Metalloid silicon, germanium, arsenic, antimony, and tellurium are commonly recognised as metalloids. Depending on the author, one or more from selenium, polonium, or astatine are sometimes added to the list. Boron sometimes is excluded, by itself, or with silicon. Sometimes tellurium is not regarded as a metalloid. The inclusion of antimony, polonium, and astatine as metalloids has been questioned. Other elements are occasionally classified as metalloids. These elements include hydrogen, beryllium, nitrogen, phosphorus, sulfur, zinc, gallium, tin, iodine, lead, bismuth, and radon. The term metalloid has also been used for elements that exhibit metallic lustre and electrical conductivity, and that are
Porous silicon Porous silicon Porous silicon (abbreviated as "PS" or "pSi") is a form of the chemical element silicon that has introduced nanopores in its microstructure, rendering a large surface to volume ratio in the order of 500 m/cm. Porous silicon was discovered by accident in 1956 by Arthur Uhlir Jr. and Ingeborg Uhlir at the Bell Labs in the U.S. At the time, the Ulhirs were in the process of developing a technique for polishing and shaping the surfaces of silicon and germanium. However, it was found that under several conditions a crude product in the form of thick black, red