Temperature dependent activation energies of exciton states on a single GaAs laterally coupled-quantum-dot molecule and quantum dot

Kim Heedae 한국물리학회 2022 Current Applied Physics Vol.39 No.-

The objective of this study was to perform spectroscopy measurements of a single GaAs laterally coupled quantum dot molecule and quantum dot. Compared to photoluminescence spectra between a single GaAs laterally coupled quantum dot molecule and a single quantum dot, the presence of optical coupling was confirmed through dipole-dipole interactions in a single coupled quantum dot molecule. Based on temperature dependence measurements, weak exciton-phonon interactions (25 meV) were observed from the ground exciton state of a single GaAs laterally coupled quantum dot molecule in comparison with a strong exciton-phonon interaction (49 meV) from the ground exciton state of a single GaAs QD. Such weak interactions were due to reduced confinement at exciton states in a single laterally coupled quantum dot molecule. In addition, weaker activation energy (~15 meV) was observed in terms of confined electrons in a single laterally coupled quantum dot molecule, where a confinement effect became reduced due to enlarged dimensional area in one direction along [1 1 0].

From the Beginning, the Synthetic Strategies of the Perovskite Quantum Dots with High Quality

이채현,강동우,전병민,정지원,김경수,한동훈,박종인,윤석준 한국공업화학회 2020 한국공업화학회 연구논문 초록집 Vol.2020 No.-

Obtaining independent synthetic method for key materials of perovskite quantum dot for next-generation energy industry, are required to be localized due to Japanese export regulations. Perovskite quantum dots formed CsPbI₃-structure using synthesized and purified precursor, PbI₂. This study seeks to find correlation of the main material’s purity and the effect of perovskite quantum dot by making up a way for the main materials of the perovskite quantum dot. Quantitative analysis about the quantum dot were performed through tunneling electron microscope, X-ray diffractometer, scanning electron microscope, UV-visible absorption spectrophotometer, photoluminescence spectrophotometer, and so on. Photoluminescence quantum yield and stability measurements were able to inform that the correlation between purity of the materials and the performance of quantum dots. As a result, as the materials were refined, the performance of the quantum dots were improved.

Feasibility Study of Synthesizing Graphene Quantum Dots From the Spent Resin in a Nuclear Power Plant

Seungbin Yoon,Woo Nyun Choi,Jaehoon Byun,Hee Reyoung Kim 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.1

The feasibility study of synthesizing graphene quantum dots from spent resin, which is used in nuclear power plants to purify the liquid radioactive waste, was conducted. Owing to radiation safety and regulatory issues, an uncontaminated ion-exchange resin, IRN150 H/OH, prior to its use in a nuclear power plant, was used as the material of experiment on synthesis of graphene quantum dots. Since the major radionuclides in spent resin are treated by thermal decomposition, prior to conducting the experiment, carbonization of ion-exchange resin was performed. The experiment on synthesis of graphene quantum dots was conducted according to the general hydrothermal/solvothermal synthesis method as follows. The carbonized ion-exchange resin was added to a solution, which is a mixture of sulfuric acid and nitric acid in ratio of 3:1, and graphene quantum dots were synthesized at 115°C for 48 hours. After synthesizing, procedure, such as purifying, filtering, evaporating were conducted to remove residual acid from the graphene quantum dots. After freeze-drying which is the last procedure, the graphene quantum dots were obtained. The obtained graphene quantum dots were characterized using atomic force microscopy (AFM), Fourier-transform infrared (FT-IR) spectroscopy and Raman spectroscopy. The AFM image demonstrates the topographic morphology of obtained graphene quantum dots, the heights of which range from 0.4 to 3 nm, corresponding to 1–4 graphene layers, and the step height is approximately 2–2.5 nm. Using FT-IR, the functional groups in obtained graphene quantum dots were detected. The stretching vibrations of hydroxyl group at 3,420 cm?1, carboxylic acid (C=O) at 1,751 cm?1, C-OH at 1,445 cm?1, and C-O at 1,054 cm?1. The identified functional groups of obtained graphene quantum dots matched the functional groups which are present if it is a graphene quantum dot. In Raman spectrum, the D and G peaks, which are the characteristics of graphene quantum dots, were detected at wavenumbers of 1,380 cm?1 and 1,580 cm?1, respectively. Thus, it was verified that the graphene quantum dots could be successfully synthesized from the ionexchange resin.

Emission of CdSe quantum dots according to the capping ligands

Lee, M.J.,Lee, J.,Yang, H.S.,Hong, K.S. Elsevier 2017 Current Applied Physics Vol.17 No.6

<P>Quantum dot nanocrystals have particular optical properties due to the quantum confinement effect and the surface effect. This study focuses on the effects of organic materials capping quantum dot on the emission properties of quantum dots. The quantum dots prepared by using 1-hexadecylamine in the synthesis show strong emission, while the quantum dots prepared by using tri-octylphosphine oxide exhibit a suppressed emission and an extra emission related with the surface energy traps. These organic materials cap the quantum dots and make the surface conditions of quantum dots different. TEM images and X-ray diffraction patterns reveal that 1-hexadecylamine constructs a layer on the surface of quantum dot during the synthesis and this surface passivation by a layer of 1-hexadecylamine reduces the surface energy traps. Differently from 1-hexadecylamine, tri-octylphosphine oxide dangles from the surface, which causes a poorly passivated surface. This generates the surface deep trap levels giving rise to a significant and broad emission in the lower energy regime. The optical mechanism is studied by measuring the emission spectra and the time-resolved spectra at various temperatures from 4 K to 300 K. (C) 2017 Elsevier B.V. All rights reserved.</P>

Shape ellipticity dependence of exciton fine levels and optical nonlinearities in CdSe and CdTe nanocrystal quantum dots

양하늬,김광석 한국광학회 2019 Current Optics and Photonics Vol.3 No.2

Shape ellipticity dependence of the exciton fine energy levels in CdTe and CdSe nanocrystal quantum dots were compared theoretically by considering the crystal structure and the Coulomb interaction of an electron and a hole. While quantum dot ellipticity changes from an oblate to prolate quantum dot via spherical shape, both the fine energy levels and the dipole moment in wurtzite structure of a CdSe quantum dot change linearly for ellipticity. In contrast, CdTe quantum dots were found to show a level crossing between the bright and dark exciton states with a significant change of the dipole moment due to the cubic structure. Shape ellipticity dependence of the optical nonlinearities in CdTe and CdSe nanocrystal quantum dots was also calculated by using semiconductor Bloch equations. For a spherical shape quantum dot, only 1 L dominates the optical nonlinearities in a CdSe quantum dot, but both 1 U and 0 U contribute in a CdTe quantum dot. As excitation pulse area becomes strong (~π), the optical nonlinearities of both CdSe and CdTe quantum dots are mainly governed by absorption saturation. However, in the case of a prolate CdTe quantum dot, the real part of the nonlinear refractive index becomes relatively significant.

Electron Transport in a Multiple Quantum Dot: Recent Progress

정윤철,최주호,H.-S. Sim 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.72 No.12

A multiple quantum dot provides an experimental tool for manipulating and detecting many-body quantum states of electrons in a level of controlling parameters of the corresponding Hamiltonians. We review recent experimental and theoretical studies on many-body states of electrons with orbital or charge degrees of freedom in multiple quantum dot systems and the resulting electron transport, focusing on triple quantum dots. This review article covers experimental backgrounds of quantum dots, orbital states and the resulting Kondo effects in a double quantum dot, charge frustration in a triple quantum dot, charge Kondo effects in a triple quantum dot, and quantum entanglement in electron states of quantum dots.

양자점 뭉쳐진 나노 와이어 제작을 위한 나노피펫-AFM을 이용한 3D프린팅 기술 소개

배연주(Yeonju Bae),안상민(Sangmin An) 한국물리학회 2024 새물리 Vol.74 No.1

In this study, we would like to introduce a 3D printing technology on the nanoscale that utilizes nanophotonics and a modified atomic force microscope (AFM) for the assembly of quantum dots. Quantum dots are semiconductor nanostructures with zero-dimensional crystal structures at the nanometer scale, exhibiting unique optical properties due to quantum confinement effects. These quantum dots, with sizes on the order of a few nanometers, have garnered significant attention in various optical fields. By printing these quantum dots onto 2D materials or other substrates in desired shapes, we open up possibilities for controlling their energy structures and utilizing them in various ways. In this technology, we inject a quantum dot solution into the nanophotonic tip and use an AFM to precisely deposit the quantum dots at desired locations and shapes. In the initial stages of this technology, we achieve this by ejecting the quantum dot solution onto the surface through the holes in the nanophotonic tip. Simultaneously, as we retract the nanophotonic tip vertically, the liquid containing quantum dots evaporates, leading to the formation of bundled quantum dot nanowires. This innovative approach holds promise for a wide range of applications where precise manipulation of quantum dots at the nanoscale is crucial.

Emission of CdSe quantum dots according to the capping ligands

이민정,이재원,양호순,홍경수 한국물리학회 2017 Current Applied Physics Vol.17 No.6

Quantum dot nanocrystals have particular optical properties due to the quantum confinement effect and the surface effect. This study focuses on the effects of organic materials capping quantum dot on the emission properties of quantum dots. The quantum dots prepared by using 1-hexadecylamine in the synthesis show strong emission, while the quantum dots prepared by using tri-octylphosphine oxide exhibit a suppressed emission and an extra emission related with the surface energy traps. These organic materials cap the quantum dots and make the surface conditions of quantum dots different. TEM images and X-ray diffraction patterns reveal that 1-hexadecylamine constructs a layer on the surface of quantum dot during the synthesis and this surface passivation by a layer of 1-hexadecylamine reduces the surface energy traps. Differently from 1-hexadecylamine, tri-octylphosphine oxide dangles from the surface, which causes a poorly passivated surface. This generates the surface deep trap levels giving rise to a significant and broad emission in the lower energy regime. The optical mechanism is studied by measuring the emission spectra and the time-resolved spectra at various temperatures from 4 K to 300 K.

Injection 온도 및 합성시간에 따른 CdSe 양자점 합성 및 특성

엄누시아,김택수,좌용호,김범성,Eom, Nu-Si-A,Kim, Taek-Soo,Choa, Yong-Ho,Kim, Bum-Sung 한국재료학회 2012 한국재료학회지 Vol.22 No.3

Compared with bulk material, quantum dots have received increasing attention due to their fascinating physical properties, including optical and electronic properties, which are due to the quantum confinement effect. Especially, Luminescent CdSe quantum dots have been highly investigated due to their tunable size-dependent photoluminescence across the visible spectrum. They are of great interest for technical applications such as light-emitting devices, lasers, and fluorescent labels. In particular, quantum dot-based light-emitting diodes emit high luminance. Quantum dots have very high luminescence properties because of their absorption coefficient and quantum efficiency, which are higher than those of typical dyes. CdSe quantum dots were synthesized as a function of the synthesis time and synthesis temperature. The photoluminescence properties were found strongly to depend on the reaction time and the temperature due to the core size changing. It was also observed that the photoluminescence intensity is decreased with the synthesis time due to the temperature dependence of the band gap. The wavelength of the synthesized quantum dots was about 550-700 nm and the intensity of the photoluminescence increased about 22~70%. After the CdSe quantum dots were synthesized, the particles were found to have grown until reaching a saturated concentration as time increased. Red shift occurred because of the particle growth. The microstructure and phase developments were measured by transmission electron microscopy (TEM) and X-ray diffractometry (XRD), respectively.

Efficient Quantum Dot−Quantum Dot and Quantum Dot−Dye Energy Transfer in Biotemplated Assemblies

Achermann, Marc,Jeong, Sohee,Balet, Laurent,Montano, Gabriel A.,Hollingsworth, Jennifer A. American Chemical Society 2011 ACS NANO Vol.5 No.3

<P>CdSe semiconductor nanocrystal quantum dots are assembled into nanowire-like arrays employing microtubule fibers as nanoscale molecular “scaffolds.” Spectrally and time-resolved energy-transfer analysis is used to assess the assembly of the nanoparticles into the hybrid inorganic biomolecular structure. Specifically, we demonstrate that a comprehensive study of energy transfer between quantum dot pairs on the biotemplate and, alternatively, between quantum dots and molecular dyes embedded in the microtubule scaffold comprises a powerful spectroscopic tool for evaluating the assembly process. In addition to revealing the extent to which assembly has occurred, the approach allows determination of particle-to-particle (and particle-to-dye) distances within the biomediated array. Significantly, the characterization is realized <I>in situ</I>, without need for further sample workup or risk of disturbing the solution-phase constructs. Furthermore, we find that the assemblies prepared in this way exhibit efficient quantum dot−quantum dot and quantum dot−dye energy transfer that affords faster energy-transfer rates compared to densely packed quantum dot arrays on planar substrates and to small-molecule-mediated quantum dot−dye couples, respectively.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2011/ancac3.2011.5.issue-3/nn102365v/production/images/medium/nn-2010-02365v_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn102365v'>ACS Electronic Supporting Info</A></P>