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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.


Related in: MedlinePlus

Low magnification HAADF images of nanowires (upper panels) and corresponding expanded view (lower panels) of trapped 2D barium layers buried within fivefold twined nanowires synthesized at the nominal temperatures of 1100 °C(a), 1200 °C (b) and 1300 °C (c), respectively. All the nanowires were aligned to the same [1–10] orientation. (d) Dependence of the average spacing of 2D impurity layers on the processing temperatures. At 1300 °C, the observation of 2D layer trapped within the crystal was rare; in this specific case, we only found two trapped 2D layers (separated by a few microns) in one of the five nanowires examined.
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f4: Low magnification HAADF images of nanowires (upper panels) and corresponding expanded view (lower panels) of trapped 2D barium layers buried within fivefold twined nanowires synthesized at the nominal temperatures of 1100 °C(a), 1200 °C (b) and 1300 °C (c), respectively. All the nanowires were aligned to the same [1–10] orientation. (d) Dependence of the average spacing of 2D impurity layers on the processing temperatures. At 1300 °C, the observation of 2D layer trapped within the crystal was rare; in this specific case, we only found two trapped 2D layers (separated by a few microns) in one of the five nanowires examined.

Mentions: The formation of the incorporated three types of dopant layers could be controlled (at least to some extent) by manipulating the processing temperatures (1100–1300 °C). As shown in Fig. 4, high densities of bright lines indicate that Ba layers were commonly present in the crystalline matrix at lower temperatures (1100–1200 °C). The existence of 2D layers became extremely rare at higher temperatures (1300 °C). As illustrated in Fig. 4(d), the occurrence of 2D Ba layers decreased greatly at higher processing temperatures. This behavior could be rationalized since Ba solute atoms were easier to escape the trapped zone during the fast ledge propagation at higher temperatures.


Embedding Ba Monolayers and Bilayers in Boron Carbide Nanowires.

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

Low magnification HAADF images of nanowires (upper panels) and corresponding expanded view (lower panels) of trapped 2D barium layers buried within fivefold twined nanowires synthesized at the nominal temperatures of 1100 °C(a), 1200 °C (b) and 1300 °C (c), respectively. All the nanowires were aligned to the same [1–10] orientation. (d) Dependence of the average spacing of 2D impurity layers on the processing temperatures. At 1300 °C, the observation of 2D layer trapped within the crystal was rare; in this specific case, we only found two trapped 2D layers (separated by a few microns) in one of the five nanowires examined.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: Low magnification HAADF images of nanowires (upper panels) and corresponding expanded view (lower panels) of trapped 2D barium layers buried within fivefold twined nanowires synthesized at the nominal temperatures of 1100 °C(a), 1200 °C (b) and 1300 °C (c), respectively. All the nanowires were aligned to the same [1–10] orientation. (d) Dependence of the average spacing of 2D impurity layers on the processing temperatures. At 1300 °C, the observation of 2D layer trapped within the crystal was rare; in this specific case, we only found two trapped 2D layers (separated by a few microns) in one of the five nanowires examined.
Mentions: The formation of the incorporated three types of dopant layers could be controlled (at least to some extent) by manipulating the processing temperatures (1100–1300 °C). As shown in Fig. 4, high densities of bright lines indicate that Ba layers were commonly present in the crystalline matrix at lower temperatures (1100–1200 °C). The existence of 2D layers became extremely rare at higher temperatures (1300 °C). As illustrated in Fig. 4(d), the occurrence of 2D Ba layers decreased greatly at higher processing temperatures. This behavior could be rationalized since Ba solute atoms were easier to escape the trapped zone during the fast ledge propagation at higher temperatures.

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.


Related in: MedlinePlus