Hollow metal nanoparticles and methods for their manufacture are disclosed. In one embodiment the metal nanoparticles have a continuous and nonporous shell with a hollow core which induces surface smoothening and lattice contraction of the shell. In a particular embodiment, the hollow nanoparticles have an external diameter of less than 20 nm, a wall thickness of between 1 nm and 3 nm or, alternatively, a wall thickness of between 4 and 12 atomic layers. In another embodiment, the hollow nanoparticles are fabricated by a process in which a sacrificial core is coated with an ultrathin shell layer that encapsulates the entire core. Removal of the core produces contraction of the shell about the hollow interior. In a particular embodiment the shell is formed by galvanic displacement of core surface atoms while remaining core removal is accomplished by dissolution in acid solution or in an electrolyte during potential cycling between upper and lower applied potentials.
STATEMENT OF GOVERNMENT RIGHTS
 The present invention was made with government support under contract number DE ACO2-98CH10886 awarded by the U.S. Department of Energy. The United States government has certain rights in the invention.