| 1. |
- Jing, Lin, et al.
(författare)
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Thermal Conductivity Enhancement of Coaxial Carbon@Boron Nitride Nanotube Arrays
- 2017
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Ingår i: ACS Applied Materials & Interfaces. - : American Chemical Society (ACS). - 1944-8252 .- 1944-8244. ; 9:17, s. 14555-14560
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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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| 2. |
- Liu, Ya, 1991, et al.
(författare)
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Thermally Conductive and Electrically Insulating PVP/Boron Nitride Composite Films for Heat Spreader
- 2019
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Ingår i: Proceedings - 2019 IMAPS Nordic Conference on Microelectronics Packaging, NORDPAC 2019. ; , s. 1-5
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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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| 3. |
- Liu, Ya, 1991, et al.
(författare)
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Thermally Conductive and Electrically Insulating PVP/Boron Nitride Composite Films for Heat Spreader
- 2019
-
Ingår i: Advancing Microelectronics. - 2222-8748. ; 2019:NOR, s. 1-5
-
Tidskriftsartikel (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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| 4. |
- Fazi, Andrea, 1992, et al.
(författare)
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Multiple growth of graphene from a pre-dissolved carbon source
- 2020
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Ingår i: Nanotechnology. - : IOP Publishing. - 1361-6528 .- 0957-4484. ; 31:34, s. 345601-
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Tidskriftsartikel (refereegranskat)abstract
- Mono- to few-layer graphene materials are successfully synthesized multiple times using Cu-Ni alloy as a catalyst after a single-chemical vapor deposition (CVD) process. The multiple synthesis is realized by extracting carbon source pre-dissolved in the catalyst substrate. Firstly, graphene is grown by the CVD method on Cu-Ni catalyst substrates. Secondly, the same Cu-Nicatalyst foils are annealed, in absence of any external carbon precursor, to grow graphene using the carbon atoms pre-dissolved in the catalyst during the CVD process. This annealing process is repeated to synthesize graphene successfully until carbon is exhausted in the Cu-Ni foils. After the CVD growth and each annealing growth process, the as-grown graphene is removed using a bubbling transfer method. A wide range of characterizations are performed to examine the quality of the obtained graphene material and to monitor the carbon concentration in the catalyst substrates. Results show that graphene from each annealing growth process possesses a similar quality, which confirmed the good reproducibility of the method. This technique brings great freedom to graphene growth and applications, and it could be also used for other 2D material synthesis.
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| 5. |
- Hansson, Josef, 1991, et al.
(författare)
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Bipolar electrochemical capacitors using double-sided carbon nanotubes on graphite electrodes
- 2020
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 451
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Tidskriftsartikel (refereegranskat)abstract
- The electrochemical capacitor (EC) is a key enabler for the miniaturized self-powered systems expected to become ubiquitous with the advent of the internet-of-things (IoT). Vertically aligned carbon nanotubes (VACNTs) on graphite holds promise as electrodes for compact and low-loss ECs. However, as with all ECs, the operating voltage is low, and miniaturization of higher voltage devices necessitates a bipolar design. In this paper, we demonstrate a bipolar EC using graphite/VACNTs electrodes fabricated using a joule heating chemical vapor deposition (CVD) setup. The constructed EC contains one layer of double-sided VACNTs on graphite as bipolar electrode. Compared to a series connection of two individual devices, the bipolar EC has 22% boost in volumetric energy density. More significant boost is envisaged for stacking more bipolar electrode layers. The energy enhancement is achieved without aggravating self-discharge (71.2% retention after 1 h), and at no sacrifice of cycling stability (96.7% over 50000 cycles) owing to uniform growth of VACNTs and thus eliminating cell imbalance problems.
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| 6. |
- Hansson, Josef, 1991, et al.
(författare)
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Effects of high temperature treatment of carbon nanotube arrays on graphite : Increased crystallinity, anchoring and inter-tube bonding
- 2020
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Ingår i: Nanotechnology. - : Institute of Physics Publishing (IOPP). - 0957-4484 .- 1361-6528. ; 31:45
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Tidskriftsartikel (refereegranskat)abstract
- Thermal treatment of carbon nanotubes (CNTs) can significantly improve their mechanical, electrical and thermal properties due to reduced defects and increased crystallinity. In this work we investigate the effect of annealing at 3000 degrees C of vertically aligned CNT arrays synthesized by chemical vapor deposition (CVD) on graphite. Raman measurements show a drastically reduced amount of defects and, together with transmission electron microscope (TEM) diffraction measurements, an increased average crystallite size of around 50%, which corresponds to a 124% increase in Young's modulus. We also find a tendency for CNTs to bond to each other with van der Waals (vdW) forces, which causes individual CNTs to closely align with each other. This bonding causes a densification effect on the entire CNT array, which appears at temperatures >1000 degrees C. The densification onset temperature corresponds to the thermal decomposition of oxygen containing functional groups, which otherwise prevents close enough contact for vdW bonding. Finally, the remaining CVD catalyst on the bottom of the CNT array is evaporated during annealing, enabling direct anchoring of the CNTs to the underlying graphite substrate.
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| 7. |
- Hansson, Josef, 1991, et al.
(författare)
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Synthesis of a Graphene Carbon Nanotube Hybrid Film by Joule Self-heating CVD for Thermal Applications
- 2018
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Ingår i: Proceedings - Electronic Components and Technology Conference. - 0569-5503. ; 2018-May
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Konferensbidrag (refereegranskat)abstract
- Hybrid films based on vertically aligned carbon nanotubes (CNTs) on graphene or graphite sheets have been proposed for application as thermal interface materials and micro heat sinks. However, the fabrication of these materials are limited to small scale, expensive and complicated chemical vapor deposition (CVD) for CNT synthesis. We present a new method for direct growth of CNTs on one or both sides of a thin graphene film (GF) using joule self-heating of the graphene film to provide the necessary heat for the thermal breakdown of carbon feedstock in a CVD process. The resulting CNT forests show good density and alignment consistent with regular CVD synthesis processes on silicon surfaces. The resulting double sided GF/CNT hybrid film is directly applicable as a thermal pad. The CNT forest has a thermal conductivity of 30 W/mK, measured by pulsed photothermal reflectance, and the total thermal interface resistance between aluminum blocks was measured to be 60 Kmm 2 /W using an ASTM D5470 compliant 1-D measurement setup. This method of directly synthesizing CNTs on graphene films is more energy efficient and capable of larger volume production compared to traditional CVD methods. It is also compatible with scaling up towards continuous roll-to-roll production for large scale commercial production, one of the major limitations preventing CVD-grown CNTs from commercial applications
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| 8. |
- Jiang, Di, 1983, et al.
(författare)
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Embedded Fin-Like Metal/CNT Hybrid Structures for Flexible and Transparent Conductors
- 2016
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Ingår i: Small. - : Wiley. - 1613-6810 .- 1613-6829. ; 12:11, s. 1521-1526
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, an embedded fin-like metal-coated carbon nanotube (Fin-M/CNT) structure is demonstrated for flexible and transparent conductor wire applications. Embedded in a polydimethylsiloxane polymeric substrate, Fin-M/CNT wires with a minimum width of 5 μm and a minimum pitch of 10 μm have been achieved. Direct current resistances of single Fin-M/CNT wires, where the supporting CNT structures have been covered by Ti/Al/Au metal coatings of different thicknesses, have been measured. The high aspect ratio of the fin-like structures not only improves the adhesion between the wires and the polymeric substrate, but also yields a low resistance at a small surface footprint. In addition, transparent Fin-M/CNT grid lines with hexagonal patterns, with a sheet resistance of as low as 45 Ω sq−1, have been achieved at an optical transmittance of 88%. The robustness of the Fin-M/CNT structures has been demonstrated in bending tests up to 500 cycles and no significant changes in wire resistances are observed.
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| 9. |
- Nylander, Andreas, 1988, et al.
(författare)
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Covalent anchoring of carbon nanotube-based thermal interface materials using epoxy-silane monolayers
- 2019
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Ingår i: IEEE Transactions on Components, Packaging and Manufacturing Technology. - 2156-3985 .- 2156-3950. ; 9:3, s. 427-433
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Tidskriftsartikel (refereegranskat)abstract
- With the ever increasing demand for improved thermal management solutions in modern electronic devices, carbon nanotubes (CNTs) have been suggested as a candidate material for thermal interface materials (TIMs). However, the interfacial resistance between CNTs and matching substrate is huge due to poor interaction at the interface. With the help of chemical functionalization, these materials can be exploited to their full potential in TIM applications. By utilizing the epoxy-silane-based monolayers, covalent anchoring can be obtained between the CNTs and target substrate in order to bridge the interface, where high resistances, otherwise, would arise. To adapt CNT arrays to the epoxy chemistry, the CNTs have subsequently been subjected to nitrogen plasma in order to activate them with amino groups. The thermal interfaces were measured, and the thermal resistance was found to be decreased by 5% in comparison with the reference samples.
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| 10. |
- NYLANDER, ANDREAS, 1988, et al.
(författare)
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Current status and progress of organic functionalization of CNT based thermal interface materials for electronics cooling applications
- 2017
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Ingår i: 2017 IMAPS Nordic Conference on Microelectronics Packaging (NordPac). - 9781538630556 ; , s. 175-181
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Konferensbidrag (refereegranskat)abstract
- The development of integrated circuitry has resulted in cheaper and more efficient computers being available every year. Unfortunately, this development comes at the expense of an exponential increase of power density that scales with miniaturisation of transistors. To counteract the hot spot issue that arises and results in poor reliability and reduced lifetime of microsystems, thermal interface materials (TIMs) can be used. TIMs play a key role in thermal management of microsystems by providing efficient thermal pathways between surfaces. Vertically aligned carbon nanotubes (CNT) have been suggested as a potential material for such TIM applications due to the combination of their high thermal conductivity, which has been reported to reach over 3000 W/mK, and unique mechanical properties. However, due to the poor interaction between individual CNT strands and the contact surface, large contact resistances are commonly measured in these interfaces. One solution to this issue is to anchor the CNT by covalent bonding using chemical functionalization which allows phonon propagation through the interface. In this paper various chemical functionalization solutions from recent literature for CNT in TIM applications will be summarized. By comparing the results from these studies to other TIM systems, CNT array based TIM hold some promise with thermal interface resistance values reaching as low as 0.6mm2K/W. However, experimental results regarding the reliability of these solutions are still uncommon and should be a suitable area for further investigations.
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