We introduce the development of conductive organic molecular assemblies including organic metals, superconductors, single component conductors, conductive films, and conductive liquids, particularl...

Development of Conductive Organic Molecular Assemblies: Organic Metals, Superconductors, and Exotic Functional Materials

Electronic structures of model interfaces of organic electroluminescent (EL) devices and porphyrin/metal interfaces were investigated by UV photoemission spectroscopy (UPS). At all the measured interfaces, shift of the vacuum level was observed, showing the formation of an interfacial electric dipole layer. For Alq/sub 3/ (tris(8-hydroxyquinolino) aluminum), TPD (N,N'-diphenyl-N,N'-(3-methylphenyl)-1,1-biphenyl-4,4'-diamine), and DP-NTCI (N,N'-diphenyl-1,4,5,8-naphthyltetracarboxylimide)/metal interfaces, interfacial energy diagrams determined by UPS correspond well with the actually observed carrier-injecting character at the interfaces. For ZnTPP (15,10,15,20-zinc-tetraphenylporphyrin), H/sub 2/TPP (5,10,15,20-tetraphenylporphyrin), and H/sub 2/T(4-Py)P (5,10,15,20-tetra(4-pyridyl) porphyrin)/metal interfaces, the shifts of the vacuum level as well as the energies of the levels in porphyrins could be expressed as a linear function of work function of the metal substrate. The slope of the linear function depended on the compound. These findings are in contrast to the traditional assumption of common vacuum level at the interfaces, For ZnTPP/metal interfaces, sample exposure to oxygen induced energy level shift in close relation with the change of the substrate work function at oxygen exposure. The present results have clearly demonstrated that direct observation of the interfacial electronic structure by microscopic method such as UPS is necessary for understanding the organic electronic devices such as EL devices and organic solar cells.

Energy level alignment at organic/metal interfaces studied by UV photoemission: breakdown of traditional assumption of a common vacuum level at the interface

Electronic structures of evaporated films of five organic light-emitting and carrier-injecting materials for organic electroluminescent devices were studied by ultraviolet photoemission spectroscopy. The compounds examined were (i) light-emitting materials tris(8-hydroxyquinolino) aluminum (Alq3) and 1,2,3,4,5-pentaphenylcyclopentadiene, (ii) a hole-injecting material N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine, and (iii) electron-injecting materials N,N′-diphenyl-1,4,5,8-naphthyletracarboxyldiimide and 1,3,5-tris(5-phenyl-1,3,4-oxadiazol-2-yl)benzene. The spectral features corresponding to the top parts of the valence states, which dominate the electric properties of the materials, were assigned by the comparison with the simulated density of states obtained from PM3 molecular orbital calculations. Using these calculations, the evolution of the electronic structure of each molecule from those of constituent parts was discussed. The characters of the unoccupied states obtained by t...

Electronic structures of organic molecular materials for organic electroluminescent devices studied by ultraviolet photoemission spectroscopy

The electronic structures of model interfaces of organic electroluminescent (EL) devices were investigated with UV photoemission spectroscopy (UPS). Interfaces of TTN (tetrathianaphthacene) and TCNQ (tetracyanoquinodimethane) were also studied as extreme cases for hole transport and electron transport material, respectively. For all organic/metal interfaces studied, the work function of metal electrode was changed by deposition of organic layer, i.e., the vacuum level was shifted at the interface, indicating the invalidity of the traditional energy level alignment model where a common vacuum level was assumed at organic/metal interface. At TCNQ/Au, DP-NTCI/Al, which are acceptor/metal interfaces, upward shift of the vacuum level of organic layer relative to that of metal was observed, suggesting the formation of interfacial dipole due to electron-transfer from metal to acceptor. At other organic/metal interfaces, TPD(N, N'-diphenyl-N, N'-(3-methylphenyl)-1, 1'-biphenyl-4, 4'-diamine)/Au or ITO (indium tin oxide), ALq/sub 3/ (tris(8-hydroxyquinolino) aluminum)/Al, DP-NTCl(N, N'-diphenyl-1,4,5,8- naphthyltetracarboxylimide)/Al or Au, downward shift of the vacuum level was observed. Such downward shift has been also observed in our previous study for porphyrin/metal interfaces, and seems to be a trend for organic/metal interfaces at which no electron-transfer from metal to organic layer occurs. This trend suggests that the traditional model tends to underestimate (overestimate) the barrier height for hole (electron) injection. On the other hand, the vacuum level shift at ALq/sub 3//TPD interface was less than 0.1 eV, leading to an apparent applicability of the traditional model. However, it is not always the case for organic/organic interfaces: finite shift of 0.2 eV was observed at TTN/TCNQ interface due to electron-transfer from TTN to TCNQ. Possible origins of vacuum level shift at organic/metal interfaces were also discussed.

Energy-level alignment at model interfaces of organic electroluminescent devices studied by UV photoemission: trend in the deviation from the traditional way of estimating the interfacial electronic structures

This article reviews the current status of inner-shell spectroscopies of free atoms and molecules using high-resolution soft-x-ray monochromators installed in the soft-x-ray beamlines at the third-generation synchrotron radiation facilities. Beamlines and endstations devoted to atomic and molecular inner-shell spectroscopies and various types of experimental techniques, such as ion yield spectroscopy, resonant photoemission spectroscopy and multiple-coincidence momentum imaging, are described. Experimental results for K-shell excitation of Ne, O K-shell excitation of H2O and CO2, C K-shell excitation and ionization of CO2 and B K-shell excitation of BF3, obtained at beamline 27SU of SPring-8 in Japan, are discussed as examples of atomic and molecular inner-shell spectroscopies using the third-generation synchrotron radiation sources.

https://iopscience.iop.org/article/10.1088/0953-4075/36/4/201/pdf

High-resolution inner-shell spectroscopies of free atoms and molecules using soft-x-ray beamlines at the third-generation synchrotron radiation sources

Design and performance of a plane-grating monochromator at UVSOR facility are described. Two monochromators of the present design have been constructed and are used for optical and photoelectron spectroscopy of solids.

A plane-grating monochromator for 2 eV ≤ hv ≤ 150 eV

Performance tests were carried out on a varied line-spacing plane grating monochromator at BL27SU of SPring-8 in the higher energy region using photoabsorption spectra of gas and solid samples and photoelectron spectra of Xe 5p3/2 A flux of 1×1011 photons/s/100 mA/002% bw was achieved at 2 keV The photon flux steeply decreased above 2 keV to 5×109 photons/s/100 mA/002% bw at 28 keV

Performance of a grating monochromator at BL27SU beamline of SPring-8 in the higher energy region

A constant‐deviation constant‐length spherical grating monochromator was constructed at the bending‐magnet beamline 8B1 of the UVSOR. The monochromator has a simple scanning mechanism with a fixed position of the entrance and exit slits, as well as fixed directions of incident and exit photon beams. The monochromator was designed to cover the photon energy of 31–620 eV with three interchangeable laminar gratings (1080 lines/mm: R=15 m, 540 lines/mm: R=15 m, 360 lines/mm: R=7.5 m). All gratings are original gratings fabricated on synthetic quartz substrates and coated with Au. The resolving power evaluated by ray tracing at the lowest energy of each grating with 10 μm slit width is ∼4400 for two high energy gratings and ∼7000 for a low energy grating. In the preliminary performance check, it was found that the output spectrum of the monochromator with G1 grating extends up to 870 eV with resolving power of ∼4000 at 400 eV with 10 μm slits.

Construction of constant‐deviation constant‐length spherical grating monochromator at UVSOR

A new plane‐grating monochromator and calibration chamber were constructed for the radiometric calibration of plasma diagnostic devices. The monochromator is designed to cover a wavelength range of 1.8–238 nm with moderate resolving power of 500±200 in λ/Δλ. To check the performance of the monochromator, spectral distribution and resolution were measured by experiments on photoemission from solids and photoionization of rare gases. The characterization of multilayer reflectors by the use of this beamline is demonstrated.

A plane-grating monochromator for radiometric calibration

Reflection spectra of single crystals of CdCl 2 , CdBr 2 and CdI 2 at 35 K were measured in the region up to 30 eV using synchrotron radiation Photoemission experiments were also performed on in-situ evaporated films of cadmium halides to determine binding energies of the outermost s -core levels of halogen ions Optical constants were derived through Kramers-Kronig analysis In the region up to 15 eV were found a number of peaks which are attributed to the transitions from the halogen valence band to the cadmium 5 s and 5 p conduction bands Around 16 eV were observed the peaks due to the Cd 4 d core excitons Weak structures in the 19-24 eV region are assigned to the transitions from the halogen s -core levels In CdI 2 , it was found that the total oscillator strength for the transition from the valence band is enhanced due to the presence of shallow core levels

Eiji Ishiguro

Papers

A plane-grating monochromator for 2 eV ≤ hv ≤ 150 eV

Performance of a grating monochromator at BL27SU beamline of SPring-8 in the higher energy region

Construction of constant‐deviation constant‐length spherical grating monochromator at UVSOR

A plane-grating monochromator for radiometric calibration

Optical Spectra of Cadmium Halide Crystals in 3–30 eV Region