The plasma chemistry of an argon/hydrogen expanding thermal arc plasma in interaction with silane injected downstream is analyzed using mass spectrometry. The dissociation mechanism and the consumption of silane are related to the ion and atomic hydrogen fluence emanating from the arc source. It is argued that as a function of hydrogen admixture in the arc, which has a profound decreasing effect on the ion-electron fluence emanating from the arc source, the dissociation mechanism of silane shifts from ion-electron induced dissociation towards atomic hydrogen induced dissociation. The latter case, the hydrogen abstraction of silane, leads to a dominance of the silyl $({\mathrm{SiH}}_{\mathrm{3}})$ radical whereas the ion-electron induced dissociation mechanism leads to ${\mathrm{SiH}}_x$ $\text{(x<3)}$ radicals. In the pure argon case, the consumption of silane is high and approximately two silane molecules are consumed per argon ion-electron pair. It is shown that this is caused by consecutive reactions of radicals ${\mathrm{SiH}}_x$ $\text{(x<3)}$ with silane. Almost independent of the plasma conditions used, approximately one ${\mathrm{H}}_{\mathrm{2}}$ is produced per consumed ${\mathrm{SiH}}_{\mathrm{4}}$ molecule. Disilane production is observed which roughly scales with the remaining silane density. Possible production mechanisms for both observations are discussed.

A supersonically expanding argon cascaded arc plasma, with different amounts of hydrogen added (0, 0.7, and 1.4 vol % ${\mathrm{H}}_2$), was studied using Thomson-Rayleigh scattering and optical emission spectroscopy. With hydrogen added, the electron density profile as a function of the distance from the onset of the expansion shows a large extra ionization loss (compared to the pure argon case), especially after the stationary shock front. This anomalous loss of ionization is attributed to molecular processes, such as associative charge transfer between ${\mathrm{Ar}}^{+}$ and ${\mathrm{H}}_2$, and dissociative recombination of the resulting ${\mathrm{ArH}}^{+}$ molecular ion. Spatially resolved emission spectroscopy shows that in the expansion the radial hydrogen emission profiles are broader than the argon profiles. The addition of hydrogen appears to change the characteristic shock behavior of pure argon. For both the argon and the hydrogen system it is shown that the uppermost levels are in Saha equilibrium with their adjacent continuum. The measurements are in agreement with the view that association of hydrogen atoms at the vessel walls results in a reentry flow of hydrogen molecules in the plasma beam.

Background: Intrinsic motivation plays a unique mediating role in student academic performance. An inquiry-based learning (IBL) physics practical is studied in terms of effects on secondary school students’ intrinsic motivation towards performing science practicals. Results: After performing IBL experiments on ionizing radiation, 38 secondary school physics students were interviewed and expressed their need for support in two main areas: the inquiry process and non-salient tasks, i.e., operating the equipment. The IBL experiments were revised accordingly, providing scaffolding through revised worksheets and videos on the use of the equipment. Subsequently, a quasi-experiment was carried out. One experimental group received both a revised worksheet and a video (N = 88), the other only received the worksheet (N = 67). Students performing the same practical on the basis of a step-by-step instruction sheet were used as a control group (N = 87). Five subscales of the intrinsic motivation inventory were used as a pre- and post-test for all three groups. Results show significant gains in the Interest/Enjoyment as well as Effort/Importance subscales favouring both IBL groups. With an instructional video, all five subscales show a significant increase as compared to the control group. Conclusions: The results point to the advantages of using an IBL approach for practicals, provided appropriate scaffolding is used in terms of equipment operation and inquiry process.

This study investigates the way students experience synchronous online and offline meetings in university education, using a qualitative approach. The context is a course in teacher training that was forced to go fully online during the Covid-19 pandemic while the course was almost halfway to completion. After completion of the course, a semi-structured interview on the experiences during the online and offline synchronous meetings was conducted with six randomly selected students out of a total of 24. The interview was transcribed, coded, and second coding was performed. The results reveal that students generally prefer offline meetings because of higher levels of all types of student interactions (student-student, student-content, and student-teacher), and the higher level of relatedness. However, students do appreciate the possibility to perform small group work outside of class in an online environment. The results support the application of blended learning. Implications are discussed.

Four ways to measure the electron density in low-temperature plasmas are presented: Thomson scattering, Langmuir probe, optical-emission spectroscopy, and continuum-radiation analysis. The results of the four methods are compared to each other and discussed. For the electron-density range of ${10}^{19}$–${10}^{21}$ ${\mathrm{m}}^{\mathrm{-}3}$, Thomson scattering proved to give the most accurate results (within a few percent); the Langmuir-probe measurements also proved acceptable (25%). A collisional-radiative-model fit through excited-level populations and continuum analysis yields results in good agreement with Thomson scattering data, although with larger margins of error (around 40%). A simple Saha fit proved to be inadequate.