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Sökning: WFRF:(Liu Johan 1960) > (2015-2019)

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1.
  • Abgrall, N., et al. (författare)
  • The large enriched germanium experiment for neutrinoless double beta decay (LEGEND)
  • 2017
  • Ingår i: Workshop on Calculation of Double-Beta-Decay Matrix Elements, MEDEX 2017. - : American Institute of Physics (AIP). - 9780735415775 ; 1894
  • Konferensbidrag (refereegranskat)abstract
    • The observation of neutrinoless double-beta decay (0νββ) would show that lepton number is violated, reveal that neu-trinos are Majorana particles, and provide information on neutrino mass. A discovery-capable experiment covering the inverted ordering region, with effective Majorana neutrino masses of 15 - 50 meV, will require a tonne-scale experiment with excellent energy resolution and extremely low backgrounds, at the level of ∼0.1 count /(FWHM·t·yr) in the region of the signal. The current generation 76Ge experiments GERDA and the Majorana Demonstrator, utilizing high purity Germanium detectors with an intrinsic energy resolution of 0.12%, have achieved the lowest backgrounds by over an order of magnitude in the 0νββ signal region of all 0νββ experiments. Building on this success, the LEGEND collaboration has been formed to pursue a tonne-scale 76Ge experiment. The collaboration aims to develop a phased 0νββ experimental program with discovery potential at a half-life approaching or at 1028 years, using existing resources as appropriate to expedite physics results.
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2.
  • Chen, Shujing, et al. (författare)
  • Manufacturing Graphene-Encapsulated Copper Particles by Chemical Vapor Deposition in a Cold Wall Reactor
  • 2019
  • Ingår i: ChemistryOpen. - 2191-1363. ; 8:1, s. 58-63
  • Tidskriftsartikel (refereegranskat)abstract
    • Functional fillers, such as Ag, are commonly employed for effectively improving the thermal or electrical conductivity in polymer composites. However, a disadvantage of such a strategy is that the cost and performance cannot be balanced simultaneously. Therefore, the drive to find a material with both a cost efficient fabrication process and excellent performance attracts intense research interest. In this work, inspired by the core-shell structure, we developed a facile manufacturing method to prepare graphene-encapsulated Cu nanoparticles (GCPs) through utilizing an improved chemical vapor deposition (CVD) system with a cold wall reactor. The obtained GCPs could retain their spherical shape and exhibited an outstanding thermal stability up to 179 degrees C. Owing to the superior thermal conductivity of graphene and excellent oxidation resistance of GCPs, the produced GCPs are practically used in a thermally conductive adhesive (TCA), which commonly consists of Ag as the functional filler. Measurement shows a substantial 74.6 % improvement by partial replacement of Ag with GCPs.
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3.
  • Cometto, O., et al. (författare)
  • Control of Nanoplane Orientation in voBN for High Thermal Anisotropy in a Dielectric Thin Film: A New Solution for Thermal Hotspot Mitigation in Electronics
  • 2017
  • Ingår i: ACS Applied Materials & Interfaces. - 1944-8252 .- 1944-8244. ; 9:8, s. 7456-7464
  • Tidskriftsartikel (refereegranskat)abstract
    • High anisotropic thermal materials, which allow heat to dissipate in a preferential direction, are of interest as a prospective material for electronics as an effective thermal management solution for hot spots. However, due to their preferential heat propagation in the in-plane direction, the heat spreads laterally instead of vertically. This limitation makes these materials ineffective as the density of hot spots increases. Here, we produce a new dielectric thin film material at room temperature, named vertically ordered nanocrystalline h-BN (voBN). It is produced such that its preferential thermally conductive direction is aligned in the vertical axis, which facilitates direct thermal extraction, thereby addressing the increasing challenge of thermal crosstalk. The uniqueness of voBN comes from its h-BN nanocrystals where all their basal planes are aligned in the direction normal to the substrate plane. Using the 3 omega method, we show that voBN exhibits high anisotropic thermal conductivity (TC) with a 16-fold difference between through-film TC and in-plane TC (respectively 4.26 and 0.26 W.m(-1).K-1). Molecular dynamics simulations also concurred with the experimental data, showing that the origin of this anisotropic behavior is due to the nature of voBN's plane ordering. While the consistent vertical ordering provides an uninterrupted and preferred propagation path for phonons in the through-film direction, discontinuity in the lateral direction leads to a reduced in-plane TC. In addition, we also use COMSOL to simulate how the dielectric and thermal properties of voBN enable an increase in hot spot density up to 295% compared with SiO2, without any temperature increase.
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4.
  • Jing, Lin, et al. (författare)
  • Thermal Conductivity Enhancement of Coaxial Carbon@Boron Nitride Nanotube Arrays
  • 2017
  • Ingår i: ACS Applied Materials & Interfaces. - 1944-8252 .- 1944-8244. ; 9:17, s. 14555-14560
  • Tidskriftsartikel (refereegranskat)abstract
    • We demonstrate the thermal conductivity enhancement of the vertically aligned carbon nanotube (CNT) arrays (from ?15.5 to 29.5 W/mK, ?90% increase) by encapsulating outer boron nitride nanotube (BNNT, 0.97 nm-thick with ?3-4 walls). The heat transfer enhancement mechanism of the coaxial C@BNNT was further revealed by molecular dynamics simulations. Because of their highly coherent lattice structures, the outer BNNT serves as additional heat conducting path without impairing the thermal conductance of inner CNT. This work provides deep insights into tailoring the heat transfer of arbitrary CNT arrays and will enable their broader applications as thermal interface material.
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5.
  • Liu, Ya, 1991, et al. (författare)
  • Effect of Boron Nitride Particle Geometry on the Thermal Conductivity of a Boron Nitride Enhanced Polymer Composite Film
  • 2019
  • Ingår i: THERMINIC 2019 - 2019 25th International Workshop Thermal Investigations of ICs and Systems.
  • Konferensbidrag (refereegranskat)abstract
    • Hexagonal Boron Nitride (h-BN) has been considered as a promising enhancement filler for thermal management due to its high thermal conductivity, structural stability, and super electrical resistivity. Numerus studies have reported using BN as an enhancement filler to achieve high thermally conductive polymer based thermal management materials. However, there are limited data regarding the influence of the flake size of BN sheets to the thermal management property of BN filled composites. In this work, three h-BN size geometries, including microscale h-BN powder, h-BN nanosheets, and a mixture of micro and nanoscale h-BN, were studied regarding its thermal transfer performance. The results show that h-BN nanosheets are able to achieve the highest in-plane thermal conductivity with loading from 0 - 5 wt% while for the through-plane thermal conductivity, all three geometries show similar thermal property when the filler loading less than 5 wt%. Through-plane thermal conductivity exhibits a sudden increase to 5.69 W m-1 K-1 at a loading of 5 wt%..
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6.
  • Liu, Ya, 1991, et al. (författare)
  • Egg albumen templated graphene foams for high-performance supercapacitor electrodes and electrochemical sensors
  • 2018
  • Ingår i: Journal of Materials Chemistry A. - 2050-7488 .- 2050-7496. ; 6:37, s. 18267-18275
  • Tidskriftsartikel (refereegranskat)abstract
    • We demonstrate a simple and scalable strategy to obtain N, S and Si co-doped biocompatible graphene foams (GFs) with different shapes using egg albumen as the template. The unique porous structure and element doping endow the GFs with a high charge-discharge rate and good wettability, which largely improve the electrochemical performance of the electrodes, including ultrahigh specific capacitance (534 F g-1at 1 A g-1), and excellent rate capability (308 F g-1at 100 A g-1) and cycling performance (96.1% retention of the initial capacitance after 10000 cycles at a high current density of 10 A g-1). Besides, when used as an electrochemical sensor for dopamine, the GF exhibits a detection limit as low as 1.2 μM with a linear response up to 70 μM, due to the low equivalent series resistance. These reveal great potential for promoting the application of 3D graphene in energy storage and electrochemical sensors.
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7.
  • Liu, Ya, 1991, et al. (författare)
  • Surface modification of graphene for use as a structural Fortifier in water-borne epoxy coatings
  • 2019
  • Ingår i: Coatings. - 2079-6412. ; 9:11
  • Tidskriftsartikel (refereegranskat)abstract
    • Graphene, the typical two-dimensional sp2 hybridized carbon allotrope, is widely used as a filler for improving the mechanical performance of polymers. However, its superhydrophobic surface makes it a big challenge to obtain stable graphene dispersions, especially in water-borne systems. On the contrary, graphene oxide (GO) shows excellent dispersibility in water, but strong oxidants and acids destroy its structure and degrade its mechanical properties. This largely limits its application in water-borne coatings. In this work, graphene from mechanical exfoliation was surface modified by p-aminophenol derived diazonium salt to achieve a homogenous dispersion. Moreover, the hydroxyl groups in p-aminophenol are able to combine with epoxy resins during the curing process to improve mechanical performance of the final coatings. The result shows that functionalized graphene shows a lower coefficient of friction and better abrasion resistance compared to GO.
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8.
  • Liu, Ya, 1991, et al. (författare)
  • Thermally Conductive and Electrically Insulating PVP/Boron Nitride Composite Films for Heat Spreader
  • 2019
  • Ingår i: Proceedings - 2019 IMAPS Nordic Conference on Microelectronics Packaging, NORDPAC 2019. ; , s. 1-5
  • Konferensbidrag (refereegranskat)abstract
    • Thermally conductive materials with electrically insulating properties have been extensively investigated for thermal management of electronic devices. The combined properties of high thermal conductivity, structural stability, corrosion resistance and electric resistivity make hexagonal boron nitride (h-BN) a promising candidate for this purpose. Theoretical studies have revealed that h-BN has a high in-plane thermal conductivity up to 400-800 W m-1 K-1 at room temperature. However, it is still a big challenge to achieve high thermally conductive h-BN thick films that are commercially feasible due to its poor mechanical properties. On the other hand, many polymers exhibit advantages for flexibility. Thus, combining the merits of polymer and the high thermal conductivity of h-BN particles is considered as a promising solution for this issue. In this work, orientated PVP/h-BN films were prepared by electrospinning and a subsequent mechanical pressing process. With the optimized h-BN loading, a PVP/h-BN composite film with up to 22 W m-1 K-1 and 0.485 W m-1 K-1 for in-plane and through-plane thermal conductivity can be achieved, respectively. We believe this work can help accelerate the development of h-BN for thermal management applications.
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9.
  • Ozolins, O., et al. (författare)
  • 7×149 Gbit/s PAM4 transmission over 1 km multicore fiber for short-reach optical interconnects
  • 2018
  • Ingår i: Optics InfoBase Conference Papers. - : Optics Info Base, Optical Society of America. - 9781557528209
  • Konferensbidrag (refereegranskat)abstract
    • We transmit 80 Gbaud/λ/core PAM4 signal enabled by 1.55 μm EML over 1 km 7-core fiber. The solution achieves single-wavelength and single-fiber 1.04 Tbit/s post-FEC transmission enhancing bandwidth-density for short-reach optical interconnects.
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10.
  • Wang, Nan, et al. (författare)
  • Highly thermal conductive and electrically insulated graphene based thermal interface material with long-term reliability
  • 2019
  • Ingår i: Proceedings - Electronic Components and Technology Conference. - 0569-5503. ; 2019-May, s. 1564-1568
  • Konferensbidrag (refereegranskat)abstract
    • High density packaging in combination with increased transistor integration inevitably leads to challenging power densities in terms of thermal management. The conventional TIMs that are widely used in the microelectronic industry today are experiencing more and more stress due to their limited thermal performance and poor reliability. Composed by particle laden polymer matrix, thermal conductivity (K) of conventional TIMs is generally limited to 5 W/mK, and such values can be even lower for electrically insulated TIMs. Conventional TIMs also suffer from severe pump-out and dry-out failures, which brought great threat to the performance and lifetime of the electronic devices. Here, we solve these problems by applying a novel highly thermal conductive, electrically insulated and reliable graphene based TIMs (I-GTs). Composed by vertical graphene structures, I-GTs provide a continuous heat pathway from top to bottom, which enables superfast heat dissipation at through-plane direction. The highest bulk through-plane thermal conductivity of the conductive body can reach up to 1000 W/mK, which is orders of magnitude higher than conventional TIMs, and even outperforms the pure indium TIMs by over ten times. The highly flexible and foldable nature of I-GT enables at least 100% compressibility upon small applied pressures. As excellent gap fillers, I-GT can provide complete physical contact between two surfaces and thereby minimize the contact resistance to heat flow. The measured minimum thermal resistance for I-GTs reaches about 30 Kmm2/W. Such values are significantly higher than the randomly dispersed composites presented above. To ensure fully electrical insulation, a smooth and soft adhesive layer with a thickness of few microns was coated on the surface of I-GT. The breakdown voltage of I-GT reaches up to 950 V. Thermal cycling test shows the highly stable nature of I-GT. The good compressibility and elasticity of I-GT ensures continued proper TIM contact with substrates, which counteracts the effect of internal stress induced by the mismatch of coefficient of thermal expansion (CTE) during temperature cycling. In addition, the I-GTs have the advantages of low density and good maintainability. The resulting I-GTs thus opens new opportunities for addressing large heat dissipation issues for form-factor driven electronics and other high power driven systems.
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