Limits...
Embedding Ba Monolayers and Bilayers in Boron Carbide Nanowires.

Yu Z, Luo J, Shi B, Zhao J, Harmer MP, Zhu J - Sci Rep (2015)

Bottom Line: Another form of bilayer complexion stabilized at stacking faults has also been identified.Numerous previous works suggested that dopants/impurities tended to segregate at the stacking faults or twinned boundaries.Moreover, we revealed the amount of barium dopants incorporated was non-equilibrium and far beyond the bulk solubility, which might lead to unique properties.

View Article: PubMed Central - PubMed

Affiliation: Beijing National Center for Electron Microscopy, School of Materials Science and Engineering, The State Key Laboratory of New Ceramics and Fine Processing, Laboratory of Advanced Materials (MOE), Tsinghua University, Beijing 100084, China.

ABSTRACT
Aberration corrected high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) was employed to study the distribution of barium atoms on the surfaces and in the interiors of boron carbide based nanowires. Barium based dopants, which were used to control the crystal growth, adsorbed to the surfaces of the boron-rich crystals in the form of nanometer-thick surficial films (a type of surface complexion). During the crystal growth, these dopant-based surface complexions became embedded inside the single crystalline segments of fivefold boron-rich nanowires collectively, where they were converted to more ordered monolayer and bilayer modified complexions. Another form of bilayer complexion stabilized at stacking faults has also been identified. Numerous previous works suggested that dopants/impurities tended to segregate at the stacking faults or twinned boundaries. In contrast, our study revealed the previously-unrecognized possibility of incorporating dopants and impurities inside an otherwise perfect crystal without the association to any twin boundary or stacking fault. Moreover, we revealed the amount of barium dopants incorporated was non-equilibrium and far beyond the bulk solubility, which might lead to unique properties.

No MeSH data available.


(a) A low magnified HAADF image showing the coexistence of monolayers and bilayers in a crystalline segment. (b) Corresponding line profiles along a buried monolayer and across trapped planar dopants. (c) A typical micrograph showing a Ba-enriched monolayer trapped in a single crystal. Pairs of typical HAADF and BF images showing cases of a Ba bilayer trapped in a stacking fault (d) and a bilayer (e) buried in a single crystalline segment. (f) A schematic of a Ba bilayer in a stacking fault. When Δx is close to zero and Δy is identical with the (001) interplanar spacing of boron carbide, the bilayer was determined as a planar impurity buried in a single crystal, otherwise they were considered to be associated with stacking faults. The inset of (f) shows the frequency of the three different solute trapping behaviors in this study (c for monolayers in single crystals, d for bilayers in stacking faults and e for bilayers in single crystals).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4660277&req=5

f3: (a) A low magnified HAADF image showing the coexistence of monolayers and bilayers in a crystalline segment. (b) Corresponding line profiles along a buried monolayer and across trapped planar dopants. (c) A typical micrograph showing a Ba-enriched monolayer trapped in a single crystal. Pairs of typical HAADF and BF images showing cases of a Ba bilayer trapped in a stacking fault (d) and a bilayer (e) buried in a single crystalline segment. (f) A schematic of a Ba bilayer in a stacking fault. When Δx is close to zero and Δy is identical with the (001) interplanar spacing of boron carbide, the bilayer was determined as a planar impurity buried in a single crystal, otherwise they were considered to be associated with stacking faults. The inset of (f) shows the frequency of the three different solute trapping behaviors in this study (c for monolayers in single crystals, d for bilayers in stacking faults and e for bilayers in single crystals).

Mentions: More generally, there were two basic forms of Ba layers that were highly ordered in the bulk: bilayers and monolayers (Fig. 3(a)). A line profile was taken across those two types of layers (Fig. 3(b), upper panel). The impurity densities in monolayers and bilayers were close as evident by the comparable HAADF intensities. Inspection of the line profile along a monolayer revealed additional information (Fig. 3(b), lower panel): the atomic column intensities of impurity did not increase monotonically when entering into the bulk but they were almost a constant with local intensity variations. This is an indication that nearly identical amounts of impurity atoms in the depth direction were collectively incorporated in the monolayer, although it sounds somewhat counterintuitively. A schematic of the cross-section structure of the trapped Ba atoms in the monolayer deduced from focal series imaging was shown in Supplementary Fig. S5. We examined 29 sets of white lines (corresponding to incorporated Ba layers, Supplementary Fig. S6) in a 1100 °C nanowire and found that, 50% of the planar impurities were monolayers that were buried in single crystals (Fig. 3(c)); ~43% were bilayers which were associated with stacking faults (Fig. 3(d,f)); the remainder (~7%, Fig. 3(e)) was trapped as bilayers in single crystals. Our statistical analysis on the structure of impurity layers revealed two unrecognized forms of dopant atoms in the crystal: monolayers and bilayers incorporated in the single crystals.


Embedding Ba Monolayers and Bilayers in Boron Carbide Nanowires.

Yu Z, Luo J, Shi B, Zhao J, Harmer MP, Zhu J - Sci Rep (2015)

(a) A low magnified HAADF image showing the coexistence of monolayers and bilayers in a crystalline segment. (b) Corresponding line profiles along a buried monolayer and across trapped planar dopants. (c) A typical micrograph showing a Ba-enriched monolayer trapped in a single crystal. Pairs of typical HAADF and BF images showing cases of a Ba bilayer trapped in a stacking fault (d) and a bilayer (e) buried in a single crystalline segment. (f) A schematic of a Ba bilayer in a stacking fault. When Δx is close to zero and Δy is identical with the (001) interplanar spacing of boron carbide, the bilayer was determined as a planar impurity buried in a single crystal, otherwise they were considered to be associated with stacking faults. The inset of (f) shows the frequency of the three different solute trapping behaviors in this study (c for monolayers in single crystals, d for bilayers in stacking faults and e for bilayers in single crystals).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4660277&req=5

f3: (a) A low magnified HAADF image showing the coexistence of monolayers and bilayers in a crystalline segment. (b) Corresponding line profiles along a buried monolayer and across trapped planar dopants. (c) A typical micrograph showing a Ba-enriched monolayer trapped in a single crystal. Pairs of typical HAADF and BF images showing cases of a Ba bilayer trapped in a stacking fault (d) and a bilayer (e) buried in a single crystalline segment. (f) A schematic of a Ba bilayer in a stacking fault. When Δx is close to zero and Δy is identical with the (001) interplanar spacing of boron carbide, the bilayer was determined as a planar impurity buried in a single crystal, otherwise they were considered to be associated with stacking faults. The inset of (f) shows the frequency of the three different solute trapping behaviors in this study (c for monolayers in single crystals, d for bilayers in stacking faults and e for bilayers in single crystals).
Mentions: More generally, there were two basic forms of Ba layers that were highly ordered in the bulk: bilayers and monolayers (Fig. 3(a)). A line profile was taken across those two types of layers (Fig. 3(b), upper panel). The impurity densities in monolayers and bilayers were close as evident by the comparable HAADF intensities. Inspection of the line profile along a monolayer revealed additional information (Fig. 3(b), lower panel): the atomic column intensities of impurity did not increase monotonically when entering into the bulk but they were almost a constant with local intensity variations. This is an indication that nearly identical amounts of impurity atoms in the depth direction were collectively incorporated in the monolayer, although it sounds somewhat counterintuitively. A schematic of the cross-section structure of the trapped Ba atoms in the monolayer deduced from focal series imaging was shown in Supplementary Fig. S5. We examined 29 sets of white lines (corresponding to incorporated Ba layers, Supplementary Fig. S6) in a 1100 °C nanowire and found that, 50% of the planar impurities were monolayers that were buried in single crystals (Fig. 3(c)); ~43% were bilayers which were associated with stacking faults (Fig. 3(d,f)); the remainder (~7%, Fig. 3(e)) was trapped as bilayers in single crystals. Our statistical analysis on the structure of impurity layers revealed two unrecognized forms of dopant atoms in the crystal: monolayers and bilayers incorporated in the single crystals.

Bottom Line: Another form of bilayer complexion stabilized at stacking faults has also been identified.Numerous previous works suggested that dopants/impurities tended to segregate at the stacking faults or twinned boundaries.Moreover, we revealed the amount of barium dopants incorporated was non-equilibrium and far beyond the bulk solubility, which might lead to unique properties.

View Article: PubMed Central - PubMed

Affiliation: Beijing National Center for Electron Microscopy, School of Materials Science and Engineering, The State Key Laboratory of New Ceramics and Fine Processing, Laboratory of Advanced Materials (MOE), Tsinghua University, Beijing 100084, China.

ABSTRACT
Aberration corrected high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) was employed to study the distribution of barium atoms on the surfaces and in the interiors of boron carbide based nanowires. Barium based dopants, which were used to control the crystal growth, adsorbed to the surfaces of the boron-rich crystals in the form of nanometer-thick surficial films (a type of surface complexion). During the crystal growth, these dopant-based surface complexions became embedded inside the single crystalline segments of fivefold boron-rich nanowires collectively, where they were converted to more ordered monolayer and bilayer modified complexions. Another form of bilayer complexion stabilized at stacking faults has also been identified. Numerous previous works suggested that dopants/impurities tended to segregate at the stacking faults or twinned boundaries. In contrast, our study revealed the previously-unrecognized possibility of incorporating dopants and impurities inside an otherwise perfect crystal without the association to any twin boundary or stacking fault. Moreover, we revealed the amount of barium dopants incorporated was non-equilibrium and far beyond the bulk solubility, which might lead to unique properties.

No MeSH data available.