共查询到20条相似文献,搜索用时 17 毫秒
1.
The epitaxial growth of Pt, Au and Ag layers on Fe3O4(0 0 1) as a function of temperature and thickness have been studied. The layers were deposited by sputtering in an ultra high vacuum chamber and the structural properties were investigated by Reflection High Energy Electron Diffraction, X-ray reflectivity and diffraction, High Resolution Transmission Electron Microscopy and Atomic Force Microscopy. Our studies give evidence for three different growth behaviours depending both on the nature of the metals and the temperature. Comparison between the growth modes of the three metals will be discussed in relation with surface and interfaces energies. 相似文献
2.
Shoudong MaoHengxiu Yang Feng HuangTingting Xie Zhenlun Song 《Applied Surface Science》2011,257(9):3980-3984
Al/Al2O3 multilayers were deposited on sintered NdFeB magnets to improve the corrosion resistance. The amorphous Al2O3 films were used to periodically interrupt the columnar growth of the Al layers. The structure of the multilayers was investigated by Scanning Electron Microscopy (SEM) and High Resolution Transmission Electron Microscopy (HRTEM). It was found that the columnar structure was effectively inhibited in the multilayers. Subsequent corrosion testing by potentiodynamic polarization in 3.5 wt.% NaCl and neutral salt spray test (NSS) revealed that the Al/Al2O3 multilayers had much better corrosion resistance than the Al single layer. Furthermore, for multilayers with similar thickness, the corrosion resistance was improved as the period decreased. 相似文献
3.
Z. Valdez-Nava S. Guillemet-Fritsch T. Lebey B. Durand 《Journal of Physics and Chemistry of Solids》2011,72(1):17-23
BaTiO3−x and Ba0.95La0.05TiO3−x nanoceramics showing colossal permittivity values have been characterized. While starting powders are of cubic symmetry, X-ray and Neutron Diffraction techniques and Raman Spectroscopy measurements show that the one-step processed ceramics obtained by Spark Plasma Sintering (SPS) contain cubic and tetragonal phases. Rather large oxygen deficiency determined in such ceramics by Electron Micro Probe analysis and Electron Energy Loss Spectroscopy analyzes is explained by the presence of Ti3+, as evidenced by X-ray Photoelectron Spectroscopy measurements. Transmission Electron Microscopy and High Resolution Transmission Electron Microscopy show that these ceramics contain 50-300 nm grains, which have single-domains, while grain boundaries are of nanometer scale. Colossal permittivity values measured in our dense nanoceramics are explained by a charge hopping mechanism and an interfacial polarization of a large number of polarons generated after sample reduction in SPS apparatus. 相似文献
4.
Ali Ekber Irmak Atilla Coskun Selcuk Akturk Yusuf Samancioglu Burak M. Kaynar 《Journal of magnetism and magnetic materials》2010,322(8):945-951
La1−xAgxMnO3 samples were synthesized by standard sol-gel method with Ag concentrations of x=0.05 and 0.25. The samples from each concentration were pressed and sintered at 1000, 1200 and 1400 °C for 24 h in air for a systematic study. They were examined structurally by Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS) and X-ray Diffraction (XRD) and magnetically by Magnetic Properties Measurements System (MPMS). AFM and SEM analyses show that surface morphology changes with Ag concentration and sintering temperature (TS). It was observed that high temperature sintering leads Ag to leave material as determined from EDS analyses. XRD spectra exhibited that the crystal structure changes with Ag concentration while showing pronounced change with the sintering temperature. From the magnetic measurements, the Curie temperatures (TC) and the isothermal magnetic entropy changes (−ΔSM) were calculated. It was observed that TC increases with Ag concentration and decreases with TS. The maximum −ΔSM was calculated to be 7.2 J/kg K under the field change of 5 T for the sample sintered at 1000 °C with x=0.25. 相似文献
5.
P.T. Phong N.V. Khiem N.V. Dai L.V. Hong 《Journal of magnetism and magnetic materials》2009,321(19):3330-3334
We report the resistivity (ρ)-temperature (T) patterns in (1-x)La0,7Ca0,3MnO3+xAl2O3 composites (0≤x≤0.05) over a temperature regime of 50-300 K. Al2O3 addition has increased the resistivity of these composites. The Curie temperature (TC) is almost independent on the Al2O3 content and is about 250 K for all the samples, while the metal-insulator transition temperature (TMI) decreases with increasing Al2O3 content. Based on the phenomenological equation for conductivity under a percolation approach, which is dependent on the phase segregation of ferromagnetic metallic clusters and paramagnetic insulating regions, we fitted the experimental data (ρ−T) from 50 to 300 K and find that the activation barrier increases as Al2O3 content increases. 相似文献
6.
Muhammad Javed Iqbal Muhammad Naeem Ashiq 《Journal of magnetism and magnetic materials》2010,322(13):1720-5126
Calcium substituted strontium hexaferrite CaxSr1−xFe12O19 (x=0.0−0.6) nanoparticles are synthesized by chemical co-precipitation method. The synthesized samples are characterized by Fourier Transform Infrared (FTIR), X-ray diffraction (XRD), Scanning Electron Microscopy, Transmission Electron Microscopy, DC electrical resistivity and dielectric measurements. FTIR data of uncalcined sample shows that nitrate ions are present which disappeared on calcination at 920 °C. The XRD data shows that a single hexagonal magnetoplumbite phase is formed in samples in which the calcium content, x, is ≤0.20. However, a nonmagnetic phase (α-Fe2O3) in addition to the hexagonal phase is also present in samples with x>0.20. The average crystallite size is found between 17 and 29 nm. The DC electrical resistivity increases with increase of calcium content up to level of x=0.2 but decreased on further addition of calcium. The enhanced resistivity of the calcium doped material has potential applications in microwave devices. The variations of dielectric constant and dielectric loss angle are explained on the basis of Maxwell-Wagner and Koops models. 相似文献
7.
Jifeng Gao Jinping Suo 《Applied Surface Science》2011,257(22):9643-9648
To increase the SiC content in Cr-based coatings, Cr-Al2O3/SiC composite coatings were plated in Cr(VI) baths which contained Al2O3-coated SiC powders. The Al2O3-coated SiC composite particles were synthesized by calcining the precursor prepared by heterogeneous deposition method. The transmission electron microscopy analysis of the particles showed that the nano-SiC particle was packaged by alumina. The zeta potential of the particles collected from the bath was up to +23 mV, a favorable condition for the co-deposition of the particles and chromium. Pulse current was used during the electrodeposition. Scanning Electron Microscopy (SEM) indicated that the coating was compact and combined well with the substrate. Energy dispersive X-ray analysis of Cr-Al2O3/SiC coatings demonstrated that the concentration of SiC in the coating reached about 2.5 wt.%. The corrosion behavior of the composite coating was studied by potentiodynamic polarization and electrochemical impedance spectroscopy techniques. The data obtained suggested that the Al2O3/SiC particles significantly enhanced the corrosion resistance of the composite coating in 0.05 M HCl solution. 相似文献
8.
GaN layers and Al1−xInxN/AlN/GaN heterostructures have been studied by scanning probe microscopy methods. Threading dislocations (TDs), originating from the GaN (0 0 0 1) layer grown on sapphire, have been investigated. Using Current-Atomic Force Microscopy (C-AFM) TDs have been found to be highly conductive in both GaN and AlInN, while using semi-contact AFM (phase-imaging mode) indium segregation has been traced at TDs in AlInN/AlN/GaN heterostructures. It has been assessed that In segregation is responsible for high conductivity at dislocations in the examined heterostructures. 相似文献
9.
R. Jangir Tapas GanguliPragya Tiwari S. PorwalHimanshu Srivastava S.K. RaiB.Q. Khattak S.M. Oak 《Applied Surface Science》2011,257(22):9323-9328
β-Ga2O3 nanostructures including nanowires, nanoribbons and nanosheets were synthesized via thermal annealing of gold coated GaAs substrates in N2 ambient. GaAs substrates with different dopants were taken as the starting material to study the effect of doping on the growth and photoluminescence properties of β-Ga2O3 nanostructures. The nanostructures were investigated by Grazing Incident X-ray Diffraction, Scanning Electron Microscopy, Transmission Electron Microscopy, Energy Dispersive X-ray Spectroscopy, room temperature photoluminescence and optical absorbance. The selected area electron diffraction and High resolution-TEM observations suggest that both nanowires and nanobelts are single crystalline. Different growth directions were observed for nanowires and nanoribbons, indicating the different growth patterns of these nanostructures. The PL spectra of β-Ga2O3 nanostructures exhibit a strong UV-blue emission band centered at 410 nm, 415 nm and 450 nm for differently doped GaAs substrates respectively. A weak red luminescence peak at 710 nm was also observed in all the samples. The optical absorbance spectrum showed intense absorption features in the UV spectral region. The growth and luminescence mechanism in β-Ga2O3 nanostructures are also discussed. 相似文献
10.
ZnO active layers on ZnO buffer layers were grown at various O2/O2 + Ar flow-rate ratios by using radio-frequency magnetron sputtering. Atomic force microscopy images showed that the surface roughnesses of the ZnO active layers grown on ZnO buffer layers decreased with decreasing O2 atmosphere, indicative of an improvement in the ZnO surfaces. The type of the ZnO active layer was n-type, and the resistivity of the layer increased with increasing O2 atmosphere. Photoluminescence spectra from the ZnO active layers grown on the ZnO buffer layers showed dominant peaks corresponding to local levels in the ZnO energy gap resulting from oxygen vacancies or interstitial zinc vacancies, and the peak positions changed significantly with the O2/O2 + Ar flow rate. These results can help improve understanding of the dependences of the surface and the optical properties on the O2/O2 + Ar ratio for ZnO thin films grown on ZnO buffer layers. 相似文献
11.
M.G. El-Shaarawy 《Journal of Physics and Chemistry of Solids》2005,66(7):1247-1251
The electrical properties of the solid electrolytes Ag7I4VO4-Al2O3 (0-40 mol% Al2O3) are investigated. The electrical conductivity, dielectric constant and dielectric loss are increased by increasing the concentration of Al2O3; showing a maximum at 30 mol% Al2O3. The conductivity is found to be increased by decreasing the particle size of Al2O3. The results are explained using the random resistor network model (RRN). This is due to the formation of a highly conducting interface layer along the matrix-particle interface. This layer is destroyed at concentrations higher than 30 mol% Al2O3. 相似文献
12.
G.F. Iriarte D.F. ReyesD. González J.G. RodriguezR. García F. Calle 《Applied Surface Science》2011,257(22):9306-9313
A pulsed DC reactive ion beam sputtering system has been used to synthesize aluminium nitride (AlN) thin films at room temperature by reactive sputtering. After systematic study of the processing variables, high-quality polycrystalline films with preferred c-axis orientation have been grown successfully on silicon and Au/Si substrates with an Al target under a N2/(N2 + Ar) gas flow ratio of 55%, 2 mTorr processing pressure and keeping the temperature of the substrate holder at room temperature. The crystalline quality of the AlN layer as well as the influence of the substrate crystallography on the AlN orientation has been characterized by high-resolution X-ray diffraction (HR-XRD). Best ω-FWHM (Full Width at Half Maximum) values of the (0 0 0 2) reflection rocking curve in the 1 μm thick AlN layers are 1.3°. Atomic Force Microscopy (AFM) measurements have been used to study the surface morphology of the AlN layer and Transmission Electron Microscopy (TEM) measurements to investigate the AlN/substrate interaction. AlN grew off-axis from the Si substrate but on-axis to the surface normal. When the AlN thin film is deposited on top of an Au layer, it grows along the [0 0 0 1] direction but showing a two-domain structure with two in-plane orientations rotated 30° between them. 相似文献
13.
V2O5-loaded Al2O3 layers were successfully grown via micro-arc oxidation (MAO) process for the first time. Surface morphology and topography of the layers were investigated by scanning electron microscope (SEM) and atomic force microscope (AFM). It was found that the composite layers had a porous structure with a rough surface which is suitable for catalytic applications. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and energy dispersive X-ray spectroscopy (EDS) techniques were also employed to study phase structure and chemical composition of the composite layers. The layers consisted of γ-alumina, α-alumina, and vanadium pentoxide phases in which their relative contents varied with the applied voltage. Meanwhile, optical properties of the composite layers were investigated using UV-vis spectrophotometry technique, and the band gap energy was calculated as 3.15 eV. Furthermore, photocatalytic performance of the synthesized composite layers was determined by measuring the decomposition rate of methylene blue solution, as a model compound, on the surface of the layers under ultra violet photo-irradiation. It was found that more than 91% of the methylene blue was degraded after 120 min with a rate constant of k = 0.0192 min−1. 相似文献
14.
R.J.S. Lima K.O. Moura P.P. Pedra J.G.S. Duque C.T. Meneses 《Physica B: Condensed Matter》2012,407(16):3196-3198
Antiferromagnetic Co3O4 nanoparticles were synthesized by the coprecipitation method. With the addition of the sucrose as chelating agent (sucrose) the size of the particles was reduced from 54 nm to 19 nm. The Co3O4 nanoparticles exhibit a cubic spinel structure identified for X-ray diffraction (XRD) and confirmed by Rietveld refinement. Scanning Electron Microscopy (SEM) images exhibit a spherical-like morphology and confirm the decrease of the particle size observed by XRD. The magnetic measurements as a function of temperature using a superconducting quantum interference device (SQUID) show a large surface anisotropy for samples obtained with the addition of sucrose accompanied by an exchange Bias effect indicating also the existence of a weak ferromagnetism. A decrease of the Néel temperature from the bulk (and other nanostructures-type) was observed, which can be associated with finite-size effect in the nanoparticles' shape. 相似文献
15.
Hongwei Chen Chuanren YangShanxue Zheng Jihua ZhangQiaozhen Zhang Guanhuan LeiFeizhi Lou Lijun Yang 《Applied Surface Science》2011,258(4):1510-1513
Modified substrates with nanometer scale smooth surface were obtained via coating a layer of CaO-Al2O3-SiO2 (CaAlSi) high temperature glaze with proper additives on the rough-95% Al2O3 ceramics substrates. (Ba0.6Sr0.4)TiO3 (BST) thin films were deposited on modified Al2O3 substrates by radio-frequency magnetron sputtering. The microstructure, dielectric, and insulating properties of BST thin films grown on glazed-Al2O3 substrates were investigated by X-ray diffraction (XRD), atomic force microscope (AFM), and dielectric properties measurement. These results showed that microstructure and dielectric properties of BST thin films grown on glazed-Al2O3 substrates were almost consistent with that of BST thin films grown on LaAlO3 (1 0 0) single-crystal substrates. Thus, the expensive single-crystal substrates may be substituted by extremely cheap glazed-Al2O3 substrates. 相似文献
16.
A. Ouerdane M. Bouslama A. Abdellaoui Z. Lounis N. Berrouachedi 《Applied Surface Science》2008,254(22):7394-7400
The goal of this research is to highlight the effectiveness of associating the spectroscopic methods EELS and EPES in the study of thin film grown on substrates. We use the great sensitivity of the Electron Energy Loss Spectroscopy (EELS) and the Elastic Peak Electron Spectroscopy (EPES) to study native InPO4 oxide of thin thickness (10 Å) grown on InP by UV/ozone oxidation. By varying the primary energy of the electron beam and the incidence angle, we give interesting results related to the chemical and the physical analyses of InPO4/InP system. These spectroscopic methods reveal the homogeneity of the chemical composition of InPO4 on the surface. Furthermore, the electron irradiation of InPO4/InP leads to the breaking of chemical bonds between the species of InPO4 and InP to form a new oxide In2O3 on the surface. We show that the heating of InPO4/InP at 450 °C in UHV allows a good reconstruction of the surface with elimination of defects on the surface and at the interface. Thus, the surface becomes more stable to impede all oxidation processes due to the electron beam irradiation even for a time as long as 30 min. 相似文献
17.
Byeol HanSeung-Won Lee Kwangchol ParkChong-Ook Park Sa-Kyun RhaWon-Jun Lee 《Current Applied Physics》2012,12(2):434-436
We produced dielectric stacks composed of ALD SiO2 and ALD Al2O3, such as SiO2/Al2O3, Al2O3/SiO2, and SiO2/Al2O3/SiO2, and measured the leakage currents through the stacks in comparison with those of the single oxide layers. SiO2/Al2O3 shows lowest leakage current for negative bias region below 6.4 V, and Al2O3/SiO2 showed highest current under negative biases below 4.5 V. Two distinct electron conduction regimes are observed for Al2O3 and SiO2/Al2O3. Poole-Frenkel emission is dominant at the high-voltage regime for both dielectrics, whereas the direct tunneling through the dielectric is dominant at the low-voltage regime. The calculated transition voltage between two regimes for SiO2 (6.5 nm)/Al2O3 (12.6 nm) is −6.4 V, which agrees well with the experimental observation (−6.1 V). For the same EOT of entire dielectric stack, the transition voltage between two regimes decreases with thinner SiO2 layer. 相似文献
18.
G. Epurescu A. Vlad M.A. Bodea O. Dumitrescu M. Elisa J.D. Pedarnig M. Filipescu A.C. Galca M. Dinescu 《Applied Surface Science》2009,255(10):5295-5298
Thin films of complex oxides have been obtained by pulsed-laser deposition (PLD) from glass targets belonging to the system Li2O-Al2O3-P2O5-(RE)2O3, with RE = Nd, Pr, Er. The films were deposited on quartz, silicon and ITO/glass substrates using a F2 laser (λ = 157 nm, ι ≈ 20 ns) for ablation in vacuum. The structural, morphological and optical properties of the oxide films were investigated through IR and UV-VIS spectroscopy, Atomic Force Microscopy (AFM), Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy (SEM-EDX) and Spectroscopic Ellipsometry. The laser wavelength was found to be the key parameter to obtain thin films with very smooth surface. In this way new possibilities are opened to grow multilayer structures for photonic applications. 相似文献
19.
The growth of Co on thin Al2O3 layers on Ni3Al(1 0 0) was investigated by Auger electron spectroscopy, high resolution electron energy loss spectroscopy (EELS), and scanning tunneling microscopy. At 300 K, Co grows in three-dimensional clusters on top of the Al2O3 layer. A defect structure of the alumina layer plays a crucial role during the early stage of Co growth. After deposition of 10 Å of Co, a complete screening of the dipoles of the Al2O3 layer due to the Co film is found in the EELS measurements. Annealing the Co film reveals a process of coalescence of Co clusters and, above 700 K, diffusion of the Co atoms through the oxide film into the substrate takes place. 相似文献
20.
The effect of alloy surface roughness, achieved by different degrees of surface polishing, on the development of protective alumina layer on Fe-10 at.% Al alloys containing 0, 5, and 10 at.% Cr was investigated during oxidation at 1000 °C in 0.1 MPa oxygen. For alloys that are not strong Al2O3 formers (Fe-10Al and Fe-5Cr-10Al), the rougher surfaces increased Fe incorporation into the overall surface layer. On the Fe-10Al, more iron oxides were formed in a uniform layer of mixed aluminum- and iron-oxides since the layer was thicker. On the Fe-5Cr-10Al, more iron-rich nodules developed on an otherwise thin Al2O3 surface layer. These nodules nucleated preferentially along surface scratch marks but not on alloy grain boundaries. For the strong Al2O3-forming Fe-10Cr-10Al alloy, protective alumina surface layers were observed regardless of the surface roughness. These results indicate that the formation of a protective Al2O3 layer on Fe-Cr-Al surfaces is not dictated by Al diffusion to the surface. More cold-worked surfaces caused an enhanced Fe diffusion, hence produced more Fe-rich oxides during the early stage of oxidation. 相似文献