Atomic Force Micrographs Research Articles

Influence of Cu doping on structural, optical and photocatalytic activity of SnO2 nanostructure thin films

In the present work, magnesium (Mg) doped SnO2 nanocrystalline thin films were synthesized by simple chemical bath deposition technique. The as-deposited films were annealed at 600 °C for 5 h in ambient atmosphere in order to improve crystallinity and structural perfection. The influence of Mg doping on structural, optical, and morphology of thin films was studied by X-ray diffraction (XRD), Raman spectra, UV–Vis Spectra, photoluminescence, and atomic force micrograph images. The XRD measurements showed that films had a tetragonal rutile type structure with P42/mnm symmetry and the results were good in agreement with the standard JCPDS data (card no: 41-1445). The surface roughness has been found to decrease with the increase of the dopant concentration as investigated by atomic force microscopy. The optical band gap energy of pure SnO2 has been found to be in the range of 3.63 eV and it is shifted to 3.42 eV for 10 wt% Mg doping. In the Raman spectrum, two active mode (A2u and Eu) were observed for Mg–SnO2 thin films. The photocatalytic activities of the films were evaluated by degradation of methylene blue rhodamine B in an aqueous solution under ultraviolet light irradiation. The photocatalytic activity of Mg (10 wt%) doped SnO2 film was much higher than that of the pure SnO2. The samples were further characterized by photoluminescence spectra analysis.

Development of graphene–nanometre-sized cerium oxide-incorporated aluminium and its electrochemical evaluation

Graphene–nanometre-sized cerium oxide-incorporated aluminium was prepared and its electrochemical and surface morphological characteristics were studied. The atomic force micrographs and scanning electron micrographs evaluation highlighted that the graphene and nanometre-sized cerium oxide in aluminium had decreased the surface roughness and improved the surface morphological characteristics. The graphene: nanometre-sized cerium oxide (ratios 1:2 or 2:1) with lesser amounts of particle in the matrix showed excellent corrosion resistance in the marine environment as evidenced by linear polarization, electrochemical impedance and weight loss studies. Introduction of graphene in the aluminium matrix showed a barrier separation between the outermost layer and inner layer, increased roughness and increased corrosion. The material is found to be a potential candidate for use in marine environment.

A simple route to synthesis of carbon doped TiO2 nanostructured thin film for enhanced visible-light photocatalytic activity

We herein report the pure and carbon doped TiO2 nanocrystalline thin films synthesized by simple chemical bath deposition technique . The as-deposited films were annealed at 600 °C for 5 h in ambient atmosphere in order to improve crystallinity and structural perfection. The influence of carbon doping on structural, optical, and morphology of thin films was studied by X-ray diffraction (XRD), Fourier Infrared spectra, UV–Vis Spectra, photoluminescence, and atomic force micrograph images. XRD results showed that both pristine and carbon doped films formed mixture of anatase (A) and rutile (R) type phase. The surface roughness has been found to decrease with the increase of the dopant concentration as investigated by atomic force microscopy. The UV–Vis spectra confirmed that incorporation of carbon in the TiO2 lattice introduced intermediate bands into its narrowed forbidden gap, leading to remarkable red-shifts in the optical absorption edges, together with significantly improved photocatalytic activity of the TiO2 thin films. The photocatalytic activities of the TiO2 films were evaluated by degradation of methylene blue rhodamine B in an aqueous solution under ultraviolet light irradiation. Carbon doped TiO2 film exhibited excellent photocatalytic activities, when compared with undoped TiO2 film. The improvement mechanism by carbon doping was also discussed.

Preparation and characterization of nanocellulose from beer industrial residues using acid hydrolysis/ultrasound

The aim of this work was to prepare nanocellulose (NC) from beer industrial residuals (BIR) by an acid hydrolysis/ultrasound method using three hydrolysis times (2, 4, and 6 hours). The atomic-force micrographs showed that the obtained NCs had whisker, oval, and spherical shapes. The average diameters of the NCs ranged between 73 and 146 nm. The chemical characterization of BIR and purified cellulose confirmed that α-cellulose content increased from 44 % to 92 % and lignin contents decreased from 32 % to 5 %. FT-IR analysis showed a substantial change in chemical structure of NCs (especially over the 2-hour hydrolysis time) compared to that of purified BIR fibers. XRD results revealed that the NCs’ crystallinity and crystallite size were positively affected by acid-hydrolysis time. TGA results showed that the thermal stability of NCs increased as a result of hydrolysis. BIR, a low-value residue, was turned to nanocellulose, a high-performance nanomaterial.

Investigations of ripple pattern formation on Germanium surfaces using 100-keV Ar(+) ions.

We have investigated the formation of nanoripples on the surface of germanium, Ge(100), due to the effect of 100-keV Ar+ ion irradiation. The irradiation was carried out at different incidence angles from 0° to 75° in steps of 15° with respect to the surface normal with a fixed ion fluence of approximately 3 × 1017 ions/cm2. Atomic force micrographs show an increase in surface roughness from 0.5 to 4.3 nm for the pristine sample and the sample irradiated at 60° incidence angle due to cos−1(θ) dependence on sputtering yield. With increase in angle of incidence, there is transition observed from nanodots to aligned nanodots perpendicular to the direction of the beam. There is an increase in size of the nanostructures observed from 44 to 103 nm with angle of incidence. The formation of nanoripples initiates at an angle of θ ~ 45°. Ripple pattern formation has taken place on the Ge surface in the energy regime of 100 keV as compared to the other reports which had been carried out using very low energy ions. Raman spectra reveal that the near surface of crystalline Ge samples becomes amorphous due to interaction of Ar+ ions due to creation of defects through collision cascades.

A Study of the Electrochemical Properties of a New Graphitic Material: GUITAR

AbstractPrevious studies of graphite from the University of Idaho thermolyzed asphalt reaction (GUITAR) indicated two unique properties that distinguish this material from other sp2 hybridized carbon electrodes. In property i, the standard heterogeneous rate constant across the basal plane (BP) of GUITAR with Fe(CN)63−/4− of 0.01 cm s−1 was 2–7 orders of magnitude greater than for BP‐graphite and graphene. With property ii, the anodic potential limit exceeds other graphite forms by 500 mV. Two new properties are now described. In iii, the hydrogen overpotential in 1 M H2SO4 exceeds other graphitic materials by 500 mV. The combination of ii and iii gives a 3 V window in 1 M H2SO4, which is the largest reported for a graphitic material and competitive with diamond electrodes. In iv, effects of air oxidation on the edge planes (EPs) is reversed by mild cathodic reduction and does not allow for electrolyte intercalation. Based on these characteristics and on atomic force micrographs, we hypothesize that GUITAR may be a new allotrope of carbon. Coupled with expected low costs, GUITAR will find a myriad of applications in electrochemical sensors, water purification, as well as energy storage and conversion.

Determination of Alpha-Fetoprotein by a Microfluidic Miniature Quartz Crystal Microbalance

The determination of serum biomarkers such as alpha-fetoprotein may be employed for early diagnosis of hepatocellular carcinoma. A miniature quartz crystal microbalance integrated with a polydimethylsiloxane microfluidic device was fabricated for on-chip determination of alpha-fetoprotein. Atomic force micrographs showed that anti-alpha fetoprotein was immobilized on the gold surface of the resonator using a cross-linking method. The integrated microfluidic device determined alpha-fetoprotein with a linear range from 0.3 to 3.74 µg/mL. By using phosphate buffer containing 200 µg/mL bovine serum albumin, 0.5 M NaCl, 500 µg/mL dextran, and 0.5% Tween 20, alpha-fetoprotein was determined in the presence of 75% human serum. Additionally, high temperature treatment allowed recovery of the resonator surface allowing limited reuse of the integrated microfluidic device.

Dynamic scaling of swift heavy ion induced surface restructuring of BaF2 thin film

Dynamic scaling of swift heavy ions induced cracks in the nanodimensional BaF2 thin films is studied using 100MeV Au+8 ions at different ion fluences. Atomic force micrographs show that, up to a fluence of 1×1012 ions/cm2, the surface morphology is almost unchanged from virgin film, but thereafter, the formation of cracks is seen. The dimensions and density of the cracks is found to increase with increase in ion fluence. Dynamic scaling of surfaces demonstrates that the surface roughness exponent (α) values are in the range of 0.2–0.5. The growth exponent values are found to be β=0.10±0.03 and 1.1±0.1 for continuous and cracked surfaces, respectively. Shift of X-ray diffraction peaks after irradiation indicates contribution of tensile stress in the crack evolution with ion fluence.

CARBOXYLATION OF SILVER NANOPARTICLES FOR THE IMMOBILIZATION OF β-GALACTOSIDASE AND ITS EFFICACY IN GALACTO-OLIGOSACCHARIDES PRODUCTION

The present study investigated the carboxylation of silver nanoparticles (AgNPs) by 1:3 nitric acid-sulfuric acid mixtures for immobilizing Aspergillus oryzae β-galactosidase. Carboxylated AgNPs retained 93% enzyme upon immobilization and the enzyme did not leach out appreciably from the modified nanosupport in the presence of 100 mmol L-1 NaCl. Atomic force micrograph revealed the binding of β-galactosidase on the modified AgNPs. The optimal pH for soluble and carboxylated AgNPs adsorbed β-galactosidase (IβG) was observed at pH 4.5 while the optimal operating temperature was broadened from 50 oC to 60 oC for IβG. Michaelis constant, Km was increased two and a half fold for IβG while Vmax decreases slightly as compared to soluble enzyme. β-galactosidase immobilized on surface functionalized AgNPs retained 70% biocatalytic activity even at 4% galactose concentration as compared to enzyme in solution. Our study showed that IβG produces greater amount of galacto-oligosaccharides at higher temperatures (50 oC and 60 oC) from 0.1 mol L-1 lactose solution at pH 4.5 as compared to previous reports.

Preparation and Characteristics of the Ag/SiO<sub>2</sub> Nanocomposite Prepared by Magnetron Sputtering and ICP Plasma

Ag/SiOXnanocomposites were successfully fabricated by inductively coupled plasma (ICP) enhanced magnetron sputtering plasma where the hexamethyldisiloxane (HMDSO) was as the monomer for SiOx deposition and Ag nanoparticles were sputtered by Ar ions from Ag target. The main motivation of this work is to clarify the feasibility of Ag/SiOXnanocomposite fabrication in a simultaneous process with plasma technology. Besides the influence of processing parameters on the microstructures and properties of the nanocomposite, such as ICP power, the deposition time and ratio of HMDSO and Argon, is investigated in this paper. With Fourier transform infrared spectroscopy (FTIR), ultraviolet visible spectroscopy (UV-Visible), and atomic force micrograph (AFM) the microstructures of the Ag/SiOXnanocomposite were characterized. It is founded that the microstructures and properties of nanocomposite depend on the discharge parameters. As an application the antibacterial behavior was tested. It indicates that the Ag/SiOx nanocomposites demonstrate an excellent antibiotic effect to colon bacillus and golden brown staphylococcus. It concludes that the Ag/SiOXnanocomposite can be facilely prepared by this processing.

Cobalt sulfide thin films: Chemical growth, reaction kinetics and microstructural analysis

CoS thin films were successfully deposited from an aqueous alkaline bath containing ammonia and TEA as the complexing agents. Under the pre-optimized conditions (temperature=80±0.5°C, speed of the substrate rotation=65±2rpm and deposition period=90min), ammonia and TEA quantities in the reaction bath were found to play a decisive role in the final product yield. Highly uniform, dark sea-green colored and tightly adherent deposits were obtained at our experimental conditions. As-obtained CoS thin films were polycrystalline in nature with hexagonal class of crystal system as derived from the X-ray diffraction analysis. Complex multifaceted webbed network of as-grown CoS crystals elongated and threaded into each other were observed through a scanning electron microscope. Atomic force micrographs revealed collapsing of the hillocks and filling of the valleys triggering decrease in the RMS roughness for increased TEA and NH3 quantities. Magnetic force microscopy (MFM) was employed to study surface topography in terms of magnetic mapping. MFM images highlighted the existence of the magnetic clusters imitating topography. Broad absorption edge with high absorption coefficient (α≈104cm−1) was observed for as-grown CoS thin films. Determined values of the optical bandgaps revealed influence of complexing environment on the final product.

CeO2 thin film as a low-temperature formaldehyde sensor in mixed vapour environment

Nanostructured cerium oxide thin film was deposited onto the glass substrate under optimized condition using spray-pyrolysis technique. X-ray diffraction result indicates polycrystalline nature of the film with fluorite-type face-centered-cubic structure. The atomic force micrograph indicates the presence of nanocrystallites over the film surface. The vapour sensing characteristics of the annealed film were studied by chemiresistive method for various concentrations of formaldehyde vapour at room temperature (~ 30 °C). For 0.5 ppm of formaldehyde vapour, the film shows a response and recovery time of 36 and 1 s, respectively. The vapour sensing properties of the cerium oxide film in mixed environment were studied and reported.

Studies on Magnetic, Transport and Dielectric Properties of Ni0.65Zn0.35Fe2O4 Thin Films Grown by Pulsed Laser Deposition

The ferrimagnetic material Ni1-xZnxFe2O4 (NZFO) has drawn tremendous attention in recent years due to its potential applications in radio frequency coils, transformer cores, rod antennas, magnetic cores of read write heads for high-speed digital tape or disk recording and microwave devices owing to its remarkable magnetic properties, high resistivity and low eddy current. Other than these the NZFO is also considered as potential candidate for multiferroic composite structures. We have chosen Ni0.65Zn0.35Fe2O4 for the present investigation as this composition exhibits the highest saturation magnetization in the entire Ni–Zn family along with high magnetic curie temperature which is ~ 575 K. NZFO thin films were grown by pulsed laser deposition (PLD) at different substrate temperatures in the range of 500-800oC using a KrF excimer laser (λ=248 nm) on LaNiO3 buffered (001) oriented (LaAlO3)0.3(Sr2AlTaO6)0.7 substrates under oxygen pressure of 150 mTorr. These films were subsequently annealed at their respective growth temperature for 30 min in oxygen ambient at a partial pressure of ~ 300 Torr. The highly c-axis oriented growth containing only (004) diffraction peak of NZFO films along with in-plane epitaxial relationship was confirmed by high resolution X-ray diffraction measurements.From the atomic force micrographs it was observed that all the films were densely packed, smooth, free from microcrack and particulates with uniform grain-size distributions. X-ray Photoelectron Spectroscopy measurements confirmed that in all films the Ni, Zn and Fe elements retain their same oxidation states as in bulk target irrespective of growth temperature. The saturation magnetization (Ms ) of NZFO film was found to enhance systematically with increasing growth temperature. The resistance of NZFO films was found to decrease with increasing temperature indicating insulating behaviour. These films showed positive magneto resistance at low magnetic fields. Detailed dielectric, magnetic, magneto resistance and transport characterizations are currently underway and results will be discussed at the meeting.

Nanoindentation and ellipsometry of Li2ZnTi3O8& Zn2TiO4single crystals

Spinel-type Li2ZnTi3O8and Zn2TiO4are useful for various industrial applications due to their interesting chemical and physical properties, for example, as promising anode materials in Li-ion batteries or as components in dielectric devices [1]. Since Li2ZnTi3O8and Zn2TiO4are expected to have high refractive indices (n calc. = 2,33 and 2,26) we tried to characterize these materials in more detail including single-crystal X-ray diffraction, nanoindentation, spectroscopic ellipsometry and electron microprobe analysis. Single crystals of Li2ZnTi3O8and Zn2TiO4were grown directly from melt at 1723 K and 1873 K, respectively. Fragments of sintered polycrystalline Li2ZnTi3O8and Zn2TiO4precursors were placed on an iridium sheet and fired in a muffle furnace from 1273 to 1723/1873 K with a heating ramp of 15 K/min. After a dwell time of 3 min the melt was cooled down to 1473 K with a ramp of 10 K/min and subsequently quenched in water. Structural investigations of the Li2ZnTi3O8and Zn2TiO4single crystals resulted in the following basic crystallographic data: cubic, P4332, a = 8.3697(2) Å, V = 586.31(3) Å3, Z = 4 and Fd-3m, a = 8.46230(17) Å, V = 605.99(2) Å3, Z = 8, respectively. Nanoindentation experiments were performed with a Berkovich diamond indenter tip to determine the hardness and elastic modulus of Zn2TiO4and Li2ZnTi3O8. For sample preparation the single crystals were embedded in resin and polished to a mirror-like surface finish. More than 150 indents with a distance of 10 µm were made with a maximum load of 20 mN. Analysis of the load-displacement curves for Zn2TiO4revealed a hardness of 10.5110.39 GPa and a reduced elastic modulus of 180.9013.92 GPa. Atomic force micrographs displayed indents with a max. depth of 28815 nm. Li2ZnTi3O8exhibited a hardness of 6.8610.45 GPa and a reduced elastic modulus of 148.8816 GPa. Zn2TiO4showed a dispersion of 0.09 due to the variation of the refractive index from 2.24 (430,8 nm, Fraunhofer G line) and 2.15 (686,7 nm, B line).

Sucrose ester-based biocompatible microemulsions as vehicles for aceclofenac as a model drug: formulation approach using D-optimal mixture design

We assessed the functionality of sucrose esters (sucrose laurate, myristate, palmitate, and stearate), relatively innocuous nonionic surfactants, in formulation of biocompatible microemulsions. The putative influence of surfactant structure on the extension of microemulsion region was explored through the construction of the pseudo-ternary phase diagrams for the isopropyl myristate/sucrose ester-isopropyl alcohol/water system, using the titration method and mixture experimental approach. Minor changes in surfactant tail length strongly affected the microemulsion area boundaries. D-optimal mixture design proved to be highly applicable in detecting the microemulsion regions. Examination of conductivity, rheology, and thermal behavior of the selected sucrose laurate and sucrose myristate-based microemulsions, upon dilution with water, indicated existence of percolation threshold and suggested the phase inversion from water-in-oil to oil-in-water via a bicontinuous structure. Atomic force micrographs confirmed the suggested type of microemulsions and were valuable in further exploring their inner structure. The solubilization capacity of aceclofenac as a model drug has decreased as the water volume fraction in microemulsion increased. High surfactant concentration and the measured solubility of aceclofenac in microemulsion components suggested that the interfacial film may mostly contribute to aceclofenac solubilization.

Adhesive properties and extracellular enzymatic activity of Staphylococcus aureus strains isolated from oral cavity

Staphylococcus aureus is one of prominent bacterial pathogen that occurs in oral region. In this study, 21 strains of S. aureus isolated from the oral cavity of Tunisian patients were investigated for slime production using Congo red agar method (CRA) and adherence assay. Biofilm formation of oral isolates on orthodontic biomaterials (Bis-GMA and PMMA) was also evaluated by MTT reduction assay. In addition, the production of hydrolytic enzymes by S. aureus strains was analyzed and the presence of protease, lipase and β-hemolysin genes (sspA, sspB, geh, hlb) was achieved by polymerase chain reaction (PCR).Qualitative biofilm production tested on CRA revealed that 91% of strains were slime producers. The result of OD570 showed that five strains isolated from the oral cavity were highly biofilm positive. The metabolic activity of S. aureus biofilm formed on Bis-GMA and PMMA did not differ between tested strains. The atomic force micrographs demonstrated that biofilm formed by S. aureus strains was organized in typical cocci cells attached to each other through production of exopolymeric substances. The production of hydrolytic enzymes showed that all S. aureus strains were protease positive. Lipase (77%) and beta hemolytic (59%) activities were also detected. Among the tested strains, 17 were positive for sspA, sspB and hlb genes. While only ten S. aureus strains harbor the geh gene (48%).These data highlight the importance of evaluation of biofilm formation and exoenzyme production in oral S. aureus isolates to investigate the role of this pathogen and its impact in oral pathology.

Self-assembled nanofilm of 1,2-dihydro-3-(octadecylthio)benzotriazine on copper for corrosion protection

The self-assembled nanofilm of 1,2-dihydro-3-(octadecylthio)benzotriazine (DOTBT) was formed on fresh copper surface obtained by etching with 7 N nitric acid at a room temperature of 30 °C. The conditions for formation of the DOTBT nanofilm have been optimized by electrochemical impedance and electrochemical quartz crystal nanobalance (EQCN) studies. The DOTBT nanofilm on copper surface was characterized by contact-angle measurement, X-ray photoelectron spectra (XPS), reflection absorption FTIR spectra and atomic force micrographs (AFM). It is inferred that formation of DOTBT film is due to chemisorption of DOTBT on copper surface through nitrogen and subsequent complex formation between DOTBT and Cu + ions. Corrosion protection ability of DOTBT nanofilm was evaluated in dilute aqueous NaCl solution using electrochemical impedance, potentiodynamic polarization, weight-loss and XPS studies. These studies inferred that the DOTBT film protects effectively copper from corrosion. Potentiodynamic polarization studies revealed that the DOTBT film inhibits corrosion by controlling the cathodic reaction. The mechanism of corrosion protection of copper by DOTBT nanofilm is discussed in this paper.

Injection moulding antireflective nanostructures

We present a method for injection moulding antireflective nanostructures on large areas, for high volume production. Nanostructured black silicon masters were fabricated by mask-less reactive ion etching, and electroplated with nickel. The nickel shim was antistiction coated and used in an injection moulding process, to fabricate the antireflective surfaces. The cycle-time was 35s. The injection moulded structures had a height of 125nm, and the visible spectrum reflectance of injection moulded black polypropylene surfaces was reduced from 4.5±0.5% to 2.5±0.5%. The gradient of the refractive index of the nanostructured surfaces was estimated from atomic force micrographs and the theoretical reflectance was calculated using the transfer matrix method and effective medium theory. The measured reflectance shows good agreement with the theory of graded index antireflective nanostructures.

Characterization of Silver Oxide Films Formed by Reactive RF Sputtering at Different Substrate Temperatures

Silver oxide (A2O) films were deposited on glass and silicon substrates held at temperatures in the range 303–473 K by reactive RF magnetron sputtering of silver target. The films formed at room temperature were single phase Ag2O with polycrystalline in nature, while those deposited at 373 K were improved in the crystallinity. The films deposited at 423 K were mixed phase of Ag2O and Ag. Atomic force micrographs of the films formed at room temperature were of spherical shape grains with size of 85 nm, whereas those deposited at 473 K were with enhanced grain size of 215 nm with pyramidal shape. Electrical resistivity of the single phase films formed at room temperature was 5.2 × 10−3 Ωcm and that of mixed phase was 4.2 × 10−4 Ωcm. Optical band gap of single phase films increased from 2.05 to 2.13 eV with the increase of substrate temperature from 303 to 373 K, while in mixed phase films it was 1.92 eV.

Structural, morphological and optical properties of spray deposited Mn-doped CeO2 thin films

Cerium oxide and manganese (Mn) doped cerium oxide thin films on glass substrates were prepared by home built spray pyrolysis system. The effect of Mn doping on the structural, morphological and optical properties of CeO2 films were studied. It was found that both the undoped and doped CeO2 films were polycrystalline in nature but the preferential orientation and grain size changed upon doping. Atomic force micrograph showed a complete changeover of surface morphology from spherical to flake upon doping. A water contact angle result displayed the hydrophobic nature of the doped CeO2 film. Optical properties indicated an increase in band-gap and a decrease in transmittance upon doping owing to Moss–Burstein effect and inverse Moss–Burstein effects. Other optical properties such as refractive index, extinction coefficient and dielectric constant as a function of doping were analysed and reported.