Polycrystalline Fe3O4 films have been prepared by reactive sputtering at room temperature. Transmission electron microscope image shows that the films consist of Fe3O4 grains well separated by grain boundaries with long-range and atomic scale disorders. The width of the long-range disordered grain boundaries observed by high resolution transmission electron microscopy is about～4nm, which is consistent with the boundary dimension derived from the resistivity and magnetization measurements. Temperature dependence of resistivity indicates that the transport properties of the films are dominated by the mechanism of fluctuation-induced tunneling of electrons across the grain boundaries. Ordinary and extraordinary Hall constants were measured to be-8.22×10-11 and～-1.45×10-8Ωcm/G, which are two and three orders of magnitude larger than those of iron, respectively.

Amorphous CoMoN/CN compound soft-X-ray multilayers were fabricated by dual-facing-target sputtering. Their structural thermal stability has been investigated by monitoring the structural evolutions of CN and CoMoN sublayers at annealing temperatures up to 800 degreesC using complementary measurement techniques, and measuring the coefficient of interfacial diffusion at annealing temperatures below 300 degreesC. The period expansion at annealing temperatures below 600 degreesC, which is usually observed in annealed metal/carbon soft-X-ray multilayers, is only 5%. The enhanced sp(2) to sp(3) bond ratio caused by the "incorporation annealing effect" of nitrogen [1] is thought to be responsible for the improved thermal stability of CN sublayers. Mo addition greatly suppresses the structural thermal evolution of CoMoN sublayers. XPS and TEM analyses indicate that the strong chemical bonding between N and Co atoms and Mo nitride aggregation in the grain boundary of cobalt are the main mechanisms for the high thermal stability of CoMoN sublayers. The layered structure of the CoMoN/CN multilayers still exists at the annealing temperature of 800 degreesC, while Co/C and CoN/CN multilayers have already been destroyed at this temperature. Compared with Co/C and CoN/CN multilayers, the smaller negative interdiffusivity measured by X-ray diffraction reveals the stable interfaces of CoMoN/CN multilayers. These results illustrate that refractory metal incorporation and strong chemical bond establishment are quite effective in obtaining thermally highly stable compound soft-X-ray optical multilayers.

At room temperature, polycrystalline Fe3O4 films with thicknesses ranging from 5 to 1120 nm have been prepared by reactive sputtering. Transmission electron microscopy image shows that uniform Fe3O4 grains are well separated by grain boundaries and their size decreases with the film thickness. The changes of resistivity as a function of temperature reveal a grain boundary dominated electron tunneling transport mechanism. The magnetoresistance MR=ρH-ρo=ρ0 measured at room temperature for the films with thickness larger than 200nm is～7.4% in 46 kOe magnetic field, which is one of the largest value have ever been reported for Fe3O4 films under the same conditions. As the thickness reduced from 80 to 5nm, MR decreases from～6.5% to～1.1% due to magnetization reduction and the enhanced spin-flip scattering at the film surface.

The thermal stability of CoMoN/CN compound soft X-ray multilayers has been investigated by monitoring the structural evolutions of CoMoN and CN sublayers at annealing temperatures up to 800℃, and the interfacial diffusion at annealing temperature below 300℃. It is shown that the thermal stability of CoN/CN multilayers can be improved significantly by enhancing the incorporation of nitrogen in CoN sublayers through doping with Mo. Both thermodynamic calculations and X-ray photoelectron spectroscopy (XPS) analyses give the information on the charge transfer from the valence band of Mo to the unfilled valence band of Co and a remarkable chemical shift of N atoms. The strong chemical bonding between N and Co atoms and Mo nitrides aggregation in the grain boundary of cobalt are thought to be the main mechanisms for the high thermal stability of CoMoN sublayers. The period expansion at annealing temperatures below 600℃, which is mainly from the density reduction of CN sublayers, was suppressed effectively by improving the incorporation of nitrogen in CN sublayers. The small negative interdiffusivity measured by X-ray diffraction reveals stable interfaces of CoMoN/CN multilayers. These results illustrate that refractory metal incorporation and strong chemical bond establishment are quite effective in obtaining high thermally stable CoMoN/CN compound soft X-ray optical multilayers.

The structural stability of CoN/CN soft X-ray multilayers has been investigated by using complementary measurement techniques. Annealing in the low-temperature range of 473-523 K, we find three interdiffusion features, different from Co/C multilayers [H.L. Bai et al.: Thin Solid Films 286, 176 (1996)]. (1) The interdiffusion critical wavelengths were calculated as 2.00-2.04nm at temperatures ranging from 473 to 523 K, which is equal to those of Co/C multilayers within the experimental error, indicating that the interdiffusion behaviours in the CoN/CN multilayers are still decided by the thermodynamic properties of the Co-C system. (2) The effective interdiffusivities and macroscopic diffusion coefficients are smaller. (3) The activation energy for diffusion is larger. The features imply that it is possible to improve the thermal stability of Co/C multilayers by doping with N atoms.