Trygve Mongstad

Transparent yttrium hydride thin films prepared by reactive sputtering

Abstract Metal hydrides have earlier been suggested for utilization in solar cells. With this as a motivation we have prepared thin films of yttrium hydride by reactive magnetron sputter deposition. The resulting films are metallic for low partial pressure of hydrogen during the deposition, and black or yellow-transparent for higher partial pressure of hydrogen. Both metallic and semiconducting transparent YH x films have been prepared directly in situ without the need of capping layers and post-deposition hydrogenation. Optically the films are similar to what is found for YH x films prepared by other techniques, but the crystal structure of the transparent films differ from the well-known YH 3− η phase, as they have an fcc lattice instead of hcp.

Surface oxide on thin films of yttrium hydride studied by neutron reflectometry

The applicability of standard methods for compositional analysis is limited for H-containing films. Neutron reflectometry is a powerful, non-destructive method that is especially suitable for these systems due to the large negative scattering length of H. In this work, we demonstrate how neutron reflectometry can be used to investigate thin films of yttrium hydride. Neutron reflectometry gives a strong contrast between the film and the surface oxide layer, enabling us to estimate the oxide thickness and oxygen penetration depths. A surface oxide layer of 5–10 nm thickness was found for unprotected yttrium hydride films.

Engineering of the band gap and optical properties of thin films of yttrium hydride

Thin films of oxygen-containing yttrium hydride show photochromic effect at room temperature. In this work, we have studied structural and optical properties of the films deposited at different deposition pressures, discovering the possibility of engineering the optical band gap by variation of the oxygen content. In sum, the transparency of the films and the wavelength range of photons triggering the photochromic effect can be controlled by variation of the deposition pressure.

Production of Silicon from SiH4 in a Fluidized Bed, Operation and Results

Abstract: For an installed silicon-based solar cell panel, about 40% of the energy needed for fabrication is consumed for production of the silicon feedstock. Reducing the energy consumption in this step is therefore crucial in order to minimize the energy payback time and cost of the technology. The most promising alternative to the conventional methods is to use fluidized bed reactors. In this article, we report the results from a novel reactor layout with a selectively cooled distribution arrangement. Important aspects of fludized bed monitoring and operation are described. Two different operation regimes are stated yielding hence porous and dense growth. Further, the method of encapsulating fines by means of more dense depositions is verified, and the nature of the scavenged material is characterized. Also, two different types of fines formation are identified and accounted for.

MgyNi1−y(Hx) thin films deposited by magnetron co-sputtering

In this work we have synthesized thin films of MgyNi1-y(H-x) metal and metal hydride with y between 0 and 1. The films are deposited by magnetron co-sputtering of metallic targets of Mg and Ni. Met ...

Annealing-induced structural rearrangement and optical band gap change in Mg-Ni-H thin films

It is well known that optical properties of Mg-Ni-H films can be tuned by hydrogen uptake from Mg-Ni-H and upload into Mg-Ni systems. In this work weshow that modulation of optical properties of Mg-Ni-H can take place as a result of thermal processing in air as well. When reactively sputter deposited semiconducting Mg-Ni-H films are annealed at temperatures of 200 °C-300 °C inair, gradual band gap change from 1.6to 2.04 eV occurs followed by change in optical appearance, from brown, toorange and, subsequently, to yellow. We investigate this phenomenon using optical and structural characterization tools, and link the changes to an atomic rearrangement and a structure reordering of the NiH44-complex. The films are x-ray amorphous up to 280 °C, where above this temperature an increase in crystallite size and establishing of long-range order lead to a formation of the cubic crystalline phase of Mg2NiH4. Also, the results suggest that even though annealing was conducted in air, no oxidation orother changes in chemical composition of the bulk of the film occurred. Therefore, the band gap of this semiconductor can be tuned permanently by heat treatment, in the range from 1.6 to2 eV.

Substoichiometric Silicon Nitride – An Anode Material for Li-ion Batteries Promising High Stability and High Capacity

Silicon is often regarded as a likely candidate to replace graphite as the main active anode material in next-generation lithium ion batteries; however, a number of problems impacting its cycle stability have limited its commercial relevance. One approach to solving these issues involves the use of convertible silicon sub-oxides. In this work we have investigated amorphous silicon sub-nitride as an alternative convertible silicon compound by comparing the electrochemical performance of a-SiNx thin films with compositions ranging from pure Si to SiN0.89. We have found that increasing the nitrogen content gradually reduces the reversible capacity of the material, but also drastically increases its cycling stability, e.g. 40 nm a-SiN0.79 thin films exhibited a stable capacity of more than 1,500 mAh/g for 2,000 cycles. Consequently, by controlling the nitrogen content, this material has the exceptional ability to be tuned to satisfy a large range of different requirements for capacity and stability.