原子尺度的欧姆表

一种高度稳定的扫描隧道显微镜(STM)可以在小于原子尺度范围精密测量金属的电学性能。扫描隧道显微镜可以在表面对单个原子成像,或者移动单个原子。研究人员最近进一步提高了这个仪器的精确性,可以对铅表面单个原子附近不同位置的电导进行测量。这个结果或许有助于揭示金属和超导体的性质的差异,未来或许可以用于纳米加工技术。一台STM的探针非常尖锐,尖端只有一个原子,将探针在真空中操控到距离表面极近的位置。电子可以在加有电势的间隙之间越过,或者称隧穿。当探针在表面运动时,记录通过探针的电流可以对表面成像。另外一种STM技术是将探针保持与表面接触,使得探针原子与样品表面形成化学键。研究人员使用这种被称为点接触技术,可以测量一种材料原子尺度的电导性质,了解在量子物理中电流是如何流动的,此时传统的欧姆定律不再成立。     

Defect orientation on the chain folded surfaces of two-arm poly(ethylene oxide) lamellar crystals

Two-arm poly(ethylene oxide) fractions (PEOs) with arm lengths of 2 220 g/mol were synthesized via a reaction using terephthaloyl (1,4-), isophthaloyl (1,3-) and phthaloyl (1,2-) dichorides as coupling agents. The center of each molecule thus includes a phenylene group as a configurational defect, and they are excluded to the crystal folded basal surfaces. In the lamellar crystals with the once-folded overall molecular conformation, observations of surface-enhanced Raman scattering experiments show that only the in-plane vibration modes are selectively enhanced. This implies that the arrangement of phenylene groups adopts a “stand-up” orientation on the basal surface, i. e., the π plane of phenylene groups in the defects is perpendicular to the lamellar basal surface.     

Modular Metal-Quinone Networks with Tunable Architecture and Functionality

Nanostructured materials with tunable structures and functionality are of interest in diverse areas. Herein, metal ions are coordinated with quinones through metal-acetylacetone coordination bonds to generate a class of structurally tunable, universally adhesive, hydrophilic, and pH-degradable materials. A library of metal-quinone networks (MQNs) is produced from five model quinone ligands paired with nine metal ions, leading to the assembly of particles, tubes, capsules, and films. Importantly, MQNs show bidirectional pH-responsive disassembly in acidic and alkaline solutions, where the quinone ligands mediate the disassembly kinetics, enabling temporal and spatial control over the release of multiple components using multilayered MQNs. Leveraging this tunable release and the inherent medicinal properties of quinones, MQN prodrugs with a high drug loading (>89 wt %) are engineered using doxorubicin for anti-cancer therapy and shikonin for the inhibition of the main protease in the SARS-CoV-2 virus.