Metal clusters in metal/C thin film nanosystems

Structure of metal clusters and of the C₆₀ matrix in Au/C₆₀ and Cu/C₆₀ nanosystems was investigated by X-ray diffraction. Results support a charge-transfer-type interaction at the metal-C₆₀ interface, which affects the size distribution of metal clusters, favouring interstitial location of metal ions in the fullerite lattice. Received 5 February 1999 and Received in final form 7 July 1999     

Gold aggregates on silica templates and decorated silica arrays for SERS applications

In this work, we report the fabrication and characterization of size controllable gold nanoparticles (NPs) aggregates for their application in surface enhanced Raman scattering (SERS). Aggregates were prepared using two methodologies: (i) by using silica particles arrays as a template to agglomerate gold NPs between the inter-particle interstices, and (ii) by functionalizing silica particles to be used as support to graft gold nanoparticles and thus to form decorated silica particle arrays. These substrates were used in the detection of Rhodamine 6G producing an enhancement factor (EF) from 10⁴ to 10⁶ that is associated to the increment of hot spot (HS) sites, and the fact that plasmon resonance from aggregates and absorption wavelength of test molecules are closely in resonance with excitation wavelength. The EF was also reduced when the plasmon resonance was red-shifted as a result of the increment of aggregate size. In spite of this, the EF is high enough to make these SERS substrates excellent candidates for sensing applications.     

Metal enhanced fluorescence of Ag-nanoshell dimer

The plasmon modes of Ag-nanoshell dimer on metal enhanced fluorescence (MEF) are studied theoretically. The amplified excitation rate of a dimer (two identical Ag nanoshells) illuminated by a plane wave for exciting a molecule located at the gap center is calculated. Subsequently, the apparent quantum yield of the emission of the excited molecule affected by the dimer is investigated. The multiple multipole method is used for the both simulations. Finally, the enhancement factor of the dimer on the overall photoluminescence of the molecule in terms of the two parameters is evaluated. Our results show that Ag-nanoshell dimer is a dual-band photoluminescence enhancer for MEF at the bonding dipole and quadrupole modes. The former is broadband, and the latter narrowband. Both bands depend on the gap size. Moreover, the average enhancement factor of Ag-nanoshell dimer for MEF with a Stokes shift is discussed.     

Surface-plasmon-mediated single-molecule fluorescence through a thin metallic film

We demonstrate that fluorescence of single molecules in the nanometric vicinity of a thin gold film can be effectively excited and detected through the film with an epi-illumination scanning confocal microscope. A full theoretical treatment of the fluorescence signal indicates that both excitation and emission are surface-plasmon mediated. Remarkably, the number of photons detectable from chromophores perpendicular to the interface is enhanced by the presence of the metal.     

Nanocluster n-CdO thin film by sol-gel for solar cell applications

The nanocluster-CdO film was successfully synthesized by sol-gel method using cadmium acetate and 2-metoxyethanol as starting materials and monoethanolamine as a stabilizer. The structural properties of the CdO film were investigated by atomic force microscopy (AFM). AFM results indicate that the CdO film is consisted of nanoclusters with grain size of 75-85 nm. The optical band gap E_g of nanocluster-CdO film was found to be 2.27 eV. The heterostructure, formed from two semiconductor layers having different optical band gaps, p-Si/n-CdO is prepared as a solar cell device. The electrical properties of the device were characterized by current-voltage and capacitance-conductance-voltage methods. The photovoltaic properties of p-Si/n-CdO device have been investigated. The p-Si/n-CdO heterojunction solar cell shows the best values of V_oc = 0.41 and J_sc = 2.19 mA/cm² under AM1.5 illumination. It is evaluated that this work is useful as a basis for the search of nanomaterial CdO and more competitive p-Si/n-CdO based solar cells, despite the fact that V_oc and J_sc are lower than those reported in the literature.     

Metal thin film ablation with femtosecond pulsed laser

Micromachining thin metal films coated on glass are widely used to repair semiconductor masks and to fabricate optoelectrical and MEMS devices. The interaction of lasers and materials must be understood in order to achieve efficient micromachining. This work investigates the morphology of thin metal films after machining with femtosecond laser ablation using about 1 μm diameter laser beam. The effect of the film thickness on the results is analyzed by comparing experimental images with data obtained using a two-temperature heat transfer model. The experiment was conducted using a high numerical aperture objective lens and a temporal pulse width of 220 fs on 200- and 500-nm-thick chromium films. The resulting surface morphology after machining was due to the thermal incubation effect, low thermal diffusivity of the glass substrate, and thermodynamic flow of the metal induced by volumetric evaporation. A Fraunhofer diffraction pattern was found in the 500-nm-thick film, and a ripple parallel to the direction of the laser light was observed after a few multiple laser shots. These results are useful for applications requiring micro- or nano-sized machining.     

The characteristics of Au:VO2 nanocomposite thin film for photo-electricity applications

Au nanoparticles have been fabricated on normal glass substrates using nanosphere lithography (NSL) method. Vanadium dioxide has been deposited on Au/glass by reactive radio frequency (rf) magnetron sputtering. The structure and composition were determined by X-ray diffraction and X-ray photoelectron spectroscope. Electrical and optical properties of bare VO₂ and Au:VO₂ nanocomposite thin films were measured. Typical hysteresis behavior and sharp phase transition were observed. Nanopartical Au could effectively reduce the transition temperature to 40 °C. The transmittance spectrum for both Au:VO₂ nanocomposite thin film shows high transmittance under transition temperature and low transmittance above transition temperature. The characteristics present the Au:VO₂ nanocomposite thin film can be used for applications, such as “smart window” or “laser protector”.     

Surface textured ZnO:Al thin films by pulsed DC magnetron sputtering for thin film solar cells applications

Transparent conducting thin films of ZnO:Al (Al-doped ZnO, AZO) were prepared via pulsed DC magnetron sputtering with good transparency and relatively lower resistivity. The AZO films with 800 nm in thickness were deposited on soda-lime glass substrates keeping at 473 K under 0.4 Pa working pressure, 150 W power, 100 μs duty time, 5 μs pulse reverse time, 10 kHz pulse frequency and 95% duty cycle. The as-deposited AZO thin films has resistivity of 6.39 × 10⁻⁴ Ω cm measured at room temperature with average visible optical transmittance, T_total of 81.9% under which the carrier concentration and mobility were 1.95 × 10²¹ cm⁻³ and 5.02 cm² V⁻¹ s⁻¹, respectively. The films were further etched in different aqueous solutions, 0.5% HCl, 5% oxalic acid, 33% KOH, to conform light scattering properties. The resultant films etched in 0.5% HCl solution for 30 s exhibited high T_total = 78.4% with haze value, H_T = 0.1 and good electrical properties, ρ = 8.5 × 10⁻⁴ Ω cm while those etched in 5% oxalic acid for 150 s had desirable H_T = 0.2 and relatively low electrical resistivity, ρ = 7.9 × 10⁻⁴ Ω cm. However, the visible transmittance, T_total was declined to 72.1%.     

A hybrid aerodynamic and electrostatic atomization system for enhanced uniformity of thin film

Droplet deposition processes by the mechanisms of either aerodynamics or electrostatic spray have been widely studied in various applications such as aerosol generators, thin film coatings, and nanoparticle formations. Among the current state-of-art methodologies, air spray deposition can produce small-sized droplets without fine control on their sizes and uniformity in deposited thin films. Conventional electrospray depositions, on the other hand, can fabricate thin films with good uniform with a relatively slow deposition speed. In this paper, a hybrid mechanism by means of aerodynamic and electrostatic deposition is investigated and demonstrated to allow high throughput and improved uniformity for thin film depositions. It utilizes both the electrostatic force and aerodynamic force to atomize the liquid and control the droplet spraying process with good stability/repeatability. A uniform thin TiO₂ film has been deposited as the demonstration example using this method. The velocities and trajectories of droplets during the deposition process have been characterized under different experimental parameters by using the technique of particle image velocimetry (PIV). This hybrid thin film fabrication method could be applicable in several industrial processes for better uniformity in making transparent electrodes, solar cells, displays, and automobiles.     

ZnO thin film deposition on butterfly shaped electrodes for ultraviolet sensing applications

ZnO thin film was deposited on patterned gold electrodes using sol–gel spin coating technique. Conventional photo-lithography with wet etching process was used to create butterfly shaped 13 μm gap from zero gap chrome mask. The deposited thin film was characterized structurally, morphologically and electrically using X-ray diffraction, scanning electron microscope and Kiethly sourcemeter. Current–voltage (I–V) characterization was captured in dark and UV conditions. The current gain of the fabricated device was 1.36 and the response and recovery time of the sensor was 76 s and 104 s, respectively, showed the fabricated device can be used for UV applications.     

掺Perylene的PVK薄膜荧光谱及发光机理

用高荧光效率的有机染料芘(perylene)掺杂聚乙烯咔唑(PVK),其荧光光谱与芘的发射光谱基本一致,而且亮度比纯芘发光提高十多倍,说明发光主要来自芘分子,并在PVK和perylene之间存在十分有效的能量传递或电荷转移过程,荧光谱强度随掺杂浓度的变化关系说明存在一个最佳的掺杂浓度比.分析PVK和perylene之间可能发生的能量转移过程,认为从PVK到perylene这种能量转移与实验不符;分析PVK和perylene薄膜的光致发光过程,认为从(PVK+)→(perylene+)和从(PVK-)→(p     

ZnO thin film on side polished optical fiber for gas sensing applications

In this work, thin ZnO films have been produced by pulsed laser deposition on side-polished fiber for optical gas sensor applications. The influence was investigated of the processing parameters, such as substrate temperature and oxygen pressure applied during deposition, on the sensitivity to ammonia of the sensing element. A shift of the spectral position of the resonance minimum to the longer wavelengths was observed at room temperature for the sample prepared at 150 °C substrate temperature and 20 Pa oxygen pressure. Spectral changes in the range 0.16-1.13 nm for NH₃ concentrations between 500 and 5000 ppm were also observed.     

Analysis of metallic nanoparticles embedded in thin film semiconductors for optoelectronic applications

This paper reports about a study of the local plasmonic resonance (LSPR) produced by metal nanoparticles embedded in a dielectric or semiconductor matrix. It is presented an analysis of the LSPR for different nanoparticle metals, shapes, and embedding media composition. Metals of interest for nanoparticle composition are Aluminum and Gold. Shapes of interest are nanospheres and nanotriangles. We study in this work the optical properties of metal nanoparticles diluted in water or embedded in amorphous silicon, ITO and ZnO as a function of size, aspect-ratio and metal type. Following the analysis based on the exact solution of the Mie theory and DDSCAT numerical simulations, it is presented a comparison with experimental measurements realized with arrays of metal nanospheres. Simulations are also compared with the LSPR produced by gold nanotriangles (Au NTs) that were chemically produced and characterized by microscope and optical measurements.     

Synthesis of the wheat-like CdSe/CdTe thin film heterojunction and their photovoltaic applications

We report on the fabrication of wheat-like CdSe/CdTe thin film heterojunction solar cells made using a simple electrochemical deposition method and close-spaced sublimation technology on indium tin oxide (ITO) substrates. Structural, optical, and electrical properties of the wheat-like CdSe/CdTe thin film junctions were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), energy dispersive spectrometry (EDS), ultraviolet–visible (UV–vis) absorption spectrum and Keithley 2400 analysis. A significant red-shift of the absorption edge is observed in this heterojunction. The heterostructure is composed of the wheat-like CdSe array and CdTe thin film, showing optical properties typical of type II heterostructures that are suited for photovoltaic applications. A photocurrent density of 8.34 mA/cm² has been obtained under visible light illumination of 100 mW/cm². This study demonstrates that the electrochemical deposition and the close-spaced sublimation technology, which are easily adapted to other chemical systems, are promising techniques for large-scale fabrication of low-cost heterojunction solar cells.     

Nanostructured Ni3Sn2 thin film as anodes for thin film rechargeable lithium batteries

Thin film Ni₃Sn₂ anodes were deposited on a Cu substrate by e-beam evaporator at room temperature. The deposited films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). They were tested as anodes for thin film rechargeable lithium batteries. These film electrodes exhibited an excellent cycle performance over 500 cycles. Ni₃Sn₂ films remained without undergoing any crystallographic phase change during cycling.     

超巨磁电阻薄膜在光探测上的新应用

混合价态钙钛矿锰氧化物在外界温度变化和磁场作用下表现出巨大的磁电阻(colossal magnetoreslstance，简记为CMR)效应，引起了人们的广泛关注．由于CMR材料在传感器、探测器以及硬盘读出磁头等应用器件研发上极具潜力，科学家们对其进行了大量研究．文章在简单介绍CMR材料结构和机理的基础上，着重报道了作者利用CMR薄膜的激光感生热电电势(LITV)制备激光功率／能量探测器和利用电阻在室温附近的巨大变化研制光热辐射探测器(bolometer)方面的新进展．     

Reflection characteristics of a copper metal-organic chemical-vapor-deposited thin film for vertical micromirror applications

We introduce Cu metal-organic chemical-vapor deposition as a potential means of conformal metal coating of the sidewalls of micromachined vertical mirrors. The optimal process temperature was experimentally found to be 215 degrees C, which gives high step coverage of better than 90%, and the surface roughness was less than 27 nm. The roughness, measured with an atomic force microscope, will induce a scattering loss less than 0.12 dB, which is small enough for vertical micromirror application. The experimental reflectances of Cu thin film were measured with a distributed-feedback laser (1550 nm) and found to be greater than 0.9 for incidence angles of 22.5 degrees and 45 degrees , and these reflectances were in good agreement with theoretical values.     

TiO2 nanoparticle thin film deposition by matrix assisted pulsed laser evaporation for sensing applications

The MAPLE technique has been used for the deposition of nanostructured titania (TiO₂) nanoparticles thin films to be used for gas sensors applications. An aqueous solution of TiO₂ nanoparticles, synthesised by a novel chemical route, was frozen at liquid nitrogen temperature and irradiated with a pulsed ArF excimer laser in a vacuum chamber. A uniform distribution of TiO₂ nanoparticles with an average size of about 10 nm was deposited on Si and interdigitated Al₂O₃ substrates as demonstrated by high resolution scanning electron microscopy-field emission gun inspection (SEM-FEG). Energy dispersive X-ray (EDX) analysis revealed the presence of only the titanium and oxygen signals and FTIR (Fourier transform infra-red) revealed the TiO₂ characteristic composition and bond. A comparison with a spin coated thin film obtained from the same solution of TiO₂ nanoparticles is reported. The sensing properties of the films deposited on interdigitated substrates were investigated, too.     

Biomolecules for development of biosensors and their applications

Biosensors are analytical devices incorporating biological materials such as enzymes, tissues, microorganisms, antibodies, cell receptors or biologically derived materials or a biomimic component intimately associated with or integrated within a physicochemical transducer or transducing microsystem which may be either optical, electrochemical, thermometric, piezoelectric or magnetic. The electronic signals produced are proportional to the concentration of specific analyte. A biomaterial may be any material, natural or man-made, that comprises whole or part of a living structure or biomedical device, which performs natural function. An essential component of molecular sensor is reagent layers. Creation of these layers require the immobilization of recognition elements for the detection method. The recognition elements are biomolecules. Laboratory methods of immobilization are numerous, but may not always appropriate for manufacture of biosensors. In the present article, we describe the use of various biomaterials for biosensors as well as their availability.     

Aluminum thin film enhanced IR nanosecond laser-induced frontside etching of transparent materials

Laser processing of glass is of significant commercial interest for microfabrication of precision optical engineering devices. In this work, a laser ablation enhancement mechanism for microstructuring of glass materials is presented. The method consists of depositing a thin film of aluminum on the front surface of the glass material to be etched. The laser beam modifies the glass material by being incident on this front-side. The influence of ablation fluence in the nanosecond regime, in combination with the deposition of the aluminum layer of various thicknesses, is investigated by determining the ablation threshold for different glass materials including soda-lime, borosilicate, fused silica and sapphire. Experiments are performed using single laser pulse per shot in an air environment. The best enhancement in terms of threshold fluence reduction is obtained for a 16 nm thick aluminum layer where a reduction of two orders of magnitude in the ablation threshold fluence is observed for all the glass samples investigated in this work.