Sharp Tip Research Articles

Coulomb blockade and quantum confinement in field electron emission from heterostructured nanotips

A new field electron emission (FE) mechanism, which includes Coulomb blockade and quantum confinement effects, is revealed for heterostructured emitters composed of quantum dots and nanowires self-assembled at diamond nanotips. The total energy distributions of the emitted electrons show multiple peaks attributed to the discrete electronic states of the quantum-confined emitter with the corresponding energy levels oscillating as a function of the applied voltage due to the Coulomb blockade. The FE current-voltage characteristics exhibit a modified Coulomb staircase with additional steps becoming more pronounced with increasing voltage. The experimentally observed behavior is consistent with numerical simulations based on the model of Coulomb blockade in quantum dots in combination with the theory of FE from sharp tips.

Assessment of needle tip geometry during infusions into a brain phantom gel

Convection-enhanced delivery (CED) is a promising method to deliver therapeutic drugs directly into the brain that has shown limited efficacy, mainly attributed to backflow, in which the infused drug flows back along the needle track rather than forward into tissue. This study evaluates the effect of sharp and blunt needle tips on backflow length under different flow rates via CED. Infusions were performed in a transparent 0.6% (w/v) brain phantom agarose hydrogel. Backflow length was significantly higher using sharp-tip needles for higher flow rates. No significant differences were observed between tip shapes for lower flow rates. In conclusion, sharp-tip needles present limitations for higher flow rates, which are needed to deliver more drug during shortest times.

Experimental and XIGA-CZM based Mode-II and mixed-mode interlaminar fracture model for unidirectional aerospace-grade composites

This article presents a fracture model for evaluation of Mode-II and Mixed-Mode (Mode-I + II) interlaminar fracture properties of unidirectional laminated composites. Mode-II and Mixed-Mode (Mode-I + II) interlaminar fracture tests have been carried out on End-Notched Flexure and Mixed-Mode bending specimens, respectively. The non pre-craked specimens are tested under pure Mode-II and Mixed-Mode loading conditions for the estimation of energy required to initiate crack growth from the natural crack tip. Pre-cracked specimens have been tested under pure Mode-II loading conditions to investigate the nature of delamination propagation from the sharp crack tip. A new set of interfacial fracture properties has been evaluated for AS4/914 laminates. An expression has been developed to correlate the experimentally obtained energy release rate (ERR) and equivalent crack growth (Δa) using a compliance based beam method. The curve-fitted expression between ERR and Δa is further introduced to the cohesive zone model for numerical modelling. Fractured surfaces at the final fracture load point in non pre-cracked specimens during Mode-II fracture tests are examined using scanning electron microscopy technique. Numerical simulations of crack initiation and propagation for all fracture tests have been performed using a combined formulation of fracture mechanics and damage mechanics. The introduction of experimentally obtained interlaminar interfacial properties into a combined formulation of extended isogeometric analysis and cohesive zone model shows a good agreement with experimentally obtained results.

Mechanical Processing of Naturally Bent Organic Crystalline Microoptical Waveguides and Junctions

Precise mechanical processing of optical microcrystals involves complex microscale operations viz. moving, bending, lifting, and cutting of crystals. Some of these mechanical operations can be implemented by applying mechanical force at specific points of the crystal to fabricate advanced crystalline optical junctions. Mechanically compliant flexible optical crystals are ideal candidates for the designing of such microoptical junctions. A vapor-phase growth of naturally bent optical waveguiding crystals of 1,4-bis(2-cyanophenylethynyl)benzene (1) on a surface forming different optical junctions is presented. In the solid-state, molecule 1 interacts with its neighbors via CH⋅⋅⋅N hydrogen bonding and π-π stacking. The microcrystals deposited at a glass surface exhibit moderate flexibility due to substantial surface adherence energy. The obtained network crystals also display mechanical compliance when cut precisely with sharp atomic force microscope cantilever tip, making them ideal candidates for building innovative T- and Δ-shaped optical junctions with multiple outputs.The presented micromechanical processing technique can also be effectively used as a tool to fabricate single-crystal integrated photonic devices and circuits on suitable substrates.

Binary Spiky/Spherical Nanoparticle Films with Hierarchical Micro/Nanostructures for High-Performance Flexible Pressure Sensors.

Flexible pressure sensors have been widely explored for their versatile applications in electronic skins, wearable healthcare monitoring devices, and robotics. However, fabrication of sensors with characteristics such as high sensitivity, linearity, and simple fabrication process remains a challenge. Therefore, we propose herein a highly flexible and sensitive pressure sensor based on a conductive binary spiky/spherical nanoparticle film that can be fabricated by a simple spray-coating method. The sea-urchin-shaped spiky nanoparticles are based on the core-shell structures of spherical silica nanoparticles decorated with conductive polyaniline spiky shells. The simple spray coating of binary spiky/spherical nanoparticles enables the formation of uniform conductive nanoparticle-based films with hierarchical nano/microstructures. The two differently shaped particles-based films (namely sea-urchin-shaped and spherical) when interlocked face-to-face to form a bilayer structure can be used as a highly sensitive piezoresistive pressure sensor. Our optimized pressure sensor exhibits high sensitivity (17.5 kPa-1) and linear responsivity over a wide pressure range (0.008-120 kPa), owing to the effects of stress concentration and gradual deformation of the hierarchical microporous structures with sharp nanoscale tips. Moreover, the sensor exhibits high durability over 6000 repeated cycles and practical applicability in wearable devices that can be used for healthcare monitoring and subtle airflow detection (1 L/min).

Fully nonlinear simulations of ferrofluid patterns in a radial magnetic field

Simulations reveal the emergence of complex starlike ferrofluid structures having sharp finger tips. These patterns result from an interplay of surface tension, magnetic, and viscous effects. This work supplements previous studies, which examined the system via linear and weakly nonlinear analyses.

Quantum Dot With a Diamond-Shaped Channel MOSFET on a Bulk Si Substrate

In this article, a p-type high- ${k}$ /metal gate (HKMG) FinFET with a special diamond-shaped channel on a bulk Si substrate for the formation of gate-induced quantum dot (QD) is reported. The electrical characteristics of the device at various temperatures and bias voltages for QD formation are extensively investigated. Remarkable oscillations in the drain current are observed for the 30-nm gate length ( ${L}_{g}$ ) transistor at ${T} =20$ K. By analyzing the experimental results as well as the simulation data obtained by TCAD, it is found that the carriers are strongly localized at the small sharp tip of the channel and the thick spacers contribute to a large confinement potential for forming QD with a large charging energy of 30 meV. This provides a promising approach for large-scale QD fabrication and integration using the mainstream bulk complementary metal oxide semiconductor (CMOS) process.

PEG J tube placement with optimization of J tube insertion.

We present a case series of 5 patients who underwent placement of a PEG tube followed by a J extension tube (PEG-J). PEG-J placement is usually performed as a 2-step procedure and is used for a variety of conditions such as gastroparesis. First, the PEG tube is placed using endoscopic transillumination, followed by tube placement with the pull method, and trimming of the PEG tube to approximately 20 cm. This is followed by insertion of the J extension tube through the PEG tube; the J extension tube is grasped by an endoscope and guided through the pylorus to a position distal to the ligament of Treitz. Two common problems related to the length of the PEG tube portion can occur when placing the J tube. A short PEG tube may not allow advancement of the J tube distal enough because of looping. On the other hand, a PEG tube that is too long can prevent adequate J tube insertion. Although the adverse events of PEG tubes are well documented, we did not find any published literature addressing problems with the placement of J tube extensions, although it is a frequently occurring problem in our clinical practice. Therefore, we have tried to address this problem. We present our technique for PEG-J tube placement, which allows optimal PEG tube length independent of the depth of J tube insertion. After PEG tube placement with the pull method, only the introducer is cut, and the entire length of the silicon PEG tube is left in situ. The tip of the J tube is lubricated and inserted into the PEG tube. In parallel, the J tube is grasped, in our cases with an endoclip, and gently maneuvered into the duodenum and eventually into the jejunum while the J tube is threaded into the PEG tube, matching the pull force from the J tube insertion by the endoscope. We use a pediatric colonoscope to achieve deep jejunal intubation; however, either the adult colonoscope or enteroscope are adequate alternative endoscopes. Once the J tube seal reaches the silicon portion of the PEG tube and further introduction is needed, a 5- to 10-cm portion of the silicon is cut using the sharp tip of the scissors provided with the PEG tube kit (Fig. 1). These steps of “peel and advance” are repeated until the J tube is advanced to the desired location and clipped to the jejunum mucosa. This technique allows optimal J tube placement without gastric looping or a too-short jejunal J tube insertion (Fig. 2). We followed all patients over 4 weeks. No PEG-J tube replacement adverse events were noted. Two patients had abdominal imaging at 4 weeks documenting optimal J tube placement without J tube loops or short J tubes resulting in proximal migration of the J tube (Video 1, available online at www.giejournal.org). All authors disclosed no financial relationships. https://www.videogie.org/cms/asset/9bec0238-72be-450f-8dbd-3862997703e4/mmc1.mp4Loading ... Download .mp4 (104.88 MB) Help with .mp4 files Video 1PEG-J tube placement with optimization of J tube insertion.

Oxidative vaporization etching for molybdenum tip formation in air

Oxidative vaporization in air using a flame with a temperature range of 1950–2300 K was employed for controlling the tip shape made from a nipper-cut metal molybdenum (Mo) wire edge. An extremely high vapor pressure of MoO3 generated on the Mo surface in flame is a driving force behind the tip shape formation. Since the MoO3 vaporization rate follows the flame temperature gradient, we could control the tip apex shape by selecting the proper flame etching condition. The best condition to obtain a sharp tip apex based on statistical tests of dozens of Mo tips was obtained by Mo wire edge insertion into the 2100 K flame from the side for one second. This was repeated twice, which reproducibly provided a tip apex with a radius of 50–100 nm and a cone angle of 20–30 degrees. The present Mo tips, fabricated without aqueous solutions, were examined for their suitability as probe tips through air-scanning tunneling microscopy (STM), ultrahigh vacuum STM, field emission spectroscopy, and conductance measurements.

Effect of Copper Electrode Geometry on Electrofreezing of the Phase-Change Material CaCl2·6H2O

Abstract The development of effective active thermal energy storage systems requires an understanding of how electrode geometry affects the electrofreezing process. This study aimed to observe the nucleation behavior of an inorganic phase-change material, CaCl2·6H2O, using a DC electric field and various copper electrode geometries. The effects of both the electrode diameter ( d = 0.5 d=0.5 and 0.7 mm) and the tip shape (flat and sharp end surfaces) were investigated. Data analysis was performed to reveal the nucleation temperature, freezing temperature, supercooling degree, supercooling time, and crystallization time period. The copper electrode with the larger diameter was found to result in a higher nucleation temperature, a smaller supercooling degree, faster nucleation, and a shorter crystallization time period. Moreover, changing from a flat tip to a sharp tip decreased the nucleation temperature and increased the supercooling degree. This study showed that the electrode geometry plays an important role in the phase-change behavior of CaCl2·6H2O.

Fluid interfaces with very sharp tips in viscous flow

When a fluid interface is subjected to a strong viscous flow, it tends to develop near-conical ends with pointed tips so sharp that their radius of curvature is undetectable. In microfluidic applications, tips can be made to eject fine jets, from which micrometer-sized drops can be produced. Here we show theoretically that the opening angle of the conical interface varies on a logarithmic scale as a function of the distance from the tip, owing to nonlocal coupling between the tip and the external flow. Using this insight we are able to show that the tip curvature grows like the exponential of the square of the strength of the external flow and to calculate the universal shape of the interface near the tip. Our experiments confirm the scaling of the tip curvature as well as of the interface's universal shape. Our analytical technique, based on an integral over the surface, may also have far wider applications, for example treating problems with electric fields, such as electrosprays.

Laser Sharpening of Carbon Fiber Microelectrode Arrays for Brain Recording.

Microwire microelectrode arrays (MEAs) are implanted in the brain for recording neuron activities to study the brain function. Among various microwire materials, carbon fiber stands out due to its small diameter (5-10 μm), relatively high Young's modulus, and low electrical resistance. Microwire tips in MEAs are often sharpened to reduce the insertion force and prevent the thin microwires from buckling. Currently, carbon fiber MEAs are sharpened by either torch burning, which limits the positions of wire tips to a water bath surface plane, or electrical discharge machining, which is difficult to implement to the nonelectrically conductive carbon fiber with parylene-C insulation. A laser-based carbon fiber sharpening method proposed in this study enables the fabrication of carbon fiber MEAs with sharp tips and custom lengths. Experiments were conducted to study effects of laser input voltage and transverse speed on carbon fiber tip geometry. Results of the tip sharpness and stripped length of the insulation as well as the electrochemical impedance spectroscopy measurement at 1 kHz were evaluated and analyzed. The laser input voltage and traverse speed have demonstrated to be critical for the sharp tip, short stripped length, and low electrical impedance of the carbon fiber electrode for brain recording MEAs. A carbon fiber MEA with custom electrode lengths was fabricated to validate the laser-based approach.

Superior antibacterial activity of sulfur-doped g-C3N4 nanosheets dispersed by Tetrastigma hemsleyanum Diels & Gilg's polysaccharides-3 solution

Bacterial resistance has become a serious global health issue over the past decades due to the misuse and abuse of antibiotics. The development of effective antibacterial drugs with a new antibacterial mechanism is thus very critical. At present, there are many reports on the antibacterial properties and mechanisms of two-dimensional materials. Currently, the modification of g-C3N4 materials, as widely used two-dimensional materials, has become a key step in extending their potential applications in the field of antimicrobial therapy. In the present work, we prepared sulfur-doped g-C3N4 nanosheets (SCNNSs), which have good water dispersibility and sharp tips. The electrostatic interaction of SCNNSs with Tetrastigma hemsleyanum Diels & Gilg's polysaccharide-3 (THDG-3) provides a new strategy that can improve the killing efficiency of SCNNSs. In addition, THDG-3 can rapidly inhibit bacterial proliferation in the early stage of administration. Combined with the antibacterial activity of the SCNNSs, TPS/SCNNSs can inhibit bacteria for a long time. Scanning electron microscopy (SEM) observation of Escherichia coli (E. coli) after administration of the materials revealed that the bacterial cells were ruptured and their intracellular contents were completely separated from the cell membrane. Therefore, we speculate that the bactericidal mechanism of the TPS/SCNNSs probably involves cell membrane damage. In summary, TPS/SCNNSs achieve fast, long-term, dual-function bacteriostatic properties.

Stiffness Tomography of Ultra-Soft Nanogels by Atomic Force Microscopy.

The softness of nanohydrogels results in unique properties and recently attracted tremendous interest due to the multi‐functionalization of interfaces. Herein, we study extremely soft temperature‐sensitive ultra‐low cross‐linked (ULC) nanogels adsorbed to the solid/water interface by atomic force microscopy (AFM). The ultra‐soft nanogels seem to disappear in classical imaging modes since a sharp tip fully penetrates these porous networks with very low forces in the range of steric interactions (ca. 100 pN). However, the detailed evaluation of Force Volume mode measurements allows us to resolve their overall shape and at the same time their internal structure in all three dimensions. The nanogels exhibit an extraordinary disk‐like and entirely homogeneous but extremely soft structure—even softer than polymer brushes. Moreover, the temperature‐sensitive nanogels can be switched on demand between the ultra‐soft and a very stiff state.

Stiffness Tomography of Ultra‐Soft Nanogels by Atomic Force Microscopy

AbstractThe softness of nanohydrogels results in unique properties and recently attracted tremendous interest due to the multi‐functionalization of interfaces. Herein, we study extremely soft temperature‐sensitive ultra‐low cross‐linked (ULC) nanogels adsorbed to the solid/water interface by atomic force microscopy (AFM). The ultra‐soft nanogels seem to disappear in classical imaging modes since a sharp tip fully penetrates these porous networks with very low forces in the range of steric interactions (ca. 100 pN). However, the detailed evaluation of Force Volume mode measurements allows us to resolve their overall shape and at the same time their internal structure in all three dimensions. The nanogels exhibit an extraordinary disk‐like and entirely homogeneous but extremely soft structure—even softer than polymer brushes. Moreover, the temperature‐sensitive nanogels can be switched on demand between the ultra‐soft and a very stiff state.

SSNOMBACTER: A collection of scattering-type scanning near-field optical microscopy and atomic force microscopy images of bacterial cells.

BackgroundIn recent years, a variety of imaging techniques operating at nanoscale resolution have been reported. These techniques have the potential to enrich our understanding of bacterial species relevant to human health, such as antibiotic-resistant pathogens. However, owing to the novelty of these techniques, their use is still confined to addressing very particular applications, and their availability is limited owing to associated costs and required expertise. Among these, scattering-type scanning near field optical microscopy (s-SNOM) has been demonstrated as a powerful tool for exploring important optical properties at nanoscale resolution, depending only on the size of a sharp tip. Despite its huge potential to resolve aspects that cannot be tackled otherwise, the penetration of s-SNOM into the life sciences is still proceeding at a slow pace for the aforementioned reasons.ResultsIn this work we introduce SSNOMBACTER, a set of s-SNOM images collected on 15 bacterial species. These come accompanied by registered Atomic Force Microscopy images, which are useful for placing nanoscale optical information in a relevant topographic context.ConclusionsThe proposed dataset aims to augment the popularity of s-SNOM and for accelerating its penetration in life sciences. Furthermore, we consider this dataset to be useful for the development and benchmarking of image analysis tools dedicated to s-SNOM imaging, which are scarce, despite the high need. In this latter context we discuss a series of image processing and analysis applications where SSNOMBACTER could be of help.

Direct Measurement of Nano-Sized Lithium Dendrite Growth Stress By in-Situ TEM

The all-solid-state Li-ion battery is attracting attention because it enables the use of a high capacity Li metal anode while easing safety concerns by employing a stable solid electrolyte. It is expected that the use of a solid electrolyte with a high shear modulus would prevent the growth and propagation of destructive lithium dendrites. However, dendrites still penetrate solid electrolytes, causing the cell to short, and the exact mechanism is still under debate. Additionally, a large compressive stress is generally applied to the cell to maintain good contact between the electrode and the solid electrolyte, which may affect the lithium deposition process and the stability of the solid electrolyte. Therefore, understanding the relationship between the mechanical stress and lithium dendrite growth is key in decoding the dendrite penetration process. We developed an in-situ transmission electron microscopy (TEM) technique to directly observe the early stages of the lithium dendrite growth process and obtain the initial force on a Li dendrite. Setup involved a sharp conductive cantilever tip contacting a relatively flat lithium metal surface and applying a potential bias initiating lithium plating at the tip. The in-situ TEM observation, as schematically illustrated in the figure below, commenced with dendrite nucleation (A) and progressed as a nano-sized lithium pillar growing vertically causing increasing stress (B). The dendrite continued its vertical growth until the force reached a critical value (C). The pillar then started to expand horizontally (D). The measured critical stress is much higher than the yield stress of bulk lithium, showing lithium can locally introduce high stresses on solid electrolytes without yielding. It is suggested that horizontal lithium growth helped to release dendritic stress buildup, unveiling a promising strategy to implement in future investigations of how to mitigate penetration through the solid electrolyte, preventing the dendrite from reaching the cathode and causing a catastrophic short. The information obtained in this work is useful for constructing a constitutive model of a lithium plating process in an all-solid-state system and understanding the mechanical stability of solid electrolytes particularly at the early stage of lithium deposition. Figure 1

Surface Plasmon Resonance-Induced Diffusion-Limited Aggregation in the Formation of Ag/AgOx Nanonetworks as Broad-Spectrum Transparent Conductors

Based on the generation and transportation of hot electrons and the diffusion-limited aggregation of Ag+ ions induced by the surface plasmon resonance of surface Ag nanoparticles (NPs) with ambient moisture, we develop a new mechanism for fabricating a surface Ag nanonetwork (NNW) structure on a slightly conductive template through Ag NP reorganization and AgOx formation. Such an extended NNW structure consists of distributed Ag NPs covered and connected by AgOx to form a highly transparent conductive network. Its sheet resistance is as low as ∼140 Ω/square while its transmittance lies between 80 and 90%. The process of diffusion-limited aggregation is regulated by electrostatic induction between diffuse Ag+ ions in a thin surface water layer condensed from moisture and the sharp tips of an NNW structure during its formation. Oxygen atoms can be dissociated from AgOx when a post-thermal treatment at a temperature higher than 412 °C is applied, leaving behind an Ag thin layer, which still connects the remaining Ag NPs to form a different conductive network of ∼240 Ω/square in sheet resistance. Such an NNW structure can stand an elevated temperature up to ∼400 °C and is thermally stable. It can extend the transparent spectrum into ultraviolet and near-infrared ranges and can be applied to touch-panel displays, ultraviolet light-emitting diodes, and flexible optoelectronics devices.

Facilitation of the thermochemical mechanism in NiO-based resistive switching memories via tip-enhanced electric fields

Transition metal oxides have attracted considerable attention as a switching material for resistive random access memory (RRAM) based on the thermochemical mechanism (TCM). However, the heat energy required for resistance switching is applied to the entire area of the RRAM without position selectivity, causing random growth of conductive filaments (CFs) and degrading device performance. This study showed that structured electrodes can promote the TCM in nickel oxide (NiO)-based RRAM by enhancing the electric field within the switching material and controlling Joule heat generation locally. Pyramid-structured electrodes with an extremely sharp tip prepared by the template-stripping method achieve an electric field in the tip region that is ∼5 times larger than that of conventional planar electrodes. The tip-enhanced electric field can induce a local temperature rise, which facilitates the TCM for nucleation and CF growth. The resulting RRAMs exhibit low and reliable forming, SET and RESET voltages (1.96±0.14V, 1.44±0.12V, and 0.64±0.05V, respectively). Moreover, their retention time and resistance ratio (RHRS/RLRS) are greatly improved, by 10 and 102 times, respectively, compared to planar devices. This approach can achieve position selectivity in TCM-based resistance switching, and could lead to the development of high-performance RRAM.

Study of Grass Shoot-Shape Silicon Nanowires Grown by Thermal Chemical Vapor Deposition

Grass shoot-shape silicon nanowires (SiNWs) with sharp tip have been successfully synthesized on an n-type Si (111) substrates at temperatures of 700 °C and various times using a thermal chemical vapor deposition (TCVD) technique. Au thin film (~10 nm thick) as catalyst were deposited on Si (111) substrates by a radio frequency magnetron sputtering system. Effect of the growth time on morphology of SiNWs has been reported. The morphologies, growth mechanism, homogeneity and crystalline structure of the nanowires were studied by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray diffractometer (XRD) and Raman spectroscopy. SEM images depict morphology of wires in form of nanoneedles (NNs) with base diameter of 60 nm, tip diameter of ∼5 nm and length up to 3 μm. TEM analysis revealed that the nanowires have core-shell structure with Au nanoparticles on the tip. Raman spectrum of as-grown SiNNs exhibited a transverse optical (TO) phonon mode. The obtained results have shown radius and length of the SiNNs increased with increase in growth time.