Epitaxial decagonal thin films on crystalline substrates

Al-Cu-Fe-Cr quasicrystalline thin films were grown on atomically flat Al 2 O 3 sapphire (0001) substrates by single-target magnetron sputtering followed by annealing. A decagonal phase with the tenfold axis A 10 parallel to the substrate surface normal was observed. The epitaxial decagonal film had two different unique orientations: a twofold P axis A 2P and a twofold D axis A 2D parallel to of the substrate. These two configurations were explained using a coincidence reciprocal lattice planes model for the interface energy. We show that this classic approach for crystal-crystal epitaxy can be applied to quasicrystal-crystal systems.     

Fragmentation testing for ductile thin films on polymer substrates

Fragmentation testing of thin films on substrates has in the past been mostly performed in situ using optical and scanning electron microscopy. While these techniques work well for brittle materials, they cannot always discern the difference between through-thickness cracks (TTCs) and localized plastic deformation of ductile films. Here, we describe fragmentation testing with atomic force microscopy and present criterion to distinguish TTCs and localized deformation for ductile films.     

Atomic force microscopy investigation of buckling patterns of nickel thin films on polycarbonate substrates

The evolution of buckling patterns of nickel thin films have been studied in situ by atomic force microscopy during cyclic tests composed of uniaxial compression followed by release of the external applied stress. After the first strain cycling, buckling structures evolve from straight-sided wrinkles to varicose patterns characterized by a debuckling of some parts of the film. Further cycling tests reveal that rebonding of the film on its substrate does not occur once decohesion has taken place.     

Fabrication of opal-like thin films

A process is described for the fabrication of opal-like thin films by controlling a solid–liquid interface moving at an inclined glass substrate. A special airflow is adopted to control solvent evaporation. SEM images and photographs show that the films, composed of polystyrene spheres, are coloured, flat, uniform, packed multilayers, and are well arrayed over a large scale. The ordered domains range in size from 10 to 15?µm. The spheres in suspension crystallized, caused by an intense interaction between the spheres on the boundary between the suspension and the substrate. A wide photonic band gap is observed in the normal-incidence transmission spectra of the films fabricated by this method. Cracks and defects in the films are examined and discussed.     

Stair-rod dislocations in perovskite films on LaAlO3 substrates

Two types of stair-rod dislocation formed at junctions of {111} stacking faults in SrTiO₃-SrRuO₃ two-layer films on LaAlO₃ substrates have been studied by high-resolution transmission electron microscopy. The first type, formed by the interaction of two stacking faults situated at the flat SrRuO₃-LaAlO₃ interface without any step, has a Burgers vector (a/3)<110>. The other type, formed by the interaction of two stacking faults, of which one starts from the SrRuO₃-LaAlO₃interface area involving an interface step, has a Burgers vector (a/3)<120>. The formation mechanism of the stair-rod dislocations and the effect of the step are discussed.     

Reversible phase transition in vanadium oxide films sputtered on metal substrates

Vanadium oxide films, deposited on aluminium (Al), titanium (Ti) and tantalum (Ta) metal substrates by pulsed RF magnetron sputtering at a working pressure of 1.5 x10^?2 mbar at room temperature are found to display mixed crystalline vanadium oxide phases viz., VO₂, V₂O₃, V₂O₅. The films have been characterized by field-emission scanning electron microscopy, X-ray diffraction, differential scanning calorimetry (DSC) and X-ray photoelectron spectroscopy, and their thermo-optical and electrical properties have been investigated. Studies of the deposited films by DSC have revealed a reversible-phase transition found in the temperature range of 45–49 °C.     

Anisotropic BaTiO3 thin films grown on MgO-buffered R-plane sapphire

Epitaxial BaTiO₃ thin films grown on MgO-buffered R-plane-cut Al₂O₃ substrates show a non-uniform distribution of planar defects. Transmission electron microscopy allows the determination of the distributions of planar defects with respect to the Al₂O₃ substrate. The BaTiO₃ film, the MgO buffer and the Al₂O₃ substrate have an orientation relationship of [100]_BaTiO3//[100]_MgO//[1120]_Al2O3, (010)_BaTiO3//(010)_MgO//(1104)_Al2O3 and (001)_BaTiO3//(001)_MgO// ≈ (1102)_Al2O3 (about 5°; deviation). Under the above relationship, most of the {111} stacking faults occur on (111) and (111) planes, that is two of four sets of {111}_BaTiO3, whereas cracks in the BaTiO₃ film (and MgO buffer) are situated on the (100) planes. The anisotropic distribution of planar defects is regarded as a consequence of an anisotropic stress in the films generated during their fabrication.     

Nano-undulations of nickel thin films on a substrate under compressive stress

Nickel thin films on a substrate have been studied in situ by atomic force microscopy during deformation. Undulations have been observed on the debonding regions, of very low amplitude and of periodicity of the order of 1mum. Attempts are made to compare these experimental results with previous models of buckling instabilities of thin plates.     

Influence of Guinier-Preston zones on deformation in Ti-rich Ti-Ni thin films

The deformed microstructure of a Ti-48.9at.%Ni thin film has been investigated by transmission electron microscopy. It was found that Guinier-Preston (GP) zones exist in the thin film and the martensite has (001) compound twins as substructure. The microstructure of the martensite shows that the GP zones do not stop both the shear deformation of martensitic transformation and the twinning shear of (001) deformation twin in the martensite phase. These results give a microstructural explanation for the previous result that Ti-rich Ti-Ni thin films with GP zones show a large transformation strain despite the presence of the GP zones.     

Electromechanical behavior of single-walled carbon nanotube thin films

Carbon nanotubes have been intensively studied owing to their great potential in nanoelectronics and nanomechanical devices. Recently, experimental results have shown that single-walled carbon nanotubes (SWCNTs) change their electronic properties when subjected to strain. In this study, the electromechanical characteristics of SWCNT networks were investigated for the application of printable strain sensors on flexible substrates. SWCNT films were formed on plastic substrates of poly(ethylene terephthalate) using a spray process. In this manner, we were able to control the transparency and obtain uniform electrical properties of the films. The films are isotropic on account of the random orientation of bundles of SWCNTs. Experimental results showed a nearly linear change in the resistance across a film when it was subjected to tensile strain, even in the inelastic range of the flexible substrate. The results demonstrate the potential use of SWCNT films for highly sensitive printable strain sensors on a macroscale.     

Epitaxial Ni-Al thin films on NaCl using a Ag buffer layer

Epitaxial nanoscale [001] films of Ni _x Al_100-x (x = 62.5) have been prepared by physical vapour deposition on to a thin film of Ag [001] on NaCl (001) faces with occasional hillocks. The Ag film contains numerous dislocations and stacking faults and has a rms surface roughness of 2 nm. The Ni-Al film is ordered in the B2 structure and reveals many dislocations as well as antiphase boundaries between ordered domains. The formation of subgrains in the Ni-Al film results in severe height variations up to 30 nm across the surface. A cross-sectional model for the growth of both films is presented.     

Modelling of dissolution kinetics of thin amorphous chalcogenide films

A theoretical relationship for the dissolution kinetics of thin chalcogenide films is proposed. The influence of light irradiation on the film dissolution is taken into account. The theoretical curves are in good agreement with the experimental dissolution results obtained for As₂S₃ thin amorphous films.     

Sol-gel-hydrothermal growth of oxide thin films at low temperatures

Lead zirconate titanate (PZT) (Pb(Zr_0.52Ti_0.48)O₃) and barium titanate (BaTiO₃) thin films have been successfully prepared using a novel sol-gel- hydrothermal (SG-HT) technique at low temperatures, which involves a combination of the conventional sol-gel process and a hydrothermal method. Highly (111)-oriented PZT thin films with a single perovskite phase and polycrystalline BaTiO thin films with well developed crystallites were obtained at a processing temperature as low as 160⁰C. The microstructural characteristics demonstrate that the SG-HT-derived PZT and BaTiO₃ thin films with good crystallinity and surface morphology are converted from the amorphous phase to the desired perovskite phase on platinum-coated and bare silicon substrates at a low processing temperature of 100-200 C. These results suggest that the SGHT technique, which is of great significance because of its low processing temperature, will become a potential and promising process for fabricating PZT, BaTiO₃ and other oxide thin films.     

Structural phase transitions in epitaxial SrRuO3 thin films

The microstructural evolution of epitaxial SrRuO₃ thin films from ambient temperature (about 293K) to about 900K has been studied by in-situ transmission electron microscopy. Upon heating from the ambient temperature, the intensities of h, k, 2n+1 and h, -h+2n+1, 0 reflections in selected-area electron diffraction patterns decrease with increasing temperature. Two structural phase transitions were observed at about 673and about 783K, revealed by the vanishing of the h, k, 2n+1 and h,-h+2n+1, 0 reflections respectively. The examination of electron diffraction patterns along several different zone axes, taking into account the possible tilting configurations of RuO₆ octahedra, indicates that, upon heating, the orthorhombic structure of SrRuO₃ transforms into a tetragonal structure at about 673K, and further transforms into a cubic structure at about 783K. Possible structural models for the high-temperature phases are considered.     

Effect of film thickness and grain size on fatigue-induced dislocation structures in Cu thin films

This letter presents systematic experimental observations of fatigue damage and corresponding dislocation structures in thin Cu films as a function of film thickness made using transmission electron microscopy and focused-ion-beam microscopy. It is found that, in thick films and grains of at least 3.0 μm diameter, coarse surface extrusions and dislocation wall and cell structures occur whereas, in thin films or in small-diameter grains, finer extrusions occur but no clearly defined dislocation structures are present. This minimum required dimension of 3.0 μm for fatigue damage formation may be caused by constrained dislocation motion in small dimensions.     

On the length scale of cyclic strain localization in fine-grained copper films

Fine-grained copper films on a flexible substrate were cyclically deformed under constant strain range control. It was found that cyclic dislocation plasticity through individual dislocation glide is still dominant at the submicrometer scale, while the ability of irreversible slip of dislocations gradually decreases and the damage was changed from extrusion-induced localization to cracking along grain boundary. Statistical evaluation of the mean spacing between slip bands and/or lines leads to a critical scale (～28 nm) below which dislocation-controlled cyclic strain localization would be shut down.     

Optical characterization of spin-coated cobalt porphyrazine thin films: effect of annealing temperature

Cobalt porphyrazine thin films were prepared by the spin-coating technique. The coated substrates were annealed at different temperatures (373, 423 and 523 K). The optical properties of the films were investigated by measuring the transmittance and reflectance spectra. The refractive index, extinction coefficient, optical band gap, dielectric constant values and thickness of the films were determined. Results showed that the refractive index, the extinction coefficient and the dielectric constants increased on annealing the films at 373 K in comparison with films annealed at other temperatures. On the other hand, the values of the band gap energy and thickness of the annealed film at 373 K were found to be the lowest in comparison with films annealed at different temperatures.     

Effect of heat treatment on the NO2-sensing properties of sputter-deposited indium tin oxide thin films

Transparent conducting indium tin oxide (ITO) films were deposited onto glass substrates by radio-frequency magnetron sputtering at 648?K, under an oxygen partial pressure of 1?Pa. The effect of annealing on the electrical properties of the films was studied. Characterization of the coatings revealed an electrical resistivity below 6.5?×?10^??3?Ω?cm. The ITO films deposited at 648?K were amorphous, while the crystallinity improved after annealing at 700?K. The surface morphology examined by scanning electron microscopy appears to be uniform over the entire surface area after annealing. The NO₂-sensing properties of the ITO films were investigated and showed sensitivity at concentrations lower than 50?ppm, at a working temperature of 600?K.