The role of direct surface interaction in surface enhanced Raman scattering by pyridine and CO on silver

The surface enhanced Raman scattering (SERS) phenomenon due to pyridine on silver and CO on silver in ultra-high vacuum (UHV) has been compared. The study was carried out for two different kinds of silver surfaces, island films and “cold” films on island films. We have reported earlier that it was necessary to warm the samples to about 70K in order to observe the full surface enhanced Raman spectrum when the pyridine was deposited on silver island films on sapphire substrates at liquid He temperatures. We call this the effect of a “low temperature anneal” and the present work indicates that this effect is more general than we originally thought. It has also been found that island films exhibit enhanced Raman scattering for pyridine but not for CO, although “cold” films enhance the Raman scattering of both CO and pyridine. This is the first clear indication that molecular specificity may be a part of the SERS phenomenon. The interpretation of these observations depends critically on our understanding of the SERS phenomenon.     

碳化硅薄膜脉冲激光晶化特性研究

采用XeCl准分子激光对非晶碳化硅(a-SiC)薄膜的脉冲激光晶化特性进行了研究.通过原子力显微镜（AFM）和Raman光谱技术对退火前后薄膜样品的形貌、结构及物相特性进行了分析.结果表明，选用合适的激光能量采用激光退火技术能够实现a-SiC薄膜的纳米晶化.退火薄膜中的纳米颗粒大小随着激光能量密度的增加而增大；Raman谱分析结果显示了退火后的薄膜的晶态结构特性并给出了伴随退火过程存在的物相分凝现象.根据以上结果并结合激光退火特性，对a-SiC的脉冲激光晶化机理进行了讨论. 关键词： 激光退火 晶化 碳化硅     

Optical and structural properties of polycrystalline CdSe deposited on titanium substrates

We report studies of photoluminescence, Raman scattering and x-ray diffraction performed on CdSe polycrystalline films deposited on titanium substrates by two different methods: chemical deposition and electroplating. We discuss the changes observed in these films as they are subjected to heat treatments. The differences observed in the energy gap of both types of film and their evolution as a function of annealing temperature are tentatively explained in terms of quantum confinement produced by the small grain size of the films.     

同质与异质外延掺杂CVD金刚石薄膜的结构与性能

采用化学气相沉积(CVD)技术,以高温高压(HTHP)合成的(100)金刚石和p型(100)Si为衬底制备了硫掺杂和硼-硫共掺杂金刚石薄膜,利用原子力显微镜(AFM)、扫描隧道显微镜(STM)及隧道电流谱(CITS)等手段分析同质和异质外延CVD掺杂金刚石薄膜的结构和性能.结果表明:异Si衬底上CVD金刚石的形核密度低,薄膜表面比较粗糙,粗糙度达到18.5nm;同质HTHP金刚石衬底上CVD金刚石薄膜晶粒尺寸约为10—50nm,表面平整,表面粗糙度为1.8nm.拉曼测试和电阻测量的结果显示,在HTHP金刚 关键词： 金刚石 掺杂 外延     

Double resonant Raman scattering in nanographite films

Experimental results are presented on Raman scattering in graphite films produced by DC plasmaenhanced chemical vapor deposition from a methane-hydrogen gas mixture. Scanning electron and probe microscopy data show that, depending on substrate material and deposition time, the deposited film is either a mesoporous material consisting of graphite nanocrystallites with basal planes oriented perpendicular to the substrate surface or an atomically flat, nanometer-thick stack of graphene layers parallel to the substrate. A comparative Raman spectroscopy analysis is performed for film samples deposited on nickel and silicon substrates for 5 and 60 min, as well as for highly ordered graphite samples. The Raman spectra of the examined samples correspond to the double resonant scattering mechanism. The behavior of Raman peak position and intensity as functions of excitation wavelength suggests a high degree of structural order in the graphite films deposited on nickel for 5 min. The results obtained are used to show that the thickness of these films is 1.5 ± 0.5 nm.     

氢化纳米硅薄膜中氢的键合特征及其能带结构分析

对氢化纳米硅薄膜中氢的键合特征和薄膜能带结构之间的关系进行了研究.所用样品采用螺 旋波等离子体化学气相沉积技术制备，利用Raman散射、红外吸收和光学吸收技术对薄膜的 微观结构、氢的键合特征以及能带结构特性进行了分析.Raman结果显示不同衬底温度下所生 长薄膜的微观结构存在显著差异，从非晶硅到纳米晶硅转化的衬底温度阈值为200℃.薄膜中 氢的键合特征与薄膜的能带结构密切相关.氢化非晶硅薄膜具有较高的氢含量，因键合氢引 起的价带化学位移和低衬底温度决定的结构无序性，使薄膜呈现较大的光学带隙和带尾宽度 .升 关键词： 氢化纳米硅 螺旋波等离子体 能带结构     

SERS study of Ag nanoparticles electrodeposited on patterned TiO2 nanotube films

In this work, Ag nanoparticles (NPs) were deposited on patterned TiO₂ nanotube films through pulse‐current (PC) electrodeposition, and as a result patterned Ag NPs films were achieved. Scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and X‐ray diffraction (XRD) were used, respectively, to study the morphology, uniformity, and phase structure of the patterned Ag NP films. The size and density of the as‐deposited Ag NPs could be controlled by changing the deposition charge density, and it was found that the patterned Ag NP films produced under a charge density of 2.0 C cm⁻² gave intense UV–vis and Raman peaks. Two‐dimensional surface‐enhanced Raman scattering (SERS) mapping of rhodamine 6G (R6G) on the patterned Ag NP films demonstrated a high‐throughput, localized molecular adsorption and micropatterned SERS effect. Copyright © 2010 John Wiley & Sons, Ltd.     

The comparison between CdS thin films grown on Si(111) substrate and quartz substrate by femtosecond pulsed laser deposition

Two kinds of cadmium sulfate (CdS) thin films have been grown at 600 °C onto Si(111) and quartz substrates using femtosecond pulsed laser deposition (PLD). The influence of substrates on the structural and optical properties of the CdS thin films grown by femtosecond pulsed laser deposition have been studied. The CdS thin films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), photoluminescence (PL) and Raman spectroscopy. Although CdS thin films deposited both on Si(111) and quartz substrates were polycrystalline and hexagonal as shown by the XRD , SEM and AFM results, the crystalline quality and optical properties were found to be different. The size of the grains for the CdS thin film grown on Si(111) substrate were observed to be larger than that of the CdS thin film grown on quartz substrate, and there is more microcrystalline perpendicularity of c-axis for the film deposited on the quartz substrate than that for the films deposited on the Si substrate. In addition, in the PL spectra, the excitonic peak is more intense and resolved for CdS film deposited on quartz than that for the CdS film deposited on Si(111) substrate. The LO and TO Raman peaks in the CdS films grown on Si(111) substrate and quartz substrate are different, which is due to higher stress and bigger grain size in the CdS film grown on Si(111) substrate, than that of the CdS film grown on the amorphous quartz substrate. All this suggests that the substrates have a significant effect on the structural and optical properties of thin CdS films. PACS 81.15.Fg; 81.05.Ea; 78.20.-e; 78.67.-n; 42.62.-b     

Gap surface plasmon polaritons enhanced by a plasmonic lens

We numerically investigate the optical field enhancement based on gap surface plasmon polaritons (GSPPs) that are enhanced by propagating surface waves launched by a circular slit at a metal-dielectric interface. The optical field enhancement originates not only from multiple scattering and coupling of GSPPs in the spacer region between two metal layers but also from propagating surface plasmon polaritons (SPPs) launched by a circular plasmonic lens. We find that the combination of the GSPPs and the propagating SPPs launched by the plasmonic lens can achieve extremely strong field confinement, and we find that the surface-enhanced Raman scattering (SERS) enhancement factor can be up to 10(15) at the tip of the equilateral triangular nanostructures. The structure proposed here is expected to find promising applications where strong field enhancement is desired, such as optical sensing with the SERS effect.     

High-energy heavy-ion induced physical and surface-chemical modifications in polycrystalline cadmium sulfide thin films

The effect of high electronic energy deposition on the structure, surface topography, optical properties, and electronic structure of cadmium sulfide (CdS) thin films have been investigated by irradiating the films with 100 MeV Ag⁺⁷ ions at different ion fluences in the range of 10¹²–10¹³ ions/cm². The CdS films were deposited on glass substrate by thermal evaporation, and the films studied in the present work are polycrystalline with crystallites preferentially oriented along (002)-H direction. It is shown that swift heavy ion (SHI) irradiation leads to grain agglomeration and hence an increase in the grain size at low ion fluences. The observed lattice compaction was related to irradiation induced polygonization. The optical band gap energy decreased after irradiation, possibly due to the combined effect of change in the grain size and in the creation of intermediate energy levels. Enhanced nonradiative recombination via additional deep levels, introduced by SHI irradiation was noticed from photoluminescence (PL) analysis. A shift in the core levels associated with the change in Fermi level position was realized from XPS analysis. The chemistry of CdS film surface was studied which showed profound chemisorption of oxygen on the surface of CdS.     

Using surface enhanced Raman scattering to study vibrations of adsorbates on thin metallic overlayers on silver

We have studied the surface enhanced Raman scattering from molecules adsorbed on thin gold overlayers on silver island films. The Raman scattering of gold cyanide species adsorbed on gold overlayers decreases in intensity with gold overlayer thickness between 0.5 – 10 Å . This intensity decrease is consistent with a simple model which takes into account the damping of the electromagnetic resonances of the silver islands by the absorbing gold overlayer. Implications of these findings for the enhancement of Raman scattering from adsorbates on other metals deposited as overlayers on silver will be discussed.     

一种新基底上的C_(60)表面增强拉曼光谱研究

利用金纳米颗粒在十八胺分子的LB膜上自组装得到了一种新的表面增强拉曼光谱(SERS)活性基底。以C60分子作为这种新基底的探针分子,得到了高质量的C60SERS光谱。不但C60的振动模式增加了,而且很多模式发生了分裂,特别是一些禁戒的模式也出现在光谱中,这说明这种新基底是一种非常高效的活性基底。C60分子在新基底上的增强机制可能来自"热点"增强。     

低温铝诱导晶化制备纳米晶硅薄膜的物相和光学性能研究

采用射频磁控溅射镀膜系统,在玻璃衬底上制备了非晶硅(α-Si)/铝(Al)复合薄膜,结合氮气(N₂)气氛中低温快速光热退火制备了纳米晶硅(nc-Si)薄膜;利用光学显微镜、共焦光学显微仪、X射线衍射(XRD)仪、拉曼散射光谱(Raman)仪和紫外-可见光-近红外分光光度计(UV-VIS-NIR)对纳米晶硅薄膜的表面形貌、物相及光学性能进行了表征,研究了退火工艺对薄膜性能的影响。结果表明： 300 ℃,25 min光热退火可使α-Si/Al膜晶化为纳米晶硅薄膜,晶化率为15.56%,晶粒尺寸为1.75 nm;退火温度从300 ℃逐渐升高到400 ℃,纳米晶硅薄膜晶粒尺寸、晶化率、带隙逐渐增加,表面均匀性、晶格畸变量逐渐减小;退火温度从400 ℃逐渐升高到500 ℃,纳米晶硅薄膜的晶粒尺寸、晶化率继续增加,带隙则逐渐降低;采用纳米晶硅薄膜的吸光模型验证了所制备的纳米晶硅薄膜的光学特性,其光学带隙的变化趋势与吸光模型得出的结果一致。     

Structural and optical characterization of wurtzite type ZnS

ZnS films were grown on (001) GaAs substrates at different temperatures by RF magnetron sputtering. The ZnS chemical stoichiometry was determined by Energy-dispersive X-ray spectroscopy (EDS), besides it allowed to find the residual impurities, mainly oxygen. The X-ray diffraction (XRD) analysis and Raman scattering reveal that ZnS deposited thin films showed hexagonal wurtzite crystalline phase. The films average crystallite size range was from 8.15 to 31.95 nm, which was determined using the Debye–Scherrer equation for the peak W(101). Besides an experimental study of first- and second-order Raman scattering of ZnS films is made. An energy level diagram involving oxygen traps and interstitial sulphur ions is used to explain the origin of the radiative transitions observed in the room temperature photoluminescence (PL) spectra.     

Effect of DC bias on microstructural rearrangement of a-SiN:H films on PET substrate

Hydrogenated amorphous silicon nitride (a-SiN:H) films were deposited on flexible polyethylene terephthalate substrates at temperature as low as 100 °C by hot-wire chemical vapor deposition using SiH₄, H₂ and NH₃ precursors. Field emission scanning emission microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy and small angle X-ray scattering were employed to study structural and microstructural properties of a-SiN:H films. The rms surface roughness increased with increase of positive bias to substrate. Intermediate range order, porosity and interface inhomogeneity in amorphous of a-SiN:H films evaluated by acoustic and optical phonon of silicon network, Guinier plot and correlated length from Raman and SAXS characterizations. The fractal behavior of a-SiN:H domains approached the perfect symmetry and the intermediate range order of a-SiN:H films deteriorate with increase of the positive substrate bias. Both correlation length and void size of the a-SiN:H amorphous domain increased with increase of the substrate bias from 0 to +200 V.     

Effects of a one-dimensional surface defect on designer surface plasmon polaritons

By using a finite difference time domain(FDTD) method,the effects of a one-dimensional(1D) surface defect on designer surface plasmon polaritons(designer SPPs) supported by a 1D metallic grating in THz domain are investigated.When the size of the defect is in a special range which is not too large,the designer SPPs reflected and scattered by the defect are weak enough to be neglected.The defect only induces a disturbance in the energy distribution of the designer SPP supported by the whole defect grating.If the defect size exceeds the said range,the reflecting and scattering are dominant in the influences of the defect on designer SPPs.Our analysis opens opportunities to control and direct designer SPPs by introducing a 1D defect,especially in low frequency domain.     

Subwavelength propagation and localization of light using surface plasmons: A brief perspective

Surface plasmons at the metal–dielectric interface have emerged as an important candidate to propagate and localize light at subwavelength scales. By tailoring the geometry and arrangement of metallic nanoarchitectures, propagating and localized surface plasmons can be obtained. In this brief perspective, we discuss: (1) how surface plasmon polaritons (SPPs) and localized surface plasmons (LSPs) can be optically excited in metallic nanoarchitectures by employing a variety of optical microscopy methods; (2) how SPPs and LSPs in plasmonic nanowires can be utilized for subwavelength polarization optics and single-molecule surface-enhanced Raman scattering (SERS) on a photonic chip; and (3) how individual plasmonic nanowire can be optically manipulated using optical trapping methods.     

Why metallic surfaces with grooves a few nanometers deep and wide may strongly absorb visible light

It is theoretically shown that nanometric silver lamellar gratings present very strong visible light absorption inside the grooves, leading to electric field enhancement of several orders of magnitude. It is due to the excitation of quasistatic surface plasmon polaritons with particular small penetration depth in the metal. This may explain the abnormal optical absorption observed a long time ago on almost flat Ag films. Surface enhanced Raman scattering in rough metallic films could also be due to the excitation of such quasistatic plasmon polaritons in grain boundaries or notches of the films.     

Characterization of RuO2 thin films by Raman spectroscopy

Raman scattering has been used as a technique for the characterization of RuO₂ thin films deposited on different substrates by the metal-organic chemical vapor deposition method and reactive sputtering under various conditions. Red shift and broadening of the linewidth of the Raman peaks are analyzed by the spatial correlation model. The intrinsic linewidth for the RuO₂ films deposited at high and low temperatures has to be adjusted to different values to achieve a good fit for the features. The lineshape and position of the Raman features vary for films deposited on different substrates under the same condition. These differences indicate the existence of stress induced by lattice mismatch and the differential thermal expansion coefficients between RuO₂ and the substrates. After annealing at 650°C in an oxygen atmosphere for 3 h, the linewidth decreases significantly for the RuO₂ thin films deposited at lower temperatures. The results show the improvement of the crystallinity of the films during the annealing process.     

Deposition of ZnO multilayer on LiNbO3 single crystals by DC-magnetron sputtering

Zinc oxide (ZnO) thin films were deposited on LiNbO₃ (LN) single crystals with 200 nm thicknesses by three different ways, where coating of zinc (Zn) film was followed by thermal oxidation for four, two, and one steps with 50, 100, and 200 nm thicknesses repeatedly. Sample, which was produced at 4-step of deposition and oxidation of Zn layer, showed high transmittance and low structural defect due to a lower photoluminescence intensity and Urbach energy. Average grain size in X-ray diffraction (XRD), scanning electron microscopy (SEM) micrograph, and atomic force microscopy (AFM) images for multilayer of ZnO was lower than monolayer of ZnO thin films. Applying multilayer coating technique leads to decrease of surface roughness and scattering on light on surface and fabrication of LiNbO₃ waveguides with lower optical loss.