Fu Dejun

Specific features of Eu3+ and Tb3+ magnetooptics in gadolinium-gallium garnet (Gd3Ga5O12)

Abstract We reported magnetooptical properties of Eu3+(4f(6)) and Tb3+(4f(8)) in single crystals of Gd3Ga5O12 (GGG), Y3Ga5O12 (YGG), and Eu3+(4f(6)) in Eu3Ga5O12 (EuGG) for both ions occupying sites of D2 symmetry in the garnet structure. Absorption, luminescence, and magnetic circular polarization of luminescence (MCPL) spectra of Tb3+ in GGG and YGG and absorption and magnetic circular dichroism (MCD) of Eu3+ in EuGG were studied. The data were obtained at 85 K and room temperature (RT). Magnetic susceptibility of Eu3+ in EuGG was also measured between 85 K and RT. The magnetooptical and magnetic susceptibility data were modeled using the wavefunctions of the crystal-field split energy (Stark) levels of Eu3+ and Tb3+ occupying D2 sites in the same garnets. The results reported gave a precise determination of these Stark level assignments and confirmed the symmetry labels (irreducible representations) of the closely-spaced Stark levels (quasi-doublets) found in the 5D1 (Eu3+) and 5D4 (Tb3+) multiplets. Ultraviolet (UV) excitation (

Effects of Bias Voltage on the Structure and Mechanical Properties of Thick CrN Coatings Deposited by Mid-Frequency Magnetron Sputtering ∗

Thick CrN coatings were deposited on Si (111) substrates by electron source assisted mid-frequency magnetron sputtering working at 40 kHz. The deposition rate, structure, and microhardness of the coatings were strongly influenced by the negative bias voltage (Vb). The deposition rate reached 8.96 μm/h at a Vb of −150 V. X-ray diffraction measurement revealed strong CrN (200) orientation for films prepared at low bias voltages. At a high bias voltage of Vb less than −25 V both CrN (200) and (111) were observed. Large and homogeneous grains were observed by both atomic force microscopy and scanning electron microscopy in samples prepared under optimal conditions. The samples exhibited a fibrous microstructure for a low bias voltage and a columnar structure for Vb less than –150 V.

Structural Characterization of Nickel-Base Alloy C-276 Irradiated with Ar Ions

The irradiation damage in nickel-base alloy C-276 irradiated with 115 keV Ar ions from low to very high doses was investigated. Structural characterization was performed using transmission electron microscopy (TEM), grazing incident X-ray diffraction (GIXRD) and atomic force microscopy (AFM). High density of interstitial type dislocation loops could be observed at a dose level of around 2.75 displacements per atom (dpa). With the irradiation dose increased to 27.5 dpa, the average size of loops increased from 5 nm to 16 nm, while the density of the loops decreased from 1.4 × 1011/cm2 to 4.6 × 1010/cm2. When the irradiation dose reached 82.5 dpa, original grains were transformed into subgrains whose sizes observed from TEM were about 20~60 nm. The fragmentation of grains was confirmed by GIXRD. The mean subgrain size was 40 nm, which was obtained from the full width at half maximum (FWHM) of the X-ray diffraction lines using the Scherrer formula and Williamson formula. AFM micrographs showed that nanometer-sized hillocks formed at the dose of 82.5 dpa, which provided further evidence of grain fragmentation at a high irradiation dose.

Magnetooptics of non-Kramers Eu3+ ions in garnets: analysis complemented by crystal-field splitting modeling calculations

Abstract Spectra of absorption, luminescence, magnetic circular dichroism (MCD), and magnetic circular polarization of luminescence (MCPL) in Gd 3 Ga 5 O 12 :Eu 3+ and Eu 3 Ga 5 O 12 garnets were studied within the visible spectral range at 300 K. Analysis of the spectral and temperature dependences of the magnetooptical and optical spectra made it possible to identify the magneto-dipole (MD) and electro-dipole (ED) 4f→4f transitions occurring between Stark sublevels of the 7 F J ( J =1, 2) and 5 D 0 multiplets in Eu 3+ -containing garnet structures. Quantum mechanical “mixing” had significant influence on quasi-degenerate states of the non-Kramers rare-earth Eu 3+ ion for Eu 3 Ga 5 O 12 in MCD due to forbidden MD transition 7 F 1 → 5 D 0 and for Gd 3 Ga 5 O 12 :Eu 3+ in MCPL due to MD 4f→4f transition 5 D 0 → 7 F 1 and forced ED-transition 5 D 0 → 7 F 2 . A parameterized Hamiltonian defined to operate within the entire 4f (6) ground electronic configuration of Eu 3+ ion was used to model the experimental Stark levels, including their irreducible representations and wavefunctions. The crystal-field parameters were determined through a Monte-Carlo method in which nine independent crystal-field parameters, B k q , were given random starting values and optimized using standard least-squares fitting between calculated and experimental levels. The final fitting standard deviation between 57 calculated-to-experimental levels was 0.73 meV.

Structure and Tribological Properties of CrTiAlN Coatings Deposited by Multi-Arc Ion Plating

CrTiAlN coatings were prepared by using a home-made industrial scale multi-arc ion plating system. The coatings were found to be composites of face-center-cubic CrN and TiN. The surface roughness, microhardness, and tribological properties of the films were significantly affected by the nitrogen pressure and dc-pulsed bias voltage applied to the substrate. The CrTiAlN coatings with the smoothest surfaces were obtained at optimum conditions of nitrogen pressure of 5.0 Pa and bias voltage of −200 V. The samples were found to exhibit a hardness of 2900 HV0.05 with an average friction coefficient of 0.16 and wear rate of 1.5×10-16 m3/N·m against cemented carbide.

Magnetic Properties and Magnetoresistance of CdMnS: Au Based Structures Prepared by Co-evaporation

Polycrystalline CdMnS and CdMnS: Au films with hexagonal structure on Si(111) substrates are prepared by co-evaporation, and exhibit ferroelectric and ferromagnetic properties, respectively Under optimized growth conditions, CdMnS: Au samples with an average crystallite size of 90 nm and Mn concentration of 5.0 at. % are obtained, and an all-semiconductor spin valve device of Co/Au/CdMnS: Au/CdMnS/Pt is fabricated. Electrical measurement of the device reveals the clear dependence of resistance on applied magnetic field, with a relative magnetoresistance of 0.06% and a switching field of 100 Oe at 77 K.

Degradation of ferroelectric and weak ferromagnetic properties of BiFeO3 films due to the diffusion of silicon atoms

Crystalline BiFeO3 (BFO) films each with a crystal structure of a distorted rhombohedral perovskite are characterized by X-ray diffraction (XRD) and high-resolution electron microscopy (HRTEM). The diffusion of silicon atoms from the substrate into the BiFeO3 film is detected by Rutherford backscattering spectrometry (RBS). The element analysis is performed by energy dispersive X-ray spectroscopy (EDS). Simulation results of RBS spectrum show a visualized distribution of silicon. X-ray photoelectron spectroscopy (XPS) indicates that a portion of silica is formed in the diffusion process of silicon atoms. Ferroelectric and weak ferromagnetic properties of the BFO films are degraded due to the diffusion of silicon atoms. The saturation magnetization decreases from 6.11 down to 0.75 emu/g, and the leakage current density increases from 3.8 × 10−4 up to 7.1 × 10−4 A/cm−2.

Structure and Mechanical Properties of CrN Thick Films Deposited by High-Rate Medium-Frequency Magnetron Sputtering

A home-made electron source assisted medium-frequency (MF) magnetron sputtering system was used to deposit thick CrN films on silicon and tungsten carbide substrates at various nitrogen flow rates with a fixed total pressure (0.3 Pa) and MF power (11.2 kW). Result from scanning electron microscopy showed that the deposited CrN films have clear columnar structure, and X-ray diffraction revealed a preferred orientation of CrN (200) for samples prepared at a rate of N2/(N2+Ar) below 60%, whereas those prepared at higher N2/(N2+Ar) rate are dominated by Cr2N. Deposition rates up to 12.5 μm/h were achieved and the hardness of the CrN coatings were in a range of 11 GPa to 18 GPa.

Investigation on diamondlike carbon films: Structure, properties and doping effect

Abstract Diamondlike carbon films (DLCFs) were prepared from benzene vapor by rf plasma chemical vapor deposition (PCVD) and non-mass-analysed (NMA) low energy ion beam deposition. It was found that the structure of the films is influenced by deposition conditions. The films deposited under various conditions were all amorphous. Their properties are consistent with the structure. The films with a large number of sp3 CH or CC bonds have high resistivity and wide optical gaps. Aluminium and phosphorus were introduced into the films by sputter and atom transferring from the substrate, respectively. The conduction type is determined by the type of impurity and its activity. Boron implantation was done in the energy range of 5–30 keV. The resistivity decreases with increase of implantation dose.

Preparation of graphene on Cu foils by ion implantation with negative carbon clusters

We report on few-layer graphene synthesized on Cu foils by ion implantation using negative carbon cluster ions, followed by annealing at 950 °C in vacuum. Raman spectroscopy reveals IG/I2D values varying from 1.55 to 2.38 depending on energy and dose of the cluster ions, indicating formation of multilayer graphene. The measurements show that the samples with more graphene layers have fewer defects. This is interpreted by graphene growth seeded by the first layers formed via outward diffusion of C from the Cu foil, though nonlinear damage and smoothing effects also play a role. Cluster ion implantation overcomes the solubility limit of carbon in Cu, providing a technique for multilayer graphene synthesis.