Metal Tip Research Articles

Molecular Identification from AFM Images Using the IUPAC Nomenclature and Attribute Multimodal Recurrent Neural Networks.

Spectroscopic methods─like nuclear magnetic resonance, mass spectrometry, X-ray diffraction, and UV/visible spectroscopies─applied to molecular ensembles have so far been the workhorse for molecular identification. Here, we propose a radically different chemical characterization approach, based on the ability of noncontact atomic force microscopy with metal tips functionalized with a CO molecule at the tip apex (referred as HR-AFM) to resolve the internal structure of individual molecules. Our work demonstrates that a stack of constant-height HR-AFM images carries enough chemical information for a complete identification (structure and composition) of quasiplanar organic molecules, and that this information can be retrieved using machine learning techniques that are able to disentangle the contribution of chemical composition, bond topology, and internal torsion of the molecule to the HR-AFM contrast. In particular, we exploit multimodal recurrent neural networks (M-RNN) that combine convolutional neural networks for image analysis and recurrent neural networks to deal with language processing, to formulate the molecular identification as an imaging captioning problem. The algorithm is trained using a data set─which contains almost 700,000 molecules and 165 million theoretical AFM images─to produce as final output the IUPAC name of the imaged molecule. Our extensive test with theoretical images and a few experimental ones shows the potential of deep learning algorithms in the automatic identification of molecular compounds by AFM. This achievement supports the development of on-surface synthesis and overcomes some limitations of spectroscopic methods in traditional solution-based synthesis.

Tracing attosecond electron emission from a nanometric metal tip.

Solids exposed to intense electric fields release electrons through tunnelling. This fundamental quantum process lies at the heart of various applications, ranging from high brightness electron sources in d.c. operation1,2 to petahertz vacuum electronics in laser-driven operation3-8. In the latter process, the electron wavepacket undergoes semiclassical dynamics9,10 in the strong oscillating laser field, similar to strong-field and attosecond physics in the gas phase11,12. There, the subcycle electron dynamics has been determined with a stunning precision of tens of attoseconds13-15, but at solids the quantum dynamics including the emission time window has so far not been measured. Here we show that two-colour modulation spectroscopy of backscattering electrons16 uncovers the suboptical-cycle strong-field emission dynamics from nanostructures, with attosecond precision. In our experiment, photoelectron spectra of electrons emitted from a sharp metallic tip are measured as function of the relative phase between the two colours. Projecting the solution of the time-dependent Schrödinger equation onto classical trajectories relates phase-dependent signatures in the spectra to the emission dynamics and yields an emission duration of 710 ± 30 attoseconds by matching the quantum model to the experiment. Our results open the door to the quantitative timing and precise active control of strong-field photoemission from solid state and other systems and have direct ramifications for diverse fields such as ultrafast electron sources17, quantum degeneracy studies and sub-Poissonian electron beams18-21, nanoplasmonics22 and petahertz electronics23.

Lateral charge migration in 1D semiconductor-metal hybrid photocatalytic systems.

Colloidal nanorods based on CdS or CdSe, functionalized with metal particles, have proven to be efficient catalysts for light-driven hydrogen evolution. Seeded CdSe@CdS nanorods have shown increasing performance with increasing rod length. This observation was rationalized by the increasing lifetime of the separated charges, as a large distance between holes localized in the CdSe seed and electrons localized at the metal tip decreases their recombination rate. However, the impact of nanorod length on the electron-to-tip localization efficiency or pathway remained an open question. Therefore, we investigated the photo-induced electron transfer to the metal in a series of Ni-tipped CdSe@CdS nanorods with varying length. We find that the transfer processes occurring from the region close to the semiconductor-metal interface, the rod region, and the CdSe seed region depend in different ways on the rods' length. The rate of the fastest process from excitonic states generated directly at the interface is independent of the rod length, but the relative amplitude decreases with increasing rod length, as the weight of the interface region is decreasing. The transfer of electrons to the metal tip from excitons generated in the CdS rod region depends strongly on the length of the nanorods, which indicates an electron transport-limited process, i.e., electron diffusion toward the interface region, followed by fast interface crossing. The transfer originating from the CdSe excitonic states again shows no significant length dependence in its time constant, as it is probably limited by the rate of overcoming the shallow confinement in the CdSe seed.

Dynamic Observation of the Coulomb Explosion and Field Evaporation of a Few-Layer Graphene Nanoribbon.

The Coulomb explosion and field evaporation are frequently observed physical phenomena for a metallic tip under an external electric field, which can modify the structures of the tip and have broad applications, such as in the atomic-probe tomography and field ion microscopy. However, the mechanistic comprehending of how they change the structures of the tip and the differences between them are not clear. Here, dynamic observations of Coulomb explosions and field evaporations on the positively biased and charged few-layer graphene (FLG) nanoribbon inside a transmission electron microscope are reported. By combining the atomic-scale molecular dynamic simulations, it is shown that the FLG is split into several sheets under Coulomb explosion. It is also observed to break by emitting the carbon ions/segments under the field evaporation. It is further demonstrated that the split and breaking of FLG can be tuned by the shape of the nanoribbon. FLG ribbons with sharp tips have splitting and breaking occur in sequence. FLG with blunt tips break without a split. These results provide a fundamental understanding of Coulomb explosion and field evaporation in graphene nanomaterials and suggest potential methods to engineer graphene-based nanostructures.

Balloon-Uncrossable Lesions: Significant Higher Recanalization-Success with Metallic-Tip Catheters 5-year Follow-Up Data from XableCath-Study

Background: The metallic tip interventional recanalization catheter XableCath showed encouraging results (95.8percentage success rate) in crossing occluding atheroma in balloon uncrossable lesions after successful passage of a guide wire. Because successful crossing of balloon-uncrossable, mostly calcified atheromatous lesions may be associated with a higher complication rate, we investigated the long-term follow-up of all twenty-two patients (24 separate lesions), who have been included into the XableCath study. Patients and Methods: We investigated the long-term outcome (5-year follow-up) of 20 lesions in 18 patients, who had successfully been treated with the XableCath metallic tip interventional recanalization catheter (XableCath Inc., Salt Lake City, Utah) for balloon-uncrossable lesions (18 femoro-popliteal (90.0 percentage), 1 below-the-knee (5.0 %), 1 common iliac (5.0 percentage), 12 total occlusions (66.7 percentage). The primary study endpoint was the rate of target lesion patency resp. target lesion complications (e.a. perforation, aneurysms, dissections, or vessel closure) achieved by duplex-sonography. Secondary endpoints were the abscence of lesion associated major adverse events (MAE) as defined as limb amputations and/or cardiovascular death during the follow-up period of 5 years. Results: Follow-up informations after 5 years (incl. duplex-sonography) could have been achieved in 18 successfully treated patients (20 lesions). 3 patients (14.3percentage) died due to not-target lesion associated cardiovascular reasons. The primary endpoint (patency rate) was 85.0 percentage, target lesion associated complications (e.a. aneurysms, perforations or dissections) were not documented in any patient (0percentage), secondary endpoint (target lesion associated major adverse cardiovascular events) did not occur in any patient (0percentage). Conclusion: The metallic-tip interventional crossing catheter XableCath is a feasible, easy to use, time and money-saving option for successful angioplasty of balloon-uncrossable PAD-lesions without a higher rate of target lesion failure or target lesion-associated adverse events during a follow-up period of 5 years after successful recanalization of a balloon uncrossable lesion.

Additive Manufactured Piezoelectric-Driven Miniature Gripper

In several cases, it is desirable to have prototypes of low-cost fabrication and adequate performance. In academic laboratories and industries, miniature and microgrippers can be very useful for observations and the analysis of small objects. Piezoelectrically actuated microgrippers, commonly fabricated with aluminum, and with micrometer stroke or displacement, have been considered as Microelectromechanical Systems (MEMS). Recently, additive manufacture using several polymers has also been used for the fabrication of miniature grippers. This work focuses on the design of a piezoelectric-driven miniature gripper, additive manufactured with polylactic acid (PLA), which was modeled using a pseudo rigid body model (PRBM). It was also numerically and experimentally characterized with an acceptable level of approximation. The piezoelectric stack is composed of widely available buzzers. The aperture between the jaws allows it to hold objects with diameters lower than 500 μm, and weights lower than 1.4 g, such as the strands of some plants, salt grains, metal wires, etc. The novelty of this work is given by the miniature gripper’s simple design, as well as the low-cost of the materials and the fabrication process used. In addition, the initial aperture of the jaws can be adjusted, by adhering the metal tips in the required position.

Development of low-temperature and ultrahigh-vacuum photoinduced force microscopy.

In this paper, we develop optical and electronic systems for photoinduced force microscopy (PiFM) that can measure photoinduced forces under low temperature and ultrahigh vacuum (LT-UHV) without artifacts. For our LT-UHV PiFM, light is irradiated from the side on the tip-sample junction, which can be adjusted through the combination of an objective lens inside the vacuum chamber and a 90° mirror outside the vacuum chamber. We measured photoinduced forces due to the electric field enhancement between the tip and the Ag surface, and confirmed that photoinduced force mapping and measurement of photoinduced force curves were possible using the PiFM that we developed. The Ag surface was used to measure the photoinduced force with high sensitivity, and it is effective in enhancing the electric field using the plasmon gap mode between the metal tip and the metal surface. Additionally, we confirmed the necessity of Kelvin feedback during the measurement of photoinduced forces, to avoid artifacts due to electrostatic forces, by measuring photoinduced forces on organic thin films. The PiFM, operating under low temperature and ultrahigh vacuum developed here, is a promising tool to investigate the optical properties of various materials with very high spatial resolution.

Driving a Third Generation Molecular Motor with Electrons Across a Surface.

Excitation of single molecules with electrons tunneling between a sharp metallic tip of a scanning tunneling microscope and a metal surface is one way to study and control dynamics of molecules on surfaces. Electron tunneling induced dynamics may lead to hopping, rotation, molecular switching, or chemical reactions. Molecular motors that convert rotation of subgroups into lateral movement on a surface can in principle also be driven by tunneling electrons. For such surface-bound motor molecules the efficiency of motor action with respect to electron dose is still not known. Here, the response of a molecular motor containing two rotor units in the form of overcrowded alkene groups to inelastic electron tunneling has been examined on a Cu(111) surface in ultrahigh vacuum at 5 K. Upon vibrational excitation, switching between different molecular conformations is observed, including conversion of enantiomeric states of chiral conformations. Tunneling at energies in the range of electronic excitations causes activation of motor action and movement across the surface. The expected unidirectional rotation of the two rotor units causes forward movements but with a low degree of translational directionality.

Examination of a Method for Estimating Solid Fraction at Flow Cessation from Flow Velocity of Mushy Formation Molten Alloys

The purpose of this study was to experimentally estimate the solid fraction at which the cessation of the flow of a molten Al–7%Si–0.3%Mg alloy and Cu–8%Sn alloy occurs in casting. The flow cessation mechanism of two alloys is known as the “mushy” formation type, which means that the flow ceases when the solid fraction at the molten metal tip reaches a certain critical value. Therefore, the flow velocity at the molten metal tip is assumed to decrease gradually. Thus, a new method for calculating the solid fraction at flow cessation based on computer simulations was examined using experimental measurements of the flow velocity and flow length. The result of the experiment shows the experimental flow length is consistent with the simulation results, the calculated solid fraction at flow cessation. The flow velocity gradually decreased from the initial stage, but there was a region where the velocity was almost constant after the initial stage. The molten metal temperature became lower from the root side to the tip side, and the solid fraction at the time of flow cessation was calculated from the measurement results, for the Al–7%Si–0.3%Mg alloy it was 0.35–0.4 near the tip, and for the Cu–8%Sn alloy it was 0.25. Computer simulations were performed by tuning the heat transfer coefficient so that the flow length and flow velocity would match the experimental results. Computer simulations were performed by tuning the heat transfer coefficients so that the flow length and flow velocity would match the experimental results and could simulate the changes in flow velocity obtained from the experiments. The solid fraction at the tip of the molten metal was almost the same as the experimental results. These results show that it is possible to estimate the solid fraction at the flow cessation from the flow velocity at the tip.

Intramolecular Force Mapping at Room Temperature.

Acquisition of dense, three-dimensional, force fields with intramolecular resolution via noncontact atomic force microscopy (NC-AFM) has yielded enormous progress in our ability to characterize molecular and two-dimensional materials at the atomic scale. To date, intramolecular force mapping has been performed exclusively at cryogenic temperatures, due to the stability afforded by low temperature operation, and as the carbon monoxide functionalization of the metallic scanning probe tip, normally required for submolecular resolution, is only stable at low temperature. In this paper we show that high-resolution, three-dimensional force mapping of a single organic molecule is possible even at room temperature. The physical limitations of room temperature operation are overcome using semiconducting materials to inhibit molecular diffusion and create robust tip apexes, while challenges due to thermal drift are overcome with atom tracking based feedforward correction. Three-dimensional force maps comparable in spatial and force resolution to those acquired at low temperature are demonstrated, permitting a quantitative analysis of the adsorption induced changes in the geometry of the molecule at the picometer level.

Near-field optical microscopy toward its applications for biological studies.

Near-field scanning optical microscopy (NSOM) is a super-resolution optical microscopy based on nanometrically small near-field light at a metallic tip. It can be combined with various types of optical measurement techniques, including Raman spectroscopy, infrared absorption spectroscopy, and photoluminescence measurements, which provides unique analytical capabilities to a variety of scientific fields. In particular, to understand nanoscale details of advance materials and physical phenomena, NSOM has been often adopted in the fields of material science and physical chemistry. However, owing to the recent critical developments showing the great potential for biological studies, NSOM has also recently gained much attention in the biological field. In this article, we introduce recent developments made in NSOM, aiming at biological applications. The drastic improvement in the imaging speed has shown a promising application of NSOM for super-resolution optical observation of biological dynamics. Furthermore, stable imaging and broadband imaging were made possible owing to the advanced technologies, which provide a unique imaging method to the biological field. As NSOM has not been well exploited in biological studies to date, several rooms need to be explored to determine its distinct advantages. We discuss the possibility and perspective of NSOM for biological applications. This review article is an extended version of the Japanese article, Development of Near-field Scanning Optical Microscopy toward Its Application for Biological Studies, published in SEIBUTSU BUTSURI Vol. 62, p. 128-130 (2022).

Impact of Metal Particles Released during Ultrasonic Scaling of Titanium Surfaces on Human Gingival Fibroblasts.

Metal particles found in tissues around dental implants have been proposed to play a pathogenic role in peri-implantitis. Ultrasonic scaling has been suggested as a mechanism by which these particles can be inadvertently released into surrounding tissues. Furthermore, risk factors like diabetes can result in exacerbation of this inflammatory condition. The current study aimed to analyze metal particles released from titanium surfaces during ultrasonic scaling and their impact on pro-inflammatory cytokine production by human gingival fibroblasts. Metal particles generated from ultrasonic scaling of titanium discs using two different tips (metal and poly-etheretherketone tips) were characterized using scanning electron microscopy and elemental analysis. Endotoxin levels and Human gingival fibroblast viability, in the presence commercial and ultrasonically generated particles were determined. Fibroblasts, cultured in high or low glucose growth medium, were incubated with commercial titanium particles or ultrasonically generated particles in the presence or absence of interluekin-1β. Interleukin 6 and interleukin 8 production were then quantified using Enzyme linked immunosorbent assay. Analysis of particles after scaling of titanium discs showed significant levels of titanium particles. Commercial titanium particles and generated particles had no effect of fibroblast viability. Endotoxin levels of all particles were too low to stimulate HGF cells. IL-1β significantly stimulated IL-6 and IL-8 production. However, commercial, and generated particles generally had no significant effect on IL- 6 and IL-8 production. Our study concluded that particles generated during ultrasonic scaling had no significant effect on viability of HGF cells and cytokine production.

Nanoscale electronic transport at graphene/pentacene van der Waals interfaces.

We report a study on the relationship between the structure and electron transport properties of nanoscale graphene/pentacene interfaces. We fabricated graphene/pentacene interfaces from 10 to 30 nm thick needle-like pentacene nanostructures down to two-three layer (2L-3L) dendritic pentacene islands, and we measured their electron transport properties by conductive atomic force microscopy (C-AFM). The energy barrier at the interfaces, i.e., the energy position of the pentacene highest occupied molecular orbital (HOMO) with respect to the Fermi energy of graphene and the C-AFM metal tip was determined and discussed with an appropriate electron transport model (a double Schottky diode model and a Landauer-Buttiker model, respectively) taking into account the voltage-dependent charge doping of graphene. In both types of samples, the energy barrier at the graphene/pentacene interface is slightly larger than that at the pentacene/metal tip interface, resulting in 0.47-0.55 eV and 0.21-0.34 eV, respectively, for the 10-30 nm thick needle-like pentacene islands, and 0.92-1.44 eV and 0.67-1.05 eV, respectively, for the 2L-3L thick dendritic pentacene nanostructures. We attribute this difference to the molecular organization details of the pentacene/graphene heterostructures, with pentacene molecules lying flat on graphene in the needle-like pentacene nanostructures, while standing upright in the 2L-3L dendritic islands, as observed from Raman spectroscopy.

Fabrication of Spindt-Type Nanometer-Sized Chromium Tips for Application as Field-Electron Emitters by Releasing the Stress of the Deposited Thin Film

Metal cone-shaped nanotip field-electron emitters which are fabricated by directional thin-film deposition (so-called Spindt-type tips) have shown promising potential for application in modern vacuum micro-/nanoelectronics. Although the fabrication processes of Spindt-type tips have been well established, the in situ release of the initial stress in the deposited metal thin film is still an open issue. Herein, an in situ stress-release process was developed to fabricate chromium (Cr) tip arrays. Patterned photoresist microcavities with surrounding trenches were designed. The microcavities were used as templates for forming the metal tips. Trenches were employed for the in situ internal stress release of the Cr film on the top of the resist. The trenches not only separated the deposited Cr film into small-sized slices (square film on the photoresist) for decreasing the deformation but also provided sufficient space for possible deformation. High-aspect-ratio (∼2) tips were achieved by plasma etching the Si substrate using the Cr tip as the mask, forming a Cr tip on a Si pillar. The Cr tips maintaining a good tip shape demonstrated that the Cr nanotips possessed good etch resistance to the SF6/O2 plasma. The gated Cr-tip array was fabricated following a self-aligned microfabrication procedure. The fabrication process was compatible with the semiconductor manufacturing technology. The gated devices showed an emission current of 33 μA at a gate voltage of 137 V. This work provides a well-developed in situ stress-releasing fabrication process to obtain Spindt-type Cr-tip field-electron emitters, which has potential for application in ionization vacuum gauges and neutralizers for propulsion.

Eyelid and scleral thermal injury following phacoemulsification in silicone oil: a case report

BackgroundPhacoemulsification has been the mainstay method for extracapsular cataract extraction surgery in the anterior segment; for cases of posterior drop of lens fragments into the vitreous, a posterior segment phacoemulsification instrument (fragmatome; Alcon, Inc., Fort Worth, TX) can be employed to remove the dislocated lens materials. Studies have reported on thermal injury to the cornea during phacmoemulsification of the anterior segment. However, few studies have investigated thermal burn in the simultaneous sclera and eyelid induced by the fragmatome. Currently, there is no reports and lack of optimal strategy for the management of nucleus drop in a vitreous cavity filled with silicon oil.Case PresentationWe present the case of a 53-year-old male patient with a thermal burn wound on the upper eyelid and sclera following phacoemulsification for a dropped lens in a silicone oil-filled vitreous. We further designed an experiment to verify our hypothesis that thermal injury could be induced by the high temperature of the metal tip during phacoemulsification in silicone oil. In our experiment, during 420 s of continuous ultrasonic wave, the temperature of the fragmatome tip in the balanced salt solution (BSS) increased from 22.0 to 24.0 ºC, while the temperature of the fragmatome tip in the silicone oil group increased from 22.0 to 43.0 ºC.ConclusionsThe temperature of the fragmatome tip increased significantly in silicone oil compared to BSS in the experiment. Thus, physicians should be aware of possible thermal complications when using fragmatome in eyes filled with silicone oil.

MD analysis of heat transfer of carbon nanotube flow on nanopumping process to improve the hydrodynamic and thermal performances

A carbon nanotube (CNT) is a promising structure for nanoscale heat and mass transfer processes and targeted drug delivery (TDD). These appropriate behavior of CNTs cause this nanometric arrangement to be used in various clinical purposes, as drug delivery process. Here, we report nanopumping behavior of CNT sample in presence of an atomic defect and external heat flux (HF). Molecular Dynamics (MD) approach in this computational research consists of two main steps. In first step, equilibrium of defined compounds is described by Temperature (T) and Total Energy (TE) reporting. Results indicated that defined samples reach an equilibrium state after 1 ns. Next, nanopumping process is done by implementing external HF and metallic tips oscillating in vicinity of defected CNT as second step. Physical quantities such as T, TE, radial distribution function (RDF), nanopumping time, kinetic energy (KE), and Velocity (V)/T profiles of defined compounds were reported after two main processes were done. MD outputs indicated C 20 molecule (target particle in nanopumping process) displaced inside CNT after 46.68 (ps), and by defining external flux, this time decreased to 43.12 (ps). Finally, we concluded that atomic defect and HF are important parameters that can be controlled nanopumping process in various clinical applications.

Local bistability under microwave heating for spatially mapping disordered superconductors

We theoretically study a strongly disordered superconducting layer heated by near-field microwave radiation from a nanometric metallic tip. The microwaves heat up the quasiparticles, which cool by phonon emission and conduction away from the heated area. Due to a bistability with two stable states of the electron temperature under the tip, the heating can be tuned to induce a submicrometer-sized normal region bounded by a sharp domain wall between high- and low-temperature states. We propose this as a local probe to access different physics from existing methods, for example, to map out inhomogeneous superfluid flow in the layer. The bistability-induced domain wall can significantly improve its spatial resolution.

Single-dopant band bending fluctuations in MoSe2 measured with electrostatic force microscopy

In this paper, we experimentally demonstrate two-state fluctuations in a metal-insulator-semiconductor device formed out of a metallic atomic force microscopy tip, vacuum gap, and multilayer ${\mathrm{MoSe}}_{2}$ sample. We show that noise in this device is intrinsically bias dependent due to the bias-dependent surface potential and does not require that the frequency or magnitude of individual dopant fluctuations are themselves bias dependent. Finally, we measure spatial nonhomogeneities in band bending (charge reorganization) timescales.

Partial Discharge Pattern Recognition Based on a Multifrequency F–P Sensing Array, AOK Time–Frequency Representation, and Deep Learning

Recognizing the patterns of partial discharge (PD) is the key to assess the hazard level of PD. This article proposes an oil-immersed transformer PD pattern recognition method based on a multifrequency fiber-optic Fabry–Perot (F–P) ultrasound sensing array and deep learning (DL). Three F–P ultrasonic probes with different resonance bands were used to form a sensing array for collecting ultrasonic signals excited by PD. Five types of PD models were prepared, including metal tip (MT) discharge in oil, PD in the air cavity (AC), and surface discharge (SD) on the pressboard, in addition to SD after pressboard blocking or after pressboard plus transformer winding blocking, to study the influence of ultrasonic attenuation on recognition accuracy. The collected PD ultrasound signal time-frequency matrix was obtained using adaptive optimal-kernel time–frequency representation to reinforce the differences in PD patterns. Then, based on the features of the PD ultrasonic signals, the signal time and frequency band for analysis were determined. The intercepted time–frequency matrix of the signals from the three F–P probes was formed into a (3, 300, 375) tensor. A modified ResNet-18 net was used for PD pattern recognition, which achieved a 98% recognition accuracy. The probabilities given by the softmax function were used to study the confidence of the model’s predictions of signals belonging to known and unknown types.

Enhancing Infrared Light-Matter Interaction for Deterministic and Tunable Nanomachining of Hexagonal Boron Nitride.

Tailoring two-dimensional (2D) materials functionalities is closely intertwined with defect engineering. Conventional methods do not offer the necessary control to locally introduce and study defects in 2D materials, especially in non-vacuum environments. Here, an infrared pulsed laser focused under the metallic tip of an atomic force microscope cantilever is used to create nanoscale defects in hexagonal boron nitride (h-BN) and to subsequently investigate the induced lattice distortions by means of nanoscale infrared (nano-IR) spectroscopy. The effects of incoming light power, exposure time, and environmental conditions on the defected regions are considered. Nano-IR spectra complement the morphology maps by revealing changes in lattice vibrations that distinguish the defects formed under various environments. This work introduces versatile experimental avenues to trigger and probe local reactions that functionalize 2D materials through defect creation with a higher level of precision for applications in sensing, catalysis, optoelectronics, quantum computing, and beyond.