Handbook of Modern Coating Technologies

Application of micro- and nanoprobes to the analysis of small-sized 2D and 3D materials, nanocomposites, and nanoobjects

• Introduction

Leading experts predict a breakthrough in the use of nanomaterials and nanotechnologies in aviation, space research, the chemical, engineering, and motor industries, medicine, biology, and environmental science by the mid-21st century. It poses the questions of diagnosing properties of nanomaterials and nanoobjects and prognostication of their properties under various conditions of application. Two routes of development of analytic techniques are conceivable:

1. Elaboration of new methods for the rapid acquisition of information at the atomic and subatomic levels.
2. Reconstruction (or extension) of the potential of the existing methods recognized as efficacious tools for obtaining microlevel information.

Traditional methods for the analysis at the substructural (nano-) level, such as high- resolution transmission electron microscopy and atomic force, scanning tunneling, and mag­netic microscopies, are currently insufficient to seek comprehensive subatomic information about a nanoobject. Hence, there is a necessity of extending the functional potential and sen­sitivity of the existing methods for nuclear-physical analysis, including—first and foremost— the analysis of angstrom-sized nanoobjects (e.g., at the level of a cell or in a single-ion acceleration mode). Therefore the use of nuclear micro- and nanoprobes, as well as pulsed scanning and transmission positron microscopes and microwave microscopes, may help to

Handbook of Modern Coating Technologies. DOI: https://doi.org/10.1016/B978-0-444-63239-5.00005-6

© 2021 Elsevier B.V. All rights reserved.

obtain reliable information on nanoobjects, nanosized particles, and cells to enable research­ers to deliberately modify the properties of nanomaterials, nanoobjects, nanoparticles, and nanosystems.

Investigations into the various properties of materials and objects at the micro- and nano­levels, as well as their diagnostics, opening opportunities for the creation of such small-sized structures, are among the top priority areas for modern science and technology. Realization of these opportunities implies the development of new multiinstrument facilities (MIFs) and methods on which to base the analysis of the microstructure and elemental composition of novel nanomaterials and nanoobjects, as well as technologies for their fabrication. The focus­ing of charged particle beams appears to be of special interest among various underlying physical principles behind the development of new MIFs due to the fact that the minimum size of a currently attainable focused beam lies in the nanometer and subnanometer ranges. Owing to this, the detection of the products of interaction between beam particles and mat­ter provides information on the microstructure and elemental composition of the test objects or allows one to locally modify their physical and chemical properties at the nanoscale level and to further treat the irradiated regions for the creation of small-sized structures.

MIFs built around focused electron beams are materialized in scanning electron micro­scopes (SEMs) and scanning transmission electron microscopes, as well as in MIFs for elec­tron probe lithography (EPL). The processes of beam generation in axisymmetric systems of these MIF are known fairly well. Various types of multipole aberration correctors and energy filters are needed to improve MIFs characteristics. These MIFs find application in electron probe microanalysis (EPMA) of the structure and elemental composition of samples under study, including energy dispersive spectroscopy (EDS), glow-discharge mass spectrometry (GDMS) and wavelength dispersive spectroscopy (WDS) [1], Auger electron spectroscopy [2], electron energy loss spectroscopy (EELS) [3], and Z-contrast imaging [4]. Despite the very high (atomic-level) resolution of some of these methods, the peculiar properties of electron beams impose important physical limitations on their application. Strong scattering of an electron beam on the electrons of atomic structures in the subjects being studied necessi­tates the use of thin samples to maintain high spatial resolution and sensitivity; it puts into question the representativeness of the data obtained with such samples for real materials. Characteristic X-ray emission induced by an electron beam and recorded by EDS or WDS is associated with a high bremsstrahlung background that impairs the sensitivity of microanaly­sis. The creation of nonprismatic small-sized 3D structures by the EPL method also encoun­ters difficulties caused by electron scattering in high-resistance materials, the formation of high-energy secondary electrons, and an additional radiation dose at the edges of the passed beam.

Focused beams of low-energy heavy ions are utilized in MIFs for secondary-ion mass spectrometry (SIMS). The beams are generated with the help of axisymmetric electrostatic optics, the characteristic mechanism of beam-matter interaction being the scattering of incident ions from atomic nuclei of the sample [5,6]. Rearrangement of atoms in the near­surface layer under the effect of beam ion momentum transfer results in chemical and struc­tural changes, such as the dispersion of atomic, molecular, and cluster structures. By way of

example, the dispersion rate for a Ga-ion beam with an energy of 30 keV varies from 1 to 10 target atoms per incident ion, depending on the type of material. Notwithstanding the high spatial resolution and sensitivity of the method, it is destructive and semiquantitative.

These brief introductory notes allow concluding that the majority of microanalytic techni­ques are suitable for investigations into the local properties of the surface layers of nanoma­terials, nanosystems, and nanoobjects or specially prepared thin samples, which determines the 2D geometry of the region of interest. EPMA is most commonly used to study bulky 3D specimens, as having a detection limit of ~100 ppm and spatial resolution of «1 pm prede­termined by the physical mechanisms of focused beam electron passage through the mate­rial. For this reason, the present review is concerned with methods using other types of charged particle beams and microwave radiation that permit increasing both spatial resolu­tion and sensitivity of analysis of small-sized 3D nanomaterials, nanosystems, and nanoobjects.

The schematic presentation of the work done in this area is provided in Fig. 5—1.