硬X射线微束掠入射实验的控制和数据采集系统及其应用

Control and Data Acquisition System for Hard X-Ray Micro-Beam Grazing Incident Experiment and Its Application

在国内发展了硬X射线微束掠入射实验方法,并将此具有微米级高空间分辨率的方法应用于纳米厚度薄膜的微区分析。该实验方法对分析样品表面或薄膜在微小区域的不均匀组分、结构、厚度、粗糙度和表面元素化学价态等信息具有重要意义。基于X射线全反射原理,以微聚焦实验站的高通量、能量可调的单色微束X射线为基础,通过集成运动控制、光强探测、衍射和荧光探测,设计了掠入射实验方法的控制和数据采集系统。此系统采用分布式控制结构,并基于Experimental Physics and Industrial Control System (EPICS)环境设计SPEC控制软件。通过建立SPEC和EPICS的访问通道,实现SPEC软件对EPICS平台上设备的控制和数据获取。在所设计的控制和数据采集系统中,运动控制系统控制多维样品台电机的运动,实现定位样品位置和调节掠入射角;光强探测系统则监测样品出射光强度,通过样品台运动控制和光强探测的联控,实现样品台的扫描定位控制;通过衍射和荧光探测系统获取不同入射深度下样品的衍射峰强度和荧光计数。此外,为准确控制掠入射角角度,必须确定样品平面与X射线平行的零角度位置,对此给出一种自动定位零角度的方法,编写了该方法的控制算法,设计了相应的控制软件。零角度自动化定位的扫描结果表明,实验系统微区分析的空间分辨率达到2.8 μm,零角度定位精度小于±0.01°。利用该系统在上海光源微聚焦实验站首次实现了具有自动化准确控制零角度的微束掠入射X射线衍射和荧光同步表征的实验方法,实验中被测样品为10 nm Au/Cr/Si薄膜材料, Si基底最上层为10 nm厚的Au薄膜,其间为一层很薄的Cr粘附层。在不同掠入射角下测量样品的衍射信号,获取不同入射深度下样品的衍射峰强度,并实现在同一掠入射角下,同步采集样品的荧光计数信号,从而确定了样品表层的相结构信息以及荧光信号强度与入射角关系,实现了对纳米厚度薄膜在微小区域的相结构和组分分析。此外,通过该技术能够选取荧光计数最大值对应的入射角度,有助于提高后续发展的低浓度样品掠入射X射线吸收近边结构实验方法的信噪比。

The hard X-ray micro-beam grazing incidence experimental method has been first developed in China. This method with micro-spatial resolution is applied to a nalyze nano-thickness films in micro-regions. It is greatly significant for a nalyzing the uneven component, structure, thickness, roughness and chemical valence of surface elements in micro-regions. In this work, according to the principle of X-ray total reflection technology, and based on the high-flux, energy-adjustable monochromatic micro-beam X-rays, a control and data acquisi tion system of the grazing incidence experimental method is designed, which integrates motion control, light intensity detection, diffraction and fluorescence detection. This system adopts the distributed control system structure, and designs the SPEC control software based on the Experimental Physics and Industri al Control System (EPICS) environment. By establishing the access channels of SPEC and EPICS, it realizes using SPEC software to control the equipment on the EPICS platform. Regarding the designed control and data acquisition system, the motion control system controls multi-dimensional sample stage motors, and it can position the sample and adjust the grazing incidence angle. The light intensit y detection system detects the intensity of the emitted light of the sample. Motion control and light intensity detection system are combined to realize sample stage scanning positioning. Diffraction and fluorescence detection system can obtain diffraction peak intensity and fluorescence counts of the sample at diffe rent incident depths. Additionally, in order to locate an accurate zero-angle position where the sample plane is parallel to the X-ray, a method of automatic controlling zero-angle is given, its control algorithm is programmed and it realizes automatic and accurate zero-angle positioning. Revealed by zero-ang le scanning positioning results, the spatial resolution of the experimental sys tem is 2.8 μm, and the zero-angle positioning accuracy is below ±0.01°. Finally, micro-beam grazing incidence X-ray diffraction and fluorescence experime nts with automatic and accurate control of zero-angle have been first performed by using this experimental system at the micro-focusing beamline of Shanghai S ynchrotron Radiation Facility. The sample was a 10 nm Au/Cr/Si thin film, the uppermost layer of the Si substrate was a 10 nm thickness Au thin film, and the re w as a very thin layer of Cr adhesion between them. Diffraction signals of the sa mple were measured at different grazing incidence angles and diffraction peak in t ensity could be obtained. Fluorescence counts were also collected at the same g raz ing incidence angles. Thereby the phase structure information and the relations hip of fluorescence counts and incidence angles were obtained. This experimenta l system realizes the analysis of phase structure and composition of nano-thick ness films in micro-regions. Additionally, according to the maximum value of fluorescence counts, an incident angle can be selected at which grazing inciden ce X-ray absorption near-edge structure experiments can be developed for low- concentration samples, and it is helpful to improve the signal-to-noise ratio of this experimental method.