Tip Potential Research Articles

The multi-dimensional joint response of the electric potential time–frequency-field in the fracture process of flawed coal under dynamic load

The fracture failure of flawed coal has always been a problem in underground engineering. Therefore, it is necessary to monitor crack propagation and damage evolution during coal fracture. In this study, the split Hopkinson pressure bar (SHPB) and digital image correlation (DIC) were combined to analyze the impact failure electric potential (EP) of flawed coal samples. The multi-dimensional joint response characteristics of coal EP time–frequency-field under dynamic load were studied and the differential expression and multi-fractal characteristics of EP responses at different measuring points were analyzed. Based on the EP signals, the evolution of damage to the coal was calculated. The results show that the time series evolution of EP and stress–strain curves during coal failure is consistent. The generation of fracture zones will excite the high-value area of local EP, and the spectral distribution of EP signals in this area shows the characteristics of low frequency and high amplitude. Each channel’s EP signal and the degree of deformation at the corresponding place are perfectly matched. The multi-fractal spectrum of the EP signal close to the fracture zone has a higher Δα and a lower Δf, which demonstrates the dominance of the large-scale EP signal produced in this region by the destruction of sample. Theoretical study indicates that the main causes of the anomalous distribution of the EP field are crack tip potential, diffusion potential, etc. The results can provide theoretical basis for the evaluation of coal fracturing by EP technology.

Evaluation of the stress corrosion crack growth behaviour of high-strength marine steel based on model of crack tip mechano-electrochemical effect

Here, the stress corrosion crack growth behaviour of a high-strength low-alloy steel under anodic potential was investigated in artificial seawater. As applied potential shifts positively, the crack growth rate first increases and then decreases. The crack growth behaviour is controlled by the mechano-electrochemical effect at the crack tip. Even under anodic potential, hydrogen embrittlement (HE) occurs at the crack tip, and HE is the main factor of crack growth. A model of mechano-electrochemical effect at the crack tip is developed to study the phenomenon. It was found that applied potentials change the crack growth behaviour via involvement in HE and anodic dissolution at the crack tip. The critical value of applied potential affecting crack growth is the crack tip potential of –0.0591 pH.

Scanning gate microscopy response for local tip potentials beyond perturbation theory

Scanning gate microscopy response for local tip potentials beyond perturbation theory

Nonvolatile memory based on the extension–retraction of bent ferroelastic domain walls: A phase field simulation

Herein, a prototype nonvolatile bent ferroelastic domain wall (DW) memory based on extension–retraction of DWs in a top electrode/bent ferroelastic DWs/bottom electrode architecture is demonstrated and the effects of mechanical condition, electrical condition, and the material parameter on ferroelastic DWs in PbTiO3 ferroelectric thin films are studied by phase field modeling. Misfit strain can be used to drive the bend of DWs in PbTiO3 thin film, resulting in a change of ferroelastic domain size, bending degree, and conductivity. Stable and reversible switching of DWs between the extendible state with high conductivity and the retractile state with low conductivity can be realized, resulting in an apparent resistance change with a large ON/OFF ratio of >102 and an excellent retention characteristic. The extension and retraction speed, corresponding to data writing speed, can be adjusted by the electric field magnitude and distributions. The memory speed increases by 5% under a homogeneous electric field and 6% under an inhomogeneous probing electric field, after the buildup of space charges in a ferroelectric thin film, and the fastest memory speed is obtained at tip potential φ = 1.8. Moreover, polarization orientations of a and c domains separated by bent ferroelastic DWs do not affect memory performance. This paper can guide the development of new ferroelectric domain wall memory.

WO x /Pt(111) Prepared As PEFC Model Anode Catalyst: Surface Structure and Suppressed Hydrogen Peroxide Generation

Introduction To achieve prolonged lifetime of polymer electrolyte fuel cell (PEFC), hydrogen-peroxide (H2O2)-induced chemical degradation of polymer electrolyte membrane (PEM) is a crucial problem. In general, oxygen (O2) crossover from cathode to anode through the PEM yields H2O2 generation on Pt/C anode catalyst surface through 2-electron pathway of O2 reduction reaction. Thus, mitigation of H2O2 generation on Pt/C surface is a key to suppress the PEM degradation. Trogadas and Ramani reported tungsten trioxide (WO3) addition to Pt/C suppressed H2O2 generation.1 The results suggest that the cooperation of Pt nanoparticles and WO3 located near-by should be effective for suppression of H2O2 generation. However, influence of the oxidation states of tungsten oxide (WO x ) on H2O2 generation at the Pt surface is not fully resolved. Furthermore, it was reported that, although fully oxidized WO3 is stable in acid solution (pH < 2),2 sub-oxides of tungsten (WO x ) could dissolve in Pt-WO x electrochemical system.3 Thus, electrochemical dissolution behaviors of WO x located on Pt substrate surface should be investigated in detail. In this study, we prepare Pt(111) surface that modified by WO x having different oxidation states, and investigated the electrochemical H2O2 generations. Experimental Pt(111) single crystal substrate surface was cleaned by repeated cycles of Ar+ sputtering and annealing in an ultrahigh vacuum (UHV; ~10-8Pa). Subsequently, WO x was deposited on the cleaned Pt(111) via an arc-plasma deposition (APD) method using a W target under partial pressures of O2 (p(O2) = 1×10-1 or 1×10-3 Pa) at ca. 298 K. Deposition amounts of the WO x was estimated to be ca. 1.5 µg/(cm2 of substrate) by using a quartz crystal microbalance installed in the UHV chamber. Then, WO x -modified Pt(111) were annealed at 703 K for 10 min. in UHV. Hereafter, the fabricated samples are referred to as p(O2)-WO x /Pt(111). X-ray photoelectron spectroscopy (XPS) was conducted for the as-fabricated samples in situ in UHV.H2O2 generation amounts were evaluated by the tip generation/substrate collection mode of scanning electrochemical microscope (SECM)4 in O2-saturated 0.1 M HClO4. Generated H2O2 was detected by a Pt tip micro-electrode (diameter: ca. 20 µm, tip potential: 1.26 V vs. RHE) positioned ca. 50 µm at surface normal of the sample electrodes, with sweeping sample electrode potential (E S) at sweep rate of 2 mV/s in negative going direction. Thereafter, potential cycles (PCs: 0.05–1.0 V vs. RHE, sweep rate: 100 mV/s, 100 cycles) were applied to the sample surfaces; then, H2O2 generation was re-evaluated. Finally, the PCs-applied sample surfaces were re-introduced to the UHV chamber to perform XPS measurements. Results and Discussion XP spectra of W4f bands for the as-fabricated and PCs-applied sample surfaces are summarized in Figure. 1 (A). Considering peak areas of deconvoluted components (solid lines), the oxidation states of WO x as-fabricated can be judged mainly to be W6+ and Wx+ (x < 4) for 10-1 Pa-WO x /Pt(111) (a) and 10-3 Pa-WO x /Pt(111) (c), respectively.Figure. 1 (B) shows SECM-estimated H2O2 generations of the WO x /Pt(111) surfaces before (as-fabricated) and after the 100 PCs. As for the as-fabricated surfaces (solid lines), H2O2 detection current (i T) of the Pt tip micro-electrode normalized by respective sample electrode current (i S) is lower for 10-1 Pa-WO x /Pt(111) than 10-3 Pa-WO x /Pt(111), yet normalized i T/|i S|-values for both surfaces are smaller than that of clean Pt(111). The results show that surface modification of Pt(111) by the small amount of WO x , particularly with higher oxidation states, effectively suppressed H2O2 generations. However, the suppression effect degraded by the 100 PCs application for both the electrode surfaces (dotted lines). Compared of W4f bands for the PCs-applied surfaces (Figure. 1 (A) (b, d)) with corresponding as-fabricated ones (a, c), the bands shifted to negative- and positive-binding-energies for 10-1 Pa-WO x /Pt(111) and 10-3 Pa-WO x /Pt(111), respectively, indicating respective reduction and oxidation of the surface WO x by the PCs. In addition, W4f bands for both surfaces decreased in intensity by the PCs application, suggesting decrease in surface amount of the WO x , probably through electrochemical dissolution during the PCs. The PCs-induced changes in oxidation states and amounts of surface WO x should correlate to the degraded H2O2 generation suppressions. Acknowledgement This study was supported by the new energy and industrial technology development organization (NEDO) of Japan, JSPS KAKENHI Grant Number JP21H01645, and JST SPRING Grant Number JPMJSP2114. References P. Trogadas and V. Ramani, J. Electrochem. Soc., 155, B696–B703 (2008).M. Anik and K. Osseo-Asare, J. Electrochem. Soc., 149, B224 (2002).A. J. Martín, A. M. Chaparro, and L. Daza, J. Power Sources, 196, 4187–4192 (2011).C. M. Sánchez-Sánchez and A. J. Bard, Anal. Chem., 81, 8094–8100 (2009). Figure 1

Energetic Radiation from Subsequent-Stroke Leaders: The Role of Reduced Air Density in Decayed Lightning Channels

Leaders of subsequent strokes in negative cloud-to-ground lightning are known to produce X-ray/gamma-ray emissions detectable at distances of a few kilometers or less from the lightning channel. These leaders usually develop in decayed but still warm channels of preceding strokes. We computed electric field waveforms at different points along the path of subsequent leader as those points are traversed by the leader tip. For a typical subsequent leader, the electric field peak is a few MV/m, which is sufficient for production of energetic radiation in a warm (reduced air density) channel. We examined the dependence of electric field peak on the leader model input parameters, including the prospective return-stroke peak current (a proxy for the leader tip potential) and leader propagation speed, and compared model predictions with measurements.

Visualization of Ion Fluxes in Nanopipettes: Detection and Analysis of Electro-osmosis of the Second Kind.

Nanopipettes are finding increasing use as nano "test tubes", with reactions triggered through application of an electrochemical potential between electrodes in the nanopipette and a bathing solution (bath). Key to this application is an understanding of how the applied potential induces mixing of the reagents from the nanopipette and the bath. Here, we demonstrate a laser scanning confocal microscope (LSCM) approach to tracking the ingress of dye into a nanopipette (20-50 nm diameter end opening). We examine the case of dianionic fluorescein under alkaline conditions (pH 11) and large applied tip potentials (±10 V), with respect to the bath, and surprisingly find that dye ingress from the bath into the nanopipette is not observed under either sign of potential. Finite element method (FEM) simulations indicate this is due to the dominance of electro-osmosis in mass transport, with electro-osmotic flow in the conventional direction at +10 V and electro-osmosis of the second kind acting in the same direction at -10 V, caused by the formation of significant space charge in the center of the orifice. The results highlight the significant deviation in mass transport behavior that emerges at the nanoscale and the utility of the combined LSCM and FEM approach in deepening understanding, which in turn should promote new applications of nanopipettes.

(PEFCE&E 21 Best Student Poster - Second Place) Hydrogen Peroxide Generation and Hydrogen Oxidation Reaction Properties of Pt/Ir(111) and Ir/Pt(111) Bimetallic Surfaces

Introduction Hydrogen peroxide (H2O2) can be generated through oxygen reduction reaction (ORR) particularly on the anode Pt/C surface due to oxygen crossover during operation of polymer electrolyte fuel cell (PEFC): such the H2O2 generation causes degradation of PEFC through reactive radical generations which severely attack the PE.1 Therefore, development of a novel anode catalyst is crucial that less-active for the H2O2 generation and, yet, active for hydrogen oxidation reaction (HOR). According to Durst et al., HOR activity of the Ir/C was about 1/3 of that of the Pt/C,2 and furthermore, we found to date that Ir(111) generates much less H2O2 than Pt(111) in low potential (< 0.3 V).3 Therefore, Pt-Ir bimetallic alloy is expected to suppress H2O2 generation with keeping practical HOR activity. Nevertheless, to our best knowledge, neither H2O2 generation nor HOR properties of Pt-Ir bimetallic surfaces has been reported. Therefore, in this study, we prepared well-defined Pt/Ir(111) and Ir/Pt(111) surfaces and investigated the H2O2 generation and HOR activity. Experimental The Pt/Ir(111) and Ir/Pt(111) bimetallic surfaces were fabricated as follows. First, Ir(111) or Pt(111) surfaces were cleaned by repeated cycles of Ar+ sputtering and annealing at 1153 K in ultra-high vacuum (UHV). Then, 0.1 monolayer (ML)-equivalent Pt or Ir were deposited on the respective Ir(111) and Pt(111) surfaces by arc-plasma deposition (APD) at room temperature. The surface morphology was verified by scanning tunneling microscopy (STM) in UHV. The electrocatalytic properties were evaluated by scanning electrochemical microscope (SECM) using Pt microelectrode (diameter: ca. 20 μm) as a tip electrode. The H2O2 generation property was investigated in O2-saturated 0.1 M HClO4.4 The substrate potential (E S; Pt/Ir(111) or Ir/Pt(111)) was swept by 2 mV/s, and the tip current (i T) due to H2O2 detection was recorded with the constant tip potential (E T) of 1.26 V and tip-substrate distance of 50 μm. The HOR activity was evaluated in an electrolyte containing 0.01 M HClO4 and 0.1 M NaClO4 solution.5 The tip electrode was set as close as possible to the substrate, and E S was swept by 5 mV/s while E T was fixed at −0.74 V. The standard rate constants (k 0) for HOR were estimated by fitting the E S-dependent i T values to the theoretical ones, following to the previous reports.6 All potentials are referenced to that of the RHE. Results and Discussion Fig. 1 shows the UHV-STM images for the Pt/Ir(111) (a) and Ir/Pt(111) (b) surfaces. The dispersed nano-sized, particle-like structures that ascribable to the AP-deposited Pt (a) or Ir (b) can be observed with the atomic steps of the single crystal substrates. The surface area differences estimated from the images were 1.05 and 1.11 for the Pt/Ir(111) and Ir/Pt(111), respectively.The potential-dependent H2O2 generation for the corresponding surfaces are shown in Fig.2 (a) with the simultaneously recorded linear sweep voltammograms (LSVs) (b). The results for clean Ir(111) and Pt(111) are also presented. As shown in Fig.2 (a), much lower i T-values for the Ir(111) than that for Pt(111) in the low potential region (< 0.3 V) indicates that the Ir(111) is much less-active to H2O2 generation than the Pt(111). The H2O2 generation of the Ir(111) in the low potential region remained almost unchanged by the Pt deposition. Also, the i T values for the Ir/Pt(111) was smaller than that for Pt(111), suggesting effective suppression of H2O2 generation of the Pt(111) surface by the deposited Ir.The estimated k 0 for HOR (i.e. HOR activity) are summarized in Fig. 2 (c). The HOR activity of Ir(111) is about 70 % of Pt(111). Though the HOR activity of Pt/Ir(111) is similar to that of Ir(111), the Pt/Ir(111) is ca. 1.5 times more HOR active than Pt(111).In conclusion, through the model catalyst studies (Pt/Ir(111) and Ir/Pt(111)), co-existence of Ir and Pt sites at the topmost surface is effective for developing novel anode catalysts having suppressed H2O2 generation property and practical HOR activity. Acknowledgement This study was supported by the new energy and industrial technology development organization (NEDO) of Japan. References R. Borup et al., Chem. Rev., 107, 3904–3951 (2007) https://pubs.acs.org/doi/10.1021/cr050182l.J. Durst, C. Simon, F. Hasché, and H. A. Gasteiger, J. Electrochem. Soc., 162, F190–F203 (2015).K. Hayashi, T. Tomimori, K. Kusunoki, N. Todoroki, and T. Wadayama, to be submitted.C. M. Sánchez-Sánchez and A. J. Bard, Anal. Chem., 81, 8094–8100 (2009).J. Zhou, Y. Zu, and A. J. Bard, J. Electroanal. Chem., 491, 22–29 (2000).R. Cornut and C. Lefrou, J. Electroanal. Chem., 621, 178–184 (2008). Figure 1

Scanning Ion Conductance Microscopy: Surface Charge Effects on Electroosmotic Flow Delivery from a Nanopipette.

Scanning ion conductance microscopy (SICM) is a powerful and versatile technique that allows an increasingly wide range of interfacial properties and processes to be studied. SICM employs a nanopipette tip that contains electrolyte solution and a quasi-reference counter electrode (QRCE), to which a potential is applied with respect to a QRCE in a bathing solution, in which the tip is placed. The work herein considers the potential-controlled delivery of uncharged electroactive molecules (solute) from an SICM tip to a working electrode substrate to determine the effect of the substrate on electroosmotic flow (EOF). Specifically, the local delivery of hydroquinone from the tip to a carbon fiber ultramicroelectrode (CF UME) provides a means of quantifying the rate of mass transport from the nanopipette and mapping electroactivity via the CF UME current response for hydroquinone oxidation to benzoquinone. EOF, and therefore species delivery, has a particularly strong dependence on the charge of the substrate surface at close nanopipette-substrate surface separations, with implications for retaining neutral solute within the tip predelivery and for the delivery process itself, both controlled via the applied tip potential. Finite element method (FEM) simulations of mass transport and reactivity are used to explain the experimental observations and identify the nature of EOF, including unusual flow patterns under certain conditions. The combination of experimental results with FEM simulations provides new insights on mass transport in SICM that will enhance quantitative applications and enable new possibilities for the use of nanopipettes for local delivery.

Local signatures of electron-electron scattering in an electronic cavity

We image equilibrium and non-equilibrium transport through a two-dimensional electronic cavity using scanning gate microscopy (SGM). Injecting electrons into the cavity through a quantum point contact close to equilibrium, we raster-scan a weakly invasive tip above the cavity regions and measure the modulated conductance through the cavity. Varying the electron injection energy between $\pm$ 2 meV, we observe that conductance minima turn into maxima beyond the energy threshold of $\pm$ 0.6 meV. This observation bears similarity to previous measurements by Jura et al. [Jura et al., Phys. Rev. B 82, 155328 (2010)] who used a strongly invasive tip potential to study electron injection into an open two-dimensional electron gas. This resemblance suggests a similar microscopic origin based on electron-electron interactions.

Accurate characterization of tip-induced potential using electron interferometry

Using the tip of a scanning probe microscope as a local electrostatic gate gives access to real-space information on electrostatics as well as charge transport at the nanoscale, provided that the tip-induced electrostatic potential is well known. Here, we focus on the accurate characterization of the tip potential, in a regime where the tip locally depletes a two-dimensional electron gas (2DEG) hosted in a semiconductor heterostructure. Scanning the tip in the vicinity of a quantum point contact defined in the 2DEG, we observe Fabry–Pérot interference fringes at low temperature in maps of the device conductance. We exploit the evolution of these fringes with the tip voltage to measure the change in the depletion radius by electron interferometry. We find that a semi-classical finite-element self-consistent model taking into account the conical shape of the tip reaches a faithful correspondence with the experimental data.

Evaluation of Anticorrosion Properties of Epoxy-Silane Hybrid Nanocomposite Coating on AA6082 Aluminum Alloy

The protection properties of (3-aminopropyl)trimethoxysilane (APTMS) incorporated epoxy coating on aluminum alloy were studied by electrochemical techniques such as electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) analysis in seawater. The epoxy-APTMS coated Al alloy displayed higher charge transfer resistance (Rct) as well as film resistance (Rf) at 1 day immersion. However, both Rct anf Rf values decreased slowly compared to pure epoxy coated alloy which showed significant decrease in Rct and Rf values with increase in immersion time in chloride media. The released Al3+ ions were detected using SECM by applying the tip potential of –0.85 V. It was evident from the SECM measurement that the dissolution of Al3+ ions was impeded at the scratch of epoxy-APTMS coated Al alloy due to the presence of electron donating amino group in APTMS which inhibited Al alloy degradation. The enrichment of Mg, Mn, Si and Al at the scratch of epoxy-APTMS coated Al alloy was confirmed by Field emission-scanning electron microscopy/energy dispersive X-Ray spectroscopy (FE-SEM/EDX) analysis. Focused ion beam-transmission electron microscopy (FIB-TEM) analysis proved the presence of thin films of nano level oxide layers containing Mg, Mn, Si and Al in the coatings, which decreased the corrosion rate of Al alloy. The enhanced adherence of epoxy-APTMS coating to Al alloy was due to the strong chemical bonding between epoxy-APTMS and Al alloy. Therefore, the pronounced protection performance against corrosion and good adhesion strength was due to the incorporation of APTMS with epoxy coatings.

Time-Resolved Fluorescence Microscopy Combined with Scanning Electrochemical Microscopy: A New Way to Visualize Photo-Induced Electron Transfer Quenching with an Electrofluorochromic Probe

The combination of Scanning Electrochemical Microscopy (SECM) and Time-Resolved Fluorescence Microscopy was successfully implemented to investigate the control of the fluorescence of a tetrazine derivative in solution according to its redox state, a phenomenon called electrofluorochromism. The normalized fluorescence intensity difference between the 'on' and 'off' states can be tuned by the tip potential and the distance between the polarized tip and the substrate. It is demonstrated for the first time that luminescence lifetime can be modulated as well, an evidence that a quenching process contributes to the fluorescence intensity drop. The experimental results demonstrate that this quenching is due to the electron transfer reaction between the excited fluorophore and the electrogenerated anion radical. A mixed dynamic and static quenching mechanism is considered to fit the variations of both luminescence intensity and lifetime ratios vs. the coulombic charge. The pertinence of a static quenching is validated by DFT calculations. Insulating (glass) and conductive (ITO) substrates have been tested and optical approach curves based on fluorescence lifetime modulation have been obtained in each case that are more sensitive than the electrochemical one based on the tip current. Finally, numerical simulations have been performed to fit these optical approach curves and validate the role of the electron transfer quenching in the variation of fluorescence intensity and lifetime.

Dissipation without resistance: Imaging impurities at quantum Hall edges

Motivated by the recent experiment by Marguerite et al. [1] on imaging in graphene samples, we investigate theoretically the dissipation induced by resonant impurities in the quantum Hall regime. The impurity induced forward scattering of electrons at quantum Hall edges leads to an enhanced phonon emission, which reaches its maximum when the impurity state is tuned to resonance by a scanning tip voltage. Our analysis of the effect of the tip potential on the dissipation reveals peculiar thermal rings around the impurities, in consistency with experimental observations. Remarkably, this impurity-induced dissipation reveals non-trivial features that are unique for chiral 1D systems such as quantum Hall edges. First, the dissipation is not accompanied by the generation of resistance. Second, this type of dissipation is highly nonlocal: a single impurity induces heat transfer to phonons along the whole edge.

Polymeric Nematics of Associating Rods: Phase Behavior, Chiral Propagation, and Elasticity

Rod-shaped colloids with attractive tips can form linear aggregates that may subsequently undergo hierarchical self-assembly into nematic fluids. Inspired by recent modelling efforts on chromonic liquid crystals, composed of discotic building blocks, we formulate a second-virial theory for reversible supramolecular rods. Unlike chromonics, these systems are capable of forming stable nematic phases in the high-temperature, monomeric limit in the absence of polymerization. Changing the tip potential from attractive to repulsive thus enables a smooth crossover from a monomeric to a polymeric nematic fluid. We analyze the isotropic-nematic phase behavior for both regimes and address the nematic elastic properties. The theory accounts for the molecular flexibility and chirality of the filaments and respects the intrinsic chain-length dependence of nematic order. We also discuss the impact of polymerization inhibitors on the phase behavior in the polymeric regime and find that the inhibitors cause a marked narrowing of the isotropic-nematic biphasic region, and generate reentrance nematization as well as a mass density inversion of the coexisting phases. We finally discuss the elastic moduli of rod-based polymeric nematics by qualitative comparing their elastic anisotropies with those of chromonic liquid crystals and other nanoparticle-based nematics.

Investigation on the anticorrosion, adhesion and mechanical performance of epoxy nanocomposite coatings containing epoxy-silane treated nano-MoO3 on mild steel

The effect of introducing MoO3 (Molybdenum oxide) nanoparticle in the epoxy coating was analyzed by EIS and SECM methods in natural seawater. The aminopropyl triethoxy silane (APTES) was treated with the nanoparticle for the proper dispersion and chemical interaction of nanoparticle with the epoxy resin. The introduction of MoO3 nanoparticle in the epoxy coating enhances the charge transfer resistance (Rct) as well as the film resistance (Rf). The observation of iron dissolution and oxygen consumption was carried out by applying the appropriate SECM tip potential in the MoO3 modified nanocomposite coated steel. The epoxy and epoxy-MoO3 nanocomposite-coated samples were used to study the mechanical, adhesion and anticorrosion properties. The analysis using SEM/EDX displayed that the enriched Mo was detected in the nanocomposite coated steel. The presence of the nano level corrosion product containing Mo was confirmed by FIB-TEM analysis. The high corrosion protection properties of the epoxy based nanocomposite coating was due to the complex nanoscale layer formed and chemical interactions of epoxy resin with surface-modified nanoparticle in nanocomposites.

Investigation into the Corrosion Behavior of Copper/Aluminum Associated with Electric/Electronic Devices in Marine Environment

Corrosion behavior of copper/aluminum was investigated using cyclic wet/dry corrosion test in natural seawater by electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM). The higher charge transfer resistance (Rct) and film resistance (Rf) at 15 d of w/d cyclic corrosion test were shown by EIS plots. The anodic surface releases Al3+ and Cu+ ions into the electrolyte, and the cathodic surface consumes dissolved oxygen. These ions and dissolved oxygen are detected by applying appropriate tip potential in SECM technique. The results showed that the corrosion activity of aluminum was accelerated due to the potential difference of the sample. The scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDX) analysis showed the enrichment of Cu and Al in corrosion products at the surface of Cu/Al sample after electrochemical analysis. The focused ion beam/transmission electron microscopy (FIB-TEM) analysis confirmed the presence of the nanoscale oxide layers containing Cu and Al in the corrosion product of the Cu/Al sample. The formation of corrosion products has a beneficial effect on corrosion resistance of Cu/Al sample.

Investigation into the Effect of Cr2O3 Nanoparticles on the Protective Properties of Epoxy Coatings on Carbon Steel in 3.5% NaCl Solution by Scanning Electrochemical Microscopy

The effect of introducing chromium oxide (Cr2O3) nanoparticles in the epoxy coatings on carbon steel was analyzed using Scanning Electrochemical Microscopy (SECM) and Electrochemical Impedance Spectroscopy (EIS). Localized measurements such as oxygen consumption and iron dissolution were observed using SECM in 3.5% NaCl in the epoxy coated sample. Line profile and topographic image analysis were measured by applying –0.70 and +0.60 V as the tip potential for the cathodic and anodic reactions, respectively. The tip current at –0.70 V for the epoxy coated sample with Cr2O3 nanoparticles decreased rapidly, which is due to cathodic reduction of dissolved oxygen. The EIS measurements were conducted in 3.5% NaCl after wet and dry cyclic corrosion test. The increase in the film resistance (Rf) and charge transfer resistance (Rct) values was confirmed by the addition of Cr2O3 nanoparticles in the epoxy coating. SEM/EDX analysis showed that Cr2O3 was enriched in corrosion products at a scratched area of the coated steel after corrosion testing. FIB-TEM analysis confirmed the presence of the nanoscale oxide layer of Cr2O3 in the rust of the steel, which had a beneficial effect on the corrosion resistance of coated steel by forming protective corrosion products in the wet/dry cyclic test.

Scanning gate experiments: From strongly to weakly invasive probes

One of the fundamental aims of scanning gate microscopy is to measure local properties of high-mobility two-dimensional electronic systems. Here, the authors present a study which sheds light on the invasiveness of the scanning probe. The two-dimensional system is shaped into a ballistic cavity, which progressively concentrates the local density of states in order to study the transition from weakly to strongly invasive measurements. A good agreement between experiment and theory allows for the identification of the imaging mechanisms according to the strength of the tip potential. The insights gained lead to a deeper understanding of weakly invasive scanning gate imaging.

In Situ Electrochemical Tip-Enhanced Raman Spectroscopy with a Chemically Modified Tip.

Chemically modified tips in scanning tunneling microscopy (STM) and atomic force microscopy (AFM) have been used to improve the imaging resolution or provide richer chemical information, mostly in ultrahigh vacuum (UHV) environments. Tip-enhanced Raman spectroscopy (TERS) is a nanoscale spectroscopic technique that already provides chemical information and can provide subnanometer spatial resolution. Chemical modification of TERS tips has mainly been focused on increasing their lifetimes for ambient and in situ experiments. Under UHV conditions, chemical functionalization has recently been carried out to increase the amount of chemical information provided by TERS. However, this strategy has not yet been extended to in situ electrochemical (EC)-TERS studies. The independent control of the tip and sample potentials offered by EC-STM allows us to prove the in situ functionalization of a tip in EC-STM-TERS. Additionally, the Raman response of chemically modified TERS tips can be switched on and off at will, which makes EC-STM-TERS an ideal platform for the development of in situ chemical probes on the nanoscale.