Corrosion protection ability of plasma-deposited amorphous hydrogenated carbon and fluorocarbon films

Hydrogenated diamond-like carbon and fluorocarbon films, deposited in a radio-frequency (rf) plasma reactor, have high chemical inertness and high electrical resistivity. These films, deposited on aluminum and type 301 stainless steel substrates at several rf power and feed gas flow rates using different gas phase precursors, were characterized for their pinhole density and stability with exposure to 0.6 M NaCl and 0.1 M NaCl and 0.1 M Na₂SO₄ solutions using electrochemical impedance spectroscopy and potentiostatic techniques, respectively. The results from electrochemical characterizations with salt water exposure indicated that films with high effective pore resistances (>10⁸ Ω · cm²)* and high stability with exposure (<10% changes in capacitance values) can be obtained over a narrow range of process conditions and gas phase compositions.     

The energy influx during plasma deposition of amorphous hydrogenated carbon films

The integral energy influx from the plasma to the substrate was determined for amorphous hydrogenated carbon (a-C:H) film deposition by magnetron sputtering and in an electron cyclotron resonance (ECR) discharge. The measurements, for which a thermal probe was designed, are based on time evolution of the substrate temperature during the deposition process. The different contributions to the integral energy influx were estimated by model calculations on the basis of assumptions for the kinetic energy of the charge carriers, their recombination, and film condensation. The energy influx during deposition in the CH₄-ECR plasma, which is in the range of 0.5–2 J s⁻¹, is predominantly determined by ions and chemical reactions, while the energy influx in magnetron sputtering, being in the range of 0.2–1.2 J s⁻¹, is mainly determined by fast neutrals and target radiation. The present results emphasise that the energy influx is a key parameter in thin film deposition and is important for comparison and scaling-up of different plasma process systems.     

Interface and superhardness of TiN/CNx multilayer films

This work attempts to reveal the microstructure of interface and the relation between interface mixing and hardening mechanism in TiN/CN_x multilayer films. The growth and microstructure of these interfacial layers are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Investigation result indicates that the interface species are mainly composed of Ti-C-N, the growth of interlayer mainly depends on the deposition temperature. The thickest interlayer (about 2.5 nm) is produced at 300 °C, and the interlayer disappears at 500 °C. Nanoindentation testing indicates that the film with a maximum interlayer thickness of about 2.5 nm exhibits superhardness up to 40 GPa. Based on the experimental results, it is suggested that the interfacial intermixing and the crystal quality of TiN are the main reasons for the superhardness effect in TiN/CN_x nanostructured multilayers.     

TiAlN/CrAlN纳米结构多层膜的结构与性能

采用射频磁控溅射方法制备了单层TiAlN、CrAlN复合薄膜以及不同调制周期和不同层厚比(lTiAlN/lCrAlN)的TiAlN/CrAlN纳米结构多层膜.薄膜采用X射线衍射仪、扫描电子显微镜、显微硬度仪进行表征.结果表明:TiAlN、CrAlN复合薄膜和TiAlN/CrAlN多层膜均为面心立方结构,呈(111)面择优取向.TiAlN/CrAlN多层膜的择优取向与调制周期和层厚比无关.层厚比为1的TiAlN/CrAlN多层膜的硬度依赖于调制周期,在调制周期为8 nm时,达到最大;固定TiAlN的厚度为4 nm,改变CrAlN层的厚度,在研究范围内,多层膜的硬度随着CrAlN层厚度的增加而增加.探讨了多层膜的致硬机制.TiAlN/CrAlN多层膜抗氧化温度比其组成单层膜高了近200 ℃,并讨论了其抗氧化机制.     

Characterization of silicon-stabilized amorphous hydrogenated carbon

The characterization of a modified form of diamondlike carbon, referred to as silicon-stabilized amorphous hydrogenated carbon (Si-AHC), is described. Auger electron spectroscopy, electron probe microanalysis, solid-state nuclear magnetic resonance, Raman scattering, nuclear reaction analysis, and optical absorption spectroscopy were used to determine chemical composition and to monitor structural changes due to the addition of silicon. Hardness, density, residual stress, and tribological properties of AHC and Si-AHC are compared. The Si-AHC coatings show much lower stress, a friction coefficient that is insensitive to moisture, an increase in optical gap compared to AHC, improved thermal stability, and equivalent hardness and wear. Some automotive applications are discussed.     

Exchange biasing in SFMO/SFWO double perovskite multilayer thin films

In the present study, we have studied the exchange bias interaction in ferromagnetic Sr₂FeMoO₆ (SFMO)/antiferromagnetic Sr₂FeWO₆ (SFWO) multilayer thin films deposited on single crystal LaAlO₃ substrates using KrF pulsed laser deposition technique. XRD pattern revealed that SFMO, SFWO and their multilayer thin films were highly oriented along the c-axis. The microstructure studied by atomic force microscopy was found to be uniform, fine, dense and homogenous in nature. The observed magnetization-temperature curves showed Neel temperature T_N ∼ 37 K for SFWO and Curie temperature T_C > 320 K for SFMO thin films. For multilayer, the field cooled magnetization-field curve was shifted horizontally and the direction of the horizontal shift is opposite to that of H_FC, indicating an exchange bias effect. Exchange bias field H_E was found to decrease with increase in temperature and approached to zero at blocking temperature.     

Buckling behaviors and adhesion energy of nanostructured Cu/X (X = Nb,Zr) multilayer films on a compliant substrate

Two sets of Cu/Nb (face-centered cubic (fcc)/body-centered cubic) and Cu/Zr (fcc/hexagonal close-packed) nanostructured multilayer films (NMFs) have been prepared on a flexible polyimide substrate, with a wide range modulation period (λ) from 250 down to 5 nm. The mechanical properties of the two NMFs have been measured upon uniaxial tensile testing and the buckling behaviors have been systematically investigated as a function of λ. A significant difference in the bucking behaviors was found between the two NMFs, with the buckles in the Cu/Nb NMF being mostly cracked, while the buckles were nearly crack-free in the Cu/Zr NMF. The different buckling behaviors, dependent on the constituent phases, are rationalized in the light of the disparity in mechanical properties. The criteria to characterize buckle cracking have been discussed with respect to the mechanical properties (e.g. yield strength, ductility and fracture toughness) of the NMFs. A modified energy balance model has been employed to estimate the adhesion energy of the NMFs on the polyimide substrate. Within the λ regime below a critical size (λ_crit) of ～50 nm a λ-independent adhesion energy of about 1.1 and 1.2 J m^?2 has been determined for the Cu/Nb and Cu/Zr NMFs, respectively, which agrees well with previous reports on the metal film/polymer substrate systems. Within the λ regime greater than λ_crit, however, the measured adhesion energy exhibit a strong size effect, i.e. increasing with increasing λ. The λ dependence of the evaluated adhesion energy is discussed in terms of the size-dependent deformation mechanism in NMFs. A micromechanics model has been utilized to quantify the critical modulation period of ～50 nm, where the deformation mechanism changes from dislocation pile-up to confined layer slip.     

Synthesis of hydrogenated amorphous carbon films with a line type atmospheric-pressure plasma CVD apparatus

In this study, hydrogenated amorphous carbon (a-C:H) films were synthesized on polyethylene terephthalate (PET) substrates with a line type atmospheric-pressure plasma chemical vapor deposition (CVD) apparatus. Acetylene and nitrogen mixture gas was used for process gas and a-C:H films having two different thickness were synthesized with varying the C₂H₂ mixing rates. We investigated the effect of chemical bonding structure on the ultraviolet ray shielding property of the films. The deposition rate increased as a function of the C₂H₂ mixing rates. Increasing the C₂H₂ mixing rate from 2.5 to 10% caused an increase in the deposition rates from 13 to 22 nm/s. The deposition rate under atmospheric pressure was faster than that of low-pressure plasma CVD (~ 5–16 nm/s). Ultraviolet transmittance of 2 μm thick a-C:H film synthesized at the C₂H₂ mixing rate of 10% on 100 μm thick PET substrates ranged from 0 to 3% as the UV wavelength ranged from 310 to 400 nm, while that of uncoated PET substrates ranged from 0 to 80%. From the result of X-ray photoelectron spectroscopy (XPS) analysis, the component of sp²-hybridized C, such as CC and CO bonds increased as the C₂H₂ mixing rate and thickness of a-C:H films increased. A decrease of sp³-hybridized C, such as CC and CO bonds and an increase of sp²-hybridized C bonds lead to an improvement of ultraviolet ray shielding property.     

Photosensitivity and optical performance of hydrogenated amorphous carbon films processed by picosecond laser beams

In this work we investigate the photosensitivity of hydrogenated amorphous Carbon films (a-C:H) and the changes in their structural features and optical properties, when they are exposed to picosecond laser beams of various wavelengths (Nd:YAG, 1st harmonic, λ = 1064 nm and 4th harmonic, λ = 266 nm). The different light-matter interactions, which take place for the various laser wavelengths, are considered and discussed. The main findings include the formation of SiC at the a-C:H film/Si interface and the film graphitization, when the 1064 nm and 266 nm beams, respectively, are used. Finally we managed to vary locally the refractive index in the range of 1.60-1.95 (20% variations) by laser processing, a fact that is very important for various applications in photonics.     

Properties of hydrogenated amorphous carbon films deposited by PECVD and modified by SF6 plasma

Hydrogenated amorphous carbon (a-C:H) films were grown at room temperature on glass and polished silicon substrates using RF-PECVD (Radio-Frequency Plasma Enhanced Chemical Vapor Deposition). Plasmas composed by 30% of acetylene and 70% of argon were excited by the application of RF signal to the sample holder with power ranging from 5 to 125 W. After deposition, the films were submitted to SF₆-plasma treatment for 5 minutes. SF₆ plasmas were generated at a pressure of 13.3 Pa by a RF power supply operating at 13.56 MHz with the output fixed at 70 W. The resulting films were characterized in terms of their molecular structure, chemical composition, surface morphology, thickness, contact angle, and surface free energy. During the SF₆ plasma treatment, fluorine species were incorporated in the film structure causing chemical alterations. The interaction of chemical species generated in the SF₆ plasmas with surface species was responsible for the decrease of the film thickness and surface energy, and for the increase of the film roughness and hydrophobicity.     

Fracture properties of hydrogenated amorphous silicon carbide thin films

The cohesive fracture properties of hydrogenated amorphous silicon carbide (a-SiC:H) thin films in moist environments are reported. Films with stoichiometric compositions (C/Si ≈ 1) exhibited a decreasing cohesive fracture energy with decreasing film density similar to other silica-based hybrid organic-inorganic films. However, lower density a-SiC:H films with non-stoichiometric compositions (C/Si ≈ 5) exhibited much higher cohesive fracture energy than the films with higher density stoichiometric compositions. One of the non-stoichiometric films exhibited fracture energy (∼9.5 J m⁻²) greater than that of dense silica glasses. The increased fracture energy was due to crack-tip plasticity, as demonstrated by significant pileup formation during nanoindentation and a fracture energy dependence on film thickness. The a-SiC:H films also exhibited a very low sensitivity to moisture-assisted cracking compared with other silica-based hybrid films. A new atomistic fracture model is presented to describe the observed moisture-assisted cracking in terms of the limited SiOSi suboxide bond formation that occurs in the films.     

Studies on local structure in hydrogenated amorphous LaNi5.0 films using extended X-ray absorption fine structure

The local structure in hydrogenated amorphous LaNi_5.0 film was analysed by means of extended X-ray absorption fine structure. The short-range order in the amorphous LaNi_5.0 film was found to be little affected by the absorption of hydrogen. The lengthening of the interatomic distance with an increase in hydrogen concentration was much smaller for an amorphous film than for a crystalline bulk, so that the amorphous film appears to have excellent durability with regard to the hydrogen absorption-desorption process.     

Fabrication, microstructure and tribological behavior of pulsed laser deposited a-CNx/TiN multilayer films

a-CN_x/TiN multilayer films were deposited onto high-speed steel substrates by pulsed laser ablation of graphite and Ti target alternately in nitrogen gas. The composition, morphology and microstructure of the films were characterized by energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. The tribological properties of the films in humid air were investigated using a ball-on-disk tribometer. The multilayer films consist of crystalline TiN, metallic Ti and amorphous CN_x (a-CN_x). With an increase in thickness ratio of CN_x to bilayer, the hardness of multilayer film decreases, friction coefficient decreases from 0.26 to 0.135, and wear rate increases. The film with thickness ratio of CN_x to bilayer of 0.47 exhibits a maximum hardness of 30 GPa and excellent wear rate of 2.5 × 10^− 7 mm³ N^− 1 m^− 1. The formation of tribo-layer was observed at contact area of Si₃N₄ ball. The film undergoes the combined wear mechanism of abrasion wear and adhesion wear.     

Synthesis of nanostructured CuxS thin films by chemical route at room temperature and investigation of their size dependent physical properties

Nanostructured semiconductors show very interesting physical properties than bulk crystal due to size effects that arises because of quantum confinement of the electronic states. Using cupric acetate and sodium thiosulphate as cationic and anionic precursor, nanostructured Cu₂S thin films were successfully prepared at room temperature by chemical bath deposition technique. By varying the deposition time from 9 to 24 h, the Cu₂S films of thickness 70-233 nm were prepared. The different characterization methods such as X-ray diffraction (XRD), scanning electron microscopy (SEM), optical absorption and electrical resistivity measurement techniques were used to investigate size dependent properties of Cu₂S thin films. As thickness increases, the hexagonal covellite phase of CuS observed at thickness 70 nm gets converted to monoclinic chalcosite phase of Cu₂S. The resistivity and activation energy is found to be thickness dependent. The optical band-gap energy increases from 2.48 to 2.90 eV as thickness decreases from 233 to 70 nm. The influence of film thickness on carrier concentration, mobility and thermo-emf is reported.     

Wear of PVD Ti/TiN multilayer coatings

The wear characteristics of PVD Ti/TiN multilayer coatings subjected to two-body abrasion and particle erosion have been studied using diamond slurry and silicon carbide particles as abrasive medium and erodant, respectively. The abrasive wear rate of the Ti/TiN multilayer coatings was found to increase with the relative amount of metallic Ti in the coatings. In erosion, the lowest wear rate was recorded for the homogeneous TiN coating. For the Ti/TiN multilayer coatings the erosion rate was found to decrease with an increasing relative amount of metallic Ti in the coatings. It is concluded that the concept of multilayered coatings offers a potent means to tailor the properties of tribological coatings. In particular, demands of different applications can be met by adjusting the relative thickness of metallic Ti in Ti/TiN coatings. The amount of metallic Ti can, for example, be used to control the coating residual stress state. Multilayered Ti/TiN coatings seem promising for combined wear and corrosion protection.     

Transparent conductive Sb-doped SnO2/Ag multilayer films fabricated by magnetron sputtering for flexible electronics

The effects of an embedded silver layer and substrate temperature on the electrical and optical properties of Sb-doped SnO₂ (ATO)/silver (Ag) layered composite structures on polyethylene naphthalate substrates have been investigated. The highest conductivity of ATO/Ag multilayer films was obtained with a carrier concentration of 1.5 × 10²² cm^?3 and a resistivity of 2.4 × 10^?5 Ω cm at the optimum Ag layer thickness and substrate temperature. The photopic averaged transmittance and Haacke figure of merit are 81.7%, and 21.7 × 10^?3 Ω^?1, respectively. In addition, a conduction mechanism is proposed to elucidate the mobility variation with increased Ag thickness. We also describe the influence of substrate temperature on the structural, electrical and optical properties of the ATO/Ag multilayer films, and propose a mechanism for the changes in electrical and optical properties at different substrate temperatures.     

Electrical properties of amorphous carbon films

Aromatic polyimide films, Upilex S partially carbonized between 700°C and 1000°C. Electrical conductivity is higher at higher temperatures. The electrical conductivity s could be expresses as s = s_o exp (−E/kT), where k is the Boltzmann constant, t is the absolute measuring temperature. s_o and E are found to be 4 × 10⁻¹ Ω⁻¹ m⁻¹ and 0.02eB, respectively. The experimental data show that the Hall coefficient R is negative, and this implies that the carriers are negatively charged, i.e. electrons. The specimens are n-type semiconductors. The carrier density η is given by η = 1/(|e|R) and the mobility μ is μ is s/(η|e|), where |e| is the absolute value of the electron charge and s is the electrical conductivity. Fitting the data, η = A₁ exp (−E₁/κT) and μ = A₂ exp (E₂/κT). E₁ and E₂ depend on carbonized temperature. The polyimide films are not completely carbonized but partially carbonized at 700°C. The partially carbonized polyimide is an n type donor. It is concluded that the “impurity level” lies about 0.36eV below the conduction band.     

Surface morphology of nanostructured anatase thin films prepared by pulsed liquid injection MOCVD

Nanostructured anatase thin films were prepared by chemical vapor deposition feeding a metal organic precursor in a pulsed liquid injection mode. The films were deposited at 500 °C on stainless steel substrates using a single molecular titanium isopropoxide liquid solution as the precursor, without any reactant gas. An effective pulsing injection mechanism for the precursor supply provides uniform concentration of the precursor in the vapor phase, allowing the formation of titanium dioxide layers from small micro-doses of the metal organic precursor. Energy-dispersive spectroscopy, scanning electron microscopy and X-ray diffraction studies show the formation of crack-free nanostructured anatase thin films, highly oriented, formed basically by stepwised nanostructures with a uniform coverage and no detectable carbon contamination. Surface crystallinity, composition, nanostructure and morphology are discussed in terms of the experimental parameters used in the deposition process.     

The effect of multilayer structure on magnetic properties of FePt thin films

The Fe/Pt multilayer films with different structures were deposited by RF magnetron sputtering on glass substrates, and the L1₀-FePt films were obtained after theas-deposited samples were subjected to vacuum annealing at various temperatures. Results show that the Fe/Pt multilayer structure can effectively reduce the ordering temperature of FePt film, and the in-plane coercivity of [Fe (5.2 nm)/Pt (5.2 nm)]₇ multilayers can reach 161.2 kA/m after annealed at 350 ℃ for 30 min. When Fe and Pt layer thickness is equal, the coercivity of the film is the largest. On the other hand, the different Fe-Pt crystalline phases such as Fe₃Pt and FePt₃ phases are formed after annealing when the thickness ratio of Fe/Pt deviates from 1 after annealing. When Fe and Pt have the same thickness, the thinner single layer gets the lower ordering temperature and the larger coercivity.