| 41. |
- Borgström, Magnus, et al.
(författare)
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Fabrication and characterization of AlP-GaP core-shell nanowires
- 2011
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 324:1, s. 290-295
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Tidskriftsartikel (refereegranskat)abstract
- We report on the particle assisted synthesis of core-shell AlP-GaP nanowires by use of metal-organic vapor phase epitaxy. The core-shell approach is chosen such as to stabilize the AlP which is highly sensitive to water. The nanowires were investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. These nanowires have an indirect band-gap and form a type II staggered heterojunction. By designed capping of the AlP cores by GaP, we find the nanowires to be stable for more than a year. (C) 2011 Elsevier B.V. All rights reserved.
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| 42. |
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| 43. |
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| 44. |
- Bulbucan, Claudiu, et al.
(författare)
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Cr-substituted Fe3O4 nanoparticles : The role of particle size in the formation of FexO sub-domains and the emergence of exchange bias
- 2023
-
Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853. ; 570
-
Tidskriftsartikel (refereegranskat)abstract
- Here we study the influence of particle size on the formation of antiferromagnetic FexO subdomains and the emergence of exchange bias in novel ferrimagnetic Cr-substituted Fe3O4 nanoparticles generated using an aerosol technique based on spark ablation. Cooling in an applied magnetic field across the Néel temperature of the FexO subdomains results in significant shifts in the hysteresis loops, which decrease in magnitude with the particle diameter for the two large systems (D≈20nm&D≈40nm), whereas only minor exchange fields are observed for the smallest system (D≈10nm). The reduced exchange bias is attributed to the metastable FexO's lower volume fraction and size due to a facile transformation into the thermodynamically stable (Fe,Cr)3O4 phase with decreasing particle diameter.
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| 45. |
- Bulbucan, Claudiu, et al.
(författare)
-
Large exchange bias in Cr substituted Fe3O4nanoparticles with FeO subdomains
- 2021
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 13:37, s. 15844-15852
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Tidskriftsartikel (refereegranskat)abstract
- Tuning the anisotropy through exchange bias in bimagnetic nanoparticles is an active research strategy for enhancing and tailoring the magnetic properties for a wide range of applications. Here we present a structural and magnetic characterization of unique FeCr-oxide nanoparticles generated from seed material with a Fe : Cr ratio of 4.71 : 1 using a physical aerosol method based on spark ablation. The nanoparticles have a novel bimagnetic structure composed of a 40 nm ferrimagnetic Cr-substituted Fe3O4 structure with 4 nm antiferromagnetic FexO subdomains. Cooling in an applied magnetic field across the Néel temperature of the FexO subdomains results in a significant shift in the hysteresis, demonstrating the presence of a large exchange bias. The observed shift of μ0HE = 460 mT is among the largest values reported for FexO-Fe3O4-based nanoparticles and is attributed to the large antiferromagnetic-ferrimagnetic interface area provided by the subdomains.
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| 46. |
- Cao, Zhen, et al.
(författare)
-
Nanoparticle-Assisted Pool Boiling Heat Transfer on Micro-Pin-Fin Surfaces
- 2021
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 37:3, s. 1089-1101
-
Tidskriftsartikel (refereegranskat)abstract
- Boiling heat transfer intensification is of significant relevance to energy conversion and various cooling processes. This study aimed to enhance the saturated pool boiling of FC-72 (a dielectric liquid) by surface modifications and explore mechanisms of the enhancement. Specifically, circular and square micro pin fins were fabricated on silicon surfaces by dry etching and then copper nanoparticles were deposited on the micro-pin-fin surfaces by electrostatic deposition. Experimental results indicated that compared with a smooth surface, the micro pin fins increased the heat transfer coefficient and the critical heat flux by more than 200 and 65–83%, respectively, which were further enhanced by the nanoparticles up to 24% and more than 20%, respectively. Correspondingly, the enhancement mechanism was carefully explored by high-speed bubble visualizations, surface wickability measurements, and model analysis. It was quantitatively found that small bubble departure diameters with high bubble departure frequencies promoted high heat transfer coefficients. The wickability, which characterizes the ability of a liquid to rewet a surface, played an important role in determining the critical heat flux, but further analyses indicated that evaporation beneath bubbles was also essential and competition between the wicking and the evaporation finally triggered the critical heat flux.
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| 47. |
- Cao, Zhen, et al.
(författare)
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Pool boiling heat transfer of FC-72 on pin-fin silicon surfaces with nanoparticle deposition
- 2018
-
Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310. ; 126, s. 1019-1033
-
Tidskriftsartikel (refereegranskat)abstract
- In the present study, two types of micro-pin–fin configurations were fabricated on silicon surfaces by a dry etching method, i.e., staggered pin fins (#1) and aligned pin fins with empty areas (#2). The micro-pin–fin surfaces were then further modified by depositing FeMn oxide nanoparticles (∼35 nm) electrostatically for 8 h and 16 h, respectively, namely #1-8h, #1-16h, #2-8h and #2-16h. Subcooled pool boiling heat transfer was experimentally studied on these surfaces at atmospheric pressure, using FC-72 as the working fluid. The results showed that in comparison to the smooth surface, pool boiling heat transfer was significantly enhanced by the micro-pin-fin surfaces and the maximum superheat was considerably decreased. Additionally, critical heat fluxes were also greatly improved, e.g., the critical heat flux on #1 was almost twice of that on the smooth surface. Generally, the nanoparticle deposition could further enhance pool boiling heat transfer, including the heat transfer coefficient and critical heat flux (CHF). High speed visualizations were taken to explore the mechanisms behind the heat transfer performance. The bubble behavior on the micro-pin–fin surfaces with and without nanoparticles was compared at low, moderate and high heat fluxes, respectively. The wickability of FC-72 on the test surfaces was measured, based on which, a modified CHF model was proposed to predict the experimental CHFs. Accordingly, a possible mechanism of CHF enhancement was described.
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| 48. |
- Cao, Zhen, et al.
(författare)
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Pool Boiling Heat Transfer of Water on Copper Surfaces With Nanoparticles Coating
- 2017
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Ingår i: ASME 2017 International Mechanical Engineering Congress and Exposition. - 9780791858431 ; 8
-
Konferensbidrag (refereegranskat)abstract
- Saturated pool boiling heat transfer is investigated experimentally on a copper substrate with copper nanoparticle coatings at atmospheric pressure, in terms of critical heat flux (CHF) and heat transfer coefficient (HTC). Experiments are carried out on the substrate surface with a diameter of 12 mm using DI water as the working fluid. The coating is formed by stacking copper nanoparticles generated by an aerosol method. The aerosol nanoparticles are generated by a spark discharge generator with nitrogen gas as carrier gas and size-selected prior to electrostatic deposition. The thickness of the coating is quantified by the deposition time. In the present study, copper particles with diameter 35± 5 nm are selected, considering better coverage on the surface, while the deposition time is controlled as 4h and 8h, respectively.The boiling curves and heat transfer coefficient of MS-1 (4h deposition) and MS-2 (8h deposition) were compared with the BS (bare surface). The results show that CHFs of MS-1 and MS-2 are increased by 24% and 36%, respectively compared with the BS, while heat transfer is enhanced as well. High speed visualization tells that the coating provides more active nucleate sites and the hydrophobicity of the coating helps bubbles departure from the surface at low and moderate heat flux. At high heat flux, a hollow well occurs on MSs to supply liquid effectively to avoid dryout. Therefore, CHF and heat transfer are both improved.
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| 49. |
- Caroff, Philippe, et al.
(författare)
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Controlled polytypic and twin-plane superlattices in iii-v nanowires.
- 2009
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Ingår i: Nature Nanotechnology. - : Springer Science and Business Media LLC. - 1748-3395 .- 1748-3387. ; 4:1, s. 50-55
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Tidskriftsartikel (refereegranskat)abstract
- Semiconductor nanowires show promise for use in nanoelectronics, fundamental electron transport studies, quantum optics and biological sensing. Such applications require a high degree of nanowire growth control, right down to the atomic level. However, many binary semiconductor nanowires exhibit a high density of randomly distributed twin defects and stacking faults, which results in an uncontrolled, or polytypic, crystal structure. Here, we demonstrate full control of the crystal structure of InAs nanowires by varying nanowire diameter and growth temperature. By selectively tuning the crystal structure, we fabricate highly reproducible polytypic and twin-plane superlattices within single nanowires. In addition to reducing defect densities, this level of control could lead to bandgap engineering and novel electronic behaviour.
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| 50. |
- Caroff, Philippe, et al.
(författare)
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InSb heterostructure nanowires: MOVPE growth under extreme lattice mismatch.
- 2009
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 20:49
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the growth of InSb-based nanowire heterostructures by metalorganic vapour phase epitaxy and use it to integrate InSb on extremely lattice-mismatched III-V nanowire templates made of InAs, InP, and GaAs. Influence of temperature, V/III ratio, and diameter are investigated in order to investigate the growth rate and morphology. The range of growth temperatures used for InSb nanowire growth is very similar to that used for planar growth due to the nature of the precursor decomposition. This makes optimization of growth parameters very important, and more difficult than for most other nanowire III-V materials. Analysis of the InSb nanowire epitaxial quality when grown on InAs, InP, and GaAs, along with InSb segment and particle compositions are reported. This successful direct integration of InSb nanowires, on nanowire templates with unprecedented strain levels show great promise for fabrication of vertical InSb devices.
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