Atomic Force Microscopy Roughness Research Articles

Characterization of Structure, Morphology, Optical and Electrical Properties of AlN–Al–V Multilayer Thin Films Fabricated by Reactive DC Magnetron Sputtering

Composite thin films of the AlN–Al–V type, grown by magnetron sputtering, were analyzed by several complementary diagnostic methods. The power of the magnetron was used as a variable parameter, while gas flows, chamber pressure, and substrate temperature remained unchanged during the film fabrication. According to grazing incidence X-ray diffraction (GIXRD) results, in most cases, it was possible to obtain an (002)-oriented aluminum nitride (AlN) layer in the films, although, with an increase in the magnetron power to 800 W, the formation of X-ray amorphous AlN was observed. Similarly, according to the Raman results, the width of the peak of the vibrational mode E1, which characterizes the correlation length of optical phonons, also significantly increased in the case of the sample obtained at 800 W, which may indicate a deterioration in the crystallinity of the film. A study of the surface morphology by atomic force microscopy (AFM) and scanning electron microscopy (SEM) showed that the AlN film grows in the form of vertically oriented hexagons, and crystallites emerge on the surface in the form of dendritic structures. During the analysis of the AFM roughness power spectral density (PSD-x) functions, it was found that the type of substrate material does not significantly affect the surface roughness of the AlN films. According to the energy–dispersive X-ray spectroscopy (SEM-EDS) elemental analysis, an excess of aluminum was observed in all fabricated samples. The study of the current-voltage characteristics of the films showed that the resistance of aluminum nitride layers in such composites correlates with both the aluminum content and the structural imperfection of crystallites.

Atomic Force Microscopy to Characterize Antimicrobial Peptide-Induced Defects in Model Supported Lipid Bilayers.

Antimicrobial peptides (AMPs) interact with bacterial cell membranes through a variety of mechanisms, causing changes extending from nanopore formation to microscale membrane lysis, eventually leading to cell death. Several AMPs also disrupt mammalian cell membranes, despite their significantly different lipid composition and such collateral hemolytic damage hinders the potential therapeutic applicability of the AMP as an anti-microbial. Elucidating the mechanisms underlying the AMP–membrane interactions is challenging due to the variations in the chemical and structural features of the AMPs, the complex compositional variations of cell membranes and the inadequacy of any single experimental technique to comprehensively probe them. (1) Background: Atomic Force Microscopy (AFM) imaging can be used in combination with other techniques to help understand how AMPs alter the orientation and structural organization of the molecules within cell membranes exposed to AMPs. The structure, size, net charge, hydrophobicity and amphipathicity of the AMPs affect how they interact with cell membranes of differing lipid compositions. (2) Methods: Our study examined two different types of AMPs, a 20-amino acid, neutral, α-helical (amphipathic) peptide, alamethicin, and a 13-amino acid, non-α-helical cationic peptide, indolicidin (which intramolecularly folds, creating a hydrophobic core), for their interactions with supported lipid bilayers (SLBs). Robust SLB model membranes on quartz supports, incorporating predominantly anionic lipids representative of bacterial cells, are currently not available and remain to be developed. Therefore, the SLBs of zwitterionic egg phosphatidylcholine (PC), which represents the composition of a mammalian cell membrane, was utilized as the model membrane. This also allows for a comparison with the results obtained from the Quartz Crystal Microbalance with Dissipation (QCM-D) experiments conducted for these peptides interacting with the same zwitterionic SLBs. Further, in the case of alamethicin, because of its neutrality, the lipid charge may be less relevant for understanding its membrane interactions. (3) Results: Using AFM imaging and roughness analysis, we found that alamethicin produced large, unstable defects in the membrane at 5 µM concentrations, and completely removed the bilayer at 10 µM. Indolicidin produced smaller holes in the bilayer at 5 and 10 µM, although they were able to fill in over time. The root-mean-square (RMS) roughness values for the images showed that the surface roughness caused by visible defects peaked after peptide injection and gradually decreased over time. (4) Conclusions: AFM is useful for helping to uncover the dynamic interactions between different AMPs and cell membranes, which can facilitate the selection and design of more efficient AMPs for use in therapeutics and antimicrobial applications.

Effect of Sodium Hypochlorite in Ground Fluorotic Enamel: Shear Bond Strength and Surface Analysis

Evaluate the effect on the shear bond strength (SBS) of 5% NaOCl applied after acid etching on ground anterior teeth with fluorosis and analyze the surface with scanning electron microscopy (SEM), also compare fluorotic and healthy ground enamel by atomic force microscopy (AFM) and Vickers microhardness (VM). For the SBS test 30 anterior teeth with moderate and severe fluorosis according Dean index were selected by an examiner previously calibrated with an expert in fluorosis by using the intraclass correlation coefficient (ICC). With the help of a calibrated high speed diamond bur for veneer preparation and a parallel chamfer high speed diamond bur the vestibular face was prepared with a uniform reduction of .3 mm under water cooling. In one half of the vestibular face of the teeth the conventional adhesive procedure was carried out while in the other half was added an additional step with 5% NaOCl applied for 1 minute and washing after acid etchant. A resin post was adhered in each half and load was applied until fracture. The failure mode was evaluated and a SEM analysis was made. Posteriorly 10 samples of fluorotic and healthy ground enamel were used to measure the nanostructural characteristics by AFM (roughness average and absolute depth profile) and the VM in three operative steps (after ground, after etchant and after deproteinization). The Shapiro-Wilks and Brown-Forsythe methods were used to test the distribution of variables. The Paired Student's t-test was used to compare the differences between mean bond strength (MPa) in the two groups for SBS test. Chi-square analyzes were performed to compare the failure modes between groups. One-way ANOVA analysis and Tukey-Kramer post hoc test were used to compare groups for roughness average, absolute depth profile and Vickers microhardness. A greater SBS (32.17±4.20 MPa) and a surface more homogeneous and less contaminated were observed in the deproteinization subgruoup compared to the conventional subgroup (27.74±4.88 MPa). AFM parameters were greater in fluorosis subgroup than in healthy enamel subgroup. VM was lower in the fluorotic enamel in each operative step in comparation with healthy enamel. The use of 5% NaOCl as a deproteinizing agent after acid etchant in ground fluorotic enamel results in better adhesion, which may imply greater success in adhesive treatments. The ground surface of fluorotic enamel shows higher values of roughness and depth and lower values of VM which proves that there is a more irregular and less hard surface.

Investigation of Aging Behavior of Biorejuvenated Asphalt with Chemical and Micromechanical Methods

Abstract Considering the increased application of high reclaimed asphalt pavement (high RAP) content mixtures, the biorejuvenator attracts increasing attention during the pavement maintenance and rehabilitation process, because this method can be implemented with ease and high effectiveness. However, the aging mechanism of biorejuvenated asphalt at a microscale is not well-understood. The microscale analysis provides a way to acknowledge how the biorejuvenator works. Therefore, this study aims to characterize the physical-structural and chemical changes of biorejuvenated asphalts of different aging levels at a microscale. The methodologies adopted include component analysis, atomic force microscopy (AFM), and Fourier-transform infrared spectroscopy (FTIR). In AFM tests, roughness and percentage of bee structures were compared in quantifying the surface morphology changes during aging. Correlation analysis was conducted between the microstructure and component analysis. Young’s modulus and adhesive forces were measured to quantify the micromechanical properties. FTIR spectra were used to investigate the aging mechanism. Results revealed that saturates, aromatics, resins and asphaltenes (SARA) fractions of original asphalts and biorejuvenated asphalts changed in the same way during aging. More special variations were found in aged biorejuvenated asphalt, and saturates content was discovered to determine the variation of bee structures’ percentage. The adhesion forces changed in different ways because of the different original asphalts, and the modulus index demonstrated that biorejuvenated asphalt aged faster than the original asphalt. The FTIR test demonstrated the new aldehyde in the biorejuvenator may be the reason for the accelerated aging of biorejuvenated asphalt.

Evaluation of clarity characteristics in a new hydrophobic acrylic IOL in comparison to commercially available IOLs

To perform invitro assessments of surface haze and roughness, subsurface nanoglistenings (SSNGs), and glistenings of a new hydrophobic acrylic intraocular lens (IOL) in comparison to commercially available IOLs. Universities of Utah and Alcalá, and Alcon Vision, LLC. Experimental study. The IOLs used were Clareon CNA0T0, Tecnis ZCB00 and Tecnis OptiBlue ZCB00V, Eternity W-60, enVista MX60, and Vivinex XY1. Surface haze was assessed by the pixel intensity units (PIU) from cross-sectional slitlamp images, and it was correlated to atomic force microscopy roughness. For SSNGs, the IOLs were artificially aged up to 10years, followed by Scheimpflug densitometry (computer-compatible tape unit [CCTU]) measurements. For glistenings, the IOLs were immersed in a water bath and subjected to temperature changes before analysis. The surface haze (n=10, PIU) was 4.25±0.87 (SD) (CNA0T0), 9.50±1.66 (ZCB00), 39.48±1.97 (ZCB00V), 46.68±3.16 (W-60), 44.70±4.00 (MX60), and 4.42±0.71 (XY1) (P<.001), which showed a strong correlation with surface roughness measurements (R=0.94, P=.006). The densitometry (n=10, CCTU at 10years) was 7.30±1.36 (CNA0T0), 11.88±3.10 (ZCB00), 38.12±2.24 (ZCB00V), 48.13±9.44 (W-60), 20.20±3.84 (MX60), and 6.75±6.66 (XY1) (P<.001), with no significant differences between CNA0T0 vs. ZCB00 and XY1. The glistenings density (n=30) was the lowest for the CNA0T0, W-60, and MX60 IOLs. The new Clareon CNA0T0, which is manufactured from a hydrophobic acrylic material, exhibited among the lowest levels of surface haze and roughness, SSNGs, and glistenings compared with other commercially available hydrophobic acrylic IOLs.

The role of spatial frequency analysis in correlating atomic force microscopy and optical profilometry with self-etch adhesive enamel bond fatigue durability.

The purpose of this study was to: (a) evaluate the role of enamel surface roughness on bond fatigue durability and (b) evaluate statistical differences in roughness values based on measurement technique, including the use of spatial filtering for optical profilometry (OP). OptiBond XTR (Kerr Corp), Prime & Bond elect (DENTSPLY Caulk), Scotchbond Universal (3 M Oral Care), and XTR pre-etched with Ultra-Etch phosphoric acid (35%) (Ultradent) self-etch adhesives were used to treat enamel. A flat ground enamel surface was included as a control. Atomic force microscopy (AFM) and OP were used to measure the surface topography of each enamel surface following the application of adhesives. AFM, OP, and filtered OP (FOP) roughness values, where FOP was designed to only include the lateral spatial resolution consistent with AFM roughness values, were collected. Spatial resolution filtering with OriginPro was used to compare line scans from the two imaging techniques and generate the FOP group. These micro- versus nanoscale lateral roughness values were correlated with shear bond and shear fatigue strengths of the adhesives bonded to enamel. Roughness values showed differences based on measurement technique and strong correlations with bond and fatigue strength. The filtered OP group demonstrated the importance of careful usage and reporting of atomic force microscopy and OP metrics in adhesive dentistry. Best practices for surface roughness analysis were also discussed.

Localized incorporation of outer membrane components in the pathogen Brucella abortus.

The zoonotic pathogen Brucella abortus is part of the Rhizobiales, which are alpha-proteobacteria displaying unipolar growth. Here, we show that this bacterium exhibits heterogeneity in its outer membrane composition, with clusters of rough lipopolysaccharide co-localizing with the essential outer membrane porin Omp2b, which is proposed to allow facilitated diffusion of solutes through the porin. We also show that the major outer membrane protein Omp25 and peptidoglycan are incorporated at the new pole and the division site, the expected growth sites. Interestingly, lipopolysaccharide is also inserted at the same growth sites. The absence of long-range diffusion of main components of the outer membrane could explain the apparent immobility of the Omp2b clusters, as well as unipolar and mid-cell localizations of newly incorporated outer membrane proteins and lipopolysaccharide. Unipolar growth and limited mobility of surface structures also suggest that new surface variants could arise in a few generations without the need of diluting pre-existing surface antigens.

Optical constants of SiO2 from 196 to 1688 nm (0.735–6.33 eV) from 20, 40, and 60 nm films of reactively sputtered SiO2 on Eagle XG® glass by spectroscopic ellipsometry

Three thicknesses of reactively sputtered SiO2, nominally 20, 40, and 60 nm, deposited on Corning Eagle XG® (EXG), an important display glass, were analyzed by spectroscopic ellipsometry. Reflection ellipsometry data from the samples were analyzed from 196 to 1688 nm at angles of 55°–60°, inclusive, in 1° increments. These angles were chosen because they bracket the Brewster angles of both EXG glass and SiO2. The backsides of the samples were roughened by sand blasting to suppress backside reflections from the substrates. A total of nine datasets were collected from nine different samples (three for each nominal thickness of SiO2), each at six different angles of incidence (54 spectra). The optical constants for each thickness of SiO2 was determined, as well as a set of constants for all the films (the material in general) via a multisample analysis (MSA). The optical constants of the SiO2 films were modeled using two poles with transparency assumed over the entire spectral range (a Sellmeier model). A Bruggeman effective medium approximation (BEMA) roughness layer was included in the model, which assumed 50/50 volume fractions that corresponded to the modeled SiO2 optical constants and void. The fit did not substantially improve when an interface layer between the Eagle XG® and the sputtered film was included, so it was omitted. Three sets of previously reported optical constants for the substrate over two wavelength ranges were considered in the modeling. The thin SiO2 films analyzed herein have very similar optical properties to those of their EXG substrate—this is a challenging analytical problem involving a transparent film on a transparent substrate. Accordingly, analysis of multiple samples, an MSA that included multiple film thicknesses analyzed at multiple angles, and an exploration of multiple modeling approaches helped ensure that the optical constants reported herein are accurate and the modeling robust. In particular, these measures helped avoid correlation between the optical constants, the layer thicknesses, and the thicknesses of the BEMA layers. Atomic force microscopy roughness measurements were made on the SiO2 films and compared to the roughness values obtained by spectroscopic ellipsometry. In summary, the authors provide here the optical constants and some accompanying physical characterization of sputtered 20–60 nm SiO2 films from 196 to 1688 nm.

Substrate-induced strain and charge doping in CVD-grown monolayer MoS2

Due to its electronic-grade quality and potential for scalability, two-dimensional (2D) MoS2 synthesized by chemical vapor deposition (CVD) has been widely explored for electronic/optoelectronic applications. As 2D MoS2 can be considered a 100% surface, its unique intrinsic properties are inevitably altered by the substrate upon which it is grown. However, systematic studies of substrate-layer interactions in CVD-grown MoS2 are lacking. In this study, we have analyzed built-in strain and charge doping using Raman and photoluminescence spectroscopy in 2D MoS2 grown by CVD on four unique substrates: SiO2/Si, sapphire, Muscovite mica, and hexagonal boron nitride. We observed decreasing strain and charge doping in grown MoS2 as the substrates become less rough and more chemically inert. The possible origin of strain was investigated through atomic force microscopy roughness measurements of the as-grown layer and substrate. Our results provide direction for device optimization through careful selection of the growth substrate and pave the way for further investigations to unravel the complex nature of the 2D monolayer-substrate interface.

Coloration of molybdenum oxide thin films synthesized by spray pyrolysis technique

Photochromiccoatings of molybdenum oxide films were deposited on glass substrates by spray pyrolysis technique. The samples were prepared at two substrate temperatures of 250°C and 400°C using spray time varying between 1 and 5 min while the other spray operating parameters are fixed at their optimum values. The crystalline nature and crystallite size of the films were investigated by grazing angle X-ray diffraction. The surface topography was characterized by atomic force microscopy roughness data and particle size histograms. The X-ray diffraction patterns prove that the films deposited at substrate temperature of 250 °C and different spray time are amorphous while the films deposited at 400°C and different spray time are crystalline with only α-phase. The particle size distribution for the prepared samples are found to be in the range from 70 to 100nm. The particle size distribution tends to be narrow as the spray time increases which indicates the improvement in homogeneity of the samples. The optical absorption spectra of selected colorless samples before and after UV light irradiation was recorded. Two distinct absorption bands were observed: a sharp one related to the energy gap and a broader one at lower energy of 1.03eV to which the blue color of the sample after UV irradiation is related. This latter band is fitted with three sub-bands E1, E2 and E4 using a Lorentzian model. The intensity and position of these sub-bands depended on UV light exposure time. The sub-bands E1 and E4 are related to the bulk and surface paramagnetic color centers while the E2 band is related to pairing diamagnetic color centers.

Atomic force microscopy study, kinetic roughening and multifractal analysis of electrodeposited silver films

We used atomic force microscopy (AFM) to study surface morphology and kinetic roughening of Ag films. X-ray diffraction (XRD) technique is used to verify the films crystalline structure. The influence of film thickness on the kinetic roughening was investigated using AFM data and roughness calculation. It is revealed that the surface roughness increases with increasing the film thickness. The data also consist with a complex behavior which is called as anomalous scaling. Scaling laws analysis for Ag films presents two distinct dynamics including large local and scale roughness and indicates a power law dependency on the thickness of film.AFM images have been characterized by the multifractal analysis. This analysis shows that the self-similar and multifractal characteristics as well as anomalous scaling exist in the Ag film morphologies. Description of the quantitative growth and surface morphology was done by the multifractal spectra, f(α)−α. It is found that the multifractal spectrum shape is left hook-like (that is difference of height interval of the multifractal spectrum, Δf=f(αmin)−f(αmax)>0). The results indicate that the surfaces having greater roughness give rise the wider multifractal spectrum width(Δα) and the greater Δf, thus, the nonuniformity of the height probabilities becomes larger. It indicates that the multifractality of the films becomes more pronounced at the higher thickness.

Relation between optical non-contact profilometry and AFM roughness parameters on coated papers with oil-filled nanoparticles

In parallel with the development of nanoparticle coatings for protection of paper substrates, detailed descriptions of the surface topography with micro- to nanoscale roughness features are needed. In this work, papers have been coated with poly(styrene-co-maleic anhydride) nanoparticles including different types of vegetable oils and the surface roughness was evaluated at 2000×2000μm2 to 0.2×0.2μm2 length scales by combining non-contact optical profilometry (NCP) and atomic force microscopy (AFM). The relationships between roughness data were studied for statistical roughness parameters, spatial roughness parameters and in the frequency domain. In order to compare AFM roughness more accurately, the original images were flattened to remove effects of the underlaying fibrous substrate and highlight features of the nanoparticle coating. More detailed information on the coating topography could be obtained by considering bearing ratio curves and histograms, where it was concluded that the oil-filled coatings form a rather thin and continuous coating that closely follows the shape of the cellulose fibers. The relation between statistical roughness parameters from NCP and AFM follows an exponential trend with relatively low coefficient of determination. The increase in surface roughness with length scale showed a transition point attributed to short- and long-range surface features. Therefore, the correlation length was used as a spatial roughness parameter that provides a successful extrapolation of the average roughness over different length scales in a double logarithmic diagram with very high coefficient of determination. Based on the power spectral density, it was difficult to exactly distinguish between the different types of SMI/oil coatings, as they include similar nanoscale features. The frequency roughness parameters were better suited for extrapolation than statistical roughness parameters but little less efficient than the spatial roughness parameters.

The influence of thermal annealing to remove polymeric residue on the electronic doping and morphological characteristics of graphene

The impact of polymer removal by forming gas and vacuum annealing on the doping, strain, and morphology of chemical vapor deposited (CVD) and mechanically exfoliated (ME) graphene is investigated using Raman spectroscopy and atomic force microscopy (AFM). The behavior of graphene exposed and unexposed to polymer is compared. It is found that the well-known doping effect after forming gas annealing is induced in CVD–ME graphene by polymeric residue/hydrogen-functionalization. Further, forming gas annealing of ME graphene is shown to induce strain via pinning of the graphene layer to the substrate. It is found that vacuum annealing removes most polymeric residue, with minor doping and strain effects. Finally, a study of AFM step height and roughness measurements provides a comprehensive understanding of those annealing-based processes which create morphological changes and directly influence doping and strain in the graphene layer, such as removal of polymer, removal of the interfacial graphene–substrate water layer, environmental doping effects and deformation of the graphene layer.

Mechanical and structural properties of RF magnetron sputter-deposited silicon carbide films for MEMS applications

In the present work, we report preparation and characterization of silicon carbide (SiC) films obtained by RF magnetron sputtering using a SiC ceramic target. The films were deposited in Ar ambient without external substrate heating. The residual stress of the films was measured as a function of sputtering parameters. The stress of the as-deposited films was observed to be compressive for the entire range of sputtering parameters used in the present work. Postdeposition annealing at 400 °C in N2 ambient was useful in reducing the stress in the films. On sequentially annealing the films at higher temperatures (600 and 800 °C), the nature of the stress changed from low compressive to high tensile. A superhard SiC film with low residual compressive stress (58.7 MPa) was obtained with hardness and Young's modulus values of 49.86 GPa and 363.75 GPa respectively. The x-ray diffraction pattern revealed that the films were either amorphous or nano-crystalline, depending on the deposition parameters and postdeposition annealing temperature. Atomic force microscopy roughness results confirmed good chemical stability of the films in potassium hydroxide and buffered hydrofluoric acid solutions. Several types of micro-structures were fabricated to demonstrate the feasibility and compatibility of these films in MEMS fabrication.

Polyimide Surface Modification by Using Microwave Plasma for Adhesion Enhancement of Cu Electroless Plating

Microwave (MW) plasma was applied to the surface of polyimide (PI) films as a treatment to enhance the adhesion between copper deposition layer and PI surface for electroless plating. The influences of nitrogen MW plasma treatment on chemical composition of the PI surface were investigated by using X-Ray photoelectron spectroscopy (XPS). The wettability was also investigated by water contact angle measurement. The surface morphologies of PI films before and after treatment were characterized with atomic force microscopy (AFM). The contact angle results show that was dramatically decreased to 16.1 degrees at the optimal treatment condition from 72.1 degrees (untreated PI). However, the root mean square (RMS) roughness of treated PI film was almost unchanged. The AFM roughness was stayed from 1.0 to 1.2 with/without plasma treatment. XPS data show a nitrogen increase when PI films exposed to N2 MW plasma. Electroless copper depositions were carried out with the free-formaldehyde method using glyoxylic acid as the reducing reagent and mixture palladium chloride, tin chloride as activation solution. Adhesion property between polyimide surface and copper layer was investigated by tape test.

New insights into the mucoadhesion of pectins by AFM roughness parameters in combination with SPR

The object of this study was to assess the mucoadhesion of the three main commercially available types of pectin by atomic force microscopy (AFM) and surface Plasmon resonance (SPR). Polyacrylic acid and polyvinyl pyrrolidone were used as positive and negative control, respectively. Image analysis of the AFM scans revealed a significant change of roughness parameters when low-ester pectin was introduced to mica supported bovine submaxillarymucin, indicating a high mucoadhesion for this type of pectin. Only minor changes were observed with high-ester and amidated pectin. The same ranking order of adhesion affinity was confirmed by SPR. In conclusion, a high specific mucin interaction of pectin with a high charge density was demonstrated directly on a molecular scale without interference from the viscoelastic properties or the intra-molecular interactions between the polymer chains themselves, using two independent methods.

Adhesion and Wettability Characteristics of Chemically Modified Banana Fibre for Composite Manufacturing

In this work banana fibre was chemically modified using various chemical agents. The surface energy of the fibre is an important parameter and one which governs the interaction of fibre with polymeric matrices. This paper describes the influence of various chemical treatments on the surface energy of the banana fibre investigated by contact angle measurements, spectroscopic analysis and surface morphology studies. The surface energy, work of adhesion, polarity, spreading coefficient, interfacial energy and interaction parameter were determined in the case of raw and chemically modified fibres. Chemical modification has been found to have a profound effect on the surface energy. The polar and dispersive components of the surface energy were also found to be dependent on the chemical treatment involved. The chemical modifications done in this work were: alkali treatment, silanation, benzoylation, formylation, potassium permanganate treatment and acetylation. Of all the modifications, the relative surface energy was found to be a maximum for alkali treated fibre and minimum for silanated fibre. Contact angle measurements were found to be an effective tool in predicting the possible interaction of the fibres with phenol formaldehyde matrix resin. Atomic force microscopy roughness analysis revealed a significant decrease in surface roughness for the chemically modified fibre. An increase both in fibre/matrix adhesion and interfacial shear strength has been observed for all surface modified fibres except for those modified by benzoylation and acetylation.

Properties of GaAs(001) surfaces thermally annealed in vacuum

Thermal degradation of GaAs(001) surfaces has been studied using spectroscopic ellipsometry (SE), optical microscopy, ex situ atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) techniques. The SE data suggest that thermal annealing causes no or little influence on the surface native oxide layer at temperatures T≤500 °C. Microscopic roughening starts to occur on GaAs surface at T&amp;gt;500 °C, giving maximum AFM roughness (rms∼14 nm) at 540 °C, and then tends to smoothened at T&amp;gt;540 °C (rms∼2.5 nm at 580 °C). Macroscopically roughened surfaces are observed at T&amp;gt;500 °C, becoming more pronounced at higher annealing temperature. The Ga droplets are also observed at T≥600 °C that lead to catastrophically damaged surfaces and make SE measurement impossible. The XPS data indicate thinning of the native GaAs oxide in the limited temperature range 450&amp;lt;T&amp;lt;580 °C; however, annealing at T≥580 °C leads to coverage with thermal oxides (Ga2O and As2O3). The naturally grown GaAs oxide is also found to act as a good passivation film against annealing-induced PL degradation.

Microscopic Investigations of the Cr(VI) Uptake Mechanism of Living Ochrobactrum anthropi

A basic understanding related to the immobilization of chromium by bacteria is essential for chromate pollutant remediation in the environment. In this work, we studied the Cr(VI) uptake mechanism of living Ochrobactrum anthropi and the influence of a bacterial culture medium on the Cr-immobilization process. It was found that the Cr-immobilization ratio of bacteria in Tris-HCl buffer is higher than in LB medium. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) analysis revealed that the chromium accumulated on bacteria were mostly in Cr(III) states. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) observations showed that noticeable Cr(III) precipitates were accumulated on bacterial surfaces. AFM roughness analysis revealed that the surface roughness of bacteria increased greatly when the bacteria-Cr(VI) interaction was in Tris-HCl buffer rather than in LB solution. Transmission electron microscopy (TEM) thin section analysis coupled with energy-dispersive X-ray spectroscopy showed that Cr(III) is also distributed in bacterial inner portions. A chromium-immobilization mechanism considering the participation of both bacterial inner portions and bacterial surfaces of living Ochrobactrum anthropi was proposed, whereas the bacterial surface was the dominant part of the immobilization of Cr(III). This work also proved that the control of Cr immobilization by living Ochrobactrum anthropi could be achieved via adjusting the bacterial culture medium.

Characterization of Bacteriocin‐Coated Antimicrobial Polyethylene Films by Atomic Force Microscopy

Antimicrobial agents can be used to give antimicrobial properties to polymeric materials used to envelope foods for packaging purposes. In this study, we exploited an atomic force microscopy (AFM) analysis for the characterization of plastic films activated with antimicrobial agents. The aim was to acquire information on the distribution of the antimicrobials on plastic materials with the ultimate scope of understanding the mechanisms of interaction between antimicrobials and materials to be used for food packaging. Four polyethylene films differing in linear, EVA, and erucamide content were activated by 3 different bacteriocins as antimicrobials, namely, nisin and bacteriocins Bac162W from Lactobacillus curvatus and BacAM09 from Lactobacillus plantarum. The spectrum of activity of the bacteriocins was assayed and shown to include several strains of Listeria monocytogenes. The plastic films were activated by a previously developed coating procedure and the surfaces of the active films were examined by AFM. In addition, roughness parameters related to the single surfaces were investigated by an appropriate software. Significant differences were found between the bacteriocin activated and control (nonactivated) films and the activated surfaces showed lower values of average roughness and surface area ratio. It was not always possible to obtain a homogeneous distribution of the bacteriocin preparation following the coating procedure. This result was dependent on the bacteriocin used and its distribution on the different plastic films. Overall, the bacteriocin Bac162W showed the most homogeneous distribution while surfaces treated with nisin, showing a sort of microtexturing, always gave the highest roughness values. Although the issue needs further investigation, the connection between AFM imaging, roughness, and antimicrobial distribution on active packaging showed the potential to improve the understanding of the interactions between plastic films and antimicrobial preparations that can be important for the innovation in food packaging and science.