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.

Energy level offset at organic semiconductor heterojunctions

Abstract: We present an investigation via ultraviolet photoemission spectroscopy of the electronic structure of three organic-organic heterojunctions formed between the standard electron-transport emissive material tris(8-hydroxy-quinoline)aluminum (Alq3) and two hole-transport materials, i.e., 3,4,9,10 perylenetetracarboxylic dianhydride (PTCDA), and N,N′-diphenyl-N,N′-bis(l-naphthyl)-1-1′biphenyl-4,4″diamine (α-NPD). We measure directly the energy offsets between highest occupied molecular orbitals during the formation of the interfaces. We show that the relative positions of the highest occupied and lowest unoccupied molecular orbitals across the Alq3/PTCDA and Alq3/α-NPD interfaces are qualitatively different and explain, in part, the difference in the performance of electroluminescent devices based on these heterojunctions. We demonstrate the existence of charge transfer-induced dipoles which shift the molecular levels of one organic with respect to the other and invalidate the usual assumption of vacuum level...

Vacuum ultraviolet photoionization mass spectrometric study of C60

Abstract: Gaseous C60 has been studied by photoionization mass spectrometry between the ionization threshold and 40.8 eV. An adiabatic threshold of 7.57±0.01 eV is observed, which may be slightly low due to hot bands. The energy derivative of the photoion yield curve is in rough agreement with the He i photoelectron spectrum on the positions of some peaks, but others are weak or absent. The discrepancy is not attributed to autoionization, but rather to selection rules governing the ejection of low energy electrons into high angular momentum waves. C++60 is observed at higher energies, and becomes ∼0.6 as intense as C+60 at 40.8 eV. The photoion yield curve of C++60, approximately linear well above threshold, appears to exhibit curvature near threshold, thwarting an attempt to make a distinction between two alternative values of the second ionization potential. Fragmentation to form C+58 is only observed at the highest energy, 40.8 eV. The unimolecular decay is modelled by quasiequilibrium theory. In this model, the...

Iron-based high transition temperature superconductors

Abstract: In a superconductor electrons form pairs and electric transport becomes dissipation-less at low temperatures. Recently discovered iron-based superconductors have the highest superconducting transition temperature next to copper oxides. In this article, we review material aspects and physical properties of iron-based superconductors. We discuss the dependence of transition temperature on the crystal structure, the interplay between antiferromagnetism and superconductivity by examining neutron scattering experiments, and the electronic properties of these compounds obtained by angle-resolved photoemission spectroscopy in link with some results from scanning tunneling microscopy/spectroscopy measurements. Possible microscopic model for this class of compounds is discussed from a strong coupling point of view.

Large Work Function Modulation of Monolayer MoS2 by Ambient Gases

Abstract: Although two-dimensional monolayer transition-metal dichalcogenides reveal numerous unique features that are inaccessible in bulk materials, their intrinsic properties are often obscured by environmental effects. Among them, work function, which is the energy required to extract an electron from a material to vacuum, is one critical parameter in electronic/optoelectronic devices. Here, we report a large work function modulation in MoS2 via ambient gases. The work function was measured by an in situ Kelvin probe technique and further confirmed by ultraviolet photoemission spectroscopy and theoretical calculations. A measured work function of 4.04 eV in vacuum was converted to 4.47 eV with O2 exposure, which is comparable with a large variation in graphene. The homojunction diode by partially passivating a transistor reveals an ideal junction with an ideality factor of almost one and perfect electrical reversibility. The estimated depletion width obtained from photocurrent mapping was ∼200 nm, which is much...

X-ray photoemission band structure of some transition-metal oxides.

Abstract: The valence-band structures of MnO, CoO, NiO, ${\mathrm{Cu}}_{2}$O, CuO, and Re${\mathrm{O}}_{3}$ have been obtained by x-ray photoemission spectroscopy. It is found that in every case a narrow metal $d$ band lies above the center of the oxygen $2p$ valence band.