Magnetic state of Nb 1 7nm Cu30Ni70 6nm superlattices revealed by Polarized Neutron Reflectometry and SQUID magnetometry

We report results of a magnetic characterization of [Cu$_{30}$Ni$_{70}$(6nm)]$_{20}$ (x=1-7nm) superlattices using Polarized Neutron Reflectometry (PNR) and SQUID magnetometry. The study has shown that the magnetic moment of the structures growths almost linearly from H = 0 to H$_{sat}$ = 1.3kOe which is an indirect evidence of antiferromagnetic (AF) coupling of the magnetic moments in neighbouring layers. PNR, however, did not detect any in-plane AF coupling. Taking into account the out-of-plane easy axis of the Cu$_{30}$Ni$_{70}$ layers, this may mean that only the out-of-plane component of the magnetic moments are AF coupled

Strategic use and perceptions of English as a Lingua Franca

English as a Lingua Franca is today a thriving and vibrant field of research which has sparkedconsiderable debate but also a wealth of studies in various directions. This paper builds on recentresearch in this field and focuses on two areas of investigation, namely pragmatic strategies andperceptions of ELF, while placing them within the larger theoretical framework of ELF studies

Building Polyelectrolyte Multilayers with Calmodulin A Neutron and X ray Reflectivity Study

We have studied the formation and functional properties of polyelectrolyte multilayers where calmodulin (CaM) is used as a polyanion. CaM is known to populate distinct conformational states upon binding Ca²⁺ and small ligand molecules. Therefore, we have also probed the effects of Ca²⁺ ions and trifluoperazine (TFP) as ligand molecule on the interfacial structures. Multilayers with the maximum sequence PEI-(PSS-PAH)_<i>x</i>-CaM-PAH-CaM-PAH have been deposited on silicon wafers and characterized by X-ray and neutron reflectometry. From the analysis of all data, several remarkable conclusions can be drawn. When CaM is deposited for the second time, a much thicker sublayer is produced than in the first CaM deposition step. However, upon rinsing with PAH, very thin CaM-PAH sublayers remain. There are no indications that ligand TFP can be involved in the multilayer buildup due to strong CaM-PAH interactions. However, there is a significant increase in the multilayer thickness upon removal of Ca²⁺ ions from holo-CaM and an equivalent decrease in the multilayer thickness upon subsequent saturation of apo-CaM with Ca²⁺ ions. Presumably, CaM can still be toggled between an apo and a holo state, when it is embedded in polyelectrolyte multilayers, providing an approach to design bioresponsive interfaces

Lithium insertion into silicon electrodes studied by cyclic voltammetry and operando neutron reflectometry

Operando neutron reflectometry measurements were carried out to study the insertion of lithium into amorphous silicon film electrodes during cyclic voltammetry CV experiments at a scan rate of 0.01 mV s amp; 8722;1. The experiments allow mapping of regions where significant amounts of Li are incorporated released from the electrode and correlation of the results to modifications of characteristic peaks in the CV curve. High volume changes up to 390 accompanied by corresponding modifications of the neutron scattering length density which is a measure of the average Li fraction present in the electrode are observed during electrochemical cycling for potentials below 0.3 V lithiation and above 0.2 V delithiation , leading to a hysteretic behaviour. This is attributed to result from mechanical stress as suggested in the literature. Formation and modification of a surface layer associated with the solid electrolyte interphase SEI were observed during cycling. Within the first lithiation cycle the SEI grows to 120 for potentials below 0.5 V. Afterwards a reversible and stable modification of the SEI between 70 delithiated state and 120 lithiated state takes plac

Electrochemical lithiation of silicon electrodes neutron reflectometry and secondary ion mass spectrometry investigations

In situ neutron reflectometry and ex situ secondary ion mass spectrometry in combination with electrochemical methods were used to study the lithiation of amorphous silicon electrodes. For that purpose specially designed closed three electrode electrochemical cells with thin silicon films as the working electrode and lithium as counter and reference electrodes were used. The neutron reflectometry results obtained in situ during galvanostatic cycling show that the incorporation, redistribution and removal of Li in amorphous silicon during a lithiation cycle can be monitored. It was possible to measure the volume modification during lithiation, which is found to be rather independent of cycle number, current density and film thickness and in good agreement with first principles calculations as given in literature. Indications for an inhomogeneous lithiation mechanism were found by secondary ion mass spectrometry measurements. Lithium tracer diffusion experiments indicate that the diffusivities inside the lithiated region D gt; 10 amp; 8722;15 m2 s amp; 8722;1 are considerably higher than in pure amorphous silicon as known from literature. This suggests a kinetics based explanation for the occurrence of an inhomogeneous lithiation mechanis

In Situ Studies of Solid Electrolyte Interphase SEI Formation on Crystalline Carbon Surfaces by Neutron Reflectometry and Atomic Force Microscopy

The solid electrolyte interphase (SEI) is a complex and fragile passivation layer with crucial importance for the functionality of lithium-ion batteries. Due to its fragility and reactivity, the use of in situ techniques is preferable for the determination of the SEI’s true structure and morphology during its formation. In this study, we use in situ neutron reflectometry (NR) and in situ atomic force microscopy (AFM) to investigate the SEI formation on a carbon surface. It was found that a lithium-rich adsorption layer is already present at the open circuit voltage on the carbon sample surface and that the first decomposition products start to deposit close to this potential. During the negative potential sweep, the growth of the SEI can be observed in detail by AFM and NR. This allows precise monitoring of the morphology evolution and the resulting heterogeneities of individual SEI features. NR measurements show a maximum SEI thickness of 192 Å at the lower cutoff potential (0.02 V vs Li/Li⁺), which slightly decreases during the positive potential scan. The scattering length density (SLD) obtained by NR provides additional information on the SEI’s chemical nature and structural evolution