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In this contribution we demonstrate doping of graphene by uncharged dibenzyl viologen (DBV0). Deposited electrochemically on chemical vapor deposited (CVD) graphene on SiO2, DBV0 forms a water-insoluble self-assembled molecular network, in contrast to water-soluble monocationic DBV˙+. The phase formation at the molecular scale is revealed by scanning tunneling microscopy (STM) and atomic force microscopy (AFM). The doping efficiency is characterized by a combination of Raman spectroscopy and Kelvin probe force microscopy (KPFM). The Raman mapping of the G-band of the DBV0 adlayer on top of CVD graphene on SiO2 shows an apparent red shift compared to the unmodified analogue indicating an n-doping effect. This observation is in line with the KPFM results of which the measured contact potential difference (CPD) displays a positive shift compared to that of the pristine graphene.

The optoelectronic performance of organic-inorganic halide perovskite (OIHP)-based devices has been improved in recent years. Particularly, solar cells fabricated using mixed-cations and mixed-halides have outperformed their single-cation and single-halide counterparts. Yet, a systematic evaluation of the microstructural behavior of mixed perovskites is missing despite their known composition-dependent photoinstability. Here, we explore microstructural inhomogeneity in (FAPbI

Probing CO at a specific site on a metal oxide surface is essential for characterizing various applications such as CO oxidation, hydrogenation, and water-gas shift reaction. Herein, we use atomic force microscopy and Kelvin probe force microscopy to probe the CO on a rutile TiO2(110) surface. Our results indicate that CO can be manipulated along the Ti row by the repulsive lateral force of “pushing” mode. Furthermore, the joint combination of precise manipulation and the distance dependence of local contact potential difference allow us to resolve the interatomic dipole moment and charge state of CO at atomic resolution. Therefore, we found that the negatively charged CO with the dipole moment of negative pole down on the rutile TiO2(110) surface. Our results suppose that both the charge state as well as the on-surface dipole interaction are very effective for CO reaction on rutile TiO2(110) surface.

Herein, we prepared CuI film by spray pyrolysis technique, and Ag nanoparticles decorated CuI thin film by photoreduction method, surface modified approach for improving the interfacial charge transfer property and work function of hole transport layer (HTL) in Perovskite Solar Cell (PSC). The concentration of the Ag was investigated by immersing the CuI thin film in the Ag solution at time intervals. The crystalline property and vibration spectra of the as-fabricated thin film were examined by an X-ray diffraction pattern (XRD) and Raman Spectroscopy. The work function of the as-fabricated thin film was analyzed by Contact Potential Difference (CPD) method as a result of Scanning Kelvin Probe (SKP). The charge transfer resistance of the working electrodes was studied, and the least dipping time sample shows the low charge transfer resistance (36.35 Ω) and less relaxation time (0.19 s).

Potential of zero charge (PZC) is an important reference for understanding the interface charge and structure at a given potential, and its difference from the work function of metal surface (ΦM) is defined as the Volta potential difference (ΔΦ). In this work, we model 11 metal/water interfaces with ab initio molecular dynamics. Interestingly, we find ΔΦ is linearly correlated with the adsorption energy of water (Eads) on the metal surface. It is revealed that the size of Eads directly determines the coverage of chemisorbed water on the metal surface and accordingly affects the interface potential change caused by electron redistribution (ΔΦel). Moreover, ΔΦ is dominated by the electronic component ΔΦel with little orientational dipole contributing, which explains the linear correlation between ΔΦ and Eads. Finally, it is expected that this correlation can be helpful for effectively estimating the ΔΦel and PZC of other metal surfaces in the future work.

In this work, a high-entropy alloy and CrZrTiNiCu coating were synthesized by mechanical alloying. It is shown that the microhardness of the CrZrTiNiCu coating is not inferior to and in most cases exceeds the hardness of high-entropy equiatomic alloys. The wear resistance of such a coating is 3·10-4 g/min, which also corresponds to special steels in terms of wear resistance. The high-entropy coating has a low coefficient of friction. It turns out to be antifrictional, which obviously leads to energy savings. For the first time, the surface energy, contact potential difference and work function of electrons for CrZrTiNiCu coating were determined.

Highly-oriented pyrolytic graphite (HOPG), i.e., the 3D stack of sp2-hybridized carbon sheets, is an attractive material thanks to its high electrical conductivity, chemical inertness, thermal stability, atomic-scale flatness, and ease of exfoliation. Despite an apparently ideal and uniform material, freshly cleaved HOPG shows domains in Kelvin probe force microscopy (KPFM) with surface potential contrast over 30 mV. We systematically investigated these domains using an integrated approach, including time-dependent KPFM and hyperspectral Raman imaging. The observed time-evolving domains are attributed to locally different hydrocarbon adsorption from the environment, driven by structural defects likely related to rotational mismatch, i.e., twisted layers. These defects affect the interlayer coupling between topmost graphene and the underlying layers. Our hypothesis was supported by Raman spectroscopy results, showing domains with G peak shifts and 2D line shape compatible with bilayer graphene. We attribute the selective sensitivity of our Raman spectroscopy results to the top graphene layers as resonances due to van Hove singularities. Our results show that the chemical and electrical properties of HOPG are far more complex than what is generally believed due to the broken symmetry at the top surface, giving rise to graphene bilayer-like behavior.

The atomic diffusion in transition metal dichalcogenides (TMDs) van der Waals heterojunctions (HJs) strongly modifies their optoelectronic properties in the nanoscale. However, probing such localized properties challenges the spatial resolution and the sensitivity of a variety of analytic tools. Herein, a multimodal nanoscopy (based on tip enhanced Raman spectroscopy (TERS) and photoluminescence (TEPL)) combined with the Kelvin probe force microscopy (KPFM) method was used to probe such nanoscale localized optoelectronic properties induced by atomic diffusion. Chemical vapor deposition (CVD)-grown lateral bilayer (2L) WS2/MoS2 HJs were imaged with a spatial resolution better than 40 nm via TERS and TEPL mapping by using intrinsic Raman and photoluminescence (PL) peaks. The contact potential difference (CPD), capacitance, and PL variation in a nanoscale vicinity of the HJ interface can be correlated to the local stoichiometry variation determined by TERS. The diffusion coefficients of W and Mo were obtained to be ∼0.5 × 10-12 and ∼1 × 10-12 cm2/s, respectively, by using Fick's second law. The obtained results would be useful to further understand the localized optoelectronic response of the TMDs HJs.

For steels of different grades, the effect of the chemical composition, structure, and surface etching on the contact potential difference is studied using the Kelvin probe method. It was shown experimentally that, with a change in the structure and chemical composition, the contact potential difference changes. Etching the surface of the steel with a 4% solution of nitric acid leads to a sharp decrease in the magnitude of the contact potential difference, which allows us to conclude that the value of the electron work function from the sample surface increases. The ability to control the composition and structure of the material by the Kelvin probe method is shown.

A free-standing high boron-doped diamond nanosheet (BDDNS) has been fabricated for the development of a flexible BDDNS strain senor. High boron-doped diamond was initially grown on a tantalum substrate in a microwave plasma-assisted chemical vapor deposition method, and was then transferred to a Kapton polymer substrate to fabricate the flexible BDDNS/Kapton device. Before performing the transfer process, the thin BDDNS’s morphology and bonding structure on the top and bottom surfaces were investigated using scanning electron microscopy and Raman spectroscopy. The contact potential difference and work function values of the BDDNS top and bottom surfaces were measured using a Kelvin probe atomic force microscope. Significant electrical conducting properties were observed from the resistance mapping of the BDDNS foil, and the average resistance value of 31 Ω attained from the top surface of the BDDNS foil. The electrical response of the BDDNS/Kapton device was investigated using a custom-made measurement system and a positive residual resistance change with strain was observed. The developed BDDNS/Kapton device was able to sustain for measuring up to 0.55% of strain, which indicates it may have great potential to be utilized in low-strain sensor applications.

The quest for the high speed, low power digital logic circuits urge an imperative demand of compatible high-κ dielectric integration on novel Germanium (Ge) based channel material. Here, first ever a methodical nanoscopic and microscopic probes were attempted to Atomic Layer Deposited, Hafnium Dioxide (HfO2) dielectrics on Molecular Beam Epitaxy (MBE) of p-Ge-on-p-Si stack. Kelvin Probe Force Microscopy based contact potential difference (CPD) analysis reveals that the disintegration of trapped charges lasting for ∼18 hours. The impact of constant voltage stress (CVS) on trapped charges results in variation of threshold voltage (Vth) and hysteresis window (W) were studied. The cyclic Capacitance-Voltage (C-V) characteristics at 0.5 MHz exhibit the shift in the flat band (ΔVfb), ΔVth, and ΔW at 10V stress were ∼0.84V, ∼0.62V, and ∼0.47V, respectively. While the computed interface trap density (Dit) and total effective charge density (Qeff) were ∼8.49 × 1012 eV−1cm−2 and ∼1.81 × 1012 cm−2, respectively. The gate leakage current density, (J) at 5V is 26.53 × 10−6 A/cm2 and reduced by a factor of ∼6.8 after 10V, CVS. Whereas the current density (J) increases from ∼26.53 × 10−6 A/cm2 at 25 °C by a factor of ∼2 at 125 °C. To study the retention and effect of charge trapping, the stress-time analysis was performed for 8000s at 3V (CVS). The r.m.s. surface roughness of HfO2 thin films was found to be ∼0.23 nm. X-ray photoelectron spectroscopy (XPS) depth profiling categorized the elemental composition of thin films. These investigations would help to HfO2/p-Ge-on-p-Si system interfacial engineering well before the Ge based nano device realization.

The paper reviews the results of a study on the surface electrostatic charges of dielectrics obtained using the contact potential difference (CPD) technique. Initially, the CPD technique was only applied to the study of metal and semiconductor surfaces. The conventional CPD measurement technique requires full compensation of the measured potential that, in the case of dielectrics, could reach very high values. Such high potentials are hard to compensate. Therefore, the conventional CPD method is rarely applied in the study of dielectric materials. Some important improvements recently made to the CPD measurement technique removed the need for compensation. The new method, which does not require compensation, has been implemented in the form of a digital Kelvin probe. The paper describes the principles of the non-compensation CPD measurement technique which was developed for mapping the electrostatic surface charge space distribution across a wide range of potential values. The study was performed on polymers such as low-density polyethylene (LDPE) and polytetrafluoroethylene (PTFE).

This article is devoted to improvement of a nondestructive control of metal machine parts by the contact potential difference method. The results of experimental studies of the effect of environmental parameters on the contact potential difference measurements with a Kelvin probe on the surface of metal samples from Al, Ti, and Ni are presented. The measured dependence of the contact potential difference on the surface of metals on the environmental parameters has been explained. Practical recommendations for measuring the contact potential difference on the surface of parts have been given. The results can be used in production, operation, and repair of metal machine parts.

The previously proposed technique of microwave volt–impedance spectroscopy of semiconductors has been experimentally verified. The technique allows one to determine the local values of electrical parameters of a semiconductor. The investigations have been carried out on a homogeneous single-crystal GaAs wafer with a system of concentric antennas formed on the top of it. The resolution is determined by the antenna central disk diameter, which has been 12, 27, and 57 μm. A dc bias voltage of 0 V ≤ U ≤ 5 V has been applied between antenna contact pads. The complex Z(f, U) impedance spectrum of each antenna has been measured on a Cascade Microtech probe station in the frequency range of f = 0.1–10 GHz. The electrical characteristics of the semiconductor have been determined from the Z(f, U) spectra by solving the inverse problem. The n-type of the semiconductor has been established, and the contact potential difference at the interface with a metal has been determined. The local values of electron density, mobility and electrical conductivity have been found have been found. The four-point probe Hall effect measurements of the surface-averaged values of the same parameters have shown good agreement of the results for the investigated homogeneous wafer.

The study of amorphous solid water (ASW) films on solid substrates has been instrumental in understanding the structure and morphology of water ices. In addition, they have the potential to help re...

Using the methods of optically stimulated electron emission (OSEE) and ambient pressure photoemission spectroscopy (APS), the energy characteristics of carbyne-containing films on copper and silicon substrates have been studied. The average contact potential difference and the work function were determined, and the positions of the Fermi level for carbyne-containing films of various thicknesses were calculated. It was found that the electrons work function and the position of the Fermi level of the studied film samples do not depend on the film thickness and the type of substrate. The information content of the OSEE and APS methods for evaluating the quality of carbon coatings on substrates is shown.

In this work, Graphene-based field-effect transistors (GFETs) are demonstrated as a highly sensitive dosimeter for gamma radiation. Graphene-based field-effect transistors exhibit p-type doping with the Dirac point shifting in the positive direction upon exposure to gamma radiation. Concurrently, an asymmetric degradation in the electron and hole mobility was observed with the former degrading more rapidly. It is shown that change in the Dirac voltage and carrier mobility is strongly dependent on the dose of gamma radiation. A sensitivity of ~1 V/kGy is reported. Gamma radiation causes partial aerial oxidation of graphene-channel which leads to p-doping as confirmed by the emergence of a higher binding energy peak (286.8 eV) in X-ray photoelectron spectra (XPS). The decrease in contact potential difference estimated through Kelvin probe force microscopy (KPFM) confirms this finding. The radiated devices showed a stable response for ~70 days. Our work demonstrates that gamma irradiation can also be used to induce large and stable hole concentrations in graphene. Such highly sensitive GFET can serve as real-time dosimeter operating in ambient conditions.

The results of a systematic study on the adsorption of polylysine molecules of different lengths on the surface of a 1,2-dimyristoyl-sn-glycero-3-phospho-L-serine (DMPS) monolayer in the liquid (LE) and condensed (LC) states are presented. A compressibility diagram and the Volta potential were recorded with the Langmuir monolayer technique and further analyzed with the empirical approach. The structure of the monolayer films with adsorbed polypeptides was studied with synchrotron X-ray reflectometry. Two- and three-layer slab models describe the reflectivity data fairly well and reveal both the significant structural changes and the dehydration of the polar groups induced by all polylysines used at the maximal coverage of the monolayer interface in both the LE and LC states. On the one hand, in the LE phase of the monolayer (area per molecule A ≅ 70 Ǻ2), the integrated electron density of the lipid headgroup region is approximately half the density contained in the clean monolayer. This indicates both significant compaction and dehydration in the polar groups of the lipids, caused by the adsorption of polypeptides. On the other hand, in the LC state (A ≅ 40 Ǻ2), the degree of the hydration of the polar region is similar to that for the initial DMPS monolayer. However, both the electron density and the thickness of the head group region differ significantly from the values of these parameters for the clean monolayer in the LC state.

The chemical states and changes in the work function of a heterogeneous multilevel film have been determined during the adsorption of cesium at 295 K on a cylindrical gas-phase polycrystalline tungsten coating (30 μm) of Nb–1%Zr alloy with a minimum concentration of residual oxygen using low-energy threshold electron spectroscopy and contact potential difference methods. The chemical states and the change in the work function of this film have been found during successive heating up to 1875 K.

Electrostatic charging of granular materials in both nature and industry usually takes place in the presence of an external electric field. Thus, it is essential to fully understand the impact charging of a single particle in such situations. Here, we used a variation of Millikan's method to measure the transferred charges by particle-plate impacting under an external electric field. The finite element method was used to determine the electric field at the impact point. We found that impact charges show different polarities under different directions of the vertical component of the electric field; meanwhile, both positive and negative impact charges were present for cases within the shielding cage. A hypothesis based on the theory of electronic energy levels was proposed to explain the total contact potential difference under an external electric field and within the shielding cage.

Two-dimensional (2D) transition-metal dichalcogenides (TMDs) are layered semiconductor materials that have recently emerged as promising candidates for advanced nano- and photoelectronic applications. Previously, various doping methods, such as surface functionalization, chemical doping, substitutional doping, surface charge transfer, and electrostatic doping, have been introduced, but they are not stable or efficient. In this study, we have developed carrier polarity modulation of molybdenum ditelluride (MoTe2) for the development of phototransistors and switching photodiodes. Initially, we treated p-MoTe2 in a N2 environment under DUV irradiation and found that the p-type MoTe2 changed to n-type MoTe2. However, the treated devices exhibited environmental stability over a long period of 60 days. Kelvin probe force microscopy (KPFM) measurements demonstrated that the values of the work function for p-MoTe2 and n-MoTe2 were ∼4.90 and ∼4.49 eV, respectively, which confirmed the carrier tunability. Also, first-principles studies were performed to confirm the n-type carrier polarity variation. Interestingly, the n-type MoTe2 reversed its polarity to p-type after the irradiation of the devices under DUV in an O2 environment. Additionally, a lateral homojunction-based p-n diode of MoTe2 with a rectification ratio of ∼2.5 × 104 was formed with the value of contact potential difference of ∼400 mV and an estimated fast rise time of 29 ms and decay time of 38 ms. Furthermore, a well self-biased photovoltaic behavior upon illumination of light was achieved and various photovoltaic parameters were examined. Also, VOC switching behavior was established at the p-n diode state by switching on and off the incident light. We believe that this efficient and facile carrier polarity modulation technique may pave the way for the development of phototransistors and switching photodiodes in advanced nanotechnology.

In this study, branch-like SnO2@ZnO heterojunction photocatalyst was successfully fabricated via a simple two-step hydrothermal process. The optical and electronic properties were characterized in detail and the results indicated that SnO2@ZnO nanocomposites (TZNCs) exhibited superior photocatalytic performance under visible light irradiation as compared to pure SnO2 and ZnO. The excellent photocatalytic performance of TZNCs can be ascribed to the heterojunction structure between ZnO and SnO2 which depresses the recombination of photogenerated electron-hole pairs. In addition, the branch-like morphology can provide large specific surface. Moreover, the density functional theory (DFT) computation on the Fermi level results confirmed that heterojunction structure between ZnO and SnO2 is more favor of the transfer of photogenerated eletrons from ZnO to SnO2, effectively improving separation of photogenerated electron-hole pairs. Noteworthy, this work would pave the route for the two semiconductor materials with a big work function difference which would lead to the high contact potential difference, surely contributing to improving the performance of photocatalysts.

Intermetallic phases on the as-polished surface of the Al-Cu-Li alloy AA2070-T8 were identified and characterized extensively with respect to microstructure and chemical composition using spectroscopic and microscopic techniques and atom probe tomography. This is the first comprehensive report of the intermetallic compounds in the 3rd generation of Al-Cu-Li alloys. A total of eleven compositional classifications and/or crystallographic phases and one GP zone were revealed, with Al7Cu2Fe(Mn) being the most abundant, comprising around 44% of all intermetallic particles. Seven types of large intermetallic compounds were found to be cathodic to the matrix and their nobility generally increases with their noble element content, e.g. Cu and Fe, and decreases with their Al content, which can be further correlated to the cathodic current densities supported by these particles. The intermetallic compound nobility is closely related to the Volta potential difference, which correlates with the extent of trenching around the particles during electrolyte exposure. Corrosion of this alloy in 0.1 M NaCl involves a series of chemical and electrochemical phenomena at the intermetallic compound/matrix/electrolyte interfacial region, including preferential dealloying of the intermetallic compound, galvanic dissolution of the peripheral matrix, trench development, hydrogen evolution at the bottom of trench, and pitting in the bulk alloy. However, after exposure, no clear corrosion attack on or around nm-scale precipitates was observed after exposure times comparable to that for large particles. These findings are essential to understand the material degradation mechanism of this alloy family and provide input into new alloy design.

Using low-energy (0–25 eV) threshold electron spectroscopy and contact potential difference in vacuum not worse than 2 × 10–8 Pa, oxygen films obtained at 295, 325–1425 (in steps of 50), and 1575 K, including in subsequent heating from the adsorption temperature to 1925 ± 50 K, on ​​the cylindrical surface of a gas-phase tungsten coating 30 μm thick on NbC-1 alloy (Nb – 1% Zr), used as a collector material for thermal emission in space-borne nuclear power plants, have been studied.

Aluminum alloy (AA) 3003 is widely used as fin and tube material in heat exchangers. In these heat exchangers, the tube and fin material are brazed together by means of an AA4xxx alloy. In this study, the effect of a simulated brazing step on the microstructure and corrosion behavior of a twin roll casted (TRC) AA3003 was studied. In particular, the effect of simulated brazing on the corrosion properties of the centre line segregation (CLS) of alloying elements and the interaction of the intermetallic particles with the surrounding matrix is explored. It is shown that the cross sections are significantly more active than the surface of the TRC AA3003, revealing the importance of the CLS on the corrosion behavior. Furthermore, it is shown that the number of pits and their depths decreased considerably on the exposed cross sections after simulated brazing, especially near the CLS. Scanning Kelvin probe force microscopy measurements show that after the simulated brazing step the Volta potential difference between the intermetallic particles and the matrix reduced significantly. This change in the Volta potential could be caused by the slight increase of Si content in the matrix.

Although step structures have generally been considered to be active sites, their role on a TiO2 surface in catalytic reactions is poorly understood. In this study, we measured the contact potential difference around the steps on a rutile TiO2(110)-(1 × 1) surface with O2 exposure using Kelvin probe force microscopy. A drop in contact potential difference was observed at the steps, indicating that the work function locally decreased. Moreover, for the first time, we found that the drop in contact potential difference at a step was larger than that at a step. We propose a model for interpreting the surface potential at the steps by combining the upward dipole moment, in analogy to the Smoluchowski effect, and the local dipole moment of surface atoms. This local change in surface potential provides insight into the important role of the steps in the catalytic reaction.

The nanonewton force facility of Physikalisch-Technische Bundesanstalt (PTB), Germany, has been significantly improved. We demonstrate the possibility of using the facility as a calibration device that can accurately determine spring constants of soft cantilevers ( $k ) with traceability to the SI units. This paper is described the possibility of increasing the range of the measured forces to 1 mN. We demonstrate the possibility of using PTB’s nanonewton force facility to accurately determine and compensate for the contact potential difference. To measure the contact potential difference and at the same time the distance between a force sensor and a measured object, a new three-voltage method was developed. For a so-called “plan–plan geometry,” the results of measuring the contact potential difference and the distance in vacuum are presented. A new method of adjusting the parallelism of the plates is also presented. The method used to measure the negative light pressure (light-induced force), which had previously been only theoretically predicted, and the first results of the measurement are presented as well.

Organic-inorganic halide perovskite materials are emerging as a new class of photoelectric materials for its low cost, easy preparation, and, especially, outstanding optoelectronic properties. Although tremendous efforts have been made on the regulation and optimization of perovskite materials and their microscopic electrical properties for high-efficiency solar cells, few reports focus on the evolution of electrical properties with temperature changes, especially at the microscopic scale, which will directly affect the device performances at varying temperatures. Here, we map the contact potential difference and photocurrent distribution of MAPbI3 at different temperatures in situ by Kelvin probe force microscopy and conductive atomic force microscopy, emphasizing the different influences of variable temperature and phase transition on the photoelectric properties of grains and grain boundaries (GBs). It is discovered that both the Fermi level and photocurrent decrease as the sample is heated from 30 to 80 °C gradually because of the variation of effective carrier concentration and the degradation of carrier mobility implicated by lattice vibration scattering. The difference between the Fermi level at GBs and that on the grains ascends first and then descends, peaking at 50 °C, near which MAPbI3 transforms from a tetragonal phase to a cubic phase. This peak is speculated as a comprehensive consequence of the increasing difference of the Fermi level of semiconductors with different doping concentrations and the converging properties of grains and GBs with the temperature rising because the lower ion activation energy of the cubic phase at higher temperatures facilitates greatly the ions' movement between grains and GB. The variation trend of the difference of the photocurrent is the same. These findings advance the knowledge on the temperature-induced variations of microscopic photoelectrical properties of organic-inorganic hybrid perovskite materials, which may guide the development of strategies for improving their thermal stability.

Halide perovskites such as methylammonium lead iodide (MAPbI3) currently attract considerable attention because of their excellent optoelectronic properties and performance in solar cell devices. Despite tremendous research efforts to elucidate their fundamental properties, ion migration with the presence of ionic defects is still not fully understood. Here, various types of ionic defects for specific (100) and (112) lattice facets in single-crystal MAPbI3 have been investigated systematically. Our measurements reveal significant anisotropic properties. Photoluminescence (PL) and electrical transport measurements show that the (100) facet has higher PL intensity and over 1 order lower trap density compared to that of the (112) facet. We find that the facet-dependent variations of contact potential difference measured with Kelvin probe force microscopy under different bias voltages and light illuminations provide insights into different types of ionic defects on the surface of MAPbI3 single crystals. We also observe a completely different ion migration behavior on specific crystal facets through nanoscale scanning probe microscopy investigations. Our results indicate that the (100) facet exhibits an n-type behavior dominated with I– vacancies, whereas the (112) facet exhibits a p-type behavior with MA+ or Pb2+ vacancies. The findings on the facet-dependent configuration of ionic defects provide deeper understanding on facet-dependent optoelectronic properties in single-crystal MAPbI3.

In this study, pH measurement was performed in a thin electrolyte droplet with a thickness

The selection of the necessary and sufficient number of Duralumin samples in determining the surface energy of metal aviation components is considered. The surface energy is determined by measuring the contact potential difference, which depends on the electron work function for the samples. The number of samples for measuring the contact potential difference must be no less than five.

Scanning Kelvin probe force microscopy (SKPFM) in nitrogen atmosphere, which can detect the variation of surface contact potential difference (CPD) caused by hydrogen ingress, was used to investigate hydrogen distribution in thermally hydrogen-precharged austenitic stainless steel with strain-induced martensite. Furthermore, the evolutions of hydrogen concentrations in lattice and trapping site are calculated by McNabb–Foster model. Results show that work function of the material is decreased by hydrogen. Hydrogen concentration evolution simulated by the model is consistent with that measured by SKPFM. Particularly, hydrogen is proved to be trapped at the phase boundary between austenite and martensite by SKPFM.

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

Beilstein journal of nanotechnology 12, 559-565 (2021). doi:10.3762/bjnano.12.46, Published by Beilstein-Institut zur Förderung der Chemischen Wissenschaften, Frankfurt, M.

The atomically precise control over the size, shape and structure of nanographenes (NGs) or the introduction of heteroatom dopants into their sp2 -carbon lattice confer them valuable electronic, optical and magnetic properties. Herein, we report on the design and synthesis of a hexabenzocoronene derivative embedded with graphitic nitrogen in its honeycomb lattice, achieved via on-surface assisted cyclodehydrogenation on the Au(111) surface. Combined scanning tunnelling microscopy/spectroscopy and non-contact atomic force microscopy investigations unveil the chemical and electronic structures of the obtained dicationic NG. Kelvin probe force microscopy measurements reveal a considerable variation of the local contact potential difference toward lower values with respect to the gold surface, indicative of its positive net charge. Altogether, we introduce the concept of cationic nitrogen doping of NGs on surfaces, opening new avenues for the design of novel carbon nanostructures.

Main methods for measuring work function values are presented in this chapter. The methods are divided primarily into two categories based on the principle of the measurements; measurements of threshold energy to excite electrons at the Fermi level (absolute value measurements) and measurements of contact potential difference (relative value measurements). The principle of work function measurement for each method is presented with equations that relates a work function value to experimentally measured quantities. For each method, explanations are described on how to obtain a work function value from experimental data. Some examples of experiments are also demonstrated. Practical experimental tips in the measurements are also explained. Described methods of measuring threshold energy include measurements of thermal emission, field emission, and photoelectron emission, electron emission spectroscopy such as photoelectron emission yield spectroscopy, ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy and Auger electron spectroscopy. As the methods of measuring contact potential difference, Kelvin probe method and diode method are explained. In addition, as a unique method, obtaining a work function value from the binding energy of Xe absorbed on the specimen surface is explained.

The nonlinear governing equations on the coupling between electromechanical fields and charge carrier in a thermal equilibrium piezoelectric pn junction subjected to asymmetric mechanical loads are established in this article. Effect of mechanical loads on the basic physical parameters of a piezoelectric pn junction, such as potential barrier region width, contact potential difference, electric potential, and carrier concentrations are analyzed numerically. Results show that asymmetry compressive stresses exert more influence on the movement of the potential barrier region’s boundary and the migration of carrier compare to asymmetry tensile stresses. It is also found that asymmetry compressive stresses lead to a pn junction with a thin potential barrier region which enhances the chance of carrier’s passing through of potential barrier region. The obtained results are useful in reducing the disadvantage of capacitance on rectification characteristic and can be used to tune the ${I}$ – ${V}$ characteristic of the pn junction working with bias voltage.

Quantifying the work function of materials is a major component of research dedicated to developing in vacuo electrical devices with high current density at low operating temperatures. These devices are regularly composites of more than one material and understanding the roles that the individual components play in determining the overall work function is at the frontier of this research [1]. The work function characterization technique outlined here is analysis using a Kelvin Probe System, which yields the opportunity to quantify a material’s work function through measuring contact potential difference (CPD) or through surface photovoltage spectroscopy (SPS). In this paper, these separate techniques are outlined and experimental data is given for W and Ba, two elements of interest in device development.

A more inclusive and detailed measurement of various physical interactions is enabled by the advance of high-speed data digitization. For surface potential characterization, this was demonstrated recently in terms of open-loop amplitude modulation Kelvin probe force microscopy (OL AM-KPFM). Its counterpart, namely open-loop frequency modulation Kelvin probe force microscopy (OL FM-KPFM), is examined here across different materials and under various bias voltages in the form of OL sideband FM-KPFM. In this implementation the changes in the amplitude and resonance frequency of the cantilever were continuously tracked as a conductive AFM probe was modulated by a 2 kHz AC bias voltage around the first eigenmode frequency of the cantilever. The contact potential difference (CPD) between the AFM probe and sample was determined from the time series analysis of the high-speed 4 MHz digitized amplitude and frequency signals of the OL sideband FM-KPFM mode. This interpretation is demonstrated to be superior to the analysis of the parabolic bias dependent response, which is more commonly used to extract the CPD in OL KPFM modes. The measured OL sideband FM-KPFM amplitude and frequency responses are directly related to the electrostatic force and force-gradient between the AFM probe and sample, respectively. As a result, clear distinction was observed for the determined CPD in each of these cases across materials of different surface potentials, with far superior spatial resolution when the force-gradient detection was used. In addition, the CPD values obtained from OL sideband FM-KPFM amplitude and frequency measurements perfectly matched those determined from their closed-loop AM-KPFM and FM-KPFM counterparts, respectively.

Understanding the stability of metal halide perovskite (MHP) surfaces is of considerable interest for the development of devices based on these materials. We present here a vacuum-based study of the surface potential and response to illumination of two different types of perovskite films, methylammonium lead bromide (MAPbBr3) and the 2D Ruddlesden–Popper phase butylammonium lead iodide (BA2PbI4, n = 1), using Kelvin probe-based contact potential difference and surface photovoltage measurements. We show that supraband gap light irradiation can induce the loss of halide species, which adsorb on the Kelvin probe tip, inducing quasi-irreversible changes of the MHP surface and tip work functions. If undetected, this can lead to misinterpretations of the MHP surface potential. Our results illustrate the effectiveness of the Kelvin probe-based technique in providing complementary information on the energetics of perovskite surfaces and the necessity to monitor the work function of the probe to avoid erroneous co...

In this work, we have demonstrated the use of DNA aptamer as a selective bio recognizable entity towards the qualitative detection of cardiac Troponin-T (cTnT), a clinically important cardiac marker protein. Prior to this, the ZnO thin film surface as an active semiconducting channel material was first biofunctionalized with DNA aptamer by using standard biotin-streptavidin chemistry. Biofunctionalization was further confirmed by analyzing the ZnO surface with atomic force microscope (AFM) and X- ray photoelectron spectroscopy (XPS) techniques. In order to understand the efficacy of biomolecular interaction between cardiac Troponin-T (cTnT) and its corresponding aptamer, Kelvin Probe Force Microscopy (KPFM) technique was performed to monitor the effective contact potential difference. Further, to realize the essential technological importance of this methodology as a sensor platform, a thin-film transistor (TFT) micro device was fabricated using ZnO as a channel material and characterized. These fabricated devices were further used to demonstrate the qualitative detection of cardiac Troponin-T protein by employing aptamer-mediated biofunctionalization of ZnO TFT.

Scanning Kelvin probe force microscopy (SKPFM) is used in corrosion studies to quantify the relative nobility of different microstructural features present within complex metallic systems and thereby elucidate possible corrosion initiation sites. However, Volta potential differences (VPDs) measured via SKPFM in the literature for metal alloys exhibit large variability, making interpretation and application for corrosion studies difficult. We have developed an improved method for referencing SKPFM VPDs by quantifying the closely related work function of the probe relative to an inert gold standard whose modified work function is calculated via density functional theory (DFT). By measuring and tracking changes in the probe vs. gold VPD, this method compensates for some of the complex effects that cause changes in an individual probe's work function. Furthermore, it provides a path toward direct, quantitative comparison of SKPFM results obtained by different researchers. Application of this method to a Cu-Ag-Ti eutectic braze of a steel sample imaged with multiple SKPFM probes of differing compositions led to enhanced repeatability both within and among probe types, as well as enabled the calculation of modified work function values for each of the microstructural constituents present.

The interplay of adsorption geometry and interface dipoles of the transition-metal complex Ir(ppy)3 on Cu(111) was studied using low-temperature scanning probe microscopy and density-functional-theory calculations. We find that the orientation of the molecule's intrinsic dipole moment with respect to the surface has a strong influence on the total energy of the different configurations, where the most stable one has the molecular dipole moment pointing out of the surface plane along the surface normal. Adsorption-induced redistribution of charges results in an additional dipole moment that also points out of the surface plane for all configurations. Submolecularly resolved maps of the resulting local contact potential difference suggest that any in-plane dipole moment is very effectively screened.

Measurement of the contact potential difference (CPD) and work functions of materials are important in analyzing their electronic structures and surface residual charges. Kelvin probe force microscopy (KPFM), an imaging technique of atomic force microscopy, has been widely used for surface potential and work function mapping at the nanoscale. However, the conventional KPFM variants are often limited in their spatial resolution to 30-100 nm under ambient conditions. The continuingly decreasing size and increasing complexity of photoactive materials and semiconductor devices will present future challenges in uncovering their nanometer-scale electrical properties through KPFM. Here, we introduce a KPFM technique based on the pulsed force mode of atomic force microscopy. Our technique, named pulsed force Kelvin Probe Force Microscopy (PF-KPFM), is a single-pass technique that utilizes the intrinsic Fermi level alignment between the AFM tip and the conductive sample without the need for an external oscillating voltage. Induced cantilever oscillations generated by a spontaneous redistribution of electrons between tip and sample are extracted and used to obtain the cantilever oscillation amplitude and to derive the surface potential. The spatial resolution of PF-KPFM is shown to be

High band gap Pb bromide perovskite (APbBr3)-based solar cells, where A is a mixture of formamidinium, methylammonium, and Cs, show significantly higher, relative, VOC losses than their iodide analogs. Using photoluminescence-, quantum efficiency-, and surface photovoltage-spectroscopy measurements, we show the absence of any significant electronically active tail states within the bulk of the (FA0.85MA0.1Cs0.05)PbBr3 absorber. All methods confirm that EG = 2.28 eV for this halide perovskite, HaP. Contact potential difference measurements for this HaP, on different substrates, reveal a Z-shape dependence between the substrate work functions and that of the HaP, deposited on it, indicating that the HaP is relatively low doped and that its Fermi level is affected by the substrate onto which it is deposited. We confirm results from electron beam-induced current (EBIC) and other measurements that most voltage loss of cells, made with these HaP films, is at the HaP/selective-contact interface, specifically the...

The application of single-pass multifrequency Kelvin probe force microscopy (KPFM) for topography and contact potential difference (CPD) measurements of organic self-assembled monolayers (SAM) is demonstrated. Four modes of mechanical and electrical cantilever excitation were tested in order to obtain the best possible resolution in the CPD measurements. The algorithm using maximum capacity of information channel for quantitative image quality assessment was proposed to compare and assess the quality of the recorded images and imaging modes. The improvement of the quality of CPD imaging in multiresonance operation was confirmed.

For the first time, the charge states of adsorbed oxygen adatoms on the rutile TiO2(110)-1×1 surface are successfully measured and deliberately manipulated by a combination of noncontact atomic force microscopy and Kelvin probe force microscopy at 78 K under ultrahigh vacuum and interpreted by extensive density functional theory modeling. Several kinds of single and double oxygen adatom species are clearly distinguished and assigned to three different charge states: Oad-/2Oad-, Oad2-/2Oad2-, and Oad--Oad2-, i.e., formal charges of either one or two electrons per atom. Because of the strong atomic-scale image contrast, these states are clearly resolved. The observations are supported by measurements of the short-range force and local contact potential difference as a function of the tip-sample distance as well as simulations. Comparison with the simulations suggests subatomic resolution by allowing us to resolve the rotated oxygen p orbitals. In addition, we manage to reversibly switch the charge states of the oxygen adatoms between the Oad- and Oad2- states, both individually and next to another oxygen, by modulating the frequency shift at constant positive voltage during both charging and discharging processes, i.e., by the tip-induced electric field of one orientation. This work provides a novel route for the investigation of the charge state of the adsorbates and opens up novel prospects for studying transition-metal-oxide-based catalytic reactions.