Core-level Line Research Articles

Unraveling the effect of annealing on the structural and microstructural evolution of NiFe2O4@SiO2 core-shell type nanocomposites

The comparison between as-received and multistage annealed NiFe2O4@SiO2 (NFO@SiO2) core-shell nanoparticles is presented. The studied ferrites were synthesized by co-precipitation followed by microemulsion. The presence of cubic inverse spinel ferrite structure with tetrahedral and octahedral iron occupancy is confirmed in all analyzed samples. The structural characterization revealed the gradual crystallization of NFO cores up to about 12 nm crystallite size at the last annealing stage. Simultaneously, a partial crystallization of the silica matrix is evidenced. The superparamagnetic (SPM) behaviour is demonstrated based on complex magnetic performance and confirmed by Mössbauer spectrometry. The spin-canting phenomenon on the surface dead magnetic layer (MDL) is revealed based on the Yafet-Kittel model. A slight change in MDL thickness versus heat treatment is proved. The X-ray photoemission and absorption studies confirmed the complex nature of the Fe-based states. The Si–O–Ni/Fe intermixing on the NFO – SiO2 nanoparticles interface is revealed by the core-level lines analysis, proving the existence of a disordered layer on the NFO surface.

Study of structural, X-ray photoelectron spectroscopy, Raman and temperature-dependent magnetic studies of NiFe2O4/CoCr2O4 nanocomposites

In recent years, cobalt chromites/nickel ferrites have been attractive candidates for significant applications as nanomagnets. In the present work, structural, electronic, vibrational and low-temperature magnetic properties of NiFe2O4, CoCr2O4, and NiFe2O4/CoCr2O4 nanocomposites were investigated. Refined XRD patterns and the Raman spectra confirm the formation of the pure crystalline spinel cubic phase. The estimated crystallite size is in the range of 14 - 29 nm. X-ray photoelectron spectroscopy (XPS) confirm the oxidation state of all elements present in the synthesized samples. The studies of the photoemission core level lines prove the cations distribution in the tetrahedral and octahedral sites with the expected valence states. The magnetic studies reveal the S-type hysteresis loops, confirming the ferrimagnetic nature. The remanent and saturation magnetization increase with increasing NiFe2O4 concentration and decrease with increasing temperature. The magnetization also increases with increase of crystallite size. The temperature-dependent magnetization curve of CoCr2O4 shows the ferrimagnetic phase transition at Curie temperature TC = 86 K. The performed density functional theory (DFT) calculations indicate a significant distribution of the density of states over the Fermi level in NiFe2O4/CoCr2O4 composites as compared to bare NiFe2O4 and CoCr2O4 materials, confirming the improved electronic properties. The overall magnetic analysis proved the magnetization enhancement by increasing x concentration.

Band Alignments of GeS and GeSe Materials

Here we present new findings of a comprehensive study of the fundamental physicochemical properties for GeS and GeSe in bulk form. UV and X-ray photoelectron spectroscopies (UPS/XPS) were employed for the experiments, which were carried out on in situ cleaned (100) surfaces free from contamination. This allowed to obtain reliable results, also unchanged by effects related to charging of the samples. The work functions, electron affinities and ionization energies as well as core level lines were found. The band gaps of the investigated materials were determined by photoreflectance and optical absorption methods. As a result, band energy diagrams relative to the vacuum level for GeS and GeSe were constructed. The diagrams provide information about the valence and conduction band offsets, crucial for the design of various electronic devices and semiconducting heterostructures.

Band bending and k -resolved band offsets at the HfO2/n+(p+)Si interfaces explored with synchrotron-radiation ARPES/XPS

$\mathrm{Hf}{\mathrm{O}}_{2}/\mathrm{Si}$ interface is among the most studied heterostructure materials due to the use of ${\mathrm{HfO}}_{2}$ in the mainstream Si microelectronic technology. Following the discovery of new functionalities in ${\mathrm{HfO}}_{2}$ such as ferroelectric and reversible resistance-switching properties, we study ultrathin ${\mathrm{HfO}}_{2}$ films grown on highly doped (${p}^{+}$ and ${n}^{+}$) Si by means of synchrotron-based soft-x-ray spectroscopy techniques, such as x-ray photoelectron spectrosopy (XPS) and angle resolved photoelectron spectroscopy (ARPES). With angular resolution, we directly obtain the electronic dispersions $E$(k) of the single-crystalline Si substrate in contact with the ${\mathrm{HfO}}_{2}$ overlayer, depending on the Si doping and heat treatment, and determine the k-resolved band offset at the interface. Analysis of the Hf and Si core-level energies and line shapes as a function of photon energy yields band bending in ${\mathrm{HfO}}_{2}$ and Si. The evolution of the Hf $4f$ linewidth upon annealing points to development of a potential distribution across ${\mathrm{HfO}}_{2}$ due to charged defects at the surface and interface with Si. The effect of intense x-ray beam on the $\mathrm{Hf}{\mathrm{O}}_{2}/\mathrm{Si}$ interfaces, distorting their pristine electronic structure, is evaluated from the time evolution of line shape and position under irradiation. We propose a model explaining the effects of both heat treatment and x-ray irradiation on the $\mathrm{Hf}{\mathrm{O}}_{2}/\mathrm{Si}$ electronic structure in terms of oxygen vacancies generated at the surface of ${\mathrm{HfO}}_{2}$ and its interface to Si, where the released O atoms react with Si to form ${\mathrm{SiO}}_{x}$ at the interface. The knowledge of the irradiation-dependent band bending is essential for precise determination of the k-dependent band offset locally at the $\mathrm{Hf}{\mathrm{O}}_{2}/\mathrm{Si}$ interface.

Core-level binding energy shifts between interior, terrace and edge atoms in MnO(001) thin films

Understanding the physical origin of core-level photoemission line shapes can offer valuable information about the chemical and physical properties of surfaces. For instance, in a large number of transition metals oxides, changes in the line shape allow the accurate determination of their oxidation states and cation site symmetry. Yet, despite this importance, experimental investigations on core-level shifts have been much neglected in recent years. In order to provide further evidence of the physical relevance, we have, in this contribution, introduced a new aspect of interior-, terrace- and edge- atom core-level binding energy shifts to describe monolayers of MnO(001) films grown on an Au(111) substrate. By this means we were able to distinguish the line shape contributions related to different types of atomic sites. We show that their relative intensities and energy shifts are able to provide information about the relative amount of under coordinated atoms on the surface and, thus give insights into their catalytic properties. Our findings reveal the importance of a detailed surface science characterization to provide the correct interpretation of distinct photoemission line shapes when considering thin film samples as well as nanostructures in general.

A Comprehensive Study of Pristine and Calcined f-MWCNTs Functionalized by Nitrogen-Containing Functional Groups.

We present the study of pristine and calcined f-MWCNTs functionalized by nitrogen-containing functional groups. We focus on the structural and microstructural modification tuned by the previous annealing. However, our primary goal was to analyze the electronic structure and magnetic properties in relation to the structural properties using a multi-technique approach. The studies carried out by X-ray diffraction, XPS, and 57Fe Mössbauer spectrometry revealed the presence of γ-Fe nanoparticles, Fe3C, and α-FeOOH as catalyst residues. XPS analysis based on the deconvolution of core level lines confirmed the presence of various nitrogen-based functional groups due to the purification and functionalization process of the nanotubes. The annealing procedure leads to a structural modification mainly associated with removing surface impurities as purification residues. Magnetic studies confirmed a significant contribution of Fe3C as evidenced by a Curie temperature estimated at TC = 452 ± 15 K. A slight change in magnetic properties upon annealing was revealed. The detailed studies performed on nanotubes are extremely important for the further synthesis of composite materials based on f-MWCNTs.

Mapping hidden space-charge distributions across crystalline metal oxide/group IV semiconductor interfaces

The electronic structures of semiconducting heterojunctions are critically dependent on composition including the presence and concentrations of dopants, both intended and unintended. Dopant profiles in the interfacial region can have major effects on band energies which in turn drive transport properties. Here we use core-level photoelectron line shapes excited with hard x rays to extract information about electric fields resulting from internal charge transfer in epitaxial ${\mathrm{La}}_{0.03}{\mathrm{Sr}}_{0.97}{\mathrm{Zr}}_{x}{\mathrm{Ti}}_{1\text{--}x}{\mathrm{O}}_{3}/\mathrm{Ge}(001)$ $(0.1\ensuremath{\le}x\ensuremath{\le}0.7)$ heterostructures. Experiments were carried out for heterojunctions involving both $n$- and $p$-type Ge substrates. These heterojunctions were not amenable to electronic characterization of all regions by transport measurements because the doped substrates act as electrical shunts, precluding probing the more resistive films and masking interface conductivity. However, the core-level line shapes were found to be a rich source of information on built-in potentials that exist throughout the heterostructure, and yielded valuable insight into the impact of band bending on band alignment at the buried interfaces. The electronic effects expected for Ge with uniform $n$- and $p$-type doping are eclipsed by those of unintended oxygen dopants in the Ge near the interface. This study illustrates the power of hard x-ray photoemission spectroscopy and related modeling to determine electronic structure in material systems for which insight from traditional transport measurements is limited.

Excitation density in time-resolved water window soft X-ray spectroscopies: Experimental constraints in the detection of excited states

Time-resolved X-ray spectroscopies have the potential of unveiling ultrafast processes with chemical sensitivity, but their widespread application is still withheld by technical and experimental constraints on two levels: the count rate and the amount of signal to be measured. In this paper, we will give a brief overview of the available pulsed X-ray sources focusing in particular on those delivering photons with energies inside the water window (280–550 eV), thus allowing to access the C1s, N1s and O1s core levels which are relevant for the characterization of thin organic films and small molecules adsorbed on surfaces. We will mainly discuss the photon fluxes delivered by such sources in relation to their repetition rates, and we will see how these factors affect time-resolved measurements. The main purpose of this work is to discuss the most crucial parameter to adjust in pump-probe spectroscopies: the excitation density, which corresponds to the fraction of photoexcited molecules/atoms. We show that such quantity may be increased up to roughly 25% in gas phase and other robust samples, however, due to a lower damage threshold, in organic films it is typically constrained to be in the order of 1–5%. Despite the initially limited population of excited states in the latter case, we show that the evolution of the system may lead to a collective response of the material, which entirely modifies the measured core level line shape, thus providing a clear signal that may nonetheless offer valuable insights into the dynamics of the studied process.

Characterization of Charge States in Conducting Organic Nanoparticles by X-ray Photoemission Spectroscopy.

The metallic and semiconducting character of a large family of organic materials based on the electron donor molecule tetrathiafulvalene (TTF) is rooted in the partial oxidation (charge transfer or mixed valency) of TTF derivatives leading to partially filled molecular orbital-based electronic bands. The intrinsic structure of such complexes, with segregated donor and acceptor molecular chains or planes, leads to anisotropic electronic properties (quasi one-dimensional or two-dimensional) and morphology (needle-like or platelet-like crystals). Recently, such materials have been synthesized as nanoparticles by intentionally frustrating the intrinsic anisotropic growth. X-ray photoemission spectroscopy (XPS) has emerged as a valuable technique to characterize the transfer of charge due to its ability to discriminate the different chemical environments or electronic configurations manifested by chemical shifts of core level lines in high-resolution spectra. Since the photoemission process is inherently fast (well below the femtosecond time scale), dynamic processes can be efficiently explored. We determine here the fingerprint of partial oxidation on the photoemission lines of nanoparticles of selected TTF-based conductors.

Correlation between Microstructure and Magnetism in Ball-Milled SmCo5/α-Fe (5%wt. α-Fe) Nanocomposite Magnets.

Magnetic nanocomposites SmCo5/α-Fe were synthesized mechanically by high-energy ball milling (HEBM) from SmCo5 and 5%wt. of α-Fe powders. The X-ray diffraction analysis reveals the hexagonal 1:5 phase as the main one accompanied by the cubic α-Fe phase and 2:17 rhombohedral as the secondary phase. The content of each detected phase is modified throughout the synthesis duration. A significant decrease in crystallite size with a simultaneous increase in lattice straining is observed. A simultaneous gradual reduction in particle size is noted from the microstructural analysis. Magnetic properties reveal non-linear modification of magnetic parameters associated with the strength of the exchange coupling induced by various duration times of mechanical synthesis. The highest value of the maximum energy product (BH)max at room temperature is estimated for samples milled for 1 and 6 h. The intermediate mixed-valence state of Sm ions is confirmed by electronic structure analysis. An increase in the Co magnetic moment versus the milling time is evidenced based on the performed fitting of the Co3s core level lines.

Influence of 3d-doping on the correlation between electronic structure and magnetism in Ho(Fe1-xCox)3 intermetallics

The series of polycrystalline Ho(Fe1-xCox)3 intermetallic compounds adopting rhombohedral PuNi3-type of crystal structure have been analyzed. The partial replacement of Fe by Co atoms is reflected in the variation within the total value of saturation magnetic moment MS from 5.21 μB/f.u (x = 0.0) to 5.60 μB/f.u (x = 1.0) and simultaneous decrease of the Curie temperature TC from about 573 K (x = 0.0) to 371 K (x = 1.0). The composition dependence of the Curie temperature TC(x) and compensation temperature Tcomp(x) is related with the change in the number of 3d electrons. The valence band spectra as well as the core level lines have been analyzed at room temperature by the use of X-ray photoemission spectroscopy (XPS). The slight modification within valence bands near the Fermi level dominated by hybridized (Fe/Co)3d states has been discussed. The analysis of 3s spectra has been performed based on multiplet splitting. The evolution of Mössbauer spectra at 300 K and 80 K and estimated hyperfine parameters versus Fe/Co doping can be associated with the itinerant electron model.

Interface formation of Al2O3 on carbon enriched 6H-SiC(0001): Photoelectron spectroscopy studies

The physical vapor deposition method is used to form layers of Al2O3 insulator on carbon enriched (0001)-oriented 6H-SiC substrate at room temperature. The substrate surface and the Al2O3/6H-SiC interface are characterized in situ by X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). The electron affinity (EA) of the pre-annealed up to 800 °C under ultrahigh vacuum 6H-SiC(0001) surface and the 7 nm thick Al2O3 layer deposited on the substrate amounts to 4.1 eV, and 1.9 eV respectively. The formation of the Al2O3 compound is confirmed by the appropriate binding energies of Al-2p and O-1s core level lines, which are 75.6 eV and 532.3 eV, respectively. The valence band offset (VBO) of the Al2O3/6H-SiC interface is found to be −3.2 eV and the conduction band offset is calculated to be 0.7 eV.

Impact of surface photovoltage on photoemission from Ni/p-GaN

Surface studies on the Ni films on p-GaN concentrated on photoelectron spectroscopies are presented. We found the surface condition on which the surface photovoltage (SPV) effect, caused by an excitation source, leads to the appearance of a quasi-Fermi level located above the Fermi level of the electron energy analyzer. The energy shifts of core-level lines were also noted due to this. This means that for meta/semiconductor systems some energy shifts of peaks observed do not have to result from a chemical reaction and may be done through SPV effects. The formation of the interface, as well as its physicochemical and structural analysis, were carried out in situ under ultrahigh vacuum. Ni films were vapour deposited onto the Mg-doped GaN, (0 0 0 1)-oriented. X-ray and ultraviolet light sources were applied in photoemission experiments. The low-energy electron diffraction technique was employed for surface structure investigation.

XPS studies on the role of arsenic incorporated into GaN

In this paper physicochemical properties of non-doped GaN0.94As0.06(0001) are presented and compared to the host material. The GaN(As) epitaxial layers were grown by molecular beam epitaxy (MBE) using an As-cracker source and studied in situ in an interconnected analytical chamber using X-ray photoelectron spectroscopy (XPS). The results achieved for the highly ordered (1 × 1), (0001)-oriented GaN(As) samples reveal changes in binding energy (BE) positions of the Ga-3d and N-1s core-level lines compared to the GaN template. These peaks are shifted by about 0.4 eV towards a lower BE and positions of As states correspond to the As-Ga bonds. The valence band (VB) shape of GaN(As) indicates the same features as the host material in the range of higher BEs, however notable changes occur in the vicinity of the Fermi level. The VB maximum of GaN(As) is considerably shifted upwards.

Layer-resolved band bending at the n−SrTiO3(001)/p−Ge(001) interface

The electronic properties of epitaxial heterojunctions consisting of the prototypical perovskite oxide semiconductor, $n\ensuremath{-}{\mathrm{SrTiO}}_{3}$, and the high-mobility Group IV semiconductor $p$-Ge have been investigated. Hard x-ray photoelectron spectroscopy with a new method of analysis has been used to determine band alignment while at the same time quantifying a large built-in potential found to be present within the Ge. Accordingly, the built-in potential within the Ge has been mapped in a layer-resolved fashion. Electron transfer from donors in the $n\ensuremath{-}\mathrm{SrTi}{\mathrm{O}}_{3}$ to the $p$-Ge creates a space-charge region in the Ge resulting in downward band bending, which spans most of the Ge gap. This strong downward band bending facilitates visible light, photogenerated electron transfer from Ge to STO, favorable to drive the hydrogen evolution reaction associated with water splitting. Ti 2p and $\mathrm{Sr}\phantom{\rule{0.28em}{0ex}}3d$ core-level line shapes reveal that the STO bands are flat despite the space-charge layer therein. Inclusion of the effect of Ge band bending on band alignment is significant, amounting to a $\ensuremath{\sim}0.4\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ reduction in valence band offset compared to the value resulting from using spectra averaged over all layers. Density functional theory allows candidate interface structural models deduced from scanning transmission electron microscopy images to be simulated and structurally optimized. These structures are used to generate multislice simulations that reproduce the experimental images quite well. The calculated band offsets for these structures are in good agreement with experiment.

Effect of oxygen vacancies at the Fe/SrTiO3(001) interface: Schottky barrier and surface electron accumulation layer

We have investigated the interface formation at room temperature between Fe and ${\mathrm{TiO}}_{2}$-terminated ${\mathrm{SrTiO}}_{3}(001)$ surface using x-ray photoelectron spectroscopy. Oxygen vacancies within the ${\mathrm{SrTiO}}_{3}$ lattice in the first planes beneath the $\mathrm{Fe}\text{/}{\mathrm{SrTiO}}_{3}$ interface are induced by the Fe deposition. Through a detailed analysis of the Fe $2p$, Sr $3d$, and Ti $2p$ core-level line shapes we propose a quantitative description of the impact of the vacancies on the electronic properties of the $\mathrm{Fe}\text{/}{\mathrm{SrTiO}}_{3}$ system. While for an abrupt $\mathrm{Fe}\text{/}{\mathrm{SrTiO}}_{3}$ junction the Schottky barrier height for electrons is expected to be about 1 eV, we find that the presence of oxygen vacancies leads to a much lower barrier height value of 0.05 eV. The deposition of a fraction of Fe monolayer also pushes the surface conduction band edge of the ${\mathrm{SrTiO}}_{3}$ below the Fermi level in favor of the formation of a surface electron accumulation layer. This change in the band bending stems from the incorporation of oxygen vacancies in the near-surface region of ${\mathrm{SrTiO}}_{3}(001)$. We deduce the conduction band profile as well as the carrier density in the accumulation layer as a function of the surface potential by solving the one-dimensional Poisson equation within the modified Thomas-Fermi approximation. Owing to the electric-field dependence of the dielectric permittivity, the ${\mathrm{SrTiO}}_{3}$ with oxygen vacancies at the surface shows original electronic properties. In particular, our simulations reveal that variations of a few percent of the vacancies concentration at the surface can cause changes of several tenths of an eV in the band bending that can lead to important lateral surface inhomogeneities for the potential. We also find through our modeling that the defect states density related to oxygen vacancies at the ${\mathrm{SrTiO}}_{3}$ surface cannot exceed, at room temperature, a critical value of $\ensuremath{\sim}8\ifmmode\times\else\texttimes\fi{}{10}^{13}/\mathrm{c}{\mathrm{m}}^{2}$.

Energy shifts in photoemission lines during the tetragonal- to cubic-phase transition in BaTiO3 single crystals and systems with CoFe2O4 and NiFe2O4 overlayers

In BaTiO3 the phase transition from tetragonal to cubic is connected with the disappearance of the ferroelectric polarization. In photoelectron spectroscopy huge transient shifts in the binding energies of all core-level photoemission lines have been observed while heating and cooling through the Curie temperature. Excitation energies from 2 keV to 6 keV have been used to show this to be a bulk effect and not a surface effect alone. These observations are discussed in terms of charging, which results from the disappearance of the ferroelectric polarization. This mechanism has previously been proposed as the origin of electron emission in ferroelectric materials. Besides the jump-like shifts, additional permanent shifts in binding energies have been observed for the tetragonal and the cubic phase. These experimental shifts have been related to theoretical ones from ab initio calculations.In addition to BaTiO3 single crystals, systems with CoFe2O4 and NiFe2O4 overlayers on BaTiO3 have been investigated. The low conductivity of these layers sets them apart from metallic overlayers like Fe or Co, where the shifts are suppressed. This difference adds further support for charging as the origin of the effect.

Studies of early stages of Mn/GaN(0001) interface formation using surface-sensitive techniques

Non-doped GaN(0001) crystals are used as substrates in this study, on which Mn films are vapour deposited in situ under ultrahigh vacuum (UHV). The early stages of the Mn/GaN(0001) interface formation at room temperature are determined by means of X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and low-energy electron diffraction (LEED). The electron affinity for the already cleaned GaN(0001)-(1 × 1) surface, achieved by thermal cleaning, is 3.5 eV. The binding energy (BE) of the Ga-3d core level line shifts from 20.3 eV to 19.8 eV and the Mn-3p state from 47.6 eV to 47.2 eV upon stepwise Mn deposition due to charge transfer, e.g. Schottky barrier (SB) formation. The splitting of the Mn-2p doublet amounts to 11.2 eV and the Mn-2p3/2 peak has a BE of 638.7 eV, these values corresponding to metallic manganese. The work function of the Mn films with the thickness of 1 nm is 3.4 eV and slightly decreases to 3.2 eV with further overlayer thickness. The SB height of the interface is determined to be 1.2 eV. The Mn films show no LEED patterns. The XPS results, generally, show the absence of any interfacial compound formation.

U-Zr alloy: XPS and TEM study of surface passivation

Surface reactivity of Uranium metal is an important factor limiting its practical applications. Bcc alloys of U with various transition metals are much less reactive than pure Uranium. So as to specify the mechanism of surface protection, we have been studying the U-20 at.% Zr alloy by photoelectron spectroscopy and transmission electron microscopy. The surface was studied in as-obtained state, in various stages of surface cleaning, and during an isochronal annealing cycle. The analysis based on U-4f, Zr-3p, and O-1 s spectra shows that a Zr-rich phase segregates at the surface at temperatures exceeding 550 K, which provides a self-assembled coating. The comparison of oxygen exposure of the stoichiometric and coated surfaces shows that the coating is efficiently preventing the oxidation of uranium even at elevated temperatures. The coating can be associated with the UZr2+x phase. TEM study indicated that the coating is about 20 nm thick. For the clean state, the U-4f core-level lines of the bcc alloy are practically identical to those of α-U, revealing similar delocalization of the 5f electronic states.

X-ray photoelectron spectroscopy: Charge transfer in Fe 2p peaks and inner-sphere reorganization of ferrocenyl-containing chalcones

A systematic analysis of the XPS Fe 2p3/2 core-level photoelectron lines and their satellite structures gave insight into the electronic properties of a series of ferrocenyl-containing chalcones with the structure FcCOCHCHC6H4R, where R is in the para-position on the phenyl ring and ROCH3 (1), CH3 (2), C6H5 (3), tBu (4), H (5), Br (6) and CF3 (7). A V-shaped correlations obtained between the binding energy of the Fe 2p3/2 photoelectron line and Hammett constants (σR) of the R-groups as well as the oxidation potential of the FeII/FeIII couple, Epa, indicates that there are different modes of zwitterion formation, of electron-donating and electron-withdrawing R-substituents, after photoemission of an electron during the XPS measurements. The intensity of the satellite peak (Iratio) within the substructure of the photoelectron line is an indication of the amount of charge being transfer from the donor (ferrocenyl-fragment) to the acceptor fragments. The link between the Gordy group electronegativities, λR, and Iratio show that more charge is being transfer from Fc in chalcone with more electron withdrawing R-groups. During electron transfer processes (like electrochemical oxidation or photoemission) the chalcone undergoes inner-sphere reorganisation to compensate for the positively charged species which is formed. The Iratio is also an indication of the degree of inner-sphere reorganisation, while the carbonyl stretching frequency (vCO as measured by ATR FTIR) is a measure of the amount of energy of required for this inner-sphere reorganisation. The link between Iratio and vCO showed that as the degree of inner-sphere reorganisation increases, more energy is required for this inner-sphere reorganisation.