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.

Characterization of lattice parameters gradient of Cu(In1-xGax)Se2 absorbing layer in thin-film solar cell by glancing incidence X-ray diffraction technique

In or Ga gradients in the Cu(In1-xGax)Se2(CIGS)absorbing layer lead to change the lattice parameters of the absorbing layer,giving rise to the bandgap grading in the absorbing layer which is directly associated with the degree of absorbing ability of the CIGS solar cell.We tried to characterize the depth profile of the lattice parameters of the CIGS absorbing layer using a glancing incidence X-ray diffraction(GIXRD)technique,and then investigate the bandgap grading of the CIGS absorbing layer.When the glancing incident angle increased from 0.50 to 5.00°,the a and c lattice parameters of the CIGS absorbing layer gradually decreased from 5.7776(3)to 5.6905(2)?,and 11.3917(3)to 11.2114(2)?,respectively.The depth profile of the lattice parameters as a function of the incident angle was consistent with vertical variation in the compositionof In or Ga with depth in the absorbing layer.The variation of the lattice parameters was due to the difference between the ionic radius of In and Ga co-occupying at the same crystallographic site.According to the results of the depth profile of the refined parameters using GIXRD data,the bandgap of the CIGS absorber layer was graded over a range of 1.222-1.532 eV.This approach allows to determine the In or Ga gradients in the CIGS absorbing layer,and to nondestructively guess the bandgap depth profile through the refinement of the lattice parameters using GIXRD data on the assumption that the changes of the lattice parameters or unit-cell volume follow a good approximation to Vegard’s law.

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.

工程陶瓷磨削表面残余应力的测量新方法

磨削加工后工程陶瓷零件表面会产生残余应力。X射线衍射法是用来测量磨削加工后工程陶瓷中残余应力的可靠测量手段。传统的X射线衍射法称之为sin2ψ法,通常只能测量工件表层的残余应力;本文介绍了一种残余应力测量新方法,该方法联合使用sin2ψ法和掠入射X射线衍射法从而得到残余应力在试件中的深度分布。如果考虑X射线的折射,在一系列掠射角下采集到的X射线衍射花样的有效穿透深度和衍射角必须进行折射校正。最后,用这种方法得到的残余应力值是X射线照射的所有层的平均值。

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.

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.