Three-Dimensional Atomic Structure of Metastable Nanoclusters in Doped Semiconductors

Martin Couillard, Guillaume Radtke, Andrew P. Knights, and Gianluigi A. Botton

Phys. Rev. Lett. 107, 186104 – Published 28 October 2011

Abstract

Aberration-corrected scanning transmission electron microscopy is used to determine the atomic structure of nanoclusters of cerium dopant atoms embedded in silicon. By channeling electrons along two crystallographic orientations, we identify a characteristic zinc-blende chemical ordering within CeSi clusters coherent with the silicon host matrix. Strain energy limits the size of these ordered arrangements to just above 1 nm. With the local order identified, we then determine the atomic configuration of an individual subnanometer cluster by quantifying the scattering intensity under weak channeling condition in terms of the number of atoms. Analysis based on single-atom visualization also evidences the presence of split-vacancy impurity complexes, which supports the hypothesis of a vacancy-assisted formation of these metastable CeSi nanophases.

Received 28 June 2011

DOI:https://doi.org/10.1103/PhysRevLett.107.186104

Authors & Affiliations

Martin Couillard^1,*, Guillaume Radtke², Andrew P. Knights³, and Gianluigi A. Botton⁴

¹Brockhouse Institute of Materials Research and Canadian Centre for Electron Microscopy, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4L7, Canada
²IM2NP UMR 6242 CNRS, Faculté des Sciences de Saint-Jérôme, case 262, Université Paul Cézanne-Aix Marseille III, 13397 Marseille cedex 20, France
³Department of Engineering Physics, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4L7, Canada
⁴Department of Materials Science and Engineering and Canadian Centre for Electron Microscopy, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4L7, Canada

^*Current address: National Research Council Canada, 1200 Montreal Road, Ottawa, Ontario K1A 0R6, Canada. martin.couillard@nrc.ca

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Vol. 107, Iss. 18 — 28 October 2011

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Images

Figure 1
ADF-STEM images of Ce dopant atoms implanted in Si(100) taken (a) before and (b) after a thermal annealing process. In (a), the image on the left was taken along the [110] zone axis, and the image on the right was taken with a 4° tilt from [110]. The depth distribution of dopant atoms is shown on the left and includes insets showing individual dopant atoms in the crystalline silicon region from an off-axis (top) and on-axis (bottom) image. The dimension of inset images is 1.2 nm. A sphere representation of a tetrahedral interstitial atom is also shown in the bottom inset. In (b), the image on the left was taken along the [100] zone axis, and the image on the right was taken with a 4° tilt from [100]. The depth distribution of dopant clusters is shown on the right and includes insets showing an on-axis (top) and off-axis (bottom) image. The dimension of inset images is 2.5 nm. Inset images have been low-pass Fourier filtered (Butterworth) using parameters that ensured no significant broadening of a 0.8 Å Gaussian function. All images are displayed on a nonlinear intensity scale.Reuse & Permissions
Figure 2
ADF-STEM images of clusters taken along the (a) [110] and (b) [100] zone axes, with their corresponding atomic models in (c) and (d). The images were taken from two different TEM specimens, have been low-pass filtered, and are displayed on a nonlinear intensity scale. Their dimension is 2 nm. Panels (e) and (f) display the (110) and (100) planes in a zinc-blende lattice.Reuse & Permissions
Figure 3
(a) ADF-STEM image (low-pass filtered and on a nonlinear intensity scale, dimension of 2 nm) taken along the [100] zone axis of a CeSi cluster, with the corresponding atomic model shown in (b). A sketch of a Ce-split-vacancy configuration is presented as an inset in (b).Reuse & Permissions
Figure 4
(a) ADF-STEM image of a CeSi cluster taken along a direction close to the [100] zone axis (not filtered and displayed on a linear intensity scale). (b) Low-pass filtered image. The specimen was tilted 6° along the (001) tilt axis, and then 4° along the orthogonal axis. The convergence semiangle is 18 mrad, and the sampling is $0.009 nm / pixel$ . The inset in (a) shows an individual atom. (c) Model of the image shown in (a) obtained following the procedure described in Ref. 25, with (d) the graph of integrated intensity for each Ce column in the cluster and for the single atom (SA) shown in (a). The inset presents a model of the cluster with an estimation of the number of atoms in each column. (e) Sphere representation of the cluster.Reuse & Permissions

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