Interfacial scattering of hot electrons in ultrathin Au/Co films

We have used room-temperature, ballistic electron emission microscopy (BEEM ) to measure hat-electron transport through ultrathin Au/Co multilayer stru ctures deposited onto Si. The samples consist of Au/Co/Si or (Au/Co)(n)/Au/ Si diodes, sputter deposited at 175 or 300 K, where n is the number of repe at layers. The thin-film Co attenuation length, lambda(Co), is extracted fr om the BEEM spectra as a function of Co thickness, in single Co layer sampl es. Similarly, the interface attenuation number, or the number of Co/Au int erfaces required for a 1/e attenuation, is determined from the multi-interf ace samples. BEEM barrier heights of Au/Co/Si decrease with increasing Co t hickness (for thicknesses <1 nm), as the film becomes continuous and develo ps a Schottky barrier for Co or CoSi2(<0.7 eV). For these diodes, lambda(Co ), increases from 0.3 to 0.5 nm, each with an estimated uncertainty of 0.1 nm, when the deposition temperature is decreased from 300 to 175K. This res ult is associated with decreased silicide formation at the lower deposition temperature. When Co is isolated from the Si with a 2 nm Au layer, the bar rier height is stable (0.82 eV), and lambda(Co), increases further to 0.8+/ -0.1 nm. The lambda(Co) values are independent of electron energy over the range measurable (1-1.8 eV). The interface attenuation number was 1.8 and 2 5 interfaces for 0.6 and 1.2 nm total Co thickness, respectively (in struct ures with a constant total Au thickness of 8 nm). Thus, significant interfa ce scattering is observed in the thinner sample and negligible scattering w hen the Co thickness was doubled. Further BEEM measurements on similar supe rlattices are being carried out to understand these results. (C) 2000 Ameri can Vacuum Society. [S0734-211X(00)08904-6].