| 1. |
- Boyd, Robert, et al.
(author)
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Characterisation of Nanoparticle Structure by High Resolution Electron Microscopy
- 2014
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In: Electron Microscopy and Analysis Group Conference (EMAG2013). - : Institute of Physics Publishing (IOPP). ; , s. 012065-
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Conference paper (peer-reviewed)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.
(author)
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Complex 3D nanocoral like structures formed by copper nanoparticle aggregation on nanostructured zinc oxide rods
- 2016
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In: Materials letters (General ed.). - : ELSEVIER SCIENCE BV. - 0167-577X .- 1873-4979. ; 184, s. 127-130
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Journal article (peer-reviewed)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.
(author)
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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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In: Materials Research Express. - : IOP Publishing. - 2053-1591. ; 1:2, s. Art. no. 025016-
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Journal article (peer-reviewed)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.
(author)
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Diagnostics and characterization of nanodust and nanodusty plasmas
- 2018
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In: European Physical Journal D. - : SPRINGER. - 1434-6060 .- 1434-6079. ; 72:5
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Journal article (peer-reviewed)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.
(author)
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Imaging Mie ellipsometry: dynamics of nanodust clouds in an argon-acetylene plasma
- 2012
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In: Plasma sources science & technology. - : Institute of Physics. - 0963-0252 .- 1361-6595. ; 21:6, s. 065005-
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Journal article (peer-reviewed)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.
(author)
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Synthesis of titanium-oxide nanoparticles with size and stoichiometry control
- 2015
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In: Journal of nanoparticle research. - : Springer Verlag (Germany). - 1388-0764 .- 1572-896X. ; 17:9, s. 353-
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Journal article (peer-reviewed)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.
(author)
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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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In: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 120:4
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Journal article (peer-reviewed)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.
(author)
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Modeling the extraction of sputtered metal from high power impulse hollow cathode discharges
- 2013
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In: Plasma sources science & technology. - : IOP Publishing. - 0963-0252 .- 1361-6595. ; 22:3, s. 035006-
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Journal article (peer-reviewed)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.
(author)
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On the work function and the charging of small (r ≤ 5 nm) nanoparticles in plasmas
- 2017
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In: Physics of Plasmas. - : American Institute of Physics (AIP). - 1070-664X .- 1089-7674. ; 24:1
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Journal article (peer-reviewed)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.
(author)
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Diagnostics of void expansion during cyclic growth and formation of layered nanoparticle clouds
- 2017
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In: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 121:11
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Journal article (peer-reviewed)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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