Aid Of Atomic Force Microscopy Research Articles

Synthesis, characterization, and antifungal properties of chrome-doped hydroxyapatite thin films

The development of thin films of chromium-doped hydroxyapatite (20CrHAp) deposited on silicon substrate by the spin coating method was realized for the first time. A coherent investigation of the physicochemical properties of 20CrHAp thin films was also carried out for the first time. The obtained thin films were studied by various techniques such as, scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR) investigations and fractal analysis. By scanning electron microscopy (SEM) studies were obtained valuable information about the surface morphology of the 20CrHAp thin films. The zeta potential (ZP), Dynamic light scattering (DLS) and ultrasound measurements (US) were used in order to evaluate the stability of 20CrHAp suspension. The ratio between the hydrodynamic diameter obtained by DLS and the particle diameter obtained by SEM was 1.6. The SEM results on 20CrHAp thin films suggested that the sample possess a conglomerate of nanoparticles unevenly distributed on their surface. The surface morphology of the 20CrHAp thin films was studied with the aid of atomic force microscopy (AFM). The AFM topography of the 20CrHAp thin film's surface highlighted that the thin films present the morphology of a continuum deposited layer composed of non-uniform particle conglomerates. The presence of hydroxyapatite on the surface of silicium substrate was revealed by the results of Fourier transform infrared spectroscopy (FTIR) investigations. The antifungal evaluation of the 20CrHAp thin films was performed using Candida albicans 10,231 ATCC fungal strain. The antifungal assays results depicted that the 20CrHAp thin films inhibited the fungal biofilm formation. More than that, the results of the antifungal studies revealed that 20CrHAp thin films exhibited good inhibitory effects on the development of the fungal cells on their surface. Furthermore, our investigation delves into the realm of Minkowski Functionals and fractal/multifractal analysis as applied to the examined films. Our findings reveal that nanocomposite coatings containing 20CrHAp exhibit robust antifungal characteristics, suggesting their viability as a compelling solution for advancing antifungal devices in biomedical contexts.

Construction of a novel efficient Z-scheme BiVO4/EAQ heterojunction for the photocatalytic inactivation of antibiotic-resistant pathogens: Performance and mechanism

To improve the bactericidal capability of the BiVO4 photocatalyst, a novel Z-scheme bismuth vanadate/2-ethylanthraquinone (BiVO4/EAQ) photocatalyst was constructed to inactivate antibiotic-resistant pathogens and degrade antibiotic-resistance genes (ARGs) in aqueous environments. The introduction of EAQ into BiVO4 enhanced the photocatalytic performance by promoting charge generation and inhibiting electron-holepair recombination. Based on the results of electron paramagnetic resonance (EPR) and fluorescent probe quantitative analyses, 60 %-BiVO4/EAQ was confirmed to be a Z-scheme heterojunction photocatalyst. The 60 %-BiVO4/EAQ composite exhibited the highest inactivation efficiency toward Shigella flexneri HL, with complete inactivation within 150 min. Scavenger experiments and radical concentration quantification assays indicated that O2− and h+ performed the major roles during photocatalytic inactivation, followed by OH. Moreover, the extracellular tetA resistance gene was almost completely degraded after a 6-hour photocatalysis reaction. The fragmentation pathway of circular DNA under photocatalysis reaction was observed with the aid of atomic force microscopy (AFM), which might also be the mechanism of ARG decomposition. Furthermore, BiVO4/EAQ composite performed good photocatalytic inactivation performance in actual water matrices. This work provides an efficient biohazard inactivation method.

Nanoindentation of single-crystal and polycrystalline yttria-stabilized zirconia: A comparative study by experiments and molecular dynamics simulations

A combination of nanoindentation experiments and molecular dynamics (MD) nanoindentation simulations is carried out in this paper to study the mechanical properties and deformation behaviors of single-crystal and polycrystalline yttria-stabilized zirconia (YSZ). Different Young’s moduli are found in the nanoindentation experiments of single-crystal and polycrystalline YSZ samples, though these two YSZ materials almost have the same hardness. In addition, with the aid of atomic force microscopy, different deformation behaviors are observed in single-crystal and polycrystalline YSZ. The different Young’s moduli and deformation behaviors of single-crystal and polycrystalline YSZ observed in experiments are explained by MD simulations. The simulation results show that during the indentation process, the slip occurs inside single-crystal YSZ but along the grain boundaries of polycrystalline YSZ. These different deformation mechanisms between single-crystal and polycrystalline YSZ account for the lager Young’s modulus and more significant pile-up phenomenon observed in single-crystal YSZ. In addition, our MD simulations also reveal that the mechanical properties of YSZ are almost independent of the temperature but can be significantly affected by the number of YSZ grains. Specifically, both the Young’s modulus and hardness of polycrystalline YSZ are found to decrease as the number of grains grows.

In-Situ Preparation of GaN Sacrificial Layers on Sapphire Substrate in MOVPE Reactor for Self-Separation of the Overgrown GaN Crystal

GaN layers on sapphire substrates were prepared by using metal organic vapor phase epitaxy (MOVPE) combined with an in-situ H2 etching process for the purpose of later self-separation of thick GaN crystals produced by hydride vapor phase epitaxy (HVPE) on such substrates. The etching process results in deep pits and long voids that formed on the surface and along the lower interface between GaN and sapphire, respectively. The pits, which were investigated by SEM analysis, can be modified in their aspect ratio and density by controlling the etching parameters. Using a proper set of in-situ etching parameters, a seed layer with internal voids can be prepared, which is suitable for HVPE overgrowth and the self-separation process. The quality of the in-situ-etched seed GaN layer and overgrown GaN crystal were characterized by X-ray diffraction (XRD) and defect selective etching (DSE). With the aid of atomic force microscopy (AFM) in tapping mode, the interface morphology of the separated GaN crystal was analyzed. The crystal quality of the separated HVPE-GaN crystal is comparable to the crystal grown on untreated GaN MOVPE-seed, which did not separate from the sapphire substrate. The introduced technique to promote the crystal separation during the HVPE process has no obvious drawback on the quality of the grown GaN crystals. Using this technique, the self-separation occurs more gently due to a weakened interface between GaN/sapphire. The conventional separation from an untreated seed by pure thermomechanical action results in higher mechanical forces on the crystal and consequently much higher risk of crystal breakage.

Water and gas barrier properties of polyvinyl alcohol (PVA)/starch (ST)/ glycerol (GL)/halloysite nanotube (HNT) bionanocomposite films: Experimental characterisation and modelling approach

In this study, ecofriendly polyvinyl alcohol (PVA)/starch (ST)/glycerol (GL)/halloysite nanotube (HNT) bionanocomposite at HNT contents of 0.25, 0.5, 1, 3 and 5 wt% were prepared in a solution casting process. Barrier properties against water vapour and gases of such bionanocomposite films were detected to consistently improve with increasing the HNT content when compared with those of PVA/ST/GL blends owing to tortuous paths generated at different HNT dispersion levels. Water vapour permeabilities of such blends and corresponding bionanocomposites increased in a linear manner when the temperature and relative humidity gradient increased from 25 to 55 °C and 10%-70%, respectively. Nonetheless, such permeabilities of bionanocomposites appeared to be less dependent of temperature and relative humidity gradient with increasing the HNT content. An accurate measurement of HNT aspect ratios with the aid of atomic force microscopy (AFM) yielded better agreement between experimental data and Nielsen model with respect to relative permeability of bionanocomposites. Overall, our fabricated bionanocomposites demonstrated good water and gas barrier properties to prolong the shelf life of avocados and peaches with great potential of being used as effective food packaging materials.

The influence of the thermal aureole asymmetry on hydrocarbon generative potential of coal beds: Insights from Raniganj Basin, West Bengal, India

The aim of the present study is to uncover hydrocarbon generation potential of an area intruded by lamprophyre dyke. Lamprophyre dyke induced a short-distance asymmetric thermal aureole in coal beds with more intense impact along the dip direction. Large ash yield, carbon content, lower volatile matter content, hydrogen indices, presence of natural coke, disordered kaolinite peaks, less pronounced aliphatic peaks, higher aromaticity under Fourier Transform Infra-Red spectroscopy (FTIR); highly rugged surface and large pores with the aid of Atomic force microscopy (AFM); abundant calcium carbonate mineral phases (calcite, dolomite, ankerite) and high-temperature silica phases (tridymite, sanidine) under X-ray diffraction (XRD) are the consequences of pronounced thermal effect and expulsion of hydrocarbons. Furthermore, the estimated vitrinite reflectance (EVRo) calculated through maximum pyrolysis temperature (Tmax) and measured mean random vitrinite reflectance (VRo) show the maximum difference in the heat-affected coal samples. In addition, parameters for source rock reconstruction and indices for quantification of FTIR spectra i.e. index of aliphaticity (IAL), index of aromaticity (IAR) and index for hydrocarbon generation (IHG) are introduced for coals. The distant (i.e. least-heat-affected) coals collected opposite to the dip direction of the coal bed have a higher potential for hydrocarbon generation. The igneous intrusion thus played a significant role in enhancing the maturity of the organic material, in turn, augmenting the hydrocarbon generation potential for targeting hydrocarbon plays of the area although at the expense of proximal samples.

Methodology for the investigation of threading dislocations as a source of vertical leakage in AlGaN/GaN-HEMT heterostructures for power devices

In this work, an AlGaN/GaN-HEMT heterostructure is exemplarily studied by a strict place-to-place correlational approach in order to help clarify some open questions in the wide field of reliability topics. Especially, vertical leakage current, its relation to dislocations in general, and specific types in particular are investigated on a highly defective material. With the aid of atomic force microscopy (AFM) in tapping mode, cathodoluminescence imaging, defect selective etching, and energy dispersive X-ray, the material’s defect content around the device relevant two dimensional electron gas is analyzed. The total dislocation density, as well as the density of threading screw, edge, and mixed type dislocations, is systematically investigated directly. The obtained result is statistically much more significant than is possible by conventional transmission electron microscopy studies and more precise than the results obtained by the indirect method of rocking curve analysis. The method of conductive AFM allowed mapping of variations in the vertical leakage current, which could be correlated with variations in barrier leakage or gate leakage. Spots of locally high leakage current could be observed and directly assigned to dislocations with a screw component, but with significant differences even within the same group of dislocation types. The electrical activity of dislocations is discussed in general, and a fundamental model for a potential dislocation driven vertical leakage is proposed.

Abrasive Wear of Polymer Fibers Investigated by Reciprocal Scratching in an Atomic Force Microscope

Three-dimensional (3D) woven fabrics have been considered by biomedical researchers to be used as load-bearing surfaces in joint and ligament replacements. In this regard, wear is a crucial phenomenon that determines material failure as well as biological response of body to wear debris. The current study evaluates various microscale screening methods with the aid of atomic force microscopy (AFM) for biocompatible polymer fibers that are used in 3D woven fabrics. Fibers in mono- and multi-filament forms were subjected to indentation, scratching, and line wear testing in dry and soaked conditions, and the effect of key parameters such as applied normal load, sliding velocity, and number of wear cycles was investigated. The area of worn material was determined by geometric approximation superimposed on the measured residual scratch of line wear. Moisture was found to lower the indentation hardness of some fibers while increasing the hardness of others. Line wear results clearly suggest ultrahigh molecular weight polyethylene (UHMWPE) to be the primary material for further investigation and that monofilament fibers should be avoided.

Structural features of ceramics based on PZT

ABSTRACTThe effect of abrasive polishing on the surface topography and domain structure of relaxor and non-relaxor ferroelectric ceramics was studied with the aid of atomic force microscopy (AFM). Two-fold effect of the surface layers on the properties of the samples was revealed: firstly, polishing treatment removes the non-ferroelectric passive layers formed during the preparation of the material; secondly, polishing results in a formation of a new surface layer having properties different from those in the bulk.

Atomic force microscopy of swelling and hardening of intact erythrocytes fixed on substrate

Peak force measurements with the aid of atomic force microscopy are used to quantitatively map nanomechanical properties of intact erythrocytes of rats under conditions that are close to physiological conditions. Erythrocytes that are immobilized on the substrate preliminary processed using poly-L-lysine predominantly exhibit plane shape. However, cells may also exhibit stepwise transformation to semispherical objects with an increase in volume and hardening. Possible reasons for such transformations are discussed.

The effect of nanocrystalline Ni-W coating on the tensile properties of copper

Nanostructured Ni-W alloy coatings containing approximately 40 wt.% tungsten were electrodeposited onto copper substrates. The effect of the coatings thickness on the surface topography, microstructure and grain size was investigated with the aid of Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) techniques respectively. In addition, this research work aims in understanding the influence and correlation between microstructure and thickness of these Ni-W coatings with the bulk mechanical properties of coated specimens. The experimental results indicated that the micro-hardness and Ultimate Tensile Strength (UTS) of the Ni-W coated copper were higher than that of bare copper, whereas both slightly increased with increasing coating thickness up to 21 μm. On the other hand, the ductility of Ni-W coated copper decreased significantly with increasing coating thickness. Thus it could be said that when applying Ni-W coatings there are certain limitations not only in terms of their composition, but their thickness, grain size and coating structure should be also taken into consideration, in order to obtain an understanding of their mechanical behavior.

Microstructural properties of warm mix asphalt before and after laboratory-simulated long-term ageing

This paper presents microstructural analysis of two original and their respective warm mix asphalt (WMA) binders, obtained with the addition of Advera® and Sasobit®. The binders were analysed before and after long-term ageing with the aid of atomic force microscopy (AFM). The AFM images highlighted the effect of ageing using rolling thin film oven (RTFO) followed by pressure ageing vessel (PAV) on the binders’ microstructure. Ageing of original binders generally increased the size of the “bee” structures. The ageing effect on the microstructure morphology of WMA binders was found to be negligible. However, ageing could affect the mechanical properties without morphology variations. The high variability inside each sample analysed makes the analysis complex. Sasobit® changed the original binders’ microstructure considerably, while Advera® did not affect it. For the original and Advera® binders, 24 hours after sample preparation, the dispersed phase expanded, and this effect was generally more pronounced for unaged than for aged binders. This could indicate a lower mobility of the species forming microstructures in aged samples. The reduced mobility of these species during heat treatment also affects the microstructure of the samples. A hypothesis on the development of “bee” structures starting from dendritic structures was proposed.

One-step construction and examination of one-dimensional plasmonic chromium nano-grating

In this paper, a low-cost one-step nano-grating fabrication has been described which is applied in the grating-coupled excitation of Surface Plasmon Polaritons (SPPs). This technique is based on a kind of physical vapor deposition technique that is so called oblique angle deposition (OAD). Our nano-gratings fabricated at angles of deposition of 60°, 70° and 80° have been investigated by the aid of atomic force microscopy, surface plasmon resonance and measurement of optical reflectance at low incidence angle. Our results show the surface plasmon resonance coupling at different azimuth angle and the sensing ability of oblique angle deposited Cr- nano-grating to the groove distance in low angle measurement system.

Atmospheric Pressure Plasma Treatment of Fused Silica, Related Surface and Near-Surface Effects and Applications

We report on an atmospheric pressure plasma (APP) treatment of fused silica and its related surface and near-surface effects. Such treatment was performed in order to improve laser micro-structuring of fused silica by a plasma-induced modification of the glass boundary layer. In this context, an APP jet applying a hydrogenous process gas was used. By the plasma treatment, the transmission of the investigated glass samples was significantly decreased. Further, a decrease in the superficial index of refraction of approx. 3.66 % at a wavelength of 636.7 nm was detected ellipsometrically. By surface energy measurements, a decrease of the surface polarity of 30.23 % was identified. These determined modifications confirm a reduction of silicon dioxide to UV-absorbing silicon suboxide as already reported in previous work. Further, a change in reflexion by maximum 0.26 % was detected which is explained by the superposition of constructive and destructive interferences due to a surface wrinkling. With the aid of atomic force microscopy, an increase of the surface root mean squared roughness by a factor of approx. 19 was determined. It was found that both the surface energy and the strength of the fused silica surface were reduced by the plasma treatment. Even though such treatment led to a clustering of carbonaceous contaminants, a surface-cleaning effect was confirmed by secondary ion mass spectroscopy and energy-dispersive X-ray spectroscopy. The increase in UV-absorption allows enhanced laser ablation results as shown in previous work.

Red, Green, and Blue Photoluminescence of Ba₂SiO₄:M (M = Eu3+, Eu2+, Sr2+) Nanophosphors.

Divalent europium doped barium orthosilicate is a very important phosphor for the production of light emitting diodes (LEDs), generally associated to the green emission color of micron-sized crystals synthesized by means of solid-state reactions. This work presents the combustion synthesis as an energy and time-saving preparation method for very small nano-sized Ba2SiO4 particles, flexibly doped to acquire different emission energies. The size of the resulting spherical nanoparticles (NPs) of the green emitting Ba2SiO4:Eu2+ was estimated to about 35 nm applying the Scherrer equation and further characterized with aid of atomic force microscopy (AFM) as well as scanning electron microscopy (SEM). This phosphor is able to build homogeneous luminescent suspensions and was successfully down-sized without changing the optical properties in comparison to the bulk phosphors. Besides the X-ray diffraction (XRD) analysis and the different types of microscopy, the samples were characterized by luminescence spectroscopy. Undoped Ba2SiO4 NPs are not luminescent, but show characteristic red emission of the 5D0 → 7FJ (J = 0–4) electronic transitions when doped with Eu3+ ions. Moreover, these orthosilicate nanoparticles generate blue light at low temperatures due to impurity-trapped excitons, introduced by the partial substitution of the Ba2+ with Sr2+ ions in the Ba2SiO4 lattice causing a substantial distortion. A model for the temperature behavior of the defect luminescence as well as for their nature is provided, based on temperature-dependent luminescence spectra and lifetime measurements.

Effect of chromium on elastic and plastic deformation of Fe3Al intermetallics

In order to evaluate the effect of chromium concentration on the mechanical properties of single phase iron aluminum intermetallics, specifically those containing 26 at.% Al, a nano-indentation technique was used. The grain orientations of samples were revealed with the aid of Electron Backscatter Diffraction (EBSD) technique. Additionally, the surface roughness of each sample was checked after electropolishing with the aid of Atomic Force Microscopy (AFM). Finally, all nano- and micro-indents were performed within the (001) orientated grains, where the surface roughness was less than 1.06 nm on average, in all samples. The Oliver–Pharr method, with correction for pile up, was used to calculate the Young's modulus and nano-hardness for Fe3Al–xCr alloys. Additionally, the effect of Cr on the shear stress needed for homogeneous dislocation nucleation, internal friction stress of dislocation motion (Peierls–Nabarro stress) and flow stress was studied.

Structural and surface properties of TiO2 thin films doped with neodymium deposited by reactive magnetron sputtering

Thin films were deposited using modified, high energy magnetron sputtering method from Ti-Nd mosaic targets. The amount of neodymium dopant incorporated into two sets of thin films was estimated to be 0.8 and 8.5 at.%, by means of energy dispersive spectroscopy. On the basis of x-ray diffraction method, the type of crystalline structure and crystallites size were evaluated directly after the deposition process and after additional post-process annealing at 800 °C temperature. The influence of annealing on the surface properties was evaluated with the aid of atomic force microscopy. Uniformity of the dopant distribution in titanium dioxide matrix was examined with the aid of secondary ion mass spectroscopy. Additionally, using atomic force microscope, diversification and roughness of the surface was determined. Chemical bonds energy at the surface of TiO2:Nd thin films was investigated by x-ray photoelectron spectroscopy method. Wettability measurements were performed to determine contact angles, critical surface tensions and surface free energy of prepared coatings. On the basis of performed investigations it was found, that both factors, the amount of neodymium dopant and the post-process annealing, fundamentally influenced the physicochemical properties of prepared thin films.

Enhanced Grain Orientation in Pb(Zr,Ti)O3 Powder-Modified SrBi2Ta2O9 Ferroelectric Ceramics

Abstract Pb(Zr,Ti)O3 (PZT) powder modified SrBi2Ta2O9 (SBT) ceramics, hereafter called SBT-PZT, were prepared by the solid phase synthesis method. With the aid of atomic force microscopy and x-ray diffractometry, the SBT-PZT ceramics were found to exhibit an enhanced c-axis orientation compared with SBT ceramics. Ferroelectric and dielectric properties of SBT-PZT ceramics were revealed to be anisotropic by relevant measurements. Because of differences in heteropolar valence and ionic radius between SBT and PZT, the PZT may be introduced into SBT as a heterogeneous system and embedded in the SBT grain boundaries. The large differences in crystal structures between SBT and PZT were proposed to be responsible for the SBT-PZT grain orientation mechanism. Obviously, the grain orientation resulted in electrical anisotropies of SBT-PZT ceramic. The internal stress, which was induced by heterogeneous system doping, was considered to affect the polarization reversal of SBT-PZT ceramics.

Use of ionic liquid in fabrication, characterization, and processing of anodic porous alumina.

Two different ionic liquids have been tested in the electrochemical fabrication of anodic porous alumina in an aqueous solution of oxalic acid. It was found that during galvanostatic anodization of the aluminum at a current density of 200 mA/cm2, addition of 0.5% relative volume concentration of 1-butyl-3-methylimidazolium tetrafluoborate resulted in a three-fold increase of the growth rate, as compared to the bare acidic solution with the same acid concentration. This ionic liquid was also used successfully for an assessment of the wettability of the outer surface of the alumina, by means of liquid contact angle measurements. The results have been discussed and interpreted with the aid of atomic force microscopy. The observed wetting property allowed to use the ionic liquid for protection of the pores during a test removal of the oxide barrier layer.

Self-Assembly in Mixed Aqueous Solutions of Amphiphilic Block Copolymers and Vesicle-Forming Surfactant

The self-assembly behavior of mixed solutions consisting of poly(isoprene-b-ethylene oxide) (IEO) copolymer micelles and vesicle-forming didodecyldimethylammonium bromide (DDAB) was investigated. Dynamic light scattering indicated the presence of two populations of nanoassemblies in the solutions. By aid of atomic force microscopy, the larger ones were identified as block copolymer modified surfactant vesicles (BCMSVs) and the smaller ones as surfactant-modified block copolymer micelles (SMBCMs). This identification is based on the amphiphilic character of the low and high molecular weight molecules and the notion that exchange of unimers of both types can take place between the initial nanoassemblies in aqueous solution. Electrophoretic light scattering experiments showed that the nanostructures carry positive charges originating from the surfactant. The sizes of the nanoassemblies depend on the relative concentrations of both components. The behavior of the mixed systems was also found to depend on block copolymer composition and temperature. Nanoassemblies of smaller sizes were formed at higher temperatures. BCMSVs and SMBCMs are thermosensitive, in contrast to the temperature stability of pure block copolymer micelles. On the other hand, BCMSVs showed lesser sensitivity to temperature increase compared to the pure DDAB vesicles. This indicates that incorporation of macromolecules into the DDAB bilayer increases the stability of the vesicles.