Photoconductive and photovoltaic evaluation of In2O3-SnO2 multilayered thin-films deposited on silicon by reactive pulsed laser ablation

In₂O₃ and SnO₂ multilayered semiconducting thin-films have been deposited on Si substrates by reactive pulsed laser ablation (RPLA), with the aim of evaluating their photoconductive and photovoltaic properties. A photo-stimulated electrical study has been performed on the films as a function of oxygen pressure during the deposition process and compared to their microstructure. Temperature-dependent resistivity measurements have been performed to determine the charge carrier transport mechanisms. The experimental demonstration of active photogeneration has been achieved and the influence of deposition parameters on the film structural properties has been correlated to the photovoltaic performance (open-circuit voltage, short-circuit current and output power).     

Evaluation of antimicrobial abilities of Cr2N/Cu multilayered thin films

Nine kinds of nanostructured Cr₂N/Cu multilayer thin films were deposited by the bipolar asymmetry reactive pulsed DC magnetron sputtering system. The antibacterial tests of coatings with various bilayer periods (Λ) and different Cr₂N/Cu thickness ratios were performed to evaluate the bactericidal ability by E. coli, S. aureus and P. aeruginosa, respectively. The Λ value, thickness values of Cr₂N to Cu layers significantly affected the bactericidal rates. The 100% bactericidal rates were achieved when the Λ value reached 20 nm. For the same Λ = 12 nm Cr₂N/Cu multilayered coatings, the thickness ratio of Cr₂N to Cu also showed strong influence on the bactericidal rates.     

Nano-scratching and nano-machining in different environments on Cr2N/Cu multilayer thin films

Five nanostructured Cr₂N/Cu multilayer coatings were deposited by a bipolar asymmetric reactive pulsed DC magnetron sputtering system, and various bilayer periods (Λ) were achieved by controlling the holding time of Si substrates in the plasma of Cr or Cu. The hardness and elastic modulus of multilayer coatings were investigated by means of a nanoindenter. Nano-scratch and nano machining experiments on multilayered coatings were conducted using atomic force microscopy (AFM) in air and DI-water, respectively. According to the groove depth, width, and coefficient of friction (COF) obtained from nano-scratch tests, influences of scratch cycle numbers and bilayer periods on the scratchability of Cr₂N/Cu multilayered thin films were examined. It was observed that after nano-scratch experiments in air and water, the COF values and the amount of removed material increased with increasing bilayer period. After nano-machining tests in air and water, different types of the cutting chip pile-ups were observed. In this work, the surface tribological properties and machinability of Cr₂N/Cu multilayered thin films when using an AFM are discussed.     

Comparison of hydrophilic properties of TiO2 thin films prepared by sol-gel method and reactive magnetron sputtering system

This article reports on preparation, characterization and comparison of TiO₂ films prepared by sol-gel method using the titanium isopropoxide sol (TiO₂ coating sol 3%) as solvent precursor and reactive magnetron sputtering from substoichiometric TiO_2 − x targets of 50 mm in diameter. Dual magnetron supplied by dc bipolar pulsed power source was used for reactive magnetron sputtering. Depositions were performed on unheated glass substrates. Comparison of photocatalytic properties was based on measurements of hydrophilicity, i.e. evaluation of water contact angle on the film surface after UV irradiation. It is shown, that TiO₂ films prepared by the sol-gel method exhibited higher hydrophilicity in the as-deposited state but has significant deterioration of hydrophilicity during aging, compared to TiO₂ films prepared by magnetron sputtering. To explain this effect AFM, SEM and high resolution XPS measurements were performed. It is shown that the deterioration of hydrophilicity of sol-gel TiO₂ films can be suppressed if as-deposited films are exposed to the plasma of microwave oxygen discharge.     

Photocatalytic activity of pulsed laser deposited TiO2 thin films in N2, O2 and CH4

We report on pulsed laser deposition of TiO₂ films on glass substrates in oxygen, methane, nitrogen and mixture of oxygen and nitrogen atmosphere. The nitrogen incorporation into TiO₂ lattice was successfully achieved, as demonstrated by optical absorption and XPS measurements. The absorption edge of the N-doped TiO₂ films was red-shifted up to ∼ 480 nm from 360 nm in case of undoped ones.The photocatalytic activity of TiO₂ films was investigated during toxic Cr(VI) ions photoreduction to Cr(III) state in aqueous media under irradiation with visible and UV light. Under visible light irradiation, TiO₂ films deposited in nitrogen atmosphere showed the highest photocatalytic activity, whereas by UV light exposure the best results were obtained for the TiO₂ structures deposited in pure methane and oxygen atmosphere.     

Effects of substrate temperature on Bi0.8La0.2FeO3 thin films prepared by pulsed laser deposition

Bi_0.8La_0.2FeO₃ thin films on Pt/TiO₂/SiO₂/Si substrates at various substrate temperatures from 500 °C to 750 °C are prepared by pulsed laser deposition, and their microstructures and ferroelectric/magnetic properties are carefully investigated using various techniques. It is observed that the crystallographic orientation and Fe-ion valence state depend significantly on the substrate temperature, which consequently influences considerably on the ferroelectric and magnetic properties of the thin films. A considerable improvement of the ferroelectric and magnetic properties of the thin films can be achieved by optimizing the substrate temperature for deposition.     

Etch characteristics of indium zinc oxide thin films in a C2F6/Ar plasma

Dry etching of indium zinc oxide (IZO) thin films was performed using inductively coupled plasma reactive ion etching in a C₂F₆/Ar gas. The etch characteristics of IZO films were investigated as a function of gas concentration, coil rf power, dc-bias voltage to substrate, and gas pressure. As the C₂F₆ concentration was increased, the etch rate of the IZO films decreased and the degree of anisotropy in the etch profile also decreased. The etch profile was improved with increasing coil rf power and dc-bias voltage, and decreasing gas pressure. An X-ray photoelectron spectroscopy analysis confirmed the formation of InF₃ and ZnF₂ compounds on the etched surface due to the chemical reaction of IZO films with fluorine radicals. In addition, the film surfaces etched at different conditions were examined by atomic force microscopy. These results demonstrated that the etch mechanism of IZO thin films followed sputter etching with the assistance of chemical reaction.     

Ferroelectric and dielectric multilayer heterostructures based on KTa0.65Nb0.35O3 and Bi1.5-xZn0.92-yNb1.5O6.92-1.5x-y grown by pulsed laser deposition and chemical solution deposition for high frequency tunable devices

Epitaxial growth of Bi_1.5-xZn_0.92-yNb_1.5O_6.92-1.5x-y (BZN) thin films was achieved on (100)_pc LaAlO₃ substrate by pulsed laser deposition (PLD) and by chemical solution deposition based on Pechini process. Effect of bismuth and zinc deficiency on the BZN thin films obtained by PLD was discussed, in relation with the starting target composition. Dielectric permittivity and bandgap values were determined from electrical and spectroscopic ellipsometry measurements performed on randomly oriented films grown on Pt/Si substrate. BZN thin films obtained by PLD exhibit, at 100 kHz, a dielectric constant of ε_r = 203 and quite low dielectric losses of tanδ = 5 × 10^− 2. Epitaxial ferroelectric − dielectric KTa_0.65Nb_0.35O₃ (KTN) − Bi_1.5-xZn_0.92-yNb_1.5O_6.92-1.5x-y (KTN on BZN and BZN on KTN) bilayers were obtained by PLD on (100)_pc LaAlO₃ with the insertion of a suitable buffer layer of KNbO₃ in the case of KTN on BZN. Such multilayer heterostructures with an epitaxial growth control of each layer are promising candidates for potential integration in microwave devices.     

Structure and microwave dielectric properties of Bi1.5Zn1.0Nb1.5O7 thin films deposited on alumina substrates by pulsed laser deposition

Bi_1.5Zn_1.0Nb_1.5O₇ (BZN) thin films were deposited on polycrystalline alumina substrates by pulsed laser deposition at different substrate temperatures. The phase structure and surface morphology were characterized using X-ray diffractometer (XRD) and atomic force microscopy. Microwave dielectric properties were performed using split-post dielectric resonator method at spot frequencies of 10, 15 and 19 GHz, respectively. The XRD results indicate that the as-deposited Bi_1.5Zn_1.0Nb_1.5O₇ thin films deposited at 650 °C are amorphous in nature. The dielectric permittivity and loss tangent of the amorphous BZN thin films are 75.5 and 0.013 at 10 GHz, respectively. As the measure frequency increased to 19 GHz, the dielectric permittivity slightly decreases and loss tangent slightly increases. BZN thin films were crystallized after the post-annealing by a rapid thermal annealing in air for 30 min. The crystallized BZN thin films exhibit the excellent dielectric properties and frequency responses. The dielectric permittivity and loss tangent of the crystallized BZN thin films are 154 and 0.038 at 10 GHz, respectively.     

Evaluation of ion conductivity of ZrO2 thin films prepared by reactive sputtering in O2, H2O, and H2O + H2O2 mixed gas

Hydrated ZrO₂ thin films were prepared by reactive sputtering in O₂, H₂O, and H₂O + H₂O₂ mixed gas, and the effect of the sputtering atmosphere on ion conductivity of the films was investigated. The results showed that the films deposited in O₂ gas exhibited poor ion conductivity; however, the ion conductivities of the films deposited in the other two kinds of atmosphere were similar and 300-500 times higher than that of the films deposited in O₂ gas. It was indicated that the higher ion conductivity of the films was caused by lower film density and higher water content.     

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.     

Er,Yb:YVO4 waveguides deposited on amorphous SiO2 by PLD and UVPLD

In this work, erbium, and erbium and ytterbium co-doped YVO₄ waveguiding thin films were deposited on amorphous SiO₂ substrates by pulsed laser deposition (PLD) and ultraviolet-assisted pulsed laser deposition (UVPLD). The influence of the deposition technique on the structure, morphology, and optical properties of the films was investigated. At lower dopant concentrations the films prepared by UVPLD show better crystallinity and optical properties. All the samples show preferred orientation of the (001) zone axes parallel to the substrate surface. The polycrystalline samples show difference in the refractive indexes ?n (?n = n_TE − n_TM) for the TE and TM polarizations.     

Structural engineering of Ba0.5Sr0.5TiO3 epitaxial films

Ba_0.5Sr_0.5TiO₃ single-layered and multilayered films were epitaxially grown on a (001) LaAlO₃ substrate using single target and dual target pulsed laser deposition, respectively. Compared to the single-layered films, the multilayered films exhibited broader phase transition and improved thermo-stability. The microstructure of these epitaxial films was investigated using high-resolution transmission electron microscopy in details. Misfit and threading dislocations were observed in the single-layered film, while the threading dislocations were dramatically decreased and no misfit dislocations were found in the multilayered film. It is suspected that the difference in dislocation densities is responsible for the different behaviors of the permittivity with temperature.     

Photocatalytic characteristics of TiO2 nanotubes with different microstructures prepared under different pulse anodizations

In this work, different positive voltages of a pulsed waveform, time intervals and electrolyte stirring were used to prepare by anodization of pure titanium plates, a series of TiO₂ thin films based on nanotubes with different morphologies and dimensions. Electrolyte stirring results in large size TiO₂ nanotubes with uneven surface morphology and less oriented directions. The titanium plates containing the TiO₂ thin films were further annealed at 450 °C for 30 min under air. It was found that only crystalline anatase was formed under this condition. Both methylene blue degradation and antibacterial tests against Escherichia coli were performed to evaluate the photocatalytic performance of these TiO₂ films. Better methylene blue degradation ability was achieved by TiO₂ nanotubes prepared under electrolyte stirring. However, the antibacterial ability of the annealed TiO₂ nanotubes was affected by their inner diameter rather than their length. It is also concluded that the anodized TiO₂ nanotube arrays fabricated in this work are promising for photo-induced methylene blue degradation and bacteria killing applications.     

Synthesis and characterization of AgInSe2 for application in thin film solar cells

AgInSe₂ (AIS) films were grown on n-type Si substrates by the ultra-high-vacuum pulsed laser deposition technique from the AIS target synthesized from high-purity materials. The X-ray diffraction and microscopic studies of the films show that films are textured having terrace-like surface morphology. The optical studies of the films show that the optical band gap is about 1.24 eV. The electrical conductivity of AgInSe₂/Si films shows excellent diode characteristics. The photoconductivity of the AgInSe₂/Si device shows photocurrent of 2.8 mA at a bias-voltage of − 1 V with an open circuit voltage of 0.15 V. This shows that AIS films are very good absorber material for solar cell technology.     

Raman spectroscopic and X-ray diffraction investigations of epitaxial BiCrO3 thin films

Epitaxial BiCrO₃ thin films were grown onto NdGaO₃ (110)- and (LaAlO₃)_0.3-(Sr₂AlTaO₆)_0.7 (100)-oriented substrates by pulsed laser deposition. High resolution X-ray diffraction and pole figure measurements were performed in order to obtain information about the crystal structure of the films, about their quality and about the mutual crystallographic orientation between the films and the substrates. The monoclinic (111) plane of BiCrO₃ was found out to be parallel to the substrate surface. The epitaxial relation between films and substrates was verified by using polarisation dependent Raman spectroscopic experiments and theoretical calculations based on symmetry.     

Deposition of hydrophobic nano-coatings with low-pressure radio frequency CH2F2/Ar plasma processing

In an attempt to perform hydrophobic nano-coating, this investigation examined various operational parameters including in RF plasma power, system gas pressure, and CH₂F₂:Ar ratio of low-pressure plasma processing. The low-pressure plasma, generated with radio frequency power at 13.56 MHz, was fed difluoromethane (CH₂F₂)/Ar gas mixture. The surface characteristics of the plasma polymerized films were studied by static contact angle measurement (CA) and atomic force microscopy (AFM). As a result, increasing deposition of CH₂F₂ plasma polymerized films was achieved in enhanced RF plasma power input. The CH₂F₂ plasma polymerized films also were conducted in a varying system gas pressure with enhanced hydrophobic surface property. The effects of CH₂F₂/Ar plasma on the surface characteristics of the plasma polymerized films were investigated as a function of the Ar content. The super hydrophobic coating under optimized operational parameters prepared in this study obtained water contact angles greater than 150°. It was found that the maximum water contact angles (161°) was obtained at 1.5:1 (CH₂F₂: Ar) ratio. In addition, AFM analysis shows that possible ion bombardment from CH₂F₂/Ar plasma can increase surface roughness, and effectively form a hydrophobic coating on the surface of heat sensitive materials.     

Effect of high temperature post-annealing of La0.7Sr0.3MnO3 films deposited by radio frequency magnetron sputtering on SiO2/Si substrates heated at low temperature

La_0.7Sr_0.3MnO₃ thin films were deposited on SiO₂/Si substrates by RF magnetron sputtering under different oxygen gas flow rates with a sputtering power of 100 W. During deposition, the substrate was heated at 623 K. To investigate post-annealing effects, the as-deposited La_0.7Sr_0.3MnO₃ thin films were thermal-treated at 973 K for 1 h. The effects of oxygen gas flow rate and post-annealing treatment on the physical properties of the films were systematically studied. X-ray diffraction results show that the growth orientation and crystallinity of the films were greatly affected by the oxygen gas flow rate and substrate heating during deposition. The sheet resistance of the films gradually decreased with increasing oxygen gas flow rate, while the post-annealed films showed the opposite behavior. The temperature coefficient of resistance at 300 K of La_0.7Sr_0.3MnO₃ thin films deposited at an oxygen gas flow rate of 40 sccm decreased from − 2.40%/K to − 1.73%/K after post annealing. The crystalline state of the La_0.7Sr_0.3MnO₃ thin films also affected its electrical properties.     

Preparation of CuAlO2 and CuCrO2 thin films by sol-gel processing

CuAlO₂ and CuCrO₂ thin films were prepared by sol-gel processing and subsequent thermal treatment in air and inert gas atmosphere. Resistivities of 700 Ω cm and 60 Ω cm with optical transmissions of 65% and 32% were achieved respectively. The crystallization temperature of 700 °C allows the preparation of CuCrO₂ on borosilicate glass. P-type conductivity was verified by Seebeck measurements and a transparent heterostructure including p-CuCrO₂ showed rectifying behavior.     

Stress relaxation of La1/2Sr1/2MnO3 and La2/3Ca1/3MnO3 at solid oxide fuel cell interfaces

Interfacial stress is thought to have significant effects on electrical and oxygen transport properties in thin films of importance in solid oxide fuel cell applications. We investigate how in-plane biaxial stress modifies the electronic structure of La_2/3Ca_1/3MnO₃ and La_1/2Sr_1/2MnO₃ thin films prepared by pulsed laser deposition on three different substrates to vary the in-plane stress from tensile to compressive. The electronic structure was probed by X-ray absorption spectroscopy of the Mn L_2,3-edge to characterize the interfacial disruption in this region in an element-specific, site-specific manner. The compressive or tensile interfacial strain modifies the relative concentrations of La and Sr in the interfacial region in order to achieve a better lattice match to the contact material. This atomic migration generates an interfacial region dominated by a compound with a single valency for the transition metal ion, resulting in a severe barrier to oxygen and electron transport through this region.