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Using N2O as an alternative background gas to O2 when growing oxide thin films by pulsed laser deposition (PLD) was previously expected to result in larger oxygen contents of as-grown thin films. In this work, we investigate the composition and kinetic energy of the pulsed laser induced plasmas that propagated in N2O and O2 by using mass spectrometry and plasma imaging. Two distinguished features were observed when using N2O instead of O2. (1) In N2O background gas as compared to O2, a larger proportion of negative oxygen ions was detected. (2) The alkaline-earth elements were fully oxidized in the N2O background, which is not achievable in O2. These observations are attributed to the smaller dissociation energy of the N2O molecules as compared to O2. The smaller dissociation energy of the background gas molecule is expected to reduce the interaction strength during their central collisions with the plasma species. As a result, the dissociable or electron detachable plasma species can be formed in larger amounts in N2O background, compared to O2. Comparing the composition of the deposited thin films indicates a larger oxygen content of the film grown in N2O background gas, as compared to O2, at pressures of ∼10−1 mbar, which is the most commonly used deposition pressure in PLD. Nevertheless, this was not achieved when performing PLD at ∼10−2 mbar, since the pressure was not high enough to trigger the formation of the shockwave front during the plasma expansion and thereby the lightest oxygen plasma species were preferentially scattered. [ABSTRACT FROM AUTHOR]

Different SrTiO3 thin films are investigated to unravel the nature of ultra‐low conductivities recently found in SrTiO3 films prepared by pulsed laser deposition. Impedance spectroscopy reveals electronically pseudo‐intrinsic conductivities for a broad range of different dopants (Fe, Al, Ni) and partly high dopant concentrations up to several percent. Using inductively‐coupled plasma optical emission spectroscopy and reciprocal space mapping, a severe Sr deficiency is found and positron annihilation lifetime spectroscopy revealed Sr vacancies as predominant point defects. From synchrotron‐based X‐ray standing wave and X‐ray absorption spectroscopy measurements, a change in site occupation is deduced for Fe‐doped SrTiO3 films, accompanied by a change in the dopant type. Based on these experiments, a model is deduced, which explains the almost ubiquitous pseudo‐intrinsic conductivity of these films. Sr deficiency is suggested as key driver by introducing Sr vacancies and causing site changes (FeSr and TiSr) to accommodate nonstoichiometry. Sr vacancies act as mid‐gap acceptor states, pinning the Fermi level, provided that additional donor states (most probably TiSr••\[{\rm{Ti}}_{{\rm{Sr}}}^{ \bullet \bullet }\]) are present. Defect chemical modeling revealed that such a Fermi level pinning also causes a self‐limitation of the Ti site change and leads to a very robust pseudo‐intrinsic situation, irrespective of Sr/Ti ratios and doping. [ABSTRACT FROM AUTHOR]

Atomic layer deposition is an appealing deposition technology for the fabrication of protective coatings for various applications, including semiconductor manufacturing chambers and related metallic parts with complex three-dimensional topographies, where a key requirement is (thermo)-mechanical robustness of the coatings. Here, we study the mechanical properties of atomic-layer-deposited Al2O3, Y2O3, and their nanolaminate (NL) coatings on an Al metal substrate. Tensile straining experiments accompanied by in situ optical and scanning electron microscopy indicate that the fragmentation onset of 100 nm thick coatings can be tailored in the strain range of 1.3–2.1% by controlling the layer structure and composition of the NLs, such that a higher Al2O3 content, denser layer spacing, and amorphization favor higher crack onset strain. Although the fracture toughness of Al2O3 and Y2O3 is found to be similar, KIC = 1.3 MPa·m1/2, the (substantially tensile) intrinsic residual stress for Y2O3 is a disadvantage for applications, where applied tensile stresses are to be expected. The films adhere well to the Al substrate as significant delamination of the films is not observed in the tensile experiments; the analysis of the fragmentation patterns indicates that insertion of an Al2O3 layer at the film/substrate interface can enhance the interface toughness. High-temperature (425 °C) tensile experiments for the Al2O3 films indicate good temperature tolerance for the coatings, and in comparison to the room-temperature data, a significant difference is seen in the increase of saturation crack spacing. Moreover, the structure and composition of the films are studied in detail through X-ray reflection and diffraction, transmission electron microscopy, Rutherford backscattering spectrometry, and elastic recoil detection analysis. The results are particularly interesting for protective coating applications. [ABSTRACT FROM AUTHOR]

The misfit-layered cobalt oxide [Ca2CoO3-δ][CoO2]1.62 is a promising material for high-temperature thermoelectric heat recovery. Here, we show that discrepancies in the numerously reported thermoelectric performances can result from Co3OM4 impurities or a change of the defects, i.e., the relative Co content in the [Ca2CoO3-δ][CoO2]1.62 phase. We observe that increasing the relative Co content in the [Ca2CoO3-δ][CoO2]1.62 phase leads to a larger figure of merit ZT. We attribute this increase of ZT to additional p-type charge carriers introduced by Ca vacancies and the resulting reduction of the electrical resistivity. For Co/Ca ratios above the miscibility limit, the increase in thermal conductivity due to the formation of Co3OM4 impurities leads to a reduction of ZT when the volume fraction of the Co3OM4 phase is increased from 1% to 3%. Hence, the best figure of merit is expected close to the upper phase boundary of the [Ca2CoO3-δ][CoO2]1.62 phase. [ABSTRACT FROM AUTHOR]

The effects of the type of background gas and pressure on the spatial distributions of plume species have been investigated by time and space resolved imaging in vacuum, 1×10-2 mbar and 1×10-1 mbar O2 and Ar. The ablation of La0.4Ca0.6MnO3 in vacuum shows dissimilar arrival times for the different neutral species and a backscattering of the impinging species from the substrate. At 1×10-2 mbar, a species-dependent plume splitting appears and preferential scattering of the lighter elements is detected generating a cation off-stoichiometry along the plume axis. In addition at 1×10-1 mbar the plume expansion in this relatively high pressure traps a portion of the background gas against the substrate holder, thereby creating a transient high local pressure with remarkable effects once the plume reaches the substrate. In an Ar background, a rebound wave is seen, which travels backwards and recoats/contaminates the target with a different composition than the original target. In O2, in addition to the rebound, a long-lived volume of excited species is created, which consists mainly of LaO I. The rebound has important effects on the film composition and is background gas dependent. The same effects are also detected during Ag ablation and are probably valid for most target materials. [ABSTRACT FROM AUTHOR]

Oxynitrides have been shown to be promising visible light water splitting photocatalysts, but rapidly degrade under operating conditions. With a custom designed photoelectrochemical cell, we perform operando grazing incidence X-ray absorption spectroscopy measurements on the oxynitride semiconductor SrTaOxNy during photocatalytic solar water splitting. We show that the nature of the A-site (Sr) and its evolution during operation have large impacts on the overall stability and catalytic activity of the material, leading to an enriched BO2 (Ta(OH)/TaO(OH)) like surface. However, this usually beneficial effect with respect to increased surface hydrophilicity has complications for the efficiency of the photocatalytic process, as the OH and O(OH) intermediates formed are in competition between O2 generation and NOx species formation in the initial stages of operation. Operando characterisation of the evolution of the electronic structure of the photocatalyst proves to be an invaluable tool for the rational design and discovery of new and better performing materials. [ABSTRACT FROM AUTHOR]

Pulsed reactive crossed-beam laser ablation is an effective technique to govern the chemical activity of plasma species and background molecules during pulsed laser deposition. Instead of using a constant background pressure, a gas pulse with a reactive gas, synchronized with the laser beam, is injected into vacuum or a low background pressure near the ablated area of the target. It intercepts the initially generated plasma plume, thereby enhancing the physicochemical interactions between the gaseous environment and the plasma species. For this study, kinetic energy resolved mass-spectrometry and time-resolved plasma imaging were used to study the physicochemical processes occurring during the reactive crossed beam laser ablation of a partially 18O substituted La0.6Sr0.4MnO3 target using oxygen as gas pulse. The characteristics of the ablated plasma are compared with those observed during pulsed laser deposition in different oxygen background pressures. [ABSTRACT FROM AUTHOR]

High mobility hydrogenated indium oxide is investigated as a transparent contact for thin film Cu(In,Ga)Se2 (CIGS) solar cells. Hydrogen doping of In2O3 thin films is achieved by injection of H2O water vapor or H2 gas during the sputter process. As-deposited amorphous In2O3:H films exhibit a high electron mobility of ~50 cm²/Vs at room temperature. A bulk hydrogen concentration of ~4 at. % was measured for both optimized H2O and H2-processed films, although the H2O-derived film exhibits a doping gradient as detected by elastic recoil detection analysis. Amorphous IOH films are implemented as front contacts in CIGS based solar cells, and their performance is compared with the reference ZnO:Al electrodes. The most significant feature of IOH containing devices is an enhanced open circuit voltage (VOC) of ~20 mV regardless of the doping approach, whereas the short circuit current and fill factor remain the same for the H2O case or slightly decrease for H2. The overall power conversion efficiency is improved from 15.7% to 16.2% by substituting ZnO:Al with IOH (H2O) as front contacts. Finally, stability tests of non-encapsulated solar cells in dry air at 80 °C and constant illumination for 500 h demonstrate a higher stability for IOH-containing devices. [ABSTRACT FROM AUTHOR]