68 research outputs found
Laser-Matter Interaction in the Bulk of Semiconductor and Dielectric
The research in the field of laser-induced materials processing is evolving continuously with new inventions in laser technology. This chapter mainly discusses the relevant physical mechanisms of laser ablation based on laser-matter interaction. Femtosecond laser excitation provides suitable conditions for studying the basic processes in irradiated materials, as compared to the duration of these processes, femtosecond laser pulses are sufficiently short. In the process of laser action on the matter, the thermal mechanism, charge carrier removal, thermal and structural effects, and other processes are extremely complex. The ultrashort laser pulse instantly puts the material in a strong nonequilibrium state characterized by hot electrons and cold ions. After the pulse ends, the electron transfers its energy to the ion through electron phonon coupling in sub-picoseconds. This heats up the phonon bath before the slow thermal effect can reconstruct the material. The electron effect plays an important and possibly dominant role in the laser ablation of nonmetallic solid surfaces. This review first describes the mechanism of laser-matter interaction from the perspective of energy, summarizes the electronic excitation and energy relaxation paths of light on semiconductors and dielectric materials, focuses on the electronic excitation and relaxation mechanisms in laser-induced ionization, desorption, and ablation, and finally analyzes the above-mentioned related processes from the perspective of material structure relaxation
Ab-initio electronic and magnetic structure in La_0.66Sr_0.33MnO_3: strain and correlation effects
The effects of tetragonal strain on electronic and magnetic properties of
strontium-doped lanthanum manganite, La_{2/3}Sr_{1/3}MnO_3 (LSMO), are
investigated by means of density-functional methods. As far as the structural
properties are concerned, the comparison between theory and experiments for
LSMO strained on the most commonly used substrates, shows an overall good
agreement: the slight overestimate (at most of 1-1.5 %) for the equilibrium
out-of-plane lattice constants points to possible defects in real samples. The
inclusion of a Hubbard-like contribution on the Mn d states, according to the
so-called "LSDA+U" approach, is rather ineffective from the structural point of
view, but much more important from the electronic and magnetic point of view.
In particular, full half-metallicity, which is missed within a bare
density-functional approach, is recovered within LSDA+U, in agreement with
experiments. Moreover, the half-metallic behavior, particularly relevant for
spin-injection purposes, is independent on the chosen substrate and is achieved
for all the considered in-plane lattice constants. More generally, strain
effects are not seen to crucially affect the electronic structure: within the
considered tetragonalization range, the minority gap is only slightly (i.e. by
about 0.1-0.2 eV) affected by a tensile or compressive strain. Nevertheless, we
show that the growth on a smaller in-plane lattice constant can stabilize the
out-of-plane vs in-plane e_g orbital and significatively change their relative
occupancy. Since e_g orbitals are key quantities for the double-exchange
mechanism, strain effects are confirmed to be crucial for the resulting
magnetic coupling.Comment: 16 pages, 7 figures, to be published on J. Phys.: Condensed Matte
Evidence of Kitaev interaction in the monolayer 1T-CrTe
The two-dimensional 1T-CrTe has been an attractive room-temperature van
der Waals magnet which has a potential application in spintronic devices.
Although it was recognized as a ferromagnetism in the past, the monolayer
1T-CrTe was recently found to exhibit zigzag antiferromagnetism with the
easy axis oriented at to the perpendicular direction of the plane.
Therefore, the origin of the intricate anisotropic magnetic behavior therein is
well worthy of thorough exploration. Here, by applying density functional
theory with spin spiral method, we demonstrate that the Kitaev interaction,
together with the single-ion anisotropy and other off-diagonal exchanges, is
amenable to explain the magnetic orientation in the metallic 1T-CrTe.
Moreover, the Ruderman-Kittle-Kasuya-Yosida interaction can also be extracted
from the dispersion calculations, which explains the metallic behavior of
1T-CrTe. Our results demonstrate that 1T-CrTe is potentially a rare
metallic Kitaev material
Multifunctional Lateral Transition-Metal Disulfides Heterojunctions
The intrinsic spin-dependent transport properties of two types of lateral
VS2|MoS2 heterojunctions are systematically investigated using first-principles
calculations, and their various nanodevices with novel properties are designed.
The lateral VS2|MoS2 heterojunction diodes show a perfect rectifying effect and
are promising for the applications of Schottky diodes. A large
spin-polarization ratio is observed for the A-type device and pure
spin-mediated current is then realized. The gate voltage significantly tunes
the current and rectification ratio of their field-effect transistors (FETs).
In addition, they all have sensitive photoresponse to blue light, and could be
used as photodetector and photovoltaic device. Moreover, they generate the
effective thermally-driven current when a temperature gratitude appears between
the two terminals, suggesting them as potential thermoelectric materials.
Hence, the lateral VS2|MoS2 heterojunctions show a multifunctional nature and
have various potential applications in spintronics, optoelectronics, and spin
caloritronics
Higher-order Topological and Nodal Superconductors MS (M = Nb and Ta) Transition-metal Sulfides
Intrinsic topological superconducting materials are exotic and vital to
develop the next-generation topological superconducting devices, topological
quantum calculations, and quantum information technologies. Here, we predict
the topological and nodal superconductivity of MS (M = Nb and Ta)
transition-metal sulfides by using the density functional theory for
superconductors combining with the symmetry indicators. We reveal their
higher-order topology nature with an index of Z4 = 2. These materials have a
higher Tc than the Nb or Ta metal superconductors due to their flat-band and
strong electron-phonon coupling nature. Electron doping and lighter isotopes
can effectively enhance the Tc. Our findings show that the MS (M = Nb and Ta)
systems can be new platforms to study exotic physics in the higher-order
topological superconductors, and provide a theoretical support to utilize them
as the topological superconducting devices in the field of advanced topological
quantum calculations and information technologies.Comment: 5 pages, 3 figure
Biogenic Synthesis of Novel Functionalized Selenium Nanoparticles by Lactobacillus casei ATCC 393 and Its Protective Effects on Intestinal Barrier Dysfunction Caused by Enterotoxigenic Escherichia coli K88
Selenium (Se) is an essential element for human and animal health. Biogenic selenium nanoparticles (SeNPs) by microorganism possess unique physical and chemical properties and biological activities compared with inorganic Se and organic Se. The study was conducted to investigate the mainly biological activities of SeNPs by Lactobacillus casei ATCC 393 (L. casei 393). The results showed that L. casei 393 transformed sodium selenite to red SeNPs with the size of 50–80 nm, and accumulated them intracellularly. L. casei 393-SeNPs promoted the growth and proliferation of porcine intestinal epithelial cells (IPEC-J2), human colonic epithelial cells (NCM460), and human acute monocytic leukemia cell (THP-1)-derived macrophagocyte. L. casei 393-SeNPs significantly inhibited the growth of human liver tumor cell line-HepG2, and alleviated diquat-induced IPEC-J2 oxidative damage. Moreover, in vivo and in vitro experimental results showed that administration with L. casei 393-SeNPs protected against Enterotoxigenic Escherichia coli K88 (ETEC K88)-caused intestinal barrier dysfunction. ETEC K88 infection-associated oxidative stress (glutathione peroxidase activity, total superoxide dismutase activity, total antioxidant capacity, and malondialdehyde) was ameliorated in L. casei 393-SeNPs-treated mice. These findings suggest that L. casei 393-SeNPs with no cytotoxicity play a key role in maintaining intestinal epithelial integrity and intestinal microflora balance in response to oxidative stress and infection
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