Microstructure analysis at the interface of Er decorated Ge nanocrystals in SiO${}_{2}$

Microstructure analysis at the interface of Er decorated Ge nanocrystals in SiO $_{2}$

A. Kanjilal, S. Gemming, L. Rebohle, A. Muecklich, T. Gemming, M. Voelskow, W. Skorupa, and M. Helm

Phys. Rev. B 83, 113302 – Published 8 March 2011

Abstract

Using scanning transmission electron microscopy and aberration-corrected high-resolution transmission electron microscopy the existence of Er around Ge nanocrystals (NCs) is established. In fact, Ge NCs with Er-rich graded interfaces are proposed experimentally and validated by theoretical modeling using a supercell structure that consists of compounds determined by x-ray diffraction. The local electronic structure of the proposed interface geometry is found to be in accordance with the hypothesis behind the inverse energy transfer process from the Er $^{3 +}$ to Ge related oxygen-deficiency centers.

Received 16 December 2010

DOI:https://doi.org/10.1103/PhysRevB.83.113302

Authors & Affiliations

A. Kanjilal^1,*, S. Gemming¹, L. Rebohle¹, A. Muecklich¹, T. Gemming², M. Voelskow¹, W. Skorupa¹, and M. Helm¹

¹Institute of Ion Beam Physics and Materials Research, Forschungszentrum Dresden-Rossendorf, PO Box 51 01 19, D-01314 Dresden, Germany
²Institute for Complex Materials, IFW Dresden, PO Box 27 01 16, D-01171 Dresden, Germany

^*akanjilal@purdue.edu

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Vol. 83, Iss. 11 — 15 March 2011

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Images

Figure 1
(a) Schematic view of the Er-rich graded interface between Ge NC core and surrounding SiO $_{2}$ , showing the setup of the supercell for DFT calculation. (b) Model supercell structure consisting of Er $_{2}$ Si $_{2}$ O $_{7}$ (001) and Er $_{2}$ Ge $_{2}$ O $_{7}$ (001) layers. (c) Spatial extension of the conduction band (cb) states, representing high-lying Er(4 $f$ ) cb $^{*}$ states localized at Er in the Ge-rich layer, occurrence of mixed (Er,Ge,O) cb states at lower energy and lower lying Er(4 $f$ ) cb states. (d) Calculated DOS ( $E_{F}$ set to zero) for the supercell depicted in (b) giving the relative energy alignment of the Er-containing cb states and the occupied valence states; colors (different gray tones) denote the character of the peak obtained from a spatial decomposition of the DOS. The inset gives a magnified view of the DOS in the vicinity of $E_{F}$ .Reuse & Permissions
Figure 2
(a) Low magnification HAADF-STEM image, showing the distribution of Ge nanoparticles in SiO $_{2}$ ; the intensity ratio of the Er- $L$ and Ge- $K$ edges in regions of A, B, C, and D is shown in the adjacent plot. (b) and (c) display the EDS and EELS profiles, respectively, taken from the region indicated by a dashed rectangle in (a). (d) High-resolution HAADF-STEM image shows the formation of Ge nanoclusters with sizes in the range 7–10 nm (white contrast), while the small features below 2 nm are mostly Si nanoparticles. The trace [shown in (d)] represents the location along which a sequence of EELS profiles was recorded where a three-dimensional view of the recorded EELS profiles is exhibited in (e). Bands marked by “1” and “2” in (e) are associated with Ge and Er. (f) Bright region represents the high Ge content in the acquired EFTEM image at the Ge $M_{4, 5}$ edge. (g) HRTEM image confirms the formation of Ge NCs, while such a typical Ge NC is screened from the surrounding SiO $_{2}$ by a dark-gray patch. The scale bars in (d) and (f) are 5 and 10 nm, respectively.Reuse & Permissions
Figure 3
$Z$ -contrast simulations were performed for (a) a Ge NC (10 nm diameter) with 1-nm-thickEr $_{2}$ Ge $_{2}$ O $_{7}$ interface layer, (b) a Ge NC (8 nm diameter) with 1-nm-thick Er covering, and (c) a pure Ge NC (10 nm diameter). (d) A quantitative comparison of the intensity profiles across the center of all three simulations shown in (a)–(c). In all cases the particles were embedded in a 30-nm-thick amorphous SiO $_{2}$ matrix and were imaged using a 0.5-nm electron probe. The color scale (grayscale) is embedded in panel (d) where the length of the scale bar in (a) is 1 nm.Reuse & Permissions

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