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In situ Rutherford Backscattering Spectrometry (RBS) and Spectroscopic Ellipsometry (SE) were applied to study the compositional and optical stability of a WAlSiN-based solar-selective coating (SSC) at high temperatures in vacuum. The samples were exposed to heating-cooling cycles between quasi room temperature and stepwise-increased high temperatures of 450 °C, 650 °C, and 800 °C, respectively. In situ RBS revealed full compositional stability of the SSC during thermal cycling. In situ SE indicated full conservation of the optical response at 450 °C and 650 °C, and minimal changes at 800 °C. The analysis of the ex situ optical reflectance spectra after the complete thermal cycling gave an unchanged solar absorptance of 0.94 and a slightly higher calculated thermal emittance at 800 °C of 0.16 compared to 0.15 after deposition. Cross-sectional element distribution analysis performed in scanning transmission electron microscopy mode confirmed the conservation of the SSC’s microstructure after the heating – cooling cycles. The study demonstrates compositional, optical, and structural stability of the WAlSiN-based solar-selective coating at temperatures targeted for the next generation of concentrated solar power plants.

The transparent conductive tantalum doped tin oxide is a potential candidate for applications in concentrated solar power technology, dye-sensitized solar cells and dynamic random access memories [1], [2], [3]. In all these fields, high-temperature stability in air is mandatory to preserve its functionality. In this work we demonstrate the compositional and structural in-air-stability of SnO2:Ta thin films at 650 °C and 800 °C for 12 hours. While the element composition and optical spectra were unchanged and the X-ray diffractograms revealed the conservation of a single-phase rutile-type crystal structure, some strong Raman lines of SnO2:Ta underwent substantial changes upon tempering. Quantum ab initio calculations of pristine and Ta-doped SnO2 with systematically varied point defects indicated that preferentially Sn vacancies and excess O atoms are responsible for these strong and unexpected Raman signatures. These defects are partially healed during high-temperature exposure, but that does not affect the functionality of SnO2:Ta as transparent conductor under these harsh conditions. This study provides a comprehensive understanding of crystal and defect structure of Ta-doped SnO2 prior to and after high temperature treatment in air for the first time and encourages its application in different fields where high-T stability, transparency and conductivity are required. [1] F. Lungwitz et al., Transparent conductive tantalum doped tin oxide as selectively solar-transmitting coating for high temperature solar thermal applications, Solar Energy Mater. Solar Cells 199, 84 (2019), doi: 10.1016/j.solmat.2019.03.012 [2] R. Ramarajan, et al. Large-area spray deposited Ta-doped SnO2 thin film electrode for DSSC application, Solar Energy 211, 547-559 (2020), doi:10.1016/j.solener.2020.09.042. [3] C. J. Cho, et al. Ta-Doped SnO2 as a reduction-resistant oxide electrode for DRAM capacitors, Journal of Materials Chemistry C 5, 9405-9411 (2017), doi:10.1039/c7tc03467a Financial support by the EU, grant No. 645725, project FRIENDS2, is gratefully acknowledged.

The treatment and coating of electrode/electrolyte interfaces is a promising route to increase lithiumion battery performance for next-generation energy storage. This work reports on the atomic layer deposition process combining lithium hexamethyl disilazide (LiHMDS) and trimethylphosphate (TMP), with an additional trimethylaluminum (TMA) pulse in between. Minimal traces of aluminum are observed, yet the deposited layer is amorphous instead of crystalline. The TMA-TMP interaction plays a key role in this process and is revealed by time-resolved full-range quadrupole mass spectrometry. We hypothesize that the interaction of unreacted OCH3 groups with TMA and the formation of Li4P2O7 units lead to higher growth and structural changes as compared to the phosphate process without TMA. The amorphous mix of Li4P2O7 and Li3PO4 units in the films grown with TMA benefits the conductive properties of the material: an ionic conductivity of 1.47±0:09·10−7 S/cm at 30°C, with an activation energy 0.58±0:02 eV is observed.

Tetrahedral, hydrogen-free amorphous carbon (ta-C) is characterized by the highest sp3-carbon content and the highest hardness of HIT > 40 GPa of the group of diamond-like carbon (DLC) coatings [1]. The formation of sp3-C bonds in this material requires impinging atoms or ions with energies of around 100 eV, provided by cathodic vacuum arc or laser arc deposition [2]. Plasma filter techniques implemented in the recent years enable the production of ta-C coatings with significantly improved surface quality. In this study, friction and wear properties of ta-C coatings deposited by filtered Laser arc are studied as a function of the environment: in humid and dry air, in nitrogen as well as in vacuum from 1 mbar to 10-7 mbar. Low friction with coefficients of friction (COF) < 0.1 is found for the friction pair ta-C/ ta-C at normal pressure, nearly independently on the relative humidity. Likewise, the wear rates are not dependent on whether dry or humid conditions are established. In vacuum, the COF and wear rates increased by a factor of approx. ten and three, respectively. Raman studies reveal a complex structure evolution of ta-C in the wear track and on the contact area of the counter body with decreasing pressure. In the wear tracks at least two types of carbon are found. One of them shows an almost unchanged G line position and an unmeasurable ID/IG ratio as the initial coating, while the second one has a by 20 cm-1 lowered G line position and an ID/IG ratio of approx. 0.4. This structure has similar Raman signatures as the counter body contact area, indicating the formation of an identical tribolayer on both friction partners. Laterally and depth resolved atomic insight in the transfer layer formation is obtained by micro-beam Rutherford backscattering spectrometry for ta-C coatings in contact with steel, brass, alumina, and silicon carbide. Financial support by the DFG, grant No. 415726702, project TRIGUS, is gratefully acknowledged. [1] J. Robertson, Diamond-like amorphous carbon. Materials Science & Engineering R-Reports 37, 129-281, doi:10.1016/s0927-796x(02)00005-0 (2002). [2] F. Kaulfuss, et al. Effect of Energy and Temperature on Tetrahedral Amorphous Carbon Coatings Deposited by Filtered Laser-Arc. Materials 14, 13, doi:10.3390/ma14092176 (2021).

The paper describes the recovery effects of pulsed electron beam treatment in Ge single crystals implanted with various doses of Sn ions at room and low temperatures. A protective coat of 100 nm Sn was applied as a sacrificial layer. The implanted layers were studied by RBS/cRBS (Rutherford BackScattering/channeled Rutherford BackScattering) method, SIMS (Secondary Ion Mass Spectrometry) and TEM (Transmission Electron Microscopy). Defects revealed in channelled RBS spectra were analysed by McChasy code. The results show that the Sn concentration attains 1% and more with very good substitutionality. They also reveal excellent lattice recovery after e-beam melting. Suggestions are derived as regards further improvement of pulsed e-beam technique.

A series of CuCr₂O₄ thin films has been successfully synthesized via a facile and cost-effective reactive Direct Current Magnetron Sputtering technique at room temperature. These coatings were deposited to evaluate their suitability as absorber material for the next generation of concentrated solar power plants [1]. The composition of the films was controlled using as key parameters the power ratio between Cu and Cr targets as well as the oxygen flux. The films deposited without intentional substrate heating were initially amorphous and needed to be annealed at 800 °C for one hour to obtain a spinel-like crystal structure [2]. RBS was used to characterize the composition of the as-deposited and annealed coatings. The structural properties were investigated by Raman spectroscopy and XRD. Structural characterization allows us to evidence that slight deviation in stoichiometry promotes the formation of secondary phases in the films. In this concern, we use in-situ Raman spectroscopy and spectroscopic ellipsometry to characterize the structural evolution of the films as a function of temperature in a controlled oxygen atmosphere. The study evidences the evolution from amorphous to fully crystallized material. Additionally, the influence of the film roughness in the optical performance of the coatings with appropriate composition was explored to enhance the optical properties of the film. References: 1) Ramón Escobar Galindo, Matthias Krause, K. Niranjan and Harish Barshilia, in Sustainable Material Solutions for Solar Energy Technologies (ed. Mariana Fraga, Delaina Amos, Savas Sonmezoglu, Velumani Subramaniam, Elsevier, 2021). 2) Matthias Krause, Johanna Sonnenberg, Frans Munnik, Jörg Grenzer, René Hübner, Aurelio Garcia-Valenzuela, Sibylle Gemming in Materialia 18 (2021) 101156.

Solid lubricants, like ta-C (hydrogen-free tetrahedral amorphous carbon) coatings, are an active area of research to replace liquid lubricants. This substitution is important because of the negative environmental impact and high material consumption of liquid lubricants. The influence of soft metal counter bodies on the unlubricated friction behaviour of hydrogen-free carbon coatings has mostly been studied for doped a-C coatings so far. All these studies show that low friction and wear can only be achieved if a tribolayer is formed to protect the contact. Even with a formed tribolayer, its composition is crucial for the frictional behaviour, making the investigation of this composition essential. A study currently underway aims to identify friction-induced surface changes like material loss of the coating, material transfer between the counter body and the coating, or the formation of a tribolayer. The current work presents Ion Beam Analysis methods to deliver laterally and depth-resolved element analysis of the wear track on the coating and the contact area of the counter bodies (CB). In a first test, a ta-C coating has been subjected to pin-on-disk tests with various metallic and ceramic CBs. He and H ion microbeams have been used to scan over the tracks and the contact areas of the CBs. Both RBS and PIXE have been used and first results are presented. It is shown that, in this case, RBS yields the more useful information. Both, a 2 MeV He ion beam and a 3 MeV H ion beam provide valuable results. The advantages of each type of ion beam depend on the sample and the information needed. As shown in this work, RBS with a 2 MeV He ion beam is useful to determine the transfer layer of a (soft) metal CB to the ta-C coating, whereas 3 MeV H RBS can be used to determine the presence of C and O on the CB because of the increased non-Rutherford cross-sections for these elements.

In situ measurements using RBS, ERD, and SE are less explored in characterizing solar absorber materials at high temperatures [1, 2]. In the present work, we report the W/WAlSiN/SiON/SiOO2 based spectrally selective solar absorber coating with excellent optical, compositional and structural properties at high temperatures [3, 4]. We have carried out in situ Rutherford backscattering spectrometry, elastic recoil detection and spectroscopic ellipsometry measurements at three different temperatures at 450°C, 650°C, and 800°C. An optical model describing perfectly the reflectance and ellipsometric data was developed. Further, the microstructural properties of the solar absorber coating are evaluated using cross-sectional transmission electron microscopy before and after annealing. Our data obtained before and after the heating experiments demonstrate excellent compositional, optical and structural stability of the coatings under the applied conditions. Furthermore, in situ ellipsometry showed the conservation of the optical properties of the W/WAlSiN/SiON/SiOO2 based spectrally selective solar absorber up to 800 °C, which is crucial for high-temperature applications. [1] Ramón Escobar Galindo, Matthias Krause, K. Niranjan and Harish Barshilia, in Sustainable Material Solutions for Solar Energy Technologies (ed. Mariana Fraga, Delaina Amos, Savas Sonmezoglu, Velumani Subramaniam, Elsevier, 2021). [2] Lungwitz, F. et al. Transparent conductive tantalum doped tin oxide as selectively solar-transmitting coating for high temperature solar thermal applications, Solar Energy Mater. Solar Cells 196, 84-93, doi:10.1016/j.solmat.2019.03.012 (2019). [3] K. Niranjan, A. Soum-Glaude, A. Carling-Plaza, S. Bysakh, S. John, H.C. Barshilia, Extremely high temperature stable nanometric scale multilayer spectrally selective absorber coating: Emissivity measurements at elevated temperatures and a comprehensive study on ageing mechanism, Solar Energy Mater. Sol. Cells 221 (2021) 110905, doi:10.1016/j.solmat.2020.110905. [4] K. Niranjan, A.C. Plaza, T. Grifo, M. Bordas, A. Soum-Glaude, H.C. Barshilia, Performance evaluation and durability studies of W/WAlSiN/SiON/SiOO2 based spectrally selective solar absorber coating for high-temperature applications: A comprehensive study on thermal and solar accelerated ageing, Solar Energy 227 (2021) 457–467, doi:10.1016/j.solener.2021.09.026.

Solid lubricants are an active research topic due to many factors, an important one being the elimination of current liquid lubrication because of its environmental impact. The tribological behaviour of different solid lubricants depends on the gas en¬vironment while testing. The most often-used solid lubricant coating is MoS2. A newer one still under research is ta-C (hydrogen-free, tetra-edic, amorphous carbon) that behaves like a polar opposite to MoS2. ta-C relies on free hydrogen and hydroxide ions to passivate free bonds resulting from the wear testing. In a first test, a ta-C coating has been subjected to tribological tests with counter bodies made of various materials. The aim is to study tribological surface changes like material loss of the coating or material transfer from the counter body, processes which aren’t fully understood yet. Both the wear tracks on the ta-C coating and the counter bodies have been subjected to Ion Beam Analysis using a high energy ion microprobe. Both PIXE (Particle Induced X-ray Emission) and RBS (Rutherford Backscattering Spectrometry) measurements have been performed using a 2 MeV He ion beam and a 3 MeV H ion beam. Results for the wear tracks obtained with a brass and a Al2O3 counter body are presented as well as results on the counter bodies themselves. The advantages and drawbacks of the results obtained with different ions and different methods are presented. These results show that it is important to combine the measurements in order to obtain a complete picture of the damage caused by the wear tests.

The (opto)electronic properties of Ta3N5 photoelectrodes are often dominated by defects, such as oxygen impurities, nitrogen vacancies, and reduced tantalum centers, impeding fundamental studies of its electronic structure, chemical stability, and photocarrier transport. Here, we synthesize high quality Ta3N5 thin films by reactive magnetron sputtering and subsequent NH3 annealing at varying temperatures. The resulting films are characterized by nearly-ideal N/Ta stoichiometry, low O content, and small Urbach energies. Both the crystallinity and material quality improve with increasing annealing temperatures up to 940 °C, while higher annealing temperatures introduce additional disorder within the Ta3N5 lattice, leading to reduced photoelectrochemical performance. These changes are also reflected in the surface and bulk composition, showing the elimination of oxygen impurities at moderate annealing temperatures and the loss of nitrogen at high annealing temperatures. As a consequence, defect-related sub-gap optical absorption initially decreases due to reduced oxygen impurity concentration, and subsequently increases due to increased formation of nitrogen vacancies. The high material quality enables us to unambiguously identify the nature of the Ta3N5 band gap as indirect, thereby resolving a long-standing controversy regarding the most fundamental characteristic of this material as a semiconductor. The assignment of Ta3N5 as indirect semiconductor is further supported by the suppression of disorder-induced band-edge photoluminescence with improved structural order within the Ta3N5 films.

The diverse physical and chemical properties of aerosols can cause a diverse impact on air quality, cloud nucleation, planetary radiation balance, public health, etc. Besides carbon particles from incomplete combustion, mineral particles from Saharan dust also present a significant contribution to the changes. It is estimated that 400 to 700 million tons of dust is transported from Sahara every year and with the particular wind directions it is carried to the Mediterranean or even to the north of Europe (Prospero, 1996). It has recently been shown that these particles induce serious problems for asthmatics (Gutierrez et al., 2020). To understand the origin of pollution, necessary input information presents knowing the source apportionment of aerosols. Techniques such as non-destructive particle induced X-ray emission (PIXE) (Lucarelli et al., 2018) and energy dispersive x-ray spectroscopy (SEM-EDS) (Longoria-Rodríguez et al., 2021) have been successfully applied for chemical microanalysis of individual particles. However, knowing both the physical and chemical properties of particles towards nm scales, which would cover all aerosol sizes, is still a challenging task. In our study, we have thus implemented the correlative approach using advanced ion beam techniques to study both physical and chemical properties of mineral particles from Saharan dust collected on quartz fiber filters on Cyprus Atmospheric Observatory (35.04oN,33.06 Eo; 535 m a.s.l.) using a combination of the virtual impactor and Aethalometer AE33 (Aerosol d.o.o.). We have implemented Helium Ion Microscopy (HIM), capable of sub-nm resolution imaging with high depth-of-field contrast, followed by micro-PIXE elemental analysis done on the same filter region. Information from backscattered high-energy ions was found particularly suitable for the registration and overlap of complementary images (Figure 1). The study has revealed the size, shape, architecture, and surface topography of individual mineral particles on nm scale, while micro-PIXE their chemical composition. Additionally, HIM resolution and surface sensitivity enabled the detection and identification of individual black carbon (BC) soot attached to the surface of mineral particles. This information can have a significant impact on our understanding of the optical properties of mineral dust and its relevance to climate changes and health effects. This finding urges for further investigations where additional focused ion beam techniques and instrumentation have been implemented and will be discussed.

Hafnium oxide was deposited from tetrakis(dimethylamino)hafnium (TDMAHf) and water by atomic layer deposition (ALD) on heated 400 Si wafers covered with native oxide in the temperature range from 100 C to 350 C. Optimized self-limiting ALD reaction and smallest hydrogen impurity level have been realized for a substrate temperature of 300 C. The stoichiometry of deposited films and hydrogen impurity level were measured by elastic recoil detection analysis. The hafnium to oxygen ratio showed the expected 1:2 value. Besides hydrogen, no other impurities could be detected. Furthermore, a strong correlation between the growth rate per cycle (GPC), film uniformity and level of hydrogen impurities was observed. Based on this result, the easily accessible GPC can be used as a first indication for the hydrogen impurity level in ALD grown thin films. Furthermore, the characterization of the crystal structure showed the appearance of some crystallites in an amorphous matrix already for a growth temperature of 250 C and a pure crystalline layer at a growth temperature of 350 C. The increased crystallinity with increasing growth temperature was attributed to a higher seed concentration and a constant crystal size.

The correlative approach of real-time aerosol measurements with offline filter analysis and ParticleInduced X-ray Emission (PIXE) can significantly enhance the scope of aerosol studies. Aerosol particles have diverse physical and chemical properties, thus having a direct impact on air quality, cloud nucleation the planetary radiation balance, public health, etc. Essential information on the chemical composition of aerosol particles can be deduced from the elemental concentrations measured simultaneously for many elements by non-destructive and undemanding PIXE (Lucarelli, 2018). Furthermore, PIXE measurements can be performed with a focused beam allowing the analysis of individual particles (Biancato, 2006). Determining elemental concentrations is also important input information for aerosol source apportionment models and consequently abatement measures in order to improve air quality (Artaxo, 1999). Complementary information of aerosol particles structure down to nm scale, can be obtained with a Helium Ion Microscope (HIM), which, to our knowledge, has never been used before for aerosol characterization. The detection of secondary electrons and backscattered ions enables sub nm lateral resolution and large depth-of-field, also on insulating samples. In addition, a concurrent secondary ion mass spectrometry (ToF-SIMS) integrated in the HIM can provide insights of the composition of elements and molecules with imaging capabilities of sub 8 nm (Klingner, 2019). In this study we coupled real-time measurements of optical properties of aerosols with an Aethalometer (Drinovec, 2015) and their carbon content with a Total Carbon Analyzer (Rigler, 2019) with PIXE and HIM analysis. Ambient aerosols were collected on quartz filters and quartz filters with Teflon coating during different pollution events (traffic or biomass burning dominated, Saharan dust dominated, etc.) at an urban background sampling site in Ljubljana, Slovenia (46o04’17’’N, 14o30’06’’E). The PM2.5 inlet was used for sampling carbonaceous aerosol while a virtual impactor was used for concentrating coarse particles during Saharan dust events. PIXE measurements have been performed on these collected samples and compared to optical properties and source apportionment obtained by the online instruments. The PIXE measurements were performed across several hundred-micrometer regions and on individual points and results are presented including a description of the procedures for quantification. Complementary high-resolution imaging and sputtered ion analysis on single black carbon and Saharian dust aerosol particles was done on the HIM to study their structure and coating composition. The combination of all methods yields a comprehensive view of the aerosol particles.

Lithium-silicon compounds are used as active material in negative electrodes of Li-ion batteries. The knowledge of Li diffusion in these materials is of importance for an optimization of charging/discharging rates and achievable maximum specific capacity as well as for an understanding of the basic lithiation mechanism. We carried out Li tracer self-diffusion experiments on ion-beam sputter-deposited LixSi(O) thin films for x ~ 0.25 and x ~ 4.5 using LixSi/6LixSi hetero-structures in combination with secondary ion mass spectrometry in line scan like mode. Measurements with elastic recoil detection analysis revealed the presence of a considerable amount of oxygen in the films. The diffusivities follow the Arrhenius law in the temperature range between 300 and 500 °C with an activation energy of 0.8 – 0.9 eV. The film containing a higher amount of Li shows faster diffusion by one order of magnitude. The Li diffusivities in the investigated Li-rich materials are several orders of magnitude higher than in Li-poor LixSi films (x = 0.02 to 0.06) as given in literature because of a lower activation energy. This indicates the presence of a direct interstitial-like mechanism. Oxygen present in samples with the same Li concentration of x = 0.06 also enhances diffusion but does not lead to a reduction in the activation energy.