Two-hole Final State Research Articles

Oxygen on-site Coulomb energy in Pr1.3−xLa0.7CexCuO4 and Bi2Sr2CaCu2O8+δ and its relation with Heisenberg exchange

We study the electronic structure of electron-doped Pr$_{1.3-x}$La$_{0.7}$Ce$_{x}$CuO$_{4}$ (PLCCO ; $T_{c}$ = 27 K, x = 0.1) and hole-doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi2212 ; $T_{c}$ = 90 K) cuprate superconductors using x-ray absorption spectroscopy (XAS) and resonant photoemission spectroscopy (Res-PES). From Res-PES across the O K-edge and Cu L-edge, we identify the O 2p and Cu 3d partial density of states (PDOS) and their correlation satellites which originate in two-hole Auger final states. Using the Cini-Sawatzky method, analysis of the experimental O 2p PDOS shows an oxygen on-site Coulomb energy for PLCCO to be $U_{p}$ = 3.3$\pm$0.5 eV and for Bi2212, $U_{p}$ = 5.6$\pm$0.5 eV, while the copper on-site Coulomb correlation energy, $U_{d}$ = 6.5$\pm$0.5 eV for Bi2212. The expression for the Heisenberg exchange interaction $J$ in terms of the electronic parameters $U_{d}$, $U_{p}$, charge-transfer energy $\Delta$ and Cu-O hopping $t_{pd}$ obtained from a simple Cu$_2$O cluster model is used to carry out an optimization analysis consistent with $J$ known from scattering experiments. The analysis also provides the effective one band on-site Coulomb correlation energy $\tilde{U}$ and the effective hopping $\tilde{t}$. PLCCO and Bi2212 are shown to exhibit very similar values of $\tilde{U}$/$\tilde{t}$ $\sim$9-10, confirming the strongly correlated nature of the singlet ground state in the effective one-band model for both the materials.

Determination of the Primary Excitation Spectra in XPS and AES

This paper reviews a procedure that allows for extracting primary photoelectron or Auger electron emissions from homogeneous isotropic samples. It is based on a quantitative dielectric description of the energy losses of swift electrons travelling nearby surfaces in presence of stationary positive charges. The theory behind the modeling of the electron energy losses, implemented in a freely available QUEELS-XPS software package, takes into account intrinsic and extrinsic effects affecting the electron transport. The procedure allows for interpretation of shake-up and multiplet structures on a quantitative basis. We outline the basic theory behind it and illustrate its capabilities with several case examples. Thus, we report on the angular dependence of the intrinsic and extrinsic Al 2s photoelectron emission from aluminum, the shake-up structure of the Ag 3d, Cu 2p, and Ce 3d photoelectron emission from silver, CuO and CeO2, respectively, and the quantification of the two-hole final states contributing to the L3M45M45 Auger electron emission of copper. These examples illustrate the procedure, that can be applied to any homogeneous isotropic material.

Single, double, and triple Auger decays from 1s shake-up states of the oxygen molecule.

The single, double, and triple Auger decays from the 1s shake-up states of O2 have been studied using a multi-electron coincidence method. Efficient populations of two-hole final states are observed in single Auger decays of the π-π* shake-up states, which is understood as a characteristic property of the Auger transitions from shake-up states of an open-shell molecule. The O23+ populations formed by double Auger decays show similar profiles for both the O1s-1 and shake-up states, which is due to the contributions from cascade double Auger processes. While the cascade contributions to the double Auger decays increase with the initial shake-up energy, the probability of direct double Auger processes remains unchanged between the O1s-1 and shake-up states, which implies a weak influence of the excited electron on the double Auger emission that originates from the electron correlation effect.

Evidence for Weakly Correlated Oxygen Holes in the Highest-T_{c} Cuprate Superconductor HgBa_{2}Ca_{2}Cu_{3}O_{8+δ}.

We study the electronic structure of HgBa_{2}Ca_{2}Cu_{3}O_{8+δ} (Hg1223; T_{c}=134 K) using photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS). Resonant valence band PES across the O K edge and Cu L edge identifies correlation satellites originating in O 2p and Cu 3d two-hole final states, respectively. Analyses using the experimental O 2p and Cu 3d partial density of states show quantitatively different on-site Coulomb energy for the Cu site (U_{dd}=6.5±0.5 eV) and O site (U_{pp}=1.0±0.5 eV). Cu_{2}O_{7}-cluster calculations with nonlocal screening explain the Cu 2p core level PES and Cu L-edge XAS spectra, confirm the U_{dd} and U_{pp} values, and provide evidence for the Zhang-Rice singlet state in Hg1223. In contrast to other hole-doped cuprates and 3d-transition metal oxides, the present results indicate weakly correlated oxygen holes in Hg1223.

Seagull and pion-in-flight currents in neutrino-induced 1N and 2N knockout

[Background] The neutrino-nucleus ($\nu A$) cross section is a major source of systematic uncertainty in neutrino-oscillation studies. A precise $\nu A$ scattering model, in which multinucleon effects are incorporated, is pivotal for an accurate interpretation of the data. [Purpose] In $\nu A$ interactions, meson-exchange currents (MECs) can induce two-nucleon ($2N$) knockout from the target nucleus, resulting in a two-particle two-hole (2p2h) final state. They also affect single nucleon ($1N$) knockout reactions, yielding a one-particle one-hole (1p1h) final state. Both channels affect the inclusive strength. We present a study of axial and vector, seagull and pion-in-flight currents in muon-neutrino induced $1N$ and $2N$ knockout reactions on $^{12}$C. [Method] Bound and emitted nucleons are described as Hartree-Fock wave functions. For the vector MECs, the standard expressions are used. For the axial current, three parameterizations are considered. The framework developed here allows for a treatment of MECs and short-range correlations (SRCs). [Results] Results are compared with electron-scattering data and with literature. The strengths of the seagull, pion-in-flight and axial currents are studied separately and double differential cross sections including MECs are compared with results including SRCs. A comparison with MiniBooNE and T2K data is presented. [Conclusions] In the 1p1h channel, the effects of the MECs tend to cancel each other, resulting in a small effect on the double differential cross section. $2N$ knockout processes provide a small contribution to the inclusive double differential cross section, ranging from the $2N$ knockout threshold into the dip region. A fair agreement with the MiniBooNE and T2K data is reached.

Contribution of two-particle–two-hole final states to the nuclear response

The excitation of two particle-two hole final states in neutrino-nucleus scattering has been advocated by many authors as the source of the excess cross section observed by the MiniBooNE Collaboration in the quasi elastic sector. We analyse the mechanisms leading to the appearance of these final states, and illustrate their significance through the results of accurate calculations of the nuclear electromagnetic response in the transverse channel. A novel approach, allowing for a consistent treatment of the amplitudes involving one- and two-nucleon currents in the kinematical region in which the non relativistic approximation breaks down, is outlined.

Spin Blocking in the Correlated Double-Electron Capture from Metal Surfaces.

The resonant capture of electrons from a metallic surface into the outer shell of a helium ion creates doubly excited states in a spin singlet (↑↓) or triplet (↑↑) configuration. Here it is shown that the capture of one or two electrons can be described in a simple quantitative model, and the capture of two electrons by He(++) proceeds in a single step. The double capture of electrons from the Fermi energy of the metal is dominated by the spin dependent electron correlation that blocks the occupation of triplet states in the ion, but creates a singlet two-hole final state at the surface, related to the concept of the exchange-correlation hole.

Resonant photoemission spectroscopy of Cu(InGa)Se2 materials for solar cells

The electron structure of CuIn1 − x Ga x Se2 single crystals is determined via resonant photoemis-sion and the main regularities of its transformation upon varying concentration x from 0 to 1 are established. The dependence of the shape of valence band spectra on the photon energy is studied. Integral photoemission intensities are shown to be determined by atomic photoionization cross sections. Processes of the direct and two-step creation of photoelectrons accompanying photoemission and the participation of internal states in the spectra of electrons from valence bands are studied. Two-hole final states in photoemission are obtained upon threshold excitation of the Cu 2p level. The strong interaction of holes leads to the multiplet splitting of these states. Partial densities of the components’ states are determined using the energy dependence of atomic photoionization cross sections.

Size-dependent Auger spectra and two-hole Coulomb interaction of small supported Cu-clusters

Auger (L3M4,5M4,5) and X-ray photoionization spectra (2p, 3d) of mass-selected CuN-clusters supported by a thin natural silica layer are presented in the size range N = 8-55 atoms per cluster. The Auger spectra of all clusters are shifted to a lower kinetic energy with respect to the spectrum of the bulk. Furthermore the Auger energy decreases systematically with decreasing cluster size. The binding energies of the 2p and 3d valence states are higher than the corresponding bulk values. Using the energy of the Auger main line, the corresponding core hole peak and the centroid of the self-convoluted 3d valence band the on-site Coulomb interaction energy Udd of the two-hole final state as a function of cluster size has been determined.

Bond Breaking, Electron Pushing, and Proton Pulling: Active and Passive Roles in the Interaction between Aqueous Ions and Water as Manifested in the O 1s Auger Decay

A core-ionized H(2)O molecule in liquid water primarily relaxes through normal Auger decay, leading to a two-hole final state in which both valence holes are localized on the same water molecule. Electronic coupling to the environment, however, allows for alternative decays resembling Intermolecular Coulombic Decay (ICD), producing final states with one of the holes delocalized on a neighboring water molecule. Here we present an experimental study of such minority processes, which adds to our understanding of dynamic interactions of electronically excited H(2)O molecules with their local surrounding in liquid water and aqueous solution. We show that the solvation of metal-halide salts considerably influences these minority decay channels from the water O 1s(-1) state. By breaking water-water bonds, both the metal cations and halide anions are found to reduce the decay into water-water delocalized states, thus having a ″passive″ effect on the Auger spectrum. The halide anions also play an ″active″ role by opening a new ICD-like decay pathway into water-halide delocalized states. The importance of this contribution increases from F(-) to I(-), which we suggest to be caused by a directional polarization of the halide anion toward the core-ionized H(2)O(+) cation in the intermediate state of the Auger process. This increases the electronic overlap between the two centers and makes delocalized decays more probable. We furthermore show that F(-), the smallest and most strongly hydrated of the halides, plays an additional role as proton puller during the core-hole lifetime, resulting in proton dynamics on the low femtosecond time scale. Our results represent a step forward toward a better understanding of how aqueous solutions, when exposed to soft X-rays, channel excess energy. This has implications for several aspects of physical and radiation chemistry, as well as biology.

Ionic-Charge Dependence of the Intermolecular Coulombic Decay Time Scale for Aqueous Ions Probed by the Core-Hole Clock

Auger electron spectroscopy combined with theoretical calculations has been applied to investigate the decay of the Ca 2p core hole of aqueous Ca(2+). Beyond the localized two-hole final states on the calcium ion, originating from a normal Auger process, we have further identified the final states delocalized between the calcium ion and its water surroundings and produced by core level intermolecular Coulombic decay (ICD) processes. By applying the core-hole clock method, the time scale of the core level ICD was determined to be 33 ± 1 fs for the 2p core hole of the aqueous Ca(2+). The comparison of this time constant to those associated with the aqueous K(+), Na(+), Mg(2+), and Al(3+) ions reveals differences of 1 and up to 2 orders of magnitude. Such large variations in the characteristic time scales of the core level ICD processes is qualitatively explained by different internal decay mechanisms in different ions as well as by different ion-solvent distances and interactions.

Many-body effect in the M 45–N 23N 45–N 45N 45N 45 coincidence spectroscopy spectra of metallic elements around Cd

The quasi-particle approximation for the 4 p4 d state of the metallic elements around Cd breaks down because of very rapid 4 p4 d–4 d 3 super Coster–Kroning (sCK) decay of the 4 p hole in the presence of the spectator 4 d hole. Here the underbar is a hole. As a result, the 4 p4 d multiplet coupling breaks down. We can examine the presence or absence of the 4 p4 d multiplet by Auger-electron sCK-electron coincidence spectroscopy measurement of the 3 d–4 p4 d–4 d 3 Auger-preceded sCK transitions. We collect the sCK-electrons in coincidence with the Auger-electrons of a selected kinetic energy (KE) and vice versa. If the multiplet coupling breaks down and does not exist, the coincidence sCK-electron (or Auger-electron) lines shift as much as the Auger-electron (or sCK-electron) analyzer's selected KE is varied. We can determine not only the three 4 d-hole sCK final-state energy but also the presence or absence of the 4 p4 d multiplet by Auger-electron sCK-electron coincidence spectroscopy. The unique capability of the coincidence measurement by which one can determine the correlation between an Auger-electron and a sCK electron generated, respectively, by creation and annihilation of the same Auger two-hole final state is very useful, even when the quasi-particle approximation of the two-hole state breaks down.

Transition from the radiationless resonant Raman scattering to the normal Auger decay in a charge transfer system

The transition from the radiationless resonant Raman scattering to the normal Auger decay in resonant Auger-electron spectroscopy (RAES) spectra of charge transfer (CT) systems is discussed by treating the relaxation and the core-hole decay of the excited core-hole state on the same footing by a many-body theory. When the resonantly excited electron remains at the excited atomic site during the core-hole decay, the RAES spectrum shows the characteristic feature of the resonant Auger–Raman effect, whereas when the excited electron has been transferred from the atomic site before the core-hole decays, the RAES spectrum shows the normal Auger decay. The present theory supports the interpretation of the variation with photon energy of the intensity ratio of the latter spectrum to the former one in the RAES spectrum by the Ar 2p → 4s resonance of Ar atoms adsorbed on Ru(0 0 1) surface reported by Keller et al. [C. Keller, M. Stichler, G. Comelli, F. Esch, S. Lizzit, D. Menzel, W. Wurth, Phys. Rev. B 57 (1998) 11951]. The transition from the radiationless resonant Raman scattering to the normal Auger decay in the RAES spectrum of CuO reported by Finazzi et al. [M. Finazzi, G. Ghiringhell, O. Tjernberg, Ph. Ohresser, N.B. Brookes, Phys. Rev. B 61 (2000) 4629] is discussed in terms of the relaxation of the resonantly excited core-hole state to the core-electron ionized main-line state by the hole–particle excitations. The merging of the resonant Raman–Auger-electron kinetic energy into the normal one about 2 eV above the absorption maximum in Cu 2O reported by Finazzi et al. [M. Finazzi, G. Ghiringhell, O. Tjernberg, Ph. Ohresser, N.B. Brookes, Phys. Rev. B 61 (2000) 4629] is explained in terms of the change in the characteristics of the screening electron in the two-hole final state. The Ti L 23-M 23V RAES spectra of TiO 2 and TiO 2− x are also analyzed.

Low-energy(5–250eV)electron-stimulated desorption ofH+,H2+, andH+(H2O)nfrom low-temperature water ice surfaces

Low-energy $(5--250\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ electron-stimulated desorption (ESD) has been used to study the production and removal of ${\mathrm{H}}^{+}$, $\mathrm{H}_{2}{}^{+}$, and ${\mathrm{H}}^{+}{({\mathrm{H}}_{2}\mathrm{O})}_{n=1--8}$ from porous amorphous solid water (PASW), amorphous solid water (ASW), and crystalline (CI) water ice films. The threshold energies for ESD of ${\mathrm{H}}^{+}$ and $\mathrm{H}_{2}{}^{+}$ from CI and ${\mathrm{H}}^{+}$ and ${\mathrm{H}}^{+}({\mathrm{H}}_{2}\mathrm{O})$ from both PASW and ASW are $\ensuremath{\sim}22\ifmmode\pm\else\textpm\fi{}3\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. There is also a $\mathrm{H}_{2}{}^{+}$ yield increase at $\ensuremath{\sim}40\ifmmode\pm\else\textpm\fi{}3\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ and a $\ensuremath{\sim}70\ifmmode\pm\else\textpm\fi{}3\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ threshold for ESD of ${\mathrm{H}}^{+}{({\mathrm{H}}_{2}\mathrm{O})}_{n=2--8}$ for all phases of ice. $\mathrm{H}_{2}{}^{+}$ production and desorption involves direct molecular elimination and reactive scattering of an energetic proton. Both of these channels likely involve localized two-hole one-electron and∕or two-hole final states containing $4{a}_{1}$, $3{a}_{1}$, and∕or $2{a}_{1}$ character. The $70\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ cluster ion threshold implicates either an initial $(2a_{1}{}^{\ensuremath{-}2})$ state localized on a monomer or the presence of at least two neighboring water molecules each containing a single hole. The resulting correlated two-hole or two-hole, one-electron configurations are localized within a complex and result in an intermolecular Coulomb repulsion and cluster ion ejection. The ${\mathrm{H}}^{+}{({\mathrm{H}}_{2}\mathrm{O})}_{n}$ yields are highest from PASW relative to ASW and CI and decrease with temperature, whereas the $\mathrm{H}_{2}{}^{+}$ yields are highest for CI and increase with temperature. The temperature effects and cluster ion distributions are accounted for by distance and temperature dependent hole screening. Changes in screening, hole lifetimes and hopping probabilities are greatest for ${a}_{1}$ levels. This is supported by valence band photoemission studies of ice as a function of temperature.

Photostimulated ion desorption from the TiO 2(1 1 0) and ZnO [formula omitted] surfaces

We used electron–ion coincidence spectroscopy to investigate the photostimulated ion desorption from clean and water-chemisorbed TiO 2(1 1 0) and ZnO ( 1 0 1 ¯ 0 ) . Desorption of O + from TiO 2(1 1 0) and ZnO ( 1 0 1 ¯ 0 ) surfaces and that of H + from water-chemisorbed TiO 2(1 1 0) and ZnO ( 1 0 1 ¯ 0 ) surfaces were observed after O1s-excitaion. These are not due to the two-hole final state caused by the ordinal single-electron excitation and its normal Auger decay but mainly due to the n-hole ( n > 2) final state which was provided by the multiple excitation/decay of the O1s electron. After metal-core excitation, meanwhile, ion (O + and H +) desorption is observed from the clean and water-chemisorbed TiO 2(1 1 0) surfaces, but not observed from clean or water-chemisorbed ZnO ( 1 0 1 ¯ 0 ) surfaces. The ion desorption following the metal-core excitation cannot be fully explained by a similar mechanism to the KF model where the inter-atomic Auger decay provides the change of the charging state of the oxygen. We therefore propose a new mechanism in which the charge transfer from the O2p orbital to the Ti3d orbital is induced by the Ti3p-core hole potential and is responsible for the creation and desorption of the O + ions.

Secondary electronic processes and the structure of X-ray photoelectron spectra of lanthanides in oxygen-containing compounds

X-ray photoelectron spectra of lanthanide compounds in the binding energy range 0–1250 eV beside the spin–orbitally split doublets exhibit fine structure. In particular, in the low-energy spectral range 0–50 eV such structure appears most likely due to the formation of the inner (IVMO) and outer (OVMO) valence molecular orbitals. The many-body perturbation shows up in the spectra of all the studied electronic shells but with different probabilities, while the multiplet splitting and dynamic effect in the spectra of just some inner shells. The present work studies the X-ray photoelectron spectral structure of lanthanide (La–Lu except for Pm) oxides and orthoniobates due to the secondary electronic processes accompanying the photoemission from the inner shells: many-body perturbation and dynamic effect. As a result, for example, the relative intensity of the line due to the many-body perturbation (shake-up process) with Δ E sat≈4 eV for LaNbO 4 was found to decrease with decreasing of the binding energy of the inner electrons from 0.72 ( E b for La 3d 5/2=834.8 eV) to 0.28 ( E b for La 4d 5/2=102.9 eV). The full-width at half-maximum of the Ln 3d 5/2 line of lanthanide oxides and orthoniobates decreases as the atomic number Z of lanthanide grows in the range 58≤ Z≤67 to the middle of the lanthanide row, and then increases. This agrees with the fact that for the beginning of the lanthanide row the Ln 3d 5/2 photoemission is accompanied by the shake-up process, while for the second half of the row—by the shake-down. It is important to note that it is connected with the Ln 4f binding energy change relative to the OVMO in compounds. The present work also confirms experimentally that the dynamic effect due to the gigantic Coster–Kronig transitions observed in the Ln 4p spectra takes place within the inner Ln 4p, 4d and outer Ln 4f shells with formation of the additional two-hole final state Ln 4p 6 4d 8 4f n+1 . The influence of the chemical environment on the Ln 4p spectral structure due to the dynamic effect was also studied.

Anomalous chemical shifts of Cu 2p and Cu LMM Auger spectra of silicate glasses

Chemical states of copper ions in various kinds of silicate glasses were investigated by X-ray photoelectron spectroscopy (XPS) and X-ray-induced Auger electron spectroscopy (XAES). Cu 2p photoelectron peaks of the melt-quenched Cu 2O–Al 2O 3–SiO 2 and Cu +/Na + ion-exchanged Cu 2O–Na 2O–Al 2O 3–SiO 2 glasses have the same binding energy assigned to Cu(I) state. On the other hand, Cu LMM Auger spectra show different spectral shapes in the respective glasses. Compared with the crystalline compounds Cu 2O and CuO and metallic Cu, the chemical shifts of the Cu LMM Auger lines are considered to represent the difference of the relaxation effect of the two-hole final state of Cu due to the electron donation ability of the surrounding elements around Cu in the glasses. Analysis of the spectra of Cu 2p and Cu LMM lines of the melt-quenched Cu 2O–Na 2O–SiO 2 glass shows remarkable X-ray irradiation effects. X-ray induces the Cu 2p peak shifts towards the lower binding energy side and finally it has a lower binding energy than that of metallic Cu. It is assigned to Cu(I) in octahedral coordination as found in the spinel structure. From the detailed analysis of Cu 2p spectra, the changes of the redox of Cu ion and the structural evolution on the glass surface are discussed.

Ion desorption induced by core-level excitation of H2O/Si(100): Evidence of desorption due to the multielectron excitation/decay

This work is an investigation of the desorption by O 1s excitation of ions from Si(100) reacted with water. Photoelectron, photostimulated desorption, and electron-ion coincidence spectroscopy are used to observe the process. When the incident photons have energy levels which are near the 1s threshold of O, they induce Auger decay that is accompanied by shakeup/off excitation and cascade Auger decay, and they are shown to be the main factor responsible for desorption in this case. When the photons have energy levels which are above the shakeup threshold, most of the desorption that occurs is a result of the shakeup excitation that accompanies the core excitation. In both cases, the desorption is induced by the respective multihole final states. The ion desorption yield for the two-hole final states of the normal process of Auger decay is small. The results are discussed, with the help of the Auger electron spectra, mainly in terms of the lifetime of the final state of Auger decay.

Spin polarized Auger electron spectroscopy of Fe and Ni

Surface sensitive experiments, in which the spin-polarized electrons are involved, play an important role for magnetic characterization, since the spin-polarized electrons are fingerprints for the local magnetization. Scanning electron microscope with polarization analysis (SEMPA) is one of the most powerful tools to investigate the surface magnetic domain structure of magnetic materials. On the other hand, at energies high enough to generate a two-hole final state arising from Auger transitions, it is possible to observe the spin polarization of the Auger electrons. These electrons reveal element-specific local magnetic information, particularly valuable for surface magnetic studies with composite systems. By using the uniqueness of the UTA-SEMPA tool, one can obtain the magnetic domain picture and also perform spin-polarized Auger electron spectroscopy studies by probing a single domain at the surface. In this study, precisely knowing the probed domain, spin polarization of electrons from super Coster–Kronig MMM Auger emissions on Fe and Ni samples have been investigated. The polarization enhancement above the 3p(M23) threshold is observed on both samples.

Angular distribution and spin polarization of Auger-electrons from a potassium (110) surface

The calculations of the spin-polarized Auger-electron emission following a core-hole excitation by circularly polarized photons from a potassium (110) surface has been performed. The angular distribution of the Auger-electron intensity is discussed and different factors determining the spin polarization of Auger-electrons are examined. It has been shown that the strong angular dependence of the Auger-electron spin polarization, predicted by the atomic model (where only the (ss) two-hole final state is considered), is substantially suppressed by contributions from the p- and d-states in the valence band of potassium crystal. This almost isotropic Auger emission can be significantly modified (particularly with respect to the angular distribution of the intensity) if the diffraction of the outgoing Auger wave on the atoms of the crystal is taken into account. In order to achieve a quantitative agreement of the calculated results with the available experimental data, the theoretical models should be improved to be valid for the accurate treatment of the scattering processes at small kinetic energies of the excited electrons.