Hafnium oxide-based ferroelectric thin-film transistor with a-InGaZnO channel fabricated at temperatures \u3c= 350°C

HfO2-based ferroelectric materials integrated with oxide-based thin-film transistors have been considered as potential candidates for back-end-of-line compatible ferroelectric field-effect transistors, which can be vertically stacked on silicon CMOS circuits to realize high-density neural network applications. However, the formation of ferroelectric orthorhombic phase in HfO2-based materials usually requires an annealing temperature of 400°C or higher. In this work, ferroelectric thin-film transistors (Fe-TFTs) were developed by monolithically integrating HfZrO2 (HZO) ferroelectric capacitors with amorphous indium-gallium-zinc oxide (a-IGZO) TFTs at a maximum processing temperature of 350°C on a glass substrate. A butterfly-shaped C-V curve was clearly observed in the low-temperature annealed metal-HZO-metal capacitor, indicating the formation of ferroelectricity in the HZO layer, as shown in Fig. 1. The positive and negative coercive voltages were 3 V and -2.4 V, respectively. The dielectric constant was 20.65. The field-effect mobility, threshold voltage, subthreshold swing and on/off current ratio of the a-IGZO TFT extracted from the transfer characteristics shown in Fig. 2 were 6.15 cm2V-1s-1, 1.5 V, 0.1 V/dec and 4.3´107, respectively. Fig. 3 shows the transfer hysteresis curves of the low-temperature Fe-TFTs in a metal-ferroelectric-metal-insulator-semiconductor configuration. The Fe-TFTs exhibited large hysteresis memory windows of 2.8 V and 3.8 V when the area ratios between ferroelectric capacitors and gate insulators (AFE / ADE) were 1/8 and 1/12, respectively. The result shows a great potential for back-end-of-line compatible memory applications. Please click Download on the upper right corner to see the full abstract

Trapping effects on inflation

We develop a Lagrangian approach based on the influence functional method so as to derive self-consistently the Langevin equation for the inflaton field in the presence of trapping points along the inflaton trajectory. The Langevin equation exhibits the backreaction and the fluctuation-dissipation relation of the trapping. The fluctuation is induced by a multiplicative colored noise that can be identified as the the particle number density fluctuations and the dissipation is a new effect that may play a role in the trapping with a strong coupling. In the weak coupling regime, we calculate the power spectrum of the noise-driven inflaton fluctuations for a single trapping point and studied its variation with the trapping location. We also consider a case with closely spaced trapping points and find that the resulting power spectrum is blue.Comment: 13 pages, 2 figure

C-H Borylation Mediated by Group 9 Pincer Complexes and Synthesis of Iridium Triflates and Triarylmethyl Species

The importance of organoboron compounds in chemical synthesis is apparent from the Nobel Prizes awarded to Herbert C. Brown (1979) and Akira Suzuki (2010) for their contribution to the development of new synthetic methodologies involving C-B bonds. Recently, dehydrogenative C-H borylation has emerged as an attractive approach to organoboron compounds. Multiple examples of catalytic conversion of unactivated C-H bonds in alkanes, benzylic and allylic C(sp3)-H bonds, as well as C(sp2)-H bonds in alkenes have been reported. Notably, the dehydrogenative C(sp)-H borylation of terminal alkynes (abbreviated as DHBTA) is missing in the list above. Here we describe the first example of DHBTA catalyzed by a new SiNN iridium pincer complex. The reaction is strictly chemoselective and can be performed under very mild conditions with terminal alkynes in high yield. We then explore Rh analogs of these SiNN iridium complexes. Although the new Rh compounds turned out to be inactive as DHBTA catalysts, they brought to light the unusual dual non-innocence behavior of the SiNN ligand. The (SiNN)Rh system also turned out to be a modest benzene borylation catalyst. Later, impressive TONs of 6500 for DHBTA were achieved by a new unsymmetric PNP iridium complex from ligand screening. The synthesis and characterization of the possible intermediates in DHBTA are also discussed. We also present the discovery of a new selective dehydrogenative diboration of the DHBTA products, alkynylboronates. The independent synthesis and characterization of the possible catalytic intermediates in the diboration are also described. Electrophilic iridium complexes have shown their great ability to activate strong bonds or serve as strong Lewis acids to catalyze reactions. We describe synthetic approaches to a highly electrophilic iridium triflate complex supported by a PNP pincer ligand and its equilibrium with ether solvents. The value of making new triarylmethyl cations is relevant to both hydrodefluorination of C(sp3)-F bonds and organometallic chemistry. We illustrate the synthesis of selected triarylmethanol and triarylmethyl chloride bearing electron withdrawing groups. Preliminary attempts to generate highly electrophilic triarylmethyl cations are also shown

Graphene reinforced biodegradable poly(3-hydroxybutyrate-co-4-hydroxybutyrate) nano-composites

Novel biodegradable poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [PHBV]/graphene nanocomposites were prepared by solution casting. The thermal properties, crystallization behavior, microstructure, and fracture morphology of the composites were investigated. Scanning electron microscope (SEM) results show that graphene layers are homogeneously dispersed in the polymer matrix. X-ray diffraction (XRD) and dynamic scanning calorimetry (DSC) studies show that the well dispersed graphene sheets act as nucleating agent for crystallization. Consequently, the mechanical properties of the composites have been substantially improved as evident from dynamic mechanical and static tensile tests. Differential thermal analysis (DTA) showed an increase in temperature of maximum degradation. Soil degradation tests of PHBV/graphene nanocomposites showed that presence of graphene doesn’t interfere in its biodegradability

Northern Hemisphere Urban Heat Stress and Associated Labor Hour Hazard from ERA5 Reanalysis

Increasing surface air temperature is a fundamental characteristic of a warming world. Rising temperatures have potential impacts on human health through heat stress. One heat stress metric is the wet-bulb globe temperature, which takes into consideration the effects of radiation, humidity, and wind speed. It also has broad health and environmental implications. This study presents wet-bulb globe temperatures calculated from the fifth-generation European Centre for Medium-Range Weather Forecasts atmospheric reanalysis and combines it with health guidelines to assess heat stress variability and the potential for reduction in labor hours over the past decade on both the continental and urban scale. Compared to 2010–2014, there was a general increase in heat stress during the period from 2015 to 2019 throughout the northern hemisphere, with the largest warming found in tropical regions, especially in the northern part of the Indian Peninsula. On the urban scale, our results suggest that heat stress might have led to a reduction in labor hours by up to ~20% in some Asian cities subject to work–rest regulations. Extremes in heat stress can be explained by changes in radiation and circulation. The resultant threat is highest in developing countries in tropical areas where workers often have limited legal protection and healthcare. The effect of heat stress exposure is therefore a collective challenge with environmental, economic, and social implications.publishedVersio

Photoelectric observations of the long-period eclipsing binaries at Yonsei University Observatory

A long term project (ten-years; 1982-92) for the photoelectric observation in the UBV passbands of selected eclipsing binaries with P 10 days has initiated at Yonsei University Observatory using 40-cm and 61-cm reflectors. The instrumentation used and the observation techniques and the reduction procedures applied to this investigation are described