In my 20 plus years of experience, I have found that nearly every specimen contaminates to some degree (some slower, some faster) in an electron microscope regardless of the manufacturer. Most of this contamination comes from the specimen, and it's magnitude is a function of the sample (metallic, semiconductor, organic, etc.), the method of preparation (electrochemical chemical, microtoming, ion milling, etc.), the microscope conditions, the probe and probe current - plus a number of less well controlled factors. Reactive gas plasmas can fortunately be used to mitigate the contamination process and frequently reduce the problem to negligible levels. Basically, one places the specimen/stage in a “tow energy plasma” where the gas acts like a catalyst for a localized surface chemical reaction, The energy of the plasma breaks weak bonds of the hydrocarbon compounds on the surface which then make these species somewhat volatile so that they can further react with the gas in the plasma.