Synthesis of (+/-)-desepoxy-4,5-didehydromethylenomycin A

An efficient and regiochemically controlled synthesis of (+/-)-desepoxy-4,5-didehydromethylenomycin A is reported.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24486/1/0000762.pd

Zero temperature coefficient of sound velocity in vitreous silicon oxynitride thin films

Vitreous silicon oxide (v-SiO2) shows anomalous phonon properties such as the positive temperature coefficient of velocity (TCV). Variation of the Si-O-Si bond angle between SiO4 tetrahedrons has been recognized to be the key, but the origin of TCV still remains unclear. In this study, we controlled the bond angle by doping nitrogen and measured TCV of vitreous silicon oxynitride thin films with various nitrogen concentrations using picosecond ultrasonics. TCV significantly decreases by adding a small amount of nitrogen, and it shows positive to negative values as the nitrogen concentration increases. We evaluated the bond-angle change by Fourier-transform infrared spectroscopy, which decreases with the increase in the nitrogen content. We also find that the temperature rise in nondoped v-SiO2 decreases the bond angle, leading to an increase in the sound velocity. We then reveal theoretically that the bond-angle change dominates the origin of the positive TCV. This study indicates the existence of a zero-TCV single material, and we discover that the specific content of v-SiO1.71N0.19 achieves this.Nagakubo A., Tsuboi S., Kabe Y., et al. Zero temperature coefficient of sound velocity in vitreous silicon oxynitride thin films. Applied Physics Letters, 114(25), 251905 (2019) https://doi.org/10.1063/1.5098354.https://doi.org/10.1063/1.509835