Circular Dichroism Control of Tungsten Diselenide (WSe2) Atomic

Subscriber access provided by - Access paid by the | UCSB Libraries

Functional Nanostructured Materials (including low-D carbon)

Circular Dichroism Control of Tungsten Diselenide (WSe2) Atomic Layers with Plasmonic Meta-Molecules Hsiang-Ting Lin, Chiao-Yun Chang, Pi Ju Cheng, Ming-Yang Li, Chia-Chin Cheng, Shu-Wei Chang, lance L. J. Li, Chih Wei Chu, Pei-Kuen Wei, and Min-Hsiung Shih ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b01472 • Publication Date (Web): 16 Apr 2018 Downloaded from http://pubs.acs.org on April 16, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Circular Dichroism Control of Tungsten Diselenide (WSe2) Atomic Layers with Plasmonic Meta-Molecules Hsiang-Ting Lin1,2, Chiao-Yun Chang1, Pi-Ju Cheng1, Ming-Yang Li1,3, Chia-Chin Cheng3, Shu-Wei Chang1,2, Lance L. J. Li,3 Chih-Wei Chu1, Pei-Kuen Wei1, and Min-Hsiung Shih1,2,4* 1

Research Center for Applied Sciences (RCAS), Academia Sinica, Taipei 11529, Taiwan

2

Department of Photonics and Institute of Electro-Optical Engineering, National Chiao Tung

University (NCTU), Hsinchu 30010, Taiwan 3

Physical Science and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900, Kingdom of Saudi Arabia

4

Department of Photonics, National Sun Yat-sen University (NSYSU), Kaohsiung 80424, Taiwan

*E-mail address: [email protected]

1 ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract Controlling circularly polarized states of light is critical to the development of functional devices for key and emerging applications such as display technology and quantum communication, and the compact circular polarization-tunable photon source is one critical element to realize the applications in the chip-scale integrated system. The atomic layers of transition metal dichalcogenide (TMDC) exhibit intrinsic circularly polarized emissions and are potential chiroptical materials for ultrathin circularly polarized photon sources. In this work, we demonstrated circularly polarized photon sources of TMDC with device thicknesses approximately 50 nm. Circularly polarized photoluminescence from atomic layers of tungsten diselenide (WSe2) was precisely controlled with chiral meta-molecules, and the optical chirality of WSe2 was enhanced more than 4 times by integrating with the meta-molecules. Both the enhanced and reversed circular dichroisms had been achieved. Through integrations of the novel gain material and plasmonic structure which are both low dimensional, a compact device capable of efficiently manipulating emissions of circularly polarized photon was realized. These ultrathin devices are suitable for important applications such as the optical information technology and chip-scale bio-sensing.

KEYWORDS: Two-dimensional materials, Transition metal dichalcogenides (TMDCs), WSe2, Surface plasmon, Metasurface, Chirality, Circular Dichroism


Page 2 of 37

Page 3 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


INTRODUCTION Controlling circularly polarized states of light is critical to their usages in various areas including display technology,1,2 quantum-based optical information processing, and communication.3–5 The distinct behaviors in the emission and absorption of two circularly polarized lights are known as the circular dichroism (CD). The phenomena take place as the light transmits through specific media which respond differently to the field components in two circular polarization states, namely left-hand circularly polarized (LCP) and right-hand circularly polarized (RCP) states. In fact, the occurrences of such events usually indicate the optical chirality of media. Since many biological molecules and organic compounds exhibit CD, the circularly polarized radiation plays an increasingly important role not only in optics but also in the fields of chemistry, biomedicine, and elementary particle physics.6–11 Recently, it has been observed that atomic layers of transition metal dichalcogenides (TMDCs)12–41 exhibit unusual absorption and emission of circularly polarized lights.12,13 TMDCs are layered semiconductors formed by transition metal atoms (M) and halogen atoms (X) with a typical chemical formula of MX2. The thickness of each layer in TMDCs is less than 1 nm. In monolayer TMDCs, the M and X atoms are separately arranged in the respective hexagonal lattice structures. Their bandgaps around the Fermi level are direct and range in 1 to 2 eV.14–18 The direct bandgaps are located at the degenerate but inequivalent K points (also known as K valleys) in the Brillouin zone. Because their crystal structure comprises two types of atoms, the inversion symmetry is broken in monolayer TMDCs, and this makes the electron-hole pairs (excitons) in the two K valleys (denoted as K1 and K2) present in different states of electric polarizations (σ 3 ACS Paragon Plus Environment


and σ ). As the circularly polarized light excites the monolayer TMDCs, the RCP and

LCP fields couple only to the σ and σ state transitions in bands at the K1 and K2 valleys, respectively, due to the angular-momentum conservation. Under such

circumstances, circularly dichroic photoluminescence (PL) could be triggered.19 Accessing different valley states through circularly polarized lights has been experimentally demonstrated with several TMDCs including molybdenum disulfide (MoS2),19–21 molybdenum diselenide (MoSe2),22 tungsten sulfide (WS2),23 and tungsten diselenide (WSe2).24–27 The phenomena of CD indicate that TMDCs are promising optical materials with a controllable optical chirality and may enable the generation of circularly polarized photons. However, the operation temperature and excitation photon energy need to be carefully controlled in order to induce observable CD in monolayer TMDCs. It had been shown that the CD of PL in monolayer MoS2 quickly diminished at a temperature more than 90 K due to the elevated intervalley scattering of carriers at the higher temperatures.19 Moreover, even in the presence of the selective coupling between circularly polarized photons and electron-hole pairs near K points, as the excitation photon energy increases and gets much higher than the direct bandgap, the degree of circular polarization of the emitted radiation would drop rapidly or simply vanish. Such trends had been observed in MoS2,19,21 MoSe2,22 and WSe2.27 To counteract these behaviors, several researchers have proposed various approaches to maintain the CD of PL in TMDCs. Such methods include the applications of an in-plane electric field,27,28 an out-of-plane magnetic field,29–33 and a localized magnetic field.34


Page 4 of 37

Page 5 of 37 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


One means of controlling circularly polarized light is to apply a chiral plasmonic metasurface. Owing to the confinement of localized surface plasmon resonance (LSPR) modes in metallic nanostructures, plasmonic metasurfaces with chiral building blocks exhibit a strong optical chirality. The optical chirality has been achieved in various plasmonic metasurfaces including helical structures,42–43 coupled achiral38 or chiral plasmonic elements,42,45-46 , Tamm plasmonic structure47 and pseudo-chirality effects.48,49 In this way, a plasmonic chiral metasurface with at least one dimension in the nanoscale can be utilized to manipulate the degree of circular polarization of the luminescence. Combining TMDCs with plasmonic metasurfaces is beneficial for several reasons. First, as the plasmonic metasurface is directly fabricated on a monolayer TMDC, tightly confined LSPR modes of the meta-surface strongly interact with the carriers within the thin sheet material. Second, the geometry-dependent LSPR modes of plasmonic nanostructures in metasurfaces provide the wavelength tunability for emission windows of different materials. Third, the ultrathin atomic layer of TMDCs ( ,

(#) + =;2( ; >

#

#

(#)

= |&|+ ?|6( (%(#) )|+ ,

. = R, L,

(#)

+ |6( (%(#) )|+ , @, (5)



Page 14 of 37

(#) +

(#)

where ( ≡ =;2( ; > are the RCP and LCP intensities from dipole . In Eq. (5), the (#)

roles played by fractions ,

(#)

and ,

appear as the information of valleys while square

modului |6(( A%(#) B|+ of the matrix elments characterize the polarization effect of chiral (::)

MMs. In this way, the circular dichroism CD

of the CP-PL in the presence of the

MM can then be expressed as a weighted sum of the local counterpart (#)

(#)

(#)

(#)

(#)

(#)

CD (%(#) , , , , ) ≡ ( − )/( + ): (::) CD

=

(::)

(::)

(::)

− +

(::)

=

Circular Dichroism Control of Tungsten Diselenide (WSe2) Atomic

Recommend Documents