Templating rare-earth hybridization via ultrahigh vacuum annealing of ErCl${}_{3}$ nanowires inside carbon nanotubes

Templating rare-earth hybridization via ultrahigh vacuum annealing of ErCl $_{3}$ nanowires inside carbon nanotubes

Paola Ayala, Ryo Kitaura, Ryo Nakanishi, Hidetsugu Shiozawa, Daisuke Ogawa, Patrick Hoffmann, Hinsanori Shinohara, and Thomas Pichler

Phys. Rev. B 83, 085407 – Published 11 February 2011

Abstract

Here we report on controlling the effective hybridization and charge transfer of rare-earth elements inside a carbon nanotube (CNT) nanoreactor. The tubular space inside CNTs can encapsulate one-dimensional (1D) crystals such as ErCl $_{3}$ , which we have used as a starting material. Applying a thermochemical reaction in ultrahigh vacuum, we obtain elemental Er nanowires still encapsulated in the CNTs. The hybridization degree and the effective charge changes were directly accessed across the Er 4 $d$ and 3 $d$ edges by high-energy spectroscopy. It was found that Er is trivalent but the effective valence is reduced for the Er-filled tube, which strongly suggests an increased hybridization between the nanotube $π$ states and the Er 5 $d$ orbitals. This was also evidenced by the conduction band response determined in C1 $s$ –x-ray absorption spectroscopy (XAS). These results have significant implications for the 1D electronic and magnetic properties of these and similar rare-earth nanowire hybrids.

Received 12 August 2010

DOI:https://doi.org/10.1103/PhysRevB.83.085407

Authors & Affiliations

Paola Ayala¹, Ryo Kitaura², Ryo Nakanishi², Hidetsugu Shiozawa³, Daisuke Ogawa², Patrick Hoffmann⁴, Hinsanori Shinohara², and Thomas Pichler¹

¹University of Vienna, Faculty of Physics, 1090 Vienna, Austria
²Department of Chemistry, Nagoya University, Nagoya 464-8602, Japan
³Advanced Technology Institute, University of Surrey, Guildford GU2 7XH, United Kingdom
⁴BESSY II, D-12489 Berlin, Germany

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Vol. 83, Iss. 8 — 15 February 2011

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Images

Figure 1
Photoemission spectra of the core level carbon C1 $s$ response for the reference (hollow SWCNTs) and filled ErCl $_{3} @$ SWCNTs as produced and after thermal e-beam heating. Top right: XPS wide scan spectra showing the Er 4 $d$ and Cl primary responses together. The lower and upper lines correspond to the as-grown ErCl $_{3} @$ SWCNTs as well as the material after heat treatment.Reuse & Permissions
Figure 2
C1 $s$ absorption edges in x-ray absorption of filled ErCl $_{3} @$ SWCNTs as produced and after e-beam heating. The inset on top shows the overall C1 $s$ edge and the main panels are a closeup into the $π^{*}$ resonance in which a foot appears at the lower energy region, which intensity increases on the sample after heat treatment. The recorded absorption edges (circles) of the ErCl $_{3} @$ SWCNTs, after and before thermal treatment in vacuum, are depicted together with the results of a fitting and line-shape analysis that includes the labels denoting the van Hove singularities (vHs) and the overall conduction band $π^{*}$ . The foot was fitted with the curves with shaded area, corresponding to the screened vHs in the conduction band: $S_{1}^{M *}$ and $S_{2}^{M *}$ .Reuse & Permissions
Figure 3
TEM micrograph of a SWCNT bundle filled with ErCl $_{3}$ (a) with an inset (b) corresponding to a high resolution TEM image of an individual ErCl $_{3}$ -filled nanotube. In (c) appears the overall morphology of the filled NT material after heat treatment at 1000 K with insets (d) and (e) showing an individual tube where partial filling remains. The EDX spectra in the lower panels correspond to the material as synthesized [top spectrum in (f)], after resistive [lower spectrum in (f)], and e-beam heat treatment (g). The agglomerates in (c) have been inspected by EDX and they have been identified as elemental nanoparticles.Reuse & Permissions
Figure 4
XAS response in the 3 $d$ levels of erbium (left) with the corresponding RES-PES study (right) of the valence band of the ErCl $_{3}$ @SWCNTs, pre- and postheat treatment. Note that the arrows indicate the energy values at which the RES-PES right-side spectra were recorded. The numbers point toward the scaling factor responsible for the resonance enhancement.Reuse & Permissions
Figure 5
XAS response in the 4 $d$ levels of erbium (left) with the corresponding RES-PES study (right) of the valence band of the hybrid material. Note that the arrows indicate the energy values at which the RES-PES right-side spectra were recorded. The numbers point toward the scaling factor responsible for the resonance enhancement.Reuse & Permissions

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