arXiv subjects

Mun Seok Jeong

Publications and source records attributed to Mun Seok Jeong.

4 recordsLinked to original sources

arXiv2021

Tip-induced strain, bandgap, and radiative decay engineering of a single metal halide perovskite quantum dot

Strain engineering of perovskite quantum dots (pQDs) enables widely-tunable photonic device applications. However, manipulation at the single-emitter level has never been attempted. Here, we present a tip-induced control approach combined with tip-enhanced photoluminescence (TEPL) spectroscopy to engineer strain, bandgap, and emission quantum yield of a single pQD. Single CsPbBr$_{x}$I$_{3-x}$ pQDs are clearly resolved through hyperspectral TEPL imaging with $\sim$10 nm spatial resolution. The plasmonic tip then directly applies pressure to a single pQD to facilitate a bandgap shift up to $\sim$62 meV with Purcell-enhanced PL quantum yield as high as $\sim$10$^5$ for the strain-induced pQD. Furthermore, by systematically modulating the tip-induced compressive strain of a single pQD, we achieve dynamical bandgap engineering in a reversible manner. In addition, we facilitate the quantum dot coupling for a pQD ensemble with $\sim$0.8 GPa tip pressure at the nanoscale. Our approach presents a new strategy to tune the nano-opto-electro-mechanical properties of pQDs at the single-crystal level.

physics.app-ph↗

arXiv2020

Adaptive tip-enhanced nano-spectroscopy

Tip-enhanced nano-spectroscopy and -imaging, such as tip-enhanced photoluminescence (TEPL), tip-enhanced Raman spectroscopy (TERS), and others, have become indispensable from materials science to single molecule studies. However, the techniques suffer from inconsistent performance due to lack of nanoscale control of tip apex structure, which often leads to irreproducible spectral, spatial, and polarization resolved imaging. Instead of refining tip-fabrication to resolve this problem, we pursue the inverse approach of optimizing the nano-optical vector-field at the tip apex via adaptive optics. Specifically, we demonstrate dynamic wavefront shaping of the excitation field to effectively couple light to the tip and adaptively control for enhanced sensitivity and polarization-controlled TEPL and TERS, with performance exceeding what can be achieved by conventional tip-fabrication and optimal excitation polarization. Employing a sequence feedback algorithm, we achieve 4.4$\times$10$^4$-fold TEPL enhancement of a WSe$_2$ monolayer which is >2$\times$ larger than the normal TEPL intensity without wavefront shaping, as well as the largest plasmon-enhanced PL intensity of a transition metal dichalcogenide (TMD) monolayer reported to date. In addition, with dynamical near-field polarization control in TERS, we demonstrate the investigation of conformational heterogeneity of brilliant cresyl blue (BCB) molecules as well as the controllable observation of IR-active modes due to a large gradient field effect. Adaptive tip-enhanced spectroscopy and imaging thus provides for a new systematic approach towards computational nanoscopy making optical nano-imaging more robust, versatile, and widely deployable.

physics.optics↗

arXiv2020

Radiative control of localized excitons at room temperature with an ultracompact tip-enhanced plasmonic nano-cavity

In atomically thin semiconductors, localized exciton (X$_L$) coupled to light shows single quantum emitting behaviors through radiative relaxation processes providing a new class of optical sources for potential applications in quantum communication. In most studies, however, X$_L$ photoluminescence (PL) from crystal defects has mainly been observed in cryogenic conditions because of their sub-wavelength emission region and low quantum yield at room temperature. Furthermore, engineering the radiative relaxation properties, e.g., emission region, intensity, and energy, remained challenging. Here, we present a plasmonic antenna with a triple-sharp-tips geometry to induce and control the X$_L$ emission of a WSe$_2$ monolayer (ML) at room temperature. By placing a ML crystal on the two sharp Au tips in a bowtie antenna fabricated through cascade domino lithography with a radius of curvature of <1 nm, we effectively induce tensile strain in the nanoscale region to create robust X$_L$ states. An Au tip with tip-enhanced photoluminescence (TEPL) spectroscopy is then added to the strained region to probe and control the X$_L$ emission. With TEPL enhancement of X$_L$ as high as ~10$^6$ in the triple-sharp-tips device, experimental results demonstrate the controllable X$_L$ emission in <30 nm area with a PL energy shift up to 40 meV, resolved by tip-enhanced PL and Raman imaging with <15 nm spatial resolution. Our approach provides a systematic way to control localized quantum light in 2D semiconductors offering new strategies for active quantum nano-optical devices.

physics.optics↗

arXiv2020

Static Rashba Effect by Surface Reconstruction and Photon Recycling in the Dynamic Indirect Gap of APbBr3 (A = Cs, CH3NH3) Single Crystals

Recently, halide perovskites have gained significant attention from the perspective of efficient spintronics owing to Rashba effect. This effect occurs as a consequence of strong spin-orbit coupling under noncentrosymmetric environment, which can be dynamic and/or static. However, there exist intense debates on the origin of broken inversion symmetry since the halide perovskites typically crystallize into a centrosymmetric structure. In order to clarify the issue, we examine both dynamic and static effects in the all-inorganic CsPbBr3 and organic-inorganic CH3NH3PbBr3 (MAPbBr3) perovskite single crystals by employing temperature- and polarization-dependent photoluminescence excitation spectroscopy. The perovskite single crystals manifest the dynamic effect by photon recycling in the indirect Rashba gap, causing dual peaks in the photoluminescence. But the effect vanishes in CsPbBr3 at low temperatures (< 50 K), accompanied by a striking color change of the crystal, arising presumably from lower degrees of freedom for inversion symmetry breaking associated with the thermal motion of the spherical Cs cation, compared with the polar MA cation in MAPbBr3. We also show that static Rashba effect occurs only in MAPbBr3 below 90 K due to surface reconstruction via MA-cation ordering, which likely extends across a few layers from the crystal surface to the interior. We further demonstrate that this static Rashba effect can be completely suppressed upon surface treatment with poly methyl methacrylate (PMMA) coating. We believe that our results provide a rationale for the Rashba effects in halide perovskites.

physics.app-ph↗