The quest for nanoscale light sources with designer radiation patterns and polarization has motivated the development of nanoantennas that interact strongly with the incoming light and are able to transform its frequency, radiation and polarization patterns. Here, we demonstrate dielectric AlGaAs nanoantennas for efficient second harmonic generation, enabling the control of both directionality and polarization of 1

Identifying the specific role of physical guidance cues in the growth of neurons is crucial for understanding the fundamental biology of brain development and for designing scaffolds for tissue engineering. Here, we investigate the structural significance of nanoscale topographies as physical cues for neurite outgrowth and circuit formation by growing neurons on semiconductor nanowires. We monitored neurite growth using optical and scanning electron microscopy and evaluated the spontaneous neuronal network activity using functional calcium imaging. We show, for the first time, that an isotropic arrangement of indium phosphide (InP) nanowires can serve as physical cues for guiding neurite growth and aid in forming a network with neighboring neurons. Most importantly, we confirm that multiple neurons, with neurites guided by the topography of the InP nanowire scaffolds, exhibit synchronized calcium activity, implying intercellular communications via synaptic connections. Our study imparts new fundamental insights on the role of nanotopographical cues in the formation of functional neuronal circuits in the brain and will therefore advance the development of neuroprosthetic scaffolds.

We report a method for growing rectangular InAs nanofins with deterministic length, width and height by dielectric-templated selective-area epitaxy. These freestanding nanofins can be transferred to lay flat on a separate substrate for device fabrication. A key goal was to regain a spatial dimension for device design compared to nanowires, whilst retaining the benefits of bottom-up epitaxial growth. The transferred nanofins were made into devices featuring multiple contacts for Hall effect and fourterminal resistance studies, as well as a global back-gate and nanoscale local top-gates for density control. Hall studies give a 3D electron density 2.5 − 5 × 10 17 cm −3 , corresponding to an approximate surface accumulation layer density 3 − 6× 10 12 cm −2 that agrees well with previous studies of InAs nanowires. We obtain Hall mobilities as high as 1200 cm 2 /Vs, field-effect mobilities as high as 4400 cm 2 /Vs and clear quantum interference structure at temperatures as high as 20 K. Our devices show excellent prospects for fabrication into more complicated devices featuring multiple ohmic contacts, local gates and possibly other functional elements, e.g., patterned superconductor contacts, that may make them attractive options for future quantum information applications.Quantum devices were underpinned for several decades by the interfacial two-dimensional (2D) electron gas found in III-V semiconductor heterostructures. 1 A top-down approach to these systems is costly, with heterostructure complexity limited by interfacial strain issues.Bottom-up approaches have thus generated massive interest with a heavy focus on onedimensional (1D) nanostructures, i.e., nanowires, where small interfaces enable greater heterostructure versatility, including the ability to integrate III-Vs on low-cost Si substrates. [2][3][4] Researcher ingenuity has meant clever new devices still arise from the nanowire geometry even after two decades. That said, we suspect we are not alone in wishing for extra spatial dimensions to work with. An attractive idea would be to take the hexagonal nanowire cross-section and stretch it to obtain a 2D 'nanofin' such that two side-facets have much larger area. These could be transferred to a separate substrate to make devices featuring, e.g., multiple contacts and gates by conventional nanofabrication methods. This concept is impossible with vapor-liquid-solid approaches. 5,6 Here we demonstrate it is possible using selective-area epitaxy, 7,8 giving 2D InAs nanofins with precise size control, and opening a path to more interesting nanostructure shapes via appropriate mask design. 9Our 2D nanofins offer some interesting potential for nanoelectronics. Firstly, they offer