Currently, the direct synthesis of inch-scale single-crystal graphene on insulating substrates is limited by the lack of metal catalysis, suitable crystallization conditions, and self-limiting growth mechanisms. In this study, we investigated the direct growth of adlayer-free ultra-flat wafer-scale single-crystal monolayer graphene on insulating substrates by the multi-cycle plasma-etching-assisted chemical vapor deposition (MPE-CVD) method. Firstly, an angstrom-scale growth nanochamber was created by fabricating single-crystal Cu(111) foils on Al2O3(0001) substrates. Graphene was then directly synthesized at the interface between Cu(111) and Al2O3(0001) by MPE-CVD. After growth, the Cu(111) foil was detached using a liquid-nitrogen-assisted separation method, and the ultra-high-quality single-crystal graphene film was experimentally achieved on Al2O3(0001). This work breaks the bottleneck in the direct synthesis of single-crystal monolayer graphene on insulating substrates and paves the way for next-generation carbon-based atomic electronics and semiconductor nanodevices.

Galaxy evolution is regulated by the interplay between galactic disks and their surrounding medium. We study this interplay by examining how the galactic coronal emission efficiency of stellar feedback depends on the (surface and specific) star formation rates (SFRs) and other parameters for a sample of 52 Chandra-observed nearby highly inclined disk galaxies. We first measure the star forming galactic disk sizes, as well as the SFRs of these galaxies, using data from the Wide-Field Infrared Survey Explorer, and then show that 1) the specific 0.5-2 keV luminosity of the coronal emission correlates with the specific SFR in a sub-linear fashion: on average, L X /L K ∝ (SFR/M * ) Γ with Γ = 0.29±0.12; 2) the efficiency of the emission L X /SFR decreases with increasing surface SFR (I SFR ; Γ = −0.44 ± 0.12); and 3) the characteristic temperature of the X-ray-emitting plasma weakly correlates with I SFR (Γ = 0.08 ± 0.04). These results, somewhat surprising and anti-intuitive, suggest that a) the linear correlation between L X and SFR, as commonly presented, is largely due to the correlation of these two parameters with galaxy mass; b) much of the mechanical energy from stellar feedback likely drives global outflows with little X-ray cooling and with a mass-loading efficiency decreasing fast with increasing I SFR (Γ < ∼ − 0.5); c) these outflows heat and inflate the medium around the galactic disks of massive galaxies, reducing its radiative cooling rate, whereas for relatively low-mass galaxies, the energy in the outflows is probably dissipated in regions far away from the galactic disks.

X-ray observations of highly ionized metal absorption lines at z = 0 provide critical information of the hot gas distribution in and around the Milky Way. We present a study of more than ten-year Chandra and XMM-Newton observations of 3C 273, one of the brightest extragalactic X-ray sources. Compared with previous work, We obtain much tighter constraints of the physical properties of the X-ray absorber. We also find a large, non-thermal velocity at ∼ 100−150 km s −1 is the main reason for the higher line equivalent width when compared with other sightlines. Using joint analysis with X-ray emission and ultraviolet observations, we derive a size of 5 -15 kpc and a temperature of (1.5-1.8)×10 6 K for the X-ray absorber. The 3C 273 sightline passes through a number of Galactic structures, including the radio Loop I, IV, the North Polar Spur, and the neighborhood of the newly discovered "Fermi bubbles". We argue that the X-ray absorber is unlikely associated with the nearby radio Loop I and IV; however, the non-thermal velocity can be naturally explained as the result of the expansion of the "Fermi bubbles". Our data implies an shock-expansion velocity of 200 − 300 km s −1 . Our study indicates a likely complex environment for the production of the Galactic X-ray absorbers along different sightlines, and highlights the significance of probing galactic feedback with high resolution X-ray spectroscopy.