DFT Studies on Van der Waals Multiferroicity and Perovskite Solar Cell

Department of ChemistryThe DFT (Density Functional Theory) method has been a powerful tool to investigate the electronic structures of molecules and atoms, especially been very useful in solid state physics. Here, the DFT method has been applied to study two interesting topicsVan der Waals Multiferroicity and Perovskite Solar cell. Materials that are simultaneously ferromagnetic and ferroelectric ??? multiferroics ??? promise the control of disparate ferroic orders, leading to technological advances in microwave magnetoelectric applications and next generation of spintronics. Single-phase multiferroics are challenged by the opposite d-orbital occupations imposed by the two ferroics, and heterogeneous nanocomposite multiferroics demand ingredients???structural compatibility with the resultant multiferroicity exclusively at inter-materials boundaries. Here, we propose the two-dimensional heterostructure multiferroics by stacking up atomic layers of ferromagnetic Cr2Ge2Te6 and ferroelectric In2Se3, thereby leading to all-atomic multiferroicity. Through first-principles density functional theory calculations, we find as In2Se3 reverses its polarization, the magnetism of Cr2Ge2Te6 is switched, and correspondingly In2Se3 becomes a switchable magnetic semiconductor due to proximity effect. This unprecedented multiferroic duality (i.e., switchable ferromagnet and switchable magnetic semiconductor) enables both layers for logic applications. Van der Waals heterostructure multiferroics open the door for exploring the low-dimensional magnetoelectric physics and spintronic applications based on artificial superlattices. In hybrid organic-inorganic halide perovskite solar cells, organic graphene nanoribbons (GNRs) can be a good candidate as carrier extraction interlayers owing to the capability of tuning the band edge energy levels through varying the size of width and the type of edge functionalization. Here, by using the density function theory (DFT) method, the electronic structures of H or F edge functionalized armchair type GNRs on MAPbI3(001) are calculated. It is shown that the H/F-passivated GNR with width of seven carbon atoms exhibits a good band alignment for hole/electron extraction. Exploiting the unzipping synthesis of carbon nanotubes in the solution phase, our result provides a facial strategy for efficient carrier extraction.clos

Growth of superconducting MgB2 thin films via postannealing techniques

We report the effect of annealing on the superconductivity of MgB2 thin films as functions of the postannealing temperature in the range from 700 C to 950 C and of the postannealing time in the range from 30 min to 120 min. On annealing at 900 C for 30 min, we obtained the best-quality MgB2 films with a transition temperature of 39 K and a critical current density of ~ 10^7 A/cm^2. Using the scanning electron microscopy, we also investigated the film growth mechanism. The samples annealed at higher temperatures showed the larger grain sizes, well-aligned crystal structures with preferential orientations along the c-axis, and smooth surface morphologies. However, a longer annealing time prevented the alignment of grains and reduced the superconductivity, indicating a strong interfacial reaction between the substrate and the MgB2 film.Comment: 7 pages, 4 figures include

Identification of keratinolytic function in Chryseobacterium camelliae Dolsongi-HT1 isolated from Green Tea

Keratin forms a major component of the epidermis, hair, feathers, nails, scales and etc. However, old keratins on the skin are not preferred for the beauty purpose. Therefore, in the highly efficient and low irritative method to remove old keratin on the skin is highly desired. For this purpose, one of the appropriate methods is the enzymatic lysis of keratin. To screen a novel keratinase, a novel microorganism having keratinolytic activity was isolated by enrichment culture. Newly screened microorganism was isolated from green tea in dolsong-i tea garden, Jeju and identified as Chryseobacterium camelliae Dolsongi-HT1. The keratinase activity of C. camelliae Dolsongi-HT1 was confirmed in the culture media. The effect of pH and temperature were studied using cell culture media. Crude keratinase showed high activity over a wide range of temperature (37 to 60°C) and showed the highest activity at 50°C. Optimum pH of keratinase activity of crude keratinase was pH 8. Interestingly, this enzyme activity was maintained over 50% at pH 6. This feature is promising for the application to cosmetics. The effect of nitrogen source for cell culture was also investigated. Among the various nitrogen sources, the highest keratinase activity (relative activity of 366.4%) was detected when cells were cultured using tryptone extract. To study the keratinolytic activity effect of keratin on the skin, the keratin of skin was obtained using tape stripping. It was found that the structure of keratin was degraded by crude keratinase. To identify the keratinase, the complete genome of C. camelliae Dolsongi-HT1 was sequenced. Because keratinases are regarded as serine or metalloprotease group, we searched for those proteases in the C. camelliae Dolsongi-HT1 genome sequence. As s result, over twenty putative keratinases could be identified. Further research to identify desired keratinases should be performed

Gene Expression Profiles are Altered in Human Papillomavirus-16 E6 D25E-Expressing Cell Lines

Previously, we have reported that the human papillomavirus (HPV) type 16 E6 D25E is the most prevalent variant in Korean women at high risk for cervical cancers. Several studies have identified an association between the increased frequency of this variant and the elevated risk of cervical intraepithelial neoplasia and invasive cervical carcinoma. To investigate whether the HPV-16 E6 D25E variant might influence cervical cancer progression, we used an oligonucleotide microarray approach to identify transcriptionally altered gene expression patterns in recombinant wild-type E6 or E6 D25E variant-expressing HPV-negative cancer cells. We found that 211 genes were significantly up- or down-regulated (at least 1.5-fold, p < 0.05). We identified 14 genes, nine down-regulated and five up-regulated upon E6 D25E expression, compared with wild-type E6 expression. These results further emphasize the unique biological activity of the HPV-16 E6 D25E variant