Layers of 1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTCDA) grown on Ag(111) at about 80 K have been investigated using Fourier transform infrared spectroscopy, spot profile analysis low-energy electron diffraction, and temperature programmed desorption. Specifically, the compressed and the relaxed monolayer, as well as the transformation between the two ordered phases have been analyzed in detail. It is found that the two monolayer phases display distinctly different vibrational spectra and can thus be discriminated with high accuracy and sensitivity. For the NTCDA/Ag(111) monolayer strong in-plane vibrational modes point at a marked dynamic charge transfer between molecule and metal substrate and provide clear evidence for an efficient electronic coupling to the Ag(111) surface in conjunction with a partially filled electronic level at the Fermi energy. The bilayer, on the other hand, is largely electronically decoupled from the substrate and, according to the vanishing infrared-active in-plane vibrational modes, is oriented parallel to the surface. On the basis of spectroscopic data the metastable nature of the bilayer phase is identified as such, leading to an improved understanding of processes encountered in the course of layer preparation and resolving inconsistencies reported in the literature.

We report a detailed crystal field analysis of Pm 3+ and Sm 3+ as well as lattice location studies of 147 Pm and 147 Nd in 2H-aluminum nitride ͑w-AlN͒. The isotopes of mass 147 were produced by nuclear fission and implanted at an energy of 60 keV. The decay chain of interest in this work is 147 Nd→ 147 Pm→ 147 Sm ͑stable͒. Lattice location studies applying the emission channeling technique were carried out using the ␤ − particles and conversion electrons emitted in the radioactive decay of 147 Nd→ 147 Pm. The samples were investigated as implanted, and also they were investigated after annealing to temperatures of 873 K as well as 1373 K. The main fraction of about 60% of both 147 Pm as well as 147 Nd atoms was located on substitutional Al sites in the AlN lattice; the remainder of the ions were located randomly within the AlN lattice. Following radioactive decay of 147 Nd, the cathodoluminescence spectra of Pm 3+ and Sm 3+ were obtained between 500 nm and 1050 nm at sample temperatures between 12 K and 300 K. High-resolution emission spectra, representing intra-4f electron transitions, were analyzed to establish the crystal-field splitting of the energy levels of Sm 3+ ͑4f 5 ͒ and Pm 3+ ͑4f 4 ͒ in cationic sites having C 3v symmetry in the AlN lattice. Using crystal-field splitting models, we obtained a rms deviation of 6 cm −1 between 31 calculated-to-experimental energy ͑Stark͒ levels for Sm 3+ in AlN. The results are similar to those reported for Sm 3+ implanted into GaN. Using a set of crystal-field splitting parameters B nm , for Pm 3+ derived from the present Sm 3+ analysis, we calculated the splitting for the 5 F 1 , 5 I 4 , and 5 I 5 multiplet manifolds in Pm 3+ and obtained good agreement between the calculated and the experimental Stark levels. Temperature-dependent lifetime measurements are also reported for the emitting levels 4 F 5/2 ͑Sm 3+ ͒ and 5 F 1 ͑Pm 3+ ͒.