Assembly of two-dimensional (2D) molecular arrays on surfaces produces a wide range of architectural motifs exhibiting unique properties, but little attention has been given to the mechanism by which they nucleate. Using peptides selected for their binding affinity to molybdenum disulfide, we investigated nucleation of 2D arrays by molecularly resolved in situ atomic force microscopy and compared our results to molecular dynamics simulations. The arrays assembled one row at a time, and the nuclei were ordered from the earliest stages and formed without a free energy barrier or a critical size. The results verify long-standing but unproven predictions of classical nucleation theory in one dimension while revealing key interactions underlying 2D assembly.

Persistent halogenated compounds (PHCs), such as dichlorodiphenyltrichloroethane and its metabolites (DDTs), hexachlorocyclohexane isomers (HCHs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), decabromodiphenylethane (DBDPE), and polybrominated biphenyl 153 (PBB 153), were quantified in muscles of five waterbird species collected from an extensive e-waste recycling region in the Pearl River Delta, South China. PCBs, at concentrations up to 1,400,000 ng/g lipid, were the dominant contaminants contributing to 80%-90% of PHCs. PBDEs and organochlorine pesticides (sum of DDTs and HCHs) contributed approximately equally to total PHCs with median concentrations ranging from 37-2200 and 530-4300 ng/g lipid, respectively. This contaminant distribution pattern was different from those acquired by most studies conducted in other regions. The concentrations of PCBs and PBDEs in Chinese-pond heron from the present study were higher than those from most other previous studies with birds having similar trophic levels. The extensive e-waste recycling activities were probably the cause of the elevated PCB and PBDE levels in the bird samples. The median concentrations of PBB 153 and DBDPE ranged from 3-140 and 10-176 ng/g lipid, respectively. The frequent detection and high concentrations of DBDPE in piscivorous birds implicate a potential environmental concern for this "new" brominated flame retardant. Additionally, the interspecies differences in the levels of contaminants and species-specific PBDE congener patterns were also elucidated in the present study.

Current rectification is well known in ion transport through nanoscale pores and channel devices. The measured current is affected by both the geometry and fixed interfacial charges of the nanodevices. In this article, an interesting trend is observed in steady-state current-potential measurements using single conical nanopores. A threshold low-conductivity state is observed upon the dilution of electrolyte concentration. Correspondingly, the normalized current at positive bias potentials drastically increases and contributes to different degrees of rectification. This novel trend at opposite bias polarities is employed to differentiate the ion flux affected by the fixed charges at the substrate-solution interface (surface effect), with respect to the constant asymmetric geometry (volume effect). The surface charge density (SCD) of individual nanopores, an important physical parameter that is challenging to measure experimentally and is known to vary from one nanopore to another, is directly quantified by solving Poisson and Nernst-Planck equations in the simulation of the experimental results. The flux distribution inside the nanopore and the SCD of individual nanopores are reported. The respective diffusion and migration translocations are found to vary at different positions inside the nanopore. This knowledge is believed to be important for resistive pulse sensing applications because the detection signal is determined by the perturbation of the ion current by the analytes.

Molybdenum disulfide (MoS2) is a layered material with outstanding electrical and optical properties. Numerous studies evaluate the performance in sensors, catalysts, batteries, and composites that can benefit from guidance by...