Optical near fields for ablation of periodic structures.

The formation mechanism of laser-induced periodic surface structures (LIPSS) has been a key to high-resolution sub-diffraction lithography or high-efficiency large-area nanotexturing. We show the evolution of LIPSS formation from a nanohole seed structure to high-spatial-frequency LIPSS by using a tightly focused and rectangular-shaped laser beam with different shape-polarization orientations. Formation of LIPSS based on light intensity distribution without invoking any long-range electromagnetic modes achieved quantitative match between modeling and experiment. Our results clearly show the entire step-like and deterministic process of LIPSS evolution based on experimental data and numerical simulations, revealing the dominant structural near-field enhancement on the ripple formation. A rectangular-shaped beam with an aspect ratio of 7:3 was used to break the symmetry of a circularly shaped focus. By azimuthally rotating the orientation of the focal spot and the polarization, it is possible to visualize the far-field effect for the initial seed structure formation and the competition between the far and near fields in the subsequent structure evolution.

Nanoscale control of non-reciprocal ripple writing.

Femtosecond laser-induced deep-subwavelength structures have attracted much attention as a nanoscale surface texturization technique. A better understanding of the formation conditions and period control is required. Herein, we report a method of non-reciprocal writing via a tailored optical far-field exposure, where the period of ripples varies along different scanning directions, and achieve a continuous manipulation of the period from 47 to 112 nm (±4 nm) for a 100-nm-thick indium tin oxide (ITO) on glass. A full electromagnetic model was developed to demonstrate the redistributed localized near-field at different stages of ablation with nanoscale precision. It explains the formation of ripples and the asymmetry of the focal spot determines the non-reciprocity of ripple writing. Combined with beam shaping techniques, we achieved non-reciprocal writing (regarding scanning direction) using an aperture-shaped beam. The non-reciprocal writing is expected to open new paths for precise and controllable nanoscale surface texturing.

Nanoscale Printing of Indium-Tin-Oxide by Femtosecond Laser Pulses.

For constructing optical and electrical micro-devices, the deposition/printing of materials with sub-1 µm precision and size (cross-section) is required. Crystalline c-ITO (indium tin oxide) nanostructures were patterned on glass with sufficient precision to form 20-50 nm gaps between individual disks or lines of ∼250 nm diameter or width. The absorbed energy density [J/cm3] followed a second-order dependence on pulse energy. This facilitated high-resolution and precise nanoscale laser-writing at a laser wavelength of 515 nm. Patterns for optical elements such as circular gratings and micro-disks were laser-printed using ITO as a resist. Unexposed amorphous a-ITO was chemically removed in aqueous 1% vol. HF solution. This use of a-ITO as a solid resist holds promise for metamaterial and micro-optical applications.

Highly Deformable High-Performance Paper-Based Perovskite Photodetector with Improved Stability.

Paper-based photodetectors have attracted extensive research interest owing to their environmentally friendly and highly deformable properties. Although perovskite crystals with outstanding optoelectronic properties have proved to be one of the most promising candidates for photodetectors, the development of paper-based photodetectors is hindered by the moisture absorptivity of paper and the instability of perovskite crystals in a humid atmosphere. In this study, we demonstrate a highly deformable and high-performance paper-based perovskite photodetector. The photodetector maintains its excellent performance even after exposure to a relative humidity of 60% for 120 h.

Perovskite Single-Crystal Microwire-Array Photodetectors with Performance Stability beyond 1 Year.

Compared with thin-film morphology, 1D perovskite structures such as micro/nanowires with fewer grain boundaries and lower defect density are very suitable for high-performance photodetectors with higher stability. Although the stability of perovskite microwire-based photodetectors has been substantially enhanced in comparison with that of photodetectors based on thin-film morphology, practical applications require further improvements to the stability before implementation. In this study, a template-assisted method is developed to prepare methylammonium lead bromide (MAPbBr3 ) micro/nanowire structures, which are encapsulated in situ by a protective hydrophobic molecular layer. The combination of the protective layer, high crystalline quality, and highly ordered microstructures significantly improve the stability of the MAPbBr3 single-crystal microwire arrays. Consequently, these MAPbBr3 single-crystal microwire-array-based photodetectors exhibit significant long-term stability, maintaining 96% of the initial photocurrent after 1 year without further encapsulation. The lifetime of such photodetectors is hence approximately four times longer than that of the most stable previously reported perovskite micro/nanowire-based photodetector; this is thought to be the most stable perovskite photodetector reported thus far. Furthermore, this work should contribute further toward the realization of perovskite 1D structures with long-term stability.

Template-confined growth of Ruddlesden-Popper perovskite micro-wire arrays for stable polarized photodetectors.

The detection of the polarization states of light is of great significance for the analysis of biological tissue morphologies, image display systems and sensors. Although organic-inorganic hybrid perovskite crystals have excellent photoelectric properties, which make them very suitable for the preparation of photodetectors, their applications in polarized light detection are hindered by their isotropy and instability. Here, we solved this problem by fabricating a stable 2D layered Ruddlesden-Popper perovskite into anisotropic micro-wire arrays with a template-confined method. Based on this anisotropic structure, a high-performance photodetector with a dark current as low as 10-12 A, high responsivity of 3.5 A W-1, detectivity exceeding 1 × 1015 Jones and a fast response with a rise time of 4.1 ms and a decay time of 3.3 ms was achieved and successfully applied for high-performance polarization detection. More importantly, the device maintained a superior performance even after being exposed to an environment of 60% relative humidity without encapsulation.

Gold nanoparticle densely packed micro/nanowire-based pressure sensors for human motion monitoring and physiological signal detection.

Flexible pressure sensors have gained ever-increasing attention because of their widespread applications in wearable devices. The sensor fabrication technologies reported so far are generally complicated, limiting their industrial applications. It is therefore of great importance to develop a simple method to fabricate high-performance flexible pressure sensors. Herein, we report an approach of assembling gold nanoparticles into strictly aligned and densely stacked micro/nanowires by imprinting for flexible pressure sensors with high performance. By our method, the whole assembly process takes only 1 min. The pressure sensor exhibits a best detection limit as low as 25 Pa. The sensors could be attached to any part of the human body and are so sensitive that even pulses in different regions of the body and the differences between a pregnant woman and a nonpregnant woman could be distinguished.

[Analysis of 61 cases undergoing sphincter-preserving procedure with intersphincteric resection by telescopic anastomosis for ultra-low rectal cancer].

OBJECTIVE: To investigate the efficacy and safety of sphincter-preserving procedure with transabdominal intersphincteric resection for ultra-low rectal cancer. METHODS: Clinical data of 61 cases with ultra-low rectal cancer (distance from anal verge ranged from 4-5 cm) were analyzed retrospectively. The patients underwent sphincter-preserving procedure with intersphincteric resection and telescopic anastomosis. RESULTS: There were 34 males and 27 females. The mean age was 56.7 years. The inferior border of the tumor was 4 cm above the anal verge in 21 cases, and 5 cm in 40 cases. There 55 patients with rectal adenocarcinoma in this cohort. The tumor was well-differentiated in 24 cases, moderately-differentiated in 29 cases, and poorly-differentiated in 2 cases. There were 6 cases with malignant adenoma. The TNM staging was T1N0M0 in 36 cases, T2N0M0 in 23, and T3N1M0 in 2. The ability to control defecation significantly improved in 1-3 months postoperatively, and returned to normal in 6-12 months. Two patients developed anastomotic leak (3.3%), and 3 anastomotic stenosis (4.9%) postoperatively. Fifty-four patients(88.5%) had follow-up. The median follow-up time was 6.2 years. The local recurrence rate was 5.6%, and the 5-year-survival rate was 73.5%. CONCLUSION: Sphincter-preserving procedure with intersphincteric resection and telescopic anastomosis is a safe and effective procedure for ultra-low rectal cancer.

[Clinical experience of 371 cases of sphincter-preservation with telescopic anastomosis after radical excision for low-middle rectal cancer].

OBJECTIVE: To evaluate the clinical efficacy, feasibility and safety of sphincter-preservation with telescopic anastomosis of colon and rectal mucosa in low-middle rectal cancer. METHODS: A retrospective analysis was carried out in 371 patients with low-middle rectal cancer in whom telescopic anastomosis was used. There were 224 males and 147 females, with a mean age of 57.9 (21-99) years. The lower margins of the tumors located between 5-8 cm from the anal verge. On histopathology, there were 361 adenocarcinomas, including 138 well-differentiated, 201 moderately differentiated, 11 poorly differentiated, 11 mucinous adenocarcinoma, and 10 adenomas with neoplastic changes. According to the Duke's stage classification, 120 were TNM stage I, 222 stage II, 26 stage III, and 3 stage IV. RESULTS: Three hundred and eighteen (318/371, 85.7%) cases were followed up, and the median follow up time was 5.8 years. Postoperative complications were observed, including 16(4.3%) cases with anastomotic leak, and 8 (2.1%) with anastomotic stenosis. All the patients resumed normal bowel function during 12-24 weeks after operation, with 1-3 times per day. The local recurrence rate was 6.3% (20/318). Hepatic and lung metastasis was 14.5% (46/318) and 2.5% (8/318), respectively. The 5-year survival rate was 69.7%. CONCLUSION: The sphincter-preservation with telescopic anastomosis procedure is safe and effective for low-middle rectal cancer, and the sphincter function can be well-preserved.