One-Dimensional Random Lasing in a Single Organic Nanofiber

New insights into the physical processes that underpin cell division and the emergence of different cellular and multicellular structures

Despite decades of focused research, a detailed understanding of the fundamental physical processes that underpin biological systems (structures and processes) remains an open challenge. Within the present paper we report on biomimetic studies, which offer new insights into the process of cell division and the emergence of different cellular and multicellular structures. Experimental studies specifically investigated the impact of including different concentrations of charged bio-molecules (cytokinin and gibberellic acid) on the growth of BaCO₃-SiO₂ based structures. Results highlighted the role of charge density on the emergence of long-range order, underpinned by a negentropic process. This included the growth of synthetic cell-like structures, with the intrinsic capacity to divide and change morphology at cellular and multicellular scales. Detailed study of dividing structures supports a hypothesis that cell division is dependent on the establishment of a charge-induced macroscopic quantum potential and cell-scale quantum coherence, which allows a description in terms of a macroscopic Schrödinger-like equation, based on a constant different from the Planck constant. Whilst the system does not reflect full correspondence with standard quantum mechanics, many of the phenomena that we typically associate with such a system are recovered. In addition to phenomena normally associated with the Schrödinger equation, we also unexpectedly report on the emergence of intrinsic spin as a macroscopic quantum phenomena, whose origins we account for within a four-dimensional fractal space-time and a macroscopic Pauli equation, which represents the non-relativistic limit of the Dirac equation.

Random Lasing Engineering in Poly-(9-9dioctylfluorene) Active Waveguides Deposited on Wrinkles Corrugated Surfaces

This paper investigates the correlation between the random lasing properties of organic waveguides made by poly-(9-9dioctylfluorene) (PFO) thin films and the morphology of wrinkled corrugated substrates. The capability to individually control the wrinkle wavelength, shape, and height allows us to separately investigate their role on the sample emission properties. We demonstrate that the main parameter determining the presence of coherent random lasing is the substrate roughness and that, contrary to what could be qualitatively expected, as the roughness increases, coherent random lasing is progressively reduced. Coherent random lasing is observed only for a substrate roughness below 33 nm, while higher roughness leads to amplified spontaneous emission (up to 70 nm) or to the absence of light amplification in the film (above 70 nm). We demonstrate that this result is due to a progressive reduction of the light amplification efficiency in the PFO film, evidencing that coherent random lasing can be obtained only with a right interplay between light amplification and scattering. Besides clarifying the basic aspects of random lasing in organic waveguides, our work opens the way to the realization of organic random lasers with predictable emission properties, thanks to the high control level of the scattering properties of the wrinkled corrugated surfaces.

Enhanced random laser by metal surface-plasmon channel waveguide

Compared with conventional lasers, the random laser is realized through strong multiple scatterings in disordered gain system. In this paper, random lasing (RL) in one-dimensional metal surface plasmon (SP) waveguide with gold-plated self-formed silicon pyramids was investigated comprehensively. Consequently, the emission intensity of RL was enhanced dramatically and the RL threshold was reduced significantly through Au-coated Si spiky tips. Meanwhile, one-dimensional metal SP channel waveguides confined the emitting light in a certain direction with a small divergence angle. Using FDTD simulations, it was found that the enhancement effect for RL is likely attributed to the localized surface plasmon (LSP) field. In addition, the LSP field nearby the spiky tips can enhance field-molecule interaction, which was benefit for lasing in small scale. The results in this letter supplied a feasible method to realize the application of RL in subwavelength optical elements.

All-Optical Switching and Two-States Light-Controlled Coherent-Incoherent Random Lasing in a Thiophene-Based Donor-Acceptor System

We describe herein the synthesis and characterization of a thiophene-based donor-acceptor system, namely (E)-2-(4-nitrostyryl)-5-phenylthiophene (Th-pNO₂ ), which was prepared under Horner-Wadsworth-Emmons conditions. The UV/Vis absorption bands, including the intramolecular charge transfer (ICT) band, were fully assigned using DFT and TD-DFT computations. The results of both efficient third-order nonlinear optical properties and light-amplification phenomena are presented. Investigations of photoinduced birefringence (PIB) in optical Kerr effect (OKE) experiments showed a great potential for this particular compound as an efficient, fully reversible, and fast optical switch. Time constants for the observed trans-cis-trans molecular transitions are in the range of microseconds and give a competitive experimental result for the well-known and exploited azobenzene derivatives. Random lasing (RL) investigations confirmed that this organic system is potentially useful to achieve strong light enhancement, observed as a multimode lasing action. Both RL and OKE measurements indicate that this material is a representative of thiophene derivatives, which can be utilized to fabricate fast all-optical switches or random lasers (light amplifiers).

A one-dimensional random laser based on artificial high-index contrast scatterers

The realization of a one-dimensional (1D) random laser (RL) by using artificially fabricated scatterers is reported in this letter, and the lasing characteristic has also been investigated comprehensively. The manipulation of the lasing mode in the 1D microwire (MW) RL can be achieved through micro-pits prepared by the laser-ablation technique. Well-defined sharp lasing peaks were realized based on the coherence feedback process in the 1D optical waveguide. The near- and far-field images exhibit excellent spatial intensity distribution, and the stability of lasing modes has also been investigated. Our results represent a novel method towards the development of a manipulated-RL, which will highlight the application of disordered systems in optoelectronic devices.

Electron-beam nanopatterning and spectral modulation of organic molecular light-emitting single crystals

The nanopatterning of light-emitting molecular crystals with semiconducting properties can be crucial for the development of future optoelectronic and nanoelectronic devices based on organic materials. In this respect, electron-beam writing is a powerful tool to realize patterns at the nanoscale, but it is still rarely applied to active organic materials. Here, sub-100-nm-scale nanopatterning is performed on the surface of quaterthiophene monocrystals by direct maskless electron-beam writing. Gratings are produced on organic crystals with periods ranging from 80 nm to 1 μm and single-line lateral dimensions ranging from 20 to 500 nm, with electron-beam exposure doses between 100 and 1500 μC/cm(2). The morphological and texturing properties of the pattern are discussed, together with the interaction mechanisms between the electron beam and the crystal. The resulting modulation of the light emission is consistent with Bragg scattering from the patterned periodic features.

Surface plasmon polariton propagation in organic nanofiber based plasmonic waveguides

Plasmonic wave packet propagation is monitored in dielectric-loaded surface plasmon polariton waveguides realized from para-hexaphenylene nanofibers deposited onto a 60 nm thick gold film. Using interferometric time resolved two-photon photoemission electron microscopy we are able to determine phase and group velocity of the surface plasmon polariton (SPP) waveguiding mode (0.967c and 0.85c at λ(Laser) = 812nm) as well as the effective propagation length (39 μm) along the fiber-gold interface. We furthermore observe that the propagation properties of the SPP waveguiding mode are governed by the cross section of the waveguide.

Stimulated resonance Raman scattering and laser oscillation in highly emissive distyrylbenzene-based molecular crystals

Three-in-one: A novel distyrylbenzene-based material forms J-type aggregates in single crystals with highly polarized and bright red emission, giving rise to optical gain narrowing, for which different mechanisms (amplified spontaneous emission, laser emission and stimulated resonance Raman scattering) are observed. These are correlated with the favorable intrinsic and macroscopic properties of the crystal, in particular to the orientation of the molecules to the crystal surface.

In situ-Directed Growth of Organic Nanofibers and Nanoflakes: Electrical and Morphological Properties

Organic nanostructures made from organic molecules such as para-hexaphenylene (p-6P) could form nanoscale components in future electronic and optoelectronic devices. However, the integration of such fragile nanostructures with the necessary interface circuitry such as metal electrodes for electrical connection continues to be a significant hindrance toward their large-scale implementation. Here, we demonstrate in situ-directed growth of such organic nanostructures between pre-fabricated contacts, which are source-drain gold electrodes on a transistor platform (bottom-gate) on silicon dioxide patterned by a combination of optical lithography and electron beam lithography. The dimensions of the gold electrodes strongly influence the morphology of the resulting structures leading to notably different electrical properties. The ability to control such nanofiber or nanoflake growth opens the possibility for large-scale optoelectronic device fabrication.

Efficient roll-on transfer technique for well-aligned organic nanofibers

A transfer technique enabling efficient device integration of fragile organic nanostructures is presented. The technique is capable of transferring organic nanofibers to arbitrary substrates, the preservation of nanofiber morphology is demonstrated, and the optical properties are unaffected or even improved by the transfer.

Self-introduction of disordered lattice distortion by a polymeric nanofiber laser

The developed molecular dynamics shows that upon photoexcitation of a conjugated polymer nanofiber, such as poly(phenylene vinylene)s or the polyfluorene family, singlet excitons initially are formed. Through continuous optical pumping, the electron populations of the excitons are reversed. Different from inorganic materials, the electron population reversion not only generates new localized electron states but also destroys the periodic structure of the polymer chain, inducing localized lattice distortion. These localized modes provide one of the channels to form localized lasing emission in a single conjugated nanofiber laser, which is consistent with recent experimental observations.

Pinning of organic nanofiber surface growth

In situ growth constitutes a very promising strategy for integrating functional nanostructures into device platforms due to the possibility of parallel, high-volume integration. Here, we demonstrate how electron-beam-lithography-defined metal nanostructures can be used to guide the surface diffusion and thereby steer the self-assembly process of organic molecules (here para-hexaphenylene) leading to morphologically well-defined molecular nanofibers with preferred growth directions. Results from a systematic investigation of the influence of the nanofiber growth parameters (such as pinning structure dimensions, substrate temperature, etc.) are presented and an appropriate parameter set is found that enables control over nanofiber length, position and orientation. The ability to achieve such parallel growth control opens a wide range of possible applications including fabrication of polarization-controlled light-emitting arrays and nanofiber growth between electrodes for direct electrical connection in organic LEDs.

The surface microstructure controlled growth of organic nanofibres

A combination of top down fabrication of microstructured growth templates and bottom up growth of oriented organic nanofibres is demonstrated. At appropriate surface temperatures blue light emitting para-hexaphenylene nanofibres are grown on gold coated silicon substrates, perpendicularly oriented to the edges of micron-sized ridges. These nanofibres have well-defined maximum lengths of a few micrometres and typical heights and widths of around a hundred and a few hundred nanometres, respectively. Previously such oriented growth has been reported solely on specific, single-crystalline growth substrates. The present finding opens up a route to direct growth of oriented organic nanofibres on microstructured substrates that can act as device platforms.

Light-emitting organic nanoaggregates from functionalized p-quaterphenylenes

Functionalized para-phenylenes are versatile building blocks for generating aligned fiber-like nanostructures by a self-assembly growth process on muscovite mica substrates upon controlled vapor deposition (molecule epitaxy). Functional groups were implemented at the 1,4‴-para-positions of p-quaterphenylenes (p4P) using a Suzuki cross-coupling strategy. The nanoaggregates possess outstanding optical properties, which can be modified in a controlled manner by functionalization. Functionalization allows the fluorescence peak emission frequency to shift within the blue spectral range, and the nanoaggregates' three-dimensional shape alters depending on the substitution. In the case of asymmetrically functionalized phenylenes due to the intrinsic non-zero hyperpolarizability of push-pull functionalized oligomers and non-centrosymmetry of the respective nanofibers, they act as frequency doublers.

Mechanical properties of organic nanofibers

Intrinsic elastic and inelastic mechanical properties of individual, self-assembled, quasi-single-crystalline para-hexaphenylene nanofibers supported on substrates with different hydrophobicities are investigated as well as the interplay between the fibers and the underlying substrates. We find from atomic-force-microscopy-based rupture experiments a rupture shear stress of about 2 x 10(7) Pa for an individual fiber. Deflecting a nanofiber suspended across a gap results in a Young's modulus of 0.65 GPa. Translational motion of intact nanofibers across the surface is demonstrated for fibers on a silicon substrate with a low-adhesion coating, whereas such motion on a noncoated substrate is limited to very short (sub-micrometer) nanofiber pieces due to strong adhesive forces.

Tailoring the growth of p-6P nanofibres using ultrathin Au layers: an organic-metal-dielectric model system

The influence of ultrathin Au cluster films on the growth of para-hexaphenyl (p-6P) fibres is investigated. Whereas p-6P at elevated temperatures forms long, mutually parallel fibres on plain mica, these fibres become shorter but taller on Au covered mica, up to a Au film thickness of approximately 8 nm. The degree to which fibres are mutually parallel decreases with increasing Au thickness. For thicker Au films the length of the fibres increases again, and their morphology changes from flat to faceted; for Au film thicknesses above 20 nm, fibre networks are formed. The spectroscopic properties of the fibres are not modified by the Au layer, enabling independent control of the fibre morphology by means of the intermediate metallic layer.