Orientational Epitaxy of van der Waals Molecular Heterostructures.

The shape of individual building blocks is an important parameter in bottom-up self-assembly of nanostructured materials. A simple shape change from sphere to spheroid can significantly affect the assembly process due to the modification to the orientational degrees of freedom. When a layer of spheres is placed upon a layer of spheroids, the strain at the interface can be minimized by the spheroid taking a special orientation. C70 fullerenes represent the smallest spheroids, and their interaction with a sphere-like C60 is investigated. We find that the orientation of the C70 within a close-packed C70 layer can be steered by contacting a layer of C60. This orientational steering phenomenon is potentially useful for epitaxial growth of multilayer van der Waals molecular heterostructures.

Tailoring the surface of ZnO nanorods into corrugated nanorods via a selective chemical etch method.

Using the chemical vapour deposition method, we successfully converted smooth ZnO nanorods (NRs) into corrugated NRs by simply increasing the reaction time. The surface morphology and crystallographic structure of the corrugated NRs were investigated. The corrugated NRs were decorated by alternant [Formula: see text] and [Formula: see text] planes at the exposed side surfaces while the conventional [Formula: see text] planes disappeared. No twinning boundaries were found in the periodically corrugated structures, indicating that they were type II corrugated NRs. Further investigation told us that they were selectively etched. We introduced a hydrothermal method to synthesize the smooth ZnO NRs and then etched them in a tube furnace at 950 °C with a flow of carbon monoxide. By separating the growth stage and the selective etching stage, we explicitly demonstrated a successfully selective etching effect on ZnO NRs with a carbon monoxide reducing atmosphere for the first time. An etching mechanism based on the selective reaction between carbon monoxide and the different exposed surfaces was proposed. Our results will improve the understanding of the growth mechanism on coarse or corrugated NRs and provide a new strategy for the application of surface controlled nanostructured materials.

Endovenous Microwave Ablation Versus Laser Ablation for Small Saphenous Vein Varicosis.

INTRODUCTION: Laser and radiofrequency ablation are two thermal ablation methods currently widely used to treat lower limb venous insufficiency. However, very few studies have been conducted on the use of microwaves, a form of thermal ablation, for the treatment of small saphenous vein (SSV) insufficiency. This study aimed to examine the efficacy and safety of endovenous microwave ablation (EMA) for the treatment of SSV insufficiency. METHODS: The clinical data of 126 patients (126 lower limbs) with SSV insufficiency (SSV trunk reflux time ≥ 500 ms on lower limb color Doppler ultrasound) treated at the Surgery Department of The Sixth People's Hospital of Zhuji from January 2020 to June 2022 were analyzed retrospectively; 64 patients underwent EMA and 62 underwent endovenous laser ablation (EVLA). The perioperative marker data [duration of surgery, duration of hospitalization, length of thermal ablation, duration of thermal ablation, number of incisions, and numerical pain rating scale (NPRS)], complication data [skin ecchymosis, skin burns, surgical site infection, paresthesia, deep vein thrombosis (DVT), and heat-induced thrombosis (EHIT)], venous clinical severity score (VCSS), chronic venous disease quality of life questionnaire (CIVIQ-20) before and 1, 3, 12 months after surgery, and SSV trunk occlusion rate at 12 months after surgery were compared between the two groups. RESULTS: No significant differences in the surgery or hospitalization durations were observed between the two groups. There were no significant differences in the length of the SSV that required thermal ablation between the two groups; however, the thermal ablation time was shorter in the EMA group than that in the EVLA group (6.14 ± 1.47 min vs 7.05 ± 1.16 min, P < 0.001). There were no statistical differences in the number of incisions, volume of tumescent solution used, or quantity of sclerosing foam used. The NPRS scores of the EMA group at 24 h and 72 h after surgery were significantly greater than those of the EVLA group (4.03 ± 0.98 vs 3.52 ± 1.28, P = 0.013; 3.78 ± 1.06 vs 3.15 ± 1.03, P = 0.001). Moreover, the two groups showed no significant difference in the NPRS score at 1 month (1.14 ± 0.84 vs 1.07 ± 0.75, P = 0.623). The EMA and EVLA group patients experienced similar postoperative complications. The VCSS and CIVIQ-20 score significantly improved at 1, 3, and 12 months after surgery. The VCSS and CIVIQ-20 scores were compared between the two groups at 12 months after surgery, and there were no significant differences (1.44 ± 0.63 vs 1.56 ± 0.56, P = 0.261; 24.24 ± 4.96 vs 25.19 ± 5.36, P = 0.304). There was no significant difference in the incidence of SSV trunk occlusion at 12 months after surgery between the two groups (95.31% vs 96.77%, OR 1.475; 95% CI 0.238-9.146, P = 1.000). CONCLUSION: EMA and EVLA are equally effective treatment methods for SSV insufficiency. EMA is associated with higher NPRS scores in the early postoperative period.

All-fiber normal-dispersion single-polarization passively mode-locked laser based on a 45°-tilted fiber grating.

An all-fiber normal-dispersion Yb-doped fiber laser with 45°-tilted fiber grating (TFG) is, to the best of our knowledge, experimentally demonstrated for the first time. Stable linearly-chirped pulses with the duration of 4 ps and the bandwidth of 9 nm can be directly generated from the laser cavity. By employing the 45° TFG with the polarization-dependent loss of 33 dB, output pulses with high polarization extinction ratio of 26 dB are implemented in the experiment. Our result shows that the 45° TFG can work effectively as a polarizer, which could be exploited to single-polarization all-fiber lasers.

[LO phonon-plasmon coupled mode in hexagonal IngaN alloy].

Raman scattering spectra of hexagonal InGaN/GaN film, excited with 532 and 488 nm visible laser lines and 325 nm UV laser line, were investigated at room temperature and 78 K. The sample was grown by metalorganic chemical vapor deposition on a sapphire substrate. Excited with 532 and 488 nm visible laser lines, the E2 and A1 (LO) modes were observed at about 571.3 and 736.4 cm(-1), respectively. These scattering signals mainly originate from GaN layer. Excited with 325 nm UV laser line, the E2 mode shifts to 569.7 cm(-1), while A1 (LO) mode shifts to 730.3 cm(-1) and resonance is enhanced. These scattering signals originate from InGaN layer. A broad feature at high frequency of A1 (LO) mode was observed in spectroscopy excited with visible laser line, and was attributed to the LO phonon-plasmon coupled mode of InGaN layer. The electron concentration of InGaN film determined from the frequency of the coupled mode is ne = 1.61 x 10(18) cm(-3). Excited with 325 nm UV laser light, the LO phonon-plasmon coupled mode is absent, and the scattering signal of A1 (LO) mode mainly originates from the surface depletion layer of the sample. The thickness of the surface depletion layer is about 40 nm. Furthermore, the scattering intensities of LO phonon-plasmon coupled mode at room temperature and 78 K were compared and analyzed. The screening wave vectors of plasmon at different temperatures were calculated. At low temperature, the screening wave vector increases, the damping of the plasmon decreases, so the LO phonon-plasmon coupled mode becomes stronger. This work is helpful in understanding the property of InGaN and in developing the optoelectronic devices of nitride.

Hole-Induced Spontaneous Mutual Annihilation of Dislocation Pairs.

Dislocations are always observed during crystal growth, and it is usually desirable to reduce the dislocation density in high-quality crystals. Here, the annihilation process of the 30° Shockley partial dislocation pairs in CdTe is studied by first-principles calculations. We found that the dislocations can glide relatively easily due to the weak local bonding. Our systematic study of the slipping mechanism of the dislocations suggests that the energy barrier for the annihilation process is low. Band structure calculations reveal that the band bending caused by the charge transfer between the two dislocation cores depends on the core-core distance. A simple linear model is proposed to describe the mechanism of formation of the dislocation pair. More importantly, we demonstrate that hole injection can affect the core structure, increase the mobility, and eventually trigger a spontaneous mutual annihilation, which could be employed as a possible facile way to reduce the dislocation density.

Excitation Dependent Phosphorous Property and New Model of the Structured Green Luminescence in ZnO.

The copper induced green luminescence (GL) with two sets of fine structures in ZnO crystal has been found for several decades (i.e., R. Dingle, Phys. Rev. Lett. 23, 579 (1969)), but the physical origin of the doublet still remains as an open question up to now. In this paper, we provide new insight into the mechanism of the structured GL band in terms of new experimental findings and theoretical calculations. It is found, for the first time, that the GL signal exhibits persistent afterglow for tens of minutes after the switch-off of below-band-gap excitation light but it cannot occur under above-band-gap excitation. Such a phosphorous property may be interpreted as de-trapping and feeding of electrons from a shallow trapping level via the conduction band to the Cu-related luminescence centers where the Cu3+ ion is proposed to work as the final state of the GL emission. From first-principles calculation, such a Cu3+ ion in wurtzite ZnO prefers a high spin 3d8 state with two non-degenerated half-filled orbitals due to the Jahn-Teller effect, probably leading to the double structures in photoluminescence spectrum. Therefore, this model gives a comprehensively new understanding on the mechanism of the structured GL band in ZnO.

Extinction of the zero-phonon line and the first-order phonon sideband in excitonic luminescence of ZnO at room temperature: the self-absorption effect.

It is firmly demonstrated in experiment that the self-absorption (SA) effect can lead to the extinction of the zero-phonon line and the first-order longitudinal optical phonon sideband of free excitonic luminescence of ZnO at room temperature. Moreover, effectiveness degree of SA effect is found to be dependent on both absorption coefficient and travelling distance of emitted photons, as well as even lattice temperature, which is uniquely reflected by the redshift amount in emission peak in ZnO. It is also unambiguously proved that the SA effect still strictly obeys the Beer-Lambert law of absorption. This work not only uncovers the long-term puzzle of significant redshift of emission peak of ZnO at higher temperatures, but also shows that the SA effect may have to be carefully taken into consideration in the study of spontaneous emission, laser and relevant optoelectronic processes in luminescent materials and optoelectronic devices.

Image recombination transform algorithm for superresolution structured illumination microscopy.

Structured illumination microscopy (SIM) is an attractive choice for fast superresolution imaging. The generation of structured illumination patterns made by interference of laser beams is broadly employed to obtain high modulation depth of patterns, while the polarizations of the laser beams must be elaborately controlled to guarantee the high contrast of interference intensity, which brings a more complex configuration for the polarization control. The emerging pattern projection strategy is much more compact, but the modulation depth of patterns is deteriorated by the optical transfer function of the optical system, especially in high spatial frequency near the diffraction limit. Therefore, the traditional superresolution reconstruction algorithm for interference-based SIM will suffer from many artifacts in the case of projection-based SIM that possesses a low modulation depth. Here, we propose an alternative reconstruction algorithm based on image recombination transform, which provides an alternative solution to address this problem even in a weak modulation depth. We demonstrated the effectiveness of this algorithm in the multicolor superresolution imaging of bovine pulmonary arterial endothelial cells in our developed projection-based SIM system, which applies a computer controlled digital micromirror device for fast fringe generation and multicolor light-emitting diodes for illumination. The merit of the system incorporated with the proposed algorithm allows for a low excitation intensity fluorescence imaging even less than 1??W/cm2, which is beneficial for the long-term, in vivo superresolved imaging of live cells and tissues.

Double-exposure optical sectioning structured illumination microscopy based on Hilbert transform reconstruction.

Structured illumination microscopy (SIM) with axially optical sectioning capability has found widespread applications in three-dimensional live cell imaging in recent years, since it combines high sensitivity, short image acquisition time, and high spatial resolution. To obtain one sectioned slice, three raw images with a fixed phase-shift, normally 2π/3, are generally required. In this paper, we report a data processing algorithm based on the one-dimensional Hilbert transform, which needs only two raw images with arbitrary phase-shift for each single slice. The proposed algorithm is different from the previous two-dimensional Hilbert spiral transform algorithm in theory. The presented algorithm has the advantages of simpler data processing procedure, faster computation speed and better reconstructed image quality. The validity of the scheme is verified by imaging biological samples in our developed DMD-based LED-illumination SIM system.