Binding Energy Scale Research Articles

Photoluminescence in the fractional quantum Hall regime

We study the photoluminescence spectrum of a low density ( ν<1) two-dimensional electron gas at high magnetic fields and low temperatures. We find that the spectrum in the fractional quantum Hall regime can be understood in terms of singlet and triplet charged-excitons. We identify the dark triplet charged-exciton and show that it is visible in the spectrum at T<2 K . We find that its binding energy scales like e 2/ l, where l is the magnetic length, and it crosses the singlet slightly above 15 T .

Charged excitons in the fractional quantum Hall regime.

We study the photoluminescence spectrum of a low-density (nu<1) two-dimensional electron gas at high magnetic fields and low temperatures. We find that the spectrum in the fractional quantum Hall regime can be understood in terms of singlet and triplet charged excitons. We show that these spectral lines are sensitive probes for the electron compressibility. We identify the dark triplet charged exciton and show that it is visible at the spectrum at T<2 K. We find that its binding energy scales as 0.1e(2)/l, where l is the magnetic length, and it crosses the singlet slightly above 15 T.

Virial theorem and scaling of shallow-donor binding energy in quantum-sized semiconductor heterostructures

The variational and fractional-dimensional space approaches are used in a thorough study of the virial theorem value and scaling of the shallow-donor binding energies versus donor Bohr radius in GaAs/(Ga,Al)As semiconductor quantum wells (QWs) and quantum-well wires (QWWs). In the case of the fractional-dimensional space approach, in which the three-dimensional actual anisotropic semiconductor heterostructure is modelled by a fractional-dimensional isotropic effective medium, we have shown that if the ground-state wave function may be approximated by a D-dimensional hydrogenic wave function, the virial theorem value equals 2 and the scaling rule for the donor binding energy versus Bohr radius is hyperbolic, both for GaAs/(Ga,Al)As wells and wires. In contrast, calculations within the variational scheme show that the scaling of the donor binding energies with quantum-sized Bohr radius is in general nonhyperbolic and that the virial theorem value is nonconstant. Moreover, calculations for the donor binding energies versus well widths or wire radii, within both the fractional-dimensional and the variational approaches, indicate that any general conclusion based on a given virial theorem value or donor energy versus Bohr radius scaling rule should be examined with caution.

Electronic structure of graphite fluorides

Abstract Results of X-ray fluorescent measurements of carbon–fluorine compounds are presented. We have measured carbon and fluorine K α X-ray emission spectra (2 p →1 s transition) of graphite fluorides ( CF ) n and ( C 2 F ) n . We found that carbon atoms are of the sp 3 type and covalently bound to fluorine. Our measurements show that results of band structure calculations based on chair-type structure of ( CF ) n are not confirmed by comparison of carbon and fluorine emission spectra in the binding energy scale. Therefore the crystal structure of graphite fluorides is still not solved and must be refined.

Summary of the American society for testing and materials practice E 2108-00 for calibration of the electron binding-energy scale of an x-ray photoelectron spectrometer

Abstract

Summary of ISO/TC 201 Standard: VII ISO 15472 : 2001—surface chemical analysis—x‐ray photoelectron spectrometers—calibration of energy scales

AbstractThis international standard specifies a method for calibrating the binding energy scales of x‐ray photoelectron spectrometers, for general analytical purposes, using unmonochromated Al or Mg x‐rays or monochromated Al x‐rays. It is only applicable to instruments that have an ion gun for sputter cleaning. This international standard further specifies a method to establish a calibration schedule, to test for the binding energy scale linearity at one intermediate energy, to confirm the uncertainty of the scale calibration at one low and one high binding energy value, to correct for small drifts of that scale and to define the expanded uncertainty of the calibration of the binding energy scale for a confidence level of 95%. This uncertainty includes contributions for behaviour observed in inter‐laboratory studies but does not cover all of the defects that could occur. This international standard is not applicable to instruments with binding energy scale errors that are significantly non‐linear with energy, to instruments operated in the constant retardation ratio mode at retardation ratios of &lt;10, to instruments with a spectrometer resolution worse than 1.5 eV or to instruments requiring tolerance limits of ±0.03 eV or less. This international standard does not provide a full calibration check, which would confirm the energy measured at each addressable point on the energy scale and would have to be performed in accordance with the manufacturer's recommended procedures. © Crown Copyright 2001. Published by John Wiley &amp; Sons, Ltd.

Summary of ISO/TC 201 Standard: VII ISO 15472 : 2001—surface chemical analysis—x‐ray photoelectron spectrometers—calibration of energy scales

This international standard specifies a method for calibrating the binding energy scales of x-ray photoelectron spectrometers, for general analytical purposes, using unmonochromated Al or Mg x-rays or monochromated Al x-rays. It is only applicable to instruments that have an ion gun for sputter cleaning. This international standard further specifies a method to establish a calibration schedule, to test for the binding energy scale linearity at one intermediate energy, to confirm the uncertainty of the scale calibration at one low and one high binding energy value, to correct for small drifts of that scale and to define the expanded uncertainty of the calibration of the binding energy scale for a confidence level of 95%. This uncertainty includes contributions for behaviour observed in inter-laboratory studies but does not cover all of the defects that could occur. This international standard is not applicable to instruments with binding energy scale errors that are significantly non-linear with energy, to instruments operated in the constant retardation ratio mode at retardation ratios of <10, to instruments with a spectrometer resolution worse than 1.5 eV or to instruments requiring tolerance limits of ±0.03 eV or less. This international standard does not provide a full calibration check, which would confirm the energy measured at each addressable point on the energy scale and would have to be performed in accordance with the manufacturer's recommended procedures. © Crown Copyright 2001. Published by John Wiley & Sons, Ltd.

Surface characterization of IM7/5260 composites by x-ray photoelectron spectroscopy

Surfaces of high-performance carbon fiber/bismeleimide (BMI) composites (IM7/5260) have been characterized by x-ray photoelectron spectroscopy. An experimental technique to separately examine the chemical natures of the carbon fibers and BMI resin in the composite form was developed. This technique uses a flood gun to establish differential charging conditions on the BMI resin. The binding energies from the BMI resin were shifted by an amount of voltage applied to the flood gun, whereas those from the carbon fibers were uniquely determined due to their electrically conducting nature. By adding external bias voltage to the sample, the binding energies for conducting fibers were further shifted from those of the BMI resin, thereby separating the IM7 phase completely from the BMI phase in the binding energy scale, allowing independent measurement of the chemical changes associated with those peaks. Using this technique, the effects of thermal aging and surface plasma treatment on the IM7/5260 composite were studied.

XPS and XES emission investigations of d–p resonance in some copper chalcogenides

Abstract Investigations of binary and ternary copper tellurides and selenides electron energy spectra are of interest because of the considerable sensitivity of their electrophysical and optical properties to the stoichiometry of these compounds. Ab initio theoretical calculations for these non-stoichiometric AI2−xBVI compounds are difficult due to the existence of 3d-electrons in copper. Thus investigations of their band structure and electron density by means of X-ray photoelectron (XPS) and X-ray emission (XES) spectroscopy are important. In this work XPS of binary Cu2Se, Cu1.84Se, Cu1.82Se, Cu2Te, Cu1.95Te, Cu1.9Te, Cu1.7Te, and ternary CuInSe2 are obtained and matched on a common binding energy scale with the corresponding XES. The results of this matching show that copper 3d-states appear to be in the center of the tellurium or selenium p-band, splitting it into two components nearly symmetrically relatively to the d-bands. The splitting value is proportional to the content of copper in all compounds and inversely proportional to the gaps in binary chalcogenides, which corresponds with the d–s, p-resonance model. Comparative analysis of the electronic structure of binary and ternary compounds raises questions about the role of indium in determining the optical properties of CuInSe2.

On the scaling of exciton and impurity binding energies and the virial theorem in semiconductor quantum wells and quantum-well wires

AbstractWe have used the variational and fractional-dimensional space approaches in a study of the virial theorem value and scaling of the shallow-donor binding energies versus donor Bohr radiusin GaAs-(Ga,Al)As semiconductor quantum wells and quantum-well wires. A comparison is made with previous results with respect to exciton states. In the case the donor ground-state wave function may be approximated by a D-dimensional hydrogenic wave function, the virial theorem value equals 2 and the scaling rule for the donor binding energy versus quantum-sized Bohr radius is hyperbolic, both for quantum wells and wires. In contrast, calculations within the variational scheme show that the scaling of the donor binding energies with quantum-sized Bohr radius is in general nonhyperbolic and that the virial theorem value is nonconstant.

Electronic structure ofCu1−xNixRh2S4andCuRh2Se4: Band-structure calculations, x-ray photoemission, and fluorescence measurements

The electronic structure of spinel-type Cu_(1-x)Ni_xRh_2S_4 (x = 0.0, 0.1, 0.3, 0.5, 1.0) and CuRh_2Se_4 compounds has been studied by means of X-ray photoelectron and fluorescent spectroscopy. Cu L_3, Ni L_3, S L_(2,3) and Se M_(2,3) X-ray emission spectra (XES) were measured near thresholds at Beamline 8.0 of the Lawrence Berkeley Laboratory's Advanced Light Source. XES measurements of the constituent atoms of these compounds, reduced to the same binding energy scale, are found to be in excellent agreement with XPS valence bands. The calculated XES spectra which include dipole matrix elements show that the partial density of states reproduce experimental spectra quite well. States near the Fermi level (E_F) have strong Rh d and S(Se) p character in all compounds. In NiRh_2S_4 the Ni 3d states contribute strongly at E_F, whereas in both Cu compounds the Cu 3d bands are only ~1 eV wide and centered ~2.5 eV below E_F, leaving very little 3d character at E_F. The density of states at the Fermi level is less in NiRh_2S_4 than in CuRh_2S_4. This difference may contribute to the observed decrease, as a function of Ni concentration, in the superconducting transition temperature in Cu_(1-x)Ni_xRh_2S_4. The density of states of the ordered alloy Cu_(1/2)Ni_(1/2)Rh_2S_4 shows behavior that is more ``split-band''-like than ``rigid band''-like.

First Results on the Electronic Distributions of Zn-Mg-Y Alloys as Investigated by Soft X-ray Spectroscopies

AbstractWe report our first results on the electronic structure of icosahedral Zn55Mg35Y10as compared to hexagonal Zn65Mg28Y7and to the conventional Zn2Mg alloy. The occupied Mg 3s,d, and Mg 3p on the one hand and empty Mg p, Zn d-s and Y d-s states on the other hand have been investigated using soft X-ray emission and photoabsorption spectroscopy, respectively. The various sub-bands presented for Mg are adjusted in the binding energy scale whereas for the other elements they are plotted in the X-ray transition energy scale. We observe that the metallic character of the samples progressively decreases when going from the pure metals to the icosahedral compound.

Systematic XPS studies of metal oxides, hydroxides and peroxides

The results of a systematic XPS study, under high controlled conditions, of different basic oxides of transition metals, alkali and alkaline-earth metals are presented; the XPS data of some hydroxides and peroxides are also reported. Variations of the O 1s binding energies are analysed and one point of interest is the large binding energy scale obtained for O 1s peaks all associated with a ‘‘2− ’’ formal charge. Through extended Hückel theory-tight binding (EHT-TB) calculations, attempts are made to rationalize the observed variations. The results illustrate the significant differences between real charges on oxygen atoms in transition metal and alkaline-earth oxides.

Charge compensation and binding energy referencing in XPS analysis

Throughout the evolution of XPS, the ability to compensate for surface charging and accurately calibrate the binding energy scale, particularly with electrically inhomogeneous samples, has remained one of the most intractable problems. The last decade, however, has seen some quite significant advances in this area. Best exemplified perhaps by the Kratos (UK) ‘in the lens’ electrostatic mirror/electron source coupled with a magnetic immersion lens, a number of concepts have been advanced that take a quite different conceptual approach to charge compensation. They differ in a number of fundamental ways from the electron flood-type compensators, which are widely used and historically are absolutely essential with instruments based on monochromatized sources. Even more recent has been the use of combined ion and electron flood systems. Thus, modern approaches to compensation represent a more sophisticated understanding both of how charging arises and how it may be mitigated to improve the accuracy and utility of XPS spectra. Copyright © 1999 John Wiley & Sons, Ltd.

Combined study of KNbO 3 and KTaO 3 by different techniques of photoelectron and X-ray emission spectroscopy

The new results of the experimental study of KNbO 3 and KTaO 3 by means of X-ray photoelectron spectroscopy, soft X-ray emission and X-ray fluorescence spectroscopy are presented. In particular, Nb M 4,5 spectra ( 5p,4f→ 3d 5/2,3/2 transition) have been measured over a range of near-threshold excitation energies 206.5–240.6 eV, and Ta N 3 spectra ( 5d,6s→ 4p 3/2 transition) over 399.4–420.4 eV at the Beamline 8.0 of the Lawrence Berkeley National Laboratory's Advance Light Source. These spectra were found to be strongly dependent on the excitation energy. Moreover, the O Kα X-ray emission spectra in both compounds as well as the valence-band photoelectron spectra are brought to the binding energy scale and discussed in combination. The trends in the spectra are explained on the basis of first-principles band-structure calculations, with the dipole transition matrix elements taken into account.

Charge correction of the binding energy scale in XPS analysis of polymers using surface deposition of PDMS

Charge correction of the binding energy scale in XPS analysis of polymers using surface deposition of PDMS

Charge correction of the binding energy scale in XPS analysis of polymers using surface deposition of PDMS

A method is described for correcting the binding energy scale for specimen charging that occurs during XPS analysis of insulating samples. A small quantity of polymeric poly (dimethyl silicone) (PDMS) is deposited from solution onto the surface of a series of polymers. After XPS analysis, the binding energy scale is then adjusted to align the Si 2p signal of the adsorbed PDMS to the value observed on conducting samples. A model is proposed that shows that the binding energies of insulating specimens are measured with respect to the sample Fermi level. Using this method, the C 1s binding energy for aliphatic hydrocarbon (CH2)x in polyethylene is measured at 284.97 eV, in excellent agreement with previously reported values based on other correction schemes. Measured energies for 12 other materials are also presented. Copyright © 1999 John Wiley & Sons, Ltd.

Measurement of data for and the development of an ISO standard for the energy calibration of X-ray photoelectron spectrometers

New values have been developed for the reference peak energies for the levels Au 4f 7/2, Ag 3d 5/2 and Cu 2p 3/2 used for calibrating the binding energy scales of X-ray photoelectron spectrometers. These values are traceable to previous values but are homogenised between X-ray sources by calculation and are now referenced to the Ag Fermi edge instead of the Ni Fermi edge used earlier. These values, which are now extended to include monochromatic Al X-rays, are typically 0.04 eV lower than previous values. These reference energies are included in a calibration procedure to allow the evaluation of the binding energy repeatability, the energy scale linearity, the energy offset and its drift with time. Evaluation of these parameters then permits the energy scale to be calibrated within a user-defined tolerance limit over the binding energy range 0 to 1040 eV by a simple regular procedure.

An XPS and XRD study of physical and chemical homogeneity of Pb(Zr,Ti)O 3 thin films obtained by pulsed laser deposition

Pb(Zr,Ti)O 3 (PZT) oriented films deposited by laser ablation on Au(111)/Si(111) have been tested by different techniques for their physico-chemical homogeneity. The samples have been divided in different zones, in order to verify the existence of chemical and structural differences between different regions. Few techniques like X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) have been employed for characterization. XRD analyses showed differences regarding the crystallographic content and the degree of orientation between zones subjected to the plasma arriving at different angles of incidence on the sample surface. In the same zones XPS studies have been performed by a VG ESCALAB 210 Spectrometer, using a non-monochromatic AlK α X-ray source (300 W) in the five channel hemispherical analyzer. Wide scans in the binding energy scale 0–1200 eV, at 50 eV analyzer pass energy, were collected both from the as received surface and after sputter cleaning in order to put into evidence all the constituents of the film. Narrow scans of Ti 2p, Zr 3d, Pb 4f and O 1s were also acquired at 20 eV and 0.1 eV/channel pass energy and 100 ms of dwell time in order to give a better insight into the chemical bonds form and a semiquantitative analyze of the present chemical species. The piezoelectric properties of different zones were also measured.

X-ray emission spectra and electronic structure of CuIr 2S 4 and CuIr 2Se 4

Measurements of X-ray emission spectra of Cu L 2,3, S Kβ 1,3, S L 2,3 and Ir N 6,7 in CuIr 2S 4 and CuIr 2Se 4 have been performed. These measurements probe the partial Cu 3 d 4 s, S 3 p, S 3 s 3 d and Ir 5 d density of states, respectively, in the valence band. The excitation energy dependence of the Cu L 2,3 X-ray emission (XES) in CuIr 2S 4 and CuIr 2Se 4 has been measured using tunable synchrotron radiation. These measurements enabled us to obtain Cu L 3 XES free from overlapping Cu L 2 XES and high-energy satellites. These spectra reproduce the distribution of Cu 3 d-states in the valence band. X-ray emission spectra of constituents atoms of CuIr 2S 4 and CuIr 2Se, were adjusted to the binding energy scale using XPS binding energies of core levels and compared with band structure calculations and valence band spectra obtained by UPS and XPS. From these measurements one concludes that Cu 3 d-states are less mixed with Ir 5 d-states in CuIr 2Se 4 and their contribution to the density of states at the Fermi level is smaller than that of CuIr 2S 4.