scholarly journals Inner-shell excitation spectroscopy of aniline, nitrobenzene, and nitroanilines

1996 ◽  
Vol 74 (6) ◽  
pp. 851-869 ◽  
Author(s):  
Cassia C. Turci ◽  
Stephen G. Urquhart ◽  
Adam P. Hitchcock
Keyword(s):  
Electronic Structure ◽  
Charge Transfer ◽  
Oscillator Strengths ◽  
Spectral Features ◽  
Excitation Spectra ◽  
Core Excitation ◽  
Substitution Pattern ◽  
Aromatic Molecules ◽  
Spectral Interpretation ◽  
Electron Energy Loss

Oscillator strengths for C 1s, N 1s, and O 1s excitation spectra of aniline, nitrobenzene, and the isomeric nitroanilines have been derived from inner-shell electron energy loss spectroscopy recorded under low momentum transfer conditions (> 2.5 keV impact energy and small scattering angle, θ ≤ 2°). Extended Hückel Molecular Orbital (EHMO) calculations carried out within the equivalent core analogy are used to aid spectral interpretation. These spectra are used to investigate the sensitivity of core excitation spectroscopy to charge transfer interactions in aromatic molecules that have both electron-donating and electron-withdrawing substituents. Strong multielectron excitation features were not found, although these had been anticipated from photoemission studies. The C 1s → π* and N 1s (NH2) → π* spectral features of the nitroanilines are found to be strongly dependent on the substitution pattern (ortho, meta, or para). Key words: electronic structure, inner-shell excitation, nitroanilines, EHMO calculations.

Core Hole Effects on Eels Near-Edge Fine Structure in Semiconductors and Insulators

2001 ◽  
Vol 7 (S2) ◽  
pp. 1174-1175
Author(s):  
Gerd Duscher ◽  
Ryszard Buczko ◽  
Stephen J. Pennycook ◽  
Sokrates T. Pantelides
Keyword(s):  
Electron Excitation ◽  
Dielectric Constants ◽  
Core Hole ◽  
Excitation Spectra ◽  
Core Excitation ◽  
Core Electron ◽  
Local Bonding ◽  
Standard Tool ◽  
Electron Energy Loss ◽  
X Ray Absorption

Electron energy-loss spectroscopy (EELS) is now a standard tool to investigate the local chemistry and bonding of defects in solids. to first order, the energy thresholds of the ionization edges in EELS spectra are determined by the identity of the element [1], while small shifts are induced by different bonding coordination and charge states [2]. The shapes of ionization edges in EELS spectra reflect the local bonding environments. We present first-principles calculations that incorporate electron-hole interactions and are in excellent agreement with experimental data obtained with X-ray absorption spectroscopy (XAS) and EELS. The superior energy resolution in XAS spectra and the new calculations make a compelling case that core-hole effects dominate core-excitation edges in all of the materials investigated: Si, SiO2, MgO, SrTiO3 and SiC. These materials differ widely in their dielectric constants leading to the conclusion that core-hole effects dominate all core-electron excitation spectra in semiconductors and insulators.

Atomic Resolution Electronic Structure Using Spatially Resolved Electron Energy Loss Spectroscopy

1994 ◽  
Vol 332 ◽  
Author(s):  
P.E. Batson
Keyword(s):  
Electronic Structure ◽  
High Energy ◽  
Dark Field ◽  
Atomic Resolution ◽  
Small Areas ◽  
Spatially Resolved ◽  
Spectral Interpretation ◽  
Core Excitations ◽  
Z Contrast ◽  
Electron Energy Loss

ABSTRACTElectronic structure in small areas is obtainable by inspection of near edge fine structure of core excitations. We can accomplish this today with near atomic resolution, using EELS at high energy. At IBM, we have obtained results using a sub-0.2nm probe at 120KeV with enough current to allow 200meV resolution studies at the Si L2,3 edge. It is especially crucial for Si-based structures that this allows us to obtain Z-contrast dark field images of the Si lattice at an acceleration voltage that is low enough to minimize radiation damage, but with a high enough current to allow good quality spectra to be obtained. A review of instrumental requirements, spectral interpretation, and applications to Si-Ge alloys is presented.

The Valence Electronic Structure of Co3O4: Is It a Charge-Transfer Insulator?

1998 ◽  
Vol 547 ◽  
Author(s):  
M.A. Langell ◽  
G.A. Carson ◽  
S. Smith ◽  
L. Peng ◽  
M.H. Nassir
Keyword(s):  
Electronic Structure ◽  
Charge Transfer ◽  
Band Structure ◽  
Valence Band ◽  
Transition Metal Oxides ◽  
Resolution Electron ◽  
Bonding Properties ◽  
Low Energy Electron ◽  
A Charge ◽  
Electron Energy Loss

AbstractDespite the relevance to a variety of materials applications, the electronic and bonding properties of spinel transition metal oxides are not well established. We report here the slow oxidation of CoO(100) to Co3O4, studied by photoemission (UPS and XPS), low energy electron diffraction (LEED) and high resolution electron energy loss spectroscopy (HREELS) with the aim of elucidating the valence band electronic structure of the Co3O4 spinel. The original Mott insulator picture of the parent CoO substrate has been revised in recent times, after careful analyses and extensive debate, to the more detailed charge-transfer insulator model which includes some admixture of oxygen 2p levels in the 3d-derived valence band. No equivalent band structure analysis has been performed on the spinel oxides, perhaps in part because of the greater complexity of the 56-atom unit cell with two different cation lattice sites and oxidation states. In this study, we determine the valence band structure of the spinel oxide and address the question of whether Co3O4 can be modeled as a charge-transfer insulator in analogy with its closely related rocksalt substrate.

Electronic Structure, Charge Transfer and Bonding in Intermetallics Using EELS and Density Functional Theory

1998 ◽  
Vol 552 ◽  
Author(s):  
C. J. Humphreys ◽  
G. A. Botton ◽  
D. A. Pankhurst ◽  
V. J. Keast ◽  
W. M. Temmerman
Keyword(s):  
Density Functional Theory ◽  
Electronic Structure ◽  
Charge Transfer ◽  
Energy Loss ◽  
Electron Energy Loss Spectroscopy ◽  
Density Functional ◽  
Ionic Component ◽  
Functional Theory ◽  
Covalent Component ◽  
Electron Energy Loss

ABSTRACTElectron energy loss spectroscopy and density functional theory have been used to show that there is a covalent component to the bonding in NiAl, CoAl and FeAl, between the transition metal atom and Al. There is no charge transfer and no ionic component to the bonding in NiAl and probably not in CoAl and FeAI. The bonding in non-stoichiometric NiAl is studied. Preliminary results are given for a Σ3 boundary in NiAl.

Electronic structure studies of conducting polymers by electron energy-loss spectroscopy

1996 ◽  
Vol 54 ◽  
pp. 160-161
Author(s):  
J. Fink
Keyword(s):  
Electronic Structure ◽  
Conducting Polymers ◽  
Conjugated Polymers ◽  
Electron Acceptors ◽  
Electron Donors ◽  
Light Emitting ◽  
One Dimensional ◽  
New Class ◽  
Electrical Conductivities ◽  
Electron Energy Loss

Conducting polymers comprises a new class of materials achieving electrical conductivities which rival those of the best metals. The parent compounds (conjugated polymers) are quasi-one-dimensional semiconductors. These polymers can be doped by electron acceptors or electron donors. The prototype of these materials is polyacetylene (PA). There are various other conjugated polymers such as polyparaphenylene, polyphenylenevinylene, polypoyrrole or polythiophene. The doped systems, i.e. the conducting polymers, have intersting potential technological applications such as replacement of conventional metals in electronic shielding and antistatic equipment, rechargable batteries, and flexible light emitting diodes.Although these systems have been investigated almost 20 years, the electronic structure of the doped metallic systems is not clear and even the reason for the gap in undoped semiconducting systems is under discussion.

Sign in / Sign up

Export Citation Format

Share Document