November AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | N O V E M B E R / D E C E M B E R 2 0 1 9 2 9 TECHNICAL SPOTLIGHT ADVANCED EDS DETECTORS DRIVE NANOPARTICLE RESEARCH The rapid ability of next-generation EDS detectors to characterize beam-sensitive materials is leading to breakthroughs in nanoparticle research. E nergy-dispersive x-ray spectrosco- py (EDS, or EDX) is an important electron microscopy tool for ma- terials characterization and is common- ly used in a wide range of applications and industries from manufacturing to energy and resource management to consumer-packaged goods. Despite the wide use of EDS, the technique has lim- itations in certain applications, such as difficulty in obtaining high-quality im- ages of polymers, catalysts, and other nanoparticles sensitive to damage from the electron beam. Next-generation EDS detectors such as Thermo Fisher Scientific’s Dual-X have helped to meet these challenges. Today’s advanced EDS detectors are overcoming the bar- riers to EDS analysis by making it quick and easy to obtain quality results with- out requiring expertise and making it possible to obtain high-resolution im- ages of beam-sensitive materials, which were previously unobtainable. The ability to apply EDS acqui- sition and automated processing to a broader range of samples will enable taking nanoparticle research to new levels, paving the way toward new ap- plications in industries ranging from food to medicine to textiles and energy research. USING X-RAYS TO PRODUCE CHEMICAL INFORMATION EDS is used to characterize the chemical composition of samples by taking advantage of the fact that ev- ery atom has a unique number of elec- trons that reside in specific positions, or shells, around the nucleus of the atom. Under normal conditions, the elec- trons in a specific shell have discrete energies. As an electron beam strikes the inner shell of an atom, it knocks an electron from the shell, leaving a hole. When the electron is displaced, it at- tracts another electron from an out- er shell to fill the void. As the electron moves from the outer to the inner shell of the atom, it loses some energy and the energy difference generates an x-ray with an energy and wavelength unique to the specific element (Fig. 1). X-rays emitted during the process are collected by silicon drift detectors, which separate the x-rays of differ- ent elements into an energy spectrum. Software is then used to analyze the spectrum and determine specific ele- ments contained within the sample. TAKING EDS DETECTORS TO THE NEXT LEVEL To obtain a high-quality image, it is necessary to maximize the number of x-rays captured from different angles. Historically, round-shaped EDS detec- tors have been used with active areas as small as 10 mm 2 , limiting the sig- nals that could be obtained. In contrast, Dual-X detectors have an oval shape, and each detector has a large active area of 100 mm 2 (or a total of 200 mm 2 ). The large racetrack-shaped 100 mm 2 detectors in Fig. 2 are positioned at ex- actly 180 degrees with respect to each other, and both are located at exactly 90 degrees with respect to the hold- er. The analytical large-gap X-twin pole pieces and detector distance and height have been optimized to place the detec- tor as close as possible to the specimen for the highest throughput of x-rays, en- abling low-dose analytics. The shadow- ing of the holder is also visible in the Fig. 1 — X-rays are generated using EDS in a two-step process: Energy transferred to the atomic electron knocks it out of its shell leaving behind a hole, which is then filled by another electron from a higher energy shell, releasing the characteristic x-ray. Fig. 2 — Dual-X detectors are symmetrically positioned at 180-degree angles in relation to the specimen, maximizing the number of x-rays that can be captured regardless of the sample tilt or orientation.