Optical and topological characterization of gold nanoparticle dimers linked by a single DNA double strand

We demonstrate that symmetric or asymmetric gold nanoparticle dimers with substantial scattering cross sections and plasmon coupling can be produced with a perfectly controlled chemical environment and a high purity using a single DNA linker as short as 7 nm. A statistical analysis of the optical properties and morphology of single dimers is performed using darkfield and cryo-electron microscopies. These results, correlated to Mie theory calculations, indicate that the particle dimers are stretched in water by electrostatic interactions.     

In-situ electrical addressing of one-dimensional gold nanoparticle assemblies

Substrates with 1-dimensional nanosize grooves were prepared using extreme-ultraviolet interference lithography (EUV-IL), wherein gold nanoparticles were self-assembled to form 1-dimensional structures. To measure the electrical properties of gold nanoparticle chains we introduce a novel in-situ measuring method based on nanomanipulator system in a scanning electron microscope. This method comprises enormous versatility for the precisely electrical addressing of low-dimensional nanoscale structures and may even be applied to routinely addressing of structures in the sub-10 nm range.     

Molecular simulation of gold nanoparticle dispersion and aggregation in supercritical CO2

We report molecular dynamics simulations for multiple passivated gold nanoparticles (NPs) in supercritical CO₂ (scCO₂). This simulation provides a direct visual observation on dispersion behavior and aggregate morphology for the NPs suspended/blended in the scCO₂ fluid. Extensive interfacial structure properties, thermodynamic free energies, and dynamics’ properties were used to characterize the effective particle interactions. The effects of surface ligand length, solvent density, and surface coverage were examined. Our simulation results indicate that the NP dispersion is controlled by both the steric repellence between the capping ligands and the solvation interaction between surface ligands and solvent. Increasing surface coverage or ligand length leads to better dispersion owing to enhancing excluded-volume effect. Meanwhile, increasing solvent density can increase repulsive interaction between the passivated NPs, thereby producing a stable dispersion. In general, the simulation presents a guide in understanding and manipulating NP interactions in supercritical fluids.     

RTP晶体光学和电学性能研究

磷酸钛氧铷(RbTiOPO4,RTP)晶体是一种新型的、有重要应用前景的电光材料。采用分光光度计、Nd:YAG锁模激光器、耐压测试仪等设备,对其光学和电学性质进行了全面测试研究,包括透过谱、折射率、消光比、电阻率、电光系数等。测试结果表明:RTP材料具有透过谱宽、吸收损耗小、消光比大、电阻率高、电光系数大、半波电压低等优点,综合性能优异,所得实验数据将为高性能RTP电光调制器件的精确设计和优化提供参考。     

Conoscopy of chiral smectic liquid crystal cells

The conoscopic method for investigating the optical properties of a liquid crystal cell is studied with the aim of determining the effects of the approximations used in the calculation on the results. We confirm that the chiral liquid crystal cell forming a helical structure can be regarded as a single biaxial plate for analyzing the conoscopic image only if the helical pitch is less than several multiples of the wavelength of light. This approximation implies that the square of the refractive index along a direction is averaged over all the layers. An incorrectly chosen value for one of the principal refractive indices to be used in the analysis of the conoscopic data can lead to an incorrect conclusion, especially for the case when the wavelength dispersion of the refractive index is neglected. A thicker cell and a longer wavelength of the incident light can minimize these limitations of the conoscopic method. We propose a novel simulation method to find the molecular distribution in a liquid crystal cell based on the average-refractive-index approximation and the conoscopic data. This is shown to be a fast, more efficient, and useful method for estimating the director distributions.     

Optical properties and electrical conductivity studies of copper selenide nanoparticle

In this work, the optical properties were studied in the UV-VIS range for copper selenide nanoparticle prepared at 160, 170 and 200 °C by solvothermal route using ethylenediamine as a solvent. Sharp absorption bands were observed at shorter wavelength due to the confinement of electrons and holes in low dimensional system producing excitonic and Coulombic attraction. The binding energy and the optical band gap were determined and the two values were found to decrease with increasing temperature and decreasing grain size. DC electrical conductivities were measured with temperature and the activation energy was calculated. The obtained data indicated that, the prepared samples behave as a semiconductor material.     

Electrically controlled fluorescence in a nematic liquid crystal doped by a chiral fluorophore

We have discovered a strong electric field sensitivity of the fluorescence intensity while studying the diffusion processes of a chiral fluorescent molecule (CFM) in a nematic liquid crystal (NLC) host. The experimental and theoretical study of this phenomenon indicates that the alignment of the CFM along two privileged orientation directions (with asymmetric distribution with respect to the NLC’s optical axis) is in the origin of this phenomenon. As a result, the obtained guest–host system demonstrates noticeable dichroism. Thus, the application of an electric field allows the reorientation of the anisotropy axis of the host, the change of CFM’s absorption (at the wavelength of excitation) and the dynamic electric control of its fluorescence intensity. The study of these phenomena allows also the identification of the angular distribution of guest CFMs suggesting that the elastic energy of orientation of the host molecules might be in the origin of the asymmetric angular distribution of CFM.     

Optical memory effect in a deformed helix ferroelectric liquid crystal

Optical memory in a deformed-helix ferroelectric liquid crystal is proposed by deforming the helix under the application of a square-voltage pulse of known magnitude and frequency. This effect is based on the electromechanical effect of helix deformation due to the electric field. When the interaction between the electric field and the dipole is sufficiently strong, all of the dipoles align along the electric field. In such a situation the interlayer dipole-dipole interaction is strong enough to balance the elastic deformation energy. When the electric field is switched off, the molecules remain in a static, balanced state owing to the dipole-dipole interaction and hence the memory effect.     

Formation of gold nanoparticles within a liquid crystalline polymeric matrix

We could prepare a novel composite consisting of a liquid crystalline polyester matrix and gold nanoparticles (7-14 nm). The polymer bears methoxy-terminated, hydrophilic, low molecular weight (350) PEG pendants on the rigid, hydrophobic aromatic polyester backbone. The polymers from a layered, sematic-like morphology at room temperature, where the interlayer is occupied by the PEG pendants. An aqueous solution of HAuCl4 was allowed to diffuse into the hydrophilic domains and the gold ions were reduced by hydrazine to gold nanoparticles. Our findings combine the concepts of self-assembly and nanoparticles, which can lead to formation of many interesting new nanocomposites.     

Optical switching of a metal-clad waveguide with a ferroelectric liquid crystal

Optical switching based on waveguide optics with a ferroelectric liquid crystal (FLC) is reported. The FLC cell was prepared as a prism coupler on which the liquid-crystal layer was sandwiched between two gold cladding layers. The role of the gold layer was examined, and the optimum thickness of the top gold layer for obtaining high contrast was determined by use of the Fresnel equation. Various optical modulations of reflectivity were predicted on the basis of theoretical calculation, taking into account the molecular reorientation of the FLC, and examined at an appropriate angle of incidence and rotational angle of the FLC cell with respect to the plane of incidence.     

Optical multi-stability of bimesogenic cholesteric liquid crystal

In this paper, we present a multi-stable property in a bimesogenic cholesteric liquid crystal material with a proper chiral additive and check its potential as an energy saving transmissive type liquid crystal display (LCD) through its electro-optic characteristics. Experimental results show that the multi-stable characteristics in the fabricated cholesteric LC cell are very stable. Such multi-stable properties depend on the driving frequency, voltage, and field direction. The contrast ratio in the fabricated transmissive type cholesteric LC cell was 15:1, which is a result produced by voltage and frequency control.     

Optical and electrical characterization of CdS thin films

Thin CdS films have been grown by chemical bath (CdCl₂, thiourea, ammonia) deposition (CBD) on SnO₂ (TO)-coated glass substrate for use as window materials in CdS/CdTe solar cells. High-resolution transmission electron microscopy revealed grains with an average size of 10 nm. The structure was predominantly hexagonal with a high density of stacking faults. The film crystallinity improved with annealing in air. Annealing in a CdCl₂ flux increased the grain size considerably and reduced the density of stacking faults. The optical transmission of the as-deposited films indicated a band gap energy of 2.41 eV. Annealing in air reduced the band gap by 0.1 eV. Annealing in CdCl₂ led to a sharper optical absorption edge that remained at 2.41 eV. Similar band gap values were obtained by photocurrent spectroscopy and electroabsorption spectroscopy (EEA) using an electrolyte contact. EEA spectra were broad for the as-deposited and air-annealed samples, but narrower for the CdCl₂-annealed films, reflecting the reduction in stacking fault density. Donor densities of ca. 10¹⁷ cm ^–3 were derived from the film/electrolyte junction capacitance.     

Time-resolved Mueller matrix analysis of a liquid crystal on silicon display

We present a full polarimetric characterization of a liquid crystal on silicon (LCoS) display, with time resolution measurements below the frame period of the device. This time-resolved analysis shows evidence of temporal fluctuations in the millisecond range in the state of polarization of the beam reflected by the display. We demonstrate that light reflected by the display is maintained fully polarized, but these temporal fluctuations result in an effective depolarization effect when detectors with long time integration intervals are used in the characterization of the display.     

Synthesis and characterization of photochromic star-like liquid crystal

A new photochromic star-like liquid crystal that is written by SiC₄ and containing four butoxyazobenzene mesogens in its periphery has been synthesized and characterized by the spectroscopic methods and thermal analysis. SiC₄ is nematic phase and its phase behavior is Cr138N147I145N118Cr. The quantum yield and photoisomerization of SiC₄ in chloroform (CHCl₃) and tetrahydrofuran (THF) have been studied by UV/Vis absorption spectra. The results indicate that the photochromism of SiC₄ in CHCl₃ and THF are in accordance with the first-order kinetics. The photochromism rate constants in CHCl₃ and THF are 10⁻¹ s⁻¹, they are 10⁷ times larger than those of side-chain liquid crystalline polymers containing the same azobenzene moieties. These results show that the star-like structure does not significantly affect the photoisomerization activity of the azobenzene mesogen in its periphery.     

Distance-dependent plasmon resonant coupling between a gold nanoparticle and gold film

We present an experimental analysis of the plasmonic scattering properties of gold nanoparticles controllably placed nanometers away from a gold metal film. We show that the spectral response of this system results from the interplay between the localized plasmon resonance of the nanoparticle and the surface plasmon polaritons of the gold film, as previously predicted by theoretical studies. In addition, we report that the metal film induces a polarization to the single nanoparticle light scattering, resulting in a doughnut-shaped point spread function when imaged in the far-field. Both the spectral response and the polarization effects are highly sensitive to the nanoparticle-film separation distance. Such a system shows promise in potential biometrology and diagnostic devices.     

Fabrication,characterization and gas sensing properties of gold nanoparticle and calixarene multilayers

Calixarenes are a group of materials that are widely used for gas sensing studies because of their simple synthesis, conformational flexibility, binding group tunability, variability in their cavity sizes and improved selectivity to different gas molecules. In recent years it has been shown that incorporation of gold nanoparticles (AuNPs) into organic layers further enhances their gas sensing performance. The present study reports on the fabrication of thin films of calixarene and AuNPs using Langmuir–Schaefer (LS) methods. The gas sensing properties of the produced films are investigated on exposure to saturated vapours of volatile organic compounds (VOCs) using surface plasmon resonance as an optical detection technique. Multilayers comprising films of AuNPs and calixarene have been investigated to evaluate the effect of AuNPs on the films sensing performances. It has been demonstrated that the hybrid layers exhibited improved sensing performance in terms of the degree of their response.     

Glass-fibre-reinforced composites with enhanced mechanical and electrical properties - Benefits and limitations of a nanoparticle modified matrix

Nanoparticles and especially carbon nanotubes (CNTs) provide a high potential for the modification of polymers. They are very effective fillers regarding mechanical properties, especially toughness. Furthermore, they allow the implication of functional properties, which are connected to their electrical conductivity, into polymeric matrices. In the present paper, different nanoparticles, as fumed silica and carbon black, were used to optimise the epoxy matrix system of a glass-fibre-reinforced composite. Their nanometre-size enables their application as particle-reinforcement in FRPs produced by the resin-transfer-moulding method (RTM), without being filtered by the glass-fibre bundles. Additionally, an electrical field was applied during curing, in order to enhance orientation of the nanofillers in z-direction. The interlaminar shear strengths of the nanoparticle modified composites were significantly improved (+16%) by adding only 0.3 wt.% of CNTs. The interlaminar toughness G_Ic and G_IIc was not affected in a comparable manner. The laminates containing carbon nanotubes exhibited a relatively high electrical conductivity at very low filler contents, which allows the implication of functional properties, such as stress-strain monitoring and damage detection.