Study on nonlinear optical,dielectric and pyroelectric properties of novel organic–inorganic hybrid material

A novel organic and inorganic hybrid material was prepared from a nonlinear, optically active imidazole derivative, 4-(nitrophenyl)-2,4-bis-(4,4′-[N,N-bis-(2-hydroxyethyl)aminophen-yl])imidazole (NPAH4), and metal alkoxide of Ta(V) via sol–gel process. The second-order nonlinear and pyroelectric properties of the hybrid film were investigated in terms of the second harmonic generation (SHG) and pyroelectric coefficient measurement. The SHG coefficient d₃₃ was found to be 28.6 pm/V at the fundamental wavelength of 1064 nm and the pyroelectric coefficient P was found to be 1.6×10⁻⁶ C/cm² K.     

Pyroelectric Ta-modified LiNbO3 thin films and devices for thermal infrared detection

High-performance pyroelectric infrared (IR) detectors have been fabricated using tantalate-doped lithium niobate LiNb_1 − xTa_xO₃ (abbreviated as LNT, with x = 0-1.0) thin films deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by diol-based sol-gel processing, in which, tantalate (Ta) is adopted as dopant in lithium niobate. The randomly oriented LNT thin film exhibits a relatively small dielectric constant and a large pyroelectric coefficient. The pyroelectric characteristics of detectors with various tantalate contents, as a function of modulation frequency, were investigated. It was found that LiNb_0.8Ta_0.2O₃ had the largest voltage responsivity of 7020 (V/W) at 70 Hz, and a specific detectivity (D^?) of 7.76 × 10⁷ cm Hz^1/2/W at 200 Hz. These results indicate that the LNT thin film with x = 0.20 is most suitable for application as high-performance pyroelectric thin-film detectors.     

Synthesis and NLO properties of hybrid inorganic-organic films containing thiophene ring

A family of second-order nonlinear optical sol-gel films with a pendent thiophene chromophore has been developed. The key step in preparation these hybrids was the syntheses of alkoxysilane dye containing thiophene ring, which was accomplished by utilizing the urethane forming reaction. Molecular structural characterization for the resultant was achieved by FTIR, ¹H NMR and UV-Visible spectra. The microscopic optical nonlinearity of the thiophene chromophore was evaluated to be 7646 × 10^− 30 esu D by solvatochromic method and second harmonic coefficients (d₃₃) of the hybrid film was also calculated to be 41.2 pm/V by second harmonic generation (SHG) measurements, respectively. Furthermore, the stability of optical nonlinearity in poled film was also investigated through a depoling experiment.     

Preparation and electro-optic properties of hybrid sol-gel films containing imidazole chromophore

An alkoxysilane precursor based on imidazole chromophore, namely 2-((4-(ethyl(2-hydroxyethyl)amino)phenyl)diazenyl)-4,5-dicyano-1H-imidazole (IZ), has been successfully synthesized through a urethane forming reaction. Following a sol-gel process of the resultant precursor, inorganic-organic hybrid films were obtained by spin-coating. Their structures were verified by ¹H NMR, FT-IR, UV-vis spectra and elemental analysis. After corona poling, the electro-optic (EO) properties of the hybrid films were characterized by a simple reflection technique, and the EO coefficient (r₃₃) of a sample was determined to be 1.6 pm/V at a wavelength of 1310 nm.     

Effects of substrate bias voltage and target sputtering power on the structural and tribological properties of carbon nitride coatings

Effects of substrate bias voltage and target sputtering power on the structural and tribological properties of carbon nitride (CN_x) coatings are investigated. CN_x coatings are fabricated by a hybrid coating process with the combination of radio frequency plasma enhanced chemical vapor deposition (RF PECVD) and DC magnetron sputtering at various substrate bias voltage and target sputtering power in the order of −400 V 200 W, −400 V 100 W, −800 V 200 W, and −800 V 100 W. The deposition rate, N/C atomic ratio, and hardness of CN_x coatings as well as friction coefficient of CN_x coating sliding against AISI 52100 pin in N₂ gas stream decrease, while the residual stress of CN_x coatings increases with the increase of substrate bias voltage and the decrease of target sputtering power. The highest hardness measured under single stiffness mode of 15.0 GPa and lowest residual stress of 3.7 GPa of CN_x coatings are obtained at −400 V 200 W, whereas the lowest friction coefficient of 0.12 of CN_x coatings is achieved at −800 V 100 W. Raman and XPS analysis suggest that sp³ carbon bonding decreases and sp² carbon bonding increases with the variations in substrate bias voltage and target sputtering power. Optical images and Raman characterization of worn surfaces confirm that the friction behavior of CN_x coatings is controlled by the directly sliding between CN_x coating and steel pin. Therefore, the reduction of friction coefficient is attributed to the decrease of sp³ carbon bonding in the CN_x coating. It is concluded that substrate bias voltage and target sputtering power are effective parameters for tailoring the structural and tribological properties of CN_x coatings.     

Effect of TiOx seed layer on the texture and electric properties in La and Ca modified PbTiO3 thin films

Lanthanum-and calcium-modified PbTiO₃ (PLCT) ferroelectric thin films were successfully prepared on Pt(111)/Ti/SiO₂/Si substrates by pulsed laser deposition. Influence of TiO_x seed layer on texture and electric properties of PLCT films was investigated. It is found the PLCT films without seed layer exhibited highly (100)-textured, while using about 9 nm TiO_x as seed layer lead to highly (301)-textured. The PLCT film with TiO_x seed layer possess higher remnant polarization (Pr = 26 µC/cm²), better pyroelectric coefficient and figure of merit at room temperature (p = 370 µC/m²k, F_d = 190 × 10^− 5 Pa^− 1/2) than that of film without seed layer. The mechanism of the enhanced electric properties was also discussed.     

Dielectric and pyroelectric properties of Ba-modified lead lanthanum zirconate stannate titanate ceramics

(Pb_0.97−xLa_0.02Ba_x)(Zr_0.75Sn_0.12Ti_0.13)O₃ ceramics in the composition range 0.1 ≤ x ≤ 0.16 were prepared by conventional solid state reaction process. On increasing Ba content from 0.1 to 0.16 mol, the specimens underwent phase transition from the first order to the second order and the Curie temperature decreased from 85 to 35 °C. With x = 0.16, the specimen showed good pyroelectric properties for practical applications. When a 500 V/mm dc bias field was applied, the specimen showed the maximum pyroelectric coefficient of 5800 μC/m² K and figure of merit of 58 × 10⁻⁵ Pa^−0.5 at Curie temperature.     

Study on electrical conduction of viologen derivatives using scanning tunneling microscopy

The electrical conduction of self-assembled monolayers (SAMs) made from viologen derivatives was measured using ultrahigh vacuum scanning tunneling microscopy (UHV-STM) with a focus on the molecular structural effect on the electrical conduction. For viologen derivative SAMs, resistances through the monolayers increased exponentially with increases in molecular length when the decay constants of transconductance β were ca. 0.35 to 0.48 nm^− 1. The estimated monolayer resistances of the viologen derivatives such as N-methyl-N′-(10-mercaptodecyl)-4,4′-bipyridinium (VC₁₀SH), N-methyl-N′-di(8-mercaptooctyl)-4,4′-bipyridinium (HSC₈VC₈SH), and N-methyl-N′-di(10-mercaptodecyl)-4,4′-bipyridinium (HSC₁₀VC₁₀SH) SAMs were 1.3 × 10⁸ Ω, 3.6 × 10⁹ Ω, and 3.8 × 10⁹ Ω, 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.     

Preparation and nonlinear optical properties of hybrid films containing dicyanomethylenepyran-based chromophores

A new nonlinear optical (NLO) chromophore 4-dicyanomethylene-2-methyl-6- {4-[4-(N-ethyl-N-hydroxyethylamino)phenylazo]}styryl-4H-pyran (AZP), which features extended conjugated chain based on DCM laser dye, was synthesized and functionalized with alkoxysilane for materials processing. Hybrid films containing chromophore AZP and DCM were prepared via a sol-gel processing. The d₃₃ values of films containing AZP are 39-48 pm/V varying with concentration of chromophores, which is similar to that containing DCM. By tuning the organic content, the thermal stability of d₃₃ values can be significantly improved by about 30 °C, about 15 °C higher than those containing DCM. The residual rotational stress, along with cavity between chromophores and matrix, is proposed to contribute to the stability of NLO activity of hybrid films.     

Use of water vapor for suppressing the growth of unstable low-κ interlayer in HfTiO gate-dielectric Ge metal-oxide-semiconductor capacitors with sub-nanometer capacitance equivalent thickness

Annealing of high-permittivity HfTiO gate dielectric on Ge substrate in different gases (N₂, NH₃, NO and N₂O) with or without water vapor is investigated. Analysis by transmission electron microscopy indicates that the four wet anneals can greatly suppress the growth of a GeO_x interlayer at the dielectric/Ge interface, and thus decrease interface states, oxide charges and gate leakage current. Moreover, compared with the wet N₂ anneal, the wet NH₃, NO and N₂O anneals decrease the equivalent permittivity of the gate dielectric due to the growth of a GeO_xN_y interlayer. Among the eight anneals, the wet N₂ anneal produces the best dielectric performance with an equivalent relative permittivity of 35, capacitance equivalent thickness of 0.81 nm, interface-state density of 6.4 × 10¹¹ eV^− 1 cm^− 2 and gate leakage current of 2.7 × 10^− 4 A/cm² at V_g = 1 V.     

l-lysine monohydrochloride dihydrate as novel elasto- and electrooptical materials

We have studied optical parametrical effects (electrooptical and elastooptical ones) at wavelength 1150 nm generated by continuous He-Ne laser. We have found that the maximal value of the effective electrooptics coefficient is equal to about 12.6 pm/V and of the elastooptical coefficient was 12 · 10¹⁴ m²/N and was achieved at temperature about 300 K. l-lysine monohydrochloride dihydrate (C₆H₁₄N₂O₂, HCl·2H₂O, LLMHCl), a semiorganic potential nonlinear optically active crystal belongs to noncentrosymmetry class P2₁. FTIR and FT Raman of this crystal have been studied at room temperature. The vibrational spectral characterization has been carried out for different Raman configurations and has been interpreted following existed crystal structural data and factor group analysis. Following the performed analysis it was discovered that the principal role in the observed electrooptics group plays the vibrational bands originating of the functional groups such as [NH₃]⁺, C=O, O-H, C-H, C-N, O-C=O, C-N-C-C ring, C-OH. For elastooptical effects the principal role belongs to the modes situated at 3500-1500 cm^− 1 originating from stretching vibrations of [NH₃]⁺, CH₂, C=O, COO⁻ and C-N groups.     

Linear and nonlinear magnetooptics of planar Au/Co/Si nanostructures

Linear and nonlinear magnetooptics are applied to study the magnetic properties of Au/Co/Si planar nanostructures. The dependence of the nonlinear magneto-optical Kerr effect on the thickness of the cobalt layer, d_Co, reaches a maximum at d_Co ≈ 2 nm. This characteristic thickness is consistent with the formation of surface magnetization. An enhancement of the second harmonic generation (SHG) intensity and of magnetization-induced SHG is attained for an island-like structure of the cobalt layer, and is associated with the excitation of localized surface plasmons in cobalt nanoislands.     

Ion beam deposition of α-Ta films by nitrogen addition and improvement of diffusion barrier property

Ta thin films were deposited on Si (100) substrates by an ion beam deposition method at various substrate bias voltages under Ar + N₂ atmosphere with different pressure ratios of Ar and N₂. The effects of nitrogen pressure in the plasma gas and the substrate bias voltage on the surface morphology, crystalline microstructure, electrical resistivity and diffusion barrier property were investigated. It was found that the fraction of a metastable β-phase in the Ta film deposited at the substrate bias voltage of − 50 V films decreased by adding nitrogen gas, while the α-Ta phase became dominant. As a result, the Ta films deposited at the substrate bias voltage of − 50 V under Ar (9 Pa) + N₂ (3 Pa) atmosphere showed a dominant α-phase with good surface morphology, low resistivity, and superior thermal stability as a diffusion barrier.     

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.     

Enhanced performance of sandwich structure Pb0.8La0.1Ca0.1Ti0.975O3 thin film for pyroelectric applications

Using the advantages of low-temperature crystallization and high orientation in Pb_0.8La_0.1Ca_0.1Ti_0.975O₃ (PLCT) film, a dense PLCT/porous PLCT/dense PLCT sandwich structure was obtained in the present study. It is found that dense PLCT layer can both sustain the porous density in the core layer and also lead to better preferential orientation of the sandwich structure. In the sandwich structure, low dielectric constant (ε_r = 43) and leakage current density (J < 9 × 10^− 5A/cm²) are simultaneously achieved. Because of high orientation in sandwich structure, the pyrocoefficient (p > 185 µC/m² K) is still keeping a relatively large value. The resulting high figure of merit (F_V′ = 4.5 µC/m² K, F_d′ = 228 µC/m² K) make the sandwich structure films good candidate for pyroelectric thin-film devices.     

Electroluminescence of a device based on europium β-diketonate with phosphine oxide complex

Rare earth (RE) ions have spectroscopic characteristics to emit light in narrow lines, which makes RE complexes with organic ligands candidates for full color OLED (Organic Light Emitting Diode) applications. In particular, β-diketone rare earth (RE³⁺) complexes show high fluorescence emission efficiency due to the high absorption coefficient of the β-diketone and energy transfer to the central ion. In this work, the fabrication and the electroluminescent properties of devices containing a double and triple-layer OLED using a new β-diketone complex, [Eu(bmdm)₃(tppo)₂], as transporting and emitting layers are compared and discussed. The double and triple-layer devices based on this complex present the following configurations respectively: device 1: ITO/TPD (40 nm)/[Eu(bmdm)₃(tppo)₂] (40 nm)/Al (150 nm); device 2: ITO/TPD (40 nm)/[Eu(bmdm)₃(tppo)₂] (40 nm)/Alq₃ (20 nm)/Al (150 nm) and device 3: ITO/TPD (40 nm)/bmdm-ligand (40 nm)/Al (150 nm), were TPD is (N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1-biphenil-4,4-diamine) and bmdm is butyl methoxy-dibenzoyl-methane. All the films were deposited by thermal evaporation carried out in a high vacuum system. These devices exhibit high intensity photo- (PL) and electro-luminescent (EL) emission. Electroluminescence spectra show emission from Eu³⁺ ions attributed to the ⁵D₀ to ⁷F_J (J = 0, 1, 2, 3 and 4) transitions with the hypersensitive ⁵D₀ → ⁷F₂ transition (around 612 nm) as the most prominent one. Moreover, a transition from ⁵D₁ to ⁷F₁ is also observed around 538 nm. The OLED light emission was almost linear with the current density. The EL CIE chromaticity coordinates (X = 0.66 and Y = 0.33) show the dominant wavelength, λ_d = 609 nm, and the color gamut achieved by this device is 0.99 in the CIE color space.     

Pyroelectric detection in glycolipid thin film

The pyroelectric and dielectric properties of glycolipid thin films have been investigated. The glycolipid under studied is (2-n-decyl-n-tetradecyl)-4-O-maltoside. From the thin film observations using polarizing optical microscopy, glycolipid molecules were found to align homeotropically, which results in non-zero temperature-dependent spontaneous polarization. The pyroelectric coefficient, dielectric constant, dielectric loss tangent and figure of merit of the glycolipid thin films are found to be in the range of 70-105 μC m^− 2 K^− 1, 5.9-16, 0.242-0.523 and 24-88 μC m^− 2 K^− 1 respectively, depending on the glycolipid concentration. Higher concentration of glycolipid renders higher pyroelectric coefficient but lower dielectric constant and dielectric loss tangent, which then results in a higher figure of merit.     

An investigation on palladium sulphide (PdS) thin films as a photovoltaic material

Polycrystalline PdS thin films with tetragonal structure have been grown by direct sulphuration of Pd layers. They are formed by crystallites of size ∼ 50 nm. As-grown PdS films show a Seebeck coefficient, S = − 250 ± 30 μV/K, which indicates an n-type conductivity. Electrical resistivity of the samples, measured by the four contact probe, is (6.0 ± 0.6) × 10^− 2 Ω·cm. Hall effect measurements, confirms n-type conductivity with a negative carrier density n = (8.0 ± 2.0) × 10¹⁸ cm^− 3 and electron mobility μ of (20 ± 2) cm²/V s. Band gap energy (E_g) and absorption coefficient (α) are determined from the optical transmission and reflectance of the films. A direct transition with energy gap E_g = (1.60 ± 0.01) eV is obtained. Optical absorption coefficient in the range of photon energies hν > 2.0 eV is higher than 10⁵ cm^− 1. All these properties make PdS thin films a good alternative material for solar applications.     

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.