Photoemission spectroscopy

About: Photoemission spectroscopy is a research topic. Over the lifetime, 10821 publications have been published within this topic receiving 250888 citations. The topic is also known as: photoelectron spectroscopy & PES.

Direct Experimental Observation of the Low Ionization Potentials of Guanine in Free Oligonucleotides by Using Photoelectron Spectroscopy

Abstract: Photodetachment photoelectron spectroscopy is used to probe the electronic structure of mono-, di-, and trinucleotide anions in the gas phase. A weak and well defined threshold band was observed in the photoelectron spectrum of 2′-deoxyguanosine 5′-monophosphate at a much lower ionization energy than the other three mononucleotides. Density function theory calculations revealed that this unique spectral feature is caused by electron-detachment from a π orbital of the guanine base on 2′-deoxyguanosine 5′-monophosphate, whereas the lowest ionization channel for the other three mononucleotides takes place from the phosphate group. This low-energy feature was shown to be a “fingerprint” in all the spectra of dinucleotides and trinucleotides that contain the guanine base. The current experiment provides direct spectroscopic evidence that the guanine base is the site with the lowest ionization potential in oligonucleotides and DNA and is consistent with the fact that guanine is most susceptible to oxidation to give the guanine cation in DNA damage.

Large quantum-spin-Hall gap in single-layer 1T' WSe2.

Abstract: Two-dimensional (2D) topological insulators (TIs) are promising platforms for low-dissipation spintronic devices based on the quantum-spin-Hall (QSH) effect, but experimental realization of such systems with a large band gap suitable for room-temperature applications has proven difficult. Here, we report the successful growth on bilayer graphene of a quasi-freestanding WSe2 single layer with the 1T' structure that does not exist in the bulk form of WSe2. Using angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy/spectroscopy (STM/STS), we observe a gap of 129 meV in the 1T' layer and an in-gap edge state located near the layer boundary. The system's 2D TI characters are confirmed by first-principles calculations. The observed gap diminishes with doping by Rb adsorption, ultimately leading to an insulator-semimetal transition. The discovery of this large-gap 2D TI with a tunable band gap opens up opportunities for developing advanced nanoscale systems and quantum devices.

Electronic structure of solids with competing periodic potentials.

Abstract: When electrons are subject to a potential with two incommensurate periods, translational invariance is lost, and no periodic band structure is expected. However, model calculations based on nearly free one-dimensional electrons and experimental results from high-resolution photoemission spectroscopy on a quasi-one-dimensional material do show dispersing band states with signatures of both periodicities. Apparent band structures are generated by the nonuniform distribution of electronic spectral weight over the complex eigenvalue spectrum.

Naphthyl Radical: Negative Ion Photoelectron Spectroscopy, Franck−Condon Simulation, and Thermochemistry

Abstract: The naphthyl anion (C10H7 - , naphthalenide) is prepared in a flow tube reactor by proton transfer between NH2 - and naphthalene (C10H8). The photoelectron spectrum of this anion is measured at a fixed laser wavelength of 364 nm. A single electronic band is observed, corresponding to the neutral naphthyl radical (C 10H7, naphthalenyl). The Franck-Condon profiles for both 1-naphthyl (R-naphthyl) and 2-naphthyl (‚-naphthyl) are simulated on the basis of density functional theory calculations of the vibrational frequencies and normal coordinates. Issues involving Franck-Condon simulations for large polyatomic molecules and Duschinsky rotation are discussed, and improved Franck-Condon simulation algorithms are presented. Comparison of the Franck-Condon simulations with the photoelectron spectrum shows that the observed band is predominantly due to the 1-naphthyl isomer, consistent with previous measurements showing the 1-naphthyl anion as more stable than the 2-naphthyl anion. The observed electron affinity of the 1-naphthyl radical is EA 0(1-C10H7) ) 1.403 ( 0.015 eV. On the basis of an evaluation of literature data, the recommended gas-phase acidity of naphthalene is ¢acidH298(1-C10H7-H) ) 1649 ( 14 kJ/mol and the recommended bond dissociation energy of naphthalene is DH298(1-C10H7-H) ) 472 ( 14 kJ/mol.

Silver Growth on TiO2(110) (1 × 1) and (1 × 2)†

Abstract: The growth and interaction of Ag with the TiO2(110) (1 × 1) and (1 × 2) surfaces were studied by X-ray photoemission spectroscopy (XPS), low-energy ion scattering (LEIS), low-energy electron diffraction (LEED), and scanning tunneling microscopy (STM). At 300 K, both LEIS and STM data indicate that Ag grows three-dimensionally on the (1 × 1) and (1 × 2) surfaces; no strong chemical interaction between Ag and TiO2 was detected by XPS. At 0.05 ML Ag exposure (corresponding to a cluster diameter of 2.0−3.5 nm), the Ag 3d core level binding energy shifts to 1.2 eV higher than that for metallic (bulk) Ag. In addition, the Ag 3d peak width increases with decreasing cluster size. The binding energy shifts and peak broadening are attributed to both initial and final state effects. The valence band as a function of Ag exposure suggests that a metal-to-nonmetal transition occurs within the Ag clusters at exposures between 0.5 and 1 ML (3.5−4.4 nm). No change in the cluster growth mode was observed upon Ag deposition...