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The ultrafast monitoring of deoxyribonucleic acid (DNA) dynamic structural changes is an emerging and rapidly growing research topic in biotechnology. The existing optical spectroscopy used to identify different dynamical DNA structures lacks quick response while requiring large consumption of samples and bulky instrumental facilities. It is highly demanded to develop an ultrafast technique that monitors DNA structural changes with the external stimulus or cancer‐related disease scenarios. Here, we demonstrate a novel photonic integrated graphene‐optofluidic device to monitor DNA structural changes with the ultrafast response time. Our approach is featured with an effective and straightforward design of decoding the electronic structure change of graphene induced by its interactions with DNAs in different conformations using ultrafast nanosecond pulse laser and achieving refractive index sensitivity of ~3 × 10−5 RIU. This innovative technique for the first time allows us to perform ultrafast monitoring of the conformational changes of special DNA molecules structures, including G‐quadruplex formation by K+ ions and i‐motif formation by the low pH stimulus. The graphene‐optofluidic device as presented here provides a new class of label‐free, ultrafast, ultrasensitive, compact, and cost‐effective optical biosensors for medical and healthcare applications.

The kagome lattice, whose electronic valence band (VB) structure includes two Dirac bands and one flat band, offers a rich space to realise tuneable topological and strongly correlated electronic phases in two-dimensional (2D) and layered materials. While strong electron correlations have been observed in inorganic kagome crystals, they remain elusive in organic systems. The latter offer versatile synthesis protocols via molecular self-assembly and metal-ligand coordination. Here, we report the synthesis of a 2D metal-organic framework (MOF) where di-cyano-anthracene (DCA) molecules form a kagome arrangement via coordination with copper (Cu) atoms on a silver surface [Ag(111)]. Low-temperature scanning tunnelling spectroscopy revealed Kondo screening--by the Ag(111) conduction electrons--of magnetic moments localised at Cu and DCA sites of the MOF. Density functional theory and mean-field Hubbard modelling show that these local moments emerge from strong interactions between kagome MOF electrons, enabling organic 2D materials as viable platforms for strongly correlated nanoelectronics and spintronics., Main text: 32 pages, 5 figures. Supplementary Information: 51 pages, 20 figures

With its monoelemental composition, various crystalline forms and an inherently strong spin-orbit coupling, bismuth has been regarded as an ideal prototype material to expand our understanding of topological electronic structures. In particular, two-dimensional bismuth thin films have attracted a growing interest due to potential applications in topological transistors and spintronics. This calls for an effective physical model to give an accurate interpretation of the novel topological phenomena shown by two-dimensional bismuth. However, the conventional semi-empirical approach of adapting bulk bismuth hoppings fails to capture the topological features of two-dimensional bismuth allotropes because the electronic band topology is heavily influenced by crystalline symmetries as well as atom spacings. Here we provide a new parameterization using localized Wannier functions derived from the Bloch states in first-principles calculations. We construct new tight-binding models for three types of two-dimensional bismuth allotropes: a Bi (111) bilayer, bismuthene and a Bi(110) bilayer. We demonstrate that our tight-binding models can successfully reproduce the band structures, symmetries and topological features of these two-dimensional allotropes. We anticipate that these models can be extended to other similar two-dimensional topological structures such as antimonene and arsenene. Moreover, these models can serve as a starting point for investigating the electron/spin transport and electromagnetic response in low-dimensional topological devices., 20 pages, 6 figures

We use angle-resolved photoemission spectroscopy to investigate the electronic structure of bilayer graphene at high n-doping and extreme displacement fields, created by intercalating epitaxial monolayer graphene on silicon carbide with magnesium to form quasi-freestanding bilayer graphene on magnesium-terminated silicon carbide. Angle-resolved photoemission spectroscopy reveals that upon magnesium intercalation, the single massless Dirac band of epitaxial monolayer graphene is transformed into the characteristic massive double-band Dirac spectrum of quasi-freestanding bilayer graphene. Analysis of the spectrum using a simple tight binding model indicates that magnesium intercalation results in an n-type doping of 2.1 $\times$ 10$^{14}$ cm$^{-2}$, creates an extremely high displacement field of 2.6 V/nm, opening a considerable gap of 0.36 eV at the Dirac point. This is further confirmed by density-functional theory calculations for quasi-freestanding bilayer graphene on magnesium-terminated silicon carbide, which show a similar doping level, displacement field and bandgap. Finally, magnesium-intercalated samples are surprisingly robust to ambient conditions; no significant changes in the electronic structure are observed after 30 minutes exposure in air., 46 pages including supporting information, 4 figures in the main paper and 9 figures in the supporting information

The edge states are of particular importance to understand fundamental properties of finite two-dimensional (2D) crystals. Based on first-principles calculations, we investigated on the bare zigzag boron nitride nanoribbons (zzBNNRs) with different spin-polarized states well localized at and extended along their edges. Our calculations examined the edge stress, which is sensitively dependent on the magnetic edge states, for either B-terminated edge or N-terminated edge. Moreover, we revealed that different magnetic configurations lead to a rich spectrum of electronic behaviors at edges. Using an uniaxial tensile strain, we proposed the magnetic phase transitions and thereby obtained the metallic to half-metallic (or reverse) phase transitions at edges. It suggests zzBNNR as a promising candidate for potential applications of non-metal spintronic devices.

Phonon polaritons (PhPs) have attracted significant interest in the nano-optics communities because of their nanoscale confinement and long lifetimes. Although PhP modification by changing the local dielectric environment has been reported, controlled manipulation of PhPs by direct modification of the polaritonic material itself has remained elusive. Here, chemical switching of PhPs in α-MoO3 is achieved by engineering the α-MoO3 crystal through hydrogen intercalation. The intercalation process is non-volatile and recoverable, allowing reversible switching of PhPs while maintaining the long lifetimes. Precise control of the intercalation parameters enables analysis of the intermediate states, in which the needle-like hydrogenated nanostructures functioning as in-plane antennas effectively reflect and launch PhPs and form well-aligned cavities. We further achieve spatially controlled switching of PhPs in selective regions, leading to in-plane heterostructures with various geometries. The intercalation strategy introduced here opens a relatively non-destructive avenue connecting infrared nanophotonics, reconfigurable flat metasurfaces and van der Waals crystals., G.Á.-P. acknowledges support through the Severo Ochoa Program from the Government of the Principality of Asturias (PA20-PF-BP19-053). P.A.-G. and J.D. acknowledge support from the European Research Council under starting grant no. 715496, 2DNANOPTICA. Q.B. acknowledges support from the Australian Research Council (ARC, FT150100450 and IH150100006). Q.B. and Q.O. acknowledge support from the Australian Research Council Centre of Excellence in Future Low-Energy Electronics Technologies (FLEET) (project number: CE170100039).

The intercalation of epitaxial graphene on SiC(0001) with Ca has been studied extensively, yet precisely where the Ca resides remains elusive. Furthermore, the intercalation of Mg underneath epitaxial graphene on SiC(0001) has not been reported. Here, we use low energy electron diffraction, x-ray photoelectron spectroscopy, secondary electron cut-off photoemission and scanning tunneling microscopy to elucidate the physical and electronic structure of both Ca- and Mg-intercalated epitaxial graphene on 6H-SiC(0001). We find that Ca intercalates underneath the buffer layer and bonds to the Si-terminated SiC surface, breaking the C-Si bonds of the buffer layer i.e. 'freestanding' the buffer layer to form Ca-intercalated quasi-freestanding bilayer graphene (Ca-QFSBLG). The situation is similar for the Mg-intercalation of epitaxial graphene on SiC(0001), where an ordered Mg-terminated reconstruction at the SiC surface and Mg bonds to the Si-terminated SiC surface are formed, resulting in Mg-intercalated quasi-freestanding bilayer graphene (Mg-QFSBLG). Ca-intercalation underneath the buffer layer has not been considered in previous studies of Ca-intercalated epitaxial graphene. Furthermore, we find no evidence that either Ca or Mg intercalates between graphene layers. However, we do find that both Ca-QFSBLG and Mg-QFSBLG exhibit very low workfunctions of 3.68 and 3.78 eV, respectively, indicating high n-type doping. Upon exposure to ambient conditions, we find Ca-QFSBLG degrades rapidly, whereas Mg-QFSBLG remains remarkably stable., 58 pages, 10 figures, 4 tables. Revised text and figures

Precipitation is accompanied by the formation and migration of heterophase interfaces. Using the combined approach of advanced imaging and atomistic simulations, we studied the precipitate-matrix interfaces in various aluminium alloy systems, aiming to resolve their detailed atomic structures and illuminate their role in phase transformations.

PN heterojunctions comprising layered van der Waals (vdW) semiconductors have been used to demonstrate current rectifiers, photodetectors, and photovoltaic devices. However, a direct or near-direct bandgap at the heterointerface that can significantly enhance optical generation, for high light absorbing few/multi-layer vdW materials, has not yet been shown. In this work, for the first time, few-layer group-6 transition metal dichalcogenide (TMD) $WSe_2$ is shown to form a sizeable (0.7 eV) near-direct bandgap with type-II band alignment at its interface with the group-7 TMD $ReS_2$ through density functional theory calculations. Further, the type-II alignment and photogeneration across the interlayer bandgap have been experimentally confirmed through micro-photoluminescence and IR photodetection measurements, respectively. High optical absorption in few-layer flakes, large conduction and valence band offsets for efficient electron-hole separation and stacking of light facing, direct bandgap $ReS_2$ on top of gate tunable $WSe_2$ are shown to result in excellent and tunable photodetection as well as photovoltaic performance through flake thickness dependent optoelectronic measurements. Few-layer flakes demonstrate ultrafast response time (5 $\mu$s) at high responsivity (3 A/W) and large photocurrent generation and responsivity enhancement at the heterostructure overlap region (10-100X) for 532 nm laser illumination. Large open-circuit voltage of 0.64 V and short-circuit current of 2.6 $\mu$A enables high output electrical power. Finally, long term air-stability and a facile single contact metal fabrication process makes the multi-functional few-layer $WSe_2$/$ReS_2$ heterostructure diode technologically promising for next-generation optoelectronic applications., Comment: Manuscript- 27 pages, 8 figures. Supporting Information- 17 pages, 17 figures

Layered indium selenides ($In_{2}Se_{3}$) have recently been discovered to host robust out-of-plane and in-plane ferroelectricity in the $\alpha$ and $\beta$' phases, respectively. In this work, we utilise angle-resolved photoelectron spectroscopy to directly measure the electronic bandstructure of $\beta '-In_{2}Se_{3}$, and compare to hybrid density functional theory (DFT) calculations. In agreement with DFT, we find the band structure is highly two-dimensional, with negligible dispersion along the c-axis. Due to n-type doping we are able to observe the conduction band minima, and directly measure the minimum indirect (0.97 eV) and direct (1.46 eV) bandgaps. We find the Fermi surface in the conduction band is characterized by anisotropic electron pockets with sharp in-plane dispersion about the $\overline{M}$ points, yielding effective masses of 0.21 $m_{0}$ along $\overline{KM}$ and 0.33 $m_{0}$ along $\overline{\Gamma M}$. The measured band structure is well supported by hybrid density functional theory calculations. The highly two-dimensional (2D) bandstructure with moderate bandgap and small effective mass suggest that $\beta'-In_{2}Se_{3}$ is a potentially useful new van der Waals semiconductor. This together with its ferroelectricity makes it a viable material for high-mobility ferroelectric-photovoltaic devices, with applications in non-volatile memory switching and renewable energy technologies., Comment: 19 pages, 4 + 1 figures; typos corrected;added references; updated figures & discussion to reflect changes in model

The Al-Ag system is thought to be a well-understood model system used to study diffusional phase transformations in alloys. Here we report the existence of a new precipitate phase, zeta, in this classical system using scanning transmission electron microscopy (STEM). The zeta phase has a modulated structure composed of alternating bilayers enriched in Al or Ag. Our in situ annealing experiments reveal that the zeta phase is an intermediate precipitate phase between GP zones epsilon and gamma prime. First-principles calculations show that z is a local energy minimum state formed during Ag clustering in Al. The layered structure of zeta is analogous to the well-known Ag segregation at the precipitate-matrix interfaces when Ag is micro- alloyed in various aluminium alloys., This is the preprint before paper submission. Please refer to Acta Materialia for the final version of the paper, supplementary materials and movies. Link: http://www.sciencedirect.com/science/article/pii/S1359645417303555

Atomic hydrogen (H) was introduced into steel (AISI 1018 mild steel) by controlled cathodic pre-charging. The resultant steel sample, comprising about 1 ppmw diffusible H, and a reference uncharged sample, were studied using atomic emission spectroelectrochemistry (AESEC). AESEC involved potentiodynamic polarisation in a flowing non-passivating electrolyte (0.6 M NaCl, pH 1.95) with real time reconciliation of metal dissolution using on-line inductively coupled plasma-atomic emission spectroscopy (ICP-OES). The presence of absorbed H was shown to significantly increase anodic Fe dissolution, as evidenced by the enhanced detection of Fe2+ ions by ICP-OES. We discuss this important finding in the context of previously proposed mechanisms for H-effects on the corrosion of steels.

A first principles many-body approach is employed to calculate the band structure and optical response of nanometer sized ribbons of SiC. Many-body effects are incorporated using the GW approximation, and excitonic effects are included using the Bethe-Salpeter equation. Both unpassivated and hydrogen passivated armchair SiC nanoribbons are studied. As a consequence of low dimensionality, large quasiparticle corrections are seen to the Kohn-Sham energy gaps. In both cases quasiparticle band gaps are increased by up to 2 eV, as compared to their Kohn-Sham energy values. Inclusion of electron-hole interactions modifies the absorption spectra significantly, giving rise to strongly bound excitonic peaks in these systems.The results suggest that hydrogen-passivated armchair SiC nanoribbons have the potential to be used in optoelectronic devices operating in the UV-Vis region of the spectrum. We also compute the formation energies of these nanoribbons as a function of their widths, and conclude that hydrogen-saturated ribbons will be much more stable as compared to the bare ones., 18 pages, 7 figures (included)