1.     Introduction

    The X-ray diffraction beamline (BL14B1) is one of the 7 phase I beamlines at Shanghai Synchrotron Radiation Facility. It is based on a bending magnet light source which is dedicated to x-ray diffraction studies. It has three critical components:a collimating mirror (Rh coated on Si), a sagittally focused double crystal monochromator and a focusing mirror (Rh coated on Si), which can further focus the beam to a size of 0.5 mm x 0.5 mm. The X-ray energy is from 4 ~ 22 keV.

    X-ray diffraction (XRD) is the coherent scattering of X-rays by atoms in the lattice. As a traditional experimental method, XRD has the strong vitality and broad applications in the frontier areas such as superconducting materials, catalyst materials, structure determination of three-dimensional biological macromolecules, drug and polymer, nano-materials, surface and interface, semiconductor superlattice, defects. BL14B1 focuses on material science, condensed matter physics fields, designs to investigate powder, surfaces and interfaces, nano-materials.

2.     Beamline Layout

3.     Techniques

High-resolution powder X-ray diffraction (HRXRD)

Grazing Incident X-ray diffraction (GIXRD)

Grazing Incident X-ray Small Angle Scattering (GISAXS)

X-ray Reflectivity measurement (XRR)

Reciprocal Space Mappings (RSM)

Polar Map

Diffraction anomalous fine structure (DAFS)

4.     Optics

Collimating Mirror (Rh coated)

Sagittal double crystal monochromator ( Si(111) )

Focusing Mirror

5.     Endstations

Huber 5021 6-circle diffractometer  

NaI Scintillation detector

Ionization chamber

Fluorescence detector

Mar345  

6.     Beamline Specifications

7.     Typical experiments

i)                 Powder diffraction

This method can be applied for the measurements of various samples, such as heterogeneous catalysts, compounds for hydrogen storage, electrodes materials for lithium battery applications, ferro-electric compounds, thermo-electric compounds, super-conductor materials, etc.

The main advantages for synchrotron-based powdered x-ray diffraction are the following: Monochromatic beam without Kα₂ diffraction peaks normally observed in the conventional XRD systems. High photon flux with much higher signal to noise ratio. Highly collimated beam with much better angular resolution.

As an example, at BL14B1, Professor Chen Ping’s group (from Dalian Institute of Chemical Physics, Chinese Academy of sciences), have successfully determine the crystal structure of a novel hydrogen storage compound, lithium ammonia borane.  It is monoclinic with a space group of p21/c. The lattice parameters are a = 7.0536 Å, b = 14.8127 Å and c = 5.1315 Å. (β = 97.491) This material is stable at ambient temperature and pressure and have very high H₂ storage capacity, which can vastly release H₂ at relatively low temperature.

             Ref: Wu, C. Z.; Wu, G. T.; Xiong, Z. T.; Han, X. W.; Chu, H. L.; He, T.; Chen, P. Chem. Mater. 2010, 22, 3-5.

ii)               Epitaxially-grown thin films and organic thin films

There are a lot of users working with thin-films, which sometimes can be as thin as one atomic layer. For these samples, especially those thin films grown on single crystal substrates, grazing-incidence XRD is often used, which normally requires a very careful calibration of the 0 position of the theta angle. With a very small incidence angle, one expect to have much higher cross-section for detection, thus to increase the sample signal and greatly suppress the signal from the substrate.

 Using the NaI point detector, there are two modes are available.

a)      In-plane scan: One can fix the incidence angle (say 0.2 degrees), and scan the two theta arm horizontally and collect the in plane diffraction signal from the sample. This signal is essentially the diffraction signal from the sample, which displays long range ordering perpendicular to the sample surface.

b)     Out of plane scan: One can collect the out of plane signal by scanning the two theta arm vertically. The sample signal, which displays long-range ordering parallel to the normal of the sample surface, can be studied.

c)      Using 2-dimensional image plate detector, the above two modes (in plane and out of plane) can be further studied, after the incidence angle of the film is determined using the NaI detector.

      Grazing-incidence X-ray diffraction can be applied widely in the field such as super-conductivity, ferro-electric thin film, thermo-electric thin film, semiconducting thin film, wet-epitaxially-grown organic film, polymer thin film transistors, etc.

   As an example, Professor Peijian’s group from Peking University studied the structure of two thin organic films of IIDDT and IIDT. They find four strong diffraction peaks of IIDDT, using GI-XRD technique, whereas there is only a weak diffraction peak for IIDT. These indicates that IIDDT has a regular long range ordering along the 0 0 1 direction, whereas IIDT is more likely with an amorphous phase. Further, the mobility and on/off ratio of the IIDDT, which are critical factors for field-effect transistors, are much superior compared with those of IIDT. Thus, a clear correlation between the structure and property could be revealed. The structures of the IIDDT and IIDT films are also confirmed using AFM technique.

   Ref: Lei, T.; Cao, Y.; Fan , Y. L.; Liu, C. J.; Yuan, S. C.; Pei, J. J. Am. Chem. Soc. 2011,133, 6099-101.

Using the diffraction and reflection techniques, professor Wu Xiaoshan from Nanjing University, proves that their thin film is with a 1x1 Epitaxially-grown superlattice structure. Their studies also proves that a single SrRuO3 unit cell can be ferromagnetic, which greatly advanced the reported results. (Ferromagnetism can only exist with a structure more than 4 unit cells) Thus electrodes can be manufactured in a much thinner manner. Besides that, their studies also find that metal-insulator transition can take place in that 1x1 superlattice under strain adjustments. This strain regulation can also incur paramagnetism to ferromagetism transition. Part of their research has been published in the top journal of physics: Phy. Rev. Lett.

                 Ref: Gu, M. Q.; Xie, Q. Y.; Shen, X.; Xie, R. B.; Wang, J. L.; Tang, G.; Wu, D.; Zhang, G. P.; Wu, X. S. Phy. Rev. Lett. 2012, 109, 157003.  

iii)             Polymer samples, silk, carbon fiber, etc.

Polymer samples (thin film) usually have some preferred orientation and can be best studied using the image plate detector. At BL14B1, polymeric samples is usually measured in the following two modes,

a)      Transmission mode. First, the sample is posed perpendicularly to the beam to collect the data (exposure time 60s); Second, the background data are collected without sample under exact the same conditions; Third, using the Fit2d code, the sample signals are obtained after the background subtracted. As an example, two typical figures before/after background subtraction of a sample in transmission mode are shown, which demonstrate much better sample signals obtained after background subtraction.

b)     Reflection mode. For polymeric samples grown on a substrate, X-ray hardly penetrate through the sample. In such a case, the measurements have to be done in the reflection mode. First, the sample is posed parallelly to the beam, with the 0 point position calibrated by using NaI point detector; Second, with a fixed incidence angle, the NaI detector is moved to 90 degrees, andthe image plate detector is moved closely to the sample; Third, the data are collected (exposure time 60s); Fourth, the sample is replaced by an identical substrate without the film, then the 0 point position is calibrated using NaI detector; Fifth, with the incidence angle fixed, the NaI is moved to 90 degrees andthe image detector is moved forward; Sixth, data are collected with the same exposure time; Seventh, using the fit2d code, the substrate signal is subtracted. The displayed two figures show typical results before/after background subtraction of a sample in reflection mode with much better sample signal.

iv)              Riciprocal Space mapping

At ambient temperature, BiFeO₃ is multi-ferroic (Both Ferro-magnetic and Ferro-electric) It has wide applications in microelectronics. However, the structure of BiFeO₃ thin film is greatly depended on the substrate. Professor Yang Ping (Singapore Light Source) successfully measured BiFeO₃ thin films grown on different substrates at BL14B1, using reciprocal space mapping techniques. For sample of BiFeO₃/LaAlO₃ 001(Left figure), the diffraction peak of (1 0 3) is a triplet, thus, it is a monoclinic Mc phase instead of the M_A or M_B phase reported by previous studies. The Polarization Rotation Path Mediated by Epitaxial Strain is showed in right Figure

                                                                                          Synchrotron XRD RSM for the fi lm on LAO near the

                                                                                       103 reflection of the tetragonal-like phase.                                                Polarization Rotation Path Mediated by Epitaxial Strain

Ref: Chen, Z. H.; Luo, Z. L.; Huang, C. W.; Qi, Y. J.; Yang, P.; You, L.; Hu, C. S.; Wu, T.;

Wang, J. L.; Gao, C.; Sritharan, T.; Chen, L. Ad.v. Funct. Mater. 2011, 21, 133-138.

v)         In situ studies.

One of the most prominent advantages of the synchrotron-based techniques is that it can provide very high photon flux, which is necessary for situ studies and not available using conventional XRD facilities. The in situ experiments can provide real time studies of the sample at non-ambient condition, which otherwise might change. For the in situ experiments, we have a high temperature chamber. Now it is mainly used either with inert gas environment or under vacuum condition. The heating is carried out using a direct Mo strip heater with a temperature of 800 ⁰C obtained with inert gas protection. With a radiation heater under Vacuum condition, even higher temperature can be achieved.

As an example, in situ study of In₂Se₃ will be shown in the following, which has wide applications in data storage, solar cells, sensors and lithium ion batteries. Typically, it has 4 phases and are α, β, γ, δ. New phase of κ phase could also exist after doping. At beamline BL14B1, Professor Sun Xuhui from Suchoo University investigated the phase transitions of In₂Se₃. Around 180 C，the intensity of 0 0 3 and 0 0 4  (κ phase) decreased, and the intensity of 0 0 2 and 0 0 4 (α phase) increased. At 500 C，κ phase almost disappeared.

Ref: Li, Y.; Gao, J.; Li, Q. L.; Peng, M. F.; Sun, X. H.; Li, Y. Y.; Yuan, G.; Wen, W.; Meyyappan, M. J. Mater. Chem. 2011, 21, 6944.

Biomass combustion tends to cause atmospheric pollution by generating nano-particles (PM2.5) and NOx. One effective solution is to convert them to heat energy or electricity through combustion in a furnace. Aerosol produced by the combustion process, however, has high alkali concentration, which will deactivate catalyst consequently. Recent research of Professor Tang Xingfu’s group (Fudan University) shows that the rapid deactivation of DeNOx catalyst is due to occupation of active sites by alkali ions. In situ XRD clearly observes the gradual melting of KCl with increasing temperature and K+ ions spontaneously migrates from surface site to internal tunnel sites of HMO unit at a temperature over 230 ℃. Due to the nano-size, the melting point of KCl is greatly lowered. Even though alkali metals are initially adsorbed on the active sites, they will automatically move to the storage sites (internal tunnels) later. As a consequence, the surface active sites of the DeNox catalyst is refreshed and active DeNox activities is restored. This catalyst has 50 times higher alkali metal resistivity than conventional DeNOx catalysts. Part of the results was published in Angew. Chem. Int. Ed. (2013, 51, 4198–420)

8.     Contacts

Wen Wen  wenwen@sinap.ac.cn +86-21-33933215

Yang Tie Ying yangtieying@sinap.ac.cn +86-21-33932091