Fabrication and characterization of multilayer films based on Keggin-type polyoxometalate and chitosan

Multilayer films based on Keggin-type polyoxometalate (POM) α-[SiW₁₂O₄₀]⁴⁻ (α-SiW₁₂), α-[PMo₁₂O₄₀]³⁻ (α-PMo₁₂) and cationic chitosan have been fabricated in aqueous solution via the layer-by-layer self-assembly technique (LBL). The resulting films were characterized by UV–Vis spectra, X-ray photoelectron spectra (XPS), atomic force microscopy (AFM) and cyclic voltammetry (CV) measurements. UV–Vis spectra show that the absorbance values at characteristic wavelengths of the multilayer films increase almost linearly with the number of chitosan/POM bilayers, suggesting that the deposition process is regular and highly reproducible from layer to layer. XPS spectra confirm the incorporation of chitosan and POMs into the films. AFM images indicate that the surface of the multilayer films is rather uniform and smooth. The antibacterial activities against Escherichia coli of the LBL films have also been investigated by optical density method.     

Preparation and characterization of LaNiO3 films grown by metal-organic deposition

We have investigated the synthesis and characterization of LaNiO₃ (LNO) layers deposited on YSZ (100) substrate by metal-organic deposition (MOD). Texture, morphology and electrical properties of the LaNiO₃ films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and electrical resistivity measurement. It has been found that the formation of (h00) orientation depends on pyrolysis temperature, annealing temperature and thickness of LaNiO₃ layers. The LaNiO₃ films prepared under optimal condition indicate highly (h00) orientation and a rather smooth surface. The LaNiO₃ films show a metallic behaviour in the measured temperature range.     

Structural and dielectric properties of (001) and (111)-oriented BaZr0.2Ti0.8O3 epitaxial thin films

We have grown and characterized BaZr_0.2Ti_0.8O₃ (BZT) epitaxial thin films deposited on (001) and (111)-oriented SrRuO₃-buffered SrTiO₃ substrates by pulsed laser deposition. Structural and morphological characterizations were performed using X-ray diffractometry and atomic force microscopy, respectively. A cube-on-cube epitaxial relationship was ascertained from the θ-2θ and φ diffractograms in both (001) and (111)-oriented films. The (001)-oriented films showed a smooth granular morphology, whereas the faceted pyramid-like crystallites of the (111)-oriented films led to a rough surface. The dielectric response of BZT at room temperature was measured along the growth direction. The films were found to be ferroelectric, although a well-saturated hysteresis loop was obtained only for the (001)-oriented films. High leakage currents were observed for the (111) orientation, likely associated to charge transport along the boundaries of its crystallites. The remanent polarization, coercive field, dielectric constant, and relative change of dielectric permittivity (tunability) of (111)-oriented BZT were higher than those of (001)-oriented BZT.     

Structure, morphology and electrical characterizations of direct current sputtered ZnO thin films

ZnO thin films were deposited on glass substrates by direct current (DC) sputtering technique at room temperature (RT) to 400 °C with a 99.999% pure ZnO target. Then the samples deposited at RT were annealed in air from the RT to 400 °C. The effects of substrate temperature (T_s) and annealing treatment (T_a) on the crystallization behavior and the morphology have been studied by X-ray diffraction and atomic force microscopy. We also compared the structural properties of samples deposited at 400 °C on glass to those deposited on Pt/silicon substrate. The resistivity, surface roughness and size of the grains have also been studied and correlated to the thickness of ZnO films deposited on Pt/Si substrates. The experimental results reveal that the substrate has a major influence on the structural and morphological properties. For the films deposited on glass, below 400 °C, T_s and T_a have a similar influence on the structure of the films. Moreover, the ZnO samples deposited at RT and annealed in air have poor electrical properties.     

Effect of high-energy electron beam irradiation on the properties of AZO thin films prepared by rf magnetron sputtering

We investigated that high-energy electron beam irradiation (HEEBI) performed in air at room temperature affected remarkably the properties of Al-doped ZnO (AZO) films grown on SiO₂ substrates by radio frequency magnetron sputtering techniques. Hall and photoluminescence measurements revealed that the n-type conductivity was preserved in HEEBI treated films with low dose up to 10¹⁵ electrons/cm² and converted to p-type conductivity with further increase in the amount of dose. X-ray photoelectron spectroscopy confirmed the conversion of conductivity by showing that in-diffusion of O₂ from the ambient as well as out-diffusion of Zn from the films took place as a result of HEEBI treatment at high dose of 10¹⁶ electrons/cm². X-ray diffraction analysis indicated that all as-grown films were found to have compressive stress, which was enhanced by HEEBI treatment with the increase of doses. It was also found that worse crystallinity with a smaller grain size was observed in HEEBI treated films with a higher dose, which was correlated with rougher surface morphologies of films observed by an atomic force microscope.     

Nanostructure, electrical and optical properties of p-type hydrogenated nanocrystalline silicon films

In this paper, p-type hydrogenated nanocrystalline (nc-Si:H) films were prepared on corning 7059 glass by plasma-enhanced chemical vapor deposition (PECVD) system. The films were deposited with radio frequency (RF) (13.56 MHz) power and direct current (DC) biases stimulation conditions. Borane (B₂H₆) was a doping agent, and the flow ratio η of B₂H₆ component to silane (SiH₄) was varied in the experimental. Films’ surface morphology was investigated with atomic force microscopy (AFM); Raman spectroscopy, X-ray diffraction (XRD) was performed to study the crystalline volume fraction X_c and crystalline size d in films. The electrical and optical properties were gained by Keithly 617 programmable electrometer and ultraviolet-visible (UV-vis) transmission spectra, respectively. It was found that: there are on the film surface many faulty grains, which formed spike-like clusters; increasing the flow ratio η, crystalline volume fraction X_c decreased from 40.4% to 32.0% and crystalline size d decreased from 4.7 to 2.7 nm; the optical band gap E_g^opt increased from 2.16 to 2.4 eV. The electrical properties of p-type nc-Si:H films are affected by annealing treatment and the reaction pressure.     

Study of the effect of the deposition parameters on the structural, electric and optical characteristics of polymorphous silicon films prepared by low frequency PECVD

In this work we present our results on the deposition and characterization of polymorphous silicon (pm-Si:H) films prepared by low frequency plasma enhanced chemical vapor deposition (LF-PECVD). We have studied the effect of the plasma deposition parameters (as the chamber pressure and gas flow rates of SiH₄ and H₂) on the structural, electric, and optical characteristics of the films.The temperature dependence of conductivity (σ(T)), activation energy (E_a), optical band gap (E_g) and deposition rate (V_d) were extracted for pm-Si:H films deposited at different pressure values and different gas flow rates. We observed that the chamber pressure is an important parameter that has a significant effect on the electric characteristics, and as well on the morphology of the pm-Si:H films (deduced from atomic force microscopy). It was found an optimal pressure range, in order to produce pm-Si:H films with high E_a and room temperature conductivity, σ_RT, which are key parameters for thermal detection applications.     

Fabrication of Cu(In,Ga)Se2 thin films by ion beam sputtering deposition from a quaternary target at different substrate temperatures

Cu(In, Ga)Se₂ (CIGS) thin films were fabricated by ion beam sputtering deposition from a single quaternary target at different substrate temperatures (T _sub). The thin films were characterized with X-ray diffractometry, scanning electron microscopy, energy-dispersive X-ray spectroscopy and four-point probe technique to study the microstructures, surface morphology, composition and electrical properties, respectively. The results show that the films grown above 400?°C are of chalcopyrite structure. Cu(In_0.7Ga_0.3)Se₂ thin film was obtained when T _sub is 550?°C. The Cu and Se atomic percentage when T _sub is above 500?°C is higher than when T _sub is below 500?°C. With the increase in T _sub, the surfaces morphology of the films is denser and the resistivity of the films decreases.     

Nickel oxide sol-gel films from nickel diacetate for electrochromic applications

Nickel diacetate tetrahydrate, [Ni(acetate)₂·4H₂O] and nickel diacetate dimethylaminoethanol, [Ni(acetate)₂(dmaeH)₂] were successfully used to deposit NiO_x thin films on conductive glass substrates by sol-gel techniques for large area electrochromic applications. Homogeneous one layer films 100 nm thick were deposited by spin coating 0.5 M [Ni(acetate)₂·4H₂O] in dmaeH at 1000 rpm and by dip coating methods. The NiO_x films were characterised by X-ray diffraction, transmission electron microscopy and atomic force microscopy. The thin film electrochromic performances were characterised by means of optical (transmittance) and electrochemical (cyclic voltammetry) methods. On early cycling NiO_x thin films present an activation period, related to an increase in capacity. The electro-optical data show an increase in the electrochromic response (i.e. an increase in contrast and colouration efficiency) upon cycling. Following this initial activation period a steady state is reached in which the thin films reversibly switch from transparent to brown. The anodically coloured NiO_x thin films are therefore suitable for use in a complete electrochromic cell with tungsten oxide as the cathodic colouring layer. However, the films are not fully stable with long cycling.     

Property change in multifunctional TiCxOy thin films: Effect of the O/Ti ratio

TiC_xO_y films with various O/Ti ratios have been deposited by DC magnetron sputtering, using C pieces incrusted in a Ti target erosion area. Composition analysis revealed the existence of three different growth regimes: (i) zone I, corresponding to films with metallic-like appearance, and atomic ratios O/Ti below one; (ii) zone II, with films revealing interference-like colours, and atomic ratios O/Ti higher than 2. Between these two regions, there was a transition zone T, where the atomic ratio O/Ti is between one and two. The films within this zone revealed a brown colour. X-ray diffraction (XRD) structural characterization results showed an evolution from a mixed Ti(C,O) phase at lower O/Ti ratio, to a quasi-amorphous structure within zone T, and poorly crystallized rutile and anatase TiO₂ at the highest O/Ti ratios (zone II). These different structural arrangements resulting from different film's compositions had clear effects on electrical resistivity, whose values increased from about 7 × 10² to 2 × 10¹¹ μΩ cm with increase of the O/Ti ratio. Fourier-transform infrared spectroscopy (FTIR) was used to further confirm the different nature of films structure and, thus, to better understand their properties variation. The observed behaviour was found to be in straight correlation with those of XRD.     

Double effects of atomic hydrogen anneal on the microstructure of hydrogenated amorphous silicon films

Hydrogenated amorphous silicon (a-Si:H) films have been deposited with pure silane and then annealed with atomic hydrogen at lower temperature (T_s=170 °C) in a novel, hot wire assisted microwave electron cyclotron resonant chemical vapor deposition system (HW-MWECR-CVD). The experimental results showed that the total hydrogen concentration (C_H) in the film decreased with H₂ flux increase in the atomic hydrogen anneal (AHA) step, but it does not obviously change, keeping at about 3% when H₂ flux increased to a higher value. This is due to double effects of AHA, the crystallization effect at lower substrate temperature and the rehydrogenation effect in low hydrogen concentration films. Furthermore, it was proposed that with increasing R(R=1/{F_hydrogen/(F_silane+F_hydrogen)}, in which F_silane is the silane gas flux in first film synthesis stage and F_hydrogen is the hydrogen gas flux during the annealing step, respectively.), polyhydrides such as SiH_x (x=2 or 3) turn into monohydrides SiH, which results in reducing the network defects, improving the film microstructure and decreasing the optical band gap from 1.644 to 1.557 eV.     

Conductivity studies of plasticized PEO-Lithium chlorate–FIC filler composite polymer electrolytes

A new report of the synthesis of (PEO/plasticizer)LiClO₄–Li_1.3Al_0.3Ti_1.7(PO₄)₃ polymer electrolyte films prepared by the solution-cast technique is represented in this work. DSC trace revealed that T_g decreased with the increase of plasticizer content in the polymer electrolyte films. SEM morphology showed that the surface morphology of films was relatively smooth and homogeneous. Conductivity studies by EIS measurement indicated that the temperature dependence of ionic conductivity of films followed Vogel–Tamman–Fulcher (VTF) equation. The pre-exponential factor (A) and the pseudo activation energy (E_a) increased with the increase of plasticizer content in the polymer electrolyte films. At the 40 wt.% plasticizer content, A and E_a respectively had a maximum.     

The influence of fluorine doping on the optical properties of diamond-like carbon thin films

Optical properties of fluorine doped diamond-like carbon (F:DLC) films deposited by the direct current plasma enhanced chemical vapor deposition (PECVD) technique were studied in detail. Surface morphologies of the F:DLC films were studied by an atomic force microscope, which indicated surface roughness increased with increase in at.% of F in the films. The chemical binding was investigated by X-ray photoelectron spectroscopic studies. Fourier transformed infrared spectroscopic studies depicted the presence of CF_x (x = 1,2,3) and CH_n (n = 1,2) bonding within the F:DLC films. Optical transparency and the optical band gap decreased with the fluorine incorporation in the DLC film. Optical band gap calculated from the transmittance spectra decreased from 2.60 to 1.95 eV with a variation of 0-14.8 at.% of F concentration in the diamond-like carbon films. Urbach parameter determined from the band tail of the transmittance spectra showed that it increased with the doping concentration.     

An investigation on electrochromic properties of (WO3)1−x-(Fe2O3)x thin films

In this research, the effect of Fe₂O₃ content on the electrochromic properties of WO₃ in thermally evaporated (WO₃)_1−x-(Fe₂O₃)_x thin films (0 ≤ x ≤ 0.4) has been studied. The atomic composition of the deposited metal oxides was determined by X-ray photoelectron spectroscopy analysis. The surface morphology of the thin films has been examined by atomic force microscopy. The surface roughness of all the films was measured about 1.3 nm with an average lateral grain size of 30 nm showing a smooth and nanostructured surface. The electrochromic properties of (WO₃)_1−x-(Fe₂O₃)_x thin films deposited on ITO/glass substrate were studied in a LiClO₄ + PC electrolyte by using ultraviolet-visible spectrophotometry. It was shown that increasing the Fe₂O₃ content leads to reduction of the optical density (ΔOD) of the colored films and also leads to increasing the optimum coloring voltage from 4 to 6 V in which ΔOD shows its maximum values, in our experimental conditions. Furthermore, by using this procedure, it is possible to make an electrochromical filter which behaves similar to the colored WO₃ film in the visible region, while it can be nearly transparent for near-infrared wavelengths, in contrast of the pure colored WO₃ film.     

Influence of Fabrication Parameters on Crystallization, Microstructure, Surface Composition, and Optical Behavior of MgO Thin Films Deposited by rf Magnetron Sputtering

In this work MgO thin films have been grown onto common glass substrates by magnetron rf sputtering from a MgO (99.99%) target with dimensions of 4″×¼″. Basically, we found the optimum conditions for deposition such as working pressure (7×10^?3 mbar), the power applied to the target (400 W) and the flow of Ar (20 sccm). The films have been characterized by X-ray diffraction (XRD) at a grazing angle at θ–2θ configuration, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and transmittance studies. The XRD results show that to reproduce the polycrystalline phase of the target, there is a power threshold of 250 W. AFM results indicate that the films present average roughness of the 200 Å and grain size of 1100 Å. XPS shows a surface composition of the films most external 5 nm, indicating the presence of MgO and Mg(OH)₂. The optical characterization indicates that the films have a high absorption coefficient for wavelengths below 310 nm, and between 450 to 850 nm they showed a transmittance average of 90%.     

Spectroscopic ellipsometry investigations of the optical properties of manganese doped bismuth vanadate thin films

The optical properties of Bi₂V_1−xMn_xO_5.5−x {x = 0.05, 0.1, 0.15 and 0.2 at.%} thin films fabricated by pulsed laser deposition on platinized silicon substrates were studied in UV-visible spectral region (1.51-4.17 eV) using spectroscopic ellipsometry. The optical constants and thicknesses of these films have been obtained by fitting the ellipsometric data (Ψ and Δ) using a multilayer four-phase model system and a relaxed Lorentz oscillator dispersion relation. The surface roughness and film thickness obtained by spectroscopic ellipsometry were found to be consistent with the results obtained by atomic force and scanning electron microscopy. The refractive index measured at 650 nm does not show any marginal increase with Mn content. Further, the extinction coefficient does not show much decrease with increasing Mn content. An increase in optical band gap energy from 2.52 to 2.77 eV with increasing Mn content from x = 0.05 to 0.15 was attributed to the increase in oxygen ion vacancy disorder.     

Preparation and electric characteristics of gadolinium-substituted bismuth titanate ferroelectric thin films

Gadolinium-substituted bismuth titanate (Bi_4 − xGd_xTi₃O₁₂, BGT) thin films were deposited on the (111)Pt/Ti/SiO₂/(100)Si substrates by a modified Sol–Gel process. With the aid of X-ray diffraction (XRD), the structure and appropriate Gd-substituted content x of BGT thin films were detected. The surface quality of the films was measured by means of an atomic force microscope (AFM) in tapping mode. The surface of BGT thin films was smooth and the phase was homogeneous. The ferroelectric properties of the films were investigated. When the Gd-substituted content x was equal to 0.75, the remanent polarization was the largest. The remanent polarization 2Pr value was equal to 15.4 μC/cm² and the coercive field Ec value was 54.17 kV/cm.     

On the annealing temperature, penetration depth of oxygen and film thickness on the DC and AC electrical properties and nano-structure of Ti thin films

Ti films of different thickness ranging from 12.3 to 246.2 nm were deposited, using resistive heat method and post-annealed at different temperatures with a flow of 5 cm³ s⁻¹ oxygen. The nano-structures of the films were obtained using X-ray diffraction (XRD) and atomic force microscopy (AFM). The results showed an initial reduction of the grain size at 373 K annealing temperature and increase of the grain size at higher temperatures. The cause of this was due to the reaction of oxygen with Ti atoms which breaks up the Ti grains and hence needle-like features form. The enhancement of activation processes at higher temperatures results in larger grains. The analysis of XRD in conjunction with AFM images showed that those films containing (004) line of anatase phase and sub-oxide phases of titanium oxide also show two types of grains in the AFM images. The resistivity of the film increased with annealing temperature, which is due to competition between increased diffusion rate and the increased reaction rate of oxygen with Ti atoms. The Hall coefficient R_H and the mobility μ decreased with increasing film thickness at all annealing temperatures, while R_H increases and μ decreases with increasing the annealing temperature. The carrier concentration increased with film thickness and decreased with annealing temperature. The impedance spectroscopy showed that all films have a pure RC behaviour, where the magnitude of R depends on the annealing temperature and film thickness. The apparent activation energies E_a, obtained from three different methods, namely σ, R_H and grain size showed good agreement within 0.30-0.46 eV for the range of film thickness examined in this work. It was found that films with thickness less than 70 nm can be recognized as Ti-oxide films while thicker films are only surface-oxidised Ti films.     

Field emission studies of CVD diamond thin films: effect of acid treatment

Field emission from CVD diamond thin films deposited on silicon substrate has been studied. The diamond films were synthesized using hot filament chemical vapor deposition technique. Field emission studies of as-deposited and acid-treated films were carried out using ‘diode’ configuration in an all metal UHV chamber. Upon acid treatment, the field emission current is found to decrease by two orders of magnitude with increase in the turn-on voltage by 30%. This has been attributed to the removal of sp² content present in the film due to acid etching. Raman spectra of both the as-deposited and acid-treated films exhibit identical spectral features, a well-defined peak at 1333 cm⁻¹ and a broad hump around 1550 cm⁻¹, signatures of diamond (sp³ phase) and graphite (sp² phase), respectively. However upon acid treatment, the ratio (I_d/I_g) is observed to decrease which supports the speculation of removal of sp² content from the film. The surface roughness was studied using atomic force microscopy (AFM). The AFM images indicate increase in the number of protrusions with slight enhancement in overall surface roughness after acid etching. The degradation of field emission current despite an increase in film surface roughness upon acid treatment implies that the sp² content plays significant role in field emission characteristics of CVD diamond films.     

Synthesis of type-II textured tungsten disulfide thin films with bismuth interfacial layer as a texture promoter

Highly textured tungsten disulfide (WS₂) thin films have been obtained by sulfurization of tungsten trioxide. The properties of WS₂ thin films prepared with bismuth interfacial layer as texture promoter has been studied. The WS₂ thin films were found to have predominant type-II orientation. The stacking of 2H-WS₂ crystallites observed with scanning electron microscopy was not reported hitherto. The films can be pictured as an assembly of WS₂ hexagonal crystallites. The energy dispersive X-ray analysis and X-ray photoelectron spectroscopy (XPS) studies confirm that the films are stoichiometric. The XPS analysis described the local environment of the tungsten atoms and the formal oxidation states of the tungsten and sulfur atoms were + 4 and − 2. Together with the high degree of crystallinity and excellent texture of the film, a relatively smooth morphology, on submicron scale, is revealed through atomic force microscopy study. The conditions for the desired textured growth with the van der Waals planes parallel to the substrate surface are reported.