The effect of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) adsorption on the physical properties of the two-dimensional (2D) atomic layer superconductor (ALSC) In/Si(111)-(7×3) has been studied by angle-resolved photoelectron spectroscopy, transport measurements, and scanning tunneling microscopy. Hole doping from the adsorbed molecules has been reported to increase the superconducting transition temperature Tc of this ALSC, and the molecular spin tends to decrease it. Owing to its large electron affinity and its nonexistent spin state, the adsorption of PTCDA was expected to increase Tc. However, the PTCDA adsorption dopes only a small number of holes in the In layers and causes a suppression of Tc with a sharp increase in the normal-state sheet resistance followed by an insulating transition. Taking the disordering of the arrangement of PTCDA into account, we conclude that the increase in resistance is due to the localization effect originating from the random potential that is induced by the disordered PTCDA molecules. The present result also indicates the importance of the crystallinity of a 2D molecular film adsorbed on ALSCs. 

Silver has been deposited on the Sn/Ge(111)-(√3×√3)-R30° surface at room temperature. The Ag growth and resulting surface morphology have been investigated using scanning tunneling microscopy. The first layer of silver forms an interface with domains of two different phases. One structure consists of short atomic rows with three-fold symmetry, oriented in the directions of the √3×√3 surface. These rows are separated by a distance equal to  and are found to fit a 2√3×√3 unit cell. The other phase is a 3×3 honeycomb structure, oriented in the Ge(111) 1 × 1 directions. Atomic structural models for the two interface phases are proposed, based on two different spin arrangements of the Sn/Ge(111)-√3×√3 surface. The results highlight the topological coupling of the two interface faces. Both interface structures are preserved with additional silver deposition. The second layer of Ag grows with a bulk-like lattice thickness on top of both interfaces. Low-energy electron diffraction on a mostly two layer Ag film reveals that it consists of domains where Ag grows in different orientations. These domains are rotated 30° with respect to each other, and thus mirror the symmetry directions of the two interfacial phases.

Silver thin films have been formed by room temperature deposition of Ag on In/Si(111)-√3 × √3. The Ag films have been investigated using both angle-resolved photoelectron spectroscopy (ARPES) and scanning tunnelingmicroscopy and spectroscopy (STM/STS). This creates a powerful link between the electronic structures and the film morphology. The valence band spectra show a clear evidence of quantum well state (QWS) formation already for a 2 monolayer (ML) film. This QWS moves towards the Fermi level for the 3 ML film, which also reveals a second QWS. The QWSs’ dispersions have been plotted along the ΓM and ΓK symmetry lines of the 1×1 surface Brillouin zone (SBZ), where the ΓM direction shows the umklapp-mediated QWSs. The valence band spectra for the 3 ML Ag film also show a strong Ag sp band close to the edge of the Ag(111) 1×1 SBZ. In the STS spectrum from 2 ML, two peaks are visible below the Shockley surface state. These peaks are compared with the ARPES data and attributed to different features of the QWS

Silver thin films have been formed on the Sn/Si(111)-(√3 ×√3)-R30 degrees surface at room temperature. The film morphologies, growth and electronic structures have been studied by scanning tunneling microscopy/spectroscopy (STM/STS), low-energy electron diffraction (LEED) and angle-resolved photoelectron spectroscopy (ARPES). The first layer of Ag forms an interface which consists of atomic rows with three-fold symmetry oriented along the Si(111)-1 x 1 directions. On top of the interface, Ag grows as an uniform thin film, following a layer-by-layer mode. The electronic structures of the films have been studied by STS for coverages between 1-5 monolayers (MLs). The STS spectra show peaks in the occupied electronic states which move towards the Fermi level with increased film thicknesses. These peaks have been attributed to quantum well states. ARPES measurements have been performed for 1 and 2 ML Ag coverage on Sn/Si(111)-(√3 ×√3)-R30 degrees, where the resulting thicknesses were confirmed by STM. The spectra reveal that quantum well states appear first for the 2 ML film.

Perylene tetracarboxylic diimide molecules were evaporated onto a Sn/Si(111)-2 root 3 x 2 root 3 surface and studied using scanning tunneling microscopy (STM) and low energy electron diffraction. At low coverages, single molecules are locked into specific adsorption geometries, which are investigated in detail using high resolution STM. The electronic structure of these individual molecules was studied using bias dependent STM images. The molecules form 1D rows that become more common with increasing coverages. Possible intermolecular O center dot center dot center dot H interactions within the rows have been identified. At around half of a monolayer (ML), the rows of molecules interact with each other and form a commensurate 4 root 3 x 2 root 3 reconstruction. In a complete monolayer, several structures emerge as molecules fill in the space between the 4 root 3 x 2 root 3 stripes. Possible intermolecular interactions within the 1 ML structures have been discussed. At coverages above 1 ML, the growth is characterized by island growth, where the molecules are arranged according to the canted structure within the layers.

Silver thin films have been formed by room temperature deposition of Ag on a Ga/Si(111) (√3 × √3)R30° surface. Scanning tunneling microscopy and spectroscopy (STM/STS) have been used to study both the clean Ga/Si(111) (√3 × √3)R30° surface and Ag films with different coverages. For the film formation, Ag first grows into 2D islands on Ga/Si(111) (√3 × √3)R30°. The first layer of the islands forms atomic lines with three-fold symmetry in the 1 × 1 direction of the underlying Si(111) substrate. From a 2 ML coverage, the growth becomes layer-by-layer mode. STS measurements have been performed on Ag films with different coverages inorder to investigate their electronic structures. Between 2–4 ML, the STS spectra reveal 2 and 3 peaks below the Fermi level. These peaks move towards the Fermi level with increased film thicknesses and thus share the same behavior as those of quantum well states (QWSs). The energy positions of the peaks have been compared with valence band photoelectron spectra in order to assign them to various parts of the QWSs. In addition, the photoemission results also confirm the existence of QWSs for a 2 ML Ag film on Ga/Si(111) (√3 × √3)R30°.

PTCDI molecules were evaporated onto a Ag/Si(111)√3×√3 surface and studied using scanning tun-resolution STM images are used to identify the delicate molecule/molecule and molecule/substrate interactions and the shapes of the molecular orbitals. The results show that the substrate/molecule interaction strongly modifies the electronic configuration of the molecules as their orbital shapes are quite different at 1 and 2 monolayer (ML) coverage. Simple models of molecular HOMO/LUMO levels and intermolecular hydrogen-bondings have been made for 1 and 2 ML PTCDI coverages to explain the STM images. Changes due to the interaction with the substrate are also found in ARUPS as extra states above the regular HOMO level at 1 ML PTCDI coverage. The ARUPS data also show that the electronic structure of the substrate remains unchanged after the deposition of molecules as the dispersion of the substrate related bands is unchanged. The changes in electronic structure ofthe molecules are discussed based on aHOMO/LUMO split.

3,4,9,10-perylene tetracarboxylic diimide molecules were evaporated onto a Ag/Si(111)-√3 x √3 surface and studied using photoelectron spectroscopy and near edge X-ray absorption fine structure (NEXAFS). All core levels related to the imide group of the molecules showed a partial shift to lower binding energies at low coverages. In NEXAFS spectra, the first transitions to the unoccupied states were weaker at low coverages compared to thicker films. Also, extra states in the valence band between the regular highest occupied molecular orbital and the Fermi level were found at low coverages. These changes were explained by two types of molecules. Due to charge transfer from the surface, these two types have different interactions between the imide group and the substrate. As a result, one type has a partially filled lowest unoccupied molecular orbital while the other type does not.

Silver thin films have been created by room temperature deposition on a Ga/Si(111)-√3 x √3 surface and their valence band structures and core levels have been measured by angle-resolved photoelectron spectroscopy (ARPES). Discrete quantum-well states (QWSs) quantized from the Ag sp valence band are observed already at 3 monolayers (ML). The characteristics of the QWSs have been examined in the phase accumulation model for thicknesses between 3 and 12 ML. The phase shift and QWSs binding energies dependence with Ag film thicknesses have all been consistently derived. In-plane energy dispersion follows a parabolic curve, and the effective mass of the QWSs shows an increasing trend with binding energies as well as with reduced film thicknesses. Furthermore, the ARPES measurements reveal umldapp mediated QWSs around the (M)over-bar points of the Si(111) 1 x 1 surface Brillouin zone. The study confirms that the Ga/Si(111)-√3 x √3 surface is a good substrate for growing uniform ultrathin Ag films in room temperature conditions.