Here, we report the design and continuous tuning of the energy levels and gaps in GQDs. Nitrogenous functionalization allows the electronic structure to be systematically modifi ed through the effective orbital resonance of nitrogen moieties with the GQD HOMO or LUMO energy levels. We used ab initio calculations to evaluate the effects of different nitrogenous functional groups on the strong orbital resonance in GQDs (see Figure 1 a). Experimentally, nucleophilic substitution and the dehydration reaction of amine moieties with oxygen-functional groups on the GQDs were used to produce nitrogen-functionalized graphene quantum dots (NGQDs). We examined potential applications of NGQDs for optoelectronic devices. The inclusion of NGQDs facilitates the separation and transport of photogenerated electrons from the CH 3 NH 3 PbI 3 absorber in perovskite solar cells by more than sixfold. We also demonstrate NGQDs hybrid phototransistors with photoconductive gain exceeding 2 × 10 10 electrons/photon and photoresponsivity as high as 3.5 × 10 4 A W -1 . These fi ndings validate a method that enables us to control the energy levels of GQDs precisely, overcoming many challenges hindering the development of graphene devices.Figure 2 a presents a preparative strategy for producing NGQDs with tunable HOMO/LUMO energy levels and gaps. We successfully functionalized NGQDs using a variety of chemical groups that had been selected based on ab initio calculations (Figure 1 a). Graphene quantum dots with a diameter of ≈4.0 nm were produced from graphite nanoparticles (GNPs) by mechanical exfoliation and then oxidized (details are given in the Methods section and Figure S1 of the Supporting Information). Functionalization occurred by the nucleophilic substitution and dehydration of the amine group on a precursor with the epoxide bridges and the hydroxyls on oxidized GQDs (o-GQDs), as shown in Figure 2 a. Although the small and uniform GNPs are better precursor for obtaining high-quality NGQDs, this nitrogen-functionalization strategy can be also applicable for other carbon sources ( Figure S3, Supporting Information). No change in the NGQD size or shape caused by functionalization was observed ( Figure S4-S6, Supporting Information); transmission electron microscopy, atomic force microscopy, and Raman spectroscopy confi rmed the persistence of monolayer graphene structures. The change in the HOMO/ LUMO levels of GQDs upon functionalization is depicted in Figure 1 b. HOMO levels were measured using photoelectron yield spectroscopy (see Figure S7, Supporting Information). LUMO levels were estimated by subtracting the bandgap from the HOMO level; the bandgap was estimated from Tauc plots ( Figure S8, Supporting Information). [ 17 ] The HOMO/ LUMO energy levels changed continuously with the different nitrogen-containing functional groups as a consequence of Graphene exhibits strong broadband saturable absorption and various unique transport phenomena that enable its use in highly effi cient photonic and optoelectronic applications. [ 1 ] Th...
We present the results from quantitative studies of physics at tE threshold, taking into account realistic experimental conditions expected at future linear e f e-colliders. A possible experimental strategy is illustrated for a sample case of mt=150 GeV, where the importance of the measurements of both total and differential cross sections is emphasized for precision determinations of various parameters. The studies are based on a recently developed theoretical formalism which includes full O(a.) corrections. An energy scan of 11 points with 1 fb-' each allows us to measure the top mass and the strong coupling constant with statistical errors of Amt=0.2 GeV and Aa.=0.005, respectively. As for the top width, AI't/I't=0.2 (stat) is expected, if both mt and a. are known. The measurement of the top momentum at some optimized energy point with 100 fb-' reduces the error on a, to Aa,=0.0015, provided that the 1S peak position is known from the threshold scan. The momentum measurement also improves the precision on the top width to ATt/Tt=0.04, if a. is known from other sources. The forward-backward asymmetry in the threshold region provides another interesting method to measure a. and I't.PACS number(s): 13.65.+i, 14.65.Ha
Due to the presence of strong magnetic resonances, high refractive index dielectric nanoantennnas have shown the ability to expand the methods available for controlling electromagnetic waves in the subwavelength region. In this work, we experimentally demonstrate that an asymmetric dielectric dimer made of silicon can lead to highly directional scattering depending on the excitation wavelength, due to the interference of the excited magnetic resonances. A back focal plane imaging system combined with a prism coupling technique enables us to explore the scattering profile parallel to the substrate. The directivity of scattering along the substrate is high enough to produce selective guiding of light along the substrate. These results showing tunable control of directional scattering will encourage the realization of novel optical applications, such as optical nanocircuitry.
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