Optical and photoluminescence studies of gold nanoparticles embedded ZnO thin films

Gold nanoparticles (AuNPs) embedded ZnO thin films were prepared by sandwiching a thin thermally evaporated Au film between two sputtered ZnO films. The films were characterized by high resolution transmission electron microscopy (HRTEM), glancing angle X-ray diffraction (GXRD), optical absorption and photoluminescence (PL) measurements. GXRD data exhibited peaks which were attributed to the reflections from various ZnO and Au planes. Size dependence of the plasmon absorption was studied by forming nanoparticles with various sizes. Optical absorption spectra showed strong absorption due to localized surface plasmons at about 608, 638 and 676 nm for films having average AuNPs sizes of 27, 40 and 67 nm respectively. AuNPs embedded ZnO film showed a strong reduction in the intensity of photoluminescence, which was prominent in the case of pure ZnO film. The rise in temperature at a single nanoparticle site was calculated to be 22 K for a particle size of 80 nm.     

微带法测试薄膜0.5～5G磁导率

提出了可以在0.5～5GHz频带扫频测量磁性薄膜复磁导率μr的微带线法,推导出了由倒置短路微带线单端口网络的反射系数R(S11)表示μr的理论公式.对微带线夹具进行了设计,并结合虚拟仪器技术,以LabVIEW为软件平台建立了一套测量薄膜微波复磁导率的自动测量系统.给出了FeCo基磁性纳米颗粒膜的磁导率测试曲线,表明微带法具有准确性较高、既适宜于面内各向异性薄膜又适合于各向同性薄膜的测量和容易操作等优点.     

Contactless method of determining the coefficient of thermal diffusivity of local domains of surface layers and thin films

A method is proposed for measuring the coefficient of thermal diffusivity of microsections of surface layers and thin films. The coefficient of thermal diffusivity is calculated from the time dependence of the heat flux emitted by the heated surface.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 31, No. 2, pp. 289–294, August, 1976.     

Preparation and optical properties of gold nanoparticles embedded in barium titanate thin films

High amount of gold nanoparticles was successfully incorporated into amorphous BaTiO₃ thin films by sol-gel process. Thiourea was applied to prevent Au ions from being reduced and aggregating as the effective stabilization agents. These films exhibited unique surface plasma resonance red-shifting and particular changes of surface plasma resonance intensity with the increase of heat-treating temperature, which could be attributed to the influence of BaTiO₃ ferroelectric domains. The films also exhibited superfast nonlinear optical response and larger third-order nonlinear susceptibility ⁽³⁾, which was attributed to hot electron contribution.     

A resonant method for determining mechanical properties of Si3N4 and SiO2 thin films

This study investigates the measurement of Poisson's ratio and Young's modulus of silicon dioxide (SiO₂) and silicon nitride (Si₃N₄) thin films using a resonant method. Two thin films, which are SiO₂ and Si₃N₄, are fabricated as the specimens of microcantilever beams and plates using the bulk micromachining. The resonant frequency of the cantilever beams and plates is measured using a laser interferometer. The Young's modulus of thin films can be calculated from the resonant frequency of the cantilever beams, and the Poisson's ratio of thin films is determined by the frequency of the cantilever plates. Experimental results show that the Poisson's ratios of SiO₂ and Si₃N₄ are 0.16 and 0.26, respectively, and the Young's moduli of SiO₂ and Si₃N₄ are, respectively, 55.6 GPa and 131.6 GPa.     

Optical properties and instrumental performance of thin gold films near the surface plasmon resonance

The optical properties of very thin gold films have been evaluated by Fresnel analysis, with optical boundary conditions pertaining to the surface plasmon resonance (SPR) at the gold-water interface. The experimental SPR characteristic was evaluated in the angular interrogation mode. Film morphology was characterized by high resolution transmission electron microscopy. The magnitude of the resonance, i.e., the SPR signal, sensitively depends on, and is affected by film thickness and morphology. A sharply defined thickness of 55 ± 5 nm is required, to achieve optimum SPR excitation conditions, and instrumental sensitivity. With decreasing film thickness, below 40 nm, the resonance angle starts to shift to larger values. A substantial increase of the intrinsic resonance broadening parameter is observed below 70 nm, associated with an increasingly asymmetric SPR line shape. A similar effect occurs in the presence of a very thin chromium adhesion layer. Surface roughness and film thickness modulations determine the experimentally observed line broadening parameter. Instrumental noise levels largely depend on accuracy and quality at which the resonance angle can be determined. Substantial improvement and instrumental sub-pixel resolution is achievable by optimum fitting routines, accounting for drastic noise reduction and improved instrumental sensitivity, up to two orders of magnitude over the inherent geometric sensor pixel resolution.     

The effect of arginine on gold nanoparticles in colloidal solutions and in thin films

Gold nanoparticles were prepared in aqueous colloidal solutions and their interaction with L-arginine solutions at different concentrations was investigated by UV-vis spectroscopy, transmission electron microscopy (TEM) and atomic force microscopy (AFM). The shift towards red of the absorption maximum of gold nanoparticles with increasing L-arginine concentration and in time, and the apparition of a new large band at higher wavelength evidence the formation of assemblies of gold nanoparticles, mediated by the amino acid. TEM images present the progress in the building process of supermolecular structures. Further, the AFM images show the self assemblies of gold nanoparticles capped with L-arginine well ordered in large domains on silanized glass. As a model for the process, we suggest that the positively charged guanidinium group of L-arginine is anchored on the negative citrate capped gold nanoparticles, while the other two functionalities of L-arginine are involved in the bonding between gold nanoparticles. The ability of arginine to specifically bind gold nanoparticles could lead to an increased ability of proteins, containing arginine, to specifically bind to nanogold. Then, they bind other target proteins or different ligands underlying numerous biological and medical applications that range from nanoscale biosensors, cell-cell communications to targeted delivery of drugs to cancer cells.     

Specific binding of dacarbazine to DNA bases and oligonucleotides based on gold nanoparticles

We studied the specific binding of an anticancer drug, dacarbazine (DTIC), to DNA bases and oligonucleotides attached to gold nanoparticles by using electrochemical methods, and the results indicate that the presence of gold nanoparticles could facilitate the binding of dacarbazine to specific DNA bases and remarkably enhance the relative detection sensitivity. The results of the study on interaction of dacarbazine with oligonucleotides also illustrate that dacarbazine could recognize some specific sequence in DNA chain and sensitively detect single-base mismatch in DNA helix.     

A simple microemulsion based method for the synthesis of gold nanoparticles

The production of gold nanoparticles and nanoplates by enzymatically-synthesized lauroyl glucose, lauroyl fructose and lauroyl ascorbate is described. These emulsifiers formed oil-in-water microemulsions with toluene and the available reducing groups brought about a rapid reduction of chloroauric acid (HAuCl₄). Gold nanoparticles could thus be synthesized without the use of an additional reducing agent. Optical images, UV–visible spectroscopy, scanning electron microscopy, energy dispersive spectra (SEM–EDS) and X-ray diffraction (XRD) analysis revealed the presence of gold nanoparticles, which on further incubation aggregated into nanoplates. This paper thus describes a novel application of the enzymatically-synthesized esters.     

A chemical method for the preparation of TlS thin films

A method has been developed for chemically depositing thin films of TlS onto glass substrates using a thallous nitrate solution, ammonia and thiourea as the reacting agents. The material was characterized through X-ray powder diffraction, optical and photoelectric studies. The films were found to be p type with an optical energy gap of about 1.02 eV.     

Analytical solutions for determining the optical constants of very thin films

A method for determining the refractive index (n), extinction coefficient (k), and physical thickness (d) of very thin films is presented. After limited development of the film characteristic matrix elements to the third order in (d/λ) (λ is wavelength), we derive simple analytical expressions for n, k, and d in terms of the film front reflectance, back reflectance and transmittance. The main advantages of the method are that the equations for n, k, and d are simpler, have a lower order and allow calculation of the optical constants with lower uncertainties than in the case of similar methods described in the literature.     

A new method for the structural analysis of thin island films

Analytical formulas for a systemic analysis of the structural coarsening of an island film on a solid substrate are obtained based on a comparison of the characteristics of theoretical and experimental distributions of the island size. This approach established a correlation between the features of transformation of the experimental distributions (histograms) and the features of processes in the island film material.     

电容位移法精确测量磁性薄膜的磁致伸缩系数

介绍了一种精确测量磁性薄膜磁致伸缩系数方法－电容位移法，并自行研制组装了一套测量装置，通过误差分析，仪器的精确标定，对稀土－铁超磁致伸缩薄膜的磁致伸缩系数进行了测量，获得满意的结果。     

Predicting and determining the bending stiffness of thin films and laminates

Three different techniques for experimentally determining the bending stiffness of flexible films and laminates have been evaluated using a number of different packaging materials. The results showed that a cantilever test was the best, giving reliable data for all kinds of films and laminates. A three‐point bending test proved to be sensitive to misalignment, whereas a bending‐under‐own‐weight test was incapable of handling curled samples and generally gave lower stiffness values. A model for predicting the bending stiffness of multilayer laminates from the elastic modulus of the constituents was developed and used to examine the influence of layer position and composition on the overall bending stiffness. Model calculations showed that thin layers, such as adhesives, print and barrier coatings, can have a large influence on the bending stiffness and that the influence often goes against what would be intuitively expected. The calculations also showed that layer modulus often is less important than layer thickness and that the position of the layer in the laminate can have a major influence on the overall stiffness. Copyright © 2001 John Wiley & Sons, Ltd.     

A method to evaluate mechanical performance of thin transparent films for flexible displays

Mechanical flexing of plastic substrates coated with thin film permeation barriers causes stress-induced cracks that may lead to device degradation. This phenomenon is of particular importance for organic light emitting diodes, an emerging display technology that can be implemented on flexible substrates but imposes stringent requirements on the barrier performance. We demonstrate a dry-etch-based method to highlight cracks in thin films of transparent materials and make them visible under a conventional optical microscope on samples in a neutral, relaxed position. This approach allows for rapid evaluation of the mechanical performance of thin film barriers on flexible substrates.     

Improved efficiency of the chemical bath deposition method during growth of ZnO thin films

Chemical bath deposition (CBD) is an inexpensive and low temperature method (25-90 °C) that allows to deposit large area semiconductor thin films. However, the extent of the desired heterogeneous reaction upon the substrate surface is limited first by the competing homogeneous reaction, which is responsible for colloidal particles formation in the bulk solution, and second, by the material deposition on the CBD reactor walls. Therefore, the CBD method exhibits low efficiency in terms of profiting the whole amount of starting materials. The present work describes a procedure to deposit ZnO thin films by CBD in an efficient way, since it offers the possibility to minimize both the undesirable homogeneous reaction in the bulk solution and the material deposition on the CBD reactor walls. In a first stage, zinc peroxide (ZnO₂) crystallizing with cubic structure is obtained. This compound shows a good average transparency (90%) and an optical bandgap of 4.2 eV. After an annealing process, the ZnO₂ suffers a transformation toward polycrystalline ZnO with hexagonal structure and 3.25 eV of optical bandgap. The surface morphology of the films, analyzed by atomic force microscope (AFM), reveals three-dimensional growth features as well as no colloidal particles upon the surface, therefore indicating the predominance of the heterogeneous reaction during the growth.