明星大學

The nucleosome is a structural and functional subunit of chromatin, and its positioning in eukaryotic genomes serves as a key platform for gene regulation. Here, we determine the positions of fully wrapped nucleosomes across the yeast genome by chemical mapping through the histone H2A-A122C residue, which cleaves near the DNA entry/exit sites. This approach reveals the most refined sequence-dependent profile of nucleosomes reported to date. Comparisons of the H2A-A122C approach with the H3-Q85C and H4-S47C methods clearly show a sequence preference for the chemical cleavage site. Notably, depletion of CC and GG dinucleotides at nucleotide positions -11 to -9 and +9 to +11 bp, respectively, from the nucleosome dyad position (zero) is consistently accompanied by enrichment of AA/AT/TA/TT dinucleotides in both yeast and mouse genomes. Introducing consecutive C center dot G base pairs to the corresponding sites in the Widom 601 sequence makes reconstituted nucleosomes more likely to shift into alternative positions without affecting the thermal stability of the nucleosome particle, implying a structural constraint imposed by the DNA sequence. Thus, CC and GG dinucleotides in the major groove blocks, in which the minor groove faces out from the histone octamer, at superhelix locations (SHL) -1.0 and +1.0, respectively, destabilize histone-DNA interactions, serving as intrinsic determinants of nucleosome positioning in eukaryotic genomes.

Bonding of sapphire and quartz glass is essential for aerospace and quantum technologies. Since the coefficient of thermal expansion (CTE) of sapphire is more than ten times that of quartz, direct bonding may fail due to excessive interfacial thermal stress. Hydroxide-catalyzed bonding (HCB) can join silicon-based materials through chemical reactions with alkaline solutions and relieve interfacial stress. However, sapphire is difficult to react due to its chemical inert, which is challenging to combine with quartz glass achieving high bonding strengths and excellent optical interfaces. Here, a reactive ion etching (RIE) plasma was employed to improve surface roughness and chemical activity. It promotes the spontaneous spreading and infiltration of Na2SiO3 solution on both sapphire and quartz surfaces. The HCB solution formulation was optimized so that high bonding strength over 8 MPa was obtained while maintaining excellent optical transmittance (similar to 95% theorical value). Moreover, the bridging interlayer of transparent inorganic networks can relieve thermal stress. The bonded sample was thus completely survived after -55 similar to +125 degrees C thermal cycles. It has great potential for hybrid integrated optical and transparent encapsulation applications.

Due to its superior nanoscale properties, cobalt (Co) is highly desirable for ultrahigh-density 3D integration into materials through metal/dielectric hybrid bonding. However, this process is very challenging through Co/SiO2 hybrid bonding, as very hydrophilic SiO2 surfaces are needed for bonding during dehydration reactions and oxidation of the Co surfaces must be avoided. Additionally, the substantial coefficient of thermal expansion mismatch between the robust capping layers (Co and SiO2 layers) necessitates hybrid bonding with minimal thermal input and compression. In this study, we introduce a ternary plasma activation strategy employing an Ar/NH3/H2O gas mixture to facilitate Co/SiO2 hybrid bonding at temperatures as low as similar to 200 degrees C, which is markedly lower than the melting point of Co (similar to 1500 degrees C). Intriguingly, non-oxide metallization at the Co-Co interface can be realized without the hindrance of a bonding barrier, thereby reducing the electrical resistance by over 40% and compression force requirements. Moreover, the enhancement in the SiO2 surface energy through active group terminations fosters extensive interfacial hydration and strengthens the mechanical properties. This research paves the way for fine-tuning bonding surfaces using a material-selective strategy, which should advance metal/dielectric hybrid bonding for future integration applications. An effective and straightforward strategy is developed for the hybrid bonding of Co and SiO2.Both homo- and heterogeneous bonding are achieved at temperatures as low as similar to 200 degrees C.Selective surface activation enhances the electrical properties of the Co surface by over 40%.The bonding mechanism involves interfacial hydration and non-oxide metallization.A defect-free hybrid bonding structure is realized for next-generation 3D integration.

Cu-based hybrid bonding, known for its high density and low latency, is widely applied in big data throughput scenarios. However, Cu joints are prone to oxidation and perform poorly at fine pitches, hindering signal transmission and leading to failures in integrated devices. One of the most promising approaches to overcome these challenges is applying a cobalt (Co) passivation layer on the Cu surface owing to its preferable electrical and anti-electromigration behavior in sub-micron scale. However, the high melting point (similar to 1500 degrees C) and inevitable oxidation of the Co film coated on Cu are scarcely evitable. In this work, a ternary plasma composed of Ar, NH3, and H2O is introduced to activate the surface of the Co-passivated Cu, facilitating bonding at a temperature of 200 degrees C. Significant surface and interface electrical resistivity reductions were observed, reduced to 67.5 % and less than 10 %, respectively. Additionally, tensile strength more than doubled with ternary plasma activation attributed to the continuous and tightly bonded Co-Co interface. The application of this Co-passivated Cu bonding structure is evaluated through signal integrity simulations for 3D interconnection with ultrafine pitch. In summary, this work provides guidelines for the future fabrication of high-performance interconnection structures.

We present a detailed analysis of the kinematics of SiO maser stars around the center of the Milky Way, Sagittarius A$^\ast$ (Sgr A$^\ast$). We used the archive data in the SiO $v=1$, J = 2–1 emission line obtained by the Atacama Large Millimeter/Submillimeter Array (ALMA) in 2017 and 2021 (#2016.1.00940.S, PI J. Darling and #2019.1.00292.S, PI J. Paine). We detected 37 SiO maser stars in the channel maps and derived their angular offsets relative to Sgr A$^\ast$ and LSR radial velocities. We derived the proper motions of 35 stars by comparing their angular offsets in the two epochs. The proper motions of Wolf–Rayet and O star in the nuclear star cluster are reported to be rather random, except for the co-moving clusters IRS13E and IRS13N (Tsuboi et al. 2022, PASJ, 74, 738). However, the derived proper motions of SiO maser stars do not look completely random. The proper motions of the SiO maser stars show a tendency to lie along the Galactic plane. The proper motion amplitudes of SiO maser stars are larger than the local standard of rest (LSR) velocity amplitudes. We estimated the 3D motions from the proper motions and LSR velocities. Many 3D velocities are near to or larger than the upper limit velocities for Kepler orbits around Sgr A$^\ast$, whose mass is assumed to be $4\times 10^6$ M$_{\odot }$. These indicate that the SiO maser stars around Sgr A$^\ast$ are members of the nuclear stellar disk rather than the nuclear star cluster.