| 1. |
- Gunnarsson, Rickard, et al.
(författare)
-
The influence of pressure and gas flow on size and morphology of titanium oxide nanoparticles synthesized by hollow cathode sputtering
- 2016
-
Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 120:4
-
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.
|
|
| 2. |
- Hasan, Mohammad I., et al.
(författare)
-
Modeling the extraction of sputtered metal from high power impulse hollow cathode discharges
- 2013
-
Ingår i: Plasma sources science & technology. - : IOP Publishing. - 0963-0252 .- 1361-6595. ; 22:3, s. 035006-
-
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.
|
|
| 3. |
- Kalered, Emil, et al.
(författare)
-
On the work function and the charging of small (r ≤ 5 nm) nanoparticles in plasmas
- 2017
-
Ingår i: Physics of Plasmas. - : American Institute of Physics (AIP). - 1070-664X .- 1089-7674. ; 24:1
-
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.
|
|
| 4. |
- Pilch, Iris, et al.
(författare)
-
Fast growth of nanoparticles in a hollow cathode plasma through orbit motion limited ion collection
- 2013
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 103:19, s. 193108-
-
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.
|
|
| 5. |
- Pilch, Iris, et al.
(författare)
-
Nanoparticle growth by collection of ions : orbital motion limited theory and collision-enhanced collection
- 2016
-
Ingår i: Journal of Physics D. - : Institute of Physics Publishing (IOPP). - 0022-3727 .- 1361-6463. ; 49:39
-
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.
|
|
| 6. |
- Pilch, Iris, et al.
(författare)
-
Size-controlled growth of nanoparticles in a highly ionized pulsed plasma
- 2013
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 102:3, s. 033108-
-
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.
|
|
| 7. |
- Pilch, Iris, et al.
(författare)
-
Synthesis of copper nanoparticles by a high power pulse hollow cathode
- 2012
-
Ingår i: Technical Proceedings of the 2012 NSTI Nanotechnology Conference and Expo, NSTI-Nanotech 2012. - 9781466562745 - 9781466562875 ; , s. 371-373
-
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.
|
|
| 8. |
- Tal, Alexey A., et al.
(författare)
-
Molecular dynamics simulation of the growth of Cu nanoclusters from Cu ions in a plasma
- 2014
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 90:16, s. 165421-
-
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.
|
|
