Memristors or memristive devices are two-terminal nanoionic systems whose resistance switching effects are induced by ion transport and redox reactions in confined spaces down to nanometer or even ...atomic scales. Understanding such localized and inhomogeneous electrochemical processes is a challenging but crucial task for continued applications of memristors in nonvolatile memory, reconfigurable logic, and brain inspired computing. Here we give a survey for two of the most powerful technologies that are capable of probing the resistance switching mechanisms at the nanoscale – transmission electron microscopy, especially in situ, and scanning tunneling microscopy, for memristive systems based on both electrochemical metallization and valence changes. These studies yield rich information about the size, morphology, composition, chemical state and growth/dissolution dynamics of conducting filaments and even individual metal nanoclusters, and have greatly facilitated the understanding of the underlying mechanisms of memristive switching. Further characterization of cyclic operations leads to additional insights into the degradation in performance, which is important for continued device optimization towards practical applications.
The initialization process of the Cu-WO x CBRAM was analyzed via in situ transmission electron microscopy (TEM). For the measurements, lateral-type devices were used to allow for clear microscopic ...observation. A widening of the electrode gap by electrochemical dissolution of the Cu anode during voltage application was experimentally confirmed. These results provide evidence for the chemical reaction occurring at the anode side of the CBRAM. The resistance gradually decreased after multiple voltage sweep applications, and deposits appeared and grew in the electrode gap region. Subsequently, sharp switching occurred, however, clear conductive filaments bridging the two electrodes were not detected within the resolution limit of the in situ TEM. Finally, a series of bipolar operations were realized; with continued bipolar operation, Cu accumulated in the switching region and device degradation occurred.
In-situ observation was performed on a transparent silica substrate during ultrasonic Al ribbon bonding, using a high-speed video camera with differing frame rates, 104 fps and 103 fps, to clarify ...the adhesion behavior. The bonding process was observed as follows. Initially, friction slip occurred, producing multiple island streaks in the direction parallel to the ultrasonic vibration. The island streaks were formed as a scratch, due to surface waviness of the Al ribbon. Momentarily, a belt-shaped bond zone was formed at the center, normally due to the ultrasonic vibration. The island streaks could be clearly observed at 104 fps. However, the central belt zone was unclear and appeared translucent at 104 fps; although it was clear when observed at 103 fps. The island streaks were unclear at 103 fps. The positional relation of the island streaks and the central belt zone was confirmed from in-situ observation results of a twist and peel test of Al ribbon bonded to silica substrate. The central belt zone was between the island streaks and the silica substrate.
Systematic control of electronic transport is demonstrated for Pt/Nb‐doped SrTiO3 (Nb:STO) junctions based on interface engineering with uniform thin layers of TaOx. By inserting TaOx layers ...fabricated via sputter deposition with different O2–Ar ratios (rO2), the current–voltage characteristics and behavior of resistive switching can be well controlled in Pt/Nb:STO junctions. Reduction of the Schottky barrier is also demonstrated via the insertion, and formation of an ideal ohmic contact with a low contact resistance of <3 Ω is achieved for rO2 = 0%. Structural and chemical characterizations show that the resistivity of the TaOx layers depends significantly on rO2 while maintaining a uniform structure independent of the resistivity. This indicates that the insertion of both insulating and metallic interface layers is possible by sputtering TaOx with no need for epitaxial growth, suggesting TaOx's potential as an interface‐layer material. Even with very thin layers (1.0 nm) of TaOx the interfacial properties can be controlled to enhance both ohmic contact formation and resistive switching. These results demonstrate an easy and reliable way to control the characteristics of Pt/Nb:STO junctions and present new insights for their memory and semiconductor device applications.
Systematic control of electron transport is demonstrated for Pt/Nb‐doped SrTiO3 Schottky junctions via interface engineering with TaOx layers having high structural uniformity. Both formation of an ideal ohmic contact and large enhancement of the interface‐type resistive switching are observed in Pt/Nb‐doped SrTiO3 junctions by inserting TaOx layers, suggesting its potential as an interface‐layer material.
This open access book is a compilation of case studies that provide useful knowledge and lessons that derive from on-the-ground activities and contribute to policy recommendations, focusing on the ...relevance of social-ecological production landscapes and seascapes (SEPLS) to “transformative change.” The concept of “transformative change” has been gaining more attention to deal with today’s environmental and development problems, whereas both policy and scientific communities have been increasingly calling for transformative change toward sustainable society. The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) has planned to start the so-called “assessment on transformative change” if approved by the IPBES plenary to be held in 2021. At present, the idea of transformative change, including its scope, methodologies, approaches and strategies, are yet to be clarified. By bringing together all of the different concerns and interests in the land/seascape, SEPLS approaches could provide practical and experience-based insights for understanding and gauging transformative change and identifying determinants of such change. This book explores how SEPLS management relates to the idea of transformative change to further the discussion of sustainable transitions in advancing sustainability science. The introductory chapter is followed by case study chapters offering real-world examples of transformative change as well as a synthesis chapter clarifying the relevance of the case study findings to policy and academic discussions. It will be of interest to scholars, policymakers and professionals in the fields related to sustainable development.
On the basis of the results of our preliminary trial suggesting that aberrant crypt foci (ACF) could be eradicated by short-term administration of sulindac, in the present study, we explored the ...feasibility of using ACF as surrogate markers for chemoprevention of colorectal cancer.
Randomly assigned to sulindac (300 mg daily), etodolac (400 mg daily), and placebo groups were 189 subjects without polyps or who had undergone polypectomy. Drugs were administered for 2 months. ACF in the rectal region were counted by magnifying endoscopy. Occurrence of polyps was evaluated at 12 months. A planned interim analysis was conducted.
ACF number at 2 months was significantly suppressed in the sulindac group (P = 0.0075), but not in the etodolac group (P = 0.73). In the sulindac group, the numbers of adenomas plus hyperplastic polyps (total polyps) and adenomas at 12 months were significantly (P = 0.02) and marginally (P = 0.064) lower, respectively, in comparison with the placebo group; no such difference was observed in the etodolac group. In analysis of only polypectomized subjects, the numbers of total polyps and adenomas in the sulindac group were even more markedly lower, with P values of 0.014 and 0.034, respectively. A similar tendency was confirmed by analyses of the incidence of polyps at 12 months. Suppression rates of total polyps and adenomas in ACF responders to sulindac were significantly greater than in nonresponders. In all groups, compliance was more than 90% and no intolerable adverse effects were observed.
ACF may be useful as surrogate lesions for chemoprevention of colorectal cancer.
In metal-based single-electron devices (SEDs), charge-offset drift has been observed, which is a time-dependent instability caused by charge noise. This instability is an issue in the application of ...new information processing devices, such as neural network devices, quantum computing devices (charge sensing), and reservoir computing devices. Therefore, the charge-offset drift in metal-based SEDs needs to be suppressed. However, the charge-offset stability of metal-based SEDs has not been investigated in depth, except in the case of Al and Al2O3 SEDs. In this work, Fe-based SEDs formed by single-layer Fe nanodot arrays embedded in MgF2 were studied with regard to their charge-offset stability. Using devices that produce simple current oscillations, the charge-offset drift (ΔQ0) of Fe-based SEDs was evaluated by focusing on peak shifts of the simple current oscillation over time, despite the use of a multi-dot system. This drift (ΔQ0 ≈ 0.3e) was shown to be much lower than in SEDs with Al-dots and Al2O3 tunnel junctions. Notably, the charge-offset drift in the metal-based SEDs was suppressed using the Fe–MgF2 system. The excellent stability of these devices was attributed to the material properties of the Fe–MgF2 system. Finally, as the Fe nanodot array contained numerous dots, the effect of satellite dots acting as traps on the charge-offset instability was discussed. The findings of this study will be important in future applications of metal-based SEDs in new information processing devices.
The purpose of this study was to evaluate and compare the effects on laboratory parameters among monotherapy with five DPP-4 inhibitors in patients with type 2 diabetes mellitus (DM).
We identified ...cohorts of new sitagliptin users (n = 879), vildagliptin users (n = 253), teneligliptin users (n = 260), alogliptin users (n = 237), and linagliptin users (n = 180) in patients with type 2 DM. We used a multivariate regression model to evaluate and compare the effects of the drugs on laboratory parameters including HbA1c concentration and serum concentrations of creatinine, estimated glomerular filtration rate, high density lipoprotein, total cholesterol, triglyceride, aspartate aminotransferase, and alanine aminotransferase among the five DPP-4 inhibitors up to 12 months.
Our study showed a favorable effect on HbA1c concentration and a slightly unfavorable effect on serum creatinine concentration in users of the five DPP-4 inhibitors, a favorable effect on lipid metabolism in sitagliptin, vildagliptin, and alogliptin users, and a favorable effect on hepatic parameters in sitagliptin, alogliptin, and linagliptin users, in comparison of the baseline and exposure periods. However, there was no significant difference in mean change in the concentration of any laboratory parameter among the five groups of DPP-4 inhibitor users.
In this study, we showed the effect of five DPP-4 inhibitors on glycemic, renal, and lipid metabolism, and hepatic parameters. DPP-4 inhibitors are well-tolerated hypoglycemic drugs.
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