Nanoindentation measurements on modified diamond-like carbon thin films

In the present study, we explored the effect of metallic interlayers (Cu and Ti) and indentation loads (5-20 mN) on the mechanical properties of plasma produced diamond-like carbon (DLC) thin films. Also a comparison has been made for mechanical properties of these films with pure DLC and nitrogen incorporated DLC films. Introduction of N in DLC led to a drastic decrease in residual stress (S) from 1.8 to 0.7 GPa, but with expenses of hardness (H) and other mechanical properties. In contrast, addition of Cu and Ti interlayers between substrate Si and DLC, results in significant decrease in S with little enhancement of hardness and other mechanical properties. Among various DLC films, maximum hardness 30.8 GPa is observed in Ti-DLC film. Besides hardness and elastic modulus, various other mechanical parameters have also been estimated using load versus displacement curves.     

Preparation and structural properties of MgO films grown on GaAs substrate

Epitaxial MgO thin films have been grown on semiinsulating GaAs (0 0 1) substrates using electron beam (e-beam) evaporation. X-ray diffraction indicates c-axis oriented MgO with (0 0 2) reflection only and rocking curve widths ∼2.2-3°. Transmission electron microscopy (TEM) analyses confirm an epitaxial growth of the MgO films. We study the microstructure and the defects at the interface between the MgO film and the GaAs substrate. Auger electron Spectroscopy (AES) concentration depth profiles reveal no contamination of the MgO films by As and Ga at different temperatures of the deposition process.     

Correlation between local hysteresis and crystallite orientation in PZT thin films deposited on Si and MgO substrates

(0 0 1)-Oriented tetragonal ferroelectric PbZr_0.53Ti_0.47O₃ (PZT) thin films (90 nm of thickness) have been grown on TiO_x/Pt/TiO₂/SiO₂/Si and TiO_x/Pt/MgO substrates. The existence of (1 0 0)-oriented crystallites in the c-axis matrix of the (0 0 1)-oriented films has been evidenced by using four circles X-ray diffraction. Depending on the substrate, the ratio of the lattice parameters c/a was found to be 1.02 (Si) and 1.07 (MgO) and this was correlated with the coercive field values. Local piezoelectric hysteresis loops produced by atomic force microscopy have been taken with profit to characterize the switching properties of the ferroelectric domains at the scale of individual crystallites. In each case, (1 0 0)-oriented crystallites require much higher voltage than (0 0 1)-oriented crystallites for switching. These results are explained by taking into account the strain imposed by the substrate in the film. We conclude that piezoelectric hysteresis loops produced by atomic force microscopy provide very rich information for addressing the local switching property of individual crystallites in PZT thin films.     

Growth of superconducting FeSe0.5Te0.5 thin films by pulsed-laser deposition

FeSe_0.5Te_0.5 thin films with PbO-type structure are successfully grown on MgO(1 0 0) and LaSrAlO₄(0 0 1) substrates from FeSe_0.5Te_0.5 or FeSe_0.5Te_0.75 polycrystalline targets by pulsed-laser deposition. The film deposited on the MgO substrate (film thickness ∼ 55 nm) shows superconductivity at 10.6 K (onset) and 9.2 K (zero resistivity). On the other hand, the film deposited on the LaSrAlO₄ substrate (film thickness ∼ 250 nm) exhibits superconductivity at 5.4 K (onset) and 2.7 K (zero resistivity). This suggests the strong influence of substrate materials and/or the c-axis length to superconducting properties of FeSe_0.5Te_0.5 thin films.     

Photosensitivity of nanocrystalline ZnO films grown by PLD

We have studied the properties of ZnO thin films grown by laser ablation of ZnO targets on (0 0 0 1) sapphire (Al₂O₃), under substrate temperatures around 400 °C. The films were characterized by different methods including X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and atomic force microscopy (AFM). XPS analysis revealed that the films are oxygen deficient, and XRD analysis with θ-2θ scans and rocking curves indicate that the ZnO thin films are highly c-axis oriented. All the films are ultraviolet (UV) sensitive. Sensitivity is maximum for the films deposited at lower temperature. The films deposited at higher temperatures show crystallite sizes of typically 500 nm, a high dark current and minimum photoresponse. In all films we observe persistent photoconductivity decay. More densely packed crystallites and a faster decay in photocurrent is observed for films deposited at lower temperature.     

Surface characteristics and nanoindentation study of Ni-Mn-Ga ferromagnetic shape memory sputtered thin films

In present paper, the off-stoichiometric Ni-Mn-Ga ferromagnetic shape memory alloy thin films are fabricated using radio frequency magnetron sputtering method. The compositions, microstructures and mechanical properties of the thin films are characterized by energy dispersive X-ray spectrum (EDAX), X-ray photoelectron spectroscopy (XPS), scanning electronic microscope (SEM), atomic force microscope (AFM) and nanoindentation test, respectively. The results show that there is a thinner layer of oxides consisting of NiO, Ga₂O₃ and an unspecified manganese oxidation (Mn_xO_y) at the surface, whereas a small amount of MnO precipitates exist in internal layers of post-annealed Ni-Mn-Ga thin films. The hardness and elastic modulus decrease with increasing film thickness. Nanoindentation tests reveal that the hardness and elastic modulus of the films can be up to 5.5 and 155 GPa, respectively. The Ni-Mn-Ga thin films have remarkably improved the ductility of Ni-Mn-Ga ferromagnetic shape memory alloys bulk materials.     

Specific features of the determination of the mechanical characteristics of thin films by the nanoindentation technique

The hardness and the elastic modulus of Cu thin films on Si, Ti, Cu, and Al substrates are investigated. It is demonstrated that the use of the Oliver-Pharr method in combination with the technique for evaluating the true hardness makes it possible to determine uniquely the hardness of Cu thin films at different ratios between the hardnesses of the film and the substrate. The elastic modulus of thin films can be correctly measured by the Oliver-Pharr method only in the case where the film and the substrate exhibit identical elastic properties. In order to determine the elastic moduli of films with the use of the parameter P/S ², the film and the substrate should have close values of both the hardness and the elastic modulus.     

A study on electrical and mechanical properties of hybrid-polymer thin films by a controlled TEOS bubbling ratio

Organic-inorganic hybrid-polymer thin films were deposited on silicon(1 0 0) substrates at room temperature by PECVD (plasma enhanced chemical vapor deposition). Ethylcyclohexane and TEOS (tetraethoxysilane) were utilized as organic and inorganic precursors with hydrogen gas for the ethylcyclohexane bubbler and argon gas for both the TEOS bubbler and as a carrier gas. To compare the electrical and the mechanical properties of the plasma polymerized thin films, we grew the hybrid-polymer thin films under conditions of various TEOS bubbling ratios. MTS nano-indenter was used to measure the hardness and Young's modulus and showed that these values increased as the TEOS bubbling ratio increased, with the highest hardness at 0.8 GPa in this experiment. An impedance analyzer was utilized for the measurements of I-V curves and capacitance, showing the lowest dielectric constant at approximately 1.83, with a leakage current density of 10⁻⁸ A/cm² at 1 MV/cm, respectively.     

Preparation and structural properties of YBCO films grown on GaN/c-sapphire hexagonal substrate

Epitaxial YBCO thin films have been grown on hexagonal GaN/c-sapphire substrates using DC magnetron sputtering and pulsed laser deposition. An MgO buffer layer has been inserted between the substrate and the YBCO film as a diffusion barrier. X-ray diffraction analysis indicates a c-axis oriented growth of the YBCO films. Φ-scan shows surprisingly twelve maxima. Transmission electron microscopy analyses confirm an epitaxial growth of the YBCO blocks with a superposition of three a-b YBCO planes rotated by 120° to each other. Auger electron spectroscopy and X-ray photoelectron spectroscopy reveal no surface contamination with Ga even if a maximum substrate temperature of 700 °C is applied.     

Optimal growth conditions for GdBa2Cu3O7 thin-film coated conductors characterized by polarized Raman scattering spectroscopy

High temperature superconducting GdBa₂Cu₃O₇ (GdBCO) thin films were grown by pulsed laser ablation. Textured MgO on metal substrates was used as a template for second generation wire applications. Growth conditions of GdBCO thin films were investigated for substrate temperature (T_s) and oxygen partial pressure (PO₂) during deposition. Superconducting critical currents of the films were obtained in the films grown at 790–810 °C of T_s and at 100–700 mTorr of PO₂. Scanning electron micrographs of the films revealed uniform and well-connected grains with some outgrown structures. X-ray θ–2θ scans of the films grown at 810 °C and 300–500 mTorr exhibited c-axis oriented texture. In-plane alignment and c-axis mosaic spread of the films were determined from X-ray Φ scans and rocking curves, respectively. Polarized Raman scattering spectroscopy was used to characterize optical phonon modes, oxygen content, cation disorder, and some possible second phases of the films. The Raman spectra of the films with large critical current density showed modes at 326–329 cm⁻¹, 444–447 cm⁻¹, 500–503 cm⁻¹ related to vibration of oxygen atoms. Origin of small peaks near 600 cm⁻¹ will be discussed as well. The information obtained from Raman scattering measurements will be useful for quality control of the conductors as well as optimization of the process conditions.     

Structural, electrical and mechanical properties of NiO thin films grown by pulsed laser deposition

Nickel oxide (NiO) thin films were prepared by reactive pulsed laser deposition on thermally oxidized Si substrates in 10 Pa oxygen pressure. The substrate temperature during deposition was varied and its influence on the structural, electrical and nanomechanical properties was studied. It was proved that the structural properties were affected by the increase of substrate temperature improving the crystalline structure. Furthermore, a higher substrate temperature resulted in a thicker NiO film, which was attributed to an increased grain size. This effect influenced the electrical properties, too. Resistivity measurements showed that it increased with the increase of substrate temperature. For the first time, the nanomechanical properties of NiO films were studied. The formation and improvement of crystalline structure affected the nanomechanical properties. Nanoindentation testing of NiO thin films revealed an increase of hardness (H) and elastic modulus (E) and a decrease of surface roughness when increasing the substrate temperature.     

Influence of target substrate distance on the properties of transparent conductive Si doped ZnO thin films

Si doped zinc oxide (SZO, Si3%) thin films are grown at room temperature on glass substrates under argon atmosphere, using direct current magnetron sputtering. The influence of the target substrate distances on structure, morphology, optical and electrical properties of SZO thin films is investigated. Experimental results show that the target substrate distances have a significance impact on the growth rate, crystal quality and electrical properties of the films, and have little impact on the optical properties of the films. SZO thin film samples grown on glasses are polycrystalline with a hexagonal wurtzite structure and have a preferred orientation along the c-axis perpendicular to the substrate. When the target substrate distance decreases from 76 to 60 mm, the degree of crystallization of the films increased, the grain size increases, and the resistivity of films decreases. However, when the distance continuously decreases from 60 to 44 mm, the degree of crystallization of the films decreased, the grain size decreases, and the resistivity of the films increases. SZO(3%) thin films deposited at a target substrate distance of 60 mm show the lowest resistivity of 5.53 × 10⁻⁴ Ω cm, a high average transmission of 94.47% in the visible range, and maximum band gap of 3.45 eV under 5 Pa of argon at sputtering power of 75 W for sputtering time of 20 min.     

Effect of oxygen pressure on microstructure and magnetic properties of strontium hexaferrite (SrFe12O19) film prepared by pulsed laser deposition

The effects of oxygen pressure during deposition on microstructure and magnetic properties of strontium hexaferrite (SrFe₁₂O₁₉) films grown on Si (100) substrate with Pt (111) underlayer by pulsed laser deposition have been investigated. X-ray diffraction pattern confirms that the films have c-axis perpendicular orientation. The c-axis dispersion (Δθ₅₀) increases and c-axis lattice parameter decreases with increasing oxygen pressure. The films have hexagonal shape grains with diameter of 150-250 nm as determined by atomic force microscopy. The coercivities in perpendicular direction are higher than those in in-plane direction, which shows the films have perpendicular magnetic anisotropy. The saturation magnetization and anisotropy field for the film deposited in oxygen pressure of 0.13 mbar are comparable to those of the bulk strontium hexaferrite. Higher oxygen pressure leads to the films having higher coercivity and squareness. The coercivity in perpendicular and in-plane directions of the film deposited in oxygen pressure of 0.13 mbar are 2520 Oe and 870 Oe, respectively.     

Preparation and characterization of Mg-doped ZnO thin films by sol-gel method

Undoped and Mg-doped ZnO thin films were deposited on Si(1 0 0) and quartz substrates by the sol-gel method. The thin films were annealed at 873 K for 60 min. Microstructure, surface topography and optical properties of the thin films have been measured by X-ray diffraction (XRD), atomic force microscope (AFM), UV-vis spectrophotometer, and fluorophotometer (FL), respectively. The XRD results show that the polycrystalline with hexagonal wurtzite structure are observed for the ZnO thin film with Mg:Zn = 0.0, 0.02, and 0.04, while a secondary phase of MgO is evolved for the thin film with Mg:Zn = 0.08. The ZnO:Mg-2% thin film exhibits high c-axis preferred orientation. AFM studies reveal that rms roughness of the thin films changes from 7.89 nm to 16.9 nm with increasing Mg concentrations. PL spectra show that the UV-violet emission band around 386-402 nm and the blue emission peak about 460 nm are observed. The optical band gap calculated from absorption spectra and the resistivity of the ZnO thin films increase with increasing Mg concentration. In addition, the effects of Mg concentrations on microstructure, surface topography, PL spectra and electrical properties are discussed.     

Influence of the crystal orientation on the electrical properties of AlN thin films on LTCC substrates

In this study, the influence of the crystal orientation on the electrical properties of sputter deposited aluminium nitride (AlN) thin films on low temperature co-fired ceramics (LTCC) substrates is investigated. The degree of c-axis orientation can be tailored by the deposition conditions such as plasma power, gas pressure and gas composition in the deposition chamber. Due to the large surface roughness of LTCC substrates (R_a = ∼0.4 μm) the quality of thin films is lower compared to silicon. Between areas of columnar grains arranged perpendicular to the LTCC surface, defects like voids are generated due to the wavy surface characteristics. The impact of crystal orientation and temperature up to 400 °C on the electrical performance is evaluated, as these layers are targeted as potential candidates for dielectric heat spreaders on multilayered ceramic substrates for high frequency applications. These AlN thin films having a good c-axis orientation exhibit lower leakage current levels over the complete temperature range compared to those with a poor alignment with respect to this crystallographic plane. The leakage current behaviour, however, is dominated according to the Pool-Frenkel electron emission independent of the degree of c-axis orientation.     

Enhanced ferroelectric properties of (Pb0.90La0.10)Ti0.975O3 multilayered thin films prepared by RF magnetron sputtering

The (Pb_0.90La_0.10)Ti_0.975O₃/PbTiO₃ (PLT/PT), PbTiO₃/(Pb_0.90La_0.10)Ti_0.975O₃/PbTiO₃ (PT/PLT/PT) multilayered thin films with a PbO_x buffer layer were in situ deposited by RF magnetron sputtering at the substrate temperature of 600 °C. With this method, highly (1 0 0)-oriented PLT/PT and PT/PLT/PT multilayered thin films were obtained. The PbO_x buffer layer leads to the (1 0 0) orientation of the films. The dielectric, ferroelectric and pyroelectric properties of the PLT multilayered thin films were investigated. It is found that highly (1 0 0)-oriented PT/PLT/PT multilayered thin films possess higher remnant polarization 2P_r (44.1 μC/cm²) and better pyroelectric coefficient at room temperature p (p = 2.425 × 10⁻⁸ C/cm² K) than these of PLT and PLT/PT thin films. These results indicate that the design of the PT/PLT/PT multilayered thin films with a PbO_x buffer layer should be an effective way to enhance the dielectric, ferroelectric and pyroelectric properties. The mechanism of the enhanced ferroelectric properties was also discussed.     

Properties of barium hexa-ferrite thin films dependent on sputtering pressure

M-type barium ferrite thin films were deposited onto sapphire (0 0 l) substrates by radio frequency magnetron sputtering. An ultra-thin layer about 20 nm was deposited and annealed before continuous deposition of the films up to 500 nm under different sputtering pressures: 0.2, 0.5, 0.8 and 1.0 Pa, respectively. It was found that the atomic ratios of Fe to Ba increased from 9.3 to 15.0 with the increase of the pressure. The films sputtered at all pressures have c-axis normal to the film plane by a four circle X-ray diffractometer, which is an improvement of the films directly sputtered on the substrate. Needle-like grains were formed on the surface of the films under higher sputter pressure with bubble domains, which is originated from high magnetocrystalline anisotropy of the film. Magnetic hysteresis loops recorded by vibrating sample magnetometer agree with them, where in-plane and out-of-plane loops of the samples prepared under high sputtering pressures are quite different, while they are almost identical of the samples under low pressures. The influence of the sputtering pressure was understood by that with the increase of the pressure, resputtering of the films was increased. Nucleation with c-axis normal to the film plane was deteriorated. Thus samples prepared under high pressure have more needle-like crystallites which have c-axis parallel to the film plane.     

TiCN/TiNbCN multilayer coatings with enhanced mechanical properties

Enhancement of mechanical properties by using a TiCN/TiNbCN multilayered system with different bilayer periods (Λ) and bilayer numbers (n) via magnetron sputtering technique was studied in this work. The coatings were characterized in terms of structural, chemical, morphological and mechanical properties by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nanoindentation. Results of the X-ray analysis showed reflections associated to FCC (1 1 1) crystal structure for TiCN/TiNbCN films. AFM analysis revealed a reduction of grain size and roughness when the bilayer number is increased and the bilayer period is decreased. Finally, enhancement of mechanical properties was determined via nanoindentation measurements. The best behavior was obtained when the bilayer period (Λ) was 15 nm (n = 200), yielding the highest hardness (42 GPa) and elastic modulus (408 GPa). The values for the hardness and elastic modulus are 1.6 and 1.3 times greater than the coating with n = 1, respectively. The enhancement effects in multilayer coatings could be attributed to different mechanisms for layer formation with nanometric thickness due to the Hall-Petch effect; because this effect, originally used to explain the increase in hardness with decreasing grain size in bulk polycrystalline metals, has also been used to explain hardness enhancements in multilayers taking into account the thickness reduction at individual single layers that make the multilayered system. The Hall-Petch model based on dislocation motion within layers and across layer interfaces, has been successfully applied to multilayers to explain this hardness enhancement.     

Effect of substrate and annealing on the structural and optical properties of ZnO:Al films

ZnO:Al thin films with c-axis preferred orientation were deposited on glass and Si substrates using RF magnetron sputtering technique. The effect of substrate on the structural and optical properties of ZnO:Al films were investigated. The results showed a strong blue peak from glass-substrate ZnO:Al film whose intensity became weak when deposited on Si substrate. However, the full width at half maxima (FWHM) of the Si-substrate ZnO:Al (0 0 2) peaks decreased evidently and the grain size increased. Finally, we discussed the influence of annealing temperature on the structural and optical properties of Si-substrate ZnO:Al films. After annealing, the crystal quality of Si-substrate ZnO:Al thin films was markedly improved and the intensity of blue peak (∼445 nm) increased noticeably. This observation may indicate that the visible emission properties of the ZnO:Al films are dependent more on the film crystallinity than on the film stoichiometry.     

Deposition of quasi-crystal Al-doped ZnO thin films for photovoltaic device applications

Quasi-crystal aluminum-doped zinc oxide (AZO) films were prepared by in situ radio frequency (RF) magnetron sputtering (sputtering without annealing) on glass substrates. The influence of deposition parameters on the optoelectronic and structural properties of the in situ deposited quasi-crystal AZO films was investigated in order to compare resulting samples. X-ray diffraction (XRD) patterns show that the quasi-crystal AZO thin films have excellent crystallization improved with increase of the RF power and substrate temperature, with an extremely preferential c-axis orientation exhibit sharp and narrow XRD pattern similar to that of single-crystal. Field emission scanning electron microscopy (FESEM) images show that quasi-crystal AZO thin films have uniform grains and the grain size increase with the increase of RF power and substrate temperature. Craters of irregular size with the columnar structure are observed in the quasi-crystal AZO thin films at a lower substrate temperature while many spherical shaped grains appeared at a higher substrate temperature. The average optical transmittance of all the quasi-crystal AZO films was over 85% in the 400-800 nm wavelength range. The resistivity of 4.176 × 10⁻⁴ Ω cm with the grain size of 76.4891 nm was obtained in the quasi-crystal AZO thin film deposited at 300 °C, under sputtering power of 140 W.