• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.213-213
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• 2012

It has been known that quantum confinement effect of CdSe nanocrystal was observed by increasing the number of deposition cycle using successive ionic layer adsorption and reaction (SILAR) method. Here, we report on thermally-induced quantum confinement effect of CdSe at the given cycle number using spin-coating technology. A cation precursor solution containing $0.3\;M\;Cd(NO_3)_2{\cdot}4H_2O$ is spun onto a $TiO_2$ nanoparticulate film, which is followed by spinning an anion precursor solution containing $0.3\;M\;Na_2\;SeSO_3$ to complete one cycle. The cycle is repeated up to 10 cycles, where the spin-coated $TiO_2$ film at each cycle is heated at temperature ranging from $100^{\circ}C$ to $250^{\circ}C$. The CdSe-sensitized $TiO_2$ nanostructured film is contacted with polysulfide redox electrolyte to construct photoelectrochemical solar cell. Photovoltaic performance is significantly dependent on the heat-treatment temperature. Incident photon-to-current conversion efficiency (IPCE) increases with increasing temperature, where the onset of the absorption increases from 600 nm for the $100^{\circ}C$- to 700 nm for the $150^{\circ}C$- and to 800 nm for the $200^{\circ}C$- and the $250^{\circ}C$-heat treatment. This is an indicative of quantum size effect. According to Tauc plot, the band gap energy decreases from 2.09 eV to 1.93 eV and to 1.76 eV as the temperature increases from $100^{\circ}C$ to $150^{\circ}C$ and to $200^{\circ}C$ (also $250^{\circ}C$), respectively. In addition, the size of CdSe increases gradually from 4.4 nm to 12.8 nm as the temperature increases from $100^{\circ}C$ to $250^{\circ}C$. From the differential thermogravimetric analysis, the increased size in CdSe by increasing the temperature at the same deposition condition is found to be attributed to the increase in energy for crystallization with $dH=240cal/^{\circ}C$. Due to the thermally induced quantum confinement effect, the conversion efficiency is substantially improved from 0.48% to 1.8% with increasing the heat-treatment temperature from $100^{\circ}C$ to $200^{\circ}C$.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.93-93
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• 2010

Semiconductor nanocrystal quantum dots (NQDs) have recently attracted considerable interest for use in photovoltaics. Band gaps of NQDs can be tuned over a considerable range by varying the particle size thereby allowing enhance absorption of solar spectrum. NQDs, synthesized using colloidal routes, are solution processable and promise for a large-area fabrication. Recent advancements in multiple-exciton generation in NQD solutions have afforded possible efficiency improvements. Various architectures have attempted to utilize the NQDs in photovoltaics, such as NQD-sensitized solar cell, NQD-bulk-heterojuction solar cell and etc. Here we have fabricated CdSe NQDs with the band gap of 1.8 eV to 2.1 eV on thin-layers of p-type organic crystallites (1.61 eV) to realize a donor-acceptor type heterojuction solar cell. Simple structure as it was, we could control the interface of electrode-p-layer, and n-p-layer and monitor the following efficiency changes. Specifically, surface molecules adsorbed on the NQDs were critical to enhance the carrier transfer among the n-layer where we could verify by measuring the photo-response from the NQD layers only. Further modifying the annealing temperature after the deposition of NQDs on p-layers allowed higher conversion efficiencies in the device.

• 한국전기전자재료학회논문지
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• 제29권12호
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• pp.737-749
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• 2016

Recently perovskite materials with much cheaper cost and marvellous optoelectronic properties have been studied for next generation LED display devices overseas. Technology development trends of inorganic $CsPbX_3$(X=halogen) based LEDs (PeLEDs) with assumed high stability were investigated on literature worldwide. It was found that syntheses methods of these nanocrystals (NCs, mainly quantum dots, QDs) made great progress. A new room temperature synthesis method showed outstanding PL (photoluminescence) properties such as high quantum yield (QY), narrow emission width, storage stability comparable with, or often exceeding those of conventional hot injection method and CdSe@ZnS type inorganic colloidal QDs. PeLEDs with shell layers might be more promising, indicating urgent real research start of this solution processing technology for small businesses in Korea.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.355-355
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• 2016

There has been an explosive development of nanocrystal (NC) synthesis and application due to their composition-dependent specific properties. Despite the composition, shape, and size of NCs foremost determine their physicochemical properties, the surface state and molecule conjugation also drastically change their characteristics. To make practical use of NCs, it is a prerequisite to understand the NC surface state and the degree to which they have been modified because the reaction occurs on the interface between the NCs and the surrounding medium. We report in here an analysis method to identify conjugated ligands and their binding states on semiconductor nanocrystals based on their molecular information. Surface science techniques, such as time-of-flight secondary-ion mass spectrometry (ToF-SIMS) and FT-IR spectroscopy, are adopted based on the micro-aggregated sampling method. Typical trioctylphosphine oxide-based synthesis methods of CdSe/ZnS quantum dots (QDs) have been criticized because of the peculiar effects of impurities on the synthesis processes. Since the ToF-SIMS technique provides molecular composition evidence on the existence of certain ligands, we were able to clearly identify the n-octylphosphonic acid (OPA) as a surface ligand on CdSe/ZnS QDs. Furthermore, the complementary use of the ToF-SIMS technique with the FT-IR technique could reveals the OPA ligands' binding state as bidentate complexes.

• Journal of Dairy Science and Biotechnology
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• 제33권4호
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• pp.271-275
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• 2015

Colloidal semiconductor CdSe-ZnS core-shell nanocrystal quantum dot (Qdot) are luminescent inorganic fluorophores that show potential to overcome some of the functional limitations encountered with organic dyes in fluorescence labeling applications. Salmonella Enteritidis has emerged as a major cause of human salmonellosis worldwide since the 1980s. A rapid, specific, and sensitive method for the detection of Salmonella Enteritidis was developed using Qdot as a fluorescence marker coupled with immunomagnetic separation. Magnetic beads coated with anti-Salmonella Enteritidis antibodies were employed to selectively capture the target bacteria, and biotin-conjugated anti-Salmonella antibodies were added to form sandwich immune complexes. After magnetic separation, the immune complexes were labeled with Qdot via biotin-streptavidin conjugation, and fluorescence measurement was carried out using a fluorescence measurement system. The detection limit of the Qdot method was a Salmonella Enteritidis concentration of $10^3$ colony-forming units (CFU)/mL, whereas the conventional fluorescein isothiocyanate-based method required over $10^5CFU/mL$. The total detection time was within 2 h. In addition to the potential for general nanotechnology development, these results suggest a new rapid detection method of various pathogenic bacteria from a complex food matrix.