Joon Kim

DIRECT FORMATION OF NANOCRYSTALLINE SILICON BY ELECTRON CYCLOTRON RESONANCE CHEMICAL VAPOR DEPOSITION

We have confirmed the direct formation of nanosized crystalline silicon during the deposition of amorphous silicon layers by electron cyclotron resonance chemical vapor deposition (ECRCVD) on silicon and silicon–dioxide substrates. Two photoluminescence (PL) peaks at 680 and 838 nm were observed at room temperature from the samples. From cross-sectional high-resolution transmission electron microscopy (HRTEM) measurements, it was confirmed that nanosize silicon crystallites of 3–5 nm in diameter were randomly distributed throughout the amorphous silicon layer. Theoretical calculations using quantum size effects gave an average crystalline size of 4 nm which was consistent with the PL peak energy at 680 nm obtained from the sample. Also, the size of the crystallites could be controlled by the change of the substrate temperature during the deposition process.

EFFECTS OF V/III RATIO ON ORDERING AND ANTIPHASE BOUNDARIES IN GAINP LAYERS

Transmission electron microscope (TEM) and transmission electron diffraction (TED) studies have been performed to investigate the effects of V/III ratio on ordering and antiphase boundaries (APBs) in organometallic vapor phase epitaxial Ga0.5In0.5P layers grown onto (001) GaAs vicinal substrates at 670 °C. TED and TEM examination showed that the degree of order is higher in the layer grown using a V/III ratio of 160 than in the layer grown using a V/III ratio of 40. TEM results showed that the higher V/III ratio could be used to suppress APBs. In addition, the growth of order-induced heterostructures, where the V/III ratio is increased abruptly during growth, could be used to block the propagation of APBs. Mechanisms are proposed to explain these phenomena.

Ssb2 is a novel factor in regulating synthesis and degradation of Gcn4 in Saccharomyces cerevisiae

Yeast cells respond to environmental stress by inducing the master regulator Gcn4 to control genes involved in biosynthesis of amino acids and purine pathways. Gcn4 is a member of the basic leucine Zipper family and binds directly as a homodimer to a conserved regulatory region of target genes. Ssb2 was discovered to rescue the mutant Gcn4 which has a point mutation that decreases DNA‐binding affinity. Ssb2 is part of the Hsp70 protein family responsible for protein quality control and it is thought that Ssb2 assists the passage of nascent polypeptide chains from the ribosomes. To characterize the mechanism behind the rescue of the mutant gcn4 phenotype, transcriptional activity and protein levels of Gcn4 were analyzed. We found that Ssb2 improved the expression of Gcn4 target genes by increasing the DNA‐binding affinity of gcn4 mutants to target gene promoters under conditions of amino acid starvation. Gcn4 levels increased at both translational and post‐translational levels without regulating GCN4 steady‐state mRNA levels. We also found that the nuclear export signal of Ssb2 is required for interaction with Gcn4 and rescue of the gcn4 mutant phenotype. These findings suggest that Ssb2 is a critical factor that modulates Gcn4 functions in the nucleus and cytosol.