Fabrication of diamond-coated germanium ATR prisms for IR-spectroscopy

Monocrystalline germanium is considered a highly useful material for infrared optical applications due to its relatively low price, low toxicity and high optical transparency in the infrared spectral range (5500–870cm−1). However, it is limited by its low chemical, mechanical, and thermal stability. The thin film diamond coating can provide a mechanical protection of a Ge surface against scratching, chemical protection against solutions, and make a well-defined hydrophilic/hydrophobic surface. Here, we compare low temperature (250–400°C) diamond growth on Ge substrates and attenuated total reflection prisms, using a chemical vapor deposition in linear antenna microwave plasma and focused microwave plasma reactors. We show that by employing a thin amorphous silicon interlayer (20–30nm), a homogeneous diamond coating with no degradation of the Ge surface is achieved. The infrared spectroscopy of proteins adsorbed on the diamond coated Ge prism demonstrates usability and advantages in comparison with bare Si or Ge prisms and even with the diamond-coated Si prism.