| 1. |
- Li, Kefei, et al.
(author)
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Long-term field exposure of structural concretes in marine environment: state-of-the-art review by RILEM TC 289-DCM
- 2022
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In: Materials and Structures/Materiaux et Constructions. - : Springer Science and Business Media LLC. - 1359-5997. ; 55:7
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Journal article (peer-reviewed)abstract
- This paper reviews the technical aspects related to the long-term field exposure practice in marine environments, based on the return of experiences of major marine exposure sites in world-wide scope. The long-term exposure practice helps both the research on durability mechanisms of structural concretes under real environments and the calibration of durability models to support the life-cycle management of concrete structures. The presentation of the field exposure data can be categorized into the information relevant to exposure sites, the data related to the exposed materials and specimens, the information of environmental actions, and the data related to the performance of materials. A standardized presentation of these data can help the efficiency of data sharing and exploitation. The exploitation of exposure data employs various models to represent the chloride ingress and the induced corrosion risk of the embedded steel bars. There are needs for models addressing the strong environment-material interactions, and simple yet reliable durability indicators for engineering use. The design and operation of exposure stations need the careful choice of exposure sites and specimens, the appropriate scheme for monitoring and inspection of exposed specimens, the systematic recording and management of exposure data, and the regular maintenance of exposure facilities. The support of exposure data for life-cycle management is demonstrated through the durability planning of a real project case. The good practice of long-term field exposure is summarized in the end.
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| 2. |
- Xu, Haoyuan, et al.
(author)
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Effect of rare earth doping on electronic and gas-sensing properties of SnO2 nanostructures
- 2022
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In: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 909
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Journal article (peer-reviewed)abstract
- Tin dioxide (SnO2) and rare earth (Y, La, Pr, Tb, and Er)-doped SnO2 materials were synthesized by a solvothermal method and used for gas sensors. The effect of rare-earth (RE) doping on structural, electronic, and gas-sensing properties of SnO2 has been investigated. According to a comparative study on the gassensing properties of SnO2 and RE-doped SnO2 gas sensors to various testing gases, the RE-doped SnO2 sensors showed enhanced sensitivities to different testing gases. Especially, the Pr-doped SnO2 sensor exhibited outstanding sensing properties to SO2, including a high response of 19.5-50 ppm SO2, excellent selectivity, repaid response and recovery rates, and superior long-term stability. According to the structural analyses, DFT calculation, and the electrochemical measurement of the SnO2 and Pr-SnO2 materials, the improved electron excitation efficiency endowed the Pr-SnO2 with a high density of free electrons that can be trapped by atmospheric oxygen species and participated in SO2-sensing reactions. Moreover, after the Pr doping of SnO2, the enhanced charge carrier transport properties, including prolonged electron lifetime, improved electron diffusion coefficient, and increased effective diffusion length, were conducive to improving the SO2-sensing property.
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| 3. |
- Zhu, Xingwang, et al.
(author)
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Mo-O-Bi Bonds as interfacial electron transport bridges to fuel CO2 photoreduction via in-situ reconstruction of black Bi2MoO6/ BiO2-x heterojunction
- 2022
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In: Chemical Engineering Journal. - : ELSEVIER SCIENCE SA. - 1385-8947 .- 1873-3212. ; 429
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Journal article (peer-reviewed)abstract
- High photogenerated carrier separation efficiency plays a crucial role in determining the rate of photocatalytic CO2 reduction, but the directional transfer of carrier remains challenging. Here, improved CO2 photoreduction rate and enhanced stability were realized by in-situ construction of BiO2-x nanoparticles on Bi2MoO6 nanoflowers using H2/Ar low temperature plasma. As evidenced by DFT calculations and photocurrent measurements, the Mo-O-Bi bonds between the Bi2MoO6 and BiO2-x interfaces act as a charge transport bridge, facilitating the directional transport of electrons and thus enhancing the rate of photocatalytic reduction reactions involving multiple electrons. Compared with pristine Bi2MoO6, Bi2MoO6/BiO2-x heterojunction has excellent photostability (12 h) and efficient photocatalytic activity (approximate to 3.0 times). This indicates that the charge transfer bridge can effectively inhibit the charge recombination and deactivation of pristine Bi2MoO6. This interatomic charge transfer bridges mode can not only solve the stability problem of bismuth-based materials, but also help to design more photocatalytic systems for efficient reduction of CO2.
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| 4. |
- Hao, Zhengming, et al.
(author)
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From n-alkane to polyacetylene on Cu (110): Linkage modulation in chain growth
- 2022
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In: Science in China Series B. - : SCIENCE PRESS. - 1674-7291 .- 1869-1870. ; 65:4, s. 733-739
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Journal article (peer-reviewed)abstract
- Direct coupling or transformation of inert alkanes based on the selective C-H activation is of great importance for both chemistry and chemical engineering. Here, we report the coupling of polyenes that are transformed from n-dotriacontane (n-C32H66) through on-surface cascade dehydrogenation on Cu (110) surface, leading to the formation of polyacetylene (PA). Three distinct linkages have been resolved by scanning tunneling microscope (STM) and noncontact atomic force microscope (nc-AFM). Apart from the alpha-type linkage which is the stemless coupling of the terminal C-C double bond in trans-configuration, beta- and gamma-type linkages appear as knots or defects which are, in fact, the C-C couplings in cis-configurations. Interestingly, the "defects" can be effectively suppressed by adjusting the surface coverage, thus making it of general interest for uniform structure modulation.
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| 5. |
- Li, Junjie, 1995
(author)
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Design and Fabrication of InP High Electron Mobility Transistors for Cryogenic Low-Noise Amplifiers
- 2022
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Licentiate thesis (other academic/artistic)abstract
- High electron mobility transistor (InP HEMT) cryogenic low noise amplifiers (LNAs) have made significant improvements in noise and gain following decades of development. Applications are found from radio astronomy to quantum computing. The noise figure for the best InP HEMT cryogenic LNA, however, is still almost one order of magnitude higher than for a quantum-noise limited amplifier. This motivates further studies to understand the physical mechanisms limiting noise reduction in the InP HEMT. In this thesis, 100-nm gate-length InP HEMTs were developed for probing the intrinsic channel noise in the transistor. Electrochemical etching was found to strongly deteriorate the gate recess etch. This was mitigated by modifying the InP HEMT fabrication scheme to a recess-first process. A comparison of two different device passivation methods, atomic layer deposition of Al2O3 and plasma enhanced chemical vapor deposition of SixNy, did not reveal any significant difference in neither gain nor noise for the InP HEMT cryogenic LNA. Channel noise of the InP HEMT was investigated by varying the spacer thickness from 1 to 7 nm in the InAlAs-InGaAs heterostructure. It was found that the optimum spacer thickness was 5 nm for lowest noise temperature in a 4-8 GHz three-stage hybrid LNA at 5 K. This was 2 nm thicker than previously reported spacer thickness used for a similar state-of-the-art InP HEMT cryogenic LNA. The 5 nm spacer InP HEMT LNA minimum average noise temperature was determined to 1.4 K. The channel noise dependence on spacer thickness for the cryogenic InP HEMT was explained by a real-space transfer mechanism associated with the injection of a minor fraction of hot electrons from channel to barrier. Finally, the subthreshold swing of the InP HEMT at 5 K was observed to exhibit a correlation with the noise temperature in the cryogenic LNA. This suggests that the subthreshold swing serves as an indicator of the amount of carrier fluctuations in the InP HEMT channel giving rise to noise.
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| 6. |
- Li, Junjie, 1995, et al.
(author)
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Influence of Spacer Thickness on the Noise Performance in InP HEMTs for Cryogenic LNAs
- 2022
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In: IEEE Electron Device Letters. - 0741-3106 .- 1558-0563. ; 43:7, s. 1029-1032
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Journal article (peer-reviewed)abstract
- InP high electron mobility transistors (InP HEMTs) with different spacer thickness 1 to 7 nm in the InAlAs-InGaAs heterostructure have been fabricated and characterized at 5 K with respect to electrical dc and rf properties. The InP HEMT noise performance was extracted from gain and noise measurements of a hybrid low-noise amplifier (LNA) at 5 K equipped with discrete transistors. When biased for optimal noise operation, the LNA using 5 nm spacer thickness InP HEMTs achieved the lowest average noise temperature of 1.4 K at 4-8 GHz. The InP HEMT channel noise was estimated from the drain noise temperature which confirmed the minimum in noise temperature for the 5 nm spacer thickness InP HEMT. It is suggested that the spacer thickness acts to control the degree of real-space transfer of electrons from the channel to the barrier responsible for the observed noise variation in the cryogenic InP HEMTs.
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| 7. |
- Li, Junjie, 1995, et al.
(author)
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On the relation between rf noise and subthreshold swing in InP HEMTs for cryogenic LNAs
- 2022
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In: Asia-Pacific Microwave Conference Proceedings, APMC. ; 2022-November, s. 10-12
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Conference paper (peer-reviewed)abstract
- 4 - 8 GHz low-noise amplifiers (LNAs) based on InP high electron mobility transistors (InP HEMTs) with different spacer thickness in the InAlAs-InGaAs heterostructure were fabricated and characterized at 5 K. A variation in the lowest average noise temperature of the LNA was observed with spacer thickness. We here report that the subthreshold swing (SS) at 5 K for the HEMT exhibited similar dependence with spacer thickness as the lowest average noise temperature of the LNA. This suggests that low-temperature characterization of SS for the HEMT can be used as a rapid assessment of anticipated noise performance in the cryogenic HEMT LNA.
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| 8. |
- Yang, Biao, et al.
(author)
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Abiotic Formation of an Amide Bond via Surface-Supported Direct Carboxyl-Amine Coupling
- 2022
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In: Angewandte Chemie International Edition. - : WILEY-V C H VERLAG GMBH. - 1433-7851 .- 1521-3773. ; 61:5
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Journal article (peer-reviewed)abstract
- Amide bond formation is one of the most important reactions in biochemistry, notably being of crucial importance for the origin of life. Herein, we combine scanning tunneling microscopy and X-ray photoelectron spectroscopy studies to provide evidence for thermally activated abiotic formation of amide bonds between adsorbed precursors through direct carboxyl-amine coupling under ultrahigh-vacuum conditions by means of on-surface synthesis. Complementary insights from temperature-programmed desorption measurements and density functional theory calculations reveal the competition between cross-coupling amide formation and decarboxylation reactions on the Au(111) surface. Furthermore, we demonstrate the critical influence of the employed metal support: whereas on Au(111) the coupling readily occurs, different reaction scenarios prevail on Ag(111) and Cu(111). The systematic experiments signal that archetypical bio-related molecules can be abiotically synthesized in clean environments without water or oxygen.
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