Persistent Energetic Electrons in Methylammonium Lead Iodide Perovskite Thin Films.

In conventional semiconductor solar cells, carriers are extracted at the band edges and the excess electronic energy (E*) is lost as heat. If E* is harvested, power conversion efficiency can be as high as twice the Shockley-Queisser limit. To date, materials suitable for hot carrier solar cells have not been found due to efficient electron/optical-phonon scattering in most semiconductors, but our recent experiments revealed long-lived hot carriers in single-crystal hybrid lead bromide perovskites. Here we turn to polycrystalline methylammonium lead iodide perovskite, which has emerged as the material for highly efficient solar cells. We observe energetic electrons with excess energy ⟨E*⟩ ≈ 0.25 eV above the conduction band minimum and with lifetime as long as ∼100 ps, which is 2-3 orders of magnitude longer than those in conventional semiconductors. The energetic carriers also give rise to hot fluorescence emission with pseudo-electronic temperatures as high as 1900 K. These findings point to a suppression of hot carrier scattering with optical phonons in methylammonium lead iodide perovskite. We address mechanistic origins of this suppression and, in particular, the correlation of this suppression with dynamic disorder. We discuss potential harvesting of energetic carriers for solar energy conversion.

Structural evolution of perfluoro-pentacene films on Ag(111): transition from 2D to 3D growth.

The structural evolution and thermal stability of perfluoro-pentacene (PF-PEN) thin films on Ag(111) have been studied by means of low-temperature scanning tunnelling microscopy (STM), low-energy electron diffraction (LEED), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and thermal desorption spectroscopy (TDS). Well-defined monolayer films can be prepared by utilizing the different adsorption energy of mono- and multilayer films and selectively desorbing multilayers upon careful heating at 380 K, whereas at temperatures above 400 K, a dissociation occurs. In the first monolayer, the molecules adopt a planar adsorption geometry and form a well-ordered commensurate (6 × 3) superstructure where molecules are uniformly oriented with their long axis along the <110> azimuth. This molecular orientation is also maintained in the second layer, where molecules exhibit a staggered packing motif, whereas further deposition leads to the formation of isolated, tall islands. Moreover, on smooth silver surfaces with extended terraces, growth of PF-PEN onto beforehand prepared long-range ordered monolayer films at elevated temperature leads to needle-like islands that are uniformly aligned at substrate steps along <110> azimuth directions.

Electronic structure at the perylene-tetracarboxylic acid dianhydride/Ag(111) interface studied with two-photon photoelectron spectroscopy.

The electronic structure of the prototype metal/organic contact 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) on a Ag(111)-surface has been investigated using time- and angle-resolved two-photon photoelectron spectroscopy (2PPE). Our analysis addresses particularly the nature of the interface state (IS) emerging at the interface due to the substrate-adsorbate interaction [C. H. Schwalb, S. Sachs, M. Marks et al., Phys. Rev. Lett. 101, 146801 (2008)]. Its free-electron-like dispersion and a possible backfolding at the surface Brillouin zone boundaries are discussed. Time-resolved pump-probe experiments reveal the inelastic electron lifetime along the dispersion parabola and show its decrease for increasing parallel momentum. The temperature dependence of the peak linewidth indicates a coupling of the IS to molecular vibrations. Moreover, additional aspects are addressed, such as the determination of the electron attenuation length of photoelectrons for low kinetic energy originating from the IS and the work function change of the sample upon PTCDA adsorption with very high energy resolution.

Enhancing the regenerative potential of guided tissue regeneration to treat an intrabony defect and adjacent ridge deformity by orthodontic extrusive force.

BACKGROUND: The biologic potential of the periodontal ligament (PDL) can be harnessed to solve complex clinical problems involving several dental disciplines. The purpose of this case report is to demonstrate that orthodontic extrusive force can enhance the regenerative potential of guided tissue regeneration (GTR) to eliminate an intrabony defect and augment a ridge deformity. METHODS: Regenerative therapy by open debridement with particulate anorganic cancellous bovine-derived bone xenograft (BDX), bioabsorbable membrane, and minocycline root conditioning was carried out. Eight weeks after the initial surgery, orthodontic extrusion and uprighting simultaneously were initiated. RESULTS: Radiographs and reentry documentation demonstrated that orthodontic extrusive force could enhance the regenerative potential of GTR. Consequently, the intrabony defect and alveolar ridge were successfully treated. CONCLUSION: This case report demonstrates that orthodontic-regenerative combined therapy can resolve complex clinical problems involving several dental disciplines.

Alveolar bone upper growth in furcation area using a combined orthodontic-regenerative therapy: a case report.

BACKGROUND: This case report demonstrates orthodontic and regenerative combined therapy in a 49-year-old male whose right maxillary premolar furcation had a bony defect with poor biologic width resulting from extensive subgingival caries. In these advanced interdisciplinary cases, crown lengthening with periodontal surgery alone does not solve the complex clinical problems. We believe that a combined orthodontic and periodontal regenerative combination therapy offers the best option for achieving a predictable outcome. METHODS: First, regenerative therapy by open debridement with a bioabsorbable synthetic bone graft, bioabsorbable membrane, and minocycline root conditioning was carried out. Eight weeks after initial surgery, orthodontic extrusion was initiated. RESULTS: Radiographs and reentry documentation suggest that the furcation defect associated with poor biologic width was successfully treated. CONCLUSION: This case report demonstrates that orthodontic-regenerative combined therapy can resolve complex clinical problems and enhance predictability.

Formation of an Organic/Metal Interface State from a Shockley Resonance.

The emergence of an organic/metal interface state is studied for the interface between 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) and Ag(100) by means of time- and angle-resolved two-photon photoemission and density functional theory. The interface state is located in the projected band gap of Ag(100), 2.3 eV above the Fermi level, and has an electron lifetime in the 10 fs range. The interface state has no direct counterpart on the clean Ag(100) surface, which only exhibits a broad resonance at ≈1 eV lower energy. Our results thus show that organic overlayers are able to shift such a resonance substantially and even qualitatively change its character to a distinct electronic state at the interface.