Raman characterization of boron doped tetrahedral amorphous carbon films

Boron doped tetrahedral amorphous carbon films, having boron content from 0.59 to 6.04 at.%, have been prepared by a filtered cathodic vacuum arc system using boron mixed graphite targets. The influence of boron on the surface morphologies and microstructures of the films was studied by atomic force microscopy and Raman spectroscopy. The surface images showed that the irregular tops on the surface of the films tended to form larger clusters as boron content increased. The Raman spectra of the films were, respectively, deconvoluted using Gaussian and Breit-Wigner-Fano line shapes. The Raman parameters, including the intensity ratios, peak positions, peak widths and coupling coefficients, obtained from both line shapes were described and compared. It was found that both line shapes could produce consistent results except the peak widths of G bands. The major effect of boron introduction was to increase the clustering of the sp² phase in the films.     

Relative fraction of sp bonding in boron incorporated amorphous carbon films determined by X-ray photoelectron spectroscopy

Boron incorporated amorphous carbon (a-C:B) films were deposited by a filtered cathodic vacuum arc system using various percentage of boron mixed graphite cathodes. X-ray photoelectron spectroscopy (XPS) was employed to determine the properties of the films as a function of boron concentration. Deconvolutions of the XPS C 1s core level spectra were carried out using four different components. The relative fraction of sp³ bonding was then evaluated from the area ratio of the peaks at 285.0, 284.1 eV which were individually attributed to sp³ C-C, sp² CC hybridizations. The results showed that the sp³ content of a-C:B film decreases from 73.8 to 58.6% for the films containing boron from 0.59 to 2.13 at.%, and then gradually reduced to 42.5% at a slower rate with boron concentration up to 6.04 at.%. Furthermore, a series of a-C:B films with fixed boron content (2.13 at.%) were prepared to identify the relationship between sp³ bonding and substrate bias. It was found that the fraction of sp³ bonding increased from 50.28% at the bias voltage of 0 V and reached a maximum value of 66.3% at −150 V. As the bias voltage increased up to −2000 V, the sp³ content decreased sharply to 43.9%.     

Structural and dielectric properties of parylene-VT4 thin films

58% semi-crystalline thin parylene-VT4 (–H₂C–C₆F₄–CH₂−)_n films, have been investigated by dielectric spectroscopy for temperature and frequency ranges of [−120 to 380 °C] and [0.1–10⁵ Hz] respectively. The study comprises a detailed investigation of the dielectric constant, dielectric loss and AC conductivity of this fluoropolymer. Dielectric behavior of parylene-VT4 is represented by a low dielectric constant with values in the range of 2.05–2.35 while the dielectric losses indicate the presence of two relaxation processes. Maxwell−Wagner−Sillars (MWS) polarization at the amorphous/crystalline interfaces with activation energy of 1.6 eV is due to the oligomer orientation. Electrical conductivity obeys to the well-known Jonscher law. The plateau in the low frequency part of this conductivity is temperature-dependent and follows an Arrhenius behavior with activation energy of 1.17 eV (deep traps) due to the fluorine diffusion. Due to its thermal stability with a high decomposition temperature (around 400 °C under air and 510 °C under nitrogen) and due to its good resistivity at low frequency (10¹⁵–10¹⁷ Ω m⁻¹), parylene-VT4 constitutes a very attractive polymer for microelectronic applications as low k dielectric. Moreover, when parylene-VT4 is subjected to an annealing, the dielectric properties can be still more improved.     

Evaluation of microstructures and mechanical properties of diamond like carbon films deposited by filtered cathodic arc plasma

Diamond-like carbon (DLC) films were deposited by a cathodic arc plasma evaporation (CAPD) process, using a mechanical shield filter combined with a magnetic filter with enhanced arc structure at substrate-bias voltage ranging from − 50 to − 300 V. The film characteristics were investigated using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and high-resolution transmission electron microscopy (HRTEM). The mechanical properties were investigated by using a nanoindentation tester, scratch test and ball on disc wear test. The Raman spectra of the films showed that the wavenumber ranging from 900 to 1800 cm^− 1 could be deconvoluted into 1140 cm^− 1, D band and G band. The bias caused a significant effect on the sp³ content which was increased with the decreasing of I_D/I_G ratio. The XPS spectra data of the films which were etched by H⁺ plasma indicated the sp³ content are higher than those of the as-deposited DLC films. This implied that there is a sp²-rich layer present on the surface of the as-deposited DLC films. The nanoindentation hardness increased as the maximum load increased. A 380 nm thick and well adhered DLC film was successfully deposited on WC-Co substrate above a Ti interlayer. The adhesion critical load of the DLC films was about 33 N. The results of the wear tests demonstrated that the friction coefficient of the DLC films was between 0.12 and 0.2.     

Effect of nitrogen doping concentration on the properties of TiO2 films grown by atomic layer deposition

N-doped TiO₂ films were grown on n⁺-silicon substrates by atomic layer deposition using titanium chloride and vapor mixture of ammonia and water as the reactants. The effects of doping concentration on the microstructure and photocurrent response of as-deposited films were investigated. The results show that the doping levels were 0.2, 0.7, 1.2, 1.5, and 4.3 at% for films grown at NH₃-to-H₂O injection volume ratios of 350, 380, 440, 520, and 550, respectively. The off-plane lattice constant of TiO₂ films increased with the increase of doping level, and the transformation of anatase to rutile was inhibited by the doping as the doping concentration reached 1.2 at%. The wavelength-dependent photocurrents suggest an optimal N doping concentration lying between 0.7 and 1.2 at% for the visible light active TiO₂ films. Doping with a too-low or a too-high nitrogen level resulted in an inefficient visible light generation or a serious carrier recombination, respectively.     

Role of ex-situ oxygen plasma treatments on the mechanical and optical properties of diamond-like carbon thin films

Role of ex-situ oxygen plasma (OP) treatment on mechanical properties of diamond-like carbon (DLC) thin films is explored. The DLC film after this treatment shows superhardness behaviour, maximum hardness of 46.3 GPa and elastic modulus of 423.2 GPa are obtained when film grown at self bias of 100 V followed by 10 min OP treatment. Moreover, the colour of the coating is fed after OP treatment, leading it to a colourless coating with significantly enhanced transmittance and improved antiglare property. Such OP treated DLC films may find their applications as protective coatings on cutting tools, automobile parts, magnetic storage media and colourless coating in packaging, as the DLC films posses brown colour.     

Photoluminescence in amorphous carbon thin films and its relation to the microscopic properties

The photoluminescence properties of amorphous hydrogenated carbon (a-C:H) films grown using a r.f. plasma have been investigated. It is found that the photoluminescence (PL) spectra exhibit a red shift, accompanied by a sharp decrease in PL efficiency and an increase in electron spin density as the applied r.f. power increases. The results can be interpreted by a model in which the a-C:H films consist of two phases with π-bonded clusters embedded in an sp³-bonded amorphous matrix. The excitation and the recombination of electron hole pairs are believed to take place in the π-bonded clusters. As a result of the confinement effect of electron hole pairs in these clusters, the cluster size becomes an important parameter in understanding the PL properties of a-C:H films.     

Adsorbed multilayer effects on the mechanical properties in nanometer indentation depth

Nanoindentation is a powerful technique for determining the mechanical properties of a material at the nanometer scale. In this study, the changes induced in the mechanical properties of a thin film by the presence of adsorbed multilayers are examined by performing nanoindentation tests with ultra-low indentation depths. The current findings suggest that the results obtained for the mechanical properties of thin films under nanoindentation will be overestimated if the effects of the adsorbed multilayers on reducing elastic recovery between the indenter and the substrate are not taken into consideration.     

Optical waveguide based on amorphous Er-doped Ga-Ge-Sb-S(Se) pulsed laser deposited thin films

Amorphous chalcogenide films play a motivating role in the development of integrated planar optical circuits due to their potential functionality in near infrared (IR) and mid-IR spectral regions. More specifically, the photoluminescence of rare earth ions in amorphous chalcogenide films can be used in laser and amplifier devices in the IR spectral domain. The aim of the present investigation was to optimize the deposition conditions for the fabrication of undoped and Er³⁺ doped sulphide and selenide thin films with nominal composition Ga₅Ge₂₀Sb₁₀S(Se)₆₅ or Ga₅Ge₂₃Sb₅S₆₇ by pulsed laser deposition (PLD). The study of compositional, morphological and structural characteristics of the layers was realized by scanning electron microscopy-energy dispersive spectroscopy, atomic force microscopy and Raman spectroscopy analyses, respectively. Some optical properties (transmittance, index of refraction, optical band gap, etc.) of prepared chalcogenide films and optical losses were investigated as well. The clear identification of near-IR photoluminescence of Er³⁺ ions was obtained for both selenide and sulphide films. The decay of the ⁴I_13/2 → ⁴I_15/2 transition at 1.54 µm in Er³⁺ doped Ga₅Ge₂₀Sb₁₀S₆₅ PLD sulphide films was studied to assess the effects of film thickness, rare earth concentration and multilayer PLD deposition on their spectroscopic properties.     

Preparation and mechanical properties of C/SiC composites with carbon fiber woven preform

C/SiC composites reinforced with multilayer carbon fiber woven preforms were fabricated by isothermal chemical vapor infiltration (ICVI) process. To characterize the mechanical properties of the composites, mechanical testing was carried out under various loading conditions, including tension, bending and shear loads. The results indicated that the composites, with superior intrinsic through-the-thickness properties, exhibited high in-plane mechanical properties. Therefore, the composites developed can well meet the demands of the reusable nose cap, i.e. the easiness of near-net shaping and the capability of withstanding multidirectional mechanical and thermal stresses.     

Anisotropic phenomena in as-evaporated amorphous chalcogenide thin films

The changes in refractive index and birefringence in as-evaporated As_xS_1−x amorphous films have been measured by means of prism-coupling technique. In particular, the time evolution, annealing and substrate temperature effects, compositional dependencies of the optical anisotropy on the fresh amorphous films are investigated. The analyse of these effects in terms of a proposed microscopic model are discussed. Such a model is shown to qualitatively explain some aspects of this phenomenon.     

Preparation and characterization of amorphous manganese sulfide thin films by SILAR method

Manganese sulfide thin films were deposited by a simple and inexpensive successive ionic layer adsorption and reaction (SILAR) method using manganese acetate as a manganese and sodium sulfide as sulfide ion sources, respectively. Manganese sulfide films were characterized for their structural, surface morphological and optical properties by means of X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis and optical absorption measurement techniques. The as-deposited film on glass substrate was amorphous. The optical band gap of the film was found to be thickness dependent. As thickness increases optical band gap was found to be increase. The water angle contact was found to be 34°, suggesting hydrophilic nature of manganese sulfide thin films. The presence of Mn and S in thin film was confirmed by energy dispersive X-ray analysis.     

Structural and electrical properties of amorphous carbon-sulfur composite films

In this paper, we discuss the synthesis of carbon-sulfur composite (a-C:S) films by vapour phase pyrolysis of maleic anhydride and sulfur. Structural changes in the system are analysed by scanning electron microscopy and powder X-ray diffraction. Microhardness test depicts an increase in the value of hardness with an increase in sulfur concentration. Electrical conductivity of composite samples varies with sulfur concentration. Magnetoresistance (MR) measurements show a drastic increase in the value of MR for the samples prepared at < 900°C. Thermal stability of these samples is analysed by thermogravimetric analysis, which depends on the host structure and the amount of intercalated species.     

High quality amorphous indium zinc oxide thin films synthesized by pulsed laser deposition

Indium zinc oxide films were grown from targets with two different In atomic concentration [In/(In + Zn)] of 40% and 80% by the pulsed laser deposition technique on glass substrates from room temperature up to 100 °C. X-ray diffraction and reflectometry investigations showed that films were amorphous and dense. Thin films (thickness < 100 nm) exhibited higher optical transmittance and resistivities than thick films (thickness > 1000 nm), probably caused by a significant decrease of oxygen vacancies due to atmosphere exposure. Films deposited from the In rich target under an oxygen pressure of 1 Pa exhibited optical transmittance higher than 85%, resistivities around 5- 7 × 10^− 4 Ω cm and mobilities in the 47-54 cm²/V s range.     

Atomistic investigation of structural and mechanical properties of silicon carbon nitride with different SiC/Si3N4 ratios

Silicon carbon nitride (SiCN) presents good performance at high temperature while it is difficult to ascertain the chemical structure of its nanodomain by experimental techniques. In this work, empirical potential based large-scale atomistic simulations are used to generate the amorphous structures of SiCN. The models obtained by melt-quench simulations reproduce the nano-domain structure of SiCN and the corresponding PDFs consist with previous DFT calculation and X-ray/Neutron Diffraction experiments. The calculated Young's moduli are comparable to the range of 160–240 GPa in experiments, moreover, it increases with an increasing SiC content and decrease with temperature increases.     

A pressure enhanced CVD method for large scale synthesis of carbon microtubes and their mechanical properties

Carbon microtubes (CMTs) are a new morphological form of carbon with micrometer scale internal diameters and thin walls made of a few graphitic layers. However, compared with carbon nanotubes, there is lack of a feasible and reliable synthetic method. Furthermore, the mechanical properties of CMTs have not been reported. In this paper, we report a gas pressure enhanced CVD method for large-scale preparation of high-purity, crystalline and thin-walled CMTs in a gas pressure furnace using urea as raw material in the absence of catalyst. The as-obtained CMTs have highly graphitized structure and have a homogenous morphology with an internal diameter of about 1 μm, a wall thickness of 5 nm and several millimeters in length. The Young's modulus of the CMTs was determined to be 0.652 TPa on average, which is comparable to that of carbon nanotubes reported in previous research.     

Optical and other physical characteristics of Ge–Se–Cd thin films

Amorphous Ge₂₀Se_80−xCd_x thin films with different compositions (x = 0, 2.5, 5, 7.5 and 10 at.%) were deposited onto glass substrates by thermal evaporation. The reflection spectra, R(λ), of the films at normal incidence were obtained in the spectral region from 400 to 2500 nm. Based on the use of the maxima and minima of the interference fringes, a straightforward analysis proposed by Minkov has been applied to derive the optical constants and the film thickness for the Ge₂₀Se_80−xCd_x thin films. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple and DiDomenico model. Tauc relation for the allowed non-direct transition describes the optical transition in the studied films. With increasing cadmium content the refractive index increases while the optical band gap decreases. The optical band gap decreases from 2 to 1.5 eV with increasing cadmium content from 0 to 10 at.%. The chemical-bond approach has been applied successfully to obtain the excess of Se–Se homopolar bonds and the cohesive energy of the Ge₂₀Se_80−xCd_x system.     

Photo-induced effects on electrical properties of Ga15Se81Ag4 chalcogenide thin films

The present work deals with the study of photo-induced crystallization on thermally evaporated Ga₁₅Se₈₁Ag₄ chalcogenide thin films. It has been achieved by shining white light using 1500 W tungsten lamp. The ambient temperature during illumination process was controlled and kept at 75 °C, which is in between the glass transition and crystallization temperature of Ga₁₅Se₈₁Ag₄ glasses. The exposure time was experimentally established for different illumination times from 0 to 120 min. After various exposure times, thin films were characterized by XRD and SEM. The dc conductivities and activation energies of these thin films were measured in temperature range of 303-403 K. It is found that the activation energy in Ga₁₅Se₈₁Ag₄ chalcogenide thin films decreases with increasing the exposure time whereas the dc conductivity increases at each temperature by increasing the illumination time.     

Effect of nitrogen addition on the properties and thermal stability of fluorinated amorphous carbon films

Continuous fluorinated amorphous carbon (a-C : F) films doped with nitrogen (a-C : F : N) were deposited by plasma enhanced chemical vapor deposition using CF₄ and C₂H₂ gases as precursors with the addition of N₂ gas. The surface morphologies, chemical compositions, deposition rates, thermal stability and mechanical properties of these films varied with the deposition parameters, including CF₄ and N₂ feed gas concentrations, processing pressure, plasma power and substrate temperature. With increasing N₂ feed gas concentration, the nitrogen content of the a-C : F : N films increased to about 6 at.% and contributed to higher mechanical properties. After thermal annealing, the a-C : F films with higher fluorine contents exhibited more obvious fluorine release and extensive film thickness shrinkage, whereas the a-C : F : N films with higher contents of nitrogen doping yielded less composition variations, smaller thickness shrinkages, higher mechanical properties, and conclusively better thermal stability.     

On the structure, stress and optical properties of CVD tungsten oxide films

Tungsten oxide thin films were prepared by low temperature chemical vapor deposition (CVD) process from a metallorganic precursor at atmospheric pressure. The influence of the deposition temperature and oxygen flow-rate on the film structure, density and built-in stress were investigated in a comparative way employing different characterization techniques. The XRD structural analysis of the films showed co-existence of WO₃ and WO_2.9 phases. On the basis of the performed studies it was inferred that the film density decreases, the film stresses change and the film transmission increases at higher oxygen flow-rate values during the deposition. The growth window for preparation of tungsten oxide films with very low density, facilitating fast kinetics of the electrochromic effect, was established.