• Journal of the Korean Chemical Society
• /
• v.60 no.6
• /
• pp.402-409
• /
• 2016

Thin films of lead sulfide colloidal quantum dots (CQDs) of 2.8 nm in diameter are fabricated and their surfaces are passivated by 3-mercaptopropionic acid (MPA) ligand or hybrid type ($MPA+CdCl_2$) ligand, respectively. The changes in valence band electronic structure and atomic composition of each PbS CQD film upon post-treatment such as air, N2 annealing or UV/Ozone have been studied by photoelectron spectroscopy. The air annealing makes the CQD fermi level to move toward the valence band leading to "p-type doping" regardless of ligand type. The UV/Ozone post-treatment generates $Pb(OH)_2$, $PbSO_x$ and PbO on both CQD surfaces. But the amount of the PbO has been reduced in hybrid type ligand case, especially. That is probably because the extra Pb cations in (111) surface are additionally passivated by $Cl_2$ ligand, which limits the reaction between the Pb cation and ozone.

• Journal of the Korean Vacuum Society
• /
• v.22 no.2
• /
• pp.92-97
• /
• 2013

The luminescence properties of InAs/GaAs quantum dots (QDs) grown by a migration enhanced epitaxy method have been investigated by using photoluminescence (PL) and time-resolved PL measurements. The MEE method supplies materials in a series of alternate depositions with migration enhancing time between each deposition. After In source was supplied for 9.3 s, the growth was interrupted for 5 s. Subsequently, As source was open for 3 (AT3), 4(AT4), 6 (AT6), or 9 s (AT9), and the growth was interrupted for 5 s again. This growth sequence was repeated 3 times for the growth of InAs QDs. The PL peak of the AT3 was 1,140 nm and the PL intensity was very weak compared with that of the other three samples. The PL peak of all samples except the AT3 sample was 1,118 nm, which is blueshifted from 1,140 nm, and the PL intensity was increased compared to that of the AT3. These results can be explained by the increased QD density and the improved QD uniformity. The AT6 sample showed the strongest PL intensity and the narrowest full width at half maximum. The PL decay time of AT6 increased with increasing emission wavelength from 940 to 1,126 nm, reaching a maximum decay time of 1.09 ns at 1,126 nm, and then decreased as the emission wavelength was increased further.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2006.02a
• /
• pp.145-145
• /
• 2006

• Korean Chemical Engineering Research
• /
• v.59 no.3
• /
• pp.450-454
• /
• 2021

Currently, gamma nuclide analysis is mainly used using inorganic scintillators or semiconductor detectors. These detectors have high resolution but there are less economical, limited in size, and low process ability than plastic scintillators. Therefore, quantum dot-based plastic scintillator was developed using the advantages of the quantum dot nanomaterial and the conventional plastic scintillator. In this study, efficient plastic scintillator was fabricated by adding CdS/ZnS based on the most widely used Cd-based nanomaterial in a polystyrene matrix. In addition, the performance of the commercial plastic scintillator was compared and it was analyzed through radiological measurement experiments. The detection efficiency of fabricated plastic scintillator was higher than commercial plastic scintillator, EJ-200. It is believed that this fabricated plastic scintillator can be used as a radioactivity analyzer in the medical and nuclear facility fields.

• Journal of the Korean Vacuum Society
• /
• v.15 no.2
• /
• pp.201-208
• /
• 2006

Optical characteristics of InGaAs quantum dot (QD) laser structures with an Al native oxide (AlOx) layer as a current-blocking layer were studied by means of photoluminescence (PL), PL excitation, and spatially-resolved micro-PL techniques. The InGaAs QD samples were first grown by molecular-beam epitaxy (MBE), and then prepared by wet oxidation and thermal annealing techniques. For the InGaAs QD structures treated by the wet oxidation and thermal annealing processes, a broad PL emission due to the intermixing effect of the AlOx layer was observed at PL emission energy higher than that of the non-intermixed region. We observed a dominant InGaAs QD emission at about 1.1 eV in the non-oxide AlAs region, while InGaAs QD-related emissions at about 1.16 eV and $1.18{\sim}1.20eV$ were observed for the AlOx and the SiNx regions, respectively. We conclude that the intermixing effect of the InGaAs QD region under an AlOx layer is stronger than that of the InGaAs QD region under a non-oxided AlAs layer.

• Journal of the Korean Chemical Society
• /
• v.60 no.2
• /
• pp.131-136
• /
• 2016

Copper ion induced photoluminescence (PL) quenching dynamics and recovery of the PL by zinc ions were investigated for CdSe based nanocrystals. When copper ions were added, CdSe quantum dots showed fast and dramatically PL quenching whereas PL of CdSe nanorod gradually decreased. In the presence of zinc ions, the PL of CdSe/CdS (core/shell) nanocrystals that have quenched by copper ions was efficiently recovered. It showed that the PL intensity of nanocrystals increased by 50% in a solution containing 1 μM zinc ions. The PL intensity was increasing with increasing zinc ions, and could be described by Langmuir binding isotherm model. We showcase that the CdSe based nanocrystals can be used as fluorescence turn-on sensor.

• Clean Technology
• /
• v.16 no.4
• /
• pp.292-296
• /
• 2010

We fabricated quantum dot sensitized solar cells(QDSSC) using PbS as a sensitizer and measured the solar energy conversion efficiency. After growing ZnO nanowires on the substrate by low temperature ammonia solution reaction, PbS QDs were deposited on ZnO nanowires by SILAR(Successive ionic layer adsorption and reaction) method. The morphology and crystallinity of PbS/ZnO nanowires were studied by SEM and XRD. In this study, the maximum conversion efficiency of QDSSC using PbS was 0.075% at one sun, which was lower than that of QDSSC using other sensitizers. The reasons it showed relatively low efficiency are i) the probability of type-I band gap arrangement between ZnO and PbS, ii) disturbance of electron migration by the various-sized PbS band gap, iii) stability dip by the chemical reaction of PbS QDs with electrolyte. To solve these problems, researches about controlling the size distribution of PbS and new type electrolyte would be needed.

• Proceedings of the Korea Crystallographic Association Conference
• /
• 2003.11a
• /
• pp.25-26
• /
• 2003

• Electrical & Electronic Materials
• /
• v.20 no.10
• /
• pp.23-34
• /
• 2007

• Proceedings of the Korean Vacuum Society Conference
• /
• 2006.02a
• /
• pp.212-212
• /
• 2006