Context. Miras are long-period variables thought to be in the asymptotic giant branch (AGB) phase of evolution. In about one percent of known Miras, the pulsation period is changing. It has been speculated that this changing period is the consequence of a recent thermal pulse in these stars. Aims. We aim to clarify the evolutionary state of these stars, and to determine in particular whether or not they are in the thermallypulsing (TP-)AGB phase. Methods. One important piece of information that has been neglected so far when determining the evolutionary state is the presence of the radio-active s-process element technetium (Tc). We obtained high-resolution, high signal-to-noise-ratio optical spectra of a dozen prominent Mira variables with changing pulsation period to search for this indicator of TPs and dredge-up. We also use the spectra to measure lithium (Li) abundances. Furthermore, we establish the evolutionary states of our sample stars by means of their present-day periods and luminosities. Results. Among the twelve sample stars observed in this programme, five were found to show absorption lines of Tc. BH Cru is found to be a carbon-star, its period increase in the past decades possibly having stopped by now. We report a possible switch in the pulsation mode of T UMi from Mira-like to semi-regular variability in the past two years. R Nor, on the other hand, is probably a fairly massive AGB star, which could be true for all meandering Miras. Finally, we assign RU Vul to the metal-poor thick disk with properties very similar to the short-period, metal-poor Miras. Conclusions. We conclude that there is no clear correlation between period change class and Tc presence. The stars that are most likely to have experienced a recent TP are BH Cru and R Hya, although their rates of period change are quite different.

We study the encapsulation of monolayers of CdSe/CdS/ZnS core/shell/shell quantum dots (QDs) in a ZnO matrix by atomic layer deposition (ALD) in order to gain insight in the interaction between quantum dots and ALD precursors and the resulting metal oxide coating. Using in situ XRF and GISAXS, we show the inhibition of ZnO growth on as-deposited QDs. Growth can, however, be triggered by exposing the QDs to a single pulse of trimethyl­aluminum (TMA) vapor. Such a TMA pretreatment results in the substitution of 35–40% of the surface Zn by Al. Whereas this drops by half the photoluminescence quantum yield of the QDs, we argue that this replacement primes the QD monolayer for ZnO growth by ALD. Finally, the evolution of the GISAXS pattern during subsequent ALD growth attests the preservation of the ordering of the QDs in the monolayer. These results illustrate the important interplay between highly reactive ALD precursors and the QD surface.

We studied the solid-phase reaction between a thin Ni film and a single crystal Ge(001) or Ge(111) substrate during a ramp anneal. The phase formation sequence was determined using in situ X-ray diffraction and in situ Rutherford backscattering spectrometry (RBS), while the nature and the texture of the phases were studied using X-ray pole figures and transmission electron microscopy. The phase sequence is characterized by the formation of a single transient phase before NiGe forms as the final and stable phase. X-ray pole figures were used to unambiguously identify the transient phase as the-phase, a non-stoichiometric Ni-rich germanide with a hexagonal crystal structure that can exist for Ge concentrations between 34% and 48% and which forms with a different epitaxial texture on both substrate orientations. The complementary information gained from both RBS and X-ray pole figure measurements revealed a simultaneous growth of both the-phase and NiGe over a small temperature window on both substrate orientations. V

The effect of thermal annealing on epitaxial GeSn (6.5% Sn) strained layers grown on Ge-buffered Si(100) wafers has been investigated using Rutherford backscattering spectrometry and X-ray diffraction to unambiguously determine the Sn substitutional content as well as the elastic strain in the layers. Vacuum annealing at temperatures below 400 C for 20 min has no noticeable effect on the strain in the epitaxial layers. Once the temperature was raised above 400 C, however, relaxation of the layer sets in and the GeSn layer has essentially completely relaxed following a 20 min anneal at 650 C. Using Rutherford backscattering and channelling spectrometry to provide compositional information as a function of depth enables one to monitor the effect of the thermal anneal on the Sn distribution throughout the layer, and also to directly extract their substitutional fraction (i.e., their solubility in the lattice). The results obtained show that when the relaxation initially sets in both the Ge and the Sn remain firmly bound in substitutional lattice sites and it is only around 600 C, and after substantial relaxation has taken place, that Sn is finally expelled from lattice sites and diffuses to the surface of the sample.

The electrical contact of the source and drain regions in state-of-the-art CMOS transistors is nowadays facilitated through NiSi, which is often alloyed with Pt in order to avoid morphological agglomeration of the silicide film. However, the solid-state reaction between as-deposited Ni and the Si substrate exhibits a peculiar change for as-deposited Ni films thinner than a critical thickness of t c =5 nm. Whereas thicker films form polycrystalline NiSi upon annealing above 450 • C, thinner films form epitaxial NiSi 2 films which exhibit a high resistance towards agglomeration. For industrial applications, it is therefore of utmost importance to assess the critical thickness with high certainty and find novel methodologies to either increase or decrease its value, depending on the aimed silicide formation. This paper investigates Ni films between 0 and 15 nm initial thickness by using of 'thickness gradients', which provide semi-continuous information on silicide formation and stability as a function of as-deposited layer thickness. The alloying of these Ni layers with 10 % Al, Co, Ge, Pd or Pt renders a significant change in the phase sequence as a function of thickness and dependent on the alloying element. The addition of these ternary impurities therefore change the critical thickness t c. The results are discussed in the framework of

Solid-state amorphization, the growth of an amorphous phase during annealing, has been studied in a wide variety of thin film structures. Whereas research on the remarkable growth of such a metastable phase has mostly focused on strictly binary systems, far less is known about the influence of impurities on such reactions. In this paper, the influence of nitrogen, introduced via ion implantation, is studied on the solid-state amorphization reaction of thin (35 nm) Ni films with Si, using in situ XRD, ex situ RBS, XTEM, and synchrotron XRD. It is shown that due to small amounts of nitrogen (< 2 at.%), an amorphous Ni-Si phase grows almost an order of magnitude thicker during annealing than for unimplanted samples. Nitrogen hinders the nucleation of the first crystalline phases, leading to a new reaction path: the formation of the metal-rich crystalline silicides is suppressed in favour of an amorphous Ni-Si alloy; during a brief temperature window between 330 and 350 • C, the entire film is converted to an amorphous phase. The first crystalline structure to grow is the orthorhombic NiSi phase. We demonstrate that this phenomenon occurs only under specific implantation conditions. In particular, the initial distribution of nitrogen upon implantation is crucial: sufficient nitrogen impurities must be present at the interface throughout the reaction. Introducing implantation damage without nitrogen impurities (e.g. by implanting a noble gas) does not cause the enhanced solid-state reaction. Moreover, we show that the stabilizing effect of nitrogen on amorphous Ni-Si films (with a composition ranging from 40% to 50% Si) is not restricted to thin film reactions, but is a general feature of the Ni-Si system.

In this study, we focus on phase formation in intermixed Ni-Ge thin films as they represent a simplified model of the small intermixed interface layer that is believed to form upon deposition of Ni on Ge and where initial phase formation happens. A combinatorial sputter deposition technique was used to co-deposit a range of intermixed Ni-Ge thin films with Ge concentrations varying between 0 and 50 at.%Ge in a single deposition on both Ge (100) and inert SiO 2 substrates. In situ X-ray diffraction and transmission electron microscopy where used to study phase formation. In almost the entire composition range under investigation, crystalline phases where found to be present in the as-deposited films. Between 36 and 48 at.%Ge, high-temperature hexagonal nickel germanides were found to occur metastabily below 300°C, both on SiO 2 and Ge (100) substrates. For Ge concentrations in the range between 36 and 42 at.%, this hexagonal germanide phase was even found to be present at room temperature in the asdeposited films. The results obtained in this work could provide more insight in the phase sequence of a pure Ni film on Ge.

We report on the growth of thin NiSi films via the thermal reaction of Ni layers (13 -35 1 nm) with Si(100) substrates modified by ion implantation. By introducing substrate 2 damage or nitrogen impurities prior to the solid-phase reaction, several properties of 3 the NiSi films can be modified: the formation temperature, texture, diffusion-limited growth rate and morphological stability. As some of the modifications to the NiSi 5 films are rooted in the early silicide phases preceding the NiSi phase, particularly its 6 formation temperature, special attention is devoted to the growth of the amorphous 7 Ni-Si alloy and the crystalline δ-Ni 2 Si and θ-Ni 2 Si phases.8We employed a number of experimental techniques, including in situ synchrotron 9 X-ray diffraction (XRD), in situ Rutherford backscattering spectrometry (RBS), in 10 situ sheet resistance measurements, ex situ ion beam channelling and ex situ pole 11 figure measurements. We show that both the formation temperature of the NiSi films and the intensity of epitaxial and axiotaxial components of the NiSi texture 13 can be either lowered or raised by selecting appropriate implantation conditions. 14 Agglomeration of the NiSi films at high temperature (> 700 • C) can be slowed down, 15 either by slowing down the mobility of the Ni and Si atoms, or by removing the 16 morphologically destabilizing axiotaxial texture. Our results emphasize the strong 17 interwoven nature of phase formation, texture and morphological degradation. We 18 illustrate that the kinetics of the early stages of thin film reactions consist of more 19 than just diffusion, i.e. nucleation can also play a crucial role. 2 Page 2 of 36 AUTHOR SUBMITTED MANUSCRIPT -JPhysD-124461.R1 14 upon further annealing. 4 Extensive research, however, has revealed the appearance of two 15 metastable phases during the reaction. The first is an amorphous interlayer, preceding the 16 crystalline phases. It forms upon deposition and grows slightly upon subsequent annealing. 17 Nucleation barriers initially prevent the formation of crystalline phases; 6 during this time 18 the amorphous phase can grow up to a few nm. 7 For most films (≥ 10 nm), the amorphous 19 phase crystallizes long before the metal supply is consumed. The second metastable phase 20 observed in the reaction is the θ-Ni 2 Si phase, which appears in the film during the growth of 21 the δ-Ni 2 Si phase; both phases grow simultaneously for a brief temperature window before 22 the θ-Ni 2 Si phase is consumed. Not only is the concurrent growth of multiple phases in thin 23 film reactions uncommon, the appearance of the θ-Ni 2 Si phase is remarkable in itself, since 24 the phase is thermodynamically unstable below 825 • C. 8 Nevertheless, it has been observed 25 in Ni-Si reaction at relatively low temperature under a variety of experimental conditions. 9 26 27 It has been found that both metastable phases mentioned above, the θ-Ni 2 Si phase and 28 the amorphous interlayer, can be stabilized (i.e., their temperature window extended) by 29 various me...