The motion of nanoscale structures made of pure crystalline silicon with different lattice conditions is simulated in vacuum by applying the molecular dynamics technique with the use of the Tersoff potential. Elastic moduli for various sized specimens are obtained by simulating flexural and longitudinal vibrations as well as simple tension tests. Compared with the bulk silicon, the elastic modulus decreases monotonically by as much as 40% as the thickness of the specimen decreases, and the presence of voids in the specimen further decreases the modulus by a significant amount. Estimation of thermal fluctuations and feasibility study of nanoscale cantilevers as molecular mass sensors demonstrate that the continuum-theory-based analysis can still be used on nanoscale structures provided the dependence of the elastic constants on dimensional scaling is accounted for. (c) 2005 Elsevier B.V. All rights reserved.