Directional antennas revolutionized modern day telecommunication by enabling precise beaming of radio and microwave signals with minimal loss of energy. Similarly, directional optical nanoantennas are expected to pave the way toward on-chip wireless communication and information processing. Currently, on-chip integration of such antennas is hampered by their multielement design or the requirement of complicated excitation schemes. Here, we experimentally demonstrate electrical driving of in-plane tunneling nanoantennas to achieve broadband unidirectional emission of light. Far-field interference, as a result of the spectral overlap between the dipolar emission of the tunnel junction and the fundamental quadrupole-like resonance of the nanoantenna, gives rise to a directional radiation pattern. By tuning this overlap using the applied voltage, we record directivities as high as 5 dB. In addition to electrical tunability, we also demonstrate passive tunability of the directivity using the antenna geometry. These fully configurable electrically driven nanoantennas provide a simple way to direct optical energy on-chip using an extremely small device footprint.

Superconducting nanowires currently attract great interest due to their application in single-photon detectors and quantum-computing circuits. In this context, it is of fundamental importance to understand the detrimental fluctuations of the superconducting order parameter as the wire width shrinks. In this paper, we use controlled electromigration to narrow down aluminium nanoconstrictions. We demonstrate that a transition from thermally assisted phase slips to quantum phase slips takes place when the cross section becomes less than ∼150 nm2. In the regime dominated by quantum phase slips the nanowire loses its capacity to carry current without dissipation, even at the lowest possible temperature. We also show that the constrictions exhibit a negative magnetoresistance at low-magnetic fields, which can be attributed to the suppression of superconductivity in the contact leads. These findings reveal perspectives of the proposed fabrication method for exploring various fascinating superconducting phenomena in atomic-size contacts.

We investigated the interaction between size-selected Au and Au clusters and graphene. Hereto preformed clusters are deposited on graphene field-effect transistors, a novel approach which offers a high control over the number of atoms per cluster, the deposition energy and the deposited density. The induced p-doping and charge carrier scattering indicate that a major part of the deposited clusters remains on the graphene flake as either individual or sub-nm coalesced entities. This is independently confirmed by scanning electron microscopy on the same devices after current annealing. Our novel approach provides perspectives for the electronic sensing of metallic clusters down to their atom-by-atom size-specific properties, and exploiting the tunability of clusters for tailoring desired properties in graphene.

COMMUNICATION (1 of 8)properties in graphene, such as (tunable) bandgaps [12] or p-n junctions. [13] Metal atoms and nanoparticles are interesting candidates to tailor graphene. [14] The charge transfer between adparticles and graphene results in tunable (surface) electronic states, which can act as active sites for heterogeneous catalysis, [4,[15][16][17] or enhance the sensitivity and selectivity of graphene gas sensors (see ref.[18] and references therein). Furthermore, metal adparticles are prime candidates to induce a (tunable) spin-orbit coupling in graphene, enhancing for instance the spin Hall effect, [19] which further augments graphene's spintronic potential. [20] Due to the extreme sensitivity of graphene devices, one desires a high level of control in adsorbing metal adparticles. Such control is offered by state-of-the-art cluster fabrication and deposition techniques, which allows to select the size and composition of clusters with atomic resolution, and tune the deposition energy and adparticle density. [21] Using these techniques, ultrasmall few-atom clusters in gas-phase showcased a distinct atom-by-atom size-dependence in the electronic and structural properties, leading to different and unique physicochemical properties. [22] The size-dependent characteristics can be preserved in the interaction of a cluster with a support. For specific gold, cobalt and germanium clusters, dedicated atomic resolution surface probe studies, using scanning tunneling microscopy [23,24] and scanning transmission electron microscopy, [25][26][27][28] have, in combination with density functional theory (DFT) simulations, allowed for a detailed morphological characterization of clusters on supports. The overall properties of a cluster-support system retain a dependence on the exact cluster size. [15] As such, cluster-support systems, engineered with atomic precision, are, among others, of interest as catalysts [29][30][31][32] and lowreactive building blocks for nanosystems. [33] In the size-regime in between single atoms and larger nanometer-sized particles, clusters offer diverse possibilities in functionalizing graphene.To the best of our knowledge, there has been no realization yet of an electronic device, in which the rich size-dependence of few-atom metal clusters is transpired in the properties of the device, although this has been proposed in several computational studies for few-atom metal clusters on graphene. [34][35][36] To that avail, we combine in this work single layer graphene (G) with few-atom gold clusters. In particular, these clusters Graphene's sensitivity to adsorbed particles has attracted widespread attention because of its potential sensor applications. Size-selected few-atom clusters are promising candidates as adparticles to graphene. Due to their small size, physicochemical properties are dominated by quantum size effects. In particular, few-atom gold clusters demonstrate a significant catalytic activity in various oxidation reactions. In this joint experimental and computational work, size-...