A Rapidly Stabilizing Water-Gated Field-Effect Transistor Based on Printed Single-Walled Carbon Nanotubes for Biosensing Applications

Biosensors are expected to revolutionize disease management through provision of low-cost diagnostic platforms for molecular and pathogenic detection with high sensitivity and short response time. In this context, there has been an ever-increasing interest in using electrolyte-gated field-effect transistors (EG-FETs) for biosensing applications owing to their expanding potential of being employed for label-free detection of a broad range of biomarkers with high selectivity and sensitivity while operating at sub-volt working potentials. Although organic semiconductors have been widely utilized as the channel in EGFETs, primarily due to their compatibility with cost-effective low-temperature solution-processing fabrication techniques, alternative carbon-based platforms have the potential to provide similar advantages with improved electronic performances. Here, we propose the use of inkjet-printed polymer-wrapped monochiral singlewalled carbon nanotubes (s-SWCNTs) for the channel of EG-FETs in an aqueous environment. In particular, we show that our EG-CNTFETs require only an hour of stabilization before producing a highly stable response suitable for biosensing, with a drastic time reduction with respect to the most exploited organic semiconductor for biosensors. As a proof-of-principle, we successfully employed our water-gated device to detect the well-known biotin-streptavidin binding event

Engineering the semiconductor/oxide interaction for stacking twin suppression in single crystalline epitaxial silicon(111)/insulator/Si(111) heterostructures

The integration of alternative semiconductor layers on the Si material platform via oxide heterostructures is of interest to increase the performance and/or functionality of future Si-based integrated circuits. The single crystalline quality of epitaxial (epi) semiconductor-insulator-Si heterostructures is however limited by too high defect densities, mainly due to a lack of knowledge about the fundamental physics of the heteroepitaxy mechanisms at work. To shed light on the physics of stacking twin formation as one of the major defect mechanisms in (111)-oriented fcc-related heterostructures on Si(111), we report a detailed experimental and theoretical study on the structure and defect properties of epi-Si(111)/Y2O 3/Pr2O3/Si(111) heterostructures. Synchrotron radiation-grazing incidence x-ray diffraction (SR-GIXRD) proves that the engineered Y2O3/Pr2O3 buffer dielectric heterostructure on Si(111) allows control of the stacking sequence of the overgrowing single crystalline epi-Si(111) layers. The epitaxy relationship of the epi-Si(111)/insulator/Si(111) heterostructure is characterized by a type A/B/A stacking configuration. Theoretical ab initio calculations show that this stacking sequence control of the heterostructure is mainly achieved by electrostatic interaction effects across the ionic oxide/covalent Si interface (IF). Transmission electron microscopy (TEM) studies detect only a small population of misaligned type B epi-Si(111) stacking twins whose location is limited to the oxide/epiSi IF region. Engineering the oxide/semiconductor IF physics by using tailored oxide systems opens thus a promising approach to grow heterostructures with well-controlled properties. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft

Preparation of WS2-PMMA composite films for optical applications

C. B. acknowledges the German research foundation DFG under Emmy-Noether grant BA4856/2-1. C. B., J. Z. and M. C. G. acknowledge the Volkswagen foundation under grant agreement no. 93404-93406. W. J. B. gratefully acknowledges support by a research grant from Science Foundation Ireland (SFI) under Grant Number 12/IA/1306.Thus far, research activities of 2D materials in optics, photonics and optoelectronics predominantly focus on micromechanically cleaved or grown nanosheets. Here, we show that high quality liquid-exfoliated nanosheets offer an alternative approach. Starting from well-defined, monolayer rich WS2 dispersions obtained after liquid exfoliation and size selection in aqueous surfactant, we present an optimised protocol facilitating transfer of the nanosheets to a polymer solution in organic media. From such dispersions, we fabricate WS2–polymer thin films by spin coating. The characteristic photoluminescence of WS2 monolayers is retained in the film at 2.04 eV without broadening (line width 40 meV) or significant changes in the line-shape. This confirms that nanosheet aggregation is efficiently prevented on transfer and deposition. The films are extremely smooth and uniform over large areas with a root mean square roughness <0.5 nm. To demonstrate the potential in optical applications, the nonlinear optical response was studied, revealing promise as optical limiter. In addition, we show that the photoluminescence can be manipulated by coupling the exciton response to cavity photons in a Ag microcavity.PostprintPeer reviewe

Photo- and electroluminescence of ambipolar, high-mobility, donor-acceptor polymers

AbstractDonor-acceptor polymers with narrow bandgaps are promising materials for bulk heterojunction solar cells and high-mobility field-effect transistors. They also emit light in the near-infrared. Here we investigate and compare the photoluminescence and electroluminescence properties of different narrow bandgap (<1.5 eV) donor-acceptor polymers with diketopyrrolopyrrole (DPP), isoindigo (IGT) and benzodipyrrolidone (BPT) cores, respectively. All of them show near-infrared photoluminescence quantum yields of 0.03–0.09% that decrease with decreasing bandgap. Bottom-contact/top-gate field-effect transistors show ambipolar charge transport with hole and electron mobilities between 0.02 and 0.7 cm2 V−1 s−1 and near-infrared electroluminescence. Their external quantum efficiencies reach up to 0.001%. The effect of polaron quenching and other reasons for the low electroluminescence efficiency of these high mobility polymers are investigated

Organic complementary-like inverters employing methanofullerene-based ambipolar field-effect transistors

Published versio

Singlet fission is incoherent in pristine orthorhombic single crystals of rubrene: no evidence of triplet-pair emission

Singlet fission (SF) and its inverse, triplet–triplet annihilation (TTA), are promising strategies for enhancing photovoltaic efficiencies. However, detailed descriptions of the processes of SF/TTA are not fully understood, even in the most well-studied systems. Reports of the photophysics of crystalline rubrene, for example, are often inconsistent. Here we attempt to resolve these inconsistencies using time-resolved photoluminescence and transient absorption spectroscopy of ‘pristine’ rubrene orthorhombic single crystals. We find the reported time-resolved photoluminescence behaviour that hinted at triplet-pair emission is found only at specific sites on the crystals and likely arises from surface defects. Using transient absorption spectroscopy of the same crystals, we also observe no evidence of instantaneous generation of triplet-pair population with ∼100 fs excitation, independent of excitation wavelength (532 nm, 495 nm) or excitation angle. Our results suggest that SF occurs incoherently on a relatively slow (picosecond) timescale in rubrene single crystals, as expected from the original theoretical calculations. We conclude that the sub-100 fs formation of triplet pairs in crystalline rubrene films is likely to be due to static disorder

Self-assembly and charge transport properties of a benzobisthiazole end-capped with dihexylthienothiophene units

The synthesis of a new conjugated material is reported; BDHTT–BBT features a central electron-deficient benzobisthiazole capped with two 3,6-dihexyl-thieno[3,2-b]thiophenes. Cyclic voltammetry was used to determine the HOMO (−5.7 eV) and LUMO (−2.9 eV) levels. The solid-state properties of the compound were investigated by X-ray diffraction on single-crystal and thin-film samples. OFETs were constructed with vacuum deposited films of BDHTT–BBT. The films displayed phase transitions over a range of temperatures and the morphology of the films affected the charge transport properties of the films. The maximum hole mobility observed from bottom-contact, top-gate devices was 3 × 10−3 cm2 V−1 s−1, with an on/off ratio of 104–105 and a threshold voltage of −42 V. The morphological and self-assembly characteristics versus electronic properties are discussed for future improvement of OFET devices

Absolute Quantification of sp3^3 Defects in Semiconducting Single-Wall Carbon Nanotubes by Raman Spectroscopy

The functionalization of semiconducting single-wall carbon nanotubes (SWCNTs) with luminescent sp$^3$ defects creates red-shifted emission features in the near-infrared and boosts their photoluminescence quantum yields (PLQYs). While multiple synthetic routes for the selective introduction of sp$^3$ defects have been developed, a convenient metric to precisely quantify the number of defects on a SWCNT lattice is not available. Here, we present a direct and simple quantification protocol based on a linear correlation of the integrated Raman D/G+ signal ratios and defect densities as extracted from PLQY measurements. Corroborated by a statistical analysis of single-nanotube emission spectra at cryogenic temperature, this method enables the quantitative evaluation of sp$^3$ defect densities in (6,5) SWCNTs with an error of ±3 defects per micrometer and the determination of oscillator strengths for different defect types. The developed protocol requires only standard Raman spectroscopy and is independent of the defect configuration, dispersion solvent, and nanotube length