Probe Force Microscopy Measurements Research Articles

The Hidden Flower in WS2 Flakes: A Combined Nanomechanical and Tip-Enhanced Raman Exploration.

We report on tungsten disulfide (WS2) flakes grown by chemical vapor deposition (CVD), which exhibit a flower-like surface structure above the primary few-layer flake with a triangular shape. The fine structure is only revealed in the mechanical, chemical, and electronic properties of the flake but not in the topography. The origin of this structure is the peculiar one-step growth during the CVD process that permits to control the sulfur concentration at any time. A high concentration of S at the onset of the deposition process leads to a rapid growth of the flake, resulting in tungsten vacancies. Reducing the sulfur concentration toward the end of the growth slows down the reaction and leads to sulfur vacancies. These microscale domains were studied by confocal- and tip-enhanced Raman spectroscopy revealing their chemical composition with high spatial resolution. A strong quenching of the photoluminescence in the tungsten-vacancy domains is observed. Atomic force microscope measurements, performed in intermittent contact mode, force modulation mode (including lateral force mode), and PeakForce quantitative nanomechanics mode, show that the mechanical properties of these domains differ. Within the tungsten-vacancy domains, the adhesion force is reduced, while the friction force increased. Kelvin probe force microscopy measurements show that the electronic properties of the flakes are modulated by these domains. The combined nanomechanical and nanospectroscopy measurements provide detailed insights on the inhomogeneous surface properties of the single WS2 flake, further highlighting how its multidomain properties can be finely tuned using CVD.

Nano-FTIR Correlation Nanoscopy for Organic and Inorganic Material Analysis

Significance: Correlation scanning probe techniques to complement nanoscale IR measurements for next generation sample characterizationScattering-type Scanning Near-field Optical Microscopy (s-SNOM) is a scanning probe approach to optical microscopy and spectroscopy, bypassing the ubiquitous diffraction limit of light to achieve a spatial resolution below 20 nanometers. s-SNOM employs the strong confinement of light at the apex of a sharp metallic atomic force microscopy (AFM) tip to create a nanoscale optical hot-spot. Analyzing the scattered light from the tip enables the extraction of the optical properties of the sample directly below the tip and yields nanoscale resolved images simultaneous to topography [1]. In addition, the technology has been advanced to enable Fourier-Transform Infrared Spectroscopy on the nanoscale (nano-FTIR) [2] using broadband radiation from the visible spectral range to THz frequencies.Recently, the combined analysis of complex nanoscale material systems by correlating near-field optical data with information obtained by other scanning probe microscopy (SPM)-based measurement methodologies has gained significant interest. For example, the material-characteristic nano-FTIR spectra of a phase-separated polystyrene/low-density polyethylene (PS/LDPE) polymer blend verifies sharp material interfaces by measuring a line profile across a ca. 1 μm sized LDPE island. Near-field reflection/absorption imaging at 1500cm-1 of the ca. 50nm thin film allows to selectively highlight the distribution of PS in the blend and simultaneously map the mechanical properties like adhesion of the different materials [3,4].Further, we present results that correlate the near-field optical response of semiconducting samples like graphene (2D) or functional SRAM devices (3D) in different frequency ranges (mid-IR & THz) to Kelvin Probe Force Microscopy (KPFM) measurements. Thus, s-SNOM systems represent an ideal platform to gain novel insights into complex material systems by different near-field and AFM-based method.[1] F. Keilmann, R. Hillenbrand, Phil. Trans. R. Soc. Lond. A 362, 787 (2004).[2] F. Huth, et al., Nano Lett. 12, 3973 (2012).[3] B. Pollard, et al., Beilstein J. of Nanotechn. 7, 605 (2016).[4] I. Amenabar, et al., Nature Commun. 8, 14402 (2017).

Fragmented graphene synthesized on a dielectric substrate for THz applications

Fragmented multi-layered graphene films were directly synthesized via chemical vapor deposition (CVD) on dielectric substrates with a pre-deposited copper catalyst. We demonstrate that the thickness of the sacrificial copper film, process temperature, and growth time essentially influence the integrity, quality, and disorder of the synthesized graphene. Atomic force microscopy and Kelvin probe force microscopy measurements revealed the presence of nano-agglomerates and charge puddles. The potential gradients measured over the sample surface confirmed that the deposited graphene film possessed a multilayered structure, which was modelled as an ensemble of randomly oriented conductive prolate ellipsoids. THz time domain spectroscopy measurements gave the ac conductivity of the graphene flakes and homogenized graphitic films as being around 1200 S cm−1 and 1000 S cm−1, respectively. Our approach offers a scalable fabrication of graphene structures composed of graphene flakes, which have effective conductivity sufficient for a wide variety of THz applications.

(Invited, Digital Presentation) Application of Polyacid Clusters in Modifying Single-Walled Carbon Nanotubes

Phosphotungstic acids (PTAs) are a typical family of polyacids with tunable composition, structure and morphology. Relying on their super strong acidity and moderate oxidizability, they may take different roles when interacting with single walled carbon nanotubes (SWCNTs).We found that PTA could be used as stable dopants for SWCNT films to reduce the resistance without damaging the transparency. By simply dipping the SWCNT films in the solution of PTAs and drying afterwards, the sheet resistance was cut in half with long term stability. The doped films showed excellent flexibility. Both Raman spectroscopic studies and Kelvin probe force microscopy measurements revealed that the strong acidity of PTAs plays a key role in the doping effect by increasing the redox potential of the ambient O2 and thus the Fermi level of the SWCNTs is brought down.The PTA clusters can be encapsulated into the inner cavity of SWCNTs when their diameters are compatible. Such a host-guest molecular interaction between SWCNTs and inner clusters with designed size was applied to separate large-diameter s-SWCNTs. When a kind of PTA of ~1 nm in size were filled within SWCNT cavities, s-SWCNTs with diameters concentrated at ~1.3–1.4 nm were selectively extracted with the purity of ~98% by a commercially available polyfluorene derivative. The sorting mechanisms associate with oxidation effect of PTA and the size-dependent electron transfer from nanotubes to inner PTA clusters. The flexible regulation of interaction between the nanotube and clusters, thus tuning the diameter of sorted s-SWCNTs.PTAs have shown great power in tuning the properties of SWCNTs, presenting amazing potentials in the applications of SWCNTs.

Mechanism of low Ohmic contact resistance to p-type GaN by suppressed edge dislocations

In this paper, an excellent Ohmic contact to p-GaN with a low specific contact resistance (ρc) of 2.0 × 10−5 Ω·cm2 is demonstrated using a patterned sapphire substrate (PSS) and oxidized Ni/Au contacts. GaN epitaxy with high crystal quality on the PSS, confirmed by high-resolution x-ray diffraction, played a key role in the improved Ohmic contact to p-GaN. The edge dislocations were annihilated during the epitaxial process on the PSS to afford a low surface dislocation density, which was in accordance with the results of transmission electron microscopy and cathodoluminescence spectroscopy. Furthermore, a reduced Fermi level and enhanced activation efficiency of Mg with suppressed segregation around the dislocations were demonstrated by Kelvin probe force microscopy and contact Hall measurements, respectively. A GaN p-channel metal oxide semiconductor device fabricated on the PSS displayed a twofold higher forward current density and superior gate controllability compared with that fabricated on a conventional sapphire substrate.

Stabilization of Three-Particle Excitations in Monolayer MoS2 by Fluorinated Methacrylate Polymers.

While extrinsic factors, such as substrates and chemical doping, are known to strongly influence visible photoemission from monolayer MoS2, key fundamental knowledge for p-type polymeric dopants is lacking. We investigated perturbations to the electronic environment of 2D MoS2 using fluorinated polymer coatings and specifically studied stabilization of three-particle states by monitoring changes in intensities and emission maxima of three-particle and two-particle emissions. We calculated changes in carrier density and trion binding energy, the latter having an additional contribution from MoS2 polarization by the polymer. Polarization is further suggested by Kelvin probe force microscopy (KPFM) measurements of large Fermi level shifts. Changes similar in magnitude, but opposite in sign, were observed in 2D MoS2 coated with an analogous nonfluorinated polymer. These findings highlight the important interplay between electron exchange and electrostatic interactions at the interface between polymers and transition metal dichalcogenides (TMDCs), which govern fundamental electronic properties relevant to next-generation devices.

Probing the charge transfer and electron–hole asymmetry in graphene–graphene quantum dot heterostructure

In recent years, graphene-based van der Waals (vdW) heterostructures have come into prominence showcasing interesting charge transfer dynamics which is significant for optoelectronic applications. These novel structures are highly tunable depending on several factors such as the combination of the two-dimensional materials, the number of layers and band alignment exhibiting interfacial charge transfer dynamics. Here, we report on a novel graphene based 0D–2D vdW heterostructure between graphene and amine-functionalized graphene quantum dots (GQD) to investigate the interfacial charge transfer and doping possibilities. Using a combination of ab initio simulations and Kelvin probe force microscopy (KPFM) measurements, we confirm that the incorporation of functional GQDs leads to a charge transfer induced p-type doping in graphene. A shift of the Dirac point by 0.05 eV with respect to the Fermi level (E F) in the graphene from the heterostructure was deduced from the calculated density of states. KPFM measurements revealed an increment in the surface potential of the GQD in the 0D–2D heterostructure by 29 mV with respect to graphene. Furthermore, we conducted power dependent Raman spectroscopy for both graphene and the heterostructure samples. An optical doping-induced gating effect resulted in a stiffening of the G band for electrons and holes in both samples (graphene and the heterostructure), suggesting a breakdown of the adiabatic Born–Oppenheimer approximation. Moreover, charge imbalance and renormalization of the electron–hole dispersion under the additional influence of the doped functional GQDs is pointing to an asymmetry in conduction and carrier mobility.

A strategy to detect the effect of electrode defects on the electrical reliability in multilayer ceramic capacitors

Multilayer ceramic capacitors (MLCCs) are indispensable devices to electronic industry due to their high capacitance and good temperature stability, which shares the largest market of passive electronic devices. However, electrode defects could adversely influence the reliability, especially for thin-layer MLCCs. It is important to understand the internal relationship between electrode quality and reliability. In this work, finite element method simulation and Kelvin probe force microscopy measurement are introduced to investigate the surface electric field distribution on the cross section of MLCCs. Successively-enhanced local electric field concentration could be detected in the vicinity of electrode roughness, electrode discontinuity, and pores based on both simulation and experimental methods. In addition, probability density of electric field curves and critical intensification factor are calculated to quantitatively characterize the electric field distribution. Electrical measurement results have revealed that MLCCs with superior electrode quality exhibit high reliability, which is further verified by studying the standard MLCCs with nearly perfect electrodes. This work innovatively utilized the Kelvin probe force microscopy test and statistical quantitative characterization of electric field distribution, which may serve as the common approaches in MLCC industries to help understand the mechanism of electrical failure.

Effect of thermally induced B2 phase on the corrosion behavior of an Al0.3CoCrFeNi high entropy alloy

The corrosion resistance of Al-Co-Cr-Fe-Ni high entropy alloys (HEAs) is probably affected by B2 phases. In this paper, the effect of B2 phases on the corrosion behavior of Al0.3CoCrFeNi HEAs in 3.5 wt% NaCl solution is clarified in this paper by purposely controlling the formation of B2 phases using annealing treatment. The microstructure characterization reveals that the content of (Al, Ni)-rich and Cr-poor B2 phases increases and the electrochemical measurements show that the pitting corrosion resistance is deteriorated as the annealing temperature decreases. Accordingly, the B2 phase is confirmed to be detrimental to the corrosion resistance of Al0.3CoCrFeNi HEAs. It can be attributed to the preferential dissolution of B2 phases causing easier pit initiation, which is evidenced by the corrosion morphology observation and scanning Kelvin probe force microscopy measurements, and to the slower repassivation rate leading to easier pit propagation, as demonstrated by the quantitative analysis of potentiostatic polarization curves.

Self-organization of agitated microspheres on various substrates.

The vibration dynamics of relatively large granular grains is extensively treated in the literature, but comparable studies on the self-assembly of smaller agitated beads are lacking. In this work, we investigate how the particle properties and the properties of the underlying substrate surface affect the dynamics and self-organization of horizontally agitated monodisperse microspheres with diameters between 3 and 10 μm. Upon agitation, the agglomerated hydrophilic silica particles locally leave traces of particle monolayers as they move across the flat uncoated and fluorocarbon-coated silicon substrates. However, on the micromachined silicon tray with relatively large surface roughness, the agitated silica agglomerates form segregated bands reminiscent of earlier studies on granular suspensions or Faraday heaps. On the other hand, the less agglomerated hydrophobic polystyrene particles form densely occupied monolayer arrangements regardless of the underlying substrate. We explain the observations by considering the relevant adhesion and friction forces between particles and underlying substrates as well as those among the particles themselves. Interestingly, for both types of microspheres, large areas of the fluorocarbon-coated substrates are covered with densely occupied particle monolayers. By qualitatively examining the morphology of the self-organized particle monolayers using the Voronoi approach, it is understood that these monolayers are highly disordered, i.e., multiple symmetries coexist in the self-organized monolayers. However, more structured symmetries are identified in the monolayers of the agitated polystyrene microspheres on all the substrates, albeit not all precisely positioned on a hexagonal lattice. On the other hand, both the silica and polystyrene monolayers on the bare silicon substrates transition into less disordered structures as time progresses. Using Kelvin probe force microscopy measurements, we show that due to the tribocharging phenomenon, the formation of particle monolayers is promoted on the fluorocarbon surface, i.e., a local electrostatic attraction exists between the particle and the substrate.

Self-Assembled Porphyrin Nanoleaves with Unique Crossed Transportation of Photogenerated Carriers to Enhance Photocatalytic Hydrogen Production

The preparation of self-assembled porphyrins with orderly stacked nanostructures for emulating natural photosynthesis has stimulated extensive efforts to optimize the energy conversion efficiency. However, the elucidation of how orderly stacked structures promote photocatalysis at the molecular level remains a great challenge. Here, unique porphyrin nanoleaves with designed and ordered structure are synthesized and show a hydrogen evolution rate higher than that of commercial powder. Photodeposition of cocatalysts and Kelvin probe force microscopy measurement suggest selective aggregation of photogenerated electrons and holes at different active sites. Combined with theoretical calculations, we find that the orderly packing changes molecular symmetry and induces a molecular dipole, which increases linearly along the π-π stacking direction and forms a strong built-in electric field. The built-in electric field drives photogenerated electrons and holes for the unique crossed transportation along different directions. These findings reveal how orderly stacked structures promote photocatalysis and provide a novel approach for highly efficient water splitting.

About the role of the hydrogen during stress corrosion cracking of a low-copper Al-Zn-Mg alloy

This study provides some clarifications about the influence of microstructural parameters on the susceptibility of low-copper Al-Zn-Mg alloy to stress corrosion cracking (SCC). Tensile tests in air were carried out on AA7046 in T4 and T4 aged at 150 °C (named 150/20) metallurgical states after pre-exposure of the specimens to a chloride solution under mechanical loading. The results showed the predominant role of the corrosion-induced hydrogen during SCC process on the loss of elongation to failure. Scanning kelvin probe force microscopy (SKPFM) measurements were performed for the T4 specimens as well as for a 530 °C heat-treated T4 specimen with a coarse-grained microstructure; this allowed the contribution of hydrogen diffusion at the grain boundaries on the hydrogen distribution to be highlighted. The analysis of the fracture modes after tensile tests and hydrogen diffusion profiles obtained by SKPFM in the framework of previous studies investigating the microstructure-hydrogen and plasticity-hydrogen relationships allowed to propose a qualitative model to describe SCC phenomena. The detrimental role of hydrogen at the grain boundaries on the mechanical behaviour was highlighted; the outcome of the evaluation of results from the present study in combination with our previous studies and literature data suggested that it can be limited by hydrogen trapping on intragranular η-MgZn2 precipitates.

Enhanced van der Waals epitaxy of germanium by out-of-plane dipole moment induced from transferred graphene on TiN/AlN multilayers

Recent advances in 3D/2D heterostructures have opened up tremendous opportunities in building highly flexible and durable optoelectronic devices. However, the inherit lack of interfacial bonding and low surface energy of van der Waals surfaces limit the nucleation and growth of 3D materials. Enhancing wettability by providing a porous buffer is effective in growing compound semiconductors on graphene while van der Waals epitaxy of Ge remains challenging. Here, the nucleation of Ge has been significantly improved from an islanded mode to granular modes by using a TiN/AlN multilayered buffer prior to Ge/graphene integration. Highly textured Ge growth with dominating (111), (220), and (311) peaks are identified by x-ray diffraction. The microstructure of the buffer TiN/AlN demonstrates a polycrystalline quality with clean interfaces between each interlayer and the substrate. Kelvin probe force microscopy measurements along the lateral TiN/AlN interface identify a potential drop corresponding to the AlN phase. This contact potential difference between TiN and AlN is the key in generating the out-of-plane dipole moment that modifies the surface energy of the monolayer graphene, resulting in enhanced wettability of the Ge adatoms nucleated on top. Surface dipole induced nucleation of 3D semiconductor thin films on 2D materials via the proper design of buffer layer is fundamentally important to enhance the 3D/2D growth toward flexible optoelectronic applications.

Controlled grain-size thermochromic VO2 coatings by the fast oxidation of sputtered vanadium or vanadium oxide films deposited at glancing angles

An original, simple and cost-effective oxidation strategy to attain thermochromic vanadium dioxide thin films is reported. This two-step procedure comprises the initial deposition of DC magnetron-sputtered vanadium or vanadium oxide films by the combination of glancing angle deposition and, if needed, reactive gas pulsing process, followed by fast oxidation of such layers in air atmosphere at high temperatures. Thanks to the careful control of the thermal treatment parameters, and taking advantage of the superior reactivity of the high surface-to-volume porous deposited structures, the formation of pure VO2 (M1) layers was achieved. The comprehensive characterization of such oxidized systems by means of scanning electron microscopy, Raman spectroscopy and scanning-transmission electron microscopy techniques such as electron energy-loss spectroscopy, not only confirmed the presence of the VO2 (M1) phase, but also allowed to shed light on the key role that reaction time plays in the selective formation of vanadium dioxide films of adjustable grain size and crystallinity. The optimal conditions to stabilize thermochromic VO2 consists in using large deposition angles (85 °) and short oxygen pulses (≤ 2 s) during the growth, followed by fast and short thermal treatments (≤ 45 s with a heating rate of 42 °C s−1) in air atmosphere at 550 °C. The metal-to-insulator response of the accomplished VO2 layers was finally evaluated by means of temperature dependent Kelvin probe force microscopy measurements, evidencing surface potential drops at heating, greater than those reported in the literature to date for VO2 thin films.

Unraveling the hysteretic behavior at double cations-double halides perovskite - electrode interfaces

Despite over a decade of research on metal halide perovskites (MHPs) in the context of photovoltaic applications, understanding the nature of electronic and ionic processes associated with current-voltage (I-V) hysteretic behavior has been limited. Here, we explore the hysteretic behavior in (FAPbI3)0.85(MAPbBr3)0.15 perovskite devices with lateral Cr electrodes by applying first order reversal curve (FORC) bias waveform in I-V, Kelvin probe force microscopy (KPFM) measurements, and in-situ chemical imaging by time-resolved time-of-flight secondary ion mass spectrometry (tr-ToF-SIMS). In dark, we reveal pronounced hysteretic behaviors of charge dynamics in the off-field by probing time-dependent current and contact potential difference (CPD). Under illumination, transient and hysteretic behaviors are significantly reduced. The tr-ToF-SIMS results reveal that the hysteretic behaviors are strongly associated with accumulation of Br- ions at the interfaces. In addition, the low mobility MA+ ions result in transient behavior and contribute to the hysteretic phenomena. It was shown that Pb2+ ions can be reduced at the interfaces due to electrochemical reactions with the electrode in the presence of charge injection and photogenerated charges. These hysteretic behaviors associated with charge dynamics, ion migration, and interfacial electrochemical reaction are critical to further improve the performance and stability of MHPs photovoltaics and optoelectronics.

On‐Surface Synthesis of a Dicationic Diazahexabenzocoronene Derivative on the Au(111) Surface

AbstractThe 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.

On-Surface Synthesis of a Dicationic Diazahexabenzocoronene Derivative on the Au(111) Surface.

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.

Charge Transfer at the Hetero‐Interface of WSe2/InSe Induces Efficient Doping to Achieve Multi‐Functional Lateral Homo‐Junctions

AbstractCharge transfer at the hetero‐interface is at the center of van der Waals (vdWs) heterostructure devices for multi‐functional applications. Compared with the extensively investigated photogenerated carrier transfer driven by the built‐in electric field from the conduction or valence band offset, the charge transfer due to the Fermi level difference of the two adjacent constitutes, and its influence on the opto‐/electronic performance of vdWs heterostructure devices are not clarified. Herein, by taking an example of WSe2/InSe heterostructure, it is demonstrated that the charge transfer at the hetero‐interface is an efficient “doping” strategy to dramatically modulate the carrier densities of atomically thin counterparts due to the extension of “band bending” across the entire heterostructure, paving the way for the creation of lateral WSe2 p‐n and n‐n+ homo‐junctions with multi‐functionalities, including promising rectification, photovoltaic, and photodetection abilities. Moreover, the device physics of lateral homo‐junctions, including potential distribution, band diagram, and photocurrent generation mechanisms, is revealed by gate‐dependent Kelvin probe force microscopy and scanning photocurrent measurements. This work not only provides a general avenue to build 2D lateral homo‐junctions, but also give deeper insights into the device physics of the junctions by coupling scanning probe and scanning photocurrent techniques.

Formation and superlattice of long-range and highly ordered alicyclic selenolate monolayers on Au(1 1 1) studied by scanning tunneling microscopy

The formation and surface structures of cyclohexanethiolate (CYH-S) and cyclohexaneselenolate (CYH-Se) self-assembled monolayers (SAMs) on Au(111) were probed to understand headgroup effects on the formation of SAMs with an alicyclic backbone using scanning tunneling microscopy (STM). CYH-S SAMs on Au(111) formed via solution deposition at room temperature (RT) were composed of small ordered domains with sizes ranging from 10 to 30 nm, whereas CYH-Se SAMs on Au(111) usually had a disordered phase. The molecular arrangements of CYH-S SAMs on Au(111) could be described as a (5 × 2√3)R30° structure. CYH-Se SAMs formed via vapor deposition at RT had a long-range ordered phase (greater than 100 nm) including missing rows and molecular defects. A highly ordered crystalline phase of CYH-Se SAMs on Au(111) with fewer structural defects was formed at 323 K for 12 h that was assigned to a (√3.5 × 2√10)R27° structure. STM observations revealed that the domain formation and surface structures of CYH-Se SAMs on Au(111) were completely different from those of CYH-S SAMs. Furthermore, we found that CYH-S and CYH-Se SAM can be utilized for bonding-induced work function modification of Au substrate through Kelvin probe force microscopy measurement.

Electrochemical characteristics of grain boundaries in gadolinium and aluminum co-doped ceria and ceria-alumina composites

The influence of 1, 2, 4 and 10 cat.% Al2O3 addition on the electrochemical characteristics of commercially available 10 cat.% Gd-doped ceria and a 1:1 cat.% mixture of CeO2:Al2O3 were evaluated in our study. Analysis of the electronic conductivity and polarization-relaxation behavior of the samples showed that an Ohmic contribution to the total electronic resistance cannot only be attributed to the electrode contact resistance but is a combined contribution from the electrode interface and decreased pO2 dependence of the grain boundary resistivity of the material. The average electrical potential barrier at the grain boundaries was calculated from impedance spectroscopy data at 50–300 °C. Kelvin probe force microscopy (KPFM) measurements were used to analyze the local Volta potential distribution at the grain boundaries of pure Ce0.9Gd0.1O1.95 and of samples with 4 and 10 cat.% Al addition at room temperature. KPFM measurements showed clear evidence for an increased Volta potential difference between bulk and grain boundary cores and for a considerable broadening of the Volta potential gradient at the grain boundaries with increasing Al concentration.