Search

We investigated the photophysical interactions between CdSe/CdS quantum dots (QDs) and a conjugated polymer (CP, P3HT). The photoluminescence intensity of P3HT in the QDs/P3HT hybrid system is sign...

In a tip-enhanced Raman spectroscopy (TERS) system, using a sharp nanotip that comprises a noble metal is critical to attaining high spatial resolution and highly enhanced Raman scattering. A strongly acidic solution is typically used to fabricate gold nanotips in a quick and reliable manner. However, using an acidic solution could corrode the etching system, thereby posing hazardous problems. Therefore, both the corrosion of the etching system and human error induced by the conventional method considerably decrease the quality and reproducibility of the tip. In this study, we significantly increased the reproducibility of tip fabrication by automating the electrochemical etching system. In addition, we optimized the etching conditions for an etchant that comprised a KCl solution to which ethanol was added to overcome the limitations of the acidic etchant. The automated etching system significantly increases the yield rate of tip-fabrication reproducibility from 65 to 95%. The standard deviation of the radius of curvature decreased to 7.3 nm with an average radius of curvature of 30 nm. Accordingly, the automated electrochemical etching system might improve the efficiency of TERS.

Thermal properties, such as thermal conductivity, heat capacity, and melting temperature, influence the efficiency and stability of two-dimensional (2D) material applications. However, existing studies on thermal characteristics—except for thermal conductivity—are insufficient for 2D materials. Here, we investigated the melting temperature of 2D Tellurium (2D Te) using the nano-thermal analysis technique and found anomalous behavior that occurs before the melting temperature is reached. The theoretical calculations present surface pre-melting in 2D Te and Raman scattering measurements suggest that defects in 2D Te accelerate surface pre-melting. Understanding the pre-melting surface characteristics of 2D Te will provide valuable information for practical applications.

We investigated the photophysical interaction between a conjugated polymer (CP) and a plasmonic gold nanoparticle (Au NP) using transient absorption spectroscopy. We prepared a hybrid system contai...

We demonstrated an effective poly(p-chloro-xylylene) (Parylene-C) encapsulation method for MAPbI3 solar cells. By structural and optical analysis, we confirmed that Parylene-C efficiently slowed the decomposition reaction in MAPbI3. From a water permeability test with different encapsulating materials, we found that Parylene-C-coated MAPbI3 perovskite was successfully passivated from reaction with water, owing to the hydrophobic behavior of Parylene-C. As a result, the Parylene-C-coated MAPbI3 solar cells showed better device stability than uncoated cells, virtually maintaining the initial power conversion efficiency value (15.5 ± 0.3%) for 196 h.

Methylammonium lead halide (MAPbI3) perovskites are considered as promising materials owing to their excellent optical and electrical properties. However, perovskite materials suffer from degradation in air, which limits their practical applications. Here, we demonstrate successful passivation of the MAPbI3 photodetectors through monochloro-para-xylylene (Parylene-C) deposition. The time-dependent photocurrent characteristics were systematically investigated, and we achieved significantly improved device performance and stability with Parylene-C passivation. Based on the excitation-power-dependent photoluminescence (PL) data, we confirmed that Parylene-C can reduce the carrier losses in MAPbI3, leading to the enhancement of photocurrent and PL in MAPbI3 photodetectors.

Hybrid organic–inorganic lead halide perovskites have recorded unprecedented improvement in efficiency as fourth-generation photovoltaic materials. Recently, they have attracted enormous interest in nonlinear optics stemming basically from their excellent optoelectronic properties. Here, we investigate multiphoton absorption (MPA) in high-quality MAPbX3 (MA = CH3NH3 and X = Cl, Br, I) bulk single crystals synthesized by an inverse-temperature crystallization (ITC) method. The two-photon absorption (2PA) coefficients under picosecond pulse excitation are determined to be β = 23 ± 2 cm/GW and 9 ± 1 cm/GW for MAPbI3 and MAPbBr3 at λ = 1064 nm, and 13 ± 2 cm/GW for MAPbCl3 at λ = 532 nm. The 2PA coefficients are comparable to those of conventional semiconductors having similar bandgaps and can be explained by a two-band model. Furthermore, we characterize the three-photon absorption behavior of MAPbCl3 at λ = 1064 nm, yielding γ = 0.05 ± 0.01 cm3/GW2. The polarization dependence of MPA is also probed to exper...

Understanding the photophysical interactions between the components in organic-inorganic nanocomposites is a key factor for their efficient application in optoelectronic devices. In particular, the photophysical study of nanocomposites based on organic conjugated polymers is rare. We investigated the effect of surface plasmon resonance (SPR) of gold nanoparticles (Au NPs) on the photoluminescence (PL) property of a push-pull conjugated polymer (PBDB-T). We prepared the hybrid system by incorporating poly(3-hexylthiophene)-stabilized Au NPs (P3HT-Au NPs) into PBDB-T. The enhanced and blueshifted PL was observed in the hybrid system compared to PL in a neat PBDB-T system, indicating that the P3HT chains attached to the Au NPs suppressed charge-transfer from PBDB-T to the Au NPs and relayed the hot electrons to PBDB-T (the band-filling effect). This photophysical phenomenon limited the auto-dissociation of PBDB-T excitons. Thus, the radiative recombination of the excitons occurred more in our hybrid system than in the neat system.

Despite the symbolism of TiO2 in photoelectrochemistry, its fundamental nanoscale properties in oxidation reaction have often reported inconsistent results. We demonstrated the simple model of TiO2 thin films (TFs) for photoelectrochemical (PEC) oxidation reaction (OR) of water, which is constituted of Indium Tin Oxide (ITO) and TiO2 TFs, by depositing it directly onto ITO coated glass substrates through Atomic Layer Deposition (ALD). Using ALD with a sub-nanometer thickness control, 9 to 90 nm in thickness (200 to 2000 in no. of ALD cycles) of TiO2 TFs were fabricated and annealed for crystallization into anatase phase. Anatase TiO2 TF photoanodes showed an optimum PEC OR performance at the thickness of 45 nm (corresponding to around 1000 ALD cycles) in the electrolyte solution of 0.1 M NaOH (pH = 12.9) under UV light illumination of 365 nm in wavelength. Different thicknesses of TiO2 TFs were characterized by electrochemical and optical measurements. Increasing bulk traps in TiO2 TFs up to the critical thickness improved charge transfer and PEC OR by increasing holes’ lifetime. However, it was found to be detrimental when it became dominant along with the increase of TFs’ thickness. This work provides insight in designing highly efficient TiO2 photoelectrodes with the precisely controlled thickness that can have a significant effect on charge transfer kinetics and thus PEC performances.

Molybdenum disulfide (MoS2) is rapidly emerging in a wide range of applications owing to its superior optical, electrical, and catalytic properties. In particular, aside from the current great interest in monolayer MoS2, MoS2 quantum dots (QDs) have received much attention in the electronics and optoelectronics fields owing to their inherent electrical and optical properties arising from the quantum confinement effect. Thus, various methods for producing MoS2 QDs, such as exfoliation, substrate growth, and colloidal synthesis, have been attempted. In this study, the method for manufacturing MoS2 QD with a size of 10 nm which is simpler than the conventional method was devised. On the basis of characterization of the prepared MoS2 QD samples, resistive switching devices was fabricated. These devices demonstrated stable unipolar resistive switching behavior without an electroforming process. This study provides a new approach for the mass production of MoS2 QD and one of their potential applications.

In this work, intermetallic compound (IMC) growth behavior in Au stud/Sn/Cu pillar bumps was investigated under annealing and current stressing conditions. AuSn2 and AuSn4 IMCs formed at the interface between the Au studs and Sn after bonding. The AuSn2 phase grew significantly as the stressing time increased, causing micro-voids to form near the (Cu, Au)6Sn5, AuSn2 and AuSn4 IMC interfaces. The interfacial reactions resulting from current stressing took place quicker than observed for pure annealing. The apparent activation energies for the growth of the AuSn2 phase during annealing and current stressing were 0.52 eV and 0.47 eV, respectively, which may be closely related to the acceleration of the interfacial reaction by electron wind forces during current stressing.

Thermal barrier coating. Thermal fatigue. Exposure time. Thermal fatigue test is one of the most widely used method to evaluate the durability of thermal barrier coating (TBC). However, thermal fatigue test can be concluded in totally different results according to the test variations. Especially, Exposure time of thermal fatigue test can affect the delamination life cycle of TBC. In this study, using the same test equipment which Kim et al. used, thermal fatigue tests were performed with different holding time at high temperature, and the test results by Kim et al. and those by this study were compared. In addition, delamination map was come to perfection from the test results to define more accurate thermal fatigue life.

TBCs (Thermal Barrier Coatings) are one technique for assuring appropriate endurance in extreme environments. DVC coating is a type of TBC that is applied by the insertion of artificial vertical cracks in a TBC to reduce the possibility of coating fracture. This study evaluates the influence crack depth and the distance between cracks, which are the main parameters of DVC coating, by FEM (Finite Element Method).

The effects of surface finishes on the in situ interfacial reaction characteristics of ball grid array (BGA) Sn-3.0Ag-0.5Cu lead-free solder bumps were investigated under annealing and electromigration (EM) test conditions of 130°C to 175°C with 5.0 × 103 A/cm2. During reflow and annealing, (Cu,Ni)6Sn5 intermetallic compound (IMC) formed at the interface of electroless nickel immersion gold (ENIG) finish. In the case of both immersion Sn and organic solderability preservative (OSP) finishes, Cu6Sn5 and Cu3Sn IMCs formed. Overall, the IMC growth velocity of ENIG was much lower than that of the other finishes. The activation energies of total IMCs were found to be 0.52 eV for ENIG, 0.78 eV for immersion Sn, and 0.72 eV for OSP. The ENIG finish appeared to present an effective diffusion barrier between the Cu substrate and the solder, which leads to better EM reliability in comparison with Cu-based pad systems. The failure mechanisms were explored in detail via in situ EM tests.

In-situ annealing tests of Cu/Ni/Au/Sn-Ag/Cu micro-bump for 3D IC package were performed in an scanning electron microscope chamber at in order to investigate the growth kinetics of intermetallic compound (IMC). The IMC growth behaviors of both and follow linear relationship with the square root of the annealing time, which could be understood by the dominant diffusion mechanism. Two IMC phases with slightly different compositions, that is, and formed at Cu/solder interface after bonding and grew with increased annealing time. By the way, and phases formed at the interfaces between and Ni/Sn, respectively, and both grew with increased annealing time. The activation energies for and IMC growths during annealing were 0.69 and 0.84 eV, respectively, where Ni layer seems to serve as diffusion barrier for extensive Cu-Sn IMC formation which is expected to contribute to the improvement of electrical reliability of micro-bump.

Ball shear test was performed by test variables such as loading speed and annealing time in order to investigate the effect of surface finishes on the bonding strength of Sn-1.2Ag-0.7Cu-0.4In Pb-free solder. The shear strength increased and the ductility decreased with increasing shear speed. With increasing shear speed, the electroless nickel immersion gold (ENIG) finish showed dominant brittle fracture mode, while organic solderability preservative (OSP) finish showed pad open fracture mode. The shear strength and toughness for both surface finishes decreased with increasing annealing time under the high-speed shear test of 500 mm/s. Typically, the thickness of intermetallic compound increased with increasing annealing time, which means that exposure of brittle fracture became much easier. With increasing annealing time, the both ENIG and OSP finishes exhibited the pad open fracture mode. Overall, ENIG finish showed higher shear strength rather than OSP finish due to its superior barrier stability.

Context-awareness as a key technology of ubiquitous computing n eeds a context model that understands and processes situational information coming f rom diverse sensors and devices, and can be applied diversely in various domains. Seman tic web based ontologies use structured standard format and express meaning of informati on, so it is possible to recognize effectively context-awareness situations, allowing th e system to share information and understand situation by inference. In this paper, we propos e a layered ontology model to support generality and scaleability of the context-awareness system, and applied the model to u-Convention domain. In addition, we propose a effecti ve reasoning method to handle compound situation by combining OWL-DL and SWRL rules.키워드: 유비쿼터스 컴퓨팅, 온톨로지, 시맨틱 웹, 온톨로지 기반 상황인지, 상황인지 모델링ubiquitous computing, ontology, semantic web, ontology-based context-awareness, context modeling * 숙명여자대학교 문헌정보학과 교수(ksh@sookmyung.ac.kr) ￭￭ 논문접수일자:2011년 5월 17일 ￭ 최초심사일자:2011년 5월 24일

This paper is concerned with formability of AZ31B magnesium alloy sheets at various temperatures. In order to acquire the forming limit curve for quantifying the formability of the magnesium alloy sheet, hemispherical punch forming tests are performed under various temperatures. The initial shape of the blank is rectangular and six different types of specimens are used with their length along the rolling direction of 175mm and widths along the transverse direction of 25, 50, 75, 100, 120 and 175mm. With the equipment of on a SIMADZU 100-ton universal testing machine, hemispherical punch forming tests are performed and a forming limit diagram is constructed at the temperature of 100°C, 200°C and 250°C. FE analyses of hemispherical punch forming tests are also conducted by considering ductile failure model in order to compare the forming limit curve obtained from the experiment and numerical analysis. The comparison examines problems in the current material model and it suggests a future research direction.

This paper is studied in order to develop the models that are appropriate for the procurement of electronic books at the school libraries. To develop the model, the following factors were reviewed: the characteristics of an electronic book, the factor analysis that affect the electronic book price, use case, environment, the role of government for the price decision model and procurement method. The models were proposed based on the above analysis and review. In addition, the proposed models reflect various opinions that the school libraries can apply.

This study examines how the lifestyle of senior citizens affects their choices of retirement communities. A survey was conducted among 256 potential customers of elderly housing, targeting citizens over 45 years old who were residents of Seoul, the capital city of Korea, at the time of the survey. Findings reveal that most respondents preferred a location based in proximity to Seoul, convenience to the suburbs, a pleasant surrounding environment, and physical equipment and facilities. Medical services and community services were also found to have an impact on preference for residency. Canonical correlation analysis between the factors of elderly lifestyle and selection attribute factors of senior housing facilities demonstrates various significant relationships with implications for developers.

The casino industry for foreign visitors has been used as a tool of economic development in Korea. The objective of the current study was to examine cultural elements of the interaction between casino workers and guests at Korea's largest casino, the Walker Hill Casino located in Seoul. The guests were grouped into five major cultural groups: Japanese, Korean residents abroad, Chinese (Mainland Chinese, Taiwanese, Hong Kong Chinese), Westerners (US citizens and Europeans), and others (mainly Sri Lankan, Philippine, Bangladeshi, Thai and Malaysian). Based on casino employees’ perceptions significant differences were observed on all 28 items of behaviours of casino customers from the five cultural groupings. As a result, it is apparent that cultural differences will have a range of implications for management including marketing, training of staff and service provision for guests.

This study is to propose the model of Digital Document Information Center at KISTI which is a representative center of science, technology and industry information in Korea. The model proposed at this study is reflected current information environment such as digitalization, Internet and various internal and external situations. Also, the study is proposed the medium and long range plans for the center.

An electronic book (eBook) has quite a few advantages over a paper-based book. However, several technical problems have not been solved until now in spite of the growing interest in eBooks, eBook industries are using different document formats with the result of difficulty in exchanging and sharing eBook contents and reinvestment in developing the related software. The US and Japan have realized the importance of a standard document format for eBooks, so they have developed the Open eBook Publication Structure (OEB PS) and JepaX, respectively, with the support from government agencies and related industries. Recently, the Electronic Book of Korea (EBK) has established a working group and developed a standard format based on the eXtensible Markup Language (XML) for eBooks. The goals of the standard include the explicit exchange of eBook contents reflecting the characteristics of the Korean publishing environment, simplicity in creation and exchangeability with the related formats. The standard supports the logical structure of various document classes as well as advanced style control such as vertical writing and multi-column editing based on XSL.

The effects of surface finishes on the in situ interfacial reaction characteristics on both ball grid array (BGA) typed Sn-3.5Ag and Sn-0.7Cu lead-free solder bumps were investigated under annealing and electromigration (EM) test conditions of 135 °C to 170°C with 5.0 × 103 A/cm2. The failure mechanisms were explored in detail via in-situ EM tests. For the shear test, the shear force of both Sn-3.5Ag and Sn-0.7Cu solder joints increased and the shear energy decreased with increasing shear speed for the high speed of 1000 mm/s.