Sponsored by LuxorReviewed by Ify IsiborJun 24 2026
Thin coatings of materials such as gold (Au) or platinum (Pt), applied via sputter coating, do not always have the "metallic appearance" we are used to in everyday life. Gold or platinum coatings with thicknesses of 15-20 nm or less lack the expected gold or platinum "appearance".
Image Credit: LUXOR
This is often misinterpreted by the operator of a sputter coater, who may believe that no or inadequate coating has been applied, when in fact the requested coating is present. To correct this common misunderstanding, LUXOR conducted a test in which layers of gold and platinum of varying thicknesses were deposited on a stub with carbon tape. These are the results:
Gold
Image Credit: LUXOR
Platinum
Image Credit: LUXOR
The characteristic gold- or platinum-like appearance becomes clearly visible only for coating thicknesses exceeding approximately 20 nm. Thinner coatings typically appear slightly reflective or grayish. Nevertheless, elemental analysis by energy-dispersive X-ray spectroscopy (EDS) in the electron microscope readily confirms the presence of a gold or platinum coating.
From a practical perspective, the observation of a distinct gold or platinum layer on a coated specimen strongly indicates that the deposited coating is substantially thicker than the generally accepted thickness required to eliminate charging in most materials (typically 2–5 nm for platinum and 5–10 nm for gold).
In such casess, the coating parameters should be adjusted to achieve thinner coatings, thereby preserving the visibility of the sample’s surface topography.
Manual coating techniques offer limited control over deposition parameters and frequently produce coatings that are either excessively thick or non-uniform. In these cases, the images shown above can serve as a useful visual reference for assessing both the thickness and overall quality of the applied coating.
What is Sample Charging?
In an electron microscope, samples are placed in a vacuum chamber and exposed to an electron beam.
During imaging, non-conductive or poorly conductive materials can accumulate electrical charges, leading to imaging artifacts such as abnormal contrast and overly bright or “overexposed” regions. To prevent these effects, a thin conductive coating, typically gold, platinum, or carbon, is applied to the sample surface.
The most commonly used coating techniques are thermal evaporation for carbon and sputter coating for gold and platinum. This sample preparation step is generally referred to as SEM coating.
Tissue Paper Uncoated (1000x Magnification)
Image Credit: LUXOR
Tissue Paper Coated with a 5 nm Gold Layer (1000x Magnification)
Image Credit: LUXOR
Why Choose LUXOR?
A2 Technology: Precision Coating for High-Resolution Imaging
LUXOR’s A2 technology generates a highly stable and precisely controlled plasma, enabling the deposition of thin, uniform coatings. The process starts by evacuating the chamber to create a vacuum, after which a proces gas or air is injected and a high voltage is applied to ionize the gas, initiating the plasma and the coating curent.
To maintain process stability, the coating current is continuously regulated through the controlled high-speed injection of small amounts of process gas into the chamber. This dynamic adjustment ensures that the target current is reached quickly and maintained throughout the coating cycle.
What sets LUXOR metal coaters apart from other commercially available systems is their distinctive approach to process monitoring and control, which provides exceptional precision and reproducibility.
Download Luxor's eBook on electron microscopy here
Image Credit: LUXOR
Innovative Upside-Down Design for Greater Functionality
LUXOR follows a "form follows function" design philosophy, which is reflected in the distinctive architecture of its mcoaters. Unlike conventional systems, the samples and are suspended upside down within the coating chamber, while the target is at the bottom. Although this configuration may initially seem unconventional, it offers several significant practical advantages.
- Safety first: The sputter device has all the high voltage and current lines safely stored within the instrument housing, decreasing the risk of electric shock. This safety function enables the machine to operate with total peace of mind.
- Effortless sample handling: The upside-down design allows for easy access to the lid, which also serves as a loading station for samples. This enables the quick application or removal of samples without the use of special tongs or tweezers. This simplicity not only improves usability but also increases productivity by expediting the process.
- Clean coating process: The clean coating procedure removes loose particles, providing maximum protection for the expensive SEM column. This results in more consistent and reliable outcomes.
- 3D coating: 3D coating improves the coating quality by removing the larger particles towards the pump rather then towards the suspended samples by gravity. LUXOR’s A2 technology eliminates the need for a rotary or planetary table, making it easier to coat three-dimensional, complex and porous samples.
Fully Automated
The coating process is fully automated. Once the samples have been loaded, simply select the appropriate coating thickness and press the Start button. This user-friendly approach significantly reduces the likelihood of human error, and new operators and lab professionals can learn to use the device after only a few minutes of basic instruction.
This information has been sourced, reviewed and adapted from materials provided by LUXOR.
For more information on this source, please visit LUXOR.