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Tailoring low-dimensional structures of bismuth on monolayer epitaxial graphene.

Chen HH, Su SH, Chang SL, Cheng BY, Chen SW, Chen HY, Lin MF, Huang JC - Sci Rep (2015)

Bottom Line: Upon Bi deposition, a little charge transfer occurs and a characteristic peak can be observed in the tunneling spectrum, reflecting the distinctive electronic structure of the Bi adatoms.When annealed to ~500 K, 2D triangular Bi islands aggregate into Bi nanoclusters (NCs) of uniform size.The approaches adopted herein provide perspectives for fabricating and characterizing periodic networks on MEG and related systems, which are useful in realizing graphene-based electronic, energy, sensor and spintronic devices.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, National Cheng Kung University, Tainan, Taiwan 701, Taiwan.

ABSTRACT
To improve graphene-based multifunctional devices at nanoscale, a stepwise and controllable fabrication procedure must be elucidated. Here, a series of structural transition of bismuth (Bi) adatoms, adsorbed on monolayer epitaxial graphene (MEG), is explored at room temperature. Bi adatoms undergo a structural transition from one-dimensional (1D) linear structures to two-dimensional (2D) triangular islands and such 2D growth mode is affected by the corrugated substrate. Upon Bi deposition, a little charge transfer occurs and a characteristic peak can be observed in the tunneling spectrum, reflecting the distinctive electronic structure of the Bi adatoms. When annealed to ~500 K, 2D triangular Bi islands aggregate into Bi nanoclusters (NCs) of uniform size. A well-controlled fabrication method is thus demonstrated. The approaches adopted herein provide perspectives for fabricating and characterizing periodic networks on MEG and related systems, which are useful in realizing graphene-based electronic, energy, sensor and spintronic devices.

No MeSH data available.


Clean MEG surface.(a) Atomically resolved STM image of MEG on 4H-SiC (0001) (6.5 nm × 6.5 nm, Vs = 40 mV, I = 0.15 nA). (b) Side view ball-and-stick representations of MEG/4H-SiC (0001). (c) dI/dV-V curve obtained on clean surface of MEG.
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f1: Clean MEG surface.(a) Atomically resolved STM image of MEG on 4H-SiC (0001) (6.5 nm × 6.5 nm, Vs = 40 mV, I = 0.15 nA). (b) Side view ball-and-stick representations of MEG/4H-SiC (0001). (c) dI/dV-V curve obtained on clean surface of MEG.

Mentions: Fig. 1(a) presents an atomically clean surface of MEG. The image reveals a well-identified honeycomb lattice of the graphene superimposed onto the 6 × 6 superstructure (bright hexagon)1617, as well as the corresponding Fast Fourier transform [FFT, inset in Fig. 1(a)]. A white solid arrow points to a 1 × 1-G spot and a green dashed arrow assigns to a 6 × 6-SiC spot1819. Fig. 1(b) schematically depicts a cross-section view of the MEG/4H-SiC (0001) structure using ball-and-stick representations. The dI/dV spectrum of the as-grown MEG in Fig. 1(c) exhibits a local minimum ~−0.37 eV, representing the Dirac point of graphene20. Although some packets are observed within the range −0.2 eV to 0.4 eV, these are likely deemed to be a result of many-body effects in graphene21 or the effect of corrugated substrate. The main feature (Dirac point) still can be identified. Upon the deposition of Bi, protrusions of approximately 0.24 nm in height are observed within different coverage of Bi. The interatomic distance distribution in different coverage is analyzed by means of statistical histogram, as shown in Fig. 2. At 0.0013 ML, dispersed protrusions and local Bi nearest neighbor distances, 1.3 nm and 1.5 nm, are obtained from the histogram [inset in Fig. 2(a)]. The protrusions exhibit linear ordering when the coverage is increased to 0.0078 ML [Fig. 2(b)]. The 1D linear structure appears (green dashed line) in accompany with a Bi-Bi nearest neighbors distance of around 1.8 nm, reflecting a characteristic 1D growth mode at low coverage. Notably, the Bi-Bi distance of 1.8 nm is almost four times the lattice spacing along the [11–20] direction of Bi nanoribbon22. At 0.039 ML, 2D triangular islands (indicated by red and white dashed lines) are observed and linear structures are still detected, as presented in Fig. 2(c), revealing the transition from 1D linear to 2D triangular structures. Such 2D triangular islands consist of Bi atoms with equally interatomic distance and form regular triangles, as displayed in Fig. 2(c). In triangular islands, the Bi-Bi distance is about 1.6 nm, which is very close to  × a = 1.57 nm {a = 4.54 Å, which is the lattice constant along the [11–20] direction of Bi nanoribbon22}. The black solid line in Fig. 2(c) delineates a unit cell of Bi adatoms. A large-scale hexagonal array of Bi atoms is formed at 0.078 ML, as presented in Fig. 2(d). The interatomic distance of Bi atoms is maintained at 1.6 nm and the same unit cell is still observed [black solid line in Fig. 2(d)] in the STM images. Therefore, the large-scale 2D hexagonal array is unambiguously identified as coverage-induced  ×  Bi reconstruction on the MEG surface. No ordered structures have been observed in previous literature232425 at such low Bi coverage. The results indicate the existence of some particular interactions between Bi adatoms and MEG. This issue will be addressed in the following discussion.


Tailoring low-dimensional structures of bismuth on monolayer epitaxial graphene.

Chen HH, Su SH, Chang SL, Cheng BY, Chen SW, Chen HY, Lin MF, Huang JC - Sci Rep (2015)

Clean MEG surface.(a) Atomically resolved STM image of MEG on 4H-SiC (0001) (6.5 nm × 6.5 nm, Vs = 40 mV, I = 0.15 nA). (b) Side view ball-and-stick representations of MEG/4H-SiC (0001). (c) dI/dV-V curve obtained on clean surface of MEG.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4477326&req=5

f1: Clean MEG surface.(a) Atomically resolved STM image of MEG on 4H-SiC (0001) (6.5 nm × 6.5 nm, Vs = 40 mV, I = 0.15 nA). (b) Side view ball-and-stick representations of MEG/4H-SiC (0001). (c) dI/dV-V curve obtained on clean surface of MEG.
Mentions: Fig. 1(a) presents an atomically clean surface of MEG. The image reveals a well-identified honeycomb lattice of the graphene superimposed onto the 6 × 6 superstructure (bright hexagon)1617, as well as the corresponding Fast Fourier transform [FFT, inset in Fig. 1(a)]. A white solid arrow points to a 1 × 1-G spot and a green dashed arrow assigns to a 6 × 6-SiC spot1819. Fig. 1(b) schematically depicts a cross-section view of the MEG/4H-SiC (0001) structure using ball-and-stick representations. The dI/dV spectrum of the as-grown MEG in Fig. 1(c) exhibits a local minimum ~−0.37 eV, representing the Dirac point of graphene20. Although some packets are observed within the range −0.2 eV to 0.4 eV, these are likely deemed to be a result of many-body effects in graphene21 or the effect of corrugated substrate. The main feature (Dirac point) still can be identified. Upon the deposition of Bi, protrusions of approximately 0.24 nm in height are observed within different coverage of Bi. The interatomic distance distribution in different coverage is analyzed by means of statistical histogram, as shown in Fig. 2. At 0.0013 ML, dispersed protrusions and local Bi nearest neighbor distances, 1.3 nm and 1.5 nm, are obtained from the histogram [inset in Fig. 2(a)]. The protrusions exhibit linear ordering when the coverage is increased to 0.0078 ML [Fig. 2(b)]. The 1D linear structure appears (green dashed line) in accompany with a Bi-Bi nearest neighbors distance of around 1.8 nm, reflecting a characteristic 1D growth mode at low coverage. Notably, the Bi-Bi distance of 1.8 nm is almost four times the lattice spacing along the [11–20] direction of Bi nanoribbon22. At 0.039 ML, 2D triangular islands (indicated by red and white dashed lines) are observed and linear structures are still detected, as presented in Fig. 2(c), revealing the transition from 1D linear to 2D triangular structures. Such 2D triangular islands consist of Bi atoms with equally interatomic distance and form regular triangles, as displayed in Fig. 2(c). In triangular islands, the Bi-Bi distance is about 1.6 nm, which is very close to  × a = 1.57 nm {a = 4.54 Å, which is the lattice constant along the [11–20] direction of Bi nanoribbon22}. The black solid line in Fig. 2(c) delineates a unit cell of Bi adatoms. A large-scale hexagonal array of Bi atoms is formed at 0.078 ML, as presented in Fig. 2(d). The interatomic distance of Bi atoms is maintained at 1.6 nm and the same unit cell is still observed [black solid line in Fig. 2(d)] in the STM images. Therefore, the large-scale 2D hexagonal array is unambiguously identified as coverage-induced  ×  Bi reconstruction on the MEG surface. No ordered structures have been observed in previous literature232425 at such low Bi coverage. The results indicate the existence of some particular interactions between Bi adatoms and MEG. This issue will be addressed in the following discussion.

Bottom Line: Upon Bi deposition, a little charge transfer occurs and a characteristic peak can be observed in the tunneling spectrum, reflecting the distinctive electronic structure of the Bi adatoms.When annealed to ~500 K, 2D triangular Bi islands aggregate into Bi nanoclusters (NCs) of uniform size.The approaches adopted herein provide perspectives for fabricating and characterizing periodic networks on MEG and related systems, which are useful in realizing graphene-based electronic, energy, sensor and spintronic devices.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, National Cheng Kung University, Tainan, Taiwan 701, Taiwan.

ABSTRACT
To improve graphene-based multifunctional devices at nanoscale, a stepwise and controllable fabrication procedure must be elucidated. Here, a series of structural transition of bismuth (Bi) adatoms, adsorbed on monolayer epitaxial graphene (MEG), is explored at room temperature. Bi adatoms undergo a structural transition from one-dimensional (1D) linear structures to two-dimensional (2D) triangular islands and such 2D growth mode is affected by the corrugated substrate. Upon Bi deposition, a little charge transfer occurs and a characteristic peak can be observed in the tunneling spectrum, reflecting the distinctive electronic structure of the Bi adatoms. When annealed to ~500 K, 2D triangular Bi islands aggregate into Bi nanoclusters (NCs) of uniform size. A well-controlled fabrication method is thus demonstrated. The approaches adopted herein provide perspectives for fabricating and characterizing periodic networks on MEG and related systems, which are useful in realizing graphene-based electronic, energy, sensor and spintronic devices.

No MeSH data available.