TEM sample preparation method: advantages and disadvantages of FIB sample preparation.
01 Overview of TEM sample preparation methods
Transmission electron microscopy enables detailed observation of the structure of a sample, even a structure made up of just one column of atoms. Its resolution is much higher than that of optical microscopes, reaching 01～0.2 nm with magnifications of tens of thousands to millions of times allows us to study and understand the microstructure and properties of the sample.
The test principle of TEM is to use the electrons that penetrate the sample for imaging and structural analysis, due to the weak penetration ability of electrons, the thickness, conductivity, magnetism and dispersion of the sample have a direct impact on the quality of the test results. As a result, TEM sample preparation is more complex and detailed.
The principle of TEM sample preparation is to be simple, not to damage the sample surface, and to obtain the largest possible observable thin area. The commonly used sample preparation methods can be divided into powder sample preparation method and block sample preparation method.
The sample preparation methods of powder samples can be divided into: solution dispersion-drip method, rubber powder mixing method.
The preparation methods of bulk samples can be divided into: resin embedding method, mechanical thinning method, ultrathin sectioning method, ion thinning method, electrolytic polishing thinning method, and focused ion beam cutting (FIB).
Among them, the Focused Ion Beam Milling (FIB) SEM dual-beam system is a dual-beam device with a focused ion beam tube added to the SEM, and cutting thin sections using FIB-SEM is the most commonly used method to obtain TEM samples. 02 Introduction to FIB sample preparation methods
2.1 FIB sample preparation principle and advantages
The principle of FIB sample preparation is to use an electric lens to accelerate the ion beam generated by the ion source (most FIBs use gallium (Ga), and some devices have helium (He) and neon (Ne) ion sources) through an ion gun, focus and act on the sample surface to realize the milling, deposition, implantation and imaging of the sample material. The integration of scanning electron microscope (SEM) and FIB into a system can give full play to their respective advantages, and the electron beam can be used to monitor the sample processing progress in real time during the processing process, so as to better control the processing accuracy, which has become the main method of nanoscale analysis and manufacturing.
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2.2 FIB sample preparation defects
While FIB systems have their unique advantages in sample preparation, there are some notable drawbacks. In particular, the use of ion beams can cause some unexpected sample damage, altering the properties of the sample surface. For example, at a gallium ion beam of 30 kV, most of the surface of the material will be affected by gallium injection in the depth range of about 30 nm, which will cause the existing atomic structure to be altered or destroyed.
Such amorphous or damaged layers are very noticeable in TEM samples prepared with FIB systems and may affect the final observations. Therefore, researchers need to pay special attention to and consider this potential damaging effect when using FIB sample preparation, and take measures to preserve the original structure and properties of the sample to the greatest extent.
2.3 FIB Sample Preparation Defect Solution
The depth of the amorphous layer induced by FIB preparation depends on the beam energy, beam angle, and the material being milled, and there are several techniques that are commonly used to reduce this amorphous layer damage in TEM samples
1.Gas-assisted etching: While the grinding rate is increased, the roughness of the crystalline-amorphous interface is increased, which further impairs the TEM image
2.Low-energy fib: At these energies, the resolution of the etch rate and position is affected, but the depth of damage can be minimized by a reduction in beam energy
3.Argon Ion Grinding Refinement: The original FIB damage layer can be removed by argon ion refinement, and the effect of removal depends on the energy, angle and time of the argon ions.
This paper focuses on the commonly used FIB focused ion beam preparation methods in TEM sample preparation, and how to solve the problem of amorphous layer formation in FIB sample preparation
In the next article, we focus on the solutions to repair the amorphous layer through two technologies: argon ion finisher and leg to fib.