Probe Tip Research Articles

Investigations of Surface-Treated Wood by a Micro-Indentation Approach: A Short Review and a Case Study

Over the past 50 years, instrumented indentation, in which an indenter tip probes the specimen surface with a regulated force and displacement to characterize its mechanical properties, has evolved. With the development of atomic force microscopy, instrumented nanoindentation has been extensively applied, and instrumented indentation in the micro range (micro-indentation) has been somewhat overshadowed by nanoindentation. However, micro-indentation remains an extremely useful technique that has the potential to investigate various properties of surface treated wood. In the first, overview-type part of the paper, instrumented micro-indentation is described and some examples of its possible applications in the field of wood science and technology are presented. To illustrate the importance of this experimental technique, some results of micro-indentation experiments carried out in our wood surface treatment laboratory are shown in the second part of the paper. The objects of the tests were untreated Scots pine wood and Scots pine wood with surface deposits of SiO2 or ZnO. The differences between the mechanical properties of early and latewood could be clearly distinguished by the micro indentation technique. On the other hand, the influence of ZnO and SiO2 particles on mechanical properties as a function of indentation depth could not be detected by this technique.

Control of optical heating of a silicon probe using near-field energy transport by localized surface plasmons

Optical heating in solids is fundamentally related to energy dissipation during absorption. Nevertheless, light absorption can be enhanced by excitation of optical resonances (plasmon, Mi, Fano, etc.). In this paper, we investigate the amplification of light absorption in nanostructured silicon by excitation of an optical near field in the gap between the tip of a silicon probe and a gold film.

SFM Fetal Therapy Practice Guidelines: Radiofrequency Ablation of Fetal Umbilical Cord

AbstractIn radiofrequency ablation (RFA), the ions in the tissue surrounding the probe's uninsulated tip are noticeably stirred up by the electrode's high-frequency alternating current. The surrounding tissue experiences thermal coagulation necrosis as a result of the frictional heat.RFA is used in complicated monochorionic twin pregnancies with selective fetal growth restriction (FGR), TRAP, and TTTS. RFA may also be considered in giant chorioangioma with favorable vascular anatomy and giant sacrococcygeal teratoma with imminent hydrops. It serves as a substitute to laser.

Predicting the placement of biomolecular structures on AFM substrates based on electrostatic interactions

Atomic force microscopy (AFM) and high-speed AFM allow direct observation of biomolecular structures and their functional dynamics. Based on scanning the molecular surface of a sample deposited on a supporting substrate by a probing tip, topographic images of its dynamic shape are obtained. Critical to successful AFM observations is a balance between immobilization of the sample while avoiding too strong perturbations of its functional conformational dynamics. Since the sample placement on the supporting substrate cannot be directly controlled in experiments, the relative orientation is a priori unknown, and, due to limitations in the spatial resolution of images, difficult to infer from a posteriori analysis, thus hampering the interpretation of measurements. We present a method to predict the macromolecular placement of samples based on electrostatic interactions with the AFM substrate and demonstrate applications to HS-AFM observations of the Cas9 endonuclease, an aptamer-protein complex, the Monalysin protein, and the ClpB molecular chaperone. The model also allows predictions of imaging stability taking into account buffer conditions. We implemented the developed method within the freely available BioAFMviewer software package. Predictions based on available structural data can therefore be made even prior to an actual experiment, and the method can be applied for post-experimental analysis of AFM imaging data.

Hold-up formation in bubble channel reactors: A bubble-scale investigation

Experiments were carried out to measure the air volume fraction and the hold-up in a bubble channel reactor fed by porous pipes.A new processing method was proposed for the signal acquired by means of a resistivity probe for the air volume fraction. This method avoids the loss of the bubble residence time on the probe tip, which affects the most used signal processing procedures. The probe measurements were compared with other studies regarding bubble curtains.The measured air hold-up was in agreement with correlations available in the literature and formulated for bubble columns fed by a porous sparger. A bubble-scale model was proposed to explain the functional form of the dependence of the hold-up on the air superficial velocity. Moreover, a link between the hold-up and the Koide equation for bubble dimensions was established.The experiments were reproduced by means of CFD simulations. The air volume fraction measurement method and the hold-up model found a confirmation in the numerical results. Moreover, the latter showed how the bubble plumes interact inside the reactor and the consequences on the air hold-up.

Preparation of atom probe tips from (nano)particles in dispersion using (di)electrophoresis and electroplating.

The behavior of catalytic particles depends on their chemical structure and morphology. To reveal this information, the characterization with atom probe tomography has huge potential. Despite progresses and papers proposing various approaches towards the incorporation of particles inside atom probe tips, no single approach has been broadly applicable to date. In this paper, we introduce a workflow that allowed us to prepare atom probe specimens from Ga particles in suspension in the size range of 50 nm up to 2 μm. By combining dielectrophoresis and electrodeposition in a suitable way, we achieve a near-tip shape geometry, without a time-consuming FIB lift-out. This workflow is a simple and quick method to prepare atom probe tips and allows for a high preparation throughput. Also, not using a lift-out allowed us to use a cryo-stage, avoiding melting of the Ga particles, while ensuring a mechanical stable atom probe tip. The specimen prepared by this workflow enable a stable measurement and low fracture rates. RESEARCH HIGHLIGHTS: Enabling cryo-preparation of (nano)particles for the atom probe. Characterization of surface and bulk elemental distribution of GaPt model SCALMS.

Interferometric metrology probe for highly sloped freeform optics.

A wide variety of systems are employed to measure the surface profile of aspheric and freeform optical surfaces. Freeform metrology systems must accurately characterize the full surface under test, which can be difficult with steep surface slopes. Here we present an interferometric surface metrology probe for highly sloped aspheric and freeform optical surfaces. The optical design of this probe allows the measurement of surface slopes up to 50deg without tilting the probe, which simplifies stage design and increases the accuracy of the system. A spectrally controlled light source is used to create a virtual ball in front of the probe tip to measure the surface distance and angle. This system produces a cloud of points, to which Zernike polynomials are fit and used to reconstruct the surface. We will show sensitivity tests and accuracy results.

Interaction of βL- and γ-Crystallin with Phospholipid Membrane Using Atomic Force Microscopy.

Highly concentrated lens proteins, mostly β- and γ-crystallin, are responsible for maintaining the structure and refractivity of the eye lens. However, with aging and cataract formation, β- and γ-crystallin are associated with the lens membrane or other lens proteins forming high-molecular-weight proteins, which further associate with the lens membrane, leading to light scattering and cataract development. The mechanism by which β- and γ-crystallin are associated with the lens membrane is unknown. This work aims to study the interaction of β- and γ-crystallin with the phospholipid membrane with and without cholesterol (Chol) with the overall goal of understanding the role of phospholipid and Chol in β- and γ-crystallin association with the membrane. Small unilamellar vesicles made of Chol/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (Chol/POPC) membranes with varying Chol content were prepared using the rapid solvent exchange method followed by probe tip sonication and then dispensed on freshly cleaved mica disk to prepare a supported lipid membrane. The βL- and γ-crystallin from the cortex of the bovine lens was used to investigate the time-dependent association of βL- and γ-crystallin with the membrane by obtaining the topographical images using atomic force microscopy. Our study showed that βL-crystallin formed semi-transmembrane defects, whereas γ-crystallin formed transmembrane defects on the phospholipid membrane. The size of semi-transmembrane defects increases significantly with incubation time when βL-crystallin interacts with the membrane. In contrast, no significant increase in transmembrane defect size was observed in the case of γ-crystallin. Our result shows that Chol inhibits the formation of membrane defects when βL- and γ-crystallin interact with the Chol/POPC membrane, where the degree of inhibition depends upon the amount of Chol content in the membrane. At a Chol/POPC mixing ratio of 0.3, membrane defects were observed when both βL- and γ-crystallin interacted with the membrane. However, at a Chol/POPC mixing ratio of 1, no association of γ-crystallin with the membrane was observed, which resulted in a defect-free membrane, and the severity of the membrane defect was decreased when βL-crystallin interacted with the membrane. The semi-transmembrane or transmembrane defects formed by the interaction of βL- and γ-crystallin on phospholipid membrane might be responsible for light scattering and cataract formation. However, Chol suppressed the formation of such defects in the membrane, likely maintaining lens membrane homeostasis and protecting against cataract formation.

First-order quantum phase transition in the hybrid metal-Mott insulator transition metal dichalcogenide 4Hb-TaS2.

Coupling together distinct correlated and topologically nontrivial electronic phases of matter can potentially induce novel electronic orders and phase transitions among them. Transition metal dichalcogenide compounds serve as a bedrock for exploration of such hybrid systems. They host a variety of exotic electronic phases, and their Van der Waals nature enables to admix them, either by exfoliation and stacking or by stoichiometric growth, and thereby induce novel correlated complexes. Here, we investigate the compound 4Hb-TaS2 that interleaves the Mott-insulating state of 1T-TaS2 and the putative spin liquid it hosts together with the metallic state of 2H-TaS2 and the low-temperature superconducting phase it harbors using scanning tunneling spectroscopy. We reveal a thermodynamic phase diagram that hosts a first-order quantum phase transition between a correlated Kondo-like cluster state and a depleted flat band state. We demonstrate that this intrinsic transition can be induced by an electric field and temperature as well as by manipulation of the interlayer coupling with the probe tip, hence allowing to reversibly toggle between the Kondo-like cluster and the depleted flat band states. The phase transition is manifested by a discontinuous change of the complete electronic spectrum accompanied by hysteresis and low-frequency noise. We find that the shape of the transition line in the phase diagram is determined by the local compressibility and the entropy of the two electronic states. Our findings set such heterogeneous structures as an exciting platform for systematic investigation and manipulation of Mott-metal transitions and strongly correlated phases and quantum phase transitions therein.

Mid-infrared photocurrent nano-spectroscopy exploiting the thermoelectric effect in graphene

We develop a conductive-atomic force microscope coupled to a mid-infrared (IR) quantum cascade laser that allows to measure mid-IR photocurrent maps and spectra with nanometric spatial resolution. Here, we exploit the photo-induced thermoelectric effect of graphene to obtain the mid-IR local absorption spectra of nanoscale devices and materials. By scanning the probe in AFM-contact mode, the thermoelectric photocurrent can be mapped throughout the graphene layer, which acts as a semitransparent transducer. At zero voltage bias applied to the probe tip, we observe very low noise (about 25 pA/Hz), which makes our technique competitive with others in measuring the local IR absorption in nanomaterials with insufficient thermal expansion coefficient, or to characterize nanoscale devices that significantly absorb IR radiation, such as mid-infrared photodetectors.

A self-balanced electron-emissive double Langmuir probe drawing no electron loss from its diagnosed plasma

In this work, a new form of double Langmuir probe (DLP) system, an emissive double Langmuir probe (EDLP), which connects a collecting probe tip and an electron-emitting probe tip to form a DLP system, has been proposed as a replacement of the currently more common asymmetric double Langmuir probes (ADLPs). The EDLP was both computationally and experimentally investigated in this work. Using an emissive probe to provide an emission current I E to balance the electron collection current I C,e, the EDLP can obtain a full I–V trace when I E,TL > I C,es and be used in a similar manner to a single Langmuir probe with the exception that the EDLP, as with the ADLP, does not measure the local plasma potential. I E,TL ≫ I C,es can be realized on an EDLP without needing the much larger ion collection area required by the ADLP, and at I E,TL ∼ 2I C,es the relative error between the EDLP and a single Langmuir probe is ∼15% due to space-charge limited effects, which is better than that of the ADLP at ∼30% under similar conditions. The performance of an EDLP depends on whether its electron emission current sufficiently offsets its electron-collecting current, making it particularly fitting for scenarios where the plasma density is low but a large probe is difficult to employ due to the limited balancing ion current. This makes the EDLP potentially useful on satellites, which operate in very low temperature plasmas with a limited ion loss area to balance a Langmuir probe’s electron-collecting current. With the advances in highly emitting materials, EDLPs are expected to significantly remove the design barriers of Langmuir probes on satellites.

Azimuthal and axial dispersion relations of low-frequency oscillations in partially magnetized plasma with crossed electric and magnetic fields

This paper presents the results of the azimuthal and axial wave diagnostics of a partially magnetized E × B Penning source. Various probes were employed, namely, a two-tip probe for azimuthal waves and two- and four-probe arrays for axial waves, to investigate the spatial characteristics of the instability using a two-point probe technique. The azimuthally aligned tips of the two-tip probe facilitated the investigation of the evolution of the azimuthal dispersion relation, which exhibited a well-known azimuthally propagative spoke at low discharge voltages. By utilizing axially aligned four-probe arrays with a probe distance of 3 mm and two-probe arrays with a relatively long probe distance of 20 mm, we sought to determine whether the rotating spoke propagated in the axial direction in the cylindrical E × B source. Our findings suggest that the rotating spoke originated near the axial center and propagated toward each cathode, rotating in a direction tilted from the azimuthal direction.

A Novel Doppler Flowmetry Shaft for Postoperative Monitoring after Head and Neck Reconstructive Surgery.

Doppler flowmetry is one of the most popular methods of monitoring Doppler signals during reconstructive surgery of the body surface. However, because of the thick and straight structure of the shaft, it is difficult to perform in areas with limited space, such as the oral cavity. We used a new type of Doppler flowmetry shaft to postoperatively monitor the flap in the oral cavity. Compared with conventional Doppler flowmetry, the new type uses a thinner metal probe shaft that can easily be inserted in narrow and limited spaces, such as the oral cavity. Additionally, the tip of the metal probe is gently bent, thereby allowing the Doppler tip to be placed perpendicular to the surface of the skin flap. We used this new type of Doppler flowmetry shaft for 30 patients after head and neck reconstruction using free flap transfer because Doppler signals were difficult to hear using conventional Doppler flowmetry. For all 30 patients, the new Doppler flowmetry shaft was able to monitor free flaps. Vascular thrombosis or vascular spasm occurred in three patients; two patients had inadequate arterial flow caused by vasospasm and arterial thrombus, and one patient had a venous thrombus. These three patients required re-exploration, and all flaps survived. This new type of Doppler flowmetry is simple and noninvasive. Furthermore, it can easily be performed by nonphysician medical personnel, and is useful for monitoring patients after head and neck reconstructive surgery.

Closed-Loop Magnetic Manipulation for Robotic Transesophageal Echocardiography

This article presents a closed-loop magnetic manipulation framework for robotic transesophageal echocardiography (TEE) acquisitions. Different from previous work on intracorporeal robotic ultrasound acquisitions that focus on continuum robot control, we first investigate the use of magnetic control methods for more direct, intuitive, and accurate manipulation of the distal tip of the probe. We modify a standard TEE probe by attaching a permanent magnet and an inertial measurement unit (IMU) sensor to the probe tip and replacing the flexible gastroscope with a soft tether containing only wires for transmitting ultrasound and IMU data and show that six-degree-of-freedom (DOF) localization and five-DOF closed-loop control of the probe can be achieved with an external permanent magnet based on the fusion of internal inertial measurement and external magnetic field sensing data. The proposed method does not require complex structures or motions of the actuator and the probe compared with existing magnetic manipulation methods. We have conducted extensive experiments to validate the effectiveness of the framework in terms of localization accuracy, update rate, workspace size, and tracking accuracy. In addition, our results obtained on a realistic cardiac tissue-mimicking phantom show that the proposed framework is applicable in real conditions and can generally meet the requirements for teleoperated TEE acquisitions.

DEM modelling of root circumnutation-inspired penetration in shallow granular materials

Plant root growth is often accompanied by circumnutative motion consisting of downward helical movement of the root tip. Previous studies indicate that circumnutations allow roots to avoid obstacles that would impede root growth, while other studies show that circumnutations can reduce the penetration resistance mobilised during root growth. Discrete-element modelling (DEM) simulations were performed on probes that employ circumnutation-inspired motion (CIM) to penetrate granular assemblies at shallow depths to evaluate the reduction in penetration resistance. These simulations investigate the effect of the ratio of tangential to vertical velocity of the circumnutative motion (i.e. relative velocity) and of the probe geometry (i.e. tip tilt angle and length). The results indicate that CIM penetration reduces the penetration force and work relative to non-rotational penetration (NRP) by changing the soil fabric and diffusing the force chains around the probe tip. However, the circumnutative motion leads to an increase in torque and associated rotational work. An optimal relative velocity and probe geometry exist for the simulated CIM probes, resulting in a smaller total work than that required for NRP. CIM penetration also mobilises smaller penetration forces and work than rotational penetration (i.e. with a straight tip), particularly at smaller relative velocities. The reduction in penetration forces induced by CIM could facilitate site investigation and monitoring activities.

Mechanical Exfoliation of Expanded Graphite to Graphene-Based Materials and Modification with Palladium Nanoparticles for Hydrogen Storage.

Hydrogen is a promising green fuel carrier that can replace fossil fuels; however, its storage is still a challenge. Carbon-based materials with metal catalysts have recently been the focus of research for solid-state hydrogen storage due to their efficacy and low cost. Here, we report on the exfoliation of expanded graphite (EG) through high shear mixing and probe tip sonication methods to form graphene-based nanomaterial ShEG and sEG, respectively. The exfoliation processes were optimized based on electrochemical capacitance measurements. The exfoliated EG was further functionalized with palladium nanoparticles (Pd-NP) for solid-state hydrogen storage. The prepared graphene-based nanomaterials (ShEG and sEG) and the nanocomposites (Pd-ShEG and Pd-sEG) were characterized with various traditional techniques (e.g., SEM, TEM, EDX, XPS, Raman, XRD) and the advanced high-resolution pair distribution function (HRPDF) analysis. Electrochemical hydrogen uptake and release (QH) were measured, showing that the sEG decorated with Pd-NP (Pd-sEG, 31.05 mC cm-2) and ShEG with Pd-NP (Pd-ShEG, 24.54 mC cm-2) had a notable improvement over Pd-NP (9.87 mC cm-2) and the composite of Pd-EG (14.7 mC cm-2). QH showed a strong linear relationship with an effective surface area to volume ratio, indicating nanoparticle size as a determining factor for hydrogen uptake and release. This work is a promising step toward the design of the high-performance solid-state hydrogen storage devices through mechanical exfoliation of the substrate EG to control nanoparticle size and dispersion.

Direct etching of nano/microscale patterns with both few-layer graphene and high-depth graphite structures by the raster STM electric lithography in the ambient conditions.

The development of raster STM electric lithography has enabled the etching of nano/microscale patterns on both few-layer graphene (FLG) and high-depth graphite structures on the bulk HOPG substrates under ambient conditions. This approach utilises a nanoscale probe tip as a machining tool to directly fabricate conductive sample surfaces without the need for resists or masks. Compared to conventional nano/micro machining methods, the capability of ultraaccurate fabrication of nanoscale patterns using this technique is unmatched. The resulting FLG structures exhibit ultrasmooth flat bottoms and uniformly controlled depths ranging from 0.34 to 3.0nm (less than 10 layers). This work represents a significant advancement as it demonstrates the perfect etching of FLG structures in designated nano/microscale regions using raster STM electric lithography in the constant current mode, which reaches the limitation of top-down manufacturing techniques. Additionally, raster STM electric lithography in the constant height mode can directly etch high-depth structures (up to ∼100nm). The geometric shape and number of layers of the etched graphene structures determined by either local anodic oxidation (LAO) or the electric discharge (ED) mechanism. The LAO mechanism results in less debris and smoother edges compared to the ED mechanism, which is caused by the random electrical discharge between the tip and the sample. The well-controlled raster STM electric lithography technique is believed to be a promising and facile approach for constructing nano/microscale graphene-based devices.

GPL-Reinforced composite piezoelectric microcantilever dynamics in atomic force microscope

Currently, Atomic Force Microscope (AFM) is utilized as an efficient tool for nanoscale measurements and nanomanipulation of particles. The central part of AFM is considered to be the microcantilever (MC) used in the device. AFM MC is generally made from silicon. Since functionally graded graphene-nanoplatelet-reinforced composite (GPLRC) materials are highly popular in industry and academic research, the present study aims to be the first attempt to investigate the possibility of utilizing these materials in AFM MC. Also, it seeks to compare the nonlinear vibrational behavior of the MC made from this type of material with that of the silicon MC and also to investigate the vibrational behavior of the GPLRC MC in interaction with the sample surface. To do so, the GPLRC MC vibrated with the piezoelectric layer on its top is utilized. In order to increase the sensitivity of the MC to the interaction force between the surface and the probe tip, the tip of the MC is considered narrower. The differential equation of the vibrational motion of the MC near the surface of the sample is derived by considering the Lennord-Jones model according to the Euler-Bernoulli theory and applying the Lagrange method. In order to solve the nonlinear differential equation of motion with partial derivatives in terms of the time and the position of each point on the MC, Galerkin variable-separation method and multiple time scale (MTS) method are applied. The results of the dynamic modeling near the surface of the sample indicate that the MC made of GPLRC is more sensitive to the nonlinearity of the interaction force as compared to the common silicon MC.

Growth of Ferroelectric Domains in Polar Direction

The forward domain growth in polar direction has been investigated on the example of the formation of isolated wedge-shaped domains and arrays of domains on lithium niobate nonpolar cuts under an electric field of a scanning probe microscope. Domain growth occurs due to the generation of steps and motion of charged kinks along charged domain walls (CDWs). A simulation of field spatial distribution showed that the generation of steps near a domain vertex is mainly caused by the effect of external field, whereas the forward growth is due to the kink motion in the field induced by neighboring kinks. Scanning by a probe tip with an applied voltage leads to the self-assembled formation of domain arrays with domain length alternation: doubling, quadrupling, and chaotic behavior under the action of the depolarizing fields formed by three neighboring domains.

A Novel Displacement Sensor Based on a Frequency Delta-Sigma Modulator and its Application to a Stylus Surface Profiler

A novel displacement sensor was proposed based on a frequency delta-sigma modulator (FDSM) employing a microwave oscillator. To demonstrate basic operation, we fabricated a stylus surface profiler using a cylindrical cavity resonator, where one end of the cavity is replaced by a thin metal diaphragm with a stylus probe tip. Good surface profile was successfully obtained with this device. A 10 nm depth trench was clearly observed together with a 10 μm trench in a single scan without gain control. This result clearly demonstrates an extremely wide dynamic range of the FDSM displacement sensors.