Binding Energy Scale Research Articles

Excitons and exciton-phonon coupling in metallic single-walled carbon nanotubes: Resonance Raman spectroscopy

The first four transitions (upper and lower branches of ${E}_{11}^{M}$ and ${E}_{22}^{M}$) for a broad diameter range (0.7--4 nm) of metallic single-walled carbon nanotubes are studied in the 1.26--2.71 eV energy range using resonance Raman spectroscopy of their radial breathing modes (RBMs). A scaling-law analysis of transition energies from 77 spectral features suggests that the transitions are excitonic in nature and that relative scaling of electron self-energies and exciton binding energies in metallic nanotubes closely matches that found in semiconductors. The previously elusive upper-branch signatures are observed at large diameters $(g1.3\text{ }\text{nm})$ for several chiralities for both ${E}_{11}^{M}$ and ${E}_{22}^{M}$ excitation. These results are discussed as a consequence of the nodal behavior of exciton-phonon coupling. Additionally, while theoretical calculations for the $(n,m)$-dependent matrix elements predict that the RBM intensity should decrease with increasing diameter, the opposite behavior is observed experimentally. We show that this is a consequence of an increase in the resonance Raman broadening factor $\ensuremath{\Gamma}$ as diameter decreases.

Photoemission, resonant photoemission, and x-ray absorption of a Ru(II) complex adsorbed on rutile TiO2(110) prepared by in situ electrospray deposition

An experimental study of the bonding geometry and electronic coupling of cis-bis(isothiocyanato)bis(2,2(')-bipyridyl-4,4(')-dicarboxylato)-ruthenium(II) (N3) adsorbed on rutile TiO(2)(110) is presented, along with supporting theoretical calculations of the bonding geometry. Samples were prepared in situ using ultrahigh vacuum electrospray deposition. Core-level photoemission spectroscopy was used to characterize the system and to deduce the nature of the molecule-surface bonding. Valence band photoemission and N 1s x-ray absorption spectra were aligned in a common binding energy scale to enable a quantitative analysis of the bandgap region. A consideration of the energetics in relation to optical absorption is used to identify the photoexcitation channel between the highest occupied and lowest unoccupied molecular orbitals in this system, and also to quantify the relative binding energies of core and valence excitons. The core-hole clock implementation of resonant photoemission spectroscopy is used to reveal that electron delocalization from N3 occurs within 16 fs.

Principal Component Analysis: A Versatile Method for Processing and Investigation of XPS Spectra

Given the relevance of principal component analysis (PCA) to the treatment of spectrometric data, we have evaluated potentialities and limitations of such useful statistical approach for the harvesting of information in large sets of X-ray photoelectron spectroscopy (XPS) spectra. Examples allowed highlighting the contribution of PCA to data treatment by comparing the results of this data analysis with those obtained by the usual XPS quantification methods. PCA was shown to improve the identification of chemical shifts of interest and to reveal correlations between peak components. First attempts to use the method led to poor results, which showed mainly the distance between series of samples analyzed at different moments. To weaken the effect of variations of minor interest, a data normalization strategy was developed and tested. A second issue was encountered with spectra suffering of an even slightly inaccurate binding energy scale correction. Indeed, minor shifts of energy channels lead to the PCA being performed on incorrect variables and consequently to misleading information. In order to improve the energy scale correction and to speed up this step of data pretreatment, a data processing method based on PCA was used. Finally, the overlap of different sources of variation was studied. Since the intensity of a given energy channel consists of electrons from several origins, having suffered inelastic collisions (background) or not (peaks), the PCA approach cannot compare them separately, which may lead to confusion or loss of information. By extracting the peaks from the background and considering them as new variables, the effect of the elemental composition could be taken into account in the case of spectra with very different backgrounds. In conclusion, PCA is a very useful diagnostic tool for the interpretation of XPS spectra, but it requires a careful and appropriate data pretreatment.

Optical study of porphyrin-doped carbon nanotubes

Porphyrin-doped carbon nanotubes in sodium dodecylbenzenesulfonate (NaDDBS) aqueous solution were obtained from NaDDBS/carbon nanotube aqueous dispersions. Several phonon-assisted absorption and recombination processes seem to occur, including one-phonon and two-phonon processes, and remain present even upon porphyrin doping. Power-law scaling of exciton binding energies and environmental dielectric screening effects are used to infer the doping from photoluminescence maps. The dielectric constant of the 5,10,15,20-tetrakis(4-trimethylammonium phenyl) porphyrin (H 2TTMAPP) in NaDDBS aqueous solution seems to be higher than the one of NaDDBS/aqueous solution apparently because the counterions have opposite net charges.

Binding energies ofL6ip-wave Feshbach molecules

We present measurements of the binding energies of $^{6}\text{L}\text{i}$ $p$-wave Feshbach molecules formed in combinations of the $|F=1/2,{m}_{F}=+1/2⟩$ $(|1⟩)$ and $|F=1/2,{m}_{F}=\ensuremath{-}1/2⟩$ $(|2⟩)$ states. The binding energies scale linearly with magnetic field detuning for all three resonances. The relative molecular magnetic moments are found to be $113\ifmmode\pm\else\textpm\fi{}7\text{ }\ensuremath{\mu}\text{K}/\text{G}$, $111\ifmmode\pm\else\textpm\fi{}6\text{ }\ensuremath{\mu}\text{K}/\text{G}$, and $118\ifmmode\pm\else\textpm\fi{}8\text{ }\ensuremath{\mu}\text{K}/\text{G}$ for the $|1⟩\text{\ensuremath{-}}|1⟩$, $|1⟩\text{\ensuremath{-}}|2⟩$, and $|2⟩\text{\ensuremath{-}}|2⟩$ resonances, respectively, in good agreement with theoretical predictions. Closed-channel amplitudes and the size of the $p$-wave molecules are obtained theoretically from full closed-coupled calculations.

P-Wave Feshbach Molecules

We have produced and detected molecules using a p-wave Feshbach resonance between 40K atoms. We have measured the binding energy and lifetime for these molecules and we find that the binding energy scales approximately linearly with the magnetic field near the resonance. The lifetime of bound p-wave molecules is measured to be 1.0+/-0.1 ms and 2.3+/-0.2 ms for the ml=+/-1 and ml=0 angular momentum projections, respectively. At magnetic fields above the resonance, we detect quasibound molecules whose lifetime is set by the tunneling rate through the centrifugal barrier.

Electronic structure of CdTe probed by Cd and Te M 4,5 X-ray emission spectra

We have investigated the bulk electronic structure of CdTe focusing on the Cd 5p and Te 5p valence states by X-ray emission spectroscopy (XES). Despite the very low fluorescence yields the Cd and Te M 4,5 (5p → 3d 3/2,5/2) spectra have been recorded successfully. A good correspondence has been found between the valence band XES and X-ray photoelectron spectra (XPS) by comparison on a common binding energy scale. We also performed a density functional theory calculation of the CdTe valence band, obtaining the Cd 4d, 5s, 5p and Te 5s, 5p local partial densities of states. The experimental Cd 5p and Te 5p derived from the X-ray emission spectra are in good agreement with the calculation. The intensity ratio of the Cd M 4,5 to the Te M 4,5 spectrum is obtained to be 0.25, in agreement with the ratio of the calculated Cd 5p to the Te 5p density of states in the CdTe upper valence band (0.22).

The interface microscopy and spectroscopy on the cleavage surfaces of the In 4Se 3 pure and copper-intercalated layered crystals

Surface properties of In 4Se 3, In 4Se 3(Cu) crystals were studied. SEM, STM surfaces micro-and nanostructure, and XPS spectra were obtained for interface on the cleavage surfaces of crystals that have been exposed to air. The intense XPS lines, viz. Se 3d, In 3d, Cu 2p, C 1s, and O 1s were recorded in an expanded binding-energy scale. In each case Gaussian line shape analysis has been done to determine the exact peak positions and peak areas. Chemical shifts have been obtained for the binding-energy values of the XPS lines for Se, In, C, and Cu. The formation of In–In metallic and In–O oxidized bindings and corresponding phases on the cleavage surfaces of In 4Se 3 and Cu–In–Se bindings for In 4Se 3(Cu) intercalated crystals have been found. Phases formation was also observed by SEM and STM.

On the bonding situation in TlCo2Se2

The electronic structure of TlCo2Se2 has been investigated by means of band structure calculations and x-ray photoelectron andemission spectroscopy (XPS and XES). The formation of the valence band is described inconnection with calculations of partial densities of states of the valence band and CoLα,β x-ray emission () aligned to the binding energy scale. The experimental results are in agreement with thecalculated distribution of Co 3d states, which lie close to the Fermi level. Theeffect of Co–Se bonding is seen as satellite structures in the XPS Co 2p signals.Thermoelectric and Hall effect data as well as resistivity measurements show thatTlCo2Se2 is metallic with electron holes as charge carriers with broadbandmobility characteristics. The observed anisotropy of the resistivity in theab planeand along c remains constant as a function of temperature, i.e. without signs of the magnetic ordering that occurs(TN∼85 K). The results of local spin density functional calculations show ferromagnetic couplingwithin the cobalt plane as a result of direct magnetic interactions between the magneticmoments.

Narrow antiadiabatic peak in optimally doped and underdoped high-Tc superconductors

Abstract We study the effect of antiferromagnetic (AF) correlations in the three-band Emery model, with respect to the experimental situation in weakly underdoped and optimally doped BSCCO. In the vicinity of the vH singularity of the conduction band there appears a central peak in the middle of a pseudogap, due to an antiadiabatic quasiparticle, which is insensitive to the energy scale of the mechanism responsible for the pseudogap. We find a quantum low-temperature regime, in which the pseudogap profile is created by zero-point motion of the magnons. Detailed analysis of the spectral functions along the (π,0)–(π,π) line shows significant agreement with experiment. We conclude that optimally doped BSCCO has a well-developed pseudogap of the order of 1000 K. This is only masked by the antiadiabatic quasiparticle, which provides the experimentally observed small binding energy scale.

Proton and Valence Quark Charge Radii for a Quasi-potential Model

The problem of calculating the root-mean-square radius of proton charge distribution is studied for a relativistic quasi-potential quark model in the approximation of the SU(6) symmetry. It is demonstrated that in the case of point quarks, the proton radius is f(m/λ)/M2, where m is the quark mass, λ is the binding energy scale parameter, M is the proton mass, and f is a dimensionless function independent of M. It is demonstrated that the root-mean-square radius of the coupled system can take a negative value in the ultrarelativistic range. For a joint description of the nucleon magnetic moments and of the proton radius, a negative root-mean-square quark radius, whose absolute value depends on the quark mass as 〈r 1q 2 〉 = −1.875 m2, must be introduced into the model with oscillator forces.

Local partial densities of states in CuInS2 upper valence band determined by soft-x-ray emission spectroscopy: Evidence for In 5p contribution

The CuL2,3, InM4,5, and SL1 soft-x-ray emission spectra of single-crystalline CuInS2 were measured using synchrotron radiation as excitation source. These spectra essentially reflect the local partial densities of states (LPDOS) of Cu 3d, In 5p, and S 3p valence states, respectively. They correspond to features in the total density of states of the upper valence band as revealed by valence-band photoelectron spectrum. On common binding-energy scale the SL1 and InM5 spectra display broad peaks positioned slightly below the Cu 3d-related peak center and a shoulder above the Cu peak center, extending towards the valence-band maximum. A density-functional calculation of the LPDOS confirms two components occurring in both S 3p and In 5p partial densities of states. From the similarity of the positions and the intensity ratios of these two components, an admixture of In 5p states to the S 3p states in the upper valence band is suggested, providing an explanation of the abnormally small band gap of ternary copper sulfides.

The effect of promoters on the electronic structure of ruthenium catalysts supported on carbon

Alkali- and earth-alkali-promoted ruthenium catalysts supported on graphitized carbon were investigated by means of X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) in order to study the effect of promoters on the electronic structure of this metal–support system. Samples were measured as prepared and after thorough reduction in hydrogen. The C 1s spectra of reduced alkali-promoted catalysts showed a shift towards higher binding energies and an asymmetric broadening. Neither non-promoted nor Ba-promoted Ru/C samples exhibited such a behaviour after similar treatments. The most important feature in the UP spectra of the reduced alkali-promoted catalysts was the appearance of a well defined Fermi edge absent in the semimetal-like electronic structure of graphite. No significant effects appeared in the case of non-promoted or Ba-promoted catalysts. The increase in the density of occupied states at the Fermi energy indicates a shift of this level into the conduction band, due to a charge transfer from the promoter to the support. This interpretation also provides an explanation for the observed higher C 1s binding energy and asymmetric broadening, due to the off-set introduced in the binding energy scale and the increasing probability of inelastic excitations near the Fermi level. In addition to photoelectron spectroscopy, low energy ion scattering (ISS) was used to obtain information about the localisation of the promoters. Based on the mild sputtering effect during prolonged series of spectra, it was possible to conclude that potassium covers both the carbon support and the Ru metal particles.

Some details of the electronic structure of tin oxide films

AbstractWe present experimental results of electronic structure investigations of SnO2 films by X‐ray emission spectroscopy and X‐ray photoelectron spectroscopy methods wherein X‐ray O Kα emission spectra for these materials are reported for the first time. The O 2p electron band shifts toward the upper edge of the valence band when oxygen vacancies increase, but, at the same time, the distance on the binding energy scale from the O 2p band centroid to the Fermi level remains constant. The O 2p valence electron band is broader on the higher binding energy side for oxides having more oxygen vacancies.

Deconstructing dimensional deconstruction

Dimensional deconstruction (DD) abstracts from higher dimensional models features of related 4-dimensional ones. DD was proposed in Refs. [1–3] as a scheme for constructing models of naturally light composite Higgs boson. These are models in which— without fine-tuning of parameters—the composite Higgs's mass M and vacuum expectation value v are much lighter than its binding energy scale Λ. We review the basic idea of DD. It is easy to arrange M ⪡ Λ. We show, however, that DD fails to give v ⪡ Λ in a model that is supposed to contain a naturally light composite Higgs [4].

On the virial theorem value and scaling of Coulomb‐bound states in semiconductor heterostructures: effects of magnetic fields

We have used the variational procedure and the fractional-dimensional space approach to study the effects of applied magnetic fields (perpendicular to the interfaces) in the virial theorem value and scaling of the shallow-donor binding energies versus quantum-sized donor Bohr radius in GaAs–(Ga,Al)As semiconductor quantum wells. In the fractional-dimensional space approach, one may show, under certain approximations, that the virial theorem value equals two and the scaling rule for the donor binding energy versus Bohr radius is hyperbolic for GaAs–(Ga,Al)As wells. In contrast, calculations within the variational scheme show that the scaling of the donor binding energies with a quantum-sized Bohr radius is, in general, non-hyperbolic and that the virial theorem value is non-constant. We conclude with a comparison with previous theoretical studies with respect to exciton states.

International Standards on Calibration of XPS and AES Spectrometer

International standards of XPS and AES spectrometers have been established. Binding energy scale calibration for XPS spectrometers was standardized as ISO 15472. The calibration of kinetic energy scale for AES spectrometers was standardized as ISO 17973 and 17974. The calibrations for the intensity scale are now discussing. The calibrations for the XPS and AES spectrometers were reviewed. The standard for XPS spectrometers specifies the calibration methods to estimate uncertainty with 95% reliability using repeatability and the linearity of binding energy scale and to correct the binding energy scales. This standard also specifies the method to establish the calibration schedule. Moreover, the standards on AES spectrometers specify the calibrations with high energy resolution for the chemical state analysis and the calibration with the medium energy resolution for elemental analysis.

Valence-band spectra of BEDT-TTF and TTF-based magnetic charge-transfer salts

The electronic structure of BEDT-TTF bis(ethylenedithio)tetrathiafulvalene, and TTF, tetrathiafulvalene, based ferrimagnetic insulating and paramagnetic semiconducting charge-transfer salts have been studied by x-ray emission spectroscopy (XES) and photoelectron spectroscopy (XPS). The counterions for the salts are the d-transition-metal complex anions $[\mathrm{Cr}(\mathrm{NCS}{)}_{4}(\mathrm{phen}){]}^{\ensuremath{-}},$ $[\mathrm{Cr}(\mathrm{NCS}{)}_{4}({\mathrm{Me}}_{2}\mathrm{phen}){]}^{\ensuremath{-}}$ and $[\mathrm{Cr}(\mathrm{NCS}{)}_{4}(\mathrm{isoq}{)}_{2}{]}^{\ensuremath{-}}$ where ${\mathrm{Me}}_{2}\mathrm{phen}=4,$ 7-dimethyl-1, 10-phenanthroline, $\mathrm{phen}=1,$ 10-phenanthroline), and $\mathrm{isoq}=\mathrm{isoquinoline}={\mathrm{C}}_{9}{\mathrm{H}}_{7}\mathrm{N}.$ The distribution of partial and total density of states was determined by comparing the XES spectra of the constituents (carbon and nitrogen $K\ensuremath{\alpha}$ and Cr ${L}_{2,3})$ with XPS valence-band spectra on the binding-energy scale. Splitting in the XPS N $1s$ and S $2p$ spectra was attributed to contributions from nonequivalent atoms, i.e., N in the NCS and phen based ligands, S in NCS and BEDT-TTF. Cr L-XES measured at the ${L}_{2}$-threshold display an unusually high ${L}_{2}$ to ${L}_{3}$ intensity ratio, which is discussed in terms of Coster-Kronig transitions and a different excitation of ${L}_{3}$ and ${L}_{2}$ levels at the ${L}_{2}$ threshold.

X-RAY EMISSION AND ABSORPTION SPECTRA AND ELECTRONIC STRUCTURE OF MgB2

Measurements of X-ray emission and absorption of the constituents of MgB 2 are presented. The results obtained are in good agreement with calculated X-ray spectra, with dipole matrix elements taken into account. The comparison of X-ray emission spectra of graphite, AlB 2, and MgB 2 in the binding energy scale supports the idea of charge transfer from σ to π bands, which creates holes at the top of the bonding σ bands and drives the high-Tc superconductivity in MgB 2.

Electronic structure ofMgB2: X-ray emission and absorption studies

Measurements of x-ray emission and absorption spectra of the constituents of MgB$_2$ are presented. The results obtained are in good agreement with calculated x-ray spectra, with dipole matrix elements taken into account. The comparison of x-ray emission spectra of graphite, AlB$_2$, and MgB$_2$ in the binding energy scale supports the idea of charge transfer from $\sigma$ to $\pi$ bands, which creates holes at the top of the bonding $\sigma$ bands and drives the high-T$_c$