Atomic Force Microscopy Characterization Research Articles

Focused Ion Beam Fabrication and Atomic Force Microscopy Characterization of Micro/Nanoroughness Artifacts With Specified Statistic Quantities

Series of roughness patterns with predetermined statistic quantities, such as standard deviation of surface heights, autocorrelation length, and height distribution were fabricated by focused ion beam (FIB) lithography and characterized by atomic force microscopy (AFM). Template-matching analysis and comparisons of surface parameters were performed to ascertain the fabrication and measurement qualities. Results show that the root-mean-square (rms) residuals are approximately 4.8, 5.2, and 15.7 nm for the fabricated Gaussian, negatively skewed, and positively skewed surfaces with the dimension of 5120 nm × 5120 nm × 121 nm. For the surfaces with the same skewness but different autocorrelation lengths, the rms residuals have no significant differences. The surface parameters of the fabricated artifacts are in close agreements with their expected values. To further elucidate the geometric interactions between the tip and roughness structure in AFM measurements, blind tip estimations were carried out on the scanned images. The tip estimation deviation increases with the increase of autocorrelation length for the Gaussian surfaces. The skewed structures help to improve the estimation accuracy. By a proper design of the surface quantities, the artifacts can serve as reference areal roughness standards at the nanoscale and a kind of tip characterizers.

Evidence of antibacterial activity on titanium surfaces through nanotextures

Abstract Nosocomial infections (Nis) are a major concern for public health. As more and more of the pathogens responsible for these infections are antibiotic resistant, finding new ways to overcome them is a major challenge for biomedical research. We present a method to reduce Nis spreading by hindering bacterial adhesion in its very early stage. This is achieved by reducing the contact interface area between the bacterium and the surface by nanoengineering the surface topography. In particular, we studied the Escheria Coli adhesion on titanium surfaces exhibiting different morphologies, that were obtained by a combination of mechanical polishing and chemical etching. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) characterization revealed that the titanium surface is modified at both micro- and nano-scale. X-ray Photoelectron Spectroscopy (XPS) revealed that the surfaces have the same composition before and after piranha treatment, consisting mainly of TiO2. Adhesion tests showed a significant reduction in bacterial accumulation on nanostructured surfaces that had the lowest roughness over large areas. SEM images acquired after bacterial culture on different titanium substrates confirmed that the polished titanium surface treated one hour in a piranha solution at a temperature of 25 °C has the lowest bacterial accumulation among all the surfaces tested. This suggests that the difference observed in bacterial adhesion between the different surfaces is due primarily to surface topography.

Correlation of shape changes of grain surfaces and reversible stress evolution during interruptions of polycrystalline film growth

Short interruptions of the growth of polycrystalline films often lead to stress evolution that is reversed when growth is resumed. Correlated in situ stress measurements and ex situ transmission electron microscopy and atomic force microscopy characterizations of grain boundary surface grooves as a function of the interruption time are reported for films deposited at different temperatures and held for different times before quenching to room temperature. These studies suggest that during film deposition surface grooves at grain boundaries are kinetically constrained to be shallow, while during a growth interruption surface diffusion allows grain boundary grooves to deepen and approach their equilibrium depth. The latter relieves a component of the compressive stress associated with trapped atoms in the grain boundaries. When growth is resumed, the non-equilibrium surface morphology is reestablished and the compressive stress increases to its pre-interruption value.

Benzothienobenzothiophene-Based Conjugated Oligomers as Semiconductors for Stable Organic Thin-Film Transistors

Two benzothienobenzothiophene (BTBT)-based conjugated oligomers, i.e., 2,2'-bi[1]benzothieno[3,2-b][1]benzothiophene (1) and 5,5'-bis([1]benzothieno[3,2-b][1]benzothiophen-2-yl)-2,2'-bithiophene (2), were prepared and characterized. Both oligomers exhibit excellent thermal stability, with 5% weight-loss temperatures (T(L)) above 370 °C; no phase transition was observed before decomposition. The highest occupied molecular orbital (HOMO) levels of 1 and 2 are -5.3 and -4.9 eV, respectively, as measured by ultraviolet photoelectron spectroscopy. Thin-film X-ray diffraction and atomic force microscopy characterizations indicate that both oligomers form highly crystalline films with large domain sizes on octadecyltrimethoxysilane-modified substrates. Organic thin-film transistors with top-contact and bottom-gate geometry based on 1 and 2 exhibited mobilities up to 2.12 cm(2)/V·s for 1 and 1.39 cm(2)/V·s for 2 in an ambient atmosphere. 1-based devices exhibited great air and thermal stabilities, as evidenced by the slight performance degradation after 2 months of storage under ambient conditions and after thermal annealing at temperatures below 250 °C.

Nano-structural, compositional and micro-architectural signs of cortical bone fragility at the superolateral femoral neck in elderly hip fracture patients vs. healthy aged controls

To unravel the origins of decreased bone strength in the superolateral femoral neck, we assessed bone structural features across multiple length scales at this cortical fracture initiating region in postmenopausal women with hip fracture and in aged-matched controls. Our combined methodological approach encompassed atomic force microscopy (AFM) characterization of cortical bone nano-structure, assessment of mineral content/distribution via quantitative backscattered electron imaging (qBEI), measurement of bone material properties by reference point indentation, as well as evaluation of cortical micro-architecture and osteocyte lacunar density. Our findings revealed a wide range of differences between the fracture group and the controls, suggesting a number of detrimental changes at various levels of cortical bone hierarchical organization that may render bone fragile. Namely, mineral crystals at external cortical bone surfaces of the fracture group were larger (65.22nm±41.21nm vs. 36.75nm±18.49nm, p<0.001), and a shift to a higher mineral content and more homogenous mineralization profile as revealed via qBEI were found in the bone matrix of the fracture group. Fracture cases showed nearly 35% higher cortical porosity and showed significantly reduced osteocyte lacunar density compared to controls (226±27 vs. 247±32#/mm2, p=0.05). Along with increased crystal size, a shift towards higher mineralization and a tendency to increased cortical porosity and reduced osteocyte lacunar number delineate that cortical bone of the superolateral femoral neck bears distinct signs of fragility at various levels of its structural organization. These results contribute to the understanding of hierarchical bone structure changes in age-related fragility.

Atomic Force Microscopy Probing of Receptor–Nanoparticle Interactions for Riboflavin Receptor Targeted Gold–Dendrimer Nanocomposites

Riboflavin receptors are overexpressed in malignant cells from certain human breast and prostate cancers, and they constitute a group of potential surface markers important for cancer targeted delivery of therapeutic agents and imaging molecules. Here we report on the fabrication and atomic force microscopy (AFM) characterization of a core–shell nanocomposite consisting of a gold nanoparticle (AuNP) coated with riboflavin receptor-targeting poly(amido amine) dendrimer. We designed this nanocomposite for potential applications such as a cancer targeted imaging material based on its surface plasmon resonance properties conferred by AuNP. We employed AFM as a technique for probing the binding interaction between the nanocomposite and riboflavin binding protein (RfBP) in solution. AFM enabled precise measurement of the AuNP height distribution before (13.5 nm) and after chemisorption of riboflavin-conjugated dendrimer (AuNP–dendrimer; 20.5 nm). Binding of RfBP to the AuNP–dendrimer caused a height increase to 26.7 nm, which decreased to 22.8 nm when coincubated with riboflavin as a competitive ligand, supporting interaction of AuNP–dendrimer and its target protein. In summary, physical determination of size distribution by AFM imaging can serve as a quantitative approach to monitor and characterize the nanoscale interaction between a dendrimer-covered AuNP and target protein molecules in vitro.

Polycrystalline indium films in the percolation threshold regime: time correlation between electric conduction and optical properties with film morphology

Polycrystalline indium films have been deposited at room temperature by electron beam evaporation on amorphous quartz substrates. Once deposited, electrical resistance and specular reflection of the films, for wavelengths between 250 and 920 nm, has been measured in situ. For these as-deposited films, these parameters decrease with time for several minutes until equilibrium is reached. At this state, additional specular and diffuse reflection, and direct transmission measurements were carried out ex situ, as well as atomic force microscope characterizations of the films’ surface. The specular reflection spectra are inverted to obtain the intrinsic scattering and absorption coefficients including their time variations. These parameters are successfully correlated with corresponding volumetric scattering and absorption cross sections of submicron- and nano-sized indium particles calculated from Mie theory. The decrease of electrical resistance with time is explained in terms of an increase of the average size of some of the nano-sized grains due to mass transfer from large submicron-sized grains, a manifestation of an inverse Ostwald ripening process. The decrease of specular reflection is related to the decoupling of the surface plasmons oscillating in neighboring nano-sized particles due to the growth of some of them.

2D Assembly of Palladium Nanoparticles and AFM Characterization

The two-dimensional (2D) assembly of the palladium nanoparticles (Pd NPs) was studied in this work. The cubic Pd NPs were successfully synthesized and assembled on mica and silicon wafer in the dip-coating way. The morphology of the Pd NPs and the topography of the Pd NPs assembly on the substrates were characterized with transmission electron microscopy (TEM) and atomic force microscopy (AFM). In the process of the fabrication, the excess cetyltrimethylammonium bromide (CTAB) was removed with the deposition-redispersion strategy, the UV-vis spectra and zeta-potential of the Pd NPs colloid were measured. It was found that the assembly and AFM characterization of the Pd NPs were affected negatively by the presence of excess CTAB. The hydrophilic property of the substrate is the crucial factor to control the 2D assembly of the Pd NPs. Compared with the washed silicon wafer, mica is ultra-hydrophilic and can attract more Pd NPs.

20pm1-E4 近接シリコン探針とFePd磁歪膜アクチュエータを搭載したデュアルAFMカンチレバー形成と動作特性評価

This paper reports on fabrication and characterization of atomic force microscopy (AFM) dual probe with narrow-gapped dual Si tip and dual cantilever with sputtered Fe_<60>Pd_<40> magneto-strictive film for switching of the cantilevers. A 600 nm-gapped dual Si tip was fabricated in a device layer of a silicon-on-insulator (SOI) wafer through self-align fabrication process based on narrow Si trench etching, refilling, polish-back, and Si crystalline anisotropic etching. After the dual Si tip fabrication. Fe_<60>Pd_<40> film (1μm)/ Si (2μm) dual cantilever was formed by MEMS fabrication process. The cantilevers were orthogonally located. By static magnetic flux of 300 Gauss along a cantilever, it was deflected to 1 μm by positive magneto-striction of the FePd film. In particular, the other cantilever orthogonal to the magnetic flax shows no deflection, resulting in sufficient individual actuation of the dual cantilever for switching.

Effect of end-groups on the photovoltaic property of diphenyl substituted diketopyrrolopyrrole derivatives

In this work, a diphenyl substituted diketopyrrolopyrrole (DPP) and its two derivatives end-capped with fluorine and n-butyl respectively, namely PDPPP, FPDPPPF, and RPDPPPR, are designed and synthesized. The resulting molecules exhibit similar energy structures, i.e. both relatively narrow optical band gaps (1.75–1.79eV) and deep highest occupied molecular orbital (HOMO) energy levels (−5.18 to −5.25eV), implying that all of them are potentially good electron donors for organic solar cells (OSCs). However, three molecules show different photovoltaic performances when they are blended with [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) to fabricate OSCs: the RPDPPPR-based device gives the highest power conversion efficiency (PCE) of 1.59%, whereas the PCEs of PDPPP and FPDPPPF-based OSCs are 0.46% and 0.55%, respectively. Through atomic force microscopy (AFM), X-ray diffraction (XRD) and space charge limited current (SCLC) characterizations, the prominent role of end-groups in the photovoltaic properties of DPP derivatives is disclosed: terminal alkyl chains in RPDPPPR can promote molecular crystallization and lead to the formation of finer phase-separation domains in the blended film, which are in favor of charge generation and transportation in the photovoltaic devices. Thus, RPDPPPR provides the best photovoltaic property among three DPP molecules.

Synthesis and characterization of La0.6Sr0.4Co0.8Fe0.2O3 films for solid oxide fuel cell cathodes

LSCF (La0.6Sr0.4Co0.8Fe0.2O3) thick and thin films were synthesized by using a Pechini method for Solid Oxide Fuel Cell cathode realization to make symmetrical half-cells. A dense LSCF thin film was deposited by spin coating between porous thick LSCF cathode film and gadolinium-doped ceria electrolyte in ceramic form. Atomic force microscopy and scanning electron microscopy characterizations were carried out on these materials to observe the microstructure and measure the thicknesses of the films. DC measurements on LSCF pellets showed that the conductivity of the material is optimized as higher than 100S/cm at temperatures above 400°C. Electrochemical Impedance Spectroscopy measurements at 700°C have shown that, thanks to the interlayer thin LSCF film, the Area Specific Resistance of the cathode has decreased by 27%.

Evolution of surface roughness parameters and microstructure in two-phase nanocrystalline Co–Cu films electrodeposited onto ITO coated glass substrates at different deposition potentials

In the present research, we have studied the effect of deposition potential on the film composition, structural, and morphological properties of the electrodeposited Co–Cu thin films grown onto indium tin oxide coated glass substrates. For this purpose, the properties of the films were analyzed by means of X-ray diffraction, energy dispersive X-ray spectroscopy (EDX), and atomic force microscopy (AFM) characterization techniques. Structural characterizations showed that all of the Co–Cu films consist of hexagonal close-packed (hcp) Co and face-centered cubic (fcc) Cu phases. The hcp Co (002)/fcc Cu (111) peak intensity ratio was found to increase as the deposition potential decreased towards more negative values. An increase in the Co content in the Co–Cu films was observed as the applied deposition potential was made more negative according to EDX analysis. The decrease of the applied deposition potential towards more negative values also induced a decrease in the average crystallite sizes of both Co and Cu particles. AFM study indicated that a granular structure of the electrodeposited Co–Cu films regardless of deposition potential. As the applied deposition potential was made more negative, the surface roughness and particle size decreased considerably. Besides, two additional roughness parameters, surface kurtosis and the surface skewness were also obtained and discussed by means of the obtained results under the study.

AFM, CLSM and EIS characterization of the immobilization of antibodies on indium–tin oxide electrode and their capture of Legionella pneumophila

The microscopic surface molecular structures and properties of monoclonal anti-Legionella pneumophila antibodies on an indium-tin oxide (ITO) electrode surface were studied to elaborate an electrochemical immunosensor for Legionella pneumophila detection. A monoclonal anti-Legionella pneumophila antibody (MAb) has been immobilized onto an ITO electrode via covalent chemical bonds between antibodies amino-group and the ring of (3-Glycidoxypropyl) trimethoxysilane (GPTMS). The functionalization of the immunosensor was characterized by atomic force microscopy (AFM), water contact angle measurement, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in the presence of [Fe(CN)₆](3-/4-) as a redox probe. Specific binding of Legionella pneumophila sgp 1 cells onto the antibody-modified ITO electrode was shown by confocal laser scanning microscopy (CLSM) imaging and EIS. AFM images evidenced the dense and relatively homogeneous morphology on the ITO surface. The formation of the complex epoxysilane-antibodies acting as barriers for the electron transfer between the electrode surface and the redox species in the solution induced a significant increase in the charge transfer resistance (Rct) compared to all the electric elements. A linear relationship between the change in charge transfer resistance (ΔRct=Rct after immunoreactions - Rct control) and the logarithmic concentration value of L. pneumophila was observed in the range of 5 × 10(1)-5 × 10(4) CFU mL(-1) with a limit of detection 5 × 10(1)CFU mL(-1). The present study has demonstrated the successful deposition of an anti-L. pneumophila antibodies on an indium-tin oxide surface, opening its subsequent use as immuno-captor for the specific detection of L. pneumophila in environmental samples.

Biosynthetic support based on dendritic poly(L-lysine) improves human skin fibroblasts attachment

Poly(L-lysine) (PLL) dendrigrafts (DGLs) are arborescent biosynthetic polymers of regular and controlled structures. They have specific properties such as biocompatibility and non-immunogenicity, and their surface density of NH2 functions can be easily modified and therefore appears as a powerful tool for the functionalization of hydrophobic polymers used in the context of tissue engineering. In this study, we evaluated several criteria of human skin fibroblasts when cultured with DGL of generations 2, 3 and 4, with linear PLL polymer as reference. In aqueous phase, DGLs and PLL displayed a similar cytotoxicity towards fibroblasts. Plastic culture plates grafted with DGLs were further characterized as homogeneous surfaces by atomic force microscopy and surface characterization by amino density estimation by colorimetric assay. Proliferation of fibroblasts was increased when cultured onto PLL and DGLs monolayers when compared with crude plates. Cellular adhesion was increased by 20% on DGLs in comparison to PLL. Integrin α5 subunit protein expression level was increased after 48 h of culture on DGLs, in comparison to control or PLL-coated surfaces. The presence of DGLs did not lead to overexpression or activation of matrix metalloproteinases 2 and 9. Finally, fibroblasts adhesion was increased by 40% on poly-(lactic-co-glycolic acid) matrices functionalized with DGLs when compared to PLL. Overall, these features make DGL promising candidates for the surface engineering of biomaterials in tissue engineering.

Three-layered coextruded cast films based on conventional and metallocene poly(ethylene/α-olefin) copolymers

Multilayer films of a conventional linear low-density poly(ethylene/α-octene) (LLDPE) and a metallocene linear low-density poly(ethylene/α-hexene) (mLLDPE) copolymers were produced by cast co-extrusion process. Coextruded films were obtained by varying the position and the relative thicknesses of the two polymers. Mechanical (tensile and impact) tests, permeability, haze and hot tack measurements were carried out on the produced films in order to verify the effect of layer composition and position on the performances of the coextruded samples. Thermal and atomic force microscopy characterizations of the three-layer structures were also performed to correlate the resulting morphology with the film properties. The experiments demonstrated that, at fixed composition, the structures having the mLLDPE copolymer as external layers exhibit generally better mechanical performances and a widening in the sealability temperature window due to a lowering of 5℃ in the seal-initiation temperature, with only a small increase (max 3.5%) in the film haze percentages. The oxygen permeability values do not seem to be significantly affected by the structure composition and layout.

AFM Characterization of Structural Evolution and Roughness of AISI 304 Austenitic Stainless Steel under Severe Deformation by Wavy Rolling

Stainless steels such as ferrritic, austenitic, martensitic and duplex stainless steels are well known for their corrosion resistance to varying extents. Among these, austenitic stainless steels exhibit superior corrosion resistance and better ductility for formability. Therefore, the ability to give simple to intricate shapes in this grade of steel brings their potential for a wide range of applications. However, the meta-stable austenite in AISI 304 is known to undergo a strain induced martensitic (SIM) transformation during conventional rolling at room temperature. This strain induced martensite causes reduction in ductility and limits formability of stainless steel. Therefore, wavy rolling technique was developed to strengthen the stainless steel through microstructural refinement. In the current study, wavy rolling with 1.5 mm amplitude was conducted on 1 mm thick stainless steel sheet to different cycles ranging from 1-4. These rolled samples were characterized by optical and Atomic Force Microscopy (AFM) with resolutions down to the nanolevel. This AFM tool is in a position to bring out the details of grain refinement and topographical roughness emerging from crystalline and microstructural defects like orientation, precipitation, stacking faults, deformation bands, slip lines and shear bands with progress in rolling as referred by the number of rolling cycles here. The structural development is semi-quantitatively related to the degree of deformation and its effect on tensile properties during wavy rolling cycle. Keywords: Structural properties; Roughness; Deformation; Wavy rolling.

Tunable Organogelator from Alkyl-Polypeptide Diblock Prepared by Ring-Opening Polymerization

Three alkyl-polypeptide hybrid amphiphiles were synthesized by the ring-opening polymerization (ROP) of γ-(2-methoxyethoxy)esteryl-l-glutamate N-carboxyanhydride (l-EG1Glu NCA) using alkylamine, i.e. C6H13NH2, C14H29NH2, and C16H33NH2, as initiators. As-prepared alkyl-poly-l-EG1Glu hybrids were found to form clear organogels in several organic solvents at low concentration. FTIR and circular dichroism characterizations suggested that poly-l-EG1Glu formed a predominantly β-sheet conformation, which accounted for the gelation. Transmission electron and atomic force microscopy characterizations revealed that these copolymers formed nanoribbon structures in THF.

Graphene Quantum Dots from Polycyclic Aromatic Hydrocarbon for Bioimaging and Sensing of Fe3+ and Hydrogen Peroxide

An easy approach for large‐scale and low‐cost synthesis of photoluminescent (PL) graphene quantum dots (GQDs) based on the carbonization of commercially available polycyclic aromatic hydrocarbon (PAH) precursors with strong acid and followed by hydrothermal reduction with hydrazine hydrate is reported. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) characterizations indicate that the size and height of GQDs are in the range of 5–10 nm and 0.5–2.5 nm, respectively. PAH, which has more benzene rings, generally forms GQDs with relatively larger size. The GQDs show high water solubility, tunable photoluminescence, low cytotoxicity, and good optical stability, which makes them promising fluorescent probes for cellular imaging. In addition, the fluorescence of GQDs shows a sensitive and selective quenching effect to Fe3+ with a detection limit of 5 × 10−9m. By combination with the Fe2+/Fe3+ redox couple, the PL GQDs are able to detect oxidant, using H2O2 as an example. This study opens up new opportunities to make full use of GQDs because of their facile availability, cost‐effective productivity, and robust functionality.

Mechanistic aspects of electrodeposition of Ni–Co–SiC composite nano-coating on carbon steel

The nucleation and early-stage growth mechanism and kinetics of electrodeposited Ni–Co–SiC composite coating on carbon steel was investigated by cyclic voltammetry, current–time transient measurements and atomic force microscopy characterization. The conventional Guglielmi's model for metal-inert particle co-deposition was modified to consider the effect of the bath electrolyte hydrodynamics on amount of nano-particles deposited in the coating. It is determined that the nucleation and early-stage growth of the coating depends on depositing overpotential. At low cathodic overpotentials, it is between an instantaneous and progressive mechanism; while at high overpotentials, it follows the instantaneous mechanism. Addition of SiC nano-particles in the bath electrolyte reduces the electrodepositing efficiency by inhibiting nucleation and growth of metallic coating. An empirical model is developed to estimate the amount of nano-particles contained in Ni–Co–SiC composite coating during pulse electrodeposition.

AFM and TEM characterization of siRNAs lipoplexes: A combinatory tools to predict the efficacy of complexation

This work aims to evaluate the effects of two different surface modification strategies: PEG conventional coupling (PEG-Lpx) and postpegylation technique (postPEG-Lpx), on lipoplexes obtained between liposomes and siRNAs. Photon correlation spectroscopy (PCS) and gel electrophoreses (as conventional techniques), and atomic force microscopy (AFM) and transmission electron microscopy (TEM) (proposed to complete the assessments of lipoplexes) were employed to investigate reorganization, structure, qualitative–quantitative stabilization of siRNAs, and PEG covering of lipoplexes. The results suggested that postPEG-Lpx exhibited high level of homogeneity with a mean diameter (Z-Average) of about 320nm, low tendency to aggregation (a polydispersion index, PDI, close to 0.06) and high loading efficiency (E.E. 82%). Otherwise, PEG-Lpx showed a Z-Average greater than 1μm, high aggregation rate (PDI>0.3) and a low E.E. (10%). The definition of the architecture by using optimized microscopical procedure allows to suggest postpegylation technique as a promising technology for the preparation of applicable complexes. This formulation strategy lead to a stable siRNA condensation and full compaction of gene material, moreover the PEG coverage generated a homogeneous hydrated surface, well described by the “phase” AFM approach.The microscopical techniques can provide a predictive and useful tool to use in the preformulative technological studies of complicated gene complexes.