Impact of Pressure on the Resonant Bonding in Chalcogenides

Resonant bonding has been appreciated as an important feature in some chalcogenides. The establishment of resonant bonding can significantly delocalize the electrons and shrink the band gap, leading to low electrical resistivity and soft optical phonons. Many materials that exhibit this bonding mechanism have applications in phase-change memory and thermoelectric devices. Resonant bonding can be tuned by various means, including thermal excitations and changes in composition. In this work, we manipulate it by applying large hydrostatic-like pressure. Synchrotron X-ray diffraction and density functional theory reveal that the orthorhombic lattice of GeSe appears to become more symmetric and the Born effective charge has significantly increased at high pressure, indicating that resonant bonding has been established in this material. In contrast, the resonant bonding is partially weakened in PbSe at high pressure due to the discontinuity of chemical bonds along a certain lattice direction. By controlling resonant bonding in chalcogenides, we are able to modify the material properties and tailor them for various applications in extreme conditions

Dithiocarbamate Self-Assembled Monolayers as Efficient Surface Modifiers for Low Work Function Noble Metals

Tuning the work function of the electrode is one of the crucial steps to improve charge extraction in organic electronic devices. Here, we show that <i>N</i>,<i>N</i>-dialkyl dithiocarbamates (DTC) can be effectively employed to produce low work function noble metal electrodes. Work functions between 3.1 and 3.5 eV are observed for all metals investigated (Cu, Ag, and Au). Ultraviolet photoemission spectroscopy (UPS) reveals a maximum decrease in work function by 2.1 eV as compared to the bare metal surface. Electronic structure calculations elucidate how the complex interplay between intrinsic dipoles and dipoles induced by bond formation generates such large work function shifts. Subsequently, we quantify the improvement in contact resistance of organic thin film transistor devices with DTC coated source and drain electrodes. These findings demonstrate that DTC molecules can be employed as universal surface modifiers to produce stable electrodes for electron injection in high performance hybrid organic optoelectronics