Preparation of boron carbon nitride thin films by radio frequency magnetron sputtering

Boron carbon nitride films were deposited by radio frequency magnetron sputtering using a composite target consisting of h-BN and graphite in an Ar-N₂ gas mixture. The samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The results suggest that the films are atomic-level hybrids composed of B, C and N atoms. The boron carbon nitride films prepared in the present experiment have a disordered structure. The sputtering power varied from 80 W to 130 W. This sputtering power was shown to have regular effect on the composition of boron carbon nitride films. The samples deposited at 80 W and 130 W are close to the stoichiometry of BC₃N. The sample deposited at 110 W is close to the stoichiometry of BCN. The samples deposited at 100 W and 120 W approach to BC₂N. It is very significant for us to synthesize boron carbon nitride compound with controllable composition by changing the sputtering power.     

A study on optical absorption and constants of doped poly(ethylene oxide)

Thin films of polymer electrolyte based on poly(ethylene oxide) doped with sodium iodide (NaI) were prepared using the solution cast method. The films obtained have average thickness of 70 μm and different NaI concentrations. Absorption and reflectance spectra of UV-radiation were studied in the wavelength range 300-800 nm. The optical results were analyzed in terms of absorption formula for non-crystalline materials.The optical energy gap and the basic optical constants, refractive index, and dielectric constants of the prepared films have been investigated and showed a clear dependence on the NaI concentration. The interpreted absorption mechanism is a direct electron transition.The observed optical energy gap for neat poly(ethylene oxide) is about 2.6 eV, and decreases to a value 2.36 eV for the film of 15 wt% NaI content. It was found that the calculated refractive index and the dielectric constants of the polymer electrolyte thin films increase with NaI content. Models were used to describe the dependences of the dielectric constant on the NaI concentration, and the refractive index on the incident photon energy.     

Femtosecond and nanosecond laser damage thresholds of doped and undoped triazenepolymer thin films

The influence of pulse duration on the laser-induced damage in undoped or infrared-absorbing-dye doped thin triazenepolymer films on glass substrates has been investigated for single, near-infrared (800 nm) Ti:sapphire laser pulses with durations ranging from 130 fs up to 540 fs and complementarily for infrared (1064 nm) Nd:YAG ns-laser single-pulse irradiation. The triazenepolymer material has been developed for high resolution ablation with irradiation at 308 nm. Post-irradiation optical microscopy observations have been used to determine quantitatively the threshold fluence for permanent laser damage. In contrast to our previous studies on a triazenepolymer with different composition [J. Bonse, S.M. Wiggins, J. Solis, T. Lippert, Appl. Surf. Sci. 247 (2005) 440], a significant dependence of the damage threshold on the pulse duration is found in the sub-picosecond regime with values ranging from ∼500 mJ/cm² (130 fs) up to ∼1500 mJ/cm² (540 fs). Other parameters such as the film thickness (50 nm and 1.1 μm samples) or the doping level show no significant influence on the material behavior upon irradiation. The results for fs- and ns-laser pulse irradiation are compared and analyzed in terms of existent ablation models.     

Step-changed period chirped long-period fiber gratings fabricated by CO2 laser

A CO₂ laser and point-by-point method are used for fabricating step-changed period chirped long-period fiber gratings (LPFG). Several types of period chirped LPFGs have been demonstrated, such as, linearly chirp, peak-shape chirp, and cascaded linearly chirp. Unlike uniform LPFGs, the spectrum change such as multiple attenuation peaks, broader spectrum can be seen in these chirp gratings, and the spectral shape can be controlled by the grating period. Especially, the cascaded linearly chirped LPFGs performs a multi-peak as interference between the core mode and cladding mode, which can be used as multi-wavelength filters in fiber optic communication and fiber optic sensors. Also, a linear tuning range of 1.6 nm with -0.559 pm/με tuning rate is achieved in these types of devices by applying an axial strain.     

Characterisation of the anodic layers formed on 2024 aluminium alloy, in tetraborate electrolyte containing molybdate ions

Anodic layer growth on 2024 aluminium alloy at 70 °C, under 40 V, during 60 min, in 50 g L⁻¹ di-sodium tetraborate solution containing di-sodium molybdate from 0.1 to 0.5 M (pH 10) is examined. Anodising behaviours strongly depend on additive concentration. Development of anodic films is favoured with weak molybdate additions (<0.3-0.4 M). The film thicknesses increase and the porosity of anodic layers decreases. Molybdenum (+VI), detected by X-ray photoelectron spectroscopy (XPS) analysis, is present in the anodic films and the Mo incorporation, studied by energy dispersive spectroscopy (EDS) analysis, increases with molybdate concentration. However, for high molybdate concentrations (>0.4 M), anodising behaviour becomes complex with the formation of a blue molybdenum oxide at the cathode. The growth of aluminium oxide is hindered. As the anodic layers are thinner, the Mo(+VI) incorporation significantly decreases. These two configurations implicate different corrosion performances in 5% sodium chloride solution at 35 °C. As the alkaline anodic layer formed with 0.3 M molybdate species is the thickest and the Mo incorporation is the more pronounced, its corrosion resistance is the highest. The effect of morphology and composition of anodic films on pitting corrosion is also discussed.     

Characterization of hydrogenated amorphous carbon thin films by end-Hall ion beam deposition

Pure hydrogenated amorphous carbon (α-C:H) and nitrogen doped hydrogenated amorphous carbon (α-C:H:N) thin films were prepared using end-Hall (EH) ion beam deposition with a beam energy ranging from 24 eV to 48 eV. The composition, microstructure and mechanical properties of the films were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, scanning probe microscopy (SPM), and nano-scratch tests. The films are uniform and smooth with root mean square roughness values of 0.5-0.8 nm for α-C:H and 0.35 nm for α-C:H:N films. When the ion energy was increased from 24 eV to 48 eV, the fraction of sp³ bonding in the α-C:H films increased from 36% to 55%, the hardness increased from 8 GPa to 12.5 GPa, and the Young's modulus increased from 100 GPa to 130 GPa. In the α-C:H:N films, N/C atomic ratio, the hardness and Young's modulus of the α-C:H:N films are, 0.087, 15 and 145 GPa, respectively. The results indicate that both higher ion energy and a small amount of N doping improve the mechanical properties of the films. The results have demonstrated that smooth and uniform α-C:H and α-C:H:N films with large area and reasonably high hardness and Young's modulus can be synthesized by EH ion source.     

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.     

Electron and lattice structure of ultra thin Ag films on Si(1 1 1) and Si(0 0 1)

We studied the low temperature (T ? 130 K) growth of Ag on Si(0 0 1) and Si(1 1 1) flat surfaces prepared by Si homo epitaxy with the aim to achieve thin metallic films. The band structure and morphology of the Ag overlayers have been investigated by means of XPS, UPS, LEED, STM and STS. Surprisingly a (√3 × √3)R30° LEED structure for Ag films has been observed after deposition of 2-6 ML Ag onto a Si(1 1 1)(√3 × √3)R30°Ag surface at low temperatures. XPS investigations showed that these films are solid, and UPS measurements indicate that they are metallic. However, after closer STM studies we found that these films consists of sharp Ag islands and (√3 × √3)R30°Ag flat terraces in between. On Si(0 0 1) the low-temperature deposition yields an epitaxial growth of Ag on clean Si(0 0 1)-2 × 1 with a twinned Ag(1 1 1) structure at coverage’s as low as 10 ML. Furthermore the conductivity of few monolayer Ag films on Si(1 0 0) surfaces has been studied as a function of temperature (40-300 K).     

Studies on poly(vinylidene fluoride-co-hexafluoropropylene) based gel electrolyte nanocomposite for sodium-sulfur batteries

Experimental investigations on a sodium ion conducting gel polymer electrolyte nanocomposite based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), dispersed with silica nanoparticles are reported. The gel nanocomposites have been obtained in the form of dimensionally stable, transparent and free-standing thick films. Physical characterization by X-ray diffraction (XRD), Fourier transform Infra-red (FTIR) spectroscopy and Scanning electron microscopy (SEM) have been performed to study the structural changes and the ion-filler-polymer interactions due to the dispersion of SiO₂ nanoparticles in gel electrolytes. The highest ionic conductivity of the electrolyte has been observed to be 4.1 × 10⁻³ S cm^− 1 at room temperature with ~ 3 wt.% of SiO₂ particles. The temperature dependence of the ionic conductivity has been found to be consistent with Vogel-Tammen-Fulcher (VTF) relationship in the temperature range from 40 to 70 °C. The sodium ion conduction in the gel electrolyte film is confirmed from the cyclic voltammetry, impedance analysis and transport number measurements. The value of sodium ion transport number (t_Na+) of the gel electrolyte is significantly enhanced to a maximum value of 0.52 on the 15 wt.% SiO₂ dispersion. The physical and electrochemical analyses indicate the suitability of the gel electrolyte films in the sodium batteries. A prototype sodium-sulfur battery, fabricated using optimized gel electrolyte, offers the first discharge capacity of ~165 mAh g^− 1 of sulfur.     

Fabrication of highly ordered CuInSe2 films with hollow nanocones for anti-reflection

Highly ordered CuInSe₂ films with hollow nanocones were fabricated by electron beam evaporation and nanospheres lithograph. From the AFM analyses, polystyrene nanospheres with diameter of 220 nm are assembled regularly on glass substrates. After reaction ion etching under different powers and residues removal, different and new surface morphologies of substrates have been obtained, such as smooth nanocones and hollow nanocones. The diffuse reflection spectra demonstrate that films on the substrates with periodic nanopatterned structure have less reflection over wavelengths ranged from 200 nm to 2500 nm due to light trapping. Especially, reflection for hollow nanocone arrays has the larger suppression value than nanocone-patterned films, which proves that surface pattern of hollow nanocones has better anti-reflection effect. Furthermore, while hollow depth increases from 6 nm to 9 nm, its optical antireflective effect becomes remarkable. These results could yield new options for solar-cell design with higher energy conversion efficiency.     

Structural and optoelectronic properties of antimony tin sulphide thin films deposited by thermal evaporation techniques

Thin films of SnSb₂S₄ have been prepared on glass substrate by using thermal evaporation techniques. The films were annealed in argon gas at low pressure in sealed glass ampoules at 85 °C, 150 °C, 275 °C and 325 °C. XRD of the films reveal that the low temperature annealed films are poly crystalline while the as deposited films and high annealed films are in amorphous states. There is no adequate variation in the photoconductivity response of the amorphous and crystalline phases. The transmittance of the films is low and having no transmittance below 740 nm. The band gap calculated by ellipsometry technique is in the range of 1.82–3.1 eV. The films have n-type conductivity but the film annealed at 325 °C show p-type conductivity.     

RF-PACVD of water repellent and protective HMDSO coatings on bell metal surfaces: Correlation between discharge parameters and film properties

Hexamethyldisiloxane (HMDSO) films have been deposited on bell metal using radiofrequency plasma assisted chemical vapor deposition (RF-PACVD) technique. The protective performances of the HMDSO films and their water repellency have been investigated as a function of DC self-bias voltage on the substrates during deposition. Plasma potential measurements during film deposition process are carried out by self-compensated emissive probe. Optical emission spectroscopy (OES) analyses of the plasma during deposition reveal no significant change in the plasma composition within the DC self-bias voltage range of −40 V to −160 V that is used. Raman and X-ray photoelectron spectroscopy (XPS) studies are carried out for film chemistry analysis and indicate that the impinging ion energy on the substrates influences the physio-chemical properties of the HMDSO films. At critical ion energy of 113 qV (corresponding to DC self-bias voltage of −100 V), the deposited HMDSO film exhibits least defective Si-O-Si chemical structure and highest inorganic character and this contributes to its best corrosion resistance behavior. The hardness and elastic modulus of the films are found to be bias dependent and are 1.27 GPa and 5.36 GPa for films deposited at −100 V. The critical load for delamination is also bias dependent and is 11 mN for this film. The water repellency of the HMDSO films is observed to be dependent on the variation in surface roughness. The results of the investigations suggest that HMDSO films deposited by RF-PACVD can be used as protective coatings on bell metal surfaces.     

The effect of annealing on the room temperature ferromagnetism in co-sputtered In2O3: C thin films

In this paper, we report investigation of room temperature (RT) ferromagnetism in In₂O₃ (InO) thin films doped with carbon prepared by the co-sputtering method. InO thin films both undoped and C doped with varied thicknesses in the range of 45 to 80 nm were synthesized on Si substrates with varied C concentrations. The carbon concentration was varied from 1.6 to 9.3 at%. The undoped InO films showed no trace of ferromagnetism. Carbon doped films (InO:C) exhibited ferromagnetism at RT, which was of the orders of 10⁻⁵ emu and varied strongly with C concentrations. It is observed that the magnetization reached a maximum value of 5.7 emu/cm³ at 4 at% C. Annealing of the InO:C films in an oxygen environment resulted in a decrease in the magnetization, indicating the crucial role of oxygen vacancies in the films. It is concluded that the oxygen vacancies were important and compete with C substitution for the RT ferromagnetism.     

Synthesis of LECBD grown cluster assembled SeO2 thin films

Cluster assembled selenium oxide (SeO₂) thin films, as a function of oxygen flow pressure (OFP) have been synthesized by a low energy cluster beam deposition (LECBD) technique. The OFP dependent surface morphology leading to well separated nanoclusters (size ranging from 50 to 200 nm) and fractal features are confirmed from transmission electron microscopic (TEM) measurements. A diffusion limited aggregation (DLA) mediated fractal growth with dimension as 1.71 ± 0.01 has been observed for high OFP (60 mbar). Structural analysis by glancing angle X-ray diffraction (GXRD) and selected area diffraction (SAD) studies identify the presence of tetragonal phase SeO₂ in the deposit. Micro-Raman studies indicate the shifts in bending and stretching vibrational phonon modes in cluster assembled SeO₂ as compared to their bulk counter part due to the phonon confinement effect.     

Highly oriented (1 0 0) ZnO thin films by spray pyrolysis

Undoped ZnO thin films have been deposited onto glass substrates by spray pyrolysis. The structural, electrical and optical properties were studied on thin films, prepared from precursor solutions with varying the ethanol concentrations. X-ray diffraction studies have shown polycrystalline nature of the films with a hexagonal wurtzite-type structure. The preferential orientation plane (1 0 0) of the ZnO thin film is found to be sensitive to ethanol concentration. The texture coefficient (TC) and grain size value have been calculated. Also ethanol concentration was found to have significant effect on sheet resistivity of the films.     

High-conductive nanocrystalline silicon with phosphorous and boron doping

Intrinsic, P- and B-doped hydrogenated amorphous silicon thin films were prepared by plasma-enhanced chemical vapor deposition technique. As-deposited samples were thermally annealed at the temperature of 800 °C to obtain the doped nanocrystalline silicon (nc-Si) films. The microstructures, optical and electronic properties have been evaluated for the undoped and doped nanocrystalline films. X-ray photoelectron spectroscopy (XPS) measurements demonstrated the presence of the substitutional boron and phosphorous in the doped films. It was found that thermal annealing can efficiently activate the dopants in films accompanying with formation of nc-Si grains. Based on the temperature-dependent conductivity measurements, it was shown that the activation of dopant by annealing increased the room temperature dark conductivity from 3.4 × 10⁻⁴ S cm⁻¹ to 5.3 S cm⁻¹ for the P-doped films and from 1.28 × 10⁻³ S cm⁻¹ to 130 S cm⁻¹ for the B-doped films. Meanwhile, the corresponding value of conductivity activation energies was decreased from 0.29 eV to 0.03 eV for the P-doped films and from 0.3 eV to 5.6 × 10⁻⁵ eV for the B-doped films, which indicated the doped nc-Si films with high conductivity can be achieved with the present approach.     

Photoemission investigations on nanostructured TiO2 grown by cluster assembling

Nanostructured titanium dioxide (ns-TiO₂) films were grown by supersonic cluster beam deposition method. Transmission electron microscopy demonstrated that films are mainly composed by TiO₂ nanocrystals embedded in an amorphous TiO₂ phase while their electronic structure was studied by photoemission spectroscopy. The cluster assembled ns-TiO₂ films are expected to exhibit several structural and chemical defects owing to the large surface to volume ratio of the deposited clusters. Ultraviolet photoemission spectra (hv = 50 eV) from the valence band unveil the presence of a restrained amount of surface Ti 3d defect states in the band gap, whereas Ti 2p core level X-ray photoelectron (hv = 630 eV) spectra do not manifestly disclose these defects.     

InSb-TiOPc interfaces: Band alignment, ordering and structure dependent HOMO splitting

Thin films of titanyl phthalocyanine (TiOPc) have been adsorbed on InSb(1 1 1) (3 × 3) and InSb(1 0 0) c(8 × 2) surfaces and studied with respect to their electronic structure using photoemission (PES), density functional theory (DFT) and scanning tunneling microscopy (STM). The interface chemical interaction is weak in both cases; no adsorbate induced surface band bending is observed and the energy level alignment across the interface is determined by the original position of the substrate Fermi level and the charge neutrality level of the molecule.Room temperature adsorption results in disordered films on both surfaces. The behaviors after annealing are different; on InSb(1 0 0) well-ordered molecular chains form along and on top of the In-rows, whereas on (1 1 1) no long range order is observed. The disorder leads to intermolecular interactions between the titanyl group and neighboring benzene rings leading to a split of TiOPc HOMO (highest occupied molecular orbital) by as much as 0.8 eV.     

Chemical synthesis of p-type nanocrystalline copper selenide thin films for heterojunction solar cells

Nanocrystalline thin films of copper selenide have been grown on glass and tin doped-indium oxide substrates using chemical method. At ambient temperature, golden films have been synthesized and annealed at 200 °C for 1 h and were examined for their structural, surface morphological and optical properties by means of X-ray diffraction (XRD), scanning electron microscopy and UV-vis spectrophotometry techniques, respectively. Cu_2−xSe phase was confirmed by XRD pattern and spherical grains of 30 ± 4 - 40 ± 4 nm in size aggregated over about 130 ± 10 nm islands were seen by SEM images. Effect of annealing on crystallinity improvement, band edge shift and photoelectrochemical performance (under 80 mW/cm² light intensity and in lithium iodide electrolyte) has been studied and reported. Observed p-type electrical conductivity in copper selenide thin films make it a suitable candidate for heterojunction solar cells.     

Electrochromic and electrochemical properties of amorphous porous nickel hydroxide thin films

Nickel hydroxide films were prepared using the chemical bath deposition (CBD) technique. The amorphous nature of the films was confirmed by X-ray diffraction measurements. X-ray photoelectron spectroscopy (XPS) measurements showed that the films exhibited nickel hydroxide nature. The porosity of the films was studied using optical measurements. The electrochromic properties of the porous nickel hydroxide layers were investigated, using cyclic voltammetry, chronoamperometry, in situ transmittance, UV-vis spectroscopy, and impedance spectroscopy. The change in the optical density (ΔOD) was found to be 0.79 for the as-deposited nickel hydroxide films, whereas it is 0.53 and 0.50 for the films annealed at 150 °C and 200 °C, respectively. The in situ transmittance and chronoamperometry curves revealed that the annealed films had a very fast colouration (t_c < 290 ms) and decolouration (t_b < 130 ms). The measured colouration efficiencies range between 30 and 40 cm²/C. The impedance measurements revealed the faster colouration and good electrochromic properties for the annealed nickel hydroxide films.