One-atom-thick crystals are impermeable to atoms and molecules, but hydrogen ions (thermal protons) penetrate through them. We show that monolayers of graphene and boron nitride can be used to separate hydrogen ion isotopes. Using electrical measurements and mass spectrometry, we found that deuterons permeate through these crystals much slower than protons, resulting in a separation factor of ≈10 at room temperature. The isotope effect is attributed to a difference of ≈60 milli-electron volts between zero-point energies of incident protons and deuterons, which translates into the equivalent difference in the activation barriers posed by two-dimensional crystals. In addition to providing insight into the proton transport mechanism, the demonstrated approach offers a competitive and scalable way for hydrogen isotope enrichment.

Controlled transport of water molecules through membranes and capillaries is important in areas as diverse as water purification and healthcare technologies. Previous attempts to control water permeation through membranes (mainly polymeric ones) have concentrated on modulating the structure of the membrane and the physicochemical properties of its surface by varying the pH, temperature or ionic strength. Electrical control over water transport is an attractive alternative; however, theory and simulations have often yielded conflicting results, from freezing of water molecules to melting of ice under an applied electric field. Here we report electrically controlled water permeation through micrometre-thick graphene oxide membranes. Such membranes have previously been shown to exhibit ultrafast permeation of water and molecular sieving properties, with the potential for industrial-scale production. To achieve electrical control over water permeation, we create conductive filaments in the graphene oxide membranes via controllable electrical breakdown. The electric field that concentrates around these current-carrying filaments ionizes water molecules inside graphene capillaries within the graphene oxide membranes, which impedes water transport. We thus demonstrate precise control of water permeation, from ultrafast permeation to complete blocking. Our work opens up an avenue for developing smart membrane technologies for artificial biological systems, tissue engineering and filtration.

We present extremely narrow collective plasmon resonances observed in gold nanostripe arrays fabricated on a thin gold film, with the spectral line full width at half-maximum (fwhm) as low as 5 nm and quality factors Q reaching 300, at important fiber-optic telecommunication wavelengths around 1.5 μm. Using these resonances, we demonstrate a hybrid graphene-plasmonic modulator with the modulation depth of 20% in reflection operated by gating of a single layer graphene, the largest measured so far.

Two-dimensional graphene plasmon-based technologies will enable the development of fast, compact and inexpensive active photonic elements because, unlike plasmons in other materials, graphene plasmons can be tuned via the doping level. Such tuning is harnessed within terahertz quantum cascade lasers to reversibly alter their emission. This is achieved in two key steps: First by exciting graphene plasmons within an aperiodic lattice laser and, second, by engineering photon lifetimes, linking graphene's Fermi energy with the round-trip gain. Modal gain and hence laser spectra are highly sensitive to the doping of an integrated, electrically controllable, graphene layer. Demonstration of the integrated graphene plasmon laser principle lays the foundation for a new generation of active, programmable plasmonic metamaterials with major implications across photonics, material sciences and nanotechnology.Among the many intriguing properties of graphene, its plasmonic characteristics are some of the most fascinating and potentially useful [1,2]. Long-lived, tunable intrinsic graphene surface plasmons (SP) have already been demonstrated in a number of experiments [3][4][5][6][7][8][9], including optical modulators [10,11], providing the potential for applications [12,13]. In contrast to the noble metals that are usually used in SP devices [13,14], graphene's Fermi energy, E F , and carrier concentration, n s (and therefore its conductivity and SP mode properties), can be altered, for example by electrical gating and surface doping [3,15,16]. Consequently, the behavior of graphene SP-based structures can be modified in situ, without the need for structural device changes. In particular, graphene's optical and plasmonic properties are tunable in the terahertz (THz) spectral region [3,17], giving rise to the possibility of compact electrically controllable THz optical components [18]. We incorporated graphene into a plasmonic THz laser microcavity to dynamically modulate round-trip modal gain values and therefore laser emission via E F . In this way gated graphene becomes a powerful tool with which to control the fundamental properties of a laser -a tool that is potentially extremely fast and all electrical in nature, with negligible electrical power requirements.The interaction between light and matter can be altered by manipulating the electromagnetic density-of-states (DOS) using a micro resonator [19,20]. By incorporating a photonic lattice or plasmonic structure into a laser, one can control the frequency and amplification of resonant modes and hence manipulate the properties of lasing emission [21][22][23]. Furthermore, by breaking the regularity of these structures it is possible to modulate the photon DOS and hence light-matter interaction at several frequencies simultaneously. This technique was used recently to develop an aperiodic distributed feedback (ADFB) cavity laser with a lattice which is in essence a computergenerated hologram [24,25]. The hologram digitally encodes the Fourier transform of a desired optica...

Umbilical defects were induced in a nematic liquid crystal with negative dielectric anisotropy, confined to Hele-Shaw cells with homeotropic boundary conditions, and their annihilation dynamics were investigated experimentally. Dynamic scaling laws, previously proposed for Schlieren defects, were verified also for electric field induced umbilical defects while varying external parameters, such as electric field amplitude, frequency, Hele-Shaw cell gap, and temperature. In all cases, scaling relations of rho(t) proportional to t(-1) for the defect density and D proportional to (t(0) - t)(1/2) for the defect pair separation were obtained, independent of external field parameters. The experimental results give evidence of the universality of scaling relations for the annihilation of topological defects in liquid crystals, extended to umbilical defects and their annihilation dynamics under applied external fields.

Graphene is known to possess strong optical nonlinearity which turned out to be suitable for creation of efficient saturable absorbers in mode locked fiber lasers. Nonlinear response of graphene can be further enhanced by the presence of graphene plasmons. Here, we report a novel nonlinear effect observed in nanostructured graphene which comes about due to excitation of graphene plasmons. We experimentally detect and theoretically explain enhanced mixing of near-infrared and mid-infrared light in arrays of graphene nanoribbons. Strong compression of light by graphene plasmons implies that the described effect of light mixing is nonlocal in nature and orders of magnitude larger than the conventional local graphene nonlinearity. Both second and third order nonlinear effects were observed in our experiments with the recalculated third-order nonlinearity coefficient reaching values of 4.5 × 10 esu. The suggested effect could be used in variety of applications including nonlinear light modulators, light multiplexers, light logic, and sensing devices.

A transverse computer-generated hologram (CGH) diffracts and provides flexible control of incident light by steering it to any point in the projected image plane -i.e.CGHs are able to direct the light to where it is needed and away from where it is not 1 .In addition, the number of resolvable points in the image projection plane is a function of the CGH's pixel count 2 . Here we report a longitudinal CGH (LCGH), a photonic structure, which swaps the ability to steer light toward fixed spatial points for digital control in the frequency domain. This is of particular interest in the context of tunable lasers. In this regard, an LCGH offers two important degrees-of-freedom (DOFs): 1) provides high-resolution wavevector or k-space resolution within the Brillouin zone; 2) enables full control to define or modify the reflectivity at each resolvable k-point, so attaining a target spectral response. We demonstrate the flexibility of our LCGH approach by achieving purely electronic tuning between six digitally-selected operating frequencies in a single-section terahertz (THz) quantum cascade laser (QCL) 3 . These switchable single-frequency devices will simplify combining the power and flexibility of (Fig. 1d) enabling switching between these modes, i.e.electronically-controlled discrete tuning.In order to understand the first DOF, consider an LCGH of 2N pixels in the form of a spatial relative permittivity distribution ε(z), where L = NΛ is the total length and Λ the 3 minimum hologram-element separation. There exists an approximate FT relationship between ε(z) and the spectral reflectivity response ρ(k)18-20 :Due to the pixelated nature of the spatial domain z, the wavevector k is unique only over the interval (0,k B ), with a maximum N number of resolvable k-points resulting in a density of states Δk = (k B /N)(n eff /n g ) 21, 22 , where k B = π/n eff Λ is the wavevector corresponding to the edge of Brillouin zone, n eff is the effective modal refractive index, n g is the group refractive index All QCLs were fabricated from a molecular beam epitaxially grown GaAs/Al 0.15 Ga 0.85 As wafer, V557, with an 11.4 µm-thick active region based on reference 25. V557 was processed (Fig. 2 caption) into SP waveguides and cleaved into ~6 mm-long Fabry-Perot (FP) cavities.All devices displayed similar performance characteristics − as a typical example Fig. 2a shows the FP spectra of device A, recorded at four driving current densities. As expected, In order to generate the real-space lattice structure (i.e. the LCGH) satisfying ρ target , we exploit equation 1. The pixelated nature of the real-space allows this design to be implemented using a discrete FT, specifically a fast Fourier transform (FFT). Identifying an "optimised" LCGH architecture is computationally non-trivial, particularly when N is large.An FFT-based simulated annealing (SA) inverse optimisation algorithm was chosen, details 5 of which, including the number of optimisation parameters, are described in references 26and 27. The choice of algorithm is not critica...

A holographically designed, aperiodic distributed feedback grating is used as a multi-resonance filter and embedded within an existing Fabry-Pérot (FP) terahertz (THz) quantum cascade laser (QCL) cavity. Balancing the feedback strengths of the filter resonances and the FP cavity creates a system capable of a high degree of single-mode selectivity, which is sensitive to changes in driving current. Multi-moded QCLs operating around 2.9 THz are thus modified to achieve purely electronic discrete tuning spanning over 160 GHz with an average tuning resolution of 30 GHz. Applying the same multi-resonance filter to QCLs with gain peaks around 2.65 and 2.9 THz leads to dual-mode lasing with an electrically controlled frequency separation of between 190 and 267 GHz. A phase sensitive mode selection mechanism is experimentally confirmed by the observation of divergent fine-tuning of the lasing modes.