Quasi-single Crystalline Research Articles

Enlargement of REBa 2Cu 3O y (RE=Y,Yb) quasi-single crystalline film by liquid phase epitaxy

Processing parameters of the liquid phase epitaxy (LPE) growth in order to grow a large REBCO LPE film of 2 in. in diameter with high quality were investigated. In the large film growth, it was clarified that both prevention against the peritectic decomposition of the seed film and suppression of the undesired crystallization were very important factors to grow a large and high quality LPE film. It was confirmed that the LPE growth of the (Y,Yb)BCO system from the YBCO seed film could realize the above requirement. The large LPE films of Y 0.9Yb 0.1Ba 2Cu 3O y with 2 in. in diameter were successfully grown to be a quasi-single crystalline film. The LPE film grown under 5 rpm of rotation had a high crystallinity and showed a high in-plane uniformity of both the crystallinity and the film thickness. The (Y,Yb)BCO LPE film also exhibited excellent superconducting properties of the T c value of 91 K and the J c value of 1.3×10 5 A/cm 2 at 77 K in 0 T.

In Situ Study of Titanium Film Growth On Different Substrates

AbstractThe chemical and microstructural properties of a surface have a strong influence on the growth mode and the morphology of a film evaporated onto this interface. Changes in the growth stress of thin titanium films, measured in situ by a cantilever beam technique, evaporated under UHV-conditions are used to monitor the chemical and microstructural properties of a substrate surface. The starting substrate film used in this study was a quasi single-crystalline TiO2-film (d=50 nm) prepared by reactive evaporation of titanium in an oxygen atmosphere and subsequent annealing (20 min, 400°C). The Ti-growth stress on this substrate is compressive up to monolayer coverage and tensile at higher film thickness, which is interpreted to indicate a strong interaction between TiO2 and the arriving Ti atoms at the interface during monolayer formation and strained (tensile) layer epitaxy at higher film thickness. In a second series of experiments the TiO2-film was covered with Al-overlayers of varying thickness. Due to oxygen interdiffusion from the TiO2-film an amorphous Al-oxide layer is formed at the interface eliminating the high degree of order of the substrate TiO2-film. On this amorphous substrate the stress vs. thickness curve of the Ti-film, in terms of our stress model, is interpreted to indicate island formation and growth of a polycrystalline Ti-film. At Al-layer thicknesses above about 3 nm the Al-interface becomes metallic. The structure of this Al-surface depends on the film thickness and substrate temperature during its deposition. During deposition of the first Ti-monolayer on metallic Al a large incremental tensile stress (up to 45 GPa) is measured. The magnitude of this tensile stress is closely related to the surface microstructure of the Al substrate. The surface roughness deduced from the tensile interface stress is compared with the surface roughness measured by AFM.For comparison, analogous experiments were made with Al2O3/Al substrate bilayers. The results of these experiments qualitatively agree with those on the TiO2/Al-substrate. The general shape of the stress vs. thickness curve is comparable, however quantitative differences are interpreted to be due to differences in the structure and/or chemical composition of the substrate Al-film.

Influence of substrate properties on the growth of titanium films: part III

The growth of thin Ti-oxide films (12 nm) on alumina substrate films formed by reactive evaporation of Ti in an oxygen atmosphere was studied by in situ internal stress measurements under ultra high vacuum conditions and transmission electron microscopy. Oxygen pressure and substrate temperatures were the varied parameters of the reactive evaporation. These Ti-oxide-films with different oxygen content (O 2/Ti-films) were then used as substrate films for the deposition of a clean titanium film. The growth stress of the titanium film on the as-deposited O 2/Ti-substrate films is comparable with that previously found for H 2O/Ti-substrates and indicates island growth and the formation of polycrystalline titanium films. Annealing (400°C, 20 min) of the as-deposited – amorphous – O 2/Ti-films gives rise to the formation of crystalline TiO 2. The amount of TiO 2 formed during annealing is strongly dependent on the oxygen content of the O 2/Ti-film. The oxygen content, in return, is dependent on oxygen partial pressure and substrate temperature during O 2/Ti-film deposition. The corresponding changes in the substrate film properties (oxygen content, crystallinity, etc.) are reflected in significant changes in the growth stress of the titanium film. The stress vs. thickness curve of these titanium films appears to indicate a superposition of the growth stress of two different growth modes, i.e. growth of a polycrystalline film with island growth on the as-deposited, amorphous oxide substrate and epitaxial growth of a quasi single crystalline film on the crystalline TiO 2-substrate.

Possibility of Quasi-Single-Crystalline Semiconductor Films

AbstractThe existence of a novel tetrahedral semiconductor Quasi-Single-Crystalline (QSC) phase is posited. In the QSC semiconductor phase, the films consist of grains with a diamond structure of tetrahedral elements, such as Si, Ge and C, and the grains have a preferred orientation, such as <111> or <100> normal to the film. The lattices perpendicular to the grain boundaries are quasi-matched with neighboring grains. The grains in the films form a regular array, and are distributed more uniformly than in conventional poly-crystalline semiconductor films. Because of the small-angle grain boundaries, a tetrahedral QSC semiconductor such as QSC Si films are expected to have extremely low energy barriers at the grain boundaries.

Evolution of Stress; Phase Formation and Microstructure in TiCux-Alloy Films

AbstractThe internal stress of TiCux-alloy films on alumina substrates was measured in situ under UHV-conditions as a function of substrate temperature and stoichiometry using a cantilever beam technique.The stress vs. thickness curves of alloy films with TiCu0.5, TiCu, TiCu2 and TiCu3 stoichiometry indicate that the film growth is amorphous at 130°C and polycrystalline at 350°C substrate temperature, which was confirmed by TEM-investigations. Furthermore TED-results of alloys deposited at 350°C imply that the TiCux-alloy-phases formed at that temperature are Ti2Cu, γ-TiCu, TiCu3 and TiCu4.The influence of substrate temperature on the growth of TiCux-alloy films (x = 1) was investigated in more detail. At substrate temperatures below 300°C the stress vs. thickness curves indicate the formation of amorphous alloy films, again confirmed by TEM- and TED-analysis. At substrate temperatures around 300°C a strong tensile stress contribution above a mean thickness of about 20 nm indicates a change in the growth mode and thus microstructure of the alloy film. The corresponding TEM- and TED-micrographs show quasi single-crystalline films. Finally at 350°C substrate temperature the stress vs. thickness curves indicate once again a change in the film growth mode, the film structure is polycrystalline and the formation of γ-TiCu is deduced fore TED-results.

Rate Mechanism of Plasticity in the Crystalline Component of Semicrystalline Nylon 6

The rate mechanism of crystal plasticity was studied in quasi-single crystalline (QSC) Nylon 6 prepared by plane strain compression in a channel die to equivalent extensional strains on the order of 1.39. Specimens of such higly oriented material were probed in simple shear experiments on the (001) [010] and (100)[010] monoclinic chain slip systems by means of strain rate change experiments in the temperature range of 255-366 K. These experiments demonstrated that while there is a well developed glass transition in the shear moduli of the material there is no corresponding transition in the plastic resistances, indicating that the plastic behavior of the QSC material is derived entirely from the crystalline component

Thin film growth of the 2122-phase of BCSCO superconductor with high degree of crystalline perfection

Thin films of the 80 K-phase of BiCaSrCu-oxide superconductor having the composition of Bi2Ca1.05Sr2.1Cu2.19Ox and high degree of crystalline perfection have been grown on c-axis oriented twin free single crystal substrates of NdGaO3. This has been achieved by carefully establishing the growth conditions of the liquid phase epitaxy (LPE) experiments. The temperature regime of 850 °C to 830 °C and quenching of the specimens on the termination of the growth period are found to be pertinent for the growth of quasi-single crystalline superconducting BCSCO films on NdGaO3 substrates. The TEM analysis reveals a single crystalline nature of these films which exhibit 100% reflectivity in infrared regions at liquid nitrogen temperature.

Very high critical current in a long YBa2Cu3O7−δ single crystalline rod

We studied by magnetic and microscopic techniques a disk (2.0 mm diam and 1.0 mm thick) sliced from a quasi single-crystalline rod prepared by very slow solidification in a small temperature gradient. The sample presents features very similar to a typical millimetric single crystal obtained by the standard flux methods. We deduced a high critical current density Jc from magnetic measurements: 2×106 A/cm2 at 4.2 K in a 3T field parallel to the c axis. The transport critical current density along the rod axis (i.e., ∼45° off the c axis) was found to be about 7000 A/cm2 at 77 K in zero applied field. It is comparable to that deduced from the hysteresis cycle at the same temperature for the same current direction.

Graphoepitaxial recrystallization of Bi films on SiO and C substrates with a surface relief structure

The oriented recrystallization of polycrystalline Bi films vapor deposited on amorphous C and SiO substrates with a well defined surface relief grating (“graphoepitaxy”) was studied by TEM and electron diffraction. Recrystallization was achieved by post-deposition annealing above the melting point of Bi and subsequent cooling down to room temperature. The influence of substrate temperature and vapor beam flux during deposition of Bi and of the thickness of the film on the orientation was investigated. It was found that the degree of orientation depends strongly on the surface coverage and accordingly on the mean thickness of the Bi film. Large area, quasi-single crystalline films were obtained for coverages exceeding 90% and having a mean layer thickness of below 42 nm. The results are interpreted by consideration of the energies of cohesion and interfacial tension.

Cristallisation par germination épitaxique

We have shown that by evaporation of any saturated solution, it is possible to get on any metallic film a number of microscopic flat and very thin single crystals (i.e. thickness smaller than 1 μm), the orientations of which are parallel. The metallic film has to be deposited on a single crystal of the same material contained in the solution. The microcrystals are either separated or closely jointed to the thickness of the metallic film. In that case we have got a quasi-single crystalline film. An explanation is given in terms of sub-microscopic holes in the film. There is first an epitaxial nucleation in the holes followed by growth at the surface of the film.