Arresting photodegradation of porous silicon by a polymer coating

Light soaking in air rapidly decreases photoluminescence (PL) of porous silicon (PS) and increases electron spin resonance (ESR) signal. In vacuum, a short light exposure (<2700 s) increases PL and decreases ESR, but longer exposures again degrade the PL. We could arrest the light-induced degradation over long periods by applying a thin polymer coating, which resulted in constant PL and ESR intensities. The PL intensity of coated PS is comparable to the PL intensity of a fresh PS sample in air. FTIR spectrum suggests new bond formations at the PS/polymer interface that may be responsible for PL stability.     

Influence of metallic coatings on the photoluminescence properties of ZnO nanowires

We report on low‐temperature photoluminescence studies of ZnO nanowires coated with thin metallic films. For all analyzed metals (Al, In, Au, Ni, Cu), we find an increased relative intensity of the green deep‐level emission. This is accompanied by a significant reduction of the relative intensity of the surface exciton band. The observed effects are most likely related to the formation of metal induced gap states in the surface region of the ZnO nanowires. A model for the band structure in the surface region of the metal‐coated nanowires is proposed that successfully explains the changes in the photoluminescence spectra after the coating process. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Au纳米颗粒和CdTe量子点复合体系发光增强和猝灭效应

利用金属蒸发真空多弧离子源注入机, 将Au离子注入到高纯石英玻璃来制备镶嵌有Au 纳米颗粒的衬底材料, 随后将化学方法合成的CdTe量子点旋涂在玻璃衬底上制备了Au纳米颗粒和CdTe量子点复合体系. 通过对镶嵌有Au纳米颗粒的衬底进行热退火处理来控制Au纳米颗粒的生长和分布, 系统研究了Au纳米颗粒的局域表面等离子体共振对CdTe量子点光致发光性能的影响. 利用光学吸收谱、原子力显微镜、透射电子显微镜和光致发光谱对样品进行了表征和测试. 光致发光谱表明, Au纳米颗粒的局域表面等离子体对CdTe量子点的发光有增强效应也有猝灭效应. 深入分析了Au纳米颗粒和CdTe量子点之间的相互作用过程, 提出了关于Au-CdTe 纳米复合体系中CdTe 发光增强和猝灭的新机理. 该实验结果为利用金属纳米颗粒表面等离子体技术制备高发光性能的光电子器件提供了较好的参考.     

Improved moisture resistance of SrS:Eu phosphors with nanoscale SiO2 coating

Orange-emitting SrS:Eu²⁺ phosphors were coated with nanoscale SiO₂ and their photoluminescence (PL) degradation behavior in moist air was investigated. The SiO₂ coating was obtained by sol-gel process using diethoxydimethylsilane (DEDMS) and the coating content was varied from 0.5 to 2 wt%. The coatings were composed of a uniform, continuous, and amorphous SiO₂ layer of 30-50 nm thickness and the coating thickness was not varied significantly with the coating content. No peak shift and no decrease of PL intensity were observed after coating. The PL intensity of the coated phosphors decreased to ∼75% of the original value after 10 h exposure to moist air, while the uncoated phosphor decreased to ∼33%, which indicates the improved moisture resistance of the nanoscale SiO₂ coated SrS:Eu²⁺ phosphors.     

Characterization of SnO2/Pb2CrO5 thin film/metal photovoltaic device

The photovoltaic behavior in a design of SnO₂/Pb₂CrO₅ thin film/metal (Au or Al) is described as functions of light intensity and wavelength for two different illumination directions. The Pb₂CrO₅ thin film in each device is formed over the SnO₂ coated glass substrate by an electron-beam evaporation technique. When illuminated from the metal side, the device with Au or Al shows the positive or the negative photovoltage, respectively. For the illumination from the SnO₂ side, the device with Au has the negative photovoltage at the short wavelength, and the positive one at the longer, while the device with Al has the negative photovoltage at both wavelength regions. These photovoltaic devices have two junctions at both sides of the Pb₂CrO₅ thin film. The band model of each device is also discussed.     

The effect of Al and B on the luminescent property of porous silicon

In this paper, we studied the PL property and the surface morphology of porous silicon prepared from N-type single silicon wafers coated with and without Al film. By introducing the Al film on the surface of silicon wafer before etching, the morphology of porous silicon exhibits obvious discrimination compared with that of the conventional porous silicon, which can be explained by the formation mechanism of the samples, and the emission property of two-type porous silicon also showed the clear difference, which may be attributed to the discrepancy in the structural configuration of the samples. Furthermore, it was found that the blue emission decreased and the green emission was almost completely quenched after boron-particle deposition, which is attributed to the structural change or annihilation of the emission defects during annealing process.     

Laser-assisted generation of gold nanoparticles and nanostructures in liquid and their plasmonic luminescence

Nanoparticles (NPs) and surface nanostructures (NS) are produced via laser ablation of a bulk gold target in liquid using second harmonics of 10 ps Nd:YAG laser (532 nm) with repetition rate of 50 kHz. The morphology and plasmon photoluminescence (PL) properties of obtained nanoscale objects are described. Transmission electron microscopy and field emission scanning electron microscopy are used for morphology characterization of NPs and NS, respectively. Plasmon PL of both gold NPs and NS is experimentally studied using the third harmonics of the Nd:YAG picosecond laser (355 nm) as a pump. The wavelength of intensity maximum of PL of Au NPs colloidal solution virtually coincides with the position of Au NPs plasmon absorption peak. Real-time excitation of both plasmon PL and Raman scattering of surrounding liquid by picosecond laser pulses in aqueous colloidal solution is also investigated. The efficient cross section of plasmon PL of Au NPs colloid is evaluated using Raman scattering of water as a comparative parameter. The results are in good agreement with values obtained in previous works. Plasmon PL from self-organized NS on the Au surface produced via laser ablation is observed for the first time. Its spectrum is compared to PL spectra of both aqueous colloidal solutions of NPs and of NPs deposited on a Si wafer. The obtained experimental data are discussed with reference to the band structure of bulk Au.     

Vibration of scanning near-field optical microscope probe with laser-induced thermal effect using Timoshenko beam theory

The Timoshenko beam theory, including the effects of rotary inertia and shear deformation, is used to analyze the resonant frequency of lateral vibration of scanning near-field optical microscope (SNOM) tapered probe with a laser-induced thermal effect. In the analysis, the thermal effect can be considered as an axial force and is dependent of temperature distribution of the probe. The Rayleigh–Ritz method is used to solve the vibration problem of the probe. According to the analysis, the frequencies of the first three vibration modes increase when the thermal effect is taken into account. The effects of shear deformation and rotary inertia on the frequency ratio of a Timoshenko beam to an Euler beam increase when the mode number increases and the contact stiffness decreases. In addition, the frequency of mode 1 increases with increasing taper angle and coating thickness of the probe. Comparison of the frequency of a SNOM probe coated with Al, Ag, or Au, the highest is with Al coating, and the lowest is with Au coating.     

Fabrication of patterned gold electrodes with spin-coated-and-fired Au(1 1 1) film by the soft lithography

We prepared high quality Au(1 1 1) film on Si wafer through the spin coating and thermal decomposition of a gold ink, spin-coated-and-fired (SCAF) Au film. The X-ray measurements, XRD and pole-figure analysis, showed that the SCAF Au film has a (1 1 1) out-of-plane orientation with a random in-plane orientation. In order to confirm the chemical activity of the SCAF Au film, we demonstrate the formation of patterned structures with the film by using soft lithography technique. The chemical activities of this physically stable SCAF Au film to the alkanethiols were at least equivalent those of physically deposited the Au films. The possibility of the mass production of micro patterned structure with the SCAF Au film was also demonstrated over the wide region on Si wafer by the microcontact lithography. These suggest that the Au film will help the easy fabrication of various nanosized devices on Si wafer and other substrates.     

Enhancement of photoluminescence emission intensity of zirconia thin films via aluminum doping for the application of solid state lighting in light emitting diode

Al doped ZrO₂ thin films were deposited on quartz substrates by sol–gel dip coating technique. X-ray diffraction pattern showed the deterioration of the crystallinity of the films with increase in Al doping concentration due to the formation of stress in the film. Scanning electron microscope images showed crack free surface. An average transmittance of >80% (in UV–vis region) was observed for all samples. Optical band gap was found to vary as a function of doping concentration. Photoluminescence spectra of the films exhibited an increase in the emission intensity with increase in Al doping concentration which is due to the increase in oxygen vacancies in the Al doped films. The “Blueshift” and “Redshift” of the PL spectra with increase in Al concentration originates from the change of stress in the films. The enhancement of PL intensity in the Al doped ZrO₂ thin films make it suitable for generation of solid state lighting in light emitting diode.     

Formation of Au nano-patterns on various substrates using simplified nano-transfer printing method

For future device applications, fabrication of the metal nano-patterns on various substrates, such as Si wafer, non-planar glass lens and flexible plastic films become important. Among various nano-patterning technologies, nano-transfer print method is one of the simplest techniques to fabricate metal nano-patterns. In nano-transfer printing process, thin Au layer is deposited on flexible PDMS mold, containing surface protrusion patterns, and the Au layer is transferred from PDMS mold to various substrates due to the difference of bonding strength of Au layer to PDMS mold and to the substrate. For effective transfer of Au layer, self-assembled monolayer, which has strong bonding to Au, is deposited on the substrate as a glue layer.In this study, complicated SAM layer coating process was replaced to simple UV/ozone treatment, which can activates the surface and form the -OH radicals. Using simple UV/ozone treatments on both Au and substrate, Au nano-pattern can be successfully transferred to as large as 6 in. diameter Si wafer, without SAM coating process. High fidelity transfer of Au nano-patterns to non-planar glass lens and flexible PET film was also demonstrated.     

Spatial polarization sensitivity of single Au bowtie nanostructures

Metallic bowtie nanostructures as plasmonic nanoantennas can create highly enhanced local fields when resonating with the incident light. With Au bowtie nanostructures fabricated by lithography method, we experimentally observed that the photoluminescence (PL) spatial profile from a single Au bowtie nanoantenna was strongly dependent on the excitation light polarization. While varying the incident light polarization, the spatial distribution of the PL intensity in the nanogap of an Au bowtie changed as predicted by the simulation results on the electromagnetic field enhancement distribution. The polarization feature of the PL intensity relative to the polarization direction of incident excitation light was also discussed. The study may find application in the design of polarization sensitive plasmonic sensors.     

Characterization of si-GaAs wafer quality by room-temperature photoluminescence

The mapping of near-band-gap photoluminescence intensity is used as a method for characterizing the uniformity of wafer properties which is an essential requirement for fabrication of integrated circuits on si-GaAs substrates.

The surface effects on PL intensity and uniformity were investigated directly after an oxide removal etch and after storage of wafers under dark and illuminated conditions. Storage results in a decrease of the PL intensity and the PL contrast. This is probably associated with changes in the native oxide composition. PL changes during storage can be reversed by suitable oxide etching and cleaning which is important for obtaining reproducible results on wafer uniformity.

The bulk PL uniformity was studied in dependence on post-growth thermal treatments and distinct improvements in PL uniformity across a wafer were found due to various annealing conditions. Very low variations of < 10% are obtained by an optimized annealing process even up to 100 mm diameter wafers. High-resolution measurements show that these changes in wafer uniformity are correlated to characteristic microscopic changes within the well known cell structure.     

Anti-Reflection Characteristics of Si Nanowires for Enhanced Photoluminescence from CdTe/CdS Quantum Dots

CdTe/CdS quantum dots(QDs) are fabricated on Si nanowires(NWs) substrates with and without Au nanoparticles(NPs). The formation of Au NPs on Si NWs can be certified as shown in scanning electron microscopy images. The optical properties of samples are also investigated. It is interesting to find that the photoluminescence(PL) intensity of Cd Te/Cd S QD films on Si nanowire substrates with Au NPs is significantly increased,which can reach 8-fold higher than that of samples on planar Si without Au NPs. The results of finite-difference time-domain simulation indicate that Au NPs induce stronger localization of electric field and then boost the PL intensity of QDs nearby. Furthermore, the time-resolved luminescence decay curve shows the PL lifetime, which is about 5.5 ns at the emission peaks of QD films on planar, increasing from 1.8 ns of QD films on Si NWs to4.7 ns after introducing Au NPs into Si NWs.     

Electron‐transfer transparency of graphene: Fast reduction of metal ions on graphene‐covered donor surfaces

The mechanism of charge transfer through nanomaterials such as graphene remains unclear, and the amount of charge that can be transferred from/to graphene without damaging its structural integrity is unknown. In this communication, we show that metallic nanoparticles can be decorated onto graphene surfaces as a result of charge transfer from the supporting substrate to an adjoining solution containing metal ions. Au or Pt nanoparticles were formed with relatively high yield on graphene‐coated substrates that can reduce these metal ions, such as Ge, Si, GaAs, Al, and Cu. However, metal ions were not reduced on graphene surfaces coated onto non‐reducing substrates such as SiO₂ or ZnO. These results confirm that graphene can be doped by exploiting charge transfer from the underlying substrate; thus graphene is not only transparent with respect to visible light, but also with respect to the charge transfer. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Photoluminescence study of the surface modified and MEH-PPV coated cotton fibers

In this paper, we report a study on the photoluminescence properties of pure cotton fibers from chemically surface and morphology modified and coated with MEH-PPV polymer samples by dip-coating method. The treated and coated fibers surfaces were characterized using scanning electron microscopy (SEM), luminescence and FT-IR spectroscopy. The SEM photos showed that cotton fiber surface was covered by a layer of MEH-PPV with the thickness around 1 μm. The effects on the crystalline structure and photoluminescence (PL) were studied as a function of the alkali modification conditions. It was found that the blue light intensity of the mercerized and bleached specimen is approximately two orders higher than the scoured one. The performance of fibers with MEH-PPV polymer as a coating component was investigated and an excellent white-light emission which consists of blue-, green-, and red-light-emitting bands was demonstrated.     

硒化镉发光量子点的制备及其在有机发光器件中的应用

硒化镉量子点具有随粒径尺寸改变,而产生发光波长调变的特性,目前已被广泛研究。本研究是由化学溶胶法合成不同粒径尺寸的核壳型CdSe／ZnS硒化镉量子点,其表面包覆十六烷基胺,避免分子团聚现象。在由硒化镉成核温度的控制,成功地制备一系列具有各种尺寸粒径的核壳型硒化镉量子点(2—6nm)。本研究也合成了含有纳米金粒子于核壳型硒化镉量子点,实验结果发现：硒化镉发光效率明显的提高。在有机发光器件的应用方面,将发光波长为505nm核壳型CdSe／ZnS量子点掺入溶有发光波长为570nm铱化合物的氯仿溶液时,其溶液的光致发光光谱表明,原量子点的发光特性消失,只有铱化合物的发光依然存在,且其发光强度呈现明显增强趋势,我们推测此现象源自于量子点到铱化合物能量转移的机制。我们也以含有核壳型硒化镉量子点的铱化合物与PVK混合材料为发光层,成功的制作发光二极管器件,器件的发光效率因核壳型硒化镉的掺杂,明显提高2倍多。     

Influence of Al-doping on the structure and optical properties of ZnO films

Al-doped ZnO (ZnO:Al) thin films with c-axis preferred orientation were deposited on glass substrates using the radio frequency reactive magnetron sputtering technique. The effect of Al concentrations on the microstructure and the luminescence properties of the ZnO:Al thin films were studied by atomic force microscopy (AFM), X-ray diffraction (XRD), and fluorescence spectrophotometer. The results showed that the crystallization of the films was promoted by appropriate Al concentrations; the photoluminescence spectra (PL) of the samples were measured at room temperature. Strong blue peak located at 437 nm (2.84 eV) and two weak green peaks located at about 492 nm (2.53 eV) and 524 nm (2.37 eV) were observed from the PL spectra of the four samples. The origin of these emissions was discussed. In addition, absorption and transmittance properties of the samples were researched by UV spectrophotometer; the UV absorption edge shifted to a shorter wavelength first as Al was incorporated, and then to a longer wavelength with the increasing Al concentrations. The optical band gaps calculated based on the quantum confinement model are in good agreement with the experimental values.     

Ethylene adsorption on thin films of Ni,Pd, Pt,Cu, Au and Al; Work function measurements

The changes in work function φ upon adsorption of C₂H₄ on clean film surfaces of six fcc metals (Ni, Pd, Pt, Cu, Au and Al) have been followed by means of photoelectron emission at 293 K. A marked difference was observed in the behaviour between Ni, Pd and Al on the one side and on Cu, Au and Pt on the other side: while with Ni, Pd and Al, φ as a function of coverage goes through a maximum, with Cu, Au and Pt, φ only decreases. In the discussion, the data obtained by work function measurements are related to other literature data. Several films covered with C₂H₄species were also submitted to a heat treatment while in other experiments H₂ was admitted to the surface covered by C₂H₄ species. In some experiments C₂h₄ was admitted to surfaces covered by H₂. In all cases φ was measured. The experiments reveal that C₂h₄is absorbed only reversibly on Cu and Au. On Ni, Pd and Pt, C₂H₄ is adsorbed initially with dissociation and this leads to an increase in φ on Ni and Pd and a decrease on Pt. Hydrogenated reactive species contribute to the lowering of φ observed with Ni, Pd and Pt. As with Cu and Au also on Ni, Pd and Pt a weakly bound C₂h₄is observed which leads to a decrease in φ as well. The behaviour of φ indicates that upon Al, C₂h₄ adsorbs first dissociatively to a small extent, while the weakly bound C₂H₄species act as intermediates for strongly adsorbed species which were observed after some time.     

金纳米颗粒光散射提高InAs单量子点荧光提取效率

采用光学方法确定InAs/GaAs单量子点在样品外延面上的位置坐标, 利用AlAs牺牲层把含有量子点的GaAs层剥离并放置在含有金纳米颗粒或平整金膜上, 研究量子点周围环境不同对量子点自发辐射寿命及发光提取效率的影响. 实验结果显示, 剥离前后量子点发光寿命的变化小于13%, 含有金纳米颗粒的量子点发光强度是剥离前的7倍, 含有金属薄膜的量子点发光强度是剥离前的2倍. 分析表明在金纳米颗粒膜上的量子点荧光强度的增加主要来自于金纳米颗粒对量子点荧光的散射效应, 从而提高量子点发光的提取效率.