The graphene/h-BN heterostructure provides a promising device for biomedical applications and biosensor. However, the friction characteristics of water on graphene/h-BN are still elusive. By means of molecular dynamics simulations, we investigated the friction coefficient of water on both sides of graphene/h-BN heterostructures under various rotation angle, which shows a non-monotonic but symmetrical variation with relative interlayer angle. Despite that friction coefficient of h-BN surface is larger than that of graphene, as the rotation angle increases, the friction coefficient of water on both sides of the graphene/h-BN heterostructure exhibits the same “M”-shaped curve. The center of symmetry of the curve is at the rotation angle of 30°; the friction coefficient is the largest when the rotation angle is 10° and 50°. It was found that graphene/h-BN heterostructure is a device whose friction coefficient is different on both sides and can be adjusted by twisting the relative interlayer angle. These results could be demonstrated by the van der Waals interaction and different pattern of free energy landscape. These findings provide detailed insights into the mechanism of the friction property of water at nanoscale, which would facilitate feasible applications of graphene/h-BN heterostructure in biosensor and biomedicine.

Rotation induced symmetry change of friction coefficient of water on graphene/h-BN heterostructures

Associating thin ferromagnetic (FM) films with two-dimensional (2D) materials appears to be a promising approach for the next-generation spintronic devices. Consequently, the control of the magnetic phenomena in the FM/2D systems is of the utmost importance. We investigate in this paper the structural, static, and dynamic magnetic properties of $\mathrm{Si}{\mathrm{O}}_{2}/\mathrm{single}\ensuremath{-}\mathrm{layer}$ graphene (SLG)/CoFeB ($3\phantom{\rule{0.16em}{0ex}}\mathrm{nm}\ensuremath{\le}{t}_{\mathrm{CFB}}\ensuremath{\le}20\phantom{\rule{0.16em}{0ex}}\mathrm{nm})/\mathrm{Cu}$ (3 nm) structures and compared them with control samples, without the SLG underlayer. The single-layer characteristics of the synthesized graphene are deduced from Raman spectroscopy investigations. Vibrating sample magnetometry measurements allowed deducting the magnetization at saturation ${M}_{s}$, the coercive field ${H}_{c}$, and the magnetic dead layer thickness ${t}_{d}$. In the absence of SLG, the nominal thickness ${t}_{\mathrm{CFB}}$ is almost preserved, while ${t}_{d}\ensuremath{\approx}2\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$ was determined in presence of graphene. Here, ${H}_{c}$ was found to increase in presence of SLG compared with the control structures, while ${M}_{s}$ are comparable. Brillouin light scattering and microstrip FM resonance measurements were employed to investigate the dynamic magnetic properties of the samples. It was found that the magnetic anisotropy results from interface and volume contributions and that the largest interface anisotropy was observed in presence of SLG. Measurements of the spin waves nonreciprocity, related to the interfacial Dzyloshinskii-Moriya interaction (iDMI), revealed weak iDMI in our samples. The magnetic damping in the SLG/CFB films was found to be dominated by the two-magnon contribution. No spin pumping was observed either without or with graphene. Our results highlight the influence of the graphene ripples on the magnetic properties of graphene/FM-based heterostructures. 

Magnetic properties of CoFeB films grown on a single-layer graphene underlayer

Based upon the observations (i) that their in-plane lattice constants match almost perfectly and (ii) that their electronic structures overlap in reciprocal space for one spin direction only, we predict perfect spin filtering for interfaces between graphite and (111) fcc or (0001) hcp Ni or Co. The spin filtering is quite insensitive to roughness and disorder. The formation of a chemical bond between graphite and the open d-shell transition metals that might complicate or even prevent spin injection into a single graphene sheet can be simply prevented by dusting Ni or Co with one or a few monolayers of Cu while still preserving the ideal spin-injection property.

Graphite and graphene as perfect spin filters

The relative orientation of successive sheets, i.e. the stacking sequence, in layered two-dimensional materials is central to the electronic, thermal, and mechanical properties of the material. Often different stacking sequences have comparable cohesive energy, leading to alternative stable crystal structures. Here we theoretically and experimentally explore different stacking sequences in the van der Waals bonded material hexagonal boron nitride (h-BN). We examine the total energy, electronic bandgap, and dielectric response tensor for five distinct high symmetry stacking sequences for both bulk and bilayer forms of h-BN. Two sequences, the generally assumed AA' sequence and the relatively unknown (for h-BN) AB (Bernal) sequence, are predicted to have comparably low energy. We present a scalable modified chemical vapor deposition method that produces large flakes of virtually pure AB stacked h-BN; this new material complements the generally available AA' stacked h-BN.

Alternative Stacking Sequences in Hexagonal Boron Nitride.

Hexagonal boron nitride (h-BN) is a promising material for implementation in spintronics due to a large band gap, low spin-orbit coupling, and a small lattice mismatch to graphene and to close-packed surfaces of fcc-Ni(111) and hcp-Co(0001). Epitaxial deposition of h-BN on ferromagnetic metals is aimed at small interface scattering of charge and spin carriers. We report on the controlled growth of h-BN/Ni(111) by means of molecular beam epitaxy (MBE). Structural and electronic properties of this system are investigated using cross-section transmission electron microscopy (TEM) and electron spectroscopies which confirm good agreement with the properties of bulk h-BN. The latter are also corroborated by density functional theory (DFT) calculations, revealing that the first h-BN layer at the interface to Ni is metallic. Our investigations demonstrate that MBE is a promising, versatile alternative to both the exfoliation approach and chemical vapour deposition of h-BN.

/pdf/structural-and-electronic-properties-of-epitaxial-multilayer-3e700opc0b.pdf

Structural and electronic properties of epitaxial multilayer h-BN on Ni(111) for spintronics applications

We carried out first-principles calculations study of the configurations, structural, electronic and magnetic properties of a graphene (h-BN) monolayer and bilayer adsorbed on Co(0001) surface. Binding energies, distances of the carbon C, boron B, or nitrogen N atoms from the Co surface and optimized lattice parameter for all configurations are reported. Induced magnetic moments on C, B and N atoms are determined as well as the magnetic moments carried by the cobalt Co surface atoms in presence of graphene or h-BN. Our results are discussed by means of hybridization of graphene (h-BN) and cobalt orbitals and charge transfer at the graphene (h-BN)/Co interface based on band structure and density of states calculations. Comparison between monolayers and bilayers systems highlighted the preponderant role of the first layer in contact with cobalt for the bilayers cases.

First-principles calculations study of the configurations, structural, electronic and magnetic properties of graphene and h-BN monolayers and bilayers adsorbed on Co(0001) surface

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First-principles calculations study of the configurations, structural, electronic and magnetic properties of graphene and h-BN monolayers and bilayers adsorbed on Co(0001) surface