Most of the solids are semiconductors.  When it is bumbarded with weak electron beam, a charge will be created. This leads to get blurred picture.  If we coat with good conductors like Pt, Au etc. they will avoid charging effect.  But how it is not clear.

From Wiki:

http://en.wikipedia.org/wiki/Scanning_electron_microscope

"For conventional imaging in the SEM, specimens must be electrically conductive, at least at the surface, and electrically grounded to prevent the accumulation of electrostatic charge at the surface. Metal objects require little special preparation for SEM except for cleaning and mounting on a specimen stub. Nonconductive specimens tend to charge when scanned by the electron beam, and especially in secondary electron imaging mode, this causes scanning faults and other image artifacts. They are therefore usually coated with an ultrathin coating of electrically conducting material, deposited on the sample either by low-vacuum sputter coating or by high-vacuum evaporation. Conductive materials in current use for specimen coating include gold, gold/palladium alloy, platinum, osmium, iridium, tungsten, chromium, and graphite. Additionally, coating may increase signal/noise ratio for samples of low atomic number (Z). The improvement arises because secondary electron emission for high-Z materials is enhanced."

In SEM we bombard specimen with electrons, negatively charged particles. Some of them get reflected (backscattered), some of them create secondary electrons, but some of them got embedded in specimen and so supply it with negative charge. When this charge became big enough it will affect electrons of incoming beam (remember – similarly charged objects are repelling each other). So, electrons of a beam will change their trajectories and image will become blurred or disappear at all.

Some materials (metals) are conductive. It means they allow electrons to move inside them without real problems. If metal specimen is grounded, additional electrons will just go away and no charge will be accumulated. Unfortunately most non-metal specimens are dielectrics, which means electrons mostly stay embedded in places where they hit a specimen. So, charge will be accumulated. If we coat specimen with thin layer of metal it will provide a path for these electrons to ground and charging will be prevended.

@M. Akram

You sited Wikipedia without acknowledgment a source. It’s a plagiarism.

Your citation has nothing to do with a question.

What it was for?

Please go through the link below for more details and better understanding.

https://www.microtonano.com/TIN-Target-material-selection-for-coating-SEM-samples-using-an-SEM-sputter-coater.php

Thank you.

Dear colleagues, where we can purchase Aurum foil for SEM polymeric samples preparation ?

I would not recommend to use pure gold target. Au-Pd is better at higher magnifications; pure Pt is better too, even if slightly more expensive. In US I usually ordered from these suppliers (do not know about their policies on shipping outside of America):

https://www.emsdiasum.com/microscopy/products/vacuum/targets.aspx

https://www.tedpella.com/cressington_html/Cressington-Targets.htm.aspx

As I understand next company has worldwide distribution, but I've never ordered from them, so no personal experience:

https://www.quorumtech.com/__assets__/ProductMultiCats/00012/Targets.pdf

Dear Vladimir!

Thanks for your answer. But why not pure Au target? Can you share the reasons behind?

Metal coatings (film on a specimen surface) at high magnification look like tiny islands, i.e. coating became visible. Au becomes visible at lower magnifications than Au-Pd or Pt. For work at low and medium magnifications it does not matter, only for high ones.