Subwavelength silver nanoparticles display a variety of unrivaled optical properties in the visible and near-IR regime, including scattering cross-sections that are orders of magnitude higher than the fluorescence emission from organic dyes as well as intense local amplification of electromagnetic fields. These phenomena result from localized surface plasmons (LSPs), where the plasma oscillations of free electrons in the metal are bound by nanoparticle geometry. Plasmon excitation occurs when a photon is absorbed at a metal-dielectric interface, transferring energy into the collective oscillations of conduction electrons, which are coupled in-phase with incident radiation. For silver and gold nanoparticles, these resonant frequencies occur at wavelengths in the visible region, giving rise to the brilliant colors that are characteristic of their colloidal solutions.For silver particles with diameter d ! l, a single dipolar plasmon mode is allowed.[1] However, for particles with lower symmetry or anisotropic dielectric surroundings, the nature of

Silver nanocrystals are ideal building blocks for plasmonic materials that exhibit a wide range of unique and potentially useful optical phenomena. Individual nanocrystals display distinct optical scattering spectra and can be assembled into hierarchical structures that couple strongly to external electromagnetic fields. This coupling, which is mediated by surface plasmons, depends on their shape and arrangement. Here we demonstrate the bottom-up assembly of polyhedral silver nanocrystals into macroscopic two-dimensional superlattices using the Langmuir-Blodgett technique. Our ability to control interparticle spacing, density, and packing symmetry allows for tunability of the optical response over the entire visible range. This assembly strategy offers a new, practical approach to making novel plasmonic materials for application in spectroscopic sensors, sub-wavelength optics, and integrated devices that utilize field enhancement effects.

Thin‐film solar cells are made by vapor deposition of Earth‐abundant materials: tin, zinc, oxygen and sulfur. These solar cells had previously achieved an efficiency of about 2%, less than 1/10 of their theoretical potential. Loss mechanisms are systematically investigated and mitigated in solar cells based on p‐type tin monosulfide, SnS, absorber layers combined with n‐type zinc oxysulfide, Zn(O,S) layers that selectively transmit electrons, but block holes. Recombination at grain boundaries is reduced by annealing the SnS films in H2S to form larger grains with fewer grain boundaries. Recombination near the p‐SnS/n‐Zn(O,S) junction is reduced by inserting a few monolayers of SnO2 between these layers. Recombination at the junction is also reduced by adjusting the conduction band offset by tuning the composition of the Zn(O,S), and by reducing its free electron concentration with nitrogen doping. The resulting cells have an efficiency over 4.4%, which is more than twice as large as the highest efficiency obtained previously by solar cells using SnS absorber layers.

Thin film solar cells made from earth-abundant, non-toxic materials are needed to replace the current technology that uses Cu(In,Ga)(S,Se) 2 and CdTe, which contain scarce and toxic elements. One promising candidate absorber material is tin monosulfide (SnS). In this report, pure, stoichiometric, single-phase SnS films were obtained by atomic layer deposition

SnS is a promising earth-abundant material for photovoltaic applications. Heterojuction solar cells were made by vapor deposition of p-type tin(II) sulfide, SnS, and n-type zinc oxysulfide, Zn(O,S), using a device structure of soda-lime glass/Mo/SnS/Zn(O,S)/ZnO/ITO. A record efficiency was achieved for SnS-based thin-film solar cells by varying the oxygen-to-sulfur ratio in Zn(O,S). Increasing the sulfur content in Zn(O,S) raises the conduction band offset between Zn(O,S) and SnS to an optimum slightly positive value. A record SnS/Zn(O,S) solar cell with a S/Zn ratio of 0.37 exhibits short circuit current density (Jsc), open circuit voltage (Voc), and fill factor (FF) of 19.4 mA/cm2, 0.244 V, and 42.97%, respectively, as well as an NREL-certified total-area power-conversion efficiency of 2.04% and an uncertified active-area efficiency of 2.46%.

Metal nanostructures that support surface plasmons are compelling as plasmonic circuit elements and as the building blocks for metamaterials. We demonstrate here the spontaneous self-assembly of shaped silver nanoparticles into three-dimensional plasmonic crystals that display a frequency-selective response in the visible wavelengths. Extensive long-range order mediated by exceptional colloid monodispersity gives rise to optical passbands that can be tuned by particle volume fraction. These metallic supercrystals present a new paradigm for the fabrication of plasmonic materials, delivering a functional, tunable, completely bottom-up optical element that can be constructed on a massively parallel scale without lithography.

Subwavelength silver nanoparticles display a variety of unrivaled optical properties in the visible and near-IR regime, including scattering cross-sections that are orders of magnitude higher than the fluorescence emission from organic dyes as well as intense local amplification of electromagnetic fields. These phenomena result from localized surface plasmons (LSPs), where the plasma oscillations of free electrons in the metal are bound by nanoparticle geometry. Plasmon excitation occurs when a photon is absorbed at a metal-dielectric interface, transferring energy into the collective oscillations of conduction electrons, which are coupled in-phase with incident radiation. For silver and gold nanoparticles, these resonant frequencies occur at wavelengths in the visible region, giving rise to the brilliant colors that are characteristic of their colloidal solutions.For silver particles with diameter d ! l, a single dipolar plasmon mode is allowed.[1] However, for particles with lower symmetry or anisotropic dielectric surroundings, the nature of

Thin films containing germanium or tin have a great variety of current and potential applications, particularly their oxides or chalcogenides. Chemical vapor deposition (CVD) and atomic layer deposition (ALD) are popular ways to make these thin films conformally even on challenging nanostructured substrates. The success of these processes depends on having precursors that are sufficiently stable, volatile, and reactive. In this paper we optimize the syntheses of the following three precursors: 1 and 2 are racemic Ge­(II) or Sn­(II) cyclic amides made from N 2 ,N 3-di-tert-butylbutane-2,3-diamine, and 3 is bis­(N,N′-diiso­propyl­aceta­midinato)­tin­(II). All three compounds are demonstrated to be effective precursors for ALD of their monosulfides, GeS or SnS, by reaction with H2S. 2 has also been reported previously to make polycrystalline SnO2 by ALD with oxidizing agents such as H2O2. The cyclic amides 1 and 2 are more volatile than the amidinate 3, vaporizing sufficiently for ALD even at precursor temperatures below 40 °C, whereas 3 vaporizes at temperatures over 90 °C. 1 and 2 can thus be used at lower substrate temperatures than 3. GeS or SnS can be deposited on substrates even at temperatures below 50 °C, while ALD of SnS from 3 becomes slow below substrate temperatures of 100 °C because of insufficient vapor pressure. The amount of growth per ALD cycle is higher for the cyclic amide 2 than for the amidinate 3. The GeS films are smooth and amorphous, while the SnS films are polycrystalline and granular. All of these films are uniformly thick inside holes with aspect ratios (depth/diameter) greater than 40:1.