基于视觉辐条图案识别方法的蓝宝石引晶机制研究

工业生产蓝宝石晶体过程中,引晶步骤有着至关重要的地位。引晶必须在温度梯度较小,温度分布趋于稳定的条件下进行。目前,工业生产蓝宝石主要依靠人工经验操控籽晶杆实现引晶操作,但是人工引晶操作的准确性不高会导致成品品质不佳、资源浪费。为此,本文提出一种基于蓝宝石视觉辐条图案识别方法来检测蓝宝石熔体状态自由液面状态,从而实现一种高效率引晶的机制。此方法利用经典骨架化算法细化辐条图案,Harris算子实现特征信息的提取,提取的特征信息放入运动轨迹模型中判断熔体稳定性,分析液面温度分布稳定性从而实现引晶。结果表明,此算法具有有效性,蓝宝石晶体引晶效率大大提高,生产出的成品良率也有提升,可有效指导蓝宝石的工业生产。     

多片导模法蓝宝石晶体的缺陷研究

使用导模法(EFG)生长了多片a面蓝宝石晶体。显微拉曼光谱结合电感耦合等离子体发射光谱(ICP-AES)测试得出晶体的气泡中可能存在含S化合物。晶体表面明显的生长条纹主要与温度、生长速度的波动以及模具的加工精度有关。化学腐蚀分析表明晶体位错密度在4.2×10⁴ cm^-2,未存在小角度晶界缺陷,双晶摇摆曲线半峰宽(FWHM)为70.63″。由于采用石墨保温材料,晶体中存在F心与F⁺色心。晶体在400~3 000 nm波段透过率高于80%,空气中退火后可减弱色心吸收。本文研究结果可为蓝宝石晶体缺陷形成理论研究提供参考,也可为导模法蓝宝石工业生产技术改进提供借鉴。     

Effects of substrate and transfer on CVD-grown graphene over sapphire-induced Cu films

We differentiated the effects of Cu films deposited on single crystalline a-,r-,and c-plane sapphire substrates upon graphene films synthesized with atmospheric pressure chemical vapor deposition(CVD).The data illustrate that the realization of high-crystalline Cu film is dependent not only on the crystallinity of underlying substrate,but also on the symmetric match of crystallographic geometry between metal film and substrate.We also systematically investigated the effects of PMMA removal on the Raman ID/IG and IG/I2D values of transferred graphene.The results reveal that different PMMA removal methods do not alter the ID/IG values;instead,the residue of PMMA increases the IG/I2D values and the thermal decomposition of PMMA leads to higher IG/I2D values than the removal of PMMA with acetone.The effects of PMMA removal on variations of the Raman spectra are also discussed.     

High-power, continuous-wave Ti:sapphire laser pumped by fiber-laser green source at 532 nm

We report the first experimental demonstration of efficient and high-power operation of a Ti:sapphire laser pumped by a simple, compact, continuous-wave (cw) fiber-laser-based green source. The pump radiation is obtained by direct single-pass second-harmonic-generation (SHG) of a 33 W, cw Yb-fiber laser in a 30-mm-long MgO:sPPLT crystal, providing 11 W of single-frequency green power at 532 nm in TEM₀₀ spatial profile with power and frequency stability better than 3.3% and 32 MHz, respectively, over 1 h. The Ti:sapphire laser is continuously tunable across 743-970 nm and can deliver an output power up to 2.7 W with a slope efficiency as high as 32.8% under optimum output coupling of 20%. The laser output has a TEM₀₀ spatial profile with M²<1.44 across the tuning range and exhibits a peak-to-peak power fluctuation below 5.1% over 1 h.     

Be扩散处理、热处理和天然双色昌乐蓝宝石的宝石学特征与鉴别

对中国山东昌乐Be扩散处理、热处理和未处理双色蓝宝石(黄色和蓝色)进行了宝石学常规测试、紫外可见光谱、红外光谱、电子探针和激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)测试,以获得它们的谱学特征,提出其鉴别方法。研究发现Be扩散处理双色蓝宝石仅出现Fe3+—Fe3+形成的紫外可见吸收峰,而且377nm吸收峰的强度异常高。红外光谱中,热处理和未处理的双色蓝宝石存在明显的3 310cm-1羟基吸收峰,而该吸收峰在Be扩散处理双色蓝宝石中消失。因此,紫外可见光谱和红外光谱可用于鉴别Be扩散处理、热处理和未处理双色蓝宝石。另外,二碘甲烷浸油实验也可识别Be扩散处理双色蓝宝石。     

GaN基高压直流发光二极管制备及其性能分析

GaN基高压直流发光二极管工艺制备, 采用蓝宝石图形衬底(PSS) 外延片制备正梯形芯粒结构的GaN基高压直流LED.相对其他结构器件, 该结构器件发光效率最高, 封装白光后, 在色温4500 K, 驱动电流20 mA时, 光效116.06 lm/W, 对应电压50 V. 测试其I-V曲线表明, 开启电压为36 V, 对应驱动电流为1.5 mA; 在电流15 mA至50 mA时, 光功率随驱动电流增加近似于线性增加, 在此区域光效随电流增加而降低的幅度比较缓慢, 表明GaN基高压直流LED适宜于采用大电流密度驱动, 而不会出现驱动电流密度增加导致量子效率明显下降(efficiency droop), 为从芯片层面研究解决量子效率下降难题提供了一种新思路.     

Improving InGaN-LED performance by optimizing the patterned sapphire substrate shape

The epitaxial growths of GaN films and GaN-based LEDs on various patterned sapphire substrates (PSSes) with different values of fill factor (f) and slanted angle (θ) are investigated in detail. The threading dislocation (TD) density is lower in the film grown on the PSS with a smaller fill factor, resulting in a higher internal quantum efficiency (IQE). Also the ability of the LED to withstand the electrostatic discharge (ESD) increases as the fill factor decreases. The illumination output power of the LED is affected by both θ and f. It is found that the illumination output power of the LED grown on the PSS with a lower production of tanθ and f is higher than that with a higher production of tanθ and f.     

高温预生长对图形化蓝宝石衬底GaN薄膜质量的提高

在图形化蓝宝石衬底生长低温缓冲层之前,通入少量三甲基镓（TMGa）和大量氨气进行短时间的高温预生长,通过改变TMGa流量制备了4个蓝光LED样品。MOCVD外延生长时使用激光干涉仪实时监测薄膜反射率,外延片使用高分辨率X射线衍射（002）面和（102）面摇摆曲线估算位错密度,并使用光致发光谱表征发光性能,制备成芯片后测试了正向电压和输出光功率。结果表明,高温预生长可促进薄膜的横向外延,使得三维岛状GaN晶粒在较小的薄膜厚度内实现岛间合并,有利于降低位错密度,提高外延薄膜质量,LED芯片的输出光功率的增强幅度达29.1%,而电学性能无恶化迹象;但高温预生长工艺中TMGa的流量应适当控制,过量的TMGa导致GaN晶粒过大,将延长岛间合并时间,降低晶体质量。     

Femtosecond petawatt laser

The high‐power femtosecond laser has now become an excellent scientific tool for the study of not only relativistic laser–matter interactions but also scientific applications. The high‐power femtosecond laser depends on the Kerr‐lens modelocking (KLM) and chirped‐pulse amplification (CPA) technique. An all‐Ti:sapphire‐based 30‐fs PW CPA laser, which is called the PULSER (Petawatt Ultrashort Laser System for Extreme Science Research) has been recently constructed and is being used for accelerating the charged particles (electrons and protons) and generating ultrashort high‐energy photon (X‐ray and γ‐ray) sources. In this review, the world‐wide PW‐level femtosecond laser systems are first summarized, the output performances of the PULSER‐I & II are described, and the future upgrade plan of the PULSER to the multi‐PW level is also discussed. Then, several experimental results on particle (electron and proton) acceleration and X‐ray generation in the intensity range of mid‐10¹⁸ W/cm² to mid‐10²⁰ W/cm² are described. Experimental demonstrations for the newly proposed phenomena and the understanding of physical mechanisms in relativistic and ultrarelativistic regimes are highly expected as increasing the laser peak intensity up to over 10²² W/cm² ～10²³ W/cm².     

Experimental Evaluation of Procedures for Heat Capacity Measurement by Differential Scanning Calorimetry

Experimental evaluation of the procedures adopted for heat capacity measurements employing differential scanning calorimetry (DSC) has been carried out by taking nickel and sapphire as test samples. Among the various methodologies reported in literature, the absolute dual step method was chosen for this purpose due to its simplicity and minimum number of measurements required. By proper temperature and heat flux calibration employing indium as reference, it was possible to obtain the calibration factor independent of temperature. This was ascertained by analysing other pure metals namely Sn, Zn, Cd, and Pb and determining their melting temperatures and heats of melting. Various operator- and sample-dependent parameters such as heating rate, sample mass, the structure of the sample, reproducibility and repeatability in the measurements were investigated. Heat capacities of both nickel and sapphire have been determined using the above method. Further, the heat capacity of nickel has also been determined using the widely employed three-step method taking sapphire as the heat flux calibration standard. Both methods yielded the comparable heat capacity values for nickel. Based on the parameters investigated and their influence, it could be concluded that reasonably precise and accurate heat capacity measurements are possible with DSC. One advantage of this method is the elimination of a separate calibration run using a reference material of known heat capacity. This revised version was published online in August 2006 with corrections to the Cover Date.