Photocatalytic properties of TiO2 thin films obtained by glancing angle deposition

Titanium dioxide (TiO₂) thin films with different nanostructures such as nano-particles and separated vertical columns were grown by glancing angle deposition (GLAD) in an electron beam evaporation system. The photocatalytic properties of grown TiO₂ films with different deposition angles and different annealing temperatures were evaluated by following decomposition of methyl orange under ultraviolet (UV) light irradiation. The results suggest that increased surface area due to the GLAD process could improve the photocatalytic properties of TiO₂ films.     

Growth of self-assembled copper nanostructure on conducting polymer by electrodeposition

In the present work, self-assembled nanostructures of copper are grown by electrodeposition on a thin conducting polymer (polypyrrole) film electropolymerized on a gold electrode. The shapes, sizes and the densities of the nanostructures are found to depend on the thickness of the polypyrrole thin film, which provides an easy means to control the morphology of these nanostructures. In particular, for the same applied potential on the gold electrode, smaller nanocrystals with a higher density are observed on thinner polymer films while bigger nanocrystals at a lower density are found on thicker films.     

Surface plasmon polariton microscope with parabolic reflectors

We report the realization of a two-dimensional optical microscope for surface plasmons polaritons (SPPs) based on parabolic Bragg mirrors. These mirrors are built from lithographically fabricated gold nanostructures on gold thin films. We show by direct imaging by leakage radiation microscopy that the magnification power of the SPP microscope follows basic predictions of geometrical optics. Spatial resolution down to the value set by the diffraction limit is demonstrated.     

Rugate filter with multi-channel grown by glancing angle deposition

Glancing angle deposition (GLAD) is an effective technique to fabricate thin films with desired nanoscale porosity variations in three dimensions. GLAD can be used to grow rugate filters characterized by a sinusoidal refractive index profile from one single source material through control of film porosity. A multi-stopband rugate filter can be achieved either by introducing a layer of constant index into the center of sinusoidal refractive index profile or by embedding discrete layers of constant refractive index to sinusoidal index profile with the GLAD technique. Transmittance measurements of the one channel filter, formed with titanium dioxide, revealed this method is one of the most valid technologies to fabricate multi-band filters.     

Local plasmon sensor with gold colloid monolayers deposited upon glass substrates

A new optical sensor that uses local plasmon resonance is proposed. A peak that is due to the local plasmon resonance appears in the absorption spectrum of a gold colloid suspension in the visible region, and its height and wavelength depend on the refractive index of the suspension. These properties are used for optical sensors. We used gold colloid monolayers in which colloidal gold particles a few tens of nanometers in diameter were immobilized upon a glass slide by a functional organic coupling agent. We measured the absorption spectra of the the gold colloid monolayers, which were immersed in liquid samples or coated with thin films. We observed increases of both the resonance wavelength and the absorbance as the refractive indices of the sample liquids or the thickness of the coated films increased. The proportional constants of the resonance wavelength to the film thickness were 3.6 and 5.7 for a 13.9- and a 20.2-nm gold colloid monolayer, respectively.     

MAPLE deposition of Mn(III) metalloporphyrin thin films: Structural, topographical and electrochemical investigations

We report the deposition by MAPLE of metallized nanostructured (5,10,15,20-tetraphenyl)porphinato manganese(III) chloride thin films onto gold screen-printed electrodes, or 〈1 1 1〉 Si substrates. The deposited nanostructures were characterized by atomic force microscopy and exhibited globular structures with average diameters decreasing with laser fluence. Raman spectroscopy showed that no major decomposition appeared. We have investigated the Mn(III)-metalloporphyrin thin films by cyclic voltammetry in order to evaluate the potential bio/chemosensing activity on dopamine neurotransmitter analyte. We have found that the manganese(III)-porphyrin is appropriate as a single mediator for dopamine sensing in the specific case of gold screen-printed electrodes.     

Morphology of periodic nanostructures for photonic crystals grown by glancing angle deposition

An enhancement of the glancing angle deposition (GLAD) technique called PhiSweep was used to grow slanted columns of silicon and titanium dioxide onto patterned substrates. The PhiSweep technique involves periodically rotating the substrate back and forth during the deposition process, which reduces column fanning caused by anisotropy in the shadowing conditions. The patterned substrates consisted of a tetragonal array of hillocks with 100, 200, and 300 nm periodicities and were fabricated using electron beam lithography. The PhiSweep method alters the tilt angle of the slanted columns compared with those grown using traditional GLAD. We present a derivation of the tilt angle of the slanted columns as a function of the parameters of the PhiSweep technique. The tilt angles of the silicon and titanium dioxide films were measured and agree with the predicted values. The films fabricated using the PhiSweep method are compared with similar films grown using traditional GLAD. The PhiSweep technique produced films with substantially less column fanning than those grown by traditional GLAD. This reduction in column fanning has extended the size range over which periodic GLAD structures, such as square spiral photonic crystals, can be grown.     

Achieving Thin Films with Micro/Nano-Scale Controllable Morphology by Glancing Angle Deposition Technique

We demonstrate that thin films with micro/nanometre controllable morphology can be fabricated by the glancing angle deposition （GLAD） technique which is a physical vapour deposition technique. In this technique, there are parameters which determine the morphology of the thin films： the incident angle, ratio of the deposition rate with respect to the substrate rotation rate, nature of the material being deposited, etc. We fabricate the morphology of column, pillar, helices, zigzag and study the parameters which determine morphology by given some examples of SEM.     

Sub-micron scale patterning using femtosecond laser and self-assembled monolayers interaction

Standard positive photoresist techniques were adapted to generate sub-micron scale patterns of gold substrate using self-assembled monolayers (SAMs) and femtosecond laser. Self-assembled monolayers formed by the adsorption of alkanethiols onto gold substrate are employed as very thin photoresists. The process underlying photopatterning of SAMs on gold is well-known at the phenomenological level. Alkanethiolates formed by the adsorption of alkanethiols are oxidized on exposure to UV light in the presence of air to alkylsulfonates. Specifically, it is known that deep UV light of wavelength less than 200 nm is necessary for oxidation to occur. In this study, solid state femtosecond laser of wavelength 800 nm is applied for photolithography. The results show that ultrafast laser of near infrared (NIR) range wavelength can replace deep UV laser source for photopatterning using thin organic films. The essential basis of our approach is the photochemical excitation of specific reactions in a particular functional group (in this case a thiolate sulfur atom) distributed with monolayer coverage on a solid surface. Femtosecond laser photolithography could be applied to fabricate the patterning of surface chemical structure and the creation of three-dimensional nanostructures by combination with suitable etching methods.     

Large-area micro/nanostructures fabrication in quartz by laser interference lithography and dry etching

Laser interference lithography (LIL) has the capability to fabricate large-area microstructures on the photoresist with only a couple of minutes’ exposure and development. In this study, LIL was adopted to fabricate micro/nanostructures in quartz by combining the following dry-etching process either reactive ion etching (RIE) or inductively coupled plasma (ICP). A layer of gold film was coated on the quartz to act as a hard mask during the dry-etching process. A microhole array in quartz with a thin gold film covered on the surface was fabricated when choosing RIE. Each hole in the microhole array was surrounded with gold nanoparticle capped silica (Au/SiO₂) cones when using ICP instead of RIE. This is due to the thin gold film that serves as the mask for creating the surface roughness required for creating the silica cone structure.     

Plasmon-enhanced fluorescence near metallic nanostructures: biochemical applications

Amplification of fluorescence is a nanoscale phenomenon which is particularly pronounced in close proximity to metal nanostructures. Due to its sharp distance dependence, it is ideally suited to monitor biorecognition reactions. Using this effect we have been able to demonstrate ultrasensitive bioassays. Two types of metal nanostructures have been employed, nanometric silver islands deposited over an ultrathin metal mirror and silver fractal structures. For the first type, metal mirrors (aluminum, gold, or silver protected with a thin silica layer) were coated with SIFs and an immunoassay (model assay for rabbit IgG or myoglobin immunoassay) was performed on this surface using fluorescently labeled antibodies. Our results show that SIFs alone (on a glass surface not coated with metal) enhance the immunoassay signal approximately 3 to 10-fold. Using a metal mirror instead of glass as support for SIFs leads to up to 50-fold signal enhancement. The second type of metal nanostructures, silver fractals, were produced by electrochemical reduction of silver nitrate deposited on sapphire covered with a thin conductive film of indium tin oxide. These structures were used as a substrate for a model rabbit IgG bioassay. The fluorescence resulting from the binding of antibody labeled with Rhodamine was highly nonuniform with distinctive hot spots. These highly fluorescent regions were correlated with areas of higher Ag thickness and coverage. Such high values of fluorescence amplification in both types of nanostructures have been interpreted by using time-resolved fluorescence data and by considering the radiative properties of plasmons in the environments which promote plasmon coupling. PACS 87.64.Ni; 81.07.-b; 87.14.-g     

Surface plasmon resonance characterization of thermally evaporated thin gold films

The heterogeneous character of thin gold films prepared by thermal evaporation and the dependence of this heterogeneity on the rate of their deposition must be considered when exploiting their optical properties for biosensor purposes. For instance, the performance of thin gold films for surface plasmon resonance (SPR) biosensors may drastically be degraded if care is not taken to prepare a film with a high fraction of gold (>95%). We use three different models to interpret the SPR response of gold films prepared by thermal evaporation. We show that the interpretation of the SPR curves requires considering both a global heterogeneity of the gold films and a surface roughness. Our conclusions are further corroborated by scanning surface plasmon microscope (SSPM) images of these thin gold films.     

Characterization and optimization of AuNPs labeled by Raman reporters on glass based on silver enhancement

In this report, gold nanoparticles (AuNPs) labeled by Raman reporters (AuNPs‐R6G) were assembled on glass and used as the seeds to in situ grow silver‐coated nanostructures based on silver enhancer solution, forming the nanostructures of AuNPs‐R6G@Ag, which were characterized by scanning electron microscopy (SEM) and UV‐visible spectroscopy. More importantly, the obtained silver‐coated nanostructures can be used as a surface enhancement Raman scattering (SERS) substrate. The different SERS activities can be controlled by the silver deposition time and assembly time of AuNPs‐R6G on glass. The results indicate that the maximum SERS activity could be obtained on AuNPs‐R6G when these nanostructures were assembled on glass for 2 h with silver deposition for 2 min. In addition, the reproducibility of SERS signal on the fabricated nanostructures is very high with the intensity error lower than 15%, which has great promise as a probe for application in bioanalysis. Copyright © 2008 John Wiley & Sons, Ltd.     

Gradient-index narrow-bandpass filter fabricated with glancing-angle deposition

Glancing-angle deposition (GLAD) is a fabrication method capable of producing thin films with engineered nanoscale porosity variations. GLAD can be used to create optical thin-film interference filters from a single source material by modification of the film refractive index through control of film porosity. We present the effects of introducing a layer of constant low density into the center of a rugate thin-film filter fabricated with the GLAD technique. A rugate filter is characterized by a sinusoidal refractive-index profile. Embedding a layer of constant refractive index, with a thickness equal to one period of the rugate index variation, causes a narrow bandpass to appear within the filter's larger stop band. Transmittance measurements of such a gradient-index narrow-bandpass filter, formed with titanium dioxide, revealed an 83% transmittance peak at a vacuum wavelength of 522 nm, near the center of the stop band, with a FWHM bandwidth of 15 nm.     

Controllable nanostructure and optical properties of ZrO2 thin films by glancing angle deposition

In this paper, nanostructured ZrO₂ films were prepared by electron beam evaporation with the glancing angle deposition (GLAD) technique. Columnar films with voids in between formed owing to the self-shadowing effect and the limited diffusion of deposited atoms. The microstructure evolves from slanted columnar structure to helical and pillar structures as the substrate rotational speed increases. The diameter of the columns is in the range of 30–50 nm. A higher rotational speed favors a larger nodule size and a greater surface roughness. Due to the porous structure, the refractive index n of GLAD ZrO₂ films varies from 1.75 to 1.80, lower than that of bulk material. A maximum value of birefringence (Δn=0.03) is obtained in a slanted columnar structure, and the relationship between birefringence and microstructure orientation is discussed. Our results demonstrate that glancing angle deposition is a feasible approach for designing the nanostructure and optical properties of thin films.     

Fabrication of segmented nanofibers by template wetting of multilayered alternating polymer thin films

Segmented polystyrene (PS) and poly-methyl methacrylate (PMMA) nanofibers were fabricated by wetting nanoporous alumina templates with multilayered polymer thin films. The order and thickness of the polymers within the thin films affected the resulting nanofiber morphology, PS and PMMA segment properties, and created unique core-shell structure in the PMMA segments. The core-shell structure suggests a complex wetting phenomenon. Fabrication of polymer nanostructures by wetting of layered thin films opens the arena of multifunctional, one-dimensional, polymer nanostructures with segments having individual and specific functionalities.     

Magnon excitation with spin-polarized scanning tunneling microscopy

Using spin-polarized scanning tunneling microscopy, the local excitation of magnons in Fe and Co has been studied. A large cross section for magnon excitation was found for bulk Fe samples while for thin Co films on Cu(111) the cross section linearly scales with film thickness. Recording inelastic tunneling spectra with Fe coated W tips in a magnetic field, the magnonic nature of the excitation was proven. Magnon excitation could be detected without the use of a separating insulating layer opening up the possibility to directly study magnons in magnetic nanostructures via spin-polarized currents.     

倾斜式生长ZnS纳米柱状薄膜及其透射性能的研究

采用倾斜式生长的方法,在本底真空为3×10-4 Pa,生长率为0.2 nm·s-1的条件下,通过改变衬底的法线方向与入射粒子流的夹角α,在ITO导电玻璃衬底上制备了ZnS纳米薄膜。在α=80°和85°时,样品的Ｘ射线衍射谱证实了不同倾斜角时所制备薄膜中均有纳米ZnS晶体形成,扫描电子显微镜(SEM)图像显示,所形成的薄膜均呈现出了柱状结构,并且倾斜角为85°时所得到的纳米柱直径大于80°时所得结果;在α=0°时,相应测量结果表明,虽然在不同衬底上也形成了纳米ZnS晶体薄膜,但并未见柱状结构,而是形成了一层均匀且致密的薄膜。对两种薄膜结构的生长动力学过程作了分析。ITO衬底上薄膜的透射光谱表明ZnS柱状薄膜能够提高可见光的透过率,因此对柱状ZnS纳米薄膜的研究将有利于提高电致发光器件的发光效率。     

Self-assembled gold nanochains hybrid based on insulin fibrils

We reported a facile method for preparing self-assembly gold nanochains by using insulin fibrils as biotemplate in aqueous environment. The gold nanochains hybrid nanostructures, which are insulin fibrils coated by gold nanoparticles, can be fabricated by simply reducing the salt precursors using DMAB. By increasing the molar ratio between salt precursors and insulin, denser hybrid nanochains can be obtained, meanwhile the mean diameter of gold nanoparticles is changing from 8 to 10 nm and then to 12 nm. The fabricated gold nanochains hybrid had helix structure, which was confirmed by circular dichroism spectra. The hybrid nanostructures were also investigated by transmission electron microscope, atomic force microscope, Fourier transform infrared spectra, and UV–Visible spectroscopy. As the wire-like structure become denser, the suspensions show color-changing, corresponding to the surface plasmon resonance red shift, which is attributed to the increasing mean size of nanoparticles. Based on the characterizations, a hypothetic mechanism was suggested to describe the formation processing of hybrid gold nanochains.     

Electrochromic switching of WO3 nanostructures and thin films

We present transmission measurements through tungsten tri-oxide nanostructures and thin films prepared by sol–gel process on micro-contact printed substrates. Identical electrochromic switching times are found for both the nanostructures and the bulk films with equal thicknesses upon intercalation of H⁺ ions. We attribute the large change in the transmission through nanostructures at 632 nm, which can not be solely explained by absorption, to diffraction effects. PACS 73.40.Cg; 73.40.Mr; 78.20.-e; 78.67.n