Realization of N-Type Semiconducting of Phosphorene through Surface Metal Doping and Work Function Study

Phosphorene becomes an important member of the layered nanomaterials since its discovery for the fabrication of nanodevices. In the experiments, pristine phosphorene shows p-type semiconducting with no exception. To reach its full capability, n-type semiconducting is a necessity. Here, we report the electronic structure engineering of phosphorene by surface metal atom doping. Five metal elements, Cu, Ag, Au, Li, and Na, have been considered which could form stable adsorption on phosphorene. These elements show patterns in their electron configuration with one valence electron in their outermost s-orbital. Among three group 11 elements, Cu can induce n-type degenerate semiconducting, while Ag and Au can only introduce localized impurity states. The distinct ability of Cu, compared to Ag and Au, is mainly attributed to the electronegativity. Cu has smaller electronegativity and thus denotes its electron to phosphorene, upshifting the Fermi level towards conduction band, resulting in n-type semiconducting. Ag and Au have larger electronegativity and hardly transfer electrons to phosphorene. Parallel studies of Li and Na doping support these findings. In addition, Cu doping effectively regulates the work function of phosphorene, which gradually decreases upon increasing Cu concentration. It is also interesting that Au can hardly change the work function of phosphorene.

Infrared spectra of hydrocarbons chemisorbed on silica-supported metals. III. 1-butene on nickel and platinum over a range of temperatures

Infrared spectra have been obtained of 1-butene chemisorbed on silica-supported platinum and nickel over the temperature range —78 to +95 °C. Virtually identical spectra were observed for 1-butene chemisorbed on platinum at — 78, 20 and 95 °C. The dominant spectral features at 2958, 2930 and 2870 cm -1 are assigned to associatively chemisorbed 1-butene, CH 3 —CH 2 —CHM—CH 2 M; a weaker band near 3010 cm -1 is attributed to olefinic surface species of the type MCH=CRM (M = surface metal atom; R — alkyl group). On hydrogenation most of the chemisorbed surface species were converted to n-butane, but at 95 °C a weak spectrum of chemisorbed w-butyl groups was observed. From the large spectral intensity increase on hydrogenation (eightfold to tenfold) it is concluded that considerable dissociative chemisorption must have occurred initially, probably to yield some surface carbide with a C 4 skeleton. A very similar spectrum, likewise attributed to an associatively adsorbed species (bands at 2958, 2920, 2870 cm -1 ), was obtained after chemisorption of 1-butene on nickel at — 78 °C. On hydrogenation at — 78 °C a large amount of n-butane was formed and the metal surface was virtually cleared of chemisorbed species. The spectral intensity increase on hydrogenation at — 78 °C was about 7.5-fold, indicating that the degree of initial dissociative chemisorption is about as great as that which occurred on platinum at all temperatures. However, after chemisorption at 20 or 95 °C, the spectra on nickel indicated that a greater number of CM bonds are formed and that some of the chemisorbed C 4 species may be attached to the surface at three or four of the carbon atoms. Also the amount of adsorption increased slowly with time. On hydrogenation at 20 °C only a small amount of n -butane was produced and many surface n -butyl groups were obtained. Also less dissociative chemisorption occurs on nickel at this temperature, for the spectral intensity increase on hydrogenation was about fourfold.