Third-order optical nonlinear absorption in Bi1.95La1.05TiNbO9 thin films

Single phase Bi_1.95La_1.05TiNbO₉ (LBTN-1.05) thin films with a layered aurivillius structure have been fabricated on fused silica substrates by pulsed laser deposition at 700 °C. The X-ray diffraction pattern revealed that the films are single-phase aurivillius. The band gap, linear refractive index and linear absorption coefficient were obtained by optical transmittance measurements. The film exhibits a high transmittance (> 70%) in visible-infrared region and the dispersion relation of the refractive index vs. wavelength follows the single electronic oscillator model. The nonlinear optical absorption property of the film was determined by the single beam Z-scan method using 800 nm with a duration of 100 fs. A large positive nonlinear absorption coefficient β = 5.95 × 10^− 8 m/W was determined experimentally. The results showed that the LBTN-1.05 is a promising material for applications in absorbing-type optical devices.     

The third-order optical nonlinearity of Bi3.25La0.75Ti3O12 ferroelectric thin film on quartz

Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin film was prepared on quartz substrates using chemical solution deposition. The sign and magnitude of both real and imaginary parts of third-order nonlinear susceptibility χ⁽³⁾ of the BLT thin film have been determined by the Z-scan technique performed at 800 nm with a femtosecond laser. The nonlinear refractive index coefficient γ and the nonlinear absorption coefficient β of the BLT thin film are − 1.915 × 10^− 12 cm² / W and − 6.764 × 10^− 8 m/W, respectively, the real part and imaginary part of the third-order nonlinear susceptibility χ⁽³⁾ of the BLT thin film are − 5.81 × 10^− 18 m² / V² and − 1.31 × 10^− 18 m² / V², respectively. Both the real and the imaginary parts of the third-order nonlinear susceptibility χ⁽³⁾ contribute to the nonlinearity of the film. These experimental results show that BLT thin film is a promising material for applications in nonlinear optical devices.     

Large third-order optical nonlinearity of SrBi2Nb2O9 thin films fabricated by pulsed laser deposition

SrBi₂Nb₂O₉ (SBN) thin films with a single phase of layered perovskite structure have been fabricated on fused quartz substrates at room temperature by pulsed laser deposition. The XRD and AFM analysis indicated that the films had better crystallinity, less rough surface morphology, and larger grain size with increasing oxygen pressure. The nonlinear optical properties of the samples were determined using a single beam Z-scan technique at a laser wavelength of 532 nm with laser duration of 25 ps. The real and imaginary parts of the third-order nonlinear optical susceptibility χ⁽³⁾ of the films were measured to be 3.18 × 10^− 8 esu and 5.94 × 10^− 9 esu, respectively.     

Large nonlinear optical response of a Bi1.5Zn1.0Nb1.5O7 thin film fabricated by pulsed laser deposition

The Bi_1.5Zn_1.0Nb_1.5O₇ (BZN) thin film has been fabricated on MgO (001) substrate by pulsed laser deposition. The nonlinear optical properties of the BZN film were investigated using Z-scan technique at a wavelength of 532 nm with 25 ps pulse duration. The two-photon absorption coefficient and the nonlinear refractive index of the BZN film were obtained to be 4.2 × 10^− 6 cm/W and 1.6 × 10^− 10 cm²/W respectively, which are comparable with those of some representative nonlinear optical materials. The large and fast response optical nonlinearities indicated that the BZN film is a promising candidate for future photonics devices.     

Nonlinear optical properties of laser deposited CuO thin films

In this work we investigate the third-order optical nonlinearities in CuO films by Z-scan method using a femtosecond laser (800 nm, 50 fs, 200 Hz). Single-phase CuO thin films have been obtained using pulsed laser deposition technique. The structure properties, surface image, optical transmittance and reflectance of the films were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and UV-vis spectroscopy. The Z-scan results show that laser-deposited CuO films exhibit large nonlinear refractive coefficient, n₂ = − 3.96 × 10^− 17 m²/W, and nonlinear absorption coefficient, β = − 1.69 × 10^− 10 m/W, respectively.     

Nanocomposite thin films of Ga5Sb10Ge25Se60 chalcogenide glass for optical limiting applications

We report a low-cost, scalable method to fabricate optical grade composite thin films for nonlinear optical applications. The transmission and reflection spectra of prepared Ga₅Sb₁₀Ge₂₅Se₆₀/PVA composite films were investigated. Optical band gap of the thin films were calculated using Tauc’s extrapolation method. The band gap of the nanocomposite thin films were found to be tunable depending on the grain size of the films. Nonlinear optical characterization of samples were studied by the Z-scan technique using an Nd:YAG laser (532 nm, 7 ns, 10 Hz). Sequential Z-scan traces were made in four regimes of intensity for films with three different grain sizes. The Z-scan spectra reveal a strong nonlinear absorption depending on the grain size of the films suggesting that the new materials are promising candidates for the development of nonlinear optical devices and are extremely perspective as optical limiters of intense short pulse radiation.     

Third order optical susceptibilities of the Cu2O thin film

By performing Z-scan method with a femtosecond laser (800 nm, 50 fs, 1 kHz), we investigated the third-order optical nonlinearities of a cuprous oxide (Cu₂O) film. Single-phase Cu₂O film deposited on a quartz substrate was obtained using the pulsed laser deposition technique. The structure properties, surface morphology and optical transmission spectrum were characterized by X-ray diffraction, scanning electron microscopy and double beam spectrophotometer, respectively. The Z-scan results show that the Cu₂O film exhibits large nonlinear refractive index, n₂ = 3 × 10^− 3 cm²/GW, while the two-photon absorption coefficient, α₂ = 40 cm/GW, is relatively small. It implies that the Cu₂O film is a promising candidate for nonlinear photonic devices.     

The optical properties of Bi3.25La0.75Ti3O12 thin films with different thickness prepared by chemical solution deposition

Bi_3.25La_0.75Ti₃O₁₂(BiLT) thin films with different thickness were successfully deposited onto fused quartz by chemical solution deposition. X-ray diffraction analysis shows that BiLT thin films are polycrystalline with (0 0 2)-preferred orientation. The dispersion of refractive indices of the BiLT thin films was investigated by the optical transmittance spectrum. The optical band gap energy was estimated from the graph of (hνα)² versus hν. The results show that the refractive index and band-gap energy of the BiLT thin films decrease with the films thickness.     

Sb2S3:C/CdS p-n junction by laser irradiation

In this paper, we report laser irradiated carbon doping of Sb₂S₃ thin films and formation of a p-n junction photovoltaic structure using these films. A very thin carbon layer was evaporated on to chemical bath deposited Sb₂S₃ thin films of approximately 0.5 μm in thickness. Sb₂S₃ thin films were prepared from a solution containing SbCl₃ and Na₂S₂O₃ at 27 °C for 5 h and the films obtained were highly resistive. These C/Sb₂S₃ thin films were irradiated by an expanded laser beam of diameter approximately 0.5 cm (5 W power, 532 nm Verdi laser), for 2 min at ambient atmosphere. Morphology and composition of these films were analyzed. These films showed p-type conductivity due to carbon diffusion (Sb₂ S₃:C) by the thermal energy generated by the absorption of laser radiation. In addition, these thin films were incorporated in a photovoltaic structure Ag/Sb₂S₃:C/CdS/ITO/Glass. For this, CdS thin film of 50 nm in thickness was deposited on a commercially available ITO coated glass substrate from a chemical bath containing CdCl₂, sodium citrate, NH₄OH and thiourea at 70 °C. On the CdS film, Sb₂S₃/C layers were deposited. This multilayer structure was subjected to the laser irradiation, C/Sb₂S₃ side facing the beam. The p-n junction formed by p-Sb₂S₃:C and n-type CdS showed V_oc = 500 mV and J_sc = 0.5 mA/cm² under illumination by a tungsten halogen lamp. This work opens up a new method to produce solar cell structures by laser assisted material processing.     

Growth and characterization of nitrogen-doped TiO2 thin films prepared by reactive pulsed laser deposition

Nitrogen-doped titanium dioxide (TiO₂) thin films were grown on (001) SiO₂ substrates by reactive pulsed laser deposition. A KrF* excimer laser source (λ = 248 nm, τ_FWHM ≅ 10 ns, ν = 10 Hz) was used for the irradiations of pressed powder targets composed by both anatase and rutile phase TiO₂. The experiments were performed in a controlled reactive atmosphere consisting of oxygen or mixtures of oxygen and nitrogen gases. The obtained thin film crystal structure was investigated by X-ray diffraction, while their chemical composition as well as chemical bonding states between the elements were studied by X-ray photoelectron spectroscopy. An interrelation was found between nitrogen concentration, crystalline structure, bonding states between the elements, and the formation of titanium oxinitride compounds. Moreover, as a result of the nitrogen incorporation in the films a continuous red-shift of the optical absorption edge accompanied by absorption in the visible spectral range between 400 and 500 nm wavelength was observed.     

Effect of lattice matching on microstructure and electrical conductivity of epitaxial ARuO3 (A = Sr, Ca and Ba) thin films prepared on (001) LaAlO3 substrates by laser ablation

(001) SrRuO₃ (SRO), (001) CaRuO₃ (CRO) and (205) BaRuO₃ (BRO) thin films were epitaxially grown on (001) LaAlO₃ substrates by laser ablation, and the effect of lattice matching on the microstructure and electrical conductivity was investigated. (001) SRO and (001) CRO thin films had a terrace with orthogonal step structure, whereas (205) BRO thin film had an orthogonal structure with tetragonal grains. Epitaxial thin films showed metallic conduction, and the (001) CRO thin films exhibited the highest electrical conductivity, i.e. 1.5 × 10⁵ S m^− 1, among the (001) SRO, (001) CRO and (205) BRO thin films. The smaller misfit between thin film and substrate could be associated with the higher electrical conductivity.     

Synthesis and electrical properties of cubic NaxWO3 thin films across the metal-insulator transition

Highly oriented (1 0 0) Na_xWO₃ thin films were fabricated in the composition range 0.1 ≤ x ≤ 0.46 by pulsed laser deposition technique. The films showed transition from metallic to insulating behaviour at a critical composition between x = 0.15 and 0.2. The pseudo-cubic symmetry of Na_xWO₃ thin films across the transition region is desirable for understanding the composition controlled metal-insulator transition in the absence of any structural phase transformation. The electrical transport properties exhibited by these films across the transition regime were investigated. While the resistivity varied as T² at low temperatures in the metallic regime, a variable range hopping conduction was observed for the insulating samples. For metallic compositions, a non-linear dependence of resistivity in temperature was also observed from 300 to 7 K, whose exponent varied with the composition of the film.     

Pb(Zr0.52Ti0.48)O3/TiNi multilayered heterostructures on Si substrates for smart systems

Ferroelectric/shape memory alloy thin film multilayered heterostructures possess both sensing and actuating functions and are considered to be smart. In this article, Pb(Zr_0.52Ti_0.48)O₃ (PZT) ferroelectric thin films and Ti-riched TiNi shape memory alloy thin films have been deposited on Si and SiO₂/Si substrates in the 400-600 °C temperature range by pulsed laser deposition technique. Deposition processing, microstructure and surface morphology of these films are described. The TiNi films deposited at 500 °C had an austenitic B2 structure with preferred (110) orientation. The surfaces of the films were very smooth with the root-mean-square roughness on a unit cell level. The structure of the TiNi films had a significant influence on that of the subsequently deposited PZT films. The single B2 austenite phase of the TiNi favored the growth of perovskite PZT films. The PZT/TiNi heterostructures with the PZT and TiNi films respectively deposited at 600 and 500 °C exhibited a polarization-electric field hysteresis behavior with a leakage current of about 2 × 10^− 6 A/cm².     

The effect of strain on nonlinear temperature dependence of resistivity in SrMoO3 and SrMoO3−xNx films

Highly oriented SrMoO₃ thin films have been fabricated by pulsed laser deposition of SrMoO₄ in hydrogen. The films are found to grow along the (1 0 0) direction on LaAlO₃ (1 0 0) and SrTiO₃ (1 0 0) substrates. The method has been extended for the fabrication of oxynitride thin films, using ammonia as the reducing medium. The resistivity measurements show nonlinear temperature dependent (Tⁿ) behaviour in the temperature interval of 10-300 K. The conduction mechanism is largely affected by the strain due to the substrate lattice. A combination of T and T² dependence of resistivity on temperature is observed for films having lesser lattice mismatch with the substrate. The X-ray photoelectron spectroscopic studies confirm the formation of SrMoO₃ and SrMoO_3−xN_x films.     

Improved dielectric and ferroelectric properties in Ti-doped BiFeO3-PbTiO3 thin films prepared by pulsed laser deposition

Ti-modified thin films of multiferroic 0.72Bi(Fe_1 − xTi_x)O₃-0.28PbTiO₃ (BFPT, x = 0 and 0.02) solid solution were prepared by pulsed laser deposition. The BFPT (x = 0 and 0.02) films possess a tetragonal structure with highly preferential (001) orientation. The effects of the ionic substitution on the properties of BFPT (x = 0 and 0.02) films have been investigated. The leakage current of the BFPT (x = 0.02) thin film is significantly reduced, and the dielectric and ferroelectric properties greatly improved by the aliovalent ionic substitution of Ti⁴⁺ for Fe³⁺. The BFPT (x = 0.02) thin film exhibits a reasonably high remnant polarization P_r with 2P_r up to 90 μC/cm² at 312 kV/cm and a switchable polarization up to 92 μC/cm² at 417 kV/cm.     

Sputter-epitaxy and electric properties of multiferroic Bim + 1Fem-3Ti3O3m + 3 thin films

Growth conditions suitable for sputter-epitaxy of Bi_m + 1Fe_m-3Ti₃O_3m + 3 (BFTO) thin films with layered structure have been investigated. The amount of oxygen during deposition was found to be specifically essential for obtaining a good-quality thin film of BFTO with a large m. The (001) epitaxial thin films of BFTO with m of nearly 10 which is expected to retain magnetic order up to room temperature have been successfully grown on (001) SrTiO₃ substrates under the determined optimum condition. The film exhibited leakage current as low as order of 10⁻²-10⁻¹ A/m² limited by Schottky emission at the interfaces between the electrodes and the film. In addition, the film showed a ferroelectric polarization curve with Pr = 6 μC/cm² for applied field of 35 MV/m at room temperature though the curve was unsaturated. These indicate that the BFTO (m = 10) thin films are promising as multiferroics at room temperature.     

Laser annealing of Pb(Zr0.52Ti0.48)O3 thin films for the pyroelectric detectors

Lead zirconate titanate (Pb(Zr_0.52Ti_0.48)O₃, PZT) thin films fabricated by magnetron sputtering technique on the Pt/Ti/SiO₂/Si substrates at room temperature, were annealed by means of CO₂ laser with resulting average substrate temperature below 500 °C. The crystal structure, surface morphology and pyroelectric properties of the PZT films before and after annealing were investigated by X-ray diffraction, atomic force microscopy, and pyroelectric measurements. The results show that the annealed PZT thin film with a laser energy density of 490 W/cm² for 25 s has a typical perovskite phase, uniform crystalline particles with a size of about 90 nm, and a high pyroelectric coefficient with 1.15 × 10^− 8 Ccm^− 2 K^− 1.     

Optical properties of TiO2 thin films deposited on polycarbonate by ion beam assisted evaporation

TiO₂ thin films were deposited on polycarbonate (PC) substrate by ion beam assisted evaporation. The grain size increased with the ion anode voltage and film thickness. The TiO₂ thin films had an amorphous structure. Moiré deflectometry was used to measure the nonlinear refractive indices of TiO₂ thin films on PC substrates. The nonlinear refractive index was measured to be of the order of 10^− 8 cm² W^− 1 and a change in refractive index was of the order of 10^− 5. Dense TiO₂ films exhibited high linear refractive indices, red-shift of the optical absorbance, and absorbance in the near-IR region.     

Third-order optical nonlinearities in anatase and rutile TiO2 thin films

Titanium dioxide (TiO₂) films have been fabricated on fused quartz and Si(001) substrates by pulsed laser deposition technique and the single-phase anatase and rutile films were obtained under the optimal conditions. The surface images and optical transmission spectra were investigated by scanning electron microscopy and double beam spectrophotometer, respectively. The values of optical band-gap and linear refractive index of the anatase and rutile films were determined. The optical nonlinearities of the films were measured by Z-scan method using a femtosecond laser (50 fs) at the wavelength of 800 nm. Through the open-aperture and closed-aperture Z-scan measurements, the real and imaginary parts of the third-order nonlinear optical susceptibility were calculated and the results show that the anatase phase TiO₂ films exhibit larger nonlinear refractive effects compared with rutile phase. The figure of merit, T, defined by T = βλ/n₂, was calculated to be 0.8 for anatase films, meeting the requirement of T < 1 and showing potential applications in all-optical switching devices.     

Enhanced ferroelectric properties of Pb(Zr0.80Ti0.20)O3/PbO thin films prepared by radio frequency magnetron sputtering

The Pb(Zr_0.80Ti_0.20)O₃ (PZT) thin films with and without a PbO buffer layer were deposited on the Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates by radio frequency (rf) magnetron sputtering method. The PbO buffer layer improves the microstructure and electrical properties of the PZT thin films. High phase purity and good microstructure of the PZT thin films with a PbO buffer layer were obtained. The effect of the PbO buffer layer on the ferroelectric properties of the PZT thin films was also investigated. The PZT thin films with a PbO buffer layer possess better ferroelectric properties with higher remnant polarization (P_r = 25.6 μC/cm²), and lower coercive field (E_c = 60.5 kV/cm) than that of the films without a PbO buffer layer (P_r = 9.4 μC/cm², E_c = 101.3 kV/cm). Enhanced ferroelectric properties of the PZT thin films with a PbO buffer layer is attributed to high phase purity and good microstructure.