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.     

Gold coated metal nanostructures grown by glancing angle deposition and pulsed electroplating

Nickel based nanostructures are grown by glancing angle deposition (GLAD) on flat and pre-patterned substrates. These fabricated porous thin films were subsequently coated by pulsed electroplating with gold. The morphology and conformity of the gold coating were investigated by scanning electron microscopy and X-ray diffraction. Controlled growth of closed gold layers on the nanostructures could be achieved, while the open-pore structure of the nanosculptured thin films was preserved. Such gold coated nanostructures are a candidate for optical sensing and catalysis applications. The demonstrated method can be applied for numerous material combinations, allowing to provide GLAD thin films with new surface properties.     

Formation of nanobumps and nanoholes in thin metal films by strongly focused nanosecond laser pulses

Nanobumps and nanoholes have been formed in gold and silver films with various thicknesses on a dielectric substrate by strongly focused single nanosecond pulses of a Nd:YAG laser. An apertureless dielectric fiber probe and an aspherical lens with a numerical aperture of 0.5 were used to focus laser radiation into a diffraction-limited spot on the surface of gold and silver films, respectively. Atomic force and electron microscopy studies have demonstrated that the shape and dimension of nanostructures, as well as the threshold parameters of laser radiation for their formation, are determined by the thickness of a modified film (“size effect”) and by the duration of a laser pulse owing to the lateral heat conduction in films (nonlocal energy deposition effect). Mechanisms of the dynamic formation of such structures in metallic films by nanosecond laser pulses due to phase transformations of their material have been discussed.     

Self‐Assembled Silver–Gold Nanoisland Films on Glass for SERS Applications

We present a study of resonant optical properties of gold‐protected silver nanoisland films. Silver nanoislands were grown on a glass substrate using out‐diffusion technique, the growth was followed by the deposition of nanometer‐thick gold coatings. Scanning electron microscopy and optical spectroscopy were used to characterize morphology and extinction spectra of the grown combined silver–gold nanostructures. Micro Raman spectroscopy of the combined nanoislands has demonstrated their signal enhancement factor exceeding that one of the initial silver nanoislands.     

Silver-enhanced conductivity of magnetoplasmonic nanochains

A method for improving the electrical properties of one-dimensional conducting structures by reductive deposition of metallic silver on a gold surface is presented. Fe₃O₄@Au core–shell nanoparticles were used to fabricate conducting magnetoplasmonic nanochains (MPNCs) through magnetic-field-induced assembly. The MPNCs were prepared on a solid substrate. Their dimension was controlled by adjusting the pH of the colloidal solution. The nanochains (NCs) were placed across gold microelectrodes, and additional metal was deposited by highly specific chemical enhancement of the colloidal gold using a silver enhancement solution. Silver-enhanced MPNCs show a remarkable morphology and an impressive enhancement in electrical properties compared to the as-prepared MPNCs.     

Fractal structure of gold clusters formed under vacuum deposition on dielectric substrates

The growth of gold island films under vacuum deposition on the surface of dielectric substrates are investigated. Fractal dimensions of the clusters formed under film deposition at different substrate temperatures and evaporation rates are estimated. The correlation between surface morphology and optical properties of the films deposited are discussed.     

Magnetic properties of Co films grown on the modified Si(111) surface

The magnetic properties and domain structure of epitaxial Co films grown on a modified Si(111) surface were studied. First, the processes of growth of copper silicide nanostructures on the Si(111) surface were investigated. Copper silicide clusters were formed on the Si(111)-5.55 × 5.55-Cu surface at a substrate temperature of ～550°C. It was established that the nanostructures formed have a perfect faceting, and the lateral edges and long wire side are oriented along the Si〈110〉 crystallographic directions. Then, Co films were deposited on the formed structures. The investigation of the coercive force and reduced remanent magnetization showed that the Co(111) films have the sixth-order crystalline anisotropy. It was found that the coercive force of the Co films deposited on the Cu buffer layer is approximately six times less than that of the Co films deposited on the Si(111)-5.55 × 5.55-Cu surface and Si(111)?5.55 × 5.55-Cu/(Cu-Si) cluster surface.     

Growth and morphology of thin films of aromatic molecules on metals: the case of perylene

The morphology and growth of perylene films on copper and gold surfaces have been characterized by XPS, AFM, SEM and polarization microscopy. Deposition at cryogenic temperatures leads to amorphous but homogeneous films whereas growth a room temperature results in a formation of disjointed crystalline islands. A similar morphology was observed after thawing the amorphous films which were grown before at low temperature and hence demonstrates a pronounced dewetting. Furthermore, it was found that the geometry of the resulting islands depends on the actual substrate surface which is attributed to the formation of seed layers and their influence on the subsequent film growth. The presently described dewetting and island formation appears to be a quite general phenomenon of organic film growth which needs to be considered in the interpretation of spectroscopic data and STM measurements for organic thin films. PACS 68.37.-d; 68.37.Ps; 68.55.Jk     

Effect of thickness on the optoelectronic properties of electrodeposited nanostructured SnS films

The present study focuses on the effect of film thickness on the physical properties of tin mono-sulfide (SnS) nanostructures deposited through an electrodeposition technique. The SnS films were characterized using X-ray diffraction (XRD) analysis, which confirmed the formation of polycrystalline orthorhombic SnS thin films. The crystallite size and lattice parameters were estimated from the XRD patterns. The effect of the deposition voltage on the surface morphology of the deposited films was evaluated by field emission electron microscopy (FESEM). The FESEM images revealed that the nanostructures possess plate-like and bulky pyramid morphologies. Also, optical plots of the thin films were considered, which determined the direct band gap energies of the samples as 1.42–1.50 eV. Finally, Mott–Schottky measurements indicated that the samples have p-type conductivity and the carrier concentrations of the SnS films improve with the increase of their thicknesses.     

Effect of crystalline microstructure on the photophysical performance of polymer／perylene composite films

To obtain high carrier mobility, better charge injection capability, and high photovoltaic device conversion efficiency, a powerful strategy is to improve the morphology of the polymer/dye composite films. Conjugated conducting polymer (CP) thin films doped with perylene derivative (PV) of various concentrations were prepared by spin-casting method, and their morphology and photovoltaic characteristics were examined. The change in morphology and molecular reorientation occurring in CP-PV composite films upon annealing at different temperatures was investigated using scanning electron microscopy, x-ray diffraction, Fourier transform infrared and UV-vis absorption. By changing the annealing temperature, PV microcrystallines of 8－10μm in size lying parallel to the substrate surface can be obtained. Annealing effect improved the photovoltaic performance of ITO/CP-PV/Al Schottky-type solar cells, which can be attributed to the formation of an electron conducting PV crystal network. Preliminary studies indicate that the morphological structure in CP-PV composite films has an important influence to their photovoltaic properties.     

Characterization of copper SERS-active substrates prepared by electrochemical deposition

Surface Enhanced Raman Scattering (SERS) on copper substrates of various morphologies, prepared by electrochemical deposition on platinum targets, was investigated. The substrate preparation procedures differed by the coating bath compositions, applied current densities and the duration of individual steps. The surface morphology of the substrates was visualized by means of Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). SERS spectra of selected organic thiols were measured and the relation between SERS spectral intensity and the surface structure of SERS-active substrates was studied. It has been shown that good Raman surface enhancement can be achieved on the copper substrates prepared by electrochemical deposition from ammoniac baths. Copper substrates fabricated from acidic baths did not show efficient Raman surface enhancement. The results of microscopic measurements demonstrated that the average surface roughness value does not play a substantial role, whereas the shape of the surface nanostructures is a key parameter.     

Study of titania nanorod films deposited by matrix-assisted pulsed laser evaporation as a function of laser fluence

The effects of annealing at 300 °C on gold nanostructures sputtered onto glass substrate were studied using XRD, SAXSees, the Van der Pauw method and ellipsometry. As-sputtered and annealed samples exhibit a different dependence of the gold lattice parameter on the sputtering time. With increasing sputtering time the average thickness of the layer and the size of gold crystallites increased. Another rapid enlargement of the crystallites is observed after annealing. The volume resistivity decreases rapidly with the increasing sputtering time for both, as-deposited and annealed structures. With increasing sputtering time initially discontinuous gold coverage changes gradually in a continuous one. Electrically continuous gold coverage on the as-sputtered and annealed samples exhibits the same concentration of free charge carriers and Hall mobility. Optical constants of as-deposited and annealed gold films determined by ellipsometry support resistivity measurements and clearly manifest the presence of plasmons in discontinuous films.     

Evolution of texture in electrodeposited Ni/Cu layered nanostructures

The objective of this research was to study the evolution of crystallographic texture in electrodeposited Ni/Cu laminated nanostructures. Thick films (14-40 µm) consisting of nickel and copper nanolayers (7-27 nm) were fabricated on annealed polycrystalline copper substrates using an electodeposition technique. The microstructure of the deposits was varied by changing the deposition time of each layer and the electrolyte temperature. X-ray diffraction, transmission electron microscopy and scanning electron microscopy were applied to characterize the deposits. Three microstructural behaviours were observed. The deposit with a very fine bilayer thickness (7 nm) was composed of coherent layers parallel to the substrate surface. This deposit replicated the cube orientation of the substrate and showed a strong ?100? texture throughout the thickness of the deposit. An increase in the bilayer thickness (17 and 27 nm) caused a change in the texture from ?100? on the substrate side to ?111? on the solution side. This change in texture is suggested to be associated with a change in the deposition front orientation from {100} to {110} and the subsequent twinning of the cube-oriented crystals. A decrease in the electrolyte temperature inhibited faceting of the interface and hence no twinning was observed.     

In situ functionalized self-assembled monolayer surfaces for selective chemical vapor deposition of copper

Recent studies show that the self-assembled monolayer (SAM) is well suited to control the selectivity of chemical vapor deposition (CVD). Here, we reported the selective CVD for copper on the functionalized SAM surfaces (with -SH, -SS-, and -SO₃H terminal groups). The -SS- and -SO₃H terminal group surfaces were obtained through in situ chemical transformation of -SH terminal group surface of a 3-mercaptopropyltrimethoxysilane-SAM (MPTMS-SAM). As a result, the -SS- terminal group surface reduces copper deposition and the -SO₃H terminal group surface enhances copper deposition comparing to the -SH terminal group surface. In addition, the MPTMS-SAM was irradiated by UV-light through a photo mask to prepare SH-group and OH-group regions. Then, copper films were deposited only on the SH-group region of the substrate in chemical vapor deposition. Finally, patterns of copper films were formed in the way of UV-light irradiation. These results are expected for use of selective deposition of copper metallization patterns in IC manufacturing processes.     

PED沉积La-Sr-Cu-O薄膜表面的有序纳米结构

采用脉冲电子束沉积(PED)技术在Si(100)衬底上生长La_Sr_Cu_O薄膜，在750℃生长温度下获得具有有序纳米结构的表面形貌.采用聚集离子束(FIB)技术对获得的纳米结构进行表征，结果表明，这种有序的纳米结构是由于Si衬底和La_Sr_Cu_O薄膜之间的热膨胀系数和晶格的 失配引起的纳米裂纹.在这些纳米裂纹处，La_Sr_Cu_O成核生长获得独立的纳米线.通过控制 这种有序的纳米结构的生长，这种有序的纳米结构可以用来构造弱连接形成的器件. 关键词： 脉冲电子束沉积 La_Sr_Cu_O薄膜 纳米结构     

LOCAL ELECTROCHEMICAL DEPOSITION OF METAL ISLANDS MECHANICALLY INDUCED WITH THE TIP OF AN ATOMIC FORCE MICROSCOPE

The investigation of electrochemical processes on the nanometer scale is of great scientific as well as technological interest. Here we study the electrodeposition of copper on a polycrystalline gold surface, and demonstrate that copper deposition can be locally induced by mechanical activation with the tip of an atomic force microscope (AFM). Whereas at higher values of the deposition voltage (>100mV), a solid copper film can grow on the gold surface without tip activation, at lower voltages (approx. 30-60mV), copper deposition only occurs at the position where the surface is activated by the AFM tip due to scanning in mechanical contact with the sample. With this mechano-electrochemical "writing" process, which can be performed at ambient conditions, the controlled local deposition of metallic islands is possible, at applied force loads of the order of 10nN. Both the size-dependence of the locally induced structures on the deposition time and the reversibility of the local deposition process are studied. Depending on the deposition parameters, individual copper islands between 50nm and 200nm in size were deposited at predefined locations on the gold surface. The investigations open perspectives for the controlled mechano-electrochemical writing of more complex nanostructures with the AFM tip.     

Optical properties of gold electrode surfaces covered with metal monolayers

The relative reflectivity changes ΔR/R of a gold electrode surface caused by the deposition of monolayers of thallium, copper and lead from electrolytic solutions at underpotentials have been studied in situ in the photon energy range between 1.8 and 5.2 eV. The optical constants of the surface layer giving rise to this measured reflectivity change have been calculated and compared to the results of the electroreflectance effect on bare gold surfaces. It is shown that the reflectance change observed during the monolayer deposition is to first order due to a change in the gold electrode surface layer and not to absorption processes in the monolayer itself. The latter ones cause a fine structure superimposed to the substrate spectrum. The relatively strong change in the gold surface optical constants upon metal monolayer deposition is explained in terms of an enhanced electroreflectance effect due to the partially ionic character of the metal adatoms, which alters the free electron concentration in the substrate surface layer. Electroreflectance spectra obtained on gold surfaces covered with a monolayer of thallium compare favourably with dielectric loss functions computed for charged gold surfaces. This supports the assumption that the reflectivity changes observed upon metal monolayer deposition are mostly due to changes in the optical properties of the substrate metal surface.     

Dispersion of nanospheres on large glass substrate by amorphous or polycrystalline silicon deposition for localized surface plasmon resonance

Nanosphere lithography is a cost-effective way to fabricate noble metal nanostructures for plasmonics. However, dispersing nanospheres on a large area of glass substrate is a difficulty encountered when transparent substrate is required in applications such as localized surface plasmon resonance or surface enhanced Raman spectroscopy. Because poly(diallyldimethyl ammonium chloride) (PDDA) on silicon surface introduces a force that can disperse nanospheres on silicon, in this article, we modify the glass surface through amorphous or polycrystalline silicon deposition and thus well disperse polystyrene or silica nanospheres over a glass area of more than 2 cm × 2 cm. Transmission loss of the glass substrate caused by amorphous or polycrystalline silicon deposition is analyzed with good agreement to experimental spectra, and localized surface plasmon resonance signals generated from the gold nanostructures fabricated on these substrates are measured and yield a sensitivity of 317 nm/RIU, which prove the feasibility and effectiveness of our method.     

Flame synthesis of WO3 nanotubes and nanowires for efficient photoelectrochemical water-splitting

Tungsten trioxide (WO₃) is a technologically important material for photoelectrochemical (PEC) water-splitting for the solar production of hydrogen fuel from water. For PEC water-splitting, high aspect ratio WO₃ nanostructures such as nanowires (NWs) and nanotubes (NTs) are superior to planar WO₃ films because they orthogonalize the directions of light absorption (along the long axis) and charge transport (across the short radius), leading to both efficient light absorption and charge carrier collection. However, PEC water-splitting requires the growth of WO₃ on delicate transparent conducting oxide (TCO) substrates that cannot tolerate high temperature processing. To date, the large-scale, rapid, economical synthesis of high aspect ratio WO₃ nanostructures on these delicate TCO substrates remains a major challenge. Previously, we synthesized WO₃ NW arrays by a rapid, atmospheric and scalable flame vapor deposition (FVD) method, in which a flame oxidizes and evaporates tungsten metal to produce tungsten oxide vapors that condense onto a colder substrate in the form of NWs. Nevertheless, at substrate temperatures low enough to ensure the health of the TCO, the growth of WO₃ NW arrays was non-uniform and sparse due to limitations of the experimental design. Herein, we significantly improve the FVD design to grow uniform and densely packed WO₃ nanostructures on TCO substrates, thereby enabling the application of these WO₃ nanostructures to PEC water-splitting. The morphology of the nanostructures varied from densely packed multi-shell NTs and single-shell NTs to NWs as we increased the substrate temperature in the range 530–700 °C. Importantly, the WO₃ NTs synthesized by FVD had higher areal number density and longer length than state-of-the-art WO₃ NW photoanodes grown by chemical vapor deposition and hydrothermal methods, resulting in stronger light absorption and superior PEC water-splitting performance. Thus, in addition to being scalable, rapid and economical, the FVD method also synthesizes materials of high quality.     

Scanning tunneling microscopy of adsorbates on insulating films. From the imaging of individual molecular orbitals to the manipulation of the charge state

Ultrathin insulating films on metal substrates are unique systems for using a scanning tunneling microscope to study the electronic properties of single atoms and molecules that are electronically decoupled from the metallic substrate. Individual gold atoms on an ultrathin insulating sodium chloride film supported by a copper surface exhibit two different charge states, which are stabilized by the large ionic polarizability of the film. The charge state and associated physical and chemical properties such as diffusion can be controlled by adding or removing a single electron to or from the adatom with a scanning tunneling microscope tip. The simple physical mechanism behind the charge bistability in this case suggests that this is a common phenomenon for adsorbates on polar insulating films. In the case of molecules on ultrathin NaCl films, the electronic decoupling allows the direct imaging of the unperturbed molecular orbitals, as will be shown in the case of individual pentacene molecules. PACS 68.37.Ef; 73.61.Ng; 73.20.Hb