In situ observation of Si(001) surface in He atmosphere at high temperatures near the bulk melting temperature

Surface melting of Si(001) surface has been investigated by x-ray reflectiv ity up to the bulk melting temperature: T-m;b. An in situ system was design ed for measurements of x-ray reflectivity at high temperatures under an atm osphere of He-gas flow. It has been shown that the surface density changes at T = T-m;s* < T-m;b-110 K. This change was observed at T=T-m;s(*) both on cooling and heating (a reversible phenomenon). The density of the near-sur face at T-m;b > T > T-m;s*, which is larger than that of the bulk solid, is 2.5(1) x 10(3) kg/m(3) which is almost the same as that of the bulk liquid , though a macroscopic melting does not occur. This reversible phenomenon i ndicates the surface melting at T = T-m;s*. (C) 2001 American Institute of Physics.