全角度高反射率DBR对GaN基蓝光Mini-LED芯片发光性能的提升

该文采用Essential Macleod软件设计了一种在420 nm～480 nm波段且具有全入射角度、高反射率(大于96%)的TiO2/SiO2分布布拉格反射镜(DBR)膜系,并采用这种全角度高反射率DBR膜系作为GaN基蓝光Mini-LED芯片的反射镜。研究结果表明,与对应唯一中心波长的传统结构DBR膜系相比,它具有全角度高反射率DBR膜系的蓝光Mini-LED芯片的I-V特性、光场分布形态且高温老化特性保持不变,在5 mA的工作电流下,输出的光功率和插座效率分别提升了5.6%和5.4%,其原因是全角度高反射率DBR膜系克服了传统结构DBR膜系在大角度入射时反射率下降的缺点。     

基于Fabry-Perot腔的高精度MEMS加速度传感器

设计了一种基于Fabry-Perot腔的高精度MEMS加速度传感器,采用动态波长调谐原理.加速度传感单元由二氧化硅支撑梁与中心质量块组成,在质量块底部与衬底层硅基凹槽内,利用薄膜沉积技术制备分布式布拉格反射镜(DBR)构成F-P光学微腔.设计了新型折叠支撑梁和维持器件可靠性的限位块结构.研究给出质量块位移引起腔长变化,...     

基于蝶翅鳞片三维结构的Au/SnO2纳米复合材料制备及其表面增强拉曼散射性能研究

利用巴黎翠凤蝶前翅翅鳞片作为模板,通过前驱体浸泡后烧结的方法制备出具有原始蝶翅鳞片准周期三维结构的SnO2(金红石相),并采用化学沉积的方法在已制备的SnO2上沉积Au纳米颗粒,合成出Au/SnO2纳米复合材料.通过SEM、XRD以及TEM等表征方法检测并分析该材料形貌结构和成分组成.采用罗丹明6G(R6G)作为分析物,测试该材料的表面增强拉曼散射光谱.通过材料形貌结构图及UV-Vis漫反射光谱谱图,分析该基底的表面增强拉曼散射机理.该基底所具有的三维结构为拉曼信号增强提供大量"热点",而基底材料中SnO2和Au纳米颗粒为拉曼增强效应提供协同作用.良好的拉曼性能以及较低的制备成本表明,该新型表面增强拉曼散射基底具有一定的应用前景.     

微波液相沉积法制备二氧化钛薄膜

采用微波液相沉积法(MWLPD),在低温下制备出了性能优异的锐钛矿型TiO2薄膜.通过XRD、SEM分析手段研究了薄膜和粉体的结晶度、晶粒尺寸、表面形貌等.实验结果表明,所得薄膜不仅具有良好的结晶形貌、表面形貌及可见光透过率,还具有特殊的表面凸起结构,能有效提高薄膜的比表面积,有助于提高TiO2薄膜的光催化性能.且整个制备过程无需热处理,成膜周期短,效率较高.     

纳米结构的倾斜角度沉积及性能优化

纳米材料发展的关键是纳米结构的制备、形貌调控和性能优化.倾斜角度沉积是以较大的角度(大于75°)倾斜入射沉积薄膜,通过控制沉积参数,得到具有特殊形貌纳米结构的方法,具有适用范围广,操作便捷,制备的薄膜面积大、纯度高、结构规整等特点,是一种理想的制备纳米材料的方法.本文介绍了采用倾斜角度沉积技术制备氧化铪抗反射薄膜和银基表面增强拉曼基底,详细分析了该方法的参数调控对纳米结构的形貌和性能的影响,并指出将倾斜角度沉积与其他先进技术相结合(以原子层沉积为例),可进一步优化纳米结构的性能,提高倾斜角度沉积的使用范围.     

应变率对Ag/Co多层膜硬度的影响及塑性变形不稳定性研究

周期结构对多层膜硬度和弹性模量的影响已有比较深入的研究,而对多层膜塑性变形特征和机理的研究还少有报道.本文采用直流磁控溅射制备了周期Λ为10 nm,20 nm,40 nm,60 nm的Ag/Co多层膜,X射线衍射表明薄膜均为Ag(111)和Co(002)织构的多晶结构,且具有很好的周期性.采用纳米压入连续刚度法在四种加载应变速率(0.025 s-1,0.05 s-1,0.1 s-1,0.5 s-1)下分别测试了不同周期薄膜的硬度,结果表明硬度随应变速率的变大而增大,且随周期的变大硬度变化随应变速率的变化更加敏感.纳米压入的载荷-位移曲线出现明显的不连续突变,压痕形貌周围有明显的剪切带,表明塑性变形的过程是不稳定的.     

调制结构对TiN/ZrN纳米多层膜的表面形貌、生长行为及力学性能的影响

利用射频反应磁控溅射方法,设计并制备了一系列不同调制周期的TiN/ZrN纳米多层膜.利用原子力显微镜、X射线衍射仪和纳米压痕仪对多层膜的表面形貌、微观结构和力学性能进行了系统表征.研究结果表明调制结构影响着薄膜的择优生长取向、沉积速率和表面形貌;在调制周期为7nm～26nm的范围内,随调制周期的增加,TiN/ZrN多层膜的织构取向有从(100)面向(111)面转变的趋势;TiN和ZrN层的沉积速率随调制周期的变化而变化.在调制周期为15nm左右时,表面粗糙度最小,减小和增加调制周期均导致粗糙度的增加.力学性能分析表明TiN/ZrN多层膜的硬度和弹性模量均高于单一TiN和ZrN的硬度和弹性模量,且随着调制周期的减小有逐渐增加的趋势.此外,根据调制结构和力学性能的分析结果,讨论了TiN/ZrN纳米多层膜的硬化机制.     

PLD法制备NiO薄膜及结构和形貌的研究

利用脉冲激光沉积法(PLD)在Si衬底上制备NiO薄膜,利用X射线衍射(XRD)和原子力显微镜(AFM)对所制备薄膜的晶体结构和表面形貌进行表征分析,研究衬底温度和脉冲激光能量对NiO薄膜结构和形貌的影响,得到生长质量较高、择优取向的多晶NiO薄膜的一种最佳制备条件.制备了p-NiO/n-Si异质结器件,Ⅰ-Ⅴ特性测试表明,器件具有良好的整流特性.     

WC/DLC纳米多层膜微观结构研究

阳极层流型气体离子源与非平衡磁控溅射复合技术沉积制备WC/DLC纳米多层膜,并在膜/基间设计了中间过渡层.用扫描电镜、拉曼光谱仪、光电子能谱仪、X衍射仪、透射电镜、干涉显微镜等,对WC/DLC纳米多层膜的微观形貌结构进行分析研究.结果表明:沉积的WC/DLC膜层表面致密、光滑细腻;多层调制周期在3～4 nn,多层界面不清晰,形成渐变过渡界面.WC/DLC膜中主要是sp2键中掺杂有一定量的sp3键,WC则以纳米晶结构弥散分布在DLC之中.     

微弧氧化TiO2涂层微结构对细胞黏附性能的影响

为改善TA2纯钛表面的生物相容性，采用微弧氧化技术，通过设置不同的电解液和电参数，在TA2纯钛基材上制备出4种具有不同微结构的氧化钛涂层，采用XRD、SEM、台阶仪、接触角测量仪测试样品的物相组成、微观形貌、粗糙度和亲水性，并以MC3T3-E1(小鼠成骨细胞)与各组具有不同微结构的氧化钛涂层样品共培养后，观察细胞与样品表面的黏附状态。结果表明：采用磷酸盐体系电解液可制备出具有大孔平整和大孔粗糙结构形貌的氧化钛涂层，采用SEM观察细胞的黏附状态发现，在具有这2种结构形貌的氧化钛涂层表面生成了丝状伪足，表面可见细胞分泌物，说明涂层表面具有一定的生物活性；采用NaOH体系电解液制备出具有细孔平整和细孔粗糙结构形貌的氧化钛涂层，在具有这2种结构形貌的氧化钛涂层表面，细胞的黏附面积明显增大，板状伪足和丝状伪足丰富，生物活性明显增强；进一步对比分析发现，氧化钛涂层在粗糙度较高时对细胞的迁移方向具有引导作用，在粗糙度较低时能够提升涂层表面对细胞的黏附能力，具有微纳二级结构的涂层对这2种能力具有整合作用。     

Electrical characterisation of p-doped distributed Bragg reflectors in electrically pumped GaInNAs VCSOAs for 1.3 μm operation

The high resistivity that is encountered in p-type DBRs is an important problem in vertical cavity surface emitting lasers and optical amplifiers (VCSELs and VCSOAs). This is because the formation of potential barriers at the interfaces between layers of high and low refractive index inhibits the carrier flow, thus increasing the DBR series resistance. In this work, the electrical characteristics of two p-type doped DBR structures grown on undoped and p-type doped GaAs substrates have been investigated. The DBRs are designed for VCSOAs operating at 1.3 μm and consist of 14-periods of alternating GaAs and Al_0.9Ga_0.1As in the first sample and 14-periods of GaAs and Al_0.3Ga_0.7As/Al_0.9Ga_0.1As in the second one. For the longitudinal transport sample, Hall mobility and sheet carrier density were measured in the temperature range from 77 to 300 K. In the vertical transport sample, current–voltage (I–V) measurements across the DBR layers were carried out at different temperatures in the range between 15 and 300 K. We achieved resistivity reduction in our samples by using an interface composition grading technique aimed at improving the VCSOA characteristics.     

Free-space-wave drop demultiplexing waveguide device fabricated by use of the interference exposure method

Integration of free-space-wave add-drop multiplexers that consist of focusing grating couplers (FGCs) and distributed Bragg reflectors (DBRs) in thin-film waveguides have been investigated for construction of an intraboard wavelength-division-multiplexing optical interconnection. Compact optics of a Lloyd mirror configuration and a contact-type mask aligner were combined as an interference exposure system for fabrication of DBRs of 300 microm coupling length. DBRs were integrated with FGCs on a thin-film waveguide on a glass substrate for two-channel wavelength-drop demultiplexing from guided waves to free-space waves. Measured outcoupled wavelengths of two free-space waves from two pairs of a FGC and a DBR agreed with the design values of 845 and 849 nm.     

GaN-based distributed Bragg reflector for high-brightness LED and solid-state lighting

A comprehensive numerical model for distributed Bragg reflectors (DBRs) based on thin-film optics is developed. Detailed refractive-index calculations for GaN, AlN, AlGaN, and InGaN can also be included in this numerical model. This model can predict DBR performances for refractive-index variations, layer-thickness fluctuations, and the number of quarter-wave stack pairs in DBR as well different light polarizations.     

Structural analysis of distributed Bragg reflector mirrors

Quantum cascade (QC) lasers and vertical-cavity surface-emitting lasers (VCSELs) are of great interest due to their potential importance for a variety of device applications. Both kinds of lasers call for very highly reflective mirrors. Usually distributed Bragg reflector (DBR) mirrors, which consist of periodic quarter wavelength stacks of high and low refractive index compound semiconductors are used. These stacks are superlattices containing more than 40 individual layers. To obtain very high reflectivity DBRs alternating GaAs and AlAs layers are used for both the high and low index mirrors.GaAs/AlAs DBR structures containing 15 periods were characterized by the complementary use of RBS/channeling, TEM and HRXRD. Since the total thickness of a DBR exceeds 2 μm the RBS analysis was performed at two He-ion energies: 1.7 MeV and 3.82 MeV. After some stopping power corrections TEM and RBS provided similar results. Discrepancies with HRXRD data were attributed to the lateral inhomogeneity of produced superlattice. Virtues and pitfalls of complementary use of these techniques were discussed.     

A study of distributed dielectric bragg reflectors for vertically emitting lasers of the near-IR range

Studies aimed at optimization of the design of a dielectric distributed Bragg reflector (DBR) produced by the reactive magnetron sputtering method for applications in near-IR vertical-cavity surface-emitting lasers with intracavity contacts (ICC-VCSELs) are carried out. It is shown that the reflectivity of the dielectric DBRs based on SiO₂/TiO₂ decreases due to the polycrystalline structure of the TiO₂ layers, which causes diffusive scattering of light. In contrast, amorphous Ta₂O₅ layers is characterized by a low surface roughness and low fluctuation in the refractive index. Single-mode ICC-VCSELs in the 980-nm spectral range with dielectric DBR based on SiO₂/Ta₂O₅ with a threshold current less than 0.27 mA, electric resistance of less than 200 Ω, and differential efficiency of more than 0.8 W/A are demonstrated.

     

Chemically vapour deposited diamond coatings on cemented tungsten carbides: Substrate pretreatments, adhesion and cutting performance

Chemical vapour deposition (CVD) of diamond films onto Co-cemented tungsten carbide (WC-Co) tools and wear parts presents several problems due to interfacial graphitization induced by the binder phase and thermal expansion mismatch of diamond and WC-Co. Methods used to improve diamond film adhesion include substrate-modification processes that create a three-dimensional compositionally graded interface. This paper reviews substrate pretreatments and adhesion issues of chemically vapour deposited diamond films on WC-Co. The combined effect of pretreatments and substrate microstructure on the adhesive toughness and wear rate of CVD diamond in dry machining of highly abrasive materials was analyzed. The role of diamond film surface morphology on chip evacuation in dry milling of ceramics was also investigated by comparing feed forces of coated and uncoated mills. The overall tribological performance of diamond coated mills depended on coating microstructure and smoothness. The use of smother films did allow to reduce cutting forces by facilitating chip evacuation.     

A capacity available-to-promise model for drum-buffer-rope systems

The capacity available-to-promise (CATP) concept, which is designed to enhance the available-to-promise (ATP) feature in MRPII for changing production strategy from make-to-stock (MTS) to make-to-order (MTO), was developed recently. In contrast to an ATP, which is the future uncommitted inventory as projected by master production schedule, a CATP provides a detailed and time-phased diagram of unused production capacity. Hence, a CATP can allow marketing personnel to establish realistic order promise dates and concentrate on selling idle capacity in the future, and enable customers to select their preferred future capacity. This study proposes a CATP model for drum-buffer-rope (DBR) systems. The DBR scheduling system is one of finite capacity schedule systems and is currently being implemented by a growing number of manufacturing companies. This CATP model can help DBR users improve the due-date promising and exploitation of bottleneck. This CATP model can also be embedded in current commercial or private DBR scheduling systems so as to enhance their effectiveness.     

Optically pumped surface-emitting lasing using self-assembled block-copolymer-distributed Bragg reflectors

A thin-film organic laser cavity using a block-copolymer-based one-dimensional (1D) photonic crystal was fabricated. Polymeric distributed Bragg reflectors (DBRs) were prepared through the self-assembly of a lamellar-forming poly(styrene-b-isoprene) (PS-b-PI) diblock copolymer having a 1D photonic stop band overlapping with the fluorescence spectrum of a gain medium. Optically pumped surface-emitting lasing was obtained using poly(methyl methacrylate) (PMMA) doped with 1,4-di-(2-methylstyryl)benzene (Bis-MSB) as an organic gain medium and the polymeric self-assembled DBR as a spectral-band selective feedback element.     

A highly distributed Bragg stack with unique geometry provides effective camouflage for Loliginid squid eyes

Cephalopods possess a sophisticated array of mechanisms to achieve camouflage in dynamic underwater environments. While active mechanisms such as chromatophore patterning and body posturing are well known, passive mechanisms such as manipulating light with highly evolved reflectors may also play an important role. To explore the contribution of passive mechanisms to cephalopod camouflage, we investigated the optical and biochemical properties of the silver layer covering the eye of the California fishery squid, Loligo opalescens. We discovered a novel nested-spindle geometry whose correlated structure effectively emulates a randomly distributed Bragg reflector (DBR), with a range of spatial frequencies resulting in broadband visible reflectance, making it a nearly ideal passive camouflage material for the depth at which these animals live. We used the transfer-matrix method of optical modelling to investigate specular reflection from the spindle structures, demonstrating that a DBR with widely distributed thickness variations of high refractive index elements is sufficient to yield broadband reflectance over visible wavelengths, and that unlike DBRs with one or a few spatial frequencies, this broadband reflectance occurs from a wide range of viewing angles. The spindle shape of the cells may facilitate self-assembly of a random DBR to achieve smooth spatial distributions in refractive indices. This design lends itself to technological imitation to achieve a DBR with wide range of smoothly varying layer thicknesses in a facile, inexpensive manner.     

Improvement in light output intensity of InGaN/GaN multiple-quantum-well blue light-emitting diode by SiO2/Si3N4 distributed Bragg reflectors and silver back mirror

In this article, the light output intensity of InGaN/GaN multiple-quantum-well (MQW) light emitting diodes (LEDs) is improved by using SiO₂/Si₃N₄ distributed Bragg reflectors (DBRs) as window layer and Ag back mirror. The SiO₂/Si₃N₄ DBRs can take several advantages, such as high reflectance with less number of DBR, passive characteristics, and high reliability due to growth in one pump down growth system. The experimental results indicated that InGaN/GaN LEDs with the 3-pair of SiO₂/Si₃N₄ DBRs show a maximum light output intensity of 64 mcd under 20 mA driving current and an improvement of 42% as compared to that of InGaN/GaN LEDs without SiO₂/Si₃N₄ DBRs. In addition, the turn-on voltage, forward resistance, and full width at half maximum (FWHM) of the emission spectra for InGaN/GaN LEDs with the 3-pair of SiO₂/Si₃N₄ DBRs and Ag back mirror are 3.23 V, 16 Ω, and 22.4 nm under 20 mA forward current.