Stability of the magnetoresistance for NiO-containing Co/Cu/Co spin valves naturally placed in air

The Co/Cu/Co spin valves with an additional NiO layer at the top (TSV) and under the bottom (BSV) were set in air at room temperature for about four years. Effects of time on the stability, the magnetoresistance (MR), and microstructures were investigated. Results show that the MR of TSV is more stable than that of BSV. The MR of BSV decreases 12.5% in the first 1000 days, while it increases 4% after another 360 days, while the MR of TSV keeps almost unchanged within the range of measurement error. Different time-dependent behavior of the MR value for BSV and TSV was ascribed to the different contribution of the roughness at NiO/Co and Co/Cu interfaces. PACS 68.60.Dv; 61.10.Eg; 68.35.Ct; 73.43.Qt; 75.25.+z     

Microstructural stability of NiO-containing spin valves annealed at room temperature

Microstructure of NiO-containing Co/Cu/Co spin valves (CCC-SV) annealed at room temperature for nearly four years has been studied by synchrotron radiation X-ray diffraction. With the annealing time expanding, the thickness of each sub-layer remains nearly unchanged while the interface roughness varies obviously compared with that of samples without annealing. The roughness at the interface of NiO/Co decreases with the annealing time increasing for both of the samples with NiO layer on the top (TSV) and under the bottom (BSV) of CCC-SV. On the other hand, the roughness at Co/Cu interface increases with the annealing time expanding for BSV while it decreases for TSV. These results indicate that the structure of TSV is more stable than that of BSV.

     

Effect of substrate temperature on the surface and interface oxidation of NiTi thin films

NiTi shape memory alloy thin films are deposited on pure Cu substrate at substrate ambient temperatures of 300 °C and 450 °C. The surface and interface oxidation of NiTi thin films are characterized by X-ray photoelectron spectroscopy (XPS). After a subsequent annealing treatment the crystallization behavior of the films deposited on substrate at different temperatures is studied by X-ray diffraction (XRD). The effects of substrate temperature on the surface and interface oxidation of NiTi thin films are investigated. In the film surface this is an oxide layer composed of TiO₂. The Ni atom has not been detected on surface. In the film/substrate interface there is an oxide layer with a mixture Ti₂O₃ and NiO in the films deposited at substrate temperatures 300 °C and 450 °C. In the films deposited at ambient temperature, the interface layer contains Ti suboxides (TiO) and metallic Ni.     

Influence of ternary addition of transition elements (Cr,Si and Mn) on the microstructure and magnetic properties of nano-structured CuCo alloy

The current state of studies presents the effect of ternary addition of transition elements such as Mn, Cr and Si (10 wt%) on the mechanically driven non-equilibrium solubility of 40 wt% Co containing Cu–Co alloy. X-ray powder diffraction analysis indicates that addition of Mn has been found to be the most effective in enhancing the solubility and formation of a complete solid solution between Co and Cu in a short duration (30 h) of ball milling. The microstructure of the ball milled CuCoMn alloy was found to be stable after the isothermal annealing up to a temperature of 450 °C for 1 h. The magnetic properties such as magnetic saturation, coercivity and remanence of ball milled CuCo alloy in the presence of Mn significantly altered after annealing in the temperature range 350–650 °C for 1 h. The best combination of magnetic properties of CuCoMn alloy has been found after annealing at 550 °C for 1 h.     

Ultrathin amorphous Ni-Ti film as diffusion barrier for Cu interconnection

5-nm-thick amorphous Ni-Ti films deposited on Si by magnetron sputtering, annealed at various temperatures in high vacuum, have been studied as diffusion barriers for Cu interconnection using X-ray diffraction, atomic force microscopy and four-probe methods. Although no Cu silicide peaks are found from X-ray diffraction patterns of the samples annealed up to 750 °C, it is found that the sheet resistance of Cu/Ni-Ti/Si decreases with the increase of annealing temperature and then slightly increases when the annealing temperature is higher than 700 °C. Root mean square roughness of Cu/Ni-Ti/Si increases with the increase of annealing temperature and many island-like grains present on the surface of the 750 °C annealed sample, which is ascribed to dewetting and agglomeration.     

Effect of tin-doped indium oxide film as capping layer on the agglomeration of copper film and the appearance of copper silicide

In this work, the effect of tin-doped indium oxide (ITO) film as capping layer on the agglomeration of copper film and the appearance of copper silicide was studied. Both samples of Cu 100 nm/ITO 10 nm/Si and ITO 20 nm/Cu 100 nm/ITO 10 nm/Si were prepared by sputtering deposition. After annealing in a rapid thermal annealing (RTA) furnace at various temperatures for 5 min in vacuum, the samples were characterized by four probe measurement for sheet resistance, X-ray diffraction (XRD) analysis for phase identification, scanning electron microscopy (SEM) for surface morphology and transmission electron microscopy (TEM) for microstructure.The results show that the sample with ITO capping layer is a good diffusion barrier between copper and silicon at least up to 750 °C, which is 100 °C higher than that of the sample without ITO capping layer. The failure temperature of the sample with ITO capping layer is about 800 °C, which is 100 °C higher than that of the sample without ITO capping layer. The ITO capping layer on Cu/ITO/Si can obstacle the agglomeration of copper film and the appearance of Cu₃Si phase.     

Magnetic properties of electroless-deposited Ni and Ni-NiO core-shell nano-arrays

Ni and Ni-NiO core-shell nano-arrays were fabricated by means of electroless deposition, where the latter was covered by a NiO shell of ∼10 nm by annealing the former at 350 °C for 30 min in an atmospheric condition. HRTEM showed that the NiO shell was developed at the expense of Ni at the array's surface. Ferromagnetic ordering of the Ni-NiO arrays was found to be suppressed compared with those of the less oxidized reference Ni arrays. This is attributed to the screening effect of the NiO shell, and weak ferromagnetism of inner Ni arrays resulted from the development of the NiO. X-ray absorption spectrum reveals that the reference Ni is partially oxidized. Also, X-ray magnetic circular dichroism suggests that the magnetic suppression of the Ni-NiO arrays is associated with a reduced spin moment.     

Effect of Co layer thickness on structural and magnetic properties of C/Co/C films

Granular C/Co/C films have been prepared by magnetron sputtering from C and Co onto glass substrates at room temperature and subsequent in situ annealing. It has been found that the structure and magnetic properties of the C/Co/C films depend strongly on the Co layer thickness. Vibrating sample magnetometer measurements indicate that the in-plane coercivities reach maximum in 20 nm Co thickness of both as-deposited and annealed films. The squareness ratio of annealed films was more than 0.8. X-ray diffraction shows that majority Co nanograins are formed as the hexagonal-close-packed (HCP) structure in 20 nm Co thickness with annealing at 400 °C. Scanning probe microscope was used to scan surface morphology and magnetic domain structures. The values of the surface roughness were lower than 0.6 nm in all annealed samples. The average magnetic cluster size was estimated to be about 10 nm in annealed 20 nm Co thickness films.     

Magnetic and magnetotransport properties in Co5Cu95 melt-spun alloys

Giant magnetoresistance (GMR) has been observed in Co₅Cu₉₅ alloys fabricated by melt-spinning. The highest MR change of 28.0% occurs for Co₅Cu₉₅ after annealing at 450°C for 30 min. Based on the super-paramagnetic assumption, the average size of Co particles embedded in Cu matrix, ranging from 3.0 to 6.0 nm, has been determined by simulating the magnetization curves at 295 K which is higher than the blocking temperatures for the samples. Comparison with phenomenological theory for GMR indicates that the interfacial spin-dependent scattering is the dominant scattering mechanism underlying GMR origin in granular systems. Additionally, for the samples in as-quenched state or annealed at temperatureT _A=350°C, the electron hybridization and super-paramagnetic behaviors of fine Co particles may be responsible for the low value of MR change.     

Giant magnetoresistance in Cu–Co films electrodeposited on n-Si

High quality Cu–Co alloy films with excellent metallic luster have been electrolytically deposited directly onto n-Si (1 0 0) substrate, thereby eliminating the need of a conducting seed layer, which is otherwise required when the films were grown on insulating substrates (Al₂O₃). The as-deposited Cu–Co films exhibit relatively higher magnetoresistance (MR) in comparison with the as-deposited films on Al₂O₃ under identical conditions. The observed increase in MR could be attributed to the reduced substrate current shunting. The MR further improves to 2.67% (at H=10 kOe) with vacuum annealing (at 425°C for 30 min) of the films on Si. This has been ascribed to the separation of Cu and Co phases resulting in a magnetic granular nanostructure. This value of MR of annealed films on Si is, however, lower in comparison with the value obtained for annealed films deposited on Al₂O₃. Glancing angle X-ray diffraction (GAXRD) has revealed the formation of copper silicide in these samples, which is responsible for the lower value of MR. Thus we have observed good MR with a copper silicide host matrix.     

Amorphous to crystalline phase transition in pulsed laser deposited silicon carbide

SiC thin films were grown on Si (1 0 0) substrates by excimer laser ablation of a SiC target in vacuum. The effect of deposition temperature (up to 950 °C), post-deposition annealing and laser energy on the nanostructure, bonding and crystalline properties of the films was studied, in order to elucidate their transition from an amorphous to a crystalline phase. Infra-red spectroscopy shows that growth at temperatures greater than 600 °C produces layers with increasingly uniform environment of the Si-C bonds, while the appearance of large crystallites is detected, by X-ray diffraction, at 800 °C. Electron paramagnetic resonance confirms the presence of clustered paramagnetic centers within the sp² carbon domains. Increasing deposition temperature leads to a decrease of the spin density and to a temperature-dependent component of the EPR linewidth induced by spin hopping. For films grown below 650 °C, post-deposition annealing at 1100 °C reduces the spin density as a result of a more uniform Si-C nanostructure, though large scale crystallization is not observed. For greater deposition temperatures, annealing leads to little changes in the bonding properties, but suppresses the temperature dependent component of the EPR linewidth. These findings are explained by a relaxation of the stress in the layers, through the annealing of the bond angle disorder that inhibits spin hopping processes.     

Long-range chemical interaction in solid-state synthesis: The formation of a CuAu alloy in Au/β-Co(001)/Cu(001) epitaxial film structures

The effect of an inert Co layer (0, 210, 480 nm) on the chemical interaction between Cu and Au in Au/β-Co(001)/Cu(001) epitaxial films has been investigated by X-ray diffraction, nuclear magnetic resonance, photoelectron spectroscopy, and magnetic structure measurements. Mixing at interfaces in Cu/β-Co(001) and Au/β-Co(001) bilayer films has not been revealed up to a temperature of 600°C. The solid-state synthesis of ordered CuAu| and CuAu∥ phases occurs through the Co inert buffer layer in Au/β-Co(001)/Cu(001) trilayer film systems with an increase in the annealing temperature. The initiation temperatures of the CuAu| and CuAu∥ phases increase only slightly with the thickness of the Co buffer layer. The assumption of the long range of the chemical interaction between Cu and Au through the chemically inert Co layer is justified using the performed investigations.     

TaN underlayers for spin valves deposited directly on top of Si substrates

TaN underlayers for spin valves were studied, which were deposited directly on top of Si substrates. The experimental results obtained with the TaN underlayer were compared with those obtained with other (Ta, Mo, and MoN) underlayers. The spin valve structure was Si/Underlayer(tÅ)/NiFe(21 Å)/CoFe(28 Å)/Cu(22 Å)/CoFe(18 Å)/IrMn(65 Å)/Ta(25 Å). The TaN underlayer for a spin valve element exhibited good adhesion to the Si substrate. The XRD patterns of the annealed TaN on bare Si substrate at 900 °C showed no Ta silicide phases, which suggests that the TaN layer may also be used as a diffusion barrier between Si substrate and the ensuing spin valve active layers, as well as an underlayer. A spin valve element having TaN underlayer deposited directly on top of a Si substrate showed a high MR ratio of about 8.3% after annealing at 200 °C. It is concluded that it is advantageous to use a TaN underlayer if one wants to fabricate spin valve elements directly on top of Si substrates.     

Dual spin valves with nano-oxide layers

A novel method is proposed for increasing the giant magnetoresistance (GMR) of dual spin valves of the CoFe/Cu/CoFe/Cu/CoFe type by inserting nano-oxide layers (NOLs) into the pinned layers. Using this method, MR ratio of 23.5% was obtained, a value equal to those of specular spin valves with antiferromagnetic oxide, e.g., NiO. This method allows the selection of metallic materials for the antiferromagnetic layer. In addition, we obtained the specularity factor of upper NOLs, 0.8, and that of lower NOLs, 0.7, by calculating Boltzmann equations taking into account the roughness of each interlayer. This model shows that the MR ratio would be 27.5% for dual spin valves with ideal NOLs.     

Influence of oxygen on diffusion in the Cu/Mo/Au system

The annealing behaviour of the Cu/Mo/Au metallization system is investigated. Backscattering spectrometry reveals a rapid diffusion of Cu and Au across the Mo film and the formation of AuCu after annealing at 600°C for 30 min in vacuum, but only when no impurity is detected in the as-deposited polycrystalline Mo layer. The Au-Cu interaction is impeded when 5.5 at% of oxygen is introduced in the as-deposited Mo layer. The thin film microstructures are analyzed using X-ray diffraction and transmission electron microscopy. The thermal stability difference between the samples with a pure Mo layer and a contaminated Mo layer is discussed in terms of fast diffusion process inhibited by a grain boundary decoration with oxygen atoms.     

Dual-facing-target-sputtered amorphous CoMoN/CN compound soft-X-ray multilayers: structures and thermal stability

Amorphous CoMoN/CN compound soft-X-ray multilayers were fabricated by dual-facing-target sputtering. Their structural thermal stability has been investigated by monitoring the structural evolutions of CN and CoMoN sublayers at annealing temperatures up to 800 °C using complementary measurement techniques, and measuring the coefficient of interfacial diffusion at annealing temperatures below 300 °C. The period expansion at annealing temperatures below 600 °C, which is usually observed in annealed metal/carbon soft-X-ray multilayers, is only 5%. The enhanced sp² to sp³ bond ratio caused by the incorporation annealing effect of nitrogen [1] is thought to be responsible for the improved thermal stability of CN sublayers. Mo addition greatly suppresses the structural thermal evolution of CoMoN sublayers. XPS and TEM analyses indicate that the strong chemical bonding between N and Co atoms and Mo nitride aggregation in the grain boundary of cobalt are the main mechanisms for the high thermal stability of CoMoN sublayers. The layered structure of the CoMoN/CN multilayers still exists at the annealing temperature of 800 °C, while Co/C and CoN/CN multilayers have already been destroyed at this temperature. Compared with Co/C and CoN/CN multilayers, the smaller negative interdiffusivity measured by X-ray diffraction reveals the stable interfaces of CoMoN/CN multilayers. These results illustrate that refractory metal incorporation and strong chemical bond establishment are quite effective in obtaining thermally highly stable compound soft-X-ray optical multilayers . PACS 68.65+g; 68.55.Ln; 68.35.Fx; 68.60.Dv     

Thermal stability of atmospheric plasma sprayed (Ni, Cu, Co)–YSZ and Ni–Cu–Co–YSZ anodes cermets for SOFC application

This paper reports the results of the thermal stability study of M–YSZ (M=Ni, Cu, Co, Cu–Co, Ni–Cu–Co) SOFC anode cermets materials at different heat treatment temperatures. The cermets were elaborated by atmospheric plasma spraying (APS) with optimized conditions and then submitted to heat treatments at 800 and 1000 °C, respectively. Scanning electron microscopy and X-ray diffraction were used to characterize, respectively, the morphology and structure of obtained films, before and after thermal annealing. A correlation was made between the differential scanning calorimetry analysis results and those obtained by X-ray diffraction. Focusing, in this study, on YSZ matrix thermal stability, the obtained results were as follows: the monometallic cermets with the lowest amount of metal and the trimetallic one exhibited a good stability at 800 °C, whereas at 1000 °C, all considered cermets were unstable with a eutectoid decomposition of YSZ matrix.     

Influence of annealing temperature on structural, optical and magnetic properties of Zn0.95Cu0.02Cr0.03O powders

Zn_0.95Cu_0.02Cr_0.03O powders have been synthesized by the sol-gel method and sintered in argon atmosphere under different temperatures. The structural, optical and magnetic properties of the powders were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and vibrating sample magnetometer (VSM). The XRD results demonstrated that Cr and Cu ions are incorporated into ZnO successfully when annealing temperatures were 600 and 700 °C. But when the samples were annealed at 500 °C, the crystallinity of the samples was not very good. However, when the annealing temperature was increased to 800 °C, the secondary phase of Cu and ZnCr₂O₄ appeared in the samples. The PL spectra revealed that the position of the ultraviolet (UV) emission peak of the samples showed a blue shift and the green emission peak enhanced significantly with the annealing temperature increasing from 600 to 700 °C. Magnetic measurements indicated that the room temperature ferromagnetism of Zn_0.95Cu_0.02Cr_0.03O was intrinsic in nature. In addition, the saturation magnetization (Ms) increased from 0.0078 to 0.0088 emu/g with the annealing temperature increased from 600 to 700 °C.     

The effects of annealing on Au/pyronine-B/MD n-InP Schottky structure

Thin film of non-polymeric organic compound pyronine-B has been fabricated on moderately doped (MD) n-InP substrate as an interfacial layer using spin coating technique for the electronic modification of Au/MD n-InP Schottky contact. The electrical characteristics have been determined at room temperature. The barrier height and the ideality factor values for Au/pyronine-B/MD n-InP Schottky diode have been obtained from the forward bias I-V characteristics at room temperature as 0.60 eV and 1.041; 0.571 and 1.253 eV after annealing at 100 and 250 °C, respectively. An increase in annealing temperature at the Au/n-InP Schottky junction is shown to increase the reverse bias leakage current by about one order of magnitude and decrease the Schottky barrier height by 0.027 eV. Furthermore, the barrier height values for the Au/pyronine-B/MD n-InP Schottky diode have also been obtained from the C-V characteristics at room temperature as 1.001 and 0.709 eV after annealing at 100 and 250 °C, respectively. Finally, it was seen that the diode parameters changed with increase in the annealing temperature.     

Failure behavior of ITO diffusion barrier between electroplating Cu and Si substrate annealed in a low vacuum

A structure of Cu/ITO(10 nm)/Si was first formed and then annealed at various temperatures for 5 min in a rapid thermal annealing furnace under 10⁻² Torr pressure. In Cu/ITO(10 nm)/Si structure, the ITO(10 nm) film was coated on Si substrate by sputtering process and the Cu film was deposited on ITO film by electroplating technique. The various Cu/ITO(10 nm)/Si samples were characterized by a four-point probe, a scanning electron microscope, an X-ray diffractometer, and a transmission electron microscope. The results showed that when the annealing temperature increases near 600 °C the interface between Cu and ITO becomes unstable, and the Cu₃Si particles begin to form; and when the annealing temperature increases to 650 °C, a good many of Cu₃Si particles about 1 μm in size form and the sheet resistance of Cu/ITO(10 nm)/Si structure largely increases.