We investigate the effects of stoichiometric imbalance on the electronic properties of lead chalcogenide nanocrystal films by introducing excess lead (Pb) or selenium (Se) through thermal evaporation. Hall-effect and capacitance-voltage measurements show that the carrier type, concentration, and Fermi level in nanocrystal solids may be precisely controlled through their stoichiometry. By manipulating only the stoichiometry of the nanocrystal solids, we engineer the characteristics of electronic and optoelectronic devices. Lead chalcogenide nanocrystal field-effect transistors (FETs) are fabricated at room temperature to form ambipolar, unipolar n-type, and unipolar p-type semiconducting channels as-prepared and with excess Pb and Se, respectively. Introducing excess Pb forms nanocrystal FETs with electron mobilities of 10 cm(2)/(V s), which is an order of magnitude higher than previously reported in lead chalcogenide nanocrystal devices. Adding excess Se to semiconductor nanocrystal solids in PbSe Schottky solar cells enhances the power conversion efficiency.

We have demonstrated amplification of luminescence in upconversion nanophosphors (UCNPs) of hexagonal phase NaYF(4) (β-NaYF(4)) doped with the lanthanide dopants Yb(3+), Er(3+) or Yb(3+), Tm(3+) by close proximity to metal nanoparticles (NPs). We present a configuration in which close-packed monolayers of UCNPs are separated from a dense multilayer of metal NPs (Au or Ag) by a nanometer-scale oxide grown by atomic layer deposition. Luminescence enhancements were found to be dependent on the thickness of the oxide spacer layer and the type of metal NP with enhancements of up to 5.2-fold proximal to Au NPs and of up to 45-fold proximal to Ag NPs. Concomitant shortening of the UCNP luminescence decay time and rise time is indicative of the enhancement of the UCNP luminescence induced by resonant plasmonic coupling and nonresonant near-field enhancement from the metal NP layer, respectively.

Herein we describe a room-temperature, chemical process to transform silver nanocrystal solids, deposited from colloidal solutions, into highly conductive, corrosion-resistant, optical and electronic materials with nanometer-scale architectures. After assembling the nanocrystal solids, we treated them with a set of simple, compact, organic and inorganic reagents: ammonium thiocyanate, ammonium chloride, potassium hydrogen sulfide, and ethanedithiol. We find that each reagent induces unique changes in the structure and composition of the resulting solid, giving rise to films that vary from insulating to, in the case of thiocyanate, conducting with a remarkably low resistivity of 8.8×10(-6) Ω·cm, only 6 times that of bulk silver. We show that thiocyanate mediates the spontaneous sintering of nanocrystals into structures with a roughness of less than 1/10th of the wavelength of visible light. We demonstrate that these solution-processed, low-resistivity, optically smooth films can be patterned, using imprint lithography, into conductive electrodes and plasmonic mesostructures with programmable resonances. We observe that thiocyanate-treated solids exhibit significantly retarded atmospheric corrosion, a feature that dramatically increases the feasibility of employing silver for electrical and plasmonic applications.

The hydrophobicity of the cicada wing originates from its naturally occurring, surface nano-structure. The nano-structure of the cicada wing consists of an array of nano-sized pillars, 100 nm in diameter and 300 nm in height. In this study, the nano-structure of the cicada wing was successfully duplicated by using hot embossing lithography and UV nanoimprint lithography (NIL). The diameter and pitch of replication were the same as those of the original cicada wing and the height was a little smaller than that of the original master. The transmittance of the hot embossed PVC film was increased by 2-6% compared with that of the bare PVC film. The hydrophobicity was measured by water contact angle measurements. The water contact angle of the replica, made of UV cured polymer, was 132 degrees +/- 2 degrees , which was slightly lower than that of the original cicada wing (138 degrees +/- 2 degrees ), but much higher than that of the UV cured polymer surface without any nano-sized pillars (86 degrees ).

An antireflection moth-eye structure was fabricated on a glass substrate by ultraviolet nanoimprint lithography (UV-NIL). A Ni template with an artificial conical structure was fabricated by laser interference lithography an used as a stamp for embossing. A transparent PVC template was fabricated by hot embossing. The embossed poly(vinyl chloride) (PVC) film was then used as an imprint template after depositing SiO 2 and a self-assembled monolayer (SAM). Using the embossed PVC film as a UV-NIL stamp, a polymer based moth-eye structure was formed on the glass template and its transmittance, parallel to surface normal, was increased to 93% for a single side patterned and 97% for a double side patterned. However, at wavelengths shorter than 430 nm, the transmittance of 30 -rotated glass substrate with a moth-eye structure became lower than that of the bare glass substrate, while the transmittance was not changed for longer wavelength regions.