Carbon nitride films have been fabricated by a dc facing-target reactive sputtering system for various N2 fractions (PN) in the gas mixture. Complementary measurement techniques, including atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and high-resolution transmission electron microscopy (HRTEM), were used to systematically study the morphology and microstructure of the films. AFM images show that the average surface roughness increases with increasing P-N. XPS analyses indicate that the concentration of N is not directly proportional to PN, and it rises quickly to a saturated value of similar to33 at% at a PN of 20%, which can be attributed to the chemical sputtering effect. The ratio N-C(sp2)/N-C(sp3) increases with increase in PN from 0% to 20%, and then decreases with further increase in P-N. However, the number of sp2-hybridized C atoms continues to increase over the whole range of PN, as evidenced by Raman and FTIR measurements. The growth of a disordered sp2 C structure at P-N below and above 20% can be attributed to the incorporation of N and the compressive stress relaxing, respectively. Raman scattering and HRTEM analyses reveal an incomplete ordering process of the sp2 C structure with increase in PN.

Fe-C granular films with different Fe volume fraction x, were fabricated using a DC facing-target sputtering system at room temperature and subsequently annealed at different temperatures. X-ray diffraction and selected area electron diffraction analyses indicate that as-deposited and low-temperature annealed (less than or equal to350℃) samples are composed of amorphous Fe and C, and higher temperature annealing makes the amorphous Fe transform to alpha-Fe, which is also confirmed by high-resolution transmission electron microscopy. Magnetic measurements indicate that at room temperature the as-deposited Fe-C (xv=58) granular films are superparamagnetic and annealed ones are ferromagnetic. The coercivity of 100 nm thick Fe-C (xv=58) granular films increases with annealing temperature (for 1h) and time (at 450℃). The coercivity of the 100 nm thick Fe-C (xv=58) samples annealed at temperatures ranging from 400 to 500℃ decreases linearly with measuring temperature T, signalling a domain wall motion mechanism. For the samples annealed at 550℃, the change of in-plane coercivity with T satisfies the relation Hc similar to T-1/2, reflecting that this system behaves better as a set of Stoner-Wohlfarth particles. It was also found that there exists a critical thickness (similar to 133nm) for the 450 oC annealed (for 1 h) Fe-C (xv=58) granular films with thickness in the range 100-200nm, below and above which the magnetization reversal is dominated by domain wall motion and by Stoner-Wohlfarth rotation, respectively.

(Fe3O4)1-x-(SiO2)x composite films have been prepared by reactive sputtering iron and SiO2 targets in Ar+O2 mixture at room temperature. Transmission electron microscopy bright field images show that with the increase of SiO2 addition, uniform Fe3O4 grains are well separated by the amorphous SiO2 matrix, forming a well-defined granular structure. Temperature dependence of resistivity ρ(T) indicates that the electron tunneling mechanism featured by dominates the transport properties of the films, which smears out the Verwey transition intrinsic to Fe2/1log−∝Tρ3O4. This tunneling transport of electrons causes a spin-dependent magnetoresistance (MR){ρ(H)-ρ(o)/ρ(0)} of about-4.7% for Fe3O4 films, and-1.8% for (Fe3O4)0.6(SiO2)0.4 composite films under 46-kOe magnetic field at room temperature. Magnetic and magnetoresistance measurements reveal that the antiferromagnetically coupled Fe3O4 grains are decoupled and show the behavior of superparamagnetism at. 4.0≥x

Polycrystalline Fe3O4 films have been prepared by reactive sputtering at room temperature. Transmission electron microscopy (TEM) images show that the films consist of quite uniform Fe3O4 grains well separated by grain boundaries. It was found that the tunneling of spin polarized electrons across the antiferromagnetic coupled grain boundaries dominates the transport properties of the films. Magnetoresistance MR=ρ(H)-ρ(o)=ρ(0) shows linear and quadratic magnetic field dependence in the low field range when the field is applied parallel and perpendicular to film plane, which is similar to the behaviors observed in the epitaxial Fe3O4 films consisting of a large fraction of antiferromagnetic antiphase domain boundaries (APBs). At 300 K, the size of MR reaches-7.4% under a 50 kOe magnetic field, which is, by far, the largest MR observed in polycrystalline Fe3O4 films.

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.

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.

We studied the structure and magnetic properties of as-deposited and subsequent annealed CoxC100-x granular films fabricated by a DC facing-target magnetron sputtering system at room temperature using atomic force microscopy, X-ray diffraction, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy and vibrating sample magnetometer. The average roughness, Ra, of the as-deposited CoxC100-x granular films is smaller than that of Si (100) substrates. X-ray diffraction and transmission electron microscopy analyses indicate that the as-deposited CoxC100-x granular films are composed of～2 nm amorphous cobalt grains dispersed in amorphous carbon matrix, and their morphology is composition independent. The high resolution TEM image of the as-deposited Co30C70 film shows that cobalt and carbon have already separated during the deposition, even if the aggregation of cobalt is not complete. Annealing at 300-450℃ causes the crystallization of amorphous cobalt followed by an increase of grain size and the graphitisation of the amorphous carbon matrix. The constrictions arising from the structural environment result in the coexistence of the hcp and fcc Co phases at temperatures higher than the phase transformation point of 425℃. Magnetic measurements reveal that the coercivity of the as-deposited CoxC100-x granular films decreases with the increasing cobalt composition, and increases with the decrease in film thickness. The enhanced coercivity can be attributed to the weakened intergrain interaction due to the increased percolation threshold and/or the destruction of long-range domain structures caused by the film thickness reduction.

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.

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.

We have investigated anomalous RF sputtering in a high magnetic field, and the effects of high magnetic fields on the microstructures and magnetic properties of Fe-Si-O films. Using a specially designed sputtering apparatus whose chamber can be set in a 6 T liquid helium-free superconducting magnet, Fe-Si-O films were successfully deposited in Ar+O2 mixture. Three typical sample appearances, hole-at-center, phase-separation and hybridization were obtained for the Fe-Si-O films prepared in the low oxygen-argon flow ratio (<1.0%), low magnetic field (<1.0 T) regime, indicating that the distribution of plasma is strongly influenced by a magnetic field, resulting in an inhomogeneous spatial distribution of sputtered atoms. In the high oxygen-argon flow ratio (>2.0%), high magnetic field (>2.0 T) regime, strong (110) orientation of Fe3O4 grains and larger remanence and coercivity measured in the direction normal to the film plane appeared in the Fe-Si-O films, indicating that the high magnetic fields not only orient the Fe-Si-O film but also induce remarkable perpendicular magnetic anisotropy during the deposition.