Recent advances in materials science allowed the incorporation of advanced two dimensional (2D) materials in electronic devices. For example, field effect transistors (FETs) using graphene channels ...have shown unprecedented carrier mobility at room temperature, which is further complemented by its intrinsic flexibility, transparency, chemical stability and even thermal heat dissipation. Other 2D materials such as transition metal dichalcogenides (TMDs) can provide additional functionalities to the devices, such as band gap induced high ON/OFF ratios in FETs. Interestingly, these 2D metallic (graphene) and 2D semiconducting materials (2D/TMDs) have been mainly implemented in devices using traditional three dimensional (3D) insulators, such as HfO2, Al2O3 and SiO2, which may not be the best solution given the complex and defective interface bonding. For this reason recently 2D insulators have been started to be used as dielectric in different electronic devices, showing interesting phenomena. A 2D insulator differs from traditional 3D insulators in that it holds a layered structure, in which the bonding in plane is covalent while the plane-to-plane interaction is governed by van der Waals interactions. This genuine structure has been demonstrated to remarkably alter some reliability phenomena like, for example, the entire dielectric breakdown process. In this review, we analyze the performance of 2D layered dielectrics, focusing on hexagonal boron nitride. Different synthesis methods, electrical characterization, reliability and variability analyses, as well as dielectric breakdown process are discussed. Moreover, it should be highlighted that, in many device applications (like capacitors or resistive switching memories), 2D dielectrics may not require the annoying transfer process usually required for graphene and 2D/TMDs, which further facilitates its introduction in the industry.
In this manuscript, we review the use of hexagonal boron nitride as dielectric, paying special attention to the synthesis methods, nanoscale homogeneity, reliability and dielectric breakdown process. In summary, hexagonal boron nitride is much more homogeneous and stable against electrical fields than other 3D dielectrics (such as HfO2) which can provide some advantages like reduced scattering effects and predictable dielectric breakdown process. Display omitted
•The synthesis, homogeneity, reliability and dielectric breakdown process of hexagonal boron nitride (h-BN) is reviewed.•BN is more homogeneous and stable vs. electrical fields than HfO2.•The layer-by-layer dielectric breakdown behavior of h-BN may have deep influence in the reliability of electronic devices.
The atomic force microscope is one of the most widespread tools in science, but many suppliers do not provide a competitive solution to make experiments in controlled atmospheres. Here, we provide a ...solution to this problem by fabricating a fast-response and user-friendly environmental chamber. We corroborate the correct functioning of the chamber by studying the formation of local anodic oxidation on a silicon sample (biased under opposite polarities), an effect that can be suppressed by measuring in a dry nitrogen atmosphere. The usefulness of this chamber goes beyond the example here presented, and it could be used in many other fields of science, including physics, mechanics, microelectronics, nanotechnology, medicine, and biology.
Injectable hydrogels have attracted a lot of attention in drug delivery, however, their capacity to deliver water-insoluble or hydrophobic anti-cancer drugs is limited. Here, we developed injectable ...graphene oxide/graphene composite supramolecular hydrogels to deliver anti-cancer drugs. Pluronic F-127 was used to stabilize graphene oxide (GO) and reduced graphene oxide (RGO) in solution, which was mixed with α-cyclodextrin (α-CD) solution to form hydrogels. Native hydrogel was used as control. GO or RGO slightly shortened gelation time. The storage and loss moduli of the hydrogels were tracked by dynamic force measurement. The storage modulus of GO or RGO composite hydrogels was larger than that of the native hydrogel. Hydrogels were unstable in solution and eroded gradually. GO or RGO in Pluronic F-127 solution could potentially improve the solubility of the water-insoluble anti-cancer drug camptothecin (CPT), especially with large drug-loaded CPT amount. Drug release behaviors from solutions and hydrogels were characterized. The nanocomponents (GO or RGO) were able to bind more drug molecules either for CPT or for doxorubicin hydrochloride (DXR) in solution. Therefore, GO or RGO composite hydrogel could potentially enable better controlled and gentler drug release (for both CPT and DXR) than native hydrogel.
The use of 2D materials to improve the capabilities of electronic devices is a promising strategy that has recently gained much interest in both academia and industry. However, while the research in ...2D metallic and semiconducting materials is well established, detailed knowledge and applications of 2D insulators are still scarce. In this paper, the presence of resistive switching (RS) in multilayer hexagonal boron nitride (h‐BN) is studied using different electrode materials, and a family of h‐BN‐based resistive random access memories with tunable capabilities is engineered. The devices show the coexistence of forming free bipolar and threshold‐type RS with low operation voltages down to 0.4 V, high current on/off ratio up to 106, and long retention times above 10 h, as well as low variability. The RS is driven by the grain boundaries (GBs) in the polycrystalline h‐BN stack, which allow the penetration of metallic ions from adjacent electrodes. This reaction can be boosted by the generation of B vacancies, which are more abundant at the GBs. To the best of our knowledge, h‐BN is the first 2D material showing the coexistence of bipolar and threshold RS, which may open the door to additional functionalities and applications.
The presence of resistive switching in multilayer hexagonal boron nitride (h‐BN) is studied using metallic and graphene electrodes, and a family of h‐BN‐based resistive random access memories with tunable capabilities is engineered.
Considering that conventional hydrogels showed limited capabilities of controlling hydrophobic drug loading and releasing and graphene materials had interactions with hydrophobic drugs, we designed a ...graphene oxide (GO) composite hydrogel for drug delivery. But GO could not disperse well in monomer solution and agglomerated badly. Thus, water-soluble GO (GO-tripolymer) was first prepared under the stabilization of amphiphilic polymer, Pluronic F-127. The GO-tripolymer showed good solubility in PBS with the increase of polymer concentration. All GO-tripolymer solutions had the same UV absorption peaks as GO. Then, GO composite hydrogels (HNG hydrogels) were formed by the polymerization of hydroxyethyl methacrylate (HEMA), N-Vinyl pyrrolidone (NVP) and GO-tripolymer mixture. The introduction of GO-tripolymer had little effect on the gelation time and equilibrium swelling ratio of hydrogel. The freeze-drying hydrogel showed porous structure. The pore size decreased and the rough surface was detected with the increase of GO concentration. HNG hydrogel could load more puerarin and norfloxacin than conventional hydrogel (HN hydrogel). Moreover, HNG hydrogel could control puerarin and norfloxacin release more steadily than HN hydrogel. HNG exhibited low cytotoxicity.
Identifying risk factors associated with obesity after craniopharyngioma (CP) resection is pivotal for the prediction and prevention of postoperative obesity. Although multiple elegant studies have ...investigated this issue, studies focusing on Asian pediatric patients are missing. Herein, we retrospectively analyzed the risk factors associated with obesity after childhood-onset CP surgery in our center, aiming to provide insights into approaches reducing the occurrence of postoperative obesity.
The clinical data of 53 children with CP who met the inclusion criteria from July 2011 to August 2020 in our center were collected for retrospective analysis. Univariate and multivariate logistic retrospective analyses were used to identify independent risk factors contributing to postoperative obesity. A review of the available literature reporting the risk factors associated with obesity after CP surgery over the past two decades was performed for comparison.
The median age at diagnosis of this cohort was 11.0 years, with a median follow-up of 44.0 months (range = 8–119 months). Eighteen (34.0%) experienced obesity at the last follow-up. Multivariate logistic regression analysis showed preoperative body mass index standard deviation score (odds ratio OR, 1.71; 95% confidence interval CI: 1.01–2.90; P = 0.046), preoperative hypothalamic involvement (OR, 29.38; 95% CI: 1.76–490.66; P = 0.019), and age at diagnosis (OR, 0.76; 95% CI: 0.61–0.95; P = 0.016) were independent risk factors for obesity after childhood-onset CP resection.
Our results combined with previous literature support preoperative body mass index standard deviation score, preoperative hypothalamic involvement, and age at diagnosis are the independent risk factors associated with obesity after childhood-onset CP resection.
Purpose
Identifying relationships between craniopharyngiomas (CPs) and contiguous structures, and tumor origin are crucial for treatments. This study attempted to explore the relationships and tumor ...origin.
Methods
CPs that underwent endoscopic surgeries were enrolled. The interfacial specimens of CPs attaching the hypothalamus, pituitary stalk (PS), pituitary grand (PG), optic chiasma (OC) and brain tissue (BT) were pathologically examined. Boundaries between CPs and these structures were observed during operations. Expression of β-catenin and stem cell markers were analyzed to explore the tumor origin. Outcomes of patients were assessed.
Results
A total of 34 CPs were categorized into two groups based on the locations of finger-like protrusions (FP). Group A comprised 18 CPs with FP only present in the specimens attaching to hypothalamus. The surface of these CPs was fused with hypothalamus under endoscopic videos. However, the specimens attaching to the PS, PG, OC, and BT showed no FP. Clear boundaries was observed between these CPs and these structures. Group B comprised 16 CPs with FP only present in the specimens attaching to PS. The tumor surface was fused with PS. Specimens attaching to the hypothalamus, PG, OC and BT showed no FP. Clear boundary was observed among these CPs with these structures. These results implied CPs only invaded a certain part of hypothalamic-pituitary axis. β-catenin and stem cells markers mainly distributed in the FP tissues of both groups. Patients in group B achieved better outcomes than group A.
Conclusions
CPs only invade the hypothalamic-pituitary axis with FP and the FP would be the tumor origin.
During the last decade, an uncountable amount of graphene prototype devices have been reported, but unfortunately none of them has faced mass production and commercialization. One of the main reasons ...is that graphene technologies are highly affected by variability problems. Although graphene presents almost unbeatable chemical and physical properties, the development of graphene devices has been heavily hindered by the difficulty of fabricating homogeneous and identical devices, due to the presence of uncontrollable amounts of defects. One of the most preoccupying aspects in the development of graphene technology is the lack of reported variability studies. Here we present the first thorough variability analysis for a graphene device, namely graphene-coated nanoprobes for atomic force microscopes. The relevancy of this work is increased by the use of a fabrication method capable of large scalability: liquid-phase exfoliated graphene inks. Our results indicate that, for this device, the presence of graphene does not introduce any performance deviation indicating that, from the variability point of view, this device is ready for mass production. Similar variability analyses should be applied to other devices in order to detect which graphene technologies are not affected by variability problems, facilitating them the introduction of graphene prototypes in the market.
•Fast and cost-effective methodology is employed for the fabrication of graphene coat AFM nanoprobes.•First quantified analysis of graphene devices indicates the intrinsic variability of the AFM technique.•The electrical properties of graphene-coated AFM tips show lower variability than those recorded with uncoated counterparts
Moisture and water penetration is one of the main phenomena altering the electrical characteristics and performance of resistive switching (RS) devices based on metal/insulator/metal nanojunctions. ...However, the effect of these phenomena in RS devices made of two dimensional (2D) materials has never been studied. In this paper it is shown that 2D materials based RS devices exposed to high relative humidity environments develop dielectric screening effects. The devices measured right after fabrication show a yield of 95% and bipolar RS characteristics, while after exposure to humid environments for two months the yield decreases to 65%. More than 30% of the devices show much lower currents than the fresh counterparts, and at high voltages they exhibit clear dielectric screening effects. This behavior is even more accentuated in RS devices that require the transfer of the 2D material, and we observe that a baking step at 120 °C for 5 min can mitigate this effect.
Dielectric screening is experimentally observed in hexagonal boron nitride based resistive switching devices. The penetration of moisture is the key factor producing a reduction of current and slow of the dielectric breakdown event. This behavior can be mitigated by adding a backing step during the fabrication process of the devices.
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