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Table of contents
The anchoring of the molecules is not only important for the stabilization of the molecular film but also for its density and the resulting surface dipole moment. In this presentation, we summarize our achievements in characterizing porphyrin based molecules equipped with carboxylic acid anchoring groups on TiO2 using scanning probe microscopy. The molecules have been thermally evaporation on TiO2 surfaces in ultrahigh vacuum conditions allowing to control the deposition conditions temperature, deposition rate, and density.
Upon adsorption the porphyrins are not covalently bound to the surface and are interacting only weakly with step edges, defects and in between each other. Upon annealing, the carboxylic acid anchors undergo deprotonation and bind to surface titanium atoms. The formation of covalent bonds is evident from the changed stability of the molecule on the surface as well as the adsorption configuration. The influence of binding on electronic coupling with the surface is investigated using current or voltage spectroscopy as well as photoelectron spectroscopy. The determined energy levels, surface potential values, and shifts of the Zn2p and N1s levels to higher binding energies indicate charging of the porphyrin core.
The strength of this charging process is influenced by the defect density below the molecules. Nanowires NWs are considered appealing and promising candidates in solar cell SC applications. It was shown that the theoretical limit, i. For this reason, intense research activities have been developed to investigate alternative materials in particular metal oxides , which would be low cost, large-area scalable and environmentally friendly, while keeping the required high performances of the NW-based SC.
In this work, we apply the conductive atomic force microscopy c-AFM with scanning spreading resistance microscopy SSRM and single pass intermodulation electrostatic force microscopy ImEFM to study the electrical properties and surface morphology on a nanometer scale of ZnO NW-based all-oxide solar cells.
The contact potential difference Vcpd , under dark and light illumination conditions, possessing high Vcpd resolution of about 1mV was as well measured with ImEFM. The great urgency of finding new energy sources resulted in an upsurge in the electrocatalysis and battery research.
However, optimization and improvement of various energy conversion and storage systems require a better understanding of the electrochemical processes limiting their performance. Thus, further development of new in-situ characterization methodologies is of great importance.
This technique can be easily combined with other commonly used methods i. The rapid illumination of the electrode surface results in an increase in its temperature directly influencing the inner Helmholtz plane of the electric double layer. As a consequence, one observes current transients whose sign, in the simplest case, corresponds to the sign of the excess electrode surface charge. The LICT is also a relatively simple technique of evaluating the potential of maximum entropy PME and, closely related to it, the potential of zero charge PZC - the fundamental properties of the electric double layer.
This indicates that the complexity of intercalation mechanisms of alkali metal cations into the films might be oversimplified. Further, we demonstrate the influence of the electrolyte pH on the net charge of the pure Pt poly electrode surface. All the obtained data emphasize the role of the electrolyte composition for the kinetics and mechanisms of the interfacial processes. Secondary ion mass spectroscopy SIMS is a characterization technique with ultra high chemical sensitivity and high depth resolution, widely established for materials analysis in the field of semiconductors. Recent advances, including the reduction of the lateral resolution to ca.
We investigate the impact of different analysis conditions which unravel the impact of the analysis conditions Bi analysis beam, sputtering with large Oxygen clusters on various artifacts induced by the ion-beam such as sputtering process, topographic ion yield variations, charging effects and bias-induced electro-migration of mobile cations.
This allows us to establish the correlation between the electrical and the chemical inhomogeneities in the materials and identify the role of nanoscopic non uniformities. Interfaces between two immiscible electrolyte solutions ITIES are a promising model mimicking some functional biomembranes in nature charge carrier separation by two interacting photocenters-z-scheme and offer novel opportunities for catalyst regeneration or exchange at the interfaces of liquids . Polarizable interface represents molecularly sharp platform suitable for assembling of nanostructured semiconductor photocatalysts which have been proposed as a novel approach, generating charge careers electron-holes pair reactants in either side of interface, involving in photo-induced charge transfer reactions at liquid-solid-liquid boundaries .
We studied O2 evolution by hyperbranched nanocrystaline BiVO4 at chemically polarized ITIES by [Co bpy 3] PF6 3 as an electron-acceptor compound in organic phase , which dramatically inhibits fast unfavorable electron-hole recombination, similar to z-schemes in natural photosynthesis . Then, it clearly influences the efficiency of the parallel reaction of photo-generated hole-driven water oxidation by increasing the O2 evolution rate. This systems also allows to interrogate the photoelectrochemical reaction by oxidation of [Co bpy 3]2 as a photo-induced electron transfer product in an organic phase of interface by utilizing detector microelectrode ME in the organic phase in a scanning electrochemical microscope SECM.
Furthermore, interfacial polarization effects on the photogenerated charge transfer reactions were investigated by recording regeneration of the reduced form of [Co bpy 3] PF6 3 in organic side of the BiVO4 layer in SECM feedback approach curves and detection of O2 as main product of water photo-oxidation in aqueous side in the generation collection mode. Firstly, the micropipette can be prepared with orifices much smaller than the Au ME so that very high collection efficiencies for [Co bpy 3]2 is attained.
This mode allows quantitative assessment of adsorbed hydroxyl radicals OH? In the interrogation step, the ME-generated titrant Co2 reacts with adsorbed hydroxyl radicals.
Interface , 10, C , , Charging and discharging of nanometer-sized and tunable-shaped objects are very important to fundamental research as well as to potential applications. For instance, isolated external charges can be used as an electrostatic gating for material transport in the nano-channels. On the other hand charging and discharging of objects provide a powerful tool to studying the electrostatic properties on the nanometer scale. Here, we report on the charging of individual graphene oxide GO sheets with varied degrees of reduction by using electrically biased atomic force microscope AFM tips.
AFM measurements indicate that the apparent height of reduced GO rGO sheets increases sharply after charging, while the charging ability is enhanced when the GO sheets are deeply reduced. Charging on isolated areas with tunable shape and size on single-layered GO has been achieved. In addition, charge transfer between rGO sheets separated in hundreds of nanometers on insulating substrates was investigated. It was found that the rGO sheet collects charges from the adjacent charged rGO sheet through the dielectric surfaces.
The efficiency of charge transfer between the separated rGO sheets is dependent on their separation distance, gap length, and the substrate type. The findings suggest that the charge interflow should not be neglected in a graphene circuit. Local dielectric property detecting is of great importance in many scientific research and application.
In the last two decades, many scanned probe microscopy SPM techniques have been developed to fast detection of surface dielectric properties of nanoscale materials. Here, we report a novel method for characterization of local dielectric property based on surface adhesion mapping by atomic force microscopy AFM. We use two dimensional 2D materials—graphene oxide GO and partially reduced graphene oxide rGO sheets, which have similar height but large difference in dielectric property, as the model systems.
By comparing with scanning polarization force microscopy SPFM , our approach is found to have higher sensitivity and lateral resolution. It is expected to provide a better and faster characterizing of local dielectric property of nanoscale materials, and will further facilitate applications in future nanomaterial based device. Efficient charge extraction within solar cells explicitly depends on the optimization of the internal interfaces. Potential barriers, unbalanced charge extraction or interfacial trap states can prevent cells from reaching high power conversion efficiencies.
In the case of perovskite solar cells, slow processes happening on timescales of seconds cause hysteresis in the current-voltage characteristics. Although hysteresis can nowadays be mostly avoided by selection of suitable selective electrode materials, its origin is not yet fully understood. Here, we report on local and time-dependent potential measurements with Kelvin probe force microscopy KPFM on cross sections of planar methylammonium lead iodide MAPI perovskite solar cells. Our experiments revealed distinct differences in the charging dynamics at interfaces of the MAPI to adjacent layers.
Measurements while switching on and off the illumination attest that more than one process is involved in hysteresis. Furthermore, we used KPFM to investigate perovskite solar cells with different electron transport materials ETM , which exhibited a different hysteretic behavior. Depending on the ETM we observed oppositely oriented electric fields within the perovskite layer, which either aid or counteract the charge carrier extraction from the active layer.
Our findings suggest that the introduction of electric fields in the perovskite layer and thus the occurrence of J-V hysteresis could be controlled by the choice of ETM. Kelvin probe force microscopy KPFM is long known as a powerful tool for mapping surface potential and topography with nanoscale resolution. The capability to correlate optoelectronic properties with local structure has been crucial to elucidate some fundamental properties responsible for the high performance of perovskite solar cells.
This work aims to go beyond previous KPFM studies through the precise quantitative analysis of tip-sample interaction in multi-dimensional spectroscopy. These measurements, combined with advanced data analysis, allow to obtain separately the contact potential difference, the capacitance, and the van der Waals interaction of the tip-sample system as a function of their relative distance. The whole preparation was based on vacuum deposition and resulted in a densely packed mesh of nanocrystals with an average grain size of nm. The first set of measurements, performed in the dark, revealed that the contact potential is determined mostly by the work function of the charge selective contact and remains constant with the tip-sample distance, indicating that there is no net charge at the perovskite surface.
When the same experiments were repeated under illumination, the contact potential difference varied according to the strength of the photovoltaic effect. Much more acute changes were observed in the second derivative of the capacitance which can be interpreted as photoinduced variation of the dielectric constant of the perovskite.
A procedure for the functionalization of BioChips for adherent biomaterials is the modification of the surface by coating or by roughening. SNEF are caused by an asymmetric electric dipole in the semiconductor surface region and detected using Kelvin probe force microscopy measurements . BioChips with a stripe-like pattern have been fabricated. The electrical properties of the implanted silicon wafers have been characterized by Hall and electrical impedance measurements. SNEF allow for a patterned adhesion of electrically polarizable biomaterials [2,3], e.
As an outlook it is discussed how the properties of adherent biomaterial, e. Finally, it is discussed how the electrical polarizability of biomaterials on the nanometer and micrometer length scale can be investigated by means of photo-induced force measurements with an AFM platform and tunable lasers.
B, , 80,  C. In polymer electrolyte membrane fuel cell PEMFC , polymer electrolyte membrane is one of the key components for high efficiency performance because proton conductivity is basically dependent on the properties of the membrane, e. Typically, Nafion membranes have been widely used in PEMFC due to its high proton conductivity and chemical stability.
Until now, most of studies have investigated macroscopic electrochemical properties of the Nafion membrane for improving their performance. Although there are numerous macroscopic studies that enable to undserstand and evaluate performance of PEMFC, there is still lack of information on fundamentals and insight of local proton conductivity at the nanoscale.
In this presentation, we investigated the tip-induced reversible and irreversible electrochemical phenomena on the Nafion membrane using atomic force microscopy. We measured local surface displacement induced by proton transport and corresponding electrochemical reactivity through current-voltage measurement and electrochemical strain microscopy. The observed results show locally different electrochemical reactivity on the Nafion membrane that may be related to the proton conducting channel.
Our observation can provide insight into not only nanoscale electrochemical reactivity but also fundamental information for improving the performance of the Nafion membrane in PEMFC. Quantitative Scanning Force Microscopy in ambient conditions Understanding tip-sample interaction in a Scanning Force Microscopy SFM setup is fundamental for optimum data acquisition as well as data interpretation.
To minimize noise and simplify the interpretation of experiments, data should be acquired in the true non-contact regime at low oscillation amplitude. Two methods will be described to characterize nanoscale systems: Alternately, normal images U x,y can be acquired by minimizing the electrostatic tip-sample interaction Kelvin Force Microscopy  in order to determine the local Contact Potential.
Experiments will be presented to demonstrate the capability of nanoscale characterization of samples in air. We will show, on the one hand, how the spatial and time evolution of the surface potential can be studied.
Scanning tunneling microscope - Wikipedia
We find strong time fluctuations of the surface potential and a static lateral corrugation of this potential. On the other hand, we will discuss how multidimensional SFM spectroscopy? From these forces, the Hamaker Constant and the Contact Potential can be determined, allowing for precise characterization of material properties on the nanoscale. Glatzel, Kelvin Probe Force Microscopy. Springer Series in Surface Sciences. Colchero, Nanotechnology , 17 21 , However, a fundamental limitation lies in its contact mode operation, leading research to focus on flat and durable samples. Considering the limitations of contact PFM, a significant barrier for quantitative analysis of these materials arises.
The IC-PFM mode stems from a scanning nanoindentation mode peakforce by Bruker , where the tip is oscillated into intermittent contact with the sample, and resulting force-curves are analysed to yield mechanical information about the sample. We superimpose an electrical signal atop this mode, and extract the piezo-response related deflection signal for each indentation point of a scanning line; notably, only data obtained when the tip contacts the sample is analyzed. The combination of optical spectroscopy and atomic force microscopy AFM is very promising, because it enables the chemical mapping far below the diffraction limit of light.
Both illuminate the tip-sample interface with a pulsed tunable laser source and utilize the resonance enhancement of AFM cantilevers. PTIR, which operates in contact mode, relies on the detection of the thermal expansion of the sample and requires a metal, often gold, substrate for best sensitivity. PiFM, presented here, senses the induced polarization of the sample via an attractive image force acting on a metalized tip and is thus applicable in a much wider wavelength range.
In PiFM, the tip-sample interaction is highly localized and provides spectrographic mapping with. We present physical principles of Apertureless Scanning Near-field Optical Microscopy ASNOM [1,2,3] and report on its application to a mapping of the nanoscale objects optical properties with nm-resolution. Normally, the dipole oscillations in a point-like object like a single molecule or nano-particle can hardly be emitted into an environmental space as a running electromagnetic wave. Its dipole momentum determined by a few oscillating electrons typically single one and angstrom-range oscillation span of charge density yields in vanishingly low efficiency in a light emission.
The situation changes dramatically if a rod-like antenna of some micrometer length is attacted? A huge amount of free electrons in a metal of a tip being involved in the charge density oscillations under an influence of the object being investigated, as well as tip large dimensions lead to increase of radiation efficiency . An external electromagnetic field can, vice versa, be applied to a surface with a help of an ASNOM tip. The dimensions of area where the field is applied are determined just by mechanical dimensions of a tip nm [5,6,7], regardless to the wavelength of a light being used up to THz range.
The amplitude and phase of the wave re-emitted by a tip antenna depend on its? Figure 2 structures of nanometer scale to demonstrate an ability of an ASNOM to map a clear material contrast, with a lateral resolution of nm. Polystyrene embedded in a PVAC matrix. We also present the maps of running surface polariton waves collected with an ASNOM on different samples. A nanometer lateral resolution of ASNOM allows for mapping the surface waves with a lateral resolution much better than a wavelength and, therefore, to investigate the polariton optics phenomena in such kind of structures with a rather good precision.
Williams, Apertureless near field optical microscope. Wickramasinghe, Scanning Interferometric Apertureless Microscopy: Optical Imaging at 10 Angstrom Resolution. Kawata, Near-field scanning optical microscope with a metallic probetip. Xie, Theory of Nanometric Optical Tweezers. Wickramasinghe, Scattering spectroscopy of molecules at nanometer resolution. Kern, Apertureless scanning near field optical microscope with sub nm resolution. The electrical behavior of materials for photovoltaics PV at the mesoscale strongly determines device performance.
Thus, spatially resolving the electrical and optical response of emerging materials, such as perovskites and polycrystalline owns, is crucial to advance our understanding of charge carrier generation, recombination and collection at the nanoscale. We use scanning probe microscopy methods to realize a novel platform to image the functionality of materials for PV.
Through time-dependent Kelvin-probe force microscopy KPFM we quantify the transient behavior of perovskite solar cells. Upon and post illumination we measure ion accumulation and migration, respectively, resulting from the occupation of trap states and in a residual Voc even when the material is under dark conditions.
We anticipate our functional imaging approach to impact the rational design of the next generation of high-efficiency and low-cost PV devices, by establishing a correlation between the materials electrical, chemical and structural properties. Further, the time-dependent KPFM could be extended to probe the stability of lead-free perovskites. CH3NH3PbI3, with perovskite structure have been received extensive attention for photovoltaic applications owing to their superior properties. V hysteresis has hindered the attainment of an even higher efficiency performance.
2017 Fall Meeting
Although recent experiemtnal studies based on piezoresponse force microscopy PFM have shown that the perovskite solar cells have ferroelectricity that causes hysteresis, there still remain an ambiguity because PFM response can originate from the surface volume change by ion migration as well as piezoresponse. V curves, we find that grain boundaries assisted ion migration can be a dominant origin of I? V hysteresis at the macroscopic scale, while ferroelectricity contributes to the I-V hysteresis at the grains. Our findings suggest that, although there is ferroelectricity in the CH3NH3PbI3 thin films, ion migration mainly contributes to the macroscopic I?
The presented results could provide basic guidance to the resolution of I-V hysteresis issues in perovskite materials. The charge carrier transport behavior and solar cells efficiency of perovskite solar cells were shown to be dramatically influenced by the existence of PbI2 phase in perovskite films. According to the investigation at the interfacial electronic configuration of individual perovskite grains under illumination, the enhanced photogenerated carrier separation and reduced back recombination were observed as an optimal interfacial PbI2 passivation layers with a thickness less than 20 nm at perovskite crystal grains was applied.
A range of emerging materials, from perovskite solar cells, to polymer batteries, and even bioelectronic transistors, show strong variations in performance associated with the nanoscale structure of the active material. In this talk, I will discuss our work using a combination of multimodal in situ probes to unravel the often complex interplay of electronic, ionic, and even ferroelectric, behaviors that connect processing, structure, and function in these materials.
For instance, by classifying local current-voltage curves according to the corresponding local photoluminescence, we show that local variations in electronic coupling between the semiconductor and electrode are present across a wide range of common hybrid perovskite semiconductor photovoltaic device architectures, pointing a clear path forward in attempts to improve Voc in these materials.
In addition, we disentangle the competing effects of electronic carrier injection with voltage bias stress, providing a clearer picture of the role of ion migration vs. Finally, we discuss nanoscale measurements of ion transport in a range of soft polymer systems, using both electrochemical strain microscopy ESM as well as time-resolved electrostatic force microscopy trEFM , showing how local polymer crystallinity influences ion uptake and motion in organic semiconductors that serve as a model for materials being studied for battery binders as well as bioelectronic transducers.
Although hybrid lead halide perovskites have shown great promise as a new cheap and flexible alternative to silicon, these so-called perovskite solar cells exhibit unusual behaviour such as current-voltage hysteresis.
Microscopy and Microanalysis 11 , — Photonik 6 , Dezember Gate-controlled atomic quantum switch, Physical Review Letters 93, 12 M. Molecular Nanowires and other Quantum Objects , Eds. Carbon , Providence, USA Switching an Electrical Current with Atoms: Carbon 41, — Y. Macromolecules 36, — E. A, 12 , 41—44 A. Surface and Interface Analysis 33 , 96—99 U. Carbon 02, 26th Conference on Carbon, , H Langmuir 18 , — Scanning Probe Techniques for Materials: Characterization at Nanometer Scale , Eds.
Siqueira Petri, and Th. Surface and Interface Analysis 32 , — Characterization and Modification of Polymer Blends. Colloids and Polymer Science , — Vitrification in Restricted Geometry: Dry Films of Colloidal Particles. Polymer 40, Journal of Materials Science, 34, B 59 12 , A 68, ff A 68, Monolayers of Graphite Rotated by a Defined Angle: Hexagonal Superstructures by STM. A 68 , Surface Modification of Thin Polystyrene Films. Langmuir 15, Depolarization Nearfield Scanning Optical Microscopy: Comparison of Experiment and Theory. Microscopy , Nachrichten Forschungszentrum Karlsruhe 32, —23 Amino-terminated self-assembled monolayers on SiO2 and their interaction chromophors, proteins and ionomers.
A, 66, S Hexagonal versus Honeycomb Structure on Graphite. Surface and Interface Analysis 25, Thin Solid Films , Surface Topography and Material Contrast. Surface and Interface Analysis 23, Correlation between Particle Geometry and Optical Properties. Metals 55—57, Ultramicroscopy 42—44, Annealing Behaviour of Ion-bombarded WSe2: Tip Shape Dependence and Writing Techniques. Annales de Chimie, 17, Properties of Highly Conducting Polyacetylene. Nanopaprika is always looking for new partners, if you have any idea, contact me at editor nanopaprika. Physicist, Engineer, Project coordinator, User of nanotechnology products My research field or area of interest innanotechnology scanning tunneling microscopy STM , atomic-force microscopy AFM , scanning probe microscopy SPM , optical profilometry OP , infrared microscopy IRM , high capacity probe storage, nanometrology, automatic surface characterization, nanolithography, nanomanipulation, nanoassembling, bottom-up nanofabrication, molecular manufacturing, nanotechnology, catalytic nanoparticles, micromechanical bimaterial infrared detectors Interest in Nalwa, volume 14, pages , American Scientific Publishers, A.
X-ray, Synchrotron and Neutron Techniques, volume 4, number 1, pages , R. X-ray, Synchrotron and Neutron Techniques, volume 1, number 6, pages , R. Drift-insensitive distributed calibration of probe microscope scanner in nanometer range: Virtual mode Posted on May 18, at 9: The main idea… Continue. STM observation of a box-shaped graphene nanostructure appeared after mechanical cleavage of pyrolytic graphite Posted on December 23, at 7: A description is given of a three-dimensional box-shaped graphene BSG … Continue.
Approach description Posted on November 28, at 4: