Revealing Optical Properties of Reduced‐Dimensionality Materials at Relevant Length Scales

Abstract

Reduced-dimensionality materials for photonic and optoelectronic applications including energy conversion, solid-state lighting, sensing, and information technology are undergoing rapid development. The search for novel materials based on reduced-dimensionality is driven by new physics. Understanding and optimizing material properties requires characterization at the relevant length scale, which is often below the diffraction limit. Three important material systems are chosen for review here, all of which are under investigation at the Molecular Foundry, to illustrate the current state of the art in nanoscale optical characterization: 2D semiconducting transition metal dichalcogenides; 1D semiconducting nanowires; and energy-transfer in assemblies of 0D semiconducting nanocrystals. For each system, the key optical properties, the principal experimental techniques, and important recent results are discussed. Applications and new developments in near-field optical microscopy and spectroscopy, scanning probe microscopy, and cathodoluminescence in the electron microscope are given detailed attention. Work done at the Molecular Foundry is placed in context within the fields under review. A discussion of emerging opportunities and directions for the future closes the review.

The important role of water in growth of monolayer transition metal dichalcogenides

“…Whereas the flakes are relatively uniform topographically, the intensity (figure 5(c)) and energy ( figure 5(d)) of the excitonic PL exhibit pronounced nanoscale variations, including a distinct peripheral edge region (~110 nm wide) of weaker PL and stronger TERS ( figure 5(e)). Qualitatively similar nanoscale heterogeneity and peripheral edge regions have been previously reported for both CVD-grown monolayer-MoS 2 [49,50] and WSe 2 [51] and are thought to arise from spatial variations in carrier density and crystalline disorder. The average TERS and nano-PL spectra of the interior and edge regions of our WS 2 are shown in figure 5(f).…”

Optoelectronic and photonic devices based on transition metal dichalcogenides

“…It is crucial to study the fundamental mechanical, electrical and optical properties of TMDCs and several recent articles have presented focused discussions on their synthesis and material-related properties which can have significant impact on device performance [29][30][31][32][33]. In this article, however, we start with a basic introduction to the physical mechanisms/phenomena in TMDC-based optoelectronic devices, followed by a brief discussion on optoelectronic device characterization, analysis and performance evaluation.…”

Layered host–guest long-afterglow ultrathin nanosheets: high-efficiency phosphorescence energy transfer at 2D confined interface

“…8–11 Recently, the transfer of light energy has attracted extensive attention, since light offers the fastest transport speed and can also be recognized and monitored easily. For example, the molecule-based fluorescence energy transfer (FET) technology has been used effectively in molecular biology 12–15 and optoelectronic applications 16 (such as optical probes, 17 information communication, 18 and light-emitting diodes 19 ). However, increasing the efficiency of light energy transfer in a typical FET process remains a considerable challenge, since the rapid release of energy from a photoactive donor (D, excited state lifetime: 10 –9 to 10 –8 s) results in an instantaneously high energy density, which cannot be effectively harvested by the acceptor (A) molecules (Fig.…”