Diamond has the highest bond energy per unit volume of all known materials, and hence it is assumed to possess the highest hardness. Diamond's hardness comes from its small atoms that each of them forms four covalent bonds. To make a structure harder than diamond, its atoms must be smaller than carbon, and/or these atoms form at least four covalent bonds. The first consideration would rule out all elements with period number higher than 2. The second criterion would eliminate all elements lighter than carbon. Hence, only C, N, O, F, and Ne are possible candidates of superdiamond. However, in order to beat diamond in hardness, these elements must form mono-atomic structures with coordination number higher than 4. Moreover, no lone pair electrons are allowed, so all of their valence electrons must be used to form single covalent bonds. The number of valence electrons in simple cubic carbon is less than the coordination number of 6. As a result, the bonds may turn metallic, so it is unlikely harder than diamond. Potential superdiamond structures include diamond-like nitrogen, simple cubic oxygen or fluorine, and body-centered cubic (BCC) neon. If these elements can form single covalent bonds that involve all their valence electrons, they could become superdiamond. Otherwise, diamond's hardness for materials may be as insurmountable as speed of light for moving objects. The above hypothetical structures of superdiamond may be synthesized by aiming collimated beams. of single ions from specific directions at a common center. Such a technique was developed by Nobel Laureate YT. Lee decades ago. The possible instantaneous formation of the predicted hypothetical structures, even though they are metastable, may be studied in situ at real times by laser strobe light flashed at femtoseconds (10(-15) S). Such femtochemistry has already been invented by Dr. Ahmed Zewail, the latest Nobel Laureate of chemistry.