Manipulation of Moiré Superlattice in Twisted Monolayer-multilayer Graphene by Moving Nanobubbles.

In the heterostructure of two-dimensional (2D) materials, many novel physics phenomena are strongly dependent on the Moiré superlattice. How to achieve the continuous manipulation of the Moiré superlattice in the same sample is very important to study the evolution of various physical properties. Here, in minimally twisted monolayer-multilayer graphene, we found that bubble-induced strain has a huge impact on the Moiré superlattice. By employing the AFM tip to dynamically and continuously move the nanobubble, we realized the modulation of the Moiré superlattice, like the evolution of regular triangular domains into long strip domain structures with single or double domain walls. We also achieved controllable modulation of the Moiré superlattice by moving multiple nanobubbles and establishing the coupling of nanobubbles. Our work presents a flexible method for continuous and controllable manipulation of Moiré superlattices, which will be widely used to study novel physical properties in 2D heterostructures.

High quality stealth dicing of sapphire with a picosecond Bessel beam by controlling the polarization direction.

Sapphire is an important substrate material in optoelectronic devices, and it is also widely used as a touch screen panel. In order to achieve high quality cutting of sapphire, the stealth dicing of 500 µm thick sapphire by a picosecond Bessel beam is studied in this paper. The influences of laser polarization direction and process parameters on cutting section roughness were studied. By controlling the laser polarization direction, different crack propagation morphologies were obtained. When the polarization direction was vertical to the cutting path, the crack propagation path was straighter, and the sapphire had better cutting quality. The laser processing parameters, including burst mode, hole spacing, and pulse energy, had a significant impact on the cutting section roughness. When the polarization direction was vertical to the cutting path under the optimal process parameters, the cutting section was uniform and flat, with no recondensable particles, no ripples, and no chamfer, and an 89.7 nm average roughness of the cutting section could be obtained.

Electrochemical assay of acetamiprid in vegetables based on nitrogen-doped graphene/polypyrrole nanocomposites.

Dual-mode electrochemical aptasensor based on nitrogen-doped graphene (NG) doped with the conducting polymer polypyrrole (PPy) nanocomposite is proposed for the determination of acetamiprid. NG/PPy was electrodeposited onto the glassy carbon electrode (GCE) using cyclic voltammetry technique. NG/PPy/GCE showed outstanding electrocatalytic activity for the oxidation of nitrite due to "active region" induced by the charge redistribution of carbon atoms. The ultrasensitive dual-mode biosensor for acetamiprid could be easily developed by coupling acetamiprid aptamers with the NG/PPy hybrid. The specific binding between acetamiprid and the aptamers resulted in the increase of differential pulse voltammetry (DPV) signal change and the decrease of chronoamperometry (CA) signal, and the concentration of acetamiprid could be measured. The working potentials of DPV and CA were - 0.2 ~ 0.4 V and - 0.4 ~ 0.4 V (vs. SCE), respectively. The dual-mode acetamiprid biosensor showed a wide linear range from 10-12 to 10-7 g mL-1, with low detection limits of 1.15 × 10-13 g mL-1 and 7.32 × 10-13 g mL-1 through DPV and CA modes, respectively. Moreover, owing to high active area and superior conductivity, as well as good electrocatalytic ability, the dual-sensing platform based on NG/PPy nanocomposite supported the quantification of acetamiprid in complex samples. A dual-mode electrochemical aptasensor based on NG/PPy nanocomposite for acetamiprid detection was proposed through both the increase of differential pulse voltammetry (DPV) signal change and the decrease of chronoamperometry (CA) signal of the nitrite oxidation electrocatalyzed by NG/PPyn in sensors and biosensors.

The Effect of Different Pulse Widths on Lattice Temperature Variation of Silicon under the Action of a Picosecond Laser.

In laser processing, due to the short interaction time between an ultrashort pulse laser and silicon, it has been difficult to study the lattice temperature change characteristics of silicon. In this paper, the interaction between a picosecond laser and silicon was studied. Based on the Fokker-Planck equation and two-temperature model (TTM) equation, a simulation model of silicon heating by different pulse-width picosecond lasers was established. The results show that within the range of 15 to 5 ps, the maximum lattice temperature tended to increase first and then decrease with the decreasing pulse width. The watershed was around 7.5 ps. The model error was less than 3.2% when the pulse width was 15 ps and the single pulse energy was 25 µJ.

Nutrient deposition over the past 60 years in a reservoir within a medium-sized agricultural catchment.

Widespread dam construction has reduced the hydrological connectivity of catchments of various sizes. Nutrients lost from upper catchments can be intercepted by dams and deposited in reservoir sediments, and this reduces downstream nutrient transportation. Few previous studies have assessed historical nutrient deposition rates (NDRs) in man-made reservoirs. Using 137Cs and 210Pbex deposition chronologies, this paper examines the total nitrogen (TN), total phosphate (TP), and organic matter (OM) concentrations in six sediment cores recovered from Xujiaya reservoir (catchment area 580 km2), provides estimates of historical NDRs by referencing the original capacity curve, and explores temporal changes to the NDR since dam construction. The results show that anthropogenic sources resulted in the increase in nutrient concentrations in the upper parts of the cores, whereas natural sources were the main contributors to nutrient deposition across the whole reservoir. In addition, sediment supply from the catchment was the main source of the nutrients deposited in the reservoir, and the changing patterns of NDRs were overall regulated by sediment yields. The TN, TP, and OM profiles in the six cores, together with the historical NDRs, reflect the pattern of nutrient deposition in the reservoir derived from this agricultural catchment over the past 60 years. The results provide new insight into the effect of dam construction on nutrient deposition at a medium-sized catchment scale against a background of recent environmental change influenced by human activity.

Ganoderic acid Sz, a new lanostanoid from the mushroom Ganoderma lucidum.

A new lanostanoid, ganoderic acid SZ (1), isolated from a lipophilic extract of the fruiting body of Ganoderma lucidum, is a geometric Z-isomer of the known ganoderic acid S (2). The structure of ganoderic SZ (1) was deduced mainly by 1D and 2D NMR studies. During the course of this study, 12 known lanostanoids have also been isolated and characterized.

Tripfordines A-C, sesquiterpene pyridine alkaloids from Tripterygium wilfordii, and structure anti-HIV activity relationships of Tripterygium alkaloids.

Three new sesquiterpene pyridine alkaloids, tripfordines A-C (1-3), were isolated from an ethanolic extract of the roots of Tripterygium wilfordii, along with eight known pyridine alkaloids, and tested for in vitro cytotoxic and anti-HIV activity. The structures of the new compounds were established on the basis of spectroscopic data interpretation. Anti-HIV structure-activity relationships (SAR) for this compound type are proposed on the basis of the screening results from the newly isolated compounds and prior data of known sesquiterpene pyridine alkaloids. The position of a carboxyalkyl chain on the pyridine moiety was not critical since both 2'- and 4'-substituted compounds exhibited high anti-HIV activity (EC(50) 0.1 microg/mL). In contrast, a hydroxy group at C-8' (carboxypropyl side chain) or C-9' (carboxybutyl side chain) was found to affect anti-HIV activity.

New lanostanoids from the mushroom Ganoderma lucidum.

From a lipophilic extract of the fruiting body of Ganoderma lucidum, three new lanostanoids, 8beta,9alpha-dihydroganoderic acid J (1), methyl 8beta,9alpha-dihydroganoderate J (2), and 20-hydroxylganoderic acid G (3), along with 12 known lanostanoids and two ergostane sterols were isolated. The structures of 1-3 were determined by interpretation of their spectroscopic data.

Dantaxusins C and D, two novel taxoids from Taxus yunnanensis.

Two new taxane diterpenes, dantaxusin C (1) and dantaxusin D (2), were isolated from an ethanol extract of the aerial parts of Taxus yunnanensis along with 14 known taxoids. All structures were established on the basis of 1D and 2D NMR and HREIMS spectroscopic methods.