共查询到20条相似文献,搜索用时 31 毫秒
1.
Dong Wang D.D. Wang C.Y. Cao L.R. Huang 《Journal of magnetism and magnetic materials》2010,322(22):3642-3647
High purity Fe2O3/ZnO nanocomposites were annealed in air at different temperatures between 100 and 1200 °C to get Fe-doped ZnO nanocrystals. The structure and grain size of the Fe2O3/ZnO nanocomposites were investigated by X-ray diffraction 2θ scans. Annealing induces an increase of the grain size from 25 to 195 nm and appearance of franklinite phase of ZnFe2O4. Positron annihilation measurements reveal large number of vacancy defects in the interface region of the Fe2O3/ZnO nanocomposites, and they are gradually recovered with increasing annealing temperature. After annealing at temperatures higher than 1000 °C, the number of vacancies decreases to the lower detection limit of positrons. Room temperature ferromagnetism can be observed in Fe-doped ZnO nanocrystals using physical properties measurement system. The ferromagnetism remains after annealing up to 1000 °C, suggesting that it is not related with the interfacial defects. 相似文献
2.
Heat treatment effects on microstructure and magnetic properties of Mn-Zn ferrite powders 总被引:1,自引:0,他引:1
Ping Hu De-an Pan Jian-jun Tian Xin-feng Wang 《Journal of magnetism and magnetic materials》2010,322(1):173-206
Mn-Zn ferrite powders (Mn0.5Zn0.5Fe2O4) were prepared by the nitrate-citrate auto-combustion method and subsequently annealed in air or argon. The effects of heat treatment temperature on crystalline phases formation, microstructure and magnetic properties of Mn-Zn ferrite were investigated by X-ray diffraction, thermogravimetric and differential thermal analysis, scanning electron microscopy and vibrating sample magnetometer. Ferrites decomposed to Fe2O3 and Mn2O3 after annealing above 550 °C in air, and had poor magnetic properties. However, Fe2O3 and Mn2O3 were dissolved after ferrites annealing above 1100 °C. Moreover, the 1200 °C annealed sample showed pure ferrite phase, larger saturation magnetization (Ms=48.15 emu g−1) and lower coercivity (Hc=51 Oe) compared with the auto-combusted ferrite powder (Ms=44.32 emu g−1, Hc=70 Oe). The 600 °C air annealed sample had the largest saturation magnetization (Ms=56.37 emu g−1) and the lowest coercivity (Hc=32 Oe) due to the presence of pure ferrite spinel phase, its microstructure and crystalline size. 相似文献
3.
Lin Cui Hua-Yu ZhangGui-Gen Wang Fang-Xu YangXu-Ping Kuang Rui SunJie-Cai Han 《Applied Surface Science》2012,258(7):2479-2485
ZnO thin films were epitaxially grown on sapphire (0 0 0 1) substrates by radio frequency magnetron sputtering. ZnO thin films were then annealed at different temperatures in air and in various atmospheres at 800 °C, respectively. The effect of the annealing temperature and annealing atmosphere on the structure and optical properties of ZnO thin films are investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), photoluminescence (PL). A strong (0 0 2) diffraction peak of all ZnO thin films shows a polycrystalline hexagonal wurtzite structure and high preferential c-axis orientation. XRD and AFM results reveal that the better structural quality, relatively smaller tensile stress, smooth, uniform of ZnO thin films were obtained when annealed at 800 °C in N2. Room temperature PL spectrum can be divided into the UV emission and the Visible broad band emission. The UV emission can be attributed to the near band edge emission (NBE) and the Visible broad band emission can be ascribed to the deep level emissions (DLE). By analyzing our experimental results, we recommend that the deep-level emission correspond to oxygen vacancy (VO) and interstitial oxygen (Oi). The biggest ratio of the PL intensity of UV emission to that of visible emission (INBE/IDLE) is observed from ZnO thin films annealed at 800 °C in N2. Therefore, we suggest that annealing temperature of 800 °C and annealing atmosphere of N2 are the most suitable annealing conditions for obtaining high quality ZnO thin films with good luminescence performance. 相似文献
4.
High-purity ZnO nanowires have been synthesized on Si substrates without the presence of a catalyst at 600 °C by a simple thermal vapor technique. Photoluminescence (PL) spectra of the annealed samples at 900 °C under oxygen and argon gases have been investigated. After O2 or Ar annealing, the PL visible-emission intensity that is related to intrinsic defects (oxygen vacancies) is greatly reduced compared with as-grown ZnO nanowires because the oxygen-gas ions or oxygen interstitials diffuse into the oxygen vacancies during annealing process. The blue-band peak of the O2- or Ar-annealed ZnO naonowires is also smaller than the green-band peak in the visible broadband because of the reduction of oxygen vacancies. Therefore, the main intrinsic defects (oxygen vacancies) of as-grown ZnO nanowires can be reduced by O2 or Ar annealing, which is an important procedure for the development of advanced optoelectronic ZnO nanowire devices. 相似文献
5.
N-In codoped ZnO thin films were prepared by ion beam enhanced deposition method (IBED) and were annealed in nitrogen and oxygen ambient after deposition. The influence of post-annealing on structure, electrical and optical properties of thin films were investigated. As-deposited and all post-annealed samples showed preferential orientation along (0 0 2) plane. Electrical property studies indicated that the as-deposited ZnO film showed p-type with a sheet resistance of 67.5 kΩ. For ZnO films annealed in nitrogen with the annealing temperature increasing from 400 to 800 °C, the conduction type of the ZnO film changed from p-type to n-type. However, for samples annealed in oxygen the resistance increased sharply even at a low annealing temperature of 400 °C and the conduction type did not change. Room temperature PL spectra of samples annealed in N2 and in O2 showed UV peak located at 381 and 356 nm, respectively. 相似文献
6.
ZnS and SiO2-ZnS nanophosphors, with or without different concentration of Mn2+ activator ions, were synthesized by using a sol-gel method. Dried gels were annealed at 600 °C for 2 h. Structure, morphology and particle sizes of the samples were determined by using X-ray diffraction (XRD), highresolution transmission electron microscopy (HRTEM) and field emission scanning electron microscopy (FESEM). The diffraction peaks associated with the zincblende and the wurtzite structures of ZnS were detected from as prepared ZnS powders and additional diffraction peaks associated with ZnO were detected from the annealed powders. The particle sizes of the ZnS powders were shown to increase from 3 to 50 nm when the powders were annealed at 600 °C. An UV-Vis spectrophotometer and a 325 nm He-Cd laser were used to investigate luminescent properties of the samples in air at room temperature. The bandgap of ZnS nanoparticles estimated from the UV-Vis data was 4.1 eV. Enhanced orange photoluminescence (PL) associated with 4T1→6A1 transitions of Mn2+ was observed from as prepared ZnS:Mn2+and SiO2-ZnS:Mn2+ powders at 600 nm when the concentration of Mn2+ was varied from 2-20 mol%. This emission was suppressed when the powders were annealed at 600 °C resulting in two emission peaks at 450 and 560 nm, which can be ascribed to defects emission in SiO2 and ZnO respectively. The mechanism of light emission from Mn2+, the effect of varying the concentration on the PL intensity, and the effect of annealing are discussed. 相似文献
7.
In Soo Kim 《Applied Surface Science》2009,255(7):4011-4014
Ag-doped ZnO (ZnO:Ag) thin films were grown on glass substrates by E-beam evaporation technique. The structural, electrical and optical properties of the films were investigated as a function of annealing temperature. The films were subjected to post annealing at different temperatures in the range of 350-650 °C in an air ambient. All the as grown and annealed films at temperature of 350 °C showed p-type conduction. The films lost p-type conduction after post annealing treatment temperature of above 350 °C, suggesting a narrow post annealing temperature window for the fabrication of p-type ZnO:Ag films. ZnO:Ag film annealed at 350 °C revealed lowest resistivity of 7.25 × 10−2 Ω cm with hole concentration and mobility of 5.09 × 1019 cm−3 and 1.69 cm2/V s, respectively. Observation of a free-to-neutral-acceptor (e,Ao) and donor-acceptor-pair (DAP) emissions in the low temperature photoluminescence measurement confirms p-type conduction in the ZnO:Ag films. 相似文献
8.
Sm-Co based nanomagnetic material was synthesized by means of a Pechini-type sol-gel process. In this method, a suitable gel-precursor was prepared using respective metal salts and complexing agent such as citric acid. The gel-precursor was dried at 300 °C and then subjected to various reductive annealing temperatures: 350, 500 and 600 °C. The nanopowders so obtained were characterized for their structure, phase composition and magnetic properties. FT-IR studies on the gel-precursor showed the binding of metal cations with the citrate molecules in the form of metal-citrate complex. The gel-precursor, which was annealed at 350 °C showed the presence of both meta-stable cobalt carbide (Co2C, Co3C) and Co3O4 phases; while the sample annealed at 500 °C indicated the sign of SmCo5 phase. Upon increasing the reductive annealing temperature to 600 °C, crystalline phase such as fcc-Co and Sm2C3 were formed prominently. FE-SEM analysis revealed the change in sample morphology from spherical to oblate spheres upon increasing the annealing temperature. VSM measurements demonstrated ferromagnetic nature at room temperature for all the nanopowders obtained irrespective of their after reductive annealing temperature. 相似文献
9.
Hu-Jie Jin 《Applied Surface Science》2008,254(7):2207-2210
Al-N-codoped ZnO films were fabricated by RF magnetron sputtering in the ambient of N2 and O2 on silicon (1 0 0) and homo-buffer layer, subsequently, annealed in O2 at low pressure. X-ray diffraction (XRD) spectra show that as-grown and 600 °C annealed films grown by codoping method are prolonged along crystal c-axis. However, they are not prolonged in (0 0 1) plane vertical to c-axis. The films annealed at 800 °C are not prolonged in any directions. Codoping makes ZnO films unidirectional variation. X-ray photoelectron spectroscopy (XPS) shows that Al content hardly varies and N escapes with increasing annealing temperature from 600 °C to 800 °C. 相似文献
10.
Huilian Liu Xin ChengHongbo Liu Jinghai YangYang Liu Xiaoyan LiuMing Gao Xu Zhang 《Superlattices and Microstructures》2012
Zn0.97Cu0.01V0.02O nanoparticles have been successfully prepared by the sol–gel method and sintered at 600 °C in argon and air atmosphere, respectively. The effects of annealing atmosphere on the structural, optical and magnetic properties of the obtained samples were studied. The X-ray diffraction result showed that the Zn0.97Cu0.01V0.02O was single phase with the wurtzite structure of ZnO. The sample annealed in air had much better crystallization. Photoluminescence shows an increase in green emission when annealing in argon. The two Zn0.97Cu0.01V0.02O samples exhibited ferromagnetism at room temperature. The ferromagnetism in this study was itself property of Cu, V co-doped ZnO and not originated from the secondary phase. 相似文献
11.
B.M. Mothudi M.A. Lephoto O.M. Ntwaeaborwa J.R. Botha H.C. Swart 《Physica B: Condensed Matter》2012,407(10):1620-1623
BaAl2O4:Eu2+,Nd3+,Gd3+ phosphors were prepared by a combustion method at different initiating temperatures (400–1200 °C), using urea as a comburent. The powders were annealed at different temperatures in the range of 400–1100 °C for 3 h. X-ray diffraction data show that the crystallinity of the BaAl2O4 structure greatly improved with increasing annealing temperature. Blue-green photoluminescence, with persistent/long afterglow, was observed at 498 nm. This emission was attributed to the 4f65d1–4f7 transitions of Eu2+ ions. The phosphorescence decay curves were obtained by irradiating the samples with a 365 nm UV light. The glow curves of the as-prepared and the annealed samples were investigated in this study. The thermoluminescent (TL) glow peaks of the samples prepared at 600 °C and 1200 °C were both stable at ∼72 °C suggesting that the traps responsible for the bands were fixed at this position irrespective of annealing temperature. These bands are at a similar position, which suggests that the traps responsible for these bands are similar. The rate of decay of the sample annealed at 600 °C was faster than that of the sample prepared at 1200 °C. 相似文献
12.
We have prepared SrTiO3/BaTiO3 thin films with multilayered structures deposited on indium tin oxide (ITO) coated glass by a sol-gel deposition and heating at 300-650 °C. The optical properties were obtained by UV-vis spectroscopy. The films show a high transmittance (approximately 85%) in the visible region. The optical band gap of the films is tunable in the 3.64-4.19 eV range by varying the annealing temperature. An abrupt decrease towards the bulk band gap value is observed at annealing temperatures above 600 °C. The multilayered film annealed at 650 ° C exhibited the maximum refractive index of 2.09-1.91 in the 450-750 nm wavelength range. The XRD and AFM results indicate that the films annealed above 600 ° C are substantially more crystalline than the films prepared at lower temperatures which were used to change their optical band gap and complex refractive index to an extent that depended on the annealing temperature. 相似文献
13.
XPS depth profiles were used to investigate the effects of rapid thermal annealing under varying conditions on the structural, magnetic and optical properties of Ni-doped ZnO thin films. Oxidization of metallic Ni from its metallic state to two-valence oxidation state occurred in the film annealed in air at 600 °C, while reduction of Ni2+ from its two-valence oxidation state to metallic state occurred in the film annealed in Ar at 600 and 800 °C. In addition, there appeared to be significant diffusion of Ni from the bottom to the top surface of the film during annealing in Ar at 800 °C. Both as-deposited and annealed thin films displayed obvious room temperature ferromagnetism (RTFM) which was from metallic Ni, Ni2+ or both with two distinct mechanisms. Furthermore, a significant improvement in saturation magnetization (Ms) in the films was observed after annealing in air (Ms = 0.036 μB/Ni) or Ar (Ms = 0.033 μB/Ni) at 600 °C compared to that in as-deposited film (Ms = 0.017 μB/Ni). An even higher Ms value was observed in the film annealed in Ar at 800 °C (Ms = 0.055 μB/Ni) compared to that at 600 °C mainly due to the diffusion of Ni. The ultraviolet emission of the Ni-doped ZnO thin film was restored during annealing in Ar at 800 °C, which was also attributed to the diffusion of Ni. 相似文献
14.
In this work zinc ferrite (ZnFe2O4) nanoparticles have been prepared by sol-gel method in two different media, one acidic and another one basic and then annealed at different temperatures from 350 to 800 °C. XRD investigations show that both samples have a single phase spinel structure. Mean crystallite sizes of the samples were calculated, using Scherrer’s formula, which are 13 and 16 nm for the samples prepared in acidic and basic media, respectively. The variation of cation distribution in the samples was estimated by the ratio of (2 2 0) and (2 2 2) intensity diffraction peaks and the results show that as-prepared nanoparticles have different ionic distributions in comparison with that of bulk zinc ferrite. Also the results show that by increasing annealing temperature the ionic distribution of the zinc ferrite nanoparticles tends to that of bulk sample. The magnetic properties of the samples were studied by VSM and the results show that zinc ferrite nanoparticles have a ferrimagnetic behavior. Also the morphology of the powders was examined by TEM. 相似文献
15.
Annealing temperature effect on microstructure,magnetic and microwave properties of Fe-based amorphous alloy powders 总被引:1,自引:0,他引:1
Fe74Ni3Si13Cr6W4 amorphous alloy powders were annealed at different temperature (T) for 1.5 h to fabricate the corresponding amorphous and nanocrystalline powders. The influences of T on the crystalline structure, morphology, magnetic and microwave electromagnetic properties of the resultant samples were investigated via X-ray diffraction, scanning electron microscopy, vibrating sample magnetometer and vector network analyzer. The results show that the powder samples obtained at T of 650 °C or more are composed of lots of ultra-fine α-Fe(Si) grains embedded in an amorphous matrix. When T increases from 350 to 750 °C, the saturated magnetization and coercivity of the as-annealed powder samples both increase monotonously whereas the relative real permittivity shows a minimal value and the relative real permeability shows a maximal value at T of 650 °C. Thus the powder samples annealed at 650 °C show optimal reflection loss under −10 dB in the whole C-band. These results here suggest that the annealing heat treatment of Fe-based amorphous alloy is an effective approach to fabricate high performance microwave absorber with reasonable permittivity and large permeability simultaneously via adjusting T. 相似文献
16.
O.M. Lemine M. Bououdina M. SajieddineA.M. Al-Saie M. ShafiA. Khatab M. Al-hilaliM. Henini 《Physica B: Condensed Matter》2011,406(10):1989-1994
Nanocrystalline zinc ferrite (ZnFe2O4) is synthesized by high-energy ball-milling after 12 h from a powders mixture of zinc oxide (ZnO) and hematite (α-Fe2O3) with balls to powders mass ratio of 20:1. X-ray diffraction, vibrating sample magnetometer (VSM), the Mössbauer spectrometry and photoluminescence (PL) are used to characterize the samples. Rietveld analysis and VSM measurements show that the powder has an average crystallites size of 10 nm and a ferrimagnetic behavior with a saturation magnetization of 30 emu/g. After annealing at 700 °C, the lattice parameter reduces from 8.448 to 8.427 Å and the sample transforms into a superparamagnetic behavior, which was confirmed as well by the room temperature Mössbauer spectrometry. Different mechanisms to explain the obtained results and the correlation between magnetism and structure are discussed. Finally, the broadband visible emission band is observed in the entire PL spectrum and the estimated energy band gap is about 2.13 eV. 相似文献
17.
One- and two-step rapid thermal annealing (RTA) for activating Mg-doped p-type GaN films had been performed to compare with conventional furnace annealing (CFA). The two-step annealing process consists of two annealing steps: the first step is performed at 750 °C for 1 min and the second step is performed at 600 °C for 5 min in pure O2 or air ambient. It is found that the samples annealed in air ambient exhibit poor electrical properties as compared to those annealed in pure O2. Compared to one-step RTA annealing and CFA annealing, the samples with two-step annealing exhibit higher hole concentration and lower resistivity. This means that the two-step annealing is a powerful method to enhance the electrical performance of Mg-doped p-type GaN films. Similar results were also evidenced by photoluminescence (PL) measurement. Possible mechanism was confirmed by secondary ion mass spectrometry analysis. 相似文献
18.
Influence of annealing temperature on structural and optical properties of ZnO: In thin films prepared by ultrasonic spray technique 总被引:4,自引:0,他引:4
Transparent conducting indium doped zinc oxide was deposited on glass substrate by ultrasonic spray method. The In doped ZnO samples with indium concentration of 3 wt.% were deposited at 300, 350 and 400 °C with 2 min of deposition time. The effects of substrate temperature and annealing temperature on the structural, electrical and optical properties were examined. The DRX analyses indicated that In doped ZnO films have polycrystalline nature and hexagonal wurtzite structure with (0 0 2) preferential orientation and the maximum average crystallite size of ZnO: In before and annealed at 500 °C were 45.78 and 55.47 nm at a substrate temperature of 350 °C. The crystallinity of the thin films increased by increasing the substrate temperature up 350 °C, the crystallinity improved after annealing temperature at 500 °C. The film annealed at 500 °C and deposited at 350 °C show lower absorption within the visible wavelength region. The band gap energy increased from Eg = 3.25 to 3.36 eV for without annealing and annealed films at 500 °C, respectively, indicating that the increase in the transition tail width. This is due to the increase in the electrical conductivity of the films after annealing temperature. 相似文献
19.
PbTiO3 thin films were successfully deposited on the LaNiO3 (LNO) substrates by the liquid-phase deposition (LPD) method and post-annealing at various temperatures. The structure, morphology and composition of the films were investigated by some analytical techniques. The as-deposited films are amorphous and composed of densely packed spherical particles. The films with the grain size of 180 nm start to decompose and crystallize into perovskite structure at 450 °C and show a perovskite single phase with tetragonal structure after annealing at 650 °C. X-ray photoelectron spectroscopy (XPS) analysis reveals that the as-deposited film contains fluorine and carbon as major impurities. Fluorine could be completely eliminated by annealing at 650 °C in air. 相似文献
20.
Zn-Sn-O (ZTO) films with continuous compositional gradient of Sn 16-89 at.% were prepared by co-sputtering of two targets of ZnO and SnO2 in a combinatorial method. The resistivities of the ZTO films were severely dependent on oxygen content in sputtering gas and Zn/Sn ratio. Except for the films with Sn 16 at.%, all the as-prepared films were amorphous and maintaining the stable amorphous states up to the annealing temperature of 450 °C. Annealing at 650 °C resulted in crystallization for all the composition, in which ZnO, Zn2SnO4, ZnSnO3, and SnO2 peaks were appeared successively with increasing Sn content. Above Sn 54 at.%, the ZTO films were deduced to have a local structure mixed with ZnSnO3 and SnO2 phases which were more conductive and stable in thermal oxidation than ZnO and Zn2SnO4 phases. The lowest resistivity of 1.9 × 10−3 Ω cm was obtained for the films with Sn 89 at.% when annealed at 450 °C in a vacuum. The carrier concentrations of the amorphous ZTO films that contained Sn contents higher than 36 at.% and annealed at 450 °C in a vacuum were proportional to the Sn contents, while the Hall mobilities were insensitive to Sn contents and leveling in the range of 23-26 cm2/V s. 相似文献