Tapping Mode Atomic Force Microscopy Research Articles

Effective Transport Tunnels Achieved by 1,2,4,5-Tetrazine-Induced Intermolecular C-H...N Interaction and Anion Radicals for Stable ReRAM Performance.

The D-A structured small-molecule-based resistive random-access memory (ReRAM) device has been well-researched in the last decade, and the switching mechanism was mainly induced by the intramolecular/intermolecular charge transfer processes from the donors to the acceptors. However, in the previous work, some small molecules with pristine electron acceptors in the backbone could still show the typical memory behaviors, of which the switching mechanism is still ambiguous. In this work, two 1,2,4,5-tetrazine based n-type small-molecular isomers, 2-DPTZ and 4-DPTZ, with the same electron acceptor, 1,2,4,5-tetrazine and pyridine, are chosen to investigate the isomeric effects on molecular packing, switching mechanism, and memory performance. Because of the abundant nitrogen atoms with a localized lone pair of electrons in the sp2 orbital, 2-DPTZ and 4-DPTZ compounds could self-assemble into a long-range ordered molecular packing through intermolecular C-H...N interactions, affording effective transporting tunnels for charge-carrier transport. As expected, the sandwich-structured ITO/2-DPTZ or 4-DPTZ/Al memory devices both showed binary memory characteristics, with 2-DPTZ based memory devices showing the write once read many times (WORM) memory behavior and 4-DPTZ based memory devices having the negative differential resistance (NDR) memory performance. These distinct ReRAM properties arose from the different morphologies of 2-DPTZ and 4-DPTZ films that were induced by the different packing styles between the adjacent molecules, as confirmed by X-ray diffraction (XRD) and tapping-mode atomic force microscopy (AFM) height images. Most importantly, the switching mechanism was thought to be attributed to the injected electrons that reduced the neutral molecules of 2-DPTZ and 4-DPTZ to their corresponding anion radicals. Thus, this present work helps us better understand the conducting mechanism of small molecules with pristine electron acceptors in the backbone and provides a supplementary guideline for designing multilevel small molecules to match the structure-stacking-property relationship.

Adsorption mechanism and flotation behavior of ammonium salt of N-Nitroso-N-phenylhydroxyamine on malachite mineral

The adsorption mechanism between malachite and a specific organic ligand of the ammonium salt of N-Nitroso-N-phenylhydroxyamine (NBH) with the NH4+ group and nitrosamine polar group has been studied. The tapping mode atomic force microscopy (AFM) imaging illustrated that irregular protrusions were covered on malachite surface at the nanoscale when malachite was treated in NBH solutions under alkaline conditions at pH 9.5. It indicated that the NBH displayed an excellent affinity to malachite, and the adsorption density was correlated with the concentration of NBH. Based on copper ammine theory and the results of Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), the intermediate transition process of the interaction between malachite and NBH can be summarized as activation, diffusion and reduction, combination, and redeposition. The copper ions removed from the ammonia-activated malachite surface combined with the NBH resonating structures to form the bidentate and monodentate complexes. Eventually, those microscopic analyses are confirmed by the macroscopic flotation test. The flotation recovery illustrated the formation of ligand–Cu complex strengthened the hydrophobicity of malachite in a three-phase system. Therefore, it is feasible using NBH as collector to selectively separate malachite from gangue minerals in flotation experiments.

Theoretical and experimental study of phase optimization of tapping mode atomic force microscope

Phase image in tapping-mode atomic force microscope (TM-AFM) results from various dissipations in a microcantilever system. The phases mainly reflect the tip-sample contact dissipations which allow the nanoscale characteristics to be distinguished from each other. In this work, two factors affecting the phase and phase contrast are analyzed. It is concluded from the theoretical and experimental results that the phases and phase contrasts in the TM-AFM are related to the excitation frequency and energy dissipation of the system. For a two-component blend, it is theoretically and experimentally proven that there exists an optimal excitation frequency for maximizing the phase contrast. Therefore, selecting the optimal excitation frequency can potentially improve the phase contrast results. In addition, only the key dissipation between the tip and sample is found to accurately reflect the sample properties. Meanwhile, the background dissipation can potentially reduce the contrasts of the phase images and even mask or distort the effective information in the phase images. In order to address the aforementioned issues, a self-excited method is adopted in this study in order to eliminate the effects of the background dissipation on the phases. Subsequently, the real phase information of the samples is successfully obtained. It is shown in this study that the eliminating of the background dissipation can effectively improve the phase contrast results and the real phase information of the samples is accurately reflected. These results are of great significance in optimizing the phases of two-component samples and multi-component samples in atomic force microscope.

Super-resolution mid-infrared spectro-microscopy of biological applications through tapping mode and peak force tapping mode atomic force microscope.

Small biomolecules at the subcellular level are building blocks for the manifestation of complex biological activities. However, non-intrusive in situ investigation of biological systems has been long daunted by the low spatial resolution and poor sensitivity of conventional light microscopies. Traditional infrared (IR) spectro-microscopy can enable label-free visualization of chemical bonds without extrinsic labeling but is still bound by Abbe's diffraction limit. This review article introduces a way to bypass the optical diffraction limit and improve the sensitivity for mid-IR methods - using tip-enhanced light nearfield in atomic force microscopy (AFM) operated in tapping and peak force tapping modes. Working principles of well-established scattering-type scanning near-field optical microscopy (s-SNOM) and two relatively new techniques, namely, photo-induced force microscopy (PiFM) and peak force infrared (PFIR) microscopy, will be briefly presented. With∼10-20nm spatial resolution and monolayer sensitivity, their recent applications in revealing nanoscale chemical heterogeneities in a wide range of biological systems, including biomolecules, cells, tissues, and biomaterials, will be reviewed and discussed. We also envision several future improvements of AFM-based tapping and peak force tapping mode nano-IR methods that permit them to better serve as a versatile platform for uncovering biological mechanisms at the fundamental level.

Force‐Induced Molecular Isomerization for the Construction of Multicolor Luminescent Segmented Molecular Crystals

AbstractMulticolor luminescent segmented materials have attracted tremendous research interest due to their potential applications as barcoding materials in information security and anti‐counterfeiting. Although much effort has been devoted to the preparation of photonic barcodes based on different light‐emitting materials, the rational design of barcoding materials with well‐controlled emission color and length at desired position remains a challenge. Here, a novel strategy to fabricate multicolor luminescent segmented 1D molecular crystals is reported by manipulating the molecular conformation and intermolecular interactions of the mechanochromic crystals, which are assembled from a rationally designed twisting conjugated molecule. The emission color of these mechanochromic crystals changes from green to orange with the mechanism of synergy effect of force‐induced molecular isomerization from trans to cis state and molecular packing changes from cross to parallel, which is revealed by single crystal X‐ray diffraction. Multicolor luminescent segmented 1D microribbons are fabricated by applying precisely controlled forces by tapping mode atomic force microscope, which shows the encoding capability. These findings provide a new method that allows the controllable fabrication of segmented materials with tunable emission color and length at desired position toward barcoding applications.

Improved Self-Assembly of P3HT with Pyrene-Functionalized Methacrylates.

A block copolymer with discotic liquid crystalline behavior was synthesized using Grignard metathesis polymerization (GRIM) and initiators for continuous activator regeneration atom transfer radical polymerization (ICAR-ATRP). A novel discotic liquid crystalline mesogen, 6-(pyren-1-yloxy)hexyl methacrylate (PyMA), comprises a block that is attached to regioregular poly(3-hexylthiophene) (rr-P3HT) generated by GRIM and subjected to end-group modification. Due to the continuous regeneration of Cu+ in the reaction mixture in ICAR-ATRP compared to conventional methods, the synthesis was successfully performed with less catalyst. The purity and yield of the final product are increased by eliminating rigorous post-synthesis purification. Stacked pyrene units have contributed to the enhanced long-range π–π interactions and aligning of the P3HT block as observed in thin-film X-ray diffraction (XRD). Furthermore, field-effect mobilities in the order of 10–2 cm2 V–1 s–1 in bottom-gate, top-contact organic field-effect transistors (OFETs) suggest an enhancement in charge transport due to the discotic electron-rich pyrene units that help mitigate the insulating effect of the methacrylate backbone. The formation of uniform microdomains of P3HT-b-poly(PyMA) observed with tapping mode atomic force microscopy (TMAFM) on the channel regions of OFETs indicates the unique packing of the block copolymer in comparison to pristine P3HT. Thermotropic properties of the novel discotic mesogen in the presence and absence of P3HT were observed with both the poly(3-hexylthiophene)-b-poly(6-(pyren-1-yloxy)hexyl methacrylate) (P3HT-b-poly(PyMA)) block copolymer and poly(6-(pyren-1-yloxy)hexyl methacrylate) (poly(PyMA)) homopolymer using polarized optical microscopy (POM) and differential scanning calorimetry (DSC).

Sample trapped charge induced signals in tapping-mode atom ic force microscopy

AFM (Atomic force microscope) has been used to measure the surface topography and electrochemical properties of the sample by the interaction between the tip on the cantilever and the sample. However, when there is a charge in the sample, an induced charge will be generated inside the tip, which will generate a new attractive force between the tip and the sample and reduce the amplitude of the tip. We found that the average amplitude of the tip decreased by about 1 nm in tapping mode AFM. As the amplitude decreasing, AFM keeps the amplitude constant by adjusting z0 with negative feedback in tapping mode. So, the average charge density will affect the measurement of surface topography.

Ultrastructural features of the corneal epithelium with micromolecular compound J2 in the corneal allograft of rats using atomic force microscopy

Objective: To study the ultrastructural features of the corneal epithelium in the corneal allograft of rats with micromolecular compound J2. Methods: An experimental study. Primarily cultured corneal epithelial cells of rats were used. Mononuclear cells (MNCs) by density gradient centrifugation were assigned into the experimental group [MNCs (2 ml)+corneal epithelial cells+J2], control group [MNCs (2 ml)+corneal epithelial cells] and blank group (corneal epithelial cells). Quantity of CD80 expression was obtained by flow cytometry after coculture. Amplitude and height images were obtained by tapping mode atomic force microscopy (AFM) with a scan rate of 2 Hz and an integral gain of 0.3 to 0.5. Statistical analysis of Ra, Rq, Rvm and Rt was performed using the single-factor analysis of variance, and P value was calculated. Results: There were obvious differences in the ultrastructure measured by AFM among groups. Ra was 86.75±12.60 in the experimental group, 120.23±12.11 in the control group, and 61.94±10.62 in the blank group (F=306.92, P<0.01). Rq was 102.53±9.45, 138.30±10.13, and 91.96±7.25, respectively, in the three groups (F=361.85, P<0.01). Rvm was -42.21±14.22, -67.36±10.89, and -32.18±19.01, respectively (F=72.22, P<0.01). Rt was 437.32±15.66, 495.32±13.96, and 339.92±11.22, respectively (F=1634.26, P<0.01). The one way analysis of variance showed significant differences in these parameters among groups. Conclusions: Corneal epithelial cells of rats activated by MNCs had higher CD80 expression, but the expression became decreased with micromolecular compound J2. The ultrastructure of the corneal epithelium became coarser after MNCs activation, and the number of protrusions increased significantly. The ultrastructural changes were alleviated by J2.(Chin J Ophthalmol, 2021, 57: 608-613).

An Insight into Amorphous Shear Band in Magnetorheological Solid by Atomic Force Microscope.

Micro mechanism consideration is critical for gaining a thorough understanding of amorphous shear band behavior in magnetorheological (MR) solids, particularly those with viscoelastic matrices. Heretofore, the characteristics of shear bands in terms of formation, physical evolution, and response to stress distribution at the localized region have gone largely unnoticed and unexplored. Notwithstanding these limitations, atomic force microscopy (AFM) has been used to explore the nature of shear band deformation in MR materials during stress relaxation. Stress relaxation at a constant low strain of 0.01% and an oscillatory shear of defined test duration played a major role in the creation of the shear band. In this analysis, the localized area of the study defined shear bands as varying in size and dominantly deformed in the matrix with no evidence of inhibition by embedded carbonyl iron particles (CIPs). The association between the shear band and the adjacent zone was further studied using in-phase imaging of AFM tapping mode and demonstrated the presence of localized affected zone around the shear band. Taken together, the results provide important insights into the proposed shear band deformation zone (SBDZ). This study sheds a contemporary light on the contentious issue of amorphous shear band deformation behavior and makes several contributions to the current literature.

Direct Visualization and Manipulation of Stacking Orders in Few-Layer Graphene by Dynamic Atomic Force Microscopy.

Stacking order plays a central role in governing a wide range of properties in layered two-dimensional materials. In the case of few-layer graphene, there are two common stacking configurations: ABA and ABC stacking, which have been proven to exhibit dramatically different electronic properties. However, the controllable characterization and manipulation between them remain a great challenge. Here, we report that ABA- and ABC-stacked domains can be directly visualized in phase imaging by tapping-mode atomic force microscopy with much higher spatial resolution than conventional optical spectroscopy. The contrasting phase is caused by the different energy dissipation by the tip-sample interaction. We further demonstrate controllable manipulation on the ABA/ABC domain walls by means of propagating stress transverse waves generated by the tapping of tip. Our results offer a reliable strategy for direct imaging and precise control of the atomic structures in few-layer graphene, which can be extended to other two-dimensional materials.

Integrated Tapping Mode Kelvin Probe Force Microscopy with Photoinduced Force Microscopy for Correlative Chemical and Surface Potential Mapping.

Kelvin probe force microscopy (KPFM) is a popular technique for mapping the surface potential at the nanoscale through measurement of the Coulombic force between an atomic force microscopy (AFM) tip and sample. The lateral resolution of conventional KPFM variants is limited to between ≈35 and 100nm in ambient conditions due to the long-range nature of the Coulombic force. In this article, a novel way of generating the Coulombic force in tapping mode KPFM without the need for an external AC driving voltage is presented. A field-effect transistor (FET) is used to directly switch the electrical connectivity of the tip and sample on and off periodically. The resulting Coulomb force induced by Fermi level alignment of the tip and sample results in a detectable change of the cantilever oscillation at the FET-switching frequency. The resulting FET-switched KPFM delivers a spatial resolution of ≈25nm and inherits the high operational speed of the AFM tapping mode. Moreover, the FET-switched KPFM is integrated with photoinduced force microscopy (PiFM), enabling simultaneous acquisitions of high spatial resolution chemical distributions and surface potential maps. The integrated FET-switched KPFM with PiFM is expected to facilitate characterizations of nanoscale electrical properties of photoactive materials, semiconductors, and ferroelectric materials.

A Point-of-Care Quartz Biosensor Chip for Detection of PF4/Heparin Complexes

BACKGROUNDOur recent studies indicate that circulating PF4/heparin complexes activate complement and contribute to a subsequent immune response seen in heparin-induced thrombocytopenia (HIT) (Khandelwal, Blood 2016). We undertook studies to develop a sensitive assay for measuring circulating PF4/heparin. To do so, we utilize a quartz crystal microbalance (QCM) device, which is a piezoelectric acoustic resonator that detects decreases in the resonance frequency of the quartz crystal due to the increased mass caused by molecules binding to the electrode surface. We hypothesize that a novel label-free QCM biosensor functionalized with PF4/heparin capture antibodies can provide for robust quantitative antigen detection and physical characterization of antigen-antibody interactions. METHODSWe formed a mixed self-assembled monolayer by using thiol-functionalized polyethylene glycols (PEGs) with -OH and biotin terminated head-groups on gold electrodes of quartz biosensor (Nelson; Langmuir 2001). PEG-backfilling of this surface provided protein non-fouling effects (1% BSA adsorbed only 10 ng/cm2), while biotin end-groups enabled close to full surface coverage of streptavidin (180 ng/cm2). This surface became our platform to immobilize biotinylated KKO (anti-PF4/heparin IgG2Κb monoclonal antibody, developed in Arepally Lab) and TRA (isotype IgG2Κb control antibody; developed in Arepally Lab).To characterize the sensor's detection ability, we flowed recombinant PF4 (provided by M. Poncz, Children's Hospital of Philadelphia) with a range of heparin (Elkins-Sinn, NJ) concentrations. The solutions are introduced to the biosensors 10 minutes after mixing the heparin and flowed through the system until the frequency readout stabilized. We determined the amount of captured PF4/heparin complexes and the layer thickness by monitoring the sensor's resonance frequency shifts and acoustic dissipation.The surface distribution of PF4/heparin complexes on KKO-functionalized surfaces was imaged by tapping-mode atomic force microscopy (AFM). The imaging results are used to verify layer thickness calculated by acoustic modeling of the QCM signal. RESULTSIn initial experiments, KKO showed no changes in the presence of buffer or PF4 alone. However, when PF4 (10 μg/ml) was infused with increasing amounts of heparin (0.2, 1 or 10 U/ml) significant binding was detected starting at 0.2 U/ml heparin (Figure A). The acoustic modeling of the KKO-bound PF4 complexes with 0.2 U/ml heparin suggested that the macromolecular complexes were nearly 25 nm high. These results are consistent with the neutralization model for the role of PF4 in heparin-induced thrombocytopenia, in which the amount of PF4/ heparin complexes peaks at a specific molar ratio of PF4:heparin (Kowalska; Thrombosis Research 2010). Comparatively, almost no binding occurred when the quartz crystal was functionalized with TRA. This result not only demonstrates the protein non-fouling capacity of the PEG backfilling of the surface, but also shows the specificity of the surface-immobilized assay.To gauge the sensitivity of the QCM biosensor to lower concentrations of PF4 and heparin that may be found in vivo, we tested 1µg/mL PF4 with lower heparin concentrations (0.02-0.05 U/ml). As shown in Figure B, a nearly linear KKO binding response was observed in this range capable of distinguishing heparin concentrations that differed by as little as 0.01 U/ml. The highest adsorption was observed at heparin concentration of 0.02 U/ml with associated atomic force microscopy (AFM) images again showing spherical particles with 25 nm diameter on the KKO immobilized surface. CONCLUSIONSHighly specific binding to PF4 complexes demonstrates the sensitivity of the QCM platform and its ability to distinguish differences between heparin concentrations of even 0.01 U/ml. Since QCM is a mass-sensing biosensor, it has a unique sensitivity advantage while sensing high molecular weight macromolecular complexes. This, combined with possible miniaturization of the sensor and integration with lab-on-a-chip systems, creates the potential for point-of-care bed-side detection of PF4/heparin. [Display omitted] DisclosuresArepally:Biokit: Patents & Royalties.

Nanoscale Material Heterogeneity of Glowworm Capture Threads Revealed by AFM.

Adhesive materials used by many arthropods for biological functions incorporate sticky substances and a supporting material that operate synergistically by exploiting substrate attachment and energy dissipation. While there has been much focus on the composition and properties of the sticky glues of these bio-composites, less attention has been given to the materials that support them. In particular, as these materials are primarily responsible for dissipation during adhesive pull-off, little is known of the structures that give rise to functionality, especially at the nano-scale. In this study we used tapping mode atomic force microscopy (TM-AFM) to analyze unstretched and stretched glowworm (Arachnocampa tasmaniensis) capture threads and revealed nano-scale features corresponding to variation in surface structure and elastic modulus near the surface of the silk. Phase images demonstrated a high resolution of viscoelastic variation and revealed mostly globular and elongated features in the material. Increased vertical orientation of 11–15 nm wide fibrillar features was observed in stretched threads. Fast Fourier transform analysis of phase images confirmed these results. Relative viscoelastic properties were also highly variable at inter- and intra-individual levels. Results of this study demonstrate the practical usefulness of TM-AFM, especially phase angle imaging, in investigating the nano-scale structures that give rise to macro-scale function of soft and highly heterogeneous materials of both natural and synthetic origins.

Theoretical model and experimental study on environmental dissipation mechanism of tapping mode atomic force microscope.

The phase information reflects the energy dissipation of the probe and sample interactions in tapping mode atomic force microscopes (TM AFMs). In this paper, we use the method of tune test in TM AFM to study the contribution of external environment to energy dissipation by changing the probe position and ambient humidity. Finally, the theoretical and experimental quality factors of air viscous damping, squeeze film damping and liquid bridge force are obtained to characterise energy dissipation. The analytically predicted values of the model established on squeeze film damping, viscous damping and liquid bridge force comparing to the experimental results in this paper is rational. And the comparative analysis results show that the main mechanism of energy dissipation is different at different probe positions and different relative humidness. This result is of great significance for understanding the mechanism of phase imaging experimentally and theoretically.

Deconvolution of dissipative pathways for the interpretation of tapping-mode atomic force microscopy from phase-contrast

Phase-contrast in tapping-mode atomic force microscopy (TM-AFM) results from dynamic tip-surface interaction losses which allow soft and hard nanoscale features to be distinguished. So far, phase-contrast in TM-AFM has been interpreted using homogeneous Boltzmann-like loss distributions that ignore fluctuations. Here, we revisit the origin of phase-contrast in TM-AFM by considering the role of fluctuation-driven transitions and heterogeneous loss. At ultra-light tapping amplitudes <3 nm, a unique amplitude dependent two-stage distribution response is revealed, alluding to metastable viscous relaxations that originate from tapping-induced surface perturbations. The elastic and viscous coefficients are also quantitatively estimated from the resulting strain rate at the fixed tapping frequency. The transitional heterogeneous losses emerge as the dominant loss mechanism outweighing homogeneous losses at smaller amplitudes for a soft-material. Analogous fluctuation mediated phase-contrast is also apparent in contact resonance enhanced AFM-IR (infrared), showing promise in decoupling competing thermal loss mechanisms via radiative and non-radiative pathways. Understanding the loss pathways can provide insights on the bio-physical origins of heterogeneities in soft-bio-matter e.g., single cancer cell, tumors, and soft-tissues.

Characterizing the coverage of anti-soiling coatings on photovoltaic modules

Anti-soiling coatings help protect solar modules against dust deposition. Tapping mode atomic force microscopy phase imaging can be used to ensure these coatings have ample coverage.

Characterization of reliability of anti-soiling coatings using tapping mode-AFM phase imaging

Power loss due to dust deposition on photovoltaic (PV) modules (also referred to as soiling) is a severe challenge to the economic viability of PV deployment in sunbelt countries like India and the Middle East. Anti-soiling coatings are nano/micrometer thick transparent coatings, which mitigate dust deposition on PV module. In this study, Tapping Mode Atomic Force Microscopy (TM-AFM) phase imaging was used to characterize the surface changes of four different commercial hydrophobic anti-soiling coatings as they were subjected to outdoor field exposure tests and three different indoor accelerated stress tests. The anti-soiling coatings were applied via manual spray coating method on solar glass substrates. The phase angle for not-coated glass shows a tight distribution around zero. The phase angle distribution of coated surface showed a larger spread. When the coatings were subjected to different environmental stressors, the phase angle distributions became tighter and, in some cases, collapsed to tight distributions around zero, indicating that the coatings were partly or completely removed from the glass surface. We demonstrate a correlation of the changes in surface coverage identified from phase angle distributions to contact angle and surface roughness, thus establishing TM-AFM phase imaging as a promising approach to characterize anti-soiling coatings subjected to environmental stress. While the analysis of the phase angle distribution is able to resolve the removal of the coating, contact angle and surface roughness cannot do so unambiguously.

Alignment of linear polymeric grains for highly stable N-type thin-film transistors

Summary Temperature-insensitive properties are attractive for most electronics, including polymeric semiconducting devices. Especially, polymeric field-effect transistors (FETs) with high mobility have been important research targets due to their broad applications. However, polymeric FETs with stable charge transport operating at extremely cold or hot zones are faced with enormous challenges. In this study, the polyacrylonitrile was found to significantly tune the sizes of pre-aggregates of polymers in solutions and the crystallinity of the polymeric films. The orientation of 5–25 μm linear grains in the films were prepared through the bar-coating process with polyacrylonitrile as an additive, which stabilized the electron mobility over a wide range of temperatures. The linear-grain morphology of the film contributed to reducing the holes and grain boundaries in the transport paths of carriers. Typically, the top-gate FETs based on P(NDI2OD-T2) displayed a stable electron transporting behavior from 200 to 460 K, with mobility greater than 3.5 cm2V−1s−1.

Atomic force microscopy studies of enamel, inner enamel, dentin, and cementum in canine teeth

The main goal of the present work is to explore the three dimensional (3-D) atomic force microscopy (AFM) images of human teeth and investigating their micromorphology. For this purpose, 10 fresh and permanent canine teeth were selected from a group of 40-year-old men who were candidate for the experimental processes. Afterward, they were all applied for studying the morphology of their hard tissues. The tapping mode of AFM was used to characterize the surface micromorphology on the square areas of 1μm × 1μm (512 × 512 pts). AFM results and surface stereometric analysis indicate the relationships between the micromorphology of the surface and the structural properties of these tissues across the length scales. As can be seen, the surface of cementum has the most irregular topography (D=2.87 ± 0.01) while the most regular topography (D=2.43 ± 0.01) is found in dentin. Furthermore, the more and less regularity of the surface have been found in inner enamel (Sq=26.26 nm) and dentin (Sq=41.28 nm), respectively. Stereometric and fractal analyses give valuable information about human canine teeth via 3-D micromorphology.

(Invited) Investigation of Corrosion Inhibitor Adsorption on Mild Steel By Electrochemical Atomic Force Microscopy

Mild steel has wide application in oil and gas industry due to its excellent mechanical properties and low costs. However, it is susceptible to corrosion attack in a typical water-containing service environment. Organic corrosion inhibitors can adsorb on steel surfaces to form protective layers even when added in a small amount. As conceptualized in the literature, the decrease in corrosion rates due to addition of inhibitor should be directly related to their surface coverage. However, studies have so far not provided any direct evidence of such a link, primarily due to limitations of conventional electrochemical analysis that have been used to investigate them. In the present work, a specially designed holder for electrochemical atomic force microscopy (EC-AFM) has been used to study the influence of a tetra-decyl-dimethyl-benzyl-ammonium inhibitor model compound on mitigation of corrosion. AFM results shows that when the bulk solution inhibitor concentration was at 0.5 CMC, partial coverage of the surface by the inhibitor film and patchy corrosion (which could lead to localized attack) of the UNS G1018 steel surface were observed by contact mode AFM imaging. When inhibitor bulk concentration was above the surface saturation value (1 CMC), full surface protection was indicated by the almost unchanged AFM topography images from 10 minutes to 4 hours exposure to the inhibited solution. The LPR results obtained with EC-AFM showed that the corrosion rates of this steel decreased as the bulk solution concentration of inhibitor in separate tests was increased from 0, 0.5 CMC to 1 CMC, while further increase of concentrations (from 1 CMC to 2 CMC) didn’t lead to any apparent reduction of general corrosion rate. Although the LPR corrosion rates at 1 CMC and 2 CMC were extremely low (0.05 - 0.1 mm/year), the values didn’t reduce to 0 under these full coverage conditions. Additional AFM tapping mode imaging results on mica indicated the formation of a porous film (a layer with ‘holes’) which is used to explain the types of adsorption layers possible and their probable influence on corrosion.