Room-Temperature Patterning of Nanoscale MoS2 under an Electron Beam.

Molybdenum disulfide (MoS2) is traditionally grown at a high temperature and subsequently patterned to study its electronic properties or make devices. This method imposes severe limitations on the shape and size of MoS2 crystals that can be patterned precisely at required positions. Here, we describe a method of direct nanoscale patterning of MoS2 at room temperature by exposing a molybdenum thiocubane single-source precursor to a beam of electrons. Molybdenum thiocubanes with various alkylxanthate moieties [Mo4S4(ROCS2)6, where R = alkyl] were prepared using a "self-assembly" approach. Micro-Raman and micro-FTIR spectroscopic studies suggest that exposure to a relatively smaller dose of electrons results in the breakdown of xanthate moieties, leading to the formation of MoS2. High-resolution transmission electron micrographs suggest that the growth of MoS2 most likely happens along (100) planes. An electron-beam-induced chemical transformation of a molybdenum thiocubane resist was exploited to fabricate sub-10 nm MoS2 lines and dense dots as small as 13 nm with a pitch of 33 nm. Since this technique does not require the liftoff and etching steps, patterning of MoS2 with interesting shapes, sizes, and thicknesses potentially leading to tunable band gap is possible.

Silica-shell cross-linked micelles encapsulating fluorescent conjugated polymers for targeted cellular imaging.

A bioinspired silification approach was successfully used to encapsulate fluorescent conjugated polymers inside silica-shell cross-linked polymeric micelles (CP-SSCL) in the highly benign synthesis environment of room temperature and near-neutral aqueous environment. Four different conjugated polymers were employed to demonstrate the versatility of the bioinspired silification, resulting in the formation of CP-SSCL with different emission wavelengths across the visible spectrum. The CP-SSCL are characterized by a large absorption coefficient and high quantum yield, indicating that they exhibit the required high fluorescence brightness for cellular imaging application. In addition, the CP-SSCL also exhibit a high colloidal stability and low cytotoxicity. The in vitro studies of using MDA-MB-231 breast cancer cells show that the CP-SSCL are successfully uptaken by the cancer cells and located at the cytoplasm of the cells. Furthermore, by conjugating folic acid on their surfaces, the uptake of CP-SSCL by MDA-MB-231 cells was enhanced significantly, suggesting their great potential for targeted imaging and early detection of cancer cells.

Intrinsically fluorescent carbon dots with tunable emission derived from hydrothermal treatment of glucose in the presence of monopotassium phosphate.

A facile method is developed to synthesize intrinsically fluorescent carbon dots by hydrothermal treatment of glucose in the presence of monopotassium phosphate. The fluorescence emission of the carbon dots thus produced is tunable by simply adjusting the concentration of monopotassium phosphate.