Laser Confocal Microscope Photoluminescence Research Articles

High hysteresis and distinctive optoelectronic memory effect for ambipolar thin-film transistors using a conjugated polymer having donor–acceptor heterojunction

π-Conjugated p-type PBDB-T and n-type N2200 macromolecular units are alternatively bonded to generate ambipolar copolymer (i.e. P(BDBT-co-N2200)) for achieving donor-acceptor (D-A) heterojunction. From the laser confocal microscope photoluminescence (PL) spectra of the P(BDBT-co-N2200) copolymer, PL characteristic peaks of PBDB-T and N2200 are simultaneously observed at 695, 760, and 860 nm. The thin-film transistors (TFTs) using P(BDBT-co-N2200) copolymer show ambipolar transistor characteristics originating from the coexistence of p-type and n-type semiconducting macromolecular units. Interestingly, a high hysteresis is observed in the transfer and output characteristics of the TFTs because of the interface traps and near-interface bulk traps. Under light irradiation, distinctive photocurrents and hysteresis are observed, suggesting the optically mediated charge release and photogating effects caused by trap states. Charge trapping with a high hysteresis and photoconduction with the photogating effect of the P(BDBT-co-N2200)-based ambipolar TFTs induce stable and repeatable writing, reading, and erasing operations. The optoelectronic memory devices using the P(BDBT-co-N2200)-based ambipolar TFTs are realized with the merit of a long charge storage time of 40 s. The π-conjugated copolymer, P(BDBT-co-N2200) exhibiting D–A heterojunction, can be applied to multifunctional devices, such as photoresponsive ambipolar transistors and optoelectronic memory devices, for image sensing and data storage. Optoelectronic memory devices using the ambipolar thin-film transistors of π-conjugated P(BDBT-co-N2200) copolymer having donor-acceptor heterojunction are realized with the merit of a long charge storage time. • π-Conjugated p-type PBDB-T and n-type N2200 macromolecular units were alternatively bonded to generate ambipolar copolymer with donor-acceptor (D-A) heterojunction. • The P(BDBT-co-N2200)-based TFT showed photoresponsive ambipolar transistor characteristics. • The P(BDBT-co-N2200)-based ambipolar TFTs were successfully operated as optoelectronic memory devices with repeatable writing, reading, and erasing processes. • Readout current charges were constant regardless of the variation in waiting times and linearly increased with increasing light exposure time.

Surface-Plasmonic-Coupled Photodetector Based on MAPbI3 Perovskites with Au Nanoparticles: Significantly Enhanced Photoluminescence and Photodetectivity

Organic–inorganic metal halide perovskites (OMHPs) are promising active materials suitable for highly efficient solar cells, photodetectors, light-emitting diodes, and sensors. In this study, methylammonium lead iodide (MAPbI3) thin sheets (TSs) were synthesized as OMHPs using both hybrid vapor-solution method for optical study and anti-solvent solution method for the photodetector. π-Conjugated polyelectrolyte (π-CPE), such as poly(9,9-bis(4′-sulfonatobutyl)fluorene-alt-1,4-phenylene) potassium (FPS-K), was spin-coated on the MAPbI3 TS, and functionalized gold nanoparticles (Au-NPs) were hybridized. The laser confocal microscope photoluminescence (PL) intensity of the MAPbI3 TS was significantly enhanced after hybridization with Au-NPs/FPS-K, owing to the passivating effect of the FPS-K and the generation of extra-photoexcited charges by local surface plasmon resonance (LSPR) coupling with Au-NPs. These results were supported by the variation in the exciton lifetime measured from the time-resolved PL decay curves. The photocurrent of the MAPbI3 photodetector increased up to 1.1 × 104 times, and the photoresponsivity (R) and photodetectivity (D*) increased by 70 and 13 times, respectively, with the hybridization of Au-NPs/FPS-K. The highest D* of the Au-NPs/FPS-K/MAPbI3 photodetector was measured to be 7.5 × 1010 Jones at 735 nm excitation. The power and wavelength dependencies of R and D* for the MAPbI3 photodetector were also significantly improved by the Au-NPs/FPS-K hybrid. These results support the development of high-performance perovskite photodetectors utilizing LSPR coupling with the π-CPE layer.

Distinctive Field-Effect Transistors and Ternary Inverters Using Cross-Type WSe2/MoS2 Heterojunctions Treated with Polymer Acid.

The electrical and optical characteristics of two-dimensional (2D) transition-metal dichalcogenides (TMDCs) can be improved by surface modification. In this study, distinctive field-effect transistors (FETs) were realized by forming cross-type 2D WSe2/MoS2 p-n heterojunctions through surface treatment using poly(methyl methacrylate-co-methacrylic acid) (PMMA-co-PMAA). The FETs were applied to new ternary inverters as multivalued logic circuits (MVLCs). Laser confocal microscope photoluminescence spectroscopy indicated the generation of trions in the WSe2 and MoS2 layers, and the intensity decreased after PMMA-co-PMAA treatment. For the cross-type WSe2/MoS2 p-n heterojunction FETs subjected to PMMA-co-PMAA treatment, the channel current and the region of anti-ambipolar transistor characteristics increased considerably, and ternary inverter characteristics with three stable logic states, "1", "1/2", and "0", were realized. Interestingly, the intermediate logic state 1/2, which results from the negative differential transconductance characteristics, was realized by the turn-on of all component FETs, as the current of the FETs increased after PMMA-co-PMAA treatment. The electron-rich carboxyl acid moieties in PMMA-co-PMAA can undergo coordination with the metal Mo or W atoms present in the Se or S vacancies, respectively, resulting in the modulation of charge density. These features yielded distinctive FETs and ternary inverters for MVLCs using cross-type WSe2/MoS2 heterojunctions.

Fine Fabrication and Optical Waveguide Characteristics of Hexagonal tris(8-hydroxyquinoline)aluminum(Ⅲ) (Alq3) Crystal

Herein, we reported on the precise growth and optical waveguide characteristics of hexagonal tris(8-hydroxyquinoline)aluminum(Ⅲ) (Alq3) micro-crystals (MCs). The hexagonal Alq3 MCs were prepared using surfactant-assisted assembly growth with the help of cetyltrimethylammoniumbromide (CTAB), in which the crystallization occurred as a result of molecular assembly and packing. Also, we adjusted the molar ratio of Alq3 and CTAB for the control degree of crystallization. The formation and structure of Alq3 MCs were investigated using field-emission scanning electron microscopy and X-ray diffraction pattern experiments, respectively. The solid-state laser confocal microscope-photoluminescence spectra and charge-coupled device images for the Alq3 MCs were measured to study the luminescence efficiency and colors, respectively. The optical waveguide performance of the hexagonal Alq3 MCs was measured for each side direction. According to our results, crystalline Alq3 micro-crystals are promising materials for application to the development of optical communication devices.

Significant enhancement of photoresponsive characteristics and mobility of MoS2-based transistors through hybridization with perovskite CsPbBr3 quantum dots

Inorganic perovskite CsPbBr3 quantum dots (QDs) are potential nanoscale photosensitizers; moreover, two-dimensional (2-D) molybdenum disulfide (MoS2) has been intensively studied for application in the active layers of optoelectronic devices. In this study, heterostructures of 2D-monolayered MoS2 with zero-dimensional functionalized CsPbBr3 QDs were prepared, and their nanoscale optical characteristics were investigated. The effect of n-type doping on the MoS2 monolayer after hybridization with perovskite CsPbBr3 QDs was observed using laser confocal microscope photoluminescence (PL) and Raman spectra. Field-effect transistors (FETs) using MoS2 and the MoS2–CsPbBr3 QDs hybrid were also fabricated, and their electrical and photoresponsive characteristics were investigated in terms of the charge transfer effect. For the MoS2–CsPbBr3 QDs-based FETs, the field effect mobility and photoresponsivity upon light irradiation were enhanced by ~ 4 times and a dramatic ~ 17 times, respectively, compared to the FET prepared without the perovskite QDs and without light irradiation. It is noteworthy that the photoresponsivity of the MoS2–CsPbBr3 QDs-based FETs significantly increased with increasing light power, which is completely contrary to the behavior observed in previous studies of MoS2-based FETs. The increased mobility and significant enhancement of the photoresponsivity can be attributed to the n-type doping effect and efficient energy transfer from CsPbBr3 QDs to MoS2. The results indicate that the optoelectronic characteristics of MoS2-based FETs can be significantly improved through hybridization with photosensitive perovskite CsPbBr3 QDs.

Energy and charge transfer effects in two-dimensional van der Waals hybrid nanostructures on periodic gold nanopost array

Two-dimensional (2D) semiconducting MoS2 and WSe2 flakes grown by chemical vapor deposition were mechanically hybridized. A hexagonal boron nitride (h-BN) dielectric flake was inserted between MoS2 and WSe2 flakes to investigate the nanoscale optical properties of 2D van der Waals hybrid nanostructures. The fabricated MoS2/WSe2 and MoS2/h-BN/WSe2 van der Waals hybrid nanostructures were loaded on a periodic gold nanopost (Au-NPo) array to study energy and charge transfer effects at the surface plasmon resonance (SPR) condition. Nanoscale photoluminescence (PL) spectra of the 2D hybrid nanostructures were measured using a high-resolution laser confocal microscope (LCM). A shift of the LCM PL peak of the MoS2/WSe2 n-p hybrid nanostructures was observed owing to the charge transfer. In contrast, the shift of the LCM PL peak of the MoS2/h-BN/WSe2 n-insulator-p hybrid nanostructure was not considerable, as the inserted h-BN dielectric layer prevented the charge transfer. The intensity of the LCM PL peak of the MoS2/h-BN/WSe2 hybrid nanostructure considerably increased once the nanostructure was loaded on the Au-NPo array, owing to the energy transfer between the 2D materials and the Au-NPo array at the SPR condition, which was confirmed by the increase in the LCM Raman intensity.

Energy transfer effect of hybrid organic rubrene nanorod with CdSe/ZnS quantum dots: Application to optical waveguiding modulators

Organic rubrene (5,6,11,12-tetraphenyltetracene) nanorods (NRs) were fabricated through the physical vapor transport method for the study of active fluorescence optical waveguiding and its modulation. The functionalized CdSe/ZnS quantum dots (QDs) with blue and green emissions were partially attached to the surface of the rubrene NR. Using a high resolution laser confocal microscope (LCM), the nanoscale photoluminescence (PL) intensity of the pristine rubrene portion of the hybrid NR/QDs was observed to be considerably enhanced after it was attached with blue (or green) QDs. The nanoscale optical waveguiding characteristics of the hybrid NR/QDs were investigated in terms of the output LCM PL spectra as a function of propagation distance. We observed more efficient optical waveguiding characteristics from the hybrid rubrene NR/blue-QDs than from the pristine NR and the hybrid rubrene NR/green-QDs. These results can be analyzed in terms of the higher Förster resonance energy transfer efficiency for hybrid rubrene NR/blue-QDs system. The results and analysis were supported by a drastic decrease of exciton lifetime of QDs in the hybrid region as measured by time-resolved PL decay curves.

Enhancement of photoresponsive electrical characteristics of multilayer MoS2 transistors using rubrene patches

Multilayer MoS2 is a promising active material for sensing, energy harvesting, and optoelectronic devices owing to its intriguing tunable electronic band structure. However, its optoelectronic applications have been limited due to its indirect band gap nature. In this study, we fabricated a new type of phototransistor using multilayer MoS2 crystal hybridized with p-type organic semiconducting rubrene patches. Owing to the outstanding photophysical properties of rubrene, the device characteristics such as charge mobility and photoresponsivity were considerably enhanced to an extent depending on the thickness of the rubrene patches. The enhanced photoresponsive conductance was analyzed in terms of the charge transfer doping effect, validated by the results of the nanoscale laser confocal microscope photoluminescence (PL) and time-resolved PL measurements.

Nanoscale optoelectronic properties of organic p–n junction P3HT/PCBM nanoparticles hybridized with CdSe/ZnS quantum dots

Organic p–n junction nanoparticles (NPs) of p-type poly(3-hexylthiophene) (P3HT) and n-type [6,6]-phenyl C61-butyric acid methyl ester (PCBM) with approximate diameters of 80–250nm were fabricated by a mini-emulsion method. Various concentrations of functionalized CdSe/ZnS quantum dots (QDs) were hybridized with P3HT/PCBM NPs. The photoluminescence (PL) spectra of the QDs mostly overlapped the absorption spectra of the P3HT/PCBM NPs, suggesting the activation of energy and/or charge-transfer effects. Using a high-resolution laser confocal microscope (LCM), we observed that the LCM PL intensity of a single P3HT/PCBM NP quenched with increasing QD concentration. Conducting atomic force microscopy revealed that the photocurrent of the P3HT/PCBM NP was enhanced as the QD concentration increased. After the hybridization of the P3HT/PCBM NPs with the QDs, the energy/charge-transfer effects and the charge dissociation of excitons with incident light have been more active, resulting in the increased photocurrent.

Luminescence enhancement by surface plasmon assisted Förster resonance energy transfer in quantum dots and light emitting polymer hybrids with Au nanoparticles

Hybrid nanowires (NWs) of light-emitting poly(3-hexylthiophene) (P3HT) blended with gold nanoparticles (Au-NPs) were fabricated by a wetting method. The functionalized CdSe/ZnS quantum dots (QDs) were attached to the surfaces of P3HT/Au-NPs NWs. The nanoscale photoluminescence (PL) characteristics of the P3HT, P3HT/Au-NPs, and QDs/P3HT/Au-NPs single NWs were investigated using a high resolution laser confocal microscope (LCM). For a P3HT/Au-NPs single NW, the LCM PL intensity of the P3HT NW decreased due to the luminescence quenching effect by the blending with Au-NPs. However, the LCM PL intensity of the P3HT/Au-NPs NW drastically increased when the QDs were attached to the surface of the NW. The PL enhancement of the P3HT NW part in the hybrid QDs/P3HT/Au-NPs single NW originated from the Förster resonance energy transfer (FRET) effect between the QDs and the P3HT NW, which was assisted by the surface plasmon (SP) coupling of Au-NPs with the QDs. Based on the analysis of time-resolved PL spectra, the exciton lifetimes of the QDs for the QDs/P3HT/Au-NPs NW were found to decrease considerably in comparison with those of the QDs/P3HT NWs without Au-NPs. We also found that the energy transfer rate of the QDs/P3HT NW increased from 0.76 to 0.93 with the Au-NPs. These observations support the notion of SP assisted FRET effect in hybrid nanosystems.

Luminescence variation of organic Alq3 nanoparticles on surface of Au nanoparticles and graphene

We demonstrate the variation of photoluminescence (PL) intensity for tris(8-hydroxyquinoline) aluminum(III) (Alq3) nanoparticles (NPs) depending on the use of a thin layer of gold (Au) NPs or a graphene substrate. The high luminescence Alq3 NPs were fabricated by a re-precipitation method. Laser confocal microscope (LCM) PL spectra were measured and used to analyze the nanoscale light-emission characteristics of the Alq3 NPs with glass, a layer of Au NPs or graphene as a substrate. PL enhancement of the Alq3 NPs attached to a layer of Au NPs was observed, while a considerable reduction of PL intensity for Alq3 NPs when a single layer of graphene was used for the substrate was observed. Color charge-coupled device and LCM PL mapping images directly confirmed the variation of PL intensities. We observed that the Raman spectra of Alq3 NPs also changed according to the substrate used. The PL enhancement of Alq3 NPs on a layer of Au NPs originated from surface plasmon resonance coupling. On a single layer of graphene substrate, the PL quenching of the Alq3 NPs occurred due to a resonance energy transfer effect.

Photoluminescence and Optical Waveguiding Characteristics of Bisalkoxy Tin(IV) Porphyrin Microcrystals

Guide me: Laser confocal microscope photoluminescence (LCM-PL) and optical waveguiding characteristics for tin(IV) porphyrin-based microcrystalline rods and plates were investigated. The efficiency of optical waveguiding for the rods (0.04 μm(-1)) was five times better than for the plate, due to stronger π-π interaction and a short layer distance (3.035 vs. 3.328 Å).

Luminescence, charge mobility, and optical waveguiding of two-dimensional organic rubrene nanosheets: Comparison with one-dimensional nanorods

Intrinsic characteristics of organic and inorganic nanostructures depend on their physical dimensions (i.e., size and shape) and crystallinity. Here, we compared the nanoscale optical and electrical properties of organic rubrene one-dimensional (1-D) nanorods (NRs) and two-dimensional (2-D) nanosheets (NSs). From high-resolution laser confocal microscope photoluminescence (PL) measurements, the light-emission characteristics of 2-D rubrene NSs varied with the crystalline domain direction, indicating intrinsic PL anisotropy, which was distinguishable from 1-D rubrene single NRs, because of anisotropy π–π stacking molecular arrangements. We also observed the variation of charge carrier mobility depending on the measured directions (i.e., anisotropy of charge transport) in rubrene NS-based field-effect transistors. The optical waveguiding properties of rubrene nanostructures were strongly correlated to the dimensionality of materials and PL anisotropy.

Nanoscale luminescence and optical waveguiding characteristics of organic CN-TFMBE nanowires and hybrid coaxial nanowires

The photoluminescence (PL) and optical waveguiding characteristics of 1-cyano-trans-1,2-bis-(3′,5′-bis-trifluoromethyl-biphenyl)ethylene (CN-TFMBE) nanowires (NWs) and their hybrid coaxial NWs with p-type poly(3-hexylthiophene) (P3HT) were investigated. For nanoscale PL and optical waveguiding experiments, we used a laser confocal microscope (LCM) with a high spatial resolution. The LCM PL peak of the CN-TFMBE single NW was observed at 490nm, indicating green-blue light emission. The LCM PL intensity of the CN-TFMBE NW as a core was considerably reduced through the hybridization with the P3HT shell, this was directly confirmed by the color CCD and LCM PL mapping images. For the CN-TFMBE single NWs, the decay constant of the optical waveguided PL intensity was estimated to be about 0.21μm−1, which is better than that of the conventional organic NWs and the CN-TFMBE/P3HT coaxial NWs. We can conclude through our analysis that the outer shell P3HT materials play the role of a luminescence quencher for the core CN-TFMBE NW due to a charge transfer effect.

Single nanoparticle of organic p-type and n-type hybrid materials: nanoscale phase separation and photovoltaic effect

We fabricated hybrid nanoparticles (NPs) of p-type poly(3-hexylthiophene) (P3HT) and n-type fullerene derivative {[6,6]-phenyl C61-butyric acid methyl ester (PCBM)} materials through a mini-emulsion method. The nanoscale photoluminescence (PL) characteristics of the non-annealed and annealed hybrid single NPs with different concentrations of P3HT and PCBM were investigated using a laser confocal microscope (LCM) with high spatial resolution. The luminescence characteristics corresponding to the P3HT and PCBM materials were observed simultaneously in the LCM PL spectra for P3HT/PCBM hybrid NP after the annealing process. We propose that the annealing process for the hybrid NPs assisted the ordering of P3HT main chains and the formation of PCBM domains through the gathering of the molecules, indicating nanoscale phase separation. This was supported by UV-Vis absorption and Raman spectroscopy results. Conducting atomic force microscope experiments on an annealed hybrid single NP allowed for the measurement of the characteristic photoresponsive current–voltage curves, and monochromatic photovoltaic characteristics and the avalanche photodiode effect were observed in the low- and high-bias regions, respectively.

Nanoscale photoluminescence of light-emitting poly (3-methylthiophene) nanotubes hybridized with Au nanoparticles

We reported on the fabrication and nanoscale luminescence characteristics of the hybrid nanotubes (NTs) of light-emitting poly (3-methylthiophene) (P3MT) NT with gold (Au) nanoparticles (NPs) (P3MT/Au-NPs). After hybridizing the Au-NPs onto the surface of P3MT NTs, the light-emitting color of P3MT NTs was dramatically changed from a green to a bright red. From laser confocal microscope photoluminescence (PL) experiments for an isolated single strand of the NTs, we observed a ∼220 times enhancement of the PL peak intensity for the hybrid NT of P3MT/Au-NPs compared to that of the P3MT single NT. The enhancement PL efficiency of the hybrid NT of P3MT/Au-NPs can be explained in terms of a surface plasmon resonance (SPR) and nanoscale local electric field enhancement effects.

Complex Nanoparticle of Light-Emitting MEH-PPV with Au: Enhanced Luminescence

Complex nanoparticles (NPs) of poly(2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene) (MEH-PPV) NP adsorbed with Au NPs (MEH-PPV/Au NPs) were fabricated through a reprecipitation method. The formation of MEH-PPV/Au NP complexes was confirmed through high-resolution transmission electron microscopy and Fourier transform infrared experiments. The laser confocal microscope photoluminescence (PL) efficiency of the complex MEH-PPV/Au single NP dramatically increased compared with that of the MEH-PPV single NP without Au NPs, which was directly confirmed through color charge-coupled device images. The enhanced PL efficiency of the MEH-PPV/Au NP complex might have originated from the energy transfer effect in a surface plasmon resonance coupling between a MEH-PPV NP and Au NPs. The strong local field enhancement due to nanogaps between Au NPs in the background of a light-emitting MEH-PPV NP might be another origin of the PL enhancement of the NP complex, as supported by finite difference time domain calculations. We also observed the blue shift of the PL peaks of the single MEH-PPV and MEH-PPV/Au NP, compared with the solution PL peaks of those NPs.

High energy ion irradiation effect on light-emitting poly(3-methylthiophene) (P3MT) nanowires

Light-emitting poly(3-methylthiophene) (P3MT) nanowires with a diameter of ∼200 nm were fabricated using an electrochemical polymerization method based on an anodic alumina oxide (Al 2O 3) nanoporous template. The relatively high energy (3 MeV) Cl 2+ ions were irradiated onto the P3MT nanowires with dosages from 1 × 10 13 to 1 × 10 15 ions/cm 2. To study the effect of high energy ion irradiation on P3MT nanowires, we measured UV/vis absorbance, Raman spectra, and laser confocal microscope photoluminescence (PL) on the nanometer scale. The relative atomic concentrations of carbon elements in the pristine and the 3 MeV Cl 2+ ion-irradiated P3MT nanowires were investigated through XPS experiments. As the dosage of the 3 MeV Cl 2+ ion irradiation increased, we observed that the P3MT nanowires changed to a partially carbonized form, and that the PL efficiency of the systems decreased.

Light‐Emitting Rubrene Nanowire Arrays: A Comparison with Rubrene Single Crystals

AbstractThis is a report on a new method of growth of a light‐emitting rubrene nanowires array with diameters of 200 ± 10 nm by using organic vapor transport through Al2O3 nanoporous templates. Nanometer‐scale laser confocal microscope (LCM) photoluminescence (PL) spectra and crystalline structures of the rubrene nanowires are compared with those of rubrene single crystals prepared with the same experimental conditions without the template. In the LCM PL spectra it is observed that the PL spectra and intensity varies with the detecting positions because of the crystal growth characteristics of the rubrene molecules. A single rubrene nanowire has a wider LCM PL band width than that of the rubrene single crystal. This may originate from the light emissions of the mixed polarized bands due to additional new crystallinity in the formation of the nanowires. From the current–voltage characteristic curves, the semiconducting nature of both the rubrene nanowires and single crystals is observed.

Partial metal coated light emitting polymers: Direct observation of enhanced photoluminescence

The enhanced photoluminescence (PL) for the partially nickel (Ni) metal coated light emitting poly(3-methylthiophene) (P3MT) or polythiophene (PTh) hybrid nanotubes was observed and analyzed. From the laser confocal microscope PL experiments of an isolated single strand of the hybrid nanotubes, we directly observed a ∼40 times and ∼16 times enhancement of the PL peak intensity for the parts of the P3MT or PTh nanotubes that were coated with the Ni metal, compared with the PL peak intensity for the parts of the P3MT or PTh nanotubes without the Ni metal coating. These were confirmed from the laser confocal microscope PL spectra of the hybrid nanotubes. The surface plasmon resonance coupling between the light emitting P3MT or PTh nanotubes and the Ni metal nanotubes contributed to the enhancement of the PL efficiency of the hybrid nanotubes.