High-repetition rate pulsed laser deposition of ZrC thin films

ZrC thin films were grown on (100) Si substrates by the pulsed laser deposition (PLD) technique using a high-repetition rate excimer laser working at 40 Hz. The substrate temperature during depositions was set at 300 °C and the cooling rate was 5 °C/min. X-ray diffraction investigations showed that the films were crystalline. Films deposited under residual vacuum or 2 × 10^− 3 Pa of CH₄ atmosphere exhibited a (200)-axis texture, while those deposited under 2 × 10^− 2 Pa of CH₄ atmosphere were found to be equiaxed. The surface elemental composition of as-deposited films, analyzed by Auger electron spectroscopy (AES), showed the usual high oxygen contamination of carbides. Once the topmost − 3-5 nm region was removed, the oxygen concentration rapidly decreased, being around 3-4% only in bulk. Scanning electron microscopy (SEM) investigations showed a smooth, featureless surface morphology, corroborating the roughness values below 1 nm (rms) obtained from simulations of the X-ray reflectivity (XRR) curves. From the same simulations we also estimated films mass density values of around 6.32-6.57 g/cm³ and thicknesses that correspond to a deposition rate of around 8.25 nm/min. Nanoindentation results showed a hardness of 27.6 GPa and a reduced modulus of 228 GPa for the best quality ZrC films deposited under an atmosphere of 2 × 10^− 3 Pa CH₄.     

Characterization of cobalt oxide thin films prepared by a facile spray pyrolysis technique using perfume atomizer

Cobalt oxide (Co₃O₄) thin films were prepared by a facile spray pyrolysis technique using perfume atomizer from aqueous solution of hydrated cobalt chloride salt (CoCl₂·6H₂O) as source of cobalt. The films were deposited onto the amorphous glass substrates kept at different temperatures (300-500 °C). The influences of molar concentration of the starting solution and substrate temperature on the structural, morphological and optical properties of (Co₃O₄) thin films were studied. It was found from X-ray diffraction (XRD) analysis that the films prepared with molar concentration greater than 0.025 M/L were polycrystalline spinel type cubic structure. The preferred orientation of the crystallites of these films changes gradually from (6 2 2) to (1 1 1) when the substrate temperature increases. By Raman spectroscopy, five Raman active modes characteristic of Co₃O₄ spinel type cubic structure were found and identified at 194, 484, 522, 620 and 691 cm⁻¹. The scanning electron microscopy (SEM) images showed micro porous structure with very fine grains less than 50 nm in diameter. These films exhibited also a transmittance value of about 70% in the visible and infra red range.     

Corrosion protection of AA2024 sealed anodic layers using the hydrophobic properties of carboxylic acids

The present study investigates the use of carboxylic acids as a post-treatment for sealed AA2024 anodised in tartaric-sulphuric acid electrolyte. Four monocarboxylic acids with different carbon chain lengths were tested ((CH₃-(CH₂)_n-COOH with n = 4, 8, 12 and 16). Hydrophobic surface properties after the post-treatment were characterized by contact angle measurements. Electrochemical impedance spectroscopy (EIS) was performed to assess the ability of the four carboxylic acids to form protective films. It was shown that stearic acid (n = 16) used in its pure molten state was the most efficient. The organic film formed very rapidly (under 5 min) and contributed to the enhancement of the protection in terms of corrosion resistance of the sealed anodic layers. EIS measurements showed the presence of the organic films on the specimen surface.     

High quality TbMnO3 films deposited on YAlO3

High quality thin films of TbMnO₃ were grown by pulsed laser deposition on orthorhombicYAlO₃ (1 0 0). The interface and surface roughness of a 55 nm thick film were probed by X-ray reflectometry and atomic force microscopy, yielding a roughness of 1 nm. X-ray diffraction revealed untwinned films and a small mosaic spread of 0.04° and 0.2° for out-of-plane and in-plane reflections, respectively. This high degree of epitaxy was also confirmed by Rutherford backscattering spectrometry. Using polarized neutron diffraction we could identify a magnetic structure with the propagation vector (0 0.27 0), identical to the bulk magnetic structure of TbMnO₃.     

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.     

Substrate temperature influence on boron carbide coatings grown by the PLD technique

Boron carbide films were synthesized by laser ablation technique, using a target of B₄C with 99.9% of purity, varying the substrate temperature between room temperature and 650 °C, in order to produce the hexagonal phase (h-BC). Films were grown on (111)-silicon wafers in an ultra high vacuum system with a base pressure in the order of 10^− 7 Pa. For the films' growth, an atmosphere of (CH₄) at a pressure of 2.5 Pa was used. During the process, the substrate temperature was varied in order to identify the influence of this parameter on the coatings' structure, composition and morphology. XRD analysis did not present peaks of BC, possibly because of the amorphous character of the film that has different phases. Films were characterized by several techniques as in situ Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and ex situ electron diffraction. Results present a concentration of 50 at.% for the sample grown to 650 °C. Electron diffraction showed an interplanar spacing (d₍₀₀₂₎ = 0.334 nm) and also other hkl reflections have been identified. Lattice parameters calculated from the interplanar spacing a = 0.585 nm and c = 1.2 nm obtained for the sample grown at 650 °C are similar to those reports for hexagonal boron carbide.     

Microstructure and tribological properties of the a-C:H films deposited by magnetron sputtering with CH4/Ar mixture

Hydrogenated amorphous carbon (a-C:H) films were deposited on steel and silicon wafers by unbalanced magnetron sputtering under different CH₄/Ar ratios. Microstructure and properties of the a-C:H films were investigated via Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, Atomic force microscopy (AFM) and substrate curvature method. The results revealed that CH₄/Ar ratio played an important role in the H content but acted a little function on the sp³/sp² ratio of the films. Also, the internal stress of those films was relatively low (< 1 GPa), and the deposition rate decreased firstly and then increased with the decrease of the CH₄ fraction. The film deposited under CH₄/Ar = 1/1 (55 sccm/55 sccm) with moderate sp³ C-H / sp³ C-C had the best tribological properties. The composition, microstructure and properties of the a-C:H films were strongly dependent on the deposition process and composition of reactant gases.     

Electrical and optical properties of tantalum oxide thin films prepared by reactive magnetron sputtering

Tantalum oxide thin films were prepared by using reactive dc magnetron sputtering in the mixed atmosphere of Ar and O₂ with various flow ratios. The structure and O/Ta atom ratio of the thin films were analyzed by X-ray diffraction and X-ray photoelectron spectroscopy (XPS). The optical and dielectric properties of the Ta₂O₅ thin films were investigated by using ultraviolet-visible spectra, spectral ellipsometry and dielectric spectra. The results reveal that the structure of the samples changes from the amorphous phase to the β-Ta₂O₅ phase after annealing at 900 °C. The XPS analysis showed that the atomic ratio of O and Ta atom is a stoichiometric ratio of 2.50 for the sample deposited at Ar:O₂ = 4:1. The refractive index of the thin films is 2.11 within the wavelength range 300-1000 nm. The dielectric constants and loss tangents of the Ta₂O₅ thin films decrease with the increase of measurement frequency. The leakage current density of the Ta₂O₅ thin films decreases and the breakdown strength increases with the increase of Ar:O₂ flow ratios during deposition.     

Investigation of niobium nitride and oxy-nitride films grown by MOCVD

Niobium nitride (NbN) and niobium oxy-nitride (NbO_xN_y) thin films were grown by metalorganic chemical vapor deposition (MOCVD) on Si(100) and Si(111) substrates using [Nb(N^tBu)(NMe₂){C(NⁱPr)₂(NMe₂)}₂] [NB; ^tBu = (CH₃)₃C; Me = CH₃; ⁱPr = (CH₃)₂CH] as a simultaneous Nb and N precursor. While NbN films were synthesized under a pure N₂ atmosphere, NbO_xN_y films were synthesized under N₂-O₂ flow (N₂:O₂ = 1-5) in the temperature range 400-600 °C, as well as by NbN deposition followed by ex-situ thermal treatments under flowing O₂ at 400-600 °C. The samples were subjected to a multi-technique characterization in order to elucidate the interplay between their structure, morphology and composition and the adopted processing parameters. Particular attention was devoted to the presence of Nb-N and Nb-O-N phases and their distribution in the films, as well as to surface oxidation phenomena. For the first time, niobium oxy-nitride coatings were obtained by CVD starting from the above precursor compound, with growth rates up to 270 Å/min on Si(111) at 600 °C. The films were characterized by a columnar-like/globular morphology when supported on Si(100)/Si(111) and revealed a higher crystallinity on the latter substrate. Surface and in-depth compositional analyses evidenced a limited carbon contamination and the Co-existence of niobium nitride, NbON and Nb₂O₅. In particular, the presence of the latter in the outermost sample layers was explained by oxidation phenomena occurring upon contact with the outer atmosphere.     

Structural, morphological and electrical properties of spray deposited nano-crystalline CeO2 thin films

Nanocrystalline, uniform, dense, and adherent cerium oxide (CeO₂) thin films have been successfully deposited by a simple and cost effective spray pyrolysis technique. CeO₂ films were deposited at low substrate and annealing temperatures of 350 °C and 500 °C, respectively. Films were characterized by differential thermal analysis, X-ray diffraction, scanning electron microscopy, atomic force microscopy; two probe resistivity method and impedance spectroscopy. X-ray diffraction analysis revealed the formation of single phase, well crystalline thin films with cubic fluorite structure. Crystallite size was found to be in the range of 10-15 nm. AFM showed formation of smooth films with morphological grain size 27 nm. Films were found to be highly resistive with room temperature resistivity of the order of 10⁷ Ω cm. Activation energy was calculated and found to be 0.78 eV. The deposited film showed high oxygen ion conductivity of 5.94 × 10⁻³ S cm⁻¹ at 350 °C. Thus, the deposited material shows a potential application in intermediate temperature solid oxide fuel cells (IT-SOFC) and might be useful for μ-SOFC and industrial catalyst applications.     

Epitaxial 0.65PbMg1/3Nb2/3O3-0.35PbTiO3 (PMN-PT) thin films grown on LaNiO3/CeO2/YSZ buffered Si substrates

Ferroelectric PMN-PT thin films with a thickness of 600 nm were epitaxially grown on buffered Si (0 0 1) substrates at a substrate temperature that ranged from 550 to 700 °C using pulsed laser deposition (PLD). LaNiO₃ (LNO) electrode thin films with a resistivity of ∼1900 μΩ cm were epitaxially grown on CeO₂/YSZ buffered Si (0 0 1) substrates. The PMN-PT thin films grown at 600 °C on LNO/CeO₂/YSZ/Si substrates had a pure perovskite and epitaxial structure. The PMN-PT films exhibited a high dielectric constant of about 1818 and a low dissipation factor of 0.04 at a frequency of 10 kHz. Polarization-electric-field (P-E) hysteresis characteristics, with a remnant polarization of 11.1 μC/cm² and a coercive field of 43 kV/cm, were obtained in the epitaxial PMN-PT films.     

Super-hydrophobic surface treatment as corrosion protection for aluminum in seawater

“Underwater super-hydrophobic” surface applied in the corrosion protection was prepared by melting myristic acid (CH₃(CH₂)₁₂COOH) adsorbed onto the anodized aluminum. The static contact angle for seawater on the surface was measured to be 154°. The surface structure and composition were then characterized by means of scanning electron microscopy (SEM) with energy dispersive X-ray spectrum (EDS) and atomic force microscope (AFM). The electrochemical measurements showed that the super-hydrophobic surface significantly improved the corrosion resistance of aluminum in sterile seawater. In addition, the mechanism of the underwater super-hydrophobic surface applied in the corrosion resistance was discussed using a schematic.     

Cu and CuO nanoparticles immobilized by silica thin films as antibacterial materials and photocatalysts

CuO nanoparticles with average diameter of about 20 nm were accumulated on surface of sol-gel silica thin films heat treated at 300 °C in air. Heat treatment of the CuO nanoparticles at 600 °C in a reducing environment resulted in effective reduction of the nanoparticles and penetration of them into the film. While the thin films heat treated at 300 °C exhibited a strong antibacterial activity against Escherichia coli bacteria, the reducing process decreased their antibacterial activity. However, by definition of normalized antibacterial activity (antibacterial activity/surface concentration of coppers) it was found that Cu nanoparticles were more toxic to the bacteria than the CuO nanoparticles (by a factor of ∼ 2.1). Thus, the lower antibacterial activity of the reduced thin films was assigned to diffusion of the initially accumulated copper-based nanoparticles into the film. The CuO nanoparticles also exhibited a slight photocatalytic activity for inactivation of the bacteria (∼ 22% improvement in their antibacterial activity). Instead, the normalized antibacterial activity of the Cu nanoparticles covered by a thin oxide layer highly increased (∼ 63% improvement) in the photocatalytic process. A mechanism was also proposed to describe the better antibacterial activity of the Cu than CuO nanoparticles in dark and under light irradiation.     

Influence of deposition conditions on mechanical and tribological properties of nanostructured TiN/CNx multilayer films

Nanostructured TiN/CN_x multilayer films were deposited onto Si (100) wafers and M42 high-speed-steel substrates using closed-filed unbalanced magnetron sputtering in which the deposition process was controlled by a closed loop optical emission monitor (OEM) to regulate the flow of N₂ gas. Multilayers with different carbon nitride (CN_x) layer thickness could be attained by varying the C target current (0.5 A to 2.0 A) during the deposition. It was found that the different bilayer thickness periods (i.e. the TiN layer thickness Λ_TiN was fixed at 3.0 nm while the CN_x layer thickness Λ_CNx was varied from 0.3 to 1.2 nm) significantly affected the mechanical and tribological properties of TiN/CN_x multilayer films. These multilayer films were characterized and analyzed by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM), Rockwell-C adhesion test, scratch test, pin-on-disc tribometer, and nanoindentation measurements. XPS analyses revealed that the chemical states, such as TiN, TiC, TiN_xO_y and TiO_2, existed in a TiN layer. Nanoindentation results showed that the hardness was highly dependent on the bilayer thickness. A maximum hardness of ~ 41.0 GPa was observed in a multilayer film at bilayer thickness Λ_TiN = 3.0 nm and Λ_CNx = 0.9 nm. All multilayer films exhibited extreme elasticity with elastic recoveries as high as 80% at 5 mN maximum load. The compressive stresses in the films (in a range of 1.5-3.0 GPa) were strongly related to their microstructure, which depended mainly on the incorporation of nitrogen in the films. By scratch and Rockwell-C adhesion tests, the multilayer films with smaller bilayer thicknesses (Λ_TiN = 3.0 nm, Λ_CNx = 0.3 and 0.6 nm) exhibited the best adhesion and cohesive strength. The critical load value obtained was as high as ~ 78 N for the films with Λ_TiN = 3.0 nm, Λ_CNx = 0.9 nm. The friction coefficient value for a multilayer at Λ_TiN = 3.0 nm and Λ_CNx = 0.9 nm was found to be low 0.11. These adhesive properties and wear performance are also discussed on the basis of microstructure, mechanical properties and tribochemical wear mechanisms.     

Electrical properties of sub-100 nm Cu films deposited by electroless plating on amino-terminated silicon oxide activated with Au nano-particles

Self-assembled organic monolayers (SAMs) are good coupling agents and diffusion barriers at Cu/SiO₂ and Cu/low-k interfaces and are considered therefore as important elements of future all-wet ULSI metallization with sub-45 nm Cu deposited by electroless plating (ELD). We formed SAM of 3-aminopropyltrimethoxy silane (APTMS) onto SiO₂/Si substrate, activated the surface of APTMS with 5, 8, 15 and 25 nm Au nano-particles (AuNPs), deposited (30-100) nm films of Cu by ELD and measured electrical resistivity ρ of the films in the as-deposited state and after vacuum annealing at 220 C. The size of AuNPs was found to be a key factor in getting low resistance sub-100 nm Cu films by ELD. The resistivity ρ ≈ 4 ± 0.8 μΩ·cm - considerably smaller compared to the previously reported data - was achieved with the use of 5 nm AuNPs. XPS and AFM revealed nano-pores, which can contribute to ρ but do not compromise likely the diffusion barrier properties of the SAM.     

Ferromagnetism in ZnTe:Cr film grown on Si(1 0 0)

Zn_1−xCr_xTe (x = 0.0 and 0.05) films were grown on Si(1 0 0) substrate by using thermal evaporation method. The structure of the films was investigated by X-ray diffraction and it showed the formation of ZnCrTe phase with an amorphous background, which indicated poor crystallinity. Composition analysis by XPS disclosed the presence of antiferromagnetic Cr₂O₃ and Cr precipitates. Magnetic domains were observed by using magnetic force microscopy at ambient temperature and the result showed anisotropic domains with an average size of 3.5 nm. Magnetic field dependence of magnetic moment measurements showed obvious hysteresis loop with a coercive field of 121 Oe at 300 K. Temperature dependence of magnetic moment showed short-range ferromagnetic order. The Curie temperature was estimated to be 354.5 K.     

Influence of europium oxide doping on the structural and optical properties of pulsed laser ablated barium tungstate thin films

Nanostructured Eu₂O₃ doped Barium tungstate (BaWO₄) crystallites are successfully synthesized using pulsed laser deposition (PLD) technique. The influence of different Eu₂O₃ doping concentrations (1,2,3 & 5 wt.%) on the structural, surface morphological and optical properties are systematically studied using XRD, micro-Raman, SEM, AFM, UV-vis and photoluminescence spectroscopy. All the films are polycrystalline with tetragonal scheelite structure. The vibrational analysis of the atoms in BaWO₄ is studied by micro-Raman spectra using factor group analysis. The surface morphological analysis by SEM and AFM reveals the presence of fine nanoparticles with distinct grain boundaries in all the films. The band gap energy variation in the Eu₂O₃ doped BaWO₄ films is in accordance with the variation of the sizes of nano particles in the films. The films with higher Eu³⁺ doping concentrations (≥2 wt.%) show a PL emission peak centered around 614 nm when excited at 394 nm which can be attributed to the ⁵D₀ → ⁷F₂ (0-2) transition of Eu³⁺ ion.     

Mechanical and tribological properties of coatings sputtered from SiC target in the presence of CH4 gas

Amorphous hydrogen-free silicon carbide (a-SiC) coatings demonstrate good adhesion to different steel substrates, low intrinsic stress and high hardness however show quite high coefficient of friction in comparison with carbon-based coatings. Some addition of carbon to SiC can promote the decrease of friction coefficient.In the present work the amorphous hydrogenated silicon-carbide (a-SiC:H) films with different C/Si ratio were prepared at room temperature using DC magnetron sputtering in two ways: (i) sputtering of silicon target; (ii) sputtering of SiC target, both in the gas mixture of Ar and CH₄. In the latter case the films contained less hydrogen at the same C/Si ratio. The mechanical and tribological properties of these films were studied to find their optimum combination.The hardness, elastic modulus (nanoindentation), intrinsic stress (Stoney's formula) and coefficient of friction (pin on disc tribometer) were examined in dependence on the technological parameters, film structure and composition (Raman spectra, electron probe microanalysis). An increase of carbon in the films from 50 to 70 at.% resulted in decrease of hardness and friction coefficient. In the first case (i) the hardness decreased from 13 to10 GPa and in the second case (ii) from 23 to 16 GPa. Thus sputtering of SiC target in the gas mixture of Ar and CH₄ allows obtaining at room temperature the films with C/Si > 1 in which relatively high hardness (16-18 GPa) and low friction coefficient (~ 0.15) are combined.     

Structural, morphological and electrical properties of spray deposited CdIn2Se4 thin films

Semiconducting n-CdIn₂Se₄ thin films have been deposited on to the amorphous and fluorine doped tin oxide (FTO) coated glass substrates using spray pyrolysis technique. The influence of solution concentration on to the photoelectrochemical, structural, morphological, compositional, thermal and electrical properties has been investigated. The PEC characterization shows that the short circuit current (I_sc) and open circuit voltage (V_oc) are at their optimum values (I_sc = 1.04 mA and V_oc = 409 mV) at the optimized precursor concentration (12.5 mM). The structural analysis shows the films are polycrystalline in nature having cubic crystal structure. The average crystallite size determined was in the range of 50-66 nm. Surface morphology and film composition have been analyzed using scanning electron microscopy and energy dispersive analysis by X-rays, respectively. The addition of solution concentration induces a decrease in the electrical resistivity of CdIn₂Se₄ films up to 12.5 mM solution concentration. The type of semiconductor was examined from thermoelectric power measurement.     

Low temperature pulsed laser deposition of textured γ′-Fe4N films on Si (1 0 0)

Low-temperature reactive pulsed laser deposition (PLD) was used to prepare iron nitride films. The textured γ′-Fe₄N films with (0 0 1)-orientation were deposited on Si (1 0 0) substrate with Fe buffer layer at a substrate temperature as low as 150 °C. The (0 0 1)-oriented γ′-Fe₄N film grew on the Fe buffer layer with a 3.5-nm thick amorphous interlayer, which eliminated the lattice mismatch stress between them. The films showed a columnar granular morphology with an average lateral grain size of approximately 110 nm. The films exhibited good soft magnetic properties with a high in-plane M_r/M_s value of 0.84. The magneto-optic Kerr effect results indicated an in-plane magnetic isotropy and confirmed the high remnant ratio of the γ′-Fe₄N films.