| 1. |
- Camut, J., et al.
(author)
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Aluminum as promising electrode for Mg-2(Si,Sn)-based thermoelectric devices
- 2021
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In: Materials Today Energy. - : Elsevier. - 2468-6069. ; 21
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Journal article (peer-reviewed)abstract
- The solid solutions of magnesium silicide and magnesium stannide Mg-2(Si,Sn) are high-performance thermoelectric (TE) materials with the advantage of being composed of light, cheap, and abundant elements. Therefore, they are especially attractive for the conversion of remnant heat into electricity in fields like the automotive sector or the aerospace industry. The optimization of Mg-2(Si,Sn)-based thermoelectric generators requires establishing a suitable electrode to ensure unhindered conduction of the electrical current through the module. We have tested aluminum for such applications and developed a technological process for joining. The obtained functionalized TE legs showed electrical contact resistances below 10 mu Omega cm(2) for both p-and n-type materials and the values are preserved or even lowered with annealing. The p-type material is found to be stable and in the n-type, there is no indication for a charge carrier compensation due to the electrode, as was previously reported e.g. for Cu and Ag. Comparison with other reported electrodes shows that aluminum is so far the most suitable electrode for an Mg-2(Si,Sn)-based module.
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| 2. |
- Minh, Hoang Van, et al.
(author)
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Tobacco Control Policies in Vietnam : Review on MPOWER Implementation Progress and Challenges
- 2016
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In: Asian Pacific Journal of Cancer Prevention. - 1513-7368. ; 17, s. 1-9
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Journal article (peer-reviewed)abstract
- In Vietnam, the WHO Framework Convention on Tobacco Control (WHO FCTC) took effect in March 2005 while MPOWER has been implemented since 2008. This paper describes the progress and challenges of implementation of the MPOWER package in Vietnam. We can report that, in term of monitoring, Vietnam is very active in the Global Tobacco Surveillance System, completing two rounds of the Global Adult Tobacco Survey (GATS) and three rounds of the Global Youth Tobacco Survey (GYTS). To protect people from tobacco smoke, Vietnam has issued and enforced a law requiring comprehensive smoking bans at workplaces and public places since 2013. Tobacco advertising and promotion are also prohibited with the exception of points of sale displays of tobacco products. Violations come in the form of promotion girls, corporate social responsibility activities from tobacco manufacturers and packages displayed by retail vendors. Vietnam is one of the 77 countries that require pictorial health warnings to be printed on cigarette packages to warn about the danger of tobacco and the warnings have been implemented effectively. Cigarette tax is 70% of factory price which is equal to less than 45% of retail price and much lower than the recommendation of WHO. However, Vietnam is one of the very few countries that require manufacturers and importers to make "compulsory contributions" at 1-2% of the factory price of cigarettes sold in Vietnam for the establishment of a Tobacco Control Fund (TCF). The TCF is being operated well. In 2015, 67 units of 63 provinces/cities, 22 ministries and political-social organizations and 6 hospitals received funding from TCF to implement a wide range of tobacco control activities. Cessation services have been starting with a a toll-free quit-line but need to be further strengthened. In conclusion, Vietnam has constantly put efforts into the tobacco control field with high commitment from the government, scientists and activists. Though several remarkable achievements have been gained, many challenges remain. To overcome those challenges, implementation strategies that take into account the contextual factors and social determinants of tobacco use in Vietnam are needed.
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| 3. |
- Pham, Ngan Hoang, et al.
(author)
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High thermoelectric power factor of p-type amorphous silicon thin films dispersed with ultrafine silicon nanocrystals
- 2020
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 127:24
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Journal article (peer-reviewed)abstract
- Silicon, a candidate as an abundant-element thermoelectric material for low-temperature thermal energy scavenging applications, generally suffers from rather low thermoelectric efficiency. One viable solution to enhancing the efficiency is to boost the power factor (PF) of amorphous silicon (a-Si) while keeping the thermal conductivity sufficiently low. In this work, we report that PF >1 m Wm−1 K−2 is achievable for boron-implanted p-type a-Si films dispersed with ultrafine crystals realized by annealing with temperatures ≤600 °C. Annealing at 550 °C initiates crystallization with sub-5-nm nanocrystals embedded in the a-Si matrix. The resultant thin films remain highly resistive and thus yield a low PF. Annealing at 600 °C approximately doubles the density of the sub-5-nm nanocrystals with a bimodal size distribution characteristic and accordingly reduces the fraction of the amorphous phase in the films. Consequently, a dramatically enhanced electrical conductivity up to 104 S/m and hence PF > 1 m Wm−1 K−2 measured at room temperature are achieved. The results show the great potential of silicon in large-scale thermoelectric applications and establish a route toward high-performance energy harvesting and cooling based on silicon thermoelectrics.
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| 4. |
- Pham, Ngan Hoang, et al.
(author)
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Self-Limited Formation of Bowl-Shaped Nanopores for Directional DNA Translocation
- 2021
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In: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 15:11, s. 17938-17946
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Journal article (peer-reviewed)abstract
- Solid-state nanopores of on-demand dimensions and shapes can facilitate desired sensor functions. However, reproducible fabrication of arrayed nanopores of predefined dimensions remains challenging despite numerous techniques explored. Here, bowl-shaped nanopores combining properties of ultrathin membrane and tapering geometry are manufactured using a self-limiting process developed on the basis of standard silicon technology. The upper opening of the bowl-nanopores is 60–120 nm in diameter, and the bottom orifice reaches sub-5 nm. Current-voltage characteristics of the fabricated bowl-nanopores display insignificant rectification indicating weak ionic selectivity, in accordance to numerical simulations showing minor differences in electric field and ionic velocity upon the reversal of bias voltages. Simulations reveal, concomitantly, high-momentum electroosmotic flow downward along the concave nanopore sidewall. Collisions between the left and right tributaries over the bottom orifice drive the electroosmotic flow both up into the nanopore and down out of the nanopore through the orifice. The resultant asymmetry in electrophoretic–electroosmotic force is considered the cause responsible for the experimentally observed strong directionality in λ-DNA translocation with larger amplitude, longer duration, and higher frequencies for the downward movements from the upper opening than the upward ones from the orifice. Thus, the resourceful silicon nanofabrication technology is shown to enable nanopore designs toward enriching sensor applications.
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| 5. |
- Tran, Tuan T., et al.
(author)
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A contactless single-step process for simultaneous nanoscale patterning and cleaning of large-area graphene
- 2023
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In: 2D Materials. - : Institute of Physics Publishing (IOPP). - 2053-1583. ; 10:2
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Journal article (peer-reviewed)abstract
- The capability to structure two-dimensional materials (2DMs) at the nanoscale with customizable patterns and over large areas is critical for a number of emerging applications, from nanoelectronics to 2D photonic metasurfaces. However, current technologies, such as photo- and electron-beam lithography, often employing masking layers, can significantly contaminate the materials. Large-area chemical vapour deposition-grown graphene is known to have non-ideal properties already due to surface contamination resulting from the transferring process. Additional contamination through the lithographic process might thus reduce the performance of any device based on the structured graphene. Here, we demonstrate a contactless chemical-free approach for simultaneous patterning and cleaning of self-supporting graphene membranes in a single step. Using energetic ions passing through a suspended mask with pre-defined nanopatterns, we deterministically structure graphene with demonstrated feature size of 15 nm, approaching the performance of small-area focused ion beam techniques and extreme ultraviolet lithography. Our approach, however, requires only a broad beam, no nanoscale beam positioning and enables large area patterning of 2DMs. Simultaneously, in regions surrounding the exposed areas, contaminations commonly observed on as-grown graphene targets, are effectively removed. This cleaning mechanism is attributed to coupling of surface diffusion and sputtering effects of adsorbed surface contaminants. For applications using 2DMs, this simultaneous patterning and cleaning mechanism may become essential for preparing the nanostructured materials with improved cleanliness and hence, quality.
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| 6. |
- Villamayor, Michelle Marie S., et al.
(author)
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Growth of two-dimensional WS2 thin films by reactive sputtering
- 2021
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In: Vacuum. - : Elsevier. - 0042-207X .- 1879-2715. ; 188
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Journal article (peer-reviewed)abstract
- We have deposited WS2 thin films on Si, SiO2/Si, and sapphire substrates by reactive sputtering from a WS2 target in an Ar/H2S atmosphere. We demonstrate that it is possible to deposit (001)-textured tungsten sulfide films that are thicker than 100 nm. However, the sputtered films are slightly substoichiometric with a composition of WS1.94. Films were deposited at different processing pressures (0.67 Pa?6.67 Pa), substrate temperatures (up to 700 ?C) and relative amounts of H2S (0%?100%) in the gas mixture. Structure, morphology, composition, and resistivity of the films were investigated for the different processing conditions. Results from X-ray diffraction show that best crystallization was achieved for the highest substrate temperatures and processing pressures. We show that the addition of H2S may help obtaining fully stoichiometric films and reduce the risk of losing the (001) texture for thicker films. The challenges of obtaining an epitaxial and fully stoichiometric film are pointed out and suggestions on how to modify the process parameters in order to obtain films with even higher quality are presented.
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| 7. |
- Yao, Yao, et al.
(author)
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On Induced Surface Charge in Solid-State Nanopores
- 2020
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In: Langmuir. - : AMER CHEMICAL SOC. - 0743-7463 .- 1520-5827. ; 36:30, s. 8874-8882
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Journal article (peer-reviewed)abstract
- Solid-state nanopores constitute a versatile platform for study of ion transport in nanoconfinement. The electrical double layer (EDL) plays a vital role in such nanoconfinements, but effects of induced surface charge on the EDL in the presence of an external transmembrane electric field are yet to be characterized. Here, the formation of induced charge on the nanopore sidewall surface and its effects, via modulation of the EDL and electroosmotic flow, on the ionic current are elucidated using a novel experimental setup with solid-state truncated-pyramidal nanopores. This study consists of three complementary approaches, i.e., an analytical model for induced surface charge, numerical simulation of induced surface charge, electroosmotic flow, and ionic current, and experimental validation with respect to the ionic current. The induced surface charge is generated by polarization in the dielectric membrane as a response to the applied electric field. This charge generation results in a nonuniform density of surface charge along the nanopore sidewall. It further causes ions in the electrolyte to redistribute, leading to a massive accumulation of single-polarity ions in the EDL and their counterions near the smaller opening of the nanopore. It also alters electrohydrodynamic properties in the nanopore, giving rise to the formation of electroosmotic vortexes in the vicinity of the smaller opening of the nanopore. Finally, the pattern of the electroosmotic flow can significantly influence the transport properties of the nanopore.
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