In the context of low-emissivity glazing, the redox reaction at a buried ZnO/Ti interface is studied in model nanometer-thick film stacks synthesized by magnetron sputtering deposition. For a given amount of Ti, the roles of annealing temperature up to 550 degrees C, of ZnO layer thickness, and of its crystalline quality are explored. The main originality of the approach is the use of hard x-ray photoemission spectroscopy to probe in situ chemical reactions at a buried interface in a non-destructive way. The detailed analysis of relevant core levels reveals the formation of a ZnxTiyOz x Ti y O z ternary compound and the nearly complete oxidation of Ti into TiO2. 2 . Thanks to complementary measurements of thermal desorption spectroscopy and electron probe microanalysis, unexpected diffusion of the Zn redox reaction by-product through the upper part of the stack and its desorption in vacuum are clearly evidenced. The reaction and mass transport pathways are rationalized through thermodynamic simulations.

By combining the well-known grid reflection method with a digital image correlation algorithm and a geometrical optics model, a new method is proposed for measuring the change of curvature of a smooth reflecting substrate, a common reporter of stress state of deposited layers. This tool, called Pattern Reflection for Mapping of Curvature (PReMC), can be easily implemented for the analysis of the residual stress during deposition processes and is sufficiently accurate to follow the compressive-tensile-compressive stress transition during the sputtering growth of a Ag film on a Si substrate. Unprecedented resolution below 10-5m-1can be reached when measuring a homogeneous curvature. A comparison with the conventional laser-based tool is also provided in terms of dynamical range and resolution. In addition, the method is capable of mapping local variations in the case of a non-uniform curvature as illustrated by the case of a Mo film of non-uniform film thickness under high compressive stress. PReMC offers interesting perspectives forin situaccurate stress monitoring in the field of thin film growth.

The post-growth stress relaxation in thin polycrystalline Ag films, deposited by direct-current magnetron sputtering under different growth conditions, was explored through wafer curvature measurements. It exhibits exponential behaviour with three distinct characteristic time components Tau. The slowest one, namely Tau(th) approximate to 200 s, is ascribed to thermal stress inherent to the deposition method. In fact, the per -formed temperature measurements match perfectly with an exponential stress variation with heating or cooling, as predicted by a thermal exchange model detailed in this work. Based on a comparison be-tween different deposition conditions (continuous/interrupted sputter deposition and evaporation), the case of Mo deposition and stress relaxation modelling, the remaining components are assigned to the out-diffusion of atoms from grain boundaries (Tau(gb) approximate to 3 s) and to changes in the grain surface shape in-duced by grain boundary grooving (Tau(sur f) approximate to 20 s). The relaxation amplitude of the first mechanism varies linearly with the steady-state stress at the end of growth in agreement with theoretical expectations. Yet, that of the second one does not. However, clues point to a kinetic limitation of atomic diffusion mechanism along grain boundaries. This study provides proofs of the simultaneous occurrence of several mechanisms of stress relaxation in thin metallic films. (c) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Growth-parameter dependence of crystalline polarity and associated electronic transport properties of zinc oxide (ZnO) thin films deposited by radio-frequency magnetron sputtering are investigated. The magnitudes of sputtering input power and distance between the substrate and ZnO target play crucial roles in controlling the polarity either the (0001) or (0001 planes. In addition, the crystallinities and surface morphologies of the films are largely different between the two types of planes. Remarkably, electrical conductivities of the (0001) films are a few orders of magnitude higher than those of the (0001>)planes, which could be attributed to differences in the carrier concentration and Hall mobility. Insights gained in this study regarding controllable polarity is significant for understanding complicated optoelectronic properties even in nominally undoped ZnO films.

Interdiffusion processes between aluminum enriched PVD-sputtered silica thin films and industrial float soda-lime silicate glass substrates are quantitatively studied using SIMS analysis. Heat treatments are performed at temperatures close or above the glass transition temperature of the float glass. Aluminum doping of the film is shown to strongly increase the migration of alkali from the glass substrate to the silica thin film. In particular the final alkali content in the film exhibits a linear scaling with the aluminum concentration. An interdiffusion process is evidenced between bulk alkali ions and protons originating from a significant water content in the as-deposited silica film. Experimental measurements of sodium concentration are shown to be consistent with a simple thermodynamic model based on the equilibration of the activity of sodium between the film and the glass substrate.

Band alignment at the interface between evaporated silver films and Zn- or O-terminated polar orientations of ZnO is explored by combining soft and hard x-ray photoemissions on native and hydrogenated surfaces. Ultraviolet photoemission spectroscopy (UPS) is used to track variations of work function, band bending, ionization energy, and Schottky barrier during silver deposition. The absolute values of band bending and the bulk position of the Fermi level are determined on continuous silver films by hard x-ray photoemission spectroscopy (HAXPES) through a dedicated modeling of core levels. Hydrogenation leads to the formation of similar to 0.3 monolayer of donorlike hydroxyl groups on both ZnO-O and ZnO-Zn surfaces and to the release of metallic zinc on ZnO-Zn. However, no transition to an accumulation layer is observed. On bare surfaces, silver adsorption is cationic on ZnO(000 (1) over bar)-O [anionic on ZnO(0001)-Zn] at the earliest stages of growth as expected from polarity healing before adsorbing as a neutral species. UPS and HAXPES data appear quite consistent. The two surfaces undergo rather similar band bendings for all types of preparation. The downward band bending of V-bb,(ZnO-O) = -0.4 eV and V-bb,(ZnO-Zn) = -0.6 eV found for the bare surfaces is reinforced upon hydrogenation (V-bb,(ZnO-O+H) = -1.1 eV, V-bb,(ZnO-Zn+H) = -1.2 eV). At the interface with Ag, a unique value of band bending of -0.75 eV is observed. While exposure to atomic hydrogen modulates strongly the energetic positions of the surface levels, a similar Schottky barrier of 0.5-0.7 eV is found for thick silver films on the two surfaces.

We study the diffusive interaction between soda-lime glass substrates and sputtered aluminum-doped silica thin films at 650 degrees C, the temperature of commercial soda-lime glass shaping or tempering. A first rapid migration of alkali ions from substrate to thin film has been described in a companion paper (J Am Ceram Soc. 2018;101:1516). Using the same samples as (J Am Ceram Soc. 2018;101:1516), we focus here on later interactions, when the layer is consumed by the substrate resulting from diffusive interactions. Using Secondary Ion Mass Spectroscopy profilometry, we show that the interdiffusion rate increases with the aluminum doping content of the layer. We show that the alkali uptake of silica layers accelerates diffusive exchanges with the substrate, consistently with a decrease of viscosity of the layer. Diffusion profiles of silicon are well reproduced when solving the diffusion equationfor a diffusivity having an exponential dependence with silicon concentration. The diffusivity of aluminum is shown to be 10 times slower than the diffusion of silicon. Specific exchanges of the two network formers with network modifiers are deduced from the composition-space trajectories, providing evidence for multicomponent diffusive couplings between species.

It is critical to reveal how crystalline polarity correlates with the electronic transport properties in polar semiconductors, such as zinc oxide (ZnO), for the development of materials with properties tailored for specific optoelectronic applications. In this paper, we investigate the structure-property relationships in ZnO films by means of tailoring the polarity of homostructural ZnO bilayers that are subjected to an external substrate bias (V-sub) during deposition. Since the probability of incorporating defects and impurities in ZnO depend on the crystalline facet, the polarity of ZnO should be a critical parameter in determining electronic conductivity. The electric conductivity and Hall mobility of the ZnO films deposited under positive V-sub were much higher than those deposited under negative V-sub. Further investigations of the homostructural ZnO bilayer films, where different signs and magnitudes of V-sub were applied, revealed that the polarity is responsible for electronic conductivity of the ZnO films in this study.

Surface differential reflectivity spectroscopy is a fast non-destructive in situ and real-time measurement technique which allows following the first stages of thin film deposition. However, when applied to sputtering technique, spectra can strongly be distorted by residual light coming from plasma in a way, as shown herein, that depends on sample reflectivity. Thanks to suitable measurements, before and after growth with and without plasma or illumination lights, a protocol of signal correction is proposed to get rid of the spurious plasma contribution. The interest of the method is illustrated in the case of silver deposition on a silicon substrate.

Effects of the nature of substrates, either crystalline or non-crystalline, on the structure and properties of ZnO films deposited by sputtering were investigated. This study focuses mainly on the role of the external electric bias applied to substrates during magnetron sputtering deposition in controlling crystalline polarity, i.e., Zn-face or O-face, and the resulting film properties. It was found that polarity control was achieved on silica and silicon substrates but not on sapphire substrates. The substrate bias did influence the lattice parameters in the structural formation; however, the selection of the substrate type had a significant influence on the defect structures and the film properties.

Thin films with low adhesion and large residual stresses may buckle and delaminate from their substrates. This delamination often results in oscillating patterns known as ‘telephone cords’. Other configurations can be observed as well, such as entangled networks of blisters. The present study aims at elucidating how these networks are generated through branching. A model coupling a geometrically non-linear plate model and a cohesive zone with mode dependent interfacial toughness is used. Previous work on the early stage delamination of initially circular blisters during interfacial crack front propagation are revisited and extended to the remote post-critical regime to capture front branching. We also build a partial phase diagram of buckling driven delamination morphologies. An intrinsic critical stress parameter is proposed which can be used to predict delamination morphology and to define ‘safe’ conditions where buckle propagation can be avoided. This critical stress also defines an intrinsic lengthscale which plays the role of a minimum nucleation size.

Thin films with low adhesion and large residual stresses may buckle. The resulting morphologies are varied, but one of the most commonly observed is an intriguing oscillating pattern – the so-called "telephone cord" – which has been extensively investigated in the recent years. We have studied the kinematics of formation of telephone cords using a geometrically non-linear plate model and mode dependent interfacial toughness, captured via a cohesive zone. Through extensive Finite Element Simulations, we have demonstrated a simple, non-trivial relation between telephone cord wavelength and interfacial toughness. To validate this prediction, highly stressed Mo thin films were deposited on Si wafers, with a well defined interface and very reproducible adhesion. Studying the morphology of the resulting buckles for different film thicknesses and stresses, we observed a trend which was fully consistent with our simulation results. From the data fit, an adhesion energy of 0.58±0.04 J m−2 for the SiO2/Ag interface was inferred, which compares well with literature estimates.

The chemistry and intermixing at buried interfaces in sputter deposited ZnO/Ti/ZnO thin layers were studied by hard x-ray photoelectron spectroscopy. The long mean free path of the photoelectrons allowed for detailed studies of the oxidation state, band bending effects, and intrinsic doping of the buried interfaces. Oxidation of the Ti layer was observed when ZnO was deposited on top. When Ti is deposited onto ZnO, Zn Auger peaks acquire a metallic character indicating a strong reduction of ZnO at the interface. Annealing of the stack at 200 °C results in further reduction of ZnO and oxidation of Ti. Above 300 °C, oxygen transport from the bulk of the ZnO layer takes place, leading to re-oxidation of ZnO at the interface and further oxidation of Ti layer. Heating above 500 °C leads to an intermixing of the layers and the formation of a ZnxTiOy compound.

In the thin film area, it is well-known that deposition rate impacts the morphology but tools to quantify online fast growth processes are scarce. Here we show that surface differential reflectivity spectroscopy (SDRS) can be used in real time to follow silver nanoparticle growth during sputtering deposition. The main experimental challenge was to avoid noise and saturation due to the plasma emission and to obtain a reasonable signal/noise ratio to monitor fast deposition. A specific setup was designed resulting in an acquisition speed in the range of hundreds of milliseconds and used to investigate the growth of silver on alumina as a test example. The evolution of the size, density and aspect ratio of growing silver islands were determined by modelling their plasmonic response and compared with previous results obtained at a much lower growth rate using physical vapour deposition (Lazzari and Jupille 2012 Nanotechnology 23 135707). During room-temperature sputter deposition, coalescence leads to significantly larger and flatter aggregates compared to evaporation at the same coverage. However, both deposition techniques lead to similar nucleation and growth behaviours. Higher substrate temperature (575 K) did not change the trend and a sticking coefficient close to one was found. The observed evolution of the particle aspect ratio is discussed in terms of supersaturation and flux driven hindrance of the coalescence.

The structures and properties of zinc oxide thin films deposited by radio-frequency magnetron sputtering were investigated for different substrate biases applied during deposition. The electrical bias determined the crystalline polarity of a nominally undoped film on an amorphous substrate: films with a (0001) surface and a (0001¯) surface were produced under positive and negative biases, respectively. Moreover, the polarity of the films was determined at an early stage of the deposition and could not be reversed by switching the substrate bias.

The evolution of the compressive stress in Mo/MoOx sputter-deposited thin films has been followed in situ during deposition as a function of two parameters: the oxygen flux and the negative voltage bias applied to the substrate. In addition the microstructure of the films has been characterized. Oxygen accumulation at the interface was observed. We describe the origins of the stress in terms of ion bombardment and oxygen incorporation.

Compressively stressed thin films weakly bound to the substrate often result in interface failure, buckling and buckling driven delamination. One of the most readily observed morphologies of a buckle in case of biaxial compression in the film is the telephone-cord blister. This morphology is rather complicated and the formation and propagation of telephone-cord buckles is not well understood. Analytical approach based on Von Karman theory of plates have provided valuable insights into straight-sided blisters, for which the coupled post-buckling elastic deformation and delamination problems are analytically tractable (Hutchinson JW, 1992). More recently, it was established that the telephone cord buckles as well as some circular shapes could be viewed as equilibrium configurations evolving out of the straight sided blisters, a phenomenon known as 'secondary buckling' (Audoly B, 1999, Parry G, 2006). Nevertheless, the complex geometry of the telephone cord buckle makes it necessary to resort to numerical simulation.