Graphene and other two-dimensional crystals can be combined to form various hybrids and heterostructures, creating materials on demand with properties determined by the interlayer interaction. This is the case even for a single material, where multilayer stacks with different relative orientation have different optical and electronic properties. Probing and understanding the interface coupling is thus of primary importance for fundamental science and applications. Here we study twisted multilayer graphene flakes with multi-wavelength Raman spectroscopy. We find a significant intensity enhancement of the interlayer coupling modes (C peaks) due to resonance with new optically allowed electronic transitions, determined by the relative orientation of the layers. The interlayer coupling results in a Davydov splitting of the C peak in systems consisting of two equivalent graphene multilayers. This allows us to directly quantify the interlayer interaction, which is much smaller compared with Bernalstacked interfaces. This paves the way to the use of Raman spectroscopy to uncover the interface coupling of two-dimensional hybrids and heterostructures.

Co-containing layered double hydroxides (LDHs) are potential non-noble-metal catalysts for the aerobic oxidation of alcohols. However, the intrinsic activity of bulk LDHs is relatively low. In this work, we fabricated ultrathin and vacancy-rich nanosheets by exfoliating bulk CoAl-LDHs, which were then assembled with graphite oxide (GO) to a ord a hybrid CoAl-ELDH/GO catalyst. TEM, AFM, and positron annihilation spectrometry indicate that the thickness of the exfoliated LDH platelets is about 3 nm, with a large number of vacancies in the host layers. Fourier transformed XAFS functions show that the Co−O and Co••••Co coordination numbers (5.5 and 2.8, respectively) in the hybrid CoAl-ELDH/GO material are significantly lower than the corresponding values in bulk CoAl-LDHs (6.0 and 3.8, respectively). Furthermore, in addition to the oxygen vacancies (VO) and cobalt vacancies (VCo), CoAl-ELDH/GO also contains negatively charged VCo−Co−OH δ− sites and exposed lattice oxygen sites. CoAl-ELDH/GO shows excellent performance as a catalyst for the aerobic oxidation of benzyl alcohol, with a TOF of 1.14 h − 1 ; this is nearly five times that of the unexfoliated bulk CoAl-LDHs (0.23 h − 1) precursor. O2-TPD and DRIFT spectroscopy declare that the oxygen storage capacity and mobility are facilitated by the oxygen vacancies and surface lattice oxygen sites. Meanwhile, DFT calculations of adsorption energy show that benzyl alcohol is strongly adsorbed on the oxygen vacancies and negatively charged VCo−Co−OH δ− sites. A kinetic isotope e ect study further illustrates that the vacancy-rich CoAl-ELDH/GO catalyst accelerates the cleavage of the O−H bond in benzyl alcohol. Finally, we show that the hybrid CoAl-ELDH/GO material exhibits excellent catalytic activity and selectivity in the oxidation of a range of other benzylic and unsaturated alcohols.

We have wrapped metallic cylinders with strongly absorbing metamaterials. These resonant structures, which are patterned on flexible substrates, smoothly coat the cylinder and give it an electromagnetic response designed to minimize its radar cross section. We compare the normal-incidence, small-beam reflection coefficient with the measurement of the far-field bistatic radar cross section of the sample, using a quasi-planar THz wave with a beam diameter significantly larger than the sample dimensions. In this geometry we demonstrate a near-400-fold reduction of the radar cross section at the design frequency of 0.87 THz. In addition we discuss the effect of finite sample dimensions and the spatial dependence of the reflection spectrum of the metamaterial.

Countering the optical network ‘capacity crunch’ calls for a radical development in optical fibres that could simultaneously minimize nonlinearity penalties, chromatic dispersion and maximize signal launch power. Hollow-core fibres (HCF) can break the nonlinear Shannon limit of solid-core fibre and fulfil all above requirements, but its optical performance need to be significantly upgraded before they can be considered for high-capacity telecommunication systems. Here, we report a new HCF with conjoined-tubes in the cladding and a negative-curvature core shape. It exhibits a minimum transmission loss of 2 dB km−1 at 1512 nm and a <16 dB km−1 bandwidth spanning across the O, E, S, C, L telecom bands (1302–1637 nm). The debut of this conjoined-tube HCF, with combined merits of ultralow loss, broad bandwidth, low bending loss, high mode quality and simple structure heralds a new opportunity to fully unleash the potential of HCF in telecommunication applications.