Microstructure and strain analysis of GaN epitaxial films using in-plane grazing incidence x-ray diffraction

This paper investigates the major structural parameters, such as crystal quality and strain state of （001）-oriented GaN thin films grown on sapphire substrates by metalorganic chemical vapour deposition, using an in-plane grazing incidence x-ray diffraction technique. The results are analysed and compared with a complementary out-of-plane x- ray diffraction technique. The twist of the GaN mosaic structure is determined through the direct grazing incidence t of （100） reflection which agrees well with the result obtained by extrapolation method. The method for directly determining the in-plane lattice parameters of the GaN layers is also presented. Combined with the biaxial strain model, it derives the lattice parameters corresponding to fully relaxed GaN films. The GaN epilayers show an increasing residual compressive stress with increasing layer thickness when the two dimensional growth stage is established, reaching to a maximum level of-0.89 GPa.

Evaluation of both composition and strain distributions in InGaN epitaxial film using x-ray diffraction techniques

The composition and stain distributions in the InGaN epitaxial films are jointly measured by employing various x-ray diffraction （XRD） techniques, including out-of-plane XRD at special planes, in-plane grazing incidence XRD, and reciprocal space mapping （RSM）. It is confirmed that the measurement of （204） reflection allows a rapid access to estimate the composition without considering the influence of biaxial strain. The two-dimensional RSM checks composition and degree of strain relaxation jointly, revealing an inhomogeneous strain distribution profile along the growth direction. As the film thickness increases from 100 nm to 450 nm, the strain status of InGaN films gradually transfers from almost fully strained to fully relaxed state and then more In atoms incorporate into the film, while the near-interface region of InGaN films remains pseudomorphic to GaN.

High resolution X-ray diffraction investigation of epitaxially grown SrTiO_3 thin films by laser-MBE

SrTiO3 thin films are epitaxially grown on DyScO3, LaAlO3 substrates with/without buffer layers of DyScO3 and SrRuO3 using laser-MBE. X-ray diffraction methods, such as high resolution X-ray diffraction, grazing incident X-ray diffraction, and reciprocal space mapping are used to investigate the lattice structure, dislocation density, in-plane lattice strain distribution along film thickness. From the measurement results, the effects of substrate on film lattice quality and microstructure are discussed.

离子注入与沉积TiN膜层中的残余应力

利用掠入射X射线衍射(GIAXRD)研究了GCr15轴承钢表面等离子体浸没离子注入与沉积(PIII&D)氮化钛(TiN)薄膜后膜层表面的应力状态。用X射线衍射(XRD)分析了处理后膜层的化学组成。探讨了薄膜厚度和掠入射角对表面膜层中应力变化规律的影响。结果表明,表面膜层中主要存在TiN相,同时含有少量的TiO2和钛氮氧的化合物。不同工艺下,TiN/GCr15轴承钢试样表面膜层中存在的应力均为压应力;且应力值随着掠入射角度的增大而减小,随着薄膜厚度的增加而降低。

Charge transport in monolayer poly(3-hexylthiophene) thin-film transistors

It is found that ultrathin poly（3-hexylthiophene） （P3HT） film with a 2.5 nm-thick layer exhibits a higher mobility of 5.0× 10-2 cm2/V-s than its bulk counterpart. The crystalline structure of the as-fabricated ultrathin P3HT layer is verified by atomic force microscopy as well as grazing incidence X-ray diffraction. Transient measurements of the as-fabricated transistors reveal the influence of the interface traps on charge transport. These results are explained by the trap energy level distribution at the interface manipulated by layers of polymer film.

Nano structure evolution in P3HT:PC_(61)BM blend films due to the effects of thermal annealing or by adding solvent

Crystallographic dynamics of blend films of regioregular poly（3-hexylthiophene）（P3HT） mixed with [6-6-]-phenylC61-butyric acid methyl ester（PC61BM） treated by thermal annealing or by adding solvent 1,8-diiodooctane（DIO） are characterized by 2D-grazing incidence x-ray diffraction（2D-GIXRD）. The results show that the P3 HT chains are primarily oriented with the thiophene ring edge-on to the substrate, with a small fraction of chains oriented plane-on. The interplanar spacing becomes narrow after being treated by DIO, and the coherence length of the P3 HT crystallites increases after being treated by thermal annealing or DIO, which is accompanied by a change in the orientation angle of the P3 HT lamellae. The increased ordering of P3 HT packing induced by thermal annealing or adding DIO contributes to enhanced photovoltaic performance.

强烘前后压印聚酰亚胺薄膜分子聚集状态研究

聚酰亚胺(PI),聚(酰胺酸)薄膜的前期要使用纳米压印技术(NIL),然后经过强烈烘焙得到压印的聚酰亚胺薄膜。通过掠入射广角X射线衍射的方法研究了强烘前后压印的聚酰亚胺薄膜的分子聚集状态,并与平整的聚酰亚胺薄膜进行了对比。发现纳米压印技术和强烘能强有力地影响聚酰亚胺薄膜的分子聚集状态。强烘前,聚酰亚胺链在线条上与直线方向平行排列。强烘后,在有序范围的排列变成聚酰亚胺分子链轴线与直线方向的垂直度显著增加了而平行度降低了。通过与平整的聚酰亚胺薄膜的比较,发现压印的聚酰亚胺薄膜的结晶度明显地提高了。

基于掠入射二维X射线衍射的陶瓷应力实验表征方法

陶瓷材料被广泛应用于航空航天关键部件的防护涂层以及功率半导体的封装材料。陶瓷材料在服役过程中受环境因素的影响会产生较大的残余应力,这是其破坏失效的主要原因。因此,发展适用于陶瓷材料应力的无损检测方法对其服役安全具有重要意义。X射线衍射(XRD)技术是一种无损、高精度的应力测试方法,在分析材料失效和优化制备工艺方面具有重要作用。然而,目前常用的X射线衍射应力分析方法和装置难以满足陶瓷材料应力快速且精准的测量需求。为此,本文提出了一种基于掠入射二维X射线衍射(GI-XRD~2)原理,采用低衍射角衍射环单次曝光的二维X射线衍射应力快速表征方法,并搭建了前向衍射的实验装置。本文基于大气等离子喷涂(APS)技术制备了8wt.%Y_(2)O_(3)稳定ZrO_(2)(8YSZ)陶瓷样品,通过实验验证了提出方法的有效性、适用性,并分析了其在兼容性、效率、灵敏度等方面相比当前其他相关方法与仪器的特点与优势。

Strong circularly polarized luminescence from quantum dots/2D chiral perovskites composites

Chiral perovskites(CPs)have attracted enormous attentions since they have combined chirality and optoelectrical properties well which is promising in circularly polarized luminescence(CPL)application and of great importance for future spin-optoelectronics.However,there is a key contradiction that in chiral perovskites chirality distorts the crystal structure,leading to poor photoluminescence(PL)properties.Achieving the balance between chirality and PL is a major challenge for strong CPL from chiral perovskites.Differently,two-dimensional(2D)chiral perovskite has shown fascinating chiral induced spin selectivity(CISS)effect which can act as spin injector under ambient conditions.Here,we propose an effective strategy to achieve high CPL activity generated from quantum dots(QDs)by introducing 2D chiral perovskite as a chiral source,providing spin polarized carriers through the CISS effect.The as-synthesized QDs/CP composites exhibit dissymmetry factors(glum)up to 9.06×10^(−3).For the first time,we performed grazing incident wide angle X-ray scattering(GIWAXS)measurements,showing the chirality originates from the distorted lattices caused by the large chiral organic cations.Besides,time-resolved PL(TR-PL)measurements verify the enhanced CPL activity should be attributed to the charge transport between two components.These findings provide a useful method to achieve CPL in QDs/2D chiral perovskite heterojunctions which could be promising in spinoptoelectronics application.

Different mechanisms of improving CH_(3)NH_(3)PbI_(3) perovskite solar cells brought by fluorinated or nitrogen doped graphdiyne

Fluorinated and nitrogen-doped graphdiyne(F/N-GDY)have been used in the active layer of perovskite solar cells(PSCs)for the first time.The introduction of heteroatoms turns out to be an effective method for boosted solar cells performance,which increases by 32.8%and 33.0%,better than the pristine or GDY doped PSCs.The enhanced performance can be attributed firstly to the superiority of F/N-GDY originated from the unique structure and optoelectronic properties of GDY.Then,both can further reduce surface defects and improve surface and bulk crystallinity than pristine GDY.What's more,efficiency increase caused by F-GDY is mainly attributed to the improvement of fill factor(FF),while the higher short-circuit current(Jsc)plays more important role by N-GDY doping.Most importantly,the detailed mechanism brought about by doping of F-GDY or N-GDY is expounded by systematical characterizations,especially the synchrotron radiation technique.Doping of F-GDY causes Pb and forms new Pb-F bonds between F-GDY and Pb ions.Doping of N-GDY or GDY brings about Pb(N-GDY doping induces more deviation than that of GDY due to the participation of imine N),improving its electron density and conductivity.

GISAXS and SAXS studies on the spatial structures of Co nanowire arrays

The spatial structures of magnetic Co nanowire array embedded in anodic aluminium membranes were investigated by grazing incidence small angle X-ray scattering （GISAXS） and conventional small angle X-ray scattering （SAXS） techniques. Compared with SEM observation, the GISAXS and SAXS measurements can get more overall structural information in a large-area scale. In this study, the two-dimensional GISAXS pattern was well reconstructed by using the IsGISAXS program. The results demonstrate that the hexagonal lattice formed by the Co nanowires is distorted （a ≈105 nm, b ≈95 nm）. These Co nanowires are isolated into many structure domains with different orientations with a size of about 2 p_m. The SAXS results have also confirmed that the nanopore structures in the AAM can be retained after depositing Co nanowires although the Co nanowires can not completely but only just fill up the nanopores. These results are helpful for understanding the global structure of the Co nanowire array.

Amorphous nonstoichiometric oxides with tunable room-temperature ferromagnetism and electrical transport

Material functionalities strongly depend on the stoichiometry,crystal structure,and homogeneity.Here we demonstrate an approach of amorphous nonstoichiometric inhomogeneous oxides to realize tunable ferromagnetism and electrical transport at room temperature.In order to verify the origin of the ferromagnetism,we employed a series of structural,chemical,and electronic state characterizations.Combined with electron microscopy and transport measurements,synchrotron-based grazing incident wide angle X-ray scattering,soft X-ray absorption and circular dichroism clearly reveal that the roomtemperature ferromagnetism originates from the In0.23Co0.77O1-v,amorphous phase with a large tunable range of oxygen vacancies.The room-temperature ferromagnetism is tunable from a high saturation magnetization of 500 emu cm-3 to below 25 emu cm-3,with the evolving electrical resistivity from5×103μΩ cm to above 2.5×105 μΩ cm.Inhomogeneous nano-crystallization emerges with decreasing oxygen vacancies,driving the system towards non-ferromagnetism and insulating regime.Our work unfolds the novel functionalities of amorphous nonstoichiometric inhomogeneous oxides,which opens up new opportunities for developing spintronic materials with superior magnetic and transport properties.