What is glow discharge mass spectrometry?
Glow discharge mass spectrometer
can be called GDMS
, is a kind of analytical instrument used in the field of material science, which has unique and irreplaceable advantages in profiling the surface and depth of materials.
Glow discharge spectroscopy is a new type of surface analysis technique, which is capable of analyzing solid samples directly. Over the years, the glow depth profiling technique has been widely used in the field of material surface analysis, and people are increasingly valuing this technique.
Application of glow discharge mass spectrometry
High purity metallic materials and alloys
Currently, the technology of glow discharge mass spectrometry
(GDMS) for the detection of trace/ultra-trace impurities in bulk high-purity metallic materials such as high-purity tantalum, high-purity copper, high-purity nickel and high-purity cobalt is well established. Since the ionic strength of the measured elements in GDMS method is not greatly influenced by the matrix, it can also be calibrated with typical RSF values in the absence of suitable specimens. After surface pre-sputtering of the sample to remove contamination and optimization of the instrument conditions, the precision of the measurement results is better than 10% for most impurities in the order of 10-6 g/g; for impurities in the order of 10-9 g/g, the precision of the measurement results The precision of the results can reach 100% for impurities in the range of 10-9 g/g.
The GDMS method has certain requirements on the shape of the sample, the diameter of the sample to be measured should be between 18.2mm and 68.5mm, the surface of the sample should be flat, and if the sample is a metal powder or particle, it needs to be pressed into a sample piece of suitable size.Semiconductor materials
GDMS method is also widely used in the analysis of high-purity semiconductor materials, such as solar cell silicon, high-purity germanium, etc. The detection limits of most elements can be lower than 1ng/g, and some elements can be detected at the pg/g level. By increasing the diameter of the sample, reducing the working resolution, increasing the number of scans and increasing the integration time, the detection limits of the elements to be measured can be reduced.Non-conductor materials
DC glow discharge mass spectrometry uses the sample to be measured as the cathode, i.e., the sample to be measured needs to be able to conduct electricity, and most inorganic non-metallic materials are poor conductors of electricity. For non-conductor materials, they are usually measured by mixing with conductor materials to make a cathode or by introducing a second cathode.
For powder samples, the mixing method is commonly used, i.e., the sample and the conductor material are mixed well and then made into needles or flakes for analysis using a specially designed press mold.Depth analysis
Glow discharge is very stable and can obtain almost identical sampling pits on the surface of the sample, and the rate of sputtering can be controlled by controlling the discharge conditions. Depth analysis is of great importance in the study of thin-layer materials, which helps to investigate the principles of some surface chemical or physical phenomena and provides guidance to the production process of corrosion protection and surface materials. As shown in Figure 3 is the depth analysis of AlOx plating on steel surface, sputtering to 5μm where the content of Fe, the main component in steel, increases significantly and the content of Al decreases, indicating that the depth of steel surface plating is 5μm.
Glow discharge mass spectrometry working principle
is an emission spectrometer, and other emission spectrometers, its basic working principle is more or less the same, that is, a light source is used to make the measured sample elements in an excited state, the sample elements from the outer electron of the high energy state back to the low energy state, the characteristic spectrum is emitted. The characteristic spectra of the elements in the sample are analyzed by the emission of the element.
The glow discharge lamp as the light source of the glow discharge instrument, there are two electrodes in a RF glow discharge light source, the diameter of 4mm tubular copper electrode for one of them, is the anode, the anode grounded. And the sample as the cathode, making a RF potential is maintained, this is the potential generated by high frequency (RF) power induction. The low-pressure argon gas is charged into the glow discharge lamp, and a small amount of argon ions are spontaneously generated in the lamp, which pass through the anode-cathode gap under the RF potential, making the high-speed oscillation generated, the accelerated argon ions and argon atoms collide, making more argon ions and electrons generated, making the plasma formed, which is called glow discharge, and the high-speed argon ions in the plasma reach the sample (cathode) surface, The material on the surface of the sample is sputtered out uniformly, diffused into the glow discharge plasma, where it is dissociated and atomized, and thus excited, causing the characteristic spectra of the sample components to be emitted.
The light from the sample is focused and spectroscopically separated by the optical system and reaches the high dynamic range detector HDD, which receives the light signal, which is converted into an electrical signal and sent to the computer for processing using the electronic control system. The computer is equipped with special software, which compares the standard curve preset in the software with the light intensity signals of various elements, so that the concentration of each element can be measured.
Glow discharge mass spectrometry advantages
Glow discharge mass spectrometer can directly sample solid samples and perform full elemental determination, the sputtering area of the sample is generally tens to thousands of m㎡, so the sample volume consumed is up to milligram level.
Wide range of elements
In principle, GDMS can cover all elements of the entire periodic table, including C, N, and O. GDMS can analyze up to 73 magazine elements at one time, and can provide a detection limit of nearly 6N, which is very suitable for analyzing the purity of solar grade silicon materials.
High sensitivity and low detection limit
GDMS has high sensitivity and low detection limit, which can be as low as 0.1-0.001ng/g for most metal elements and ug/g for C, N, O.
Types of glow discharge mass spectrometry
DC glow discharge mass spectrometer
DC glow discharge mass spectrometry
dominates the analytical applications and is currently the main mode of testing.
When a DC glow discharge mass spectrometer is coupled with a DC voltage between the cathode and anode, the remaining electrons and ions in the working gas in the cavity move in a directional manner under the action of the electric field, and the current increases from zero.
When the voltage between the electrodes is large enough for all charged ions to reach their respective electrodes, the current reaches a certain maximum (i.e. saturation value).
When the discharge voltage between the electrodes is greater than a certain critical value (ignition glow voltage), the discharge current will rise suddenly and rapidly, and the voltage between the cathode and anode will drop steeply and remain at a low and stable value. The working gas is breakdown, ionization, and produce plasma and self-sustaining glow discharge, which is the basic process of "Townsend discharge", also known as small current normal glow discharge.
The cathode of the magnetron target is connected to the negative terminal of the target power supply, and the anode is connected to the positive terminal of the target power supply. Its characteristics are, with the adjustment of the power output of the magnetron target voltage increases, sputtering current should also be synchronized with a slow rise.
Pulsed glow discharge mass spectrometer
Pulsed glow discharge mass spectrometer is mainly used to analyze non-conductor samples
The gas discharge of a single pulse of a pulsed or sinusoidal half-wave IF target power supply should be consistent with the variation pattern of the abnormal glow discharge section of the DC gas discharge volt-ampere characteristic curve and the preceding section. It can be regarded as the gas discharge volt-ampere characteristics in a single pulse of the discharge reproduction. The pulsed DC target power supply starts the glow sputtering during the pulse and naturally extinguishes the glow between pulses, which is difficult to distinguish with the naked eye because of the high frequency.
Sputtering target after the glow discharge, when the power supply output pulse repetition frequency is high enough because the conductive ions in the vacuum cavity body have not been completely neutralized, the second (later) repeat the pulse of the re-glow voltage and sputtering target work voltage close or the same. When the power supply output pulse repetition frequency is very low (for example, a few hundred HZ below) or arc extinguishing time is too long (more than 100ms), the sputtering target after the glow discharge, because the conductive ions in the vacuum cavity have been basically neutralized, the second (later) repeat pulse of the re-glow voltage back to a higher value, and ignition glow when the high voltage is close to or the same.
RF glow discharge mass spectrometer
RF glow discharge mass spectrometers can provide stronger ion signals at the same power as DC glow discharge by applying a DC voltage periodically between the two poles.
Glow discharge mass spectrometry specifications
RF glow discharge mass spectrometer
1. RF glow discharge mass spectrometer uses RF generator-standard configuration, compound D standard, high stability, extremely flat sputtering beam spot, very short plasma stabilization time and no distortion of surface information.
2. The pulsed working mode can analyze both conventional coating/plating layers and thin films as well as coatings/plating layers and thin films with poor thermal conductivity and thermal fragility very well.
3. The multi-channel spectrometer provides full spectral coverage from 110nm to 800nm and can test far-UV elements C, H, O, N and Cl.
4. The original ion etched holographic grating ensures that the instrument has the maximum luminous flux and therefore has excellent optical efficiency and sensitivity.
5.T he High Dynamic Detector (HDD) provides fast, highly sensitive detection of elements at ppm-100%. The dynamic range is 5 x 1010.
6. Suitable for large sample chambers for easy loading of all types of samples.
Glow discharge mass spectrometer operating conditions
1. Supply voltage:
Independent power supply required AC380V/220V(±10%),50Hz
2. Working ambient temperature:
3. Ambient relative humidity:
4. Instrument operation durability:
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