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/I2Dvalues 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.
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 BiFeO3film 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 × 10-4up to 7.1 × 10-4A/cm-2.
CrN microspheres were synthesized by using a cathodic arc plasma source system. The obtained samples were annealed in air at temperatures of 300-800 ℃ for 60 min. The influence of annealing temperature on the microstructure and surface morphology of the CrN microspheres was investigated. The CrN microspheres were characterized by means of scanning electron microscopy, transmission electron microscopy and X-ray diffraction analysis. The results show that the CrN nanoparticles arranged into leaf-like structures before annealing. With the rising of the annealing temperature, the size of CrN crystal nanoparticals became larger. When the annealing temperature exceeded the oxidation point(500 ℃), the CrN was oxidized and the leaf-like structure was broken. With further increase of the annealing temperature(700 ℃), the arrangement of CrN nanoparticles was changed from leaf-like structure to be discrete.
The ion implantation uniformity is of vital importance for an ion implanter.In this paper,we report the,uniformity measurement for a large current ion implanter(LC-16 type) by implanting of 190-keV Ar ions into Si to 3×1016 atoms/cm2,followed by Rutherford backscattering spectroscopy(RBS) and sheet resistance measurement providing quantitative information on spatial distribution of dopants.The implant doses obtained from RBS at selected points of the sample give a spatial uniformity of <5%,which are confirmed by the sheet resistance measurement.While sheet resistance is an indirect method for dose evaluation of ion-implanted samples,RBS provides a competent technique for calibration of the ion implantation system.And both measurements show that good uniformity can be achieved for the ion implanter by tuning of the scanning process.
Hui LiZe-Song WangSheng-Jun ZhangVasiliy O.PelenovichFeng RenDe-Jun FuChuan-Sheng LiuZhi-Wei Ai
Spectra of absorption,luminescence,magnetic circular dichroism(MCD),and magnetic circular polarization of luminescence(MCPL) in Gd3 Ga5 O12 :Eu3+and Eu3 Ga5 O12 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 the7FJ(J=1,2) and5D0 multiplets in Eu3+-containing garnet structures.Quantum mechanical "mixing" had significant influence on quasi-degenerate states of the non-Kramers rare-earth Eu3+ion for Eu3 Ga5 O12 in MCD due to forbidden MD transition7F1 →5D0 and for Gd3 Ga5 O12 :Eu3+in MCPL due to MD 4f→4f transition5D0 →7F1 and forced ED-transition5D0 →7F2.A parameterized Hamiltonian defined to operate within the entire 4f(6)ground electronic configuration of Eu3+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,Bk 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.
Uygun V.ValievJohn B.GruberAnvar K.MukhammadievVasiliy O.Pelenovich付德君Gary W.Burdick
