Formation mechanisms of dust particles due to interaction between carbon walls and plasmas in fusion devices have attracted considerable attention, because they pose two potential problems: they can contain a large amount of tritium and... more
Formation mechanisms of dust particles due to interaction between carbon walls and plasmas in fusion devices have attracted considerable attention, because they pose two potential problems: they can contain a large amount of tritium and their existence in fusion devices may lead to deterioration of plasma confinement. To obtain information on formation mechanisms of dust particles of nm in size in fusion devices, we have generated deuterium helicon discharge plasmas which simulate divertor plasmas in fusion devices and then we have collected and analyzed dust particles produced due to interaction between graphite and the plasmas. Dust particles are made of carbon and can be classified into three kinds: small dust particles below 1 mum in size, large flakes above 1 mum in size, and agglomerates which consist of primary particles of 10 nm. These three kinds suggest three formation mechanisms, that is, CVD growth, carbon films peeled from walls, and agglomeration [1]. There exist a lar...
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A plasma enhanced atomic layer deposition process for synthesizing titanium dioxide (TiO2) films, which allows the film properties to be modified by tuning the ion energies of the discharges, was performed. The films were deposited via... more
A plasma enhanced atomic layer deposition process for synthesizing titanium dioxide (TiO2) films, which allows the film properties to be modified by tuning the ion energies of the discharges, was performed. The films were deposited via the oxidation of titanium tetrachloride in a typical capacitively coupled radio frequency (CCRF) discharge in argon/oxygen mixtures at a low temperature of 100 °C, resulting in all the films synthesized being amorphous. The energy distributions of ions hitting on the lower electrode (wafer surface) in the CCRF discharges were varied by tuning the impedance of the lower electrode, aimed at controlling the film properties. The wet etching rate of TiO2 films shows a clear correlation with the mean ion energy, 〈ei〉, i.e., a higher 〈ei〉 realizes a higher value of the wet etching rate. The variation of the film properties is explained by a change in the balance between the ion bombardment and the oxidation; the former is greatly affected by 〈ei〉, whereas the latter is mainly dete...
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Abstract A plasma enhanced atomic layer deposition (PEALD) process combined with ion energy control of capacitively couples radio frequency (CCRF) discharges in Ar/H 2 gas mixture for fabricating Ti films was performed, and the impact of... more
Abstract A plasma enhanced atomic layer deposition (PEALD) process combined with ion energy control of capacitively couples radio frequency (CCRF) discharges in Ar/H 2 gas mixture for fabricating Ti films was performed, and the impact of the ion energies on the film characteristics was evaluated. Titanium tetrachloride (TiCl 4 ) was adsorbed on a silicon wafer and Ti films were synthesized via the reduction of Cl atoms from TiCl 4 via the CCRF discharges. The growth per cycle of the films clearly increases with increasing the mean ion energy, ⟨ e i ⟩, suggesting that increase in the ion energies of the discharges promotes the reduction process of Cl atoms. Also, the film stress shows a clear dependence on ⟨ e i ⟩; it changes towards compressive with increasing ⟨ e i ⟩. On the other hand, the resistivity and the film density are almost constant independent of ⟨ e i ⟩, which indicates that the reduction reaction is saturated through the sequential PEALD cycles independent of ⟨ e i ⟩. In this paper, a simulation model based on one-dimensional (1D) Particle-in-Cell/Monte Carlo Collision (PIC/MCC) has been utilized for CCRF discharges in Ar/H 2 gas mixture.
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Abstract Ion energies in capacitively coupled radio frequency (RF) discharges were controlled by tuning the impedance at the upper and lower electrodes as well as their RF power ratio, and the technique was applied to plasma enhanced... more
Abstract Ion energies in capacitively coupled radio frequency (RF) discharges were controlled by tuning the impedance at the upper and lower electrodes as well as their RF power ratio, and the technique was applied to plasma enhanced atomic layer deposition (PEALD) process for synthesizing titanium dioxide films. The film characteristics show a clear correlation with the mean ion energy, ⟨ei⟩, which is explained by the formation of fine pores in the films due to the bombardments of high energetic ions during PEALD process in case of a high ⟨ei⟩ condition. The method to control ⟨ei⟩ by changing the RF power ratio in addition to tuning the impedance of the electrodes realizes a wider range of change in ⟨ei⟩ and thus the film characteristics, compared with the method without changing the RF power ratio. Although the films deposited on amorphous carbon patterns show a good step-coverage even for a low ⟨ei⟩, the etching (deformation) of the patterns becomes pronounced with increasing ⟨ei⟩. In this paper, a simple numerical approach using the ion incident depth to express the ion etching is introduced. Based on this approach, the contribution of ions and radicals to the etching of the patterns is discussed.
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This paper demonstrates thermal atomic layer deposition (ALD) combined with periodic oxidation for synthesizing titanium oxynitride (TiON) thin films. The process used a typical ALD reactor for the synthesis of titanium nitride (TiN)... more
This paper demonstrates thermal atomic layer deposition (ALD) combined with periodic oxidation for synthesizing titanium oxynitride (TiON) thin films. The process used a typical ALD reactor for the synthesis of titanium nitride (TiN) films wherein oxygen was supplied periodically between the ALD-TiN cycles. The great advantage of the process proposed here was that it allowed the TiN films to be oxidized efficiently. Also, a uniform depth profile of the oxygen concentration in the films could be obtained by tuning the oxidation conditions, allowing the process to produce a wide variety of TiON films. The resistivity measurement is a convenient method to confirm the reproducibility of metal film fabrication but may not be applicable for TiON films depending upon the oxidation condition because the films can easily turn into insulators when subjected to periodic oxidation. Therefore, an alternative reproducibility confirmation method was required. In this study, spectroscopic ellipsometry was applied to moni...
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Using the combination of a fundamental frequency and its second harmonic (e.g. 13.56 MHz + 27.12 MHz), the symmetry of capacitive discharges is controlled by the phase between the two frequencies. Here, this concept is studied in an... more
Using the combination of a fundamental frequency and its second harmonic (e.g. 13.56 MHz + 27.12 MHz), the symmetry of capacitive discharges is controlled by the phase between the two frequencies. Here, this concept is studied in an electronegative oxygen discharge by an experiment, a PIC/MCC simulation, and an analytical model. The results show that the generation of a dc self-bias is controlled via the phase. Meanwhile, the dissipated power and the total densities are kept constant. At low pressure, the self-excitation of plasma series resonance oscillations occurring due to the electrical asymmetry leads to resonance structures inside the plasma bulk. Funding: German Federal Ministry for the Environment (0325210B), Alexander von Humboldt Foundation, RUB Research Department Plasma, National Natural Science Foundation of China (Grant No. 10635010), and Research Fund for Doctoral Program of Higher Education of China (Grant No. 20090041110026).
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To obtain information on formation mechanisms of dust particles of nm in size in fusion devices, in-situ collection of dust particles produced due to interaction between graphite target as plasma facing materials and the plasmas was... more
To obtain information on formation mechanisms of dust particles of nm in size in fusion devices, in-situ collection of dust particles produced due to interaction between graphite target as plasma facing materials and the plasmas was carried out in a helicon discharge chamber and in Large Helical Device (LHD). Dust particles produced in the helicon discharges are made of carbon and can be classified into three kinds: small spherical dust particles below 1 �m in size, large flakes above 1 �m in size, and agglomerates which consist of primary particles of 10 nm. These features are quite close to those of dust particles collected in LHD, suggesting that the helicon plasma can simulate dust formation processes in divertor region in LHD. Three kinds of dust particles suggest three formation mechanisms: CVD growth of carbon radicals, carbon films peeled from walls, and agglomeration.
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ABSTRACT
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ABSTRACT We have developed a novel method to control the dust particle transport in capacitively coupled plasmas via the electrical asymmetry effect (EAE) [1]. At low pressures the EAE allows controlling the spatial potential profile and... more
ABSTRACT We have developed a novel method to control the dust particle transport in capacitively coupled plasmas via the electrical asymmetry effect (EAE) [1]. At low pressures the EAE allows controlling the spatial potential profile and the ion density distribution by adjusting the phase angle between a fundamental frequency and its second harmonic, resulting in control of forces exerted on dust particles such as electrostatic and ion drag forces. We report the experimental results of this method using SiO2 particles of 1.5 μm in size, which are inserted into an argon discharge. Initially dust particles tend to be confined at the sheath edge near the bottom electrode, and the change of their equilibrium position with plasma due to the adiabatic phase shift can be well understood by the electric field profile obtained from a simple analytical model. By applying the abrupt change of phase angle from 90 to 0 dust particles are transported between both sheaths through the plasma bulk [1]. Based on the model of this transport [1] the potential profile can be obtained by experimental results.[4pt] [1] Iwashita S et al., Plasma Sources Sci. Technol. 21 (2012) 032001.
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Materials Science and APS
We have proposed a novel nano-system construction method using plasmas [1-3]. We have succeeded in realizing size control of nano-blocks and their rapid transport towards a substrate by using pulse discharges with amplitude modulation... more
We have proposed a novel nano-system construction method using plasmas [1-3]. We have succeeded in realizing size control of nano-blocks and their rapid transport towards a substrate by using pulse discharges with amplitude modulation (AM) of the discharge voltage [1- 3]. We are developing a method for their three dimensional transport using a capacitively coupled RF discharge reactor having a grounded electrode with needles. During the period of AM nano-blocks are transported from their generated region rear the powered electrode to the top of the needle. Such three dimensional transport needs an asymmetric electric potential profile, in other words, a large voltage drop across the sheath near the powered electrode. We will report the experimental results and discuss the mechanism of the three dimensional transport.[4pt] [1] S. Nunomura, et al. J. Appl. Phys., 99, 083302 (2006).[0pt] [2] K. Koga, et al. J. Phys. D, 40, 2267 (2007).[0pt] [3] M. Shiratani, et al. Faraday Discuss., 13...
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... Authors: Shinya Iwashita (Ruhr-University Bochum). Giichiro Uchida (Kyushu University). Julian Schulze (Ruhr-University Bochum). Edmund Schuengel (Ruhr-University Bochum). PeterHartmann (Hungarian Academy of Science). Masaharu... more
... Authors: Shinya Iwashita (Ruhr-University Bochum). Giichiro Uchida (Kyushu University). Julian Schulze (Ruhr-University Bochum). Edmund Schuengel (Ruhr-University Bochum). PeterHartmann (Hungarian Academy of Science). Masaharu Shiratani (Kyushu University). ...
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We have proposed a novel nano-system construction method, which consists of production of nano-blocks and radicals (adhesives) in reactive plasmas, their transport towards a substrate, arrangement of nano-blocks on the substrate [1-3].... more
We have proposed a novel nano-system construction method, which consists of production of nano-blocks and radicals (adhesives) in reactive plasmas, their transport towards a substrate, arrangement of nano-blocks on the substrate [1-3]. For the method, size of nano-blocks is controlled by the duration of pulse RF discharges [1] and their rapid transport towards a substrate is realized using pulse RF discharges with amplitude modulation (AM) of the discharge voltage [2, 3]. During the period of AM nano-blocks can be transported from their generation region near the powered electrode to a substrate at a velocity more than 67 cm/s, which is at least 6 times that after turning off the unmodulated discharges. Such rapid transport needs an asymmetric potential profile, in other words, a large voltage drop across the sheath near the powered electrode. We will report the experimental results and discuss the mechanism of the rapid transport in this presentation. [1] S. Nunomura, et al. J. App...
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ABSTRACT We propose the concept of 'nano-factory in plasma' which is a miniature version of a macroscopic conventional factory. A nano-factory in plasma produces nanoblocks and radicals (adhesives) in reactive plasmas,... more
ABSTRACT We propose the concept of 'nano-factory in plasma' which is a miniature version of a macroscopic conventional factory. A nano-factory in plasma produces nanoblocks and radicals (adhesives) in reactive plasmas, transports nanoblocks towards a substrate and arranges them on the substrate. We describe several key control methods for a nano-factory in plasma: size and structure control of nanoparticles, control of their agglomeration, transport and sticking, and then explain the combination of several types of control. Finally we point out remaining important issues in nano-factories in plasma.
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Transport of nano-particles in rf discharges without and with an amplitude modulation (AM) of the discharge voltage has been examined using a two-dimensional laser-light-scattering method. During the discharging period, nano-particles are... more
Transport of nano-particles in rf discharges without and with an amplitude modulation (AM) of the discharge voltage has been examined using a two-dimensional laser-light-scattering method. During the discharging period, nano-particles are mainly generated in the plasma/sheath boundary region near the powered electrode. They move away from their generation region towards the upper grounded electrode after turning off discharges due to
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Hydrogenated amorphous silicon (a-Si:H) films of high stability against light exposure have been deposited by using a newly developed multi-hollow plasma chemical vapor deposition (CVD) method. Films deposited in the upstream region in... more
Hydrogenated amorphous silicon (a-Si:H) films of high stability against light exposure have been deposited by using a newly developed multi-hollow plasma chemical vapor deposition (CVD) method. Films deposited in the upstream region in the multi-hollow plasma CVD reactor are a-Si:H films without incorporating a-Si:H nano-particles (clusters), while those in the downstream region are a-Si:H films with incorporating clusters. A-Si:H films
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We have observed transport of nano-particles having, on average, a fractional elementary charge in single pulse and double pulse capacitively-coupled rf discharges both without and with an Amplitude Modulation (AM) of the discharge... more
We have observed transport of nano-particles having, on average, a fractional elementary charge in single pulse and double pulse capacitively-coupled rf discharges both without and with an Amplitude Modulation (AM) of the discharge voltage, using a two-dimensional laser-light scattering method. Rapid transport of nano-particles towards the grounded electrode is realized using rf discharges with AM. Two important parameters for the rapid transport of nano-particles are the discharge voltage and the period of AM. An important key of the rapid transport is fast redistribution of ion current over the whole discharge region; that is, fast change of spatial distribution of forces exerted on nano-particles. The longer period of the modulation is needed for rapid transport for the larger nano-particles. The higher discharge voltage of the modulation is needed for rapid transport of nano-particles having a smaller mean charge. Local perturbation of electric potential using a probe does not bring about global rapid transport of nano-particles, whereas it leads to their local transport near the probe.