K. Tao

Phase evolution upon ion mixing and solid‐state reaction and thermodynamic interpretation in the Ni‐Nb system

The amorphization of Ni‐Nb multilayered alloy films by xenon ion irradiation at room temperature and by high‐temperature solid‐state reaction was studied. The composition range favoring amorphization was carefully determined to be 20–85 at. % Ni by energy‐dispersive spectroscopy attached to the transmission electron microscope. A new metastable crystalline phase (MX) of hexagonal structure was formed in Ni75Nb25 and Ni70Nb30 multilayered films. Interestingly, in the Ni75Nb25 multilayered films, with increasing mixing dose an amorphous phase was first formed and then the MX‐phase was observed, while in the Ni70Nb30 multilayered films the MX phase was formed at relatively low doses and turned amorphous upon further mixing or 400 °C annealing for 2 h. Besides, annealing of the as‐deposited Ni70Nb30 multilayered films at 300 °C for half an hour also resulted in the formation of the MX phase. The thermal stability of the ion‐mixed amorphous alloys was also studied by subsequent annealing. To give semiquantitat...

C54‐TiSi2 formed by direct high current Ti‐ion implantation

We report, in this letter, the formation of TiSi2 by direct Ti‐ion implantation into silicon wafers using a metal vapor vacuum arc ion source. Implantation was conducted by 80 KeV Ti ions to a dose of 5×1017/cm2 with various ion current densities. When the ion current density exceeded 100 μA/cm2, the equilibrium TiSi2 of the C54 structure was uniquely formed. Additional evidence of the formation of C54‐TiSi2 was given by the resistivity measurements, i.e., the sheet resistivity was below 3.0 Ω/⧠. The formation mechanism is also discussed in terms of the beam heating effect during implantation.

Materials science communication formation of aln films by al evaporation with nitrogen ion beam bombardment

Abstract Aluminum nitride films were synthesized by electron gun evaporation of aluminum on to Si (111) wafer with simultaneous bombardment by nitrogen ions. Under special conditions, polycrystalline AlN films of fine crystallinity were obtained.

STRUCTURE AND MAGNETIC PROPERTIES OF FE-N FILMS PREPARED BY ION-BEAM-ASSISTED DEPOSITION

Fe–N films were prepared by ion‐beam‐assisted deposition at different N/Fe atomic arrival ratios to the substrates. Films consisted of nitrogen‐rich α‐Fe and different phases of iron nitrides including ζ‐Fe2N, e‐Fe2‐3N, and γ′‐Fe4N were formed. The phase composition of Fe–N films was found to depend sensitively on the N/Fe atomic arrival ratio and deposition temperature. The magnetic properties of the films mainly depends on phase composition. It was found that nitrogen‐rich α‐Fe films exhibited higher Ms than that of the pure iron film, and their Ms could be increased further by vacuum annealing at relatively low temperatures.

Polarization of Pd atoms in Ni/Pd magnetic multilayers

Ni/Pd multilayered films with various Ni and Pd layer thicknesses were prepared by electron gun evaporation. These films were all polycrystals with (111) preferential orientation. Also, both experimental analysis and computer simulation results indicated the existence of a diffusion layer at the Ni-Pd interfaces. The nominal magnetic moment per Ni atom measured for these multilayered films varied with change in the Ni layer thickness. For a thinner Ni layer, the magnetic moment was smaller than that of bulk Ni, while it was larger for the thicker Ni layer. This variation is attributed to the opposite effects of two factors, namely the favourable effect of Pd atom polarization versus the magnetic degradation mainly due to the decrease in the Curie temperature with decreasing Ni layer thickness. The effect of Pd atoms polarized by their neighbouring Ni atoms was also verified by the results of thermal annealing the multilayers.

Influence of Si doping on optical characteristics of cubic GaN grown on (001) GaAs substrates

The photoluminescence (PL) properties of Si-doped cubic GaN with different carrier concentrations were investigated at room temperature. The epilayers were grown on GaAs (001) by radio-frequency molecular-beam epitaxy. It was found that when the carrier concentration is increased from 5×1015 to 2×1018 cm−3, the PL peak shifted towards low energy, from 3.246 to 3.227 eV, and the PL linewidth increased from 77.1 to 121 meV. The PL peak shift is explained by the band gap narrowing effect due to the high doping concentration. The PL linewidth includes two parts: one is doping concentration independent, which is caused by the imperfection of samples and phonon scattering; the other is doping concentration dependent. We assign the second part to the broadening by the microscopic fluctuation of the doping concentration. The experimental measurements are in good agreement with the model.

Investigation of the interface reactions of Ti thin films with AlN substrate

Pure bulk AIN substrates were prepared by hot-pressing to eliminate the influence of an aid-sintering substance on the interface reactions, AlN thin films were deposited on Si(lll) substrates to decrease the influence of charging on the analysis of metal/AlN interfaces with x-ray photoelectron spectroscopy (XPS), Thin films of titanium were deposited on bulk ALN substrates by e-gun evaporation and ion beam assisted deposition (IBAD) and deposited on AlN films in situ by e-gun evaporation. Solid-state reaction products and reaction mechanism of the Ti/AlN system annealed at various temperatures and under LEAD were investigated by XPS, transmission electron microscopy (TEM), x-ray diffraction (XRD), and Rutherford backscattering spectrometry (RES). Ti reacted with AlN to form a laminated structure in the temperature range of 600 degrees C to 800 degrees C, The TiAl3 phase was formed adjacent to the AlN substrate, TiN, and Ti4N3-x as well as Ti2N were formed above the TiAl3 layer at the interface, Argon ion bombardment during Ti evaporation promoted the interface reactions. No reaction products were detected for the sample as-deposited by evaporation. However, XPS depth profile of the Ti/AlN/Si sample showed that Ti-N binding existed at the interface between the AIN thin films and the Ti thin films.

A preliminary study of the formation of WSi2 by high-current W ion implantation

Two differently structured WSi2 phases were formed by direct W ion implantation, for the first time, into silicon wafers using a metal vapour vacuum arc ion source. Implantation of W ions was conducted with an extract voltage of 40 kV, various beam densities from 50 to 115 mu A cm-2 and a fixed dose of 5*1017 cm-2. It was found that the formation of WSi2 with either a hexagonal or a tetragonal structure depended on the ion current density. The temperature rise caused by beam heating and the beam-striking time related to the dose were calculated, and they were responsible for the formation and evolution related to the differently structured WSi2 phases.

Solid‐state reaction of Ti and Ni thin films with aluminum nitride

Pure bulk AlN substrates were prepared by hot pressing to eliminate the influence of an aid‐sintering substance on the interface reactions. AlN thin films were deposited on Si(111) substrates to decrease the influence of charging on the analyses of metal/AlN interfaces with x‐ray photoelectron spectroscopy (XPS). Thin films of titanium and nickel were deposited on bulk AlN substrates by e‐gun evaporation and ion‐beam assisted deposition (IBAD) and deposited on AlN films in situ by e‐gun evaporation. The samples of the evaporated Ti films on bulk AlN and Ni films on bulk AlN were annealed at temperatures from 600 to 800 °C and from 600 to 850 °C for 1 h, respectively. Solid‐state reaction products between the metal films and bulk AlN substrates under annealing and IBAD were investigated by x‐ray diffraction (XRD) and Ruthford backscattering spectroscopy (RBS). TiAl3, TiN, and Ti4N3−x including Ti2N were found at the interface between the Ti films and AlN substrates for the annealed samples and IBAD sample....

Enhancement of magnetic moment of iron atoms in the Fe/Au nanomultilayers

Fe/Au multilayers were prepared by alternative vapor deposition. The periodicity, thickness, chemical composition, microstructure, and the magnetic moment of the films were determined and measured by various methods. The magnetic moment per Fe atom in Fe/Au multilayers was considerably enhanced when the Fe layer thickness was thinner than 8 nm and it was up to 2.59 μB, i.e., about 1.2 times of that of bulk Fe, at an Fe layer thickness of 4.5 nm. The experimental results also revealed that as the thickness of the Fe layer decreased, there was an increasing tendency towards perpendicular magnetization in the Fe/Au multilayers. The possible mechanism responsible for the modification of magnetic properties is also discussed.