氧气DBD等离子体处理PBO纤维表面及其对双马树脂基复合材料界面性能的影响

采用氧气介质阻挡放电(DBD)等离子体处理PBO纤维表面,用以改善PBO纤维与双马来酰亚胺(BMI)树脂之间的界面粘结性能。结果表明,用氧气等离子体处理PBO纤维能大幅度提高PBO/BMI复合材料的层间剪切强度(ILSS)值,最佳处理条件为功率30 W/m³、时间24 s,ILSS值从43.9 MPa提高到62.0 MPa。经过氧气DBD等离子体处理的PBO纤维其表面的氧含量明显提高,氮含量变化不大,甚至在过度处理时降低;官能团-O-C=O基团的含量从0提高到3.16%,-C-O-的含量也明显提高;在氧气DBD等离子体处理后的PBO纤维表面产生大量凹凸不平和沟壑,使纤维表面的粗糙度提高。而表面氧含量的提高和表面形貌与粗糙度的变化,是PBO/BMI复合材料ILSS值提高的重要原因。单丝拉伸实验结果表明,适当的DBD等离子体处理不会对PBO纤维表面产生不良影响,不影响其在复合材料中的作用。     

射频等离子体改性工艺与氧化铟锡薄膜性能研究

采用正交实验方法研究了氧气等离子体表面改性中各工艺因素对ITO薄膜表面性质的影响,获得了IID表面改性的最佳工艺条件,并且通过XPS,AFM,透射光谱的分析以及薄膜表面接触角和方块电阻的测量,表征了优化工艺条件下氧气等离子体处理前后ITO薄膜的表面性质.结果表明,氧气等离子体处理降低了ITO表面的粗糙度和方块电阻,改善了ITO表面的化学组分和浸润性能.另外,以表面处理前后的ITO基片作为空穴注入电极,采用真空热蒸镀技术制备了有机薄膜电致发光(OTFEL)器件,并对器件的电流.电压.亮度特性以及电流效率进行了测试和分析,实验结果显示,氧气等离子体处理降低了启亮电压和驱动电压,提高了发光亮度和电流效率,有效地改善了OTFEL器件的光电性能.     

氧化钛薄膜表面等离子体处理引发官能团形成的研究

采用水/氧气,丙烯酸/氧气脉冲射频等离子体处理方法,对氧化钛薄膜进行表面改性.结果表明,水蒸气/氧气混合气体等离子体处理在氧化钛薄膜表面产生了吸附水及游离羟基,丙烯酸/氧气混合气体等离子体处理在氧化钛薄膜表面形成了羟基、羧基和羰基官能团.经水蒸气/氧气、丙烯酸/等离子体处理的氧化钛薄膜的水接触角分别降低了67.3和58.5°,极性分量分别增加了36.5和50.9mJ/m2,表现出很好的亲水性.     

氧等离子体处理对国产芳III纤维表面性能的影响

用氧气等离子体处理芳III纤维的表面,考察了等离子体处理前后芳III纤维表面性能的变化。使用红外光谱分析(FT-IR)、X射线光电子能谱(XPS)、扫描电子显微镜(SEM)、原子力显微镜(AFM)和动态接触角等手段研究了等离子体处理前后芳III纤维化学结构、表面元素组成、表面形貌、表面粗糙度和表面浸润性能的变化。结果表明,在保持纤维本体结构不变的前提下用氧等离子体处理在纤维的表面引入了含量分别为20.1%和8.1%的新极性官能团(C-O和COO)。经氧等离子体处理后纤维表面的沟槽和起伏增多,粗糙度增大。用等离子体处理使纤维表面的浸润性能明显提高,总表面自由能由49.9 m J/m~2提高到67.1 m J/m~2。     

等离子体处理高密度聚乙烯表面形态的研究

应用扫描电镜研究了经不同等离子体条件处理的高密度聚乙烯表面形态的变化。结果表明随处理功率增大、处理时间增长和处理压力增高,表面刻蚀随之加深,刻蚀由非晶区向晶区发展,刻蚀条纹渐趋明显,表面粗糙度增加。不同处理气体的作用顺序是氧气>空气≈氩气>氮气。     

氧气等离子体处理对CFRP表面特性及胶接界面力学性能的影响EI北大核心CSCD

为改善碳纤维增强复合材料(CFRP)胶接界面力学性能,采用低温氧气等离子体处理设备对CFRP进行表面处理。利用接触角测量仪、扫描电子显微镜(SEM)、原子力显微镜(AFM)、X射线光电子能谱(XPS)对CFRP表面润湿性、表面能、表面形貌、表面化学组分等进行表征,通过双悬臂梁实验(DCB)对CFRP胶接界面力学性能进行研究。结果表明:随氧气等离子体处理时间从0 s增加至30 s,表面水接触角从97°降至29°,CFRP表面润湿性达到最佳,极性分量占比显著增多;随处理时间的增加,CFRP表面粗糙度和最大高低差降低,形成较多谷峰分布的纳米级沟壑,基体表面积增大;同时,表面C—O和C■O等含氧极性官能团含量明显增加,C—C/C—H和Si—C官能团含量减少,表面污染物得到有效清除和转化;与未处理相比,经氧气等离子体处理20 s后,CFRP胶接界面最大剥离载荷和Ⅰ型断裂韧度分别提高了1.01倍(62.73 N)和1.92倍(649.21 J/m 2)。研究发现,氧气等离子体处理可以显著改善CFRP表面物理化学特性,有利于CFRP与胶黏剂更好的黏结,提高胶接界面剥离强度与韧性。     

HDPE薄膜低温等离子体改性与粘接性能研究

利用氧气低温等离子体,在真空度为20 Pa,处理功率为30 W的条件下,对高密度聚乙烯(HDPE)薄膜进行了表面改性。研究结果表明:在20~200 s的处理时间内,单位面积的失重率随处理时间的增加线性增大,表面粗糙度也随着增加;处理后薄膜表面的接触角显著减小;接触角越小,剥离强度就越大;处理后能在薄膜表面形成羟基、羰基和羧基等各种极性基团。     

等离子体表面处理技术的应用

作为表面处理技术之一的等离子体表面处理技术已经获得广泛的应用。等离子体表面处理方法的优点是利用其处理后的表面化学活性状态增快反应速度。在较低温度下,这类反应也能进行。在这种处理方法中,使置放在等离子体中的固体表面产生新的化合物,改变固体表面的性质。等离子体表面氧化是使半导体表面经过辉光放电处理形成表面氧化膜。若把试样放在等离子体中进行表面处理,试样会直接受到带电粒子的冲击。为了弥补这个缺点,可以在半导体上加盖保护膜,使其产生界面氧化。这个方法叫做界面氧化。作为保     

等离子体时效性对芳纶表面及复合材料界面性能的影响

利用氧气等离子体处理芳纶纤维表面,采用溶液预浸渍工艺制备芳纶纤维增强含氮杂萘聚醚砜酮(PPESK)树脂基复合材料。利用X射线光电子能谱、原子力显微镜和短梁剪切等分析测试手段研究了等离子体时效性对芳纶纤维表面元素组成、表面形貌、表面粗糙度及纤维复合材料层间剪切强度(ILSS)的影响。结果表明,随着等离子体处理的纤维在空气中放置时间的延长,表面化学组成变化较大,表面形貌和表面粗糙度变化不大。经等离子体处理的纤维在空气中放置较短时间内,其复合材料界面性能基本保持,继续延长放置时间到10d,ILSS值由52.0 MPa下降到43.9 MPa,下降了15.5%。     

等离子体处理对PLA膜亲水性及与CNF膜粘附性的影响

目的利用低温等离子体处理PLA膜以提高其亲水性及粘附性,为制备PLA/纳米纤维素复合膜提供一种方法。方法利用单因素试验法探究低温等离子体处理时的放电电压(50～175V)和放电时间(10～50s)对PLA膜表面亲水性和粘附性的影响规律。通过测定PLA膜表面接触角及PLA/纳米纤维素复合膜的剥离强度,分析亲水性及粘附性的变化。利用原子力显微镜观察其微观表面形貌、X射线光电子能谱分析PLA膜表面由疏水性向亲水性转变的机理,并对PLA膜的力学性能及阻隔性能进行分析。结果 PLA膜在低温等离子体条件(放电电压为125V、放电时间为40s、电极距离为4.5cm,氧气流速为1 mL/min,真空度为16.0 kPa)下处理后,其亲水性及与纳米纤维素膜的粘附性达到最佳。此时,PLA膜的接触角由90.0°降至42.4°,PLA/纳米纤维素复合膜的剥离强度为39.5 N/m。结论低温等离子体处理使PLA膜表面由疏水性转变为亲水性,且处理后的PLA可较为牢固地与纳米纤维素膜粘附在一起,从而为PLA/纳米纤维素复合膜的制备提供了一种可行方法。同时,低温等离子体处理对PLA膜的力学性能及阻隔性能没有显著影响。     

Characterization of AlGaN/GaN Metal- Semiconductor-Metal Photodetectors With a Low-Temperature AlGaN Interlayer

AlGaN/GaN metal-semiconductor-metal photodetectors (MSM PDs) with a low-temperature (LT) AlGaN interlayer (IL) were fabricated. Compared with the conventional AlGaN/GaN MSM PD, it was found that leakage current can be suppressed by insertion of a LT AlGaN IL due to the reduction of surface pits and improvement of crystalline quality. It was also found that larger photoresponsivity can be achieved due to the enhanced electric field strength as a result of inserting a LT AlGaN IL. Furthermore, suppressed photoconductive gain, lower noise level, and larger detectivity of MSM PD can also be achieved by using a LT AlGaN IL.      

AlGaN/GaN HEMT栅槽低损伤刻蚀技术

对AlGaN/GaN HEMT栅槽低损伤刻蚀技术进行研究,通过加入小流量的具有钝化缓冲作用的C2H4,对Cl2/Ar/C2H4的工艺条件进行了优化,有效地降低了栅槽刻蚀造成的AlGaN表面损伤和器件退化,同时防止反应生成物淀积在栅槽表面,改善了肖特基结特性,提高了栅极调控能力,实现凹栅槽的低损伤刻蚀.     

The effects of LT AlN buffer thickness on the properties of high Al composition AlGaN epilayers

To fabricate nitride-based ultraviolet optoelectronic devices, a deposition process for high-Al-composition AlGaN (Al content > 50%) films with reduced dislocation densities must be developed. This paper describes the growth of high-Al-composition AlGaN film on (0001) sapphire via a LT AlN nucleation layer by low pressure metalorganic chemical vapor deposition (LPMOCVD). The influence of the low temperature AlN buffer layer thickness on the high-Al-content AlGaN epilayer is investigated by triple-axis X-ray diffraction (TAXRD), scanning electron microscopy (SEM), and optical transmittance. The results show that the buffer thickness is a key parameter that affects the quality of the AlGaN epilayer. An appropriate thickness results in the best structural properties and surface morphology.     

Nanoscale investigation of AlGaN/GaN-on-Si high electron mobility transistors

AlGaN/GaN HEMTs are devices which are strongly influenced by surface properties such as donor states, roughness or any kind of inhomogeneity. The electron gas is only a few nanometers away from the surface and the transistor forward and reverse currents are considerably affected by any variation of surface property within the atomic scale. Consequently, we have used the technique known as conductive AFM (CAFM) to perform electrical characterization at the nanoscale. The AlGaN/GaN HEMT ohmic (drain and source) and Schottky (gate) contacts were investigated by the CAFM technique. The estimated area of these highly conductive pillars (each of them of approximately 20-50?nm radius) represents around 5% of the total contact area. Analogously, the reverse leakage of the gate Schottky contact at the nanoscale seems to correlate somehow with the topography of the narrow AlGaN barrier regions producing larger currents.     

Effect of high temperature AlGaN buffer thickness on GaN Epilayer grown on Si(111) substrates

Crack-free GaN epitaxial layer was obtained through inserting 80 nm graded AlGaN buffer layer between GaN epilayer and high temperature AlN buffer on 2-in Si(111) substrates by metal organic chemical vapor deposition. This paper investigated the influence of AlGaN buffer thickness on the structural properties of the GaN epilayer. It was confirmed from the optical microscopy and scanning electronic microscopy that the graded AlGaN buffer with optimized thickness had a remarkable effect on introducing relative compressive strain to the top GaN layer and preventing the formation of cracks. X-ray diffraction and atomic force microscopy analysis showed that AlGaN buffer with proper thickness could improve the crystal quality and surface morphology of the GaN film. Transmission electron microscopy analysis revealed that a significant reduction in threading dislocations was achieved in GaN epilayer by the insertion of graded AlGaN buffer.     

Surface acoustic wave excitation on SF6 plasma-treated AlGaN/GaN heterostructure

In this work, we introduce a new modified approach to the formation of interdigital transducer (IDT) structures on an AlGaN/GaN heterostructure. The approach is based on a shallow recess-gate plasma etching of the AlGaN barrier layer in combination with “in-situ” SF₆ surface plasma treatment applied selectively under the Schottky gate fingers of IDTs. It enables one to modify the two-dimensional electron gas (2DEG) density and the surface field distribution in the region of the IDTs, as is needed for the excitation of a surface acoustic wave (SAW). The measured transfer characteristics of the plasma-treated SAW structures revealed the excitation of SAW at zero bias voltage due to fully depleted 2DEG in the region of the IDTs. High external bias voltages are not necessary for SAW excitation. SIMS depth distribution profiles of F atoms were measured to discuss the impact of SF₆ plasma treatment on the performance of the AlGaN/GaN-based IDTs.     

AlGaN/GaN HEMTs passivated by Cat-CVD SiN Film

We demonstrate the excellent performance of a 140 W AlGaN/GaN HEMT in the C-band, which is passivated by a Cat-CVD SiN film. The interface trap density of the AlGaN surface passivated by Cat-CVD film after NH₃ treatment is 3 × 10¹² cm^− 2, which is the smallest of investigated deposition techniques. The lowest interface trap density achieved by the Cat-CVD technique makes it possible to operate the AlGaN/GaN HEMT in the C-band. We clarify that the Cat-CVD technique is necessary for developing future amplifiers.     

Isolated photosystem I reaction centers on a functionalized gated high electron mobility transistor

In oxygenic plants, photons are captured with high quantum efficiency by two specialized reaction centers (RC) called Photosystem I (PS I) and Photosystem II (PS II). The captured photon triggers rapid charge separation and the photon energy is converted into an electrostatic potential across the nanometer-scale (~6 nm) reaction centers. The exogenous photovoltages from a single PS I RC have been previously measured using the technique of Kelvin force probe microscopy (KFM). However, biomolecular photovoltaic applications require two-terminal devices. This paper presents for the first time, a micro-device for detection and characterization of isolated PS I RCs. The device is based on an AlGaN/GaN high electron mobility transistor (HEMT) structure. AlGaN/GaN HEMTs show high current throughputs and greater sensitivity to surface charges compared to other field-effect devices. PS I complexes immobilized on the floating gate of AlGaN/GaN HEMTs resulted in significant changes in the device characteristics under illumination. An analytical model has been developed to estimate the RCs of a major orientation on the functionalized gate surface of the HEMTs.     

Growth of InGaN quantum dots with AlGaN barrier layers via modified droplet epitaxy

The growth of c-plane InGaN quantum dots via modified droplet epitaxy with AlGaN barrier layers is reported. The growth of the AlGaN layer underlying the InGaN quantum dot layer was carried out under H₂ at 1050 °C, while the capping AlGaN layer was grown at the same temperature (710 °C) and using the same carrier gas (N₂) as that used to grow the InGaN quantum dot layer to prevent decomposition of the InGaN. Atomic force microscopy of InGaN epilayers grown and annealed on high temperature AlGaN using identical growth conditions used for the quantum dot samples highlighted a narrower distribution of nanostructure heights than that obtained for similar growth on GaN. Scanning transmission electron microscopy (STEM) imaging combined with energy dispersive X-ray (EDX) analysis revealed the presence of a thin high aluminium content layer at the surface of both AlGaN layers, which is believed to be related to loss of Ga during temperature ramping processes. Micro-photoluminescence studies carried out at low temperature revealed near resolution-limited peaks while time-resolved measurements on these peaks demonstrated mono-exponential decay times between 1 and 4 ns, showing that quantum dots had successfully been formed between the AlGaN barriers. Temperature-dependant measurement of the emission lines revealed that quenching of the peak often occurred at ∼60–70 K, with some of the peaks exhibiting significant line broadening whilst others remained narrow.     

Cathodoluminescence study of crystalline quality of (Al, In, Ga)N heterostructures

Wurtzite InGaN/GaN and AlGaN/GaN heterostructures grown by metal organic vapor phase epitaxy were studied using cathodoluminescence (CL) combined with secondary electron microscopy (SEM) and scanning transmission electron microscopy (STEM). The surface morphology of samples containing InGaN layers is dominated by three types of defects: mesa-like hexagonal structures, hexagonal pyramids and micropipes. At the positions of pyramids the whole epilayer is thicker than at defect free positions, while at the positions of micropipes the whole epilayer is much thinner. The luminescence efficiency as well as the emission wavelength are influenced by these defects. In SL structures an increasing SL period thickness in the growth direction was observed. Panchromatic CL images show intensity inhomogeneity in both InGaN/GaN and AlGaN/GaN heterostructure, which are related to local variations of the interface quality. In AlGaN/GaN SQW structures a broad deep-level luminescence band at around 543 nm was observed, which is generally absent in InGaN/GaN heterostructures. This deep-level emission is strongly enhanced in defect positions.