Moiré superlattices in graphene supported on various substrates have opened a new avenue to engineer graphene’s electronic properties. Yet, the exact crystallographic structure on which their band structure depends remains highly debated. In this scanning tunneling microscopy and density functional theory study, we have analysed graphene samples grown on multilayer graphene prepared onto SiC and on the close-packed surfaces of Re and Ir with ultra-high precision. We resolve small-angle twists and shears in graphene, and identify large unit cells comprising more than 1,000 carbon atoms and exhibiting non-trivial nanopatterns for moiré superlattices, which are commensurate to the graphene lattice. Finally, a general formalism applicable to any hexagonal moiré is presented to classify all reported structures. K and K′ corners of the Brillouin zone, giving rise to a linear energy dispersion of its quasiparticles close to the Fermi levelK and K′ points of the Brillouin zone are called Dirac cones.Graphene (gr) is a two-dimensional crystal with honeycomb structure, whose peculiar electronic properties have raised considerable interest in the past few years. Indeed, its electronic bands cross at the Such exotic electronic properties are predicted for pristine graphene, but are altered when graphene is supported by a substrate. Indeed, due to the structural mismatch between graphene and its support, graphene has periodically varying stacking configurations with its substrate45678101112131720212221222420252628Other surfaces interact more strongly with graphene, and are prone to exchange electrons with it, establishing partially covalent bonds. Graphene-substrate bonding then implies both van der Waals forces (physisorption) and partial covalent bonding (chemisorption), and is modulated along the moiré periodicity111230313436383541The usual structural model used to describe moirés assumes  top that47474951There are many ways the above assumption for commensurability can be fulfilled, as can be shown by considering strains and rotation of the graphene with respect to its substrate43Here we present the straightforward extension of Hermann’s formalism to the latter case. Besides, we derive the relationships that establish the consistency between this formalism, and another one, recently presented by Zeller and Günther to describe the number of beatings a moiré can compriseWe apply this description to resolve the structure of the moiré superlattices in graphene on multilayer graphene prepared on SiC, and in monolayer graphene on Re(0001) and Ir(111). For this purpose, we resort to scanning tunneling microscopy (STM) in both direct and reciprocal (Fourier) space, in the latter case achieving better than 0.1 pm precision on the lattice parameter determination, owing to distortion-less imaging with atomic resolution across several 10 nm fields of view. We find rotated and sheared moiré superlattices. Similarly to the rotation, shear appears more obviously in the moiré than in the graphene, as confirmed by our density functional theory (DFT) calculations. Some of these moirés comprise several moiré beatings in the case of metal substrates. Strikingly, commensurability between graphene and moiré superlattices provides a fine description of even very large moiré supercells, comprising above 1,000 carbon atoms.am is an integer number times graphene’s (agr) or the support’s (as) lattice parameters: am = i agr = m as, with i and m two coprime integers.In most cases, supported graphene and its substrate do not share the same lattice parameter and/or graphene lies twisted by some angle with respect to its support. Assuming commensurability between the two lattices, a supercell can be defined which comprises the smallest integer numbers of unit cells of both graphene and the support. This supercell defines the moiré superlattice. Formally, in a one-dimensional picture, the moiré superlattice parameter km), of graphene (kgr) and of the support (ks) hence fulfil i km = kgr and m km = ks. We stress that these two equations constitute the general definition of a moiré superlattice. On the contrary, the definition usually proposed in the literature, km = kgr − ks, does not require commensurability. It can be obtained in the particular case of a commensurate system, with i − m = 1, i.e. with i and m two consecutive integer numbers. This particular case is sketched in i − m = 2. Strikingly, at first sight the two moirés in i − m = 1 moiré  described as a i − m = 1 moiré. In fact it has a richer Fourier spectrum than the latter, as can be seen on i − m = 2 moiré is km = (kgr − ks)/(i − m) = (kgr − ks)/2, and not (kgr − ks) as is the case for the i − m = 1 moiré. The predominant intensity of the second harmonic (kgr − ks) translates nothing else than the close (but not exact) lattice coincidence observed at half the moiré period  space unit vectors of the moiré superlattice , uniaxial strain in a given direction εu (2 and 3), and a rotation (4) of the graphene layer. It can be noted that the so far overlooked shearing contribution is taken into account by combining a rotation, biaxial and uniaxial strains. The impact of such a combination on a moiré has only been predictedIn the most general case, graphene is twisted, strained and sheared with respect to its substrate. The combination of all these contributions can be separated into four elementary geometrical transformations represented on i, j, k, l, m, n, q, r), which are determined through atomically-resolved microscopy, is then necessary :On the other hand, one can equivalently describe the graphene-substrate relation by explicitly writing the commensurate relation defining the moiré superlattice. In order to account for its structural complexity in two dimensions, a set of eight integers :i, j, k, l, m, n, q, r) integers used here correspond to the decomposition of the superstructure lattice vectors i, j, k, l), and the supporting material lattice vectors , as sketched on The . The extended Wood’s notation reads as (p1Rφ1 × p2Rφ2). This notation gives the reader the ability to easily capture the graphene-substrate relation, and imagine how sheared it is by comparing p1 and p2, and φ1 and φ2. Once again, these quantities relate to the  integers, as explained in the P1RΦ1 × P2RΦ2), with:Although using a set of eight integers is efficient to describe a moiré superlattice, it is a relatively cumbersome notation that does not give an immediate picture of the structure. A clearer formulation of such sheared structures is then desirable. In the simple case of graphene experiencing only deformations preserving its pristine with i, j, k, l, m, n, q, r) integers is here discussed to justify this necessity.The geometrical formalism developed so far proves necessary to properly interpret the refined twist angles and shearings observed in atomically-resolved microscopy images. The experimental uncertainty on the identification of the  can be lowered by precisely determining 2. The latter effect translates into an uncertainty as low as km and kgr is ~1%. For , this precision translates through propagation of uncertainty into 2%.Quantitatively, the uncertainty on  is liable to put shears in evidence. At first thought, atomic resolution imaging can artificially produce sheared images. Such shears may result from imaging artefacts, for instance, in the case of scanning probe microscopy, thermal drift of the piezoelectric scanners or inequivalent calibration of these scanners along the two scan directions. However, these artefacts have no influence on the decomposition of The above described determination of . For a N = 1 moiré, First, the case of multilayer graphene on the C-rich  in  see . Here, ti, j, k, l, m, n, q, r) = . Using Equation (4a–d), such a structure can be analysed as two graphene layers sharing the same lattice parameter p1 = p2 = 1), and rotated by This commensurability relation gives a complete structural description, by decomposing the moiré lattice vectors in the basis of each graphene layer, using the set of integers  through a self-limiting processN = 1 moiré superlattice with 10 graphene cells on 9 Re cellsThe case of multilayer graphene on C-face SiC has shown a situation where a moiré superlattice is related to a single structural parameter: the twisting angle A direct analysis of the STM topograph along the same lines as for pz-like orbital of a C atom in atop position with the d-like orbitals of the underlying metal atom is then maximal. Consequently, the local electronic density of states is modified, making it appear low in STMFirst, depending on the position within the beatings, the apparent height accessed by STM shows a varying number of visible C: in a valley, only 3 atoms out of a 6-C ring are seen, whereas on a hill, all 6 are observed. This is due to the sites occupied by the C atoms on the terminal metallic layer, which fall into three typical configurations: a C on top of a metal atom (atop), or on top of a hollow site. Two kinds of hollow site can be distinguished, depending on the presence (hcp) or absence (fcc) of another metal atom of the second terminal metallic layer below the hollow site. In a valley, the sites occupied by the C atoms are either atop and hcp, or atop and fcc. The overlap of the Second, the apparent atomic rows of C oscillate with the same periodicity as the beatings. This phenomenon has been reported and discussed in the case of gr/Ru see ref. , and obs6364N = 1 moiré superlattice of gr/Re, comprising a sufficiently small number of atoms to be treated numerically. This moiré is characterized by the set  = . On Using DFT calculations, these two effects have been reproduced in the case of a sheared and twisted On N = 1 superlattice  = . As a signature of the anisotropy, the moiré cell contains a different number of beatings N1 = 1 and N2 = 2 in each of its main directions, as can be deduced from The corresponding set of integers therefore is (P1RΦ1 × P2RΦ2) extended Wood’s notation, with N = 1 superlattice, comprising 308 carbon atoms, as well as a sizeable shear. The corresponding shear of the graphene lattice is obvious in the corresponding extended Wood’s notation (p1Rφ1 × p2Rφ2). Using Equation (4a–d), one gets R0.73 × 0.886 R0.36). This structure is close but different from the previously reported assignment of a (7 × 7)R0, N = 1 moiré  in the case of gr/Re, graphene is biaxally compressed by e.g. in the case of gr/Ir. Similarly to gr/Re, the FFT-image of N > 1). In addition, the position of the graphene spots with respect to the moiré reciprocal lattice is not the same in each main direction, which means the structure is sheared. Actually, along the close-to-horizontal direction in reciprocal space  = , as interpreted in P1RΦ1 × P2RΦ2), with R0° structurep1Rφ1 × p2Rφ2), with This description of the superlattice can be summarized with . Shear and strain of such extents have already been reported beforeUsing Equation , this shearing translates into a combination of biaxial compression Using an extended Wood’s notation for a pictorial description using two scaling factors and two angles,In more physical terms with rotation angles, and uniaxial and biaxial strains,With eight integers that decompose independently the two moiré lattice vectors onto those of graphene and of its support.Three support lattices have been considered so far, revealing that a moiré structure can be rotated, strained and sheared. It also demonstrates that moiré superlattices comprising more than one beating are commonly encountered. Three equivalent ways have been presented to describe moiré superlattices with ease:N > 1 beatings superlattices, and of sheared superlattices, which both display specific properties. N > 1 beatings superlattices indeed exhibit inequivalent moiré hills12 cm−2 , hence with shifted Dirac conesi.e. by considering two sets of four integers,  and , which obey the same equations. Below, we introduce these equations in the case of  from The notation relying on eight integers enables to enumerate all the possible structures by combining every possible value for each integer. The system can also be treated by addressing two independent directions separately, as, one can express the moiré lattice constant am, the biaxial strain ε (assuming the lattice parameter of HOPG as a zero-strain situation), and the twist angle φ between graphene and its support  Rφ can be established straightforwardly , it is then possible to enumerate every possible structure. Using a limited set of parameters such as those defined by Nkm = kgr − ks. The representation of these curves is given by:With increasing values of (N the number of beatings given by N1 = N2.where N (see This series of parametrized curves highlights moiré superlattices with increasing numbers of beatings N see . The aboε = 2.51% (11), ε = −1.73% (19) and ε = 3.45% (20), and ε = −2.38% (21). Higher number of beatings are in fact probable for such structures. Such a high number of beatings was determined in the case of the so-called R30 phase of gr/Ir (see ref. μ-LEED) and STM study showed that within a moiré unit cell of ~3.02 nm lattice parameter, N = 37 beatings separated by ~0.47 nm occur N = 37 moiré is described with  =   =   = , ε = −0.02%  = , ε = −2.73% , even in growth conditions quite far from thermodynamic equilibrium. Presumably, the strong bonds of covalent character between carbon and metal atoms inside the growing flake are not readily broken, as would be required for twisting.Gr/Ir and gr/Pt are typical of the first situation. Numerous moiré phases have been reported for them, as shown on φ ~ 0° can be grown, as observed in STMμ-LEED61N = 4 (N1 = N2 = 2) superlattice  = ) using surface x-ray diffractionAlthough large-angle graphene twists are almost prohibited for gr/Re, slightly twisted graphene phases of gr/Re coexist. These numerous very similar structures can be assumed to be local minima in the energy landscape of gr/Re. Their coexistence then implies a high activation energy between each of them, so the formation of a large-scale uniform graphene phase is kinetically limited. In other words, graphene needs to be heated to high enough temperature to rearrange into the most stable phase of gr/Re. However, at high temperature, graphene growth competes with bulk dissolution and carbide formation, so the growth is performed by annealing cyclesi, j), such that  = . For instance,  =  in the present work, and  =  in ref. Graphene on C-face SiC grows with rotational disorder between the adjacent graphene layersN > 1 number of beatings will produce rich electronic modulations in graphene.In conclusion, different supported graphene systems have been studied with STM. A consistent analysis of moiré superlattices involving both direct and FFT STM images has been presented. The geometry of the superlattices, as apparent in STM images, has been rationalized by calculating electronic density maps derived from DFT calculations. A spatial precision of a tenth of 1 pm is achieved, revealing that graphene lying on a substrate is actually twisted, strained and sheared, which breaks its rotational symmetry. A geometrical model enables to classify all moiré superlattices. This model gives a global picture assuming commensurability between graphene and its substrate , yielding various numbers of beatings. While a very large number of structures is possible, only a few have actually been reported. In the case of strong graphene-substrate interaction, it is unlikely that all predicted superlattices are discovered, since for instance phases corresponding to a substantial rotation of graphene with respect to the substrate do not tend to form. For low interaction graphene-substrate systems, the complexity of the moiré superlattices has been undetected or overlooked, leading to possibly simplified interpretations. We anticipate that moiré superlattices with 2 pieces. The growth has been performed in a RF-furnace following the recipe in ref. 2 and Ar atmosphere at 1,560 °C, and subsequently annealed in Ar atmosphere at the same temperature.Graphene has been grown on undoped double-polished 4H-SiC−10 mbar) by cycles of Ar+ ion bombardment at 2 keV at 750 °C and subsequent annealing at ~1,300 °C. The gr/Re was prepared following the recipe presented in ref. 2H4 at room temperature (introduced with a 3 · 10−8 mbar pressure), and two subsequent cycles of flash-annealing/cooling at 750 °C with a 5 · 10−7 mbar C2H4 pressure.Re single crystal cut in the (0001) surface purchased from Surface Preparation Laboratory was cleaned in a ultrahigh vacuum (UHV) chamber  surface purchased from Surface Preparation Laboratory was cleaned in the same UHV chamber as for gr/Re, by cycles of ArFor multilayer gr/SiC, STM measurements were performed at 4 K in a home-made He-cooled STM, using a commercial Pt/Ir tip bought from Bruker. For gr/Re and gr/Ir, STM measurements were performed at room temperature under UHV, using a commercial Omicron UHV-STM 1, with a W chemically etched tip. Before analysing STM images, thermal drift and miscalibrations have been corrected.DFT calculations were performed using the VASP code, with the projector augmented wave (PAW) approach78How to cite this article: Artaud, A. et al. Universal classification of twisted, strained and sheared graphene moiré superlattices. Sci. Rep.6, 25670; doi: 10.1038/srep25670 (2016).


The inversion symmetry preserved antidot would then further split the πa (πz) bands into πa1 (πz1) and πa2 (πz2) bands with an energy interval Ed, which accounts for the bandgap opening in a kind of superlattices with Dirac cone being folded to Γ point. However, such antidot would not affect the semimetal nature of the other superlattices, showing a novel mechanism for bandstructure engineering as compared to the sublattice-equivalence breaking. For a superlattice with bandgap of ~Ed opened at Γ point, the Es could be increased by strengthening strain to close the bandgap, suggesting a reversible switch between the high velocity properties of massless Fermions attributed to the linear dispersion relation around Dirac cone and the high on/off ratio properties associated with the sizable bandgap. Moreover, the gap width actually could be continuously tuned by controlling the strain, showing attractive application potentials.Using the density functional theory with generalized gradient approximation, we have studied in detail the cooperative effects of degenerate perturbation and uniaxial strain on bandgap opening in graphene. The uniaxial strain could split π bands into π The linear energy dispersion relation around Dirac point brings us many unique and amazing properties, showing fascinating application potentials. The charge carriers, which could be tuned continuously between electrons and holes, have the group velocity as high as 106 m/s being close to that of light. Therefore, the graphene-based nanostructures are believed to be promising materials for next-generation high-performance nanoelectronic devices12356789101112131415161718Graphene consisting of hexagonally arranged carbon atoms has attracted tremendous research interests on both theory and experiment. Attributed to the etc. have been proved to be efficient for synthesizing graphene nanomesheset al. reported the nicely patterned graphene nanomesh fabricated by using the block copolymer lithographyet al. reported the CVD growth of large area smooth-edged graphene nanomesh by nanosphere lithographyet al. These progresses in fabricating advanced nanomaterials suggest the possibilities in preparing graphene nanomeshes in experiment with nice precision. In fact, this could be regarded as to pattern graphene into superlattice with carbon vacancies, which would modulate the corresponding Born-von Karman boundary conditions24252021222 surface2 surface folds the Dirac cone to Γ point. So, to shed light on the experimental studies, we have carried out detailed studies of hexagonal-antidot-patterned graphene superlattice in which the inversion symmetry remains. The novel mechanism differing with the sublattice-equivalence breaking for bandstructure engineering and the effects of uniaxial strain on electronic properties are carefully discussed. Most interesting, for a kind of graphene superlattices whose bandgaps are opened at Γ point, the gap width could be continuously tuned by applying uniaxial strain until it is closed. So, for such superlattices, one could reversibly switch between the massless Fermion properties attributed to the linear dispersion relation around Dirac cone and the high on/off ratio properties associated with the sizable bandgap.In the field of bandstructure engineering of graphene, an issue needs to be addressed. Along with the bandgap opening, the linear energy dispersion relationship around Dirac cone would be usually destroyed, which in turn would obviously reduce the charge carrier mobility. Usually, the wider bandgap opened in graphene to gain higher on/off ratio would lower the carrier mobility much more. Hence, it would be interesting if the bandgap could be switched on/off for a specific graphene-based nanomaterial toward different application demands. Interestingly, the advanced nanotechnologies have been successfully used in fabricating antidot-patterned graphene nanostructures–the graphene nanomeshes. The block copolymer lithography, nanoparticles local catalytic hydrogenation, nanosphere lithography, nanoimprint lithography, D6h high symmetry antidots in this paper for: (1) it could shed light on the circular mesh hole of the synthesized graphene nanomesh, and (2) it preserves the inversion symmetry. This kind of antidots in fact do not break the sublattice equivalence, which however could still open bandgap of some graphene superlattices, showing a novel mechanism for bandstructure engineering.The studied graphene superlattice is schematically illustrated in A × B periodic unit as shown in A and B are along the armchair and zigzag edges, respectively. The smallest rectangle unit cell defined by A1 = a + b and B1 = −a + b is illustrated in a × b primitive unit cell of graphene. As compared to the graphene studied with primitive unit cell, we would like to hereafter refer the pristine graphene studied with supercell A × B as pseudo graphene superlattice (PGS). If a perturbation such as an antidot was introduced in the A × B unit cell, the PGS would turn to be a real superlattice. In order to facilitate discussion, we would like to use the notation  to account for the lattice A × B with A = AP1 and B = BQ1. Therefore, the  stands for the smallest rectangle lattice A1 × B1. In h-BZ) and the rectangle one (r-BZ) corresponding to the primitive unit cell and the  PGS are shown, respectively. One can see that the K point in h-BZ would be folded to the T1r-BZ. The energy bandstructure of  PGS is presented in 1 point, confirming the above band-folding analysis. Based on our detailed analysis for the  PGSes with different P, we could conclude that the Dirac point would be always folded onto r-BZ. Interestingly, the Dirac point could be folded to Γ point when Q = 3m (m is an integer). In r-BZ is presented in h-BZ of primitive unit cell is equivalent to the Γ2 point in r-BZ of  lattice. The energy bandstructure shown in 2.Firstly, we start the discussion of electronic properties with the energy band-folding analysis. In this paper, the orthogonal superlattice with the P,Q) (Q = 3m) PGS by introducing an inversion symmetry preserved defect, such as the D6h hexagonal antidot, which does not coincide with the sublattice-equivalence breaking mechanism. For illustration, we have studied the electronic properties of , , and  superlattices. According to our energy band folding analysis, the ,  PGSes should have Dirac points at r-BZs while the  PGS should have Γ as Dirac point in its r-BZ. After introducing a C12 hexagonal antidot in the unit cell , their bandstructures are studied and shown in Aany × Bany, the lattice vectors could be expressed as Aany = N11a + N12b and Bany = N21a + N22b (a and b are the basis vectors of primitive unit cell of graphene). If the coefficients satisfy the conditions of 2N11 + N12 = 3m1 and 2N21 + N22 = 3m2 or N11 + 2N12 = 3m3 and N21 + 2N22 = 3m4 , the Dirac cone would be folded to Γ point and the introduced inversion symmetry preserved defect in the repeated unit cell would then open a bandgap in such superlattice.A bandgap can be opened in the  superlattice with Q = 3m could be closed by moving Dirac cone away Γ point ? Hence, in this subsection, we would like firstly to concentrate on discussing the effects of uniaxial strain on the Dirac cone move.In the above discussion, the hexagonal antidot acts differently on bandgap engineering of the free-standing graphene superlattice, which strongly depends on the position of the Dirac point. Only for the lattice with A1 lattice) and zigzag (B1 lattice) edges, respectively. In our studies, the Dirac cone was found to move along the 1 point in a applied along the armchair edge would move Dirac cone away T1 point with z along the zigzag edge would move it toward Γ point In D6h-defect-patterned superlattice, the  PGS lattice is adopt as a prototype example. As shown in a and σz are investigated in detail. Both of them could shift the Dirac cone away Γ. In z are illustrated. The band closing point at Γ is degenerate in z as shown in z and πa respectively. The charge densities of the πz and πa bands are plotted in z band accounts for the orbitals along zigzag edge while the πa is for the orbitals along armchair edge. This suggests that the Dirac point move could be attributed to the splitting between the energy degenerate bands πz and πa. Interesting it is that the density distributions of πa and πz bands show anisotropic characters. However, due to the fact that they would cross with each other at Fermi level in the neighborhood of Γ point, the anisotropic characters could not be observed in the conducting property studies. But, as to be discussed, the peculiar phenomena may be obtained in the strain engineered defect-patterned suplattice. For the  PGS without strain, the bond lengths of πz and πa bonds are exactly the same, which are around 1.425 Å. By applying the 5% σz strain along zigzag edge, the πz bond is elongated by ~3% while the πa bond remains almost unchanged. The tight binding (TB) method is well known in treating π bands of graphene, which could help to understand the physical origin of the electronic properties of graphene-based nanostructures. By considering only the nearest neighbor atoms, the related energy Enna could be obtained through28ti is the transfer integral, ki is the component of wavevector k, ai is the corresponding lattice constant, and z and πa orbitals at Fermi level make two separated Dirac points adjacent to Γ. In the spirit of the concept of pseudospin, two valleys with different chiralities of the corresponding electrons are located at K and K′ points in the h-BZ of primitive unit cell of graphene. In the pseudo superlattice , the valleys are folded onto Γ point in the corresponding r-BZ. The effects of the uniaxial strain are to split the degenerate valleys by shifting them away Γ in opposite directions, which would still keep them equivalent in energy with the apexes of corresponding Dirac cones being located at Fermi level.In order to investigate the effects of Dirac cone move on the bandgap opening of the D6h-antidot-patterned superlattice studied in this paper may be a potential candidate. In  (Q = 3m) PGS, the Dirac point would be folded to Γ point. Then, the high symmetry D6h antidot can open a bandgap in the corresponding graphene superlattice, which however could not change the semimetal nature of the other superlattices with Q≠3m (the Dirac point is not at Γ). Interestingly, by controlling strain, one can manipulate whether the Dirac point is located at Γ point or not of the  (Q = 3m) PGS, which suggests the possibilities in switching on/off bandgap of such superlattice.On a hand, due to the linear dispersion relationship around Dirac cone, the charge carriers gain high group velocity, which could also be tuned between the holes and electrons. On the other hand, the semimetal nature of graphene does not favor its usage as for high-performance nano-transistors, which requires high on/off ratio. In order to obtain high on/off ratio, a bandgap needs to be opened for the graphene-based nanostructure. However, along with the bandgap opening, the linear dispersion relation of graphene crystal would be destroyed also, which in turn harms the velocity properties of the charge carriers. So, it would be interesting to explore the possibilities in switching between the high velocity properties of massless Fermions and the high on/off ratio properties. The 6 hexagon  PGS, the introduced defect could open a bandgap at Γ point according to the discussion of the bandgap opening mechanism. Applying a strain σz of ~5%, we have then studied its electronic properties again. The corresponding bandstructure along Y′-Γ-Y path is shown in As to the  PGS, in order to facilitate discussion, we would like to first study the effects of a defect in the unit cell by contracting a Cz strain, where the strain makes the splitting between πz and πa orbitals, the D6h defect also induce band splitting. As shown in a1, πa2, πz1, and πz2, respectively, for which the corresponding band-decomposed charge densities are studied in D6h defect breaks the equivalence among πa (πz) orbitals, resulting in different bonding strengthes between πa1 (πz1) and πa2 (πz2) bonds. As compared to the corresponding C-C bonds of  PGS studied in 6 hexagon induces about 0.8% elongation of πa1 bonds and 0.6% contraction of πa2 bonds, respectively. As to the πz1 and πz2 bonds, the corresponding elongation and contraction are about 1.0% and 0.7%, respectively. In the spirit of the TB methoda2 and πz1 bands are lower in energy compared to the corresponding πa1 and πz2 bands, accounting for the splitting of πa and πz bands. Actually, the herein discussed splitting could also be understood by the intervalley scattering. The periodically arranged defects could be approximately treated as introducing a periodic potential Vd(r) to the pristine grephene. If the wavervectors of the opposite K and K ′ valleys differ with each other by a reciprocal lattice G, the intervalley scattering would induce band splitting. The energy interval Ed would be proportional to the integration K and K ′ pointsCompared to the electronic properties shown in a and πz bands and (2) the defect could break the equivalence among the armchair edge bonds (zigzag edge bonds) inducing the band splitting also. In fact, the competition between the band-split interval Es induced by the uniaxial strain and the Ed induced by the introduced defect dominates whether the bandgap could be switched on or off. Actually, we have also examined the free-standing defect-patterned  superlattice. The studied D6h defect also induces the band split Ed between πa1 (πz1) and πa2 (πz2) orbitals. For there is no strain applied to the lattice, the corresponding Es equals to zero. So, an obvious bandgap could be opened at Γ point. However, for the  superlattice studied in s is larger than the Ed, which makes the πa1 and πz1 to cross to form new Dirac cone.Now, one can see that (1) the strain along either armchair or zigzag edges could make the degenerate π bands to split into πD6h-antidot-patterned graphene superlattice by applying strain. In z = 0 in s increases as the strain σz enhances from 0% to 5%. As shown in 12 antidot patterned superlattice has been studied. Besides of the experimental fact of the successful fabrication of vacancy hole patterned graphene superlattice, we have performed the molecular dynamics simulations to evaluate the stability of the C12 patterned superlattice. We find that it can withstand the temperature of 1,500 K, implying that this superlattice structure is separated by high-energy barriers from other local minima on the potential energy surface. In this superlattice, the C12 antidot further splits the πa and πz orbitals, which brings the Ed ≈ 0.28 eV energy interval. For the studied  superlattice, the Ed remains almost the same as the applied strain increases. For the σz = 2% strain, the Es is smaller than the Ed. This still keeps the bandgap opening though the bandgap becomes narrower. An interesting point needs to be addressed. Now, the conduction band minimum (CBM) and the valence band maximum (VBM) consist of only πa- and πz-type bands, respectively, hinting the possibilities in obtaining anisotropic conducting properties. The electron and hole charge carriers may respectively transport along armchair and zigzag directions. However, for the case of the σz = 3% strain, the split energy interval Es gets larger than the Ed. The Dirac cone starts to form. For the condition with σz = 5% strain, the formation of the Dirac cone is obvious. So, for the energy interval Ed induced by the defect keeps almost constant, one could then switch on/off the bandgap by manipulating the energy interval Es through controlling uniaxial strain. This would be interesting for that the high velocity properties of massless Fermions attributed to the linear energy dispersion around Dirac cone and the high on/off ratio properties associated with the sizable bandgap could be switched with each other in the same material. For comparison, the superlattice patterned with (BN)6 flake (patching the C12-antidot hole with this nanoflake) has also been studied. For the graphene and BN sheet materials, the atoms are correspondingly hexagonally arranged in a plane to form the honeycomb structures. The calculated lattice constants of graphene and BN sheets are 2.47 and 2.51 Å, respectively. By using (BN)6 nanoflake to patch the vacancy hole in graphene, the local strain around the nanoflake should stand due to the lattice mismatch. Considering the fact that the ratio of the area of nanoflake against the one for the graphene is only around 0.04, the local strain would probably be released to some sense at the aid of the structural relaxation of graphene, which would help to stabilize the patched superlattice structure. In order to evaluate the structural stability, we have also carried out the MD simulations of the (BN)6 patched  superlattice, which suggest the stability at temperature of 1,500 K.In order to benefit experimental studies of patterning graphene nanomesh with circular antidots, we have also studied the bandgap on/off switching of the 12-antidot-patterned superlattice. The (BN)6 flake breaks the inversion symmetry by destroying the sublattice equivalence, opening ~0.13 eV bandgap. This bandgap seems unaffected in gap width by the uniaixal strain in our studies. Also, the deformed bandstructures induced by the uniaxial strain presented in 6 patched superlattice may have topological semiconducting properties due to the anticrossing bands shown in the neighborhood of Γ point, which are worthy of further investigations on both theory and experiment. As discussed the above, the uniaxial stretching strain would modify the electronic properties accordingly. Because of the linear dispersion relation around Dirac cone, the group velocity of massless Fermions could be estimated by the band energy gradient (k and E(k) are the wave vector and dispersion relation, respectively. For the fact that the mobilities of the charge carrier electrons and holes are almost same, we would like to concentrate on discussing their average values, with the purpose to illustrate the effects of strain. The average velocities of the PGSes studied in 5 m/s for the corresponding graphene superlattices under 0%, 2%, 3% and 5% strains, agreeing with the experimentally measured Fermi velocity of ~106 m/s for graphene228In 12-antidot-patterned  superlattice, the opened bandgap would be continuously reduced by enhancing strain, and the corresponding effective mass would be decreased also. According to the simple relationship μ) and effective mass (m) (τ is the scattering time of charge carrier)−13 s for scattering time, we have also estimated the carrier mobilities of the semiconducting superlattices to be ~103 cm2V−1s−1. Once the bandgap starts to close, the band energy dispersion would gain linear relationship again, resulting in high charge carrier mobility. For the case studied in z = 5% strain, the group velocity of the massless Fermions has been calculated to be ~6.12 × 105 m/s.In z and σa, the degeneracy between πa and πz bands would be removed, resulting in an energy interval Es to make the Dirac cone to move. The free-standing  (Q = 3m) PGS should have Dirac cone at Γ point according to the energy band folding analysis. Upon introducing a hexagonal antidot in the unit cell, the patterned superlattice would open a bandgap, showing a novel mechanism for bandstructure engineering as compared to the sublattice-equivalence breaking. In comparison with the defect-free PGS, the πa orbitals are split. The studied D6h defect has different effects on πa1- and πa2-type C-C bonds, making the former to contract and the latter to elongate. Similar effects are also observed for the πz-type C-C bonds. The energy interval between πa1 and πa2 energy bands and the value between πz1 and πz2 energy bands are same, which is referred as Ed. For the hexagonal-antidot-patterned  (Q = 3m) superlattice under uniaxial strain, the competition between Es and Ed dominates whether the bandgap remains open or not. For a given superlattice, the Ed keeps almost unchanged while the Es could be increased by enhancing the strain. Starting from the free-standing  (Q = 3m) superlattice, which has a bandgap opened by the energy split between πa1 (πz1) and πa2 (πz2) oribitals, the bandgap decreases along with the increase of the applied uniaxial strain until it closes. Upon this critical point, the energy bands πa1 and πz1 start to cross to form new Dirac cone. So, the electronic properties of  (Q = 3m) superlattice have been switched from the high on/off ratio properties to the high carrier velocity properties. Also, the transformation is reversible along with the strain releasing. Besides, the gap width could be continuously tuned by controlling strain, showing attractive application potentials.In conclusion, the possibilities, for switching between the high velocity properties of massless Fermions attributed to the linear dispersion relation around Dirac cone and the high on/off ratio properties associated with the sizable bandgap for a specific graphene superlattice, are carefully investigated. Upon applying uniaxial strain, such as the strains σab initio simulation package22pn with n = 1–3, respectively; for H, the configuration was 1sk-point sampling was performed with the Monkhorst-Pack techniquek-mesh. The structural parameters of the primitive unit cell of pristine graphene were firstly optimized, which were then used to construct superlattice. In our studies, the in plane lattices of the hexagonal primitive unit cell were calculated to be 2.466 Å, which is in good agreement with the previous datak-meshes of 7 × 9 × 1 and 3 × 5 × 1 were used for studying their electronic properties, respectively. Correspondingly, the charge densities and the local potentials were respectively calculated by using the 128 × 72 × 160 and 336 × 224 × 160 grid meshes. The convergence of the electronic properties was set to 10−5 eV. In the structural optimization, all the atoms were fully relaxed until the force acting on each atom converged to 0.01 eV/Å. As to the superlattice, we have also carefully checked the effects of antidot on lattice vectors of the repeated unit. The regularly arranged antidots in fact would not change the angle between lattice vectors, which would only affect the lattice constant. Thus, the symmetry of the superlattice could be preserved, which plays an important role in determining the position of Dirac cone in reciprocal space. For the superlattices simulated in our studies, the lattice constants were carefully optimized. As for testing the accuracy of the method, we also studied the lattice constant of diamond, which was calculated to be 3.571 Å in good agreement with the experimental value of 3.567 ÅWe have carried out spin-polarized first-principles calculations within the framework of density functional theory with a plane wave basis set as implemented in the Vienna How to cite this article: Jia, T.-T. et al. Dirac cone move and bandgap on/off switching of graphene superlattice. Sci. Rep. 6, 18869; doi: 10.1038/srep18869 (2016).


Directed self-assembly of block copolymers is a scalable method to fabricate well-ordered patterns over the wafer scale with feature sizes below the resolution of conventional lithography. Typically, lithographically-defined prepatterns with varying chemical contrast are used to rationally guide the assembly of block copolymers. The directed self-assembly to obtain accurate registration and alignment is largely influenced by the assembly kinetics. Furthermore, a considerably broad processing window is favored for industrial manufacturing. Using an atomically-thin layer of graphene on germanium, after two simple processing steps, we create a novel chemical pattern to direct the assembly of polystyrene-block-poly(methyl methacrylate). Faster assembly kinetics are observed on graphene/germanium chemical patterns than on conventional chemical patterns based on polymer mats and brushes. This new chemical pattern allows for assembly on a wide range of guiding periods and along designed 90° bending structures. We also achieve density multiplication by a factor of 10, greatly enhancing the pattern resolution. The rapid assembly kinetics, minimal topography, and broad processing window demonstrate the advantages of inorganic chemical patterns composed of hard surfaces. The self-assembly of block copolymers through microphase separation yields patterns with various morphologies and feature sizes ranging from 3 to 100 nm123467910111213b-PMMA) system20The Liu-Nealey (LiNe) flow is a paradigm of chemoepitaxy, as it seamlessly integrates with state-of-the-art 193 nm immersion lithography17Alternatively, if a material that wets PS or PMMA is patterned on a neutral surface, only lithography and plasma etching are needed to prepare the chemical contrast pattern. Here, monolayer graphene grown on a germanium wafer is proposed as an appealing template to perform directed self-assembly. Graphene has similar wetting behavior as an X-PS mat23282931In this work, we demonstrate that atomically-thin graphene stripe arrays can be used as chemical patterns for directed assembly of block copolymers, resulting in well-registered lamellae patterns with complex architectures. The graphene/germanium chemical patterns enable block copolymer assembly on templates with incommensurate periods and in 90° bending structures. Faster assembly dynamics are observed on graphene/germanium templates than on conventional patterns based on polymer mats and brushes. Density multiplication by a factor of 10 is also demonstrated, which means that the period of the assembled block copolymer is one-tenth the template periodicity. These results indicate that graphene/germanium chemical patterns enable robust, reproducible directed self-assembly of block copolymers.2  are used to ensure that the germanium surface is not etched and that the single-atom step height of the graphene stripes is preserved  (PMMA) mask over the continuous graphene monolayer films using electron-beam lithography . The expreserved . The sampe array  indicateb-PMMA is directed to assemble on the graphene/germanium chemical patterns via thermal annealing  of 78 nm. The graphene ribbon arrays are spin-coated with ~60 nm of PS-b-PMMA and the sample is annealed at 250 °C for 5–10 min in an inert N2 environment (O2 < 1 ppm and H2O < 1 ppm). b-PMMA assembles into lamellae that closely follow the underlying graphene chemical pattern and are not disrupted by the germanium terracing. In Ls, is chosen to be equivalent to L0 = 78 nm to ensure that the PS-b-PMMA assembles under optimum conditions.Finally, PS-nnealing . PS-b-PMb-PMMA on graphene/germanium templates and conventional chemical patterns based on X-PS (2) substrate. The graphene and X-PS films are patterned into similar line-space arrays with Ls = L0. The samples are spin-coated with PS-b-PMMA and annealed at 250 °C for 2–30 min to reach equilibrium. Directed assembly occurs more rapidly on the graphene-based chemical pattern than on the X-PS-based chemical pattern. Within 2 min, the block copolymer is largely ordered, following the underlying graphene template on >65% of the surface area . The line width of the graphene guiding stripes is chosen to be 1.5 L0 for n > 1 to clearly identify the underlying graphene stripes with SEM after directed assembly. The PS-b-PMMA is spin-coated onto the graphene ribbon array and the sample is annealed at 250 °C for 5–10 min to induce assembly. Despite the lack of guiding stripes for n periods of L0, the block copolymer segregates into regular domains between the graphene ribbons. On the wide graphene stripes, the PS and PMMA domains assemble into lamellae in which the bottom domains are nearly parallel to the surface, creating a U-shaped cross-section; this likely occurs because the PS preferentially wets the graphene surface when the width of a stripe is greater than L0, as previously reported on X-PS based chemical patternsb-PMMA is further characterized, below. Density multiplication by a factor of 10 is achieved using the graphene chemical pattern  film is determined to provide an indirect measurement of their surface affinity towards each of the domains in PS-b-PMMA. The water contact angle on a continuous monolayer graphene film (81°) is similar to that of the PS film (91°). Furthermore, the contact angle on a bare germanium surface after plasma treatment (72°) is similar to that of the PMMA film (68°). These results suggest that PS and PMMA preferentially wet the graphene and germanium regions, respectively, during assembly.Investigations of water contact angles and the wetting behavior of block copolymer filmsb-PMMA (molecular weight of 22k-b-22 k g mol−1) thin films with thicknesses of 1.5 L0, 1.75 L0 and 2.0 L0 are spin-coated onto continuous graphene films after growth on germanium, and onto bare germanium surfaces after being treated with an oxygen plasma to etch the graphene. The samples are annealed at 190 °C for 1 h to induce self-assembly and AFM is used to resolve the equilibrium morphology of the block copolymer films. At 190 °C, PS has lower surface energy than PMMA, so it is energetically favored to wet the free surface. Thus, from the morphology of the self-assembled films, the surface affinity of graphene and germanium toward each block copolymer domain can be determined.The wetting behavior of the block copolymer domains on graphene and germanium is further verified with a hole/island experimentb-PMMA films are shown in L0 and 1.75 L0 have featureless terraces with step heights of 1.0 L0, whereas films with thickness of 2.0 L0 are flat and featureless. These results are consistent with symmetric wetting of the PS-b-PMMA, as shown in the assembly schematics in L0, which is consistent with assembly on a nearly neutral surfaceL0 and 2.0 L0. The film is flat for the 1.5 L0 case, whereas the featureless regions are higher than the fingerprint regions for the 2.0 L0 case. As shown in the schematic of the assembled block copolymer domains in The morphologies of the assembled PS-0LS that deviates from L0The difference in surface energy between the graphene and the germanium likely provides the chemical contrast needed for directed assembly; the PS and PMMA preferentially wet the graphene and germanium regions, respectively. This chemical contrast also provides a favorable template for directed self-assembly with density multiplication, as both the PS and PMMA domains can wet the nearly neutral germanium substrate to form well-ordered patterns, despite the lack of guiding stripes every LThe above results were obtained using graphene guiding stripes that are grown directly on germanium. The direct synthesis of the graphene chemical pattern on a target substrate is desirable for wafer-scale assembly of block copolymers because (1) CVD is an inherently scalable process, yielding uniform continuous graphene films over large areas that are only limited in extent by the size of the substrate or the size of the reaction chamber422 is chosen as the target substrate because it is preferential to the PMMA domains over the PS domains, and thus provides suitable chemical contrast and surface energetics with respect to graphene to direct the assembly of PS-b-PMMA. After transfer onto SiO2, the continuous graphene films are patterned into guiding stripes using electron-beam lithography and reactive ion etching, as described above. The 85k-b-91k PS-b-PMMA is directed to assemble into aligned lamellae on the graphene guiding stripes on SiO2 wafers with Ls of 78 nm  by patterning the guiding stripes using extreme ultraviolet (EUV) lithography. After directed assembly, the PS-b-PMMA is well-ordered over the entire patterned region, demonstrating that our approach is compatible with state-of-the-art planar lithographic techniques used for high-throughput patterning  provide faster assembly kinetics, (2) enable assembly on patterns with high degree of incommensurability, (3) allow assembly on irregular and complex templates, and (4) provide density multiplication by a factor of 10, even for relatively high molecular weight block copolymers. In future work, chemical contrast may be alternatively patterned by exposing the sample to chemical or plasma treatment, by forming a self-assembled monolayer, or by depositing a second two-dimensional atomic layer . These graphene-based chemical patterns may enable the directed self-assembly of ultranarrow block copolymer domains for manufacturing of high resolution features, both in the semiconductor electronics industry and in high density magnetic media. This work also opens the door for directed assembly studies on chemical patterns based on the large library of two-dimensional materials.In conclusion, we demonstrate that an atomically-thin monolayer graphene/germanium chemical pattern can be easily prepared and successfully used to direct the assembly of PS-−5 torr. The chamber is filled to atmospheric pressure with a flow of 200 sccm of Ar (99.999%) and 100 sccm of H2 (99.999%). The samples are annealed for 30 min at 910 °C before introducing 4.6 sccm of CH4 (99.99%), which serves as the carbon precursor, to start the graphene synthesis. Growth occurs for 12 h to ensure complete graphene coverage on the germanium surface. The samples are rapidly cooled by sliding the furnace away from the growth region, which terminates growth.Ge(111)  and Ge(110) (University Wafer) substrates are used to catalyze graphene growth, as described previously42b-PMMA. The quality and thickness of graphene after growth and after patterning is assessed via Raman spectroscopy (Thermo Scientific DXRxi) using an excitation wavelength of 532 nm, power of 10 mW, and spot size of 0.6 μm. Contact angle measurements (Dataphysics OCA 15) are conducted using deionized water.AFM (Veeco MultiMode SPM) in tapping mode and SEM (Zeiss LEO 1530) are used to characterize the samples after graphene growth, after patterning of graphene into guiding stripes, and after directed assembly of PS-How to cite this article: Chang, T.-H. et al. Directed self-assembly of block copolymer films on atomically-thin graphene chemical patterns. Sci. Rep.6, 31407; doi: 10.1038/srep31407 (2016).


The use of carbon based materials on the removal of antibiotics with high concentrations has been well studied, however the effect of this removal method is not clear on the actual concentration of environments, such as the hospital wastewater, sewage treatment plants and aquaculture wastewater. In this study, experimental studies on the adsorption of 7 antibiotics in environmental concentration of aqueous solutions by carbon based materials have been observed. Three kinds of carbon materials have shown very fast adsorption to antibiotics by liquid chromatography–tandem mass spectrometry (LC-MS-MS) detection, and the highest removal efficiency of antibiotics could reach to 100% within the range of detection limit. Surprisedly, the adsorption rate of graphene with small specific surface area was stronger than other two biochar, and adsorption rate of the two biochar which have approximate specific surface and different carbonization degree, was significantly different. The key point to the present observation were the π-π interactions between aromatic rings on adsorbed substance and carbon based materials by confocal laser scanning microscope observation. Moreover, adsorption energy markedly increased with increasing number of the π rings by using the density functional theory (DFT), showing the particular importance of π-π interactions in the adsorption process. Antibiotics have been used for several decades in both human and animals for treatment of microbial infections, and also as feed additives for promotion of growth of livestock animals124811523242526272811Carbon based materials are widely used in biomedicineIn this paper, seven commonly used antibiotics with near actual environmental concentrations were taken as examples, and two kinds of biochar with large surface area and a graphene with small surface area were chosen as sorbents. The objectives of this study were: (1) to determine the adsorption ability of biochar or graphene on antibiotics in environmental concentration, and draw support from fluorescence experiments to directly observe the adsorption process, (2) to reveal the effects of antibiotics with different aromatic rings on adsorption, (3) to explain the adsorption mechanism by experiment and density functional theory. The concentration of antibiotics in the samples were detected by liquid chromatography–tandem mass spectrometry (LC-MS-MS). We found that three sorbents showed rapid adsorption to antibiotics. The graphene with small specific surface area had the best adsorption capacity. For the same sorbents, the number of aromatic rings on antibiotics is a main factor affecting the adsorption rate, which is in agreement with the results of density functional calculations. The main adsorption mechanism is π-π interactions deduced by observing the adsorption process in confocal laser scanning microscope from fluorescence experiments. The cheap carbon materials with more aromatic ring area  can rapidly and efficiently remove the antibiotics from the actual environment. It is also expected to have great applications in removal of polycyclic aromatic hydrocarbons in water.−1), C=C (at approximately 1630 cm−1), C-OH (at approximately 1400 cm−1), and C-O-C groups (at approximately1050 cm−1) were observed on the surface for graphene and biochar37−1, 1630 cm−1, 1400 cm−1 and 1050 cm−1, showing the surface contained carboxyl, phenolic hydroxyl and oxygen containing groups. The broad peak at approximately 3450 cm−1 was assigned as stretching vibration of adsorbed water, and there was not a distinction among three carbon materials. But the absorption peaks of GN and B2 at 1630 cm−1 were stronger than that of B1, which means that the content of aromatic ring on the surface of GN and B2 was higher than on B1. This C-O-C (1050 cm−1) functional group, suggested that oxygen-containing groups were introduced into the graphene.The morphologies of graphene and biochar were visualized by using scanning electron microscope (SEM). As shown in −1, and a D band at 1320–1350 cm−1. The D band relates to disordered sp2-hybridized carbon atoms containing vacancies, impurities, or other symmetry-breaking defects, such as oxygen containing groups, whereas the G band represents the structural integrity of sp2-hybridized carbon atoms. The extent of carbon-containing defects in the biochars and graphene can be estimated by an intensity ratio of D band to G band (ID/IG)D/IG ratios for the B1, B2 and graphene are 1.03, 1.00 and 0.52, respectively. The higher ID/IG ratio in biochars suggests that biochars possessed fewer aromatic rings structures and more carbon-containing defects that led to the formation of oxygen-containing functional groups on the surface of biochars2/g, 881.6748 m2/g and 49.3840 m2/g, respectively. The surface area of biochar was obviously higher than that of graphene.Raman spectra of the B1, B2 and graphene can be found in The adsorption processes of various antibiotics on carbons is shown in e and qt (ug/g) is the mass of antibiotics adsorbed on per unit mass of adsorbent at equilibrium and at time t (h), respectively. k1 (1/h) is rate constant of the first-order kinetic model, k2 (g/ug/h) is rate constant of the second-order kinetic model. Adsorption data of biochar and graphene adsorbed antibiotic are modeled by the above two kinetic models, and the results are shown in Table 2S. Comparison of fitting results of Table 2S, the correlation coefficients (R2) of pseudo-first-order kinetic and pseudo-second-order kinetic model are almost the same, however the theoretical values of equilibrium adsorption amount (qe), calculated from the first-order kinetics models were in good agreement with the experimental values. According to the adsorption rate parameter (K1) of first order adsorption kinetics equations, as shown in e and k1 parameters. For SD and SMX, the qe of B2 is larger than that of GN since the BET surface area of B2 is significant higher than that of GN which means larger adsorption capacity of B2. Thus, the smaller BET surface area of GN affect the decreasing of concentration after 2 hours.The adsorption test is the study on the adsorption of trace antibiotics of different carbon based materials, thus some antibiotics reached the removal in the adsorption balance. More concern was given to the adsorption rate of carbon based materials to antibiotics. In order to qualificatory compare the adsorption rate of biochar and graphene with 7 kinds of antibiotics, the adsorption kinetics model was used to simulate the experimental data. Adsorption kinetics is commonly interpreted by first- and second-order kinetic models. When the concentration of the antibiotic was lower than the detection limit, we decided it was 0 ng/ml. According to equations41e for B1, B2, GN were 105.7, 199.0, 190.3 ug/g respectively.The researches of carbon based materials for adsorption of antibiotics confirmed that carbon based materials had a strong adsorption capacity523242526272829Researche can reach 25 mg/gIt is worth noting that the concentration of antibiotics has an important influence on the adsorption process. The adsorption equilibrium time of activated carbon for high concentration AMOX (317 mg/L) is only 35 min, and the values of qIt was observed that graphene had an obvious adsorption effect on FITC in one hour. The fluorescence images at different times  were observed under the same conditions in the same field. The fluorescence results of graphene adsorption of FITC with time were shown in 471) as shown in As previously reported, the adsorption behavior of organic compounds on carbon based material in general follows mechanisms such as π-π interaction4948In order to verify the adsorption mechanism of π rings on graphene and biochar, and the adsorption correlation between graphene and π rings with various number, here, we analyzed the adsorption of a series of increased size π rings on a graphene flake at the ωB97X-D/6-31 + G levels of theory. The optioned structures are showed in Carbon based materials are increasingly recognized as effective, inexpensive, and environmentally friendly sorbents for abating organic contaminants. In this paper, the adsorption of 7 antibiotics by 2 biochar and graphene were studied in actual concentration of environments such as the hospital wastewater, sewage treatment plants and aquaculture wastewater, which pose antibiotics resistance genes, potential human health and ecological risks. In the three cabon based materials, the B1 has large surface area and less aromatic ring area by 800 °C carbonization degree; the B2 has porous, large surface area, high aromatic ring area by 1000 °C carbonization degree; and the GN has high aromatic ring areas, and small specific surface area with few pores and functional groups. The adsorption kinetics model was used to simulate the experimental data. And adsorption processes of FITC, which has similar groups and molecular weight with antibiotics, by graphene particles were visualized by fluorescence microscope.The results show that the three carbon based materials have good adsorption proporties for antibiotics in actual concentration of environments, by which the highest removal efficiency of antibiotics can be up to 100%. The adsorption ability follows this order: GN > B2 > B1. From the view of antibiotics adsorption on same adsorbents, the number of aromatic rings on antibiotics was also an important factor in determining the adsorption rate, the more aromatic ring is, the faster the adsorption rate will be. The adsorption process by graphene lead to fast fluorescence quenching of FITC in 1 hour via π-π interaction. We have used density functional theory simulations to find the strong interaction between π rings and graphene, and the adsorption energies increased with number of the π rings. It is concluded that the main adsorption mechanism is the π-π interaction, and it also should be mentioned that other adsorption mechanism such as hydrophobic interaction, H-bonding interaction, electrostatic interaction, pore-filling could not be excluded, which may be auxiliary adsorption mechanism.Comparing the sorption of antibiotics by 3 kind carbon based materials, the biochar with high carbonization degree or graphene, which has rich aromatic ring areas, were more effective in adsorption of antibiotics. From the view of adsorption mechanism, antibiotics with more aromatic rings should be recommended in applications for the easy removal of antibiotics in the environment. At the same time, an efficient, fast and simple sewage treatment process is needed to remove the antibiotics from hospital wastewater, pharmaceutical wastewater and sewage treatment plants.Seven antibiotic standards  including Ofloxacin (OFL), Sulfadiazine (SD), Sulfamethoxazole (SMX), Sulfamethazine (SMZ), Cefalexin (CFX), Amoxicillin (AMOX), Tetracycline (TC) were purchased from Dr. Ehrenstofer GmbH (Germany). Chemical structures are shown in Two types of commercial biochars  and one kind of homemade grapheneIn order to keep the biochar particles size uniformity, eliminate the interference of other substances and microbial interference in biochars, the original samples were treated as follows: the particle size of the biochar was 0.4–0.8 mm after grinding. The biochars and graphene samples were washed by deionized water to an invariable pH value and desiccated by vacuum freeze–drying. The microbial interference was excluded by 30 min UV irradiation. Finally, the carbon materials were characterized by SEM, FTIR spectrum and Raman spectrometer . Surface area of adsorbents (biochar and garphene) were determined by nitrogen adsorption using ASAP 2020 V3.04 H (Micromeritics).0) was chosen as initial concentration.The concentrations of antibiotics in the sewage of hospitals, pharmaceutical plants and sewage treatment plants have been reported in the range of from 64 ng/ml to 540 ng/ml6789Static adsorption method41In order to visually observe the carbon-based material adsorbed antibiotic, the fluorescence properties of the 7 kinds of antibiotics were detected, the results showed that the fluorescence brightness was not suitable for direct observation of the adsorption process. The fluorescent agent fluorescein isothiocyanate (FITC), whose structure is similar to antibiotics  was chosen to directly observe the adsorption process. The molecular weight of FITC is 389.4, which is in the range of antibiotics (251.2-445.2) as listed in The suitable amount of graphene particles was added to the solution of FITC with concentration of 0.1 mg/ml, and then the sample was placed on the stage. By using visual mode, the magnification of the objective was adjusted; the need to test the samples under the fluorescence microscope was found (FLUOVIEW FV1000). By switching to a scanning mode, the double needle and laser intensity parameters, could get clear confocal images. Under the same parameters, we observed the fluorescence change in the same field within one hour.How to cite this article: Peng, B. et al. Adsorption of Antibiotics on Graphene and Biochar in Aqueous Solutions Induced by π-π Interactions. Sci. Rep.6, 31920; doi: 10.1038/srep31920 (2016).


Long INterspersed Element-1 (LINE-1 or L1) retrotransposon, the only currently active autonomous family of retroelements. Though L1 elements have helped to shape mammalian genome evolution over millions of years, L1 activity can also be mutagenic and result in human disease. L1 expression has the potential to contribute to genomic instability via retrotransposition and DNA double-strand breaks (DSBs). Additionally, L1 is responsible for structural genomic variations induced by other transposable elements such as Alu and SVA, which rely on the L1 ORF2 protein for their propagation. Most of the genomic damage associated with L1 activity originates with the endonuclease domain of the ORF2 protein, which nicks the DNA in preparation for target-primed reverse transcription.Approximately 17 % of the human genome is comprised of the Bioinformatic analysis of full-length L1 loci residing in the human genome identified numerous mutations in the amino acid sequence of the ORF2 endonuclease domain. Some of these mutations were found in residues which were predicted to be phosphorylation sites for cellular kinases. We mutated several of these putative phosphorylation sites in the ORF2 endonuclease domain and investigated the effect of these mutations on the function of the full-length ORF2 protein and the endonuclease domain (ENp) alone. Most of the single and multiple point mutations that were tested did not significantly impact expression of the full-length ORF2p, or alter its ability to drive Alu retrotransposition. Similarly, most of those same mutations did not significantly alter expression of ENp, or impair its ability to induce DNA damage and cause toxicity.Overall, our data demonstrate that the full-length ORF2p or the ENp alone can tolerate several specific single and multiple point mutations in the endonuclease domain without significant impairment of their ability to support Alu mobilization or induce DNA damage, respectively.The online version of this article (doi:10.1186/s13100-016-0064-x) contains supplementary material, which is available to authorized users. Long INterspersed Element-1 (LINE-1 or L1) retrotransposon is the only currently active autonomous non-LTR retroelement in the human genome. Most of the approximately 500,000 L1 loci have been truncated or mutated and are incapable of further retrotransposition  supplemented with 10 μl/ml each of the Halt protease inhibitor cocktail (Pierce) and Phosphatase inhibitor cocktails 2 and 3 (Sigma). Harvested cells were sonicated three times for 10 s each at 12 W using a Microson XL-2000 sonicator (Misonix). Cell lysates were collected after centrifugation at 14,000 rpm for 15 min at 4 °C. Total protein concentration was calculated using the Bio-Rad Protein Assay.Tris Glycine gels were used for western blot analysis in Figs. Bis Tris gels were used for western blot analysis in Fig. t-test for samples of equal variance. Error bars in figures represent standard deviations.All western blots were developed using Clarity Western ECL blotting substrate (Bio-Rad) and the images were captured using a Bio-Rad Gel Doc XR+ imager. The signal intensity of observed bands was quantified before saturation, using Image Lab 4.0.1 software. Statistical significance was evaluated using Student’s


A315T transgenic mice exacerbated the pathological TDP-43 accumulation in the cytoplasm of spinal motor neurons and it enhanced the levels of TDP-43 aggregation. These results suggest that inflammation may contribute to development or exacerbation of TDP-43 proteinopathies in neurodegenerative disorders.TAR DNA-binding protein 43 (TDP-43) is a major component in aggregates of ubiquitinated proteins in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). Here we report that lipopolysaccharide (LPS)-induced inflammation can promote TDP-43 mislocalization and aggregation. In culture, microglia and astrocytes exhibited TDP-43 mislocalization after exposure to LPS. Likewise, treatment of the motoneuron-like NSC-34 cells with TNF-alpha (TNF-α) increased the cytoplasmic levels of TDP-43. In addition, the chronic intraperitoneal injection of LPS at a dose of 1mg/kg in TDP-43 Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by the loss of motor neurons in the brain and spinal cord, causing progressive muscle weakness and typically leading to death by paralysis within a few years. Mutations in over twenty genes are known to be associated with familial forms of ALS –2 which Under normal conditions TDP-43 is mostly localized in the nucleus, where it is mainly involved in RNA processing –19. In dPreviously, we reported that levels of messenger RNA (mRNA) and protein for TDP-43 and nuclear factor κ B (NF-κB) p65 were higher in the spinal cord of ALS patients than of control individuals . Surprisin vivo effect of chronic LPS administration in transgenic mice expressing genomic fragment of human TDP-43 A315T gene (hTDP-43A315T) [A315T transgenic mice. These results suggest that chronic brain inflammation may contribute to TDP-43 proteinopathies.Here, we report that LPS exposure induced cytoplasmic redistribution of TDP-43 in cultured microglia and astrocytes. Similarly, NF-κB activation in motor neuron-like cell line NSC-34 by TNF-α enhanced TDP-43 cytoplasmic level. We also tested the 43A315T) –12. InteA315T (hTDP-43A315T) has been generated and characterized by us [The heterozygous transgenic mouse line expressing the human mutant TDP-43ed by us , 23. All2), the tissue was triturated. The cell suspension was washed in glial culture medium  and cultured at 37°C, 5% CO2 in 25 cm2 Falcon tissue culture flasks  coated with 10 mg/ml poly-d-lysine  for overnight and then rinsed thoroughly with sterile distilled water. Four to five days later medium was changed and supplemented with 5ng/ml of mouse recombinant macrophage colony stimulating factor  and every second day thereafter, for a total culture time of 10–14 days. At the moment of tissue dissection the genotype of each pup was unknown. Each brain was then dissected and cultured separately (one brain/25 cm2 flask). The transgenic pups were identified by DNA extraction from tails and PCR amplification of the human TARDBP gene. After 10–14 days, when the genotype of each pup was known, cultures with the same genotype were pulled together during the separation of astrocytes from microglia.Primary astroglial cultures from brain tissues of neonatal (P2-P3) mice were prepared as described previously . In brie2 and astrocytes at 40,000 cell/cm2 in 16-well chamber slides (Thermo scientific) for immunocytochemical analysis and 6-well-plates for protein or RNA extraction. Astrocytes and microglia cultures were treated with LPS (Sigma) at different concentration and for different periods as indicated in figures and results section.The procedure followed to separate astrocytes from microglia is based in previous published protocols . In brieA315T mice and their non-transgenic (wild-type) littermates received intraperitoneal (i.p.) injection of LPS  diluted in 100 μl of vehicle (Veh) solution . Mice were i.p. injected once a week for duration of two months. Mice were not exhibiting overt phenotypes due to LPS injection. Control mice were given same volume of saline.To trigger a systemic innate immune response in the CNS, presymptomatic 6-month-old hTDP-43After two months of systemic injections, animals were deeply anesthetized by i.p. injection of pentobarbital (50mg/kg) and then rapidly perfused transcardially with 0.9% saline, followed by 4% paraformaldehyde in 0.1 M borax buffer, pH 9.5, at 4°C. Spinal cords were rapidly removed from the animals. Dissected spinal cord tissues were postfixed for 24 h in 4% paraformaldehyde and equilibrated in a solution of PBS-sucrose (20%) for 48 h. Spinal cord tissues were cut in 25 μm thick sections with a Leica frozen microtome and kept in a cryoprotective solution at -20°C. Immunohistochemistry was performed on 25μm-thick sections. TDP-43 was probed (1:200) with Rabbit polyclonal (ProteinTech) or (1:200) mouse monoclonal (Abnova) antibodies. Neu N was immunostained with (1: 500) monoclonal (Invitrogen) antibody.Real-time RT-PCR was performed with a LightCycler 480 (Roche) sequence detection system using Light-Cycler SYBR green I at the Quebec Genomics Centre. Total RNA was extracted from cell cultures using TRIZOL reagent (Life Technologies). Total RNA was treated with DNase (QIAGEN) to get rid of genomic DNA contaminations. Total RNA was then quantified using Nanodrop, and its purity was verified by Bioanalyzer 2100 (Agilent Technologies). Gene-specific primers were constructed using the GeneTools software (Biotools Inc.). Three genes, Atp5, Hprt1, and GAPDH, were used as internal control genes. The mRNA copy number of each analyzed gene was divided by the mRNA copy number of the house-keeping gene Atp5 in the same sample, in order to take in account variations in samples size. Then, in order to get the fold changes in the expression of each gene with the LPS-treatment, levels of mRNA in the LPS-treated sample were divided by the levels of mRNA in the respective untreated control. Fold change equal to 1 indicate no effect of LPS in the gene expression, while fold changes higher than 1 indicate that the LPS treatment led to a higher expression of the analyzed gene.For sub-cellular fractionation, cells were lysed by a hypotonic buffer  and protease inhibitor (Sigma)) for 30 min on ice. Cells were further broken down by passing 30 times though a 22.5/27 G needle. Membranes were separated from the remaining cellular components by centrifugation at 3000 rpm, 10 min., 4°C. Pellet was then resuspended in extraction buffer  and protease inhibitor (Sigma)) and incubated for 60 min at 4°C with rotation. Nuclear fraction was then separated from the cytosolic fraction by ultra centrifugation at 30,000g for 30 min at 4°C. Pellet containing the cytosolic fraction was resuspended in RIPA buffer. Protein concentration was estimated using the Bradford method.It was done as previously described by Hart et al, with some modifications as described below . Frozen Total protein was extracted from cells using the RIPA buffer  and protease inhibitor (Sigma)). Protein concentration was estimated using the Bradford method. After denaturation, protein samples were resolved by 12% sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and transferred onto nitrocellulose membrane . Membranes were incubated in blocking solution  solution) for 1h at room temperature. Membranes were then incubated with a primary antibody diluted in blocking solution at 4°C overnight. After rinsing 3 times with 0.1% Tween-20 in TBS solution, membranes were incubated in a horseradish peroxidase-conjugated secondary antibody made in goat  diluted 1:5000 in blocking solution. After rinsing 3 times with 0.1% Tween-20 in TBS solution, immunoreactive proteins were visualized by chemiluminescence with the Renaissance kit . Primary antibodies used were the following: (1) Anti human TDP-43 monoclonal antibody  (2) anti-TDP43 rabbit polyclonal antibody , which reacts with both human (transgenic) and mouse (endogenous) proteins and (3) anti-actin mouse monoclonal . Bands intensity was measured using Image J 1.45p . The intensity of all TDP-43 bands was divided by the intensity of the respective actin band to take in account the differences in the protein loading. Fold change is the ratio of the band intensity in the LPS-treated cultures over the band intensity in the respective untreated controls, after normalized by the intensity of the correspondent actin bands.Paraformaldehyde (4%) fixed cell cultures and 20-um-thick spinal cord sections were incubated in blocking solution  for 1h at room temperature. Cells were then incubated in primary antibodies diluted in blocking solution at room temperature overnight. After rinsing 3 times with PBS, cells were incubated with Alexa 488 or Alexa 594 conjugated secondary antibody made in goat (Life Technologies), diluted 1:200 in blocking solution for 2h at room temperature. Nucleus was stained with 4', 6-diamidino-2-phenylindole  and then rinsing 3 times with PBS. Cover slips with stained cells were mounted on glass slides with mounting medium. The primary antibodies used were the following: anti-glial fibrillary acidic protein (GFAP) mouse ; anti-Iba1 rabbit ; anti-CD11b rat ; anti-TDP43 rabbit polyclonal antibody  and anti-TDP-43 mouse monoclonal . Cells were viewed using a 40X objective on a DM5000B microscope (Leica). Statistical analyses were performed with GraphPad Prism 5.A315T transgenic mice went from a ‘resting’ form with long branching processes and small cellular body, in the absence of LPS, to a large ameboid form when treated with LPS    or CD11b marker) .A315T transgenic astrocytes resulted in redistribution of TDP-43 from nucleus to cytoplasm. As observed in A315T mice.As shown in Subcellular fractionation of astrocyte cultures was performed. Nuclear and cytoplasmic fractions were analyzed by Western blot . TDP-43 As shown in The cellular/molecular events that may lead to abnormal neuronal distribution of TDP-43 in neuronal cells are largely unknown. We investigated whether inflammatory stimuli could promote mislocalization of TDP-43 from nucleus to cytoplasm in motor neuron-like NSC-34 cell lines. Non-transfected NSC-34 cells and NSC-34 cells stably transfected with hTDP-43WT-HA were treated with recombinant mouse TNF-α at a concentration of 10 ng/mL for 6h. Non-TNF treated cells served as controls. Following treatment, the subcellular distribution of TDP-43 was determined by Western blot analysis complemented by immunocytochemistry. As expected, the majority of TDP-43 was located in nucleus. However, TNF-α treatment induced cytoplasmic mislocalization of TDP43 in non-transfected cells as well as in cells stably transfected with hTDP-43WT-HA . Thus, tin vivo, 6 months old non-transgenic mice and hTDP-43A315T transgenic mice were chronically i.p. injected once a week with LPS (1 mg/kg) or vehicle solution starting at 6 months of age for a duration of 2 months. After two months of LPS treatment, the spinal cords were collected and examined by immunostaining or western blotting for TDP-43 immunodetection. Spinal cord sections double immunostained with polyclonal antibody for TDP-43 and neuronal marker (Neu N) showed increased cytoplasmic immunostaining in motor neurons of transgenic mice treated with LPS  (A315T transgenic mice (Fold change > 1)  . In contnge > 1) . The effnic mice .A315T transgenic mice exhibited more cytoplasmic TDP-43 immunostaining when injected with LPS rather than vehicle. LPS treatment increased the number of neuronal cells with nuclear depletion of TDP-43 and with cytoplasmic TDP-43 aggregates (in vivo results are in agreement with our findings with in vitro cell cultures that activation of NF-κB pathway by inflammatory stimuli (LPS or TNF-α) can promote cytoplasmic mislocalization and aggregation of TDP-43.To further confirm the effect of LPS treatment on abnormal distribution of TDP-43, spinal cord sections from LPS and vehicle-treated mice were immunostained with monoclonal antibody specific for human TDP-43. As revealed by immunostaining, spinal neurons from hTDP-43gregates . These iThe results presented here demonstrate that inflammatory stimuli such as TNF-α or LPS can promote cytoplasmic mislocalization and aggregation of TDP-43 in glial and neuronal cells, a proteinopathy similar to what has been observed in ALS cases . Some faA315T linked to familial ALS [A315T mice overexpress at moderate levels the TDP-43 transgene ubiquitously under its own promoter. Thus, it was possible to derive from the hTDP-43A315T transgenic mice primary cultures of astrocyte and microglia that expressed TDP-43A315T mutant. The LPS treatment increased the total amount of TDP-43 protein in both microglia and astrocyte cultures  Primary astroglia and microglia cultures were prepared from brain tissues of neonatal mice and then subjected to LPS treatment as described in Materials and Methods. (B) To trigger a systemic innate immune response in the CNS, presymptomatic 6-month-old hTDP-43A315T mice and their non-transgenic (wild-type) littermates received intraperitoneal i.p. injection of LPS (1 mg/kg of body weight) diluted in 100 μl of saline. Mice were i.p. injected once a week for duration of two months.(PDF)Click here for additional data file.


Nanoelectromechanical systems constitute a class of devices lying at the interface between fundamental research and technological applications. Realizing nanoelectromechanical devices based on novel materials such as graphene allows studying their mechanical and electromechanical characteristics at the nanoscale and addressing fundamental questions such as electron–phonon interaction and bandgap engineering. In this work, we realize electromechanical devices using single and bilayer graphene and probe the interplay between their mechanical and electrical properties. We show that the deflection of monolayer graphene nanoribbons results in a linear increase in their electrical resistance. Surprisingly, we observe oscillations in the electromechanical response of bilayer graphene. The proposed theoretical model suggests that these oscillations arise from quantum mechanical interference in the transition region induced by sliding of individual graphene layers with respect to each other. Our work shows that bilayer graphene conceals unexpectedly rich and novel physics with promising potential in applications based on nanoelectromechanical systems. Graphene nanoelectromechanical systems enable the study of the interplay between electrical conductivity and mechanical properties. Here, the authors observe oscillations in the electromechanical response of bilayer graphene due to wrinkling, rather than the linear response seen in single layers. Separating graphene3581011121310On the other hand, bilayer graphene has been reported to show appealing physical properties such as the possibility of opening and tuning an electronic bandgap17Here we integrate mono- and bilayer graphene into NEMS to study the effect of strain on their transport properties. Mono- and bilayer GNRs with widths between 60 and 300 nm are investigated using nanoindentation techniques based on atomic force microscopy (AFM) for high-resolution imaging and controlled deformation of the GNRs. Electrical conductance of the suspended GNR is measured simultaneously with mechanical deformation using a low-noise lock-in amplifier. While monolayer graphene displays increasing resistance with strain, we observe oscillations in the electromechanical response of bilayer graphene. This behaviour is explained from the point of view of quantum interference in the transition region induced by sliding of individual graphene layers with respect to each other.Vs to the source electrodes and a back-gate voltage Vg to the degenerately doped silicon substrate. The drain current is measured using a current–voltage converter connected to a lock-in amplifier. The transfer and output characteristics of a monolayer- and a bilayer-suspended device are presented in Is–Vs characteristic typical of ohmic contacts. The gating dependence Is–Vg shows ambipolar dependence with the charge neutrality point VCN lying at the conductivity minimum and corresponding to the Dirac point.Our samples consist of field-effect transistors based on suspended GNRs . The devDcantilever, (lower graph) as a function of the position of the stage, Zpiezo. We extract the deformation of the GNR ribbon at the point where load is applied by the AFM tip (DGNR) from the expression Zpiezo=Dcantilever+DGNR  and chemical vapour deposition (CVD) grapheneIn the case of monolayer graphene, we have performed electromechanical measurements on five devices with widths varying between 60 and 300 nm , resistaR/R0 as a function of nanoribbon deflection DGNR  defined as GF=(ΔR/R0)/ɛ. This observed strain-induced resistance increase is in agreement with the previous reports on monolayer graphene142122To compare the electromechanical response of the various GNRs, we represent the relative variation of the resistance Δion DGNR . In almo2  of the individual graphene layers with respect to each other. This lateral displacement is expected due to the weak van der Waals force between the two graphene layers25272829303132333435383926293335362732342830W1 and W2, is different  in one of the layers of bilayer graphene, as illustrated in W of the charge carriers in the decoupled graphene layers. Increasing the strain leads to higher amount of local corrugation and changes ΔW, which would cause constructive or destructive interference.We note, however, that the effective width of the transition region within the two individual graphene layers measured on the graphene lattice, E and momentum parallel to the transition region, k||, for various carrier path differences a=0.246 nm—the lattice constant of graphene). The trivial case of ΔW=0  reveals the massive character of Dirac fermions in bilayer graphene. Finite path differences ΔW result in significant amount of backscattering developing a clear sub-band sequence resulting from the quantum confinement of massless Dirac fermions in the transition region (indicated by the dashed line in the last panel of k=4π/(3a). Therefore, one period of oscillations corresponds to the deformation-induced lateral displacement of 3a=0.74 nm.To verify this hypothesis, we perform numerical simulations of electronic transport in a model bilayer graphene device . The simRC, act as a ‘bottleneck' in a realistic device and are thus responsible for most of its total resistance. We obtained RC=41 kΩ by fitting both the average value of the calculated resistance and the magnitude of oscillations to the experimental data reported in a. The direct comparison of W=0 corresponds to the minimum of resistance (no backscattering) while in experiments resistance oscillates reaching both higher and lower values compared with the zero-displacement point. This implies that the stacking domain boundary was already present before indentation. In other words, the origin in experimental resistance curves corresponds to a finite value of ΔW in To gain further insight, we compare the calculated resistance with actual experimental observation. A quantitative comparison requires accounting for the role of contacts as well as for the diffusive transport in the rest of device. Both factors, below collected in a single value et al.In summary, we have investigated the electromechanical response of mono- and bilayer GNRs. Monolayer graphene devices show an increase in resistance under strain, which is related to a change in the Fermi velocity under strain. Within our experimental conditions at room temperature, we observe neither a spectral nor a transport bandgap larger than 4 meV for strain under 5%, in agreement with theoretical predictions by Pereira 2 layer2 plasma, followed by mask removal in acetone. The electron beam lithography step was used to define contacts using a standard bilayer technique (methyl methacrylate (MMA)/PMMA) followed by metallization and lift-off in acetone. The graphene channel is released and suspended using hydrofluoric acid wet etching and critical point drying.Single- and bilayer sheets of graphene have been exfoliated from commercially available crystals of graphite (NGS Naturgraphite GmbH) using the scotch-tape micromechanical cleavage techniqueElectrical characterization of the devices is carried out using Agilent E5270B parameter analyser and a home-built shielded probe station with micromanipulated probes. AFM imaging and electromechanical nanoindentation experiments are performed using a home-built set-up combining the Asylum Research Cypher AFM with the low-noise lock-in amplifier (SRS-830). We use nonconductive Si AFM tips, model NSC36/AlBS from MikroMash .How to cite this article: Benameur, M. M. et al. Electromechanical oscillations in bilayer graphene. Nat. Commun. 6:8582 doi: 10.1038/ncomms9582 (2015).Supplementary Figures 1-11, Supplementary Table 1, Supplementary Notes 1-8 and Supplementary References


An approximate growth model was employed to predict the time required to grow a graphene film by chemical vapor deposition (CVD). Monolayer graphene films were synthesized on Cu foil at various hydrogen flow rates from 10 to 50 sccm. The sheet resistance of the graphene film was 310Ω/□ and the optical transmittance was 97.7%. The Raman intensity ratio of the G-peak to the 2D peak of the graphene film was as high as ~4 when the hydrogen flow rate was 30 sccm. The fitting curve obtained by the deviation equation of growth model closely matches the data. We believe that under the same conditions and with the same setup, the presented growth model can help manufacturers and academics to predict graphene growth time more accurately. Graphene as a TCE has a wide range of applications, including in solar cells, solid-state lighting, and detectors, owing to not only its higher optical transmittance but also its more favorable conductance[Graphene, comprising two-dimensional monolayer of spductance-4 than tductance. (Additiductance. Howeverductance. Neverthductance. Four-laductance. Additioductance-14. This3PO4 in deionized water of 100 mL) was utilized to smooth out the foil, and a voltage from 2 to 4 V was applied until the Cu foil glowed. Thereafter, the Cu foil was rinsed in a large amount of deionized water with sonication and then blow-dried with nitrogen gas. The Cu foil was placed in the reaction chamber, the Ar and H2  gases were introduced into the chamber during temperature ramp-up. The Cu foil was annealed at 1,070°C for an hour. Then, 0.3 sccm of methane  was used as a source of carbon to grow the graphene. The H2 flow rate was varied from 10 to 50 sccm prior to observation of the morphology of the graphene domains and the nucleation density. Following the growth process, the as-grown graphene/Cu foil was removed from the heating zone for rapid cooling. Polymethyl methacrylate (PMMA) was spin-coated on the as-grown graphene/Cu foil as a supporting layer to prevent any cracking during the transfer process. The graphene grew on both sides of the Cu foil. The graphene at the back of the foil was removed by floating on nitride acid solution (30% in deionized water) for 10 s. The Cu foil was etched away overnight using an ammonium persulfate solution (0.1 M) and then rinsed three times in deionized water. The PMMA/graphene was placed on the substrate, and the PMMA was then dissolved in hot acetone bath for 24 h. The residual PMMA was removed by annealing in air at 200°C for an hour and reduced to pristine graphene using an H2/Ar (7/20 sccm) mixture. The morphology and the nucleation density of the graphene domain were measured by scanning electron microscopy (SEM); The surface profile of Cu foils were measured by atomic force microscopy (AFM); the sheet resistance was measured using a four-probe stage; the Raman shift of the graphene was measured by Raman spectroscopy using a laser with a wavelength of 532 nm, the laser power at the focused spot was 2 mW, and the numerical aperture value was 0.75 on the sample with an area of 1 μm2.Graphene films were grown by chemical vapor deposition (APCVD) on 25-μm-thick Cu foils  in a 3-in. quartz tube furnace under atmospheric pressure. Beforehand, electrochemical polishing  and the red spots represent the growth times of graphene that yield the specified area, based on Equation 7. A red spot at the dashed line indicates that the graphene fully covered the Cu foil. Figure -1, verifying the presence of a single-layer graphene[The graphene.An approximate growth model of the synthesis of graphene by APCVD was developed. When the hydrogen flow rate was 30 sccm, the transmittance as a function of wavelength for single-layer graphene reached its maximum of 97.7% at λ =550 nm. The 2D/G ratio and the FWHM indicated that the graphene comprised a single layer of high quality. The lowest obtained sheet resistance of a single layer of graphene was about 310Ω/□. The results of the experiments closely matched the fitting curve. We believe that, under the same conditions and with the same experimental setup, the proposed growth model can help manufacturers and academics predict the growth time of graphene more accurately.The authors declare that they have no competing interests.SHC (Chan) designed the study and wrote the paper. JWC, HSW, MCL, and HBC analyzed the data. SHC (Chen), CCL, and CCK are advisors. All authors read and approved the final manuscript.