Third-order nonlinear optical properties of an ultrathin film containing a porphyrin derivative

An ultrathin nanoscopic multilayer film has been fabricated through the electrostatic layer-by-layer self-assembly of negatively charged 5,10,15,20-tetrakis(3,4,5-trihydroxyphenyl)porphyrin (DHP) and oppositely charged polyethylenimine (PEI). UV-vis spectra showed a continuous and uniform deposition process of PEI and DHP. The film structure was characterized by small-angle X-ray diffraction measurement and AFM images. The nonlinear optical properties of ultrathin film were studied by Z-scan technique with laser duration of 8 ns at a wavelength of 532 nm. The film sample exhibited strong nonlinear saturated absorption and a self-defocusing effect. The nonlinear absorption coefficient and refractive index of the self-assembly ultrathin film are -9.7 x 10(-5) m/W and -7.56 x 10(-12) m(2)/W, respectively.     

(苄基三乙基铵)双(1,3-二硫杂环戊烯-2-硫酮-4,5-二硫基)-金的三阶非线性光学性质

合成了一种新的配位化合物(苄基三乙基铵)双(1,3-二硫杂环戊烯-2-硫酮-4,5-二硫基)-金(BTEAADT). 利用旋涂技术制备了该材料与聚甲基丙烯酸甲酯(PMMA)掺杂的复合薄膜, 该材料在复合薄膜中的质量分数为1%. 采用Z扫描方法, 分别测试了该材料的乙腈溶液和该材料与PMMA复合薄膜在波长为1064 nm, 脉宽为20 ps条件下的三阶非线性光学特性. 同时还研究了复合薄膜的线性光学性质. Z扫描的结果表明, 复合薄膜和该材料的乙腈溶液都具有自散焦效应, 非线性折射率都是负值. 在实验条件下, 两者的非线性吸收效应都是可以忽略的. 经过计算得出溶液样品的非线性折射率为-1.459×10^-18 m²·W^-1, 复合薄膜样品的非线性折射率为-3.978×10^-15 m²·W^-1. 该材料在1064 nm处的非线性光学器件方面有潜在应用价值.     

Photocurrent generation in multilayer self-assembly films fabricated from water-soluble poly(phenylene vinylene)

A novel, water-soluble, cationic PPV derivative poly[(2,5-bis(3-bromotrimethylammoniopropoxy)-phenylene-1,4-divinylene)-alt-1,4-(2,5-bis(2-(2-hydroxyethoxy)ethoxy))phenylene vinylene] (BH-PPV) has been synthesized by a Heck coupling reaction. Multilayered assemblies of the BH-PPV and the sodium salt of hexa(sulfobutyl)fullerenes (C(60)-HS) were fabricated successfully by an alternate deposition technique. The multilayer structures were studied by UV/Vis spectroscopy, small angle X-ray diffraction, and atomic force microscopy. The photoinduced charge transfer property of the self-assembled multilayer film was also measured by a three-electrode cell technique. A steady and rapid cathodic 5.5 microA cm(-2) photocurrent response was measured as the irradiation of the multilayer film was switched on and off. Importantly, the response of on/off cycling is prompt and reproducible. A possible mechanism for the electron-transfer process is proposed.     

Nonlinear studies of acid fuchsin dye in liquid and solid media

Solid-state dye-doped polymers are attractive alternative to the conventional liquid dye solutions. In this paper, nonlinear properties of the dye Acid Fuchsin has been studied. The third-order nonlinear optical properties of Acid Fuchsin dye in 1-butanol and dye-doped polymer film were measured by the Z-scan technique using 532 nm diode pumped Nd:Yag laser. This material exhibits negative optical nonlinearity. The dye at 0.4 mM concentration exhibited nonlinear refractive coefficient (n(2)=-8.72 x 10(-8) and -10.308 x 10(-8) (cm(2)/W) in liquid and solid media, respectively), nonlinear absorption coefficient (beta=-7.69 x 10(-4) and -8.294 x 10(-4)cm/W in liquid and solid media, respectively) and susceptibility (chi(3)=4.33 x 10(-6) and 5.13 x 10(-5)esu in liquid and solid media, respectively). These results show that Acid Fuchsin dye has potential applications in nonlinear optics.     

Nonlinear studies of Pararosanilin dye in liquid and solid media

Solid-state dye-doped polymers are attractive alternative to the conventional liquid dye solutions. In this paper, nonlinear properties of the dye Pararosanilin has been studied. The third-order nonlinear optical properties of Pararosanilin dye in 1-butanol and dye-doped polymer film were measured by the Z-scan technique using 532 nm diode pumped Nd:Yag laser. This material exhibits negative optical nonlinearity. The dye at 0.4 mM concentration exhibited nonlinear refractive coefficient (n(2) = -6.8 x 10(-8) and -7.11 x 10(-8) (cm(2)/W) in liquid and solid media, respectively), nonlinear absorption coefficient (beta = -7.7 x 10(-4) and -7.93 x 10(-4)cm/W in liquid and solid media, respectively) and susceptibility (chi((3))=3.38 x 10(-6) and 3.53 x 10(-5)esu in liquid and solid media, respectively). These results show that Pararosanilin dye has potential applications in nonlinear optics.     

Enhancement of third-order optical nonlinearities in 3-dimensional films of dielectric shell capped Au composite nanoparticles

The composite nanoparticles of Au-core capped by CdS shells of different thickness were prepared and assembled into densely packed 3-dimensional films by the layer-by-layer self-assembly (LBL) technique. These films exhibited the 3-dimensional structure of densely packed Au@CdS composite nanoparticles and the shell thickness was tunable by changing the concentration of Cd2+-thiourea complexes. These multilayer films exhibited enhanced third-order optical nonlinear responses and ultrafast response times (several picoseconds). The third-order nonlinear optical susceptibility of the film with the CdS shell thickness of 4.4 nm was estimated to be 1.48 x 10(-9) esu and the value decreases with the increase of the CdS shell thickness. The enhancement of the optical nonlinearity was explained based on the calculation according to the electrostatic approximation by the solution of Laplace's equation under the boundary conditions appropriate to the model of core-shell nanoparticles, and mainly attributed to localized electric field effects in the CdS shell region. Additionally, the nonlinearity was optimized by determination of the values of the dielectric constant and thickness of the different shell.     

Fabrication of electrochemical transistor based on pi-conjugate polymer Langmuir-Blodgett film

We fabricated an efficient organic electrochemical transistor (OECT) composed of polymer Langmuir-Blodgett (LB) film. The pi-conjugated polymer LB film, which was constructed from a poly(N-dodecylacrylamide) (pDDA) and poly(3-hexylthiophene) (PHT) mixture, was used as a conduction channel layer to connect source and drain electrodes. The mixed-polymer LB film was characterized using UV-vis spectroscopy, X-ray diffraction (XRD), atomic force microscopy (AFM), and cyclic voltammetry. Subsequent UV spectra measurements, XRD measurements, and AFM measurements show that PHT forms a crystalline lamellar domain in the layered structure of pDDA. The OECT included 10 layers of the mixed-polymer LB film as the conduction channel layer. The OECT showed an on/off ratio of 1.1x10(4) and mobility of 7.5x10(-2) cm2 V(-1) s(-1) at low gate (VG=-1.2 V) and source-drain voltages (VDS=-0.5 V). Moreover, the necessary charge to operate the OECT was 1.1x10(-9) mol of e(-1) cm(-2), which was 2 orders smaller than the value reported using a similar device structure. The relatively high on/off ratio and low charge consumption suggest that this OECT, which is fabricated from pi-conjugated polymer LB films, is applicable to macroelectronic devices.     

Optical nonlinear absorption and refraction of CdS and CdS-Ag core-shell quantum dots

The CdS and CdS-Ag core-shell quantum dots (QDs) have been prepared. The nanostructures of the QDs were revealed by transmisson electron microscopy and absorption spectra, respectively. The third-order nonlinear optical properties of the core-shell QDs have been studied by using Z-scan technique with femtosecond pulses at the wavelength of 790 nm. The value of the effective nonlinear absorption coefficient beta(eff) of CdS-Ag QDs is measured to be about 16.8 cm/GW, which is about 400 times larger than that of bare CdS QDs of 3.9 x 10(-2) cm/GW. The nonlinear refraction index gamma of CdS-Ag QDs is about -2.3 x 10(-4) cm(2)GW, which is about 200 times larger than that of bare CdS QDs of 1.0 x 10(-6) cm(2)GW.     

Interaction forces in thin liquid films stabilized by hydrophobically modified inulin polymeric surfactant. 2. Emulsion films

The interaction forces in emulsion films stabilized using hydrophobically modified inulin (INUTEC SP1) were investigated by measuring the disjoining pressure of a microscopic horizontal film between two macroscopic emulsion drops of isoparaffinic oil (Isopar M). A special measuring cell was used for this purpose whereby the disjoining pressure Pi was measured as a function of the equivalent film thickness hw. The latter was determined using an interferometric method. In this way Pi-hw curves were established at a constant INUTEC SP1 concentration of 2x10(-5) mol.dm-3 and at various NaCl concentrations. At a constant disjoining pressure of 36 Pa, a constant temperature of 22 degrees C, and a film radius of 100 microm, hw decreased with an increase in the NaCl concentration, Cel, and reached a constant value of 11 nm at Cel=5x10(-2) mol.dm-3. This reduction in film thickness is due to the compression of the electrical double layer, and at the above critical NaCl concentration any electrostatic repulsion is removed and only steric interaction remains. This critical electrolyte concentration represents the transition from electrostatic to steric interaction. At a NaCl concentration of 2x10(-4) mol.dm-3 the Pi-hw isotherms showed a gradual decrease in hw with an increase in capillary pressure, after which there was a jump in hw from approximately 30 to approximately 7.2 nm when Pi reached a high value of 2-5.5 kPa. This jump is due to the formation of a Newton black film (NBF), giving a layer thickness of the polyfructose loops of approximately 3.6 nm. The film thickness did not change further when the pressure reached 45 kPa, indicating the high stability of the film. Pi-hw isotherms were obtained at various NaCl concentrations, namely, 5x10(-2), 5x10(-1), 1.0, and 2.0 mol.dm-3. The initial thicknesses are within the range 9-11 nm, after which a transition zone starts, corresponding to a pressure of about 0.5 kPa. In this zone all films transform to an NBF with a jump, after which the thickness remains constant with a further increase in the disjoining pressure up to 45 kPa, with no film rupture. This indicates the very high stability of the NBF in the presence of high electrolyte concentrations. The high emulsion film stability (due to strong steric repulsions between the strongly hydrated loops of polyfructose) is correlated with the bulk emulsion stability.     

Synthesis, linear, and quadratic-nonlinear optical properties of octupolar D3 and D2d bipyridyl metal complexes

A series of D3 (Fe(II), Ru(II), Zn(II), Hg(II)) and D2d (Cu(I), Ag(I), Zn(II)) octupolar metal complexes featuring different functionalized bipyridyl ligands has been synthesized, and their thermal, linear (absorption and emission), and nonlinear optical (NLO) properties were determined. Their quadratic NLO susceptibilities were determined by harmonic light scattering at 1.91 microm, and the molecular hyperpolarizability (beta0) values are in the range of 200-657 x 10(-30) esu for octahedral complexes and 70-157 x 10(-30) esu for tetrahedral complexes. The octahedral zinc(II) complex 1 e, which contains a 4,4'-oligophenylenevinylene-functionalized 2,2'-bipyridine, exhibits the highest quadratic hyperpolarizability ever reported for an octupolar derivative (lambdamax=482 nm, beta1.91(1 e)=870 x 10(-30) esu, beta0(1 e)=657 x 10(-30) esu). Herein, we demonstrate that the optical and nonlinear optical (NLO) properties are strongly influenced by the symmetry of the complexes, the nature of the ligands (donor endgroups and pi linkers), and the nature of the metallic centers. For example, the length of the pi-conjugated backbone, the Lewis acidity of the metal ion, and the increase of ligand-to-metal ratio result in a substantial enhancement of beta. The contribution of the metal-to-ligand (MLCT) transition to the molecular hyperpolarizability is also discussed with respect to octahedral d6 complexes (M=Fe, Ru).     

N+离子注入聚对苯乙炔衍生物的非线性光学性能

以对甲氧基苯酚和溴代异戊烷为原料,用脱氯化氢反应制备可溶性聚[2-甲氧基-5-(3'-甲基)丁氧基]对苯乙炔(MMB-PPV),通过核磁氢谱(1HNMR)和红外光谱(FTIR)对产物分子的结构进行表征.用能量为15keV、剂量为3.8×1015～9.6×1016ions/cm2的氮正离子(N+)对MMB-PPV薄膜进行注入改性.紫外-可见吸收光谱(UV-Vis)显示,注入离子在MMB-PPV薄膜内部引入杂质能级,破坏了分子的共轭结构.随着注入剂量增加,吸收边逐渐向长波方向移动,且分子激发态和基态间的光学带隙由2.12eV减小至1.81eV.用简并四波混频(DFWM)技术研究了离子注入MMB-PPV薄膜的三阶非线性光学性能.结果表明,未注入薄膜的三阶非线性极化率(χ(3))值为7.1×10-10esu,随着注入剂量的增加,χ(3)值逐渐增大,当注入剂量达到3.8×1016ions/cm2时,χ(3)值提高到9.3×10-9esu,继续增加注入剂量,χ(3)值开始下降,当注入剂量为9.6×1016ions/cm2时,χ(3)值降低到1.5×10-10esu.对离子注入MMB-PPV薄膜χ(3)值变化的机理进行了探讨.     

Insights into adsorption of uncharged macrocyclic complexes into a Nafion Film: Adsorption characteristics and analysis of tetraphenylporphyrine zinc(II)

Tetraphenylporphine zinc(II) (ZnTPP) was found to be adsorbed from its CH2Cl2 solution into a Nafion (Nf) film. The characteristics of the adsorption of ZnTPP into the Nf film were studied using a visible absorption spectroscopic technique. The initial rate (v0, mol cm(-2) s(-1)) for uptake of ZnTPP was saturated with increasing ZnTPP concentration (c0, M) in the solution. This kinetic profile was analyzed in terms of a Michaelis-Menten model considering preequilibrium of ZnTPP adsorption between the solution and the outer layer of the Nf film, followed by diffusion to an inner bulk region, giving a maximum diffusion reflux of v(max) = (2.2 +/- 0.2) x 10(-13) mol cm(-2) s(-1). This is different from the kinetics for the Nf/phthalocyanine zinc(II) (ZnPc) film, which gives a linear plot of v(0) vs c(0). This can be explained by the relatively slow diffusion of ZnTPP in the film compared to that of ZnPc because of steric factors: ZnTPP contains bulky tetraphenyl moieties attached perpendicular to a porphyrin ring, whereas ZnPc has higher planarity. The isotherm for the adsorption of ZnTPP into the Nf film was analyzed using a Langmuir isotherm equation, yielding an equilibrium constant of (3.6 +/- 1.1) x 10(6) M(-1) and a saturated amount of adsorbed ZnTPP of (1.8 +/- 0.1) x 10(-9) mol cm(-2), suggesting monolayer adsorption of ZnTPP on the hydrophobic polymer network interfacial with hydrophilic transport channels without significant intermolecular overlap. This is in contrast to the multilayer adsorption mode suggested for the ZnPc adsorption. The tetraphenyl moieties could prevent the stacking of ZnTPP for multilayer adsorption.     

60]Fullerene-containing polyurethane films with large ultrafast nonresonant third-order nonlinearity at telecommunication wavelengths

A significantly enhanced, ultrafast third-order optical nonlinearity at the wavelengths of 1150-1600 nm was demonstrated with cross-linked C60-containing polyurethane films using the Z-scan technique. Good-quality polymer films with a high loading of C60 derivative were obtained by cross-linking of the hydroxyl-containing C60 derivative and a triisocyanate. The positive Kerr coefficient with nonresonant nonlinear refractive index n2 falls in the range of (3.7 +/- 0.80) x 10-4 to (2.0 +/- 0.6) x 10-3 cm2/GW, and the calculated chi(3) and gamma values are up to 9.7 x 10-11 and 9.6 x 10-32 esu at 1550 nm, which are several orders of enhancement in third-order optical nonlinearity over pristine C60 in solution and 1-2 orders of enhancement over recently reported C60 derivatives and conjugated polymers.     

Layer-by-layer growth on Ge(100) via spontaneous urea coupling reactions

We have demonstrated the layer-by-layer growth, via a urea coupling reaction between two bifunctional molecules, ethylenediamine and 1,4-phenylene diisocyanate, to form an ultrathin film on Ge(100)-2 x 1 at room temperature under vacuum conditions. The initial adsorption and subsequent growth of each layer was studied with multiple internal reflection Fourier transform infrared (MIR-FTIR) spectroscopy. Ethylenediamine reacts with Ge(100)-2 x 1 to produce a surface-bound amine group which is available for additional reaction. Subsequent exposure of 1,4-phenylene diisocyanate leads to a spontaneous urea coupling reaction between the surface-bound amine and the highly reactive isocyanate functional group. Three bands at 1665, 1512, and 1306 cm(-)(1) are characteristic of a urea linkage and provide evidence of the coupling reaction. The coupling procedure can be repeated in a binary fashion to create covalently bound ultrathin films at room temperature, and in the present work, we demonstrate the successful growth of four layers. In addition, we have found that an initial exposure of 1,4-phenylene diisocyanate to Ge(100)-2 x 1 produces an isocyanate-functionalized surface which, upon exposure to ethylenediamine, also forms urea linkages. This layer-by-layer deposition method provides a strategy with which to design and produce precisely tailored organic materials at semiconductor interfaces.     

Surface-plasmon-resonance-enhanced cavity ring-down detection

The cavity ring-down technique is used to probe the absolute optical response of the localized surface plasmon resonance (SPR) of a gold nanoparticle distribution to adsorption of trichloroethylene (TCE) and perchloroethylene (PCE) from the gas phase. Extended Mie theory for a coated sphere with a particle-size-dependent dielectric function is used to elucidate size-dispersion effects, the size-dependence of the SPR sensitivity to adsorption, and the kinetics of adsorption. An approximate Gaussian distribution of nanospheres with a mean diameter of 4.5 nm and a standard deviation of 1.1 nm, as determined by atomic force microscopy, is provided by the intrinsic granularity of an ultrathin, gold film, having a nominal thickness of approximately 0.18 nm. The cavity ring-down measurements employ a linear resonator with an intracavity flow cell, which is formed by a pair of ultrasmooth, fused-silica optical flats at Brewster's angle, where the Au film is present on a single flat. The total system intrinsic loss is dominated by the film extinction, while the angled flats alone contribute only approximately 5 x 10(-5)/flat to the total loss. Based on a relative ring-down time precision of 0.1% for ensembles averages of 25 laser shots from a pulsed optical parametric oscillator, the minimum detectable concentrations of PCE and TCE obtained by probing the SPR response are found to be 2 and 7 x 10(-8) mol/L, respectively, based on a 30 s integration time.     

Classical trajectory study of the reaction between H and HCO

The thermal reaction between H and HCO was studied by classical trajectory calculations on an ab initio potential. The formation of H2+CO, the exchange of hydrogen atoms, and nonreactive encounters, proceeding either via direct or via complex-forming pathways, were separated. The reaction H+HCO-->H2+CO, with direct and complex-forming components, was found to have a low-pressure rate coefficient of 2.0(+/-0.15)x10(-10) cm3 molecule(-1) s(-1), being nearly independent of temperature between 200 and 1000 K. This value is in agreement with the recent experimental value of 1.83(+/-0.4)x10(-10) cm3 molecule(-1) s(-1). Thermal lifetime distributions of H2CO* complexes formed in the reaction are only weakly temperature dependent due to a compensation of energy and angular momentum effects.     

Measurement of apparent diffusion coefficients within ultrathin nafion Langmuir-Schaefer films: comparison of a novel scanning electrochemical microscopy approach with cyclic voltammetry

The use of scanning electrochemical microscopy (SECM) to evaluate the apparent diffusion coefficient, Dapp, of redox-active species in ultrathin Nafion films is described. In this technique, an ultramicroelectrode (UME) tip, positioned close to a film on a macroscopic electrode, is used to oxidize (or reduce) a species in bulk solution, causing the tip-generated oxidant (reductant) to diffuse to the film/solution interface. The oxidation (reduction) of film-confined species regenerates the reductant (oxidant) in solution, leading to feedback to the UME. A numerical model is developed that allows Dapp to be determined. For these studies, ultrathin films of Nafion were prepared using the Langmuir-Schaefer (LS) technique and loaded with an electroactive species, either the ferrocene derivative ferrocenyltrimethylammonium cation, FA+, or tris(2,2'-bipyridyl)ruthenium(II), Ru(bpy)32+. The morphology and the thickness of the Nafion LS films (1.5 +/- 0.2 nm per layer deposited) were evaluated using atomic force microscopy (AFM). For comparison with the SECM measurements, cyclic voltammetry (CV) was employed to evaluate the concentration of electroactive species within the Nafion LS films and to determine Dapp. The latter was found to be essentially invariant with film thickness, but the value for Ru(bpy)32+ was 1 order of magnitude larger than for FA+. CV and SECM measurements yield different values of Dapp, and the underlying reasons are discussed. In general, the Dapp values for these films are considerably smaller than for recast Nafion films, which can be attributed to the compactness of Nafion LS films. Nonetheless, the ultrathin nature of the films leads to fast response times, and we thus expect that these modified electrodes could find applications in sensing, electroanalysis, and electrocatalysis.     

Synthesis, structures, and physical properties of copper(II)-gadolinium(III) complexes combining ferromagnetic coupling and quadratic nonlinear optical properties

Two copper(II)-gadolinium(III) metal complexes of formula CuIIGdIIILX3 are reported. H2L stands for the Schiff base ligand obtained by condensation of 3,4-dimethoxysalicylaldehyde with ethylenediamine (complex 1) or 1R,2R-(+)-1,2-diphenylethylenediamine (complex 2). While 1 reveals a centrosymmetric crystal structure, 2 crystallizes in the noncentrosymmetric P212121 space group and exhibits an efficiency 0.3 time that of urea in second harmonic generation. Due to a trend for dissociation in solution, the molecular hyperpolarizabilities (beta) cannot be determined experimentally for 1 and 2. Nevertheless, the electric field induced second harmonic (EFISH) technique, in connection with spectroscopic data and a ZINDO semiempirical approach, leads to a beta value of -6.5 x 10(-30) cm5 esu(-1), for the related CuIIL monomers, as an indicative range of magnitude in all these Schiff base complexes. In addition, 1 and 2 exhibit a ferromagnetic coupling in solid state with J = 3.3 and 1.3 cm-1, respectively (J being the parameter of the exchange Hamiltonian = -JSCu x SGd).     

PAn/PEO-LiClO4界面的交流阻抗研究

近年来,交流阻抗方法已成功地应用于固体电极-电解质界面电化学性能的研究.特别是最近几年,聚氧化乙烯-锂盐复合物(PEO-LiX)系列高分子电解质材料研究的深入,研制以高分子电解质为隔膜的全固态锂电池的设想已成可能.前人用交流阻抗方法对Li/PEO-LiX和钒氧阴极/PEO-LiX界面行为研究已作了大量工作,并获得相关锂电池电极界面电化学性能的理论数据.本文用化学氧化法合成聚苯胺(PAn)阴极材料和本室改进的PEO-LiClO_4复合物作室温固体电解质,研究PAn/PEO-LiClO_4电极界面的电化学性能,获得一些新的结果。