Thin films of yttrium oxyhydride (YHO) exhibit reversible light-induced resistivity and transmission changes at room temperature and ambient pressure. Establishing how the physical properties of YHO films are influenced by their chemical composition is an important challenge that can open the way toward practical applications. In this work, we have prepared YHO thin films with lateral gradient of oxygen and hydrogen concentrations by reactive magnetron sputtering deposition. This enables us to efficiently investigate the effect of changes in the composition of the films on their structural, electrical and optical properties. The as-deposited YHO film appeared to be black opaque and non-photochromic in the oxygen-poor part of the film, and it changed to yellow transparent and photochromic in the oxygen-rich part of the film. We report a gradual increase in the lattice constant with increasing oxygen content of the film, as revealed by grazing incidence X-ray diffraction measurements. Electrical resistivity measurements unveiled that persistent photoconductivity was strongly enhanced as the oxygen content decreased in the photochromic yellow transparent film. Analysis of the kinetics of the photochromic reaction indicated that the bleaching speed increased with increasing oxygen content in the photodarkened film. Unusual large persistent photochromism was discovered in the same yellow YHO film with lowest oxygen content which lasted for almost 10 days. Moreover, it was shown that the optical constants can be tuned by varying the oxygen content in the photochromic film as well.

In this work, the composition of oxygen-containing yttrium hydride (YHO) thin films was investigated. The films were prepared by reactive sputter deposition, and were found for have oxygen contents on the order of several tens of per cents. We present depth-resolved atomic composition profiles of photochromic YHO films to study the connection between composition, photochromic properties and growth parameters. Two films, deposited at different pressures, were prepared and characterized using ion beam analysis techniques, i.e. Rutherford backscattering spectrometry and elastic recoil detection analysis. We found that an increase of deposition pressure results in larger [O]/[Y] ratios, while the ratio [H]/[Y] becomes reduced. We also report a gradual oxidation of the films exposed to air as well as hydrogen release under ion bombardment.

There is a deficit of ways to detect higher order silane isomers during silane pyrolysis. Thus, a novel instrument utilizing gas chromatography-mass spectrometry (GC-MS) for detection of higher order silanes has been developed. The instrument enables us to separate higher order silane species using gas chromatography before they are introduced to the mass spectrometer, thereby obtaining spectra of separate isomers, rather than overlaid spectra. In this contribution we describe the details of the GC-MS system. We compare our GC-separated mass spectra of mono-, di- and trisilane to mass spectra of these species available in the literature. Further, we present mass spectra of the tetrasilane isomers n-tetrasilane (n-Si4H10), silyltrisilane (i-Si4H10) and cyclotetrasilane (cyclo-Si4H8) and of the pentasilane isomers n-pentasilane (n-Si5H12), silyltetrasilane (i-Si5H12) disilyltrisilane (neo-Si5H12) and cyclopentasilane (cyclo-Si5H10). Six of these mass spectra are previously unpublished. Based on the fragmentation pattern in the tetra- and pentasilane mass spectra, we are able to acquire mass spectra of silanes with up to eight silicon atoms. Finally, we apply the novel detection technique to a silane pyrolysis reactor to track the outlet concentration of higher order silanes as function of reactor temperature. We believe that the detection technique that we present here may open the door for validation of monosilane pyrolysis models, and thus constitute a roadmap for future research in this field. (C) 2018 The Authors. Published by Elsevier B.V.

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.

Mg-Ni-H thin films were deposited by reactive magnetron sputtering. As-deposited samples were Mg-rich and annealed in air by two steps at T=220 and 290°C in order to increase crystallinity. A reversible, thermochromic effect was detected when the crystalline yellow colour sample underwent a colour transition and changed its colour from yellow to red. The change in transmission spectra of the prepared thin films in visible range of spectra was induced by in situ heating setup. The continuous shifts of the transmission spectra at T=200°C towards lower band gap was observed. Additionally, a photochromic effect was detected and confirmed by exposing the sample to visible light, as grey-coloured area appeared on the sample.

Processes taking place during hydrogen desorption from MgH2 thin films were investigated in as-prepared samples and samples modified by argon ion irradiation. Irradiation was used to produce well-defined defects with depth distribution. It was shown that the size, shape, and concentration of Mg nuclei formed during hydrogen desorption from MgH2 thin films depend on the characteristics and distribution of the induced defects. In as-prepared samples the shape of Mg nuclei is spherical, while in irradiated samples, it is highly irregular. Variations in sample colour were observed during hydrogen desorption and before the creation of Mg nuclei. DFT calculations showed that the observed variations in the optical properties of samples can be explained by changes in MgH2 electronic structure –the appearance of an H-vacancy band within the MgH2 energy gap.

Photochromic oxygen-containing yttrium hydride (YHO) thin films with switchable optical properties have recently emerged as a promising material for the utilization in smart windows and sensor applications. In the present study, we have prepared YHO thin films with a lateral gradient of oxygen and hydrogen concentrations, which allows us to systematically investigate the effect of changes in chemical composition on their optical properties. We show that when the average lateral oxygen content exceeded a threshold level at a certain location in the as-deposited film, its appearance was abruptly changed from black opaque to yellow transparent, in which only yellow YHO exhibited photochromism. Moreover, we show that a small region (typically ∼5–10 mm lateral size) in the black opaque part of the as-deposited film, located adjacent to the yellow transparent part of the film, was observed to transform permanently to yellow transparent upon exposure to oxygen in air in the dark for several weeks. The black to yellow color transformation was caused by an increase in the oxygen concentration, originating from the oxidation process. Optical characterization revealed pronounced photochromic response in the transformed region as compared to the rest of the yellow film. This finding demonstrates that the switchable optical properties can be tailored by changing the chemical composition of YHO 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 we show 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 degrees C-300 degrees C in air, gradual band gap change from 1.6 to 2.04 eV occurs followed by change in optical appearance, from brown, to orange 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 [NiH4]4-complex. The films are x-ray amorphous up to 280 degrees 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 or other 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 to 2 eV.

Thermal decomposition experiments with monosilane diluted in hydrogen have been conducted in a free-space reactor with an extendable reaction zone, allowing for easy variation of residence time. Reactor effluent was analyzed by gas-chromatography combined with mass-spectrometry (GC-MS). The applied analysis technique enables detection of silanes with up nine silicon atoms, as well as absolute quantification of the concentrations of mono-, di-, and trisilane. For all the detected silanes, our gas analyses show a peak in reactor outlet concentration as function of temperature whose position and shape depend on the number of silicon atoms (nSi) contained in the silane species. The peak width decreases and the peak position shifts to higher temperatures with increasing nSi. At increased residence time, the concentration peak shifts to lower temperatures and the SiH4 consumption rate increases. This is consistent with the expected behavior for a system described by Arrhenius kinetics. The maximum outlet concentrations of all the measured silanes decrease with increasing residence time. However, the dependence of silane concentrations on temperature and residence time is not trivial: At a fixed temperature the measured outlet concentrations will increase with increasing residence time in some temperature regions and decrease with residence time in other temperature regions. By mapping outlet concentrations as function of temperature and residence time we attempt to decouple the effect of these two parameters and to untangle their effect from that of reactor geometry and operation.

Today's most frequently used production path for polysilicon and solar grade silicon (SG-Si) is based on thermal decomposition of trichlorosilane (SiHCl3) in a Siemens-type reactor. Due to the batch-wise mode of its operation and its requirement for heating and cooling, the Siemens technology is an energy demanding procedure. As an alternative to this process, SG-Si can be produced through the thermal decomposition of monosilane (SiH4), for example in a fluidized bed reactor or a centrifugal chemical vapour deposition reactor. In order to avoid production of fine particulates and related clogging, this process requires knowledge of the nucleation properties of silane. In this work, the critical concentration for particle nucleation from SiH4, diluted in H-2 has been determined for temperatures in the range 400 - 700 degrees C. For this purpose, we used a free space reactor and an optical particle detector of own design for in-situ monitoring of the reactor exhaust. In a plot of logarithmic critical nucleation concentration against inverse temperature, an almost linear relation was found for temperatures below approximately 500 degrees C and above approximately 600 degrees C. Between 500 and 600 degrees C, a less temperature dependent behavior is observed. Apparent activation energies are estimated to be 32 kcal/mol for temperatures below 500 degrees C, 8 kcal/mol for temperatures between 500 and 600 degrees C and 23 kcal/mol for temperatures above 600 degrees C. The first and last of these values agree well with existing literature. The low temperature dependence in the range 500 degrees C to 600 degrees C, however represents a deviation from earlier studies. Investigations of reactor exhaust by GC-MS (gas chromatography- mass spectrometry), allowing detection of the concentrations of higher order silanes (disilane (Si2H6), trisilane (Si3H8), etc) as function of reactor temperature, suggest that the low temperature dependence of the nucleation concentration for some conditions is related to an increase of the concentration of Si2H6 and Si3H8 at the same temperature range. (C) 2016 The Authors. Published by Elsevier Ltd.

SUMMARY Using an industry-relevant method of production we have demonstrated production of doped silicon nanoparticles for Li-ion batteries. The particles have been characterized and tested in Li-ion battery half-cells for demonstration of the performance as Li ion storage material in the anode. In this presentation we will show the results regarding the characterization of the particles as well as the performance results of the material in Li-ion half cells. BACKGROUND The use of silicon as part of the anode in Li-ion batteries enhances the potential storage capacity greatly. While the graphite anode used in standard Li-ion batteries has a theoretical capacity of 372 mAh/g, the theoretical capacity for Si is 3,572 mAh/g [1]. However, to be able to absorb the sufficient amount of Li ions reversibly, the silicon material needs to be nanostructured [2]. EXPERIMENTAL IFE has earlier demonstrated production of silicon particles prepared using a silane-based free-space reactor, which allows control of particle size distribution and crystallinity and a high production capacity [3]. In this work, the setup was modified to allow for introduction of phosphine gas in the production process. The intention was to introduce phosphorous dopant atoms to modify the electrical conductivity of the silicon material. The current particles were produced with a silane flow rate of 5 slm, and 5 slm of 3% phosphine diluted in He. Thus, the P concentration in the process gases was 3% with respect to Si. The production rate at 100% yield would be about 400 g/h, while the product recovered from the process typically was between 100 and 200 g/h. The processing temperature was varied from 475 °C to 600 °C to produce particles with different properties. All electrochemical tests were performed in a crimped 2032 coin cell with lithium metal used as a counter electrode, with a polymer separator (Celgard 3401) and 1 M LiPF6 in 1:1 EC/DMC electrolyte (LP30, BASF). For some experiments, 10 wt% fluoroethylene carbonate (FEC) was used as electrolyte additive. The cells were cycled at 25 °C between 0.05 and 1.0 V with a constant C-rate of C/10 (after initial 3 cycles at C/20) using an Arbin Battery cycler (Arbin Instruments). RESULTS AND CONCLUSIONS The phosphorus content of the particles was by inductively coupled plasma mass spectrometry (ICP-MS) and energy-dispersive x-ray spectroscopy (EDS) measured to be in the range of 1.7-1.8% with respect to silicon. Thus, it seems that the utilization of the phosphine is not complete, or phosphorous binds to materials which are not recovered from the production process. The particle size distribution was centered around 600 nm as measured by laser scattering in a Malvern Mastersizer 2000. SEM and TEM revealed that the particles consisted of aggregates of spherical silicon particles with a primary particle size of 50-400 nm. X-ray diffraction showed that we could produce amorphous or crystalline particles depending on the temperature of the process. Cycling of the particles in lithium battery half cells showed a life time of about 300 cycles for doped and undoped particles. Some measurements indicate a better conductivity of the doped material but the results were not conclusive. The cells were cycled with a limited capacity regime where the capacity was set to 1000 mAh/g(Si) and thus the end-voltage could vary. The most pronounced difference in the cycling performance between doped and undoped silicon particles was a shift in the increase in end voltage for the doped particles: While end-voltage increased from 0.4 V to 0.6 V over the first 25 cycles, this development is stretched out over the first 50 cycles or more for doped particles. See the attached figure for further details. References [1] D. Larcher, S. Beattie, M. Morcrette, K. Edström, J.-C. Jumas, and J.-M. Tarascon, “Recent findings and prospects in the field of pure metals as negative electrodes for Li-ion batteries,” J. Mater. Chem., vol. 17, no. 36, p. 3759, 2007. [2] H. Kim, M. Seo, M. H. Park, and J. Cho, “A critical size of silicon nano-anodes for lithium rechargeable batteries,” Angew. Chemie - Int. Ed., vol. 49, no. 12, pp. 2146–2149, 2010. [3] H. F. Andersen, W. O. Filtvedt, J. P. Mæhlen, T. Mongstad, M. Kirkengen, and A. Holt, “Production of Silicon Particles for High-Capacity Anode Material, Yielding Outstanding Production Capacity,” ECS Trans., vol. 62, no. 1, pp. 97–105, 2014. Figure 1

In this paper we demonstrate production of doped silicon nanoparticles and testing of the material in Li-ion battery half cells. Incorporation of 3 at% of phosphorous in the reactants of the free-space reactor used resulted in a doping level of 1.8 at%, a very high level of doping with regards to the standard in semiconductor silicon. However, even with this high level of doping, no significant effect was observed for cycling of silicon anodes using 60 wt% silicon. We propose that the benefit of doping silicon is masked by the effect of the conductive carbon and other additives used in preparation of the test cells.

Silicon is often studied as an alternative to graphite for negative electrodes in lithium-ion battery technology due to its high theoretical specific capacity (3579 mAh/g [1]). However, silicon expands during lithiation, which leads to fast degradation and limited practical use of silicon-based anodes. In order to overcome these challenges a deeper understanding of the degradation mechanisms is needed. However, a common problem with electrode testing is the lack of control of factors such as thickness and loading which effectively conceals the variation in degradation behavior of silicon. A change in the silicon treatment is often concealed by more prominent factors such as loading and thickness variations. To better understand the influence of the silicon material and electrode preparation a better control of these factors is needed, i.e. improving the “signal-to-noise ratio” by improving the process control. All components used in the electrode and the interaction between them will influence the processes towards the resulting battery cell. The current work focuses on optimizing one of these processes to improve the homogeneity of the electrode. The coating method can give severe differences in both thickness and loading properties, and it is of great importance to keep these differences as low as possible. Only cells with similar loading and thickness can give comparable results and yield better understanding of the degradation mechanisms in the silicon anodes. In the search of a uniform electrode, the coating methods play a large role and can be optimized. For laboratory based research, tape casting is often the preferred method as it requires simple equipment and the material consumption is low. An alternative coating method is screen printing which has been applied in various industries, such as clothing, photovoltaics and printed electronics due to the low cost and reliable quality. This work compares silicon-based electrodes prepared with two coating methods; tape casting and screen printing. A water-based mixture of 60 % silicon (0.3 µm, produced at IFE [2]), 10 % graphite (KS6L), 15 % carbon black (Super C65) and 15 % binder (CMC) was prepared and deposited on a structured copper foil with the two different coating techniques. Tape casting was used as a reference method, while parameters for the screen printing process, such as mesh size, printing speed, pressure and snap off, were varied to achieve thickness and loading variations. Issues such as slurry preparation and slurry requirements, cleaning procedure and ease of electrode preparation were compared. The electrodes were analyzed in terms of morphology (cross section and surface), resistance, adhesion testing, thickness and loading parameters as well as final cycling properties. Initial results show a more homogeneous thickness distribution from the screen printed electrode, and the loading variations in terms of active material per area are accordingly decreased. The beneficial homogeneity in thickness distribution for the screen printing can be seen in the attached figure, while the electrode coated via tape casting shows a higher variation in thickness over the entire electrode. The improved control of thickness and loading for the screen printed electrodes led to an improved understanding of the degradation mechanism of the electrodes as the noise in cycleability results was reduced. [1] U. Kasavajjula et al. J. Power Sources 163 (2007) 1003-1039 [2] H. F. Andersen et al. ECS Trans. 62(1) (2014) 97–105 Figure 1

For practical applications of the oxygen-containing yttrium hydride-based photochromic films, knowledge about deposition on substrates of different types and sizes is an important issue. In this article, we report on the dynamic reactive sputter deposition of the films on small and large-area glass and plastic substrates. By analysis of the optical properties we show that all the deposited films exhibited photochromic effect. Surface morphology and structural properties of the films have been studied.

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.

Thin films of yttrium hydride have for almost 20 years been under investigation for optoelectronic and solar energy applications due to the hydrogen-induced switching in electronic state from the metallic elemental yttrium and yttrium dihydride to the transparent semiconductor material yttrium trihydride. In this study, we investigate the electronic structure of yttrium, yttrium hydride and yttrium oxide by using X-ray photoelectron spectroscopy and kelvin probe measurements. The investigated samples have been prepared by reactive sputtering deposition. We show that the electronic work function of transparent yttrium hydride is of 4.76eV and that the recently discovered photochromic reaction lowers the electronic work function of the transparent hydride by 0.2eV.

The application of silicon as an anode material for lithium-ion batteries requires cost-effective fabrication routes and facile processing of the material. Here we present the production and characterization of silicon particles prepared using a silane-based free-space reactor, allowing control of particle size distribution and crystallinity and an outstanding production capacity. The synthesized silicon particles were chemically characterized, prepared as anode material electrodes and electrochemically characterized. The effect of active material loading and electrolyte additives was studied.

Silicon is proven to have a great potential as an anode material in lithium-ion batteries due to its high theoretical electrochemical capacity. The standard, commercial graphite anode has a theoretical capacity of less than 400 mAh/g, whereas the silicon anode can potentially deliver a tenfold capacity as a result of multiple Li-ion incorporation in the structure. However, silicon anodes deteriorate quickly during cyclic charging and discharging, rendering them useless in only a few cycles. This has been attributed to stresses induced by the large volume change of the material during cycling. The methods explored in order to overcome these problems such as using lithography, advanced nanotechnology, incorporation of silicon in carbon nanotubes or similar methods are too slow and too expensive for commercial use. This work presents results from using a silane-based decomposition reactor in order to produce silicon particles with a suitable nanostructure for use in lithium-ion battery anodes. The silane gas is decomposed in a controlled environment at a temperature of 500-600 °C. The current pilot reactor has demonstrated production of up to 350 g/hour in an easily up-scalable lab version. Particles of diameter ranging from 50 nm and up to 500 nm have been produced with relatively narrow size distribution. This method may produce both amorphous and crystalline particles and the surface of the particles can be terminated by hydrogen or other elements if desired. The silicon particles were mixed with an organic binder in an aqueous slurry and coated on a Cu-foil, The electrochemical performance was tested with CR-2032 coin cells. In the course of the presented work studies of cyclic voltammetry, cycling stability (Figure 1), voltage profiles and electrochemical impedance were performed. Besides electrochemical methods, SEM (Figure 2), XRD, ICP-MS and particle size distribution measurements were implemented. The silicon particles achieved a high capacity, relatively good stability, as well as a high yield and production capacity. Further developments on the silicon particles, such as doping of Si and in-line surface coating, are feasible.