Atomic Force Micrographs Research Articles

Lead-free ferroelectric thin films obtained by pulsed laser deposition

Na0.5Bi0.5TiO3-BaTiO3 (NBT-BT) thin films grown by pulsed laser deposition have been investigated by X-ray diffraction, scanning electron microscopy, and dielectric spectroscopy in order to clarify the role of substrate temperature on crystalline structure, grain morphology, and dielectric properties. We have shown that the structural and dielectric properties of NBT-BT thin films with composition at morphotropic phase boundary (6% BT) critically depend on the substrate temperature: small variations of this parameter induce structural changes, shifting the morphotropic phase boundary toward tetragonal or rhombohedral side. Higher deposition temperature (1000 K) favor the formation of rhombohedral phase, films deposited at 923 K and 973 K have tetragonal symmetry at room temperature. Grains morphology depends also on the deposition temperature. Atomic force micrographs show grains with square or rectangular shape in a compact structure for films grown at lower temperatures, while grains with triangular shape in a porous structure are observed for films grown at 1000 K. Dielectric spectroscopy measurements evidenced the phase transition between ferroelectric and antiferroelectric phase at 370 K. Films grown at 1000 K shown low electrical resistivity due to their porous structure. High dielectric constant values (about 800 at room temperature and 2700 at 570 K) have been obtained for films grown at temperatures up to 973 K.

Planarization of Polymeric Field‐Effect Transistors: Improvement of Nanomorphology and Enhancement of Electrical Performance

AbstractThe planarization of bottom‐contact organic field‐effect transistors (OFETs) resulting in dramatic improvement in the nanomorphology and an associated enhancement in charge injection and transport is reported. Planar OFETs based on regioregular poly(3‐hexylthiophene) (rr‐P3HT) are fabricated wherein the Au bottom‐contacts are recessed completely in the gate‐dielectric. Normal OFETs having a conventional bottom‐contact configuration with 50‐nm‐high contacts are used for comparison purpose. A modified solvent‐assisted drop‐casting process is utilized to form extremely thin rr‐P3HT films. This process is critical for direct visualization of the effect of planarization on the polymer morphology. Atomic force micrographs (AFM) show that in a normal OFET the step between the surface of the contacts and the gate dielectric disrupts the self‐assembly of the rr‐P3HT film, resulting in poor morphology at the contact edges. The planarization of contacts results in notable improvement of the nanomorphology of rr‐P3HT, resulting in lower resistance to charge injection. However, an improvement in field‐effect mobility is observed only at short channel lengths. AFM shows the presence of well‐ordered nanofibrils extending over short channel lengths. At longer channel lengths the presence of grain boundaries significantly minimizes the effect of improvement in contact geometry as the charge transport becomes channel‐limited.

Structural Evolution Mechanism of Early-Stage Nanocrystallization of Finemet Amorphous Ribbons

The Finemet alloy is used to make transformers for its excellent soft magnetic property. In order to study its distinctive character, it is essential to clarify the structural evolution mechanism especially in early nanocrystallization. The Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">73.5</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13.5</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> amorphous ribbons were prepared by single-roller melt-spinning process under argon atmosphere, and then annealed at 350°C, 380°C and 400°C for 10 mins respectively. We conduct the X-ray photoelectron spectrum (XPS) and the atom force microscope (AFM) to investigate the structural evolution mechanism in early nanocrystallization of Finemet. The X-ray photoelectron spectrum present the Cu atoms enrich in the surface and the Nb atoms redistribute to the iron-rich layer following with the increasing annealing temperature. The atomic force micrographs for the annealed specimens present a significant increase in the amount of the clusters and a dramatic drop in their average size. The structure evolution as observed is subjected to the atomic redistribution, which is crucial to the formation of the Cu-enriched clusters. In this paper, we discuss the behavior of different elements and elaborate the transformation of microstructure during the process of atomic migration.

Defect engineering and opto electronic property modifications by 1.5 MeV Li+ implantation on nano crystalline MgIn2O4 thin films

Spinel MgIn2O4 thin films were deposited on quartz substrates by the chemical spray pyrolysis technique using metal organic precursors at 450°C. Energetic 1.5 MeV Li+ ions were implanted to various fluences of 1013, 1014 and 1015 ions/cm2 onto insulating MgIn2O4 films using a 9 SDH-2, NEC, 3MV accelerator to modify the material properties and surface nature. X-ray diffraction analysis was carried out to identify the changes in the crystallinity and grain orientations before and after implantations. Before implantation, the grains of polycrystalline MgIn2O4 were randomly oriented [(222), (311), (442) and (511)], and after implantation they exhibited a tendency to realign the crystallites along the even (hkl) planes [(222) and (442)]. On the Li+-implanted sample, one or more grains combine together and form bigger grains along with shallow pits, as observed through the atomic force micrographs. The as-deposited films have a percentage transmittance of 70–80% in the wavelength range 400–800 nm and the observed optical transmittance was less in Li+-implanted MgIn2O4 films. The index of refraction and the extinction co-efficient values were respectively n=1.98 and k=10−2 in the visible region. However, the DC electrical conductivity of Li+-implanted films to a fluence of 1015 ions/cm2 was nearly 0.7 S/cm at room temperature. The efficiency of the carrier generation was increased from 13.41% to 26.81% on annealing the implanted sample to lower fluence (1013 ions/cm2).

In vitro formation and thermal transition of novel hybrid fibrils from type I fish scale collagen and type I porcine collagen

Novel type I collagen hybrid fibrils were fabricated by neutralizing a mixture of type I fish scale collagen solution and type I porcine collagen solution with a phosphate buffer saline at 28 °C. Their structure was discussed in terms of the volume ratio of fish/porcine collagen solution. Scanning electron and atomic force micrographs showed that the diameter of collagen fibrils derived from the collagen mixture was larger than those derived from each collagen, and all resultant fibrils exhibited a typical D-periodic unit of ∼67 nm, irrespective of volume ratio of both collagens. Differential scanning calorimetry revealed only one endothermic peak for the fibrils derived from collagen mixture or from each collagen solution, indicating that the resultant collagen fibrils were hybrids of type I fish scale collagen and type I porcine collagen.

Scaling law analysis of paraffin thin films on different surfaces

The dynamics of paraffin deposit formation on different surfaces was analyzed based on scaling laws. Carbon-based films were deposited onto silicon (Si) and stainless steel substrates from methane (CH4) gas using radio frequency plasma enhanced chemical vapor deposition. The different substrates were characterized with respect to their surface energy by contact angle measurements, surface roughness, and morphology. Paraffin thin films were obtained by the casting technique and were subsequently characterized by an atomic force microscope in noncontact mode. The results indicate that the morphology of paraffin deposits is strongly influenced by substrates used. Scaling laws analysis for coated substrates present two distinct dynamics: a local roughness exponent (αlocal) associated to short-range surface correlations and a global roughness exponent (αglobal) associated to long-range surface correlations. The local dynamics is described by the Wolf–Villain model, and a global dynamics is described by the Kardar–Parisi–Zhang model. A local correlation length (Llocal) defines the transition between the local and global dynamics with Llocal approximately 700nm in accordance with the spacing of planes measured from atomic force micrographs. For uncoated substrates, the growth dynamics is related to Edwards–Wilkinson model.

Adhesive Properties and Hydrolytic Enzymes of Oral Candida albicans Strains

Several virulence factors in Candida albicans strains such as production of hydrolytic enzymes and biofilm formation on surfaces and cells can contribute to their pathogenicity. For this, control of this opportunistic yeast is one of the factors reducing the nosocomial infection. The aim of this study was to investigate biofilm formation on polystyrene and polymethylmethacrylate and the production of hydrolytic enzymes in Candida albicans strains isolated from the oral cavity of patients suffering from denture stomatitis. All strains were identified by macroscopic, microscopic analysis and the ID 32 C system. Our results showed that 50% of the total strains produced phospholipase. Furthermore, protease activity was detected in seven (35%) strains. All Candida albicans strains were beta haemolytic. All C. albicans strains adhered to polystyrene 96-well microtiter plate at different degrees, and the metabolic activity of C. albicans biofilm formed on polymethylmethacrylate did not differ between tested strains. The atomic force micrographs demonstrated that biofilm of Candida albicans strains was organized in small colonies with budding cells.

XRD and XPS characterization of mixed valence Mn 3O 4 hausmannite thin films prepared by chemical spray pyrolysis technique

Spray pyrolysis technique has been employed successfully for the synthesis of single phase mixed valence spinel hausmannite (Mn 3O 4) thin films using alcoholic start solution of manganese acetate (Mn(CH 3COO) 2·4H 2O) on pyrex glass substrates at atmospheric pressure using air as a carrier gas. Thermal decomposition of the precursor in the temperature range 320–490 °C led to the formation of Mn 3O 4 phase as revealed from the thermogravimetry analysis. Prepared samples are characterized by X-ray diffraction that shows spinel structure with space group I4 1/ amd. Pure and well crystallized specimen is subjected to X-ray photoelectron spectroscopy for the surface chemistry investigation of these systems at a molecular level. Surface Mn/O ratio is compared to the bulk composition of the sample. Atomic force micrographs revealed that the morphology and the surface grains of the films largely influenced by the substrate temperature.

Fabrication of single-walled carbon nanotubes dotted with Au nanocrystals: Potential DNA delivery nanocarriers

Single-walled carbon nanotubes (SWCNTs) dotted with Au nanocrystals (Au-SWCNTs) were fabricated by using a two-phase reduction of hydrogen tetrachloroaurate in the presence of thiol groups anchored to SWCNTs for their potential applications in DNA (deoxyribonucleic acid) delivery. To allow a surface reaction on SWCNTs during the metal nucleation and growth processes, Au nanocrystals were grown using a two-phase system. Raman, XPS and transmission electron microscopy results show that the Au nanocrystals were grafted primarily to the sidewalls of the SWCNTs. DNA probes were immobilized on Au-SWCNTs by the conjugation of DNA functionalized at the 3′ end with a thiol group with Au dots of SWCNTs, followed by hybridizion of complementary oligonucleotides, as verified by fluorescence-based measurements. To investigate whether the target DNA hybridized to DNA probes immobilized on Au-SWCNTs, 618-base-pair fragments of amplified DNA were prepared by polymerase chain reaction using plasmid pET-22b as a template. Atomic force micrograph (AFM) images show that the nanorod-bound DNA is recognizable with excellent specificity, indicating the potential use of such material as a versatile gene delivery carrier in gene-based disease therapy.

Determination of the diffusion of poly(ethylene glycol) in polypropylene using ATR-FTIR

The diffusion of poly(ethylene glycol) (PEG) in polypropylene (PP) was investigated using attenuated total reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), Atomic Force Micrograph (AFM), and Scanning Electron Microscopy (SEM). It has been found that the diffusion of PEG in PP was greatly affected by the annealing temperature and the molecular weight of PEG. Higher temperature was in favor of PEG to diffuse in PP with fast velocity and reached diffusion equilibrium with shorter time. PEG with higher molecular weight was distributed in PP with bigger phase domains and had lower diffusivity, which resulted in its lesser enrichment on the surface of the PP blend film.

Structural and electrical properties of metal contacts on n-type ZnO thin film deposited by vacuum coating technique

The authors report on fabrication and characterization of Al and Pt metal contacts on ZnO thin films grown on ITO coated glass substrates using thermal evaporation technique. The structural and surface properties of ZnO thin film were studied by using x-ray diffraction and atomic force microscopy techniques. Atomic force micrographs revealed that ZnO microparticles have perfect pyramidal shape with small surface roughness (average rms value of 3nm). The current voltage characteristics of Pt∕ZnO and Al∕ZnO contacts were studied by scanning tunneling microscopy. The Pt contact on ZnO thin films behaves as a rectifying contact with a barrier height of 0.72eV, while Al contact on ZnO thin film turns out to be Ohmic in nature. The band gap of ZnO thin film was estimated to be 3.10eV from absorption spectroscopic measurements.

A novel procedure for preparation of submicron liposomes-lyophilization of oil-in-water emulsions

A novel liposome preparation method is described involving the freeze-drying of oil-in-water emulsions containing sucrose in the aqueous phase as a lyoprotectant and phospholipids in the oil as emulsifiers. The oil-in-water emulsions can be prepared by emulsification and then lyophilized to obtain dry products that will, upon rehydration, form unilamellar liposomes with a mean size of less than 200 nm, as proved by dynamic light scattering, atomic force micrographs, freeze-fracture electron micrographs, and small-angle X-ray scattering (SAXS). With or without combination with active loading, this method can be used successfully to encapsulate amphiphilic or lipophilic drugs into liposomes, although it cannot be applied to hydrophilic drugs. The lyophilized products are stable and can be rehydrated to form liposomes, even after a storage period of 10 months. Based on the encapsulation efficiency for hydrophilic drugs, as well as the scanning electron micrograph and SAXS of the freeze-dried products, a unique liposome formation mechanism is proposed.

Blueshift in optical band gap in nanocrystalline Zn1−xCaxO films deposited by sol-gel method

A blueshift in the optical band gap of nanocrystalline Zn1−xCaxO thin films has been obtained. A 12.72% enhancement in the band gap of ZnO thin films has been obtained using Ca dopant for the first time. The band gap widens from 3.38 to 3.81 eV as the Ca concentration increases from x=0 to x=0.15. The films are deposited by sol-gel method and have a hexagonal wurtzite phase with no indication of calcium. Grain size lies in the range of 12–92 nm. Atomic force micrographs indicate much smaller rms surface roughness showing significantly smooth surfaces.

On the complex behavior of strain relaxation in (In,Ga)As/GaAs(001) quantum dot molecules

A detailed growth scenario of surface quantum dot molecules (QDM) in the system (In,Ga)As/GaAs(001) has been investigated in terms of shape and elastic strain evolution. QDMs are grown by a combined approach using droplet epitaxy for initial homoepitaxial GaAs mounds, which subsequently serve as nucleation spots for surrounding (In,Ga)As surface quantum dots. Atomic force micrographs trace a detailed pathway toward the final QDM containing up to six quantum dots with perfect inherent symmetry. Synchrotron-based grazing incidence diffraction together with grazing incidence small angle x-ray scattering reveal a relaxation behavior, which for all growth stages comprises a strained lattice along [1¯10] and partial elastic relaxation along [110]. Numerical finite element calculations on the three-dimensional strain profile support the experimental findings.

Lateral variations in self-assembled InGaAs quantum dot distributions

The lateral uniformity of self-assembled InGaAs quantum dots grown by molecular beam epitaxy (MBE) was assessed as a function of growth conditions. Variations in the dot density and height were determined from atomic force micrographs. Growth rate had a large influence on lateral uniformity. The most uniform dot distributions were grown at low rates, 0.15 monolayers/s (ML/s). Dots deposited at a rate of 1.15 ML/s had large variations in both height and density. These variations decreased as the dot density increased; however, they remained larger than those of dots deposited slowly. The lateral uniformity of dots deposited quickly also improved for the top layer of dots in stacked layers, even though these layers had decreased dot densities. There were negligible differences in the lateral height and density uniformities of dots as functions of continuous versus pulsed growth, wafer diameter and mole fraction of In.

“Mechanically Docked” Metallodendrimers about Single-Walled Carbon Nanotubes

We report experimental support for “mechanical docking” of an optically active rigid molecule, ruthenium metallodendrimer (decamer), to single-walled carbon nanotubes (SWNTs) with some diameter selectivity. Binding of these rigid metallodendrimers onto dispersed single-walled carbon nanotubes has been studied by Raman and UV−vis−near-infrared (NIR) absorption spectroscopy. Atomic force and scanning electron micrographs indicate strong binding of these molecules specifically to the ends of nanotubes and are consistent with the spectroscopic evidence for diameter selectivity presented here. Near-IR absorption and radial breathing mode Raman spectra of these “end-functionalized” SWNTs show preferential diameter-selective separation, along with a red shift of the optical transitions. A concentration-dependent red shift is observed for the NIR absorption for decamer-bound nanotubes. This indicates a strong interaction between selective SWNTs and the decamer, forming a mechanically docked supramolecular complex. Spectral shifts and intensity variations in specific radial breathing mode bands of the functionalized SWNTs are complementary to our observations of the UV−vis−NIR absorption spectra and atomic force microscopy data.

Gold Nanoparticles: Microbial Synthesis and Application in Water Hygiene Management

A green chemical method to synthesize nanogold-bioconjugate and its eco-friendly promising role to purify contaminated waters has been described. Gold nanoparticles of 10 nm average diameter are produced on the surface of Rhizopus oryzae , a fungal strain, by in situ reduction of chloroauric acid (HAuCl(4)). The nanogold-bioconjugate (NGBC) showed strong adsorption capacity toward different organophosphorous pesticides. The EDXA study confirms adsorption of pesticides on the conjugate material surface. Morphological changes of the NGBC material after adsorption of organophosphorous pesticides were detected by atomic force micrographs. NGBC shows high antimicrobial activity against several Gram-negative and Gram-positive pathogenic bacteria as well as the yeasts Saccharomyces cerevisiae and Candida albicans . The treatment of microbial cells with NGBC caused rupture of cell membrane as revealed in scanning electron and fluorescence micrographs. These unique characteristics of NGBC have been successfully utilized to obtain potable water free from pathogens and pesticides in a single operation.

Key role of molecular kinetic energy in early stages of pentacene island growth

Organic molecular beam deposition is studied systematically at thermal and hyperthermal regimes aiming at investigating the role of molecular kinetic energy on the growth mechanism of pentacene submonolayers on SiOx/Si. We show that the kinetic energy of the impinging molecule (Ek) plays a crucial role in determining island structure and shape, distribution of island sizes, the crystalline quality of the first monolayer, and even the growth mode of subsequent layers. With increasing Ek, the island structure changes from fractal to nonfractal, the shape becomes more anisotropic and the island size more uniform, pointing to correlated island growth. Moreover, while 3D island growth is observed for thermal organic molecular beam deposition, supersonic molecular beam deposition gives rise to layer-by-layer growth, at least for the first two layers. When Ek≥5.0 eV, the first monolayer is composed of large single crystalline domains which can extend over up to 10 μm, inferred from comparing atomic force micrographs of height and net transverse shear force. In these growth conditions both the high surface diffusivity and energy redistribution play a major role. We propose a mechanism where the energy dissipation occurring during the molecule–surface collision leads to the reorientation of whole islands during island coalescence, resulting in the elimination of grain boundaries.

Corrosion Inhibition by Sodium Gluconate‐Zn2+‐DTPMP System

The inhibition efficiency of a phosphonic acid, Diethylene Triamine Pentamethylene Phosphonic acid (DTPMP) in controlling corrosion of carbon steel immersed in an aqueous solution containing 60 ppm of Cl- has been evaluated by weight loss method in the absence and presence of Zn2+. The formulation consisting of DTPMP and Zn2+ has excellent inhibition efficiency (IE). A synergistic effect is noticed between Zn2+ and DTPMP. Addition of sodium gluconate (SG) enhances the IE of Zn2+ and DTPMP system. The DTPMP‐Zn2+‐SG system function as a mixed inhibitor as revealed by polarization study. AC impedance spectrum, optical and atomic force micrographs reveal the formation of a protective film on the metal surface. FTIR spectra reveal that the protective film consists of Fe2+‐DTPMP complex, Fe2+‐SG complex and Zn(OH)2.

Computational and experimental studies of phase separation in pentacene:C60 mixtures

Phase separation in molecular donor-acceptor mixtures composed of pentacene and C60 is examined using a combination of computational and experimental methods. Classical molecular dynamics simulations of the relaxation process of pentacene:C60 mixtures predict the formation of pentacene stacks and C60 clusters in the equilibrated structures. These findings are consistent with experimental observations, where x-ray diffraction and atomic force microscopy characterization of the mixed films confirm the existence of polycrystalline pentacene domains. The scanning electron and atomic force micrographs of mixed films deposited at different rates as well as with various mixing ratios show that the aggregation of pentacene, and therefore the degree of phase separation in the mixtures, can be manipulated by the processing conditions. Finally, bulk heterojunction photovoltaic devices using different pentacene:C60 mixtures as an active layer are fabricated and their photovoltaic performance characteristics are compared. It is found that the device with 1:5.5 (by weight) mixing ratio of pentacene:C60 shows nearly 400 times higher power conversion efficiency than the 1:1 device due to successful control of nanoscale phase separation that leads to better exciton diffusion and charge collection.