高效率的蓝色磷光有机电致发光器件

制备了基于双母体结构的高效率蓝色磷光有机电致发光器件。通过与采用单母体结构和双发光层结构的器件性能进行对比,发现双母体结构的应用对蓝光器件的性能起到了明显的提升作用。双母体蓝光器件的最大效率为14.9 cd/A(13.3 lm/W),最大亮度达到10 440 cd/m~2,其开启电压仅为2.7 V。蓝光器件同时展示出低的效率滚降特性,在100~5 000 cd/m~2范围内,器件的效率滚降仅为35.3%。在3~8 V的电压变化内,器件的色坐标一直位于蓝光区域。     

6H-SiC衬底上AlGaN基垂直结构紫外LED的制备

利用金属有机物化学气相沉积方法,在n型6H-SiC衬底上制备了15对Si掺杂Al_(0.19)Ga_(0.81)N/Al_(0.37)Ga_(0.63)N DBR,并采用低温AlN缓冲层有效抑制了DBR结构中裂纹的产生,得到了表面均方根粗糙度仅为0.4 nm且导电性能良好的n型DBR,其在369 nm处峰值反射率为68%,阻带宽度为10 nm。在获得导电DBR的基础上,进一步在n型6H-SiC衬底上构建了有、无DBR的垂直结构紫外LED。对比两者电致发光光谱,发现DBR结构的引入有效增强了LED紫外发光强度。     

绿肥对华北潮土土壤可溶性有机物的影响

在华北潮土上种植不同绿肥,于绿肥翻压前原位采集其地上部及土壤样品,进行56d的绿肥翻压模拟试验。设毛叶苕子(Vicia villosa Roth.)、二月兰(Orychophragmus Violaceus L.)、黑麦(Secale cereale L.)三个绿肥处理和无绿肥对照处理,分析培养过程中土壤可溶性有机物(DOM)组分及其紫外-可见光谱参数的变化,以探究绿肥对土壤DOM的影响。种植和翻压绿肥增加土壤可溶性有机碳(DOC)、总有机酸碳(TOAs)和总碳水化合物碳(TCs)含量,三者的变化趋势一致,各处理均在培养第1 d上升至峰值后迅速下降。毛叶苕子提高DOC和TOAs的效果最好,最高比对照增加114.01%(培养第1d)和109.10%(培养第14 d)。黑麦提高TCs的效果最好,最高比对照增加323.18%(培养第42 d)。种植和翻压绿肥增加土壤可溶性有机氮(DON)含量,与DOC变化趋势不同,各处理在培养第1 d上升后迅速下降一段时间后又迅速上升。毛叶苕子提高DON的效果最好,最高比对照增加305.83%(培养第42d)。绿肥增加了SUVA₂₅₄,SUVA₂₆₀,SUVA₂₇₂,SUVA₂₈₀,SAUC_240-400,降低了A₂₅₀/A₃₆₅和A₂₄₀/A₄₂₀。紫外-可见光谱参数的主成分分析显示SUVA₂₅₄,SUVA₂₆₀,SUVA₂₇₂,SUVA₂₈₀间有很高正相关性,A₂₅₀/A₃₆₅和A₂₄₀/A₄₂₀间亦有很高正相关性,SAUC_240-400是这些参数中表征DOM性质的关键因子。综上结果表明,种植翻压绿肥增加了土壤DOM含量,提高了土壤DOM的芳香性、疏水性、腐殖化程度、平均分子量,增加了土壤DOM的稳定性。     

应用遗传算法结合连续投影算法近红外光谱检测土壤有机质研究

应用遗传算法结合连续投影算法近红外光谱检测土壤有机质研究。采集浙江省文城地区农田土壤样品近红外光谱数据,土壤样品数为394个。为简化模型,采用遗传算法结合连续投影算法挑选出18个特征波长建模,应用偏最小二乘回归建立有机质预测模型,建模集的决定系数为0.81,均方根预测误差为0.22, 剩余预测偏差为2.31,预测集的决定系数为0.83,均方根预测误差为0.20,剩余预测偏差为2.45。研究发现,遗传算法结合连续投影算法在简化模型同时,模型的预测评价指标同采用全谱波长建模并没有明显降低。因此,遗传算法结合连续投影算法挑选的特征波长可以应用于近红外光谱检测土壤有机质含量。     

采用瞬态电致发光研究磷光掺杂体系发光瞬时过冲的发射机理

掺杂型有机电致发光器件中载流子累积、载流子复合等物理过程的深入了解对提高器件效率和稳定性有重要作用。通过瞬态电致发光测量可以研究掺杂型有机电致发光器件内部载流子累积。对结构为: ITO/NPB(30 nm)/host: Ir(ppy)₃/BCP(10 nm)/Alq₃(20 nm)/LiF(0.7 nm)/Al(100 nm)的器件分别研究主体材料以及客体掺杂浓度变化对有机掺杂型器件瞬态发光行为的影响。实验发现,当单脉冲驱动电压关闭后,只有TAZ: Ir(ppy)₃掺杂器件出现发光瞬时过冲现象,即发光强度衰减到一定时间时突然增强;且随着客体掺杂浓度的增加,瞬时过冲强度逐渐增强。通过分析TAZ: Ir(ppy)₃掺杂器件的瞬时过冲强度对主体材料与掺杂浓度的依赖关系,进一步发现,瞬时过冲效应强度主要受限于发光层内部积累的电子载流子;TAZ: Ir(ppy)₃发光层内电子容易被客体材料分子俘获并积累,电场突变时陷阱电子容易跳跃到主体材料上并与主体材料上积累的空穴形成激子,激子能量传递到客体材料上并复合发光继而出现发光强度的瞬时过冲现象。研究发光瞬时过冲行为可探究器件发光层内的载流子和激子的动态行为,有利于指导器件的设计,从而减少积累电荷的影响,提高器件的性能。     

Ar-buffer-assisted deposition of Cu13 on Cu(1 1 1) surfaces

In this paper, the deposition of Cu₁₃ onto Cu(1 1 1) surface through argon buffer layers was investigated by molecular dynamics (MD) simulations. The interactions between Cu-Cu, Cu-Ar, and Ar-Ar were described by Finnis-Sinclair (FS) tight-binding potential and L-J potential, respectively. The impact energy was chosen to be 2-6 eV/atom in order to compare with experimental results. It was observed that with Ar-buffer layers, the Cu cluster deposited on the surface may retain its free cluster symmetry (I_h). Whereas, on originally bare Cu surface, the deposited Cu cluster lost its original symmetry completely and was recrystalized to have the same fcc structure as the substrate. The Ar-buffer dissipates most of the translational energy of the incident cluster. Therefore, it prevents the cluster from being overheated upon impinging. Furthermore, the interaction between Ar and Cu benefits the confinement of the cluster structure. Our study shows that with Ar-buffer layers, the lateral spread of deposited clusters is 20% smaller than that on the bare Cu surface. This is consistent with the experimental findings.     

para-Sexiphenyl thin film growth on Cu(1 1 0) and Cu(1 1 0)-(2 × 1)O surfaces

We present a reflectance difference spectroscopy (RDS) study of para-sexiphenyl (p-6P) thin film growth on Cu(1 1 0) and Cu(1 1 0)-(2 × 1)O substrates. The RDS spectra show pronounced anisotropies for p-6P films formed on both substrates at room temperature, demonstrating that the molecules are uniaxially aligned within the films. Based on the RD spectra and the evolution of the optical transitions with p-6P coverage the growth mode on both substrates could be identified. From the dominating RDS feature, assigned to the lowest energy HOMO-LUMO transition, the orientation of the molecular chain can be determined. On Cu(1 1 0), the p-6P molecular chains align in the direction, i.e., along the Cu atomic rows, whereas on the Cu(1 1 0)-(2 × 1)O surface, the molecules are oriented in the orthogonal [0 0 1] direction, i.e., along the “added” Cu-O rows of the Cu(1 1 0)-(2 × 1)O surface. The energetic position and line shape of the main RDS feature differs for the two substrates and varies with p-6P coverage. This fine structure is discussed in terms of different molecular conformations, adlayer structure and vibronic replicas.     

The chemisorption of pentacene on Si(0 0 1)-2 × 1

Adsorption structures of the pentacene (C₂₂H₁₄) molecule on the clean Si(0 0 1)-2 × 1 surface were investigated by scanning tunneling microscopy (STM) in conjunction with density functional theory calculations and STM image simulations. The pentacene molecules were found to adsorb on four major sites and four minor sites. The adsorption structures of the pentacene molecules at the four major sites were determined by comparison between the experimental and the simulated STM images. Three out of the four theoretically identified adsorption structures are different from the previously proposed adsorption structures. They involve six to eight Si-C covalent chemical bonds. The adsorption energies of the major four structures are calculated to be in the range 67-128 kcal/mol. It was also found that the pentacene molecule hardly hopped on the surface when applying pulse bias voltages on the molecule, but was mostly decomposed.     

Optical–optical double resonance spectroscopy of the transition of CaOH

The state of CaOH was investigated using optical–optical double resonance spectroscopy. A combined least-squares fit of the double resonance transition data along with optical transition data and the millimeter-wave pure rotational data of the state was performed using an effective Hamiltonian. The spin–rotation constant was determined for the state for the first time. An analysis of these constants showed that the Ca–O bond length and spin–rotation parameter of the state have the smallest values of all the observed ²Σ⁺ states of CaOH. This evidence suggests the assignment of the state as arising from a Ca⁺ atomic orbital of mainly 5sσ character. This atomic orbital assignment was shown to be consistent with both previous work on CaF and recent theoretical calculations on CaOH.