Shifts in Valence States in Bimetallic MXenes Revealed by Electron Energy-Loss Spectroscopy (EELS)

2D Materials ◽  
2022 ◽  
Author(s):  
Alexandre C. Foucher ◽  
Meikang Han ◽  
Christopher E. Shuck ◽  
Kathleen Maleski ◽  
Yury Gogotsi ◽  
...  
Keyword(s):  
Solid Solution ◽  
Energy Loss ◽  
Electron Energy ◽  
Oxidation State ◽  
Electron Energy Loss Spectroscopy ◽  
Valence State ◽  
Fine Tuning ◽  
Valence States ◽  
The Impact ◽  
Electron Energy Loss

Abstract MXenes are an emergent class of two-dimensional materials with a very wide spectrum of promising applications. The synthesis of multiple MXenes, specifically solid-solution MXenes, allows fine tuning of their properties, expands their range of applications, and leads to enhanced performance. The functionality of solid-solution MXenes is closely related to the valence state of their constituents: transition metals, oxygen, carbon, and nitrogen. However, the impact of changes in the oxidation state of elements in MXenes is not well understood. In this work, three interrelated solid-solution MXene systems (Ti2-yNbyCTx, Nb2-yVyCTx, and Ti2-yVyCTx) were investigated with scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS) to determine the localized valence states of metals at the nanoscale. The analysis demonstrates changes in the electronic configuration of V upon modification of the overall composition and within individual MXene flakes. These shifts of oxidation state can explain the nonlinear optical and electronic features of solid-solution MXenes. Vanadium appears to be particularly sensitive to modification of the valence state, while titanium maintains the same oxidation state in Ti-Nb and Ti-V MXenes, regardless of stoichiometry. The study also explains Nb's influential role in the previously observed electronic properties in the Nb-V and Nb-Ti systems.

Fast Mapping of the Cobalt-Valence State in Ba0.5Sr0.5Co0.8Fe0.2O3-dby Electron Energy Loss Spectroscopy

2013 ◽  
Vol 19 (6) ◽  
pp. 1595-1605 ◽  
Author(s):  
Philipp Müller ◽  
Matthias Meffert ◽  
Heike Störmer ◽  
Dagmar Gerthsen
Keyword(s):  
Energy Loss ◽  
Electron Energy ◽  
Electron Energy Loss Spectroscopy ◽  
Valence State ◽  
Hexagonal Phase ◽  
Fast Method ◽  
White Line ◽  
Valence States ◽  
Electron Energy Loss

AbstractA fast method for determination of the Co-valence state by electron energy loss spectroscopy in a transmission electron microscope is presented. We suggest the distance between the Co-L3and Co-L2white-lines as a reliable property for the determination of Co-valence states between 2+ and 3+. The determination of the Co-L2,3white-line distance can be automated and is therefore well suited for the evaluation of large data sets that are collected for line scans and mappings. Data with a low signal-to-noise due to short acquisition times can be processed by applying principal component analysis. The new technique was applied to study the Co-valence state of Ba0.5Sr0.5Co0.8Fe0.2O3-d(BSCF), which is hampered by the superposition of the Ba-M4,5white-lines on the Co-L2,3white-lines. The Co-valence state of the cubic BSCF phase was determined to be 2.2+ (±0.2) after annealing for 100 h at 650°C, compared to an increased valence state of 2.8+ (±0.2) for the hexagonal phase. These results support models that correlate the instability of the cubic BSCF phase with an increased Co-valence state at temperatures below 840°C.

Atomic resolution characterisation of interface structures by Electron Energy Loss Spectroscopy

1993 ◽  
Vol 51 ◽  
pp. 576-577
Author(s):  
N. D. Browning ◽  
M. M. McGibbon ◽  
M. F. Chisholm ◽  
S. J. Pennycook
Keyword(s):  
High Resolution ◽  
Energy Loss ◽  
Electron Energy ◽  
Electron Energy Loss Spectroscopy ◽  
Imaging Technique ◽  
Atomic Scale ◽  
Atomic Resolution ◽  
Reference Image ◽  
The Impact ◽  
Electron Energy Loss

The recent development of the Z-contrast imaging technique for the VG HB501 UX dedicated STEM, has added a high-resolution imaging facility to a microscope used mainly for microanalysis. This imaging technique not only provides a high-resolution reference image, but as it can be performed simultaneously with electron energy loss spectroscopy (EELS), can be used to position the electron probe at the atomic scale. The spatial resolution of both the image and the energy loss spectrum can be identical, and in principle limited only by the 2.2 Å probe size of the microscope. There now exists, therefore, the possibility to perform chemical analysis of materials on the scale of single atomic columns or planes.In order to achieve atomic resolution energy loss spectroscopy, the range over which a fast electron can cause a particular excitation event, must be less than the interatomic spacing. This range is described classically by the impact parameter, b, which ranges from ~10 Å for the low loss region of the spectrum to <1Å for the core losses.

A Study of [Cr-O6]-based rutile analogues by means of EELS

2008 ◽  
Vol 1148 ◽  
Author(s):  
Angel M. Arevalo-Lopez ◽  
Elizabeth Castillo-Martinez ◽  
Miguel Ángel Alario-Franco
Keyword(s):  
Energy Loss ◽  
Linear Relationship ◽  
Electron Energy ◽  
Oxidation State ◽  
Electron Energy Loss Spectroscopy ◽  
Oxidation States ◽  
Formal Oxidation State ◽  
Electron Energy Loss

AbstractWe present in here the study by means of electron energy loss spectroscopy (EELS) of several rutile based oxides, having in common the presence of octahedrally oxygen coordinated chromium, [Cr-O6], in three different formal oxidation states: Cr4+ in CrO2, a regular rutile; Cr3+ in CrOOH, a H bonded orthorrombic distorted rutile and in CrTaO4, a metal disordered rutile and Cr2+ in CrTa2O6 an ordered trirutile structure. A linear relationship is observed between the formal oxidation state of chromium in all these rutile oxides and the separation between the Cr-L2,3 and O-K energy loss peaks.

The determination of the Pr valence state in (Pr1.5Ce0.5)Sr2Cu2NbO10 compound by Electron Energy Loss Spectroscopy

1995 ◽  
Vol 53 ◽  
pp. 378-379
Author(s):  
S. C. Cheng ◽  
V. P. Dravid
Keyword(s):  
Energy Loss ◽  
Electron Energy ◽  
Electron Energy Loss Spectroscopy ◽  
Valence State ◽  
Energy Position ◽  
Measured Energy ◽  
Electron Energy Loss

The debate on the Pr valence state in PrBCO compounds is well documented. Recently (Pr1.5Ce0.5)Sr2Cu2NbO10(RCeSCNO) system has been synthesized and studied. In this paper, the results of our study to determine the valence of Pr in PrCeSCNO, which has similar property of PrBCO are presented. Typical EELS spectrum of Pr M45 edges with Ce M45 edges from (Pr1.5Ce0.5)Sr2Cu2NbO10 is shown in Fig. 1. In Fig. 1 the energy position of Ce M45 edges were taken at 883.0 eV and 901.0 eV. The Ce M45 edges were used to calibrate the energy axis, so that the position of Pr M45 edges could be accurately measured. The measured energy positions of Pr M45 edges in PrCeSCNO and in Pr2Ce2O7 and Pr2Ce2O8, which were used to obtain the spectra of trivalent and tetravalent Pr compounds, are also listed in table 1. The spectra taken from these compounds are shown in Fig. 1 (a) and (b).

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