Bitumen morphologies by phase-detection atomic force microscopy

Bitumen is a complex mixture of hydrocarbons for which microstructural knowledge is incomplete. In an effort to detail this microstructure, 13 bitumens were analysed by phase‐detection atomic force microscopy. Based on morphology, the bitumens could be classified into three distinct groups. One group showed fine domains down to 0.1 µm, another showed domains of about 1 µm, and a third group showed up to four different domains or phases of different sizes and shapes. No correlation was found between the atomic force microscopy morphology and the composition based on asphaltenes, polar aromatics, naphthene aromatics and saturates. A high correlation was found between the area of the ‘bee‐like’ structures and the vanadium and nickel content in bitumen, and between the atomic force microscopy groups and the average size of molecular planes made of fused aromatics. The morphology and the molecular arrangements in bitumen thus appear to be partly governed by the molecular planes and the polarity defined by metallic cations.     

纳米压痕硬度尺寸效应分析及其试验研究

针对材料纳米压痕硬度的压痕尺寸效应(Indentation size effect,ISE),利用纳米压痕技术测得单晶铝和单晶硅的载荷-压深曲线,获得最大载荷和最大压深,并结合原子力显微镜,获得压痕的三维形貌,计算出压痕的真实残余面积。根据最大压深和残余面积提出了一个新的模型——残余面积最大压深模型,此模型能更好地理解和描述材料硬度的压痕尺寸效应,并与其他几种典型的理论和模型进行了比较和分析。     

A comparative study of colloidal particles as imaging standards for microscopy

Colloidal particles have long been used as imaging standards for electron microscopy and, more recently, for scanning probe microscopy. We have analysed gold, polystyrene and silica colloidal particles by both transmission electron microscopy and atomic/scanning force microscopy in an attempt to determine if any can be truly used as 'standards' of shape and/or size. From the transmission electron micrographs, we have obtained precise information of the particle circumference and mean diameter. By comparing the ratio of these to the value for π, we obtained a measure of the sphericity of the particles. We have also shadowed the particles with metal at a known angle and have analysed the shadow length to determine the particles' heights and shapes. The height information obtained from the shadow length data collected from the transmission electron micrographs was then compared with that obtained by atomic/scanning force microscopy. Our results show that cleaned (washed) silica or polystyrene particles closely approach true spheres. In the case of gold particles, height data obtained from shadow lengths analysed in transmission electron micrographs show good agreement with that obtained from the atomic/scanning force microscopy images even without washing. However, the gold particles often deviate from sphericity. Based upon both the shape and the physical properties of the colloidal particles, silica would be the best choice as a standard. We also have noticed that metal shadowing of colloidal particle samples used for atomic/scanning force microscopy offers an advantage which we call a 'nanoscale metric' visible in the image directly at each particle site. This information can be important if one wishes to use samples prepared from colloidal particles simply and reliably to determine the probe shape for scanning probe microscopy from image deconvolution/restoration methods or as a calibration sample.     

Theoretical analysis of the atomic force microscopy characterization of columnar thin films

In this paper, the theoretical analysis of the influence of finite linear dimensions of an atomic force microscope tip on profiles of the upper boundaries of columnar thin films and their statistical quantities is performed. This analysis is based on a numerical evaluation of the main statistical quantities, i.e. the standard deviations of the heights and slopes, one-dimensional distributions of the probability density of heights and slopes and power spectral density function, corresponding to a simulated columnar structure of the thin films. It is shown that the strongest misrepresentation of the measured profiles of the upper boundaries of the columnar films originates in the cases when the linear dimensions of the columns are smaller or comparable with the linear dimensions of the tip. Further, it is shown that using a surface reconstruction procedure one can correct (improve) the boundary profiles and their statistical quantities partially. The results of this analysis enable us to perform rough estimation of the errors achieved within atomic force microscopy studies of the real columnar thin films. Moreover, these results allow to estimate the corrections of the statistical quantities mentioned above to be obtained using the surface reconstruction.     

Mechanical Property Investigation of Soft Materials by Cantilever‐Based Optical Interfacial Force Microscopy

Cantilever‐based optical interfacial force microscopy (COIFM) was applied to the investigation of the mechanical properties of soft materials to avoid the double‐spring effect and snap‐to‐contact problem associated with atomic force microscopy (AFM). When a force was measured as a function of distance between an oxidized silicon probe and the surface of a soft hydrocarbon film, it increases nonlinearly in the lower force region below ∼10 nN, following the Herzian model with the elastic modulus of ∼50 MPa. Above ∼10 nN, it increases linearly with a small oscillatory sawtooth pattern with amplitude 1–2 nN. The pattern suggests the possible existence of the layered structure within the film. When its internal part of the film was exposed to the probe, the force depends on the distance linearly with an adhesive force of −20 nN. This linear dependence suggests that the adhesive internal material behaved like a linear spring with a spring constant of ∼1 N/m. Constant‐force images taken in the repulsive and attractive contact regimes revealed additional features that were not observed in the images taken in the noncontact regime. At some locations, however, contrast inversions were observed between the two contact regimes while the average roughness remained constant. The result suggests that some embedded materials had spring constants different from those of the surrounding material. This study demonstrated that the COIFM is capable of imaging mechanical properties of local structures such as small impurities and domains at the nanometer scale, which is a formidable challenge with conventional AFM methods. SCANNING 35:59‐67, 2013. © 2012 Wiley Periodicals, Inc.     

Observation of recording pits on phase-change film using a scanning probe microscope

A phase-change film is a key material for optical data storage media such as rewritable compact disks (CD-RW) and digital versatile disk random access memory (DVD-RAM). Data pits are recorded as differences in crystal state (crystallized state vs. amorphous state) on phase-change film. It is very important to distinguish the crystal state difference in a very small area for material research of phase-change film. Measuring size and shape of recorded data pits is also very important for the development to achieve good data reliability and high data density of optical data storage media. The crystal state difference in very small areas of phase-change film is successfully observed by Kelvin probe force microscopy (KFM) and scanning near-field optical/atomic force microscopy (SNOAM). The advantage of KFM and SNOAM for measuring physical property differences in a very small area is demonstrated.     

Characterization of spatial patterns of dental restorative nanocomposites

The aim of this study was to provide important insights into the effects of four different dental polishing protocols (one single‐step and one multi‐step either followed or not by diamond paste polishing) on the 3D surface morphology of two representative dental resin‐based nanocomposites (a nanofilled and a nanohybrid composite) by means of digital image analysis and processing techniques. The 3D surface morphology was investigated by atomic force microscopy. Segmentation, statistics of height distributions (described by statistical parameters, according to ISO 25178‐2: 2012) and Minkowski functionals were applied to the images to characterize the spatial patterns of analyzed samples at micrometer scale. The nanofilled composite had significantly lower values of height parameters in comparison with nanohybrid one. Multi‐step polishing protocol generated a statistically significant smoother finish for both tested materials, than one‐step polishing protocol, even when it was followed by diamond paste polishing. Diamond paste polishing generated a statistically significant smoother surface of tested samples. This suite of surface analysis tools is important in the research and manufacture of these dental resin‐based nanocomposites, where material surfaces have a key role in the functionality of objects.     

Kinetics of adhesion on a viscoelastic sample by force microscopy

Indentation of the tip of an atomic force microscope is carried out under purely adhesive force, on a sample that is in a viscoelastic state. A characteristic size of the contact area is also measured by recording the tangential force while a small lateral modulation of the sample position is applied. Both the contact size and the penetration depth of the tip follow the compliance function of the material. It is shown that the kinetics of the adhesion can be described as the adhesive equilibrium of the tip on an elastic material whose compliance is the instantaneous value of the compliance function of the viscoelastic material. Implications for the analysis of the force–distance curves are discussed.     

Fractal features and surface micromorphology of diamond nanocrystals

This paper analyses the three‐dimensional (3‐D) surface texture of growing diamond nanocrystals on Au thin films as catalyst on p‐type Si substrate using hot filament chemical vapour deposition (HFCVD). Rutherford backscattering spectrometry (RBS), atomic force microscopy (AFM), Raman, X‐ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were applied also to characterize the 3‐D surface texture data in connection with the statistical, and fractal analyses. This type of 3‐D morphology allows a deeper understanding of structure/property relationships and surface defects in prepared samples. Our results indicate a promising way for preparing high‐quality diamond nanocrystals on Au thin films as catalyst on p‐type Si substrate via HFCVD method.     

Aspects of latex particle size control for improved water blush resistance

Latex films have a tendency to "blush" when exposed to water. The swelling of trapped hydrophilic material, which results in pockets with different refractive indices, is proposed as a possible model for blushing. A pressure-sensitive latex was developed on the basis of this model. The blush was improved by the choice of the surfactant and control of the particle diameter. The resulting latex has an unusual particle growth behavior during polymerization. The particle size distribution (PSD) was characterized by dynamic light scattering (DLS), electron microscopy (SEM/TEM) and atomic force microscopy (AFM). The data are in a good agreement with our proposed growth model.     

Application of atomic force microscopy to the study of natural and model soil particles

The structure and surface chemistry of soil particles has extensive impact on many bulk scale properties and processes of soil systems and consequently the environments that they support. There are a number of physiochemical mechanisms that operate at the nanoscale which affect the soil's capability to maintain native vegetation and crops; this includes soil hydrophobicity and the soil's capacity to hold water and nutrients. The present study used atomic force microscopy in a novel approach to provide unique insight into the nanoscale properties of natural soil particles that control the physiochemical interaction of material within the soil column. There have been few atomic force microscopy studies of soil, perhaps a reflection of the heterogeneous nature of the system. The present study adopted an imaging and force measurement research strategy that accounted for the heterogeneity and used model systems to aid interpretation. The surface roughness of natural soil particles increased with depth in the soil column a consequence of the attachment of organic material within the crevices of the soil particles. The roughness root mean square calculated from ten 25 microm(2) images for five different soil particles from a Netherlands soil was 53.0 nm, 68.0 nm, 92.2 nm and 106.4 nm for the respective soil depths of 0-10 cm, 10-20 cm, 20-30 cm and 30-40 cm. A novel analysis method of atomic force microscopy phase images based on phase angle distribution across a surface was used to interpret the nanoscale distribution of organic material attached to natural and model soil particles. Phase angle distributions obtained from phase images of model surfaces were found to be bimodal, indicating multiple layers of material, which changed with the concentration of adsorbed humic acid. Phase angle distributions obtained from phase images of natural soil particles indicated a trend of decreasing surface coverage with increasing depth in the soil column. This was consistent with previous macroscopic determination of the proportions of organic material chemically extracted from bulk samples of the soils from which specimen particles were drawn. Interaction forces were measured between atomic force microscopy cantilever tips (Si(3)N(4)) and natural soil and model surfaces. Adhesion forces at humic acid free specimen surfaces (Av. 20.0 nN), which are primarily hydrophilic and whose interactions are subject to a significant contribution from the capillary forces, were found to be larger than those of specimen surfaces with adsorbed humic acid (Av. 6.5 nN). This suggests that adsorbed humic acid increased surface hydrophobicity. The magnitude and distribution of adhesion forces between atomic force microscopy tips and the natural particle surfaces was affected by both local surface roughness and the presence of adsorbed organic material. The present study has correlated nanoscale measurements with established macroscale methods of soil study. Thus, the research demonstrates that atomic force microscopy is an important addition to soil science that permits a multiscale analysis of the multifactorial phenomena of soil hydrophobicity and wetting.     

Direct probing of solvent-induced charge degradation in polypropylene electret fibres via electrostatic force microscopy

Electrostatic force microscopy was used to directly probe solvent‐induced charge degradation in electret filter media. Electrostatic force gradient images of individual polypropylene electret fibres were used to quantify the extent of charge degradation caused by the immersion of the fibres into isopropanol. Electrostatic force gradient images were obtained by monitoring the shifts in phase and frequency between the oscillations of the biased atomic force microscopy (AFM) cantilever and those of the piezoelectric driver. Electrostatic force microscopy measurements were performed using non‐contact scans at a constant tip‐sample separation of 75 nm with varied bias voltages applied to the cantilever. Mathematical expressions, based on the capacitance of the tip‐sample system, were used to model the phase and frequency shifts as functions of the applied bias voltage to the tip and the offset voltage due to the fibre's charge. Quantitative agreement between the experimental data and the simplified model was observed.     

Transmission electron microscopy analysis of phase separation in GaInAsSb films grown on GaSb substrate

The GaSb‐based quaternary alloys are a good choice for thermophotovoltaic applications. The thermophotovoltaic cell converts infrared radiation to electricity, using the same principles as photovoltaic devices. The aim of the present work was the microstructural study of such an alloy, namely Ga_0.84In_0.16As_0.12Sb_0.88. A thin film of the material was grown by metal organic vapour phase epitaxy on a (100)α→[111]B (α = 2°, 4°, 6°) GaSb substrate. The GaInAsSb alloy has an appropriate band gap, but suffers from a phase separation consisting of GaAs‐rich and InSb‐rich regions that is disadvantageous for cell efficiency. In this work, we employed a morphological approach to phase separation, with the use of conventional transmission electron microscopy and atomic force microscopy. The phase separation occurs in two different orientations: parallel to the growth direction (vertical) and inclined (lateral). After application of fast Fourier transformation filtering, the vertical periodicity was found to be λ = 5 nm for the pair (black and white) of layers independently of the cut‐off angle, whereas the lateral periodicity was related to it.     

Near-field imaging of surface plasmon on gold nano-dots fabricated by scanning probe lithography

We obtained scanning near‐field optical microscopy images to study the excitation of surface plasmons on metallic dots fabricated using scanning probe lithography. Gold nano‐dots were fabricated by applying electric voltages to conducting probes installed in an atomic force microscope using the mechanism of field‐induced diffusion and nano‐oxidation plus Au‐coating. High spatial resolution of scanning near‐field optical microscopy revealed a ‘bifold’ pattern of surface plasmon mode on fabricated Au dots in the polarization direction of incident light. We found that scanning near‐field optical microscopy imaging combined with scanning probe lithography is able to provide a systematic study of surface plasmon excitation on nano‐metallic structures.     

In vivo assessment of the corrosion of nickel–titanium orthodontic archwires by using scanning electron microscopy and atomic force microscopy

This study was undertaken to assess in vivo the corrosion in two commercial nickel–titanium (NiTi) orthodontic archwires removed from the oral cavity of patients using fluoride mouthwashes. Five volunteers took part in this study on the corrosion behavior of two brands of NiTi archwires (3M and AO (brand of archwire)) during use of two mouthwashes with neutral sodium fluoride 1.1%, one with acidulated fluoride 1.1%, and one with placebo and a control group. Each patient used one mouthwash in three different periods of time for 1 min a day for 30 days. The archwires were assessed with scanning electron microscopy and atomic force microscopy for qualitative and quantitative analysis. The values obtained with atomic force microscopy (AFM) were submitted to normality test, two‐way analysis of variance, and Tukey's test at a significance level of 5%. The AFM images showed a gradual qualitative increase in the roughness of both types of wire between the treatments: control < placebo < neutral fluoride < acidulated fluoride. The arithmetic average of the roughness and root mean square of the roughness were similar. As for 3M archwires, only the acidulated fluoride group differed statistically from the others. As for AO archwires, the control and placebo groups did not differ from each other, but differed from the other fluoride treatments. The group using neutral fluoride also differed significantly from the acidulated fluoride group. 3M archwires were not affected by daily oral challenges. AO archwires were not affected by daily oral challenges either; their association with fluoride, either neutral or acidulated, increased their roughness.     

Error analysis and regression mode of the V‐grooved sample in the atomic force microscope simulation measurement mode by the molecular mechanics

Based on the molecular mechanics, this study uses the two‐body potential energy function to construct a trapezoidal cantilever nano‐scale simulation measurement model of contact mode atomic force microscopy (AFM) under the constant force mode to simulate the measurement the nano‐scale V‐grooved standard sample. We investigate the error of offset distance of the cross‐section profile when using the probes with different trapezoidal cantilever probe tip radii (9.5, 8.5, and 7.5 Å) to scan the peak of the V‐grooved standard sample being reduced to one‐tenth (1/10) of its size, and use the offset error to inversely find out the regression equation. We analyze how the tip apex as well as the profile of the tip edge oblique angle and the oblique edge angle affects the offset distance. Furthermore, a probe with a larger radius of 9.5 nm is used to simulate and measure the offset error of scan curve, and acquire the regression equation. By the conversion proportion coefficient of size (ω), and revising the size‐reduced regression equation during the small size scale, a revised regression equation of a larger size scale can be acquired. The error is then reduced, further enhancing the accuracy of the AFM scanning and measurement. SCANNING 31: 147–159, 2009. © 2009 Wiley Periodicals, Inc.     

Detection of Brucella abortus by a platform functionalized with protein A and specific antibodies IgG

Oriented immobilization of antibodies on a sensor surface is critical for enhancing both the antigen‐binding capacity and the sensitivity of immunosensors. In this study, we describe a strategy to adsorb immunoglobulin G (IgG) anti‐Brucella antibodies onto a silicon surface, oriented by protein A obtained from Staphylococcus aureus (SpA). X‐ray photoelectron spectroscopy and atomic force microscopy were used to characterize topographically, morphologically, and chemical changes of the sensor functionalization. The activity of the biosensor was assessed by confocal microscopy, scanning electronic microscopy, and bacteria capture assays (BCA). According to the BCA, the efficiency of Brucella abortus detection with the SpA‐IgG anti Brucella biosensor was three‐fold higher than that of the random orientated IgG anti Brucella biosensor. The limit of detection was 1 × 10⁶ CFU/ml. These data show that the orientation of antibodies immobilization is crucial to developing immunosensors for bacterial antigen detection as Brucella spp and improve its sensibility level. Functionalization with protein A increases Brucella detection by an antibody‐coated surface. Functionalized silicon surface for Brucella detection was characterized by atomic force microscopy, X‐ray photoelectron spectroscopy and confocal microscopy.     

Atomic force microscopy imaging of actin cortical cytoskeleton of Xenopus laevis oocyte

In this study we report an atomic force microscopy (AFM) investigation of the actin cortical cytoskeleton of Xenopus laevis oocytes. Samples consisted of inside‐out orientated plasma membrane patches of X. laevis oocytes with overhanging cytoplasmic material. They were spread on a freshly cleaved mica surface, subsequently treated with Triton X‐100 detergent and chemically fixed. The presence of actin fibres in oocyte patches was proved by fluorescence microscopy imaging. Contact mode AFM imaging was performed in air in constant force conditions. Reproducible high‐resolution AFM images of a filamentous structure were obtained. The filamentous structure was identified as an actin cortical cytoskeleton, investigating its disaggregation induced by cytochalasin D treatment. The thinnest fibres showed a height of 7 nm in accordance with the diameter of a single actin microfilament. The results suggest that AFM imaging can be used for the high‐resolution study of the actin cortical cytoskeleton of the X. laevis oocyte and its modifications mediated by the action of drugs and toxins.     

Grain size distribution analysis in polycrystalline LiF thin films by mathematical morphology techniques on AFM images and X-ray diffraction data

The influence of the deposition temperature on the grain size of polycrystalline lithium fluoride (LiF) thin films is studied using a mathematical morphology method. On atomic force microscopy images of the LiF surface, the grain sizes and shapes are determined by applying the watershed technique, together with a shape factor algorithm. Also, the domain size of the film structure, determined by an X-ray diffraction data analysis, is compared and correlated with the mean grain size as a function of the deposition temperature. In both cases a linear increase with temperature and a very good agreement among the two structural parameters (grain and domain size) was found.