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Atomic characterization of Si nanoclusters embedded in SiO2 by atom probe tomography.

Roussel M, Talbot E, Gourbilleau F, Pareige P - Nanoscale Res Lett (2011)

Bottom Line: Such a technique and its analysis give information on the structure at the atomic level and allow obtaining complementary information with respect to other techniques.An atomic scale description of the Si nanoclusters/SiO2 ML will be fully described.This system is composed of 3.8-nm-thick SiO layers and 4-nm-thick SiO2 layers annealed 1 h at 900°C.

View Article: PubMed Central - HTML - PubMed

Affiliation: Groupe de Physique des Matériaux, Université et INSA de Rouen, UMR CNRS 6634, Av, de l'université, BP 12, 76801 Saint Etienne du Rouvray, France. manuel.roussel@etu.univ-rouen.fr.

ABSTRACT
Silicon nanoclusters are of prime interest for new generation of optoelectronic and microelectronics components. Physical properties (light emission, carrier storage...) of systems using such nanoclusters are strongly dependent on nanostructural characteristics. These characteristics (size, composition, distribution, and interface nature) are until now obtained using conventional high-resolution analytic methods, such as high-resolution transmission electron microscopy, EFTEM, or EELS. In this article, a complementary technique, the atom probe tomography, was used for studying a multilayer (ML) system containing silicon clusters. Such a technique and its analysis give information on the structure at the atomic level and allow obtaining complementary information with respect to other techniques. A description of the different steps for such analysis: sample preparation, atom probe analysis, and data treatment are detailed. An atomic scale description of the Si nanoclusters/SiO2 ML will be fully described. This system is composed of 3.8-nm-thick SiO layers and 4-nm-thick SiO2 layers annealed 1 h at 900°C.

No MeSH data available.


Concentration profile deduced from APT experiments. a. Concentration profile along the analyzed volume; b. Concentration profile across a precipitate.
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Figure 4: Concentration profile deduced from APT experiments. a. Concentration profile along the analyzed volume; b. Concentration profile across a precipitate.

Mentions: APT analysis gives a chemical map of the sample and allows us to measure the composition of each phase. These compositions can easily be estimated by counting the atoms present into phases. The composition in SiO2 layers is estimated to be 34.3 ± 0.3 at.% of Si. This measurement is very close to the theoretical composition of SiO2 (33.3 at.% of Si). The composition of the SRSO layers is estimated to be 51.0 ± 0.3 at.% of Si which is very close to the composition of SRSO layers estimated during the elaboration process. This composition corresponds to a silicon excess of ≈26% in SiO2. The stacking sequence of silicon-rich and silica layers can be clearly identified on the composition profile realized along the axis of the analyzed volume (Figure 4a). APT technique gives a local composition at the atomic scale and allows us to study the phase separation within the SRSO layers. The annealing treatment (1 h at 900°C) realized on the samples induce the precipitation of the silicon excess. Two phases are observed: SiO2-matrix, and Si-precipitates. The matrix is composed of 41.9 ± 0.3 at.% of Si. This silicon concentration is significantly higher than in pure silica. An excess of silicon is still present in the matrix evidencing an incomplete phase separation between Si and SiO2 after the 1-h annealing at 900°C. Si-nc composition can be measured with the help of composition profiles as shown in Figure 4b. This composition profile shows the oxygen and silicon concentrations across a 4-nm-diameter Si-nc. Si-nc core compositions measured in this way systematically is 80 ± 3 at.% of Si for almost all clusters. This result is not coherent with HRTEM observations. Indeed previous electron microscopy studies have proven that Si-nc are pure silicon [21,22,33]. This difference is due to a well-known APT artifact: the local magnification effect. This effect is caused by the difference between the evaporation fields of Si-nc, which is significantly lower than that of the silica surrounding (matrix). It means that silicon atoms belonging to clusters evaporate more easily than silicon and oxygen atoms of the matrix, causing local variation of curvature radius and trajectory aberrations. Because of this phenomenon, some SiO2 is artificially introduced into Si-nc during the virtual reconstruction of the tip. The local magnification is well known in the APT community and can easily be corrected [34]. Talbot et al. [35] have proposed and used a correction to study matrix/cluster interface in SRSO layers.


Atomic characterization of Si nanoclusters embedded in SiO2 by atom probe tomography.

Roussel M, Talbot E, Gourbilleau F, Pareige P - Nanoscale Res Lett (2011)

Concentration profile deduced from APT experiments. a. Concentration profile along the analyzed volume; b. Concentration profile across a precipitate.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211216&req=5

Figure 4: Concentration profile deduced from APT experiments. a. Concentration profile along the analyzed volume; b. Concentration profile across a precipitate.
Mentions: APT analysis gives a chemical map of the sample and allows us to measure the composition of each phase. These compositions can easily be estimated by counting the atoms present into phases. The composition in SiO2 layers is estimated to be 34.3 ± 0.3 at.% of Si. This measurement is very close to the theoretical composition of SiO2 (33.3 at.% of Si). The composition of the SRSO layers is estimated to be 51.0 ± 0.3 at.% of Si which is very close to the composition of SRSO layers estimated during the elaboration process. This composition corresponds to a silicon excess of ≈26% in SiO2. The stacking sequence of silicon-rich and silica layers can be clearly identified on the composition profile realized along the axis of the analyzed volume (Figure 4a). APT technique gives a local composition at the atomic scale and allows us to study the phase separation within the SRSO layers. The annealing treatment (1 h at 900°C) realized on the samples induce the precipitation of the silicon excess. Two phases are observed: SiO2-matrix, and Si-precipitates. The matrix is composed of 41.9 ± 0.3 at.% of Si. This silicon concentration is significantly higher than in pure silica. An excess of silicon is still present in the matrix evidencing an incomplete phase separation between Si and SiO2 after the 1-h annealing at 900°C. Si-nc composition can be measured with the help of composition profiles as shown in Figure 4b. This composition profile shows the oxygen and silicon concentrations across a 4-nm-diameter Si-nc. Si-nc core compositions measured in this way systematically is 80 ± 3 at.% of Si for almost all clusters. This result is not coherent with HRTEM observations. Indeed previous electron microscopy studies have proven that Si-nc are pure silicon [21,22,33]. This difference is due to a well-known APT artifact: the local magnification effect. This effect is caused by the difference between the evaporation fields of Si-nc, which is significantly lower than that of the silica surrounding (matrix). It means that silicon atoms belonging to clusters evaporate more easily than silicon and oxygen atoms of the matrix, causing local variation of curvature radius and trajectory aberrations. Because of this phenomenon, some SiO2 is artificially introduced into Si-nc during the virtual reconstruction of the tip. The local magnification is well known in the APT community and can easily be corrected [34]. Talbot et al. [35] have proposed and used a correction to study matrix/cluster interface in SRSO layers.

Bottom Line: Such a technique and its analysis give information on the structure at the atomic level and allow obtaining complementary information with respect to other techniques.An atomic scale description of the Si nanoclusters/SiO2 ML will be fully described.This system is composed of 3.8-nm-thick SiO layers and 4-nm-thick SiO2 layers annealed 1 h at 900°C.

View Article: PubMed Central - HTML - PubMed

Affiliation: Groupe de Physique des Matériaux, Université et INSA de Rouen, UMR CNRS 6634, Av, de l'université, BP 12, 76801 Saint Etienne du Rouvray, France. manuel.roussel@etu.univ-rouen.fr.

ABSTRACT
Silicon nanoclusters are of prime interest for new generation of optoelectronic and microelectronics components. Physical properties (light emission, carrier storage...) of systems using such nanoclusters are strongly dependent on nanostructural characteristics. These characteristics (size, composition, distribution, and interface nature) are until now obtained using conventional high-resolution analytic methods, such as high-resolution transmission electron microscopy, EFTEM, or EELS. In this article, a complementary technique, the atom probe tomography, was used for studying a multilayer (ML) system containing silicon clusters. Such a technique and its analysis give information on the structure at the atomic level and allow obtaining complementary information with respect to other techniques. A description of the different steps for such analysis: sample preparation, atom probe analysis, and data treatment are detailed. An atomic scale description of the Si nanoclusters/SiO2 ML will be fully described. This system is composed of 3.8-nm-thick SiO layers and 4-nm-thick SiO2 layers annealed 1 h at 900°C.

No MeSH data available.