Enhancing the photocatalytic properties of PbS QD solids: the ligand exchange approach

Surface engineering of nanomaterials is a promising tool towards the design of new materials for conversion of solar energy into chemical energy. In this work, we examine the influence of ligand exchange on the photocatalytic performance of solution-processed PbS films. We test different ligands such as oleylamine (OAm), 1,2-ethanedithiol (EDT), 3-mercaptopropionic acid (MPA) and tetrabutylammonium iodide (TBAI). The study demonstrates that PbS films capped with MPA and EDT exhibit 3.5-fold enhanced photocatalytic performance for the photodecomposition of methyl orange upon sunlight exposure. Both band energy alignment and charge carrier transport have a strong impact on the generation of reactive oxygen species (ROS), which play a key role in the photodecomposition process. Moreover, the stability and reusability of the photocatalysts are clearly improved after ligand exchange. We prove how both MPA and EDT provide much more stability to PbS QD films to operate very efficiently up to 8 cycles of photocatalysis. As observed in XPS, the oxidation of PbS is prevented after ligand exchange. We demonstrate how surface chemistry engineering of solution-processed QD films can open a new approach towards the design of highly efficient and stable visible-light-driven photocatalysts, which paves the way to low cost and large area fabrication of high-performance photocatalytic devices.

Nanotexturing To Enhance Photoluminescent Response of Atomically Thin Indium Selenide with Highly Tunable Band Gap

Manipulating properties of matter at the nanoscale is the essence of nanotechnology, which has enabled the realization of quantum dots, nanotubes, metamaterials, and two-dimensional materials with tailored electronic and optical properties. Two-dimensional semiconductors have revealed promising perspectives in nanotechnology. However, the tunability of their physical properties is challenging for semiconductors studied until now. Here we show the ability of morphological manipulation strategies, such as nanotexturing or, at the limit, important surface roughness, to enhance light absorption and the luminescent response of atomically thin indium selenide nanosheets. Besides, quantum-size confinement effects make this two-dimensional semiconductor to exhibit one of the largest band gap tunability ranges observed in a two-dimensional semiconductor: from infrared, in bulk material, to visible wavelengths, at the single layer. These results are relevant for the design of new optoelectronic devices, including heterostructures of two-dimensional materials with optimized band gap functionalities and in-plane heterojunctions with minimal junction defect density.

Strongly-coupled PbS QD solids by doctor blading for IR photodetection

In this work, doctor blading is proposed for the fabrication of strongly-coupled QD solids from a PbS nanoink for photodetection at telecom wavelengths.

Polymer waveguide couplers based on metal nanoparticle-polymer nanocomposites

In this work Au nanoparticles (AuNPs) are incorporated into poly(methyl methacrylate) (PMMA) waveguides to develop optical couplers that are compatible with planar organic polymer photonics. A method for growing AuNPs (of 10 to 100 nm in size) inside the commercially available Novolak resist is proposed with the intention of tuning the plasmon resonance and the absorption/scattering efficiencies inside the patterned structures. The refractive index of the MNP-Novolak nanocomposite (MNPs: noble metal nanoparticles) is carefully analysed both experimentally and numerically in order to find the appropriate fabrication conditions (filling factor and growth time) to optimize the scattering cross section at a desired wavelength. Then the nanocomposite is patterned inside a PMMA waveguide to exploit its scattering properties to couple and guide a normal incident laser light beam along the polymer. In this way, light coupling is experimentally demonstrated in a broad wavelength range (404-780 nm). Due to the elliptical shape of the MNPs the nanocomposite demonstrates a birefringence, which enhances the coupling to the TE mode up to efficiencies of around 1%.

UV-patternable nanocomposite containing CdSe and PbS quantum dots as miniaturized luminescent chemo-sensors

We have developed a patternable nanocomposite sensor based on luminescent CdSe QDs and a polyisoprene-based photoresist (PIP) as host matrix that showed chemosensing response against MET and EDA in vapour with a LOD around 0.1 pg and 15 ng, respectively.

Efficient excitation of photoluminescence in a two-dimensional waveguide consisting of a quantum dot-polymer sandwich-type structure

In this Letter, we study a new kind of organic polymer waveguide numerically and experimentally by combining an ultrathin (10-50 nm) layer of compactly packed CdSe/ZnS core/shell colloidal quantum dots (QDs) sandwiched between two cladding poly(methyl methacrylate) (PMMA) layers. When a pumping laser beam is coupled into the waveguide edge, light is mostly confined around the QD layer, improving the efficiency of excitation. Moreover, the absence of losses in the claddings allows the propagation of the pumping laser beam along the entire waveguide length; hence, a high-intensity photoluminescence (PL) is produced. Furthermore, a novel fabrication technology is developed to pattern the PMMA into ridge structures by UV lithography in order to provide additional light confinement. The sandwich-type waveguide is analyzed in comparison to a similar one formed by a PMMA film homogeneously doped by the same QDs. A 100-fold enhancement in the waveguided PL is found for the sandwich-type case due to the higher concentration of QDs inside the waveguide.

Demonstration of near infrared gas sensing using gold nanodisks on functionalized silicon

In this work, we demonstrate experimentally the use of an array of gold nanodisks on functionalized silicon for chemosensing purposes. The metallic nanostructures are designed to display a very strong plasmonic resonance in the infrared regime, which results in highly sensitive sensing. Unlike usual experiments which are based on the functionalization of the metal surface, we functionalized here the silicon substrate. This silicon surface was modified chemically by buildup of an organosilane self-assembled monolayer (SAM) containing isocyanate as functional group. These groups allow for an easy surface regeneration by simple heating, thanks to the thermally reversible interaction isocyanate-analyte, which allows the cyclic use of the sensor. The technique showed a high sensitivity to surface binding events in gas and allowed the surface regeneration by heating of the sensor at 150 °C. A relative wavelength shift ∆λ(max)λ(0)=0.027 was obtained when the saturation level was reached.

Charge dissipation in e-beam lithography with Novolak-based conducting polymer films

Charging of common resist materials during electron beam (e-beam) writing leads to deflection of the electron beam path, which can result in significant pattern displacement. Here we report a new conducting polymer to eliminate charging. A common approach is to place the conducting layer underneath the e-beam resist layer. Conductivity equal or greater than 10(-4) S cm(-1) has been reported to prevent pattern displacement. Some other properties such as a flat surface layer, chemical inertness and insolubility in both the top resist solvent and the developer are also necessary. The way to achieve all these properties consisted in synthesizing a conducting polymer inside an insulating polymer to form an interpenetrating polymer network (IPN) which could combine their properties. Novolak was used as the host polymer and terthiophene (3T) as the monomer to polymerize. Cu(ClO(4))(2) initiates simultaneously the oxidative polymerization of the 3T and its subsequent doping inside Novolak during the bake step in a one-step reaction. Solvent-resistant and homogeneous conducting films with smooth surfaces were achieved. The conductivity was of the order of 10(-2) S cm(-1). Patterning of the top resist was carried out without disturbing its lithographic performance.