Direct observation and analysis of yolk-shell materials using low-voltage high-resolution scanning electron microscopy: Nanometal-particles encapsulated in metal-oxide, carbon, and polymer

Abstract

Nanometal particles show characteristic features in chemical and physical properties depending on their sizes and shapes. For keeping and further enhancing their features, the particles should be protected from coalescence or degradation. One approach is to encapsulate the nanometal particles inside pores with chemically inert or functional materials, such as carbon, polymer, and metal oxides, which contain mesopores to allow permeation of only chemicals not the nanometal particles. Recently developed low-voltage high-resolution scanning electron microscopy was applied to the study of structural, chemical, and electron state of both nanometal particles and encapsulating materials in yolk-shell materials of Au@C, Ru/Pt@C, Au@TiO2, and Pt@Polymer. Progresses in the following categories were shown for the yolk-shell materials: (i) resolution of topographic image contrast by secondary electrons, of atomic-number contrast by back-scattered electrons, and of elemental mapping by X-ray energy dispersive spectroscopy; (ii) sample preparation for observing internal structures; and (iii) X-ray spectroscopy such as soft X-ray emission spectroscopy. Transmission electron microscopy was also used for characterization of Au@C.

Investigation of the Image Contrast in an Ultra-Low Voltage Scanning Electron Microscope Using an Auger Electron Spectrometer

“…Recently, FE-SEMs with low incident electron energy (LE-SEMs) with a spatial resolution of less than 1 nm, even at 1 keV, have been developed, making it possible to obtain SEM images at high magnification at several tens of eV (Asahina et al, 2014). LE-SEM is more commonly referred to as low voltage SEM (Asahina et al, 2014).…”

“…Recently, FE-SEMs with low incident electron energy (LE-SEMs) with a spatial resolution of less than 1 nm, even at 1 keV, have been developed, making it possible to obtain SEM images at high magnification at several tens of eV (Asahina et al, 2014). LE-SEM is more commonly referred to as low voltage SEM (Asahina et al, 2014). We used an LE-SEM column in this study with the ability to apply a sample bias to create low incident electron energy by decelerating the primary electron beam, both in an SEM and an Auger electron spectrometer (AES).…”

Low-Temperature Synthesis and Structure of Hybrid Ni@C Nanomaterials Fabricated by Method of Reactive Magnetron Sputtering

“…Гибридные материалы обычно представляют собой металл, инкап-сулированный в углеродную оболочку (Me@C) [1][2][3][4]. Углеродная оболочка, покрывающая металлическую частицу, обеспечивает ей не только защиту от механических повреждений, но и предохраня-ет от окисления [5,6], тем самым увеличивая диапазон возможного практического применения.…”

Damage-less Chemical State Analysis by Using Soft X-ray Emission Spectroscopy in Low Voltage SEM

“…However, it was known that the SXES is not suitable for electron beam sensitive samples because it needs high electron probe current to detect enough X-rays. In this report, we focused on the chemical state analysis with less electron damage using low voltage method and the cooling stage.The SXES is possible to analyze chemical bonding states because it has high energy resolution at X-ray energy of about 200 eV or even below such as 0.3 eV at the Al Fermi edge [1]. The SXES is installed in the low voltage (LV) FE-SEM JSM-7800FPRIME.…”

“…The SXES is possible to analyze chemical bonding states because it has high energy resolution at X-ray energy of about 200 eV or even below such as 0.3 eV at the Al Fermi edge [1]. The SXES is installed in the low voltage (LV) FE-SEM JSM-7800FPRIME.…”