Nanoporous structure of a GdF(3) thin film evaluated by variable angle spectroscopic ellipsometry

As excimer lasers extend to deep-ultraviolet and vacuum-ultraviolet wavelengths at 193 and 157 nm, optical coatings experience the challenge of eliminating possible environmental contamination, reducing scattering loss, and increasing laser irradiation durability. Wide bandgap metal fluorides become the materials of choice for the laser optics applications. To understand the optical properties of nanostructure fluoride films, thin GdF(3) films grown on CaF(2) (111) substrates were evaluated by variable angle spectroscopic ellipsometry. An effective medium approximation model was used to determine both the film porosity and the surface roughness. Structural evolution of the GdF(3) film was revealed with improved ellipsometric modeling, suggesting the existence of multilayer structure, a densified bottom layer, middle layers with increasing porosity, and a rough surface. The nanostructure of the film and the surface roughness were confirmed by atomic force microscopy. The attraction of the nanostructure to environmental contamination was experimentally demonstrated.     

Étude de surfaces de couches minces d'argent par microscopie électronique

The relationship between the surface irregularities and crystallographic structure of thin silver films are investigated as a function of the conditions of film preparation. Information on the film surface is deduced mainly from electron microscope examination of carbon surface replicas, while information on the film structure is obtained by studies of the films themselves by electron microscopy and diffraction as well as X-ray diffraction. The roughness of the Ag-air interface is shown to arise from (a) crystallization defects of Ag (e.g. twinning), or in some cases, grain boundaries; (b) the roughness of the substrate due to polishing; (c) the slow and gradual sulfuration of Ag. The conditions of preparation are determined for films in which less than 5% of the film surface is perturbed by irregularities with height (as estimated by microstereography) less than 30 or 50 Å.     

Fabrication of a polymer-coated silver hollow optical fiber with high performance

The techniques for fabricating a hollow optical fiber with an inner silver layer and a cyclic olefin polymer (COP) layer have been improved to reduce the surface roughness of these two layers. The loss spectrum was thereby drastically reduced over a wide wavelength range, from visible to near infrared. Optimization of the COP layer thickness resulted in low loss simultaneously at several key laser wavelengths. Infrared hollow fiber with low loss was developed for Er:YAG and Nd:YAG lasers. It can also deliver green and red pilot beams with low loss. Use of this fiber in therapeutic and pilot lasers should prove useful for research and development in laser medicine.     

Silver-island films as substrates for enhanced Raman scattering: effect of deposition rate on intensity.

The relationship between surface-enhanced resonance Raman scattering (SERRS) intensity and the rate of deposition during silver-island film preparation was examined, using zinc tetraphenylporphine (ZnTPP) as the adsorbate. The effect of the deposition rate on the optical properties of the films at specific wavelengths was also analyzed. The data show that the film extinction (the term extinction is used rather than absorption because the spectra have not been corrected for reflection or scattering losses) increases exponentially at 514 and 458 nm as the deposition rate is decreased. SERRS intensities also increase exponentially at these two excitation wavelengths with a decrease in the deposition rate. The optical density is linearly related to the SERRS intensity, and maximal enhancement is observed for films with the greatest extinction at these excitation wavelengths. In contrast, neither the extinction at 406 nm nor the SERRS scattering intensities resulting from excitation at this wavelength differ substantially. The surface-enhanced Raman scattering (SERS) intensity and the electronic spectra of 4,4'-bipyridine (BP) adsorbed onto silver films as a function deposition rate were also examined. The behavior of the nonresonantly enhanced BP is comparable to that of the resonantly enhanced ZnTPP samples. The effects of the surface morphology, as determined from transmission electron micrographs of the films at various deposition rates, on the corresponding electronic spectra and SERS/SERRS spectra are described.     

Carbon fiber coating with silver using intervening Au/Pd nanoparticle films produced using a spark discharge

A low roughness conductive silver film on a fiber substrate was fabricated via a catalytic surface activation (needed to initiate electroless silver deposition) with spark produced gold aerosol nanoparticles. Gold had a similar lattice parameter with silver in crystallinity and thus a crystallographic misfit between gold activated substrate and silver was minimized during the deposition, resulting in formation of a flat silver film. Properties were compared with those obtained with palladium aerosol activation, the gold activation enhanced thin-metallic film properties in surface root-mean-square roughness (nm: 8, gold vs 44, palladium) and electrical resistivity (μΩ cm: 64, gold vs 498, palladium) at 88 mg/g (silver/substrate) in deposition amount.     

Dual layer and multilayer enhancements from silver film over nanostructured surface-enhanced Raman substrates

Novel dual layer and multilayer silver film over nanostructure (SFON) substrates have been developed that provide surface-enhanced Raman scattering (SERS) signal enhancements of greater than 1000% compared to conventional single layer SFON substrates. These substrates provide signal enhancement factors of 3.8 x 10(5) and greater for a variety of SERS active analytes. Substrate preparation is accomplished by vapor depositing a thick (approximately 100 nm) layer of silver on top of an underlying layer of alumina nanoparticles, followed by deposition of additional layers of silver with silver oxide layers between them. Unlike previous dual layer silver island based substrates that have been developed, these substrates do not rely on achieving an optimal morphology via deposition of silver. Instead, these substrates rely on the roughness being provided by the original under-layer, providing enhanced substrate homogeneity and more reproducible signals than either silver island substrates or colloidal substrates. In addition, the signal enhancement gives these substrates extended lifetimes compared to conventional single layer SFON substrates. Finally, this study also shows that geometric surface structure and surface roughness factors play little or no role in this enhancement process, allowing for this multilayer fabrication process to be applied to many different types of substrates achieving similar or even greater results.     

Morphology and Structure of Nb Thin Films Grown by Pulsed Laser Deposition at Different Substrate Temperatures

This paper reports the fabrication of Nb thin films through pulsed laser deposition at different substrate temperatures, ranging from 300 to 660 K. While the variation of the substrate temperature does not affect significantly the excellent Nb thin film adhesion to the Si(100) substrate surface, the increase of the substrate temperature up to 570 K promotes an improvement of the grown film in terms of morphology and roughness. Such improvement is achieved through the formation of wider columnar structures with a reduced superficial roughness, around 5 nm, as shown by scanning electron microscopy(SEM) and atomic force microscopy. The use of temperatures over 570 K increases the substrate roughness due to the formation of irregular structures inside the film, as observed by SEM cross section analysis, and does not produce a relevant improvement on the crystalline structure of the material.     

基于分子动力学的丝网印刷柔性传感器电极导电性机理研究

目的 研究提高丝网印刷柔性传感器电极的导电性,为提升柔性传感器的电学性能提供参考依据。方法 首先采用分子动力学（Molecular Dynamic,MD）模拟方法,建立在Wenzel模型下导电银浆团簇在不同粗糙因子下的对苯二甲酸乙二醇酯（Polyethylene Terephthalate,PET）表面铺展的分子动力学模型,其次分别计算各体系下的结合能,用以表征不同体系下PET表面对导电银浆团簇结合能力,接下来通过丝网印刷实验的方法探究银浆与不同粗糙因子PET的结合能力对传感器电极的导电性的影响。结果 仿真结果表明,导电银浆团簇在不同粗糙因子的PET表面的铺展过程中会陷入粗糙表面的凹陷处,且导电银浆与基材的结合能随着PET粗糙因子的增加而增加。实验结果表明,使用不同粗糙因子的PET作为承印物能显著提升电极的导电性。相比于未处理的PET,随着粗糙因子的增加,导电线条的电导率逐渐升高,电阻率逐渐降低,方块电阻逐渐降低。电导率最大提升了77%,电阻率最大下降了43%,方块电阻最大下降了38%。结论 导电银浆在粗糙表面铺展的过程中会渗入基材的凹陷处,增加了吸附点位,使得银浆与基材的结合更加紧密...     

纳秒激光调控CFRP复合材料表面润湿性及其对胶接性能的影响

采用纳秒激光对碳纤维增强树脂基(CFRP)复合材料进行表面预处理,调控其表面成分、粗糙度和表面润湿性,然后采用SEM、接触角测量仪、光学轮廓仪、XPS等表征CFRP复合材料的表面微观形貌、接触角、粗糙度和化学成分,并通过拉伸剪切实验评价和分析激光表面处理对CFRP复合材料胶接强度的影响规律和机制.结果表明:优化激光表面...     

AgOx薄膜的形貌、光谱以及激光烧蚀研究

制备了不同氧分压比的AgOx薄膜,对其进行了原子力(AFM)形貌观察,发现分压比0.4时,薄膜的粗糙度最小,均匀性也最好.光谱性质表明:随着分压比的增加,存在着金属向半导体的转变;经过热处理后的共振吸收峰和扫描电(SEM)表明了金属银粒子的析出.不同激光功率下的烧蚀实验表明:在激光照射下存在着两记录(烧蚀)形态,一种是银粒子散布在其间的气泡型;另一种是形成中间烧蚀孔,银粒子在孔附近密集的破裂气泡型.     

Long-range surface plasmon polariton waveguides containing very thin spin-coated silver films

We fabricated very thin solid silver films with thicknesses below 50 nm using a spin coating method. An aqueous silver ionic complex solution was spin-coated and then thermally cured for a few minutes at a low temperature. The properties of the spin-coated silver films were compared to the properties of silver films deposited by thermal evaporation. The spin-coated thin silver films possessed silver crystallinity and a surface roughness of ~ 2.83 nm, while the thermally evaporated thin silver films also possessed silver crystallinity with a surface roughness of ~ 2.44 nm. Long-range surface plasmon polariton (LR-SPP) waveguides fabricated by both spin coating and thermal evaporation were also characterized and compared. The propagation losses of the 23 nm thick spin-coated and the 19 nm thick evaporated LR-SPP waveguides with strip widths of 7 μm were 3.6 and 4.2 dB/cm, respectively, and their coupling losses were 1.4 and 1.0 dB/2facets, respectively. The use of the spin coating method is a very cost effective solution because the films can be formed at low temperature in a short period of time without requiring a vacuum system. In addition, there are many potential applications of using spin-coated very thin solid silver films in LR-SPP waveguides and nano electrical circuit patterns.     

Chemical-mechanical polishing of SiO2 thin films studied by X-ray reflectivity

Specular X-ray reflectivity from SiO₂ thin films prepared on silicon substrates by plasma-enhanced chemical vapor deposition showed the films to have a characteristic width of the decay in density at the free surface of 17 Å, to be about three-quarters the density of -quartz, and to have an interfacial layer at the silicon interface that was of the order of 100 Å wide and less dense than the bulk of the film. After chemical-mechanical polishing the characteristic width of the decay in density at the free surface was reduced to 10 Å; furthermore, the near-surface region to a depth of 30 Å had a greater density than the as-deposited film. Off-specular reflectivity confirmed that the decrease in characteristic width at the free surface was due to reduced roughness upon polishing and also revealed that the lateral correlation length in the limit of long wavelengths was the same for both polished and unpolished samples. The compression of the near-surface region during polishing is believed to enhance the dissolution of SiO₂ into the slurry which is necessary to achieve smooth surfaces.     

Characterization on pulsed laser deposited nanocrystalline ZnO thin films

Nanocrystalline zinc oxide thin films were deposited on glass and silicon substrates by using pulsed laser deposition at different laser energy densities (1.5, 2, and 3 J/cm²). The film thickness, surface roughness, composition, optical and structural properties of the deposited films were studied using an α-step surface profilometer, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), optical transmittance, and X-ray diffraction (XRD), respectively. The film thickness was calculated as 244 nm. AFM analysis shows that the root-mean-square roughness increases with increasing laser energy density. XPS analysis shows that the interaction of zinc with oxygen atoms is greatly increased at high laser energy density. In the optical transmittance spectra, a shift of the absorption edge towards higher wavelength region confirms that the optical band gap increases with an increase in laser energy density. The particle size of the deposited films was measured by XRD, it is found to be in the range from 7.87 to 11.81 nm. It reveals that the particle size increases with an increase in laser energy density.     

Preparation of silver nanoparticles by photo-reduction for surface-enhanced Raman scattering

A substrate for surface-enhanced Raman scattering (SERS) has been developed. Based on the surface-catalyzed reduction of Ag⁺ by citrate on the silver nanoparticles surface under light irradiation, small silver seeds on a quartz slide can be enlarged. The optical properties and characteristics of the silver films have been investigated by ultraviolet-visible spectroscopy, scan electron microscope and atomic force microscopy (AFM). The results indicate that the particle size and shape are different at different reduction time. At the first 3 h, some triangular and hexagonal nanoparticles formed; with the reduction proceeding, the shape of the silver particles became irregular and the size became larger. The silver films obtained are very suitable as SERS active substrate. The relationship between SERS intensity and the reduction time has been investigated for 1,4-bis[2-(4-pyridyl)ethenyl]-benzene molecule adsorbed on the silver film. The SERS intensity reached a maximum at 8 h reduction. The AFM measurements indicate that roughness features with an average size of 100 nm are present on the surface, which yielded the strongest SERS signal. Pyridine was used as a probe molecule to investigate the enhancement factor (EF) of the silver films. According to the formalism of Tian and co-workers, the EF of the silver films is estimated to be 3.4 × 10⁵. The silver film that can remain active for more than 50 days would seem to be suitable for various analytical applications.     

Reflectance measurements and optical constants in the extreme ultraviolet-vacuum ultraviolet regions for SiC with a different C/Si ratio

Reflectance versus incidence angle measurements have been performed from 5 to 152 nm on samples of SiC with a different C/Si ratio deposited with rf magnetron sputtering. The optical constants of the material at different wavelengths have been determined by using a curve-fitting technique of reflectance values versus incidence angle. Complementary measurements of the incident beam polarization, film thickness, surface roughness, and stoichiometry were performed to complete the analysis of the samples.     

High‐Performance Doped Silver Films: Overcoming Fundamental Material Limits for Nanophotonic Applications

The field of nanophotonics has ushered in a new paradigm of light manipulation by enabling deep subdiffraction confinement assisted by metallic nanostructures. However, a key limitation which has stunted a full development of high‐performance nanophotonic devices is the typical large losses associated with the constituent metals. Although silver has long been known as the highest quality plasmonic material for visible and near infrared applications, its usage has been limited due to practical issues of continuous thin film formation, stability, adhesion, and surface roughness. Recently, a solution is proposed to the above issues by doping a proper amount of aluminum during silver deposition. In this work, the potential of doped silver for nanophotonic applications is presented by demonstrating several high‐performance key nanophotonic devices. First, long‐range surface plasmon polariton waveguides show propagation distances of a few centimeters. Second, hyperbolic metamaterials consisting of ultrathin Al‐doped Ag films are attained having a homogeneous and low‐loss response, and supporting a broad range of high‐k modes. Finally, transparent conductors based on Al‐doped Ag possess both a high and flat transmittance over the visible and near‐IR range.     

基于干共混法控制柔性模板上金属薄膜微裂纹形貌

以500 nm的SiO₂纳米粒子为填料,聚二甲基硅氧烷(PDMS)为包覆纳米粒子的聚合物,通过一种新颖的干共混法制备了SiO₂纳米粒子含量高达83.8wt%的SiO₂/PDMS柔性模板。所制备柔性模板的弹性模量为16.58 MPa,热膨胀系数为96×10?6/℃,较SiO₂直接掺入PDMS中湿共混制备的纯PDMS柔性模板,弹性模量提高了91.56%,热膨胀系数降低了69.23%,且该柔性模板具有良好的透明度。最后,在柔性模板表面采用磁控溅射法沉积银薄膜,利用SEM和AFM对银薄膜表面形貌进行表征。结果显示,银薄膜表面光滑,粗糙度很小,且具有良好稳定性。干共混法制备的柔性模板有效抑制了金属薄膜微裂纹的产生,为制造导电性良好的电极及大面积的金属薄膜提供了新方案。      

Layer-by-layer self-assembled mutilayer films of gold nanoparticles for surface-assisted laser desorption/ionization mass spectrometry

Layer-by-layer (LBL) self-assembled multilayer films of gold nanoparticles (AuNPs) on a silicon wafer were demonstrated to be promising substrates for surface-assisted laser desorption/ionization (SALDI) mass spectrometry (MS) of peptides and environmental pollutants for the first time. LBL multilayer films, (AuNPs/PAHC)n, consisting of alternating layers of ammonium citrate capped AuNPs and poly(allylamine hydrochloride) (PAHC) were prepared on a silicon surface. Silicon plates with aggregated AuNPs were more suitable than those with dispersed AuNPs for the SALDI-MS of peptides. The number of particle layers had a significant effect on the laser desorption/ionization of angiotensin I; the peak intensity of the peptide (molecular ion amount) increased with an increase in the number of layers of AuNPs. As a result, the (AuNPs/PAHC)5 multilayer films increased the sensitivity of the angiotensin I to subfemtomoles and raised the useful analyte mass range, thus making it possible to detect small proteins (a 12 kDa cytochrome c). The signal enhancement when using (AuNPs/PAHC)5 may be due to (i) the high absorption of the UV laser light at 337 nm by the AuNP layers, (ii) the low thermal conductivity due to the AuNPs being covered with a thin monolayer of PAHC, and (iii) the increase in the surface roughness (approximately 100 nm) with the number of AuNP layers. Thus, laser-induced rapid high heating of AuNPs for effective desorption/ionization of peptides is possible. In addition, it was found that (AuNPs/PAHC)5 could be used to extract environmental pollutants (pyrene and dimethyldistearylammonium chloride) from very dilute aqueous solutions with concentrations less than 10(-10) mg/mL, and the analytes trapped in the LBL film could be identified by introducing the film directly into the SALDI mass spectrometer without needing to elute the analytes out of the film.     

Fabrication of hollow waveguides for CO2 lasers

Germanium-coated metal (silver, gold, and copper) hollow waveguides for CO(2) laser energy delivery have been fabricated by electron-beam evaporation and plating techniques in which an acid-soluble glass mandrel with small surface roughness was used. The transmission characteristics of Ge-coated metal hollow waveguides were studied. Ge-coated Ag hollow waveguides showed smaller loss, 0.2 dBm, for CO(2) laser light than Ge-coated Au and Cu waveguides. The transmission characteristics of Ge-coated Ag hollow waveguides were measured in relation to a core diameter and a bending radius.     

Surface assessment of CaF2 deep-ultraviolet and vacuum-ultraviolet optical components by the quasi-Brewster angle technique

The requirements for optical components have drastically increased for the deep-ultraviolet and vacuum-ultraviolet spectral regions. Low optical loss, high laser damage threshold, and long lifetime fluoride optics are required for microlithographic applications. A nondestructive quasi-Brewster angle technique (qBAT) has been developed for evaluating the quality of optical surfaces including both top surface and subsurface information. By using effective medium approximation, the negative quasi-Brewster angle shift at wavelengths longer than 200 nm has been used to model the distribution of subsurface damage, whereas the positive quasi-Brewster angle shift for wavelengths shorter than 200 nm has been explained by subsurface contamination. The top surface roughness depicted by the qBAT is consistent with atomic force microscopy measurements. The depth and the microporous structure of the subsurface damage measured by the qBAT has been confirmed by magnetorheological finishing. The technique has been extended to evaluate both polished and antireflection-coated CaF(2) components.