Heterovalent dopant ions, such as Sn 4+ , in In 2 O 3 nanocrystals (NCs) provide free electrons for localized surface plasmon resonance (LSPR). But the same heterovalent dopants act as electron scattering centers, both independently and by forming complexes with interstitial oxygen, thereby increasing LSPR line width. Also, such complexes decrease free carrier density. These detrimental effects diminish the figureof-merit of LSPR known as the quality factor (Q-factor). Herein, we designed colloidal Cr−Sn codoped In 2 O 3 NCs, where both high carrier density and low carrier scattering can be achieved simultaneously, yielding a high LSPR Q-factor of 7.2, which is a record high number compared to prior reports of doped In 2 O 3 NCs. Q-factors increase systematically from 3.2 for 6.6% Sn doped In 2 O 3 NCs to 7.2 for 23.8% Cr−6.6% Sn codoped In 2 O 3 NCs by increasing the Cr codoping concentration, which is also accompanied by an increase in NC size from 6.7 to 22.1 nm. Detailed characterization and analysis of LSPR spectra using Drude model suggest that the increase in NC size (induced by Cr codoping) is mainly responsible for the enhanced LSPR Q-factor. Sn 4+ dopants on the surface of NCs are more vulnerable to form irreducible complexes with interstitial oxide ions, compared to Sn 4+ ions in the core. Therefore, an increase in the concentration ratio of [Sn core ]/[Sn surface ] (or [Sn]/ [interstitial oxide]) by increasing the size of NCs, increases the carrier density. Furthermore, such increase in both NC size and Cr doping influences multiple factors reducing the scattering of charge carriers, thereby increasing the optical carrier mobility. This unique combination, which increases both the density and mobility of charge carriers, improves the LSPR Q-factor.

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We report the direct exclusive modification of the edge of a single graphene monolayer with nanoparticles or organic functionalities under ambient conditions.

We present here the electrochemistry at a photolithographically created isolated monolayer graphene edge (GrEdge). The millimeter-long GrEdge is found to behave like a nanowire, exhibiting very high mass transport rates, characteristic of nanoelectrodes. Accordingly, the voltammetric response at such electrodes is dictated by the kinetics of heterogeneous electron transfer (HET). We observe high electron transfer rates at GrEdge electrodes, at least 14 cm/s for the outer-sphere probe ferrocenemethanol and 0.06 cm/s or higher for the innersphere probe Fe(CN) 6 3− . Upon selective modification of the edge with gold nanoparticles, the HET is found to be reversible, with the voltammetric curve showing a typical mass-transport-limited Nernstian response for both kinds of probes. Subsequently, the electrodes are evaluated as electrochemical sensors for the detection of reduced form of nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD). The nanoscale geometry with a unique diffusional profile of the unmodified GrEdge enables the sensing of NADH down to micromolar concentrations. Taken together, our simple strategy for the realization of graphene edge electrodes enables the availability of a versatile high-aspect one-dimensional nanoelectrode with the capability to study fast electron transfer kinetics. Moreover, such electrodes allow for facile detection of small amounts of electroactive species and hence will find applications in chemical sensing and biosensing.

Electron transfer rates at graphene are found to vary with pH, attributed to electrostatic effects at the graphene-liquid interface.