Focusing of x-rays emitted by a pyroelectric x-ray generator for micro x-ray fluorescence

• Published in: Journal of vacuum science and technology. B, Nanotechnology & microelectronics Vol. 37; no. 1
• Main Authors: Wilke, Markus, Harnisch, Karsten, Knapp, Wolfram, Ecke, Martin, Halle, Thorsten
• Format: Journal Article
• Language: English
• Published: 01.01.2019
• DOI: 10.1116/1.5067322
• ISSN: 2166-2746

Micro x-ray fluorescence spectroscopy (μXRF) is a technique for local chemical analyses of materials. There are several advantages in comparison to other similar methods like energy dispersive x-ray spectroscopy in a scanning electron microscope (SEM). The main advantage is the possible abdication of an evacuated sample chamber, which offers the possibility to analyze wet and oil contaminated specimens as well as specimens with intrinsic pores in addition to conventional samples used in SEM analyses. The subject of this report is the investigation of the pyroelectric effect with regard to its application for the generation of focused x-rays and first steps to a successive usage of the generated radiation for μXRF applications. In order to answer questions concerning the energy and intensity of primary radiation and geometric parameters for a successful focusing, this paper describes several experiments and results against the background of the described aims. Different setups and measurements have been used, optimizing the experimental setups to find the basic parameters to potentially generate focal spots of the primary x-rays. Emission behavior of electrons has been visualized and characterized by using a phosphor screen positioned in front of a pyroelectric crystal. Radiation has been measured and characterized by using an energy dispersive silicon drift x-ray detector. All x-ray experiments were executed in a vacuum test rig. This allowed the optimization of the working pressure of the residual gas surrounding the crystal in an evacuated atmosphere (rarefied air). It has been shown that emitted x-ray energies are strongly influenced by the vacuum pressure. Lithiumniobate and lithiumtantalate of different geometries were used as the pyroelectric material. Different target materials and target angles have been compared to optimize the combination of the constructed x-rays source with an aperture as well as with an x-ray optic to focus the primary x-rays. A glass fiber capillary lens was used as the focusing optic. A first step to a μXRF application is shown.