Electron Microscope Sample Preparation and Target Material Selection

Electron microscopes (EM) are crucial tools for exploring micro/nano structures. To ensure high-resolution and clear images of samples under various types of electron microscopes, conductive thin films must be prepared on the sample surface. The choice and preparation of the target materials for the film directly affect imaging quality. Therefore, understanding the characteristics and suitable applications of different materials (targets) is essential.

Target Material Selection

1.     Gold (Au)Gold is the most commonly used conductive coating material for electron microscope samples, especially for imaging at magnifications greater than 30,000x. Gold offers excellent conductivity and has small particle sizes (around 5 nm), making it highly effective for high-resolution imaging. Gold is a non-oxidizing material, making it suitable for deposition using low vacuum sputtering systems. VPI’s SD-900M Magnetron Sputtering Coater is an ideal system for depositing gold coatings (target), providing high-quality metal coatings for electron microscope samples, ensuring stable high-resolution images.

2.     Carbon (C)Carbon is often used as an alternative to gold in EDX analysis. With a lower atomic number, carbon does not affect X-ray spectra, making it suitable for applications where avoiding interference with X-ray background peaks is critical. VPI’s SD-980 Pulsed Thermal Evaporation Coater is an ideal device for depositing carbon coatings in low vacuum environments, ensuring uniformity and quality of the coatings.

3.     Platinum (Pt)Platinum provides finer particle sizes, making it suitable for high magnification imaging. It has a very high secondary electron emission rate, ideal for high-precision imaging. Platinum has a lower sputtering rate than gold and typically requires deposition in a high vacuum environment. VPI’s SD-900M Low Vacuum Coater can also fulfill sample preparation requirements for platinum coatings.

4.     Palladium (Pd)Palladium (target) coatings are suitable for low to medium magnification imaging. The secondary electron signal from palladium is lower than that from gold, but it is an excellent alternative material, particularly for EDX analysis. Palladium has good solubility and can be removed from the sample surface, allowing researchers to return the sample to its original state after the experiment.

5.     Gold/Palladium (Au/Pd)Gold/Palladium alloys (such as 60/40 or 80/20 ratios) are commonly used to obtain smaller particle sizes compared to pure gold, especially when deposited in high vacuum conditions. This material is very effective in high-resolution applications, but it is not suitable for EDX analysis because palladium increases X-ray peaks.

6.     Chromium (Cr)Chromium is a common oxidizing material, especially for conductive coatings in semiconductor materials. It provides very fine particle sizes, suitable for high-resolution imaging. Due to its susceptibility to oxidation in the air, chromium requires a pre-sputtering process to remove oxides. VPI’s SD-650MH High Vacuum Magnetron Sputtering Coater is ideal for chromium target sputtering and sample preparation, while also removing oxidation and ensuring coating purity.

Which Samples Need Coating?

1.     Beam-sensitive SamplesCertain samples (e.g., biological samples) may be damaged when exposed to high-energy electron beams. To reduce radiation damage, a protective thin film is applied to the sample surface.

2.     Non-conductive SamplesNon-conductive samples tend to accumulate charge on their surface due to electron beam impact, leading to surface charge buildup. To solve this issue, a thin conductive coating (such as gold, platinum, or carbon) helps to remove excess charge and ensures stable imaging of the sample.

Types of Electron Microscopes and Their Magnification Ranges

Different types of electron microscopes are suited to different magnification ranges and applications, as outlined below:

• Scanning Electron Microscope (SEM)

  SEM is suitable for medium to high magnification imaging, typically ranging from 10x to 500,000x. It is used for observing the surface structure and morphology of samples, particularly for larger samples and surface feature analysis.

• Field Emission Scanning Electron Microscope (FESEM)

  FESEM is a high-resolution scanning electron microscope, suitable for magnifications ranging from 500,000x to 2,000,000x. It uses a field emission electron source to provide more detailed surface features and higher resolution, making it ideal for observing nanoscale details.

• Transmission Electron Microscope (TEM)

  TEM is used for high-resolution analysis of thin films and internal material structures, with magnifications typically ranging from 100,000x to 10,000,000x. TEM provides extremely high resolution, suitable for detailed nanoscale analysis.

VPI Sputtering Coaters: Supporting High-Resolution Electron Microscope Imaging

In the preparation of electron microscope samples, choosing the right sputtering coating system is crucial. VPI’s SD-900M Magnetron Sputtering Coater and SD-650MH High Vacuum Magnetron Sputtering Coater offer high-quality thin film coatings to ensure optimal imaging results under electron microscopes.

• SD-900M Magnetron Sputtering Coater: This device is ideal for fast deposition of conductive coatings using gold, silver, platinum, and palladium targets. It meets the sample preparation needs for SEM and FESEM, providing uniform films that ensure high-resolution images.

• SD-650MH High Vacuum Magnetron Sputtering Coater: This system is perfect for fine coating deposition in high vacuum environments, offering higher quality films. It is especially suitable for samples requiring high purity and uniform coatings, making it advantageous for TEM analysis, material science, semiconductor, biochemistry, and battery research.

Choosing the appropriate coating materials and sputtering deposition technology is crucial for electron microscope imaging. Materials such as gold, platinum, and palladium are widely used in sample preparation due to their excellent conductivity and suitability for high-resolution imaging. VPI’s SD-900M Magnetron Sputtering Coater and SD-650MH High Vacuum Magnetron Sputtering Coater provide high-quality coating solutions, ensuring your sample preparation meets the requirements of different electron microscope analyses and delivers the best imaging results.