Simulation of the light extraction efficiency of nanostructure light-emitting diodes

The light extraction efficiencies have been calculated for various InGaN/GaN multiple quantum well nanostructure light-emitting diodes including nanopillar,nanorough of P-GaN surface,coreshell and nano-interlayer structure.From the calculated results we can see that the light extraction efficiency is remarkably improved in the nanostructures,especially those with an InGaN or AlGaN nano-interlayer.With a 420-nm luminescence wavelength,the light extraction efficiency can reach as high as 65% for the InGaN or AlGaN nano-interlayer structure with appropriate In or Al content while only 26% for the planar structure.     

精密测量中的纳米计量技术

随着纳米科学的迅速发展,对纳米计量技术也提出了更高要求。目前,纳米计量技术已经实现在几十微米量程范围内具有亚纳米甚至皮米量级的测量分辨率。回顾了现在主要的纳米计量技术,包括激光干涉仪、差拍F P干涉仪、X射线干涉仪、光学+X射线干涉仪、基于频率测量技术和光频梳技术等,介绍了其工作原理、技术特点、应用范围及其最新研究进展。     

8-epi-Liphagal的合成研究

四环杂萜类天然产物Liphagal含有新奇的[6-7-5-6]四环骨架, 是磷酸肌醇3-激酶(PI3K)的有效抑制剂之一, 可以选择性抑制细胞增殖和促进细胞死亡, 在治疗炎症、免疫紊乱、癌症以及心血管疾病中有潜在的医用价值. 从廉价的2,4,5-三甲氧基苯甲醛出发, 通过Wittig反应、Cu催化的环化反应、选择性氢化、分子内Friedel-Crafts反应, 以直线步骤最长7步, 8.72%的总收率实现了8-epi-Liphagal高级中间体10的合成.     

Effect of surface treatment of GaN based light emitting diode wafers on the leakage current of light emitting diode devices

To form low-resistance Ohmic contact to p-type GaN, InGaN/GaN multiple quantum well light emitting diode wafers are treated with boiled aqua regia prior to Ni/Au (5~nm/5~nm) film deposition. The surface morphology of wafers and the current--voltage characteristics of fabricated light emitting diode devices are investigated. It is shown that surface treatment with boiled aqua regia could effectively remove oxide from the surface of the p-GaN layer, and reveal defect-pits whose density is almost the same as the screw dislocation density estimated by x-ray rocking curve measurement. It suggests that the metal atoms of the Ni/Au transparent electrode of light emitting diode devices may diffuse into the p-GaN layer along threading dislocation lines and form additional leakage current channels. Therefore, the surface treatment time with boiled aqua regia should not be too long so as to avoid the increase of threading dislocation-induced leakage current and the degradation of electrical properties of light emitting diodes.     

Microstructure and strain analysis of GaN epitaxial films using in-plane grazing incidence x-ray diffraction

This paper investigates the major structural parameters,such as crystal quality and strain state of (001)-oriented GaN thin films grown on sapphire substrates by metalorganic chemical vapour deposition,using an in-plane grazing incidence x-ray diffraction technique.The results are analysed and compared with a complementary out-of-plane xray diffraction technique.The twist of the GaN mosaic structure is determined through the direct grazing incidence measurement of (100) reflection which agrees well with the result obtained by extrapolation method.The method for directly determining the in-plane lattice parameters of the GaN layers is also presented.Combined with the biaxial strain model,it derives the lattice parameters corresponding to fully relaxed GaN films.The GaN epilayers show an increasing residual compressive stress with increasing layer thickness when the two dimensional growth stage is established,reaching to a maximum level of-0.89 GPa.     

Time delay in InGaN multiple quantum well laser diodes at room temperature

This paper reports that a long delay between the beginning of pumping current pulse and the onset of optical pulse is observed in InGaN laser diodes.The delay time decreases as the pumping current increases,and the speed of the delay time reduction becomes slower as the current amplitude increases further.Such delay phenomena are remarkably less serious in laser diodes grown on GaN substrate than those on sapphire.It attributes the delay to the traps which cause a large optical loss by saturable absorption and retard the laser action.The traps can be bleached by capturing injected carriers.The effect of GaAs laser irradiation on InGaN laser action demonstrates that the traps responsible for the delay are deep centres which can be filled by the photo-assisted processes.     

Modulation instability of femtosecond pulses in fibres with slowly decreasing dispersion

In this paper,we investigate the modulation instability for generating femtosecond pulses in fibres with slowly decreasing dispersion.Higher-order dispersion and higher-order nonlinear effects are taken into account when the continuous wave or quasi-continuous wave evolves into sub-picosecond and femtosecond pulses by modulation instability in the optical fibres.Our research results show that the gain spectrum of the dispersion-decreasing fibres is much wider than that in conventional fibres.The third-order dispersion effect has no contribution to gain spectrum,while the self-steepening effect reduces the maximum value and gain bandwidth,and the Raman self-scattering effect widens the extent to which the modulation instability occurs.     

用于测量液面高度的光纤光栅传感器

提出并实验了一种精密的用光纤光栅作为敏感元件测量液面高度的方法,讨论了传感系统设计的关键问题。该传感器可用于中等深度的液面高度的精密测量,其灵敏度可达0.15mm/pm。     

弯曲振动型薄板扬声器

分析了动圈扬声器的性能,讨论了弯曲振动型振膜构成的NXT扬声器及其频率响应和声辐射。薄板扬声器在新世纪中将有发展前途。     

绿色合成氧化铈构建导尿管抗菌水凝胶涂层

因导尿管引起的微生物感染严重危害患者健康,并容易导致细菌耐药性。基于纳米材料的抗菌涂层是应对导尿管感染的最有效策略之一。本文利用绿色小球藻自身及其分泌物的还原性环境,制备合成高表面活性的纳米氧化铈Bio-CeO₂,能够高效产生活性氧自由基,实现对大肠杆菌、铜绿假单胞菌等致病菌的抑制和杀伤。在这种绿色合成的模拟酶纳米材料基础上,将其与壳聚糖、京尼平等生物基材料协同作用,在导尿管表面构建稳定的抑菌水凝胶涂层。结果显示,包覆有Bio-CeO₂水凝胶抗菌涂层的硅胶导尿管比裸导管的抑菌效果显著增强,尤其是在低浓度的过氧化氢溶液环境下,对铜绿假单胞菌的抑菌效率可提升至54%,这为未来新型广谱抗菌导尿管的设计和感染性疾病的预防控制提供了潜在新材料和技术手段。