Atomic Force Microscopy Observations Research Articles

Nanogroove Formation By Ag-Assisted Chemical Etching to Separate Neighboring Terraces on Vicinal Si(111)

We aim to form nanogrooves to separate neighboring terraces on a Si surface for the fabrication of functional devices such as nanogap electrodes. For this purpose, we propose a self-assembled process composed of multiple wet-chemical treatments of a vicinal Si(111) surface. In this scheme, we used p-type Si(111) wafers with resistivity 10–20 Ω･cm. The miscut angle was 0.2°. After both metallic and organic contaminants were removed from the Si wafer by wet cleaning, it was dipped into a dilute HF solution to passivate the surface with H atoms. The sample was then immersed for 25 minutes in water with an ultralow level of dissolved oxygen, which is referred to hereafter as LOW. LOW was obtained by adding the deoxygenation agent ammonium sulfite monohydrate to deionized water [1] in which the O2 concentration was less than 3 ppb. This treatment with LOW led to anisotropic etching of Si(111) to form atomically flat terraces together with atomic steps. Each terrace width was approximately 90 nm. Next, the flattened Si sample was immersed for 2–5 seconds in LOW containing Ag+ ions at a concentration of 5 ppm. Atomic force microscopy (AFM) observations revealed that Ag atoms were selectively adsorbed at the edges of atomic steps on Si(111). In other words, Ag nanowires were formed along the step edges. Nanowire width and height were approximately 10 and 3 nm, respectively. Based on previous reports [2,3], it is speculated that the immersion of a flattened Si(111) surface into LOW caused the decoration of the step edge with hydroxyl (OH ) species. The oxygen atom in OH strongly interacted with Ag+ ions, promoting the transfer of electrons from the Si substrate to the ions. As a result, reduced Ag atoms were adsorbed at the step edges, and a Si dioxide (SiO2) film was formed locally underneath the Ag nanowires. Finally, the Si sample with Ag nanowires was immersed into a mixture of HF, H2O2, and deionized water for a few minutes. The HF and H2O2 concentrations were 4.6 and 0.005 M, respectively. AFM images indicated that adsorbed Ag atoms at step edges were replaced by perforated grooves. Groove width and depth were about 10 and 2 nm, respectively. The Ag nanowires are interpreted as acting as a catalyst to enhance chemical etching of the Si surface underneath, thus forming the nanogrooves. It is supposed that the Ag atoms dissolved gradually during the immersion into the solution containing H2O2. Finally, a likely explanation for formation of a “perforated” groove, rather than a continuous one, is that Ag atoms did not align to form a continuous wire during the deposition process; this finding indicates that the deposition process needs improvement. Nevertheless, these results present a possibility in which nanogrooves can be formed along a step edge on a Si(111) surface by catalyst-assisted chemical etching using a template of Ag nanowires. Because this process enables the separation of neighboring Si terraces, it is expected to be of use for future Si-based nanodevices.[1] H. Fukidome and M. Matsumura, Jpn. J. Appl. Phys., 38, L1085 (1999).[2] N. Tokuda, D. Hojo, S. Yamasaki, K. Miki and K. Yamabe, Jpn. J. Appl. Phys. 42, L1210 (2003).[3] A. Yoshimatsu, T. Shigetoshi, J. Uchikoshi, M. Morita and K. Arima et al., Surf. Interface Anal., 40, 1134 (2008).

BioAFMviewer: An interactive interface for simulated AFM scanning of biomolecular structures and dynamics.

We provide a stand-alone software, the BioAFMviewer, which transforms biomolecular structures into the graphical representation corresponding to the outcome of atomic force microscopy (AFM) experiments. The AFM graphics is obtained by performing simulated scanning over the molecular structure encoded in the corresponding PDB file. A versatile molecular viewer integrates the visualization of PDB structures and control over their orientation, while synchronized simulated scanning with variable spatial resolution and tip-shape geometry produces the corresponding AFM graphics. We demonstrate the applicability of the BioAFMviewer by comparing simulated AFM graphics to high-speed AFM observations of proteins. The software can furthermore process molecular movies of conformational motions, e.g. those obtained from servers which model functional transitions within a protein, and produce the corresponding simulated AFM movie. The BioAFMviewer software provides the platform to employ the plethora of structural and dynamical data of proteins in order to help in the interpretation of biomolecular AFM experiments.

Atomic force microscope observation of athletes' hemoglobin imaging

Hemoglobin (Hb) is a protein and its functional form has a tetrameric structure. This structure is the result of a combination of four sub-units called globin and indicates the dynamic interaction between them. Each subunit has a ring-shaped organic molecule called a heme that contains an iron atom; Heme is a group that mediates the reversible binding of oxygen by hemoglobin. This research was performed to observe the image of Hb by an atomic force microscope (AFM) and measure the physical function of athletes. For this purpose, based on the principle of AFM imaging, the hemoglobin crosslinking method was used to measure the morphology and size of cross-linked Hb, glutaraldehyde and Hb diameter were detected to prepare cross-linked Hb samples with different molar ratio, the activity of peroxidase was detected by Trinder reaction. The AFM was used to detect the influence of physiological environment changes such as pH, temperature, oxygen partial pressure and osmotic pressure on the absorption spectrum of Hb imaging. Results showed that the size of the uncrosslinked Hb was 6.64 nm. With the increase of the molar ratio of glutaraldehyde to Hb, the number of Hb molecules involved in the crosslinking increased, and the molecular size increased. During the crosslinking process, the aggregation of the cross-linked molecules would make the particle size of some Hb molecules reach 80-100 nm. The peak height, peak position and peak shape of the characteristic absorption peaks of pH to hemoglobin at 550 and 589 nm occurred. When the temperature changes continuously in the range of 30-55℃, the peak height of Hb absorption spectrum of normal red blood cells at 550 nm and 589 nm decreases gradually with the increase of temperature, and the peak shape at 610 nm changes obviously at 42℃, which indicates that the molecular structure of Hb changes; the absorption spectrum curve of deoxygenation disappears at 500 nm, the oxygen-binding capacity of Hb is very low, and the oxygen affinity and oxygenated hemoglobin are low (The concentration of HbO2) decreased, the osmotic pressure increased, the RBC dehydrated, the volume decreased, and the concentration of Hb increased. Conclusion: It is more accurate and comprehensive to use AFM to observe athletes' hemoglobin.

Antibacterial and Antifungal Activities of PMMAs Implanted Fluorine and/or Silver Ions by Plasma-Based Ion Implantation with Argon.

The purpose of this study was to examine the anti-oral microorganism effects of fluorine and/or silver ions implanted into acrylic resin (PMMA) using plasma-based ion implantation (PBII) with argon gas. The experimental PMMA specimens were implanted with F and Ag ions alone or simultaneously by the PBII method using Ar or Ar/F2 gases and Ag mesh. The surface characteristics were evaluated by X-ray photoelectron spectroscopy (XPS), contact angle measurements, and atomic force microscopy (AFM). Moreover, the antibacterial activity against Streptococcus mutans (S. mutans) and the antifungal activity against Candida albicans (C. albicans) were examined by the adenosine-5’-triphosphate (ATP) emission luminescence method. XPS spectra of the modified specimens revealed peaks due to F in the Ar/F and the Ar/F+Ag groups, and due to Ag in the Ar+Ag and the Ar/F+Ag groups. The water contact angle increased significantly due to the implantation of Ar, F, and Ag. In the AFM observations, the surface roughness of the Ar/F and the Ar/F+Ag groups increased significantly by less than 5 nanometers. The presence of F and Ag was found to inhibit S. mutans growth in the Ar+Ag and the Ar/F+Ag groups. However, this method provided no significant antifungal activity against C. albicans.

In situ AFM Observation of the Movements of Isolated Isotactic Poly(methyl methacrylate) Chains in a Precursor Film of an Oligo(methyl methacrylate) Droplet Spreading on Mica.

Atomic force microscopy (AFM) is a powerful tool to observe polymer chains at the molecular level. In this study, we show that the movements of isolated linear polymer chains in a precursor film of a droplet of an oligomer spreading on a substrate could be visualized in situ at the molecular level by AFM for the first time. The system was an isotactic poly(methyl methacrylate) (it-PMMA) solubilized in an oligo(MMA) matrix (it-PMMA/oligo(MMA) = 1/10,000 w/w) spreading on mica under high humidity. Because of the limited resolution of the AFM instrument, condensed linear polymer chains could not be visualized, but a small amount of it-PMMA chains that were solubilized as isolated chains in the oligo(MMA) matrix could be visualized in the precursor film, the contrast of which came from a large difference in glass transition temperature (Tg) of it-PMMA and oligo(MMA). The it-PMMA chains in the precursor film spread in the radial direction of the droplet with vigorously changing chain conformations. The spreading rate of it-PMMA chains under 72% relative humidity was ∼1/30 of the spreading rate of the oligo(MMA) matrix, which was estimated based on the decrease in the volume of the macroscopic droplet. The spreading of the it-PMMA chains and droplet strongly depended on humidity and was suppressed with the decrease in humidity, most likely because of the increase in friction with the substrate. The difference in the spreading rate of it-PMMA and oligo(MMA) further increased under low humidity. The dynamic molecular information of a precursor film by AFM should help to elucidate the wetting dynamics on a substrate.

Optimizing a fabricating program for wearable super-hydrophobic cotton by clean production technology of plasma and reducing chemical consumption

The atmospheric-pressure cold plasma jet was used as a clean production technology together with fluorine-free water repellent agent (FfWRA) to optimize the fabricating program for wearable super-hydrophobic cotton. By the contrasting test of sample surfaces treated via FfWRA and by plasma in advance with fluorine-free agent (P-FfWRA), it was concluded that the plasma can evidently strengthen the hydrophobic finishing effect. Hydrophobicity study indicates the contact angle on sample treated by P-FfWRA reached 153°. Even more important, meantime a 44.4% reduction in the chemical consumption can be achieved with the optimization method. Scanning electron microscope (SEM) and atomic force microscope (AFM) observations verified that large amounts of nano-scaled roughness uniformly presented on the modified fiber surface. X-ray photoelectron spectroscopy (XPS) measurements reveals that there was a reduction of up to 40% in oxygenous groups on the cotton fabric processed by P-FfWRA. The washing test show that the P-FfWRA treated sample still have a strong hydrophobic surface with a contact angle of 147°even after washing 25 times. The breathability of the modified sample even has a small increase due to the variation in fiber diameter after the modification. The optimized fabricating program has been proved to be an environmentally friendly, high efficiency production technology. This paper provides theoretical support and practical significance for further research on the saving of the chemical consumption.

Highly crystalline metal oxide thin films on plastic substrates prepared via firing and transfer: key role of the “lost” organic underlayer

Our sol–gel transfer technique realizes highly crystalline metal oxide thin films on plastic substrates. In that technique a precursor gel film is fired at temperatures as high as 700 °C on an organic underlayer that is deposited beforehand on a single crystal silicon substrate. The resultant crystalline oxide film is transferred to a plastic substrate by heating the film on a hot plate and pressing a plastic substrate on it. The organic underlayer, which is completely lost during firing, critically facilitates the oxide film delamination from the silicon substrate. In order to answer the question how such a “lost” organic underlayer could be the key for the transfer, the effect of the underlayer thickness on the oxide film transferrability was investigated. Titania and zinc oxide precursor films were prepared by spin-coating on polyimide-polyvinylpyrrolidone and polyimide layers on Si(100) substrates, respectively, followed by firing and transfer to polycarbonate (PC) substrates. Quantitative evaluation based on image analysis demonstrated that thicker “lost” underlayers result in larger area fractions of the successfully transferred oxide films. Depth profile analyses by X-ray photoelectron spectroscopy excluded the residual carbon at the film/Si(100) interface as the delamination facilitator. On the other hand, atomic force microscopic observations demonstrated that thicker “lost” underlayers create larger surface roughness on both sides of the oxide films. It was concluded that such an increase in roughness decreased the contact area and brought the anchoring effect, reducing and increasing the film/Si(100) and film/PC adhesions, respectively, which facilitates the film transfer.

In-situ electrochemical SPR study of gold surface smoothing by repetitive cathodic deposition and anodic dissolution of copper in an ionic liquid

Abstract We performed in-situ analysis of the initial process of copper electrodeposition in an ionic liquid (IL), 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide (C4mimTFSA), using electrochemical surface plasmon resonance (ESPR), where the SPR resonance angle (Δθ) was recorded simultaneously with cyclic voltammograms (CVs) at the gold interface of C4mimTFSA. Δθ shifted at the potentials where faradaic current appears in the CVs, indicating that SPR probes the redox processes of copper between Cu2+, Cu+, and Cu metal. In stark contrast to the fact that the CVs are not cycle dependent, the amount of the Δθ shift due to the copper electrodeposition decreased with increasing the CV cycle. A model reflectivity analysis using the Bruggeman effective medium approximation predicted that this decrease in Δθ is due to the decrease in the roughness of the gold surface, and it was actually confirmed by ex-situ atomic force microscopy observation. Since the dissolution of gold was found to be negligible from the atomic absorption measurement of IL after the ESPR measurements, the roughness decrease of the gold surface is likely due to the surface diffusion of gold atoms promoted during copper electrodeposition and dissolution processes. It was found that ESPR can track the surface roughness change of the gold electrode in an in-situ manner in the order of A.

Opuntia ficus-indica as a durable and eco-friendly corrosion inhibitor on AISI 410 stainless steel in $$0.5~\hbox {M}\,\hbox {H}_{{2}}\hbox {SO}_{{4}}$$

In the dental office, surgical instruments must be sterilized for each patient, following their contamination by saliva and blood. Repeated sterilization cycles cause corrosion. A worn out and corroded instrument may cause toxicity to the patient. The aim of our study is to improve the corrosion resistance of orthodontic pliers during sterilization using green inhibitors. The behaviour of AISI 410 stainless steel with respect to corrosion was studied in a $$0.5~\hbox {M H}_{{2}}\hbox {SO}_{{4}}$$ , using cladodes of Opuntia ficus-indica (OFI) as a green inhibitor. Temperature effect on OFI efficacy was studied for different ranges (25, 35 and $$45^{\circ } \hbox {C}$$ ). The study was carried out using the weight loss method, the stationary electrochemical techniques (polarization curves), the transients (electrochemical impedance spectroscopy), and the scanning electron microscopy associated with X-ray dispersive energy spectroscopy (SEM–EDX) and atomic force microscopy (AFM) observations. OFI behaves as a mixed inhibitor, with a physisorbed adsorption obeying to Langmuir isotherm and, with an efficacy ranging from 95.12 to 15% (v/v) obtained after 12 h immersion at a temperature of $$25^{\circ } \hbox {C}$$ . The SEM–EDX and AFM observations confirm the obtained results. In conclusion, OFI improves corrosion resistance of AISI 410 stainless steels in $$0.5~\hbox {M H}_{{2}}\hbox {SO}_{{4}}$$ at $$25^{\circ } \hbox {C}$$ .

Characterization of a New M4 Metalloprotease With Collagen-Swelling Ability From Marine Vibrio pomeroyi Strain 12613.

The ocean harbors a variety of bacteria that contain huge protease resources and offer a great potential for industrial and biotechnological applications. Here, we isolated a protease-secreting bacterium Vibrio pomeroyi strain 12613 from Atlantic seawater and purified a protease VP9 from strain 12613. VP9 was identified as a metalloprotease of the M4 family. VP9 could hydrolyze casein and gelatin but not elastin and collagen. With gelatin as the substrate, VP9 showed the highest activity at 40°C and pH 6.0–8.0. It was stable at temperatures of 50°C and less and in the range of pH 5.0–11.0. VP9 also had good tolerance to NaCl, non-ionic detergents, and organic solvent methanol. Unlike other M4 metalloproteases, VP9 has distinct collagen-swelling ability, and its collagen-swelling effect was concentration dependent. The relative expansion volume of collagen increased by approximately eightfold after treatment with 10 μM VP9 at 37°C for 12 h. The collagen-swelling mechanism of VP9 on bovine-insoluble type I collagen was further studied. Atomic force microscopy observation and biochemical analyses showed that VP9 can degrade proteoglycans in collagen fibers, resulting in the release of collagen fibrils from collagen fibers and the swelling of the latter. In addition, VP9 can degrade glycoproteins, a non-collagenous constituent interacting with collagen in the skin. The characteristics of VP9, such as sufficient specificity toward proteoglycans and glycoproteins but no activity toward collagen, suggest its promising potential in the unhairing and fiber-opening processing in leather industry.

Convergent evolution of processivity in bacterial and fungal cellulases

Cellulose is the most abundant biomass on Earth, and many microorganisms depend on it as a source of energy. It consists mainly of crystalline and amorphous regions, and natural degradation of the crystalline part is highly dependent on the degree of processivity of the degrading enzymes (i.e., the extent of continuous hydrolysis without detachment from the substrate cellulose). Here, we report high-speed atomic force microscopic (HS-AFM) observations of the movement of four types of cellulases derived from the cellulolytic bacteria Cellulomonas fimi on various insoluble cellulose substrates. The HS-AFM images clearly demonstrated that two of them (CfCel6B and CfCel48A) slide on crystalline cellulose. The direction of processive movement of CfCel6B is from the nonreducing to the reducing end of the substrate, which is opposite that of processive cellulase Cel7A of the fungus Trichoderma reesei (TrCel7A), whose movement was first observed by this technique, while CfCel48A moves in the same direction as TrCel7A. When CfCel6B and TrCel7A were mixed on the same substrate, "traffic accidents" were observed, in which the two cellulases blocked each other's progress. The processivity of CfCel6B was similar to those of fungal family 7 cellulases but considerably higher than those of fungal family 6 cellulases. The results indicate that bacteria utilize family 6 cellulases as high-processivity enzymes for efficient degradation of crystalline cellulose, whereas family 7 enzymes have the same function in fungi. This is consistent with the idea of convergent evolution of processive cellulases in fungi and bacteria to achieve similar functionality using different protein foldings.

Nanoscale oligopeptide adsorption behaviour on chlorite as revealed by scanning probe microscopy and density functional simulations

In the present work, the interaction between simple oligopeptides of L-alanine (di-L-alanine) and the (001) surface of clinochlore was characterized in details by employing cross-correlated atomic force microscopy (AFM) observations and Density Functional Theory (DFT) simulations. The AFM results showed that the mineral surface is able to stably bind L-alanine peptides preferentially onto the brucite-like sheets of clinochlore during an interaction in a water suspension. In particular, the (001) surface acted as a condensing and agglomerating system, where AFM evidenced di-L-alanine oligopeptides organized in dot-like, agglomerates and filament-like structures up to more than 160 nm in length, in the experimental conditions here used. DFT simulations were conducted to analyse at the atomic scale the interaction between di-L-alanine oligopeptides and the mineral, finding the molecular conformation with the lowest energy, the adsorption (binding) energy between the oligopeptide and the brucitic surface and also the hydrogen bonding scheme. The reported findings constitute a further step towards the comprehension of the interaction mechanisms between fundamental biomolecules and clay mineral surfaces, of paramount importance for environmental sequestration and biotechnological purposes, but also for prebiotic chemistry research.

Assembly of a patchy protein into variable 2D lattices via tunable multiscale interactions

Self-assembly of molecular building blocks into higher-order structures is exploited in living systems to create functional complexity and represents a powerful strategy for constructing new materials. As nanoscale building blocks, proteins offer unique advantages, including monodispersity and atomically tunable interactions. Yet, control of protein self-assembly has been limited compared to inorganic or polymeric nanoparticles, which lack such attributes. Here, we report modular self-assembly of an engineered protein into four physicochemically distinct, precisely patterned 2D crystals via control of four classes of interactions spanning Ångström to several-nanometer length scales. We relate the resulting structures to the underlying free-energy landscape by combining in-situ atomic force microscopy observations of assembly with thermodynamic analyses of protein-protein and -surface interactions. Our results demonstrate rich phase behavior obtainable from a single, highly patchy protein when interactions acting over multiple length scales are exploited and predict unusual bulk-scale properties for protein-based materials that ensue from such control.

Effect of atmospheric pressure plasma treatment on surface physicochemical properties of carbon fiber reinforced polymer and its interfacial bonding strength with adhesive

To study the effect of surface physicochemical properties of carbon fiber reinforced polymer (CFRP) on its interfacial bonding strength with adhesive, atmospheric pressure plasma treatment (APPT) using three gases (i.e., argon (Ar), nitrogen (N2) and air (Air)) was conducted on surfaces of CFRP substrates. Atomic force microscope (AFM) observation indicates that APPT only changes the surface morphology of CFRP in a depth of tens of nanometers, and this minor change contributes little to the interfacial bonding strength of CFRP joints. X-ray photo electron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analyses reveal that the release agent (mainly the -Si-CH3 group) and other contaminations on CFRP substrate surfaces were effectively removed by APPT, which improves the shear strength of CFRP joints from 8.6 MPa to 23.1 MPa. In addition, polar chemical functional groups (i.e., –NH2, –OH, –COOH) were generated on the CFRP substrate surfaces after APPT when nitrogen and air were used as plasma gases, which not only enhances the surface free energy of CFRP substrate but also combines with adhesive molecules through the form of hydrogen bonds and covalent bonds. With this mechanism, the shear strength of CFRP joints increased further to 28.7 MPa and 31.5 MPa when nitrogen and air were used as the plasma gases, respectively. After a quantitative study, the interfacial bonding strength between CFRP substrate and adhesive is expressed as a function of the concentration of -Si-CH3, –NH2 and –OH groups.

Evaluating the Effect of Azole Antifungal Agents on the Stress Response and Nanomechanical Surface Properties of Ochrobactrum anthropi Aspcl2.2.

Azole antifungal molecules are broadly used as active ingredients in various products, such as pharmaceuticals and pesticides. This promotes their release into the natural environment. The detailed mechanism of their influence on the biotic components of natural ecosystems remains unexplored. Our research aimed to examine the response of Ochrobactrum anthropi AspCl2.2 to the presence of four azole antifungal agents (clotrimazole, fluconazole, climbazole, epoxiconazole). The experiments performed include analysis of the cell metabolic activity, cell membrane permeability, total glutathione level and activity of glutathione S-transferases. These studies allowed for the evaluation of the cells’ oxidative stress response to the presence of azole antifungals. Moreover, changes in the nanomechanical surface properties, including adhesive and elastic features of the cells, were investigated using atomic force microscopy (AFM) and spectrophotometric methods. The results indicate that the azoles promote bacterial oxidative stress. The strongest differences were noted for the cells cultivated with fluconazole. The least toxic effect has been attributed to climbazole. AFM observations unraveled molecular details of bacterial cell texture, structure and surface nanomechanical properties. Antifungals promote the nanoscale modification of the bacterial cell wall. The results presented provided a significant insight into the strategies used by environmental bacterial cells to survive exposures to toxic azole antifungal agents.

Analysis of soft and hard nanoparticle alternating multilayers for the development of theory for long-period stacking order structure prepared by Langmuir-Blodgett method

Two types of hard and soft nanoparticles with a size of 5 nm were alternately layered to adjust the multi-particle structure with high regularity, and structural analysis was performed. Specifically, we alternately transferred two kinds of single-particle layers composed of surfactant-modified organo-magnetite and a hydrophobic polymer to a solid substrate using the Langmuir-Blodget (LB) method. The morphology of two-dimensional particle integration in each single particle layer was confirmed by atomic force microscopy observations. The obtained LB multilayers exhibited almost the same periodicity, crystallite size, and lattice distortion, based on X-ray diffraction (XRD) analysis. The alternating multilayers composed of hard and soft particle monolayers were not inferior to single component multilayers in terms of periodicity and regularity. The utilization of this preparation method facilitates effective control of the period of hard and soft layers. It is asserted that the high degree of regularity was attained due to the affinity and miscibility between the organic polymer particle layer and the modified organic chains on the inorganic nanoparticle surface. The most notable result is that in the XRD data, the spacing between inorganic nanoparticles was not enhanced, and the period of the hard-soft particle correlation was confirmed. Therefore, it seems that both layers have the same high degree of regularity.

Hydrogen gas sensor based on nanofibers TiO2-PVP thin film at room temperature prepared by electrospinning

TiO2/PVP nanofibers (NFs) have been deposited onto glass substrate by electrospinning method. X-ray diffraction analysis confirms the formation of anatse phase with high crystallinity and Field emission scanning electron microscopy and atomic force microscopy observations reveal the formation of fibrous nanostructure with a mean diameter in the range 41–281 nm and high porosity. A sensor was fabricated based on TiO2/PVP nanofibers (NFs) by sputtering Pt electrodes onto glass substrate and hydrogen (H2)-sensing performance was examined at room temperature over broad range of concentrations (167–1000 ppm). The results show that the sensor has good response towards H2 with a good sensitivity reaching 63% upon exposure to 1000 ppm of H2 gas at a low power consumption of 60 mW. The improved sensing performance is associated with surface morphology, high porosity and high surface-to-volume ratio of one-dimensional NFs.

Studied on the interaction between Ag-DNA nanocomposites and lipids monolayers

The adsorption behavior of AgNPs-DNA nanocomposites on 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-dimyristoyl-sn-glycero-3-phosphoserine (DMPS) lipid monolayers has been investigated by analyzing adsorption dynamic process, surface pressure-area isotherms (π-A), excess mean area ( $${\Delta \mathrm{A}}_{\mathrm{e}\mathrm{x}\mathrm{c}}$$ ), excess Gibbs free energy ( $$\Delta {\mathrm{G}}_{\mathrm{e}\mathrm{x}}$$ ) and the atomic force microscopy (AFM). The nanocomposites were prepared by sliver nanoparticles (AgNPs) and deoxyribonucleic acid (DNA) via electrostatic attraction. The result of ∆π/π and π-A isotherms indicated that the binding of AgNPs-DNA tends to adsorb on DMPC while the concentration of DNA exceeds 0.4 μg/mL. Excess mean area and thermodynamic analysis of excess Gibbs energy demonstrated that AgNPs-DNA enlarged the interval between DMPC and DMPS molecules, whose phenomena might be the electrostatic repulsion of each AgNPs-DNA molecule. AFM observation showed that the adsorption behavior of AgNPs-DNA on DMPS monolayers had a saturation point, while DMPC was not. Taken together, this work might provide a novel idea and useful basis for the development of metal nanoparticles-based biological materials.

Electrochemical adsorption and passivation on gold surface in alkaline thiourea solutions

An electrochemical method was used to examine Au surface absorption and passivation under the most commonly employed pH conditions in an alkaline Au leaching system. The polarization at different pH values was obtained through the current step curve. At pH 10, no absorption layer was formed. When the pH was increased to 11, an absorption layer was formed through the Au electrode reaction. At pH 12, the entire system could not be stabilized, even after long durations because of the thiourea oxidation and decomposition. The samples were analyzed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and atomic force microscopy (AFM). AFM observations of the Au plating surface and SEM–EDS analyses for the Au-coated graphite surface indicated that a passivation membrane was formed on the Au surface after its use in the alkaline thiourea Au leaching system. Two-step leaching was used to confirm the conclusions drawn from the experimental results. The two-stage experimental results further confirmed the existence of a passivation membrane.

Determination of solid electrolyte interphase formation mechanism on negative electrode surface in Li-O2 battery electrolyte by operando electrochemical atomic force microscopy observation

Solid electrolyte interphase (SEI) on the negative electrode surface affect the electrochemical operation and cycle performance of the Li-O2 batteries. Two-type of SEI formation processes involving the O2 molecule on negative electrode surface have been suggested: (i) direct electrochemical reaction and (ii) indirect multi-step chemical reaction. In this research, the operando electrochemical atomic force microscopy observation was conducted to determine the proper model. Well-polished cupper substrate was used as model working electrode and was observed during the cyclic-voltammetry operation in the tetraglyme (G4) based electrolyte with and without dissolved O2. In the pristine electrolyte, in which O2 is not dissolved, no solid formation was observed. In the O2-dissolved electrolyte, the solid formation was suddenly observed from 1.3 V vs. Li counter electrode (LiCE) in the negative scan, which voltage is remarkably lower than the onset voltage of reduction current at 1.8 V vs. LiCE. This significant delay of solid formation against the electron transfer reaction strongly supported the multi-step solid formation model. The direct observation of electrode surface coupled with electrochemical operation determine the SEI formation mechanism in the Li-O2 battery.