Simultaneous Topography Research Articles

Comparison of Anterior Segment Measurements with a New Multifunctional Unit and Five Other Devices

PurposeTo evaluate the clinical availability of a multifunctional ocular biometric unit, MR-6000, for simultaneous keratometry, tonometry, topography, and pachymetry evaluation, and compare anterior segment measurements with five other devices: autokeratometer (KR-1), Scheimpflug camera (Pentacam HR), swept-source optical coherence tomography (IOLMaster 700), Placido disk scanning-slit topography (Orbscan II), and noncontact tonometry (FT-1000).MethodsThirty eyes from thirty patients who visited Severance Hospital for cataract surgery were examined using MR-6000 and the other devices. The mean keratometry, central corneal thickness (CCT), white-to-white (WTW) distance, and intraocular pressure (IOP) values were compared. Repeated measures analysis of variance, Wilcoxon signed-rank test, intraclass correlation coefficient (ICC), and Bland-Altman plot were used to assess the correlation and agreement between devices.ResultsThirty eyes of thirty patients were evaluated. Statistically significant differences in mean keratometry between MR-6000, KR-1, Pentacam HR, and IOLMaster 700 were not observed (p > 0.05). All five devices, including Orbscan II, had almost perfect agreement in measuring keratometry (ICC > 0.80, p < 0.05). CCT measured by MR-6000 was significantly different from that of Pentacam HR and Orbscan II measurements (p < 0.05) but correlated with that of Pentacam HR and Orbscan II measurements (ICC > 0.60, p < 0.05). The WTW distance measured by MR-6000 was not significantly different from that measured by IOLMaster 700 but was different from that measured by Orbscan II. IOP measured by MR-6000 was not correlated with FT-1000.ConclusionsKeratometric values obtained through MR-6000 can be used interchangeably with other devices based on good correlation and agreement. However, the CCT, WTW, and IOP values were not interchangeable with a single multifunctional unit for cataract surgery preoperative examination.

Simultaneous Corneal Topography and Epithelial Thickness Mapping from a Single Measurement Using Optical Coherence Tomography.

Purpose To evaluate the performance of corneal epithelial thickness mapping (ETM) and demonstrate simultaneous measurement of ETMs and corneal topography using REVO NX (Optopol Technology, Zawiercie, Poland)—an OCT device for anterior and posterior segment imaging. Methods One hundred thirty-seven eyes of 137 normal subjects and patients with corneal diseases were recruited to the study. Each subject was scanned with REVO NX. ETMs and corneal topography maps were reconstructed from a single measurement. Corneal topography was also carried out using Pentacam (Oculus, Wetzlar, Germany). One hundred twenty-eight eyes were qualified for the final analysis. Forty healthy eyes were used to evaluate the performance of ETM, and 88 eyes were used to compare ETMs and corneal topography. The repeatability and reproducibility of ETMs in healthy subjects were assessed on the basis of 17 spatial zones derived from an 8-mm diameter corneal scan using within-subject standard deviation, test-retest repeatability, within-subject coefficient of variation (CoV), and intraclass correlation coefficient (ICC). Results The ICC for both repeatability and reproducibility of ETMs for the central sector was 0.95. The ICC value for the other sectors was only moderately lower. However, the CoV for repeatability (≤1.55%) was slightly higher than the value reported for the RTVue device (Optovue, Inc, Fremont, California, USA), for which a CoV in the central zone of 1.07% was reported in unoperated eyes. The superior quadrants were found to be the thinnest while the inferior ones were the thickest. ETMs and topography maps created from a single OCT measurement present a complementary image of the cornea. Conclusions ETMs obtained using REVO NX show high levels of repeatability and reproducibility in normal eyes. Because the topographic and epithelial thickness analyses are performed using the same data, which means they are based on the exact same 3D corneal model, they do not require reciprocal centration and map matching. This ensures a complete point-to-point correlation between ETMs and corneal topography maps, which paints a fuller picture of a given pathology.

Molecular Recognition of Proteins through Quantitative Force Maps at Single Molecule Level.

Intermittent jumping force is an operational atomic-force microscopy mode that produces simultaneous topography and tip-sample maximum-adhesion images based on force spectroscopy. In this work, the operation conditions have been implemented scanning in a repulsive regime and applying very low forces, thus avoiding unspecific tip-sample forces. Remarkably, adhesion images give only specific rupture events, becoming qualitative and quantitative molecular recognition maps obtained at reasonably fast rates, which is a great advantage compared to the force–volume modes. This procedure has been used to go further in discriminating between two similar protein molecules, avidin and streptavidin, in hybrid samples. The adhesion maps generated scanning with biotinylated probes showed features identified as avidin molecules, in the range of 40–80 pN; meanwhile, streptavidin molecules rendered 120–170 pN at the selected working conditions. The gathered results evidence that repulsive jumping force mode applying very small forces allows the identification of biomolecules through the specific rupture forces of the complexes and could serve to identify receptors on membranes or samples or be applied to design ultrasensitive detection technologies.

Boxcar Averaging Scanning Nonlinear Dielectric Microscopy.

Scanning nonlinear dielectric microscopy (SNDM) is a near-field microwave-based scanning probe microscopy method with a wide variety of applications, especially in the fields of dielectrics and semiconductors. This microscopy method has often been combined with contact-mode atomic force microscopy (AFM) for simultaneous topography imaging and contact force regulation. The combination SNDM with intermittent contact AFM is also beneficial for imaging a sample prone to damage and using a sharp microscopy tip for improving spatial resolution. However, SNDM with intermittent contact AFM can suffer from a lower signal-to-noise (S/N) ratio than that with contact-mode AFM because of the shorter contact time for a given measurement time. In order to improve the S/N ratio, we apply boxcar averaging based signal acquisition suitable for SNDM with intermittent contact AFM. We develop a theory for the S/N ratio of SNDM and experimentally demonstrate the enhancement of the S/N ratio in SNDM combined with peak-force tapping (a trademark of Bruker) AFM. In addition, we apply the proposed method to the carrier concentration distribution imaging of atomically thin van der Waals semiconductors. The proposed method clearly visualizes an anomalous electron doping effect on few-layer Nb-doped MoS2. The proposed method is also applicable to other scanning near-field microwave microscopes combined with peak-force tapping AFM such as scanning microwave impedance microscopy. Our results indicate the possibility of simultaneous nanoscale topographic, electrical, and mechanical imaging even on delicate samples.

Utilization of AFM for Observing Early-Onset Mechanisms of Lithium-Metal

Lithium metal is seen as a “Holy Grail” material for battery technology, due to its high capacity and low electrochemical potential. However, the intrinsic plating/stripping mechanism of lithium metal, coupled with heterogeneous ionic pathways leads to treacherous dendrite growth and rapid consumption of active materials, diminishing cycle life. Variability in the mechanical and electrochemical properties of lithium’s surface initiates a cascading effect that ultimately ends in the failure mechanisms that plague lithium metal.Simulations and ultra-resolved techniques (e.g., cryo-TEM) can provide fundamental understanding of certain phenomena but need to be closely coupled with realistic conditions to drive commercialization of lithium. Cell-level studies can provide clarity between different parameters, such as temperature, pressure, lithium preparation, electrolyte optimization, and cathode characteristics. However, cell-to-cell variability makes repeatability of results difficult, slowing the advancement in the readiness-level of novel cell designs. In this work, phenomena at the micro- to nanoscale were observed to better understand the behavior of lithium. At this scale, investigation of Li+ flux during deposition and dissolution is a crucial piece to solving the lithium-metal battery puzzle. This was accomplished with the use of different atomic force microscopy (AFM) techniques, coupled with other characterization tools to correlate to cell-level evaluation. The multi-functional capabilities of AFM may provide a bridge between atomistic/fundamental studies and cell-level testing, thanks in part to its non-destructive nature, high reproducibility, and ability to decipher the effect of various parameters on reaction mechanisms at the electrode-electrolyte interface.Scanning Kelvin probe force microscopy (SKPFM), electrochemical AFM (EC-AFM) and quantitative nanomechanical mapping (QNM) were utilized to acquire spatially resolved properties for different use conditions and under different design parameters. SKPFM is a tool used to measure the surface potential, which directly relates to the work function. With this tool, local heterogeneities can be distinguished as a function of surface treatment or operation in a cell-level build. EC-AFM is utilized to observe mechanistic variations in-situ, detecting morphological changes caused by either lithiation/de-lithiation or solid-electrolyte interphase (SEI) breakdown/formation. Coupled with QNM, EC-AFM can also provide simultaneous topography and mechanical properties such as adhesion, modulus, and deformation.These AFM tools can provide high-resolution insight into mechanistic phenomena such as dendrite/pit growth, “dead” Li formation, as well as SEI formation, furthering the understanding of the lithium-metal anode. The investigations accomplished with AFM advances the field of battery technologies, providing insight into the initiation and propagation of failure mechanisms, along with how to solve them.

Adaptive Simultaneous Topography and Broadband Nanomechanical Mapping of Heterogeneous Materials on Atomic Force Microscope

In this article, an approach is proposed to achieve simultaneous imaging and broadband nanomechanical mapping of heterogeneous soft materials in air by using atomic force microscope (AFM). Simultaneous imaging and mechanical mapping (SIMM) is developed to, for example, correlate morphological and mechanical evolutions of the sample together. Current methods, however, are limited to nanomechanical mapping at a single frequency one at a time, or at frequencies much higher than those of interests for majority of soft polymers and live biological species. These limitations have been tackled through the recently-developed simultaneous imaging and broadband nanomechanical mapping (SIBNM) technique for materials of relatively small mechanical spatial variations. We propose, in this work, to extend the SIBNM technique to heterogeneous materials by developing a gradient-based adaptive Kalman-filtering technique to account for spatial variations of the sample mechanical properties when decoupling the sample topography tracking and the nanomechanical mapping from each other. A compressed-sensing technique is introduced to adaptively tune the gain of the adaptive Kalman filter. Experimental implementation of the proposed approach shows that both the topography and the broadband mechanical mapping of a heterogeneous soft sample can be reliably quantified.

Simultaneous X-ray radiography and diffraction topography imaging applied to silicon for defect analysis during melting and crystallization

One of the key issues to be resolved to improve the performance of silicon solar cells is to reduce crystalline defect formation and propagation during the growth-process fabrication step. For this purpose, the generation of structural defects such as grain boundaries and dislocations in silicon must be understood and characterized. Here, in situ X-ray diffraction imaging, historically named topography, is combined with radiography imaging to analyse the development of crystal defects before, during and after crystallization. Two individual indirect detector systems are implemented to record simultaneously the crystal structure (topographs) and the solid–liquid morphology evolution (radiographs) at high temperature. This allows for a complete synchronization of the images and for an increased image acquisition rate compared with previous studies that used X-ray sensitive films to record the topographs. The experiments are performed with X-ray synchrotron radiation at beamline ID19 at the European Synchrotron Radiation Facility. In situ observations of the heating, melting, solidification and holding stages of silicon samples are presented, to demonstrate that with the upgraded setup detailed investigations of time-dependent phenomena are now possible. The motion of dislocations is recorded throughout the experiment, so that their interaction with grain boundaries and their multiplication through the activation of Frank–Read sources can be observed. Moreover, the capability to record with two camera-based detectors allows for the study of the relationship between strain distribution, twinning and nucleation events. In conclusion, the simultaneous recording of topographs and radiographs has great potential for further detailed investigations of the interaction and generation of grains and defects that influence the growth process and the final crystalline structure in silicon and other crystalline materials.

Simultaneous removal of nonrotationally symmetric errors in tilted wave interferometry

The tilted wave interferometer has been developed as a fast and accurate instrument for the measurement of aspheric and freeform surfaces. We present a method for increasing its robustness and flexibility. Tilted wave interferometry crucially depends on accurate calibration and any changes to a calibrated setup require, in general, a recalibration. Therefore, we propose a method for simultaneous topography reconstruction and elimination of errors arising from such changes. An approach to identify trends in systematic errors for the complex non-null setup with a large number of blackbox model parameters is worked out. The procedure allows deriving an error removal scheme for nonrotationally symmetric components based on measurements in different rotational positions. The feasibility and benefit of the error elimination method are shown both by simulation methods and dedicated experiments. A significant reduction of systematic errors even in a miscalibrated state is achieved. Hence, recalibrations are avoided and measurement time and flexibility are improved.

Portable hyperspectral lidar utilizing 5 GHz multichannel full waveform digitization.

The Finnish Geospatial Research Institute hyperspectral LiDAR (FGI HSL) was one of the first multichannel terrestrial LiDARs capable of producing simultaneous 3-dimensional topography with spectral data. Supercontinuum-based HSL instruments developed so far have suffered from portability and sensitivity issues, severely restricting potential applications. Recently, we have implemented a new robust field design of the FGI HSL together with an improved pulse digitizing scheme. Small size and significantly improved measuring accuracy of this new system enable a range of novel applications that so far have been impractical for multichannel terrestrial LiDARs. Particularly, this new design has enabled us to perform measurements in underground mines and detect minute spectral differences in various rock types. In this paper, we present the design of our new LiDAR and preliminary algorithms together with a brief performance assessment of the device. In addition, we provide example measurements of typical rock samples found in a ferrochrome mine.

Modified wavelength scanning interferometry for simultaneous tomography and topography of the cornea with Fourier domain optical coherence tomography.

Visual acuity is dependent on corneal shape and size. A minor variation in surface geometry can cause a deformation of corneal geometry, which affects its optical performance. In this work we demonstrate an algorithm for the simultaneous measurement of corneal tomography and topography with a traditional point-scanning Fourier domain optical coherence tomography (FD-OCT) system. A modified wavelength scanning interferometry (mWSI) algorithm enabled topographical evaluation of the surface with nanometer-scale resolution, which is superior to the micrometer-scale resolution of traditional OCT structural imaging. We validated the technique with an optically flat mirror, standard roughness gauges, and atomic force microscopy (AFM). The mirror results show nanometer-scale sensitivity (~3.5 nm), and the mWSI measurements were in good agreement (error ~5%) with the specifications of the roughness comparator and AFM, demonstrating the accuracy of the technique. Following validation, the measurements were made on pig corneas in situ at various artificially controlled intraocular pressures (IOP) and before and after cross-linking (CXL). The results show that the mean surface roughness increased by ~65% after removal of the epithelium in preparation for CXL but did not change as a function of IOP. The demonstrated method could be used for simultaneous measurement of tissue tomography with micrometer-precision and topography with nanometer-precision.

(Invited) Investigation of Solid Electrolyte Interphase on Amorphous Siox/Si Films Using Tip Enhanced Raman Spectroscopy

The composition, morphology and thickness of solid electrolyte interphase (SEI) on silicon anodes are dictated by multiple factors such as surface chemistry, electrolyte composition, chemical passivation effects etc. Further the SEI constantly evolves, as it is electrochemically lithiated (delithiated) during the enormous volume changes. SEI on silicon typically is reported to be in the range of tens of nanometers and can be compositionally heterogeneous. Normal vibrational spectroscopy techniques such as micro-Raman and FT-IR while pretty useful, provide chemical information at a relatively bulk scale, typically much > 100 nm from the sample surface.This makes it harder for getting information from the real SEI, which can be only order of tens of nanometer. Tip Enhanced Raman Spectroscopy (TERS) is based on the field enhancement of Raman active signal locally at regions close to the tip. The Raman cross section is enhanced at least several orders of magnitude due to resonance coupling between surface plasmon modes (of the tip) and the electromagnetic field of the excitation laser. TERS enables simultaneous chemical mapping and topography at a nanoscale spatial resolution. TERS mapping of cycled amorphous silicon show the SEI composition and morphology changing as a function of electrochemical cycles. These observations will be compared with results from other techniques such as X-ray photoelectron spectroscopy

Glycan distribution and density in native skin's stratum corneum.

BackgroundThe glycosylation of proteins on the surface of corneocytes is believed to play an important role in cellular adhesion in the stratum corneum (SC) of human skin. Mapping with accuracy the localization of glycans on the surface of corneocytes through traditional methods of immunohistochemistry and electron microscopy remains a challenging task as both approaches lack enough resolution or need to be performed in high vacuum conditions.Materials and methodsWe used an advanced mode of atomic force microscope (AFM), with simultaneous topography and recognition imaging to investigate the distribution of glycans on native (no chemical preparation) stripped samples of human SC. The AFM cantilever tips were functionalized with anti‐heparan sulfate antibody and the lectin wheat germ agglutinin (WGA) which binds specifically to N‐acetyl glucosamine and sialic acid.ResultsFrom the recognition imaging, we observed the presence of the sulfated glycosaminoglycan, heparan sulfate, and the glycans recognized by WGA on the surface of SC corneocytes in their native state. These glycans were found associated with bead‐like domains which represent corneodesmosomes in the SC layers. Glycan density was calculated to be ~1200 molecules/μm2 in lower layers of SC compared to an important decrease, (~106 molecules/μm2) closer to the surface due probably to corneodesmosome degradation.ConclusionGlycan spatial distribution and degradation is first observed on the surface of SC in native conditions and at high resolution. The method used can be extended to precisely localize the presence of other macromolecules on the surface of skin or other tissues where the maintenance of its native state is required.

Two Years Follow up Evaluating Progression of Ectasia for Keratoconus Patients Treated with Simultaneous Topography - Guided PRK Plus Cross Linking

This retrospective study was designed to evaluate the efficacy and safety of simultaneous topography-guided PRK plus cross linking for patients with mild to moderate keratoconus and to evaluate the stability of the cone. The patients were evaluated over two years for the progression and stability of the cone by the Allegro Pentacam Oculyzer to assess the changes of corneal curvatures (K readings) and the stability of the cone after the surgery and evaluating uncorrected distance (UDVA) and best corrected (CDVA) visual acuities. The follow-up results showed that UDVA improved from 0.4±0.3 to 0.7±0.1 and CDVA changed from 0.6±0.1 to 0.8±0.1 (P < 0.001). The keratometry value decreased from 44.1±2.2 to 41.4±1.6 D for K1, and from 46.4±2.6 to 43.5±1.7 for K2 (P < 0.001). This combined procedure offers a promising method to stabilize the corneal surface with reducing higher order aberrations so enhancing quality of vision in keratoconus patients.

Quantitative Visualization of Nanoscale Ion Transport.

Understanding ion transport properties at various interfaces, especially at small length scales, is critical in advancing our knowledge of membrane materials and cell biology. Recently, we described potentiometric-scanning ion conductance microscopy (P-SICM) for ion-conductance measurement in polymer membranes and epithelial cell monolayers at discrete points in a sample. Here, we combine hopping mode techniques with P-SICM to allow simultaneous nanometer-scale conductance and topography mapping. First validated with standard synthetic membranes and then demonstrated in living epithelial cell monolayers under physiological conditions, this new method allows direct visualization of heterogeneous ion transport of biological samples for the first time. These advances provide a noncontact local probe, require no labeling, and present a new tool for quantifying intrinsic transport properties of a variety of biological samples.

Simultaneous topography imaging and broadband nanomechanical mapping on atomic force microscope

In this paper, an approach is proposed to achieve simultaneous imaging and broadband nanomechanical mapping of soft materials in air by using an atomic force microscope. Simultaneous imaging and nanomechanical mapping are needed, for example, to correlate the morphological and mechanical evolutions of the sample during dynamic phenomena such as the cell endocytosis process. Current techniques for nanomechanical mapping, however, are only capable of capturing static elasticity of the material, or the material viscoelasticity in a narrow frequency band around the resonant frequency(ies) of the cantilever used, not competent for broadband nanomechanical mapping, nor acquiring topography image of the sample simultaneously. These limitations are addressed in this work by enabling the augmentation of an excitation force stimuli of rich frequency spectrum for nanomechanical mapping in the imaging process. Kalman-filtering technique is exploited to decouple and split the mixed signals for imaging and mapping, respectively. Then the sample indentation generated is quantified online via a system-inversion method, and the effects of the indentation generated and the topography tracking error on the topography quantification are taken into account. Moreover, a data-driven feedforward-feedback control is utilized to track the sample topography. The proposed approach is illustrated through experimental implementation on a polydimethylsiloxane sample with a pre-fabricated pattern.

Simultaneous Topography and Reaction Flux Mapping at and around Electrocatalytic Nanoparticles

The characterization of electrocatalytic reactions at individual nanoparticles (NPs) is presently of considerable interest but very challenging. Herein, we demonstrate how simple-to-fabricate nanopipette probes with diameters of approximately 30 nm can be deployed in a scanning ion conductance microscopy (SICM) platform to simultaneously visualize electrochemical reactivity and topography with high spatial resolution at electrochemical interfaces. By employing a self-referencing hopping mode protocol, whereby the probe is brought from bulk solution to the near-surface at each pixel, and with potential-time control applied at the substrate, current measurements at the nanopipette can be made with high precision and resolution (30 nm resolution, 2600 pixels μm-2, <0.3 s pixel-1) to reveal a wealth of information on the substrate physicochemical properties. This methodology has been applied to image the electrocatalytic oxidation of borohydride at ensembles of AuNPs on a carbon fiber support in alkaline media, whereby the depletion of hydroxide ions and release of water during the reaction results in a detectable change in the ionic composition around the NPs. Through the use of finite element method simulations, these observations are validated and analyzed to reveal important information on heterogeneities in ion flux between the top of a NP and the gap at the NP-support contact, diffusional overlap and competition for reactant between neighboring NPs, and differences in NP activity. These studies highlight key issues that influence the behavior of NP assemblies at the single NP level and provide a platform for the use of SICM as an important tool for electrocatalysis studies.

Characterization of the specific interaction between the DNA aptamer sgc8c and protein tyrosine kinase-7 receptors at the surface of T-cells by biosensing AFM

We studied the interaction of the specific DNA aptamer sgc8c immobilized at the AFM tip with its corresponding receptor, the protein tyrosine kinase-7 (PTK7) embedded in the membrane of acute lymphoblastic leukemia (ALL) cells (Jurkat T-cells). Performing single molecule force spectroscopy (SMFS) experiments, we showed that the aptamer sgc8c bound with high probability (38.3 ± 7.48%) and high specificity to PTK7, as demonstrated by receptor blocking experiments and through comparison with the binding behavior of a nonspecific aptamer. The determined kinetic off-rate (koff = 5.16 s−1) indicates low dissociation of the sgc8c–PTK7 complex. In addition to the pulling force experiments, simultaneous topography and recognition imaging (TREC) experiments using AFM tips functionalized with sgc8c aptamers were realized on the outer regions surface of surface-immobilized Jurkat cells for the first time. This allowed determination of the distribution of PTK7 without any labeling and at near physiological conditions. As a result, we could show a homogeneous distribution of PTK7 molecules on the outer regions of ALL cells with a surface density of 325 ± 12 PTK7 receptors (or small receptor clusters) per μm2.Graphical The specific interaction of the DNA aptamer sgc8c and protein tyrosine kinase-7 (PTK7) on acute lymphoblastic leukemia (ALL) cells was characterized. AFM based single molecule force spectroscopy (SMFS) yielded a kinetic off-rate of 5.16 s−1 of the complex. Simultaneous topography and recognition imaging (TREC) revealed a PTK7 density of 325 ± 12 molecules or clusters per μm2 in the cell membrane

Recent Progress in Molecular Recognition Imaging Using Atomic Force Microscopy.

Atomic force microscopy (AFM) is an extremely powerful tool in the field of bionanotechnology because of its ability to image single molecules and make measurements of molecular interaction forces with piconewton sensitivity. It works in aqueous media, enabling studies of molecular phenomenon taking place under physiological conditions. Samples can be imaged in their near-native state without any further modifications such as staining or tagging. The combination of AFM imaging with the force measurement added a new feature to the AFM technique, that is, molecular recognition imaging. Molecular recognition imaging enables mapping of specific interactions between two molecules (one attached to the AFM tip and the other to the imaging substrate) by generating simultaneous topography and recognition images (TREC). Since its discovery, the recognition imaging technique has been successfully applied to different systems such as antibody-protein, aptamer-protein, peptide-protein, chromatin, antigen-antibody, cells, and so forth. Because the technique is based on specific binding between the ligand and receptor, it has the ability to detect a particular protein in a mixture of proteins or monitor a biological phenomenon in the native physiological state. One key step for recognition imaging technique is the functionalization of the AFM tips (generally, silicon, silicon nitrides, gold, etc.). Several different functionalization methods have been reported in the literature depending on the molecules of interest and the material of the tip. Polyethylene glycol is routinely used to provide flexibility needed for proper binding as a part of the linker that carries the affinity molecule. Recently, a heterofunctional triarm linker has been synthesized and successfully attached with two different affinity molecules. This novel linker, when attached to AFM tip, helped to detect two different proteins simultaneously from a mixture of proteins using a so-called "two-color" recognition image. Biological phenomena in nature often involve multimolecular interactions, and this new linker could be ideal for studying them using AFM recognition imaging. It also has the potential to be used extensively in the diagnostics technique. This Account includes fundamentals behind AFM recognition imaging, a brief discussion on tip functionalization, recent advancements, and future directions and possibilities.

Utilizing intentional internal resonance to achieve multi-harmonic atomic force microscopy

During dynamic atomic force microscopy (AFM), the deflection of a scanning cantilever generates multiple frequency terms due to the nonlinear nature of AFM tip–sample interactions. Even though each frequency term is reasonably expected to encode information about the sample, only the fundamental frequency term is typically decoded to provide topographic mapping of the measured surface. One of main reasons for discarding higher harmonic signals is their low signal-to-noise ratio. Here, we introduce a new design concept for multi-harmonic AFM, exploiting intentional nonlinear internal resonance for the enhancement of higher harmonics. The nonlinear internal resonance, triggered by the non-smooth tip–sample dynamic interactions, results in nonlinear energy transfers from the directly excited fundamental bending mode to the higher-frequency mode and, hence, enhancement of the higher harmonic of the measured response. It is verified through detailed theoretical and experimental study that this AFM design can robustly incorporate the required internal resonance and enable high-frequency AFM measurements. Measurements on an inhomogeneous polymer specimen demonstrate the efficacy of the proposed design, namely that the higher harmonic of the measured response is capable of enhanced simultaneous topography imaging and compositional mapping, exhibiting less crosstalk with an abrupt height change.

Simultaneous Interfacial Reactivity and Topography Mapping with Scanning Ion Conductance Microscopy.

Scanning ion conductance microscopy (SICM) is a powerful technique for imaging the topography of a wide range of materials and interfaces. In this report, we develop the use and scope of SICM, showing how it can be used for mapping spatial distributions of ionic fluxes due to (electro)chemical reactions occurring at interfaces. The basic idea is that there is a change of ion conductance inside a nanopipet probe when it approaches an active site, where the ionic composition is different to that in bulk solution, and this can be sensed via the current flow in the nanopipet with an applied bias. Careful tuning of the tip potential allows the current response to be sensitive to either topography or activity, if desired. Furthermore, the use of a distance modulation SICM scheme allows reasonably faithful probe positioning using the resulting ac response, irrespective of whether there is a reaction at the interface that changes the local ionic composition. Both strategies (distance modulation or tuned bias) allow simultaneous topography-activity mapping with a single channel probe. The application of SICM reaction imaging is demonstrated on several examples, including voltammetric mapping of electrocatalytic reactions on electrodes and high-speed electrochemical imaging at rates approaching 4 s per image frame. These two distinct approaches provide movies of electrochemical current as a function of potential with hundreds of frames (images) of surface reactivity, to reveal a wealth of spatially resolved information on potential- (and time) dependent electrochemical phenomena. The experimental studies are supported by detailed finite element method modeling that places the technique on a quantitative footing.