Scanning Kelvin Probe Microscopy Research Articles

Manipulation of domain structures in LiNbO3 thin films using focused ion beam

In this study, we utilized focused ion beam (FIB) technology to generate domains with a size of approximately 500 nm in LiNbO3 thin films. These films were synthesized using the rf sputtering technique. To investigate these domains, we employed scanning Kelvin probe microscopy (SKPM) and Piezoresponse force microscopy (PFM) techniques. PFM was specifically employed to examine the polarization characteristics of these domains. Notably, we observed distinct contrast in the phase data of neighboring domains. A phase contrast of 180° indicated that the polarization direction in the two neighboring polarized domains was antiparallel. Within the ferroelectric phase, the SKPM method measured a characteristic potential change of approximately 35 mV across neighboring ferroelectric domains with opposite polarization directions (180°-domains). Moreover, we observed that upon illumination, the average surface potential increased by approximately 80 mV. This increase has been attributed to the light-induced population of surface states.

Kinetic Suppression of Photoinduced Halide Migration in Wide Bandgap Perovskites via Surface Passivation.

In this work, we study the kinetics of photoinduced halide migration in FA0.8Cs0.2Pb(I0.8Br0.2)3 wide (∼1.69 eV) bandgap perovskites and show that halide migration slows down following surface passivation with (3-aminopropyl) trimethoxysilane (APTMS). We use scanning Kelvin probe microscopy (SKPM) to probe the contact potential difference (CPD) shift under illumination and the kinetics of surface potential relaxation in the dark. Our results show that APTMS-passivated perovskites exhibit a smaller CPD shift under illumination and a slower surface potential relaxation in the dark. We compare the evolution of the photoluminescence spectra of APTMS-passivated and unpassivated perovskites under illumination. We find that APTMS-passivated perovskites exhibit more than 5 times slower photoluminescence red-shift, consistent with the slower surface potential relaxation as observed by SKPM. These observations provide evidence for kinetic suppression of photoinduced halide migration in APTMS-passivated samples, likely due to reduced halide vacancy densities, opening avenues to more efficient and stable devices.

Surface Passivation Suppresses Local Ion Motion in Halide Perovskites.

We use scanning probe microscopy to study ion migration in formamidinium (FA)-containing halide perovskite semiconductor Cs0.22FA0.78Pb(I0.85Br0.15)3 in the presence and absence of chemical surface passivation. We measure the evolving contact potential difference (CPD) using scanning Kelvin probe microscopy (SKPM) following voltage poling. We find that ion migration leads to a ∼100 mV shift in the CPD of control films after poling with 3 V for only a few seconds. Moreover, we find that ion migration is heterogeneous, with domain interfaces leading to a larger CPD shift than domain interiors. Application of (3-aminopropyl)trimethoxysilane (APTMS) as a surface passivator further leads to 5-fold reduction in the CPD shift from ∼100 to ∼20 mV. We use hyperspectral microscopy to confirm that APTMS-treated perovskite films undergo less photoinduced halide migration than control films. We interpret these results as due to a reduction in the halide vacancy concentration after APTMS passivation.

Influence of the Mn Content on the Corrosion Behaviour of HEA CoCrFeN-iMnX (X=5, 20, 35 at.%) Prepared via MA+SPS

The high entropy alloys with intended chemical compositions of CoCrFeNiMnX (X=5, 20 and 35 at.%) were prepared by the means of mechanical alloying. Prepared powders were then compacted using the progressive spark plasma sintering, which minimizes the deleterious microstructural coarsening. The compacts were, regardless of the actual chemical composition, composed of a solid solution with FCC crystallographic lattice and a small amount of carbides identified as Cr7C3. The dimensions of those carbides increased with the content of Mn, which was confirmed also by atomic force microscopy (AFM) and scanning kelvin probe microscopy (SKPM). The surface topography measured by AFM confirmed its presence as they emerged from the surface, perfectly matching the positive potential measured by the SKPM. It was found, that the HEAs are showing rather worse corrosion resistance in the aqueous environment containing 9 g/l NaCl compared to the reference 316L stainless steel. Moreover, the higher the content of Mn, the worse the corrosion resistance increasing the corrosion current density and shifting open circuit potential towards more negative values. When exposed to the elevated temperature of 600 °C, the alloys formed a poor protective oxidic layer that tended to chip off due to thermal stresses.

Lateral Controlled Doping and Defect Engineering of Graphene by Ultra-Low-Energy Ion Implantation

In this paper, the effectiveness of ultra-low-energy ion implantation as a means of defect engineering in graphene was explored through the measurement of Scanning Kelvin Probe Microscopy (SKPM) and Raman spectroscopy, with boron (B) and helium (He) ions being implanted into monolayer graphene samples. We used electrostatic masks to create a doped and non-doped region in one single implantation step. For verification we measured the surface potential profile along the sample and proved the feasibility of lateral controllable doping. In another experiment, a voltage gradient was applied across the graphene layer in order to implant helium at different energies and thus perform an ion-energy-dependent investigation of the implantation damage of the graphene. For this purpose Raman measurements were performed, which show the different damage due to the various ion energies. Finally, ion implantation simulations were conducted to evaluate damage formation.

Surface-Doping-Induced Mobility Modulation Effect for Transport Enhancement in Organic Single-Crystal Transistors.

Molecular doping has conventionally been an effective way to improve the electrical-transport performances in organic field-effect transistors (OFETs), while corresponding mechanisms associated with specific doping techniques have been less investigated and discussed in detail. Here, based on ultrathin dinaphtho[2,3-b:2',3'-f]-thieno[3,2-b]thiophene (DNTT) single crystals, robust transconductance enhancements are realized in OFETs upon surface molecular doping realized via van der Waals epitaxially growing crystalline 1,3,4,5,7,8-hexafluoro-tetracyanonaphthoquinodimethane (F6TCNNQ) onto the single crystal's surface. It is proposed that it is the mobility modulation effect (MME) from the interactions between charge-transfer interface and gate electric field, that contributes to more weighted bulk carriers, and finally improves charge-transport performances. The evaluations are further supported by scanning Kelvin probe microscopy(SKPM) surface potential characterizations, which manifest the gate-induced more delocalized holes near the charge-transfer interfaces. Space-charge-limited current (SCLC) investigations, numerical calculations, and theoretical mobility modeling are also performed to corroborate the analysis. This study can deepen the understanding of charge transport in doped semiconductors and provide effective ways for optimizing the electrical performance of organic devices.

Tailoring surface electronic properties of GO-TiO2 hybrid nanostructures through interface modifications

The tailoring of electronic properties in carbon-based hybrid functional materials is essential for improving their overall physicochemical behavior. In this work, graphene oxide (GO)-titanium dioxide (TiO2) hybrid nanostructures are irradiated with 120 MeV Ag9+ swift heavy ions (SHI) for tailoring its surface electronic properties through defect-mediated interface modifications. The microscopic and spectroscopic characterizations indicate a gradual reduction of GO into reduced graphene oxide (rGO) with increasing ion dose. The work function (WF) measurement of GO-TiO2 by scanning Kelvin probe microscopy (SKPM) exhibits systematic variation with the ion fluence and agrees well with the variation in the Fermi energy of GO obtained from the Raman spectroscopy. Moreover, the semiconducting behavior of GO can be effectively tuned by TiO2-controlled Fermi level modulation in GO-TiO2 hybrid nanostructures with ion fluence. The Monte Carlo-based simulations, stopping range of ions in matter (SRIM) and transport of ions in matter (TRIM) codes, reveal that the mutual interplay of defects created in the nanostructures, substrate, and their interfacial regions are responsible for the systematic modulation of the WF in the GO-TiO2.

Electron transfer behaviour of green synthesized carbon quantum dot sensor towards VOC and heavy metal ion sensing

Present day world, the leakage of volatile organic compound (VOC) such as ethanol in industries, as well as presence of heavy metal ions in drinking water pose a serious threat to human health. This research develops a quantum dot sensor (nitrogen-doped carbon quantum dots (n-CDs)) for multifaceted applications. n-CDs were synthesized using hydrothermal from Citrus medica fruit and analysed using XPS, HRTEM, Zeta-potential, PL, and EDS. The study is unique, which employs the Scanning Kelvin Probe microscope (SKP) technique to investigate VOC sensing by n-CDs with contact potential difference mapping for ethanol gas sensing. n-CDs were first-ever characterized by SKP to resolute work function, and VOC interactions were examined. Energy level diagrams were used to study electron transitions. The luminescence quenching caused by electron transfer from n-CDs to receptors was manipulated to detect Fe3+ metal ions with a detection limit of 1.2 µM, which is well below the WHO’s acceptable limit.

Scanning Kelvin Probe Microscopy investigation of optically induced charge in Au nanoparticles embedded into ZrO-=SUB=-2-=/SUB=-(Y) films

Accumulation and relaxation of optically induced electric charge in ZrO2(Y) films with embedded single-layered arrays of Au nanoparticles (NPs) of 2-3 nm in diameter have been studied subject to the depth of the Au NPs in the ZrO2(Y) layers and the optical excitation power at the wavelengths of 473 and 633 nm by Scanning Kelvin Probe Microscopy (SKPM). Keywords: thin film systems, zirconia, nanoparticles, plasmon resonance.

Изучение оптически наведенного заряда наночастиц Au в пленках ZrO-=SUB=-2-=/SUB=-(Y) методом сканирующей Кельвин-зонд микроскопии

Accumulation and relaxation of optically induced electric charge in ZrO2(Y) films with embedded single-layered arrays of Au nanoparticles (NPs) of 2-3 nm in diameter have been studied subject to the depth of the Au NPs in the ZrO2(Y) layers and the optical excitation power at the wavelengths of 473 and 633 nm by Scanning Kelvin Probe Microscopy (SKPM).

Substrate-assisted Fermi level shifting of CVD graphene by swift heavy ions

The systematic modulation of surface electronic properties of graphene can be achieved through surface and interface engineering using swift heavy ion (SHI) irradiation. The effects of dense electronic excitation on the optical and surface electronic properties of chemical vapor deposited (CVD) graphene sheets are investigated in this work. The spectroscopic and microscopic results indicate that the sputtered substrate atoms are trapped in the graphene sheet during irradiation and alter the Fermi level of graphene. The change in the Fermi level calculated from the Raman spectra is investigated through the surface potential measurement by scanning Kelvin probe microscope (SKPM). The shifting of the Fermi level towards the valence band verifies the hole-doping of the graphene sheet by sputtered substrate atoms. The mechanism of ion interaction and its subsequent effects on the graphene and substrate material are further studied rigorously through Monte Carlo simulations using stopping and range of ions in matter (SRIM) and Surface Sputtering sub-routine of transport of ions in matter (TRIM) packages. This work offers a novel way of analyzing defect-induced modifications in the electronic properties of graphene by Raman spectroscopic features in combination with SKPM.

In Operando Visualization of Interfacial Band Bending in Photomultiplying Organic Photodetectors.

Charge injection is a basic transport process that strongly affects performance of optoelectronic devices such as light-emitting diodes and photodetectors. In these devices, the charge injection barrier is related to the band bending at the active layer/electrode interface and exhibits sophisticated dependence on interface structure and device operating conditions, making it difficult to determine via either theoretical prediction or experimental measurements. Here, in operando cross-sectional scanning Kelvin probe microscopy (SKPM) has been applied in organic photodetectors to visualize the interfacial band bending. The photoinduced interfacial band bending becomes more significant with increasing reverse bias voltage, resulting in reduced charge injection barrier and facilitated charge injection. The photoinduced injection current is orders of magnitude higher than the photocurrent directly generated from light absorption and thus leads to significant photomultiplication. Furthermore, the interfacial structure is tuned to further enhance photoinduced interfacial band bending and the photomultiplication factor.

A study of dopant incorporation in Te-doped GaAsSb nanowires using a combination of XPS/UPS, and C-AFM/SKPM

We report the first study on doping assessment in Te-doped GaAsSb nanowires (NWs) with variation in Gallium Telluride (GaTe) cell temperature, using X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), conductive-atomic force microscopy (C-AFM), and scanning Kelvin probe microscopy (SKPM). The NWs were grown using Ga-assisted molecular beam epitaxy with a GaTe captive source as the dopant cell. Te-incorporation in the NWs was associated with a positive shift in the binding energy of the 3d shells of the core constituent elements in doped NWs in the XPS spectra, a lowering of the work function in doped NWs relative to undoped ones from UPS spectra, a significantly higher photoresponse in C-AFM and an increase in surface potential of doped NWs observed in SKPM relative to undoped ones. The carrier concentration of Te-doped GaAsSb NWs determined from UPS spectra are found to be consistent with the values obtained from simulated I–V characteristics. Thus, these surface analytical tools, XPS/UPS and C-AFM/SKPM, that do not require any sample preparation are found to be powerful characterization techniques to analyze the dopant incorporation and carrier density in homogeneously doped NWs.

Mechanism of the Alcohol-Soluble Ionic Organic Interlayer in Organic Solar Cells.

In this article combining density functional theory (DFT) calculations and corresponding experimental measurements, the adsorption behaviors and working mechanism of the alcohol-soluble ionic organic interlayer on different electrode substrates were studied. The results suggest that, when the ionic organic bipyridine salt interlayer (FPyBr) is adsorbed on the Ag surface, Br- will break away from molecule chains and form new chemical bonds with the Ag substrate, as confirmed by both the X-ray photoelectron spectroscopy (XPS) study and DFT study for the first time. Charges are further found to transfer to the Ag substrate from the new interlayer molecular structure without Br-, resulting in adsorption dipoles directed from Ag to the interlayer. Moreover, the direction of the intrinsic dipole of the molecule itself on the Ag substrate is also verified, which is the same as that of the adsorption dipole. Subsequently, the superposition of the two dipoles results in a large reduction of the Ag substrate work function. In addition, the dipole formation mechanism of the interlayer on the ITO surface was also studied. The change in the work function of the ITO substrate by this interlayer is found to be smaller than that of Ag as confirmed by both a DFT study and scanning Kelvin probe microscopy (SKPM) results, which is mainly due to the reversed direction of the molecular intrinsic dipole with respect to the interfacial dipole. The worst device performance of organic solar cells based on the ITO-FPyBr substrate is considered to be one of the consequences of the feature. The findings here are of great importance for the study of the mechanism of the ionic organic interlayer in organic electronic devices, providing insightful understandings on how to further improve the material and device performance.

Imaging Graphene Moiré Superlattices via Scanning Kelvin Probe Microscopy.

Moiré superlattices in van der Waals heterostructures are gaining increasing attention because they offer new opportunities to tailor and explore unique electronic phenomena. Using a combination of lateral piezoresponse force microscopy (LPFM) and scanning Kelvin probe microscopy (SKPM), we directly correlate ABAB and ABCA stacked graphene with local surface potential. We find that the surface potential of the ABCA domains is ∼15 mV higher (smaller work function) than that of the ABAB domains. First-principles calculations show that the different work functions between ABCA and ABAB domains arise from the stacking-dependent electronic structure. Moreover, while the moiré superlattice visualized by LPFM can change with time, imaging the surface potential distribution via SKPM appears more stable, enabling the mapping of ABAB and ABCA domains without tip-sample contact-induced effects. Our results provide a new means to visualize and probe local domain stacking in moiré superlattices along with its impact on electronic properties.

Balanced Ambipolar Charge Transport in Phenacene/Perylene Heterojunction-Based Organic Field-Effect Transistors.

Electronic devices relying on the combination of different conjugated organic materials are considerably appealing for their potential use in many applications such as photovoltaics, light emission, and digital/analog circuitry. In this study, the electrical response of field-effect transistors achieved through the evaporation of picene and PDIF-CN2 molecules, two well-known organic semiconductors with remarkable charge transport properties, was investigated. With the main goal to get a balanced ambipolar response, various device configurations bearing double-layer, triple-layer, and codeposited active channels were analyzed. The most suitable choices for the layer deposition processes, the related characteristic parameters, and the electrode position were identified to this purpose. In this way, ambipolar organic field-effect transistors exhibiting balanced mobility values exceeding 0.1 cm2 V–1 s–1 for both electrons and holes were obtained. These experimental results highlight also how the combination between picene and PDIF-CN2 layers allows tuning the threshold voltages of the p-type response. Scanning Kelvin probe microscopy (SKPM) images acquired on picene/PDIF-CN2 heterojunctions suggest the presence of an interface dipole between the two organic layers. This feature is related to the partial accumulation of space charge at the interface being enhanced when the electrons are depleted in the underlayer.

Correction: Space-charge accumulation and band bending at conductive P3HT/PDIF-CN2 interfaces investigated by scanning-Kelvin probe microscopy

Correction for ‘Space-charge accumulation and band bending at conductive P3HT/PDIF-CN2 interfaces investigated by scanning-Kelvin probe microscopy’ by Federico Chianese et al., J. Mater. Chem. C, 2021, DOI: 10.1039/d1tc04840f.

Space-charge accumulation and band bending at conductive P3HT/PDIF-CN2 interfaces investigated by scanning-Kelvin probe microscopy

Charge transfer processes and space charge accumulation phenomena are fundamental topics concerning the technological applications of organic heterointerfaces.

Scanning Kelvin Probe Microscopy Reveals That Ion Motion Varies with Dimensionality in 2D Halide Perovskites

We study ion migration in 2D lead halide perovskites of varying dimensionality using scanning Kelvin probe microscopy (SKPM). We perform potentiometry on micrometer-scale lateral junctions in the a...

English

In this work, Zn1-xCoFe2AlxO4 (x=0, 0.2, 0.4, 0.6, 0.8 and 1.0) ferrites were synthesized using the sol-gel method. XRD analysis was done and confirmed the formation of spinel structure, where the particle size and lattice parameter decrease with increase of aluminum concentration. This may be attributed to a shift of the bigger Al3+ ions, from the tetrahedral to the octahedral sites, interchanging with smaller Zn2+ ions and that consequently result to a decreased unit cell size. The Scanning Kelvin Probe Microscopy (SKPM) showed that the work function average ranges between 200 and 680 mV for the different concentration of aluminum in the samples. Fractural analysis indicated a small fracture between the samples of different ratios which can be attributed to the method used to prepare as well as the shifting of the Al3+ ions. The UV-vis spectroscopy showed variation of energy gap with increasing aluminum concentration, and an increased optical absorbance as the Al3+ ions were introduced in the samples. Key words: Scanning kelvins probe microscopy, UV-vis spectroscopy, work function, and absorbance.