Kelvin Probe Force Microscopy Research Articles

Role of Smart-Release Pigments in Preventing Corrosion Driven Cathodic Disbondment of Organically Coated Hot Dip Galvanised Steel

The role of smart-release corrosion inhibitive pigments in preventing cathodic delamination of organically coated hot-dip galvanized steel (HDG) is investigated. The pigments consisted of hydrotalcite (HT) exchanged with a range of inorganic and organic anionic species and were dispersed in a model PVB coating. A scanning Kelvin probe (SKP) technique was used to determine cathodic delamination rates, and the inhibition efficiencies obtained for inorganic ions increased in the order < < < < < < The inhibition efficiencies for organic-based pigments increased in the order triazole <phenylphosphonate <trans-cinnamate <benzoate <salicylate <benzotriazole. The inhibition efficiency afforded by the best performing organic inhibitor, benzotriazole (BTA), rivalled that of HT containing stored chromate anions. Findings are consistent with HT-BTA acting to sequester anions from the underfilm electrolyte, releasing BTA− which subsequently strongly adsorbs on the underfilm metal surface but can also form an insoluble Zn-BTA precipitate at the coating-defect boundary.

Direct Z-scheme heterojunction of PCN-222/CsPbBr3 for boosting photocatalytic CO2 reduction to HCOOH

Exploring photocatalysts with efficient charge separation to boost CO2 reduction to valuable chemicals is of great significance. Herein, we develop a PCN-222/CsPbBr3 hybrid with direct Z-scheme heterojunction for high-efficiency photoreduction of CO2 to HCOOH. By delicately controlling the interface of the PCN-222/CsPbBr3 hybrid, effective electron transfer from CsPbBr3 to PCN-222 is achieved, leading to the construction of an internal electric field (IEF). The photo-induced electrons transfer from PCN-222 to CsPbBr3 under visible light irradiation derived from IEF is confirmed by in-situ X-ray photoelectron spectroscopy (XPS), transient absorption (TA), and Kelvin probe force microscopy (KPFM), resulting in the impactful spatial separation of electron-hole pairs. The optimized PCN-222/CsPbBr3 catalyst with direct Z-scheme heterojunction finally offers a 7.0- and 2.1-times enhancement in CO2 photoreduction to HCOOH compared to pristine PCN-222 and CsPbBr3, respectively. This work provides a facile strategy for developing superior perovskite-based CO2RR photocatalysts with both high catalytic activity and selectivity of value-added products.

Quantifying nanoscale charge density features of contact-charged surfaces with an FEM/KPFM-hybrid approach

Kelvin probe force microscopy (KPFM) is a powerful tool for studying contact electrification (CE) at the nanoscale, but converting KPFM voltage maps to charge density maps is nontrivial due to long-range forces and complex system geometry. Here we present a strategy using finite-element method (FEM) simulations to determine the Green's function of the KPFM probe/insulator/ground system, which allows us to quantitatively extract surface charge. Testing our approach with synthetic data, we find that accounting for the atomic force microscope (AFM) tip, cone, and cantilever is necessary to recover a known input and that existing methods lead to gross miscalculation or even the incorrect sign of the underlying charge. Applying it to experimental data, we demonstrate its capacity to extract realistic surface charge densities and fine details from contact-charged surfaces. Our method gives a straightforward recipe to convert qualitative KPFM voltage data into quantitative charge data over a range of experimental conditions, enabling quantitative CE at the nanoscale.

Utilizing the surface potential of a solid electrolyte region as the potential reference in Kelvin probe force microscopy.

In electrochemical measurements, monitoring the electrode potential using a stable reference is essential for controlling the redox reactions that occur at the electrodes. In Kelvin probe force microscopy (KPFM) measurements on electrochemical cells, the surface potential is generally measured relative to electrical ground instead of a stable reference. Here, we show that the changes in the surface potential, measured using KPFM relative to the surface potential in the electrolyte region, is consistent with the changes in the electrode potential measured using a voltmeter relative to a reference electrode. These results demonstrate that the surface potential in the electrolyte region can be utilized as a stable potential reference when analyzing KPFM data.

Nanoscale probing of surface potential landscape at MoS2/BP van der Waals p–n heterojunction

2D van der Waals heterostructure paves a path towards next generation semiconductor junctions for nanoelectronics devices in the post silicon era. Probing the band alignment at a real condition of such 2D contacts and experimental determination of its junction parameters is necessary to comprehend the charge diffusion and transport through such 2D nano-junctions. Here, we demonstrate the formation of the p–n junction at the MoS2/Black phosphorene (BP) interface and conduct a nanoscale investigation to experimentally measure the band alignment at real conditions by means of measuring the spatial distribution of built-in potential, built-in electric field, and depletion width using the Kelvin probe force microscopy (KPFM) technique. We show that optimization of lift scan height is critical for defining the depletion region of MoS2/BP with nanoscale precision using the KPFM technique. The variations in the built-in potential and built-in electric field with varying thicknesses of MoS2 are revealed and calibrated.

Synthesis of ((CeO2)0.8(Sm2O3)0.2)@NiO Core-Shell Type Nanostructures and Microextrusion Printing of a Composite Anode Based on Them.

The process of the hydrothermal synthesis of hierarchically organized nanomaterials with the core-shell structure with the composition ((CeO2)0.8(Sm2O3)0.2)@NiO was studied, and the prospects for their application in the formation of planar composite structures using microextrusion printing were shown. The hydrothermal synthesis conditions of the (CeO2)0.8(Sm2O3)0.2 nanospheres were determined, and the approach to their surface modification by growing the NiO shell with the formation of core-shell structures equally distributed between the larger nickel(II) oxide nanosheets was developed. The resulting nanopowder was used as a functional ink component in the microextrusion printing of the corresponding composite coating. The microstructure of the powders and the oxide coating was studied by scanning (SEM) and transmission electron microscopy (TEM), the crystal structure was explored by X-ray diffraction analysis (XRD), the set of functional groups in the powders was studied by Fourier-transform infrared spectroscopy (FTIR) spectroscopy, and their thermal behavior in an air flow by synchronous thermal analysis (TGA/DSC). The electronic state of the chemical elements in the resulting coating was studied using X-ray photoelectron spectroscopy (XPS). The surface topography and local electrophysical properties of the composite coating were studied using atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM). Using impedance spectroscopy, the temperature dependence of the specific electrical conductivity of the obtained composite coating was estimated.

D 6 h Symmetric Radical Donor–Acceptor Nanographene Modulated Interfacial Carrier Transfer for High-Performance Perovskite Solar Cells

<i>D</i> ^{6 <i>h</i>} Symmetric Radical Donor–Acceptor Nanographene Modulated Interfacial Carrier Transfer for High-Performance Perovskite Solar Cells

Dual-bias modulation heterodyne Kelvin probe force microscopy in FM mode

The use of a heterodyne detection scheme in Kelvin probe force microscopy (KPFM) is an effective way for enhancing the performance of KPFM. However, this detection scheme generally has difficulty in detecting the first- and second-harmonic electrostatic forces simultaneously. To overcome this problem, we propose dual-bias modulation heterodyne frequency modulation KPFM (DM-hetero-FM KPFM), in which dual AC biases at 2f1±fm are applied between the tip and the sample. DM-hetero-FM KPFM enables us to measure the contact potential difference and capacitance gradient simultaneously at high frequencies (in the MHz range) beyond the bandwidth of phase-lock loop. Moreover, the present method allows us to perform it in the open-loop mode, which is highly desired for performing KPFM on semiconductors or in liquids at high frequencies.

Extended Work Function Shift of Large‐Area Biofunctionalized Surfaces Triggered by a Few Single‐Molecule Affinity Binding Events

AbstractFew binding events are here shown to elicit an extended work function change in a large‐area Au‐surface biofunctionalized with ≈108 capturing antibodies. This is demonstrated by Kelvin probe force microscopy (KPFM), imaging a ≈105 µm2 wide Au‐electrodes covered by a dense layer (≈104 µm−2) of physisorbed anti‐immunoglobulin‐M (anti‐IgM). A 10 min incubation in 100 µL phosphate buffer saline solution encompassing ≈10 IgM antigens (10−19 mole L−1  102 × 10−21 m) produces a work function shift ΔW ≈ –60 meV. KPFM images prove that this shift involves the whole inspected area. Notably, no work function change occurs upon incubation in highly concentrated (3 × 10−15 m) nonbinding IgG solutions. The ΔW measured by KPFM is in quantitative agreement with the threshold voltage shift of an electrolyte‐gated single‐molecule large‐area transistor (SiMoT). The findings provide direct experimental evidence for the SiMoT ultrahigh sensitivity, by imaging the extensive shift of the gate work function, likely arising from collective surface phenomena, elicited by single‐molecule binding events.

Morphology and Luminescence Regulation for CsPbBr3 Perovskite Light-Emitting Diodes by Controlling Growth of Low-Dimensional Phases.

At present, the high defect density and strong nonradiative recombination rate of all-inorganic cesium lead bromide (CsPbBr3) perovskite light-emitting diodes (PeLEDs) seriously inhibit the improvement of their quantum efficiency. In this paper, the addition of a short-chain additive, diethylammonium bromide (DEABr), aims to control the generation of a quasi-2D large n-phase to optimize the surface morphology and construct two-dimensional/three-dimensional (2D/3D) heterojunction perovskite structures to enhance the EL efficiency of PeLEDs. Through Kelvin probe force microscopy (KPFM) characterization, we confirmed that the 2D phase grains with a low potential are locally formed on the surface of the perovskite film under the action of DEABr. The existence of the 2D phase effectively improved the surface morphology and suppressed surface defects. In addition, the in situ constructed 2D/3D heterojunction perovskite structure further increases the exciton radiative recombination rate and significantly improves the electroluminescent performance. By optimizing its doping concentration, the optimal all-inorganic PeLED displays a current efficiency (CE) of 30.3 cd A-1, an external quantum efficiency (EQE) of 9.6%, and a maximum brightness of 32,500 cd m-2. According to our results, the formation of 2D structures on the surface of the CsPbBr3 film can improve surface morphology issues and optoelectronic properties of the film.

Influence of self-doping on band-edges and Fermi energy of CsPbBr3

The electronic properties of CsPbBr 3 thin films cast through a solution route are known to depend on the stoichiometry of the precursors. In this work, with the aid of Kelvin probe force microscopy (KPFM) and scanning tunneling spectroscopy (STS) studies, a complete energy landscape has been derived for the all-inorganic perovskite formed with a wide range of precursor stoichiometries. While the optical band gap of the perovskite is known to remain unchanged with a variation in the stoichiometry, we show the manner in which their Fermi energy, valence band (VB), and conduction band (CB) edges shift. The variation in the energy levels has been correlated to the presence of defects. Since the formation energy of different intrinsic point defects depends on the growth environment, the nature of defects has depended on the precursor stoichiometry used during the formation of the perovskites. The presence of defects has thereby tuned the Fermi energy and the type of electronic conductivity in CsPbBr 3 as well. Here, the CB and VB edges have responded due to the self-doping process. Finally, we have presented the energy landscape of the perovskite with a variation in the precursor stoichiometry, since the energy levels are indeed crucial in designing any optoelectronic devices based on CsPbBr 3 . • Fermi level and band edges of CsPbBr 3 are affected by the precursor stoichiometry. • Energy landscape of the perovskite derived from a combination of KPFM and STS. • CsPbBr 3 formed with CsBr-rich precursors has p -type conductivity. • CsPbBr 3 formed with PbBr 2 -rich growth condition exhibits an n -type behavior. • Bands moved away from vacuum level in perovskites formed in PbBr 2 -rich environment.

Suppressing piezoelectric screening effect at atomic scale for enhanced piezoelectricity

Zinc oxide (ZnO) is one of the most popular piezoelectric materials since it is non-toxic and environmentally friendly. However, its widespread adoption is largely hindered by its lower piezoelectricity. Herein, we report a generalizable approach to improving the piezoelectricity of ZnO via suppressing its piezoelectric screening effect at an atomic scale via rare earth (RE) ions doping. The developed Y3+: ZnO demonstrates a 91.8%-dropped carrier concentration and a 53.8%-increased surface piezoelectric response compared to undoped ZnO. Combining work function from Kelvin probe force microscopy (KPFM) and piezoelectric response distribution from piezoresponse force microscopy (PFM), this work reveals that the RE ion doping strategy can indeed suppress the piezoelectric screening effect and thus greatly enhance the piezoelectricity. The contribution of the atomic suppression strategy of screening effect to the community is two-fold: 1. it provides a fundamental understanding of intrinsic piezoelectric mechanism in the ZnO. 2. it could be extended and adapted to other piezoelectric materials. Overall, this work opens a new strategy for piezoelectric enhancement and applicative piezoelectrics.

Enwrapping g-C3N4 on In2O3 hollow hexagonal tubular for photocatalytic CO2 conversion: Construction, characterization, and Z-scheme mechanism insight

The reduction of CO2 achieved by photocatalysis can simultaneously alleviate the energy crisis and solve environmental issues. Nevertheless, it remains challenging for the rational design of photocatalysts with high-efficiency carrier migration ability. Herein, the Z-scheme g-C3N4/In2O3 (CN/INO) heterostructure was fabricated via metal–organic frameworks (MOFs) assisted thermal deposition which could form a fully encapsulated hollow tubular structure. The unique structure was based on the MOFs-derived hollow hexagonal In2O3 tubular integrated with ultrathin g-C3N4. The Z-scheme CN/INO heterojunction exhibited a larger specific surface area and excellent charge separation efficiency. Benefiting from the above features, the Z-scheme CN/INO heterojunction demonstrated superior performance on photocatalytic CO2 reduction. The formation of CO and CH3OH over the optimized CN/INO-2 catalyst was 7.94 and 1.44 µmol⋅g−1⋅h−1, respectively. Moreover, the density functional theory (DFT) calculations and Kelvin probe force microscopy (KPFM) was carried out to further investigate the situation of charge transfer on the interface of CN/INO. The in-situ Fourier transform infrared spectroscopy (FTIR) was measured to confirm the immediate products and the possible mechanism of photocatalytic CO2 reduction was proposed. This work provided a MOFs-assisted strategy to construct a Z-scheme system for photocatalytic CO2 reduction.

Microextrusion Printing of Hierarchically Structured Thick V2O5 Film with Independent from Humidity Sensing Response to Benzene.

The process of V2O5 oxide by the combination of sol-gel technique and hydrothermal treatment using heteroligand [VO(C5H7O2)2-x(C4H9O)x] precursor was studied. Using thermal analysis, X-ray powder diffraction (XRD) and infra-red spectroscopy (IR), it was found that the resulting product was VO2(B), which after calcining at 300 °C (1 h), oxidized to orthorhombic V2O5. Scanning electron microscopy (SEM) results for V2O5 powder showed that it consisted of nanosheets (~50 nm long and ~10 nm thick) assembled in slightly spherical hierarchic structures (diameter ~200 nm). VO2 powder dispersion was used as functional ink for microextrusion printing of oxide film. After calcining the film at 300 °C (30 min), it was found that it oxidized to V2O5, with SEM and atomic force microscopy (AFM) results showing that the film structure retained the hierarchic structure of the powder. Using Kelvin probe force microscopy (KPFM), the work function value for V2O5 film in ambient conditions was calculated (4.81 eV), indicating a high amount of deficiencies in the sample. V2O5 film exhibited selective response upon sensing benzene, with response value invariable under changing humidity. Studies of the electrical conductivity of the film revealed increased resistance due to high film porosity, with conductivity activation energy being 0.26 eV.

The surface charge decay: A theoretical and experimental analysis

The ability to retain localized charges at the surface or interface of dielectric materials is a universal property that applies to many different fields such as tribocharging, charge nanopatterning, nanoxerography, etc. Once the surface is charged, its stability and subsequent discharging rate will determine the potential applications of a given system. This decay rate is properly defined by the macroscopic equations which depend on dielectric constants and conductivities of the two media. Here, we derive the equations to model the decay of charge distributions localized at the surface/interface of materials and solve them avoiding additional approximations made so far. Addressing the problem in the Fourier space, we arrive to a compact generic equation which provides a useful tool to determine both the bulk and surface conductivities of a material. Furthermore, we show that Kelvin Probe Force Microscopy (KPFM) is a particularly suited method to exploit this tool. Monitoring the charge decay of previously injected charge patches on silicon dioxide (SiO2), together with an appropriated data analysis, we verify the behavior predicted by our equations. This allows us to characterize the surface and bulk conductivities of SiO2 layers as well as its dependence with the relative humidity.

Biomimetic liquid infused surface based on nano-porous array: Corrosion resistance for tin metal and self-healing property

Tin material corrosion has been recognized as an important problem for electronic products. Biomimetics strategies have been adopted to develop intriguing materials to combat corrosion. In this paper, by anodic oxidation, mussel inspired dopamine hydrochloride modification and thiol grafting, lotus leaf inspired superhydrophobic surface (SHS) based on porous SnO2 coating is prepared on tin. Further, a stable liquid infused surface (LIS) enlightened by Nepenthes plant is formed by infusing dimethyl silicone oil into SHS. The wettability, microstructure and chemical composition of tin surface with different modification are characterized by contact angle, scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and so forth. The porous SnO2 structure endows superhydrophobicity with a contact angle up to 155.9°. The corrosion resistance of SHS and LIS coating is revealed by scanning Kelvin probe (SKP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) curves. Corrosion data show that the prepared LIS exhibits better corrosion resistance than SHS. After being soaked in a representative 3.5 wt% NaCl solution for 180 h, the corrosion inhibition efficiency of LIS maintains 99.6%, which is much better than that of SHS. In addition, when being fold or bent to induce cracks, the LIS shows slight change in corrosion inhibition efficiency, indicating the high tolerance to mechanical torsion. Moreover, in response to externally imposed mechanical scratching, LIS demonstrates good self-healing capability, illustrating the high potential for practical usage.

Investigating local corrosion processes of magnesium alloys with scanning probe electrochemical techniques: A review

The study of corrosion of magnesium and its alloys has emerged a hot topic in the applications of lightweight structural materials. The inherently high electrochemical activity of bare magnesium surfaces still lacks a convincing mechanism to describe the observed experimental characteristics, and it has prompted the development of various types of protective coatings with the aim of slowing metal dissolution. In recent years, new instruments and techniques have been developed to study with spatial resolution the local corrosion processes that occur in metallic materials in general, and for magnesium and its alloys in particular, both for bare surfaces and coated. Scanning microelectrochemical techniques, such as local electrochemical impedance spectroscopy (LEIS), scanning electrochemical microscopy (SECM), scanning vibrating electrode technique (SVET), scanning ion-selective electrode technique (SIET) and scanning Kelvin probe (SKP) can provide information about the local electrochemical activity of metallic surfaces. In the present work, the applications of these techniques in corrosion studies of magnesium and its alloys are reviewed. Assessment of corrosion mechanisms, barrier properties of conventional coatings and active corrosion behavior of self-healing coatings are examined. Limitations and future developments in this area are discussed.

Modifying transparent electrode with conjugated organic semiconductor hole transport material as interface for enhancing performance of organic solar cell

Indium tin oxide (ITO) is used as a substrate was covered with 4-[4-(4-methoxy-N-naphthalen-2-ylanilino) phenyl] benzoic acid (MNA) as a self-assembled monolayer (SAM). Poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6) C61 (PCBM) were mixed and used as a donor–acceptor in organic solar cell (OSC). The MNA (SAM) layer is used as an interface instead of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS) for hole injection. The HOMO-LUMO energy level of MNA-SAM molecule and the electronic charge distribution were calculated theoretically using Chemissian software. The HOMO-LUMO energy level of the MNA is calculated as EHOMO = −5.10 eV and ELUMO = −1.60 eV. The OSC modified with MNA showed an efficient performance in the absence of PEDOT: PSS as hole transport layer. The annealing of the ITO/SAM/P3HT: PCBM films at different temperatures are also investigated to study the effect of reducing defects. The interface structures of the organic semiconductor layer on ITO were characterized by Atomic Force Microcopy (AFM). In addition, Kelvin Probe Microscopy (KPM) is used to understand how the annealing changes the surface potential energy of the ITO/SAM substrate. Using the KPM method, which measures the surface potential energy of the films, the energy bands of the ITO were increased to maximum 5.09 eV. The ITO/SAM/P3HT: PCBM film's surface potential was determined to be 0.18 eV after being annealed at 80 °C. The surface potential of the modified films was discovered to be 0.33 V and 0.39 V when the annealing temperature was raised from 80 °C to 120 °C and 160 °C. The maximum device efficiency was demonstrated by the ITO/SAM/P3HT: PCBM film after an hour of annealing at 160 °C.

Charge-biased nanofibrous membranes with uniform charge distribution and hemocompatibility for enhanced selective adsorption of endotoxin from plasma

Endotoxin has been recognized as the crucial inducer for sepsis, and selective removal of endotoxin from plasma in vitro is the popular therapeutic strategy, such as hemoperfusion technology based on adsorption. Construction of hemoperfusion adsorbents with high endotoxin adsorption capacity in plasma is critical to meet the demands of hemoperfusion therapy for sepsis. However, it has proven to be challenging because of the adhesion of plasma protein. Inspired by the antiadhesion property of mixed-charge polymers and the endotoxin adsorption property of polyethyleneimine, here, a charge-bias, endotoxin selectively adsorbable and hemocompatible layer was constructed on nanofibrous surface of polysulfone (PSF) electrospun nanofibrous membrane (ENM) by the co-deposition of positively-charged polyethyleneimine (PEI) and negatively-charged polydopamine (PDA). The charge-bias degree of PEI/PDA co-deposition layer was quantified through zeta potential measurement, and firstly visualized through Kelvin probe force microscopy (KPFM) measurement. The continuity and integrity of PEI/PDA layer were characterized by XPS and TEM. We showed that the light positive charge-bias of the PEI/PDA layer in physiological environment (pH = 7.4) can macroscopically drove the adsorption selectivity towards endotoxins via electrostatic interaction, and uniformly distributed positive and negative charges can microscopically drove the anti-protein adhesion property. The resultant PEI/PDA@PSF ENM exhibited high adsorption capacity of 9049 EU/g in plasma, which is much higher than commercial endotoxin adsorbents. Notably, PEI/PDA@PSF ENM possessed satisfactory anti-plasma protein adhesion property, hemocompatibility and had no adverse effects on blood components, especially plasma protein. This work suggests a feasible approach for producing ENMs-based hemoperfusion adsorbent matrix for endotoxin-induced sepsis.

Enhanced Optoelectronic Performance Induced by Ion Migration in Lead-Free CsCu2I3 Single-Crystal Microrods.

Lead-free perovskite has attracted great attention in realizing high-performance optoelectronic devices due to their excellent atmospheric stability and nontoxic characteristics. Although a pronounced ion migration effect has been observed in this new class of materials, its potential in enhancing the overall device performance is yet to be fully explored. In this work, we studied the effect of ion migrations on the carrier transport behavior and found that the recoverable migration process can contribute to enhancing the on/off ratio in a lead-free CsCu2I3 single-crystal microrod-based photodetector. In detail, we synthesized CsCu2I3 single-crystal microrods via an in-plane self-assembly supersaturated crystallization approach. These microrods with well-defined morphologies were then used to construct ultraviolet (UV)-band photodetectors, which outperform most reported lead-free perovskite photodetectors based on individual single crystals. Simultaneously, ion migration can result in asymmetric band bending in the two-terminal device, as confirmed by surface potential profiling with Kelvin probe force microscopy (KPFM). Such an effect can be harnessed to increase the on/off ratio by almost an order of magnitude. Furthermore, the lead-free CsCu2I3 single crystal exhibits excellent thermal and air stabilities. These findings demonstrate that the CsCu2I3 single-crystal microrods can be used in stable and efficient photodetection, and the ion migration effect can potentially be utilized for improving the optoelectronic performance of lead-free devices.