Metal Tip Research Articles

Клинический случай обширного субконъюнктивального разрыва склеры с благоприятным исходом

Aim. To present a clinical case of severe open injury of the eyeball of a con-tusion nature with the presence of intraocular complications and to show that de-spite the significant severity of the injury, good results can be achieved. Material and methods. Patient injured his right eye at home with a metal tip on a rubber band, after which his vision sharply decreased, pain and lacrimation of the right eye appeared. Objectively: vision of the right eye pr. l. certae, intraocular pressure (palpation) - hypotension. No foreign body was found on the survey radi-ograph of the orbits. An ultrasound B-scan revealed hemophthalmus, and subse-quently (after 7 days) retinal detachment appeared. The patient underwent vitrec-tomy, tamponade of the vitreous cavity with silicone oil, endolaser coagulation of the retina. Results. On the 1st day after the operation, the visual acuity increased to 0.4 with correction (shp +8.0). 3 months after discharge from the hospital, the patient had complete safety of the eyeball and stable functional results were achieved, where the visual functions of the injured eye were 0.5 with correction (shp + 8.0). Conclusions. A clinical case of severe open eye injury with extensive sub-conjunctival rupture of the sclera, hemophthalmos and retinal detachment demon-strates that, despite the severity of the injury, with timely provision of high-tech surgical care, there is a real chance of saving the eyeball and get high visual func-tions. Key words: Traumatic vitreous haemorrhage; vitrectomy; subconjunctival rupture of the sclera; retinal detachment.

Imaging signatures of the local density of states in an electronic cavity

We use Scanning Gate Microscopy to study electron transport through an open, gate-defined resonator in a Ga(Al)As heterostructure. Raster-scanning the voltage-biased metallic tip above the resonator, we observe distinct conductance modulations as a function of the tip-position and voltage. Quantum mechanical simulations reproduce these conductance modulations and reveal their relation to the partial local density of states in the resonator. Our measurements illustrate the current frontier between possibilities and limitations in imaging the local density of states in buried electron systems using scanning gate microscopy.

Nanoscale coating on tip geometry by cryogenic focused ion beam deposition

We report application of nanoscale in-situ cryo-condensation coating technique on needle-shaped specimens and frozen hydrated cells. By using a cryogenic focused ion beam/ scanning electron microscopy (cryo-FIB/SEM) instrument, phase transformation of the metal–organic precursor gas has been demonstrated to occur at the cryogenically cooled metal tip of 50 nm in radius, and the properties of the deposited layer can be tuned by the control parameters. Revealed surface morphologies on the needle tip include nanoscale columns using glancing angle deposition (GLAD). With deposition performed at multiple orientations, a continuous frozen shell as thin as 40 nm can be formed. The physical mechanisms of curing by ion beam/electron beam irradiation have been further investigated with characterization tools including transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy (EDS), and the results confirm the feasibility of constructing a platinum-rich conductive layer. The proposed approach is also demonstrated by depositing a thin conductive layer on frozen hydrated bacterial cells to facilitate sectioning and high-resolution electron imaging. The proposed approach opens a novel route to nanofabrication on tip geometry as well as site-specific conductive protection to facilitate nanocharacterisation.

(Invited) Scanning Gate Imaging of Charge Transport in Graphene Nanodevices

Quantum transport in nanodevices is usually probed thanks to measurements of the electrical resistance or conductance, which lack the spatial resolution necessary to probe local-scale electron behaviour. Here, we will discuss how to get real-space local information on peculiar quantum transport phenomena inside graphene constrictions. The results were obtained using low temperature scanning gate microscopy (SGM), which consists in mapping the electrical conductance of a device as an electrically-biased sharp metallic tip scans in its vicinity [1].If the tip-induced perturbation is relatively small, SGM is an imaging technique giving access to the local density of states inside mesoscopic devices [2]. Here, we will focus on the regime of large tip-induced perturbation. This regime is particularly interesting in the case of graphene: depending on tip voltage and tip-sample distance, one can tune the shape, size, and smoothness of the moving scattering region associated with the tip, and eventually create a moving circular pn-junction within the device. We use this moving pn-junction to probe peculiar aspects of relativistic charge carrier dynamics within graphene devices: Klein tunnelling and current focusing and defocusing [3], Fabry-Pérot interferometry [4], signatures of whispering gallery modes [5] and tunneling between counterpropagating quantum Hall edge states [6]. This work unlocks new possibilities in the field of electron optics in graphene.[1] M.A. Eriksson et al., Appl. Phys. Lett. 69, 671 (1996); M. Topinka et al., Science 289, 671 (2000).[2] F. Martins et al., Phys. Rev. Lett. 99, 136807 (2007) ; M. Pala et al., Phys. Rev. B 77, 125310 (2008).[3] B. Brun et al., Phys. Rev. B 100, 041401 (2019).[4] B. Brun et al., 2D Materials, 7, 025037 (2020).[5] B. Brun et al., submitted.[6] N. Moreau et al., submitted.

Very weak bonds to artificial atoms formed by quantum corrals.

We explored the bonding properties of the quantum corral (a circle of 48 iron atoms placed on a copper surface) reported by Crommie et al. in 1993, along with variants, as an artificial atom using an atomic force microscope (AFM). The original corral geometry confines 102 electrons to 28 discrete energy states, and we found that these states can form a bond to the front atom of the AFM with an energy of about 5 millielectron volts. The measured forces are about 1/1000 of typical forces in atomically resolved AFM. The confined electrons showed covalent attraction to metal tips and Pauli repulsion to CO-terminated tips. The repulsion at close distance was evident from the response of corral states created by deliberately placing single iron atoms inside the corral. The forces scaled appropriately with a 24-atom corral.

Laser ray bundle: a thermometry method for HIFU heating

High-intensity focused ultrasound (HIFU) is a therapeutic modality that heats tissue by focusing a sound beam into a narrow, localized region. This paper is concerned with the thermo-optic lensing effect observed by Al-Qraini et al (Ultrasound Med. Biol. 39 647–59) when visible light was shone at a transparent tissue-mimicking phantom heated by HIFU. Thermal lensing was caused by light refraction as it passed through the thermal gradient region. HIFU thermal lensing was reproduced experimentally and studied analytically using the geometric (eikonal) ray equation to devise a method for temperature measurement. Under the Gaussian thermal field assumption, explicit closed form solutions were found for the forward thermo-optic ray deflection problem, and for the inverse opto-thermal conversion problem that yielded the underlying temperature field from measured ray deflections. Neither temperature calibration nor iterative computations were needed. In the experimental setup, a bundle of thin laser rays illuminated the HIFU-heated spot in a clear tissue-mimicking phantom. The ray deflections were recorded and directly converted into temperature with very good temporal and spatial resolution. These compared reasonably well against the output of an embedded thermocouple (TC)—considering the absorptive and viscous heating artifacts which were also investigated. The TC metallic tip junction was carefully positioned to coincide with the axis of peak heating. It was found that the TC stem (wire) transferred heat by conduction from the tip into the tissue located off the HIFU heating axis. The proposed thermometry method can be useful in elucidating heating from focused ultrasound sources, or from other sources of localized heating such as lasers.

Comparative Apex Electrostatics of Atom Probe Tomography Specimens.

Rigorous electrostatic modeling of the specimen-electrode environment is required to better understand the fundamental processes of atom probe tomography (APT) and guide the analysis of APT data. We have developed a simulation tool that self-consistently solves the nonlinear electrostatic Poisson equation along with the mobile charge carrier concentrations and provides a detailed picture of the electrostatic environment of APT specimen tips. We consider cases of metals, semiconductors, and dielectrics. Traditionally in APT, and regardless of specimen composition, the apex electric field has been approximated by the relation , which was originally derived for sharp, metallic conductors; we refer to this equation as the "k-factor approximation". Here, is tip-electrode bias, is the radius of curvature of the tip apex, and is a dimensionless fitting parameter with . As expected, our Poisson solver agrees well with the k-factor approximation for metal tips; it also agrees remarkably well for semiconductor tips-regardless of the semiconductor doping level. We ascribe this finding to the fact that even if a semiconductor tip is fully depleted of majority carriers under the typical conditions used in APT, an inversion layer will appear at the apex surface. The inversion forms a thin, conducting layer that screens the interior of the tip -thus mimicking metallic behavior at the apex surface. By contrast, we find that the k-factor approximation applied to a purely dielectric tip results in values far greater than the typical range for metallic tips. We put our numerical results into further context with a brief discussion of our own, separate, experimental work and the results of other publications.

Understanding the Role of 2D Nature on the Junction Properties in WS2 Layers; Effect of AFM Tip Induced Loading Force on Spatially Varying Contact

In the present study, AFM metal tip induced loading force dependent electrical transport behaviour of WS2 domains synthesized using chemical vapour deposition technique has been investigated. Raman spectroscopy, optical microscopy and atomic force microscopy (AFM) techniques have been employed to characterize the synthesized two-dimensional (2D) domains. The local nanoscale I-V measurements have been carried out as a function of loading force (53 – 300 nN) using conductive atomic force microscopy to probe the interface formed between AFM tip (Pt coated) and 2D domains of WS2 layers. An interesting phenomena of decreasing junction current with increasing loading force obtained at the centre of single layer WS2 sample is opposed by an increasing junction current at the edges of domain. Loading force induced spatially varying, compressive and tensile strain resulting in charge polarization causing an opposite flow of majority electron carriers away and towards the tip-WS2 domain has been explained as the possible mechanism for the applied opposing uniaxial strains. This study reports the influence of single layer nature of WS2 constituting polar edges and wrinkle terminations on electronic properties of metal-semiconductor contacts. These results are crucial for understanding the junction properties and application of 2D material based devices in next-generation electronics.

Thermic Epidermic Tissue Surgical Generator Using Bipolar Electrode

Hemostasis remains the foremost vital role of cautery, without hemostasis we have the danger of bleeding which results in the worst-case of a retro neural structure intumescence and visual impairment. Hemostasia permits for a safer and a lot of favorable outcomes, besides hemostasia cautery is used for different functions. We use it ordinarily in medicine to induce timely structure for patients with dry eyes, to shut conjunctivas incisions also as a surgical marker. Heat is generated through associate electrical current and flows to a metal tip to coagulate blood vessels to stop bleeding. Electrocautery comes within the monopolar or bipolar style with monopolar electrocautery and is applied through a hand-held active conductor which travels back to the generator through an inactive conductor connected to the patient (the grounding pad). Therefore, the patient is an element of the circuit. The inactive conductor is usually placed on the outsized space of the body to avoid physical heat phenomenon. With bipolar electrocautery, the existing is passed between one extractor tip to the opposite and a restricted quantity of tissue is cauterized in between. The existing is unfolded with monopolar electrocautery in which there's a lot of tissue harm and the tissue recovery takes a longer time.

Electrostatic tip effects in scanning probe microscopy of nanostructures

Electrical scanning probe microscopies (SPM) use ultrasharp metallic tips to obtain nanometer spatial resolution and are a key tool for characterizing nanoscale semiconducting materials and systems. However, these tips are not passive probes; their high work functions can induce local band bending whose effects depend sensitively on the local geometry and material properties and thus are inherently difficult to quantify. We use sequential finite element simulations to first explore the magnitude and spatial distribution of charge reorganization due to tip-induced band bending (TIBB) for planar and nanostructured geometries. We demonstrate that tip-induced depletion and accumulation of carriers can be significantly modified in confined geometries such as nanowires compared to a bulk planar response. This charge reorganization is due to finite size effects that arise as the nanostructure size approaches the Debye length, with significant implications for a range of SPM techniques. We then use the reorganized charge distribution from our model to describe experimentally measured quantities, using in operando scanning microwave impedance microscopy measurements on axial p-i-n silicon nanowire devices as a specific example. By incorporating TIBB, we reveal that our experimentally observed enhancement (absence) of contrast at the p-i (i-n) junction is explained by the tip-induced accumulation (depletion) of carriers at the interface. Our results demonstrate that the inclusion of TIBB is critical for an accurate interpretation of electrical SPM measurements, and is especially important for weakly screening or low-doped materials, as well as the complex doping patterns and confined geometries commonly encountered in nanoscale systems.

Nanoscale investigation of two-photon polymerized microstructures with tip-enhanced Raman spectroscopy

We demonstrate the use of tip-enhanced Raman spectroscopy (TERS) on polymeric microstructures fabricated by two-photon polymerization direct laser writing (TPP-DLW). Compared to the signal intensity obtained in confocal Raman microscopy, a linear enhancement of almost two times is measured when using TERS. Because the probing volume is much smaller in TERS than in confocal Raman microscopy, the effective signal enhancement is estimated to be ca. 104. We obtain chemical maps of TPP microstructures using TERS with relatively short acquisition times and with high spatial resolution as defined by the metallic tip apex radius of curvature. We take advantage of this high resolution to study the homogeneity of the polymer network in TPP microstructures printed in an acrylic-based resin. We find that the polymer degree of conversion varies by about 30% within a distance of only 100 nm. The combination of high resolution topographical and chemical data delivered by TERS provides an effective analytical tool for studying TPP-DLW materials in a non-destructive way.

Understanding the Role of Different Substrate Geometries for Achieving Optimum Tip-Enhanced Raman Scattering Sensitivity.

Tip-enhanced Raman spectroscopy (TERS) has experienced tremendous progress over the last two decades. Despite detecting single molecules and achieving sub-nanometer spatial resolution, attaining high TERS sensitivity is still a challenging task due to low reproducibility of tip fabrication, especially regarding very sharp tip apices. Here, we present an approach for achieving strong TERS sensitivity via a systematic study of the near-field enhancement properties in the so-called gap-mode TERS configurations using the combination of finite element method (FEM) simulations and TERS experiments. In the simulation study, a gold tip apex is fixed at 80 nm of diameter, and the substrate consists of 20 nm high gold nanodiscs with diameter varying from 5 nm to 120 nm placed on a flat extended gold substrate. The local electric field distributions are computed in the spectral range from 500 nm to 800 nm with the tip placed both at the center and the edge of the gold nanostructure. The model is then compared with the typical gap-mode TERS configuration, in which a tip of varying diameter from 2 nm to 160 nm is placed in the proximity of a gold thin film. Our simulations show that the tip-nanodisc combined system provides much improved TERS sensitivity compared to the conventional gap-mode TERS configuration. We find that for the same tip diameter, the spatial resolution achieved in the tip-nanodisc model is much better than that observed in the conventional gap-mode TERS, which requires a very sharp metal tip to achieve the same spatial resolution on an extended metal substrate. Finally, TERS experiments are conducted on gold nanodisc arrays using home-built gold tips to validate our simulation results. Our simulations provide a guide for designing and realization of both high-spatial resolution and strong TERS intensity in future TERS experiments.

Are charged tips driving TERS-resolution? A full quantum chemical approach.

Experimental evidence suggests an extremely high, possibly even sub-molecular, spatial resolution of tip-enhanced Raman spectroscopy (TERS). While the underlying mechanism is currently still under discussion, two main contributions are considered: The involved plasmonic particles are able to highly confine light to small spatial regions in the near-field, i.e., the electromagnetic effect and the chemical effect due to altered molecular properties of the sample in close proximity to the plasmonic tip. Significant theoretical effort is put into the modeling of the electromagnetic contribution by various groups. In contrast, we previously introduced a computational protocol that allows for the investigation of the local chemical effect-including non-resonant, resonant, and charge transfer contributions-on a plasmonic hybrid system by mapping the sample molecule with a metallic tip model at the (time-dependent) density functional level of theory. In the present contribution, we evaluate the impact of static charges localized on the tip's frontmost atom, possibly induced by the tip geometry in the vicinity of the apex, on the TERS signal and the lateral resolution. To this aim, an immobilized molecule, i.e., tin(II) phthalocyanine (SnPc), is mapped by the plasmonic tip modeled by a single positively vs negatively charged silver atom. The performed quantum chemical simulations reveal a pronounced enhancement of the Raman intensity under non-resonant and resonant conditions with respect to the uncharged reference system, while the contribution of charge transfer phenomena and of locally excited states of SnPc is highly dependent on the tip's charge.

Revised electrochemical etching system for a reproducible fabrication of ultra-sharp tungsten tips

This article proposes an improved version of the drop-off electrochemical etching technique, developed for a reproducible production of ultra-sharp metal tips. Firstly, a comprehensive survey of other mechanical and physicochemical procedures is made in order to individuate three issues commonly neglected: (i) the influence of external perturbations, (ii) the positions of the electrode (a W wire) and counter-electrode (a Pt ring) and (iii) the counter-electrode shape. These issues need to be carefully fixed, in an enclosed and geometrically well-defined configuration, to better control the opening angle, radius of curvature and aspect ratio. The quality of the tips produced is evaluated comparing their performances, in imaging a reference sample with scanning tunnelling microscopy, to those of commercial tips. Using established procedures and data reported in the literature, an optimal set of the parameters can be identified obtaining high-quality tips with an opening angle < 10° and a radius of curvature ~ 30 nm. Furthermore, achieving a higher reproducibility allows us to investigate the electrochemical process monitoring the time dependence of the current from the etching parameters, such as the wire immersion, electrolyte concentration and applied bias voltage. Thus, the current versus time curves can be analysed in terms of linear scan voltammetry and electrochemical impedance spectroscopy, in order to investigate the phenomena occurring during the wire etching. In particular, at the beginning of the electrochemical process, the replacement of the native W oxide with a thicker layer of WO3(H2O)x oxide is observed, in agreement with previous observations.

The effects of physical decontamination methods on zirconia implant surfaces: a systematic review.

PurposePeri-implantitis therapy and implant maintenance are fundamental practices to enhance the longevity of zirconia implants. However, the use of physical decontamination methods, including hand instruments, polishing devices, ultrasonic scalers, and laser systems, might damage the implant surfaces. The aim of this systematic review was to evaluate the effects of physical decontamination methods on zirconia implant surfaces.MethodsA systematic search was conducted using 5 electronic databases: Ovid MEDLINE, PubMed, Scopus, Web of Science, and Cochrane. Hand searching of the OpenGrey database, reference lists, and 6 selected dental journals was also performed to identify relevant studies satisfying the eligibility criteria.ResultsOverall, 1049 unique studies were identified, of which 11 studies were deemed suitable for final review. Air-abrasive devices with glycine powder, prophylaxis cups, and ultrasonic scalers with non-metal tips were found to cause minimal to no damage to implant-grade zirconia surfaces. However, hand instruments and ultrasonic scalers with metal tips have the potential to cause major damage to zirconia surfaces. In terms of laser systems, diode lasers appear to be the most promising, as no surface alterations were reported following their use.ConclusionAir-abrasive devices and prophylaxis cups are safe for zirconia implant decontamination due to preservation of the implant surface integrity. In contrast, hand instruments and ultrasonic scalers with metal tips should be used with caution. Recommendations for the use of laser systems could not be fully established due to significant heterogeneity among included studies, but diode lasers may be the best-suited system. Further research—specifically, randomised controlled trials—would further confirm the effects of physical decontamination methods in a clinical setting.

Interaction of Tungsten tips with Laguerre-Gaussian beams

Interaction of femtosecond laser pulses with metallic tips have been studied extensively and they have proved to be a very good source of ultrashort electron pulses. We present our study of interaction of Laguerre-Gaussian (LG) laser modes with Tungsten tips. We report a change in the order of the interaction for LG beams and the difference in the order of interaction is attributed to ponderomotive shifts in the energy levels corresponding to the enhanced near field intensity supported by numerical simulations.

One-dimensional polymer-derived ceramic nanowires with electrocatalytically active metallic silicide tips as cathode catalysts for Zn-air batteries.

New metallic nickel/cobalt/iron silicide droplets at the tips of polymer-derived ceramic (PDC) nanowires have been identified as stable and efficient cathode catalysts for Zn–air batteries. The as-prepared catalyst having a unique one-dimensional (1D) PDC nanowire structure with the presence of metallic silicide tips of 1D-PDC plays a crucial role in facilitating oxygen reduction/evolution reaction kinetics. The Zn–air battery was designed using Ni/PDC, Co/PDC and Fe/PDC as air electrode catalysts. In electrochemical half-cell tests, it was observed that the catalysts have a good bifunctional electrocatalytic activity. The efficiency of the catalysts to function as a cathode catalyst in real-time primary and mechanically rechargeable Zn–air battery configurations was determined. The primary battery testing results revealed that Ni/PDC and Co/PDC exhibited a stable discharge voltage plateau up to 29 h. The Fe/PDC sample, on the other hand, performed up to 23 h with an operating potential of 1.20 V at the discharge current density of 5 mA cm−2 after which the battery ceased to perform. The Ni/PDC, Co/PDC, and Fe/PDC cathode catalysts performed galvanostatic 1200 charge–discharge cycles in a mechanically rechargeable secondary Zn–air battery configuration. The results demonstrate that the Ni/PDC, Co/PDC, and Fe/PDC materials serve as excellent and durable bifunctional cathode electrocatalysts for Zn–air batteries.

Tip-sample interactions in terahertz scattering scanning near-field optical microscopy and its influences

Terahertz scattering scanning near-field optical microscopy (s-SNOM), as an important means to break through the limits of conventional optical diffraction, can achieve super-resolution imaging on a nanoscale and has a wide range of applications in biological nano-imaging, terahertz nano-spectroscopy, nanomaterials imaging, and the study of polarized excitations. As an important component of the terahertz s-SNOM, the atomic force microscope tip plays a key role in implementing the near-field excitation, detection, and enhancement. However, the tip-sample interaction can greatly affect the results. In this paper, the effects of tip-sample interaction on near-field excitation, near-field detection, and terahertz near-field spectrum in terahertz s-SNOM are revealed through simulations and experiments. First, the wave vector coupling weight of the near field excited by the tip is investigated, and it is found that the wave vector is concentrated mainly on the order of 10&lt;sup&gt;5&lt;/sup&gt; cm&lt;sup&gt;–1&lt;/sup&gt;, which differs from that of the general terahertz excitations by 2 to 3 orders of magnitude, indicating that the terahertz near field is difficult to excite terahertz excitations. Secondly, through theoretical and experimental studies, it is found that the metal tip interferes with the surface near-field of the graphene disk structure, which indicates the limitations of the terahertz s-SNOM in probing the near-field distribution of the structure. Finally, the influence of the tip on the near-field spectrum is studied. It is found that the tip length and cantilever length are important parameters affecting the near-field spectrum, and the influence of the tip on the near-field spectrum can be reduced by increasing the tip length or cantilever length.

Systematic electrochemical etching of various metal tips for tunneling spectroscopy and scanning probe microscopy.

Hard point-contact spectroscopy and scanning probe microscopy/spectroscopy are powerful techniques for investigating materials with strong expandability. To support these studies, tips with various physical and chemical properties are required. To ensure the reproducibility of experimental results, the fabrication of tips should be standardized, and a controllable and convenient system should be set up. Here, a systematic methodology to fabricate various tips is proposed, involving electrochemical etching reactions. The reaction parameters fall into four categories: solution, power supply, immersion depth, and interruption. An etching system was designed and built so that these parameters could be accurately controlled. With this system, etching parameters for copper, silver, gold, platinum/iridium alloy, tungsten, lead, niobium, iron, nickel, cobalt, and permalloy were explored and standardized. Among these tips, silver and niobium's new recipes were explored and standardized. Optical and scanning electron microscopies were performed to characterize the sharp needles. Relevant point-contact experiments were carried out with an etched silver tip to confirm the suitability of the fabricated tips.

Critically Charged Superfluid 4He Surface in Inhomogeneous Electric Fields

We have studied the spatial distribution of charges trapped at the surface of superfluid helium in the inhomogeneous electric field of a metallic tip close to the liquid surface. The electrostatic pressure of the charges generates a deformation of the liquid surface, leading to a “hillock” (called “Taylor cone”) or “dimple”, depending on whether the tip is placed above or below the surface. We use finite element simulations for calculating the surface profile and the corresponding charge density in the vicinity of the tip. Typical electric fields E are in the range of a few kV/cm, the maximum equilibrium surface deformations have a height on the order of (but somewhat smaller than) the capillary length of liquid 4He (0.5 mm), and the maximum number density of elementary charges in a hillock or dimple, limited by an electrohydrodynamic instability, is some 1013 m−2. These results can be used to determine the charge density at a liquid helium surface from the measured surface profile. They also imply that inhomogeneous electric fields at a bulk helium surface do not allow one to increase the electron density substantially beyond the limit for a homogeneous field, and are therefore not feasible for reaching a density regime where surface state electrons are expected to show deviations from the classical behavior. Some alternative solutions are discussed.