Unveiling Nanoscale Heterogeneities at the Bias-Dependent Gold-Electrolyte Interface.

Electrified solid-liquid interfaces (SLIs) are extremely complex and dynamic, affecting both the dynamics and selectivity of reaction pathways at electrochemical interfaces. Enabling access to the structure and arrangement of interfacial water in situ with nanoscale resolution is essential to develop efficient electrocatalysts. Here, we probe the SLI energy of a polycrystalline Au(111) electrode in a neutral aqueous electrolyte through in situ electrochemical atomic force microscopy.

High Aspect Ratio Silver Nanogrids by Bottom-Up Electrochemical Growth as Transparent Electrode.

A scalable selective-area electrochemical method is reported for the fabrication of interconnected metal nanostructures. In this work, the fabrication of silver nanowire grids for the application of transparent electrodes is explored. The presented method is based on a through-the-mask electrodeposition method, where the mask is made by using substrate conformal imprint lithography.

Optical Characterization of Plasmonic Indium Lattices Fabricated via Electrochemical Deposition.

The optical properties of periodic metallic nanoparticle lattices have found many exciting applications. Indium is an emerging plasmonic material that offers to extend the plasmonic applications given by gold and silver from the visible to the ultraviolet spectral range, with applications in imaging, sensing, and lasing. Due to the high vapor pressure/low melting temperature of indium, nanofabrication of ordered metallic nanoparticles is nontrivial.

The role of Pb oxidation state of the precursor in the formation of 2D perovskite microplates.

Two-dimensional (2D) lead halide perovskites are an exciting class of materials currently being extensively explored for photovoltaics and other optoelectronic applications. Their ionic nature makes them ideal candidates for solution processing into both thin films and nanostructured crystals. Understanding how 2D lead halide perovskite crystals form is key towards full control over their physical properties, which may enable new physical phenomena and devices.

Influence of the crystallographic texture of ITO on the electrodeposition of silver nanoparticles.

The electrochemical control over nucleation and growth of metal nanoparticles on foreign substrates is an active field of research, where the surface properties of the substrate have a key role in nucleation dynamics. Polycrystalline indium tin oxide (ITO) films are highly desired substrates for many optoelectronic applications, for which the only parameter that is often specified is the sheet resistance. As a result, growth on ITO is highly irreproducible.

Ion Current Rectification and Long-Range Interference in Conical Silicon Micropores.

Fluidic devices exhibiting ion current rectification (ICR), or ionic diodes, are of broad interest for applications including desalination, energy harvesting, and sensing, among others. For such applications a large conductance is desirable, which can be achieved by simultaneously using thin membranes and wide pores. In this paper we demonstrate ICR in micrometer sized conical channels in a thin silicon membrane with pore diameters comparable to the membrane thickness but both much larger than the electrolyte screening length.

Over 65% Sunlight Absorption in a 1 μm Si Slab with Hyperuniform Texture.

Thin, flexible, and invisible solar cells will be a ubiquitous technology in the near future. Ultrathin crystalline silicon (c-Si) cells capitalize on the success of bulk silicon cells while being lightweight and mechanically flexible, but suffer from poor absorption and efficiency. Here we present a new family of surface texturing, based on correlated disordered hyperuniform patterns, capable of efficiently coupling the incident spectrum into the silicon slab optical modes.

Confined pulsed diffuse layer charging for nanoscale electrodeposition with an STM.

Regulating the state of the solid-liquid interface by means of electric fields is a powerful tool to control electrochemistry. In scanning probe systems, this can be confined closely to a scanning (nano)electrode by means of fast potential pulses, providing a way to probe the interface and control electrochemical reactions locally, as has been demonstrated in nanoscale electrochemical etching. For this purpose, it is important to know the spatial extent of the interaction between pulses applied to the tip, and the substrate.

Directional quantum dot emission by soft-stamping on silicon Mie resonators.

We present a soft-stamping method to selectively print a homogenous layer of CdSeTe/ZnS core-shell quantum dots (QDs) on top of an array of Si nanocylinders with Mie-type resonant modes. Using this new method, we gain accurate control of the quantum dot's angular emission through engineered coupling of the QDs to these resonant modes. Using numerical simulations we show that the emission into or away from the Si substrate can be precisely controlled by the QD position on the nanocylinder.

Photonics for Photovoltaics: Advances and Opportunities.

Photovoltaic systems have reached impressive efficiencies, with records in the range of 20-30% for single-junction cells based on many different materials, yet the fundamental Shockley-Queisser efficiency limit of 34% is still out of reach. Improved photonic design can help approach the efficiency limit by eliminating losses from incomplete absorption or nonradiative recombination. This Perspective reviews nanopatterning methods and metasurfaces for increased light incoupling and light trapping in light absorbers and describes nanophotonics opportunities to reduce carrier recombination and utilize spectral conversion.

Directed nanoscale metal deposition by the local perturbation of charge screening at the solid-liquid interface.

Understanding and directing electrochemical reactions below the micrometer scale is a long-standing challenge in electrochemistry. Confining reactions to nanoscale areas paradoxically requires both isolation from and communication with the bulk electrolyte in terms of electrochemical potential and access of ions, respectively. Here, we demonstrate the directed electrochemical deposition of copper nanostructures by using an oscillating nanoelectrode operated with an atomic force microscope (AFM).

Combining 1D and 2D waveguiding in an ultrathin GaAs NW/Si tandem solar cell.

As an effective means to surpass the Shockley-Queisser efficiency limit, tandem solar cells have been successfully designed and used for years. However, there are still economical and design set-backs hampering the terrestrial implementation of tandem solar cells. Introducing high efficiency, thin Si-based tandem cells that are flexible in design (shape and curvature) will be the next major step towards integrating highly efficient solar cells into fashionable designs of today's buildings and technologies.

Visual Understanding of Light Absorption and Waveguiding in Standing Nanowires with 3D Fluorescence Confocal Microscopy.

Semiconductor nanowires are promising building blocks for next-generation photonics. Indirect proofs of large absorption cross sections have been reported in nanostructures with subwavelength diameters, an effect that is even more prominent in vertically standing nanowires. In this work we provide a three-dimensional map of the light around vertical GaAs nanowires standing on a substrate by using fluorescence confocal microscopy, where the strong long-range disruption of the light path along the nanowire is illustrated.

Morphology and composition of oxidized InAs nanowires studied by combined Raman spectroscopy and transmission electron microscopy.

Any device exposed to ambient conditions will be prone to oxidation. This may be of particular importance for semiconductor nanowires because of the high surface-to-volume ratio and only little is known about the consequences of oxidation for these systems. Here, we study the properties of indium arsenide nanowires which were locally oxidized using a focused laser beam.

Efficient Multiterminal Spectrum Splitting via a Nanowire Array Solar Cell.

Nanowire-based solar cells opened a new avenue for increasing conversion efficiency and rationalizing material use by growing different III-V materials on silicon substrates. Here, we propose a multiterminal nanowire solar cell design with a theoretical conversion efficiency of 48.3% utilizing an efficient lateral spectrum splitting between three different III-V material nanowire arrays grown on a flat silicon substrate.

From Twinning to Pure Zincblende Catalyst-Free InAs(Sb) Nanowires.

III-V nanowires are candidate building blocks for next generation electronic and optoelectronic platforms. Low bandgap semiconductors such as InAs and InSb are interesting because of their high electron mobility. Fine control of the structure, morphology, and composition are key to the control of their physical properties.

Polarization response of nanowires à la carte.

Thanks to their special interaction with light, semiconductor nanowires have opened new avenues in photonics, quantum optics and solar energy harvesting. One of the major challenges for their full technological deployment has been their strong polarization dependence in light absorption and emission. In the past, metal nanostructures have been shown to have the ability to modify and enhance the light response of nanoscale objects.

Modulation of fluorescence signals from biomolecules along nanowires due to interaction of light with oriented nanostructures.

High aspect ratio nanostructures have gained increasing interest as highly sensitive platforms for biosensing. Here, well-defined biofunctionalized vertical indium arsenide nanowires are used to map the interaction of light with nanowires depending on their orientation and the excitation wavelength. We show how nanowires act as antennas modifying the light distribution and the emitted fluorescence.

Light generation and harvesting in a van der Waals heterostructure.

Two-dimensional (2D) materials are a new type of materials under intense study because of their interesting physical properties and wide range of potential applications from nanoelectronics to sensing and photonics. Monolayers of semiconducting transition metal dichalcogenides MoS2 or WSe2 have been proposed as promising channel materials for field-effect transistors. Their high mechanical flexibility, stability, and quality coupled with potentially inexpensive production methods offer potential advantages compared to organic and crystalline bulk semiconductors.

BiVO4 thin film photoanodes grown by chemical vapor deposition.

BiVO4 thin film photoanodes were grown by vapor transport chemical deposition on FTO/glass substrates. By controlling the flow rate, the temperatures of the Bi and V sources (Bi metal and V2O5 powder, respectively), and the temperature of the deposition zone in a two-zone furnace, single-phase monoclinic BiVO4 thin films can be obtained. The CVD-grown films produce global AM1.

Raman spectroscopy of self-catalyzed GaAs(1-x)Sb(x) nanowires grown on silicon.

Thanks to their wide band structure tunability, GaAs(1-x)Sb(x) nanowires provide exciting perspectives in optoelectronic and energy harvesting applications. The control of composition and strain of these ternary alloys is crucial in the determination of their optical and electronic properties. Raman scattering provides information on the vibrational properties of materials, which can be related to the composition and strain.

Efficient photovoltaic current generation at ferroelectric domain walls.

We elucidate the mechanism of a newly observed photovoltaic effect which occurs in ferroelectrics with periodic domain structures. Under sufficiently strong illumination, domain walls function as nanoscale generators of the photovoltaic current. The steps in the electrostatic potential function to accumulate electrons and holes on opposite sides of the walls while locally reducing the concentration of the oppositely charged carriers.

Gold nanoring trimers: a versatile structure for infrared sensing.

In this work we report on the observation of surface plasmon properties of periodic arrays of gold nanoring trimers fabricated by electron beam lithography. It is shown that the localized surface plasmon resonances of such gold ring trimers occur in the infrared spectral region and are strongly influenced by the nanoring geometry and their relative positions. Based on numerical simulations of the optical extinction spectra and of the electric near-field intensity maps, the resonances are assigned to surface plasmon states arising from the strong intra-trimer electromagnetic interaction.

Dual wavelength sensing based on interacting gold nanodisk trimers.

Fabrication and surface plasmon properties of gold nanostructures consisting of periodic arrays of disk trimers are reported. Using electron beam lithography, disk diameters as small as 96 nm and gaps between disks as narrow as 10 nm have been achieved with an unprecedented degree of control and reproducibility. The disk trimers exhibit intense visible and infrared surface plasmon resonances which are studied as a function of the disk diameter and of the pitch between trimers.