  Reports published in the last 25 years on the synthesis of carbon-based
materials significantly superior to diamond in hardness and elastic properties
have been critically examined, and three groups of recently appearing myths
have been analyzed. The first group concerns the possibility of producing
materials with bulk moduli much higher than that of diamond. The second group
regards to "experimentally measured" hardness significantly higher than that of
diamond. Myths of the third group state that quantum confinement effects
supposedly provide "theoretical" foundations for a several-fold (!) increase in
the hardness of covalent materials. The fundamental impossibility of
synthesizing materials with elastic moduli noticeably exceeding the diamond
value under normal conditions has been demonstrated. The problems of hardness
measuring have been discussed; it was shown that the formation of obstacles for
motion of dislocations can allow increasing the measured hardness of superhard
materials by 20-40%. It was demonstrated that other hypothetical ways for
hardness increase, e.g. owing to quantum confinement have no any real physical
grounds. The superior mechanical properties of diamond are due to reliably
established physical laws. Accordingly, any statements on the possibility of
obtaining materials with elastic characteristics and/or hardness several times
higher than the corresponding values for diamond cannot be considered as
scientifically reliable.
