Why is tungsten used for the probe tip in a scanning tunneling microscope?

In a scanning tunneling microscope (STM), the probe tip is typically fashioned from a sharp tungsten needle. Tungsten is chosen for this application primarily due to its unique physical properties, which allow it to function effectively as an electron emitter and maintain structural integrity at the atomic scale.12

Key reasons for using tungsten include:

• High Conductivity: Tungsten possesses high electrical conductivity, which is essential for facilitating the flow of tunneling current between the probe tip and the sample surface.13
• Mechanical Strength and Durability: While brittle at room temperature, tungsten is an exceptionally strong refractory metal with the highest melting point of all metals (3,410 °C). This durability allows the tip to be sharpened to an extremely fine point—often just a few atoms wide—which is necessary to achieve the high resolution required to image individual atoms.142
• Stability: Its resistance to wear and its ability to maintain its form under various conditions make it a reliable material for the precise, nanometer-scale positioning required during the scanning process.124