Abstract
Metal oxides are archetypal CO
2
reduction reaction electrocatalysts, yet inevitable self-reduction will enhance competitive hydrogen evolution and lower the CO
2
electroreduction ...selectivity. Herein, we propose a tangible superlattice model of alternating metal oxides and selenide sublayers in which electrons are rapidly exported through the conductive metal selenide layer to protect the active oxide layer from self-reduction. Taking BiCuSeO superlattices as a proof-of-concept, a comprehensive characterization reveals that the active Bi
2
O
2
2+
sublayers retain oxidation states rather than their self-reduced Bi metal during CO
2
electroreduction because of the rapid electron transfer through the conductive Cu
2
Se
2
2-
sublayer. Theoretical calculations uncover the high activity over Bi
2
O
2
2+
sublayers due to the overlaps between the Bi
p
orbitals and O
p
orbitals in the OCHO* intermediate, thus achieving over 90% formate selectivity in a wide potential range from −0.4 to −1.1 V. This work broadens the studying and improving of the CO
2
electroreduction properties of metal oxide systems.
An effective passivation approach to protect black phosphorus (BP) from degradation based on multi‐scale simulations is proposed. The self‐assembly of perylene‐3,4,9,10‐tetracarboxylic dianhydride ...monolayers via van der Waals epitaxy on BP does not break the original electronic properties of BP. The passivation layer thickness is only 2 nm. This study opens up a new pathway toward fine passivation of BP.
Abstract
We present a statistical study of the C
i
(
3
P
1
3
P
0
), C
i
(
3
P
2
3
P
1
) lines (hereafter C
i
(1–0) and C
i
(2–1), respectively) and the CO(1–0) line for a sample of ...(ultra-)luminous infrared galaxies ((U)LIRGs). We explore the correlations between the luminosities of CO(1–0) and C
i
lines, and find that
correlates almost linearly with both
and
, suggesting that C
i
lines can trace total molecular gas mass, at least for (U)LIRGs. We also investigate the dependence of
/
,
/
, and
/
on the far-infrared color of 60-to-100
μ
m, and find non-correlation, a weak correlation, and a modest correlation, respectively. Under the assumption that these two carbon transitions are optically thin, we further calculate the C
i
line excitation temperatures, atomic carbon masses, and mean C
i
line flux-to-H
2
mass conversion factors for our sample. The resulting
masses using these C
i
-based conversion factors roughly agree with those derived from
and CO-to-H
2
conversion factor.
Activating basal plane inert sites will endow MoTe
2
with prominent hydrogen evolution reaction (HER) catalytic capability and arouse a new family of HER catalysts. Herein, we fabricated single MoTe
...2
sheet electrocatalytic microdevice for
in situ
revealing the activated basal plane sites by vacancies introducing. Through the extraction of electrical parameters of single MoTe
2
sheet, the in-plane and interlayer conductivities were optimized effectively by Te vacancies due to the defect levels. More deeply, Te vacancies can induce the delocalization of electrons around Mo atoms and shift the d-band center, as a consequence, facilitate the adsorption of H from the catalyst surface for HER catalysis. Benefiting by the coordinated regulation of band structure and local charge density, the overpotential at −10 mA·cm
−
2
was reduced to 0.32 V after Te vacancies compared to 0.41 V for the basal plane sites of same MoTe
2
nanosheet. Meanwhile, the insights gained from single nanosheet electrocatalytic microdevice can be applied to the improved HER of the commercial MoTe
2
power. That the
in situ
testing of the atomic structure-electrical behavior-electrochemical properties of a single nanosheet before/after vacancies introducing provides reliable insight to structure-activity relationships.
Searching for room temperature magnetic two-dimensional (2D) materials is a charming goal, but the number of satisfied materials is tiny. Strain can introduce considerable deformation into the ...lattice structure of 2D materials, and thus significantly modulate their intrinsic properties. In this work, we demonstrated a remarkable strain-modulated magnetic properties in the chemical vapor deposited Cr
2
Te
3
nanoflakes grown on mica substrate. We found the Curie temperature of Cr
2
Te
3
nanoflakes can be positively and negatively modulated under tensile and compressive strain respectively, with a maximum varied value of ∼ 40 and −90 K, dependent on the thickness of samples. Besides, the coercive field of Cr
2
Te
3
nanoflakes also showed a significant decrease under the applied strain, suggesting the decrease of exchange interaction or the change of the magnetization direction. This work suggests a promise to employ interfacial strain to accelerate the practical application of room temperature 2D magnetics.
We present maps of atomic carbon C i( ) and C i( ) emission (hereafter C i (1−0) and C i (2−1), respectively) at a linear resolution ∼1 kpc scale for a sample of one H ii, six LINER, three Seyfert, ...and five starburst galaxies observed with the Herschel Space Observatory. We compare spatial distributions of two C i lines with that of CO (hereafter CO (1−0)) emission, and find that both C i lines distribute similarly to CO (1−0) emission in most galaxies. We present luminosity ratio maps of / , / , (hereafter ) and 70-to-160 m far-infrared color of f70/f160. / , and are centrally peaked in starbursts; whereas they remain relatively constant in LINERs, indicating that star-forming activity can enhance carbon emission, especially for C i (2−1). We explore the correlations between the luminosities of CO (1−0) and C i lines, and find that correlates tightly and almost linearly with both and , suggesting that C i lines, similar to CO (1−0), can trace total molecular gas in H ii, LINER, Seyfert, and starburst galaxies on kpc scales. We investigate the dependence of / , / and C i excitation temperature, Tex, on dust temperature, Tdust, and find noncorrelation and a weak and modest correlation, respectively. The ratio of / stays a smooth distribution in most galaxies, indicating that the conversion factor of C i (1−0) luminosity to H2 mass ( ) changes with CO (1−0) conversion factor ( ) proportionally. Under optically thin and local thermodynamical equilibrium assumptions, we derive a galaxy-wide average carbon excitation temperature of , and an average neutral carbon abundance of in our resolved sample, which is comparable to the usually adopted value of 3 × 10−5, but ∼3 times lower than the carbon abundance in local (ultra)luminous infrared galaxies. We conclude that the carbon abundance varies in different galaxy types.
A Study of the Merging Dwarf Galaxy VCC322 Zhang, Lan-Yue; Zhao, Yinghe; Zhang, Hong-Xin
Astrophysical journal/The Astrophysical journal,
04/2024, Volume:
965, Issue:
1
Journal Article
Peer reviewed
Open access
Abstract
Galaxy interactions and mergers can enhance or reduce star formation, but a complete understanding of the involved processes is still lacking. The effect of dwarf galaxy mergers is even less ...clear than their massive counterpart. We present a study on a dwarf merger remnant in the Virgo cluster, VCC322, which might form a triple system with VCC334 and VCC319. We identify a prominent long and straight tail-like substructure that has a size comparable to its host galaxy VCC322. By comparing the color–color (
g
−
r
versus
r
−
H
) distribution with simple stellar population models, we infer that the metallicity and stellar age of this tail are
Z
⋆
∼ 0.02
Z
⊙
and
t
⋆
∼ 10 Gyr, respectively. In VCC319, we find a sign of isophotal twisting. This suggests that VCC319 may be subject to tidal interaction. An analysis of the Sloan Digital Sky Survey optical spectra of VCC322 indicates mass- and light-weighted ages of about 10
9.8
yr and 10
7.5
yr, respectively, indicating an ongoing star formation activity. However, the star formation in VCC322 seems suppressed when compared to other star-forming dwarfs of comparable stellar masses. Our finding of shock excitation of optical emission lines indicates that interaction-induced shock may contribute to the heating of cold gas and suppression of star formation.
We present results of a statistical study of the cosmic evolution of the mass-dependent major-merger rate since z = 1. A stellar mass limited sample of close major-merger pairs (the CPAIR sample) was ...selected from the archive of the COSMOS survey. Pair fractions at different redshifts derived using the CPAIR sample and a local K-band-selected pair sample show no significant variations with stellar mass. The pair fraction exhibits moderately strong cosmic evolution, with the best-fitting function of functionof sub(pair) = 10 super(-1.88(+ or - 0.03))(1 + z) super(2.2(+ or - 0.2)). The best-fitting function for the merger rate is R sub(mg) (Gyr super(-1)) = 0.053 x (M sub(star)/10 super(10.7) M sub(middot in circle)) super(0.3)(1 + z) super(2.2)/(1 + z/8). This rate implies that galaxies of M sub(star) ~ 10 super(10)-10 super(11.5) M sub(middot in circle) have undergone ~0.5-1.5 major mergers since z = 1. Our results show that, for massive galaxies (M sub(star) > or =, slanted 10 super(10.5) M sub(middot in circle)) at z < or =, slant 1, major mergers involving star-forming galaxies (i.e., wet and mixed mergers) can account for the formation of both ellipticals and red quiescent galaxies (RQGs). On the other hand, major mergers cannot be responsible for the formation of most low mass ellipticals and RQGs of M sub(star) <, ~ 10 super(10.3) M sub(middot in circle). Our quantitative estimates indicate that major mergers have significant impact on the stellar mass assembly of the most massive galaxies (M sub(star) > or =, slanted 10 super(11.3) M sub(middot in circle)), but for less massive galaxies the stellar mass assembly is dominated by the star formation. Comparison with the mass-dependent (ultra)luminous infrared galaxies ((U)LIRG) rates suggests that the frequency of major-merger events is comparable to or higher than that of (U)LIRGs.
Abstract
We describe a
Herschel Space Observatory
194–671
μ
m spectroscopic survey of a sample of 121 local luminous infrared galaxies and report the fluxes of the CO
J
to
J
–1 rotational transitions ...for
, the N
ii
205
μ
m line, the C
i
lines at 609 and 370
μ
m, as well as additional and usually fainter lines. The CO spectral line energy distributions (SLEDs) presented here are consistent with our earlier work, which was based on a smaller sample, that calls for two distinct molecular gas components in general: (i) a cold component, which emits CO lines primarily at
J
≲ 4 and likely represents the same gas phase traced by CO (1−0), and (ii) a warm component, which dominates over the mid-
J
regime (4 <
J
≲ 10) and is intimately related to current star formation. We present evidence that the CO line emission associated with an active galactic nucleus is significant only at
J
> 10. The flux ratios of the two C
i
lines imply modest excitation temperatures of 15–30 K; the C
i
370
μ
m line scales more linearly in flux with CO (4−3) than with CO (7−6). These findings suggest that the C
i
emission is predominantly associated with the gas component defined in (i) above. Our analysis of the stacked spectra in different far-infrared (FIR) color bins reveals an evolution of the SLED of the rotational transitions of
vapor as a function of the FIR color in a direction consistent with infrared photon pumping.
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