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Amplitude modulation scanning Kelvin probe microscopy (AM-SKPM) is widely used to measure the contact potential difference (CPD) between probe and samples in ambient or dry inert atmosphere. However, AM-SKPM is generally considered quantitatively inaccurate due to crosstalk between the cantilever and the sample. Here we demonstrate that the accuracy of AM-SKPM-based CPD measurements is drastically improved by exciting the SKPM probe at its second eigenmode. In the second eigenmode of oscillation, there exists a stationary node at the cantilever towards its free end, across which the displacement bears opposite signs; therefore driving the SKPM probe at its second eigenmode helps to partially cancel the virtual work done by the cantilever and reduce the crosstalk effect. The improvement in accuracy is experimentally confirmed with interdigitating electrodes calibration samples as well as practical samples such as the cross-section of wafer-bonded GaAs/GaN heterojunction.

The micro-galvanic interactions between Cu-Fe-Mn-Li-containing aluminides and the alloy matrix of aluminium alloy AA2099 during chloride-induced corrosion were investigated in-situ with real-time monitoring of the local contact potential difference (VCPD) using the scanning Kelvin probe force microscopy (SKPFM) at controlled relative humidities. The aluminides showed noble potentials and were able to ennoble their neighbouring matrix sites when a cluster of aluminides surrounded the matrix. The matrix, hence, adopted a more positive VCPD, towards that of the aluminides. The anode-to-cathode ratio changed throughout the corrosion exposure and was seen to show a dynamic character. Much higher local VCPD activities were recorded during the earliest stages of corrosion, when the Al-Li AA2099 surface was first exposed to high humidities, than in later RH cycles; a phenomenon not seen in other aluminium alloys.

Tribocharging is utilized in a large number of applications and is meanwhile hazardous. Controlling of the charging and the following discharging during the friction contacts is urgently needed. Here, the triboluminescence has first been investigated and we found that the position reversal of the friction pairs has a dramatic impact on the triboluminescence. Such a position dependence was then explained by the combined effect of the contact potential difference and the temperature difference between the contacting surfaces on the charge transfer during the friction process. This work may provide a new perspective for understanding the tribocharging process and may propose a simple yet effective approach to modulate the intensities of tribocharging and tribodischarging.

Endogenous microscopic electric cues play an essential role in bone's remodeling and self-repair. Modulating the extracellular electrical environment, by means of external electric stimulation or changing surface potential of implants, was manifested to facilitate the osteointegration. The microscopic potential difference, originating from heterogeneous microstructures of materials, may mimic the endogenous electric signals to stimulate surrounding cells. In this study, the spark-plasma sintered Ti/Ta hybrid metal was fabricated and utilized to realize a surface microscopic potential difference at the same magnitude as endogenous potentials. Activated by the electric stimulation, the mesenchymal stem cells exhibited the anisotropic and polygonal cellular morphology on the Ti/Ta hybrid metal. The microscopic electric potential difference coordinated the cells proliferation on the subsequent days. Moreover, the results showed that the osteo-lineage differentiation on Ti/Ta hybrid metal were in vitro boosted over the control groups. Tailoring microstructures of material to obtain a reasonable electric microenvironment may be a necessary principle to achieve more favorable cell responses to implants, suggesting an extra degree of freedom in bone-repairing material design.

We have examined the capabilities of a Tip-On-Gate of Field-Effect Transistor (ToGoFET) probe for characterization of FIB-induced damage in Si surface. A ToGoFET probe is the SPM probe which the Field Effect Transistor(FET) is embedded at the end of a cantilever and a Pt tip was mounted at the gate of FET. The ToGoFET probe can detect the surface electrical properties by measuring source-drain current directly modulated by the charge on the tip. In this study, a Si specimen whose surface was processed with Ga+ ion beam was prepared. Irradiation and implantation with Ga+ ions induce highly localized modifications to the contact potential. The FET embedded on ToGoFET probe detected the surface electric field profile generated by schottky contact between the Pt tip and the sample surface. Experimentally, it was shown that significant differences of electric field due to the contact potential barrier in differently processed specimens were observed using ToGOFET probe. This result shows the potential that the local contact potential difference can be measured by simple working principle with high sensitivity.

Influence of oxygen concentration in the measurement atmosphere on detection of hydrogen using Kelvin probe was studied. The studied material was a 100-m-thick palladium foil, which was mounted in a 3D printed electrochemical flow cell. The used setup enables hydrogen loading with in-situ contact potential measurement of the hydrogen exit side of the Pd electrode. The hydrogen loading and unloading procedure, including insertion of different amounts of hydrogen into the Pd membrane and recording resulting values of contact potential difference, was performed at distinct oxygen concentrations ranging between 1 and 80 vol%. An increasing amount of oxygen in the atmosphere surrounding the hydrogen-loaded Pd electrode resulted in an accelerated removal of hydrogen from the Pd. The kinetics of this reaction was studied based on Kelvin probe measurements, and a reaction mechanism is discussed. (VLID)4848449 Version of record

Graphene with a zero-bandgap energy is easily doped using a chemical dopant, and a shift upwards or downwards in the Fermi level is generated. Moreover, the integration of inorganic material into the doped graphene changes the physical and chemical properties of the material. For this purpose, we successfully fabricated a p-n junction device by depositing an n-typed ZnO layer on p-doped graphene and studied the ultraviolet (UV) photoresponse properties under a photocurrent (UV light on) and a dark current (UV light off). Two devices, lateral and vertical, were developed by alternating the thickness of the ZnO layer, and the photoresponse mechanisms were described on the basis of the contact potential difference.

The types of cells and methods of electrochemical reduction of graphene oxide films were described. The possibility of creating ultrathin membrane–electrode assemblies of supercapacitor cells was demonstrated. The peculiarities of the electrochemical behavior of films of different thicknesses that contact with carbon and metal current collectors were shown. The limiting charge (1500–2000 C/g) for complete electrochemical reduction of graphene oxide was determined. Possible mechanisms of proton conductivity along the basal faces of graphene oxide flakes were proposed. The nature of the current collector was shown to affect the electron–hole conductivity of graphene oxide films and the observed contact potential difference.

Four binary cast Mg-Ga alloys containing 1, 2, 3 and 4 wt% Ga were studied in terms of microstructure and degradation behavior. The alloys present two types of intermetallics: (i) the second phase Mg5Ga2, which volume increases with the amount of Ga in the alloy, and (ii) inclusions containing impurities. For the first time, the binary Mg-Ga system is analyzed paying particular attention to the effect of secondary phases (Mg5Ga2) and impurities on the localized corrosion mechanism using AFM/SKPFM. Inclusions containing impurities reveal a high Volta potential difference, enough to form an active galvanic couple. However, localized electrochemical activities decrease with time leading to uniform degradation. For short immersion times, there is no clear influence of the element Ga on the corrosion behavior, measured by electrochemical and hydrogen evolution tests. However, for longer immersion times, increasing the amount of Ga in the alloy shows a clear negative effect. Electrochemical measurements reveal that higher Ga containing alloys form faster an oxide layer which is not stable.

This work contributes to the better understanding of Kelvin microprobe response to iron re-deposition related surface morphology changes resulting from Mg corrosion caused by iron-rich impurities. Scanning Kelvin probe force microscopy (SKPFM) was performed on polished Mg samples at well-defined surface conditions occurring from corrosive exposure to 0.05 M NaCl electrolyte or dissolved FeCl2. Volta potential difference was measured and mapped across iron-rich areas, unaffected areas of α-Mg, and on FeCl2 exposed areas. Afterward, the obtained potential values were evaluated via the derived mathematical expression, based on model assumptions. Subsequently, they were compared and then correlated to the corrosion process. The article demonstrates what kind of information can be obtained by SKPFM and what conclusion can be drawn toward the detailed explanation of recently reported iron re-deposition mechanism on corroding Mg surface. Finally, suggestions toward the improved application of SKPFM for Mg corros...

To explain the initiation mechanism of alternating current in an electric circuit containing the dynamic capacitor a model of mechanic- electrical transformation is suggested to use. In such a model, electric charges disposed between the capacitor plates serve as a cause of measured signal in contrast to the contact potential difference, which is considered as the main base in the Kelvin’s model. If one of the plates moves periodically, then the conditions of the charges screening are changed and thereby the capacitor recharging current is arise. The measuring is based on compensation of the recharging current by current, which generated by a source of electromotive force (EMF). The compensation voltage depends on both the distribution of ions or dipoles over the studied surface and the charges creating the surface potential barrier. This voltage is independent on the bulk electro-physical characteristics of a solid.

A combination of scanning Kelvin probe force microscopy (SKPFM) and electron backscatter diffraction (EBSD) has been applied to investigate the hydrogen release from thermally hydrogen-precharged type 304 austenitic stainless steel (γ-SS). The evolution of contact potential difference (CPD) well exhibits the evolution of hydrogen concentration in the near surface area. It is found for the first time that the hydrogen diffusivity in γ-SS depends on the crystallographic orientation. The hydrogen diffusion out from (001) and (101) grains is faster than from (111) grains while no obvious difference is found between (001) and (101) grains.

The manufacturing process of wide-band-gap matrix photodetector devices and miniaturization of their individual pixels gave rise to increased demands on the material quality and research methods. In the present paper we propose using the methods of atomic-force microscopy to study the local distribution of electrical properties of the V-defects that form in epitaxial films of HgCdTe during their growth process via molecular beam epitaxy. We demonstrate that a complex approach to studying the electrical properties of a predefined region of a V-defect allows one to obtain more detailed information on its properties. Using scanning spreading resistance microscopy, we show that, for a V-defect when the applied bias is increased, the surface area that participates in the process of charge carrier transfer also increases almost linearly. The presence of a potential barrier on the periphery of individual crystal grains that form the V-defect interferes with the flow of current and also affects the distribution of surface potential and capacitive contrast.

Two microscale numerical models are developed in this work using a moving-mesh approach to investigate the growth process of pitting in different iron phases and the corrosion prevention capability of polyaniline (PANi) on steels. The distributions of corrosion potential and current in the electrolyte-coating-steel system are computed to evaluate the anti-corrosion ability of PANi. The arbitrary Lagrangian–Eulerian approach was used to accomplish the continuous remesh process as was needed to simulate the dynamic growing forefront of the modeled pitting domain. Experimental validation of the numerical models was conducted using the technique of scanning kelvin probe force microscopy (SKPFM). The SKPFM-scanned surface topography and Volta potential difference exhibit comparable results to and thereby prove the numerical results. The potential distribution in the electrolyte phase of the validated models shows that the corrosion pit grows faster in the epoxy-only-coated steel than that in the PANi-primer-coated steel over the simulation time; also, the corrosion pit grows faster in the ferrite phase than in the cementite phase. The simulation results indicate that the epoxy-only coating lost its anti-corrosion capability as the coating was penetrated by electrolyte, while the PANi-based coating can still protect the steel from corrosion after the electrolyte penetration. The models developed in this work can be used to study the mechanisms of pitting corrosion as well as develop more effective corrosion prevention strategies for general metallic materials.

We are presenting a combination of two measurement methods for simultaneous generation of optical and electrical signals out of one gasochromic film. For this purpose we combined the UV–vis spectroscopy with the contact potential difference (CPD) measurement. To demonstrate the advantages of this combined measurement we chose a well-known gasochromic system. For testing the benefits and limitations of the concept, we used a phenol red based film with known sensitivity to CO2. Getting in contact with CO2 the phenol red based sensitive layer shows changes in absorption spectra and in contact potential difference (CPD). Due to the combination of both measurement techniques the influence of temperature and humidity, which is always a challenge in gas detection, can be identified and eliminated. We see different signal behaviour of the two measurement methods at humidity and temperature changes. In dry conditions the optical signal response towards CO2 is reduced, whereas the electrical signal is increased. Whereas the optical signal response is strongly dependent on the temperature, the electrical signal seems to be independent. These reactions look promising for future gas sensor applications in the field of gasochromic sensor dye evaluation.

The work concerns the research on patterns of the electron work function (EWF) distribution over the sample surface, depending on the fatigue tests. When studying samples made of high-temperature alloy EP866 used for highly loaded parts of gas turbine engine (GTE) compressors, we determined a stage of reversible structural rearrangements when the EWF value for a given surface point decreases and increases periodically fluctuating around a particular average amount. At the initial stages of testing, the EWF oscillates near a specific value, which indicates the reversibility of the process of accumulation of fatigue damage and the change in the hardening processes – relaxation at these stages. Then a stage of irreversible structural changes in the material of the surface layer is observed when the EWF decreases monotonously until the sample is destructed. It was found that in the process of cyclic deformation, the material areas experiencing the same mechanical stresses correspond to the surface areas with the similar EWF values. The deformation processes preparing the formation of a fatigue crack to cause the creation of a “deformation” dip on all the EWF distribution curves, and, accordingly, the contact potential difference (CPD). It can be assumed that the maximum change in EWF in the dip corresponds to the most intensive flow of deformation processes. The EWF distribution over the sample surface makes it possible to predict the place of fatigue cracks initiation at the early testing stages.

Cerium-based conversion coatings have emerged as promising green alternatives to the harmful chromium-based ones, but the mechanism of corrosive protection still remains a subject of academic and industrial research. This study focuses at small scale phenomena of corrosion inhibition imparted by ceria (CeO2) to AA7075. Ceria nanoparticles were deposited from diluted and concentrated CeO2 sols by immersion. A multi-analytical approach, combining Atomic Force microscopy (AFM), Scanning Kelvin Probe Force Microscopy, Glow Discharge Optical Emission Spectroscopy, open circuit potential and electrochemical impedance spectroscopy was employed. Deposition of ceria films led to deactivation of cathodic sites, i.e. decreased Volta potential difference, resulting in increased corrosion inhibition. In situ AFM real-time monitoring revealed that during exposure to NaCl electrolyte, the changes in size of deposited ceria aggregates occurred: nanoparticles disintegrated/desorbed and re-deposited at the coating surface. The process was found to be dynamic in nature. Small particles size and inherent reactivity are believed to accelerate this phenomenon. Due to the greater CeO2 reservoir, this phenomenon was more pronounced with a thicker film, imparting longer term protection.

The effect of Sn content on the mechanical properties and corrosion behavior of Mg-3Al-xSn alloys was investigated by SEM-EDXS, XRD, electrochemical measurements, and scanning Kelvin probe force microscopy (SKPFM). The results showed that when the Sn content was 1.4 wt%, Sn dissolved in the α-Mg matrix and then precipitated as an intermetallic compound (Mg2Sn). The combined results of mass loss, hydrogen evolution, and electrochemical measurements indicated that Mg-3Al-1Sn had a low corrosion rate. The SKPFM results showed that the Volta potential of Mg2Sn particles, Al-Mn, and β-Mg17Al12 phases were 100, 80, and 50 mV higher than the matrix, respectively. Therefore, the Mg2Sn phase that formed in Mg-3Al-xSn served as a local cathode due to its high potential, which accelerated microgalvanic corrosion along with the secondary local cathode (Al-Mn). The Sn solution strengthening and secondary phase strengthening (fine Mg2Sn particles) improved the mechanical properties of the Mg-3Al-xSn alloys.

A novel method for synthesis of Boron Nitride nano-sheets (BNNS) using chemical route is presented here. Being chemically inert synthesis of BNNS is pretty much difficult yet the suitable selection of solvent and sonication time results in a good amount of BNNS. The UV-VIS spectrum and Raman spectrum of synthesized BNNS prove that an efficient quality of sample has been synthesized. The surface potential mapping of the BNNS has been taken using Scanning Kelvin Probe Microscope (SKPM), which allows us to measure the work function (WF) value using the contact potential difference (CPD) of synthesized BNNS on Si substrate and gold tip embedded in SKPM. The value of WF of BNNS/Si comes out to be ∼5.8 eV. This result will be helpful to understand the substrate effect on the WF of hBN as well as to explore the possibility of robust BNNS to use in photoelectric devices.

Phase transition in Molybdenum disulfide (MoS2) from 2H to 1T has attracted a considerable research interest in recent years due to its far exceeding unique potential applications. This paper describes the coexistence of 1T and 2H phases of MoS2 after microwave irradiation. The irradiation of microwaves on MoS2 can modify its structural and surface electronic properties. We have studied this behavior using X-ray diffraction (XRD), UV-vis (UV) spectrophotometer and scanning Kelvin probe microscopy (SKPM). A change in the contact potential difference of 2H-1T phase MoS2 has been observed.

Electron emission can be utilised to measure the work function of the surface. However, the number of significant digits in the values obtained through thermionic-, field- and photo-emission techniques is typically just two or three. Here, we show that the number can go up to five when angle-resolved photoemission spectroscopy (ARPES) is applied. This owes to the capability of ARPES to detect the slowest photoelectrons that are directed only along the surface normal. By using a laser-based source, we optimised our setup for the slow photoelectrons and resolved the slowest-end cutoff of Au(111) with the sharpness not deteriorated by the bandwidth of light nor by Fermi-Dirac distribution. The work function was leveled within $\pm$0.4 meV at least from 30 to 90 K and the surface aging was discerned as a meV shift of the work function. Our study opens the investigations into the fifth significant digit of the work function., Comment: For an associated blog-type posting, see https://devicematerialscommunity.nature.com/posts/measuring-the-work-function-precisely-by-using-laser-arpes

The surface energy, contact potential difference, and electron work function for highly entropic coatings were first determined in the work. These coatings were applied by the magnetron method in a high vacuum installation. The targets themselves were fabricated by mechanical alloying followed by heat treatment. The measurements were carried out at facilities developed by the authors.

The energetics of adsorption of H2O layers and H2O layers partially replaced with OH or Cl on an Al(111) surface and on selected surfaces of intermetallic phases, Mg2Si and Al2Cu, was studied by first-principle calculations using the density function theory (DFT). The results show that H2O molecules tended to bind to all investigated surfaces with an adsorption energy in a relatively narrow range, between &ndash, 0.8 eV and &ndash, 0.5 eV, at increased water coverage. This can be explained by the dominant role of networks of hydrogen bonds at higher H2O coverage. On the basis of the work function, the calculated Volta potential data suggest that both intermetallic phases became less noble than Al(111), also, the Volta potential difference was larger than 1 V when the coverage of the Cl-containing ad-layer reached one monolayer. The energetics of H2O dissociation and substitution by Cl as well as the corresponding work function of each surface were also calculated. The increase in the work function of the Al(111) surface was attributed to the oxidation effect during H2O adsorption, whereas the decrease of the work function for the Mg2Si(111)&ndash, Si surface upon H2O adsorption was explained by atomic and electronic rearrangements in the presence of H2O and Cl.

Spin-coating of poly(ethylenimine) (PEI) has been used to reduce the work function of GaAs (001), (110), (111)A and (111)B. The magnitude of the reduction immediately after coating varies significantly from 0.51 eV to 0.69 eV and depends on the surface crystal face, on the GaAs bulk doping and on the atomic termination of the GaAs. For all samples, the work function reduction shrinks in ambient air over the first 20 hours after spin coating, but reductions around 0.2–0.3 eV persist after 1 year of storage in air. Core-level photoemission of thin film PEI degradation in air is consistent with a two-stage reaction with CO2 and H2O previously proposed in carbon capture studies. The total surface dipole from PEI coating is consistent with a combination of internal neutral amine dipole and an interface dipole whose magnitude depends on the surface termination. The contact potential difference measured by Kelvin probe force microscopy on a cleaved GaAs heterostructure is smaller on p-doped regions. This can be explained by surface doping due to the PEI, which increases the band bending on p-doped GaAs where Fermi level pinning is weak. Both surface doping and surface dipole should be accounted for when considering the effect of PEI coated on a semiconductor surface.

With nanoelectronics reaching the limit of atom-sized devices, it has become critical to examine how irregularities in the local environment can affect device functionality. Here, we characterize the influence of charged atomic species on the electrostatic potential of a semiconductor surface at the subnanometer scale. Using noncontact atomic force microscopy, two-dimensional maps of the contact potential difference are used to show the spatially varying electrostatic potential on the (100) surface of hydrogen-terminated highly doped silicon. Three types of charged species, one on the surface and two within the bulk, are examined. An electric field sensitive spectroscopic signature of a single probe atom reports on nearby charged species. The identity of one of the near-surface species has been uncertain in the literature, and we suggest that its character is more consistent with either a negatively charged interstitial hydrogen or a hydrogen vacancy complex.

When graphene supported on SiO 2 is fluorinated, XPS reveals an increase in concentration of chemically-adsorbed fluorine (higher F/C ratio with C-CF, C-CF 2 , C-F and C-F 2 but no C-F 3 ) on the graphene surface with time. Raman I D /I G ratio, i.e. a measure of non-sp2to Sp2 bonding states, increases with time before showing a decrease suggesting a surface morphology change owing to C-F bonding followed by disordering of the π-electron system. AFM surface morphology scans reveal that defects (holes), which increases in size with time, are observed to form preferentially at the boundary of the graphene flakes. Synchronized Kelvin-Probe Force-Microscopy (KPFM) mapping of the graphene region surrounding these holes shows a higher work-function, ϕ, giving rise to a donut-shape contact potential difference (CPD) which increases from 4.9 ± 0.1 eV to 5.4 ± 0.1 eV with fluorination. Together with XPS and Raman results, the increase in ϕ can be attributed to the presence of a higher concentration of fluorine in the graphene region (C-F/C-F 2 bonds) surrounding these holes. The formation of the hole-defects on graphene and its subsequent increase in size with fluorination is thus a result of aggregation of adsorbed fluorine and removal of carbon likely in the form of CF 4 or C 2 F 4 .

Careful surface analysis is essential to understand the electronic and ionic behaviors in perovskite absorbers. In this contribution we discuss Kelvin probe force microscopy performed in ultra-high vacuum on as-grown and annealed co-evaporated methylammonium lead iodide perovskite thin films. By comparing the contact potential difference upon annealing and illumination, we find that annealing increases the average workfunction, indicating a change either in doping or in surface composition. Illumination also increases the average workfunction, indicating a p-type absorber, by reducing band bending as the photo-generated carriers screen the surface states. The effect of light shows a two-step process, with a first fast trend, linked to the surface photovoltage and a second slower trend indicating a possible redistribution of mobile charges.

Historically, high carbon steels have been used in mechanical applications because their high surface hardness contributes to excellent wear performance. However, in aggressive environments, current bearing steels exhibit insufficient corrosion resistance. Martensitic stainless steels are attractive for bearing applications due to their high corrosion resistance and ability to be surface hardened via carburizing heat treatments. Here three different carburizing heat treatments were applied to UNS S42670: a high-temperature temper (HTT), a low-temperature temper (LTT), and carbo-nitriding (CN). Magnetic force microscopy showed differences in magnetic domains between the matrix and carbides, while scanning Kelvin probe force microscopy (SKPFM) revealed a 90&ndash, 200 mV Volta potential difference between the two phases. Corrosion progression was monitored on the nanoscale via SKPFM and in situ atomic force microscopy (AFM), revealing different corrosion modes among heat treatments that predicted bulk corrosion behavior in electrochemical testing. HTT outperforms LTT and CN in wear testing and thus is recommended for non-corrosive aerospace applications, whereas CN is recommended for corrosion-prone applications as it exhibits exceptional corrosion resistance. The results reported here support the use of scanning probe microscopy for predicting bulk corrosion behavior by measuring nanoscale surface differences in properties between carbides and the surrounding matrix.

In this work metallic pins made of Mg5Gd alloy were coated with magnetron sputtered PVD Mg5Gd layers. Immersion tests in Hank’s balanced salt solution (HBSS) were performed. The PVD coating drastically reduced the corrosion rate of the Mg5Gd pin. The corrosion mechanism of the coating was studied in model electrochemical measurements by Scanning Vibrating Electrode Technique and galvanic current measurements. The tests revealed the preferential anodic dissolution of the Mg5Gd coating galvanically coupled with the bulk Mg5Gd pin. Local measurements of Volta potential difference revealed the VPD contrast between the pin and the coating surfaces only after immersion in HBSS.

This work studies the corrosion behavior of β-Sn and intermetallic compounds (IMCs) in Sn96.5Ag3.0Cu0.5 (SAC305) alloy through micro-structure observation, in-situ electrochemical technique and first-principles calculation. The results show that corrosion behavior of SAC305 is affected by galvanic corrosion, electronic structure and material microstructure. The Volta potential difference between Cu6Sn5, Ag3Sn and Sn is up to 234 and 174 mV. The length percentage of high angle grain boundaries (HAGBs) for β-Sn and eutectic phase is 11.61 % and 35.18 %. The calculated electronic density of state explains the corrosion behavior of SAC305 from corrosion kinetics perspective. The corresponding corrosion failure mechanism is proposed.

The nanoscale characteristics of semiconducting transition metal dichalcogenides (TMDCs) are largely determined by their photonic, mechanical, magnetic, thermal, and electronic properties, which can be modulated by adjusting thickness and radiation treatments. In this paper, gamma-rays were applied to irradiate the materials with one to six layers, based on which a comparison was drawn of the frictional and electrical properties before and after irradiation. The changes on a few-layer WSe2 were investigated using Raman spectroscopy, photoluminescence spectroscopy, scanning electron microscopy, transmission electron microscopy, force friction microscopy, and Kelvin probe force microscopy. Under the context of irradiation, there was a phenomenon found different than previously reported. The friction force of WSe2 nano-flakes increased from monolayer to bilayer, decreased at tri-layer, and then increased on a continued basis with thickness. It is suggested that the gamma-ray irradiation treatment could be effective in improving frictional and electronic properties. The range of change to the surface contact potential difference (CPD) was narrowed, and the stability of the device surface potential was enhanced. The continuum mechanics theory was applied to explore the friction force variation between different thickness layers. Based on the puckering effect of tip-flake adhesion, the friction force was determined by bending stiffness. The thermal treatment of WSe2 nanoflakes had a significant impact on the CPD between the sample and the test tip. After thermal treatment, the surface potential increased from one to five layers with thickness. These phenomena were explained in detail. The research contributes to enriching nanotribology and electrical theory in addition to promoting the use of semiconducting TMDCs for nano-components’ design.

The article is devoted to solving the problem of determining the electron work function of aircraft metal parts of aviation technology by the Kelvin probe method. The features of the application of the Kelvin probe method for contact potential difference measurement for aircraft metal parts are considered. Requirements for the Kelvin probe developed for measuring the contact potential difference of metal parts are formulated. A comparative analysis of materials for the manufacture of the measuring electrode of the sensor is carried out. A technique is proposed to ensure the stability of the measurement results of the contact potential difference, and the factors influencing it are assessed. Practical recommendations are given for the Kelvin probe development of the contact potential difference measuring on the aircraft metal parts surface.

Fe is a promising alloying element for the development of high strength Ti alloys. However, the distribution and phase structure of Fe in Ti alloys would have an important effect on their corrosion resistance. Therefore, the effect of Fe content on the corrosion behavior of dual-phase Ti–6Al–4V alloys was studied using a galvanic coupling technique together with the electron probe X–ray microanalysis (EPMA) and Kelvin probe force microscope (KPFM). The results indicate that the Fe is enriched in the β phases, resulting in an increase in Volta potential difference between the β and α phases. Ti–6Al–4V alloy with high Fe content (TC4-H) shows worse crevice corrosion resistance than Ti–6Al–4V alloy with low Fe content (TC4-L), which can be attributed to the worse compactness and passivation ability of the passive film on TC4-H due to Fe doping.

Currently, the use of probe electrometry in non-destructive testing is constrained by the complexity of measurement results interpretation. An output signal of electrometric probe depends on a number of physical and chemical parameters of surface including chemical composition variations, stresses, dislocations, crystallographic orientation of a surface, etc. The study aims to the use of probe electrometry methods for nondestructive testing and analysis of precision metal surfaces’ defects after different treatment or processing. Control of surface defects of aluminum and its alloys was performed with a scanning Kelvin probe technique. The results of scanning were plotted in a form of contact potential difference (CPD) distribution map. Additionally, a histogram of CPD values distribution and statistical characteristics including the expectation of CPD mean value and histogram half-width were calculated either for the whole distribution or for each individual mode in a case of multimodal distribution. The spatial CPD distribution of A99 aluminum and AMG-2 alloy surfaces after electrochemical polishing and diamond finishing was studied. An additional study was held for AMG-2 surface after the formation of 30 microns thick specific nanostructured alumina oxide surface layer. Higher quality surfaces have characterized as more homogeneous distribution of the physical properties (at half-width distribution histogram). Surfaces with higher mechanical strength and overall better mechanical properties found to have lower CPD values that correspond to higher electron work function and surface energy. The presence of the second mode in the CPD distribution histogram indicates the significant proportion of defect areas on the sample surface. Analysis of visualized CPD distribution maps using defined criteria allows detecting and characterizing such defects as residual stress areas, areas with reduced microhardness, surface contamination spots, corrosion defects. This provides the possibility of rapid nondestructive testing and diagnostic of precision metal surfaces, in particular the starting substrates for sensitive elements and sensory devices manufacture.

The transformations in nanosized Ni–MoO3 systems were studied by optical spectroscopy, microscopy, and gravimetry depending on the thickness of the Ni (d = 1–40 nm) and MoO3 (d = 3–50 nm) films, temperature (473–773 K), and thermal treatment time. The contact potential difference was measured for Ni and MoO3 films; photovoltage, for Ni–MoO3 systems. An energy band diagram of the Ni–MoO3 systems was constructed. A model of the thermal transformation of MoO3 films in Ni–MoO3 systems was suggested, which involves a redistribution of equilibrium charge carriers at the contact, formation of a [(Vа)++е] center during the preparation of the MoO3 film, the transformation of this center into an [е(Vа)++е] center during the formation of Ni–MoO3 systems, and the thermal transition of an electron to the level of the [(Vа)++е] center to form an [е(Vа)++е] center.

In this study we compared three diamond substrate grades: polycrystalline, optical grade single crystal, and electronic grade single crystal for detector application. Beside the bulk type, the choice of contact material, pre-treatment, and sputtering process details have shown to alter significantly the diamond detector performance. Characterization of diamond substrate permittivity and losses indicate grade and crystallinity related, characteristic differences for frequencies in 1 kHz–1 MHz range. Substantial grade related variations were also observed in surface electrostatic characterization performed by contact potential difference (CPD) mode of an atomic force microscope. Study of conductivity variations with temperature reveal that bulk trap energy levels are also dependent on the crystal grade.

We present a study of the energy levels in a FTO/TiO2/CH3NH3PbI3/Spiro solar cell device. The measurements are performed using a novel ambient pressure photoemission (APS) technique alongside Contact Potential Difference data from a Kelvin Probe. The Perovskite Solar Cell energy band diagram is demonstrated for the device in dark conditions and under illumination from a 150W Quartz Tungsten Halogen lamp. This approach provides useful information on the interaction between the different materials in this solar cell device. Additionally, non-destructive macroscopic DC and AC Surface Photovoltage Spectroscopy (SPS) studies are demonstrated of different MAPBI3 device structures to give an indication of overall device performance. AC-SPS measurements, previously used on traditional semiconductors to study the mobility, are used in this case to characterise the ability of a perovskite solar cell device to respond rapidly to chopped light. Two different device structures studied showed very different characteristics: Sample A (without TiO2): (ITO/PEDOT:PSS/polyTPD/CH3NH3PbI3/PCBM) had ∼4 times the magnitude of AC-SPS response compared to Sample B (including TiO2): (ITO/TiO2/ CH3NH3PbI3/Spiro). This demonstrates that the carrier speed characteristics of device architecture A is superior to device architecture B. The TiO2 layer has been associated with carrier trapping which is illustrated in this example. However, the DC-SPV performance of sample B is ∼5 times greater than that of sample A. The band gap of the MAPBI3 layer was determined through DC-SPS (1.57 ± 0.07 eV), Voc of the devices measured and qualitative observations made of interface trapping by DC light pulsing. The combination of these (APS, KP, AC/DC-SPV/SPS) techniques offers a more general method for measuring the energy level alignments and performance of Organic and Hybrid Solar Cell Devices.

Triple cation based perovskite solar cells offer enhanced moisture tolerance and stability compared to mixed perovskites. Slight substitution of methyl ammonium or formamidinium cation by cesium (Cs+), was also reported to eliminate halide segregation due to its smaller size. To elucidate the device kinetics and understand the role of the Cs, we undertook different modes of scanning probe microscopy and electrochemical impedance spectroscopy (EIS) experiments. Kelvin probe force microscopy revealed that the incorporation of the Cs cation increases the contact potential difference (CPD), this CPD further increases when Spiro-OMeTAD is used as a hole transport material. The current at the nanoscale level shows improvement with Cs inclusion and further enhancement by the Spiro-OMeTAD deposition, studied under light illumination, which supports the high photocurrent density obtained from the cells. EIS demonstrates that in a triple cation environment, reduced carrier recombination at the TiO2/perovskite interface was also obtained which in turn allow us to achieve a higher Voc value.

Photo-generated charge behaviors in the bulk heterojunctions (BHJs) of all-polymer solar cells (PSCs) are studied by Kelvin probe force microscopy (KPFM). Root-mean-square deviations (RMSDs, Rq) of the contact potential difference (CPD) images are applied to quantitatively characterize the phase segregations of the BHJs. When the BHJs are illuminated, CPD values and Rq of CPD images are changed, which attributes to the photo-generated charge transfer and accumulation. Inner structures of the BHJ are thus extrapolated by studying the charge behaviors, demonstrating KPFM an effective technique to study the relationship between inner structures and photovoltaic activities in all-PSCs.

The present research is devoted to creation of a new low-cost miniaturised measurement system for determination of potential difference in real time and with high measurement resolution. Furthermore, using the electrode of the reference probe, Kelvin method leads to both an indirect measurement of electronic work function or contact potential of the sample and measurement of a surface potential for insulator type samples. The bucking voltage in this system is composite and comprises a periodically variable component. The necessary steps for development of signal processing and tracking are described in detail.