Memristors are a leading candidate for future storage and neuromorphic computing technologies 1-10 due to characteristics such as device scalability, multi-state switching, fast switching speed, high switching endurance and CMOS compatibility 6,[11][12][13][14][15][16] . Most research and development efforts have been focused on improving device switching performance in optimal conditions, and the reliability of memristors in harsh environments such as at high temperature and on bending substrates has so far received much less attention. Since the programming processes in memristors based on traditional oxide materials mostly rely on ion moving and ionic valence changing 16,17 , the thermal instability at elevated temperatures could result in device failure 18 . Thus, to the best of our knowledge, there has been no reliable switching behaviours observed in memristors at temperatures above 200 °C 18,19 , which limits their potential application in harsh electronics such as those demanded in aerospace, military, automobile, geothermal, oil and gas industries. Common high temperature electronic materials, such as SiC and III-nitride 20,21 , are not adoptable in fabricating memristors, and therefore searching for new materials and structures for robust memristors with good performance is desirable.By stacking two-dimensional (2D) layered materials together 22-30 , van der Waals (vdW) heterostructures can combine the superior properties of each 2D component. 2D materials have shown excellent structural stability 31,32 and electrical properties, which could provide significant improvements in the robustness of electronic devices. For example, graphene possesses unparalleled breaking strength, and ultra-high thermal and chemical stabilities 33 ; molybdenum disulfide (MoS 2 ) has shown good flexibility, large Young's modulus (comparable to stainless steel), 34 and excellent thermal stability up to 1,100 °C 32 ; and various functionalized 2D material layers, or certain grain boundaries within 2D materials, have shown switching behaviours [35][36][37][38][39][40][41][42][43][44] . Since both the thickness and roughness of 2D layered materials can be controlled accurately at the atomic scale, the reliability and uniformity of the electronic devices based on such materials and their vdW heterostructures could also be optimized.In this Article, we report robust memristors based on a vdW heterostructure made of fully layered 2D materials (graphene/MoS 2−x O x / graphene), which exhibit repeatable bipolar resistive switching with endurance up to 10 7 and high thermal stability with an operating temperature of up to 340 °C. The MoS 2−x O x layer was found to be responsible for the high thermal stability of the devices by performing high temperature in situ high-resolution transmission electron microscopy (HRTEM) studies. Further in situ scanning transmission electron microscopy (STEM) investigations on the cross section of a functional device revealed a well-defined conduction channel and a switching mechanism based on the migr...

No abstract

No abstract

No abstract

Two-dimensional materials with out-of-plane (OOP) ferroelectric and piezoelectric properties are highly desirable for the realization of ultrathin ferro- and piezoelectronic devices. We demonstrate unexpected OOP ferroelectricity and piezoelectricity in untwisted, commensurate, and epitaxial MoS 2 /WS 2 heterobilayers synthesized by scalable one-step chemical vapor deposition. We show d 33 piezoelectric constants of 1.95 to 2.09 picometers per volt that are larger than the natural OOP piezoelectric constant of monolayer In 2 Se 3 by a factor of ~6. We demonstrate the modulation of tunneling current by about three orders of magnitude in ferroelectric tunnel junction devices by changing the polarization state of MoS 2 /WS 2 heterobilayers. Our results are consistent with density functional theory, which shows that both symmetry breaking and interlayer sliding give rise to the unexpected properties without the need for invoking twist angles or moiré domains.

Layered metal chalcogenide materials provide a versatile platform to investigate emergent phenomena and two-dimensional (2D) superconductivity at/near the atomically thin limit. In particular, gate-induced interfacial superconductivity realized by the use of an electric-double-layer transistor (EDLT) has greatly extended the capability to electrically induce superconductivity in oxides, nitrides, and transition metal chalcogenides and enable one to explore new physics, such as the Ising pairing mechanism. Exploiting gate-induced superconductivity in various materials can provide us with additional platforms to understand emergent interfacial superconductivity. Here, we report the discovery of gate-induced 2D superconductivity in layered 1T-SnSe, a typical member of the main-group metal dichalcogenide (MDC) family, using an EDLT gating geometry. A superconducting transition temperature T ≈ 3.9 K was demonstrated at the EDL interface. The 2D nature of the superconductivity therein was further confirmed based on (1) a 2D Tinkham description of the angle-dependent upper critical field B, (2) the existence of a quantum creep state as well as a large ratio of the coherence length to the thickness of superconductivity. Interestingly, the in-plane B approaching zero temperature was found to be 2-3 times higher than the Pauli limit, which might be related to an electric field-modulated spin-orbit interaction. Such results provide a new perspective to expand the material matrix available for gate-induced 2D superconductivity and the fundamental understanding of interfacial superconductivity.

How to cite:Please refer to published version for the most recent bibliographic citation information. If a published version is known of, the repository item page linked to above, will contain details on accessing it.

Background : The systemic immune-inflammation index (SII) has been reported to be associated with patient survival in various kinds of solid tumors. However, just few studies have focused on its prognostic value in patients with surgically resected esophageal squamous cell carcinoma (ESCC). Materials and Methods : This study was a single-institution, retrospective analysis of 468 ESCC patients who underwent curative esophagectomy at the Department of Thoracic Surgery, National Cancer Center/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College between 2005 and 2008. The receiver operating curve (ROC) was plotted to compare the discrimination ability of the SII and other inflammatory factors for overall survival (OS) and disease-free survival (DFS). Univariate and multivariate analyses were performed based on the Cox proportional hazards regression model. Results : The SII, neutrophil-lymphocyte ratio (NLR), and platelet-lymphocyte ratio (PLR) were all associated with OS in ESCC patients. The SII, NLR, and PLR were independent prognostic factors for OS (hazard ratio (HR) = 1.604, 95% confidence interval (CI) 1.247-2.063, P < 0.001; HR = 1.396, 95% CI 1.074-1.815, P = 0.013; HR = 1.370, 95% CI 1.067-1.758, P = 0.013, respectively) and DFS (HR = 1.681, 95% CI 1.307-2.162, P < 0.001; HR = 1.376, 95% CI 1.059-1.788, P = 0.017; HR = 1.398, 95% CI 1.089-1.794, P = 0.009, respectively). The area under the curve (AUC) for SII was bigger than NLR, PLR, and MLR (0.553, 0.540, 0.532, and 0.521, respectively). Conclusion : The SII is a simple and promising prognostic predictor for patients with surgically resected ESCC. The prognostic value of SII is superior to those of the NLR, PLR and MLR. Moreover, the SII retained prognostic significance in stage I-II ESCC subgroup (OS, DFS) and stage III ESCC subgroup (DFS).