晶粒尺寸对Ba0.70Sr0.30TiO3陶瓷介电性能的影响规律及机理研究

通过制备晶粒尺寸处于0.1-10 μm之间的致密Ba0.70Sr0.30TiO3陶瓷,系统研究了晶粒尺寸对居里温度TC、铁电相介电常数εF、峰值介电常数εM的影响规律,并深入分析了其内在的影响机理.研究表明:晶粒尺寸减小时,TC刚开始基本不变,直到晶粒尺寸小到一定程度时才开始降低,此变化规律可由Buesseum的内应力模型解释;随晶粒尺寸的增加,εF先增加后减小,此变化规律可由Shaikh的串并联模型来解释,主要影响因素有内应力、畴、晶界;εM随晶粒尺寸的增加,在晶粒尺寸较小时先增加后减小,晶粒尺寸较大时略有增加,此变化规律可由弥散相变理论和串并联模型共同解释,在晶粒尺寸较小时主要影响因素为内应力、微畴和晶界,晶粒尺寸较大时主要影响因素为晶界.     

双波长激光路面气象传感方法

为解决传统接触式路面气象传感器寿命低、安装不便、易破坏路基等问题,用1 310 nm、1 430 nm两种波长的激光器作为探测光源,结合红外测温辅助,研究了一种非接触的路面气象传感方法。该方法通过测量不同路面状态下由光源照射形成的后向散射光强,得到水、冰介质膜在两个特征波长下的反射率;通过设定反射率和红外温度信号的判别逻辑,可以分辨多种路面状态,包括干燥、潮湿、积水、结冰和结霜;以朗伯比尔定律为基础建模实现积水、结冰厚度检测,利用反射率零点自动判别校准测量模型参数,无需现场标定即可在不同道路条件下实现精准测量。实验证明,该方法路面状态判别准确,水/冰厚度检测量程达到3 mm,精度均为±0.2 mm,具有结构简单、探测距离远、成本低等特点,有良好的实用价值。     

Effects of Hydrogen Treatment in Barrier on the Electroluminescence of Green InGaN/GaN Single-Quantum-Well Light-Emitting Diodes with V-Shaped Pits Grown on Si Substrates

Effect of hydrogen(H_2) treatment during the GaN barrier growth on the electroluminescence performance of green In GaN/GaN single-quantum-well light-emitting diodes(LEDs) grown on Si substrates is experimentally investigated. We prepare two LED samples with different carrier gas compositions during the growth of GaN barrier. In the H_2 free LED, the GaN barrier is grown in full nitrogen(N_2) atmosphere. For the other H_2 treated LED, a mixture of N_2 and H_2 was used as the carrier gas. It is observed that V-shaped pits decrease in size after H_2 treatment by means of the scanning electron microscope. Due to the fact that the p–n junction interface would be closer to the p-GaN as a result of smaller V-shaped pits, the tunneling barrier for holes to inject into the In GaN quantum well would become thicker after H_2 treatment. Hence, the external quantum efficiency of the H_2 treated LED is lower compared to the H_2 free LED. However, LEDs would exhibit a better leakage behavior after H_2 treatment during the GaN barrier growth because of more effective blocking of the threading dislocations as a result of the H_2 etching at V-shaped pits.     

晶粒尺寸对Ba$lt;sub$gt;0.70$lt;/sub$gt;Sr$lt;sub$gt;0.30$lt;/sub$gt;TiO$lt;sub$gt;3$lt;/sub$gt;陶瓷介电性能的影响规律及机理研究

通过制备晶粒尺寸处于0.1—10 μm之间的致密Ba_0.70Sr_0.30TiO₃陶瓷,系统研究了晶粒尺寸对居里温度T_C、铁电相介电常数ε_F、峰值介电常数ε_M的影响规律,并深入分析了其内在的影响机理.研究表明：晶粒尺寸减小时,T_C刚开始基本不变,直到晶粒尺寸小到一定程度时才开始降低,此变化规律可由Buesseum的内应力模型解释;随晶粒尺寸的增加,ε_F先增加后减小,此变化规律可由Shaikh的串并联模型来解释,主要影响因素有内应力、畴、晶界;ε_M随晶粒尺寸的增加,在晶粒尺寸较小时先增加后减小,晶粒尺寸较大时略有增加,此变化规律可由弥散相变理论和串并联模型共同解释,在晶粒尺寸较小时主要影响因素为内应力、微畴和晶界,晶粒尺寸较大时主要影响因素为晶界. 关键词： 0.70Sr_0.30TiO₃陶瓷')" href="#">Ba_0.70Sr_0.30TiO₃陶瓷 介电常数 居里温度 晶粒尺寸     

加高喷头MOCVD压强对生长影响的研究

以低速旋转、加高喷头、垂直喷淋的MOCVD反应室为对象,运用三维数学输运模型分析与计算.在模拟过程中分析了压强的变化对高喷头反应室流场的影响,着重分析与讨论了操作压强变化与GaN薄膜的沉积一致性及平均生长速率的关系,其次探讨了实验值与模拟值对比结果,从而对薄膜的均匀性及平均生长速率进行一定的预测,最终得到以基准工艺参数为前提的最佳压强设定范围为6650～13300 Pa.模拟跟实验结果表明:减小压强有利于薄膜的均匀性,压强较大时,平均生长速率大,但压强较大时极易引起流场不稳.     

Carrier Dynamics Determined by Carrier-Phonon Coupling in InGaN/GaN Multiple Quantum Well Blue Light Emitting Diodes

Phonon sidebands in the electrolumiescence(EL) spectra of InGaN/GaN multiple quantum well blue light emitting diodes are investigated. S-shaped injection current dependence of the energy spacing(ES) between the zero-phonon and first-order phonon-assisted luminescence lines is observed in a temperature range of 100–150 K.The S-shape is suppressed with increasing temperature from 100 to 150 K, and vanishes at temperature above200 K. The S-shaped injection dependence of ES at low temperatures could be explained by the three stages of carrier dynamics related to localization states:(i) carrier relaxation from shallow into deep localization states,(ii) band filling of shallow and deep localization states, and(iii) carrier overflow from deep to shallow localization states and to higher energy states. The three stages show strong temperature dependence. It is proposed that the fast change of the carrier lifetime with temperature is responsible for the suppression of S-shaped feature.The proposed mechanisms reveal carrier recombination dynamics in the EL of InGaN/GaN MQWs at various injection current densities and temperatures.     

基于银膜的自准直光纤法布里-珀罗腔设计及声源定位研究

提出一种基于银膜的自准直外腔式光纤法布里-珀罗(EFPI)干涉仪声传感器阵列,用于中低频声信号的检测以及二维平面声源定位。传感器阵列由三个相同结构的EFPI组成,结构简单、制作简便。银膜的应用和准直器的引入提高了传感器的声压灵敏度,扩大了声源定位范围。实验结果表明：单个传感器声压灵敏度为185 mV/Pa,最小可探测声压为52.7μPa/Hz^1/2@500 Hz。在声源指向性实验中,声源设置在传感器正前方时,其声压灵敏度达到185 mV/Pa,声源设置在传感器侧面(90°,270°)时,其声压灵敏度衰减仅为4.5%。传感器阵列结合到达时间差技术,成功实现高精度的声源定位,系统的理论空间分辨率为0.71 cm,最大定位误差不超过2.8 cm,定位范围为200 cm×200 cm,具有成本低、实用性高等优点。