Thin films of rare-earth (RE)–oxygen–hydrogen compounds prepared by reactive magnetron sputtering show a unique color-neutral photochromic effect at ambient conditions. While their optical properties have been studied extensively, the understanding of the relationship between photochromism, chemical composition, and structure is limited. Here we establish a ternary RE–O–H composition-phase diagram based on chemical composition analysis by a combination of Rutherford backscattering and elastic recoil detection. The photochromic films are identified as oxyhydrides with a wide composition range described by the formula REOxH3–2x where 0.5 ≤ x ≤ 1.5. We propose an anion-disordered structure model based on the face-centered cubic unit cell where the O2– and H– anions occupy tetrahedral and octahedral interstices. The optical band gap varies continuously with the anion ratio, demonstrating the potential of band gap tuning for reversible optical switching applications.

AlO on Si is known to form an ultrathin interfacial SiO during deposition and subsequent annealing, which creates a negative fixed charge ( Q) that enables field-effect passivation and low surface recombination velocities in Si solar cells. Various concepts were suggested to explain the origin of this negative Q. In this study, we investigate Al-O monolayers (MLs) from atomic layer deposition (ALD) sandwiched between deliberately grown/deposited SiO films. We show that the Al atoms have an ultralow diffusion coefficient (∼4 × 10 cm/s at 1000 °C), are deposited at a constant rate of ∼5 × 10 Al atoms/(cm cycle) from the first ALD cycle, and are tetrahedral O-coordinated because the adjacent SiO imprints its tetrahedral near-order and bond length into the Al-O MLs. By variation in the tunnel-SiO thickness and the number of Al-O MLs, we demonstrate that the tetrahedral coordination alone is not sufficient for the formation of Q but that a SiO/AlO interface within a tunneling distance from the substrate must be present. The Al-induced acceptor states at these interfaces have energy levels slightly below the Si valence band edge and require charging by electrons from either the Si substrate or from Si/SiO dangling bonds to create a negative Q. Hence, tunneling imposes limitations for the SiO and AlO layer thicknesses. In addition, Coulomb repulsion between the charged acceptor states results in an optimum number of Al-O MLs, i.e., separation of both interfaces. We achieve maximum negative Q of ∼5 × 10 cm (comparable to thick ALD-AlO on Si) with ∼1.7 nm tunnel-SiO and just seven ALD-AlO cycles (∼8 Å) after optimized annealing at 850 °C for 30 s. The findings are discussed in the context of a passivating, hole-selective tunnel contact for high-efficiency Si solar cells.

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The (opto)electronic properties of Ta3N5 photoelectrodes are often dominated by defects, but precise control of these defects provides new insight into the electronic structure, photocarrier transport, and photoelectrochemical function.

Lithium−silicon compounds are used as active material in the negative electrodes of Li-ion batteries. The knowledge of Li diffusion in these materials is of importance for the 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 sputterdeposited Li x Si(O) thin films for x ≈ 0.25 and 4.5 using Li x Si/ 6 Li x Si heterostructures in combination with secondary-ion mass spectrometry in the 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 of 300−500 °C with an activation energy of 0.8−0.9 eV. The film containing a higher amount of Li shows faster diffusion by 1 order of magnitude. The Li diffusivities in the investigated Li-rich materials are several orders of magnitude higher than in Li-poor Li x Si films (x = 0.02−0.06) as given in the literature because of a lower activation energy. This indicates the presence of a direct interstitial-like mechanism. The 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.