Asynchronous propagation of atomic force and excited electronic charge in GaAs under proton irradiation.

The studies for the interaction of energetic particles with matter have greatly contributed to the exploration of material properties under irradiation conditions, such as nuclear safety, medical physics and aerospace applications. In this work, we theoretically simulate the non-adiabatic process for GaAs upon proton irradiation using time-dependent density functional theory, and find that the radial propagation of force on atoms and the excitation of electron in GaAs are non-synchronous process. We calculated the electronic stopping power on proton with the velocity of 0.1-0.6 a.u., agreement with the previous empirical results. After further analyzing the force on atoms and the population of excited electrons, we find that under proton irradiation, the electrons around the host atoms at different distances from the proton trajectories are excited almost simultaneously, especially those regions with relatively high charge density. However, the distant atoms have a significant hysteresis in force, which occurs after the surrounding electrons are excited. In addition, hysteresis in force and electron excitation behavior at different positions are closely related to the velocity of proton. This non-synchronous propagation reveals the microscopic dynamic mechanism of energy deposition into the target material under ion irradiation.

Crossover of energy deposition and semi-stable chemical bonding in the nonadiabatic dynamics of GaN under proton irradiation.

Understanding the ion-solid interactions of charged particles in materials facilitates the development of ion beam irradiation techniques. Combining Ehrenfest dynamics and time-dependent density-functional theory, we investigated the electronic stopping power (ESP) of an energetic proton in GaN crystal and studied the ultrafast dynamic interaction between the proton and target atoms during the nonadiabatic process. We found a crossover phenomenon of ESP at 0.36 a.u. along the <100> and <110> channels, which is interpreted by the charge transfer between the host material and the projectile and the stopping force exerted on the proton. At velocities of 0.2 and 1.7 a.u., we demonstrated that the reversal of the average number of charge transfer and the average axial force resulted in the reversed energy deposition rate and ESP in the corresponding channel. Further analysis of the evolution of non-adiabatic electronic states revealed the existence of the transient and semi-stable N-H chemical bonding during irradiation process, which is introduced by the electron clouds overlap of Nsp3hybridization and thesorbitals of the proton. These results provide meaningful information for the interactions between energetic ions and matter.

Stretching effects on non-adiabatic electron dynamic behavior in poly(dG)-poly(dC) DNA upon the proton irradiation.

The electronic excitations caused by DNA when exposed to ion radiation is essential to DNA damage. In this paper, we investigated the energy deposition and electron excitation process of DNA with reasonable stretching range upon proton irradiation based on time-dependent density functional theory. Stretching changes the strength of hydrogen bonding between the DNA base pairs, which in turn affects the Coulomb interaction between the projectile and DNA. As a semi-flexible molecule, the way of energy deposition is weakly sensitive to the stretching rate of DNA. However, the increase of stretching rate causes the increase of charge density along the trajectory channel, sequentially resulting in an increase in proton resistance along the intruding channel. The Mulliken charge analysis indicates that the guanine base and guanine ribose are ionized, meanwhile the cytosine base and cytosine ribose are reduced at all stretching rates. In a few femtoseconds, there exists an electron flow passing through the guanine ribose, guanine, cytosine base and the cytosine ribose in turn. This electron flow increases electron transfer and DNA ionization, promoting the side chain damage of the DNA upon ion irradiation. Our results provide a theoretical insight for deciphering the physical mechanism of the early stage of the irradiation process, and are also of great significance for the study of particle beam cancer therapy in different biological tissues.

Dynamic interplay between thionine and DNA under carbon ion irradiation: a real-time first-principles study.

Understanding the interactions between deoxyribonucleic acid (DNA) and photosensitizer under ion irradiation benefits the development of aptasensors, DNA biosensors and cancer diagnosis. Using real-time time-depended density functional theory, by simulating high-energy C ion passing through DNA with poly(dG)·poly(dC) sequence and that with embedded thionine (3,7-diamino-5-phenothiazinium, TH), we compared the electronic stopping power (ESP), evolution of the structure and charge, and absorption spectrum. TH inserting leads the increase in space charge density, a larger electron de-excitation and a larger ESP, but the speed corresponding to the maximum ESP is almost same. When C ion passes through TH-DNA, the structure of TH slightly changes and there still exists noncovalent interaction between TH and DNA, but the absorption coefficient depends on the electron occupied state of TH when the ion passes through. These results indicate that at low radiation doses, TH still can be a DNA detector, although its response wavelength and intensity have been slightly changed, and provide a theoretical reference to improve the possible application of phenothiazine dye in DNA biosensor under ion irradiation.

Optimizing the Synthetic Conditions of "Green" Colloidal AgBiS2 Nanocrystals Using a Low-Cost Sulfur Source.

Colloidal AgBiS2 nanocrystals (NCs) have attracted increasing attention as a near-infrared absorbent materials with non-toxic elements and a high absorption coefficient. In recent years, colloidal AgBiS2 NCs have typically been synthesized via the hot injection method using hexamethyldisilathiane (TMS) as the sulfur source. However, the cost of TMS is one of the biggest obstacles to large-scale synthesis of colloidal AgBiS2 NCs. Herein, we synthesized colloidal AgBiS2 NCs using oleylamine@sulfur (OLA-S) solution as the sulfur source instead of TMS and optimized the synthesis conditions of colloidal AgBiS2 NCs. By controlling the reaction injection temperature and the dosage of OLA-S, colloidal AgBiS2 NCs with adjustable size can be synthesized. Compared with TMS-based colloidal AgBiS2 NCs, the colloidal AgBiS2 NCs based on OLA-S has good crystallinity and fewer defects.

Real-time first-principles calculations of ultrafast carrier dynamics of SnSe/TiO2heterojunction under Li+implantation.

Ion implantation has been widely used in biomaterials, alloys, and semiconductors modification. Basing on the studying of trapping states in the equilibrium state, we investigate the ultrafast carrier dynamics of SnSe/TiO2and SnSe/Li/TiO2heterojunctions under Li+implantation by the real-time time-dependent density functional theory. The special type II band alignment and Li+interfacial states in SnSe/TiO2heterojunction effectively facilitate the exciton dissociation in a benign process and suppresses the interfacial nonradiative recombination. By monitoring the instantaneous ion-solid interaction energy, electronic stropping power and the excitation electron evolution, we find that atomic reconstruction introduced by the Li inserting layer changes the charge density and crystal potential field in the injection channel, and thus weakens the violent oscillation force and electron excitation on the Ti and O atoms. There exists a weaker and shorter charge excitation at the interface for SnSe/Li/TiO2implantation system, which suggests that the Li ion layer weakens the e-ph coupling between the interface electrons and the moving ion. Meanwhile, only the hot electrons are produced in the interface region, reducing the probability of carrier recombination. These results provide an understanding for the behavior of carriers in SnSe based heterojunctions and the electron-phonon coupling mechanism at the phase/grain boundary under ion implantation.

Anion-Coordination-Assisted Assembly of Supramolecular Charge-Transfer Complexes Based on Tris(urea) Ligands.

Charge-transfer (CT) complexes, formed by noncovalent bonding between electron-rich (donor, D) and electron-deficient (acceptor, A) molecules (or moieties) have attracted considerable attention due to their fascinating structures and potential applications. Herein, we demonstrate that anion coordination is a promising strategy to promote CT complex formation between anion-binding, electron-rich tris(urea) donor ligands (D) and electron-deficient viologen cation acceptors (A), which form co-crystals featuring infinite ⋅⋅⋅DADA⋅⋅⋅ or discrete (circular DADA or three-decker DAD) π-stacking interactions. These CT complexes were studied by X-ray diffraction, UV/Vis spectroscopy, electric conductivity measurements, charge displacement curve (CDC) calculations, and DFT computations.

Effect of High-Dose Statin Pretreatment for Myocardial Perfusion in Patients Receiving Percutaneous Coronary Intervention (PCI): A Meta-Analysis of 15 Randomized Studies.

BACKGROUND For coronary artery disease, percutaneous coronary intervention (PCI) is the preferred treatment. Reperfusion injury is a common and serious complication of PCI. Studies showed that early statin therapy has a favorable prognostic impact for patients undergoing PCI. However, the effects of statins on improving post-PCI myocardial perfusion are still unclear. In this study we evaluated the potential effect of high-dose statin pretreatment on postprocedure myocardial perfusion and MACE rate in patients receiving PCI. MATERIAL AND METHODS We searched randomized controlled trials that evaluated the effect of high-dose statin pretreatment on post-PCI TIMI flow grade and MACE in patients undergoing PCI from the databases of PubMed, Embase, and Cochrane Library. All data were pooled for analysis and were stratified by type of statin, clinical presentation, and current statin therapy status in subgroup. RESULTS Fifteen RCTs with 4240 individuals were selected. The pooled analysis showed that high-dose statin pretreatment before PCI significantly improved the final TIMI flow grade compared with the control group (OR=0.61, 95% CI: 0.46 to 0.80, p=0.0005), and showed reduced incidence of MACE (OR=0.53, 95%CI: 0.39 to 0.71, p<0.0001). In subgroup analysis, the beneficial effect of high-dose statin was significant in statin-naive treatment patients, ACS patients, and patients on atorvastatin therapy, but no difference occurred in rosuvastatin, previous statin therapy, and stable angina patients. CONCLUSIONS High-dose statin pretreatment has an important effect on postprocedure myocardial perfusion by improving the TIMI flow in patients undergoing PCI, and high-dose statin preloading also reduces the incidence of MACE.

The origin of enhanced optical absorption of the BiFeO3/ZnO heterojunction in the visible and terahertz regions.

Optical absorption is improved for the BiFeO3/ZnO heterostructure prepared by a sol-gel process, especially, in the terahertz energy region. A dipole-corrected slab model is used to describe the bilayer film, and first-principles calculations agree with the experiments which present unambiguous explanation for the enhancement of the optical properties. Two-dimensional electrons in the ZnO side of the heterostructure are found to play an essential role in forming the photoinduced carriers and the enhancement of the absorption. The conducting layers tend to penetrate into the interface and decrease the band gap, leading to the transport of carriers through the interface to the BiFeO3 side. The photoinduced carriers can be separated by the ferroelectric domains in BiFeO3, and this mechanism makes the heterostructure an ideal candidate for BiFeO3-based ferroelectric photovoltaic cells.

Tunable Optical Properties and Charge Separation in CH3NH3Sn(x)Pb(1-x)I3/TiO2-Based Planar Perovskites Cells.

A sharp potential drop across the interface of the Pb-rich halide perovskites/TiO2 heterostructure is predicted from first-principles calculations, suggesting enhanced separation of photoinduced charge carriers in the perovskite-based photovoltaic solar cells. The potential drop appears to be associated with the charge accumulation at the polar interface. More importantly, on account of both the ß phase structure of CH3NH3Sn(x)Pb(1-x)I3 for x < 0.5 and the α phase structure of CH3NH3Sn(x)Pb(1-x)I3 for x ≥ 0.5, the computed optical absorption spectra from time-dependent density functional theory (TD-DFT) are in very good agreement with the measured spectra from previous experiments. Our TD-DFT computation also confirms the experimental structures of the mixed Pb-Sn organometal halide perovskites. These computation results provide a highly sought answer to the question why the lead-based halide perovskites possess much higher power conversion efficiencies than the tin-based counterparts for solar-cell applications.