Deposition and wettability of silver nanostructures on Si(1 0 0) substrate based on galvanic displacement reactions

A new route for silver electroless deposition on Si(1 0 0) substrate is developed based on the galvanic displacement process. The basic electroless bath contains NaF and AgNO₃ with different concentrations. The morphologies of electrolessly deposited silver nanostructures, including silver nanowires and nanoparticles, are strongly dependent on the electrolyte composition. Adding an excess dosage of polyvinylpyrrolidone into the basic electrolyte yields final silver films of porous structures composed by multitudinous Ag nanoparticles. The porous silver films possess the surface hydrophobic property after the modification with n-dodecanethiol. Unidirectional wetting and spreading of a water droplet are also demonstrated on the patterned porous Ag films.     

Fabrication of silver nanoparticles deposited on boehmite sol for surface enhanced Raman scattering

The composite consisting of silver nanoparticles deposited on boehmite hybrid was synthesized by NaBH₄ reduction technique. The morphology of the composite was studied by TEM, UV/Vis spectrophotometer and particle sizer. The size of the silver nanoparticles deposited on the surface of the boehmite ranged from 10 nm to 100 nm. The contact of silver nanoparticles increased by means of deposition of silver nanoparticles on the boehmite sol and the aggregation of the composites. This leads to the appearance of a shoulder at 450 nm in the UV-Vis absorption spectra with the addition of 0.15 mg and 1.5 mg boehmite. It was found that the intensity of the SERS in the case of the composite was higher than for silver colloids consisting of a concentration of silver greater than 3.2 mM.     

A facile method for preparing highly conductive and reflective surface-silvered polyimide films

A novel method was developed for the preparation of reflective and electrically conductive surface-silvered polyimide (PI) films. The polyimide films were functionalized with poly(dopamine), simply by dipping the PI films into aqueous dopamine solution and mildly stirring at room temperature. Electroless plating of silver was readily carried out on the poly(dopamine) deposited PI (PI-DOPA) surface. The surface compositions of the modified PI films were studied by X-ray photoelectron spectroscopy (XPS). XPS results show that the PI-DOPA surfaces were successfully deposited with ploy(dopamine) and were ready for electroless deposition of silver. The poly(dopamine) layer was used not only as the chemi-sorption sites for silver particles during the electroless plating of silver, but also as an adhesion promotion layer for the electrolessly deposited silver. The as-prepared silvered PI films show high conductivity and reflectivity, with a surface resistance of 1.5 Ω and a reflectivity of 95%, respectively.     

Spatially defined silver mirror reaction on a micropatterned aldehyde-terminated self-assembled monolayer

A simple microfabrication technique for silver (Ag) based on spatially defined silver mirror reaction using a photolithographically micropatterned aldehyde (CHO)-terminated self-assembled monolayer (SAM) is proposed. First, both a Si substrate covered with native oxide and a quartz glass plate were exposed to a vapor of triethoxysilylundecanal (TESUD) diluted with absolute toluene for 3 h at 403 K. This vapor phase treatment produced a 1.2-nm-thick TESUD-SAM with a flat, homogeneous surface. Several samples were then photolithographically micropatterned using an excimer lamp radiating 172 nm vacuum ultraviolet light, and subsequently employed as templates for area-selective electroless Ag plating. Optical microscopy, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) confirmed that Ag metal was preferentially deposited on the CHO-terminated regions, resulting in the formation of well-ordered Ag microstructures composed of rectangular 5 μm × 25 μm features. The CHO terminal groups of the TESUD-SAM were found to be effective in reducing Ag ionic species at the solid/liquid interface.     

Optical and structural properties of CdS thin films grown by chemical bath deposition doped with Ag by ion exchange

In this work thin CdS films using glycine as a complexing agent were fabricated by chemical bath deposition and then doped with silver (Ag), by an ion exchange process with different concentrations of AgNO₃ solutions. The CdS films were immersed in silver solutions using different concentrations during 1 min for doping and after that the films were annealed at 200 °C during 20 min for dopant diffusion after the immersion on the AgNO₃ solutions. The aim of this research was to know the effects of different concentrations of Ag on the optical and structural properties of CdS thin films. The optical band gap of the doped films was determined by transmittance measurements, with the results of transmittance varying between 35% and 70% up to 450 nm in the electromagnetic spectra and the band gap varying between 2.31 and 2.51 eV depending of the silver content. X-ray photoelectron spectroscopy was used to study the influence of silver on the CdS:Ag films, as a function of the AgNO₃ solution concentration. The crystal structure of the thin CdS:Ag films was studied by the X-ray diffraction method and the film surface morphology was studied by atomic force microscopy. Using the ion exchange process, the CdS films’ structural, optical and electric characteristics were modified according to silver nitrate concentration used.     

Effect of temperature and silicon resistivity on the elaboration of silicon nanowires by electroless etching

The morphology of silicon nanowire (SiNW) layers formed by Ag-assisted electroless etching in HF/H₂O₂ solution was studied. Prior to the etching, the Ag nanoparticles were deposited on p-type Si(1 0 0) wafers by electroless metal deposition (EMD) in HF/AgNO₃ solution at room temperature. The effect of etching temperature and silicon resistivity on the formation process of nanowires was studied. The secondary ion mass spectra (SIMS) technique is used to study the penetration of silver in the etched layers. The morphology of etched layers was investigated by scanning electron microscope (SEM).     

Synthesis of hollow silver spheres using poly-(styrene-methyl acrylic acid) as templates in the presence of sodium polyacrylate

Hollow silver spheres were successfully prepared by reducing AgNO₃ with ascorbic acid and using negatively charged poly-(styrene-methyl acrylic acid) (PSA) spheres as templates in the presence of sodium polyacrylate as a stabilizer. Firstly, silver cations adsorbed on the surface of PSA spheres via electrostatic attraction between the carboxyl groups and silver cations were reduced in situ by ascorbic acid. The silver nanoparticles deposited on the surface of PSA spheres served as seeds for the further growth of silver shells. After that, extra amount of AgNO₃ and ascorbic acid solutions were added to form PSA/Ag composites with thick silver shells. In order to obtain compact silver shells, the as-prepared PSA/Ag composites were heated at 150 °C for 3 h. Then hollow silver spheres were prepared by dissolving PSA templates with tetrahydrofuran.     

Electrochemical synthesis of Ag nanoparticles supported on glassy carbon electrode by means of p-isopropyl calix[6]arene matrix and its application for electrocatalytic reduction of H2O2

The silver nanoparticles were prepared on the glassy carbon (GC) electrode, modified with p-iso propyl calix[6]arene, by preconcentration of silver ions in open circuit potential and followed by electrochemical reduction of silver ions. The stepwise fabrication process of Ag nanoparticles was characterized by scanning electron microscopy and electrochemical impedance spectroscopy. The prepared Ag nanoparticles were deposited with an average size of 70 nm and a homogeneous distribution on the surface of electrode. The observed results indicated that the presence of calixarene layer on the electrode surface can control the particle size and prevent the agglomeratione and electrochemical deposition is a promising technique for preparation of nanoparticles due to its easy-to-use procedure and low cost of implementation. Cyclic voltammetry experiments showed that Ag nanoparticles had a good catalytic ability for the reduction of hydrogen peroxide (H₂O₂). The effects of p-isopropyl calix[6]arene concentration, applied potential for reduction of Ag⁺, number of calixarene layers and pH value on the electrocatalytic ability of Ag nanoparticles were investigated. The present modified electrode exhibited a linear range from 5.0 × 10⁻⁵ to 6.5 × 10⁻³ M and a detection limit 2.7 × 10⁻⁵ M of H₂O₂ (S/N = 3) using amperometric method.     

Growth behavior of electroless Ni-Co-P deposits on Fe

The electroless Ni-Co-P films were deposited on Fe film in plating baths using sodium hypophosphite as reducing agent and nickel and cobalt sulphates as ion source at pH value of 9 and plating temperature from 60 to 85 °C. The effect of the mol ratio of CoSO₄/CoSO₄ + NiSO₄ in plating bath on the growth behavior of electroless Ni-Co-P films was studied. The electroless Ni-Co-P films were characterized by transmission electron microscopy for the microstructure and thickness, and energy dispersive spectrometer for the composition. The results showed that the electroless Ni-Co-P films can be deposited on Fe films without the step of sensitization and activization; the surface of electroless Ni-Co-P film on Fe is quite even; the more the Co²⁺ ion in plating bath, the larger the activation energy and the smaller the plating rate of electroless Ni-Co-P films; and the mol ratio of Co/Co + Ni in film is larger than that in plating bath (with the exception of the film deposited in the bath with 0.9 mol ratio of CoSO₄/CoSO₄ + NiSO₄)     

Effect of electromagnetic interactions on plasmon excitations in silver particle ensembles

The optical properties of silver nano-particle ensembles are studied as a function of particle density by analyzing the light emission excited via electron injection from an STM tip. The particles are prepared with distinct dome and disk-like shapes on a Al₂O₃/NiAl(1 1 0) support. The particle density is varied over one order of magnitude by changing the Ag deposition temperature and the defect concentration in the oxide surface. With increasing density, a pronounced blue shift of the Ag plasmon mode is observed for ensembles of dome-like particles, whereas disk-like particles show relatively constant resonance energies. The observed evolution of plasmon energy as a function of particle density reflects the influence of electromagnetic interactions in the ensemble, as verified by model calculations.     

The effect of the deposition parameters on size, distribution and antimicrobial properties of photoinduced silver nanoparticles on titania coatings

Controlled photodeposition of silver nanoparticles (AgNP) on titania coatings using two different sources of UV light is described. Titania (anatase) thin films were prepared by the sol-gel dip-coating method on silicon wafers. AgNPs were grown on the titania surface as a result of UV illumination of titania films immersed in aqueous solutions of silver nitrate. UV xenon lamp or excimer laser, both operating at the wavelength 351 ± 5 nm, was used as illumination sources. The AFM topography of AgNP/TiO₂ nanocomposites revealed that silver nanoparticles could be synthesized by both sources of illumination, however the photocatalysis carried out by UV light from xenon lamp illumination leads to larger AgNP than those synthesized using the laser beam. It was found that the increasing concentration of silver ions in the initial solution increases the number of Ag nanoparticles on the titania surface, while longer time of irradiation results the growth of larger size nanoparticles. Antibacterial tests performed on TiO₂ covered by Ag nanoparticles revealed that increasing density of nanoparticles enhances the inhibition of bacterial growth. It was also found that antibacterial activity drops by only 10-15% after 6 cycles compared to the initial use.     

Electron spectroscopy studies of surface In-Ag alloy formation on the tungsten surface

XPS and UPS investigations of ultrathin films of In/Ag and Ag/In, deposited onto the W(1 1 0) surface in the ultrahigh vacuum conditions have been performed. Indium and silver films were formed by “in-situ” evaporation on W(1 1 0) substrate. XPS and UPS studies have been performed by means of SCIENTA ESCA200 instrument. The changes of In4d core-level and Ag4d valence band emissions with increasing Ag and In coverage were monitored to observe the energy shift and shape of the spin-orbit doublet of In4d and Ag4d lines in the Ag/In/W and In/Ag/W systems. UPS (HeI and HeII) measurements were supported by XPS AlK_α measurements of In3d and W4p levels, as well as by investigations of Ag3d levels. XPS and UPS data allowed to evaluate the coverage and make conclusions concerning intermixing and surface alloying in the In/Ag/W and Ag/In/W systems. W(1 1 0) substrate can be cleaned after each deposition by thermal desorption and no alloying in the In/W and Ag/W systems is observed.     

AgSbSe2 and AgSb(S,Se)2 thin films for photovoltaic applications

Silver antimony selenide (AgSbSe₂) thin films were prepared by heating sequentially deposited multilayers of antimony sulphide (Sb₂S₃), silver selenide (Ag₂Se), selenium (Se) and silver (Ag). Sb₂S₃ thin film was prepared from a chemical bath containing SbCl₃ and Na₂S₂O₃, Ag₂Se from a solution containing AgNO₃ and Na₂SeSO₃ and Se thin films from an acidified solution of Na₂SeSO₃, at room temperature on glass substrates. Ag thin film was deposited by thermal evaporation. The annealing temperature was 350 °C in vacuum (10⁻³ Torr) for 1 h. X-ray diffraction analysis showed that the thin films formed were polycrystalline AgSbSe₂ or AgSb(S,Se)₂ depending on selenium content in the precursor films. Morphology and elemental analysis of these films were done using scanning electron microscopy and energy dispersive X-ray spectroscopy. Optical band gap was evaluated from the UV-visible absorption spectra of these films. Electrical characterizations were done using Hall effect and photocurrent measurements. A photovoltaic structure: glass/ITO/CdS/AgSbSe₂/Al was formed, in which CdS was deposited by chemical bath deposition. J-V characteristics of this structure showed V_oc = 435 mV and J_sc = 0.08 mA/cm² under illumination using a tungsten halogen lamp. Preparation of a photovoltaic structure using AgSbSe₂ as an absorber material by a non-toxic selenization process is achieved.     

Electrolytical production of Ni + Mo + Si composite coatings with enhanced content of Si

Ni + Mo + Si composite coatings were prepared by co-deposition of nickel with molybdenum and silicon powders from a nickel solution in which Mo and Si particles were suspended by stirring. The layers have been deposited on a carbon steel substrate (St3S) under galvanostatic conditions. The content of Si in deposited layers was about 2-5 wt.% depending on deposition current density and the value of electric charge. For comparison Ni + Mo composite coatings were obtained under analogous current conditions. Composite coatings of enhanced Si content (15 wt.%) were deposited from an electrolyte in which 40 g/dm³ of Si covered with electroless plated nickel was dispersed. Deposition current density was equal 0.1 A/cm² and the value of electric charge Q = 500 C/cm². The thickness of the coatings was about 100-300 μm depending on their kind, electric charge and the deposition current density. Surface and cross-section morphology were investigated by scanning electron microscope (SEM). All deposited coatings are characterized by great, developed surface area. No internal stresses causing their cracking were observed. Chemical composition of the layers was determined by X-ray fluorescence spectroscopy (XRF) method and quantitative X-ray analysis (QXRD). It was stated, that the content of molybdenum and silicon in Ni + Mo + Si coatings depends on deposition current density and the amount of the powder in bath. The results of structural investigation of the obtained layers by the X-ray diffraction (XRD) method show, that they consist in crystalline Mo or Mo and Si phases built into Ni matrix. Moreover, Ni + Mo + Si composite coatings were modified by thermal treatment. It has been found that the thermal treatment of Ni + Mo + Si composite coatings caused that the new phases (NiSi, Mo₂Ni₃Si and Ni₆Mo₆C_1.06) were obtained.     

Ageing of plasma-mediated coatings with embedded silver nanoparticles on stainless steel: An XPS and ToF-SIMS investigation

Nanocomposite thin films (∼170 nm), composed of silver nanoparticles enclosed in an organosilicon matrix, were deposited onto stainless steel, with the aim of preventing biofilm formation. The film deposition was carried out under cold plasma conditions, combining radiofrequency (RF) glow discharge fed with argon and hexamethyldisiloxane and simultaneous silver sputtering. XPS and ToF-SIMS were used to characterize Ag-organosilicon films in native form and after ageing in saline solution (NaCl 0.15 M), in order to further correlate their lifetime with their anti-fouling properties. Two coatings with significantly different silver contents (7.5% and 20.3%) were tested. Surface analysis confirmed the presence of metallic silver in the pristine coating and revealed significant modifications after immersion in the saline solution. Two different ageing mechanisms were observed, depending on the initial silver concentration in the film. For the sample exhibiting the low silver content (7.5%), the metal amount decreased at the surface in contact with the solution, due to the release of silver from the coating. As a result, after a 2-day exposure, silver nanoparticles located at the extreme surface were entirely released, whereas silver is still present in the inner part of the film. The coating thickness was not modified during ageing. In contrast, for the high silver content film (20.3%), the thickness decreased with immersion time, due to significant silver release and matrix erosion, assigned to a percolation-like effect. However, after 18 days of immersion, the delamination process stopped and a thin strongly bounded layer remained on the stainless steel surface.     

Growth of silver structures on silicon surfaces observed in vivo by scanning tunneling microscopy

Early stages of growth of silver thin films on oriented silicon surfaces Si(1 0 0)2 × 1 and Si(1 1 1)7 × 7 were studied directly during deposition at room temperature by the scanning tunneling microscopy. Single Ag atoms deposited on the Si(1 0 0)2 × 1 surface diffuse too fast on the surface to be imaged by the microscope. Nucleation on C-type defects of the Si(1 0 0)2 × 1 reconstruction has been observed. During further growth, the defects represent stable terminations of silver chains. Ag nanoclusters growing on the Si(1 1 1)7 × 7 surface have been studied as a system with low diffusivity at room temperature. On this surface, presence of effective interaction between Ag clusters and individual Ag atoms in neighboring cells of the reconstruction has been identified. The interaction results in lowering the barrier for Ag atom hopping to an adjacent unit cell occupied by an Ag cluster. Unique possibilities arising from scanning the surface directly during growth are demonstrated.     

The synthesis and kinetic growth of anisotropic silver particles loaded on TiO2 surface by photoelectrochemical reduction method

Silver nanorods with average diameters of 120-230 nm and aspect ratio of 1.7-5.0 were deposited on the surface of TiO₂ films by photoelectrochemical reduction of Ag⁺ to Ag under UV light. The composite films prepared on soda-lime glass substrates were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results show that the TiO₂ film after UV irradiation in AgNO₃ solution is composed of anatase phase TiO₂ and metallic silver with face centered cubic structure. Other compounds cannot be found in the final films. The maximum deposition content of silver particles on the surface of TiO₂ film was obtained with the AgNO₃ concentration of 0.1 M. The kinetic growth rates of silver particles can be controlled by photocatalytic activity of TiO₂ films. The studies suggest that the growth rates of silver particles increase with the enhancement of photocatalytic activity of TiO₂ films. The maximum growth rate of silver particles loaded on TiO₂ films can be up to 0.353 nm min⁻¹ among samples 1#, 2# and 3#, while the corresponding apparent rate constant of TiO₂ is 1.751 × 10⁻³ min⁻¹.     

Growth and electronic properties of ultra-thin Ag films on Ni(1 1 1)

We studied the growth mode and electronic properties of ultra-thin silver films deposited on Ni(1 1 1) surface by means of scanning tunnelling microscopy (STM) and angle resolved photoemission spectroscopy (ARPES). The formation of the 4d-quantum well states (QWS) was analysed within the phase accumulation model (PAM). The electronic structure of the 1 ML film is consistent with the silver layer which very weakly interacts with the supporting surface. The line-shape analysis of Ag-4d_xz,yz QWS spectrum support the notion of strong localization of these states within the silver layer. The asymmetry of the photoemission peaks implies that the decay of the photo-hole appears to be influenced by the dynamics of the electrons in the supporting surface.     

Influence of Si substrate preparation on surface chemistry and morphology of L-CVD SnO2 thin films studied by XPS and AFM

Results of experimental studies of the influence of substrate preparation on the surface chemistry and surface morphology of the laser-assisted chemical vapour deposition (L-CVD) SnO₂ thin films are presented in this paper. The native Si(1 0 0) substrate cleaned by UHV thermal annealing (TA) as well as thermally oxidized Si(1 0 0) substrate cleaned by ion bombardment (IBA) have been used as the substrates. X-ray photoemission spectroscopy (XPS) has been used for the control of surface chemistry of the substrates as well as of deposited films. Atomic force microscopy (AFM) has been used to control the surface morphology of the L-CVD SnO₂ thin films deposited on differently prepared substrates. Our XPS shows that the L-CVD SnO₂ thin films deposited on thermally oxidized Si(1 0 0) substrate after cleaning with ion bombardment exhibit the same stoichiometry, i.e. ratio [O]/[Sn] = 1.30 as that of the layers deposited on Si(1 0 0) substrate previously cleaned by UHV prolonged heating. AFM shows that L-CVD SnO₂ thin films deposited on thermally oxidized Si(1 0 0) substrate after cleaning with ion bombardment exhibit evidently increasing rough surface topography with respect to roughness, grain size range and maximum grain height as the L-CVD SnO₂ thin films deposited on atomically clean Si substrate at the same surface chemistry (nonstoichiometry) reflect the higher substrate roughness after cleaning with ion bombardment.     

Electrochemical investigation of the surface energy: Effect of the HF concentration on electroless silver deposition onto p-Si (1 1 1)

Electroless silver deposition onto p-silicon (1 1 1) from 0.005 mol l⁻¹ AgNO₃ solutions with different HF concentration was investigated by using an electrochemical direct current polarization method and open circuit potential-time (Ocp-t) technique. The fact that three-dimensional (3D) growth of silver onto silicon is favored with increasing the HF concentration was ascribed to the drop of the surface energy and approved by electrochemical direct current polarization, Ocp-t technique and atomic force microscopy (AFM). The drop slope of open-circuit potential, K_{−ΔE(OCP)/t}, was educed from the mixed-potential theory. K_{−ΔE(OCP)/t} as well as the deposition rate determined by an inductively coupled plasma atomic emission spectrometry (ICP-AES), increased with the HF concentration, yet was not a linear function. Results were explained by the stress generation and relaxation mechanisms.