Atomically thin optical lenses and gratings

Yang, Jiong; Wang, Zhu; Wang, Fan; Xu, Ruijuan; Tao, Jin; Zhang, Shuang; Qin, Qing Hua; Luther‐Davies, Barry; Jagadish, Chennupati; Yu, Zongfu; Lu, Yuerui

doi:10.1038/lsa.2016.46

Cited by 118 publications

(103 citation statements)

References 30 publications

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“…The measured OPL values agree very well with our theoretical calculations (Figure 1d). Recently, we also successfully used PSI to quickly and precisely identify the layer numbers of TMD atomically thin semiconductors 21 .…”

Section: Resultsmentioning

confidence: 99%

Optical tuning of exciton and trion emissions in monolayer phosphorene

et al. 2015

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Monolayer phosphorene provides a unique two-dimensional (2D) platform to investigate the fundamental dynamics of excitons and trions (charged excitons) in reduced dimensions. However, owing to its high instability, unambiguous identification of monolayer phosphorene has been elusive. Consequently, many important fundamental properties, such as exciton dynamics, remain underexplored. We report a rapid, noninvasive, and highly accurate approach based on optical interferometry to determine the layer number of phosphorene, and confirm the results with reliable photoluminescence measurements. Furthermore, we successfully probed the dynamics of excitons and trions in monolayer phosphorene by controlling the photo-carrier injection in a relatively low excitation power range. Based on our measured optical gap and the previously measured electronic energy gap, we determined the exciton binding energy to be ,0.3 eV for the monolayer phosphorene on SiO 2 /Si substrate, which agrees well with theoretical predictions. A huge trion binding energy of ,100 meV was first observed in monolayer phosphorene, which is around five times higher than that in transition metal dichalcogenide (TMD) monolayer semiconductor, such as MoS 2 . The carrier lifetime of exciton emission in monolayer phosphorene was measured to be ,220 ps, which is comparable to those in other 2D TMD semiconductors. Our results open new avenues for exploring fundamental phenomena and novel optoelectronic applications using monolayer phosphorene. Keywords: exciton; monolayer phosphorene; optical injection; two-dimensional materials INTRODUCTION Phosphorene is a recently developed two-dimensional (2D) material that has attracted tremendous attention owing to its unique anisotropic manner 1-6 , layer-dependent direct band gaps 7,8 , and quasi-onedimensional (1D) excitonic nature 9,10 , which are all in drastic contrast with the properties of other 2D materials, such as graphene 11 and transition metal dichalcogenide (TMD) semiconductors [12][13][14] . Monolayer phosphorene has been of particular interest in exploring technological applications and investigating fundamental phenomena, such as 2D quantum confinement and many-body interactions 9,15 . However, such unique 2D materials are unstable in ambient conditions and degrade quickly 8,16 . Particularly, monolayer phosphorene is expected to be much less stable than few-layer phosphorene 16 , hence making its identification and characterization extremely challenging. There is a huge controversy on the identification of very few-layer (one or two layers) phosphorene and thus on their properties [16][17][18] . This controversy was primarily due to the lack of a robust experimental technique to precisely identify the monolayer phosphorene. Consequently, many important fundamental properties of monolayer phosphorene, such as its excitonic nature, remain elusive. In this study, we propose and implement a rapid, noninvasive,

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Section: Resultsmentioning

confidence: 99%

Optical tuning of exciton and trion emissions in monolayer phosphorene

et al. 2015

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“…In recent years layered materials, also known as van der Walls crystals, have attracted major attention across multiple fields of nanoscale science and technology 1,2,3,4,5 . For instance, transition metal carbides and nitrides (MXens) have been promising building blocks for energy storage and capacitors, 1,6 .…”

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Engineering and Localization of Quantum Emitters in Large Hexagonal Boron Nitride Layers

Choi

Tran

Elbadawi

et al. 2016

ACS Appl. Mater. Interfaces

174

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Hexagonal boron nitride is a wide-band-gap van der Waals material that has recently emerged as a promising platform for quantum photonics experiments. In this work, we study the formation and localization of narrowband quantum emitters in large flakes (up to tens of micrometers wide) of hexagonal boron nitride. The emitters can be activated in as-grown hexagonal boron nitride by electron irradiation or high-temperature annealing, and the emitter formation probability can be increased by ion implantation or focused laser irradiation of the as-grown material. Interestingly, we show that the emitters are always localized at the edges of the flakes, unlike most luminescent point defects in three-dimensional materials. Our results constitute an important step on the roadmap of deploying hexagonal boron nitride in nanophotonics applications.

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“…Recently, nano-patterned periodic sub-wavelength gratings made of vdW materials at mid-infrared frequencies have been reported 24 , although wavefront engineering in the far-field has not been demonstrated. Additionally, ultrathin Fresnel lenses made of molybdenum disulfide have been demonstrated 25 . These lenses, however, do not exploit nano-meter scale patterning and rely on phase accumulation from the variable thickness.…”

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Ultrathin van der Waals Metalenses

et al. 2018

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+ These two authors contributed equally.Ultrathin and flat optical lenses are essential for modern optical imaging, spectroscopy, and energy harvesting 1-5 . Dielectric metasurfaces comprising nanoscale quasi-periodic resonator arrays are promising for such applications, as they can tailor the phase, amplitude, and polarization of light at subwavelength resolution, enabling multi-functional optical elements 2-6 . To achieve 2π phase coverage, however, most dielectric metalenses need a thickness comparable to the wavelength, requiring fabrication of high-aspect-ratio scattering elements. Here, we report ultrathin dielectric metalenses made of van der Waals (vdW) materials, leveraging their high refractive indices and the incomplete phase design approach 7,8 to achieve device thicknesses down to ~/10, operating at infrared and visible wavelengths. These materials have generated strong interest in recent years due to their advantageous optoelectronic properties 9-13 . Using vdW metalenses, we demonstrate near diffraction-limited focusing and imaging, and exploit their layered nature to transfer the fabricated metalenses onto flexible substrates to show strain-induced tunable focusing. Our work enables further downscaling of optical elements and opportunities for integration of metasurface optics in ultra-miniature optoelectronic systems.Sub-wavelength diffractive optical elements, also known as metasurfaces, have fostered considerable interest in the photonics community in recent years. A sub-wavelength scatterer can provide different phaseshifts to the incident light by virtue of their lateral geometry, while having the same thickness. A metasurface exploits this effect to realize ultra-thin and flat optical elements, with uniform thickness, which can be fabricated by a single stage lithography. Although several works in this field have successfully demonstrated metalenses 14,15 and other optical components 2,3,16 using deep sub-wavelength-thick metallic nano-antennas, these devices usually suffer from high absorption loss and strong polarization sensitivity. An alternative approach is to exploit arrays of dielectric resonators 17,18 . Thus far, a diverse set of low-loss dielectric metasurface optical elements operating in the infrared and visible wavelength ranges have been reported 4,17-20 . However, these dielectric elements are much thicker (on the order of the wavelength) to achieve a full 2π phase shift. At the same time, to impart small phase shifts the resonators need to have narrower lateral dimensions. As the thickness is uniform for all the scatterers, several pillars end up having high high-aspect-ratio (typically > 5). Fabricating these delicate structures while simultaneously keeping a low sidewall roughness is a challenging nanofabrication task and may limit the practical applications of metalenses. Although thinner and efficient dielectric metasurfaces can be ideally realized at near-infrared wavelengths using high-index materials with low absorption loss, such as group III-V compounds like AlGaAs (...

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Atomically thin optical lenses and gratings

Cited by 118 publications

References 30 publications

Optical tuning of exciton and trion emissions in monolayer phosphorene

Optical tuning of exciton and trion emissions in monolayer phosphorene

Engineering and Localization of Quantum Emitters in Large Hexagonal Boron Nitride Layers

Ultrathin van der Waals Metalenses

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