Phase-selective staining of metal salt for scanning electron microscopy imaging of block copolymer film

Three metal salts, i.e., AgNO3, HAuCl4, and KCl, were proposed as novel staining reagents instead of traditional RuO4 and OsO4 labeled with expensive price and extreme toxicity for scanning electron microscopy (SEM) imaging of microphase separated block copolymer film. A simple and costless aqueous solution immersion procedure could ensure selective staining of the metal slat in specific phase of the nanostructured copolymer film, leading to a clear phase contrasted SEM image. The heavy metal salt has better staining effect, demonstrating stable and high signal-to-noise SEM image even at an acceleration voltage as high as 30 kV and magnification up to 250,000 times.