Blanka Detlefs

Disentangling multipole resonances through a full x-ray polarization analysis

Complete polarization analysis applied to resonant x-ray scattering at the Cr K edge in K2CrO4 shows that incident linearly polarized x rays can be converted into circularly polarized x rays by diffraction at the Cr pre-edge (E=5994eV) . The physical mechanism behind this phenomenon is a subtle interference effect between purely dipole (E1-E1) and purely quadrupole (E2-E2) transitions, leading to a phase shift between the respective scattering amplitudes. This effect may be exploited to disentangle two close-lying resonances that appear as a single peak in a conventional energy scan, in this way allowing one to single out and identify the different multipole order parameters involved.

Probing deeper by hard x-ray photoelectron spectroscopy

We report an hard x-ray photoelectron spectroscopy method combining high excitation energy (15 keV) and improved modelling of the core-level energy loss features. It provides depth distribution of deeply buried layers with very high sensitivity. We show that a conventional approach relying on intensities of the core-level peaks is unreliable due to intense plasmon losses. We reliably determine the depth distribution of 1 ML La in a high-κ/metal gate stack capped with 50 nm a-Si. The method extends the sensitivity of photoelectron spectroscopy to depths beyond 50 nm.

Structural consequences of hydrogen intercalation of epitaxial graphene on SiC(0001)

The intercalation of various atomic species, such as hydrogen, to the interface between epitaxial graphene (EG) and its SiC substrate is known to significantly influence the electronic properties of the graphene overlayers. Here, we use high-resolution X-ray reflectivity to investigate the structural consequences of the hydrogen intercalation process used in the formation of quasi-free-standing (QFS) EG/SiC(0001). We confirm that the interfacial layer is converted to a layer structurally indistinguishable from that of the overlying graphene layers. This newly formed graphene layer becomes decoupled from the SiC substrate and, along with the other graphene layers within the film, is vertically displaced by ∼2.1 A. The number of total carbon layers is conserved during the process, and we observe no other structural changes such as interlayer intercalation or expansion of the graphene d-spacing. These results clarify the under-determined structure of hydrogen intercalated QFS-EG/SiC(0001) and provide a precise model to inform further fundamental and practical understanding of the system.

PEALD ZrO2 Films Deposition on TiN and Si Substrates

a STMicroelectronics 850 rue Jean Monnet 38926 Crolles, France. b SIMaP, Grenoble-INP-CNRS-UJF, 1130 rue de la piscine 38402 Saint Martin d’Heres, France. c CMTC, Grenoble-INP, 1260 rue de la piscine 38402 Saint Martin d’Heres, France. d ESRF 6 rue Jules Horowitz 38043 Grenoble, France. e CEA-LETI, Minatec 17 rue des Martyrs 38054 Grenoble, France. f LPCML, Universite Lyon 1 UMR 5620, CNRS, 10 rue Andre-Marie Ampere 69622 Villeurbanne, France.

Resonant x-ray scattering study of Np Rh Ga 5 and Np Co Ga 5

We report a resonant x-ray scattering (RXS) study of antiferromagnetic neptunium compounds NpCoGa_5 and NpRhGa_5 at the Np M_4 and Ga K-edges. Large resonant signals of magnetic dipole character are observed below the Neel temperatures at both edges. The signals at the Np edges confirm the behaviour determined previously from neutron diffraction, i.e. the moments along [001] in NpCoGa_{5} and in NpRhGa_5 a reorientation of the moments from the c-axis direction to the ab plane. In the latter material, on application of magnetic field of 9 Tesla along the [010] direction we observe a change in the population of different [110]-type domains. We observe also a magnetic dipole signal at the Ga K-edge, similarly to the reported UGa_3 case, that can be interpreted within a semi-localized model as an orbital polarization of the Ga 4p states induced via strong hybridization with the Np 5f valence band. Quantitative analysis of the signal shows that the Ga dipole on the two different Ga sites follows closely the Np magnetic moment reorientation in NpRhGa_5. The ratios of the signals on the two inequivalent Ga sites are not the same for the different compounds.

Influence of static Jahn-Teller distortion on the magnetic excitation spectrum of PrO2: A synchrotron x-ray and neutron inelastic scattering study

A synchrotron x-ray diffraction study of the crystallographic structure of PrO{sub 2} in the Jahn-Teller distorted phase is reported. The distortion of the oxygen sublattice, which was previously ambiguous, is shown to be a chiral structure in which neighboring oxygen chains have opposite chiralities. A temperature dependent study of the magnetic excitation spectrum, probed by neutron inelastic scattering, is also reported. Changes in the energies and relative intensities of the crystal field transitions provide an insight into the interplay between the static and dynamic Jahn-Teller effects.

Flatband Voltage Tuning of HfSiON-based Gate Stacks: Impact of High Temperature Activation Annealing and LaOx Capping Layers

INTRODUCTION The aggressive scaling of metal-oxide-semiconductor field-effects transistors (MOSFETS) faces the challenge of metal gate (MG) and high-k (HK) dielectric integration to reduce power consumption [1]. Hf-based oxides and silicates, such as HfSiON, are considered as the most promising candidates for next-generation gate dielectrics, owing to their high permittivity, with a sufficiently wide band gap and a good thermal stability [2]. However, the control of the threshold voltage (Vth) for the advanced nFET and pFET devices is challenging [3]. In gate first approach, the incorporation of LaOx capping layer has been reported to provide Vth shift towards the nFET band edge, yielding the necessary decrease of the effective work function (EWF) of the gate [4]. The mechanism of this voltage shift is attributed to La-induced dipoles at the HK/Si interface [5]. For this reason, the location of LaOx capping layer within the gate stack is a key factor for optimizing the transistor Vth. So far, detailed studies of La-capped gate systems have been focused on HfO2/SiO2 stacks. In this work, we have investigated the impact of high temperature thermal annealing and LaOx capping layer on electronic structure and band discontinuity for TiN/LaOx/HfSiON/SiON/Si gate stacks by coupling hard X-ray photoelectron spectroscopy (HAXPES) with synchrotron radiation and capacitance versus voltage (CV) measurements.

Resonant x-ray scattering study of NpRhGa5 and NpCoGa5

We report a resonant x-ray scattering (RXS) study of antiferromagnetic neptunium compounds NpCoGa_5 and NpRhGa_5 at the Np M_4 and Ga K-edges. Large resonant signals of magnetic dipole character are observed below the Neel temperatures at both edges. The signals at the Np edges confirm the behaviour determined previously from neutron diffraction, i.e. the moments along [001] in NpCoGa_{5} and in NpRhGa_5 a reorientation of the moments from the c-axis direction to the ab plane. In the latter material, on application of magnetic field of 9 Tesla along the [010] direction we observe a change in the population of different [110]-type domains. We observe also a magnetic dipole signal at the Ga K-edge, similarly to the reported UGa_3 case, that can be interpreted within a semi-localized model as an orbital polarization of the Ga 4p states induced via strong hybridization with the Np 5f valence band. Quantitative analysis of the signal shows that the Ga dipole on the two different Ga sites follows closely the Np magnetic moment reorientation in NpRhGa_5. The ratios of the signals on the two inequivalent Ga sites are not the same for the different compounds.

Multi-k magnetic structures in USb0.9Tc0.1 and UAs0.8Se0.2 observed via resonant x-ray scattering at the U M4 edge

Experiments with resonant photons at the U M4 edge have been performed on a sample of USb_{0.9}Te_{0.1}, which has an incommensurate magnetic structure with k = 0.596(2) reciprocal lattice units. The reflections of the form , as observed previously in a commensurate k = 1/2 system [N. Bernhoeft et al., Phys. Rev. B 69 174415 (2004)] are observed, removing any doubt that these occur because of multiple scattering or high-order contamination of the incident photon beam. They are clearly connected with the presence of a 3k configuration. Measurements of the reflections from the sample UAs_{0.8}Se_{0.2} in a magnetic field show that the transition at T* ~ 50 K is between a low-temperature 2k and high-temperature 3k state and that this transition is sensitive to an applied magnetic field. These experiments stress the need for quantitative theory to explain the intensities of these reflections.

X-ray Raman spectroscopy of lithium-ion battery electrolyte solutions in a flow cell

The effects of varying LiPF6 salt concentration and the presence of lithium bis(oxalate)borate additive on the electronic structure of commonly used lithium-ion battery electrolyte solvents (ethylene carbonate-dimethyl carbonate and propylene carbonate) have been investigated. X-ray Raman scattering spectroscopy (a non-resonant inelastic X-ray scattering method) was utilized together with a closed-circle flow cell. Carbon and oxygen K-edges provide characteristic information on the electronic structure of the electrolyte solutions, which are sensitive to local chemistry. Higher Li+ ion concentration in the solvent manifests itself as a blue-shift of both the π* feature in the carbon edge and the carbonyl π* feature in the oxygen edge. While these oxygen K-edge results agree with previous soft X-ray absorption studies on LiBF4 salt concentration in propylene carbonate, carbon K-edge spectra reveal a shift in energy, which can be explained with differing ionic conductivities of the electrolyte solutions.