Thickness effects of Bi3.5Nd0.5Ti3O12 buffer layers on structure and electrical properties of BiFeO3 films

BiFeO₃ (BFO) thin films deposited on various thicknesses (0, 40, 80, and 160 nm) of Bi_3.5Nd_0.5Ti₃O₁₂ (BNT) buffer layers were fabricated on indium tin oxide (ITO)/Si substrates using a metal organic decomposition process. X-ray diffraction (XRD) measurements reveal that the BNT buffer layers can favor the growth of (110)-oriented grains in the BFO films. Well-saturated P–E hysteresis loops can be obtained in BFO films with BNT buffer layers due to their lower leakage current densities compared with that in BFO film deposited directly on ITO/Si substrate. A remanent polarization (P _r) as large as 70.2 ± 2 μC/cm² can be achieved in BFO film with 40-nm-thick BNT buffer layer. Further increase of the buffer layer thickness results in the degradation of the rectangularity of P–E hysteresis loops, reduction of the P _r value, as well as deterioration of the charge-retaining ability for the double-layered films.     

X-ray diffraction analysis of 10,12-pentacosadiynoic acid Langmuir-Blodgett films during polymerization

10,12-pentacosadiynoic acid (PCDA) LB films were deposited on two different subphases of CdCl₂ and TbCl₃ respectively and polymerized under UV-irradiation. It is found that the different subphase influenced the molecular packing, and in turn, influenced the polymerization behavior in the LB films. The molecular arrangement structures of unpolymerized and photopolymerized LB films were investigated by low angle X-ray diffraction. The periodic spacing of molecules in the LB films and the inclination angle of molecules on the substrate were calculated from the X-ray diffraction profiles. The unpolymerized PCDA LB film had one set of diffraction peaks, however, two sets of diffraction peaks were clearly observed in partly-polymerized PCDA LB films deposited on CdCl₂ subphase and reduced to one set of diffraction peaks corresponding to the polymerized LB films. On the other hand, the PCDA LB films deposited on TbCl₃ subphase had only one set of diffraction peaks throughout. This is interpreted to correspond to different mechanisms of chain propagation, i.e., heterogeneous chain propagation for the PCDA LB film deposited on CdCl₂ subphase and homogeneous polymerization for the LB film deposited on TbCl₃ subphase. A molecular arrangement model in LB film was employed to explain the phenomenon of the even-odd intensity oscillation qualitatively.     

Effect of SiO2 buffer layer thickness on the properties of ITO/Cu/ITO multilayer films deposited on polyethylene terephthalate substrates

Transparent conductive ITO/Cu/ITO films were deposited on polyethylene terephthalate (PET) substrates with a SiO₂ buffer layer by magnetron sputtering using three cathodes at room temperature. The effect of the SiO₂ buffer layer thickness on the electrical and optical properties of ITO/Cu/ITO films was investigated. The ITO/Cu/ITO film deposited on the 40 nm thick SiO₂ buffer layer exhibits a sheet resistance of 143Ω/sq and transmittance of 65% at 550 nm wavelength. Highly transparent ITO/Cu/ITO films with a transmittance of 80% and a sheet resistance of 98.7Ω/sq have been obtained by applying −60 V substrate bias.     

Effect of SiO2 buffer layer thickness on the properties of ITO/Cu/ITO multilayer films deposited on polyethylene terephthalate substrates

Transparent conductive ITO/Cu/ITO films were deposited on polyethylene terephthalate (PET) substrates with a SiO₂ buffer layer by magnetron sputtering using three cathodes at room temperature. The effect of the SiO₂ buffer layer thickness on the electrical and optical properties of ITO/Cu/ITO films was investigated. The ITO/Cu/ITO film deposited on the 40 nm thick SiO₂ buffer layer exhibits a sheet resistance of 143Ω/sq and transmittance of 65% at 550 nm wavelength. Highly transparent ITO/Cu/ITO films with a transmittance of 80% and a sheet resistance of 98.7Ω/sq have been obtained by applying −60 V substrate bias.     

ITO substrate resistivity effect on the properties of CuInSe<Subscript>2</Subscript> deposited using two-electrode system

The purpose of this work is to deposit the CuInSe₂ films on the ITO substrate by electrodeposition technique using a simplified two electrodes system and to investigate the effect of ITO sheet resistance on the fundamental properties of the resulting films. The as deposited films were annealed under argon atmosphere at 300 °C during 30 min. The structural, morphological and electrical properties were characterized respectively by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrical resistivity measurements. The optical band gap of samples was estimated using the optical absorption technique. After annealing, the XRD spectra show diffraction peaks corresponding to the single-phase chalcopyrite CuInSe₂ with (112) as main reflection. The SEM images reveal a homogeneous surface and the estimated grain size was calculated from Scherrer’s Equation with (112) peak lay in the range of 165–272 Å. The band gap, E _g, is a decreasing function with the ITO sheet resistance.     

Surface morphology,structural and electrical properties of RF-sputtered ITO thin films on Si substrates

Series of indium tin oxide (ITO) thin films were deposited onto Si(100) substrate by RF sputtering. The film thickness ranges from 61 to 768 nm. X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) experiments were performed to study the structure and the surface morphology of these films. The electrical properties were obtained by a Hall effect measurement system; the electrical resistivity \(\rho \), the carrier concentration n and the mobility \(\mu \) were measured. Annealing experiments were carried out in the air at \(400{^{\circ }}\hbox {C}\) for 60 min. The different physical parameters were investigated as a function of thickness before and after annealing. The effects of power and deposition rate were also addressed. We noted that the behaviour of some parameters with thickness is different before and after annealing. All these results are discussed and correlated in this article. Also, the results of the present ITO/Si system were compared to those of the ITO/glass, we have previously published.     

Structural,electrical, optical properties and reliability of ultra-thin tin doped indium oxide films for touch panels

Ultra-thin ITO films with thickness of 4–56 nm were deposited on glass by dc magnetron sputtering using 5 wt% SnO₂ doped ITO target. The effect of film thickness on the structural, electrical, optical properties and reliability was investigated for its application to touch panels. The 4 nm thick ITO film shows amorphous structure and other films present polycrystalline structure and the (222) preferred orientation. The ultra-thin ITO films show smooth surface with low Ra surface roughness smaller than 1 nm. The sheet resistance and visible transmittance of the ITO films decrease with the increase in film thickness. The 4 nm thick ITO film shows the highest resistivity (3.08 × 10^?3 Ω cm) with low carrier density and Hall mobility, and other films have excellent conductivity (<4.0 × 10^?4 Ω cm). The ITO films show high transmittance (>85 %) in visible light range and do not generate interference ripples between film and substrate interface. The ITO films with thickness of 18–56 nm show stable reliability under high temperature, high temperature & high humidity and alkaline environmental conditions. The only electrical degradation corresponds to the increase of sheet resistance in the ITO films with thickness of 4–12 nm.     

Influence of Ag thickness on electrical, optical and structural properties of nanocrystalline MoO3/Ag/ITO multilayer for optoelectronic applications

In this study, MoO₃/Ag/ITO/glass (MAI) nano-multilayer films were deposited by the thermal evaporation technique and then were annealed in air atmosphere at 200 °C for 1 h. The effects of Ag layer thickness on electrical, optical and structural properties of the MoO₃(45 nm)/Ag(5-20 nm)/ITO(45 nm)/glass nano-multilayer films were investigated. The sheet resistance decreased rapidly with increasing Ag thickness. Above a thickness of 10 nm, the sheet resistances became somewhat saturated to a value of 3(Ω/□). The highest transparency over the visible wavelength region of spectrum (85%) was obtained for 10 nm Ag layer thickness. Carrier mobility, carrier concentrations, transmittance and reflectance of the layers were measured. The allowed direct band-gap for an Ag thickness range 5-20 nm was estimated to be in the range 3.58-3.71 eV. The XRD pattern showed that the films were polycrystalline. X-ray diffraction has shown that Ag layer has a (111) predominant orientation when deposited. The figure of merit was calculated for MAI multilayer films. It has been found that the Ag layer thickness is a very important factor in controlling the electrical and optical properties of MAI multilayer films. The optimum thickness of the Ag layer for these films was determined. The results exhibit that the MAI transparent electrode is a good structure for use as the anode of optoelectronic devices.     

Crystalline β-C3N4 synthesized by MPCVD

Carbon nitride films were grown on Si and Pt substrates by microwave plasma chemical vapor deposition (MPCVD) method. Scanning electron microscope (SEM) observations show that the films deposited on Si substrates consisted of densely populated hexagonal crystalline rods. Energy dispersive X-ray (EDX) analyses show that N/C ratios of the rods were in the range of 1.0 to 2.0 depending on deposition condition. X-ray diffraction experiments show that the films consisted of crystalline phase -C₃N₄. Comparison with films grown on Pt substrate show that the main X-ray diffraction peaks of -C₃N₄ are existed in films deposited on both substrate. XPS study showed that carbon and nitride atoms are covalent bounded to each other. IR results show that the film is predominantly C-N bonded. Raman measurement showed characteristic peaks of -C₃N₄ in the low wave number region. Temperature dependent growth experiments show that the amount of Si₃N₄ in the films grown on Si substrates can be significantly reduced to negligible amount by controlling the substrate temperature.     

Spectrographic ellipsometry study of a liquid crystal display substrate consisting of thin films of SiO2, polyimide and indium tin oxide on glass

Variable angle spectrometric ellipsometry at room temperature is used to determine thin film parameters of substrates used in liquid crystal displays. These substrates consist of sequential thin films of polyimide (PI), on indium tin oxide (ITO),on SiO₂ deposited on a glass backing approximately 1.1 mm thick. These films were studied by sequentially examining more complex systems of films (SiO₂, SiO₂-ITO, SiO₂-ITO-PI). The SiO₂ layer appears to be optically uniform and flat. The ITO film is difficult to characterize. When this surface film's lower surface is SiO₂ and upper surface is an air-ITO-interface it is found that including surface roughness and variation of the optical properties with ITO thickness in the model improved the fit; suggesting that both phenomena exist in the ITO films. However, the surface roughness and graded nature of optical properties could be not determinable by ellipsometry when the ITO is coated with a polyimide film. The PI films are ellipsometrically flat and over the wavelength range from 500 to 1400 nm the real refractive index of polyimide films varying in thickness between 25 and 80 nm is well modeled by a two-term Cauchy model with no absorption. The ellipsometric thickness of the ITO layer is the same as the profilometric thickness; however, the ellipsometric thickness of the polyimide layers is roughly 10 nm larger than that obtained from the profilometer. These final observations are consistent with the literature.     

Structural, electrical and optical properties of ITO films with a thin TiO2 seed layer prepared by RF magnetron sputtering

Tin-doped indium oxide (ITO) films were deposited by RF magnetron sputtering on TiO₂-coated glass substrates (the TiO₂ layer is usually called seed layer). The properties of ITO films prepared at a substrate temperature of 300 °C on bare and TiO₂-coated glass substrates have been analyzed by using X-ray diffraction, atomic force microscope, optical and electrical measurements. Comparing with single layer ITO film, the ITO film with a TiO₂ seed layer of 2 nm has a remarkable 41.2% decrease in resistivity and similar optical transmittance. The glass/TiO₂ (2 nm)/ITO film achieved shows a resistivity of 3.37 × 10⁻⁴ Ω cm and an average transmittance of 93.1% in the visible range. The glass/TiO₂ may be a better substrate compared with bare glass for depositing high quality ITO films.     

ITO deposited by pyrosol for photovoltaic applications

The goal of this work is to investigate morphology, electrical and optical properties of indium-tin-oxide (ITO) deposited by pyrosol on glass and Si substrates at different temperatures and to implement such layers for the processing of Si-based solar cells. The influence of the methanol/H₂O ratio on general properties of ITO was investigated. Atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission spectra, ellipsometry and resistivity measurements were used for the analysis. It is shown that properties of ITO layers depend dramatically on the substrate used. It is shown that the resistivity of ITO layers deposited on a glass substrate is higher up to 2.5 times, compared to that of ITO layers deposited on a Si substrate at the same conditions, but in both cases decreases if the deposition temperature increases. Moreover, ITO layers deposited on a glass substrate are more flat and their refractive indexes are always lower for all deposition temperatures. An increase of the H₂O concentration in a film-forming solution leads to a decrease of the ITO film resistivity and to a slight increase of the roughness. An application of pyrosol deposited ITO films as the top transparent electrodes for the (p⁺nn⁺)Si and heterojunction ITO/n-Si solar cells is demonstrated.     

Evidence of hexagonal diamond in plasma-deposited carbon films

Hexagonal diamond grains of 30 nm diameter together with graphite and SiC are seen in predominantly amorphous carbon films deposited at low temperature on Si substrates from a CH₄ plasma vapour source. The different crystalline phases are identified by grazing-angle X-ray diffraction which allows for substrate rotation and tilting to enable the 2 peaks to be correlated with the angular displacements of specific planes. Electron energy-loss spectroscopy shows the chemical composition of the films to be predominantly carbon with traces of oxygen. Raman spectroscopy shows the peaks to be associated with amorphous carbon and graphite, together with a peak at 1170 cm^–1 which is attributed to microcrystalline hexagonal diamond.     

Effect of substrate temperature and deposited thickness on the formation of iron silicide prepared by ion beam sputter deposition

Ion beam sputter deposition (IBSD) method was employed to find optimum conditions for the formation of epitaxial β-FeSi₂ films on Si(100) substrate. It was found that crystal structure of the films as determined by X-ray diffraction (XRD) analysis is dependent on the substrate temperature as well as on the deposited thickness of sputtered Fe. The film with best crystal properties was obtained either at 873 K with the deposited Fe thickness of 15 nm, or at 973 K with the deposited Fe thickness of 30 nm. The obtained results indicate the importance of Fe and/or Si diffusion in determining the crystal properties of β-FeSi₂ film.     

Nanodomain and interface structure in epitaxial BaTiO<Subscript>3</Subscript> thin films on MgO deposited by magnetron sputtering

High epitaxial quality BaTiO₃ films were deposited on the MgO (001) substrate using RF magnetron sputtering at 800 °C by manipulating processing parameters. The BaTiO₃ films have a ~200 nm thickness with a very low surface roughness but a rough interface structure with respect to the substrate. The epitaxial BaTiO₃ films have a tetragonal crystal structure (a = 4.02 Å and c = 4.11 Å) with a tetragonality (c/a) of 1.02. The c-axis of the film is parallel to the growth direction as characterized by X-ray diffraction, electron diffraction, and high-resolution transmission electron microscopy. The orientation relationship between the film and the MgO is (001)_BTO//(001)_MgO and 〈100〉_BTO//〈100〉_MgO. Epitaxial nanodomains were formed in the film with a size ranging from 3 to 20 nm. The formation of the nanodomains is associated with the rough film/substrate interface due to the modification of the substrate surface characteristics (steps, terraces, and kinks) during the process. The two-dimensional interface structure between the film and the substrate was studied and its influence on the film microstructure is discussed.     

Fabrication of transparent conductive films with a sandwich structure composed of ITO/Cu/ITO

New transparent conductive films that had a sandwich structure composed of ITO/Cu/ITO multilayer films were prepared by a conventional RF and DC magnetron sputtering process on a polycarbonate substrate without intentional substrate heating. The thickness of each layer in the ITO/Cu/ITO films was kept constant at 50 nm/5 nm/45 nm. The optoelectrical and structural properties of the films were compared with conventional ITO single-layer films and ITO/Cu/ITO multilayered films. Although both films had identical thickness, 100 nm, the ITO/Cu/ITO films showed a lower resistivity, 3.5 × 10⁻⁴ Ω cm. In optical transmittance measurements, however, the ITO single-layer films showed a higher transmittance of 74% in the wavelength range of 300-800 nm. XRD spectra showed that both the ITO and ITO/Cu/ITO films were amorphous. The figure of merit, φ_TC, reached a maximum of 5.2 × 10⁻⁴ Ω⁻¹ for the ITO/Cu/ITO films, which was higher than the φ_TC of the ITO films (1.6 × 10⁻⁴ Ω⁻¹). The φ_TC results suggested that ITO/Cu/ITO films had better optoelectrical properties than conventional ITO single-layer films.     

Quality enhancement of AZO thin films at various thicknesses by introducing ITO buffer layer

Due to the simultaneously superior optical transmittance and low electrical resistivity, transparent conductive electrodes play a significant role in semiconductor electronics. To enhance the electrical properties of these films, one approach is thickness increment which degrades the optical properties. However, a preferred way to optimize both electrical and optical properties of these layers is to introduce a buffer layer. In this work, the effects of buffer layer and film thickness on the structural, electrical, optical and morphological properties of AZO thin films are investigated. Al-doped zinc oxide (AZO) is prepared at various thicknesses of 100 to 300 nm on the bare and 100 nm-thick indium tin oxide (ITO) coated glass substrates by radio frequency sputtering. Results demonstrate that by introducing ITO as a buffer layer, the average values of sheet resistance and strain within the film are decreased (about 76 and 3.3 times lower than films deposited on bare glasses), respectively. Furthermore, the average transmittance of ITO/AZO bilayer is improved nearly 10% regarding single AZO thin film. This indicates that bilayer thin films show better physical properties rather than conventional monolayer thin films. As the AZO film thickness increases, the interplanar spacing, d₍₀₀₂₎, strain within the film and compressive stress of the film in the hexagonal lattice, decreases indicating the higher yield of AZO crystal. Moreover, with the growth in film thickness, carrier concentration and optical band gap (E_g) of AZO film are increased from 4.62?×?10¹⁹ to 8.21?×?10¹⁹ cm^?3 and from 3.55 to 3.62 eV, respectively due to the Burstein-Moss (BM) effect. The refractive index of AZO thin film is obtained in the range of 2.24–2.26. With the presence of ITO buffer layer, the AZO thin film exhibits a resistivity as low as 6?×?10^?4 Ω cm, a sheet resistance of 15 Ω/sq and a high figure of merit (FOM) of 1.19?×?10⁴ (Ω cm)^?1 at a film thickness of 300 nm. As a result, the quality of AZO thin films deposited on ITO buffer layer is found to be superior regarding those grown on a bare glass substrate. This study has been performed over these two substrates because of their significant usage in the organic light emitting diodes and photovoltaic applications as an enhanced carrier injecting electrodes.     

Near infrared quazi-omnidirectional reflector in chalcogenide glasses

The quazi-omnidirectional reflector was designed as a planar quarter wave stack consisting of the alternating amorphous chalcogenide Ge₂₅S₇₅ and Sb₄₀Se₆₀ films. Photonic bandgap calculation of the intended reflector predicted 240 nm omnidirectional and 450 nm normal incidence first-order bandgaps centred near 1.55 μm for appropriate values of the index of refraction and thickness of the films. The TEM and HR-TEM images of the prepared 7.5 pairs reflector verified good periodicity, smooth interface and amorphous structure of the chalcogenide films deposited by thermal and flash evaporation, respectively. The optical reflectivity measurements revealed 98.8% normal incidence stopband of the reflector at 1.55 μm. We also report the ellipsometry study of the prepared reflector. The TEM and ellipsometry studies confirmed the thickness variation of prepared individual layers to be ±7 and ±9 nm, respectively, compared to theoretical predictions.     

Thickness dependence of H2 gas sensor in amorphous SnQx films prepared by ion-beam sputtering

Amorphous SnO_x films were deposited by ion-beam sputtering on sintered alumina substrates. Amorphous film sensors were prepared by annealing the films at 300° C for 2 h in air. The thickness dependence of resistivity and hydrogen gas sensitivity were measured at 150° C over the thickness range 1 to 700 nm. A resistivity maximum was observed in ultrathin films. Resistivity increased by three orders of magnitude with increasing film thickness from 0.9 to 7.4 nm and then decreased by five orders of magnitude from 7.4 to 35 nm. Ultrathin film sensors showed sensitivity maxima around a thickness of 10 nm. Sensitivity and resistivity of ultrathin films were significantly influenced by the thermal expansion coefficient and the surface state of the substrate.     

Characterization of strain relaxation of (0 0 1) oriented SrTiO3 thin films grown on LaAIO3 (1 1 0) by means of reciprocal space mapping using x-ray diffraction

The strain relaxation of SrTiO₃ r.f. magnetron sputter-deposited thin films on LaAlO₃ substrates have been studied by x-ray diffraction mapping. An investigation of different x-ray optics shows that a, so called, hybrid mirror monochromator in combination with a triple-bounce analyser crystal provides very good conditions for characterization of thin distorted films grown epitaxially onto substrates with high structural order. The in-plane and out-of-plane lattice parameters of the SrTiO₃ films could accurately be determined since the x-ray diffraction optics enabled the splitting of substrate peaks, caused by the twinning in the rhombohedral LaAlO₃ to be resolved and, provided film peak intensities are high enough, to precisely establish their positions. Films in the thickness range 9.3–144.0 nm were found to be partially relaxed, having a tetragonal distortion due to in-plane strain that was found to decrease with increasing film thickness, approaching an undistorted SrTiO₃ lattice parameter of 0.3927 nm. This value is 0.6% larger than the bulk indicating that the compositions of the films were slightly non-stoichiometric. The strain relaxation of the grown films was found to follow the general trend of a predicted strain–thickness relation based on energy density balance considerations regarding misfit dislocations and lattice strain.