Hyungsub Kim

Adsorption kinetics of alkanethiols studied by quartz crystal microbalance

Abstract The quartz crystal microbalance (QCM) has been employed extensively for measurement of mass changes at metal surface while the metal coated electrode is immersed in a liquid. We report the real time in-situ adsorption kinetic trends of alkanethiol CH3(CH2)n–1SH (n=8, 12, 16) monolayers with different chain lengths and solvents using QCM. Regarding 1-octanethiol monolayer formation on gold surface, we could identify the two distinct monolayer formation steps in hexane and ethanol solutions. The adsorption process of alkanethiols is characterized by two distinct steps. In the kinetically controlled initial monolayer formation step, the adsorption rate of short chain alkanethiols is faster than that of long chain alkanethiols. The second step is a thermodynamically controlled ordering and packing process. In case of short chain alkanethiols, these two separated adsorption steps were clearly observed, but in the case of long chain alkanethiols (over 10 carbon numbers) only one step of monolayer formation was observed.

Synthesis of CdS with Graphene by CBD(Chemical Bath Deposition) Method and Its Photocatalytic Activity

Synthesis of RGO (reduced graphene oxide)-CdS composite material was performed through CBD (chemical bath deposition) method in which graphene oxide served as the support and Cadmium Sulfate Hydrate as the starting material. Graphene-based semiconductor photocatalysts have attracted extensive attention due to their usefulness for environmental and energy applications. The band gap (2.4 eV) of CdS corresponds well with the spectrum of sunlight because the crystalline phase, size, morphology, specic surface area and defects, etc., of CdS can affect its photocatalytic activity. The specific surface structure (morphology) of the photocatalyst can be effective for the suppression of recombination between photogenerated electrons and holes. Graphene (GN) has unique properties such as a high value of Young`s modulus, large theoretical specific surface area, excellent thermal conductivity, high mobility of charge carriers, and good optical transmittance. These excellent properties make GN an ideal building block in nanocomposites. It can act as an excellent electron-acceptor/transport material. Therefore, the morphology, structural characterization and crystal structure were observed using various analytical tools, such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. From this analysis, it is shown that CdS particles were well dispersed uniformly in the RGO sheet. Furthermore, the photocatalytic property of the resulting RGO-CdS composite is also discussed in relation to environmental applications such as the photocatalytic degradation of pollutants. It was found that the prepared RGO-CdS nanocomposites exhibited enhanced photocatalytic activity as compared with that of CdS nanoparticles. Therefore, better efficiency of photodegradation was found for water purification applications using RGO-CdS composite.

Role of inserting layer controlling wavelength in InGaAs quantum dots

Emission wavelength from the self-assembled In(Ga)As QDs on GaAs is typically around 1.0 /spl mu/m. In order to be applied to optical fiber communication, the extension of its optical emission wavelength to 1.3 /spl mu/m and further is necessary. Several groups have demonstrated GaAs-based InGaAs QDs with 1.3 /spl mu/m photoluminescence (PL). During the formation of such ternary dots, the variation of composition and dot size make it difficult to reproducibly achieve long wavelength emission. Long emission wavelength up to 1.3 /spl mu/m at room temperature cannot be realized until the In(Ga)As dots are placed in or below and InGaAs matrix. Among the proposed origins of achieving long wavelength emission from InAs quantum dots, we believe that the residual strain in quantum dots plays a key role. In this study, we have investigated the role of inserting layers tuning emission wavelength in InGaAs quantum dots.