Low-damage direct patterning of silicon oxide mask by mechanical processing

To realize the nanofabrication of silicon surfaces using atomic force microscopy (AFM), we investigated the etching of mechanically processed oxide masks using potassium hydroxide (KOH) solution. The dependence of the KOH solution etching rate on the load and scanning density of the mechanical pre-processing was evaluated. Particular load ranges were found to increase the etching rate, and the silicon etching rate also increased with removal of the natural oxide layer by diamond tip sliding. In contrast, the local oxide pattern formed (due to mechanochemical reaction of the silicon) by tip sliding at higher load was found to have higher etching resistance than that of unprocessed areas. The profile changes caused by the etching of the mechanically pre-processed areas with the KOH solution were also investigated. First, protuberances were processed by diamond tip sliding at lower and higher stresses than that of the shearing strength. Mechanical processing at low load and scanning density to remove the natural oxide layer was then performed. The KOH solution selectively etched the low load and scanning density processed area first and then etched the unprocessed silicon area. In contrast, the protuberances pre-processed at higher load were hardly etched. The etching resistance of plastic deformed layers was decreased, and their etching rate was increased because of surface damage induced by the pre-processing. These results show that etching depth can be controlled by controlling the etching time through natural oxide layer removal and mechanochemical oxide layer formation. These oxide layer removal and formation processes can be exploited to realize low-damage mask patterns.     

EUROCAT oxide: an European V2O5–WO3/TiO2 SCR standard catalyst study: Characterisation by electron microscopies (SEM, HRTEM, EDX) and by atomic force microscopy

The morphology and the homogeneity in chemical compositions of fresh and used V₂O₅–WO₃/TiO₂ EUROCAT SCR samples, in their original monolith form and after gentle grinding, have been investigated by means of electron microscopies and EDX analyses. It appears clearly that the monoliths were constituted of fibres rich in Si, Al and Ca embedded without preferential orientation in a nearly homogeneous oxide phase containing Ti, V, and W. This phase was in the form of small particles of homogeneous size of around 20–40 nm. The used catalyst was very similar to the fresh one, only the presence of S element and of more defects and more fibres were observed on the surface of the monolith. This observation was confirmed by a higher roughness detected using AFM technique.

EDX–TEM studies on the powders obtained by gently grinding the monoliths have shown that W and V species were well distributed in TiO₂ support and that the repartition of the W species, very homogeneous in the fresh sample, became somewhat slightly more heterogeneous in the used sample. V species were not so well dispersed that W species and even, some particles rich in V were observed on the used sample. This may be due to the migration and agglomeration of some of the V species. More particles, very rich in Si, were also observed for the used sample suggesting that the coating of the fibres by the active phase was partly deteriorated during SCR reaction. This observation was supported by an AFM analysis which showed a higher surface roughness for the used sample.

It was also observed by high resolution TEM that the first one or two atomic layers at the surface of all crystallites appear amorphous, while the further layers are well crystallised with the anatase structure. For the used sample this amorphous layer is slighly larger. This is an important feature for electrical conductivity (mainly at the surface) and catalytic properties.     

Electrodeposition of copper: the nucleation mechanisms

The nucleation mechanisms of copper during electrodeposition of thin films from sulfate solutions were studied by utilizing the electrochemical techniques (cyclic voltammetry and chronoamperometry) and atomic force microscopy (AFM). Near atomically smooth glassy carbon was used as the deposition substrate (electrode). The copper nucleation mechanisms were examined as a function of solution pH, copper concentration, deposition potential, temperature, and background electrolyte. It was found that with pH and copper concentration increase, the nuclei size increased, while the nuclei population density decreased. An increase of deposition potential produced smaller nuclei and higher nuclei population density. Temperature affected the morphology of deposited copper. The presence of background electrolyte also influenced the morphology and population density of copper nuclei. The nucleation mechanisms were examined by fitting the experimental data (chronoamperometry) into the Scharifker-Hills nucleation models. It was found that at pH 1, in the absence of background electrolyte, copper nucleation was instantaneous. At pH 2 and 3, the mechanism was inconclusive. In the presence of background electrolyte, the mechanism at pH 1 and 2 was mixed, while at pH 3, the mechanism was progressive nucleation.     

Electrodeposition of Pt-Fe(III) nanoparticle on glassy carbon electrode for electrochemical nitric oxide sensor

An electrochemical sensor for the detection of nitric oxide (NO) was developed by electrodeposition of Pt-Fe(III) nanoparticle on a glassy carbon electrode. This sensor exhibits excellent electrocatalytic activity for the oxidation of NO. A Nafion membrane coating was used to avoid the interference of nitrite and other potential interferences which may co-exist with NO in the biological systems. The effect of scan number in the electrodeposition process and the behavior of the sensor with respect to bulk pH have been studied. The catalytic peak current is found to be linear with the NO concentration over a wider range of 8.4 × 10⁻⁸ to 7.8 × 10⁻⁴ M, with a detection limit of 1.8 × 10⁻⁸ M (s/n = 3). In addition, the sensor has also good stability and anti-interference ability.     

Evaluation of biosynthesized nickel oxide nanoparticles from Clerodendrum phlomidis: A promising photocatalyst for methylene blue and acid blue dyes degradation

In the present investigation, nickel oxide nanoparticles (NiO) were biosynthesized utilizing an extract of Clerodendrum phlomidis leaves. Their size, phase study, and shape were investigated using a variety of research methods. In addition, we assessed the photocatalytic effects of NiO nanoparticles on the degradation of methylene blue (MB) and acid blue (AB) dyes. Throughout the research process, we found that these nanoparticles had extraordinary potential for photocatalysis when exposed to UV light. This is a 100% environmentally friendly method that makes no use of any harmful or poisonous solvents. High-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and ultraviolet–visible spectroscopy (UV–Vis) were used to analyze the biosynthesized NiO nanoparticles. The catalytic activity of the newly synthesized nanoparticles was evaluated by seeing how well they degraded dyes called methylene (MB) and acid blue (AB). Following the first-order reaction, kinetics was the photocatalytic effectiveness against the methylene blue (MB) and acid blue (AB) dyes, both of which exhibited a maximum degradation efficiency of 92% and 63%. Because of this, the biosynthesized NiO nanoparticles synthesized utilizing the extract of Clerodendrum phlomidis leaves have the potential to be used in photocatalytic applications.     

Immobilization of silver nanoparticles on polyethylene terephthalate

Two different procedures of grafting with silver nanoparticles (AgNP) of polyethylene terephthalate (PET), activated by plasma treatment, are studied. In the first procedure, the PET foil was grafted with biphenyl-4,4′-dithiol and subsequently with silver nanoparticles. In the second one, the PET foil was grafted with silver nanoparticles previously coated with the same dithiol. X-ray photoelectron spectroscopy and electrokinetic analysis were used for characterization of the polymer surface at different modification steps. Silver nanoparticles were characterized by ultraviolet-visible spectroscopy and by transmission electron microscopy (TEM). The first procedure was found to be more effective. It was proved that the dithiol was chemically bonded to the surface of the plasma-activated PET and that it mediates subsequent grafting of the silver nanoparticles. AgNP previously coated by dithiol bonded to the PET surface much less.     

Electrochemical and AFM study of cobalt nucleation mechanisms on glassy carbon from ammonium sulfate solutions

Nucleation mechanisms of cobalt on a glassy carbon electrode (gce) from aqueous ammonium sulfate solutions were investigated through the electrochemical techniques of cyclic voltammetry (cv) and chronoamperometry (ca), coupled with atomic force microscopy (AFM) studies. The studied parameters were pH, cobalt concentration, temperature, scanning rate, and deposition potential. It was found that scanning in the cathodic direction produced two peaks, corresponding to cobalt and hydrogen reduction, respectively. Scanning in the anodic direction was characterized by cobalt dissolution, which was interrupted by formation of cobalt hydroxide, causing a second anodic peak. The amperometric study found progressive nucleation mechanisms, in contrast to the instantaneous nucleation mechanisms determined by the AFM study. An explanation for the contradictory nucleation mechanisms shown in the two studies is provided.     

Electrochemical and AFM study of nickel nucleation mechanisms on vitreous carbon from ammonium sulfate solutions

Reaction and nucleation mechanisms of nickel in ammoniacal solutions have been investigated as a function of nickel concentration, solution pH, deposition potential, temperature and conditioning potential. Electrochemical mechanisms of nickel reduction were found to be pH dependent, while their kinetics was concentration dependent. A surface film formed by anodic oxidation passivates nickel clusters preventing their further oxidation. Nickel nucleation on vitreous carbon, which proceeds according to the progressive nucleation model, shows a large degree of inhibition at both pH 6 and pH 9. Cluster sizes were larger when electrodeposition was carried out from solutions with higher nickel concentrations. The clusters were also larger at more negative deposition potentials and at higher solution pH. Cluster population density increased with the increasing solution temperature. Different activation energies for the nickel-aquo and nickel-ammino complexes calculated from Arrhenius diagram indicate that electroreduction of nickel-ammino complex is energetically more demanding. All electrochemical results were further verified by the atomic force microscopy investigations.     

Reduction of nickel oxide on alpha alumina: coalescence of nickel to metallic crystallites

Reduction of alpha-alumina-supported nickel oxide was studied with hydrogen consumption, magnetization and XRD measurements. Rupture of Ni-O bonds at 270–350 ° C is much faster than nucleation of metallic nickel and precedes growth into crystallites. Water vapor and low hydrogen flows retard both processes. At higher temperatures, growth is more rapid than Ni-O bond rupture.     

The application of lateral force microscopy to particle removal in aqueous polymer solutions

Abstraet-An atomic force microscope (AFM) has been used to examine the effect of a typical polymeric dispersant on the adhesion between an iron oxide sphere and a silicon wafer in the presence and absence of shear. Two separate methods for the determination of the lateral spring constant (k₁) of AFM cantilevers were employed. Determination of k₁ allows the absolute, rather than relative, shear force to be extracted from the lateral force output of the AFM. A comparison is made between the pull-off force (no shear) and the lateral force as the dispersant concentration and loading force are varied. While in both cases the magnitude of the forces decrease with increasing dispersant concentration, the effect is much less marked for the lateral force. A linear increase in removal forces with increasing loading force was observed. For a given load, the removal force is typically an order of magnitude smaller in the presence of shear.     

Electrodeposition of copper on Ru(0 0 0 1) in sulfuric acid solution: Growth kinetics and nucleation behavior

The electrodeposition of Cu on Ru(0 0 0 1) from 0.1 M CuSO₄/0.5 M H₂SO₄ solution has been studied by cyclic voltammetry, current-time transient measurements, and by in situ electrochemical atomic force microscopy (EC-AFM). Cyclic voltammetry measurements show that the as-prepared Ru(0 0 0 1) electrode exhibits a UPD peak, while EC-AFM data indicate a broadly terraced surface with step heights of atomic dimensions. Kinetic data show that the electrodeposition/nucleation process is not well described by 3D or 2D nucleation models. The EC-AFM data show that at potentials near the OPD/UPD threshold, Cu crystallites exhibit pronounced growth anisotropy, with lateral dimensions greatly exceeding vertical dimensions. AFM data also show that deposition at more cathodic potentials result in smaller crystallites.     

Effect of hexagonal structure nanoparticles on the morphological performance of the ceramic scaffold using analytical oscillation response

Porous bony scaffolds are utilized to manage the growth and migration of cells from adjacent tissues to a defective position. In the current investigation, the effect of titanium oxide (TiO₂) nanoparticles on mechanical and physical properties of porous bony implants made of polymeric polycaprolactone (PCL) is studied. The bio-nanocomposite scaffolds are prepared with composition of nanocrystalline hydroxyapatite (HA) and TiO₂ powder using the freeze-drying technique for different weight fractions of TiO₂ (0 wt%, 5 wt%, 10 wt%, and 15 wt%). In order to identify the microstructure and morphology of the fabricated porous bio-nanocomposites, the X-ray diffraction (XRD), atomic force microscope (AFM) and scanning electron microscopy (SEM) are employed. Also, the biocompatibility and biodegradability of the manufactured scaffolds are examined by placing them in a simulated body fluid (SBF) for 21 days, their weight and pH changes are measured. The rate of degradation of the PCL-HA scaffold can be controlled by varying the percentage of its constituent components. Due to an increasing growth and activity of bone cells and the apatite formation on the free surface of the fabricated bio-nanocomposite implants as well as their reasonable mechanical properties, they have the potential to be used as a bone substitute. Additionally, with the aid of the experimentally extracted mechanical properties of the scaffolds, the vibrational characteristics of a beam-type implant made of the proposed porous bio-nanocomposites are explored. The results obtained from SEM image indicate that the scaffolds produced by the employed method have high total porosity (70%–85%) and effective porosity. The pore size is obtained between 60 and 200 μm, which is desirable for the growth and propagation of bone cells. Also, it is revealed that the addition of TiO₂ nanoparticles leads to reduce the rate of dissolution of the fabricated bio-nanocomposite scaffolds.     

Enhanced direct electron transfer reactivity of hemoglobin in cationic gemini surfactant-room temperature ionic liquid composite film on glassy carbon electrodes

A novel composite film comprising cationic gemini surfactant butyl-α,ω-bis(dimethylcetylammonium bromide) (C₁₆H₃₃N(CH₃)₂-C₄H₈-N(CH₃)₂C₁₆H₃₃, C₁₆-C₄-C₁₆) and ionic liquid 1-octyl-3-methylimidazolium hexafluorophate (OMIMPF₆) has been prepared. The composite film shows good biocompatibility and it can promote the direct electron transfer between hemoglobin (Hb) and glassy carbon (GC) electrode. On the C₁₆-C₄-C₁₆ (dissolved in ethanol)-OMIMPF₆ film coated GC electrode, the immobilized Hb can exhibit a pair of well-defined, quasi-reversible and stable redox peaks with a formal potential of −0.317 V (vs SCE) in 0.10 M pH 7 phosphate buffer solutions. The electron transfer coefficient (α) of Hb is calculated to be 0.44 and the heterogeneous electron transfer rate constant is 6.08 s⁻¹. With the length of alkyl chains of gemini surfactant increasing and the ethanol concentration rising, the redox peaks of the resulting electrode C₁₆-C₄-C₁₆-OMIMPF₆-Hb/GC become bigger. The electrode presents good electrocatalytic response to peroxide hydrogen. The kinetic parameters I_max and k_m for the catalytic reaction are estimated. In addition, UV-vis spectra and reflectance absorption infrared spectra demonstrate that the Hb immobilized in the C₁₆-C₄-C₁₆-OMIMPF₆ film almost retains the structure of native Hb.     

Direct electrochemical behavior of cytochrome c on DNA modified glassy carbon electrode and its application to nitric oxide biosensor

Cytochrome c/DNA modified electrode was achieved by coating calf thymus DNA onto the surface of glassy carbon electrode firstly, then immobilizing cytochrome c on it by multi-cyclic voltammetric method and characterized by the electrochemical impedance. The electrochemical behavior of cytochrome c on DNA modified electrode was explored and showed a quasi-reversible electrochemical redox behavior with a formal potential of 0.045 ± 0.010 V (versus Ag/AgCl) in 0.10 M, pH 5.0, acetate buffer solution. The peak currents were linearly with the scan rate in the range of 20-200 mV/s. Cytochrome c/DNA modified electrode exhibited elegant catalytic activity for the electrochemical reduction of NO. The catalytic current is linear to the nitric oxide concentration in the range of 6.0 × 10⁻⁷ to 8.0 × 10⁻⁶ M and the detection limit was 1.0 × 10⁻⁷ M (three times the ratio of signal to noise, S/N = 3).     

Effect of post annealing treatment on electrochromic properties of spray deposited niobium oxide thin films

Niobium oxide thin films were deposited on the glass and fluorine doped tin oxide (FTO) coated glass substrates using simple and inexpensive spray pyrolysis technique. During deposition of the films various process parameters like nozzle to substrate distance, spray rate, concentration of sprayed solution were optimized to obtain well adherent and transparent films. The films prepared were further annealed and effect of post annealing on the structural, morphological, optical and electrochromic properties was studied. Structural and morphological characterizations of the films were carried out using scanning electron microscopy, atomic force microscopy and X-ray diffraction techniques. Electrochemical properties of the niobium oxide thin films were studied by using cyclic-voltammetry, chronoamperometry and chronocoulometry.     

Effect of cerium oxide nanoparticles coating on the electrodes of benthic microbial fuel cell

Benthic microbial fuel cell is a power source for low-power devices. For enhancement of power, Cerium oxide (CeO₂) nanoparticles (NPs) were coated on anode and cathode electrodes and compared separately. CeO₂ NPs were synthesized by hydrothermal method and characterized by Dynamic light scattering. Polyvinylidene fluoride and graphite powder were used as a conductive matrix for binding CeO₂ NPs. Coated electrodes were characterized by physical and electrochemical analysis. Maximum power densities generated by CeO₂ coated cathode and anode were 60 and 43 mW/m³ respectively; whereas conductive matrix only produced 14 mW/m³. Results demonstrated that CeO₂ at cathode performed better than at anode. NPs show their effectiveness as an oxygen reduction reaction catalyst in the sea water.     

Gas-phase radical generation by Ti oxide clusters supported on silica: application to the direct epoxidation of propylene to propylene oxide using molecular oxygen as an oxidant

A new catalytic system consisting of titanium oxide clusters supported on silica was found for radical production at relatively low temperature (~573 K). The clusters give rise to selective oxidation products, such as propylene oxide, through gas-phase chain reactions.     

Transition from ripples to faceted structures under low-energy argon ion bombardment of silicon: understanding the role of shadowing and sputtering

Abstract

In this study, we have investigated temporal evolution of silicon surface topography under 500-eV argon ion bombardment for two angles of incidence, namely 70° and 72.5°. For both angles, parallel-mode ripples are observed at low fluences (up to 2 × 10¹⁷ ions cm^-2) which undergo a transition to faceted structures at a higher fluence of 5 × 10¹⁷ ions cm^-2. Facet coarsening takes place at further higher fluences. This transition from ripples to faceted structures is attributed to the shadowing effect due to a height difference between peaks and valleys of the ripples. The observed facet coarsening is attributed to a mechanism based on reflection of primary ions from the facets. In addition, the role of sputtering is investigated (for both the angles) by computing the fractional change in sputtering yield and the evolution of surface roughness.

PACS

81.05.Cy, 81.16.Rf, 61.80.Jh, 87.64.Dz     

Force spectrum of a few chains grafted on an AFM tip: Comparison of the experiment to a self-consistent mean field theory simulation

A simulation model based on self-consistent mean field theory (SCMFT) has been developed to inspect the approaching process of the polymer chain grafted AFM tip to a substrate. The effects of various controlling parameters, such as grafting position, chain number, chain length, as well as solvent- and substrate-chain interactions, on the force curve were investigated. Real force spectroscopy of AFM tips modified by poly(ethylene glycol) (PEG) chains interacting with the fresh mica has been recorded, and several typical types of the force curves that correspond to the different states of the grafting chain were assorted. The simulations fit the experimental results well, providing a strong support to the model.     

Effects of linker molecules on the attachment and growth of gold nanoparticles on indium tin oxide surfaces

As a linker molecule to attach gold nanoparticles (AuNPs) on indium tin oxide (ITO) surfaces, cysteamine was examined together with well-known 3-mercaptopropyltrimethoxysilane (MPTMS) and 3-aminopropyltrimethoxysilane (APTMS). Systematic comparisons of AuNPs’ nanostructures formed on ITO were carried out after the room temperature treatment in an ethanol solution of linker molecules followed by the attachment of AuNPs using (i) one-step immersion into the 20-nm Au colloidal solution or (ii) two-step immersion, i.e., a seed-mediated growth treatment. Consequently, in case (i), it was found that APTMS was most effective for denser and homogeneous attachment of AuNPs on ITO surfaces with keeping the dispersion. With the MPTMS or cysteamine linkers in case (i), AuNPs aggregated on the ITO surfaces, and the attached amount of AuNPs were larger with the MPTMS linker. In contrast, in case (ii), nanostructural growth of AuNPs was possible with MPTMS or cysteamine using the seed-mediated growth, while the growth of AuNPs was significantly suppressed with the APTMS linker. Because quite different results were obtained between APTMS and cysteamine, it was found that the attachment and nanostructural growth of AuNPs on the organic linker layers cannot be simply governed by the functional groups, -NH₂, on the outer surfaces.