SunHyung Lee

Growth of well-developed sodium tantalate crystals from a sodium chloride flux

Well-developed cubic crystals of NaTaO3 and NaTaO3 : La were successfully grown by cooling an NaCl flux at 650–1000 °C. Colourless and transparent NaTaO3 and NaTaO3 : La crystals were obtained from relatively low-temperature solutions containing 20 mol% solute, with a smallest average size of 0.18 μm. The crystal sizes and forms were highly dependent on the holding temperature, cooling rate, and starting composition. In particular, when La2O3 powders were added to the starting compositions, NaTaO3 : La crystals with a very unique surface morphology were grown from the NaCl flux. Additionally, the average size of the NaTaO3 : La crystals decreased dramatically when compared with that of the NaTaO3 crystals prepared under the same conditions. Furthermore, the NaTaO3 and NaTaO3 : La crystals exhibited high dye photodegradation activity. These results demonstrate that NaCl is adequate for synthesizing high quality and well-developed tantalate crystals.

Highly crystalline niobium oxide converted from flux-grown K4Nb6O17 crystals

Highly crystalline niobium oxide (Nb2O5) nanotubes without defects such as bent and node were successfully prepared by a two-step process. The first step entails making high quality, layered K4Nb6O17 crystals as a precursor material. In this study, well-developed, highly crystalline, layered K4Nb6O17 crystals were readily grown by the rapid cooling of a KCl flux at a holding temperature of 800 °C and a cooling rate of 300 °C h−1. The grown layered crystals of K4Nb6O17 were transparent-colorless and had a median diameter of 530 nm. They were plate-like with well-developed faces. The second step is to transform the layered K4Nb6O17 crystals into highly crystalline Nb2O5nanotubes. In order to make the nanotubes, an intercalation–exfoliation process using tetra(n-butyl)ammonium hydroxide (TBA+OH−) aqueous solution was carried out, and highly crystalline Nb2O5nanotubes having a uniform diameter were successfully fabricated in this medhod. The crystallinity, uniformity and size (diameter and length) of nanotubes were significantly dependent on those of the precursor crystals. The flux-grown crystals, therefore, played a very important role in the nanotube fabrication. The average length and outer diameter were, respectively, about 100–500 nm and 15–25 nm. The photocatalytic properties of the layered K4Nb6O17 crystals and the Nb2O5nanotubes were basically almost the same, although their Brunauer–Emmett–Teller (BET) surface areas were quite different from each other. The BET surface area of the Nb2O5nanotubes (108.71 m2 g−1) was ca 20 times larger than that of the layered K4Nb6O17 crystals (5.14 m2 g−1). As compared with the flux-grown K4Nb6O17 crystals, the Nb2O5nanotubes exhibited high photocatalytic activity for the photodegradation of trichloroethylene. The grown layered K4Nb6O17 crystals and Nb2O5nanotubes were investigated thoroughly by means of field emission scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction analysis, energy-dispersive X-ray spectrometry, BET surface area and pore size distribution analysis, and spectrophotometry.

Reversible nanochemical conversion

Local chemical conversion of an organic surface that consists of a surface-confined monolayer is demonstrated in a reversible manner based on electrochemical reactions induced beneath a conductive probe tip of an atomic force microscope. The monolayer was prepared by a self-assembling technique from the precursor, p-aminophenyltrimethoxysilane. The chemical state of this self-assembled monolayer was regulated by probe-tip scanning with a bias voltage applied between the tip and substrate. With a positive substrate bias scanning, the monolayer surface was oxidized to be nitroso-terminated. With a negative bias scanning, this monolayer could be amino-terminated. These oxidation and reduction processes could be reversibly repeated.

The growth of highly crystalline, idiomorphic potassium titanoniobate crystals by the cooling of a potassium chloride flux

Highly crystalline, well-developed potassium titanoniobate (KTiNbO5 and KTi3NbO9) crystals were successfully grown at temperatures ranging from 700 to 1000 °C by a KCl flux cooling method. Colourless and transparent KTiNbO5 crystals with a smallest average size of 750 nm were grown at a relatively low temperature of 700 °C. The sizes of grown crystals were observed to greatly dependent on the holding temperature and solute concentration. HRTEM observations indicated that the flux-grown KTiNbO5 crystals were of high quality. The band gap energies of the fabricated KTiNbO5 and KTi3NbO9 crystals, as estimated from their absorption edges in UV-vis diffuse reflectance spectra, were approximately 3.54 and 3.35 eV, respectively. Furthermore, these crystals exhibited good photocatalytic activities under UV light irradiation. The photodecomposition of TCE gas occurred via a photocatalytic process under UV light irradiation. This study demonstrates that KCl flux cooling is an environmentally friendly and nature-mimetic process for growing high-quality, well-developed, and photocatalytic KTiNbO5 and KTi3NbO9 crystals.

Exploration of the chemical bonding forms of alkoxy-type organic monolayers directly attached to silicon

Alkoxy-type organic monolayers on hydrogen-terminated silicon were prepared from 1-undecanol (UN), 1-nonanol (NO), 1-heptanol (HP), and 4-phenylphenenol (PP). These monolayers were characterized based on x-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). XPS spectra showed that the lowest amount of SiOx oxide on the sample of the UN monolayer. On the other hand, a SiOx peak was clearly observed for the HP, NO, and PP monolayers. The generation of SiOx in the PP monolayer may have been due to steric hindrance of the aromatic rings. The–CH2–region in the FT-IR spectra showed that shorter alkyl chains promoted the formation of gauche conformers in the monolayer. This increase of gauche conformers was determined to have caused the generation of SiOx in the alkyl monolayers.

Selective growth of highly crystalline hydroxyapatite in a micro-reaction cell of agar gel

High quality, idiomorphic hydroxyapatite (HAp) nanocrystals were directly, selectively and successfully grown on the hydrophobic/hydrophilic patterned surface via gel method. The patterned agar gel acted successfully as the micro reaction cell between raw materials. The HAp nanocrystals densely covered the hydrophilic surface, but their shape depended greatly on growth period. After 20 d growth, they were highly crystalline and well developed, and their crystal shape changed to form the one-dimensional (1-D) structure. Furthermore, idiomorphic, hexagonal cylindrical HAp nanocrystals were obtained after annealing at 600 °C for 5 h. It is expected to become considerably important in researching the direct growth/patterning of biocrystals.

Scanning Probe Lithography on Organic Monolayers

Lithographic technologies for the surface modification of inorganic and organic surfaces have been developed for various devices such as sensing, data memory, single molecule electronics and biological systems. Nano and micropatterning of organic monolayers have attracted attentions for applications to biological systems in which proteins or DNA are fixed. Photolithography, microcontact printing, and electron beam lithography have usually been used as patterning techniques for organic monolayers (Hayashi et al., 2002; Hong et al., 2003; Saito et al., 2003; Hahn et al., 2004; Kidoaki & Matsuda, 1999). Although the electronbeam lithography can fabricate very small patterns, it requires an ultra-high vacuum system (Harnett et al., 2001). The resolution of photolithography is limited by the light wavelength. Moreover, these methods are based on destructive lithography, i.e., they cause damages to the organic materials. In particular, nano-lithographic technologies have evolved in order to satisfy persistent demands for miniaturization and high-density integration of semiconductor electric circuits. Scanning probe microscopy (SPM) has been a key tool in achieving this goal. SPM can be used not only as the means that observe surface structure at sub-molecule level by a probe but also as the means that control the atomic and molecular arrangement on a substrate. As a local nano-fabrication means, the lithography technique in nanoscale range by using SPM is called to the scanning probe lithography (SPL) (Kaholek et al., 2004; Blackledge et al., 2000; Tello et al., 2002; Liu et al., 2002). In particular, a variety of lithographic techniques using SPM probe can fabricate nano-scale patterns on an organic monolayer, such as nanoshaving, nanografting, anodization SPL, dip-pen nanolithography (DPN), and electrochemical SPL. The lithography technique is used to break the material surface by using various energy sources. SPM can also be used to break the organic monolayer. For instance, nanoshaving involves mechanical scratching by physical pressure of the probe, and anodization lithography involves anodic oxidation of the substrate surface by an applied bias voltage (above 9 V) between the probe and the substrate (Jang et al., 2002; Kaholek et al., 2004; Sugimura, & Nakagiri, 1995). In the case of the anodization lithography, the oxide layer can be fabricated by anodic oxidation. As another SPL technique, the

High Functionalization of Magnesium Alloy Surface by Superhydrophobic Treatment

Magnesium and its alloys have excellent physical and mechanical properties such as low density, good electromagnetic shielding, and high strength/weight ratio (Gray & Luan, 2002; Yong et al., 2008). Thus, they are expected to be applied to various industries such as the aerospace, automobile, and railway industries (Mordike & Ebert, 2001; Phani et al., 2006; Ha & Kim, 2006). Their poor corrosion resistance, however, hinders their use on a larger scale. The corrosion of magnesium and magnesium alloys occurs via the following reaction (Baril et al., 2007; Song el al., 1997):