Synergistic Effect of Laser, Water Vapor, and Electron-Beam on the Degradation of Quasi-Two-Dimensional Ruddlesden-Popper Perovskite Flakes.

Understanding the effects of laser light, water vapor, and energetic electron irradiation on the intrinsic properties of perovskites is important in the development of perovskite-based solar cells. Various phase transition and degradation processes have been reported when these agents interact with perovskites separately. However, detailed studies of their synergistic effects are still missing. In this work, the synergistic effect of three factors (exposure to laser light, water vapor, and e-beam) on the optical and physical properties of two-dimensional (2D) Ruddlesden-Popper (RP) perovskite flakes [(BA)2(MA)2Pb3Br10] has been investigated in an environmental cell. When the perovskite flakes were subjected to moderate laser irradiation in a humid environment after prior e-beam irradiation, the photoluminescence (PL) peak centered at 480 nm vanished, while a new PL peak centered at 525 nm emerged, grew, and then quenched. This indicates the degradation process of the 2D RP perovskite was a phase transition to a three-dimensional (3D) perovskite [MAPbBr3] followed by the degradation of 3D perovskite. The spatial distribution of the 525 nm PL signal shows that this phase-transition process spreads across the flake to the area as far as ∼40 µm from the laser spot. Without humidity, the phase transition happened in the laser-irritated area but did not spread, which suggests that moisture enhanced the ion migration from the laser-scanned area to the rest of the flake and accelerated the phase transition in the nearby area. Experiments with no prior e-beam irradiation show that e-beam irradiation is the key to activating the 2D-3D phase transition. Therefore, when the three factors work synergistically, a conversion from the 2D RP perovskite into the 3D perovskite is not localized and propagates through the perovskite. These findings contribute to our understanding of the complex interactions between external stimuli and perovskite materials, thereby advancing the development of efficient and stable perovskite-based solar cells.

Transfer Printing of Ordered Plasmonic Nanoparticles at Hard and Soft Interfaces with Increased Fidelity and Biocompatibility Supports a Surface Lattice Resonance.

Transfer printing, the relocation of structures assembled on one surface to a different substrate by adjusting adhesive forces at the surface-substrate interface, is widely used to print electronic circuits on biological substrates like human skin and plant leaves. The fidelity of original structures must be preserved to maintain the functionality of transfer-printed circuits. This work developed new biocompatible methods to transfer a nanoscale square lattice of plasmon resonant nanoparticles from a lithographed surface onto leaf and glass substrates. The fidelity of the ordered nanoparticles was preserved across a large area in order to yield, for the first time, an optical surface lattice resonance on glass substrates. To effect the transfer, interfacial adhesion was adjusted by using laser induction of plasmons or unmounted adhesive. Optical and confocal laser scanning microscopy showed that submicron spacing of the square lattice was preserved in ≥90% of transfer-printed areas up to 4 mm2. Up to 90% of ordered nanoparticles were transferred, yielding a surface lattice resonance measured by transmission UV-vis spectroscopy.

Effects of geometry and composition of soft polymer films embedded with nanoparticles on rates for optothermal heat dissipation.

Embedding soft matter with nanoparticles (NPs) can provide electromagnetic tunability at sub-micron scales for a growing number of applications in healthcare, sustainable energy, and chemical processing. However, the use of NP-embedded soft material in temperature-sensitive applications has been constrained by difficulties in validating the prediction of rates for energy dissipation from thermally insulating to conducting behavior. This work improved the embedment of monodisperse NPs to stably decrease the inter-NP spacings in polydimethylsiloxane (PDMS) to nano-scale distances. Lumped-parameter and finite element analyses were refined to apportion the effects of the structure and composition of the NP-embedded soft polymer on the rates for conductive, convective, and radiative heat dissipation. These advances allowed for the rational selection of PDMS size and NP composition to optimize measured rates of internal (conductive) and external (convective and radiative) heat dissipation. Stably reducing the distance between monodisperse NPs to nano-scale intervals increased the overall heat dissipation rate by up to 29%. Refined fabrication of NP-embedded polymer enabled the tunability of the dynamic thermal response (the ratio of internal to external dissipation rate) by a factor of 3.1 to achieve a value of 0.091, the largest reported to date. Heat dissipation rates simulated a priori were consistent with 130 µm resolution thermal images across 2- to 15-fold changes in the geometry and composition of NP-PDMS. The Nusselt number was observed to increase with the fourth root of the Rayleigh number across thermally insulative and conductive regimes, further validating the approach. These developments support the model-informed design of soft media embedded with nano-scale-spaced NPs to optimize the heat dissipation rates for evolving temperature-sensitive diagnostic and therapeutic modalities, as well as emerging uses in flexible bioelectronics, cell and tissue culture, and solar-thermal heating.

Asymmetric reduction of gold nanoparticles into thermoplasmonic polydimethylsiloxane thin films.

Polymer thin films containing gold nanoparticles (AuNPs) are of growing interest in photovoltaics, biomedicine, optics, and nanoelectromechanical systems (NEMs). This work has identified conditions to rapidly reduce aqueous hydrogen tetrachloroaurate (TCA) that is diffusing into one exposed interface of a partially cured polydimethylsiloxane (PDMS) thin film into AuNPs. Nanospheroids, irregular gold (Au) networks, and micrometer-sized Au conglomerates were formed in a ∼5 µm layer at dissolved TCA contents of 0.005, 0.05, and 0.5 mass percent, respectively. Multiscale morphological, optical, and thermal properties of the resulting asymmetric AuNP-PDMS thin films were characterized. Reduction of TCA diffusing into the interface of partially cured PDMS film increased AuNP content, robustness, and scalability relative to laminar preparation of asymmetric AuNP-PDMS thin films. Optical attenuation and thermoplasmonic film temperature due to incident resonant irradiation increased in linear proportion to the order of magnitude increases in TCA content, from 0.005 to 0.05 to 0.5 mass percent. At the highest TCA content (0.05 mass percent), an asymmetric PDMS film 52-µm-thick with a 7 µm AuNP-containing layer was produced. It attenuated 85% of 18 mW of incident radiation and raised the local temperature to 54.5 °C above ambient. This represented an increase of 3 to 230-fold in photon-to-heat efficiency over previous thermoplasmonic AuNP-containing systems.

Gold nanoparticles reduced in situ and dispersed in polymer thin films: optical and thermal properties.

Optical and thermal activity of plasmon-active nanoparticles in transparent dielectric media is of growing interest in thermal therapies, photovoltaics and optoelectronic components in which localized surface plasmon resonance (LSPR) could play a significant role. This work compares a new method to embed gold nanoparticles (AuNPs) in dense, composite films with an extension of a previously introduced method. Microscopic and spectroscopic properties of the two films are related to thermal behavior induced via laser excitation of LSPR at 532 nm in the optically transparent dielectric. Gold nanoparticles were incorporated into effectively nonporous 680 µm thick polydimethylsiloxane (PDMS) films by (1) direct addition of organic-coated 16 nm nanoparticles; and (2) reduction of hydrogen tetrachloroaurate (TCA) into AuNPs. Power loss at LSPR excitation frequency and steady-state temperature maxima at 100 mW continuous laser irradiation showed corresponding increases with respect to the mass of gold introduced into the PDMS films by either method. Measured rates of temperature increase were higher for organic-coated NP, but higher gold content was achieved by reducing TCA, which resulted in larger overall temperature changes in reduced AuNP films.