Sejeong Kim graduated from Sogang University (Summa Cum Laude), Korea in 2009 with a degree in Physics and Integrated Biotechnology. She received her Ph.D. in Physics from Korea Advanced Institute of Science and Technology (KAIST) in 2014. Dr. Sejeong Kim spent two and half years as a postdoctoral researcher at KAIST. She joined the University of Technology Sydney (UTS) as a postdoctoral researcher since 2017. Her doctoral research interests include semiconductor optical resonator design, fabrication and optical characterization. The title of doctoral thesis is “Study of photonic crystal nanobeam lasers and their applications”. Since then, her interest was to efficiently collect light from GaN single emitters. Sejeong Kim’s research at UTS will focus on the introduction of micro/nano cavities for new materials.
Can supervise: YES
Fröch, JE, Hwang, Y, Kim, S, Aharonovich, I & Toth, M 2019, 'Photonic Nanostructures from Hexagonal Boron Nitride', Advanced Optical Materials, vol. 7, no. 4.View/Download from: UTS OPUS or Publisher's site
© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Growing interest in devices based on layered van der Waals (vdW) materials is motivating the development of new nanofabrication methods. Hexagonal boron nitride (hBN) is one of the most promising materials for studies of quantum photonics and phonon polaritonics. A promising nanofabrication process used to fabricate several hBN photonic devices using a hybrid reactive ion etching (RIE) and electron beam-induced etching (EBIE) technique is reported in detail here. The shortcomings and benefits of RIE and EBIE are highlighted and the utility of the hybrid approach for the fabrication of suspended and supported device structures with nanoscale features and highly vertical sidewalls are demonstrated. Functionality of the fabricated devices is proven by measurements of high-quality cavity optical modes (Q ≈ 1500). This nanofabrication approach constitutes an advance toward an integrated, monolithic quantum photonics platform based on hBN and other layered vdW materials.
Shandilya, PK, Froech, JE, Mitchell, M, Lake, DP, Kim, S, Toth, M, Behera, B, Healey, C, Aharonovich, I & Barclay, PE 2019, 'Hexagonal Boron Nitride Cavity Optomechanics', NANO LETTERS, vol. 19, no. 2, pp. 1343-1350.View/Download from: UTS OPUS or Publisher's site
Duong, NMH, Xu, Z-Q, Kianinia, M, Su, R, Liu, Z, Kim, S, Bradac, C, Li, L-J, Solntsev, A, Liu, J & Aharonovich, I 2018, 'Enhanced Emission from WSe2 Monolayers Coupled to Circular Bragg Gratings', ACS Photonics, vol. 5, pp. 3950-3955.View/Download from: UTS OPUS or Publisher's site
Two-dimensional transition-metal dichalcogenides (TMDC) are of great interest
for on-chip nanophotonics due to their unique optoelectronic properties. Here,
we propose and realize coupling of tungsten diselenide (WSe2) monolayers to
circular Bragg grating structures to achieve enhanced emission. The interaction
between WSe2 and the resonant mode of the structure results in Purcell-enhanced
emission, while the symmetric geometrical structure improves the directionality
of the out-coupling stream of emitted photons. Furthermore, this hybrid
structure produces a record high contrast of the spin valley readout (> 40%)
revealed by the polarization resolved photoluminescence (PL) measurements. Our
results are promising for on-chip integration of TMDC monolayers with optical
resonators for nanophotonic circuits.
Kianinia, M, Bradac, C, Sontheimer, B, Wang, F, Tran, TT, Nguyen, M, Kim, S, Xu, Z-Q, Jin, D, Schell, AW, Lobo, CJ, Aharonovich, I & Toth, M 2018, 'All-optical control and super-resolution imaging of quantum emitters in layered materials.', Nature communications, vol. 9, no. 1, pp. 874-874.View/Download from: UTS OPUS or Publisher's site
Layered van der Waals materials are emerging as compelling two-dimensional platforms for nanophotonics, polaritonics, valleytronics and spintronics, and have the potential to transform applications in sensing, imaging and quantum information processing. Among these, hexagonal boron nitride (hBN) is known to host ultra-bright, room-temperature quantum emitters, whose nature is yet to be fully understood. Here we present a set of measurements that give unique insight into the photophysical properties and level structure of hBN quantum emitters. Specifically, we report the existence of a class of hBN quantum emitters with a fast-decaying intermediate and a long-lived metastable state accessible from the first excited electronic state. Furthermore, by means of a two-laser repumping scheme, we show an enhanced photoluminescence and emission intensity, which can be utilized to realize a new modality of far-field super-resolution imaging. Our findings expand current understanding of quantum emitters in hBN and show new potential ways of harnessing their nonlinear optical properties in sub-diffraction nanoscopy.
Kim, S, Fröch, JE, Christian, J, Straw, M, Bishop, J, Totonjian, D, Watanabe, K, Taniguchi, T, Toth, M & Aharonovich, I 2018, 'Photonic crystal cavities from hexagonal boron nitride.', Nature Communications, vol. 9, no. 1, pp. 2623-2623.View/Download from: UTS OPUS or Publisher's site
Development of scalable quantum photonic technologies requires on-chip integration of photonic components. Recently, hexagonal boron nitride (hBN) has emerged as a promising platform, following reports of hyperbolic phonon-polaritons and optically stable, ultra-bright quantum emitters. However, exploitation of hBN in scalable, on-chip nanophotonic circuits and cavity quantum electrodynamics (QED) experiments requires robust techniques for the fabrication of high-quality optical resonators. In this letter, we design and engineer suspended photonic crystal cavities from hBN and demonstrate quality (Q) factors in excess of 2000. Subsequently, we show deterministic, iterative tuning of individual cavities by direct-write EBIE without significant degradation of the Q-factor. The demonstration of tunable cavities made from hBN is an unprecedented advance in nanophotonics based on van der Waals materials. Our results and hBN processing methods open up promising avenues for solid-state systems with applications in integrated quantum photonics, polaritonics and cavity QED experiments.
Kim, S, Toth, M & Aharonovich, I 2018, 'Design of photonic microcavities in hexagonal boron nitride.', Beilstein journal of nanotechnology, vol. 9, pp. 102-108.View/Download from: UTS OPUS or Publisher's site
We propose and design photonic crystal cavities (PCCs) in hexagonal boron nitride (hBN) for diverse photonic and quantum applications. Two dimensional (2D) hBN flakes contain quantum emitters which are ultra-bright and photostable at room temperature. To achieve optimal coupling of these emitters to optical resonators, fabrication of cavities from hBN is therefore required to maximize the overlap between cavity optical modes and the emitters. Here, we design 2D and 1D PCCs using anisotropic indices of hBN. The influence of underlying substrates and material absorption are investigated, and spontaneous emission rate enhancements are calculated. Our results are promising for future quantum photonic experiments with hBN.
Nguyen, M, Kim, S, Tran, TT, Xu, Z-Q, Kianinia, M, Toth, M & Aharonovich, I 2018, 'Nanoassembly of quantum emitters in hexagonal boron nitride and gold nanospheres.', Nanoscale, vol. 10, no. 5, pp. 2267-2274.View/Download from: UTS OPUS or Publisher's site
The assembly of quantum nanophotonic systems with plasmonic resonators is important for fundamental studies of single photon sources as well as for on-chip information processing. In this work, we demonstrate the controllable nanoassembly of gold nanospheres with ultra-bright narrow-band quantum emitters in 2D layered hexagonal boron nitride (hBN). We utilize an atomic force microscope (AFM) tip to precisely position gold nanospheres to close proximity to the quantum emitters and observe the resulting emission enhancement and fluorescence lifetime reduction. The extreme emitter photostability permits analysis at high excitation powers, and delineation of absorption and emission enhancement caused by the plasmonic resonators. A fluorescence enhancement of over 300% is achieved experimentally for quantum emitters in hBN, with a radiative quantum efficiency of up to 40% and a saturated count rate in excess of 5 × 106 counts per s. Our results are promising for the future employment of quantum emitters in hBN for integrated nanophotonic devices and plasmonic based nanosensors.
Tran, TT, Kianinia, M, Nguyen, M, Kim, S, Xu, ZQ, Kubanek, A, Toth, M & Aharonovich, I 2018, 'Resonant Excitation of Quantum Emitters in Hexagonal Boron Nitride', ACS Photonics, vol. 5, no. 2, pp. 295-300.View/Download from: UTS OPUS or Publisher's site
© 2017 American Chemical Society. Quantum emitters in layered hexagonal boron nitride (hBN) have recently attracted a great deal of attention as promising single photon sources. In this work, we demonstrate resonant excitation of a single defect center in hBN, one of the most important prerequisites for employment of optical sources in quantum information processing applications. We observe spectral line widths of an hBN emitter narrower than 1 GHz while the emitter experiences spectral diffusion. Temporal photoluminescence measurements reveal an average spectral diffusion time of around 100 ms. An on-resonance photon antibunching measurement is also realized. Our results shed light on the potential use of quantum emitters from hBN in nanophotonics and quantum information processing applications.
Xu, Z-Q, Elbadawi, C, Tran, TT, Kianinia, M, Li, X, Liu, D, Hoffman, TB, Nguyen, M, Kim, S, Edgar, JH, Wu, X, Song, L, Ali, S, Ford, M, Toth, M & Aharonovich, I 2018, 'Single photon emission from plasma treated 2D hexagonal boron nitride.', Nanoscale, vol. 10, no. 17, pp. 7957-7965.View/Download from: UTS OPUS or Publisher's site
Artificial atomic systems in solids are becoming increasingly important building blocks in quantum information processing and scalable quantum nanophotonic networks. Amongst numerous candidates, 2D hexagonal boron nitride has recently emerged as a promising platform hosting single photon emitters. Here, we report a number of robust plasma and thermal annealing methods for fabrication of emitters in tape-exfoliated hexagonal boron nitride (hBN) crystals. A two-step process comprising Ar plasma etching and subsequent annealing in Ar is highly robust, and yields an eight-fold increase in the concentration of emitters in hBN. The initial plasma-etching step generates emitters that suffer from blinking and bleaching, whereas the two-step process yields emitters that are photostable at room temperature with emission wavelengths greater than ∼700 nm. Density functional theory modeling suggests that the emitters might be associated with defect complexes that contain oxygen. This is further confirmed by generating the emitters via annealing hBN in air. Our findings advance the present understanding of the structure of quantum emitters in hBN and enhance the nanofabrication toolkit needed to realize integrated quantum nanophotonic circuits.
Zhou, Y, Wang, Z, Rasmita, A, Kim, S, Berhane, A, Bodrog, Z, Adamo, G, Gali, A, Aharonovich, I & Gao, W-B 2018, 'Room temperature solid-state quantum emitters in the telecom range.', Science advances, vol. 4, no. 3, pp. eaar3580-eaar3580.View/Download from: UTS OPUS or Publisher's site
On-demand, single-photon emitters (SPEs) play a key role across a broad range of quantum technologies. In quantum networks and quantum key distribution protocols, where photons are used as flying qubits, telecom wavelength operation is preferred because of the reduced fiber loss. However, despite the tremendous efforts to develop various triggered SPE platforms, a robust source of triggered SPEs operating at room temperature and the telecom wavelength is still missing. We report a triggered, optically stable, room temperature solid-state SPE operating at telecom wavelengths. The emitters exhibit high photon purity (~5% multiphoton events) and a record-high brightness of ~1.5 MHz. The emission is attributed to localized defects in a gallium nitride (GaN) crystal. The high-performance SPEs embedded in a technologically mature semiconductor are promising for on-chip quantum simulators and practical quantum communication technologies.
Cho, JH, Kim, YM, Lim, SH, Yeo, HS, Kim, S, Gong, SH & Cho, YH 2018, 'Strongly Coherent Single-Photon Emission from Site-Controlled InGaN Quantum Dots Embedded in GaN Nanopyramids', ACS Photonics, vol. 5, no. 2, pp. 439-444.View/Download from: UTS OPUS or Publisher's site
© 2017 American Chemical Society. Group III-nitride materials have drawn a great deal of renewed interest due to their versatile characteristics as quantum emitters including room-temperature operation, widely tunable wavelengths from ultraviolet to infrared, and a high degree of linear polarization. However, most reported results for III-nitride-based quantum emitters show large inhomogeneous line width broadening in comparison to their lifetime-limited values, which is detrimental to achieving indistinguishability with high visibility. To overcome this, we propose an unprecedented InGaN quantum dot formation technique at the apex of GaN nanopyramid structures, which significantly suppresses inhomogeneous line width broadening. Using high-resolution transmission electron microscopy, a site-controlled InGaN quantum dot with small height (<2 nm) was estimated. No measurable screening effect or frequency jitter of the single-photon emission was observed, which leads to the narrow homogeneous emission line width (64 ± 8 μeV) beyond the spectral resolution limit via Fourier-transform spectroscopy. The emitted photons exhibited superb antibunching characteristics with a near-unity degree of linear polarization, which is highly relevant for polarized nonclassical light sources for applications in quantum information processing.
Gong, SH, Kim, S, Kim, JH, Cho, JH & Cho, YH 2018, 'Site-Selective, Two-Photon Plasmonic Nanofocusing on a Single Quantum Dot for Near-Room-Temperature Operation', ACS Photonics, vol. 5, no. 3, pp. 711-717.View/Download from: UTS OPUS or Publisher's site
© 2018 American Chemical Society. Although the study of single quantum dot (QD) properties without the background noise and dephasing processes caused by surrounding carriers is a crucial issue, the spatial-selective excitation of a single QD is still challenging, due to the diffraction nature of light. Here, we demonstrate a deep subwavelength excitation of a single QD using two-photon plasmonic nanofocusing. Self-aligned plasmonic nanofocusing on a single QD was achieved using metal coated nanopyramid structures. The highly enhanced local electric field generated by the plasmonic nanofocusing gives rise to a large increase in the optical nonlinear effect (i.e., two-photon excitation). As a result of the enhanced field enhancement on the metal-pyramid hybrid structure, the two-photon luminescence intensity was enhanced by a factor of 5000, and the selective excitation of a single QD enabled us to observe InGaN QD emission at near room temperature, due to the large suppression of the background emission. Our approach opens promising perspectives for quantum optics experiments with highly reduced background emissions.
Hwang, Y, Lee, S, Kim, S, Lin, J & Yuan, XC 2018, 'Effects of Fano Resonance on Optical Chirality of Planar Plasmonic Nanodevices', ACS Photonics, vol. 5, no. 11.View/Download from: UTS OPUS or Publisher's site
© 2018 American Chemical Society. The effects of Fano resonance on the optical chirality of planar plasmonic nanodevices in the visible wavelength range are experimentally observed and theoretically explained. The nanodevice consists of a nanodisk at the center with surrounding six gold nanorods with an orientation angle to exhibit optical chirality under dark-field illumination. The chiral response induced by the gold nanorods is affected by the presence of the nanodisk with different diameters which causes Fano resonance of different coupling strength. An intriguing change to the opposite selection preference of different handedness of the circularly polarized light has been clearly observed experimentally. This change of the preference is understood based on the coupled localized surface plasmon model. Moreover, electrostatic analysis and the time-dependent simulations provide a further understanding of the phenomenon. The observed and understood effects of Fano resonance on optical chirality enables effective manipulation of chiral characteristics of planar subwavelength nanodevices.
Bray, K, Regan, B, Trycz, A, Previdi, R, Seniutinas, G, Ganesan, K, Kianinia, M, Kim, S & Aharonovich, I 2018, 'Single Crystal Diamond Membranes and Photonic Resonators Containing Germanium Vacancy Color Centers', ACS Photonics, vol. 5, no. 12, pp. 4817-4822.View/Download from: UTS OPUS or Publisher's site
Copyright © 2018 American Chemical Society. Single crystal diamond membranes that host optically active emitters are highly attractive components for integrated quantum nanophotonics. In this work we demonstrate bottom-up synthesis of single crystal diamond membranes containing germanium vacancy (GeV) color centers. We employ a lift-off technique to generate the membranes and perform chemical vapor deposition in the presence of a germanium source to realize the in situ doping. Finally, we show that these membranes are suitable for engineering of photonic resonators such as microdisk cavities with quality factors of ∼1500. The robust and scalable approach to engineer single crystal diamond membranes containing emerging color centers is a promising pathway for the realization of diamond integrated quantum nanophotonic circuits on a chip.
Tran, TT, Kianinia, M, Bray, K, Kim, S, Xu, Z-Q, Gentle, A, Sontheimer, B, Bradac, C & Aharonovich, I 2017, 'Nanodiamonds with photostable, sub-gigahertz linewidth quantum emitters', APL Photonics, vol. 2, no. 11, pp. 116103-116103.View/Download from: UTS OPUS or Publisher's site
Single-photon emitters with narrow linewidths are highly sought after for applications
in quantum information processing and quantum communications. In this
letter, we report on a bright, highly polarized near infrared single photon emitter
embedded in diamond nanocrystals with a narrow, sub-GHz optical linewidth
at 10 K. The observed zero-phonon line at ∼780 nm is optically stable under low
power excitation and blue shifts as the excitation power increases. Our results highlight
the prospect for using new near infrared color centers in nanodiamonds for
Kim, S, Gong, S, Cho, J & Cho, Y 2016, 'Unidirectional emission of a site-controlled single quantum dot from a pyramidal structure', Nano Letters, vol. 16, no. 10, pp. 6117-6123.View/Download from: UTS OPUS or Publisher's site
Emission control of a quantum emitter made of semiconductor materials is of significance in various optical applications. Specifically, the realization of efficient quantum emitters is important because typical semiconductor quantum dots are associated with low extraction efficiency levels due to their high refractive index contrast. Here, we report bright and unidirectional emission from a site-controlled InGaN quantum dot formed on the apex of a silver-coated GaN nanopyramidal structure. We show that the majority of the extracted light from the quantum dot is guided toward the bottom of the pyramid with high directionality. We also demonstrate that nanopyramid structures can be detached from a substrate, thus demonstrating great potential of this structure in various applications. To clarify the directional radiation, the far-field radiation pattern is measured using Fourier microscopy. This scheme will pave the way toward the realization of a bright and unidirectional quantum emitter along with easy fabrication and large-area reproducibility
Kim, S, Ko, H, Lee, C, Kim, M, Kim, KS, Lee, Y, Shin, K & Cho, Y 2016, 'Semiconductor Photonic Nanocavity on a Paper Substrate', Advanced Materials, vol. 28, no. 44, pp. 9765-9769.View/Download from: UTS OPUS or Publisher's site
Direct integration of semiconductor photonic nanocavities with paper substrates is demonstrated for the first time. 1D photonic crystal nanocavities successfully show lasing action on paper substrates. The device has great synergy as a sensor because paper has good wicking ability while a photonic crystal cavity has high figure of merit. The research provides a platform for eco-friendly and sustainable devices.
Kim, S, Kim, H & Lee, Y 2015, 'Single nanobeam optical sensor with a high Q-factor and high sensitivity', Optics Letters, vol. 40, no. 22, pp. 5351-5354.View/Download from: UTS OPUS or Publisher's site
The miniaturization of optical sensors is essential for the realization of compact, portable, and cost-effective devices. Photonic crystal-based optical sensors, which have an ultra-small mode volume and footprint, have demonstrated remarkable recent progress in achieving a high figure-of-merit (FOM) in a sensor. Here, we report an optical sensor with a high Q-factor and high sensitivity based on a photonic crystal nanobeam using the second lowest air band-edge mode. We calculated that a nanobeam ( =3.4)(n=3.4) in a water environment ( =1.33)(n=1.33) has refractive-index sensitivity of ∼631 nm/RIU∼631 nm/RIU, while the quality factor is greater than 23,300. Accordingly, a theoretical FOM of the sensor corresponds to >9500>9500. To the best of our knowledge, experimental refractive-index sensitivity of 461 nm/RIU is the highest value among photonic crystal single nanobeam geometry. The simple geometry of uniform air hole sizes and lattice constants in the proposed nanobeam sensor allows easy fabrication and mechanical stability.
Kim, S, Kim, H, Son, J, Kim, Y, Ok, JM, Kim, KS, Jung, H, Min, B & Lee, Y 2014, 'Low-voltage-tunable nanobeam lasers immersed in liquid crystals', Optics express, vol. 22, no. 25, pp. 30707-30712.View/Download from: UTS OPUS or Publisher's site
A low-voltage-tunable one-dimensional nanobeam laser is realized by employing lithographically defined lateral electrodes. An InGaAsP nanobeam with a sub-micrometer width is transfer-printed in the middle of two electrodes using a polydimethylsiloxane stamp. Spectral tuning is achieved by controlling the molecular alignment of the surrounding liquid crystals (LCs). From μm-scale-gap structures, a total wavelength shift that exceed 6 nm is observed at a low voltage of less than 10 V. A measured spectral tuning rate of 0.87 nm/V, which is the largest value ever reported to our knowledge among LC-tuned photonic crystal lasers, was also noted.
Son, B, Kim, S, Kim, YH, Käläntär, K, Kim, H, Jeong, H, Choi, SQ, Shin, J, Jung, H & Lee, Y 2014, 'Optical vortex arrays from smectic liquid crystals', Optics express, vol. 22, no. 4, pp. 4699-4704.View/Download from: UTS OPUS or Publisher's site
We demonstrate large-area, closely-packed optical vortex arrays using self-assembled defects in smectic liquid crystals. Self-assembled smectic liquid crystals in a three-dimensional torus structure are called focal conic domains. Each FCD, having a micro-scale feature size, produces an optical vortex with consistent topological charge of 2. The spiral profile in the interferometry confirms the formation of an optical vortex, which is predicted by Jones matrix calculations.