Direct imaging and determination of the crystal structure of six-layered graphdiyne.
ABSTRACT:
Since its disclosure, the immediate imaging and assurance of the gem structure of few-layer graphdiyne
has demonstrated troublesome in light of the fact that it is excessively sensitive under illumination by an
electron pillar. In this work, the gem construction of a six-layered graphdiyne nanosheet was
straightforwardly seen by low-voltage transmission electron microscopy (TEM) utilizing low current
thickness. The joined utilization of high-goal TEM (HRTEM) reproduction, electron energy-misfortune
spectroscopy, furthermore, electron diffraction uncovered that the as-incorporated nanosheet was
glasslike graphdiyne with a thickness of 2.19 nm (relating to a thickness of six layers) and showed ABC
stacking. Subsequently, this work gives direct proof tothe presence and gem construction of few-layer
graphdiyne, which is another sort of two-layered carbon material integral to graphene.
1 Introduction
Since their most memorable forecast by Baughman et al. [1-3], two-layered (2D) materials, for example,
graphyne, graphdiyne, graphtriyne, and graphtetrayne have produced huge interest as logical interests
what's more, for their possible innovative applications in nanoelectronics, energy capacity, batteries [413]. Graphdiyne, one of the main two 2D graphyne materials that have been acknowledged by tests [1418], is shaped by the diacetylene linkage s of carbon iotas: three-crease
facilitated sp2-hybridized and two-overlap facilitated sp-hybridized. Such level carbon (sp2 +sp)
-combination, consistently dispersed pores, more modest thickness
than graphene, and tunable electronic properties [19]. Like other 2D materials [20-22], layered
graphdiyne has different stacked translucent designs, including the AA, AB, and ABC stacking modes.
Stacking mode and thickness are two pivotal elements that assistance characterize the gem designs and
in this manner the electronic structures/properties of graphdiyne [4, 15, 23]. For model, monolayer
graphdiyne is a semiconductor with a direct bandgap [24-26] and its determined electron versatility
ultimately depends on 105 cm2 ·V-1·s-1 at room temperature. Zeng et al. [23] have determined the
bandgaps of bilayer furthermore, trilayer graphdiynes, showing that their AB and ABC stacked structures
are more steady contrasted with those in the AA stacking mode. The direct bandgap of bilayer
graphdiyne with the AB stacking (0.35 eV) is bigger than that of the trilayer with the ABA structure (0.18
eV). Qian et al. [15] have revealed thatthe deliberate versatility of graphdiyne nanowires with lengths
going fro
the scope of 20 to 50 nm was ~ 7.1 × 102 cm2 ·V-1·s-1 at room
temperature. Huge region graphdiyne films have been manufactured on the outer layer of copper
through a cross-coupling response utilizing hexaethynylbenzene [4, 14]. Likewise, translucent
graphdiyne has additionally been effectively incorporated by a few gatherings [15-17]. Be that as it may,
the immediate imaging also, portrayal of the precious stone designs of not many layer graphdiyne is as
yet troublesome, in light of the fact that their structures are effortlessly harmed by the electron shaft of
transmission electron microscopy (TEM). Utilizing high-goal TEM (HRTEM) and chose region electron
diffraction (SAED) with an electron light emission 300 kV from a field-discharge firearm, Zhou et al.
showed that graphdiyne nanowalls with a thickness of about 15.5 nm (relating to roughly 42 layers)
were translucent with a layer dividing of ~ 0.365 nm [16]. By utilizing a 75 kV electron bar from a fieldoutflow firearm, Matsuoka et al. showed that graphdiyne nanosheets with a thickness of 2.97 nm (or
nine layers) were stacked in an ABC-type mode [17]. These forward leaps demonstrate that
accomplishing great is very difficult HRTEM pictures straightforwardly for not many layer graphdiyne. In
this work, we combined not many layer graphdiyne nanosheets utilizing a changed Glaser−Hay coupling
response. HRTEM utilizing an electron light emission kV from a LaB6 firearm and a 60 kV pillar from a
fieldemission weapon with low current densities was utilized to empower the immediate excellent
imaging of the gem designs of the nanosheets. A few portrayal strategies, to be specific, SAED, electron
energy-misfortune spectroscopy (EELS), and HRTEM reenactments were performed. HRTEM imaging
demonstrated that the as-blended nanosheet was translucent graphdiyne with a thickness of 2.19 nm
(six layers) and the ABC stacking mode. This thickness was additionally affirmed by nuclear power
microscopy (AFM). Consequently, we had the option to acquire obvious proof of the presence of fewlayer graphdiyne and decided its precious stone design.
2 Results and discussion
2.1 Characterization of graphdiyne nanosheets by Raman and X-ray photoelectron spectroscopy (XPS)
The nanosheets were combined by a changed Glaser-Hay coupling response as per a past report [16].
The subtleties of the engineered strategy are given in the Methods area. As displayed in Fig. 1(a),
the Raman range of the nanosheets has four unmistakable tops, which are predictable with the four
normal groups of graphdiyne [14, 17]. In particular, the tops at 1,384.2 furthermore, 1,569.3 cm-1
compare to the D and G groups, like those of graphite, while those at 1,931.2 furthermore, 2,170.9 cm-1
can be credited to the vibration of the formed diyne linkage. These phantom pinnacles exhibit a fruitful
combination of graphdiyne. The high-goal C1s XPS range given in Fig. 1(b) further affirms the
arrangement of graphdiyne; the C1s pinnacle can be deconvoluted into four sub-tops, of which those at
284.3 and 285.0 eV can be relegated to C=C (sp2) furthermore,
ndividually. Besides,
the nuclear proportion of sp2 /sp is around 0.5, which is as per the synthetic structure of graphdiyne
[17].
2.2 Direct imaging of graphdiyne nanosheets
Figures 2(a) and 2(b) outline the morphology and a HRTEM picture of a graphdiyne nanosheet,
individually. The HRTEM picture shows a reasonable 2D cross section what's more, along with its quick
Fourier change (FFT) design shows that the nanosheet is a solitary gem lying on an indistinct carbon (aC) substrate. This excellent imaging was gotten utilizing an electron light emission kV from a LaB6
firearm, whose ongoing thickness of 2.3 × 104 A·m-2 utilized here is by and large lower than those from
field-discharge firearms. To decide the thickness of this nanosheet, EELS estimations were acted in the
nanosheet and formless areas, as displayed in Fig. 2(b). As indicated by the EELS philosophy for
estimating the example thickness [27-29], the thickness of the nanosheet along with the a-C substrate
and that of the a-C itself were estimated to be 78.5 and 76.1 nm, separately (see subtleties in Fig. S1 in
the Electronic Supplementary Material (ESM)). In this manner, the thickness of the nanosheet was
determined as 2.4 nm, which is identical to 6.6 layers. This proposes that this nanosheet is by the same
token six-or seven-layered. For reevaluating the graphdiyne thickness, we described it utilizing an AFM.
The results displayed in Fig. S2 (in the ESM) show that the thickness of graphdiyne is 2.25 ± 0.17 nm.
Inside the wiggle room, this worth is equivalent to 2.4 nm. It ought to be noticed that Fig. S3 (in the
ESM) shows a HRTEM picture of another graphdiyne nanosheet also, its two FFT designs. The thickness
of this nanosheet estimated by EELS went from ~ 2 to 11 nm. Despite the fact that the differences of the
two regions with various thicknesses in the HRTEM picture are not quite the same as one another, their
cross section pictures and FFT designs are something similar as those displayed in Fig. 2(b). In this way,
the graphdiyne thickness has no enormous effect in the HRTEM portrayal technique. Subsequently, it is
important to play out the EELS and AFM estimations on the graphdiyne thickness.
Figures 2 and 3(a) show that the sheet plane of the graphdiyne nanosheet is typical to the [001] bearing
what's more, has a width of a few microns. In the event that the nanosheet is expected to be seen along
the [100] or [010] bearing, then it is important to shift it by 90° to acquire a picture. In any case, this
shifting and imaging strategy may be difficult to execute on the grounds that regardless of whether
some TEM holders can shift the examples by 90°, the thickness of the nanosheet along the [100] or [010]
course is on a micron-scale, which is tragically excessively thick for fruitful HRTEM imaging.
2.3 Determination of the crystal structure of graphdiyne nanosheets
Figure 3(a) shows a test SAED example of the nanosheet. To decide the stacking mode comparing to the
SAED design, we assembled three graphdiyne models with AA, AB, and ABC stacking modes, and
mimicked their SAED designs, as displayed in Figs. 3(b)- 3(g). On examination of the exploratory
furthermore, the recreated SAED designs, it is apparent that the trial design coordinates with that of the
ABC stacking mode and not those of one or the other AA or AB modes. Consequently, it was affirmed
that the nanosheet is stacked in the ABC way. In this way, if the nanosheet is six-layered (or sevenlayered), its stacking structure would be ABCABC (or ABCABCA). As the ABCABCA stack is essentially less
steady than the ABCABC structure, it was presumed that the nanosheet is six-layered, or 2.19 nm thick.
This is the most slender graphdiyne at any point announced in Refs. [14-17]. The distinction between the
6-and the 6.6-layer thicknesses can be credited to the estimation mistake. To additionally confirm the
precious stone design (counting the stacking mode and the thickness) of the nanosheet, HRTEM
recreations were performed with the revealed crystallographic boundaries of graphdiyne (a = b = 0.96
nm, c =
0°,
tilizing the worth of thickness as 2.19
nm, and differen
shows the mimicked pictures. For a cautious correlation
of the reenacted and the trial pictures, the HRTEM picture in Fig. 2(b) was sifted by the Wiener sifting
technique. The outcome is given in Fig. 5 (see subtleties in Fig. S4 in the ESM). The Wiener separating
strategy has been broadly used to eliminate clamor in HRTEM pictures [31, 32]. In this manner, Figs. 4
and 5 were analyzed and it was seen that as the recreated
50 nm is in generally
excellent concurrence with the exploratory and separated HRTEM pictures, as shown by the primary
board and the inset in Fig. 5. Thusly, we could additionally affirm that the graphdiyne nanosheet is
stacked in the ABC way furthermore, has a thickness of 2.19 nm, which compares to a heap of six layers.
What's more, we gathered center misfortune EELS spectra from the imaged region in Fig. 2(b). These
spectra are displayed in Fig. S5 in the ESM, in which just the C and O edges exist, and there are no edges
of Si, Al, K, and different components. Since both the SAED design and HRTEM picture from the
graphdiyne nanosheet are steady with the relating reproduced designs of ABC-stacked graphdiyne, the
sign of O edge ought to emerge from the a-C underneath the graphdiyne nanosheet. In this manner, it is
apparent that the graphdiyne nanosheet contains unadulterated carbon. We additionally attempted to
utilize an electron light emission kV from the field-emanation firearm in a Titan TEM instrument to play
out the HRTEM imaging on the equivalent graphdiyne nanosheet as displayed in Figs. 2 and 5. The
current thickness was acclimated to a low worth (7 × 103 A·m-2) also, the got HRTEM pictures (Fig. S6 in
the ESM) were viewed as like those in Figs. 2 and 5. Accordingly, 60-120 kV energy pillar TEMs with low
current densities of 103 -104 A·m-2 are reasonable for the HRTEM imaging of graphdiyne.
3 Conclusions
The precious stone construction of a graphdiyne nanosheet was straightforwardly still up in the air by
low-voltage TEM with low current thickness. Its cross section picture could be obviously saw by HRTEM,
and its stacking mode what's more, thickness were additionally affirmed by SAED EELS, and HRTEM
reenactment to be ABC and 2.19 nm (comparing to six layers), separately. This work gives a technique to
describe and get the precious stone design of not many layer graphdiyne and presents obvious proof of
the presence of this 2D material.
4 Methods
4.1 Synthesis, refinement, and transfer of graphdiyne nanosheets
The monomer hexaethynylbenzene was dropped slowlyinto a mixed arrangement of CH3)2CO, pyridine,
and tetramethylethylenediamine with Cu foil as the impetus source. The response combination was held
under an argon climate and safeguarded from light, as illustrated in Fig. S7 in the ESM. The response was
done for 20 h and it was found that graphdiyne nanosheets were available in the arrangement.
Presently, this engineered process doesn't permit command over the thickness of graphdiyne. In this
way, a high velocity rotator was utilized to refine the thickness in the accompanying way. After their
blend, the graphdiyne nanosheets were first washed with warmed dimethyl formamide (DMF) and
CH3)2CO, and afterward dried under argon. The dried powders were scattered in ethanol by sonicating
them for 10 min. Hence, the ethanolic scattering was centrifuged at 5,000 upsets each moment (rpm)
for 5 min and the supernatant was isolated. The supernatant fundamentally contained graphdiyne
nanosheets with a thickness of 2-11 nm, like those portrayed in Fig. 2, and Figs. S2 and S3 in the ESM.
For TEM portrayals, a volume of ~ 5 μL was gotten from the supernatant and dropped onto a TEM
matrix. The TEM matrix was dried in vacuum at room temperature for 1 h before estimation.
4.2 TEM characterization
The TEM pictures and SAED design displayed in Figs. 2, 3, and 5 were gotten by utilizing a FEI Tecnai G2
Soul TWIN with a LaB6 weapon and a speeding up voltage of 120 kV. The ongoing thickness of the
electron shaft was 2.3 × 104 A·m-2. The EELS estimation was performed by utilizing a Gatan Enfinium ER
Model 977 on a filtering TEM (FEI Titan Cubed Themis G2 300) worked at 60 kV. The HRTEM recreations
were performed with the MacTempas programming. The total boundaries utilized in the recreation are
as per the following: circular distortion coefficient = 2 mm, chromatic deviation coefficient = 1.3 mm,
intermingling point = 0.1 mrad, graphdiyne thickness = 2.19 nm, and 16 values with a stage of 10 nm in
the reach from - 70 to 80 nm for the defocus. It was tracked down that the reproduction result acquired
with 50 nm defocus showed the best concurrence with the trial HRTEM picture, as outlined in Figs. 4 and
5. The TEM picture shown in Fig. S6 in the ESM was gotten by utilizing the TEM method of the FEI Titan
Cubed Themis G2 300 with a field-emanation weapon and a speeding up voltage of 60 kV, in which the
ongoing thickness of the electron shaft was set to be 7 × 103 A·m-2.
4.3 AFM characterization
Some graphdiyne nanosheets were scattered on the level surface of a mica substrate. Thusly, an AFM
instrument with the model name of Dimension Icon created by Bruker was utilized to acquire pictures of
the nanosheets and measure their thicknesses.
Acknowledgements
This work was financially supported by the National Natural Science Foundation of China (Nos.
11604241, 21790052 and 21331007), the National Program for Thousand Young Talents of China, the
Postdoctoral Science Foundation of China (No. 2015M580209), the Tianjin Municipal Education
Commission, the Tianjin Municipal Science and Technology Commission (No. 15JCYBJC52600), and the
Fundamental Research Fund of Tianjin University of Technology.
Electronic Supplementary Material:
Supplementary material (the thickness measurements with EELS and AFM, more HRTEM images and
EELS spectra, the Wiener filtering details and the synthesis process) is available in the online version of
this article at https://doi.org/10.1007/s12274-017-1789-7.
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