A STUDY ON ATOMICALLY THIN ULTRA SHORT CONDUCTING CHANNELS, BREAKDOWN, AND ENVIRONMENTAL EFFECTS

We have developed a novel method of producing ultra-short channel graphene field effect devices on SiO2 substrates and have studied their electrical transport properties. A nonlinear current behavior is observed coupled with a quasi-saturation effect. An analytical model is developed to explain this behavior using ballistic transport, where the charge carriers experience minimal scattering. We also observe multilevel resistive switching after the device is electrically stressed. In addition, we have studied the evolution of the electrical transport properties of few-layer graphene during electrical breakdown. We are able to significantly increase the time scale of break junction formation, and we are able to observe changes occurring close to breakdown regime. A decrease in conductivity along with p−type doping of the graphene channel is observed as the device is broken. The addition of structural defects generated by thermal stress caused by high current densities is attributed to the observed evolution of electrical properties during the process of breakdown. We have also studied the effects of the local environment on graphene devices. We encapsulate graphene with poly(methyl methacrylate) (PMMA) polymer and study the electrical transport through in situ measurements. We have observed an overall decrease in doping level after low-temperature annealing in dry-nitrogen, indicating that the solvent in the polymer plays an important role in doping. For few-layer encapsulated graphene devices, we observe stable n−doping. Applying the solvent onto encapsulated devices demonstrates enhanced hysteretic switching between p and n−doped states

Nanogaps on Atomically Thin Materials as Non-Volatile Read/Writable Memory Devices

The present invention relates to the presence of nanogaps across a metal dispersed over an atomically-thin material, such that the nanogap exposes the atomically-thin material. The resulting device offers an ultra-short gap with ballistic transport and demonstrated switching in the presence of a gate or dielectric material in close proximity to the channel

Electrostatic Force Microscopy and Electrical Isolation of Etched Few-Layer Graphene Nano-Domains

Nanostructured bi-layer graphene samples formed through catalytic etching are investigated with electrostatic force microscopy. The measurements and supporting computations show a variation in the microscopy signal for different nano-domains that are indicative of changes in capacitive coupling related to their small sizes. Abrupt capacitance variations detected across etch tracks indicates that the nano-domains have strong electrical isolation between them. Comparison of the measurements to a resistor-capacitor model indicates that the resistance between two bi-layer graphene regions separated by an approximately 10 nm wide etch track is greater than about 1×1012 Ω with a corresponding gap resistivity greater than about 3×1014 Ω⋅nm . This extremely large gap resistivity suggests that catalytic etch tracks within few-layer graphene samples are sufficient for providing electrical isolation between separate nano-domains that could permit their use in constructing atomically thin nanogap electrodes, interconnects, and nanoribbons

Preparation and characterization of Fe-doped TiO<SUB>2</SUB> powders for solar light response and photocatalytic applications

Different amounts of Fe-doped TiO2 (with 0.1 to 10 wt.% Fe) powders were prepared at temperatures in the range of 400 and 800 °C following a conventional co-precipitation technique and were thoroughly characterized by means of X-ray diffraction (XRD), Fourier-transform infrared (FT-IR), Fourier-transform Raman (FT-Raman), diffuse reflectance spectroscopy (DRS), BET surface area, zeta potential and flat band potential measurements. Photocatalytic ability of Fe-doped TiO2 powders was evaluated by means of methylene blue (MB) degradation experiments conducted under the irradiation of simulated solar light. Characterization results suggested that as a dopant Fe stabilized TiO2 in the form of anatase phase, reduced its band gap energy and adjusted its flat band potentials in such a way that these powders can be employed for photoelectrolysis of water into hydrogen and oxygen in photoelectrochemical (PEC) cells. The 0.1 wt.% Fe-doped TiO2 exhibited highest activity in the photocatalytic degradation of MB. The kinetic studies revealed that the MB degradation reaction follows the Langmuir-Hinshelwood first order reaction rate

Nonlinear Ballistic Transport in an Atomically Thin Material

Ultrashort devices that incorporate atomically thin components have the potential to be the smallest electronics. Such extremely scaled atomically thin devices are expected to show ballistic nonlinear behavior that could make them tremendously useful for ultrafast applications. While nonlinear diffusive electron transport has been widely reported, clear evidence for intrinsic nonlinear ballistic transport in the growing array of atomically thin conductors has so far been elusive. Here we report nonlinear electron transport of an ultrashort single-layer graphene channel that shows quantitative agreement with intrinsic ballistic transport. This behavior is shown to be distinctly different than that observed in similarly prepared ultrashort devices consisting, instead, of bilayer graphene channels. These results suggest that the addition of only one extra layer of an atomically thin material can make a significant impact on the nonlinear ballistic behavior of ultrashort devices, which is possibly due to the very different chiral tunneling of their charge carriers. The fact that we observe the nonlinear ballistic response at room temperature, with zero applied magnetic field, in non-ultrahigh vacuum conditions and directly on a readily accessible oxide substrate makes the nanogap technology we utilize of great potential for achieving extremely scaled high-speed atomically thin devices

Hot snare vs. cold snare polypectomy for endoscopic removal of 4\u200a-\u200a10\u200amm colorectal polyps during colonoscopy: a systematic review and meta-analysis of randomized controlled studies

Introduction \u2002In recent years, cold snare polypectomy (CSP) has increasingly been used over hot snare polypectomy (HSP) for the removal of colorectal polyps (4\u200a-\u200a10\u200amm in size). However, the optimal technique (CSP vs. HSP), in terms of complete polyp resection and complications, is uncertain. Our aim was to compare incomplete resection rate (IRR) of polyps and complications using CSP vs. HSP. Methods \u2002Randomized controlled studies (RCTs) comparing CSP and HSP for removal of 4\u200a-\u200a10\u200amm colorectal polyps were considered. Studies were included in the analysis if they obtained biopsy specimens from the resection margin to confirm the absence of residual tissue and reported complications. IRR and complication rate were the outcome measures. Pooled rates were reported as Odds Ratios (OR) or risk difference with 95\u200a% Confidence Interval (CI). Results \u2002In total, three RCTs were included in the final analysis. A total of 1051 patients with 1485 polyps were randomized to either HSP group (n\u200a=\u200a741 polyps) or CSP group (n\u200a=\u200a744 polyps). The overall IRR did not differ between the two groups (HSP vs. CSP: 2.4\u200a% vs. 4.7\u200a%; OR 0.51, 95\u200a%CI 0.13\u200a-\u200a1.99, P \u200a=\u200a0.33, I2 \u200a=\u200a73\u200a%). The HSP group had a lower rate of overall complications compared to the CSP group (3.7\u200a% vs. 6.6\u200a%; OR 0.53, 95\u200a% CI 0.3\u200a-\u200a0.94, P \u200a=\u200a0.03, I2 \u200a=\u200a0&nbsp;%). Polyp retrieval rates were not different between the two groups (99\u200a% vs. 98.1\u200a%). Conclusion \u2002Our results suggest that HSP and CSP techniques can be effectively used for the complete removal of 4\u200a-\u200a10\u200amm colorectal polyps; however, HSP has a lower incidence of overall complications

Abstract Number ‐ 22: Hemorrhagic Outcomes in Patients Demonstrating Early Venous Filling After Mechanical Thrombectomy For Acute Ischemic Stroke

Introduction Endovascular thrombectomy (EVT) for acute ischemic infarcts with large vessel occlusion have been shown to improve functional outcomes. However, there is still the risk of hemorrhagic transformation (HT). Early identification of patients at risk of HT is paramount to enhance EVT outcomes. EVF can be an indicator of the hyperemia that occurs following an infarct. We evaluated if early venous filling (EVF) defined as contrast filling of any cerebral vein within the arterial phase on angiogram can predict individuals at a higher risk of HT after EVT. Methods From the SELECT cohort,EVT patients with evaluable digital subtraction angiography were included in the study. Baseline clinical and imaging characteristics as well as clinical and hemorrhagic outcomes were compared between patients demonstrating EVF and no EVF. Association between EVF with symptomatic ICH and parenchymal hemorrhage was examined using multivariable logistic regression models. Results 46/254 (18%) patients had EVF at the end of the procedure. Age and NIHSS were similar between the patients with and without EVF, although patients with EVF presented earlier (1.39 (0.88‐2.75) hours vs 2.62 (1.10‐4.28) hours, p = 0.024), and demonstrated lower CT ASPECTS (7 (6‐9) vs 8 (7‐9), p = 0.022). The presence of EVF was associated with significantly higher odds of sICH (EVF: 8.7% vs no EVF: 5.6%, aOR: 4.72, 95% CI: 1.05‐21.28, p = 0.043) and demonstrated a trend towards higher odds of parenchymal hemorrhage type 1 or 2 (EVF: 10.9% vs no EVF: 6.3%, aOR: 3.64, 95% CI: 0.96‐13.73, p = 0.057) and mortality (EVF: 17% vs no EVF: 12%, aOR: 3.22, 95% CI: 0.93‐11.13, p = 0.064). Functional outcomes did not differ at 90 days between the two groups Conclusions Early identification of EVF may help to identify patients with increased risk of hemorrhagic transformation after EVT. This finding was independent from time last known well. While EVF is suggestive of hyperemia it is also a biomarker of infarct volume and may help to implement early therapeutic measurements to reduce hemorrhagic transformation risk such as strict blood pressure control. Further studies to evaluate EVF as a potential marker for hemorrhagic transformation are required

Solid–Liquid–Vapor Synthesis of Negative Metal Oxide Nanowire Arrays

Nanowires grown using the vapor–liquid–solid (VLS) mechanism are highly attractive components for functional nanomaterials since they grow along unique crystallographic axes to form defect-free single crystals with well-controlled dimensions. To date, however, these free-standing wires have been put to little use, since their ordered arrangement or placement is highly challenging. Here, we report an approach to create ordered arrays of nanoscale interfaces, in which we utilize the reverse of the VLS mechanism (the solid–liquid–vapor (SLV) mechanism) to etch the inverse of a nanowire, a “negative nanowire”, into a single crystal. In this way, we achieve essentially the same array of crystallographic surfaces as would be achieved by growing a large array of nanowires but in a way that creates a single object which is easy to handle. The SLV mechanism is a unique approach in that it is governed by the same crystallography which makes the VLS mechanism attractive but, additionally, poses several key advantages, such as the tendency for negative nanowires to grow along a preferred etch direction inherently leading to arrays of negative nanowires with related alignment and orientation. Here, we present proof-of-principle experiments to show that SLV etching to synthesize negative nanowires can be performed in a nonreactive atmosphere and on single-crystalline zinc oxide and tin­(IV) oxide substrates, demonstrating control over shape, size, alignment, and growth direction