Epitaxial （0001）-oriented Zn1-xCoxO （x= 0.01, 0.05 and 0.1） thin films were grown on c-sapphire substrates by pulsed laser deposition. The XRD analysis, optical transmittance and XPS measurements revealed that the...Epitaxial （0001）-oriented Zn1-xCoxO （x= 0.01, 0.05 and 0.1） thin films were grown on c-sapphire substrates by pulsed laser deposition. The XRD analysis, optical transmittance and XPS measurements revealed that the Co2＋ substituted Zn2＋ ions were incorporated into the lattice of ZnO in Zn1-xCoxO thin films. The electrical properties measurements revealed that the Co concentration had a non- monotonic influence on the electrical properties of the Zn1-xCoxO thin films due to the defects resulted from imperfections induced by Co substitution. The resistivity remarkably increased and the carrier concentration remarkably decreased in Zn1-x CoxO thin films after oxygen annealing at 600 ℃ under 15 Pa O2 pressure for 60 mins. Room-temperature ferromagnetic was observed and the ferromagnetic Co amount was smaller than the nominal Co concentration for Zn1-xCoxO samples before oxygen annealing. After oxygen annealing, the Zn1-x CoxO thin films exhibited paramagnetic behavior. It is suggested that the room-temperature ferromagnetic ofZn1-x CoxO thin films may attribute to defects or carriers induced mechanism.展开更多
We investigate the electronic and magnetic properties of the diluted magnetic semiconductors Zn1-xMnxS（001） thin films with different Mn doping concentrations using the total energy density functional theory. The en...We investigate the electronic and magnetic properties of the diluted magnetic semiconductors Zn1-xMnxS（001） thin films with different Mn doping concentrations using the total energy density functional theory. The energy stability and density of states of a single Mn atom and two Mn atoms at various doped configurations and different magnetic coupling state were calculated. Different doping configurations have different degrees of p-d hybridization, and because Mn atoms are located in different crystal-field environment, the 3d projected densities of states peak splitting of different Mn doping configurations are quite different. In the two Mn atoms doped, the calculated ground states of three kinds of stable configurations are anti-ferromagnetic state. We analyzed the 3d density of states diagram of three kinds of energy stability configurations with the two Mn atoms in different magnetic coupling state. When the two Mn atoms are ferromagnetic coupling, due to d-d electron interactions, density of states of anti-bonding state have significant broadening peaks. As the concentration of Mn atoms increases, there is a tendency for Mn atoms to form nearest neighbors and cluster around S. For such these configurations, the antiferromagnetic coupling between Mn atoms is energetically more favorable.展开更多
Zn1-xCuxO thin films were synthesized by the radio frequency （RF） magnetron sputtering technique using a ZnO target containing different pieces of small Cu-chips. X-ray diffraction （XRD） and scanning electron micr...Zn1-xCuxO thin films were synthesized by the radio frequency （RF） magnetron sputtering technique using a ZnO target containing different pieces of small Cu-chips. X-ray diffraction （XRD） and scanning electron microscopy （SEM） were employed to analyze the crystalline and microstructure of the film, and X-ray photoelectron spectroscopy （XPS） was used to establish the bonding characteristics and oxidation states of copper inside the ZnO host. Room temperature （RT） ferromagnetism was observed in the Znl-xCuxO films by a Quantum Design superconducting quantum interference device （SQUID） and the saturation magnetic moment of the films was found to decrease with the increase in Cu content.展开更多
Zn1-xCoxO films were grown on glass by sol-gel spin coating process. A homogeneous and stable Zn1-xCoxO sol was prepared by dissolving zinc acetate dihydrate, cobalt acetate tetrahydrate and aluminium chloride hexahyd...Zn1-xCoxO films were grown on glass by sol-gel spin coating process. A homogeneous and stable Zn1-xCoxO sol was prepared by dissolving zinc acetate dihydrate, cobalt acetate tetrahydrate and aluminium chloride hexahydrate as solutes in solution of isopropanol and monoethanolamine. The films were postheated and vacuum annealed, and investigated for c-axis preferred orientation and electromagnetic properties. Zn1-xCoxO films with different Co concentrations were oriented well along the c-axis, especially the Zn1-xCoxO film with 10% Co(atom fraction) was highly c-axis oriented. The transmittance spectra show that Zn1-xCoxO films occur d-d transition and sp-d exchange interaction between Co2+ ions. The electrical resistivity of the films at 10% Co had the lowest value because the crystallite size became largest and the crystallinity of the c-axis was improved. X-ray photoelectron spectroscopy and alternating gradient magnetometer analyses indicated that no Co metal cluster was formed, and the ferromagnetism at room temperature appeared. The characteristics of the electrical resistivity and room temperature ferromagnetism of sol-gel derived Zn1-xCoxO films suggest a potential application of dilute magnetic semiconductor devices.展开更多
Zn1-xCoxO diluted magnetic semiconductor bulks were prepared by hot pressing.Mixed powders of pure ZnO and CoO were compacted under pressure of 10 MPa at the temperature of 1 073 K.Then the samples were annealed in va...Zn1-xCoxO diluted magnetic semiconductor bulks were prepared by hot pressing.Mixed powders of pure ZnO and CoO were compacted under pressure of 10 MPa at the temperature of 1 073 K.Then the samples were annealed in vacuum at the temperature from 673 K to 873 K for 10 h.The crystal structure and magnetic properties of Zn1-xCoxO bulks have been investigated by X-ray diffraction（XRD） and vibrating sample magnetometer（VSM）.X-ray photoelectron spectroscopy（XPS） was used to study chemical valence of zinc and cobalt in the samples.The results showed that Zn1-xCoxO samples had c-axis oriented wurtzite symmetry,neither cobalt or cobalt oxide phase was found in the samples if x was less than 0.15.Zn and Co existed in Zn0.9Co0.1O sample in Zn2＋ and Co2＋ states.The results of VSM experiment proved the room temperature ferromagnetic properties（RTFP） of Co-doped ZnO samples.The saturation magnetization and the coercivity of Zn0.9Co0.1O sample,observed in the M-H curve,were about 0.20 emu/g and 200 Oe,respectively.展开更多
基金Funded by New Century Excellent Talents in University(No.NCET-10-0662)International Science and Technology Cooperation Project of Hubei Province(No.2010BFA017)International Science&Technology Cooperation Program of China(No.2011DFA52650)
文摘Epitaxial （0001）-oriented Zn1-xCoxO （x= 0.01, 0.05 and 0.1） thin films were grown on c-sapphire substrates by pulsed laser deposition. The XRD analysis, optical transmittance and XPS measurements revealed that the Co2＋ substituted Zn2＋ ions were incorporated into the lattice of ZnO in Zn1-xCoxO thin films. The electrical properties measurements revealed that the Co concentration had a non- monotonic influence on the electrical properties of the Zn1-xCoxO thin films due to the defects resulted from imperfections induced by Co substitution. The resistivity remarkably increased and the carrier concentration remarkably decreased in Zn1-x CoxO thin films after oxygen annealing at 600 ℃ under 15 Pa O2 pressure for 60 mins. Room-temperature ferromagnetic was observed and the ferromagnetic Co amount was smaller than the nominal Co concentration for Zn1-xCoxO samples before oxygen annealing. After oxygen annealing, the Zn1-x CoxO thin films exhibited paramagnetic behavior. It is suggested that the room-temperature ferromagnetic ofZn1-x CoxO thin films may attribute to defects or carriers induced mechanism.
基金This work was supported by the National Natural Science Foundation of China （No.60776039 and No.60406005）, the Natural Science Foundation of Beijing （No.3062016）, and the School Foundation of Beijing Jiaotong University.
文摘We investigate the electronic and magnetic properties of the diluted magnetic semiconductors Zn1-xMnxS（001） thin films with different Mn doping concentrations using the total energy density functional theory. The energy stability and density of states of a single Mn atom and two Mn atoms at various doped configurations and different magnetic coupling state were calculated. Different doping configurations have different degrees of p-d hybridization, and because Mn atoms are located in different crystal-field environment, the 3d projected densities of states peak splitting of different Mn doping configurations are quite different. In the two Mn atoms doped, the calculated ground states of three kinds of stable configurations are anti-ferromagnetic state. We analyzed the 3d density of states diagram of three kinds of energy stability configurations with the two Mn atoms in different magnetic coupling state. When the two Mn atoms are ferromagnetic coupling, due to d-d electron interactions, density of states of anti-bonding state have significant broadening peaks. As the concentration of Mn atoms increases, there is a tendency for Mn atoms to form nearest neighbors and cluster around S. For such these configurations, the antiferromagnetic coupling between Mn atoms is energetically more favorable.
基金National Natural Science Foundation of China (Nos.10275047,10575073)the Natural Science Foundation of Jiangsu Province of China (03KJB140116)
文摘Zn1-xCuxO thin films were synthesized by the radio frequency （RF） magnetron sputtering technique using a ZnO target containing different pieces of small Cu-chips. X-ray diffraction （XRD） and scanning electron microscopy （SEM） were employed to analyze the crystalline and microstructure of the film, and X-ray photoelectron spectroscopy （XPS） was used to establish the bonding characteristics and oxidation states of copper inside the ZnO host. Room temperature （RT） ferromagnetism was observed in the Znl-xCuxO films by a Quantum Design superconducting quantum interference device （SQUID） and the saturation magnetic moment of the films was found to decrease with the increase in Cu content.
文摘Zn1-xCoxO films were grown on glass by sol-gel spin coating process. A homogeneous and stable Zn1-xCoxO sol was prepared by dissolving zinc acetate dihydrate, cobalt acetate tetrahydrate and aluminium chloride hexahydrate as solutes in solution of isopropanol and monoethanolamine. The films were postheated and vacuum annealed, and investigated for c-axis preferred orientation and electromagnetic properties. Zn1-xCoxO films with different Co concentrations were oriented well along the c-axis, especially the Zn1-xCoxO film with 10% Co(atom fraction) was highly c-axis oriented. The transmittance spectra show that Zn1-xCoxO films occur d-d transition and sp-d exchange interaction between Co2+ ions. The electrical resistivity of the films at 10% Co had the lowest value because the crystallite size became largest and the crystallinity of the c-axis was improved. X-ray photoelectron spectroscopy and alternating gradient magnetometer analyses indicated that no Co metal cluster was formed, and the ferromagnetism at room temperature appeared. The characteristics of the electrical resistivity and room temperature ferromagnetism of sol-gel derived Zn1-xCoxO films suggest a potential application of dilute magnetic semiconductor devices.
基金Funded by the Innovative Scientific Research Foundation of Shanghai Education Committee (No.09YZ367)
文摘Zn1-xCoxO diluted magnetic semiconductor bulks were prepared by hot pressing.Mixed powders of pure ZnO and CoO were compacted under pressure of 10 MPa at the temperature of 1 073 K.Then the samples were annealed in vacuum at the temperature from 673 K to 873 K for 10 h.The crystal structure and magnetic properties of Zn1-xCoxO bulks have been investigated by X-ray diffraction（XRD） and vibrating sample magnetometer（VSM）.X-ray photoelectron spectroscopy（XPS） was used to study chemical valence of zinc and cobalt in the samples.The results showed that Zn1-xCoxO samples had c-axis oriented wurtzite symmetry,neither cobalt or cobalt oxide phase was found in the samples if x was less than 0.15.Zn and Co existed in Zn0.9Co0.1O sample in Zn2＋ and Co2＋ states.The results of VSM experiment proved the room temperature ferromagnetic properties（RTFP） of Co-doped ZnO samples.The saturation magnetization and the coercivity of Zn0.9Co0.1O sample,observed in the M-H curve,were about 0.20 emu/g and 200 Oe,respectively.
