Nanomaterial is a kind of material with special properties that at least one dimension in three-dimensional space is in the order of nanometer (1~100 nm), or is composed of nanostructure units. It is known as "one of the most important strategic high-tech materials in the 21st century". Due to its special structure and extremely unstable thermodynamics, nanomaterials have many special properties such as small size effect, surface effect, quantum size effect and macroscopic quantum tunnel effect, as well as many physical and chemical properties that traditional materials do not have, such as high chemical activity, strong adsorption, special catalysis, special optical properties, special electromagnetic properties, hydrogen storage properties, etc., so they are widely used in medicine, manufacturing, materials, communications, biology, environment, energy, food and other fields.
Characterization and testing technology is the fundamental way to scientifically identify nanomaterials, recognize their diverse structures, and evaluate their special properties. The main purpose of characterization of nanomaterials is to determine some physicochemical properties of nanomaterials such as morphology, size, particle size, chemical composition, crystal structure, band gap, and absorption characteristics.
The characterization of nanomaterials can be divided into the following parts:
(1) Morphological characterization: TEM, SEM, AFM;
(2) Component analysis: AAS, ICP-AES, XPS, EDS;
(3) Structural characterization: XRD, ED, FT-IR, Raman, DLS;
(4) Characterization of properties: optical, electrical, magnetic, thermal, force.
Some common testing methods.
- Scanning electron microscopy (SEM)
SEM mainly uses the secondary electron signal imaging to observe the surface morphology of the sample, that is, using a very narrow electron beam to scan the sample and produce various effects through the interaction of the electron beam with the sample. Secondary electrons can produce a magnified image of the sample surface, which is established chronologically as the sample is scanned, i.e., using point-by-point imaging to obtain a magnified image.
SEM can acquire the information of various physical and chemical properties of the tested sample itself, such as morphology, composition, crystal structure and electronic structure. SEM is also a conventional instrument for characterizing the morphology, particle size, and size of nanomaterials, which are generally used in the literature of nanomaterials. In addition, SEM is usually equipped with EDS, which is used to analyze the elemental composition and the proportion of the material.
- Transmission electron microscopy (TEM)
TEM is the projection of an accelerated and aggregated electron beam onto a very thin sample, where electrons collide with atoms in the sample and change direction, resulting in solid angle scattering. The magnitude of the scattering angle is related to the density and thickness of the sample, so that different light and dark images can be formed. TEM with a resolution of 0.1 to 0.2 nm and a magnification of tens of thousands to millions of times was used to observe the ultrastructure, i.e., structures less than 0.2 microns and invisible under a light microscope. TEM is a conventional instrument for characterizing the morphology, particle size, and size of nanomaterials, which are generally used in the literature of nanomaterials.
In general, TEM is equipped with High-Resolution TEM, EDX (Energy Dispersive X-ray Spectroscopy) and SAED (Selected Area Electron Diffraction). High-resolution TEM is used to observe the crystal plane parameters of nanomaterials and deduce the crystal form of nanomaterials; EDX is generally used to analyze the elements contained in the sample, as well as the ratio of elements occupied; SAED is used to realize the in situ analysis of the morphological characteristics and crystallographic properties of crystalline samples.
- Atomic force microscopy (AFM)
AFM is an analytical instrument that can be used to study the surface structure of solid materials, including insulators. It studies the surface structure and properties of a substance by measuring the very weak interatomic force between the surface of the sample to be measured and a micro-force sensitive element.
The advantage of AFM is that the sample surface can be observed at high magnification under atmospheric conditions and can be used for almost all samples (there is a certain requirement for surface finish) without the need for other sample preparation to obtain a three-dimensional topography image of the sample surface.
- X-ray Diffraction (XRD)
XRD is a research method to analyze the diffraction pattern of a material by means of X-ray diffraction and obtain information on the composition of the material, the crystalline structure of the material, the structure or morphology of atoms or molecules inside the material.