Ryan Pate

Room-temperature, mid-infrared photodetection in colloidal quantum dot/conjugated polymer hybrid nanocomposites: a new approach to quantum dot infrared photodetectors

A unique and distinct approach to unipolar, intraband transitions appropriate for room-temperature, mid- and long-wave-infrared (IR) photodetection is to use active regions comprising colloidal quantum dots (CQDs) synthesized by inorganic chemistry embedded in conjugated polymers. The polymer not only enhances quantum confinement of and electron localization in CQDs, but it also assists in the conduction of electrons photogenerated by the absorption of IR light. Preliminary demonstrations of intraband, mid-wave IR absorption and Fourier transform IR (FTIR) spectral response at room temperature in CdSe/MEH-CN-PPV hybrid nanocomposite thin films are promising, yet the inherent lack of control over hybrid nanocomposite morphology due to solution-based deposition is an inherent challenge. Matrix-assisted pulsed laser evaporation is a vacuum-based deposition technique that could address this challenge by providing more homogeneous distributions of CQDs in hybrid nanocomposite thin films.

Colloidal quantum dot absorption enhancement in flexible Fano filters

We report here modified absorption property of colloidal quantum dots (CQDs) inside flexible Fano filters—made of patterned single crystalline silicon nanomembrane transferred onto flexible plastic substrates. Enhanced optical absorption was obtained both experimentally and theoretically, when the CQD absorption peak spectrally overlaps with Fano resonance peak. On the other hand, suppressed absorption was observed when the Fano resonance has no spectral overlap with the CQD absorption bands.

Comparison of conjugated polymer deposition techniques by photoluminescence spectroscopy

The effects of various deposition techniques on the photoluminescence spectra of the conjugated polymer poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-(1-cyanovinylene) phenylene] (MEH-CN-PPV) are investigated. Photoluminescence spectroscopy provides insight to the internal morphology of organic thin films through the identification of interchain or intrachain recombination peaks. Thin films were deposited on glass substrates by drop casting, spin casting, and resonant-infrared matrix-assisted pulsed laser evaporation (RIR-MAPLE) and were compared to the photoluminescence of the polymer in solution. The photoluminescence measurements reported in this article demonstrate that samples deposited by evaporative RIR-MAPLE have an internal morphology similar to that of MEH-CN-PPV in solution, leading to an enhancement of intrachain transitions in the conjugated polymer.

Resonant Infrared Matrix‐Assisted Pulsed Laser Evaporation Of Inorganic Nanoparticles And Organic/Inorganic Hybrid Nanocomposites

In this research, resonant infrared matrix‐assisted pulsed laser evaporation (RIR‐MAPLE) has been used to deposit different classes of inorganic nanoparticles, including bare, un‐encapsulated ZnO and Au nanoparticles, as well as ligand‐encapsulated CdSe colloidal quantum dots (CQDs). RIR‐MAPLE has been used for thin‐film deposition of different organic/inorganic hybrid nanocomposites using some of these inorganic nanoparticles, including CdSe CQD‐poly[2‐methoxy‐5‐(2’‐ethylhexyloxy)‐1,4‐(1‐cyanovinylene)phenylene] (MEH‐CN‐PPV) nanocomposites and Au nanoparticle‐poly(methyl methacrylate) (PMMA) nanocomposites. The unique contribution of this research is that a technique is demonstrated for the deposition of organic‐based thin‐films requiring solvents with bond energies that do not have to be resonant with the laser energy. By creating an emulsion of solvent and ice in the target, RIR‐MAPLE using a 2.94 μm laser can deposit most material systems because the hydroxyl bonds in the ice component of the emulsion...

RIR-MAPLE deposition of conjugated polymers and hybrid nanocomposites for application to optoelectronic devices

Resonant infrared matrix-assisted pulsed laser evaporation (RIR-MAPLE) is a variation of pulsed laser deposition that is useful for organic-based thin films because it reduces material degradation by selective absorption of infrared radiation in the host matrix. A unique emulsion-based RIR-MAPLE approach has been developed that reduces substrate exposure to solvents and provides controlled and repeatable organic thin film deposition. In order to establish emulsion-based RIR-MAPLE as a preferred deposition technique for conjugated polymer or hybrid nanocomposite optoelectronic devices, studies have been conducted to demonstrate the value added by the approach in comparison to traditional solution-based deposition techniques, and this work will be reviewed. The control of hybrid nanocomposite thin film deposition, and the photoconductivity in such materials deposited using emulsion-based RIR-MAPLE, will also be reviewed. The overall result of these studies is the demonstration of emulsion-based RIR-MAPLE as a viable option for the fabrication of conjugated polymer and hybrid nanocomposite optoelectronic devices that could yield improved device performance.

Direct measurement of spectrally selective absorption enhancement in Fano resonance photonic crystal cavities on plastic substrates

We report direct measurement of spectrally selective absorption properties of PbSe and PbS colloidal quantum dots (CQDs) in Si nanomembrane photonic crystal cavities on flexible polyethylene terephthalate (PET) substrates. Enhanced optical absorption was obtained when CQD absorption overlaps with photonic crystal Fano resonances. On the other hand, no absorption was observed when the Fano resonance has no spectral overlap with the CQD absorption bands. The measurement results agree well with the simulation results obtained based on 3D FDTD and RCWA simulation techniques. Measured angular and polarization properties also agree well with Fano resonance transmission properties, which were obtained experimentally and, theoretically based on simulated dispersion properties and transmission properties. Bending induced spectral shifts were characterized for potentially flexible photonic device applications.