Use Of Scanning Probe Microscopy Research Articles

Unveiling Nanoscale Heterogeneities at the Bias-Dependent Gold-Electrolyte Interface.

Electrified solid-liquid interfaces (SLIs) are extremely complex and dynamic, affecting both the dynamics and selectivity of reaction pathways at electrochemical interfaces. Enabling access to the structure and arrangement of interfacial water in situ with nanoscale resolution is essential to develop efficient electrocatalysts. Here, we probe the SLI energy of a polycrystalline Au(111) electrode in a neutral aqueous electrolyte through in situ electrochemical atomic force microscopy. We acquire potential-dependent maps of the local interfacial adhesion forces, which we associate with the formation energy of the electric double layer. We observe nanoscale inhomogeneities of interfacial adhesion force across the entire map area, indicating local differences in the ordering of the solvent/ions at the interface. Anion adsorption has a clear influence on the observed interfacial adhesion forces. Strikingly, the adhesion forces exhibit potential-dependent hysteresis, which depends on the local gold grain curvature. Our findings on a model electrode extend the use of scanning probe microscopy to gain insights into the local molecular arrangement of the SLI in situ, which can be extended to other electrocatalysts.

Submolecular Insights into Interfacial Water by Hydrogen-Sensitive Scanning Probe Microscopy.

ConspectusWater-solid interfaces have attracted extensive attention because of their crucial roles in a wide range of chemical and physical processes, such as ice nucleation and growth, dissolution, corrosion, heterogeneous catalysis, and electrochemistry. To understand these processes, enormous efforts have been made to obtain a molecular-level understanding of the structure and dynamics of water on various solid surfaces. By the use of scanning probe microscopy (SPM), many remarkable structures of H-bonding networks have been directly visualized, significantly advancing our understanding of the delicate competition between water-water and water-solid interactions. Moreover, the detailed dynamics of water molecules, such as diffusion, clustering, dissociation, and intermolecular and intramolecular proton transfer, have been investigated in a well-controlled manner by tip manipulation. However, resolving the submolecular structure of surface water has remained a great challenge for a long time because of the small size and light mass of protons. Discerning the position of hydrogen in water is not only crucial for the accurate determination of the structure of H-bonding networks but also indispensable in probing the proton transfer dynamics and the quantum nature of protons.In this Account, we focus on the recent advances in the H-sensitive SPM technique and its applications in probing the structures, dynamics, and nuclear quantum effects (NQEs) of surface water and ion hydrates at the submolecular level. First, we introduce the development of high-resolution scanning tunneling microscopy/spectroscopy (STM/S) and qPlus-based atomic force microscopy (qPlus-AFM), which allow access to the degrees of freedom of protons in both real and energy space. qPlus-AFM even allows imaging of interfacial water in a weakly perturbative manner by measuring the high-order electrostatic force between the CO-terminated tip and the polar water molecule, which enables the subtle difference of OH directionality to be discerned. Next we showcase the applications of H-sensitive STM/AFM in addressing several key issues related to water-solid interfaces. The surface wetting behavior and the H-bonding structure of low-dimensional ice on various hydrophilic and hydrophobic solid surfaces are characterized at the atomic scale. Then we discuss the quantitative assessment of NQEs of surface water, including proton tunneling and quantum delocalization. Moreover, the weakly perturbative and H-sensitive SPM technique can be also extended to investigations of water-ion interactions on solid surfaces, revealing the effect of hydration structure on the interfacial ion transport. Finally, we provide an outlook on the further directions and challenges for SPM studies of water-solid interfaces.

Scanning probe microscopy study of cobalt ferrite-barium titanate coreshell magnetoelectric nanoparticles

Cobalt ferrite – barium titanate coreshell composite nanoparticles are an important part of the emerging field of magnetoelectric materials. Understanding the structure of these nanoparticles is vital towards controlling and adjusting their key properties for specific applications. Although transmission electron microscopy can reveal nanoparticle size, shape, and crystallinity, key information regarding the magnetic properties and the compositional makeup of the coreshell configuration remains elusive at nanoscale. This paper covers the use of scanning probe microscopy to directly measure these features using topography imaging, magnetic force imaging, and phase imaging. This technique provides significant insights into the intrinsic magnetoelectric coupling between the magnetostrictive cobalt ferrite core and the piezoelectric barium titanate shell. Particularly, this technique was applied to obtain phase images that directly exhibited the coreshell configuration, including an intermediate transition region between the core and the shell. The samples examined include 20 nm and 50 nm cobalt ferrite-barium titanate coreshell nanoparticles fabricated via co-precipitation and sol–gel synthesis. The results revealed a cuboid shape for the cobalt ferrite cores, and an oval shape for the cobalt ferrite-barium titanate coreshell nanoparticles. This result was confirmed by transmission electron microscopy. Additionally, the paper comprehensively analyzes the samples in their powder form via X-ray diffraction. The results indicate that the crystallinity of barium titanate is enhanced as the cobalt ferrite concentration is increased because of heterogeneous nucleation requiring a lower nucleation barrier compared to homogeneous nucleation.

Studying signal compartmentation in adult cardiomyocytes.

Multiple intra-cellular signalling pathways rely on calcium and 3′–5′ cyclic adenosine monophosphate (cAMP) to act as secondary messengers. This is especially true in cardiomyocytes which act as the force-producing units of the cardiac muscle and are required to react rapidly to environmental stimuli. The specificity of functional responses within cardiomyocytes and other cell types is produced by the organellar compartmentation of both calcium and cAMP. In this review, we assess the role of molecular localisation and relative contribution of active and passive processes in producing compartmentation. Active processes comprise the creation and destruction of signals, whereas passive processes comprise the release or sequestration of signals. Cardiomyocytes display a highly articulated membrane structure which displays significant cell-to-cell variability. Special attention is paid to the way in which cell membrane caveolae and the transverse-axial tubule system allow molecular localisation. We explore the effects of cell maturation, pathology and regional differences in the organisation of these processes. The subject of signal compartmentation has had a significant amount of attention within the cardiovascular field and has undergone a revolution over the past two decades. Advances in the area have been driven by molecular imaging using fluorescent dyes and genetically encoded constructs based upon fluorescent proteins. We also explore the use of scanning probe microscopy in the area. These techniques allow the analysis of molecular compartmentation within specific organellar compartments which gives researchers an entirely new perspective.

GaN nanowires as probes for high resolution atomic force and scanning tunneling microscopy

GaN nanowires are potential candidates for use in scanning probe microscopy due to their well-defined, reproducible, geometric shapes, their hardness, and their light guiding properties. We have developed and investigated probes for high resolution atomic force microscopy and scanning tunneling microscopy utilizing GaN nanowires as probes. The nanowires are n-doped and the morphology of the nanowires has been tailored for scanning probe microscopy by growing them with a sharp tip for measurements and high thickness for robustness. The individual GaN nanowires were removed from their growth substrate and attached onto commercial atomic force microscopy cantilevers or etched tungsten wires for scanning tunneling microscopy. A standard scanning electron microscope equipped with a nanoprobe, a focused ion beam column and a gas injection system was used to locate, transfer, and attach the nanowires. We evaluated the properties of the GaN probes on different substrates including HOPG, Au, SiO2, InAs, and GaAs. We demonstrate both atomic force microscopy and scanning tunneling microscopy measurements with single atomic layer resolution and evaluate the robustness of the tips by monitoring them before and after scanning. Finally, we explore the use of the tips for scanning tunneling spectroscopy demonstrating that reliable results, which can reveal information on the electronic properties of the surface-tip system, are obtainable. The fundamental properties of these probes, which are demonstrated in this work, show promise for future use of the probes in exploring semiconductor-semiconductor tunneling junctions at the nanoscale as well as for other scanning probe techniques where high resolution is required.

Corrosion Initiation and Propagation on Carburized Martensitic Stainless Steel Surfaces Studied via Advanced Scanning Probe Microscopy.

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 90–200 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.

Selecting suitable image dimensions for scanning probe microscopy

The use of scanning probe microscopy to acquire topographical information from surfaces with nanoscale features is now a common occurrence in scientific and engineering research. Image sizes can be orders of magnitude greater than the height of the features being analysed, and there is often a trade-off between image quality and acquisition time. This work investigates a commonly encountered problem in nanometrology - how to choose a scan size which is representative of the entire sample. The topographies of a variety of samples are investigated, including metals, polymers, and thin films.

AFM characterization of the shape of surface structures with localization factor

Although with the use of scanning probe microscopy (SPM) methods the topographical imaging of surfaces is now widely available, the characterization of surface structures, especially their shape, and the processes which change these features is not trivial with the existing surface describing parameters. In this work the application of a parameter called localization factor is demonstrated for the quantitative characterization of surface structures and for processes which alter the shape of these structures. The theory and optimal operation range of this parameter are discussed with three application examples: microstructure characterization of gold thin films, characterization of the changes in the grain structure of these films during thermal annealing, and finally, characterization of the oxidation processes on a polished tin surface.

Temperature mapping of operating nanoscale devices by scanning probe thermometry.

Imaging temperature fields at the nanoscale is a central challenge in various areas of science and technology. Nanoscopic hotspots, such as those observed in integrated circuits or plasmonic nanostructures, can be used to modify the local properties of matter, govern physical processes, activate chemical reactions and trigger biological mechanisms in living organisms. The development of high-resolution thermometry techniques is essential for understanding local thermal non-equilibrium processes during the operation of numerous nanoscale devices. Here we present a technique to map temperature fields using a scanning thermal microscope. Our method permits the elimination of tip–sample contact-related artefacts, a major hurdle that so far has limited the use of scanning probe microscopy for nanoscale thermometry. We map local Peltier effects at the metal–semiconductor contacts to an indium arsenide nanowire and self-heating of a metal interconnect with 7 mK and sub-10 nm spatial temperature resolution.

Efficient Carrier Separation and Intriguing Switching of Bound Charges in Inorganic-Organic Lead Halide Solar Cells.

We fabricated a mesoporous perovskite solar cell with a ∼14% conversion efficiency, and we investigated its beneficial grain boundary properties of the perovskite solar cells through the use of scanning probe microscopy. The CH3NH3Pb(I0.88,Br0.12)3 showed a significant potential barrier bending at the grain boundary and induced passivation. The potential difference value in the x = 0.00 sample is ∼50 mV, and the distribution of the positive potential is lower than that of the x = 0.12 sample. We also investigated the polarization and hysteretic properties of the perovskite thin films by measuring the local piezoresponse. Specifically, the charged grain boundaries play a beneficial role in electron-hole depairing and in suppressing recombination in order to realize high-efficiency perovskite solar cells.

Microstructure and erosion characteristics of Ni-AlN thin films prepared by electrodeposition

AbstractNi-AlN thin films were successfully fabricated via direct-current (DC), pulse-current (PC), and ultrasonic-assisted pulse-current (UAPC) deposition. The microstructure, microhardness, and erosion characteristics of the Ni-AlN thin films were determined with the use of scanning probe microscopy (SPM), X-ray diffraction (XRD), Vickers hardness test, electrochemical station, and scanning electron microscopy (SEM). SPM results revealed that the Ni-AlN thin films synthesized by UAPC deposition have a compact and fine morphology with average grain diameters of the Ni and AlN particles of approximately 97.7 and 40.2 nm, respectively. Based on the XRD results, the Ni-AlN thin films consist of Ni and AlN phases. The Ni-AlN thin films prepared by DC, PC, and UAPC deposition at 4.5 A/dm2 current density exhibited an optimum microhardness value of 904, 943, and 987 HV, respectively. Based on the erosion test results, the films prepared by UAPC deposition possesses the best corrosion resistance among the prepared thin films. The corrosion potentials of the DC-, PC-, and UAPC-deposited films were -0.552, -0.473, and -0.446 V vs. SCE, respectively.

Mineral surface–organic matter interactions: basics and applications

The ability to control the binding of biological and organic molecules to a crystal surface is central in several fields; for example, in biotechnology, catalysis, molecular microarrays, biosensors preparation and environmental sciences. The nano-morphology and nanostructure at the surface may have physico-chemical properties that are very different from those of the underlying mineral substrate. Recent developments in scanning probe microscopy (SPM) have widened the spectrum of possible investigations that can be performed at the nanometric level on the surface of minerals. They range from the study of physical properties such as surface potential, electric field topological determination, Brønsted–Lowry site distributions, to chemical and spectroscopic analysis in air, in liquid or in gaseous environments. After an introduction to SPM modes of operation and new SPM-based technological developments, we will present recent examples of applications in the study of interactions between organic matter and mineral surface and report on the advances in knowledge that have been made by the use of scanning probe microscopy.

Use of scanning probe microscopy to study the evolution of nanometer sized liquid structures

The evolution of the profile of nanometer sized water drops on a mica surface has been studied through hydration scanning probe microscopy. A time range from a few seconds down to a fraction of millisecond after the formation of the drop has been explored. This high time resolution has been obtained by sampling a series of statistically equivalent drops. This approach also avoids any probe interference during the drop evolution process.

(Invited) Electrical Scanning Probe Microscopy Techniques for the Detailed Characterization of High-k Dielectric Layers

The use of scanning probe microscopy (SPM) techniques for the electrical characterization of high-k dielectric layers is reviewed, focusing on conductive atomic force microscopy (cAFM) and scanning capacitance microscopy (SCM). It is demonstrated exemplarily for ZrO2 high-k layer stacks that cAFM enables a detailed analysis of the morphological and electrical layer characteristics. Film morphologies can be determined even for surfaces where topography mapping can not detect distinct surface roughness like grain structures. For as-deposited amorphous layers, the current distribution is random whereas increased leakage currents at grain boundaries can be observed for nano-crystalline samples. The dominant current mechanisms through the layers can be determined from current voltage curves at distinct local points. Comparison with conventional techniques proofs the findings by cAFM. The quantitative interpretation of SCM measurement results often suffers from parasitic capacitances and light induced effects. Local thickness variation of dielectrics, however, can be detected very sensitively.

Availability of Feature-Oriented Scanning Probe Microscopy for Remote-Controlled Measurements on Board a Space Laboratory or Planet Exploration Rover

Prospects for a feature-oriented scanning (FOS) approach to investigations of sample surfaces, at the micrometer and nanometer scales, with the use of scanning probe microscopy under space laboratory or planet exploration rover conditions, are examined. The problems discussed include decreasing sensitivity of the onboard scanning probe microscope (SPM) to temperature variations, providing autonomous operation, implementing the capabilities for remote control, self-checking, self-adjustment, and self-calibration. A number of topical problems of SPM measurements in outer space or on board a planet exploration rover may be solved via the application of recently proposed FOS methods.

Nanoimaging in SiC and Related Materials: Beyond Surface Morphology to Charge Transport and Physical Parameters Mapping

We describe the potential use of scanning probe microscopy (SPM) to image at nanoscale the charge transport in conductive layers, through dielectrics and barriers and in general for mapping of physical properties in wide band gap materials, processing and devices. Measurements through conductive layers are described discussing the limits and potentialities. Carrier profiling by SPM is presented and critically discussed as a complex method, crossing information from several techniques, to extract more insights related to carrier distribution.

Imaging of charge trapping in distorted carbon nanotubes by x-ray excited scanning probe microscopy

We have observed the distribution of electron trapping centers on distorted carbon nanotubes (CNTs) by a unique x-ray analysis technique that has both elemental and spatial selectivities. This technique involves the use of scanning probe microscopy (SPM) under synchrotron radiation excitation of the inner shell of carbon. The probe detects the Coulomb force that results from the relaxation of an electron bound to a defect site into the core hole state created by x-ray photon absorption. This results in a change in charge state of the defect. At the spatial resolution provided by the SPM technique, we observed the electron trapping centers distributed on the compressed and torsionally distorted CNTs. This direct association of mechanical distortion with defect sites indicates a potential risk of deterioration of electric properties during the fabrication and processing of CNT networks.

Mechanical Properties of Sharpened Carbon Nanotube Tips

We investigate the mechanical properties of sharpened nanotube tips for use in scanning probe microscopy in terms of tip bending under a force acting on the side of the tip. The sharpened nanotube probe fabricated by means of a modified electrical breakdown process effectively acts as a probe with high lateral resolution not only in the topographic measurement but also in the potential distribution measurement. Based on molecular mechanics calculations for a sharpened triple-walled nanotube probe, although the interlayer van-der-Waals interaction weakens the probe stiffness expected on the basis of the continuum model, the stiffness of the tapered nanotube is confirmed to be 10 times higher than that for a single-walled nanotube with the same tip radius and the same length.

Ferroelectric domain engineering using atomic force microscopy tip arrays in the domain breakdown regime

One of the main obstacles to ultrahigh-density scanning probe ferroelectric-based devices is the writing speed of the device when using a single tip. We report here on the application of atomic force microscopy tip arrays for nanodomain engineering in ferroelectric crystals under the domain breakdown conditions. Using a multiple-tip array, it is shown that domain writing in 200-μm-thick RbTiOPO4 crystals results in a regular one-dimensional domain grating that penetrates throughout the bulk crystal as in the case of single tip writing. This multiple tip approach paves the way to the use of scanning probe microscopy for fabrication of various nanodomain configurations for advanced optoelectronic and microelectronic devices.

Change of internal stress of carbon superhard condensates at a process of annealing

Superhard carbon coatings with thickness from 5 nm up to 10 μm were obtained by vacuum-arc deposition of carbon plasma on sublayers from stainless steels, titanium and silicon under the temperature from 50 up to 150 °C. Correlation dependences between conditions of formation of carbon condensates and change of internal stresses in them at a process of annealing in a range of temperatures from 200 up to 475 °C were examined. It was shown that the character of internal stresses changing at a process of annealing of carbon condensates had proof correlation with the parameters of deposition (the temperature of sublayer, duration of a pulse of discharge) and it could be used for identification of coatings and for control of their properties. It was determined that superthin layers of carbon obtained by impulse vacuum-arc method effectively protected a surface from oxidation in an atmosphere of air up to 425 °C. Researches of surface structures of coatings by use of scanning probe microscopy (SPM) were carried out. It was classified as fractal and an explanation of mechanism of change of internal stress value in carbon coatings at a process of annealing was given.