Situ Second Harmonic Generation Research Articles

In Situ Heterodyne-Detected Second-Harmonic Generation Study of the Influence of Cholesterol on Dye Molecule Adsorption on Lipid Membrane.

Cholesterol plays an essential role in regulating the functionality of biomembranes. This study employed in situ second-harmonic generation (SHG) to investigate the adsorption behavior of the dye molecule 4-(4-(diethylamino)styryl)-N-methyl-pyridinium iodide (D289) on a biomimic membrane composed of 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (sodium salt) (DPPG) and cholesterol. The time-dependent polarization SHG intensity exhibited an initial rapid increase, followed by a subsequent decline. The initial increased SHG intensity is responsible for the electrostatic interaction-driven adsorption of D289 onto the membrane, while the decrease in the SHG signal results from the broadening of the orientation distribution within the membrane. Heterodyne-detected SHG (HD-SHG) measurements demonstrated that the adsorption of dye molecules influenced the phase of the induced electric field. The interfacial potential Φ(0) as a function of time was measured, and we found that even after reaching a stable Stern layer state, the diffusion layer continued to exhibit a dynamic change. This study offers a comprehensive understanding of the influence of cholesterol on adsorption, reorientation dynamics, and dynamic changes in the reorientation of water in the diffusion layer.

Adsorption and Oxidation Dynamics of Disperse Orange 3 on a Polycrystalline Pt Electrode Studied by In Situ Second Harmonic Generation

Adsorption mechanisms and electrochemical reaction mechanisms at the molecular level are fundamental issues in electrochemistry. Here, we used in situ second harmonic generation (SHG) combined with in situ UV–vis spectra and potential step techniques to investigate the dynamics of the adsorption and oxidation of 4-amino-4′-nitroazobenzene (disperse orange 3, DO3) molecules on a polycrystalline Pt electrode. Time-dependent SHG spectra with different polarization combinations under certain potential steps confirmed that the SHG intensity change in the DO3 molecules resulted from the number density change rather than the orientation angle change. A double potential step experiment and UV–vis spectra verified that the number density change arose from the cooperative effects of adsorption and oxidation of DO3 at the interfaces. Under an applied potential, the adsorption rate of DO3 was greater than the electrooxidation rate in the first hundred seconds until full coverage was achieved and the maximum SHG intensity was reached. Subsequently, the oxidation of DO3 dominated until equilibrium was established, while the SHG intensity stabilized. In addition, the time-dependent SHG spectra showed that the rate constants of the adsorption process and the oxidation reaction were strongly dependent on the potential. This work provides in-depth insights into the adsorption and electrochemical reaction at electrode/solution interfaces.

Monitoring the Seed-Mediated Growth of Gold Nanoparticles Using in Situ Second Harmonic Generation and Extinction Spectroscopy

In situ second harmonic generation (SHG) coupled with extinction spectroscopy is used for real-time monitoring of seed-mediated growth dynamics of colloidal citrate-stabilized gold nanoparticles in water. The time-dependent in situ SHG results capture an early stage of the growth process where a large enhancement in the SHG signal is observed, which is attributed to the formation of plasmonic hot spots from a rough and uneven nanoparticle surface. The temporal peak in the SHG signal is followed by a decay that is fit to an exponential function to characterize the size-dependent nanoparticle growth lifetime, which varies from 0.45 to 1.7 min for final nanoparticle sizes of 66 and 94 nm, respectively. This early growth stage also corresponds to a broadening of the plasmon spectra, as monitored using time-dependent in situ extinction spectroscopy. Over the course of the seed-mediated growth reaction, the nanoparticle becomes more thermodynamically stable through surface reconstruction resulting in a smoother...

Self-powered photovoltaic photodetector established on lateral monolayer MoS2-WS2 heterostructures

With the rapid development of modern semiconductor industry, power free or self-powered devices become an indispensable part in the electronic components and optoelectronic products. Epitaxial connected TMDs lateral heterojunctions with the maximum built-in potential at the hetero-interface offer fast separation of the photo-generated electron-hole (e-h) pairs without an external bias, which make them promising for self-powered devices. However, so far, the photovoltaic performance of such structures are rarely studied. Here, we report the photovoltaic light sensors based on individual monolayer MoS2-WS2 in-plane heterostructures that were created through a one-step synthesis strategy. The in situ second-harmonic generation (SHG) characterizations of this monolayer in-plane heterostructures directly demonstrate their underlying symmetry and high orientation. The photovoltaic photodetectors designed on individual MoS2-WS2 in-plane samples that operate in a self-powered mode (zero bias) exhibits a spectral responsivity (Rλ) of 4.36 mA/W and detectivity (D*) of 4.36 × 1013 Jones under 28.64 mW/cm2 @ 532 nm. The primary characteristics of the lateral heterostructure devices are attributed to the built-in potential at the interface. The initial self-powered light sensor in a monolayer heterostructures combined with the scalable growth can be further applied in other 2D heterostructures.

Structural dependency of collagen fibers on ion types revealed by in situ second harmonic generation (SHG) imaging method

Ionic species in aqueous solutions alter protein solubility and aggregation behavior through a variety of complex interactions.

Synthesis and properties of a second‐order, nonlinear‐optical, addition‐type polyimide with high thermal and temporal stability

AbstractA highly thermally and temporally stable, second‐order, nonlinear‐optical polyimide with an X‐type chromophore (2‐{4‐[4,5‐di(4‐nitrophenyl)imidazolyl]phenyl}‐4,5‐di(4‐aminophenyl)imidazole) was synthesized by the Michael addition reaction. The structure of the prepolymer was characterized with Fourier transform infrared (FTIR). Its thermal stability and curing behavior were studied with differential scanning calorimetry, thermogravimetric analysis, and FTIR. After the curing, the glass‐transition temperature of the polyimide greatly increased. The FTIR results suggested that addition and/or crosslinking reactions were carried out during the thermal curing of the prepolymer. A poling polyimide film was achieved, and the thermal and temporal stability of the poling‐induced orientation were evaluated with a multistep corona‐poling technique at an elevated temperature and with in situ second harmonic generation (SHG) measurements. The temporal orientation of the poled polyimide film was over 1000 h at 150°C; it retained 85% of the initial second‐order, nonlinear‐optical coefficient. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Effect of pendant group on the second-order optical nonlinearity of sol–gel films

A series of organically modified sol–gel films with various acceptor groups were prepared and characterized. All the chromophores exhibit much larger microscopic optical nonlinearity compared with the classical chromophore DR1 in solvatochromic measurement. Using in situ second harmonic generation (SHG) technique, the optimal poling temperatures (Topt) for sol–gel films were obtained. The second harmonic coefficients (d33) of hybrid films at the wavelength of 1,064 nm were in the range of 50.1–70.3 pm/V after corona poling under their Topt. The NLO stabilities of these poled films were also investigated by tracing the d33 value as a function of temperature and time. One of the hybrid films, which was prepared from chromophore 2,4-dinitro-4′-(N,N-dihydroxyethyl) aminoazobenzene exhibited a combination of large optical nonlinearity and high NLO stability. Furthermore, the effects of molecular structure on the NLO property and thermal stability of the hybrid films were also discussed.

Preparation and second-order optical nonlinearity of inorganic–organic hybrid films

Abstract The sol–gel technique has been used to prepare a thin film for second-order nonlinear optics (NLO). An azo-dye molecule 2,5-dimethyl-4-(4′-nitrophenylazo)phenol (DMNPAP) was covalently bonded to the silicon oxide network through hydrolysis and co-condensation between the alkoxysilane dye and tetraethyl silicate (TEOS) in relatively high loading densities (43 wt%). The resulting film showed a thermal stability up to 302 °C in thermogravimetric analysis (TGA) thermograms and a flat surface morphology in atomic force microscope (AFM) image. The orientation behavior of the poled film was studied by UV–visible spectroscopy. The NLO activity (d33), which was estimated to be 6.5 pm/v at 1064 nm by in situ second harmonic generation (SHG) measurement, the thermal stability of the second-order nonlinearity was also reported.

A second harmonic generation study of the oxidation of copper electrodes

The oxidation of copper in basic media has been studied by in situ second harmonic generation (SHG), where the SHG signal was recorded alongside the cyclic voltammogram. The SHG signal changes markedly as the copper surface is oxidised to first Cu 2O and then CuO in a duplex structure. The development of Cu 2O gives rise to a resonant SHG signal because of the band-gap of the material then the upper CuO layer produces an electric-field induced second harmonic (EFISH) response. A correlation of charge with the SHG signal is informative with regard to the mechanism of reduction of CuO and SHG is shown to be a useful method for the examination of oxidation of electrode surfaces.

Second-order nonlinear optical properties of cross-linked silica films prepared through sol–gel process

In this paper, second-order NLO chromophores containing two reactive sites have been synthesized and characterized by 1H NMR, FTIR and elemental analysis. The transparent films have silica network of matrix and covalently bonded chromophore of NLO segment were then fabricated via sol–gel process. The SHG coefficients ( d 33) of the poled films were calculated to be around 50 pm/V by in situ second harmonic generation (SHG) measurement. The thermal stability of the NLO coefficient was investigated by the depoling experiment and temporal decay test, showing that the cross-linked films had a good thermal stability up to 160 °C.

Synthesis and characterization, second-order nonlinear optical and photorefractive properties of new multifunctional polysiloxane with broad optical transparent pentafluorophenyl azo chromophore

A new polysiloxane P1 with pendant carbazoly groups and a high density of the pentafluorophenyl azo chromophore as side chain was synthesized in moderate yield by two successive postfunctionalization reaction including Vilsmeir formylated reaction and Knoevenagel condensation. Its structure was verified by 1H NMR, IR, and UV–Vis spectra. The polymer P1 exhibited good solubility in common organic solvents and was thermally stable up to 282 °C. The maximum absorption appeared at about 407 nm for P1 in THF, which was blue-shifted about 87 nm compared to the corresponding polysiloxane P2 with a well-known nitro acceptor azo chromophore, resulting in a wider transparency window. The value of the NLO coefficient d 33 of P1 thin film, measured by in situ second harmonic generation (SHG), was 11.9 pm/V. Preliminary photorefractive experiments showed that P1 obtained diffraction efficiency of 78% and a time constant of 1.19 sec.

Enhanced thermal stability of optical nonlinearity for anilino–silane derived inorganic–organic hybrid thin films

A series of chromophore-bonded inorganic–organic hybrid films were successfully prepared via a sol–gel process using the alkoxysilane dye (ICTES-DR1), anilinomethyltriethoxysilane (AMTES) and tetraethoxysilane (TEOS) as precursors. Second-order NLO properties and their thermal stability of the hybrid films were investigated by in situ second harmonic generation (SHG) measurement. The poled films exhibit large second harmonic coefficient (d33) in the range of 32–41pm/V at 1064nm. The aniline group of the AMTES was found to be effective for improving the thermal stability of optical nonlinearity due to the formation of hydrogen bonds between the carbonyl and aniline group, which was confirmed by virtue of FTIR and UV–visible spectra.

Effect of thermal treatment on the nonlinear optical response and stability of hybrid inorganic–organic films

Abstract Hybrid inorganic–organic second-order nonlinear optical (NLO) materials have been obtained through hydrolysis and co-condensation between tetraethyl silicate (TEOS), Vinyltriethoxysilane (VTES) and an alkoxysilane dye (ICTES-DR1). The hybrid materials showed a thermal stability up to 306 °C in thermogravimetric analysis (TGA) thermograms and no visible glass transition temperature ( T g ) was observed in the range 50–200 °C in differential scanning calorimetry (DSC) thermograms. The poling profiles of the hybrid films were investigated by using the in situ second harmonic generation (SHG) measurement. The thermal stability of the second order NLO properties of the poled films were also investigated by the in situ SHG intensity probing. It has been shown that the NLO response and its thermal stability were strongly dependent on the thermal pretreatment of the films.

Preparation and Nonlinear Optical Properties of Inorganic−Organic Hybrid Films with Various Substituents on Chromophores

Four kinds of hydroxy-ended azobenzene-type chromophores containing different substituent groups as electron donor or electron acceptor were synthesized and further reacted with 3-isocyanatopropyltriethoxysilane (ICTES) to give alkoxysilane dyes via a urethane reaction. Following a sol-gel process of the alkoxysilane dyes, the inorganic-organic hybrid nonlinear optical (NLO) films were successfully prepared. Molecular structures of the resultant films were confirmed by elemental analysis, FTIR, and 1H NMR. The betaCT mu(g) values of the chromophores were evaluated by a solvatochromic method, and the second harmonic coefficients (d33) of the hybrid films were measured by in situ second harmonic generation (SHG) measurement. The hybrid films exhibited large optical nonlinearity and full transparency in the visible range. The effects of substituent group and position on betaCT mu(g) values of the chromophores and d33 values of the films were also discussed.

Two new poly(arylene ether sulfone)s containing second-order nonlinear optical chromophores

Two new poly(arylene ether sulfone)s, P1 and P2, with pendant nonlinear optical (NLO) chromophores (60 and 84%, respectively) have been easily prepared by post-esterification reaction of poly(arylene ether sulfone) P under mild conditions. P1 and P2 are readily soluble in common organic solvents at room temperature and thermally stable up to 200 °C in both air and argon. The glass transition temperatures (T g's) of P1 and P2 are 174 and 189 °C, respectively. The resonant nonlinear optical coefficient (d 33) values were estimated to be 29.2 and 16.5 pm/V for P1 and P2, respectively, by in situ second harmonic generation (SHG) measurements at 1064 nm fundamental wavelength. By using the approximation two-level model, the nonresonant NLO coefficient (d 33(∞)) values of P1 and P2 were estimated to be 6.6 and 4.8 pm/V, respectively.

A Comparative Study of Hydroxide Adsorption on the (111), (110), and (100) Faces of Silver with Cyclic Voltammetry, Ex Situ Electron Diffraction, and In Situ Second Harmonic Generation

Hydroxide adsorption on the (111), (110), and (100) faces of silver electrodes from mixed NaOH/NaF solution is studied using cyclic voltammetry and in situ second harmonic generation (SHG). Cyclic voltammograms for the three low index silver planes in alkaline electrolytes are for the first time compared. They show two pairs of anodic and cathodic peaks in the potential interval below the equilibrium Ag/Ag(2)O potential. These are attributed to the specific adsorption of hydroxide ions followed by submonolayer oxide formation. The differences in the cyclic voltammograms for the (111), (110), and (100) planes are attributed to different (i) work functions, (ii) surface atomic densities, and (iii) corrugation potentials for these surfaces. Ex situ low energy electron diffraction (LEED) and reflection high energy electron diffraction (RHEED) show that disordered adlayers are formed on Ag(111) and Ag(100), in contrast to Ag(110), where ordered structures are produced in the region of the first pair of current peaks. In the region of the second pair of peaks, LEED indicates disordered oxide phases on each crystal plane and RHEED shows the presence of small islands of c(2 x 2) structure at some potentials on (110) and (100). SHG measurements were performed (i) in the potential scan mode at constant rotational angle and (ii) at constant potential as a function of the rotational angle. The isotropic (for the (111), (110), and (100) planes) and anisotropic (for the (110) and (111) planes) contributions to the SHG intensity were calculated by fitting the experimental data and are discussed in terms of their dependence on the charge density at the interface, on hydroxide adsorption, and on submonolayer oxide formation.

Hydroxide Adsorption on Ag(110) Electrodes: An in Situ Second Harmonic Generation and ex Situ Electron Diffraction Study

The adsorption of hydroxide on the Ag(110) surface has been studied with cyclic voltammetry, in situ second harmonic generation (SHG), and ex situ low energy electron diffraction (LEED) and reflection high energy electron diffraction (RHEED). OH- is found to be adsorbed on the Ag(110) surface at potentials negative of the potential of zero charge, forming small antiphase domains of c(2 × 6) symmetry. Further adsorption leads to longer-range order and the removal of antiphase domain boundaries and is associated with a current peak in the cyclic voltammogram (CV). Concurrently, a change in symmetry patterns is observed in SHG. A c(2 × 2) pattern gradually replaces the c(2 × 6) pattern as the potential, and the OH- coverage, is increased. At the beginning of the second current wave, another symmetry change takes place which is accompanied by a sharp change in the LEED pattern from a c(2 × 2) pattern to a (1 × 1) pattern with strong background, indicating a disordered adlayer. However, RHEED results show that...

Synthesis and characterization of second-order nonlinear optical polyurethane with high thermal stability

A second-order nonlinear optical polyurethane was formed with an X-type multi-dimensional charge-transfer (CT) chromophore (DNPIPDHPI) and 3,3 ′-dimethoxy-4,4 ′-diphenyl diisocyanate. Simultaneous poling and polymerization and in situ second harmonic generation (SHG) measurement technique was carried on to evaluate the thermal stability of the poling induced orientation. The SHG signal of the poled polymer film was not decay below 150 °C and remains 90% of relative d 33 value at 200 °C, which is better than the results reported in literature. Comparison of thermal stability indicates that the X-type chromophores possess better property in controlling the decay of the SHG activity than classic chromophores.

Polysilanes with NLO chromophores as pendant groups by utilizing different synthetic strategies

This paper summarizes our research on the synthesis and properties of several kinds of functionalized polysilanes (FPSs) containing nonlinear optic (NLO) chromophores in the side chain. They have been synthesized successfully through utilizing different synthetic strategies: chloromethylation of poly(methylphenylsilanes) and the following etherification with the hydroxy-containing NLO chromophore in water–chloroform two-phase system with Brij35 as a phase-transfer catalyst; hydrosilylation of polyhydrosilanes with the NLO chromophore containing the terminal double bond; etherification of chlorine-containing polysilanes with the hydroxy-containing NLO chromophore; and post-functionalization of phenyl group-containing polysilanes through azo coupling with p-nitrobenzenediazonium fluoroborate or tricyanovinylation with the oxidant tetracyanoethylene. FPSs were characterized with FT-IR, UV–vis spectra, differential scanning calorimetry (DSC), gel permeation chromatography (GPC), and elemental analysis. The second-order optical nonlinear properties of the polysilanes were determined by in situ second harmonic generation (SHG) experiments.

An in situ second harmonic generation study of the electrochemical oxidation of silicon in fluoride media

The electrochemical oxidation of p-type Si in fluoride solutions has been studied by in situ second harmonic generation (SHG) with the SHG signal being recorded simultaneously with the cyclic voltammogram. The SHG signal is shown to change in tandem with the electrochemical response enabling the identification of transition points between different surface conditions such as hydrogen-terminated, hydrated oxide and oxide. Interpretation of the changes in SHG suggests that the initial response is due to the electric field-induced second harmonic (EFISH) due to the electric field gradient at the interface. It then becomes dominated by the variation in the resonant surface non-linear susceptibility as the changes in local bonding affect the response. SHG signals display a much greater sensitivity to surface conditions than the voltammetric response and allow the real-time identification of the potentials at which significant changes take place in the state of the surface.