Zinc oxide thin film transistors using MgO-Bi1.5Zn1.0Nb1.5O7 composite gate insulator on glass substrate

We report on high mobility ZnO thin film transistors (TFTs) (< 5 V), utilizing a room temperature grown MgO-Bi_1.5Zn_1.0Nb_1.5O₇ (BZN) composite gate insulator on a glass substrate. 30 mol% MgO added BZN composite gate insulators exhibited greatly enhanced leakage current characteristics (~< 2 × 10^− 8 A/cm² at 0.3 MV/cm) due to the high breakdown strength of MgO, while retaining an appropriate high-k dielectric constant of 32. The ZnO-TFTs with MgO-BZN composite gate insulators showed a high field-effect mobility of 37.2 cm²/Vs, a reasonable on-off ratio of 1.54 × 10⁵, a subthreshold swing of 460 mV/dec, and a low threshold voltage of 1.7 V.     

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.     

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.     

Z-scan measurement for the nonlinear absorption of Bi2.55La0.45TiNbO9 thin films

Bi_2.55La_0.45TiNbO₉ (BLTN-0.45) thin films with layered aurivillius structure were fabricated on fused silica substrates by pulsed laser deposition technique. Their structure, fundamental optical constants, and nonlinear absorption characteristics have been studied. The film exhibits a high transmittance (> 60%) in visible-infrared region. The optical band gap energy was found to be 3.44 eV. The optical constant and thickness of the films were characterized using spectroscopic ellipsometric (SE) method. The nonlinear optical absorption properties of the films were investigated by the single-beam Z-scan method at a wavelength of 800 nm laser with a duration of 80 fs. We obtained the nonlinear absorption coefficient β = 4.64 × 10^− 8 m/W. The results show that the BLTN-0.45 thin film is a promising material for applications in absorbing-type optical device.     

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.     

Enhanced tunable dielectric properties of Ba0.5Sr0.5TiO3/Bi1.5Zn1.0Nb1.5O7 multilayer thin films by a sol-gel process

Ba_0.5Sr_0.5TiO₃(BST)/Bi_1.5Zn_1.0Nb_1.5O₇(BZN) multilayer thin films were prepared on Pt/Ti/SiO₂/Si substrates by a sol-gel method. The structures and morphologies of BST/BZN multilayer thin films were analyzed by X-ray diffraction (XRD) and field-emission scanning electron microscope. The XRD results showed that the perovskite BST and the cubic pyrochlore BZN phases can be observed in the multilayer thin films annealed at 700 °C and 750 °C. The surface of the multilayer thin films annealed at 750 °C was smooth and crack-free. The BST/BZN multilayer thin films annealed at 750 °C exhibited a medium dielectric constant of around 147, a low loss tangent of 0.0034, and a relative tunability of 12% measured with dc bias field of 580 kV/cm at 10 kHz.     

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.     

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.     

Influences of post-annealing on structural and electrical properties of Bi1.5Zn1.0Nb1.5O7 thin films prepared by pulsed laser deposition

Bi_1.5Zn_1.0Nb_1.5O₇ (BZN) thin films were prepared on Pt/TiO₂/SiO₂/Si(100) substrates at 650 °C under an oxygen pressure of 10 Pa by using pulsed laser deposition process. The crystallinity, microstructure and electrical properties of BZN thin films were investigated to verify the influences of post-annealing thermal process on them. The X-ray diffractometer (XRD) results indicate that all Bi_1.5Zn_1.0Nb_1.5O₇ thin films without post-annealing process or with post-annealing in situ vacuum chamber and in oxygen ambient exhibit a cubic pyrochlore structure. The improved crystallinity of BZN thin films through post-annealing was confirmed by XRD and scanning electron microscope (SEM) analysis. Dielectric constant and loss tangent of the as-deposited BZN thin films are 160 and 0.002 at 10 kHz, respectively. After annealing, dielectric properties of thin films are significantly improved. Dielectric constant and loss tangent of the in situ annealed films are 181 and 0.0005 at 10 kHz, respectively. But the films post-annealed in O₂ oven show the largest dielectric constant of 202 and the lowest loss tangent of 0.0002, which may attribute to the increase in grain size and the elimination of oxygen vacancies. Compared with the as-deposited BZN thin films, the post-annealed films also show the larger dielectric tunability and the lower leakage current density.     

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.     

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.     

Ion beam modification of TiO2 films prepared by Cat-CVD for solar cell

The effects of nitrogen ion bombardment on TiO₂ films prepared by the Cat-CVD method have been studied to improve the optical and electrical properties of the material for use in Si thin film solar cells. The refractive index n and the dark conductivity of the TiO₂ film increased with irradiation time. The refractive index n of the TiO₂ film was changed from 2.1 to 2.4 and the electrical conductivity was improved from 3.4 × 10^− 2 to 1.2 × 10^− 1 S/cm by the irradiation. These results are due to the formation of Ti-N bonds and oxygen vacancies in the film.     

Interfacial characteristics and dielectric properties of Ba0.65Sr0.35TiO3 thin films

Ba_0.65Sr_0.35TiO₃ (BST) thin films were deposited on Pt/Ti/SiO₂/Si substrates by radio frequency magnetron sputtering technique. X-ray photoelectron spectroscopy (XPS) depth profiling data show that each element component of the BST film possesses a uniform distribution from the outermost surface to subsurface, but obvious Ti-rich is present to BST/Pt interface because Ti⁴⁺ cations are partially reduced to form amorphous oxides such as TiO_x (x < 2). Based on the measurement of XPS valence band spectrum, an energy band diagram in the vicinity of BST/Pt interface is proposed. Dielectric property measurements at 1 MHz reveal that dielectric constant and loss tangent are 323 and 0.0095 with no bias, while 260 and 0.0284 with direct current bias of 25 V; furthermore, tunability and figure of merit are calculated to be 19.51% and 20.54, respectively. The leakage current density through the BST film is about 8.96 × 10^− 7 A/cm² at 1.23 V and lower than 5.66 × 10^− 6 A/cm² at 2.05 V as well as breakdown strength is above 3.01 × 10⁵ V/cm.     

Third-order nonlinear optical properties of Bi2S3 nanocrystals doped in sodium borosilicate glass studied with Z-scan technique

The third-order nonlinear optical properties of Bi₂S₃ nanocrystals doped in sodium borosilicate glass are measured by Z-scan technique. The microstructures of the glass are characterized by means of X-ray diffraction, transmission electron microscopy, scanning transmission electron microscopy, energy dispersion X-ray spectra, and high-resolution transmission electron microscopy. The results show that the Bi₂S₃ nanocrystals ranging from 10 to 30 nm are determined to be of the orthorhombic crystalline phase, and the third-order optical nonlinear refractive index γ, absorption coefficient β, and susceptibility χ⁽³⁾ of the glass are determined to be 2.56 × 10⁻¹⁶ m² W⁻¹, 4.13 × 10⁻¹⁰ mW⁻¹, and 1.43 × 10⁻¹⁰ esu, respectively.     

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.     

Growth, linear and nonlinear optical and, laser damage threshold studies of organometallic crystal of MnHg(SCN)4

Single crystals of bimetallic MnHg(SCN)₄ (abbreviated as MMTC) are grown by slow cooling method and the second and third order optical nonlinearities are investigated by Kurtz and Perry powder SHG test and single beam Z-scan technique respectively. The influences of SCN ligand in modifying the NLO properties are discussed and the results are compared with other organometallic crystals. The nonlinear refractive index, absorption coefficient and third order susceptibility are estimated to be −1.88 × 10⁻¹¹ cm²/W, 8.65 × 10⁻⁶ cm/W and 6.58 × 10⁻⁹ esu, respectively. The optical absorption of MMTC single crystal was recorded and the corresponding direct band gap is found to be 4.2 eV. The phase matching and laser induced damage threshold studies are also carried out. The FT-IR and photoluminescence spectroscopic techniques were employed to identify the composition and luminescence nature of the crystal.     

Chemical diffusion coefficient of lithium ion in Li3V2(PO4)3 cathode material

The kinetic properties of monoclinic lithium vanadium phosphate were investigated by potential step chronoamperometry (PSCA) and electrochemical impedance spectroscopy (EIS) method. The PSCA results show that there exists a linear relationship between the current and the square root of the time. The D?_Li values of lithium ion in Li_3-xV₂(PO₄)₃ under various initial potentials of 3.41, 3.67, 3.91 and 4.07 V (vs Li/Li⁺) obtained from PSCA are 1.26 × 10^− 9, 2.38 × 10^− 9, 2.27 × 10^− 9 and 2.22 × 10^− 9 cm²·s^− 1, respectively. Over the measuring temperature range 15-65 °C, the diffusion coefficient increased from 2.67 × 10^− 8 cm²·s^− 1 (at 15 °C) to 1.80 × 10^− 7 cm²·s^− 1 (at 65 °C) as the measuring temperature increased.     

Third harmonic generation in LiKB4O7 single crystal

The third order nonlinear optical properties of the lithium potassium borate (LiKB₄O₇) single crystal have been investigated by means of the rotational Maker fringe technique using Nd:YAG laser at 1064 nm working in picosecond regime. The value of the third order nonlinear optical susceptibility was calculated using the theoretical model of Kajzar et al. and was found to be about 1.4 × 10⁻²¹ m² V⁻² that is one order higher than that of fused silica.     

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.     

Exceptionally large third-order optical susceptibility in Ag:SrBi2Nb2O9 composite films

Thin films of SrBi₂Nb₂O₉ with and without the inclusion of Ag nanocrystals were prepared on MgO (001) substrates by alternative pulsed laser ablation of SrBi₂Nb₂O₉ ceramic and Ag metal in a nitrogen atmosphere. The size of the Ag nanocrystals can be brought down to ca. 5.0 nm, as revealed by transmission electron microscopy and X-ray diffraction. We measured the third-order susceptibility χ⁽³⁾ of the deposits by single beam z-scan technique at a wavelength of 532 nm. It is found that SrBi₂Nb₂O₉ is an effectively nonlinear optical medium, exhibiting a very large χ⁽³⁾. With the inclusion of Ag nanocrystals the χ⁽³⁾ was nearly doubled (Reχ⁽³⁾ = 8.052 × 10^− 7 esu, and Imχ⁽³⁾ = − 1.717 × 10^− 7 esu), which comes very close to the maximum value available in the current time. This indicates that the Ag:SrBi₂Nb₂O₉ composite structure can be an excellent candidate for nonlinear optical applications. A general approach for further enhanced third-order susceptibility by tailoring the dielectric constant of the metal inclusion is briefly discussed.