01 GDMS Overview
glow discharge mass spectrometry method (Glow Discharge Mass Spectrometry, GDMS) is an analysis method that uses the glow discharge power supply as an ion source to connect it to the mass spectrometry instrument for mass spectrometry. GDMS has been used in many disciplines. In the field of materials science, GDMS has become a tool for controlling and characterizing reactive and non-reactive plasma deposition processes. GDMS is considered to be the most effective means to directly analyze trace and supertrace elements on solid conductive material . Because it can directly inject solids, it has become a powerful method for the analysis of impurity components of inorganic solid materials, especially high-purity metals, alloys and other materials.
Figure 1. Glow discharge mass spectrometer
02 GDMS principle
Glow discharge mass spectrometer consists of two parts: glow discharge ion source and mass spectrometer analyzer. The glow discharge ion source (GD source) uses an inert gas (usually argon gas, pressure of about 10 to 100Pa) to impact the surface of the sample surface to sputter. The sample atoms generated by sputtering diffuse into the plasma and further ionize, and then collect and detect by the mass spectrometer analyzer. glow discharge is a low-voltage discharge. The large number of electrons and metastable inert gas atoms generated by the discharge frequently collide with the sample atoms, causing the sample to be greatly sputtered and ionized. At the same time, since the atomization and ionization of the sample in the GD source are carried out in two different regions, the cathode dark region near the sample surface and the negative radiance region near the anode, the matrix effect is greatly reduced. The responses of GD sources to different elements are small (usually within 10 times) and have a wide linear dynamic range (about 10 orders of magnitude). Therefore, even without standard samples, more accurate multi-element semi-quantitative analysis results can be given, which is very conducive to the semi-quantitative analysis of ultrapure samples.
Figure 2. Basic principles of glow discharge mass spectrometry
GD source power supply methods can be divided into three types: DC glow discharge (DC-GD), radio frequency glow discharge (RF-GD) and pulsed glow discharge (pulsed-GD). Among them, DC sources are the most used, and the other two combinations with mass spectrometry are still in the laboratory stage, and no commercial instruments have appeared.
03 GDMS features
- direct solid state sampling;
- ion source ion source ionization ability;
- high sensitivity and high resolution;
- measurement process is stable, Good reproducibility and reproducibility;
- can perform qualitative or quantitative analysis of almost all elements in the periodic table (except C, O, H, N);
- GDMS can directly detect inorganic powders, coatings/substrates and non-conductive materials without sample preparation, providing information on various elements;
◮ Detection area: ~ 50 mm2;
◮ Detection range: % - ppt;
◮ Vertical resolution: = 0.1 µm.
04 GDMS The main purpose of the application of
DC glow discharge mass spectrometry (DC-GDMS) is to analyze trace impurities of conductive materials such as high-purity metals and semiconductors, and in-depth analysis of layered samples prepared by plating, electrodeposition, permeation and other processes. In addition, it can also be used in impurity analysis of non-metallic materials such as sediments and oxides, as well as isotope abundance analysis with low accuracy requirements.
, high-purity material analysis
There are two main difficulties in the analysis of impurities of high-purity materials: one is that the concentration of impurities is very low, which requires high requirements for the instrument's detection ability, background control, and elimination of interference; the other is that the concentration of matrix elements is very high, which is easy to interfere with the elements being tested. High-resolution GDMS has strong interference removal ability and wide dynamic range. It can realize constant, trace, trace, and ultra-trace analysis, and is easier to overcome the above difficulties, so it is particularly suitable for the analysis of high-purity substances.
2, Deep Analysis
GDMS sputtering injection method determines that it can perform in-depth analysis. The glow discharge is very stable, and almost the same sampling pit can be obtained on the sample surface, and the rate of sputtering can be controlled by controlling the discharge conditions. Many literatures have reported the application of GDMS in in-depth analysis. In-depth analysis is of great significance in studying thin-layer materials, and it helps to study the principles of some surface chemical or physical phenomena and provide guidance on the production processes of anti-corrosion and surface materials.
3. Conductor Materials Analysis
DC-GDMS cannot directly analyze non-conductor materials. There are two main methods for analyzing non-conductor material treatment: the second cathode method and the mixing method. The second cathode method has strict requirements on the material of the second cathode. Generally speaking, the signal strength of the matrix is weaker than that of the conductor, has poor stability, and it is impossible to distinguish the background of the second cathode impurity from the sample impurities; for powder samples, it can be mixed with conductive substances, such as graphite , gold, copper, tantalum, silver powder , press-molded, and then analyzed. This method is prone to contamination, and the additions will increase the background signal and dilute the sample to reduce sensitivity.
