Depth-resolved X-ray Absorption Spectroscopy Research Articles

Chemical States of Stainless Steel in nm to Several Tens of nm Region from Surface Observed by the Depth-Resolved X-ray Absorption Spectroscopy.

Chemical states of Fe, Cr, Ni, Mn, and O in stainless steel, SS304, are nondestructively observed over a wide range of depth from nanometer (nm) to several tens of nm by means of the depth-resolved X-ray absorption spectroscopy in the soft X-ray region. It is revealed that Cr is more oxidized in the surface region than the inner region, while Fe is also oxidized at the surface though the oxidation is less prominent compared to Cr. The chemical states of Cr are described by a mixture of Cr-O and Cr-OH coordinations, with more OH components at the surface. Mn and Ni spectra show MnO and metallic Ni features, respectively, throughout the depth of at least up to several tens of nm.

Understanding the Overlithiation Properties of LiNi0.6Mn0.2Co0.2O2 Using Electrochemistry and Depth-Resolved X-ray Absorption Spectroscopy

One known drawback of Ni-containing layered cathodes is their poor first cycle efficiency of 85%–90%, upon cycling in a practical potential window. The poor first cycle efficiency is likely a result of surface overlithiation due to significant lithium ion diffusion limitation at this bulk state of charge, but the overlithiation properties of Ni-containing cathodes are currently insufficiently understood. This work focuses on one Ni-containing cathode, LixNi0.6Mn0.2Co0.2O2, and performs detailed characterization of its intercalation properties both in the poor cycling efficiency region as well as in the overlithiation region, where the bulk lithium ion content rises above the value of 1. The results of the study first demonstrate that it is possible to recover the capacity this cathode “loses” in the first cycle by lowering the applied potential. Then, they establish the possibility to overlithiate LixNi0.6Mn0.2Co0.2O2 cathodes by as much as 300 mAhg−1 relative to the pristine electrode. Through complementary characterization using ex situ X-ray diffraction and X-ray absorption spectroscopy both the structural changes and the oxidation state variations in the material throughout the overlithiation process are elucidated. The generated knowledge can be used in developing more accurate physics-based models of industrially-relevant batteries.

Effect of introducing interlayers into electrode/electrolyte interface in all-solid-state battery using sulfide electrolyte

Introduction of an interlayer between a cathode and a sulfide solid electrolyte is a well-known method for reducing the interfacial resistance and improving the performance of all-solid-state batteries. However, the mechanism responsible for the interlayer remains unclear because it is difficult to observe the reactions at the nanometer-scale range. In this study, thin-film model interface of LiCoO2/80Li2S·20P2S5 and LiCoO2/Li3PO4/80Li2S·20P2S5 are fabricated by pulsed-laser deposition. The model interfaces are investigated by performing electrochemical measurements and depth-resolved X-ray absorption spectroscopy to clarify the effect of the Li3PO4 interlayer. The results indicate that a reaction product layer forms between the LiCoO2 cathode and the 80Li2S·20P2S5 electrolyte during charge/discharge processes, resulting in high interfacial resistance. Meanwhile, the formation of the reaction product layer can be suppressed by the introduction of a Li3PO4 interlayer.

Observation of an electric field-induced interface redox reaction and magnetic modification in GdOx/Co thin film by means of depth-resolved X-ray absorption spectroscopy.

We study an electric field-induced redox reaction at the interface of GdOx/Co thin film, by means of soft X-ray absorption spectroscopy (XAS). The fluorescence-yield depth-resolved XAS analysis reveals that the interfacial Co layer at GdOx/Co is composed of ∼50% Co oxide when the negative field is applied, while metallic Co is dominant in the case of the positive field. We suppose that the interfacial layer is oxidized by oxygen migration from the GdOx layer with the negative field while the interfacial layer shows the metallic state with the positive field, which means that the redox reaction is induced by the electric field. In addition, it is found from the X-ray magnetic circular dichroism (XMCD) measurement that the orbital magnetic moment of Co is larger when the negative electric field is applied to the film, as compared to the positive field. Moreover, the depth-resolved XMCD analysis reveals that the interfacial Co layer shows no or little magnetization regardless of the electric field, while for the inner layer, an increase of the orbital magnetic moment is suggested with the negative field. The field-induced magnetic modification could be attributed to the change of the orbital moment in the inner Co layer due to interfacial modifications. We thus succeed in the direct observation of the redox reaction-induced change in the interface magnetic state.

Elucidation of Reaction Mechanism at the Cathode/Electrolyte Interface in All-Solid-State Battery By Using Depth-Resolved X-Ray Absorption Spectroscopy

As one of the next-generation batteries, all-solid-state batteries have attracted a lot of attention due to their outstanding safety performance and energy density. However, their power performance are still far from traditional lithium ion batteries using liquid electrolyte, which is considered as a result of interfacial resistance existing between cathode and solid electrolyte. To overcome this inherent interfacial problem of all-solid-state batteries, there is an urgent need to understand the reaction mechanism at the cathode/electrolyte interface. As the origin of the interfacial resistance, so far there are three hypotheses have been proposed: the space-charge layer [1], the reaction product layer [2] and the mechanical structure change [3]. In this study, two types of LiCoO2 thin-film model electrodes with and without interface modification by using Li3PO4 interlayer were fabricated by pulsed laser deposition (PLD). The electrodes were applied for electrochemical measurement and depth resolved X-ray absorption spectroscopy (DR-XAS) measurement to investigate the reaction mechanism of interface between LiCoO2 cathode and Li2S-P2S5 solid electrolyte. In order to analyze the interfacial reaction, thin-film model electrode with LiCoO2 cathode and Li2S-P2S5 solid electrolyte was deposited on mirror-polished platinum substrate by PLD. A Li3PO4 interlayer was also deposited between cathode and solid electrolyte by PLD. Electrochemical measurements were performed by using liquid electrolyte (1M LiClO4 in propylene carbonate) and lithium metal anode. Cyclic voltammetry (CV) measurement was carried out from 3.2 V to 4.4 V at 0.1 mV/s. Electrochemical impedance spectroscopy (EIS) measurement was performed at 3.9 V, 4.0 V, 4.1 V, 4.2 V, 4.3 V and 4.4 V with a 30 mV amplitude during first charge and discharge cycle. The frequency range of EIS was limited from 10-2 to 106 Hz. DR-XAS measurements were conducted using the BL37XU beamline, SPring-8, Japan, with a two-dimensional pixel array detector, PILATUS (Dectris, Switzerland). Comparing to the thin-film electrode with Li3PO4 interlayer, the first cycle of CV curves of the electrode without Li3PO4 interlayer shows a current peak around 3.2 V, which is considered to come from the reaction between cathode and electrolyte. EIS measurements show that Li3PO4 interlayer can suppress the increase of interface resistant during charge and discharge, which means a more stable interface can be kept by interface modification. In order to make a more detailed observation of the interfacial structure, DR-XAS near edge structure of the electrodes are analyzed at Co K-edge. The energy shift around the interface in the electrodes with Li3PO4 interlayer is smaller than that of samples without Li3PO4 interlayer. These results indicate that valence changes of cobalt ions near cathode/solid electrolyte interface are suppressed by interface modification. The introducing of Li3PO4 interlayer reduces the inter-diffusion between cathode and solid electrolyte. The results of both electrochemical and DR-XAS measurements present that the reaction mechanism is the reaction product layer at cathode/electrolyte interface in all-solid-state battery using sulfide electrolyte. Reference [1] K. Takada, N. Ohta, L. Zhang, K. Fukuda, I. Sakaguchi, R. Ma, M. Osada, T. Sasaki , Solid State Ionics, 179 (2008) 1333. [2] A. Sakuda, A. Hayashi, M. Tatsumisago, Chem Mater, 22 (2010) 949. [3] K. Kishida, N. Wada, H. Adachi, K. Tanaka, H. Inui, C. Yada, Y. Iriyama, Z. Ogumi., Acta Materialia, 55 (2007) 4713. Acknowledgement This research was financially supported by the Japan Science and Technology Agency (JST), Advanced Low Carbon Technology Research and Development Program (ALCA), Specially Promoted Research for Innovative Next Generation Batteries (SPRING) Project.

Depth-Resolved X-Ray Absorption Spectroscopic Studies on Reaction Mechanism at the Cathode/Electrolyte Interface in All-Solid-State Battery

As one of the next-generation batteries, all-solid-state batteries have attracted attention due to their outstanding safety performance and energy density. However, their power performance are still far from the increasing demand of electric vehicles, which seems to be caused by the large interfacial resistance between cathode and solid electrolyte. To overcome the inherent interfacial problem of all-solid-state batteries, there is an urgent need to understand the reaction mechanism at the cathode/electrolyte interface. As the origin of the interfacial resistance, three hypotheses have been proposed: the space-charge layer [1], the reaction product [2] and the mechanical structure change [3]. In this study, we applied thin-film model electrode for electrochemical measurement and depth resolved X-ray absorption spectroscopy (DR-XAS) measurement to investigate the reaction mechanism of interface between LiCoO2 cathode and Li2S-P2S5 solid electrolyte with interface modification by using Li3PO4 interlayer. In order to analyze the interfacial reaction between cathode and electrolyte, thin-film model electrode with LiCoO2 cathode and Li2S-P2S5 solid electrolyte was deposited on mirror-polished platinum substrate by pulsed laser deposition (PLD). A Li3PO4 interlayer was also deposited between cathode and solid electrolyte by PLD. Electrochemical measurements were performed by using liquid electrolyte (1M LiClO4 in propylene carbonate) and lithium metal anode. Cyclic voltammetry measurement (CV) was carried out from 3.2 V to 4.4 V at 0.1 mV/s. EIS measurement was performed at 3.9 V, 4.0 V, 4.1 V, 4.2 V, 4.3 V and 4.4 V with a 30 mV amplitude. The frequency range of EIS was limited from 10-2 to 106 Hz. Depth-resolved XAS measurements were conducted using the BL37XU beamline, SPring-8, Japan, with a two-dimensional pixel array detector, PILATUS (Dectris, Switzerland). The first cycle of CV curves of the film without Li3PO4 interlayer shows a current peak around 3.2 V, which is considered to come from the reaction between cathode and electrolyte. EIS measurements show that the interfacial resistance of the films with Li3PO4 interlayer does not increase compared with the film without Li3PO4 interlayer. In order to discuss the interfacial structure, depth resolved X-ray near edge structure at Co K-edge is analyzed. The energy shift around the interface in the film with Li3PO4 interlayer is smaller than that of sample without Li3PO4 interlayer. These results indicate that valence changes of cobalt ions near cathode/solid electrolyte interface are suppressed by using Li3PO4 interlayer. The introducing of Li3PO4 interlayer reduces the inter-diffusion between cathode and solid electrolyte. Reference [1] K. Takada, N. Ohta, L. Zhang, K. Fukuda, I. Sakaguchi, R. Ma, M. Osada, T. Sasaki., Solid State Ionics, 179 (2008) 1333. [2] A. Sakuda, A. Hayashi, M. Tatsumisago., Chem Mater, 22 (2010) 949. [3] K. Kishida, N. Wada, H. Adachi, K. Tanaka, H. Inui, C. Yada, Y. Iriyama, Z. Ogumi., Acta Materialia, 55 (2007) 4713. Acknowledgement This research was financially supported by the Japan Science and Technology Agency (JST), Advanced Low Carbon Technology Research and Development Program (ALCA), Specially Promoted Research for Innovative Next Generation Batteries (SPRING) Project.

Chemical state of Ag in Conducting Bridge Random Access Memory cells: a depth resolved X-ray Absorption Spectroscopy investigation.

Conducting Bridge Random Access Memories (CBRAM) are a promising substitute for FLASH technology but problems with limited retention of the low resistance ON state still hamper their massive deployment. Depth resolved X-ray Absorption Spectroscopy has been used to describe the chemical state of the atoms of the active electrode (in this case Ag) and to reveal the role of Sb as stabilizer of the metallic state.

Depth-Resolved X-ray Absorption Spectroscopy by Means of Grazing Emission X-ray Fluorescence.

Grazing emission X-ray fluorescence (GEXRF) is well suited for nondestructive elemental-sensitive depth-profiling measurements on samples with nanometer-sized features. By varying the grazing emission angle under which the X-ray fluorescence signal is detected, the probed depth range can be tuned from a few to several hundred nanometers. The dependence of the XRF intensity on the grazing emission angle can be assessed in a sequence of measurements or in a scanning-free approach using a position-sensitive area detector. Hereafter, we will show that the combination of scanning-free GEXRF and fluorescence detected X-ray absorption spectroscopy (XAS) allows for depth-resolved chemical speciation measurements with nanometer-scale accuracy. While the conventional grazing emission geometry is advantageous to minimize self-absorption effects, the use of a scanning-free setup makes the sequential scanning of the grazing emission angles obsolete and paves the way toward time-resolved depth-sensitive XAS measurements. The presented experimental approach was applied to study the surface oxidation of an Fe layer on the top of bulk Si and of a Ge bulk sample. Thanks to the penetrating properties and the insensitivity toward the electric conduction properties of the incident and emitted X-rays, the presented experimental approach is well suited for in situ sample surface studies in the nanometer regime.

Surface Strontium Segregation of Solid Oxide Fuel Cell Cathodes Proved by In Situ Depth-Resolved X-ray Absorption Spectroscopy

Surface Strontium Segregation of Solid Oxide Fuel Cell Cathodes Proved by In Situ Depth-Resolved X-ray Absorption Spectroscopy

Effects of ZrO2 Coating on LiCoO2 Thin-Film Electrode Studied by In Situ X-ray Absorption Spectroscopy

Surface modification effects on interfacial reaction for zirconia (ZrO2) coated lithium cobalt oxide (LiCoO2) are studied. ZrO2-coated LiCoO2 thin-film electrodes are prepared by a pulsed laser deposition with different preparation periods. Cyclic voltammetry measurements clearly show that cycle performance and high-potential durability are improved by the ZrO2 coating. AC impedance spectroscopy reveals that there are two types of resistance associated with ZrO2 coating; one is the charge transfer resistance which depends on the Li+-containing electrolyte concentration, and the other is the ZrO2-layer resistance which depends on the deposition periods of ZrO2 coatings. In situ total-reflection fluorescence X-ray absorption spectroscopy for ZrO2-coated LiCoO2 thin-film electrodes reveals that the ZrO2 coating layer suppresses the reduction reaction by electrolyte contact, leading to improving its cycle performance. Depth-resolved X-ray absorption spectroscopy reveals that the ZrO2 coating layer can prevent the increase of local distortion of the LiCoO2 electrode when overcharged, leading to high-potential durability.

Sub-nm resolution depth profiling of the chemical state and magnetic structure of thin films by a depth-resolved X-ray absorption spectroscopy technique

Development and recent progress of a depth-resolved X-ray absorption spectroscopy (XAS) technique are presented, together with future prospects. The technique has been developed by controlling the probing depth of the electron-yield XAS data, which depends on the electron emission angle. This novel technique enables us to achieve depth profiling of the magnetic structure of thin films with a sub-nm depth resolution by using X-ray magnetic circular dichroism (XMCD) in X-ray absorption, which provides quantitative information on the element-specific spin and orbital magnetic moments. The chemical state and electronic structure at the surface and interface are also investigated by depth-resolved XAS analysis. As for future prospects, a three-dimensional micro XAS technique is being developed by combining an X-ray microbeam with depth-resolved XAS. Moreover, it is expected to manipulate magnetic anisotropy by using element-specific and depth-resolved magnetic anisotropy energies obtained from the depth-resolved XMCD to design thin films and multilayers with proper elements and proper thicknesses. The observation of the spin dynamics at the interface will be also possible in future by adopting the pump-probe method.

Cation Extraction Process in Bilayer Cyanide Film as Investigated by Depth-Resolved X-ray Absorption Spectroscopy

Cation Extraction Process in Bilayer Cyanide Film as Investigated by Depth-Resolved X-ray Absorption Spectroscopy

Cation Extraction Process in Bilayer Cyanide Film as Investigated by Depth-Resolved X-ray Absorption Spectroscopy

The cation extraction process in the bilayer cyanide film with an epitaxial interface, Na0.84-yCo2+[Fey3+Fe1-y2+(CN)6]0.713.8H2O (NCF71)/Na1.60-x(Cox3+Co1-x2+)[Fe2+(CN)6]0.902.8H2O (NCF90), was investigated by depth-resolved X-ray absorption spectroscopy. Assuming stepwise depth (z) distributions of Co3+ and Fe3+, we estimated the step depths, dCo and dFe, and concentrations, δCo and δFe, of the respective ions against the average quantity (δav) of cation extraction. The Na+ extraction was found to be dominant in the NCF90 surface layer, consistent with the lower redox potential in the NCF90 layer. We found that the magnitude of dFe (∼600 nm) is much deeper than the actual depth (d = 200 nm) of the NCF71/NCF90 interface, and interpreted the behavior in terms of the redox interaction in the vicinity of the interface.

Nanoscale Observation of the Electronic and Local Structures of LiCoO2 Thin Film Electrode by Depth-Resolved X-ray Absorption Spectroscopy

The electronic and local structural changes during electrochemical delithiation processes occurring at the electrode/electrolyte interface of LiCoO2 thin film electrode prepared by pulsed laser deposition were clarified by using depth-resolved X-ray absorption spectroscopy technique. We successfully obtained detailed microstructural information around the Li1–xCoO2 electrode surface with a depth resolution of ca. 3 nm using a spectro-electrochemical cell. Our results revealed a remarkable increase in the local distortions at the Li1–xCoO2 surface after charging, and the distortions extended to the bulk of Li1–xCoO2. Such unprecedented local distortions might be attributable to the marked deterioration of the electrodes.

NiO-like single layer formed on a Ni/Cu(001) thin film revealed by the depth-resolved x-ray absorption spectroscopy

The formation of a 1-ML-thick NiO-like layer on a 5.5 ML Ni ultrathin film by Ni deposition on oxygen precovered Cu(001) is revealed by the depth-resolved x-ray absorption spectroscopy, and its magnetic properties are investigated. The surface layer exhibits a NiO-like x-ray absorption spectrum, while the underlying layers show a typical spectrum for a metallic Ni film. An uncompensated spin moment is observed in the NiO-like layer, which is antiparallel to the spin moment in the underlying Ni layers. These results demonstrate a potential to fabricate a sharp interface between ferromagnetic and antiferromagnetic materials.

Depth-resolved X-ray absorption spectroscopic study on nanoscale observation of the electrode–solid electrolyte interface for all solid state lithium ion batteries

Depth-resolved X-ray absorption spectroscopy (DR-XAS) measurements were performed for the direct observation of the chemical state and local structure at the LiCoO2 electrode–solid electrolyte model interface, which can contribute towards the enhancement of the power density in all solid-state lithium batteries. The charge transfer resistance, measured by AC impedance spectroscopy, of the LiCoO2 electrode–solid electrolyte interface decreased with the introduction of a NbO2 interlayer at the interface, while the resistance increased with ZrO2 and MoO2 interlayers. Using DR-XAS with a depth resolution of about 7 nm, the changes in electronic structure and local structure of the LiCoO2 electrode were clarified. The extended X-ray absorption fine structure of DR-XAS revealed that the introduction of the NbO2 layer is effective for restricting the large Co–O bond change at the interface during delithiation. This interlayer relieved the stress at the interface due to the volume change of LiCoO2 during delithiation and then decreased the activation energy for the charge transfer process.

Depth-Resolved X-ray Absorption Spectroscopy for all Solid-State Lithium-Ion Battery

not Available.

Characterization of Manganese Oxide-Enriched Surface Layers of Fe-Mn Alloys

Alloying elements are added to steel for improving surface properties such as corrosion resistance. The alloying elements exhibit different chemical characters, and they are often enriched to the surface of the alloys during annealing at high temperatures. In this study, depth-resolved X-ray absorption spectroscopy (XAS) measurements were carried out using a two-dimensional detector with geometrical arrangement of grazing exit in detection of fluorescence X-ray emitted from sample surface, in order to characterize the enrichment and oxidation of manganese on the surface layers of an Fe-Mn alloy annealed under low oxygen partial pressure. This technique facilitates non-destructive measurement for characterizing the compositional distribution of manganese in the depth direction. The results showed that manganese was enriched to surface layers of the Fe-Mn alloys during annealing at high temperatures and formed as manganese oxide. The preferential oxidation of manganese by annealing under low oxygen partial pressure is considered the driving force for their enrichment on the alloy surface.