H.W. Tian

Growth, structural, and magnetic properties of iron nitride thin films deposited by dc magnetron sputtering

Abstract FeN thin films were deposited on glass substrates by dc magnetron sputtering at different Ar/N 2 discharges. The composition, structure and the surface morphology of the films were characterized using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and atomic force microscopy (AFM). Films deposited at different nitrogen pressures exhibited different structures with different nitrogen contents, and the surface roughness depended on the mechanism of the film growth. Saturation magnetization and coercivity of all films were determined using superconducting quantum interference device, which showed that if N 2 /(Ar+N 2 ) flow ratio was equal to or larger than 30% the nonmagnetic single-phase γ″-FeN appeared. If N 2 /(Ar+N 2 ) flow ratio was less than 10%, the films consisted of the mixed phases of FeN 0.056 and γ′-Fe 16 N 2 , whose saturation magnetizations were larger than that of α-Fe. If N 2 /(Ar+N 2 ) flow ratio was 10%, the phases of γ′-Fe 4 N and e-Fe 3 N appeared, whose saturation magnetizations were lower than that of α-Fe.

Effects of radio frequency power on the chemical bonding, optical and mechanical properties for radio frequency reactive sputtered germanium carbide films

Germanium carbide (Ge1−xCx) films have been prepared by radio frequency (RF) reactive sputtering of a pure Ge(111) target in a CH4/Ar mixture discharge, and their composition, chemical bonding, optical and mechanical properties have been investigated as a function of RF power. The relationship between the chemical bonding and the optical and mechanical properties of the Ge1−xCx films has been explored. The results show that the refractive index of Ge1−xCx films increases from 1.9 to 3.2 and the optical gap decreases from 1.9 to 1.0 eV as RF power increases from 80 to 250 W, which is due to an increase in the germanium content with increasing RF power. Also, it is found that the hardness of Ge1−xCx films increases with increasing RF power, which can be attributed to an increase in the fraction of sp3 Ge–C bonds at the expense of the sp2 C–C bonds in the Ge1−xCx films.

Nature of substitutional impurity atom B/N in zigzag single-wall carbon nanotubes revealed by first principle calculations

We present systematic calculations for the single-walled zigzag (n,0) carbon nanotubes containing the substitutional impurity atom B/N using the ab initio density- functional theory. It is found that the formation energies of the single-walled zigzag carbon nanotubes with substitutional impurity atom B/N depend on the tube diameters as well as the electric properties, and show periodic features. The nature of these periodic features has been revealed, which results from the different bonding structures of the perfect zigzag carbon tubes with different diameters, rather than the defects (substitutional impurity atom B/N) in the zigzag tubes

Modulation periodicity dependent structure, stress, and hardness in NbN/W2N nanostructured multilayer films

NbN/W2N nano-multilayer films with a modulation periodicity, Λ, ranging from 5.1 to 157.4 nm have been deposited on a Si(100) substrate by reactive magnetron sputtering in Ar/N2 mixtures. The Λ dependent structural and mechanical properties for the resulting NbN/W2N multilayers have been evaluated by means of low-angle x-ray reflectivity, x-ray diffraction, high-resolution transmission electron microscope, and nanoindentation measurements. The finding is that for films with Λ ≤ 10.6 nm, fcc NbN layers are coherent with cubic W2N layers, resulting in NbN layers and W2N layers that are in the compressive and tensile states, respectively. In contrast, as Λ is larger than 10.6 nm, a phase transition from W2N to W occurs in the W2N layer, which is a result of the coherent interface strain relaxation. For this case, all layers are in the compressive state, and the coherent interface disappears. The intrinsic compressive stress evolution with Λ can be interpreted in terms of interface stress. The formation of co...