Hydrogen interaction with tungsten is becoming a highly relevant topic since tungsten was recognized as the most promising candidate for the first wall of future fusion reactors. Prediction of hydrogen isotopes migration and their abundance in the reactor after plasma exposure is uncertain. Namely, a part of gaseous tritium is not interacted completely with deuterium and is also not completely removed in the gas phase after the plasma shots. A part of it may be retained everywhere inside reactor surface. A great role represents the structural disorder that is formed on the W surface or by W and Be/W deposits. Vacancy sites are theoretically predicted to trap multiple H atoms exothermically, but their density and their potential influence on permeability has not been experimentally investigated yet. In our work, long-term hydrogen outgassing and permeation studies of structurally highly disordered tungsten films, deposited on 40 mm diameter highly permeable Eurofer substrates, using the Pulsed Laser Deposition technique have been realized. Permeability of W films having different thicknesses (1 and 10 micrometers) was initially extremely low, and was gradually increasing over a several-day campaign. The final values at 400 °C, lying between P = 1.46x10-15 mol H2/(m s Pa0.5) and P = 4.8x10-15 mol H2/(m s Pa0.5), were substantially lower than those known for well ordered films. Surprisingly, the 10 micrometer thick W film initially contained a very high amount of hydrogen, ~ 0.1 H/W, which was gradually releasing during the twenty-day campaign.
COBISS.SI-ID: 25908263
We present experimental data and numerical simulations in order to show that the mechanism of spinodal dewetting is active during ion beam irradiation of thin solid films. The expected scaling law for the characteristic wavelengths versus the initial film thickness is modified by the presence of sputtering. The conclusion is fully supported by model simulation which shows a square law dependence for null sputtering yield and a bimodal trend when sputtering is included. This result is in contrast to earlier studies and opens the possibility to control and use ion induced dewetting for the fabrication of functional nanostructures.
COBISS.SI-ID: 914090
Amorphous silicon nitride films, 500-nm and 700-nm thick, were deposited on Eurofer substrates by applying reactive radio-frequency magnetron sputtering from pure Si targets in an argon/nitrogen atmosphere. The hydrogen permeation through such double-layered, 40-mm-diameter membranes at 400 °C and 1 bar upstream pressure involved the use of a conventional technique with enhanced sensitivity. The extremely high barrier efficiency for these films with respect to hydrogen, expressed as a permeation-reduction factor in excess of 2000, was only achieved with films containing 6–7 atomic percent of hydrogen. The achieved permeation-reduction factor at 400 °C corresponds to the permeability of silicon nitride, which is as low as P = 1×10-17 mol H2/m s Pa0.5. The hydrogen concentration was determined with an ERDA, which indicated that this high concentration represents only the strongly bound hydrogen that is not mobile at this low temperature. A silicon nitride film with a low hydrogen content is a far less efficient barrier, which supports the role of the strongly bound hydrogen
COBISS.SI-ID: 25978663
Gas-discharge tube (GDT) surge protectors are known for many decades as passive units used in low-voltage telecom networks for protection of electrical components from transient over-voltages (discharging) such as lightning. A cold field electron emitter source is used as the trigger for the gas discharge. We present experimental results which show that stable cold field electron emission current in the high vacuum range originating from the nano-structured edge of the graphite layer is well correlated to the stable breakdown voltage of the GDT surge protector filled with a mixture of clean gases.
COBISS.SI-ID: 25752615
Due to outgassing from the walls of vacuum calibration chambers, the generation of the calibration pressure in primary vacuum calibration systems operating below 10[sup]{-6} Pa becomes un-accurate. Austenitic stainless steel (SS) is the most common construction material for ultrahigh vacuum (UHV) and extremely high vacuum (XHV) chambers. Hydrogen is the predominant residual gasat very low pressures in SS vacuum systems, i.e., in the UHV and XHV range. Therefore, the reduction of the hydrogen outgassing rate is the most challenging problem in achieving pressures in those ranges. In this paper, a vacuum chamber with a wall thickness of 2.62 mm and made from AISI type 304 L SS was examined with the aim of mitigating the outgassing rate. The heat treatments were carried out at 250 °C for 380 h and at 350 °C for 140 h. After baking at 250 °C for 380 h (corresponding to a dimensionless time Fo = 3.09), an outgassing rate q = 2.86 * 10[sup]{-13} mbar L s[sup]{-1} cm[sup]{-2} was achieved at room temperature (RT). This RT outgassing rate was further reduced to q = 5.7 * 10[sup]{-14} mbar L s[sup]{-1} cm[sup]{-2} after baking for another 140 h at 350 °C (Fo = 8.66, resulting in a total dimensionless time SFo = 11.75).
COBISS.SI-ID: 905642