Unoccupied electronic band structure of pentagonal Si nanoribbons on Ag(110).

Silicon nanoribbons - one dimensional silicon structures with a pentagonal atomic structure and mixed sp2- and sp3-hybridisation - grow on Ag(110) upon deposition of silicon. These nanostructures are viewed as promising candidates for modern day electronics as they are comprised of the same element as today's semiconductor devices. Even though they have been studied extensively over the last decade, only little is known about their unoccupied band structure which is important for possible future optoelectronics, semiconductor, and spintronics applications. In order to elucidate the unoccupied band structure of the nanoribbons, k-resolved inverse photoemission spectroscopy (KRIPES) studies were performed on both nanoribbon structures reported in the literature as well as on the bare Ag(110) substrate within the energy range of E-EF = 0-6.5 eV. The obtained experimental results are compared to density functional theory (DFT) calculated band structures to assign individual spectral features to specific bands. Since even small changes in the structural model of the nanoribbons lead to a change in the calculated band structure, this comparison allows us to assess the validity of the proposed structural models.

Tip-induced oxidation of silicene nano-ribbons.

We report on the oxidation of self-assembled silicene nanoribbons grown on the Ag (110) surface using scanning tunneling microscopy and high-resolution photoemission spectroscopy. The results show that silicene nanoribbons present a strong resistance towards oxidation using molecular oxygen. This can be overcome by increasing the electric field in the STM tunnel junction above a threshold of +2.6 V to induce oxygen dissociation and reaction. The higher reactivity of the silicene nanoribbons towards atomic oxygen is observed as expected. The HR-PES confirm these observations: even at high exposures of molecular oxygen, the Si 2p core-level peaks corresponding to pristine silicene remain dominant, reflecting a very low reactivity to molecular oxygen. Complete oxidation is obtained following exposure to high doses of atomic oxygen; the Si 2p core level peak corresponding to pristine silicene disappears.

Concurrent Sensing of CO2 and H2O from Air Using Ultramicroporous Fluorinated Metal-Organic Frameworks: Effect of Transduction Mechanism on the Sensing Performance.

Conventional materials for gas/vapor sensing are limited to a single probe detection ability for specific analytes. However, materials capable of concurrent detection of two different probes in their respective harmful levels and using two types of sensing modes have yet to be explored. In particular, the concurrent detection of uncomfortable humidity levels and CO2 concentration (400-5000 ppm) in confined spaces is of extreme importance in a great variety of fields, such as submarine technology, aerospace, mining, and rescue operations. Herein, we report the deliberate construction and performance assessment of extremely sensitive sensors using an interdigitated electrode (IDE)-based capacitor and a quartz crystal microbalance (QCM) as transducing substrates. The unveiled sensors are able to simultaneously detect CO2 within the 400-5000 ppm range and relative humidity levels below 40 and above 60%, using two fluorinated metal-organic frameworks, namely, NbOFFIVE-1-Ni and AlFFIVE-1-Ni, fabricated as a thin film. Their subtle difference in a structure-adsorption relationship for H2O and CO2 was analyzed to unveil the corresponding structure-sensing property relationships using both QCM- and IDE-based sensing modes.

Silicon sheets by redox assisted chemical exfoliation.

In this paper, we report the direct chemical synthesis of silicon sheets in gram-scale quantities by chemical exfoliation of pre-processed calcium disilicide (CaSi2). We have used a combination of x-ray photoelectron spectroscopy, transmission electron microscopy and energy-dispersive x-ray spectroscopy to characterize the obtained silicon sheets. We found that the clean and crystalline silicon sheets show a two-dimensional hexagonal graphitic structure.