Preparation and photodetection performance of high crystalline quality and large size β-Ga_(2)O_(3)microwires

Ultrawide band gap semiconductors are promising solar-blind ultraviolet(UV)photodetector materials due to their suitable bandgap,strong absorption and high sensitivity.Here,β-Ga_(2)O_(3)microwires with high crystal quality and large size were grown by the chemical vapor deposition(CVD)method.The microwires reach up to 1 cm in length and were single crystalline with low defect density.Owing to its high crystal quality,a metal–semiconductor–metal photodetector fabricated from a Ga_(2)O_(3)microwire showed a responsivity of 1.2 A/W at 240 nm with an ultrahigh UV/visible rejection ratio(R_(peak)/R_(400 nm))of 5.8×10^(5),indicating that the device has excellent spectral selectivity.In addition,no obvious persistent photoconductivity was observed in the test.The rise and decay time constants of the device were 0.13 and 0.14 s,respectively.This work not only provides a growth method for high-quality Ga_(2)O_(3)microwires,but also demonstrates the excellent performance of Ga_(2)O_(3)microwires in solar-blind ultraviolet detection.

Formation of nano-twinned 3C-SiC grains in Fe-implanted 6H-SiC after 1500-℃annealing

A nano-twinned microstructure was found in amorphous SiC after high-temperature annealing.Grazing incidence x-ray diffraction,high-resolution transmission electron microscopy,and electron diffraction were performed to characterize the microstructure and phase transition in the recrystallization layer.After 1500℃or 2-h annealing,3C-SiC grains and numerous stacking faults on the{111}planes were visible.Some 3C-SiC grains have nano-twinned structure with{011}planes.Between the nano-twinned 3C-SiC grains,there is a stacking fault,indicating that the formation mechanisms of the nano-twinned structure are related to the disorder of Si atoms.The increase in the twin thickness with increasing annealing temperature demonstrates that the nano-twinned structure can sink for lattice defects,in order to improve the radiation tolerance of SiC.

Comparison of cavities and extended defects formed in helium-implanted 6H-SiC at room temperature and 750 ℃

The formation of cavities in silicon carbide is vitally useful to“smart-cut”and metal gettering in semiconductor industry.In this study,cavities and extended defects formed in helium(He)ions implanted 6H-SiC at room temperature(RT)and 750℃ followed by annealing at 1500℃are investigated by a combination of transmission electron microscopy and high-resolution electron microscopy.The observed cavities and extended defects are related to the implantation temperature.Heterogeneously distributed cavities and extended defects are observed in the helium-implanted 6H-SiC at RT,while homogeneously distributed cavities and extended defects are formed after He-implanted 6H-SiC at 750℃.The possible reasons are discussed.

Effect of helium concentration on irradiation damage of Fe-ion irradiated SIMP steel at 300℃and 450℃

SIMP steel is newly developed fully martensitic steel for lead-cooled fast reactors and accelerator-driven systems.It is important to evaluate its radiation resistance via high flux neutron irradiation,where dense He atoms can be formed via(n,α)transmutation reaction.Co-irradiation with Fe and He ions,instead of neutron,was performed.Specimens were irradiated with 6.4-MeV Fe ions to the damage dose of 5 dpa at a depth of 600 nm.Three different helium injection ratios of 60-appm He/dpa(dpa:displacements per atom),200-appm He/dpa and 600-appm He/dpa at a depth of 600 nm,were performed.Two different irradiation temperatures of 300℃and 450℃were carried out.The effect of helium concentration on the microstructure of Fe-irradiated SIMP steel was investigated.Microstructural damage was observed using transmission electron microscopy.The formed dislocation loops and bubbles depended on the helium injection ratio and irradiation temperature.Lots of dislocation loops and helium bubbles were homogeneously distributed at 300℃,but not at 450℃.The causes of observed effects are discussed.

Comparison of helium bubble formation in F82H, ODS, SIMP and T91 steels irradiated by Fe and He ions simultaneously

Ferritic-martensitic steels and ODS steels are attractive candidates for structural materials in advanced nuclear-power systems due to their good swelling resistance. Four kinds of steels, F82 H, 15 Cr-ODS, SIMP and T91, are investigated in this study. We take 6.4 Me V Fe3+ ions and energy-degraded 1.0 Me V He+ ions in the irradiation of these materials to 5 dpa and 60 appm He/dpa, 200 appm He/dpa and 600 appm He/dpa at 300℃ and 450℃, respectively. The bubble formation and distribution are investigated by transmission electron microscopy(TEM). Formation and distribution of the bubbles in the four investigated steels are compared. The influence of irradiation temperature and helium injection ratio on bubble formation is discussed. It is found that there appears to be homogenously distributed bubbles at 300℃ irradiation while heterogeneously distributed bubbles at 450℃ irradiation.

Risk factors and clinical outcomes of incomplete endoscopic resection of small rectal neuroendocrine tumors in southern China:a 9-year data analysis

Background:The histologically complete resection(CR)rate of small rectal neuroendocrine tumors(RNETs)is unsatisfactory at the first endoscopy.Risk factors and clinical outcomes associated with incomplete resection(IR)have not been explicitly elucidated.This study aims to explore the relevant factors of IR.Methods:This retrospective study reviewed patients with small RNETs(10mm)in eight centers from January 2013 to December 2021.Clinicopathological characteristics and clinical outcomes were compared between the CR and IR groups,and the polypectomy and advanced treatment groups.Results:Of the 326 patients included,83(25.5%)were diagnosed with IR.Polypectomy(odds ratio[OR]=16.86),a central depression(OR=7.50),and treatment in the early period(OR=2.60)were closely associated with IR.Further analysis revealed that an atypical hyperemic appearance(OR=7.49)and treatment in the early period(OR=2.54)were significantly associated with the inappropriate use of polypectomy(both P<0.05).In addition,a total of 265(81.3%)were followed up with a median follow-up period of 30.9 months.No death,metastasis,or recurrence was found during the follow-up period.Conclusions:Polypectomy,a central depression,and treatment in the early period were risk factors for IR.Further,an atypical hyperemic appearance and treatment in the early period were significant predisposing factors for inappropriate choice of polypectomy.For histologically incompletely resected small RNETs,follow-up may be a safe and feasible alternative to rigorous salvage therapy.

Suppression of persistent photoconductivity in high gain Ga_(2)O_(3) Schottky photodetectors

The defect-related photoconductivity gain and persistent photoconductivity(PPC)observed in Ga_(2)O_(3)Schottky photodetectors lead to a contradiction between high responsivity and fast recovery speed.In this work,a metal-semiconductor-metal(MSM)Schottky photodetector,a unidirectional Schottky photodetector,and a photoconductor were constructed on Ga_(2)O_(3)films.The MSM Schottky devices have high gain(>13)and high responsivity(>2.5 A/W)at 230-250 nm,as well as slow recovery speed caused by PPC.Interestingly,applying a positive pulse voltage to the reverse-biased Ga_(2)O_(3)/Au Schottky junction can effectively suppress the PPC in the photodetector,while maintaining high gain.The mechanisms of gain and PPC do not strictly follow the interface trap trapping holes or the self-trapped holes models,which is attributed to the correlation with ionized oxygen vacancies in the Schottky junction.The positive pulse voltage modulates the width of the Schottky junction to help quickly neutralize electrons and ionized oxygen vacancies.The realization of suppression PPC functions and the establishment of physical models will facilitate the realization of high responsivity and fast response Schottky devices.

Review on carbon dots:Synthesis and application in biology field

As a multifunctional fluorescent nanomaterial, carbon dots (CDs) not only have small size, stable chemical properties, excellent photoluminescence characteristics, but also exhibit good biocompatibility and low toxicity. It has attracted considerable attention in the field of nanotechnology and biological science. CDs contain abundant functional groups on the surface, which not only retain part of the properties of raw materials, but also may have new photoelectric, catalytic, biomedical, and other functions. In this review, we systematically summarize the synthesis methods, modifications, optical properties, and main biological functions of CDs in recent years. The application of functionalized modified CDs in biological detection, biological imaging, photodynamic therapy, photothermal therapy, targeted therapy, drug delivery, gene delivery, protein delivery, and other biomedical fields is introduced. The latest progress of CDs with its own biomedical function in antioxidant, anti-pathogen, and disease treatment is summarized. Finally, we discuss some problems in the practical application of CDs and look forward to the future development trend of self-functional CDs combined with surface modification to achieve multimodal treatment of diseases.

Inhibition of LIM kinase reduces contraction and proliferation in bladder smooth muscle

Overactive bladder(OAB)is the most bothersome symptom in lower urinary tract symptoms(LUTS).Current pharmacologic treatment aims to inhibit detrusor contraction;however,shows unsatisfied efficacy and high discontinuation rate.LIM kinases(LIMKs)promote smooth muscle contraction in the prostate;however,their function in the bladder smooth muscle remains unclear.Here,we studied effects of the LIMK inhibitors on bladder smooth muscle contraction and proliferation both in vitro and in vivo experiments.Bladder expressions of LIMKs are elevated in OAB rat detrusor tissues.Two LIMK inhibitors,SR7826 and LIMKi3,inhibit contraction of human detrusor strip,and cause actin filament breakdown,as well as cell proliferation reduction in cultured human bladder smooth muscle cells(HBSMCs),paralleled by reduced cofilin phosphorylation.Silencing of LIMK1 and LIMK2 in HBSMCs resulted in breakdown of actin filaments and decreased cell proliferation.Treatment with SR7826 or LIMKi3 decreased micturition frequency and bladder detrusor hypertrophy in rats with bladder outlet obstruction.Our study suggests that LIMKs may promote contraction and proliferation in the bladder smooth muscle,which could be inhibited by small molecule LIMK inhibitors.LIMK inhibitors could be a potential therapeutic strategy for OAB-related LUTS.

On the helium bubble swelling in nano-oxide dispersion-strengthened steels

The development of structural materials resistant to harsh radiation environments requires an in-depth understanding of the early stage of the aging processes.In radiation environments with high transmutation helium production rates such as in fusion and spallation applications,even materials with otherwise acceptable radiation stability may suffer from radiation embrittlement related to helium bubble formation.While theoretical modeling of helium-assisted cavity nucleation in pure metals and simple alloys provides some useful guidelines at the atomic scale level,these,however,do not overlap with the size resolution of available experimental techniques.In this study,we employed slow positron beam spectroscopy to characterize the nucleation and growth of nano-scale helium bubbles in martensitic steels strengthened by thermodynamically stable nano-oxide dispersoids.In combination with transmission electron microscopy,we experimentally characterized the evolution of helium bubbles from small clusters of radiation-induced vacancies to large cavities well resolvable by TEM.Superior radiation resistance of oxide-dispersion strengthened steels dominates only in the early stages of bubble evolution,where positron lifetime measurements provide a missing piece of the microstructural puzzle conventionally constructed by TEM.

Photoluminescence and Raman Spectroscopy Study on Color Centers of Helium Ion-Implanted 4H-SiC

Color centers in silicon carbide(SiC)are promising candidates for quantum technologies.However,the richness of the polytype and defect configuration of SiC makes the accurate control of the types and position of defects in SiC still challenging.In this study,helium ion-implanted 4H-SiC was characterized by atomic force microscopy(AFM),confocal photoluminescence(PL),and confocal Raman spectroscopy at room temperature.PL signals of silicon vacancy were found and analyzed using 638-nm and 785-nm laser excitation by means of depth profiling and SWIFT mapping.Lattice defects(C-C bond)were detected by continuous laser excitation at 532 nm and 638 nm,respectively.PL/Raman depth profiling was helpful in revealing the three-dimensional distribution of produced defects.Differences in the depth profiling results and SRIM simulation results were explained by considering the depth resolution of the confocal measurement setup,helium bubbles,as well as swelling.

Strong room-temperature emission from defect states in CVD-grown WSe2 nanosheets

Monolayer transition metal dichalcogenides （TMDCs）, as direct bandgap semiconductors, show promise for applications in ultra-thin flexible optoelec- tronic devices. However, the optical properties and device performance are greatly affected by defects, such as vacancies, present in these materials. Vacancies exist unavoidably in mechanically exfoliated or grown by chemical vapor deposition （CVD） monolayer TMDCs; therefore, their influence on the electric and optical properties of host materials has been widely studied. Here, we report a new defect state located at 1.54 eV, which is 70 meV lower than the neutral exciton energy in as-prepared WSe2 monolayers grown by CVD. This defect state is clearly observed in photoluminescence （PL） and Raman spectra at ambient conditions. PL mapping, Rarnan mapping, and atomic force microscopy analysis indicate a solid-vapor reaction growth mechanism of the defect state formation. During a certain growth stage, nuclei with the composition of WOxSey do not fully react with the Se vapor, leading to the defect formation. This type of defects permits radiative recombination of bound neutral excitons, which can make the PL intensity as strong as the intrinsic excitation. Our findings reveal a new way to tailor the optical properties of two-dimensional TMDCs without any additional processes performed after growth.