Nondestructive Material Homogeneity Characterization by Millimeter Waves

Millimeter wave bridge technique for nondestructive material homogeneity characterization is described. The idea of this technique is the local excitation of millimeter waves in testing material and the measurement of the transmitted amplitude and phase in it different places. Some results of the homogeneity measurements for the dielectric substrates are presented.     

Coherent magnetic vortex motion in optically formed channels for easy flow in YBa2Cu3O7−x superconducting thin films

We report our results of investigation of electric and magnetic properties of partially oxygen-depleted channels for easy vortex motion in YBa₂Cu₃O_7?x (YBCO) superconducting, 50-μm-wide, and 100-μm-long microbridges at temperatures below the onset of the superconducting state critical temperature T _c ^on . The channels were produced by means of a laser-writing technique. The writing was performed using a 0.1–0.3 W power, continuous-wave laser radiation focused down to a ~ 5 μm spot on the surface of a superconducting film in a nitrogen gas atmosphere, and resulted in perpendicular stripes (channels) with partial (x ~ 0.2) reduction of the oxygen content in the YBCO stripe. The oxygen-depleted channels exhibit a depressed T _c and lower both the critical current density and the first critical magnetic field, as compared with the laser-untreated areas. The bias current applied to the bridge self-produced a magnetic flux that penetrated the channels in a form of Abrikosov magnetic vortices that, subsequently, moved coherently (a quasi-Josephson effect) along the channels in the narrow temperature range of 0.943 T _c ^on –0.98 T _c ^on and manifested themselves as steps on the current–voltage characteristics of our microbridges. Our results demonstrate that laser-induced formation of artificial channels of the flux flow can be used for a precise control of vortex nucleation and their coherent motion in pre-assigned regions of thin-film YBCO devices.     

Synthesis and characterisation of Hf(thd)2X2 derivatives [X = N(SiMe3)2, OSiMe3 and OSiBuMe2] as precursors for MOCVD of hafnium silicate films

Hafnium β-diketonatochlorides HfCl₂(thd)₂ (1), HfCl(thd)₃ (2) as well as β-diketonato-silylamide and/or siloxide derivatives of 1 namely Hf(thd)₂[N(SiMe₃)₂]₂ (3), Hf(thd)₂(OSiMe₃)₂ (4) and Hf(thd)₂(OSi^tBuMe₂)₂ (5) (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) were synthesized and characterized by elemental analysis, FT-IR, ¹H NMR and TGA. 2 and 5 were also characterized by single-crystal X-ray diffraction. The siloxide ligands are in cis position for 5 and exert a strong trans effect. The new volatile compounds were tested as single-source precursors for the deposition of HfSi_xO_y films by pulsed liquid injection MOCVD on Si(1 0 0) and R plane sapphire. The as-deposited at 600–800 °C films were essentially amorphous, Hf-rich (Hf/Hf + Si = 0.7–0.85) and smooth.     

Preparation of dense, ultra-thin MIEC ceramic membranes by atmospheric spray-pyrolysis technique

Dense ceramic mixed ionic and electronic conducting membranes have been deposited by atmospheric spray-pyrolysis technique onto porous ceramic substrates. Perovskite oxide layers, i.e. manganites La_1−xSr_xMnO₃, ferrites La_1−xSr_xFe_1−y(Co,Ni)_yO₃, gallates La_1−xSr_xGa_1−y(Co,Ni,Fe)_yO₃, cobaltites La_1−xSr_xCoO₃ and related perovskites such as lanthanum nickelate La₂NiO₄ layers have been prepared. The structure, morphology and composition of the layers were characterised by XRD, SEM and WDS, respectively. Density and gas tightness of the layers were studied as a function of deposition process parameters, film thickness (from 0.5 to 3 μm) and preparation procedure. The presence of cracks and defects due to thermo-mechanical stresses applied during or after the preparation process were correlated with the membrane composition and the corresponding thermal expansion coefficient differences between substrates and membranes.