when i was using Scanning Electron Microscope to investigate fracture surface of a metal sample,the results of composition of it appeared so different to what the composition should be, that sample contains 2% carbon comparing to normally 0.1%. i thought there are 3 ways of doing that: 1.hand--i need to use my hand to handle the operation during the process. scurf and sweat may pollute the sample surface. 2.Enviroment--instrument;air with high content of carbon dioxide; residual grease. 3.Chemical reaction--with all possible source. what is the major reason of that happened? any possibility else? it's about my project,thank you!!!