The in situ metalation of monolayers and multilayers of 2H-tetraphenylporphyrin (2HTPP) with Fe atoms on Ag(111) was studied with scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). This surface-confined coordination reaction results in the formation of adsorbed iron(II)-tetraphenylporphyrin (FeTPP). It is demonstrated that metalation of 2HTPP is achieved either by depositing iron atoms onto a monolayer of 2HTPP at room temperature or, alternatively, by depositing 2HTPP onto a Ag(111) surface with predeposited iron. The latter route requires elevated temperatures, indicating that this reaction includes at least one step with an activation barrier. In addition, it is demonstrated that vapor deposited Fe atoms also react with multilayers of the porphyrin at room temperature under the formation of FeTPP.

We address the dynamic behavior and the surface chemical bond of 2H-tetraphenylporphyrin (2HTPP) on Cu(111) around room temperature by variable-temperature scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) in ultrahigh vacuum. Between 280 and 345 K, the molecules predominantly display unidirectional diffusion along one of the three densely packed substrate AE110ae directions, which is attributed to a high site selectivity of the adsorbateÀsubstrate bond. Above 305 K, the diffusion direction is found to change occasionally by (120°. The activation barriers for the unidirectional diffusion and for rotation of the diffusion direction are determined to 0.71 ( 0.08 and 1.28 ( 0.12 eV, respectively. XPS shows that the iminic nitrogen atoms of 2HTPP interact strongly with the Cu surface. It is postulated that the local bonding situation is similar as in the initial complex (sitting-atop complex), which has previously been observed during the surface-confined in situ metalation of porphyrins.

The self-assembly of molecular building blocks on flat surfaces opens up the perspective to engineer molecular architectures with tailored functionalities. [1,2] Porphyrins appear as ideal candidates for such building blocks: they combine a rigid-structural theme, that is, the macrocycle, which often triggers long-range order, and a central metal atom as active site; this determines the intrinsic functionality. [3] Indeed, the generation of multicomponent porphyrinoid adlayers has successfully been realized and characterized by scanning tunneling microscopy (STM) on different surfaces in ultrahigh vacuum (UHV) [4][5][6] and in solution. [7] The key for the fabrication of tailored supramolecular networks is detailed understanding of the adsorption behavior of the involved molecules, which is determined by the interplay of molecule-substrate and molecule-molecule interactions. (111) (U = À1.94 V, I = 27 pA). e) STM image of an individual 2HTPP with the corresponding, scaled, space-filling model (U = À1.49 V, I = 30 pA). A closed-packed Cu atomic row is indicated, highlighting the coordinative bond between the iminic nitrogens of 2HTPP and the copper substrate atoms. f) STM image of a single CoTPP with the corresponding, scaled, space-filling model (U = À1.48 V, I = 27 pA).

Layers of CdSe quantum dots (QDs) with fixed diameter (4.5 nm) and various ligands were deposited on ITO substrates and investigated by photoluminescence (PL) and surface photovoltage (SPV) techniques. The distance between QDs decreased after washing and ligand exchange. The PL signals in the first excitonic peak as well as in the defect range strongly decreased with successive ligand exchange. In contrast to multilayer deposition, no PL signal related to CdSe QDs has been observed for a monolayer of QDs with pyridine surfactants on ITO. Neither modulated nor transient SPV signals were found for pristine CdSe QD layers. The modulated SPV signals strongly increased with successive ligand exchange. SPV transients became longer with successive ligand exchange. The experiments gave evidence for strong generation of surface defect states with ongoing ligand exchange and for fast initial charge separation of electrons from the first monolayer of CdSe QDs to the ITO surface. SPV transients could be described within a single QD approximation model, in which the number of surface defect states per QD, the energy distributions of defect states, hopping and distant dependent recombination were considered.

We demonstrate that Cu(111) surfaces pre-covered with a submonolayer of copper oxide or metallic nickel are suitable model-templates for the selective adsorption and/or localized functionalization of functional molecules such as different free base porphyrins and metalloporphyrins. The oxide/Cu(111) model-template is able to steer the adsorption of tetraphenylporphyrins (TPP): 2HTPP selectively adsorbs on the bare Cu areas, and for CoTPP anchoring at the rim of the copper oxide islands is found. On the Ni/Cu(111) model-template TPP molecules are pinned on the Ni areas while they are mobile on the bare Cu surface. Interestingly, adsorption of free base octaethylporphyrin on Ni/Cu(111) leads to a local functionalization, namely the metalation to NiOEP on the Ni areas. Model-template preparation and characterization by scanning tunneling microscopy is performed at room temperature.

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Layers of pyridine terminated CdSe quantum dots (QDs) with thicknesses from a monolayer (ML) to 80 nm were deposited on ITO substrates by dip coating. Transient surface photovoltage measurements showed dominant charge separation within the first ML of QDs at short times and an increasing influence of layer thickness at long times. Auger recombination limited the maximum of separated charge carriers to about 1 × 1012 cm‐2.magnified imageSeparation of photo‐generated electron‐hole pairs within a ML of CdSe‐QDs. Electrons were either trapped on ITO surface states or separated due to a built‐in electrical field created by a transferred electron from the ITO to a trap state at the QD. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Lattice positions of Sn in kesterite Cu2ZnSnS4 and Cu2SnS3 nanoparticles and thin films were investigated by XANES (x-ray absorption near edge structure) analysis at the S K-edge. XANES spectra were analyzed by comparison with simulations taking into account anti-site defects and vacancies. Annealing of Cu2ZnSnS4 nanoparticle thin films led to a decrease of Sn at its native and defect sites. The results show that XANES analysis at the S K-edge is a sensitive tool for the investigation of defect sites, being critical in kesterite thin film solar cells.