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Auger Electron Spectrometer

Auger electron spectrometer in laboratory

What is auger electron spectroscopy?

Auger electron spectroscopy(AES) is an analytical technique for surface and materials science. Therefore, the technique is named mainly by the analysis of the Osher effect. In 1953, the OSCE spectroscopy was gradually applied to the analysis of the chemical properties and composition of the surface of a sample. It is characterized by the fact that the Roche electrons come from a shallow surface and only bring out information from the surface, and the energy position of the spectrum is fixed and easy to analyze.

Application of auger electron spectroscopy

Elemental analysis of the surface of nanoceramic powder specimens
In the process of nanoceramic powder preparation, auger electron spectrometer is trying to enrich the surface of powder particles with certain dopants to form an inclusions layer for the purpose of reducing powder agglomeration, improving grain boundary properties and inhibiting grain growth. Usually, the thickness of the surface enrichment layer can only be in the order of a few atomic layers. The Osher surface analysis technique has a very small sampling depth. When the characteristic peaks of elemental kinetic energy or binding energy characterizing the chemical composition of powder particles are drowned by the characteristic peaks of dopants, the surface is indeed enriched with dopants.

Elemental analysis and depth analysis of thin film, multilayer film and thick film specimens
Since the AES instrument is equipped with an ion gun etching system, another major application, in addition to surface cleaning of the specimen, is the analysis of the distribution of elements with the depth of the specimen (depth range from a few nanometers to several hundred nanometers). This analysis technique is required for passivation films, thermal insulation films, ferroelectric films, hard films, etc. After layer peeling and layer collection of spectra, the quality of film formation, diffusion width at the interface, diffusion mechanism and film making process parameters that need to be adjusted can be analyzed.

Elemental analysis on the surface of block specimens
Certain specimens have thin surface generation and small generation zones, such as the analysis of contamination and anti-pollution on the surface of steel plates and silver coins, and the analysis of the causes of failure of microelectronic devices. Other specimens contain ultra-light elements, such as the analysis of Li, B, C and N in SiC-based composite ceramics with SiC fibers coated with BN and C layers, and Li-doped calcium titanate functional ceramics.

Auger electron spectroscopy working principle

The basic principle of auger electron spectroscopy is that when a high-energy electron beam interacts with a solid sample, the electrons in the inner shell of the atom are excited by ionization and leave a vacancy, and the outer electrons jump to this energy level. In the process of releasing energy, the atom can emit an X-ray light with characteristic energy, or it can transfer this energy to another outer electron, causing further ionization and thus emitting a RSE with characteristic energy. The detection of the energy and intensity of the Roche electron gives qualitative and quantitative information about the chemical composition of the surface layer. For an atom, the excited atom can only emit one type of energy: characteristic X-rays or Roche electrons. For elements with a high atomic number, the characteristic X-rays are more likely to be emitted, and for elements with a low atomic number, the oscillating electrons are more likely to be emitted, and when the atomic number is 33, the two types of emission are approximately equal. Therefore,AES is suitable for the analysis of light elements. If an electron beam excites an electron in the K-layer of an atom as a free electron, the L-layer electron jumps to the K-layer, and the energy released excites another electron in the L-layer as an interstitial electron, this interstitial electron is called a KLL interstitial electron. Likewise, the LMM electron is an electron in the L-layer that is excited, and the M-layer electron is filled into the L-layer, and the energy released causes another M-layer electron to be excited.

Advantages of auger electron spectrometer

AES is mainly an analytical technique to obtain information on the elemental species, composition, and chemical state of the sample surface, and its advantages are as follows:
① Thin analytical layer, which can provide information on the composition of a thin layer in the 0-3 nm region on the surface of a solid sample.
② Wide range of analyzed elements, can analyze all elements except H and He, sensitive to light elements.
③ Small analysis area, can be used for the analysis of compositional changes in the region ≤ 50 nm in materials.
④ Ability to provide chemical states of elements.
⑤ Ability to determine depth-to-composition distribution.
⑥ For most elements, the sensitivity of quantitative detection is 0.1% to 1.0%. The accuracy of quantitative analysis is limited to 4-30% of the elements present when elemental sensitivity coefficients are used for calculation, and it is possible to improve quantitative results when standards of similar samples are used.

Structure of auger electron spectroscopy

AES instrument mainly consists of an electron optical system, electron energy analyzer, sample placement system, ion gun, and ultra-high vacuum system.

Electron optical system
The electron optical system consists of an electron excitation source (hot cathode electron gun), an electron beam focusing (electromagnetic lens), and a deflection system (deflection coil). The main indicators of the electron optical system are the incident electron beam energy, the beam intensity, and the beam diameter. The minimum area for AES analysis depends on the minimum beam spot diameter of the incident electron beam; the detection sensitivity depends on the beam intensity. These two metrics are often somewhat contradictory, as a smaller beam diameter will result in a significant decrease in beam current, and therefore a compromise is generally required.

Electron energy analyzer

This is the heart of AES and its function is to collect and separate electrons of different kinetic energies. Because of the extremely low energy of the oscillator electrons, special devices must be used to achieve the required sensitivity of the instrument. Almost all current OSCE spectrometers use a device called a cartridge analyzer.
The main body of the analyzer is two concentric cylinders. The sample and the inner cylinder are grounded simultaneously, a negative deflection voltage is applied to the outer cylinder, a circular electron inlet and outlet is opened on the inner cylinder, and the excitation electron gun is placed in the inner chamber of the cartridge analyzer (it can also be placed outside the cartridge analyzer). The electrons with certain energy emitted from the sample enter the two cylinders from the inlet position, and finally, the electrons enter the detector from the outlet because of the deflection voltage applied to the outer cylinder. If the deflection voltage on the outer cylinder is continuously changed, the interstitial electrons with different energies can be received at the detector in turn. The electrons output from the energy analyzer enter the pulse counter after the electron multiplier and preamplifier, and finally, the X-Y recorder or fluorescent screen displays the distribution curve of the number of interstitial electrons N with the electron energy E.
If the barrel mirror analyzer is combined with the electron beam scanning circuit, a scanning OSCE microscope can be formed (right figure). The electron gun works similarly to the scanning electron microscope, where the two-stage lens reduces the electron beam spot to 3 microns, and the scanning system controls the electron beam to produce simultaneous scanning on the sample and the fluorescent screen of the picture tube.

Sample placement system
The system usually consists of a sample introduction system, a sample stage, a heating or cooling apparatus, etc. To reduce the time required for sample change and to maintain a high vacuum in the sample chamber, the OSCE spectrometer uses a rotating sample stage, capable of holding 6-12 samples simultaneously and delivering the samples to be analyzed to the test position as required.
The sample for the OSCE spectrometer must be able to withstand the vacuum environment without serious decomposition under electron beam irradiation. Organic and volatile substances cannot be analyzed by OSI. Powder samples can be briquettes and placed in the sample chamber.

Ion gun
It consists of an ion source and beams focusing lens and other parts, has the following functions:
clean the sample surface for analysis the sample requires very clean, in the analysis before the commonly used sputtering ion gun on the sample surface cleaning, to remove the dirt attached to the sample surface.
layer by layer etching sample surface, sample composition of the depth profile analysis. Generally use differential argon ion gun, that is, the use of differential pressure pumping so that the ion gun in the gas pressure than the analysis chamber is about 103 times higher. This way when the ion gun work, the analysis chamber can still be in a high vacuum. The ion beam energy can be adjusted in the range of 0.5 to 5 keV, and the beam spot diameter is adjustable from 0.1 to 5 mm. To exclude the influence of the sputtering trap edge, the sputtering etching area should be much larger than the diameter of the incident electron beam spot. The ion beam can also be scanned over a wide range.

Ultra-high vacuum system
This is an important component of AES. This is because a high vacuum level minimizes the staining of the specimen surface during the measurement process, resulting in correct surface analysis results. The high vacuum level of current commercial AES can reach about 10-10 Torr. Without sufficient vacuum, gas particles will adhere to the surface, and a monolayer can be adsorbed in about 1 second at 10-6 torr. Even in a vacuum of 10-10 torr, a considerable amount of carbon and oxygen will be adsorbed on the active surface within 30 minutes, almost approaching a monolayer. That is why environmental contamination of vacuum systems is important.

Auger electron spectroscopy sample pre-treatment

Auger electron spectroscopy has specific requirements for the analysis of samples, and in general only solid conductive samples can be analyzed. Insulating solids can be analyzed with special treatment. In principle, powder samples cannot be analyzed by ERS, but they can be analyzed by special sample preparation. The samples to be analyzed are usually subjected to some pretreatment because of the transfer and placement of the samples in a vacuum.

Handling of powder samples
There are two common methods of sample preparation for powder samples. One is to use conductive tape to fix the powder directly on the sample stage, and the other is to press the powder sample into a thin sheet and then fix it on the sample stage.

Handling of volatile samples
For samples containing volatile substances, the volatile substances must be removed before the sample enters the vacuum system of AES. Generally, the sample can be heated or cleaned with solvent. For samples containing oily substances, the samples are generally cleaned by ultrasonic cleaning with hexane, acetone, and ethanol in turn, and then dried in infrared before entering the vacuum system.

Surface contamination of the sample processing
For samples contaminated with organic substances such as oil, the sample must be cleaned with oil before entering the auger electron spectrometer. Before entering the vacuum system, the sample must be cleaned with oil-soluble solvents, such as cyclohexane, acetone, etc., and finally washed with ethanol to remove the organic solvents. To ensure that the sample surface is not oxidized, natural drying is generally used. Some samples can be polished.

Auger electron spectroscopy specification

1. Auger electron spectroscopy instrumentation is fully automated multi-sample depth analysis is available for rapid depth analysis of small areas at specific micron levels.

2. Equipped with a sensitive hemispherical energy analyzer, it can provide high sensitivity and significantly reduce sample analysis time. In addition, the AES can measure multiple samples in a short period.

3. Floating column type ion gun: high current high energy ion beam is used for thick films, the low energy ion beam is used for ultra-thin films, floating column type to ensure high etch rate with low acceleration voltage, physical bending column will block high energy neutral atoms, thus improving sputtering pit shape and reducing sputtering to adjacent areas.

How to order auger electron spectroscopy?

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