| 1. |
- Boyd, Robert, et al.
(författare)
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Characterisation of Nanoparticle Structure by High Resolution Electron Microscopy
- 2014
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Ingår i: Electron Microscopy and Analysis Group Conference (EMAG2013). - : Institute of Physics Publishing (IOPP). ; , s. 012065-
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Konferensbidrag (refereegranskat)abstract
- Whilst the use of microscopic techniques to determine the size distributions of nanoparticle samples is now well established, their characterisation challenges extend well beyond this. Here it is shown how high resolution electron microscopy can help meet these challenges. One of the key parameters is the determination of particle shape and structure in three dimensions. Here two approaches to determining nanoparticle structure are described and demonstrated. In the first scanning transmission electron microscopy combined with high angle annular dark field imaging (HAADF-STEM) is used to image homogenous nanoparticles, where the contrast is directly related to the thickness of the material in the electron beam. It is shown that this can be related to the three dimensional shape of the nano-object. High resolution TEM imaging, combined with fast Fourier transform (FFT) analysis, can determine the crystalline structure and orientation of nanoparticles as well as the presence of any defects. This combined approach allows the physical structure of a significant number of nano-objects to be characterised, relatively quickly.
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| 2. |
- Boyd, Robert, et al.
(författare)
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Complex 3D nanocoral like structures formed by copper nanoparticle aggregation on nanostructured zinc oxide rods
- 2016
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Ingår i: Materials letters (General ed.). - : ELSEVIER SCIENCE BV. - 0167-577X .- 1873-4979. ; 184, s. 127-130
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports a new strategy for nanoparticle surface assembly so that they form anisotropic fibril like features, consisting of particles directly attached to each other, which can extend 500 nm from the surface. The particles are both formed and deposited in a single step process enabled via the use of a pulsed plasma based technique. Using this approach, we have successfully modified zinc oxide rods, up to several hundred nanometers in diameter, with 25 nm diameter copper nanoparticles for catalytic applications. The resulting structure could be modelled using a diffusion limited aggregation based approach. This gives the material the appearance of marine coral, hence the term nanocoral. (C) 2016 Elsevier B.V. All rights reserved.
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| 3. |
- Boyd, Robert, et al.
(författare)
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Double oxide shell layer formed on a metal nanoparticle as revealed by aberration corrected (scanning) transmission electron microscopy
- 2014
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Ingår i: Materials Research Express. - : IOP Publishing. - 2053-1591. ; 1:2, s. Art. no. 025016-
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Tidskriftsartikel (refereegranskat)abstract
- Determining the extent of oxidation in batches of metal nanoparticles is essential to predict the behaviour of the material. Using aberration corrected transmission electron microscopy (TEM) it was possible to detect the formation of an oxide shell, of thickness 3 nm, on the surface of copper nanoparticles. Further analysis showed that this shell actually consists of two layers, both of which were polycrystalline in nature with domains in the size range of 1-2 nm, and having a thickness of 1.5 nm each. Energy dispersive x-ray spectroscopy confirms that the layers arise due to the formation of oxides, but it was not possible to determine their exact nature. Analysis of the intensity variation within images obtained via probe corrected scanning TEM combined with a high angle annular dark field detector indicates that the shell consists of an inner layer of cuprous oxide (Cu2O) and an outer layer of cupric oxide (CuO). This work was complemented by conventional TEM which provided size distribution and revealed that the majority of particles have a core consisting of a single crystal of copper. This demonstrates the ability of TEM to help to determine the oxidation state of nanoparticles and its potential to be applied to a wide range of homogenous and heterogeneous nanoparticles.
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| 4. |
- Greiner, Franko, et al.
(författare)
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Diagnostics and characterization of nanodust and nanodusty plasmas
- 2018
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Ingår i: European Physical Journal D. - : SPRINGER. - 1434-6060 .- 1434-6079. ; 72:5
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Tidskriftsartikel (refereegranskat)abstract
- Plasmas growing or containing nanometric dust particles are widely used and proposed in plasma technological applications for production of nano-crystals and surface deposition. Here, we give a compact review of in situ methods for the diagnostics of nanodust and nanodusty plasmas, which have been developed in the framework of the SFB-TR24 to fully characterize these systems. The methods include kinetic Mie ellipsometry, angular-resolved Mie scattering, and 2D imaging Mie ellipsometry to get information about particle growth processes, particle sizes and particle size distributions. There, also the role of multiple scattering events is analyzed using radiative transfer simulations. Computed tomography and Abel inversion techniques to get the 3D dust density profiles of the particle cloud will be presented. Diagnostics of the dust dynamics yields fundamental dust and plasma properties like particle charges and electron and ion densities. Since nanodusty plasmas usually form dense dust clouds electron depletion (Haynes effect) is found to be significant.
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| 5. |
- Greiner, Franko, et al.
(författare)
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Imaging Mie ellipsometry: dynamics of nanodust clouds in an argon-acetylene plasma
- 2012
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Ingår i: Plasma sources science & technology. - : Institute of Physics. - 0963-0252 .- 1361-6595. ; 21:6, s. 065005-
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Tidskriftsartikel (refereegranskat)abstract
- For the in situ analysis of nano-sized particles in a laboratory plasma, Mie ellipsometry is a well established technique. We present a simple setup with two CCD cameras to gain online spatiotemporal resolved information of the growth dynamics of particles which are produced by plasma chemical processes in an argon-acetylene plasma. Imaging Mie ellipsometry proves to be a powerful technique to study the growth processes of nanodust in all its details.
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| 6. |
- Gunnarsson, Rickard, et al.
(författare)
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Synthesis of titanium-oxide nanoparticles with size and stoichiometry control
- 2015
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Ingår i: Journal of nanoparticle research. - : Springer Verlag (Germany). - 1388-0764 .- 1572-896X. ; 17:9, s. 353-
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Tidskriftsartikel (refereegranskat)abstract
- Ti-O nanoparticles have been synthesized via hollow cathode sputtering in an Ar-O-2 atmosphere using high power pulsing. It is shown that the stoichiometry and the size of the nanoparticles can be varied independently, the former through controlling the O-2 gas flow and the latter by the independent biasing of two separate anodes in the growth zone. Nanoparticles with diameters in the range of 25-75 nm, and with different Ti-O compositions and crystalline phases, have been synthesized.
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| 7. |
- Gunnarsson, Rickard, et al.
(författare)
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The influence of pressure and gas flow on size and morphology of titanium oxide nanoparticles synthesized by hollow cathode sputtering
- 2016
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 120:4
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Tidskriftsartikel (refereegranskat)abstract
- Titanium oxide nanoparticles have been synthesized via sputtering of a hollow cathode in an argon atmosphere. The influence of pressure and gas flow has been studied. Changing the pressure affects the nanoparticle size, increasing approximately proportional to the pressure squared. The influence of gas flow is dependent on the pressure. In the low pressure regime (107 <= p <= 143 Pa), the nanoparticle size decreases with increasing gas flow; however, at high pressure (p = 215 Pa), the trend is reversed. For low pressures and high gas flows, it was necessary to add oxygen for the particles to nucleate. There is also a morphological transition of the nanoparticle shape that is dependent on the pressure. Shapes such as faceted, cubic, and cauliflower can be obtained. Published by AIP Publishing.
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| 8. |
- Hasan, Mohammad I., et al.
(författare)
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Modeling the extraction of sputtered metal from high power impulse hollow cathode discharges
- 2013
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Ingår i: Plasma sources science & technology. - : IOP Publishing. - 0963-0252 .- 1361-6595. ; 22:3, s. 035006-
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Tidskriftsartikel (refereegranskat)abstract
- High power impulse hollow cathode sputtering is studied as a means to produce high fluxes of neutral and ionized sputtered metal species. A model is constructed for the understanding and optimization of such discharges. It relates input parameters such as the geometry of the cathode, the electric pulse form and frequency, and the feed gas flow rate and pressure, to the production, ionization, temperature and extraction of the sputtered species. Examples of processes that can be quantified by the use of the model are the internal production of sputtered metal and the degree of its ionization, the speed and efficiency of out-puffing from the hollow cathode associated with the pulses, and the gas back-flow into the hollow cathode between pulses. The use of the model is exemplified with a special case where the aim is the synthesis of nanoparticles in an expansion volume that lies outside the hollow cathode itself. The goals are here a maximum extraction efficiency, and a high degree of ionization of the sputtered metal. It is demonstrated that it is possible to reach a degree of ionization above 85%, and extraction efficiencies of 3% and 17% for the neutral and ionized sputtered components, respectively.
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| 9. |
- Kalered, Emil, et al.
(författare)
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On the work function and the charging of small (r ≤ 5 nm) nanoparticles in plasmas
- 2017
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Ingår i: Physics of Plasmas. - : American Institute of Physics (AIP). - 1070-664X .- 1089-7674. ; 24:1
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Tidskriftsartikel (refereegranskat)abstract
- The growth of nanoparticles (NPs) in plasmas is an attractive technique where improved theoretical understanding is needed for quantitative modeling. The variation of the work function W with size for small NPs, rNP≤ 5 nm, is a key quantity for modeling of three NP charging processes that become increasingly important at a smaller size: electron field emission, thermionic electron emission, and electron impact detachment. Here we report the theoretical values of the work function in this size range. Density functional theory is used to calculate the work functions for a set of NP charge numbers, sizes, and shapes, using copper for a case study. An analytical approximation is shown to give quite accurate work functions provided that rNP > 0.4 nm, i.e., consisting of about >20 atoms, and provided also that the NPs have relaxed close to spherical shape. For smaller sizes, W deviates from the approximation, and also depends on the charge number. Some consequences of these results for nanoparticle charging are outlined. In particular, a decrease in W for NP radius below about 1 nm has fundamental consequences for their charge in a plasma environment, and thereby on the important processes of NP nucleation, early growth, and agglomeration.
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| 10. |
- Pilch, Iris, et al.
(författare)
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Diagnostics of void expansion during cyclic growth and formation of layered nanoparticle clouds
- 2017
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Ingår i: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 121:11
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Tidskriftsartikel (refereegranskat)abstract
- Nanoparticles were grown in an argon-acetylene plasma, and the particle size was characterized during growth using imaging Mie ellipsometry (I-Mie). The typical cyclic growth was observed, and the previously reported expansion and contraction of the void before depletion of nanoparticles [van de Wetering et al., J. Phys. D: Appl. Phys. 48, 035204 (2015)] was independently confirmed in our measurements. The cyclic growth was interrupted by repetitively turning the acetylene flow on and off. The nanoparticles that were confined in the discharge proceeded to grow slowly but more importantly a new growth cycle started with nucleation and growth taking place in the void region. The additional growth burst in the void region leads to a structured dust cloud with regions of nanoparticles with different sizes that were sharply separated. The advantages of using the I-Mie diagnostics for the observation of nanoparticles compared to standard video microscopy are demonstrated for the structured dust cloud. The results are discussed in relation to the growth processes for nucleation and coagulation.
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| 11. |
- Pilch, Iris, et al.
(författare)
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Fast growth of nanoparticles in a hollow cathode plasma through orbit motion limited ion collection
- 2013
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 103:19, s. 193108-
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Tidskriftsartikel (refereegranskat)abstract
- Plasma-based nanoparticle synthesis techniques are attractive in many respects but suffer from a major drawback-low productivity. We demonstrate a technique by which the growth rate of copper nanoparticles has been substantially increased by collection of copper ions. A growth rate as high as 470 nm/s was obtained as compared to a growth rate of less than 3 nm/s in the case of growth by neutrals. The increased trapping of copper is explained as orbital motion limited (OML) collection of ions. Experimentally obtained nanoparticle growth rates are in good agreement with theoretical estimates of the OML ion collection rates.
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| 12. |
- Pilch, Iris, et al.
(författare)
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Nanoparticle growth by collection of ions : orbital motion limited theory and collision-enhanced collection
- 2016
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Ingår i: Journal of Physics D. - : Institute of Physics Publishing (IOPP). - 0022-3727 .- 1361-6463. ; 49:39
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Tidskriftsartikel (refereegranskat)abstract
- The growth of nanoparticles in plasma is modeled for situations where the growth is mainly due to the collection of ions of the growth material. The model is based on the classical orbit motion limited (OML) theory with the addition of a collision-enhanced collection (CEC) of ions. The limits for this type of model are assessed with respect to three processes that are not included: evaporation of the growth material, electron field emission, and thermionic emission of electrons. It is found that both evaporation and thermionic emission can be disregarded below a temperature that depends on the nanoparticle material and on the plasma parameters; for copper in our high-density plasma this limit is about 1200 K. Electron field emission can be disregarded above a critical nanoparticle radius, in our case around 1.4 nm. The model is benchmarked, with good agreement, to the growth of copper nanoparticles from a radius of 5 nm-20 nm in a pulsed power hollow cathode discharge. Ion collection by collisions contributes with approximately 10% of the total current to particle growth, in spite of the fact that the collision mean free path is four orders of magnitude longer than the nanoparticle radius.
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| 13. |
- Pilch, Iris, et al.
(författare)
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Size-controlled growth of nanoparticles in a highly ionized pulsed plasma
- 2013
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 102:3, s. 033108-
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Tidskriftsartikel (refereegranskat)abstract
- Copper nanoparticles (NPs) were synthesized using a high power pulsed hollow cathode technique and the produced NPs were studied as a function of pulse parameters, i.e., frequency, peak current, and pulse width. It was found that the particle size can be altered in a range from 10 to 40 nm by changing any one of the pulse parameters. The mechanisms of NP synthesis with respect to a pulsed discharge and a high degree of ionization of the sputtered material are discussed.
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| 14. |
- Pilch, Iris, et al.
(författare)
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Synthesis of copper nanoparticles by a high power pulse hollow cathode
- 2012
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Ingår i: Technical Proceedings of the 2012 NSTI Nanotechnology Conference and Expo, NSTI-Nanotech 2012. - 9781466562745 - 9781466562875 ; , s. 371-373
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Konferensbidrag (refereegranskat)abstract
- A novel plasma-based nanoparticle synthesis method was used for synthesizing copper nanoparticles. High power pulses were applied to a cylindrical hollow cathode providing a high density and a high degree of ionization of the sputtered material. The variation of the nanoparticle size distributions were analyzed from scanning electron microscopy images and studied with respect to varied pulse parameters, e.g., pulse width and peak current. It was found that the nanoparticle size can be changed in a range between 10 and 40 nm by varying the pulse parameters.
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| 15. |
- Pilch, Iris, et al.
(författare)
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The use of highly ionized pulsed plasmas for the synthesis of advanced thin films and nanoparticles
- 2014
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Ingår i: Kona. - : Hosokawa Powder Technology Foundation. - 0288-4534 .- 2187-5537. ; 31:1, s. 171-180
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Tidskriftsartikel (refereegranskat)abstract
- Pulsed plasma processes open up the possibility of using very high plasma densities and modulated deposition in the synthesis of thin films and nanoparticles. The high plasma densities lead to a high degree of ionization of the source material, which creates new possibilities for surface engineering. Ions can, in contrast to atoms, be easily controlled with regard to their energy and direction, which is beneficial for thin film growth. Furthermore, ions can also increase the trapping probability of material on nanoparticles growing in the gas phase. The pulsed sputter ejection of source material also has other consequences: the material in the plasma and the material arrival on the growth surface will fluctuate strongly resulting in high level of supersaturation during pulse-on time. In this paper, an overview of the generation and properties of highly ionized pulsed plasmas is given. In addition, the use and importance of these types of discharges in the fields of thin-film and nanoparticle growth are also summarized. ©2014 Hosokawa Powder Technology Foundation.
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| 16. |
- Tal, Alexey A., et al.
(författare)
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Molecular dynamics simulation of the growth of Cu nanoclusters from Cu ions in a plasma
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 90:16, s. 165421-
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Tidskriftsartikel (refereegranskat)abstract
- A recently developed method of nanoclusters growth in a pulsed plasma is studied by means of molecular dynamics. A model that allows one to consider high-energy charged particles in classical molecular dynamics is suggested, and applied for studies of single impact events in nanoclusters growth. In particular, we provide a comparative analysis of the well-studied inert gas aggregation method and the growth from ions in a plasma. The importance to consider of the angular distribution of incoming ions in the simulations of the nanocluster growth is underlined. A detailed study of the energy transfer from the incoming ions to a nanocluster, as well as the diffusion of incoming ions on the cluster surface, is carried out. Our results are important for understanding and control of the nanocluster growth process.
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| 17. |
- Vermang, Bart, et al.
(författare)
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Highly reflective rear surface passivation design for ultra-thin Cu(In,Ga) Se-2 solar cells
- 2015
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 582, s. 300-303
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Tidskriftsartikel (refereegranskat)abstract
- Al2O3 rear surface passivated ultra-thin Cu(In,Ga)Se-2 (CIGS) solar cells with Mo nano-particles (NPs) as local rear contacts are developed to demonstrate their potential to improve optical confinement in ultra-thin CIGS solar cells. The CIGS absorber layer is 380 nm thick and the Mo NPs are deposited uniformly by an up-scalable technique and have typical diameters of 150 to 200 nm. The Al2O3 layer passivates the CIGS rear surface between the Mo NPs, while the rear CIGS interface in contact with the Mo NP is passivated by [Ga]/([Ga] + [In]) (GGI) grading. It is shown that photon scattering due to the Mo NP contributes to an absolute increase in short circuit current density of 3.4 mA/cm(2); as compared to equivalent CIGS solar cells with a standard back contact.
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