Structural, optical and electrical properties of CuIn5S8 thin films grown by thermal evaporation method

Stoichiometric compound of copper indium sulfur (CuIn₅S₈) was synthesized by direct reaction of high purity elemental copper, indium and sulfur in an evacuated quartz tube. The phase structure of the synthesized material revealed the cubic spinel structure. The lattice parameter (a) of single crystals was calculated to be 10.667 Å. Thin films of CuIn₅S₈ were deposited onto glass substrates under the pressure of 10⁻⁶ Torr using thermal evaporation technique. CuIn₅S₈ thin films were then thermally annealed in air from 100 to 300 °C for 2 h. The effects of thermal annealing on their physico-chemical properties were investigated using X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDX), scanning electron microscope (SEM), optical transmission and hot probe method. XRD studies of CuIn₅S₈ thin films showed that as-deposited films were amorphous in nature and transformed into polycrystalline spinel structure with strong preferred orientation along the (3 1 1) plane after the annealing at 200 °C. The composition is greatly affected by thermal treatment. From the optical transmission and reflection, an important absorption coefficient exceeds 10⁴ cm⁻¹ was found. As increasing the annealing temperature, the optical energy band gap decreases from 1.83 eV for the as-deposited films to 1.43 eV for the annealed films at 300 °C. It was found that CuIn₅S₈ thin film is an n-type semiconductor at 300 °C.     

A comparison of the oxidation behavior of CrN films deposited using continuous dc,pulsed dc and modulated pulsed power magnetron sputtering

The study is aimed at comparing the oxidation behavior of the stoichiometric CrN films deposited by continuous dc magnetron sputtering (dcMS), mid-frequency pulsed dc magnetron sputtering (PMS), and modulated pulsed power (MPP) magnetron sputtering techniques in a closed field unbalanced magnetron sputtering system. These as-deposited CrN films exhibited a cubic structure and similar stoichiometric compositions, but with different microstructures and residual stresses. After annealing in the ambient air from 600 to 1000 °C, the changes in the crystal phase, microstructure, and hardness of the films were characterized using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy line scan, and nanoindentation. The oxidation activation energies of the films were calculated using Arrhenius equation. It was found that the MPP CrN film exhibited superior oxidation resistance than dcMS and PMS CrN films. After annealing at 900 °C, the MPP CrN film exhibited an extremely dense structure and the cubic phase was well maintained. On the other hand, the dcMS and PMS CrN films were severely oxidized into a porous structure with the development of β-Cr₂N and Cr₂O₃ phases and a rapid degradation of the cubic phase after 700 and 800 °C, respectively. The results indicate that all films showed a parabolic oxidation rate below 900 °C. The oxidation activation energies for the dcMS, PMS and MPP CrN films are 116 kJ/mol, 141 kJ/mol, and 195 kJ/mol, respectively. The better oxidation resistance of the MPP CrN film is attributed to its dense microstructure and low residual stress.     

Perpendicular magnetic anisotropy in 70 nm CoFe2O4 thin films fabricated on SiO2/Si(1 0 0) by the sol-gel method

Cobalt ferrite CoFe₂O₄ films were fabricated on SiO₂/Si(1 0 0) by the sol-gel method. Films crystallized at/above 600 °C are stoichiometric as expected. With increase of the annealing temperature from 600 °C to 750 °C, the columnar grain size of CoFe₂O₄ film increases from 13 nm to 50 nm, resulting in surface roughness increasing from 0.46 nm to 2.55 nm. Magnetic hysteresis loops in both in-plane and out-of-plane directions, at different annealing temperatures, indicate that the films annealed at 750 °C exhibit obvious perpendicular magnetic anisotropy. Simultaneously, with the annealing temperature increasing from 600 °C to 750 °C, the out of plane coercivity increases from 1 kOe to 2.4 kOe and the corresponding saturation magnetization increases from 200 emu/cm³ to 283 emu/cm³. In addition, all crystallized films exhibit cluster-like structured magnetic domains.     

Oxidation resistance and mechanical property of cosputtered quasi-amorphous Ta-Si-N films under vacuum rapid thermal annealing

The oxidation resistance and mechanical properties of Ta-Si-N films at high temperature are important issues for application. In this paper, quasi-amorphous Ta-Si-N thin films were fabricated by using reactive magnetron co-sputtering at different Si/Ta power ratios and nitrogen flow ratios (FN₂% = FN₂/(FAr + FN₂) × 100%). Vacuum rapid thermal annealing at 600-900 °C at 2.6 Pa was performed to investigate the oxidation resistance of films. At the higher Si/Ta power ratio and increased FN₂%, there is low oxygen fraction (O/(O + N) ≤ 0.2) of films at high annealing temperature which corresponds to benefit oxidation resistance. The crystalline δ-Ta₂O₅ phase was formed at 900 °C for all films. The islands of oxide were formed on the surface of films at low-Si-content (≤ 20 at.%) after 900 °C annealing. The hardness of all as-deposited Ta-Si-N films was between 16 and 24 GPa. The low-Si-content Ta-Si-N films has higher hardness than high-Si-content (≥ 20 at.%) ones due to lower fraction of soft amorphous SiN_x. The effect of annealing temperature on the correlation among process parameters, microstructure, phase transformation and hardness is discussed. The Ta-Si-N formed at 6 FN₂% and Si/Ta power ratio of 2/1 can be the best candidate for good oxidation resistance with appropriate mechanical property.     

Synthesis and characterization of (0001)-textured wurtzite Al1-xBxN thin films

Al_1-xB_xN films of the wurtzite structure and a strong c-axis texture have been grown at room temperature by reactive sputter deposition with B concentrations of up to 10 at.%. The crystallographic structure of the films has been studied with XRD and HRTEM/SAED with stoichiometry and chemical bonding determined by XPS. Nanoindentation experiments show that the films have a hardness in excess of 30 GPa, which is retained after annealing for 1 h at 1000 °C. An amorphous phase is observed at the interface, the thickness of which increases with the B concentration in the film, while the film crystallinity is seen to improve with film thickness.     

N-doped Sb2Te phase change materials for higher data retention

Crystallization temperatures of the Sb₂Te films increase remarkably from 139.4 °C to 223.0 °C as the N₂ flow rates increasing from 0 sccm to 1.5 sccm. Electrical conduction activation energies for amorphous and crystalline states increase by doping nitrogen. A small amount of nitrogen atoms can locate at interstitial sites in the hexagonal structure, generating a strain field, and improving the thermal stability of amorphous state. The best 10-years lifetime at temperature up to 141 °C is found in Sb₂TeN₁ films. Doping excessively high nitrogen in Sb₂Te film will form nitride and make Te separate out. As a result, the activation energy for crystallization decreases instead, accompanying with the deterioration of thermal stability. The power consumption of PCRAM test cell based on Sb₂TeN₁ film is ten times lower than that of PCRAM device using Ge₂Sb₂Te₅ films.     

A study of the oxidation behavior of CrN and CrAlN thin films in air using DSC and TGA analyses

Freestanding CrN_x and Cr_1 − xAl_xN films with two different Al atomic percentages with respect to the metal sublattice (x = 0.23 and x = 0.60) were produced by pulsed closed field unbalanced magnetron sputtering (P-CFUBMS). The dynamic oxidation behavior of the films has been characterized by thermal analysis using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The structure of the films at different thermal-annealing temperatures were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) in an effort to understand different phase transitions and oxidation reactions observed on the DSC curves. The peak temperatures of the main exothermic/endothermic oxidation reactions in the DSC signals at different heating rates were applied to the Kissinger model for determination of activation energies. The mechanical properties of the films at different heat-annealing states were measured by nano-indentation.It was found that the CrN_x films oxidized in air after 600 °C by the dissociation of fcc (face center cubic)-CrN to h(hexagonal)-Cr₂N and nitrogen and, after 900 °C by the dissociation of h-Cr₂N to Cr and nitrogen in the film. The addition of Al to CrN film can further improve the oxidation resistance, especially for the high temperature above 800 °C. The oxidation degradation in two Cr-Al-N films started with dissociation of fcc-CrAlN to h-Cr₂N and nitrogen in the film. The presence of thermally stable Al-N bonding in the fcc-CrAlN structure can suppress the reduction of nitrogen in the film. A dense (Cr,Al)₂O₃ layer (either amorphous or crystalline) formed at early oxidation stage (< 700 °C) can act as an effective diffusion barrier slowing down the inward diffusion of the oxygen at high temperatures. Precipitation of h-AlN phase in Cr_0.77Al_0.23N and Cr_0.40Al_0.60N films were found at 900 and 1000 °C respectively, accompanied with crystalline Al₂O₃ formation. After that, both Cr-Al-N films oxidized rapidly after the dissociation of h-Cr₂N to Cr and nitrogen. In addition, Cr_0.40Al_0.60N films exhibit higher oxidation resistance than Cr_0.77Al_0.23N films. The fcc-CrAlN was retained up to 900 °C and the precipitation of h-AlN phase took place after 1000 °C in Cr_0.40Al_0.60N films. Cr_0.40Al_0.60N films also retained a hardness of 25 GPa after annealing at 800 °C in ambient air for 1 h. The activation energies of the final oxidation exothermic peaks in CrN_x, Cr_0.77Al_0.23N and Cr_0.40Al_0.60N films in the current study were found to be 2.2, 3.2 and 3.9 eV atom^− 1 respectively.     

Properties of magnetron sputtered Al-Si-N thin films with a low and high Si content

The article reports on properties of Al-Si-N films with a low (≤ 10 at.%) and high (≥ 25 at.%) Si content reactively sputtered using a closed magnetic field dual magnetron system operated in ac pulse mode. The films were sputtered from a composed target (a Si plate fixed by an Al ring with inner diameter Ø_i = 15 or 26 mm). Main attention was devoted to the investigation of a relationship between the structure of the films and their mechanical properties, thermal stability of hardness, and oxidation resistance. It was found that (1) while the films with a low (≤ 10 at.%) Si content are crystalline (c-(Al-Si-N)), those with a high (≥ 25 at.%) Si content are amorphous (a-(Al-Si-N)) when sputtered at the substrate temperature T_s = 500 °C, (2) both groups of the films exhibit (i) a high hardness H = 21 and 25 GPa, respectively, and high values of the oxidation resistance exceeding 1000 °C; 1100 °C (Δm = 0 mg/cm²) and 1300 °C (Δm ≈ 0.003 mg/cm²), respectively, (3) the hardness of a-(Al-Si-N) does not vary with increasing annealing temperature T_a up to 1100 °C even after 4 h, and (4) a high oxidation resistance of c-(Al-Si-N) film with a low (< 10 at.%) Si content is due to the formation of a dense, nearly amorphous Al₂O₃ surface layer which is formed in reaction of free Al atoms with ambient oxygen and prevents the fast penetration of oxygen into bulk of the film. Obtained results contribute to understand the effect of Al and Si in the Al-Si-N thin film on its mechanical properties, thermal stability and oxidation resistance.     

Electric and dielectric behavior of CaCu3Ti4O12-based thin films obtained by soft chemical method

CaCu₃Ti₄O₁₂ (stoichiometric) and Ca_1.1Cu_2.9Ti₄O₁₂ (non-stoichiometric) thin films have been prepared by the soft chemical method on Pt/Ti/SiO₂/Si substrates, and their electrical and dielectric properties have been compared as a function of the annealing temperature. The crystalline structure and the surface morphology of the films were markedly affected by the annealing temperature and excess calcium. The films show frequency-independent dielectric properties at room temperature which is similar to those properties obtained in single-crystal or epitaxial thin films. The room temperature dielectric constant of the 570-nm-thick CCTO thin films annealed at 600 °C at 10 kHz was found to be 124. The best non-ohmic behavior (α = 12.6) presented by the film with excess calcium annealed at 500 °C. Resistive hysteresis on the I-V curves was observed which indicates these films can be used in resistance random access memory (ReRAM).     

Low temperature growth of nanocrystalline TiO2 films with Ar/O2 low-field helicon plasma

TiO₂ thin films were deposited on silicon wafer substrates by low-field (1 < B < 5 mT) helicon plasma assisted reactive sputtering in a mixture of pure argon and oxygen. The influence of the positive ion density on the substrate and the post-annealing treatment on the films density, refractive index, chemical composition and crystalline structure was analysed by reflectometry, Rutherford backscattering spectroscopy (RBS) and X-ray diffraction (XRD). Amorphous TiO₂ was obtained for ion density on the substrate below 7 × 10¹⁶ m^− 3. Increasing the ion density over 7 × 10¹⁶ m^− 3 led to the formation of nanocrystalline (~ 15 nm) rutile phase TiO₂. The post-annealing treatment of the films in air at 300 °C induced the complete crystallisation of the amorphous films to nanocrystals of anatase (~ 40 nm) while the rutile films shows no significant change meaning that they were already fully crystallised by the plasma process. All these results show an efficient process by low-field helicon plasma sputtering process to fabricate stoichiometric TiO₂ thin films with amorphous or nanocrystalline rutile structure directly from low temperature plasma processing conditions and nanocrystalline anatase structure with a moderate annealing treatment.     

Oxidation resistance of decorative (Ti,Mg)N coatings deposited by hybrid cathodic arc evaporation-magnetron sputtering process

Titanium-magnesium nitride coatings (Ti,Mg)N were deposited on steels and silicon substrates by hybrid reactive arc evaporation-magnetron sputtering process from cathodic Ti and sputter Mg targets in an argon/nitrogen gas mixture. X-ray diffraction analyses (XRD) of as-deposited coatings with various Mg/Ti atomic ratios gave evidence of a fcc TiN-like structure strongly oriented in the [111] direction. The TiN lattice parameter increases with the addition of Mg resulting from the substitution of Ti atoms by Mg ones. Optical investigations by spectrophotometry revealed that Mg addition to TiN leads to a change in colour from golden through coppery and violet to grey. Nanoindentation measurements showed that increasing Mg content does not alter the hardness of coatings. As-deposited films were annealed in air from 450 to 750 °C with a 100 °C step. XRD and Raman analyses revealed the formation of rutile TiO₂ and MgTiO₃ phases. Secondary neutral mass spectrometry measurements were performed to study the elemental depth profiles after air annealing. A diffusion of Mg atoms towards the film surface was evidenced above 650 °C, leading to the formation of the MgTiO₃ phase. However, thermogravimetric measurements showed that this oxide phase did not protect the films against high temperature oxidation. On the contrary, below 650 °C Mg affords to TiN a beneficial protective effect, able to reduce the oxidation kinetics by half.     

Effect of annealing temperature on the structure and optical properties of sputtered TiO2 films

TiO₂ thin films were deposited by DC reactive magnetron sputtering. Some TiO₂ thin films samples were annealed for 5 min at different temperatures from 300 to 900 °C. The structure and optical properties of the films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (SEM) and ultraviolet-visible (UV-vis) spectrophotometry, respectively. The influence of the annealing temperature on the structure and optical properties of the films was investigated. The results show that the as-deposited TiO₂ thin films are mixtures of anatase and rutile phases, and possess the column-like crystallite texture. With the annealing temperature increasing, the refractive index and extinction coefficient increase. When the annealing temperature is lower than 900 °C, the anatase phase is the dominant crystalline phase; the weight fraction of the rutile phase does not increase significantly during annealing process. As the annealing temperature rises to 900 °C, the rutile phase with the large extinction coefficient becomes the dominant crystalline phase, and the columnar structure disappears. The films annealed at 300 °C have the best optical properties for the antireflection coatings, whose refractive index and extinction coefficient are 2.42 and 8 × 10⁻⁴ (at 550 nm), respectively.     

Oxidation behavior of Al4SiC4 ceramic up to 1700 °C

Isothermal oxidation behavior of Al₄SiC₄ ceramics at the temperature range from 1200 °C to 1700 °C in air for 10-20 h was investigated. The results indicated that this material had an excellent oxidation resistance from 1200 °C to 1600 °C, and the kinetics of oxidation obeyed the parabolic law with an activation energy of 220 ± 20 kJ mol⁻¹. The oxide scales consisted of an outer oxide layer with higher density, a middle oxide layer with a few of large size pores and a reaction layer which is near to the matrix with a number of small size pores over the temperature ranges. A number of pores exist in the middle oxide scale. The oxide surface and cross-sectional morphologies were observed by scanning electron microscope (SEM) technique and the formation mechanism of the oxidation layers was also analyzed.     

Influence of air oxidation on the properties of decorative NbOxNy coatings prepared by reactive gas pulsing

In this work the oxidation resistance of DC reactive sputtered niobium oxynitrides and its influence on the properties of the films are studied. The depositions have been carried out by DC magnetron sputtering with a reactive gas pulsing process. The nitrogen flow was kept constant and the oxygen flow was pulsed. Pulse durations of 10 s produced multilayer coatings with a period of λ = 10 nm. Three sets of films with increasing duty cycle (= on-time of high oxygen flow / pulse duration) have been deposited. The films were subsequently annealed in air at 400, 500 and 600 °C, respectively.X-ray diffraction measurements showed a clear and progressive change from a roughly amorphous nature of the films to a crystalline oxide-type compound for those annealed at 600 °C, which was consistent with the composition analysis. For annealing temperatures of 500 and 600 °C, the coatings presented a significant reduction in hardness, approaching the values characteristic of Nb₂O₅-type films. Moreover, the residual stress measurements performed by using the deflection method revealed low values in all the coatings nearly independent on the annealing temperature.Color variation in the CIE − L^?a^?b^? color space and the reflectance in the UV-visible spectrum range of these niobium oxynitrides were investigated and correlated to their chemical composition and structural features. For both properties, the variation tendencies are quite similar, showing the transition from a nitride-type alloy to an oxide-type one with increasing annealing temperature.     

The nanostructured phase transition and thermal stability of superhard f-TiN/h-AlSiN films

The superhard Ti–Al–Si–N films were synthesized by multi-arc ion plating technology and the influence of vacuum annealing on the structures and properties of the films was investigated. Transmission electron microscopy observation confirmed that the as-deposited Ti–Al–Si–N films were consisted of fcc-TiN/hcp-AlSiN multilayers with a period of 8 nm. The result also showed that a minute layer of cubic structure was observed in hcp-AlSiN layer at the interface between TiN layers and AlSiN layers, which resulted in an epitaxial growth between TiN layers and AlSiN layers. The annealing experiment of the Ti–Al–Si–N films was performed in vacuum furnace for 2 h at temperatures ranging from 700 to 1100 °C. With increasing annealing temperatures, no novel phases were observed indicating that the film retained the sharp interfaces. The grains of the film coarsened and showed mixed orientations at 1100 °C. The transformation of h-AlSiN into h-AlN and Al-depleted AlSiN_x and partial crystalline SiN_x was speculated during the annealing process by the XPS and DSC results. The film retained super hardness of above 47 GPa even at 1100 °C due to the formation of crystalline SiN_x and the minute c-(Al, Si)N layer between c-TiN layers and h-AlSiN layers which delayed the transformation of (Al, Si)N from cubic phase to hexagonal phase. The adhesion strength of the film was also discussed and that vacuum annealing could improve the adhesion strength.     

Transparent p-type CuxS thin films

The effect of different mild post-annealing treatments in air, at 270 °C, for 4-6 min, on the optical, electrical, structural and chemical properties of copper sulphide (Cu_xS) thin films deposited at room temperature are investigated. Cu_xS films, 70 nm thick, are deposited on glass substrates by vacuum thermal evaporation from a Cu₂S:S (50:50 wt.%) sulphur rich powder mixture. The as-deposited highly conductive crystalline CuS (covellite) films show high carrier concentration (∼10²² cm⁻³), low electrical resistivity (∼10⁻⁴ Ω cm) and inconclusive p-type conduction. After the mild post-annealing, these films display increasing values of resistivity (∼10⁻³ to ∼10⁻² Ω cm) with annealing time and exhibit conclusive p-type conduction. An increase of copper content in Cu_xS phases towards the semiconductive Cu₂S (chalcocite) compound with annealing time is reported, due to re-evaporation of sulphur from the films. However, the latter stoichiometry was not obtained, which indicates the presence of vacancies in the Cu lattice. In the most resistive films a Cu₂O phase is also observed, diminishing the amount of available copper to combine with sulphur, and therefore the highest values of optical transmittance are reached (65%). The appearance on the surface of amorphous sulphates with annealing time increase is also detected as a consequence of sulphur oxidation and replacement of sulphur with oxygen. All annealed films are copper deficient in regards to the stoichiometric Cu₂S and exhibit stable p-type conductivity.     

Lanthanum silicate thin films for SOFC electrolytes synthesized by magnetron sputtering and subsequent annealing

Thin films of La and Si with Si/(La + Si) atomic ratios ranging from 0.36 to 0.44 were produced by magnetron sputtering in pure Ar. For all compositions, the apatite-like La_9.33Si₆O₂₆ phase was formed during annealing in air at 900 °C. A preferential orientation was developed during annealing of the films with higher silicon content while formation of oxide impurities was detected for the films with less silicon. Silicon segregation to the thin film/substrate interface was observed after annealing for thin films with higher Si/(La + Si) atomic ratios. The higher ionic conductivity values were obtained with the films with lower silicon content (2.81 × 10^− 3 Scm^− 1 at 800 °C for the film with Si/(La + Si) atomic ratio of 0.36). This film presented the lower activation energy E_a (0.94 eV).     

Effect of annealing temperature on optical band-gap of amorphous indium zinc oxide film

The effect of annealing temperature on the electrical and optical properties of indium zinc oxide (IZO) (In₂O₃:ZnO = 90:10 wt.%) thin films has been investigated. The IZO thin films were deposited on glass substrates by radio frequency magnetron sputtering and then subjected to annealing in a mixed ambient of air and oxygen at 100, 200 and 300 °C. All the IZO films were found to have amorphous structure. With the increase of the annealing temperature, the carrier concentration decreased and the resistivity increased. The average transmittance of IZO thin films decreased slightly with annealing temperature. Interestingly, a systematic reduction of the optical band-gap from 3.79 eV to 3.67 eV was observed with annealing temperature. The change in optical band-gap was observed to be caused predominantly by Burstein-Moss band-gap widening effect suggesting unusual absence of band narrowing effect. The effects on optical and electrical properties of IZO films have been discussed in detail.     

Characterization of Sn and Si nanocrystals embedded in SiO2 matrix fabricated by magnetron co-sputtering

Sn and Si nanocrystals were prepared by depositing Sn-Si-rich SiO₂ films using a co-sputtering process and a subsequent annealing. The microstructure and optical properties of Sn and Si nanocrystals were characterized by scanning electron microscopy (SEM), Raman spectra, X-ray diffraction and photoluminescence spectra. The crystallization of Sn has started at the annealing temperature of 400 °C, and was accomplished at 700 °C. However, the phase of amorphous Si starts to transform into nanocrystal Si when the annealing temperature is higher than 700 °C. These results illustrate that Sn existence as an element may played an important role in lowering the crystallization temperature of Si, and the crystallization rate of Si will be enhanced when Sn atom serves as the nucleation centre. Because quantum confinement effects are expected at relatively large radius for nanocrystal Sn, the redshift of high-energy PL peak may result from quantum confinement effects of nanocrystal Sn. However, the low-energy PL peak may be attributed to defects.     

Structure and mechanical properties of TiAlSiN/Si3N4 multilayer coatings

TiAlSiN/Si₃N₄ multilayer coatings which have different separate layer thicknesses of TiAlSiN or Si₃N₄ were deposited onto glass sheets, single-crystal silicon wafers and polished WC-Co substrates by reactive magnetron co-sputtering. The morphology, crystalline structure and thickness of the as-prepared multilayer coatings were characterized by TEM, SEM, XRD and film thickness measuring instrument. The mechanical properties of the coatings were evaluated by a nanoindenter. The effects of monolayer thickness on the microstructure and properties of TiAlSiN/Si₃N₄ multilayer coatings were explored. The coatings showed the highest hardness when the thickness of Si₃N₄ and TiAlSiN monolayers was 0.33 nm and 5.8 nm, respectively. The oxidation characteristics of the coatings were studied at temperatures ranging from 700 °C to 900 °C for oxidation time up to 20 h in air. It was found that the coatings displayed good oxidation resistance.