406 research outputs found
Probing Carrier Dynamics in sp(3)-Functionalized Single-Walled Carbon Nanotubes with Time-Resolved Terahertz
Low disordered, stable, and shallow germanium quantum wells: a playground for spin and hybrid quantum technology
Buried-channel semiconductor heterostructures are an archetype material
platform to fabricate gated semiconductor quantum devices. Sharp confinement
potential is obtained by positioning the channel near the surface, however
nearby surface states degrade the electrical properties of the starting
material. In this paper we demonstrate a two-dimensional hole gas of high
mobility ( cm/Vs) in a very shallow strained germanium
channel, which is located only 22 nm below the surface. This high mobility
leads to mean free paths , setting new benchmarks for holes in
shallow FET devices. Carriers are confined in an undoped Ge/SiGe
heterostructure with reduced background contamination, sharp interfaces, and
high uniformity. The top-gate of a dopant-less field effect transistor controls
the carrier density in the channel. The high mobility, along with a percolation
density of , light effective mass (0.09
m), and high g-factor (up to ) highlight the potential of undoped
Ge/SiGe as a low-disorder material platform for hybrid quantum technologies
Impact of Dielectric Environment on Trion Emission from Single-Walled Carbon Nanotube Networks
Trions are charged excitons that form upon optical or electrical excitation
of low-dimensional semiconductors in the presence of charge carriers (holes or
electrons). Trion emission from semiconducting single-walled carbon nanotubes
(SWCNTs) occurs in the near-infrared and at lower energies compared to the
respective exciton. It can be used as an indicator for the presence of excess
charge carriers in SWCNT samples and devices. Both excitons and trions are
highly sensitive to the surrounding dielectric medium of the nanotubes, having
an impact on their application in optoelectronic devices. Here, the influence
of different dielectric materials on exciton and trion emission from
electrostatically doped networks of polymer-sorted (6,5) SWCNTs in top-gate
field-effect transistors is investigated. The observed differences of trion and
exciton emission energies and intensities for hole and electron accumulation
cannot be explained with the polarizability or screening characteristics of the
different dielectric materials, but they show a clear dependence on the charge
trapping properties of the dielectrics. Charge localization (trapping of holes
or electrons by the dielectric) reduces exciton quenching, emission blue-shift
and trion formation. Based on the observed carrier type and dielectric material
dependent variations, the ratio of trion to exciton emission and the exciton
blue-shift are not suitable as quantitative metrics for doping levels of carbon
nanotubes
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
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Temperature dependence of strainâphonon coefficient in epitaxial Ge/Si(001): A comprehensive analysis
We investigate the temperature dependence of the Ge Raman mode strainâphonon coefficient in Ge/Si heteroepitaxial layers. By analyzing the temperature-dependent evolution of both the Raman Ge-Ge line and of the Ge lattice strain, we obtain a linear dependence of the strainâphonon coefficient as a function of temperature. Our findings provide an efficient method for capturing the temperature-dependent strain relaxation mechanism in heteroepitaxial systems. Furthermore, we show that the rather large variability reported in the literature for the strainâphonon coefficient values might be due to the local heating of the sample due to the excitation laser used in ”-Raman experiments. © 2020 The Authors. Journal of Raman Spectroscopy published by John Wiley & Sons Lt
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 (<1.5Â eV) donor-acceptor polymers with diketopyrrolopyrrole (DPP), isoindigo (IGT) and benzodipyrrolidone (BPT) cores, respectively. All of them show near-infrared photoluminescence quantum yields of 0.03â0.09% 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 0.7Â cm2Â Vâ1Â sâ1 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
temperature dependence of strain phonon coefficient in epitaxial ge si 001 a comprehensive analysis
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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 WS2Â 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 WS2âpolymer thin films by spin coating. The characteristic photoluminescence of WS2Â 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
Structural and optical quality of GaN grown on Sc2O3/Y2O3/Si(111)
Thick (âŒ900ânm) GaN layers were grown by molecular beam epitaxy on cost-effective Sc2O3/Y2O3/Si(111) substrates and characterized by x-ray diffraction and photoluminescence. Samples grown in Ga-rich condition show superior structural and optical quality with reduced density of cubic GaN inclusions within the hexagonal matrix and a relatively strong photoluminescence emission at 3.45âeV at 10âK. Cubic inclusions are formed in the initial growth stage and their concentration is reduced with increasing film thickness and after rapid thermal annealing
Triptycene EndâCapped Benzothienobenzothiophene and Naphthothienobenzothiophene
Previously it was demonstrated that triptycene endâcapping can be used as a crystal engineering strategy to direct the packing of quinoxalinophenanthrophenazines (QPPs) towards cofacially stacked Ï dimers with large molecular overlap resulting in high charge transfer integrals. Remarkably, this packing motif was formed under different crystallization conditions and with a variety of derivatives bearing additional functional groups or aromatic substituents. Benzothienobenzothiophene (BTBT) and its derivatives are known as some of the best performing compounds for organic fieldâeffect transistors. Here, the triptycene endâcapping concept is introduced to this class of compounds and polymorphic crystal structures are investigated to evaluate the potential of triptycene endâcaps as synthons for crystal engineering
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