| 1. |
- Nakaso, K, et al.
(författare)
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Evaluation of the change in the morphology of gold nanoparticles during sintering
- 2002
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Ingår i: Journal of Aerosol Science. - 0021-8502. ; 33:7, s. 1061-1074
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Tidskriftsartikel (refereegranskat)abstract
- Morphological changes of agglomerates consisting of nanometer primary gold particles were studied experimentally and theoretically. Gold aerosol nanoparticles were produced using the evaporation/condensation method, and the change in agglomerate size by reheating was examined experimentally using a tandem DMA setup. Numerical calculations, based on two extreme mechanisms to reshape agglomerates, i.e., subsequent coalescence of primary particles and subsequent rearrangement of primary particles, were carried out. By comparison with the experimental results, the sintering time and the rate constant of restructuring were obtained. Using these values, the change in particle size for different generation conditions could be calculated. The change in morphology of agglomerates can be explained from the comparison of the experimental results with the theoretical calculations: agglomerates with smaller primary particles will compact mainly by the subsequent coalescence of primary particles, while agglomerates with larger primary particles will compact mainly by a rearrangement of primary particles.
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| 2. |
- Bayer, K., et al.
(författare)
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Targeted deposition of Au aerosol nanoparticles on vertical nanowires for the creation of nanotrees
- 2007
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Ingår i: Journal of Nanoparticle Research. - : Springer Science and Business Media LLC. - 1572-896X .- 1388-0764. ; 9:6, s. 1211-1216
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Tidskriftsartikel (refereegranskat)abstract
- Complex tree-like nanostructures with controlled morphology are becoming increasingly important for the development of nanoscale devices. The position of branches on III-V semiconductor nanotrees is determined by the distribution of Au seed particles. Here we report the dependence of the distribution of Au aerosol nanoparticles on nanowires on parameters including distance between wires, particle size, wire length, wire diameter, III-V material and particle charge. It was observed that different wire lengths and separation distances as well as different particle polarities have a significant effect on the resulting particle distribution while different wire diameters, particle diameters, materials and deposition voltages do not.
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| 10. |
- Dick Thelander, Kimberly, et al.
(författare)
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Growth of GaP nanotree structures by sequential seeding of 1D nanowires
- 2004
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 272:1-4, s. 131-137
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Tidskriftsartikel (refereegranskat)abstract
- Complex nanostructures are becoming increasingly important for the development of nanoscale devices and functional nanomaterials. Precise control of size and morphology of these structures is critical to their fabrication and exploitation. We have developed a method for stepwise growth of tree-like nanostructures via the vapour liquid-solid (VLS) growth mode, demonstrated for III-V semiconductor materials. This method uses the initial seeding of nanowires by catalytic aerosol nanoparticles to form the trunk, followed by sequential seeding of branching structures. Here we present a detailed study of the growth of these complex structures using Gap. Diameter of each level of nanowires is directly determined by seed particle diameters, and number of branches is determined by seed particle density. Growth rate is shown to increase with temperature to a maximum corresponding to the temperature of complete decomposition of the Group-III precursor material, and subsequently decrease due to competition with bulk growth. Growth rate also depends on flow of the Group-III precursor, but not on the Group-V precursor. Finally, there is a relationship between the number of branches and their growth rate, suggesting that material diffusion plays a role in nanowire branch growth. (C) 2004 Elsevier B.V. All rights reserved.
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| 11. |
- Hamed, Tareq Abu, et al.
(författare)
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Multiscale in modelling and validation for solar photovoltaics
- 2018
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Ingår i: EPJ Photovoltaics. - : EDP Sciences. - 2105-0716. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Photovoltaics is amongst the most important technologies for renewable energy sources, and plays a key role in the development of a society with a smaller environmental footprint. Key parameters for solar cells are their energy conversion efficiency, their operating lifetime, and the cost of the energy obtained from a photovoltaic system compared to other sources. The optimization of these aspects involves the exploitation of new materials and development of novel solar cell concepts and designs. Both theoretical modeling and characterization of such devices require a comprehensive view including all scales from the atomic to the macroscopic and industrial scale. The different length scales of the electronic and optical degrees of freedoms specifically lead to an intrinsic need for multiscale simulation, which is accentuated in many advanced photovoltaics concepts including nanostructured regions. Therefore, multiscale modeling has found particular interest in the photovoltaics community, as a tool to advance the field beyond its current limits. In this article, we review the field of multiscale techniques applied to photovoltaics, and we discuss opportunities and remaining challenges.
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| 14. |
- Kohut, A., et al.
(författare)
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From plasma to nanoparticles : Optical and particle emission of a spark discharge generator
- 2017
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 28:47
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Tidskriftsartikel (refereegranskat)abstract
- The increased demand for high purity nanoparticles (NPs) of defined geometry necessitates the continuous development of generation routes. One of the most promising physical techniques for producing metal, semiconductor or alloy NPs in the gas phase is spark discharge NP generation. The technique has a great potential for up-scaling without altering the particles. Despite the simplicity of the setup, the formation of NPs in a spark discharge takes place via complex multi-scale processes, which greatly hinders the investigation via conventional NP measurement techniques. In the present work, time-resolved optical emission spectroscopy (OES) was used to provide information on the species present in the spark from as early as approximately 100 ns after the initiation of the discharge. We demonstrate that operando emission spectroscopy can deliver valuable insights into NP formation. The emission spectra of the spark are used to identify, among others, the main stages of material erosion and to calculate the quenching rate of the generated metal vapour. We demonstrate that the alteration of key control parameters, that are typically used to optimize NP generation, clearly affect the emission spectra. We report for Cu and Au NPs that the intensity of spectral lines emitted by metal atoms levels off when spark energy is increased above an energy threshold, suggesting that the maximum concentration of metal vapour produced in the generator is limited. This explains the size variation of the generated NPs. We report a strong correlation between the optical and particle emission of the spark discharge generator, which demonstrate the suitability of OES as a valuable characterization tool that will allow for the more deliberate optimization of spark-based NP generation.
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| 16. |
- Lee, S. -K, et al.
(författare)
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Reduction of the barrier height and enhancement of tunneling current of titanium contacts using embedded Au nano-particles on 4H and 6H silicon carbide
- 2002
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Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 389-393:2, s. 937-940
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the electrical characteristics of Ti Schottky contacts with embedded Au nano-particles on various types of epilayers of SiC (4H- and 6H-SiC). From our current-voltage (I-V) and capacitance-voltage (C-V) measurements, we observed that Ti Schottky contacts with embedded Au nano-particles had 0.19 eV (n-4H-SiC) and 0.15 eV (n-6H-SiC) lower barrier height than those of particle free Ti Schottky contacts. In order to understand this reduction of the Schottky barrier height (SBH) for Ti Schottky contacts with embedded Au nano-particles, it has been proposed that SBH lowering is caused by an enhanced electric field due to the small size of the Au nano-particles and the large SBH difference. We have also tested these contacts on highly doped n-and p-type SiC material to study ohmic contacts using linear TLM measurements.
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| 17. |
- Lee, S. K., et al.
(författare)
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Reduction of the Schottky barrier height on silicon carbide using Au nano-particles
- 2002
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Ingår i: Solid-State Electronics. - 0038-1101 .- 1879-2405. ; 46:9, s. 1433-1440
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Tidskriftsartikel (refereegranskat)abstract
- By the incorporation of size-selected Au nano-particles in Ti Schottky contacts on silicon carbide, we could observe considerably lower the barrier height of the contacts. This result could be obtained for both n- and p-type Schottky contacts using current-voltage and capacitance voltage measurements. For n-type Schottky contacts, we observed reductions of 0.19-0.25 eV on 4H-SiC and 0.15-0.17 eV on 6H-SiC as compared with particle-free Ti Schottky contacts. For p-type SiC, the reduction was a little lower with 0.02-0.05 eV on 4H- and 0.10-0.13 eV on 6H-SiC. The reduction of the Schottky barrier height is explained using a model with enhanced electric field at the interface due to the small size of the circular patch and the large difference of the barrier height between Ti and Au.
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| 18. |
- Lehmann, Sebastian, et al.
(författare)
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Simultaneous Growth of Pure Wurtzite and Zinc Blende Nanowires
- 2019
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 19:4, s. 2723-2730
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Tidskriftsartikel (refereegranskat)abstract
- The opportunity to engineer III-V nanowires in wurtzite and zinc blende crystal structure allows for exploring properties not conventionally available in the bulk form as well as opening the opportunity for use of additional degrees of freedom in device fabrication. However, the fundamental understanding of the nature of polytypism in III-V nanowire growth is still lacking key ingredients to be able to connect the results of modeling and experiments. Here we show InP nanowires of both pure wurtzite and pure zinc blende grown simultaneously on the same InP [100]-oriented substrate. We find wurtzite nanowires to grow along «111»B and zinc blende counterparts along «111»A. Further, we discuss the nucleation, growth, and polytypism of our nanowires against the background of existing theory. Our results demonstrate, first, that the crystal growth conditions for wurtzite and zinc blende nanowire growth are not mutually exclusive and, second, that the interface energies predominantly determine the crystal structure of the nanowires.
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| 19. |
- Mårtensson, T, et al.
(författare)
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III-V nanowires on Si and nanowire arrays
- 2005
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Ingår i: Book of abstracts: 342nd WE-Heraeus-Seminar Sci and Technol of Inorganic Nanowires, Bad Honnef, Germany (2005).
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 20. |
- Ohlsson, B. J., et al.
(författare)
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Size-, shape-, and position-controlled GaAs nano-whiskers
- 2001
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 79:20, s. 3335-3337
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Tidskriftsartikel (refereegranskat)abstract
- We have developed a technique for the synthesis of size-selected, GaAs, epitaxial nano-whiskers, grown on a crystalline substrate. As catalysts, we used size-selected gold aerosol particles, which enabled us to fully vary the surface coverage independently of the whisker diameter. The whiskers were rod shaped, with a uniform diameter between 10 and 50 nm, correlated to the size of the catalytic seed. Furthermore, by the use of nano-manipulation of the aerosol particles by means of atomic force microscopy, we can nucleate individual nano-whiskers in a controlled manner at specific positions on a substrate with accuracy on the nm level.
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| 21. |
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| 22. |
- Seifert, Werner, et al.
(författare)
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Growth of one-dimensional nanostructures in MOVPE
- 2004
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248. ; 272:1-4, s. 211-220
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Tidskriftsartikel (refereegranskat)abstract
- The use of metal organic vapor-phase epitaxy (MOVPE) for growth of one-dimensional nanostructures in the material systems GaAs, GaP, InAs and InP is investigated. Some kinetic effects are discussed, especially the general finding that in MOVPE thinner whiskers grow faster than thicker whiskers. Effects of growth temperature on growth rate and shape of the whiskers, the effects of different growth directions on the perfection of the materials and the possibilities to grow heterostructures in axial and lateral directions are reported. Ways to overcome the randomness in whisker growth by controlled seeding of the Au particles and by using lithography for site control are demonstrated.
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| 23. |
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| 24. |
- Wolff, M. F. H., et al.
(författare)
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Synthesis and magnetic characterization of MnAs nanoparticles via nanoparticle conversion
- 2011
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 22:5
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Tidskriftsartikel (refereegranskat)abstract
- We report on the synthesis of ferromagnetic manganese arsenide (MnAs) nanoparticles via the conversion of primary Mn particles which are generated in an aerosol process in a spark discharge generator. After sintering and size selection in an aerosol setup, the particles are deposited on GaAs(100) B and Si(111) substrates. Subsequent conversion to MnAs particles takes place in an annealing process under a hydrogen atmosphere with an arsine background pressure. The magnetic properties are studied using a SQUID magnetometer. The annealed MnAs particles exhibit hexagonal facets and show anisotropic magnetic behaviour on GaAs(100) B substrates, whereas on Si(111) they remain spherical and show isotropic magnetic behaviour. Scanning transmission electron microscopy studies are used to confirm the conversion from Mn to MnAs.
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