273 research outputs found
The effect of substrate temperature on cadmium telluride films in high temperature vapor deposition process
Physical vapor high-temperature deposition of CdTe thin films is one of the
main methods for preparing high-efficiency CdTe solar cells, but
high-temperature deposition also has an impact on the internal structure of the
film. The difference in thermal expansion coefficients between the substrate
and CdTe leads to the generation of internal stress in the CdTe thin film
during the cooling process. In this work, we prepared thin films with different
substrate temperatures using a homemade GVD device, and observed by SEM that
the crystallization quality of the film gradually improved with the increase of
substrate temperature, but accompanied by the shift of XRD peak position. We
calculated the internal stress situation of the film by the shift amount, and
the possible causes of stress generation were speculated by the results of TEM
and SAED to be the combined effects of the different thermal expansion
coefficients between the substrate and the film and the stacking fault defects
inside the film
Donor–Acceptor Fluorophores for Energy-Transfer-Mediated Photocatalysis
Triplet–triplet energy transfer (EnT) is a fundamental activation pathway in photocatalysis. In this work, we report the mechanistic origins of the triplet excited state of carbazole-cyanobenzene donor–acceptor (D–A) fluorophores in EnT-based photocatalytic reactions and demonstrate the key factors that control the accessibility of the 3LE (locally excited triplet state) and 3CT (charge-transfer triplet state) via a combined photochemical and transient absorption spectroscopic study. We found that the energy order between 1CT (charge transfer singlet state) and 3LE dictates the accessibility of 3LE/3CT for EnT, which can be effectively engineered by varying solvent polarity and D–A character to depopulate 3LE and facilitate EnT from the chemically more tunable 3CT state for photosensitization. Following the above design principle, a new D–A fluorophore with strong D–A character and weak redox potential is identified, which exhibits high efficiency for Ni(II)-catalyzed cross-coupling of carboxylic acids and aryl halides with a wide substrate scope and high selectivity. Our results not only provide key fundamental insight on the EnT mechanism of D–A fluorophores but also establish its wide utility in EnT-mediated photocatalytic reactions
Photometry of Variable Stars from THU-NAOC Transient Survey I: The First 2 Years
In this paper, we report the detections of stellar variabilities from the
first 2-year observations of sky area of about 1300 square degrees from the
Tsinghua University-NAOC Transient Survey (TNTS). A total of 1237 variable
stars (including 299 new ones) were detected with brightness < 18.0 mag and
magnitude variation >= 0.1 mag on a timescale from a few hours to few hundred
days. Among such detections, we tentatively identified 661 RR Lyrae stars, 431
binaries, 72 Semiregular pulsators, 29 Mira stars, 11 slow irregular variables,
11 RS Canum Venaticorum stars, 7 Gamma Doradus stars, 5 long period variables,
3 W Virginis stars, 3 Delta Scuti stars, 2 Anomalous Cepheids, 1 Cepheid, and 1
nove-like star based on their time-series variability index Js and their phased
diagrams. Moreover, we found that 14 RR Lyrae stars show the Blazhko effect and
67 contact eclipsing binaries exhibit the O'Connell effect. Since the period
and amplitude of light variations of RR Lyrae variables depend on their
chemical compositions, their photometric observations can be used to
investigate distribution of metallicity along the direction perpendicular to
the Galactic disk. We find that the metallicity of RR Lyrae stars shows large
scatter at regions closer to the Galactic plane (e.g., -3.0 < [Fe/H] < 0) but
tends to converge at [Fe/H]~ -1.7 at larger Galactic latitudes. This variation
may be related to that the RRAB Lyrae stars in the Galactic halo come from
globular clusters with different metallicity and vertical distances, i.e. OoI
and OoII populations, favoring for the dual-halo model.Comment: 18 pages, 19 figures, published in AJ, 150, 10
Extended Wiener-Khinchin theorem for quantum spectral analysis
The classical Wiener-Khinchin theorem (WKT), which can extract spectral
information by classical interferometers through Fourier transform, is a
fundamental theorem used in many disciplines. However, there is still need for
a quantum version of WKT, which could connect correlated biphoton spectral
information by quantum interferometers. Here, we extend the classical WKT to
its quantum counterpart, i.e., extended WKT (e-WKT), which is based on
two-photon quantum interferometry. According to the e-WKT, the
difference-frequency distribution of the biphoton wavefunctions can be
extracted by applying a Fourier transform on the time-domain Hong-Ou-Mandel
interference (HOMI) patterns, while the sum-frequency distribution can be
extracted by applying a Fourier transform on the time-domain NOON state
interference (NOONI) patterns. We also experimentally verified the WKT and
e-WKT in a Mach-Zehnder interference (MZI), a HOMI and a NOONI. This theorem
can be directly applied to quantum spectroscopy, where the spectral correlation
information of biphotons can be obtained from time-domain quantum interferences
by Fourier transform. This may open a new pathway for the study of light-matter
interaction at the single photon level.Comment: 13 pages, 5 figure
- …