Effect of annealing temperature on the microstructure and optical–electrical properties of Cu–Al–O thin films

We have successfully prepared Cu–Al–O thin films on silicon (100) and quartz substrates by radio frequency (RF) magnetron sputtering method. The as-deposited Cu–Al–O film is amorphous in nature and post-annealing treatment in argon ambience results in crystallization of the films and the formation of CuAlO₂. The annealing temperature plays an important role in the surface morphology, phase constitution and preferred growth orientation of CuAlO₂ phase, thus affecting the properties of the film. The film annealed at 900 °C is mainly composed of CuAlO₂ phase and shows smooth surface morphology with well-defined grain boundaries, thus exhibiting the optimum optical–electrical properties with electrical resistivity being 79.7 Ω·cm at room temperature and optical transmittance being 80% in visible region. The direct optical band gaps of the films are found in the range of 3.3–3.8 eV depending on the annealing temperature.     

The influence of lithium excess in the target on the properties and compositions of Li<Subscript>1+<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>2</Subscript>O<Subscript>4−<Emphasis Type="Italic">δ</Emphasis></Subscript> thin films prepared by PLD

Li–Mn–O thin films were deposited by pulsed laser deposition (PLD) onto stainless steel substrates using targets containing different concentrations of added Li₂O. The influence of the target composition on the stoichiometry of the resulting thin films, the surface morphology and the electrochemical properties was studied. The application of the target with added 7.5 mol% Li₂O results in an almost ideal lithium content, while all films were still oxygen deficient. The thin films were applied as electrodes in Li//Li_1+x Mn₂O_4−δ cells (i.e. model cells for a rechargeable Li-ion battery) and characterized by cyclic voltammetry and galvanostatic charge/discharge experiments. The electrochemical measurements of the thin films confirmed that the thin films can serve as good model systems and that they show a sufficient cyclability.     

Electrical transport properties of CaMnO3 thermoelectric compound: a theoretical study

The electrical transport coefficients of anti-ferromagnetic CaMnO₃ have been investigated by density functional theory calculation within generalized gradient approximation. The calculated transport coefficients exhibit the anisotropic nature, in agreement with its electronic states. The transport property results reveal the stronger carrier transport along the O1–Mn–O1 plane within the O–Mn–O octahedron, indicating that the Mnd and O1p orbitals are mainly responsible for electrical transport. The maximum power factor values as a function of relaxation time reach 8.4×10²³ Wm⁻¹ K⁻² s⁻¹, 7.9×10²³Wm⁻¹ K⁻² s⁻¹ and 4.9×10²³ Wm⁻¹ K⁻² s⁻¹ within c, a and b direction, respectively. The dimensionless figure of merit ZTxx, ZTyy as well as ZTzz is estimated with 1.28, 0.8 and 1.37 at 1000 K, respectively.     

Multi-functional properties of iron-based ferromagnetic shape memory ribbons

This paper presents measured multi-functional properties of Fe–Mn–Cr–Si–Tb–B ribbons developed by means of the melt-spinning technique in air. The alloys are multi-functional materials, which have both ferromagnetic and shape memory properties. If we can simultaneously improve the material properties, the applications of the shape memory alloys will be widened dramatically in the field of the electromagnetic sensors and actuators. The base shape memory material, Fe–Mn–Si alloy, is nonmagnetic due to its high manganese content (28–34 Mn, 4–6.5Si wt%). In order to improve ferromagnetic function of the Fe–Mn–Si alloy, we have investigated the addition of rare earth elements. Addition of about 0.7–1.0 wt% Tb was effective in increasing the saturation magnetization. However, ductility of the samples was not good and it was difficult to evaluate the shape memory properties with shape recovery strain measurements. The detailed magnetic and shape memory properties of the Fe–Mn–Cr–Si–Tb–B alloys are discussed in this paper.     

Iron-based soft magnetic composites with Mn–Zn ferrite nanoparticles coating obtained by sol–gel method

This paper focuses on iron-based soft magnetic composites which were synthesized by utilizing Mn–Zn ferrite nanoparticles to coat iron powder. The nanocrystalline iron powders, with an average particle diameter of 20 nm, were obtained via the sol–gel method. Scanning electron microscopy, energy dispersive X-ray spectroscopy and distribution maps show that the iron particle surface is covered with a thin layer of Mn–Zn ferrites. Mn–Zn ferrite uniformly coated the surface of the powder particles, resulting in a reduced imaginary permeability, increased electrical resistivity and a higher operating frequency of the synthesized magnets. Mn–Zn ferrite coated samples have higher permeability and lower magnetic loss when compared with the non-magnetic epoxy resin coated compacts. The real part of permeability increases by 33.5% when compared with the epoxy resin coated samples at 10 kHz. The effects of heat treatment temperature on crystalline phase formation and on the magnetic properties of the Mn–Zn ferrite were investigated via X-ray diffraction and a vibrating sample magnetometer. Ferrites decomposed to FeO and MnO after annealing above 400 °C in nitrogen; thus it is the optimum annealing temperature to attain the desired permeability.     

Structural, optical and electrical properties of Al-N codoped ZnO films by RF-assisted MOCVD method

N-doped ZnO films were produced using N₂ as N source by metal-organic chemical vapor deposition (MOCVD) system which has been improved with radio-frequency (RF)-assisted equipments. The data of secondary ion mass spectroscopy (SIMS) indicate that the concentration of N in N-doped ZnO films is around 5 × 10²⁰ cm⁻³, implying that sufficient incorporation of N into ZnO can be obtained by RF-assisted equipment. On this basis, the structural, optical and electrical properties of Al-N codoped ZnO films were studied. Then, the effect of RF power on crystal quality, surface morphologies, optical properties was analyzed using X-ray diffraction, atomic force microscopy and photo-luminescence methods. The results illustrate that the RF plasma is the key factor for the improvement of crystal quality. Then the observation of A⁰X recombination associated with N_O acceptor in low-temperature PL spectrum proved that some N atoms have occupied the positions of O atoms in ZnO films. Hall measurements shown that p-type ZnO film deposited on quartz glasses was obtained when RF power was 150 W for the Al-N codoped ZnO films, while the resistivity of N-doped ZnO films was rather high. Compared with the Al-doped ZnO film, the obviously increased resistivity of codoped films indicates that the formation of N_O acceptors compensate some donors in ZnO films effectively.     

The evolution of magnetic,electrical and structural properties of nanogranular [FeCoBN/SiN]×n thin films

Some results concerning the magnetic, electrical and microstructural properties of multilayer [FeCoBN/Si₃N₄]×n films in view of their utilization for manufacturing thin film magnetic inductors are presented. A comparison between the magnetic, electrical and structural properties of FeCoBN and [FeCoBN/Si₃N₄]×n thin films is also reported. The [FeCoBN/Si₃N₄]×n thin films with the thickness of the FeCoBN layers varied from 10 to 30 nm, exhibit good soft magnetic characteristics and high values for electrical resistivity such as Ms of 172–185 A m²/kg, Hc of 318–1433 A/m and ρ of 82–48×10⁻⁷ Ω m, respectively. These physical properties of the samples are discussed in relation with the microstructure of the multilayer system.     

Electrical and mechanical properties of graphene oxide on flexible substrate

Graphene oxide (GO) was deposited via the electrophoretic deposition (EPD) method to lower the oxygen concentration of graphene sheets for large-scale production. In addition, the direct synthesis of large-scale GO films using transfer processes on a polydimethylsiloxane (PDMS) substrate was conducted. The thickness of the GO films was controlled to adjust the optical, electrical, and mechanical properties. The Young's modulus values of films with thicknesses of 100–200 nm were 324–529 GPa. Moreover, the GO films exhibited excellent conductivity, with a sheet resistance of 276–2024 Ω/sq at 23–77% transparency. Experiments show that transfer processes for flexible substrates can produce high-quality cost-effective transparent conductive films.     

Influence of radiofrequency power on compositional, structural and optical properties of amorphous silicon carbonitride films

The silicon carbonitride (SiCN) films were deposited on n-type Si (1 0 0) and glass substrates by the radiofrequency (RF) reactive magnetron sputtering of polycrystalline silicon target under mixed reactive gases of acetylene and nitrogen. The films have been characterized by energy dispersive spectrometer (EDS), atomic force microscope (AFM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectrophotometer (UVS). The influence of RF power on the compositional, morphological, structural and optical properties of the SiCN films was investigated. The SiCN films deposited at room temperature are amorphous, and the C, Si and O compositions except N in the films are sensitive to the RF power. The surface roughness and optical band gap decrease as the RF power increases. The main bonds in the SiCN films are C-N, N-H_n, C-H_n, C-C, CN, Si-H and Si-C, and the intensities of the CN, Si-H and C-H_n bonds increase with increment of the RF power. The mechanisms of the influence of RF power on the characteristics of the films are discussed in detail.     

Synthesis and characterization of ZnO thin films by thermal evaporation

ZnO thin films have been successfully synthesized by thermal evaporation of pure zinc at 900 °C under the flow of different percentages of argon and oxygen gases. The films were characterized by X-ray diffraction (XRD), variable pressure scanning electron microscopy (VPSEM), energy dispersive X-ray spectroscopy (EDS) and UV–vis spectroscopy. The aim of this paper is to study the influence of the oxygen percentage on the structural and morphological properties of the ZnO films. VPSEM results show that very thick needle structures were produced at high oxygen percentages. EDS results revealed that only Zn and O are present in the sample, indicating a composition of pure ZnO. XRD results showed that the ZnO synthesized under different quantities of oxygen were crystalline with the hexagonal wurtzite structure. UV–vis spectroscopy results indicated that the optical band gap energies from the transmission spectrum are between 3.62 and 3.69 eV for ZnO thin films.     

Study on crystalline properties of Er-Si-O compounds in relation to Er-related 1.54 μm photoluminescence and electrical properties

Er-Si-O crystalline compounds, which exhibit superlattice structures and sharp and strong Er-related 1.54 μm photoluminescence (PL) spectra at room temperature have been formed by self-assembling growth mechanism. Oxidation of the starting materials which have Si and Er at an atomic ratio of 2:1 are prepared and then oxidation and succeeding high-temperature annealing in Ar above 1250 °C cause a self-assembled superlattice-structured Er-Si-O crystalline compounds. The control of the ratio of Si and Er, as well as the following oxidation and annealing processes, is found to be sensitive to the crystalline properties, PL spectra and electrical properties. In this study, Er-Si-O crystalline thin films are formed on Si substrates by sol-gel and MOMBE methods, and their crystalline properties such as crystalline orientation and concentration ratio of Er, Si and O are investigated. Crystalline Er-Si-O films of high orientation are successfully grown on Si(1 0 0) and its inclined surface. The PL and excitation spectra, fluorescence decay and the electrical properties are found to be strongly related to the crystalline properties. Excess O causes a broader 1.54 μm PL spectra, slower fluorescence decay, lower carrier-mediated excitation and higher resistivity. A precise control of O is found to be necessary to grow superlattice-structured Er-Si-O compounds, which are semiconducting and are excitable via carrier-mediated excitation mechanism.     

The improvement of the superconducting Y–Ba–Cu–O magnet characteristics through shape recovery strain of Fe–Mn–Si alloys

Since bulk Y–Ba–Cu–O superconductors are brittle ceramics, reinforcement of mechanical properties is important for practical applications. It has been reported that bulk Y–Ba–Cu–O can be reinforced with Al or Fe based alloy ring, in that compression force acts on bulk Y–Ba–Cu–O due to a difference in thermal expansion coefficients. However, the shrinkage of the metal ring was not so large, and therefore careful adjustment of the circumference of the bulk and the metal rings was necessary. In this study, we employed Fe–Mn–Si shape memory alloy rings to reinforce bulk Y–Ba–Cu–O. The advantage of the shape memory alloy is that the shrinkage can take place on heating, and furthermore, the alloy shrinks and compresses the bulk body on cooling. Bulk Y–Ba–Cu–O superconductor 22.8 mm in diameter was inserted in a Fe–Mn–Si ring 23.0 mm in inner diameter at room temperature. Beforehand, the Fe–Mn–Si ring was expanded by 12% strain at room temperature. Then the composite was heated to 673 K. At room temperature, the Fe–Mn–Si ring firmly gripped the bulk superconductor. We then measured trapped fields before and after the ring reinforcement, and found that the trapped field was improved through the treatment.     

Influence of polarity inversion on the electrical properties of Ga‐doped ZnO thin films

This study investigates how polarity inversion influences the relationship between the electrical properties of heavily Ga‐doped ZnO (GZO) films deposited by RF magnetron sputtering and their thickness. The electrical properties observed in very thin films are correlated with a change of polarity from O‐polar to Zn‐polar face upon increasing the film thickness based on results of valence band spectra measured by X‐ray photoelectron spectroscopy. It is found that the electrical properties of very thin GZO films deposited on Zn‐polar ZnO templates are significantly improved compared to those deposited on O‐polar face. A low resistivity of 2.62 × 10^–4 Ω cm, high Hall mobility of 26.9 cm²/V s, and high carrier concentration of 8.87 × 10²⁰ cm^–3 being achieved with 30 nm‐thick GZO films using Zn‐polar ZnO templates on a glass substrate. In contrast, the resistivity of 30 nm‐thick GZO films on bare glass that shows more likely O‐polar is very poor about 1.44 × 10^–3 Ω cm with mobility and carrier concentration are only 11.9 cm²/V s and 3.64 × 10²⁰ cm^–3, respectively. It is therefore proposed that polarity inversion plays an important role in determining the electrical properties of extremely thin GZO films. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Structural, optical and electrical properties of cadmium zinc oxide films for light emitting devices

Structural, optical and electrical properties of Cd_yZn_1-yO (y=0–0.1) ternary alloy thin films have been investigated for the films prepared using the spin coating method on the glass substrate. XRD pattern confirmed the nano-size polycrystalline hexagonal wurtzite structure for all the samples. The size of nano-crystals was found to be varied in between 21 and 30 nm. Optical band gap calculated from the absorption coefficient signifies the shift in direct band gap from 3.2 to 2.97 eV with cadmium composition. Through EDAX spectrum, it was confirmed that Cadmium was successfully incorporated into ZnO. SEM studies make clear that even after Cadmium incorporation, the surface morphology of the films remained smooth. The current–voltage characteristics obtained from semiconductor characterization system reveals that resistance of the films was found to be decreased with the increase in cadmium composition. Our investigations lead to the applicability of CdZnO as an active layer in CdZnO/ZnO heterostructure for light emitting devices.     

Enhanced exchange bias in magnetron-sputtered Ni–Mn–Sb–Al ferromagnetic shape memory alloy thin films

In the present study, the influence of aluminium (Al) addition on the martensite-austenite phase transformation and exchange bias of Ni–Mn–Sb films have been investigated. Ni–Mn–Sb–Al films with different Al concentration (∼0–5.6%) were deposited by co-sputtering of Ni–Mn–Sb and Al targets. Experimental results revealed the decrease in martensitic transformation temperature with increasing Al content upto a certain extent (3.3%) beyond which martensitic transformation was suppressed. Paramagnetic to ferromagnetic transition temperature (T_C) also decreased with increasing Al concentration. Ni₅₀Mn_36.3Sb_10.4Al_3.3 thin film showed significant improvement in exchange bias field as compared to pure Ni_50.3Mn_36.9Sb_12.8 thin film. This enhancement in the exchange bias field H_EB = 611 Oe at 10 K is attributed to the increase of AFM-FM interactions that result from the decrease of Mn–Mn distance due to the incorporation of Al atoms. This behaviour is an additional property of the FSMA thin films apart from various other multifunctional properties and therefore, is of technological importance for their applications in magnetic storage devices.     

Characterization of SnO2 obtained from the thermal oxidation of vacuum evaporated Sn thin films

Tin oxide has been prepared by thermal oxidation of evaporated tin thin films onto pyrex glass substrates. Films oxidation was achieved in air at a temperature of 600 °C with varied duration from 20min to 3 h. Structural, optical and electrical properties of the films were characterized by means of X-ray diffraction, UV–vis spectroscopy and electrical resistivity measurements respectively. The X-ray analysis revealed the transformation of Sn into SnO₂ with preferential orientation along (101) plans. No intermediate phases such as SnO and Sn₃O₄ were evidenced. It was also found that the SnO₂ crystallites orientation changed with the annealing time due to the strain energy effect. Both band gap energy and electrical resistivity decrease with annealing time due to the crystalline quality improvement and films densification. We have noticed that oxidation at 600 °C for 3 h leads to transparent and conductive films with suitable properties for photovoltaic applications.     

Magnetic properties of Cr substituted Li–Sb ferrites

The magnetic properties, such as initial permeability and hysteresis loop properties of the chromium substituted Li–Sb ferrite system have been investigated. The SEM micrographs reveal the microstructure of the samples. The initial permeability is observed to decrease with the increase of chromium concentration. Frequency variation of permeability indicates that for all samples the resonance peak due to domain wall oscillations is at a frequency above 15 MHz. The hysteresis loop parameters have been calculated from the hysteresis loop studies. The magnetic parameters are observed to decrease with higher level of substitution.     

Room-temperature deposition of transparent conducting Al-doped ZnO films by RF magnetron sputtering method

Transparent conductive Al-doped zinc oxide (AZO) films with highly (0 0 2)-preferred orientation were deposited on quartz substrates at room temperature by RF magnetron sputtering. Optimization of deposition parameters was based on RF power, Ar pressure in the vacuum chamber, and distance between the target and substrate. The structural, electrical, and optical properties of the AZO thin films were investigated by X-ray diffraction, Hall measurement, and optical transmission spectroscopy. The 250 nm thickness AZO films with an electrical resistivity as low as 4.62 × 10⁻⁴ Ω cm and an average optical transmission of 93.7% in the visible range were obtained at RF power of 300 W, Ar flow rate of 30 sccm, and target distance of 7 cm. The optical bandgap depends on the deposition condition, and was in the range of 3.75-3.86 eV. These results make the possibility for light emitting diodes (LEDs) and solar cells with AZO films as transparent electrodes, especially using lift-off process to achieve the transparent electrode pattern transfer.     

High-performance zig-zag and meander inductors embedded in ferrite material

This paper describes the design, modeling, simulation and fabrication of zig-zag and meander inductors embedded in low- or high-permeability soft ferrite material. These microinductors have been developed with ceramic coprocessing technology. We compare the electrical properties of zig-zag and meander inductors structures installed as surface-mount devices. The equivalent model of the new structures is presented, suitable for design, circuit simulations and for prediction of the performance of proposed inductors. The relatively high impedance values allow these microinductors to be used in high-frequency suppressors. The components were tested in the frequency range of 1 MHz–3 GHz using an Agilent 4287A RF LCR meter. The measurements confirm the validity of the analytical model.     

High-frequency properties of thin amorphous ribbons

Magnetic energy losses have been investigated in Co-based near-zero-magnetostriction amorphous ribbons from DC to 10 MHz. Attention has been devoted to the properties of field-annealed ribbons thinned down to 5.8 μm and their behavior at high frequencies. A rationale is provided for the frequency dependence of the magnetic losses over the investigated many-decade range through analysis of the loss components. Ribbons annealed under transverse field benefit by limited irreversible domain wall activity and correspondingly reduced hysteresis and excess losses. Based on the near-linear response of the material and the permeability–energy loss relationship, the separate contributions of domain wall displacements and rotations to the magnetization process and the related dissipation effects are singled out at all frequencies. Very thin amorphous ribbons are shown to display lower loss and higher permeability (i.e. higher Snoek's product) than Mn–Zn ferrites at all frequencies.