According to an example, a spark stand assembly for an OES instrument is provided, the spark stand assembly including: a spark stand body that at least partially defines a plasma chamber; an exciter at least partially disposed inside the plasma chamber; and an optical transmission path from the plasma chamber for providing a view to a plasma generated in the plasma chamber, wherein the plasma chamber is provided with an opening for exposing a part of a sample positioned on the opening for excitation from the exciter so as to generate plasma on a surface of the sample upon activation of the exciter, and wherein a coating layer that includes a tribological coating is arranged to cover at least a portion of surfaces of the plasma chamber.