Low-voltage SEM of air-sensitive powders: From sample preparation to micro/nano analysis with secondary electron hyperspectral imaging. (May 2022)

• Record Type: Journal Article
• Authors: Nohl, James F.; Farr, Nicholas T.H.; Sun, Yige; Hughes, Gareth M.; Cussen, Serena A.; Rodenburg, Cornelia
• Is Part Of: Micron. Volume 156(2022)
• Publication Date: 2022-05
• Subjects: AE Auger electron -- AES Auger electron spectroscopy -- AM Additive manufacturing -- AV Accelerating voltage -- BD Beam deceleration -- BSE Backscatter electron -- CB Carbon black -- CD Critical dimension -- CF Carbon fiber -- CM CarbonMide® -- CT Computerized tomography -- DOS Density of states -- EBID Electron beam induced deposition -- EDX Energy dispersive X-ray -- EF Energy filtered -- EL Landing energy, energy at which PEs interact with the specimen -- EOS Electro Optical Systems -- ETD Everhart-Thornley detector -- FIB Focussed ion beam -- FOV Field of view -- HeIM Helium ion microscope -- HFW Horizontal field width -- HOPG Highly oriented pyrolytic graphite -- HV High-voltage -- I0 Incident beam current -- IMFP Inelastic mean free path, mean distance the SE travels between inelastic collisions -- KPAFM Kelvin probe atomic force microscopy -- LIB Lithium-ion battery -- LV Low-voltage -- MAI Methylamonium iodide -- MAPbI3 Methylamonium lead iodide -- MAST-SEY MAterial Simulation Toolkit for Secondary Electron Yield -- MED Mean escape depth, average depth from the surface that SEs are emitted from -- MV Mirror Voltage -- NMC Nickel manganese cobalt oxide -- NMP N-methyl pyrrolidone -- NRMSD Normalized root mean square deviation -- OPV Organic photovoltaic -- P3HT poly(3-hexylthiophene) -- PA Polyamide -- PE Primary electron, electron in the incident electron beam -- PFIB Plasma focussed ion beam -- PVDF Polyvinylidene fluoride -- ROI Region of interest -- SAM Scanning Auger microscope -- SD Standard deviation -- SDD Silicon drift detector -- SE Secondary electron -- SE1 SE emissions localized to the PE interaction from which UHR SE images are formed -- SE2 SE emissions delocalized in time and space from the PE interaction -- SEHI Secondary electron hyperspectral imaging -- SEM Scanning electron microscope/microscopy -- SLS Selective laser sintering -- STEM Scanning transmission electron microscope -- SEY Secondary electron yield, the ratio of emitted SEs to PEs -- TEM Transmission electron microscope -- TLD Through-lens detector -- UC UniColore -- UHR Ultra-high resolution -- UHV Ultra-high vacuum -- WD Working distance, distance between where the electron beam is focussed and the pole piece -- XPS X-ray photoelectron spectroscopy -- φ Work function, minimum energy required to remove an electron from a metal surface; Low-voltage scanning electron microscopy (LV-SEM) -- Secondary electron hyperspectral imaging (SEHI) -- Powder characterization -- Energy storage materials -- Additive manufacturing (AM) materials; Microscopy -- Periodicals; Electron Probe Microanalysis -- Periodicals; Microscopy -- Periodicals; Microscopie -- Périodiques; Microscopy; Periodicals; 502.82
• DOI: 10.1016/j.micron.2022.103234
• Languages: English
• ISSNs: 0968-4328

Abstract

Abstract: Powder materials are used in all corners of materials science, from additive manufacturing to energy storage. Scanning electron microscopy (SEM) has developed to meet morphological, microstructural and bulk chemical powder characterization requirements. These include nanoscale elemental analysis and high-throughput morphological assays. However, spatially localized powder surface chemical information with similar resolution to secondary electron (SE) imaging is not currently available in the SEM. Recently, energy filtered (EF-) SEM has been used for surface chemical characterization by secondary electron hyperspectral imaging (SEHI). This review provides a background to existing powder characterization capabilities in the low voltage SEM provided by SE imaging, EDX analysis and BSE imaging and sets out how these capabilities could be extended for surface chemical analysis by applying SEHI to powders, with particular emphasis on air and beam sensitive powder surfaces. Information accessible by SEHI, its advantages and limitations, is set into the context of other chemical characterization methods that are commonly used for assessing powder surface chemistry such as by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The applicability of existing powder preparation methods for SEM to SEHI is also reviewed. An alternative preparation method is presented alongside first examples of SEHI characterization of powder surfaces. The commercial powder materials used as examples were carbon-fiber/polyamide composite powder feedstock (CarbonMide®) used in additive manufacturing and powders consisting of lithium nickel cobalt oxide (NMC). SEHI is shown to differentiate bonding present at carbonaceous material surfaces and extract information about the work function of metal oxide surfaces. The surface sensitivity of SEHI is indicated by comparison of pristine powders to those with surface material added in preparation. A minimum spatial localization of chemical information of 55 nm was achieved in differentiating regions of NMC surface chemistry by distinct SE spectra.