Summary of 7 major material testing methods!

Ingredient analysis

Component analysis can be divided into two types: trace sample analysis and trace component analysis according to the analysis object and requirements. According to the different purposes of analysis, it is divided into bulk element component analysis, surface component analysis and micro-component analysis.

Bulk elemental composition analysis refers to the analysis of bulk elemental composition and its impurity composition, including atomic absorption, atomic emission ICP, mass spectrometry, and X-ray fluorescence and X-ray diffraction analysis methods. Among them, the first three analytical methods need to be dissolved before the sample is measured, so they are destructive sample analysis methods, while X-ray fluorescence and diffraction analysis methods can directly determine solid samples, so they are also called non-destructive element analysis methods.

Surface & Micro Composition Analysis:

1. X-ray Photoelectron Spectroscopy (XPS), (10nm, surface)

2. Auger electron spectroscopy (AES), (6nm, surface)

3. Secondary Ion Mass Spectrometry (SIMS), (μm, surface)

4. Electron probe analysis method, (0.5 μm, bulk phase)

5. Energy spectroscopy by electron microscopy, (1 μm, bulk phase)

6. Electron energy loss spectroscopy by electron microscopy, (0.5nm)

In order to achieve this purpose, compositional analysis is divided into spectroscopic analysis, mass spectrometry analysis and energy spectroscopy analysis according to different analysis methods.

spectroscopic analysis

The main methods include flame and electrothermal atomic absorption spectroscopy (AAS), inductively coupled plasma atomic emission spectroscopy (ICP-OES), X-ray fluorescence spectroscopy (XFS) and X-ray diffraction spectroscopy (XRD).

Atomic Absorption Spectrometry (AAS)

Also known as atomic absorption spectrophotometry. Atomic absorption spectroscopy is an instrumental analysis method based on the resonance absorption of the ground state atom of the measured element in the vapor phase of the sample to the characteristic narrow-frequency radiation emitted by the light source, and its absorbance is proportional to the concentration of the ground state atom of the measured element in the vapor phase within a certain range, so as to determine the content of the element in the sample.

Atomic Absorption Analysis Features:

1. The content of the measured element in the sample is determined according to the absorption intensity of the ground state atom of the measured element in the vapor phase to its atomic resonance radiation;

2. It is suitable for the quantitative determination of trace metal impurity ions in nanomaterials, and the detection limit is low;

3. The measurement accuracy is very high, 1% (3~5%);

4. Good selectivity, no need for separation detection;

5. A wide range of elements are analyzed, more than 70 kinds.

It should be a disadvantage (uncertain): refractory elements, rare earth elements and non-metallic elements, which cannot be analyzed by multiple elements at the same time.

Inductively coupled plasma atomic emission spectrometry (ICP-AES)

ICP is a method that uses inductively coupled plasma as an excitation source, and analyzes the elements to be measured according to the characteristic spectral lines emitted when the atoms of the element to be measured in the excited state return to the ground state, which can be analyzed by multiple elements at the same time, suitable for the analysis of nearly 70 kinds of elements, with a very low detection limit, which can reach 10-110-5μg/cm-3, with good stability and high precision, and a relative deviation of 1% The linear range can reach 46 orders of magnitude, but the detection sensitivity of non-metallic elements is low.

X-ray fluorescence spectrometry (XFS)

It is a non-destructive analytical method for the direct determination of solid samples. It has great advantages in the composition analysis of nanomaterials, and there are two basic types of X-ray fluorescence spectrometer, wavelength dispersion type and energy dispersion type, which has good qualitative analysis ability and can analyze all elements with atomic number greater than 3. The intensity is low, the analytical sensitivity is high, and its detection limit reaches 10-5~10-9g/cm3, which can determine the thickness of the film from a few nanometers to tens of microns.

X-ray diffraction analysis (XRD)

Mass spectrometry

It mainly includes inductively coupled plasma mass spectrometry (ICP-MS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS).

Inductively coupled plasma mass spectrometry (ICP-MS)

ICP-MS is an elemental mass spectrometry method that uses an inductively coupled plasma as an ion source. The sample ions generated by this ion source are passed through a mass analyzer and detector for mass spectrometry to obtain mass spectrometry. Low detection limits (most elements are ppb-ppt levels), wide linear range (up to 7 orders of magnitude), fast analysis speed (70 elements can be obtained in 1 minute), less spectral interference (1 atomic weight difference can be separated), and isotopic analysis can be performed.

Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS)

It is an extremely high-resolution measurement technology that excites the surface of the sample with a primary ion, produces an extremely small amount of secondary ions, and determines the ion mass according to the time it takes for the secondary ions to fly to the detector depending on the mass of the secondary ions.

How it works:

a. Using a focused primary ion beam to carry out a stable bombardment on the sample, the primary ion may be backscattered by the sample surface (with a small probability), or it may penetrate some atomic layers on the surface of the solid sample to a certain depth, and a series of elastic and inelastic collisions occur during the penetration process. The primary ion transfers part of its energy to the lattice atoms, some of which move towards the surface and transfer the energy to the surface ions for emitting, a process known as particle sputtering.

When a primary ion beam bombards a sample, other physical and chemical processes can occur: primary ions enter the lattice, causing lattice distortion, causing chemical reactions on surfaces covered with adsorption layers, etc. Most of the sputtering particles are neutral atoms and molecules, and a small part are atoms, molecules and molecular fragments with positive and negative charges.

b. Ionized secondary particles (sputtered atoms, molecules, clusters, etc.) are separated by mass spectrometry according to the mass-to-charge ratio;

c. Collect the secondary ions separated by mass spectrometry to know the elemental composition and distribution of the sample surface and body. In the analysis process, the mass analyzer can not only provide multi-element analysis data for each moment of the surface, but also provide a secondary ion image of the distribution of a certain element on the surface.

d. TOF (Time of Flight) is unique in that its ion flight time depends only on their mass. Due to the fact that a full spectrum can be obtained in a single pulse, the ion utilization rate is the highest, and the almost non-destructive static analysis of the sample can be achieved in the best way, and its more important feature is that the mass range can be extended by simply reducing the repetition rate of the pulse, which is not limited in principle.

Spectroscopy analysis

It mainly includes X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES).

X-ray Photoelectron Spectroscopy (XPS)

X-ray photoelectron spectroscopy (XPS) is to use X-rays to irradiate the surface of a sample, so that the electrons of its atoms or molecules are stimulated and emitted, and the energy distribution of these photoelectrons is measured to obtain the required information. With the development of microelectronic technology, XPS is also constantly improving, and at present, the small area X-ray photoelectron spectroscopy has been developed, which greatly improves the spatial resolution ability of XPS. By scanning the sample completely, all or most of the elements can be detected in a single measurement.

As a result, XPS has developed into a powerful surface analysis instrument with surface element analysis, chemical state and band structure analysis, and micro-chemical state imaging analysis. The theoretical basis for X-ray photoelectron spectroscopy is Einstein's formula of photoelectron divergence.

As one of the most important means to study the electronic and atomic structure of materials on the surface and interface, XPS can in principle determine all elements on the periodic table except hydrogen and helium. Its main functions and applications are threefold:

First, it can provide qualitative and quantitative information and chemical state information of elements in several atomic layers on the surface of the substance.

Second, the depth distribution analysis of the heterogeneous overburden can be carried out to understand the distribution of elements with depth.

Thirdly, the elements and their chemical states can be imaged, and the distribution images of different elements in different chemical states on the surface can be given.

Auger electron spectroscopy (AES)

Auger electron spectroscopy is a method of using an electron beam (or X-ray) with a certain energy to excite the Auger effect of a sample, and by detecting the energy and intensity of Auger electrons, information about the chemical composition and structure of the surface of the material can be obtained. The surface composition of the sample microregion was qualitatively and quantitatively analyzed by using the Auger electrons emitted during the Auger transition de-excitation process of the excited atoms.

Auger spectrometers are used in conjunction with low-energy electron diffractometers to analyze the surface composition and crystal structure of specimens, hence the name surface probes.

Electron microscopy-energy spectroscopy analysis method: Electron microscope electron beam and solid micro-area X-ray generated by the interaction of electron beam for energy spectroscopy (EDAX), combined with electron microscope (SEM, TEM), micro-component analysis can be carried out, qualitative and quantitative analysis can be carried out.

Topography analysis

The main content of phase analysis is to analyze the geometric morphology of the material, the particle size of the material, the distribution of the particle size, the composition and phase structure of the morphology micro-area.

The main morphology analysis methods are: optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and scanning tunneling microscopy, STM) and Atomic force microscopy (AFM).

SEM

Scanning electron microscopy analysis can provide topography images in the range from a few nanometers to millimeters, with a large field of view, and its resolution is generally 6 nanometers, and for field emission scanning electron microscopy, its spatial resolution can reach the order of 0.5 nanometers.

The information provided mainly includes the geometry of the material, the dispersion state of the powder, the size and distribution of nanoparticles, and the elemental composition and phase structure of specific morphological regions. The SEM has relatively low requirements for samples, and whether it is a powder sample or a large sample, the topography can be directly observed.

TEM

TEM has high spatial resolution and is particularly suitable for the analysis of nanopowder materials. It is characterized by a small amount of sample use, which can not only obtain the morphology, particle size and distribution of the sample, but also obtain the elemental composition and phase structure information of a specific region.

Transmission electron microscopy is more suitable for the morphology analysis of nanopowder samples, but the particle size should be less than 300nm, otherwise the electron beam will not be transparent. For the analysis of bulk samples, TEM generally requires thinning of the sample.

Transmission electron microscopy can be used to observe the size, morphology, particle size, distribution, particle size distribution range, etc. of particles, and use statistical average method to calculate particle size. High-resolution electron microscopy (HRTEM) can directly observe the structure of microcrystallites, especially for the analysis of interfacial atomic structure, it can observe the solid appearance of tiny particles, and the growth direction of crystals can be studied according to the crystal morphology and the corresponding diffraction pattern and high-resolution image.

STM and AFM topography analysis

Scanning tunneling microscopy (STM) is mainly used for the topography analysis of some special conductive solid samples. It can achieve atomic-level resolution, but it is only suitable for morphology analysis and surface atomic structure distribution analysis of conductive thin film materials, and cannot be analyzed for nano-powder materials.

Scanning tunneling microscopes have high resolution at the atomic level, with resolutions of 0.1 nm and 0.01 nm in parallel and perpendicular directions to the surface, respectively, that is, they can distinguish individual atoms, so they can directly observe the near-atomic image of the crystal surface, and secondly, they can obtain a three-dimensional image of the surface, which can be used to measure the surface structure with or without periodicity.

Probes can manipulate and move individual molecules or atoms, arrange molecules and atoms according to people's wishes, and realize nanoscale micromachining of surfaces, and at the same time, when measuring the surface topography of samples, a scanning tunneling spectrum of the surface can be obtained to study the electronic structure of the surface.

Scanning atomic force microscopy (AFM) can analyze the morphology of nanofilms, and the resolution can reach tens of nanometers, which is worse than STM, but it is suitable for conductor and non-conductor samples, and is not suitable for the morphology analysis of nanopowders.

These four topography analysis methods have their own characteristics, and EM analysis has more advantages, but STM and AFM have the characteristics of in-situ topography analysis under atmosphere.

Phase structure analysis

Commonly used phase analysis methods include X-ray diffraction analysis, laser Raman analysis, Fourier transform infrared analysis, and micro-electron diffraction analysis.

X-ray diffraction analysis

XRD phase analysis is based on the diffraction effect of X-rays on a polycrystalline sample to analyze the presence and morphology of each component in the sample. The structure and content of various crystalline components can be determined by measuring the crystallization situation, crystal phase, crystal structure and bonding state. The sensitivity is low, and generally only the phase content in the sample can be determined by more than 1%, and at the same time, the accuracy of quantitative determination is not high, generally in the order of 1%. XRD phase analysis requires a large amount of sample (0.1g) to obtain more accurate results, and amorphous samples cannot be analyzed.

The main uses of X-ray diffraction analysis are: qualitative analysis of XRD phases, quantitative analysis of phases, determination of grain size, determination of mesoporous structure (small-angle X-ray diffraction), multilayer analysis (small-angle XRD method), and identification of material states (distinguishing between crystalline and amorphous states).

Raman analysis

When a photon of an excitation light interacts with a molecule that is the center of scattering, most of the photons simply change direction and scatter, while the frequency of the light remains the same as that of the excited light source, which is called Rayleigh scattering.

But there are also very small amounts of photons that not only change the direction of light propagation, but also change the frequency of light waves, this kind of scattering is called Raman scattering, and the intensity of the scattered light accounts for about 10-6~10-10 of the total scattered light intensity.

Raman scattering occurs due to the energy exchange that occurs between the photon and the molecule, changing the energy of the photon. There are many mechanisms of Raman activation in solid materials, and the range of reflections is also wide: such as molecular vibrations, various meta-excitations (electrons, phonons, plasmas, etc.), impurities, defects, etc. Raman spectroscopy can be used to analyze the molecular structure, physical and chemical properties and qualitative identification of materials, and reveal vacancy, interstitial atoms, dislocations, grain boundaries and phase boundaries in materials.

Infrared analysis (IR)

Infrared spectroscopy is mainly used to detect organic functional groups. Fourier transform infrared spectroscopy can detect the chemical environment and changes such as the bonding of metal ions and non-metal ions, and the coordination of metal ions.

Micro-electron diffraction analysis

Electron diffraction, like X-rays, follows the Bragg equation, and the electron beam is very thin, making it suitable for microanalysis. Therefore, it is mainly used to determine the phases of the objects and their orientation relationship with the matrix, as well as structural defects in the material, etc.

Particle size analysis

In general, the particle size of solid materials can be described by the concept of particle size. However, due to the complexity of particle shape, it is generally difficult to directly describe a particle size with a scale, so the concept of equivalent particle size is widely used in the process of describing particle size.

For particle size analysis instruments with different principles, the measurement principles are different, and their particle characteristics are also different, so they can only be compared with each other, and can not be compared horizontally and directly.

1. Microscopy

SEM, TEM, 1nm~5μm range, suitable for particle size and morphology analysis of nanomaterials. The advantage is that it can provide data on particle size, distribution, and shape, and in addition, the size of the particles can be measured from 1 nanometer to several microns in the order of magnitude, and the intuitive data of the particle image is easy to understand. However, the disadvantage is that the sample preparation process can have a serious impact on the results, such as the dispersion of the sample preparation, which directly affects the quality of the EM observation and the analysis results. The small amount of electron microscopy sampling will produce a non-representative sampling process.

2. Sedimentation Size Analysis

The principle of sedimentation method is based on the balance of gravity (or centrifugal force), buoyancy and viscous resistance of the particles themselves when the particles are in the suspension system, and the viscous force obeys Stokes' law to carry out the measurement, at this time, the particles settle at a constant speed in the suspension system, and the sedimentation rate is proportional to the square of the particle size, 10nm~20μm particles.

3. Light Scattering

Laser diffraction particle size analyzer is only accurate for samples with a particle size of more than 5 μm, while dynamic light scattering particle size analyzer is accurate for the analysis of nano samples with a particle size of less than 5 μm. The laser light scattering method can measure the particle size distribution of 20nm-3500μm, and the equivalent spherical volume distribution is obtained, which is accurate, fast, representative, and repeatable, and is suitable for the measurement of mixed materials.

Photon coherence spectroscopy can be used to measure the particle size distribution in the range of 1nm-3000nm, which is especially suitable for the particle size analysis of ultrafine nanomaterials. Measuring volume distribution with high accuracy, fast measurement speed and wide dynamic range, the stability of the dispersed system can be studied. The disadvantage is that it is not suitable for the determination of samples with wide particle size distributions.

Characteristics of light scattering particle size test method: wide measurement range, now the most advanced laser light scattering particle size tester can measure 1nm3000μm, which basically meets the requirements of ultrafine powder technology. The measurement speed is fast, the degree of automation is high, and the operation is simple, generally only 11.5min. Accurate measurements, good reproducibility, and particle size distributions can be obtained.

Laser coherence spectroscopy particle size analysis: With photon correlation spectroscopy (PCS), the migration rate of particles can be measured. Whereas, nanoparticles in liquids are dominated by Brownian motion, and their movement speed depends on factors such as particle size, temperature and viscosity. Under constant temperature and viscosity conditions, the corresponding particle size distribution can be obtained by measuring the migration rate of the particles by photon correlation spectroscopy (PCS).

Photon correlation spectroscopy (PCS) is capable of measuring suspended solids particles with nanometer sizes, and has a wide range of applications in the fields of nanomaterials, bioengineering, pharmacology, and microbiology.

Thermogravimetric analysis

Thermal analysis is commonly used in differential scanning calorimetry (DSC) and thermogravimetry (TG), referred to as DSC-TG.

Thermogravimetric Analysis (TG or TGA) refers to a thermal analysis technique that measures the relationship between the mass of the sample to be measured and the temperature change at a programmed temperature to study the thermal stability and composition of materials. It is worth mentioning that the change in mass rather than the change in weight is based on the fact that when a strong magnetic material reaches the Curie point, it has an apparent weightlessness when it reaches the Curie point.

TGA is a commonly used testing method in R&D and quality control. Thermogravimetric analysis is often used in conjunction with other analytical methods in actual material analysis to perform comprehensive thermal analysis and analyze materials comprehensively and accurately.