• Journal of Powder Materials
• /
• v.24 no.1
• /
• pp.1-5
• /
• 2017

We have investigated the washing method of as-synthesized CdSe/ZnS core/shell structure quantum dots (QDs) and the effective surface passivation method of the washed QDs using PMMA. The quantum yield (QY%) of as-synthesized QDs decreases with time, from 79.3% to 21.1%, owing to surface reaction with residual organics. The decreased QY% is restored to the QY% of as-synthesized QDs by washing. However, the QY% of washed QDs also decreases with time, owing to the absence of surface passivation layer. On the other hand, the PMMA-treated QDs maintained a relatively higher QY% after washing than that of the washed QDs that were kept in toluene solution for 30 days. Formation of the PMMA coating layer on CdSe/ZnS QD surface is confirmed by HR-TEM and FT-IR. It is found that the PMMA surface coating, when combined with washing, is useful to be applied in the storage of QDs, owing to its long-term stability.

• Korean Chemical Engineering Research
• /
• v.46 no.6
• /
• pp.1081-1086
• /
• 2008

QDs-LEDs(quantum dot light emitting device) should contain well-organized arrays of QDs on an electron transport layer. Thin films of CdSe/ZnS core-shell QDs were successfully fabricated on $TiO_2$ substrates by using PDMS stamp and micro contact printing method. 2-Carboxyethylphosphonic acid(CAPO) and 1,6-hexanedithiol(HDT) were employed as molecular linkers in assembling CdSe/ZnS core-shell QDs with high-density and uniform array. The CAPO increased the binding strength between the QDs and the substrates, and the HDT induced the strong inter-particle attractions of assembled QDs. The assembling properties of QDs thin films were characterized by SEM, AFM, optical microscope and photoluminescence spectroscope(PL).

• Fashion & Textile Research Journal
• /
• v.4 no.3
• /
• pp.266-272
• /
• 2002

This research is compared and analyzed variations of the heavy metal contents in human hairs according to treating permanent wave manipulation before and after and permanent wave agents. This is the survey of women's hairs in 19 years old. On the basis of this we would like to analyze a extend of exposing of heavy metal scientifically. Also, we would to show a basic data for the permitted limits of heavy metal to keep the healthy hair The conclusion is as follows.; Mean contents of heavy metal in hairs is 2.11 ppm (Pb), 0.25 ppm (Cd), 2.62 ppm (Ni), 256 ppm (Zn), 8.45 ppm (Cu). In reducing agents (processing lotions) of perm, 1.50 ppm (Pb), 0.03 ppm (Cd), 0.05 ppm (Ni), 15.45 ppm (Zn), 0.86 ppm (Cu) in a perm (S), 2.30 ppm (Pb), 0.05 ppm (Cd), 0.05 ppm (Ni), 13.05 ppm (Zn), 0.65 ppm (Cu) in a perm (T). In oxidizing agents (neutralizer) of perm, 1.40 ppm (Pb), 0.03 ppm (Cd), 0.09 ppm (Ni), 9.05 ppm (Zn), 0.65 ppm (Cu) in a perm (S), 1.50 ppm (Pb), 0.02 ppm (Cd), 0.16 ppm (Ni), 8.00 ppm (Zn), 0.85 ppm (Cu) in a perm (T). Mean contents of lead(Pb) didn't show significant differences according to treating cysteine perm agents, showed it according to 3 treating thioglycolic acid perm agents (p<0.05). Mean contents of cadmium(Cd) showed significant differences (p<0.001) according to 2 treating both perm agents. Mean contents of nickel (Ni) showed neither. Mean contents of zinc (Zn) showed significant differences according to 2 treating cysteine perm agents (p<0.001) and 1 treating thioglycolic acid perm agents (p<0.01). Mean contents of copper (Cu) didn't show significant differences according to treating cysteine perm agents, showed it according to 1 treating thioglycolic acid perm agents (p<0.001).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2003.05c
• /
• pp.71-74
• /
• 2003

Photoconductor for direct detection fiat-panel imager present a great materials challenge, since their requirement include high X-ray absorption, ionization and charge collection, low leakage current and large area deposition, CdTe is practical material. We report studies of detector sensitivity, That is an CdTe with $5{\mu}m$ thickness on glass. That is hybrid layer of depositting ZnS:AgCl phosphor with $100{\mu}m$ on CdTe. The leakage current of hybrid is similar to it of a-Se, but photocurrent is larger than a-Se. Both of them have high spatial resolution, but hybrid has higher sensitivity than a-Se at comparable bias voltage.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2010.05a
• /
• pp.35.1-35.1
• /
• 2010

The Cu(In,Ga)Se2(CIGS) thin film solar cells have been achieved until almost 20% efficiency by NREL. These solar cells include chemically deposited CdS as buffer layer between CIGS absorber layer and ZnO window layer. Although CIGS solar cells with CdS buffer layer show excellent performance, many groups made hard efforts to overcome its disadvantages in terms of high absorption of short wavelength, Cd hazardous element. Among Cd-free candidate materials, the CIGS thin film solar cells with Zn compound buffer layer seem to be promising with 15.2%(module by showa shell K.K.), 18.6%(small area by NREL). However, few groups were successful to report high-efficiency CIGS solar cells with Zn compound buffer layer, compared to be known how to fabricate these solar cells. Each group's chemical bah deposition (CBD) condition is seriously different. It may mean that it is not fully understood to grow high quality Zn compound thin film on the CIGS using CBD. In this study, we focused to clarify growth mechanism of chemically deposited Zn compound thin film on the CIGS, especially. Additionally, we tried to characterize junction properties with unfavorable issues, that is, slow growth rate, imperfect film coverage and minimize these issues. Early works reported that film deposition rate increased with reagent concentration and film covered whole rough CIGS surface. But they did not mention well how film growth of zinc compound evolves homogeneously or heterogeneously and what kinds of defects exist within film that can cause low solar performance. We observed sufficient correlation between growth quality and concentration of NH3 as complex agent. When NH3 concentration increased, thickness of zinc compound increased with dominant heterogeneous growth for high quality film. But the large amounts of NH3 in the solution made many particles of zinc hydroxide due to hydroxide ions. The zinc hydroxides bonded weakly to the CIGS surface have been removed at rinsing after CBD.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2015.08a
• /
• pp.191.2-191.2
• /
• 2015

Details of carrier dynamics in self-assembled quantum dots (QDs) with a particular attention to nonradiative processes are not only interesting for fundamental physics, but it is also relevant to performance of optoelectronic devices and the exploitation of nanocrystals in practical applications. In general, the possible processes in such systems can be considered as radiative relaxation, carrier transfer between dots of different dimensions, Auger nonradiactive scattering, thermal escape from the dot, and trapping in surface and/or defects states. Authors of recent studies have proposed a mechanism for the carrier dynamics of time-resolved photoluminescence CdTe (a type II-VI QDs) systems. This mechanism involves the activation of phonons mediated by electron-phonon interactions. Confinement of both electrons and holes is strongly dependent on the thermal escape process, which can include multi-longitudinal optical phonon absorption resulting from carriers trapped in QD surface defects. Furthermore, the discrete quantized energies in the QD density of states (1S, 2S, 1P, etc.) arise mainly from ${\delta}$-functions in the QDs, which are related to different orbitals. Multiple discrete transitions between well separated energy states may play a critical role in carrier dynamics at low temperature when the thermal escape processes is not available. The decay time in QD structures slightly increases with temperature due to the redistribution of the QDs into discrete levels. Among II-VI QDs, wide-gap CdZnTe QD structures characterized by large excitonic binding energies are of great interest because of their potential use in optoelectronic devices that operate in the green spectral range. Furthermore, CdZnTe layers have emerged as excellent candidates for possible fabrication of ferroelectric non-volatile flash memory. In this study, we investigated the optical properties of CdZnTe/ZnTe QDs on Si substrate grown using molecular beam epitaxy. Time-resolved and temperature-dependent PL measurements were carried out in order to investigate the temperature-dependent carrier dynamics and the activation energy of CdZnTe/ZnTe QDs on Si substrate.

• Spatial Information Research
• /
• v.10 no.2
• /
• pp.201-213
• /
• 2002

Chemical analyzes were carried out the samples from roadsides of the Gwangju city. The purpose of this research is to investigate the concentrations and distribution patterns of heavy metals due to urbanization and industrialization in the Gwangju city This study area is not significantly contaminated based on the concentrations of Cd, Cu, Fe, Mn, Pb and Zn. However, the concentrations of the chemical elements analyzed are locally higher than those of serious contamination level indicated by Ministry of environment. The dust pH is in the rage of 5.60-7.09 and was generally neutral, and there are no difference in pollution area and nonpollution area. Chemical analyses utilized are dilution by 0.1N HCl. In result of analysis by the method using 0.1N HCl, concentrations of Cd and Cu are a little high in Gwangchondong of Seo-Gu. Concentrations of Mn and Pb are a little high in Buk-Gu and Nam-gu, and Concentrations of Zn are generally higher than average of soils. Zn, in the study area, keeps polluting greatly as Zn concentration of average is 150.9ppm. All of P.I values are lower than 1, it means heavy metal pollution is not serious.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.25 no.2
• /
• pp.42-53
• /
• 2020

In this study, heavy metal in road-deposited sediments (RDS) and marine sediment around Gwangyang Bay area have been investigated to assess the pollution status of metals and to understand the environmental impact of RDS as a potential source of metal pollution. Zn concentration for <63 ㎛ size fraction was the highest (2,982 mg/kg), followed by Cr, Ni, Pb, Cu, As, Cd, and Hg. Metal concentrations in RDS increased with decreasing particle size and relatively higher concentrations were observed around the metal waste and recycling facilities. For particle size in RDS smaller than 125 ㎛, EF values indicated that Zn was very high enrichment and Cr, Cd, Pb were significant enrichment. The concentrations of metals in marine sediments were mostly below the TEL value of sediment quality guidelines of Korea. However, the Zn concentrations has increased by 30~40% compared to 2010 year. The amounts of Zn, Cd and Pb in less than 125 ㎛ fraction where heavy metals can be easily transported by stormwater runoff accounted for 54% of the total RDS. The study area was greatly affected by Zn pollution due to corrosion of Zn plating materials by traffic activity as well as artificial activities related to the container logistics at Gwangyang container terminal. The fine particles of RDS are not only easily resuspended by wind and vehicle movement, but are also transported to the surrounding environments by runoff. Therefore, further research is needed on the adverse effects on the environment and ecosystem.

• Journal of the Korean Institute of Telematics and Electronics D
• /
• v.35D no.6
• /
• pp.21-27
• /
• 1998

Electrical and optical characteristics of ZnS:Mn/ZnS:Tb multilayer TFEL devices were investigated for multi-color electroluminescent display applications. Emission spectra of M $n^{2+}$ and T $b^{3+}$ ions were observed from ZnS:Mn/ZnS:Tb multi-layer TFEL devices, and were very broad from 540 nm to 640 nm. Saturation luminance measured at 155 V was 1025 Cd/$m^2$. C-V, $Q_{t}$ - $V_{p}$ curves showed that the phosphor capacitance ( $C_{p}$ ) and the insulator capacitance ( $C_{i}$ ) were 13.5nF/$\textrm{cm}^2$ and 60 nF/$\textrm{cm}^2$, respectively. Threshold voltage( $V_{thl}$) was shown to decrease from 126 V to 93 V due to the increase of the applied voltage from 155 V to 185 V, which was attributed to the increase of the polarization charge. The equation for the calculation of the threshold voltage as a function of the applied voltage was proposed for the first time. The calculated threshold voltage agreed well with the data obtained from the measurement.t.t.t.

• Journal of Preventive Medicine and Public Health
• /
• v.21 no.2 s.24
• /
• pp.320-328
• /
• 1988

This study was carried out to investigate the heavy metal contents and their correlationship between paddy soil and brown rice near the Kum-River area. In this study, eighty soil samples and forty brown rice samples were taken from the paddy soil. The contents of heavy metals were measured by flame atomic absorption spectrophotometry. The results were as follows: 1. The average contents of soluble heavy metals in surface soil were Cd 0.19, Cu 15.31, Zn 18.10 and Pb 9.08 ppm. The average contents of soluble heavy metals in subsurface soil were Cd 0.19, Cu 14.52, Zn 17.75 and Pb 8.11 ppm. There was no statistically significant difference between the two layers. 2. The contens of Cu, Zn and Pb of Taejeon(S6) and Cd of Sinbyung(S5) in surface soil were higher than those of other areas. The contents of Cd and Cu of Taejeon(S6) and Zn and Pb of Kumnam(S3) in brown rice were higher than those of other areas and four heavy metals in soil and brown rice of Simchon(S7) were lower than those of other areas. 3. The ratio of soluble contents(Cd:Cu:Zn:Pb) in surface soil was 1:79:93:47, that of soluble contents in subsurface soil was 1:76:94:43, and that of total contents in brown rice was 1:84:294:12. 4. The correlationship of the content between soluble heavy metals in surface(0-15 cm depth) soil total heavy metals in brown rice was found to be order of Cd>Cu>Zn>Pb. The correlationship of the content between soluble heavy metals in subsurface(20-30 cm depth) soil and total heavy metals in brownricewasfoundtobeorderofcu>Cd>Zn>Pb.