicrobials, respectively). Conclusion A high prevalence of HAIs was observed, mainly caused by Gram-negative bacteria with high carbapenem resistance rates. This in combination with a high rate of antimicrobial use illustrates the urgent need to improve rational antimicrobial use and infection control efforts.
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| 2. |
- Son, Hoang Nghia, et al.
(författare)
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Effects of simulated microgravity on the morphology of mouse embryonic fibroblasts (MEFs)
- 2020
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Ingår i: Romanian Biotechnological Letters. - Bucharest : University of Bucharest. - 1224-5984 .- 2248-3942. ; 25:6, s. 2156-2160
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Tidskriftsartikel (refereegranskat)abstract
- This study aimed to assess the effects of simulated microgravity on mouse embryonic fibroblast (MEF) morphology. The results showed that the area of MEFs under simulated microgravity was 7843.39 +/- 551.31 mu m(2) which was lower than the control group (9832.72 +/- 453.86 mu m(2)) (p < 0.001). The nuclear area of MEFs under simulated microgravity (290.76 +/- 4.58 mu m(2)) and the control group (296.8 +/- 4.58 mu m(2)) did not statistically differ. In addition, the nuclear shape value of the MEFs under simulated microgravity and the control group did not statistically differ (0.86 +/- 0.006 vs. 0.87 +/- 0.003, respectively). The nuclear intensity of MEFs under simulated microgravity (19361 +/- 852) was higher than the control group (16997 +/- 285) (P <0.05). Moreover, the flow cytometry analysis indicated the reduced GO/G1 phase cell ratio and the increased S phase and G2/M phase cell ratio in MEFs under simulated microgravity. Simulated microgravity also induced a decrease in diameter of actin filament bundles of the MEFs under simulated microgravity (1.61 +/- 0.33 mu m) compared to the control group (1.79 +/- 0.32 mu m) (P <0.01). These results revealed that simulated microgravity is capable of inducing the morphological changes of mouse embryonic fibroblasts.
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| 3. |
- Le, Son Phuong, et al.
(författare)
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Electron mobility anisotropy in InAs/GaAs(001) heterostructures
- 2021
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Ingår i: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 118:18
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Tidskriftsartikel (refereegranskat)abstract
- Electron transport properties in InAs films epitaxially grown on GaAs(001), InAs/GaAs(001) heterostructures, were systematically investigated through the dependence on crystal direction, thickness, and temperature. As a result, we found a pronounced electron mobility anisotropy, in which the mobility is highest and lowest along [1 (1) over bar0] and [110] crystal directions, respectively. The mobility anisotropy intensifies as the InAs thickness decreases, while it diminishes in thick regimes, where the InAs films are relatively immune to effects from the epitaxial heterointerface. We observed the anisotropy in a wide temperature range, 5-395 K, with an enhancement at high temperatures. Our analysis indicates that the electron mobility anisotropy can be attributed to anisotropic electron scatterings by both interface roughness and random piezoelectric polarization near the interface. Published under license by AIP Publishing.
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| 4. |
- Le, Son Phuong, et al.
(författare)
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GaN-based light-emitting materials prepared by hot-wall metal-organic chemical vapor deposition
- 2022
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Ingår i: Applied Physics A. - : SPRINGER HEIDELBERG. - 0947-8396 .- 1432-0630. ; 128:9
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Tidskriftsartikel (refereegranskat)abstract
- GaN-based structures grown on SiC substrates by means of horizontal hot-wall metal-organic chemical vapor deposition (MOCVD) were systematically characterized, revealing high crystal quality. The hot-wall MOCVD grown GaN, doped by Mg and Si, respectively showed low-resistivity hole and electron transport, competitive with the state-of-the-art GaN. High concentrations of free holes (similar to 2 x 10(17) cm(-3)) were achieved for the as-grown Mg-doped GaN without thermal annealing, thanks to advantageous heating characteristics of the "hot-wall" reactor. The analysis of optical and electrical properties brought a picture, where Mg is the only impurity defining energy levels in the hot-wall MOCVD p-type doped GaN. Besides, InGaN/GaN light-emitting diodes employing such doped GaN materials in the carrier-transport layers were fabricated, resulting in high device performances. The devices exhibited bright electroluminescence with very narrow full widths at half maximum as well as negligible spectral shifts at high current levels (greater than or similar to 10 A/cm(2)). These results exemplified the rewards of the hot-wall MOCVD for development of high-quality nitrides-based structures, providing an attractive growth method to realize the demonstration of light-emitting devices with favorable properties.
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| 5. |
- Le, Son Phuong, et al.
(författare)
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GaN-based pyramidal quantum structures for micro-size light-emitting diode applications
- 2021
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Ingår i: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 118:14
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Tidskriftsartikel (refereegranskat)abstract
- GaN-based pyramidal quantum structures, InGaN nanostructures located on top of micro-sized GaN pyramids, were fabricated by selective-area growth on SiC substrates by means of hot-wall metal-organic chemical vapor deposition. Arrays of GaN-based pyramidal structures exhibit micro-size pyramids possessing high uniformity, precise hexagonal bases, and InGaN/GaN quantum-well layers with well-defined interfaces. Each pyramid comprises a p-i-n InGaN/GaN structure, which is separated from that of other pyramids by a dielectric layer, serving as a building block for micro-emitters. Moreover, interconnected micro-size light-emitting diodes (microLEDs) built on the GaN-based pyramidal quantum structures were demonstrated, resulting in well-determined electroluminescence in the near-ultraviolet regime with negligible spectral shifts at high current levels. The results elucidated the rewards for development of these light-emitting designs and their potential for microLED applications.
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| 6. |
- Le, Son Phuong, 1983-, et al.
(författare)
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Insulator-semiconductor interface fixed charges in AlGaN/GaN metal-insulator-semiconductor devices with Al2O3 or AlTiO gate dielectrics
- 2018
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 123:3, s. 034504-1-034504-7
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated insulator-semiconductor interface fixed charges in AlGaN/GaN metal-insulator-semiconductor (MIS) devices with Al2O3 or AlTiO (an alloy of Al2O3 and TiO2) gate dielectrics obtained by atomic layer deposition on AlGaN. Analyzing insulator-thickness dependences of threshold voltages for the MIS devices, we evaluated positive interface fixed charges, whose density at the AlTiO/AlGaN interface is significantly lower than that at the Al2O3/AlGaN interface. This and a higher dielectric constant of AlTiO lead to rather shallower threshold voltages for the AlTiO gate dielectric than for Al2O3. The lower interface fixed charge density also leads to the fact that the two-dimensional electron concentration is a decreasing function of the insulator thickness for AlTiO, whereas being an increasing function for Al2O3. Moreover, we discuss the relationship between the interface fixed charges and interface states. From the conductance method, it is shown that the interface state densities are very similar at the Al2O3/AlGaN and AlTiO/AlGaN interfaces. Therefore, we consider that the lower AlTiO/AlGaN interface fixed charge density is not owing to electrons trapped at deep interface states compensating the positive fixed charges and can be attributed to a lower density of oxygen-related interface donors.
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| 7. |
- Le, Son Phuong, 1983-, et al.
(författare)
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Low-frequency noise in AlTiO/AlGaN/GaN metal-insulator-semiconductor heterojunction field-effect transistors.
- 2016
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 119:20, s. 204503-1-204503-6
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Tidskriftsartikel (refereegranskat)abstract
- Using aluminum titanium oxide (AlTiO, an alloy of Al2O3 and TiO2) as a high-k gate insulator, we fabricated and investigated AlTiO/AlGaN/GaN metal-insulator-semiconductor heterojunction field-effect transistors. From current low-frequency noise (LFN) characterization, we find Lorentzian spectra near the threshold voltage, in addition to 1/f spectra for the well-above-threshold regime. The Lorentzian spectra are attributed to electron trapping/detrapping with two specific time constants, ~25 ms and ~3ms, which are independent of the gate length and the gate voltage, corresponding to two trap level depths of 0.5-0.7 eV with a 0.06 eV difference in the AlTiO insulator. In addition, gate leakage currents are analyzed and attributed to the Poole-Frenkel mechanism due to traps in the AlTiO insulator, where the extracted trap level depth is consistent with the Lorentzian LFN. [ABSTRACT FROM AUTHOR]
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| 8. |
- Le, Son Phuong, 1983-, et al.
(författare)
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Low-frequency noise in InAs films bonded on low-k flexible substrates.
- 2015
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 107:19, s. 192103-1-192103-4
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Tidskriftsartikel (refereegranskat)abstract
- We have systematically investigated low-frequency noise (LFN) in InAs films with several thicknesses (≃10-100 nm) bonded on low-k flexible substrates (InAs/FS), comparing with that in InAs films epitaxially grown on GaAs(001) substrates (InAs/GaAs). We obtain current LFN spectra exhibiting approximate 1/f characteristics and consequent effective Hooge parameters α depending on the thickness, where we find that α in the InAs/FS is larger than that in the InAs/GaAs. The behavior of α can be attributed to the fluctuation of the electron mobility dominated by surface/interface charge scattering and by thickness fluctuation scattering. [ABSTRACT FROM AUTHOR]
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| 9. |
- Papamichail, Alexis, et al.
(författare)
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Mg-doping and free-hole properties of hot-wall MOCVD GaN
- 2022
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 131:18
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Tidskriftsartikel (refereegranskat)abstract
- The hot-wall metal-organic chemical vapor deposition (MOCVD), previously shown to enable superior III-nitride material quality and high performance devices, has been explored for Mg doping of GaN. We have investigated the Mg incorporation in a wide doping range (2.45 × 10 18 cm-3 up to 1.10 × 10 20 cm-3) and demonstrate GaN:Mg with low background impurity concentrations under optimized growth conditions. Dopant and impurity levels are discussed in view of Ga supersaturation, which provides a unified concept to explain the complexity of growth conditions impact on Mg acceptor incorporation and compensation. The results are analyzed in relation to the extended defects, revealed by scanning transmission electron microscopy, x-ray diffraction, and surface morphology, and in correlation with the electrical properties obtained by Hall effect and capacitance-voltage (C-V) measurements. This allows to establish a comprehensive picture of GaN:Mg growth by hot-wall MOCVD providing guidance for growth parameters optimization depending on the targeted application. We show that substantially lower H concentration as compared to Mg acceptors can be achieved in GaN:Mg without any in situ or post-growth annealing resulting in p-type conductivity in as-grown material. State-of-the-art p-GaN layers with a low resistivity and a high free-hole density (0.77 ω cm and 8.4 × 10 17 cm - 3, respectively) are obtained after post-growth annealing demonstrating the viability of hot-wall MOCVD for growth of power electronic device structures.
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| 10. |
- Son Phuong, Le, 1983-, et al.
(författare)
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Low-frequency noise in AlN/AlGaN/GaN metal-insulator-semiconductor devices: A comparison with Schottky devices.
- 2014
-
Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 116:5
-
Tidskriftsartikel (refereegranskat)abstract
- We have systematically investigated low-frequency noise (LFN) in AlN/AlGaN/GaN metalinsulator- semiconductor (MIS) devices, where the AlN gate insulator layer was sputteringdeposited on the AlGaN surface, in comparison with LFN in AlGaN/GaN Schottky devices. By measuring LFN in ungated two-terminal devices and heterojunction field-effect transistors (HFETs), we extracted LFN characteristics in the intrinsic gated region of the HFETs. Although there is a bias regime of the Schottky-HFETs in which LFN is dominated by the gate leakage current, LFN in theMIS-HFETs is always dominated by only the channel current. Analyzing the channel-current-dominated LFN, we obtained Hooge parameters α for the gated region as a function of the sheet electron concentration ns under the gate. In a regime of small ns, both the MIS- and Schottky-HFETs exhibit α ∝ ns–1. On the other hand, in a middle ns regime of the MIS-HFETs, α decreases rapidly like ns–ξ with ξ~2-3, which is not observed for the Schottky- HFETs. In addition, we observe strong increase in α ∝ ns3 in a large ns regime for both the MIS- and Schottky-HFETs. [ABSTRACT FROM AUTHOR]
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