Yudian Fan

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.

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.

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....

A first-principles LMTO-ASA study of crystalline metastable phases in NiNb system

Abstract The phase stability, electronic structure and cohesive properties of metastable crystalline phases Ni 3 Nb and Nb 3 Ni with their cubic L1 2 and hexagonal D0 19 structures have been studied by using the linearized muffin-tin-orbital method with the atomic sphere approximation (LMTO-ASA). The structure preferences are predicted correctly for both the Ni 3 Nb and the Nb 3 Ni metastable phases. Our results show that the calculated equilibrium lattice constants of the metastable phases in NiNb system are in good agreement with the experiment values. The relative stability of different structures are further analyzed in terms of the density of states.

Investigation of diffusion across the interface between metal films and AlN or A12O3 substrates

Abstract Vacuum annealing of W films/AlN samples, followed by Rutherford backscattering spectrometry (RBS) measurements, showed that medium energy ion beam assisted deposition (IBAD) techniques could remarkably hinder the interdiffusion of interfacial atoms at elevated temperatures in comparison with evaporated W films/AlN samples. Similar results were observed in Mo thin films/AlN and Mo (or W) thin films/Al 2 O 3 (0001) systems. An IBAD Mo films/Al 2 O 3 (0001) sample was selected so as to investigate the mechanism of medium energy IBAD resulting in a stable interface by high-resolution electron microscopy (HREM). An amorphous layer of 10–12 nm thickness between IBAD Mo films and A1 2 O 3 (0001) substrate was observed.

First‐principles calculation of the hexagonal‐closed‐packed Ni75Ta25 metastable phase

The total energy and electronic structure of the hcp Ni76Ta25 metastable phase have been obtained by the self‐consistent discrete variational method and the local Xα exchange approximation. The total energy of this phase was calculated as a function of lattice constant, a, for a fixed c/a of 1.63, which is determined experimentally. The predicted lattice constant, i.e., a=4.93 a.u. is very close to the experimental value of a=4.97 a.u. In addition, the density of states and bonding charge density were used to clarify the characteristics of bonding in this metastable crystalline phase.

A first-principles investigation of the solid-state phase transition in the Mo - Fe system

The first-principles linear-muffin-tin-orbital method has been applied in studying the two-step phase transition induced by ion mixing in Mo - Fe multilayers which has been observed recently. Three different structures, i.e., cubic , hexagonal , and tetragonal , of have been considered in our study. The results are presented in the form of the total energy as a function of the lattice constant, the cohesive properties, and the density of states for the three structures. In agreement with experiment, the structure is found to be more stable than either the or structures, which indicates the possibility of a phase transition from the hexagonal close-packed (hcp) to the face-centred cubic (fcc) form. The predicted lattice constants of these two phases fit very well with the experimental ones. The densities of states are also used to analyse the relative stability of different structures in the Mo - Fe system.

Electronic structure of the hcp Ni-Nb metastable crystalline phase

Abstract The electronic structure of the hcp Ni 75 Nb 25 metastable crystalline phase has been investigated by using the first-principles discrete variational X α method. The total energy curve of this metastable crystalline phase is calculated as a function of the lattice constant using a 19-atom cluster. The predicted equilibrium lattice parameter of this hcp phase agreed well with the experimental value.