Solvatochromism in single-walled carbon nanotubes

Choi, Jong Hyun; Strano, Michael S.

doi:10.1063/1.2745228

Cited by 208 publications

(331 citation statements)

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“…Electrical measurements have also been performed and the reported mobility gaps were smaller than those found by photoluminescence (see mobility and optical gaps, Table 1), a result that is surprising because the mobility gap should be larger than the optical gap in a semiconductor with few interband states. 59,60 However, the study did provide a detailed analysis of many flake thicknesses, and revealed that bulk properties begin to transition towards quantumconfined properties at flake sizes as large as 30 layers. Table 2.…”

Section: Optical Absorption In 2d Phosphorus: Backgroundmentioning

confidence: 99%

Phosphorene: Synthesis, Scale-Up, and Quantitative Optical Spectroscopy

et al. 2015

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Phosphorene, a two-dimensional (2D) monolayer of black phosphorus, has attracted considerable theoretical interest, although the experimental realization of monolayer, bilayer, and few-layer flakes has been a significant challenge. Here we systematically survey conditions for liquid exfoliation to achieve the first large-scale production of monolayer, bilayer, and few-layer phosphorus, with exfoliation demonstrated at the 10-gram scale. We describe a rapid approach for quantifying the thickness of 2D phosphorus and show that monolayer and few-layer flakes produced by our approach are crystalline and unoxidized, while air exposure leads to rapid oxidation and the production of acid. With large quantities of 2D phosphorus now available, we perform the first quantitative measurements of the material's absorption edgewhich is nearly identical to the material's band gap under our experimental conditions-as a function of flake thickness. Our interpretation of the absorbance spectrum relies on an analytical method introduced in this work, allowing the accurate determination of the absorption edge in polydisperse samples of quantum-confined semiconductors. Using this method, we found that the band gap of black phosphorus increased from 0.33 ± 0.02 eV in bulk to 1.88 ± 0.24 eV in bilayers, a range that is larger than any other 2D material. In addition, we quantified a higherenergy optical transition (VB-1 to CB), which changes from 2.0 eV in bulk to 3.23 eV in bilayers. This work describes several methods for producing and analyzing 2D phosphorus while also yielding a class of 2D materials with unprecedented optoelectronic properties.

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Section: Optical Absorption In 2d Phosphorus: Backgroundmentioning

confidence: 99%

Phosphorene: Synthesis, Scale-Up, and Quantitative Optical Spectroscopy

et al. 2015

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“…This could be partly ascribed to the different stoichiometry of the SiO 2 layers used as a substrate, which induces a shift in the emission because of the different dielectric constant of the surrounding medium. 38 To verify this hypothesis, we have transferred black phosphorus flakes onto a Si substrate covered by a thin (∼ 2 nm) layer of native oxide. Such a substrate has a larger dielectric constant than the standard Si/SiO 2 substrates.…”

Section: 1819mentioning

confidence: 99%

Excitons in atomically thin black phosphorus

et al. 2016

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Raman scattering and photoluminescence spectroscopy are used to investigate the optical properties of single layer black phosphorus obtained by mechanical exfoliation of bulk crystals under an argon atmosphere. The Raman spectroscopy, performed in situ on the same flake as the photoluminescence measurements, demonstrates the single layer character of the investigated samples. The emission spectra, dominated by excitonic effects, display the expected in plane anisotropy. The emission energy depends on the type of substrate on which the flake is placed due to the different dielectric screening. Finally, the blue shift of the emission with increasing temperature is well described using a two oscillator model for the temperature dependence of the band gap.Black phosphorus, the most stable of all the allotropes of phosphorus, has been intensively studied by different experimental methods from the early fifties of the last century.1-7 Bulk black phosphorus is a semiconductor, with a band gap of about 0.335 eV.1,4 The orthorombic bulk crystal has a layered structure, with atomic layers bound by weak van der Waals interactions. A single atomic layer is puckered, with the phosphorus atoms being parallel in the (010) plane. 3,8,9 Atomically thin monolayers have been recently isolated using mechanical exfoliation, 10 adding black phosphorus to the rapidly growing family of emerging two dimensional materials. The band gap of black phosphorus is always direct and can be tuned from 0.3 eV to the nearly visible part of the spectrum 11,12 . In contrast, graphene is gapless, 13 and the transition metals dichalcogenides (TMDs) have an indirect gap in bulk phase and only monolayer TMDs have a direct gap.14 Moreover, black phosphorus exhibits a strong in-plane anisotropy 11,12,[15][16][17] , absent in graphene and TMDs. Additionally, the relatively high mobilities measured at room temperature combined with the direct band gap result in an on/off ratio for FET transistors of the order of 10 5 . 26 The exciton binding energy and consequently the emission energy strongly depend on the dielectric environment (substrate) 10,27 . This could partially explain the wide range of values for the black phosphorus emission energy found in the literature, possibly related also to a slightly different composition of the SiO 2 substrates employed. Moreover, owing to the limited life time of the samples, the various characterization techniques used to identify monolayer black phosphorus (e.g. atomic force microscopy, Raman spectroscopy) could not always be performed on the same flake where the optical response was investigated.In this paper we present a systematic investigation of the optical properties of monolayers of black phosphorus. We analyze the properties of the emission as a function of the dielectric constant of the substrate, excitation power, polarization and temperature. The single layer character of the investigated flakes is demonstrated using in situ Raman measurements on the same flake used for the PL. We show that the PL emission ...

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“…The chiralities of the SWNTs present in the sample are determined using an empirical equation. [ 48,49 ] In the inset, the structure of SWCNT-P3DDT hybrid is displayed. b) Sketch of the inkjet printing process for the deposition of s-SWCNTs solution.…”

Section: Doi: 101002/aelm201600094mentioning

confidence: 99%