title: Atomically Thin Graphene Windows That Enable High Contrast Electron Microscopy without a Specimen Vacuum Chamber.
abstract: Scanning electron microscopes (SEMs) require a high vacuum environment to generate and shape an electron beam for imaging; however, the vacuum conditions greatly limit the nature of specimens that can be examined. From a purely scattering physics perspective, it is not necessary to place the specimen inside the vacuum chamber-the mean free paths (MFPs) for electron scattering in air at typical SEM beam voltages are 50-100 μm. This is the idea behind the airSEM, which removes the specimen vacuum chamber from the SEM and places the sample in air. The thickness of the gas layer is less than a MFP from an electron-transparent window to preserve the shape and resolution of the incident beam, resulting in comparable imaging quality to an all-vacuum SEM. Present silicon nitride windows scatter far more strongly than the air gap and are currently the contrast and resolution limiting factor in the airSEM. Graphene windows have been used previously to wrap or seal samples in vacuum for imaging. Here we demonstrate the use of a robust bilayer graphene window for sealing the electron optics from the room environment, providing an electron transparent window with only a 2% drop in contrast. There is a 5-fold-increase in signal/noise ratio for imaging compared to multi-MFP-thick silicon nitride windows, enabling high contrast in backscattered, transmission, and surface imaging modes for the new airSEM geometry.
authors.affiliation: Department of Applied and Engineering Physics, Cornell University , Ithaca, New York 14853, United States.
authors.forename: Yimo
authors.initials: Y
authors.lastname: Han
authors.affiliation: Department of Chemistry and Chemical Biology, Cornell University , Ithaca, New York 14853, United States.
authors.forename: Kayla X
authors.initials: KX
authors.lastname: Nguyen
authors.affiliation: Department of Chemistry and Chemical Biology, Cornell University , Ithaca, New York 14853, United States.|Institute for Materials Chemistry and Engineering, Kyushu University , Kasuga, Fukuoka 816-8580, Japan.
authors.forename: Yui
authors.initials: Y
authors.lastname: Ogawa
authors.affiliation: Department of Chemistry and Chemical Biology, Cornell University , Ithaca, New York 14853, United States.|Kavli Institute at Cornell for Nanoscale Science , Ithaca, New York 14853, United States.
authors.forename: Jiwoong
authors.initials: J
authors.lastname: Park
authors.affiliation: Department of Applied and Engineering Physics, Cornell University , Ithaca, New York 14853, United States.|Kavli Institute at Cornell for Nanoscale Science , Ithaca, New York 14853, United States.
authors.forename: David A
authors.initials: DA
authors.lastname: Muller
keywords: AirSEM; SEM; STEM; electron scattering; graphene