有机自旋光电子学的基本过程

有机自旋光电子学的研究方向分为磁场效应和自旋注入两个方面.研究表明,外加低磁场能够显著改变非磁性有机半导体材料的光致发光、注入电流、电致发光和光电流.这称为有机半导体材料的磁场效应.近年来,非磁性有机半导体材料的磁场效应引起了广泛的关注和研究兴趣.首先,有机半导体材料的磁场效应是强有力的实验手段,用以研究有机电学、光学和光电器件中电荷传输和激发态中的有用和无用过程,为解决电荷传输和激发态过程中的瓶颈问题提供有效的实验手段,为实现磁-光-电多功能集成提供科学原理,尤其是磁场效应能够为提高能量转换效率、探测和传感光电子学器件的响应频谱范围和灵敏度提供新思路.同时利用磁电极,有机半导体材料和器件中自旋注入及其对电荷传输和激发态过程的调控可以用于发展新型功能化的自旋光电子学器件.本文综述并讨论了有机半导体材料和器件中的磁场效应和自旋注入的光电子学效应.     

主链含酞和芴结构的无定形聚芳醚酮的合成

通过共聚改性在酚酞聚芳醚酮(PEK-C)的主链上引入含芴侧基,制备了一系列主链含酞和芴结构的线性高分子量无定形聚芳醚酮无规共聚物.通过傅里叶红外光谱(FTIR)、核磁共振谱(1H,13C NMR)等手段确定了共聚物结构.凝胶渗透色谱(GPC)数据表明,共聚物的Mn>6.0×104,Mw>1.0×105,PDI(Mw/Mn)范围在1.6~1.7之间.X射线衍射(XRD)数据表明共聚物系无定形结构,差示扫描量热法(DSC)和热重分析(TGA)测试表明聚合物具有良好的耐热性;初始热分解温度高于467℃;700℃时残炭率大于58.9%;共聚物呈现单一的玻璃化转变温度(Tg>243℃).当酚酞与双酚芴摩尔比在3∶7~5∶5范围时,共聚物的弹性模量和断裂伸长率显著提高,可分别达到3.1 GPa和58%,是酚酞聚芳醚酮的1.4倍和8.3倍.这类含酞和芴侧基的无定形聚芳醚酮保持了在氯仿、二氯甲烷、四氢呋喃(THF)和甲基吡咯烷酮(NMP)等极性非质子溶剂中良好的溶解性能,并显著提高了聚合物的力学性能和热性能.     

Investigation of passivation effects in AlGaN/GaN metal-insulator-semiconductor high electron-mobility transistor by gate-drain conductance dispersion study

This paper studies the drain current collapse of AlGaN/GaN metal-insulator-semiconductor high electron-mobility transistors (MIS-HEMTs) with NbAlO dielectric by applying dual-pulsed stress to the gate and drain of the device.For NbAlO MIS-HEMT,smaller current collapse is found,especially when the gate static voltage is 8 V.Through a thorough study of the gate-drain conductance dispersion,it is found that the growth of NbAlO can reduce the trap density of the AlGaN surface.Therefore,fewer traps can be filled by gate electrons,and hence the depletion effect in the channel is suppressed effectively.It is proved that the NbAlO gate dielectric can not only decrease gate leakage current but also passivate the AlGaN surface effectively,and weaken the current collapse effect accordingly.     

Hot‐electron drift velocity and hot‐phonon decay in AlInN/AlN/GaN

A nanosecond‐pulsed current–voltage technique was applied to study hot‐electron transport along the two‐dimensional electron gas channel confined at a nominally undoped AlInN/AlN/GaN heterointerface. Hot‐electron drift velocity was deduced under the assumptions of uniform longitudinal electric field and field‐independent electron sheet density. At a fixed electric field strength, a resonance‐type non‐monotonous dependence of the velocity on the electron density was found in the investigated range from 1 to When the electric field increased from 20 kV/cm to 80 kV/cm, the peak velocity increased from ～1.1 to cm/s, and the position of the resonance shifted from ～1.1 to ～1.2 respectively. The resonance position correlates with that for the fastest decay of hot phonons known from independent experiment. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Enhancement in hydrophobicity of silica films using metal acetylacetonate and heat treatment

Water is one of the most affecting chemicals that can cause damage to the solid surface. To protect the surface due to the action of water, the surface should be made hydrophobic. In the present study, the improvement in hydrophobicity of silica films using metal acetylacetonate (M-acac) by employing heat treatment to methyltrimethoxy silane (MTMS) based silica coatings is reported as a novel attempt. Instead of following the established trends of the surface derivatization or co-precursor method, iron acetylacetonate Fe(acac)₃, copper acetylacetonate Cu(acac)₂ and heat treatment were used to incorporate hydrophobicity with silica coatings. As M-acac is readily soluble in organic solvents, Fe(acac)₃ and Cu(acac)₂ were dissolved in methanol (MeOH) and their concentration was varied from 0 to 0.025 M. The coating solution was prepared by optimizing molar ratio of MTMS:MeOH:basic H₂O to 1:7.15:6.34, respectively. Gelation time (t_g) for Cu(acac)₂ containing silica sol and that containing Fe(acac)₃ were noted to be 30 and 55 min, respectively. The substrates were taken out after gelation and heat treated at 150 °C for 2 h. The heat treated films showed a dramatic increase in the static water contact angle from 82° to as high as 142°.     

Ultra-high repetition rate InAs/InP quantum dot mode-locked lasers

We have designed, grown and fabricated InAs/InP quantum dot (QD) waveguides as the gain materials of mode-locked lasers (MLLs). Passive InAs/InP QD MLLs based on single-section Fabry-Perot (F-P) cavities with repetition rates from 10 GHz to 100 GHz have been demonstrated in the C- and L-band. Femtosecond (fs) pulses with pulse duration of 295 fs have been achieved. The average output power is up to 50 mW at the room temperature of 18 °C. By using the external fiber mixed cavities fs pulse train with a repetition rate of 437 GHz has been generated. We have also discussed the working principles of the developed QD MLLs.     

Structural and magnetic characterization of rhombohedral Ga1.2Fe0.8O3 ceramics prepared by high-pressure synthesis

The rhombohedral α- Ga_1.2Fe_0.8O₃ ceramics have been synthesized by using a high pressure technique at a pressure of 5 GPa and a temperature of 800 °C from orthorhombic ε- Ga_1.2Fe_0.8O₃ ceramics, which were identified to be isostructural with α- Fe₂O₃ and α- Ga₂O₃. The low temperature magnetism has been studied for α- Ga_1.2Fe_0.8O₃, the saturation magnetization is at 5 K, and the Morin temperature has not been found. Moreover, it is most probable that the spin reorientation of α- Ga_1.2Fe_0.8O₃ has been found at 50 K resulted from the change of magnetic dipole anisotropy and single-ion anisotropy with temperature.     

Power-law scaling of proton conductivity in amorphous silicate thin films

Amorphous hafnium silicate, a-Hf_0.1Si_0.9O_x, thin film with thickness of 32, 41, 55, 80, 110, 120, 180 and 320 nm was prepared by multiple spin-cast process and the proton conductivity across the films was measured at intermediate temperatures (100-400 °C) in dry atmosphere. The morphologically- and compositionally-uniform films were prepared on a substrate as confirmed by SEM, RBS and XPS measurements. a-Hf_0.1Si_0.9O_x thin film clearly revealed the H/D isotope effect on ionic conductivity, indicating that protonic conduction is dominant in the measured temperature range. The films did not reveal thickness-dependent proton conductivity in dry air and the σ at given temperatures is almost constant at any thickness. No increment of σ in a-Hf_0.1Si_0.9O_x thin films by reduction of thickness might be related to the absence of the highly-conductive acid network with mesoscopically-sized length because of the relatively low concentration of Brønsted acid sites inside films.     

Multilayer laser printing for Organic Thin Film Transistors

Functional laser printed Organic Thin Film Transistors (OTFTs) have been achieved from multilayer substrates composed with semiconductor and electrodes. The p-type copper phthalocyanine (CuPc) was used to form the active layer. Different kinds of metallic materials were used for source and drain electrodes. Multilayer donor substrates were prepared by the successive depositions of materials by either thermal evaporation under vacuum or laser printing. The materials were transferred together in a single step onto a receiver substrate by laser pulses in the picosecond regime. The latter substrate formed the gate and the dielectric of the transistor. The results are compared with the step-by-step laser printing process, where electrodes and organic layer were successively printed from two different donor substrates. The multilayer laser printing reveals an improvement of the performances of the OTFT devices.     

Comparison study on structure of Si and Cu doping CrN films by reactive sputtering

CrN, CrSiN and CrCuN films were deposited by DC magnetron reactive sputtering with hot pressed pure Cr, CrSi, and CrCu targets, respectively. As substrate bias increased from −50 V to −200 V, the preferred orientation of CrN films changed from (1 1 1) to (2 0 0). And the Si doping did not change this condition. However, the Cu doping films kept (2 0 0) orientation all along. CrN films presented typical columnar structure, and the alloying of Si and Cu could restrain columnar growth leading to dense structure. The CrSiN film was composed of nanocrystallites distributed in amorphous Si₃N₄, while no amorphous phase existed in CrCuN films.