Unoccupied electronic band structure of the semi-metallic Bi(111) surface probed with two-photon photoemission

While many photoemission studies have dealt with both the bulk band structure and various surface states and resonances, the unoccupied electronic structure above the Fermi level of the Bi(111) surface has not yet been measured directly although understanding of this model semi-metal is of great interest for topological insulators, spintronics and related fields. We use angle-resolved two-photon photoemission to directly investigate the occupied and unoccupied p bands of Bi, including the bulk hole pocket at the T point, as well as the image potential states and surface states of Bi(111).Comment: 9 pages, 7 figure

Photo-induced and thermal reactions in thin films of an azobenzene derivative on Bi(111)

Azobenzene is a prototypical molecular switch which can be interconverted with UV and visible light between a trans and a cis isomer in solution. While the ability to control their conformation with light is lost for many molecular photoswitches in the adsorbed state, there are some examples for successful photoisomerization in direct contact with a surface. However, there the process is often driven by a different mechanism than in solution. For instance, photoisomerization of a cyano-substituted azobenzene directly adsorbed on Bi(111) occurs via electronic excitations in the substrate and subsequent charge transfer. In the present study we observe two substrate- mediated trans–cis photoisomerization reactions of the same azobenzene derivative in two different environments within a multilayer thin film on Bi(111). Both processes are associated with photoisomerization and one is around two orders of magnitude more efficient than the other. Furthermore, the cis isomers perform a thermally induced reaction which may be ascribed to a back-isomerization in the electronic ground state or to a phenyl ring rotation of the cis isomer

Economic Boom or Political Boondoggle? Florida\u27s Atlantic Gulf Ship Canal in the 1930s

In the 1930s, the federal government began construction on one of the grandest public works projects in Florida. More than twice the length of the Suez and four times larger than the Panama Canal, the Atlantic Gulf Ship Canal was perhaps the most opulent single symbol of the New Deal. 1 Yet, despite the labor and massive expenditures on the part of state and federal officials, the project ended within a year of its groundbreaking. Plagued by political controversy from start to finish, the Ship Canal can be seen as a dress-rehearsal for the decades-long debate over the Cross-Florida Barge Canal that followed the Depression-era project. Canal boosters asserted that, because the canal would be part of a regional trade network, the project would expand economic growth and guarantee prosperity for the nation as well as the state. Amid the Depression, that promise seemed at least partially fulfilled with the Ocala construction boom that accompanied the dig. The canal prompted a wave of criticism, however, as opponents tried to block future funding for the project. Nationally, anticanal forces saw the project as one of many examples of New Deal profligacy and government waste. Locally, the canal pitted region against region and interest against interest over the conservation of one of the state\u27s most precious natural resources-Florida\u27s freshwater aquifer. The result was a contentious debate that, while ending the Ship Canal, entrenched interests and produced a bureaucratic inertia that continually pushed for a canal for much of the rest of the twentieth century

Polaron dynamics in thin polythiophene films studied with time-resolved photoemission

Femtosecond time-resolved two-photon photoemission spectroscopy is employed to study the dynamics of an excited state in a thin regioregular poly(3-hexylthiophene) (RR-P3HT) film deposited on a conducting polymer poly(3,4-ethylene-dioxythiophene): poly-(styrenesulfonate) (PEDT:PSS) electrode following optical excitation at 2.1 eV. We found that the biexponential decay of this excited state has a fast component (2.6 ps) assigned to bound polaron pairs which recombine quickly or separate to be added to the slow component (7.6 ps). The latter is attributed to polarons generated via charge transfer between adjacent polymer chains

Dynamics of optically excited electrons in the conducting polymer PEDT:PSS

Femtosecond time-resolved two-photon photoemission spectroscopy is employed to study the dynamics of the non-equilibrium electron distribution in the conducting polymer poly(3,4-ethylene-dioxythiophene): poly-(styrenesulfonate) (PEDT:PSS) film following optical excitation at 2.1 eV. We found that the electron thermalization occurs on a ultrafast timescale of around 60 fs analogous to the relaxation times of optically excited electrons in Au(111)

The role of cGMP and PKG-I in spinal nociceptive processing

First paragraph (this article has no abstract) Persistent stimulation of nociceptors results in sensitization of nociceptive sensory neurons, which is associated with hyperalgesia and allodynia. The release of NO and subsequent synthesis of cGMP in the spinal cord are involved in this process. cGMP-dependent protein kinase I (PKG-I) has been suggested to act as a downstream target of cGMP, but its exact role in nociception hadn't been characterized yet. To further evaluate the NO/cGMP/PKG-I pathway in nociception we assessed the effects of PKG-I inhibiton and activaton in the rat formalin assay and analyzed the nociceptive behavior of PKG-I-/- mice. Open access article

Electronic structure of an iron porphyrin derivative on Au(1 1 1)

Surface-bound porphyrins are promising candidates for molecular switches, electronics and spintronics. Here, we studied the structural and the electronic properties of Fe-tetra-pyridil-porphyrin adsorbed on Au(1 1 1) in the monolayer regime. We combined scanning tunneling microscopy/spectroscopy, ultraviolet photoemission, and two-photon photoemission to determine the energy levels of the frontier molecular orbitals. We also resolved an excitonic state with a binding energy of 420 meV, which allowed us to compare the electronic transport gap with the optical gap

Azobenzene versus 3,3',5,5'-tetra-tert-butyl-azobenzene (TBA) at Au(111): Characterizing the role of spacer groups

We present large-scale density-functional theory (DFT) calculations and temperature programmed desorption measurements to characterize the structural, energetic and vibrational properties of the functionalized molecular switch 3,3',5,5'-tetra-tert-butyl-azobenzene (TBA) adsorbed at Au(111). Particular emphasis is placed on exploring the accuracy of the semi-empirical dispersion correction approach to semi-local DFT (DFT-D) in accounting for the substantial van der Waals component in the surface chemical bond. In line with previous findings for benzene and pure azobenzene at coinage metal surfaces, DFT-D significantly overbinds the molecule, but seems to yield an accurate adsorption geometry as far as can be judged from the experimental data. Comparing the trans adsorption geometry of TBA and azobenzene at Au(111) reveals a remarkable insensitivity of the structural and vibrational properties of the -N=N- moiety. This questions the established view of the role of the bulky tert-butyl-spacer groups for the switching of TBA in terms of a mere geometric decoupling of the photochemically active diazo-bridge from the gold substrate.Comment: 9 pages including 6 figures; related publications can be found at http://www.fhi-berlin.mpg.de/th/th.htm

Progranulin contributes to endogenous mechanisms of pain defense after nerve injury in mice

Progranulin haploinsufficiency is associated with frontotemporal dementia in humans. Deficiency of progranulin led to exaggerated inflammation and premature aging in mice. The role of progranulin in adaptations to nerve injury and neuropathic pain are still unknown. Here we found that progranulin is up-regulated after injury of the sciatic nerve in the mouse ipsilateral dorsal root ganglia and spinal cord, most prominently in the microglia surrounding injured motor neurons. Progranulin knockdown by continuous intrathecal spinal delivery of small interfering RNA after sciatic nerve injury intensified neuropathic pain-like behaviour and delayed the recovery of motor functions. Compared to wild-type mice, progranulin-deficient mice developed more intense nociceptive hypersensitivity after nerve injury. The differences escalated with aging. Knockdown of progranulin reduced the survival of dissociated primary neurons and neurite outgrowth, whereas addition of recombinant progranulin rescued primary dorsal root ganglia neurons from cell death induced by nerve growth factor withdrawal. Thus, up-regulation of progranulin after neuronal injury may reduce neuropathic pain and help motor function recovery, at least in part, by promoting survival of injured neurons and supporting regrowth. A deficiency in this mechanism may increase the risk for injury-associated chronic pain