Neutron irradiation effects on AlGaN/GaN high electron mobility transistors

AlGaN/GaN high electron mobility transistors (HEMTs) were exposed to 1 MeV neutron irradiation at a neutron fluence of 1 × 10¹⁵ cm^-2. The dc characteristics of the devices, such as the drain saturation current and the maximum transconductance, decreased after neutron irradiation. The gate leakage currents increased obviously after neutron irradiation. However, the rf characteristics, such as the cut-off frequency and the maximum frequency, were hardly affected by neutron irradiation. The AlGaN/GaN heterojunctions have been employed for the better understanding of the degradation mechanism. It is shown in the Hall measurements and capacitance-voltage tests that the mobility and concentration of two-dimensional electron gas (2DEG) decreased after neutron irradiation. There was no evidence of the full-width at half-maximum of X-ray diffraction (XRD) rocking curve changing after irradiation, so the dislocation was not influenced by neutron irradiation. It is concluded that the point defects induced in AlGaN and GaN by neutron irradiation are the dominant mechanisms responsible for performance degradations of AlGaN/GaN HEMT devices.     

三芳胺和二氢吲哚作为给体的染料对钴电解质的染料敏化太阳能电池性能的影响

合成了两种有机染料,三芳胺染料XS51和二氢吲哚染料XS52,并分别用于钴基电解质和碘基电解质的染料敏化太阳能电池中. 考察了染料结构对光物理性能、电化学性能和电池性能的影响. XS51为含有四个己氧基的三芳胺结构,表现出较好的空间位阻,从而提高了光电压. XS52中二氢吲哚的给电子能力强,从而短路电流较大. 同碘电解质相比,所合成的染料更适合用于钴电解质的染料敏化电池中. 在100 mW/cm²的光强下,基于染料XS52的钴电解质太阳能电池总的光电转换效率达到6.58%.     

基于多维随机森林的番茄灰霉病高光谱图像早期检测

植物病害的自动早期检测对于作物精确保护至关重要。提出了一种基于多维光谱序列（multi-dimensional spectral series, MDSS）和加权随机森林（weighted random forest, WRF）的番茄灰霉病早期诊断与鉴别方法。目的是利用叶片多个观测维度的光谱曲线整体变化趋势建立作物病害检测模型,以期在肉眼明显可见叶面病斑前对作物病害实现诊断。将健康叶片接种灰霉病菌第3天作为叶片成功染病第1天。试验首先采集番茄健康叶片和染病叶片7天内每天的高光谱图像,提取感兴趣区域并计算平均光谱作为初始光谱数据,经筛选共得到(156×7)组有效样本。将样本数据按时间顺序拆分成分别包含1～7个维度的光谱数据形成多维原始光谱序列,为增加维度间差异性,相邻原始光谱序列相减构成多维关联光谱序列。分别采用符号聚合近似估计（symbolic aggregate approximation, SAX）和符号傅里叶近似估计（symbolic Fourier approximation, SFA）两种符号化方法将光谱序列离散成局部辨别性特征。基于多维光谱序列的局部辨别性特征建立加权随机森林（MDSS-SAX-SFA-WRF）分类模型,实现病害早期检测。相应地,基于单维光谱序列（single-dimensional spectral series, SDSS）的番茄灰霉病识别模型被作为基准模型与MDSS-SAX-SFA-WRF模型比较。试验结果显示,MDSS-SAX-SFA-WRF检测模型在包含2至7个光谱序列维度的56个测试样本数据中均获得90%以上识别准确率,在包含5个光谱序列维度测试集中得到最高99%的识别准确率,较SDSS-SAX-SFA-MRF检测模型在染病第5天的识别率高8.2个百分点。另外受随机干扰的影响,SDSS-SAX-SFA-MRF模型准确率在染病5～7 d出现大幅度回落至最低84%,MDSS-SAX-SFA-WRF模型识别率在肉眼可见病斑阶段依然保持超过98%的较高检测水准,未过度回落。因此,提出的基于多维光谱曲线整体变化趋势和加权随机森林（MDSS-SAX-SFA-WRF）的分类模型能够有效实现番茄灰霉病早期检测,并具有较强的鲁棒性,为染病初期的番茄灰霉病鉴别提供新思路。     

关于非齐次马氏过程散度的极限性质

将数列上的绝对平均收敛性推广到平面上,并得出相应的引理.利用这个概念给出非齐次马氏过程散度率存在的一个条件.     

分形结构稀疏孔径阵列的成像性能

根据分形的自相似性理论提出一种分形稀疏孔径阵列结构.该阵列是以Golay-3为分形结构单元,按自相似方式扩展构成的一种多层分形阵列结构.采用无量纲约化参数对其结构进行表征,给出光瞳函数和调制传递函数解析表达式.通过数值计算分形结构在不同填充因子和不同外层旋转角下的调制传递函数、实际截止频率和中频特性,比较分析了当孔径数分别为N=3,N=9,N=18阵列的MTF及特性参数.结果表明,当填充因子为0.0952F≤0.2246d0=1时,其变化对MTF曲线影响较小.外层旋转具有周期性,转角的变化对实际截止频率没有大的影响.当约化孔径参数,填充因子为22.46%时,N=18阵列的中频特性更加平稳,实际截止频率也更高.利用分形自相似性可以在相对保持中频特性的前提下有效地扩展系统孔径.由于采用约化孔径参数,数值计算结果具有标度不变性.     

Effect of Si doping in wells of AlGaN/GaN superlattice on the characteristics of epitaxial layer

An AlGaN/GaN superlattice grown on the top of a GaN buffer induces the broadening of the full width at half maximum of (102) and (002) X-ray diffraction rocking curves. With an increase in the Si-doped concentration in the GaN wells, the full width at half maximum of the (102) rocking curves decreases, while that of the (002) rocking curves increases. A significant increase of the full width at the half maximum of the (002) rocking curves when the doping concentration reaches 2.5 × 1019 cm-3 indicates the substantial increase of the inclined threading dislocation. High level doping in the AlGaN/GaN superlattice can greatly reduce the biaxial stress and optimize the surface roughness of the structures grown on the top of it.     

O2对燃煤烟气中As2 O3均相反应生成途径影响研究

应用量子化学密度泛函理论研究了燃煤烟气中As和AsO与O_2均相生成As_2O_3的反应机理。首先计算确定了各反应物、中间体、过渡态和产物的结构和能量,然后运用热力学和动力学方法对As_2O_3均相生成过程进行分析。结果表明,由As和AsO与O_2均相生成As_2O_3的最大反应能垒分别为32.9和157.2kJ/mol,在烟气中由As转化为As_2O_3更为容易进行。在500-1900 K下,各反应的正逆反应速率常数均随温度的提高而增大,但不同反应过程受温度影响的程度不同。As与O_2反应生成AsO和AsO_2的两个反应过程的平衡常数在所研究的温度范围内均大于10~5,能完全反应,可以认为是单向反应。AsO与O_2反应生成AsO_2的过程平衡常数在所研究的温度范围内小于10~5,反应不完全,转化率低。AsO与AsO_2生成As_2O_3(D3H)构型的平衡常数极低,反应难以进行,而生成As_2O_3(GAUCHE)构型反应能垒低,可自发进行。     

Hot carrier injection degradation under dynamic stress

In this paper,we have studied hot carrier injection(HCI) under alternant stress.Under different stress modes,different degradations are obtained from the experiment results.The different alternate stresses can reduce or enhance the HC effect,which mainly depends on the latter condition of the stress cycle.In the stress mode A(DC stress with electron injection),the degradation keeps increasing.In the stress modes B(DC stress and then stress with the smallest gate injection) and C(DC stress and then stress with hole injection under V g = 0 V and V d = 1.8 V),recovery appears in the second stress period.And in the stress mode D(DC stress and then stress with hole injection under V g = 1.8 V and V d = 1.8 V),as the traps filled in by holes can be smaller or greater than the generated interface states,the continued degradation or recovery in different stress periods can be obtained.     

磷酸二氢根溶液标准物质研制

研制磷酸二氢根溶液标准物质.以磷酸二氢钾和去离子水为原料,采用重量–容量法制备磷酸二氢根溶液标准物质.采用F检验和回归曲线法对研制的标准物质进行均匀性和稳定性检验,并对定值结果的不确定度进行评定.结果表明,研制的标准物质具有良好的均匀性和稳定性,标准值为1000μg/mL,相对扩展不确定度为1.4％(k=2),有效期为...     

钡-玫红酸络合物荧光光谱法测定钡餐在水中的溶解度

以荧光衍生光谱法研究了氯化钡与玫红酸形成络合物的荧光光谱,建立了钡离子的荧光光谱分析方法,在优化条件下:溶液pH=11.2,反应时间为5min,乙醇与水溶剂的比为15％.在2.5×10-11-5×10-5mol/L范围内,络合物的荧光强度与钡离子浓度存在两段线性关系,检出限为2.5×10-11mol/L.方法用于钡餐在水中溶解度的测定,结果与文献报道值一致.