RESUMO
Molecular layer deposition (MLD) is a strongly emerging thin-film technique for deposition of ultra-thin inorganic-organic hybrid ("metalcone") coatings directly from the gas phase, even on complex three-dimensional surfaces. In particular alucones (Al-based hybrids) have been found interesting e.g. for Li-ion battery and gas-barrier applications owing to the promise for enhanced mechanical performance provided by the organic fragments in the materials' structure. However, the metalcones based on short/small organic fragments are relatively brittle from the mechanical perspective. Here, we demonstrate an efficient approach for tailoring mechanical properties of MLD-fabricated hybrid inorganic-organic thin films through control over the organic precursor chain length. The proof-of-concept data is presented for alucones prepared using trimethyl aluminum together with 1,6-hexanediol or 1,10-decanediol as the precursors. Tensile testing coupled with in situ optical microscopy reveals a gradual increase in stretchability with the increasing chain length, such that the crack onset strain value of 9.9 ± 0.2% is obtained for the 1,10-decanediol-based 100 nm-thick film. Through the demonstration of substantially suppressed crack propagation-as a sign of brittle-to-ductile transition-and the decrease in the elastic modulus value down to 4.6 ± 2.1 GPa, the mechanical performance of the alucone family is extended to the polymeric regime. The substantial increase in the mechanical performance within the metalcone material family makes the results particularly interesting for high-capacity high-volume-change battery electrodes requiring mechanically highly robust coatings.
RESUMO
Pliable and lightweight thin-film magnets performing at room temperature are indispensable ingredients of the next-generation flexible electronics. However, conventional inorganic magnets based on f-block metals are rigid and heavy, whereas the emerging organic/molecular magnets are inferior regarding their magnetic characteristics. Here we fuse the best features of the two worlds, by tailoring ε-Fe2O3-terephthalate superlattice thin films with inbuilt flexibility due to the thin organic layers intimately embedded within the ferrimagnetic ε-Fe2O3 matrix; these films are also sustainable as they do not contain rare heavy metals. The films are grown with sub-nanometer-scale accuracy from gaseous precursors using the atomic/molecular layer deposition (ALD/MLD) technique. Tensile tests confirm the expected increased flexibility with increasing organic content reaching a 3-fold decrease in critical bending radius (2.4 ± 0.3 mm) as compared to ε-Fe2O3 thin film (7.7 ± 0.3 mm). Most remarkably, these hybrid ε-Fe2O3-terephthalate films do not compromise the exceptional intrinsic magnetic characteristics of the ε-Fe2O3 phase, in particular the ultrahigh coercive force (â¼2 kOe) even at room temperature.
RESUMO
Mechanical fracture properties were studied for the common atomic-layer-deposited Al2O3, ZnO, TiO2, ZrO2, and Y2O3 thin films, and selected multilayer combinations via uniaxial tensile testing and Weibull statistics. The crack onset strains and interfacial shear strains were studied, and for crack onset strain, TiO2/Al2O3 and ZrO2/Al2O3 bilayer films exhibited the highest values. The films adhered well to the polyimide carrier substrates, as delamination of the films was not observed. For Al2O3 films, higher deposition temperatures resulted in higher crack onset strain and cohesive strain values, which was explained by the temperature dependence of the residual strain. Doping Y2O3 with Al or nanolaminating it with Al2O3 enabled control over the crystal size of Y2O3, and provided us with means for improving the mechanical properties of the Y2O3 films. Tensile fracture toughness and fracture energy are reported for Al2O3 films grown at 135 °C, 155 °C, and 220 °C. We present thin-film engineering via multilayering and residual-strain control in order to tailor the mechanical properties of thin-film systems for applications requiring mechanical stretchability and flexibility.
RESUMO
Atomic/molecular layer deposited (ALD/MLD) inorganic-organic thin films form a novel class of materials with tunable properties. In selected cases, hybrid materials are reported to show environmental instability, specifically towards moisture. In this article, we focus on zinc oxide/zincone multi-layers with the theoretical formula of (ZnO)a(Zn-O-C6H4-O)b. We show by means of ellipsometric porosimetry that micro-porosity in the range of 0.42 and 2 nm in the pristine zincone layer is responsible for its environmental degradation. During degradation, it is found that a relative micro-porosity content of 1.2 ± 0.1 vol% in the pristine zincone films evolves into micro-mesoporosity with a relative content of 39 ± 1 vol%. We also show that the micro-porosity in the zincone layer can be gradually suppressed when few cycles (a = 1-10) of ZnO are introduced. The resulting (ZnO)a(Zn-O-C6H4-O)b = 1 periodic multilayer is an environmentally stable film with a = 10. It is found that the suppressed micro-porosity is due to the development of continuous ZnO layers with a≥ 10.
RESUMO
A combined atomic layer deposition (ALD) and molecular layer deposition (MLD) process was developed to fabricate inorganic-organic [(TiO2)m(Ti-O-C6H4-O-)k]n thin films from TiCl4, water and hydroquinone (HQ) precursors, and in particular, superlattice structures where single-molecular organic layers (k = 1) are periodically sandwiched between thicker TiO2 layers (m > 1). The incorporation of organic layers was found to systematically blue-shift the optical band gap of TiO2 with decreasing superlattice period and--most importantly--to sensitize the TiO2 layers to visible light over a considerable part of the visible range below 700 nm, a fact that could be of substantial interest for photocatalysis and solar cell applications.
