Spin- and angle-resolved photoemission studies of the electronic structure of Si(110)“ 16×2 ” surfaces

The electronic structure of Si(110) `$16\times2$' double-domain, single-domain and $1\times1$ surfaces has been investigated using spin- and angle-resolved photoemission at sample temperatures of 77 K and 300 K. Angle-resolved photoemission was conducted using horizontally- and vertically-polarised 60 eV and 80 eV photons. Band-dispersion maps revealed four surface states ($S_1$ to $S_4$) which were assigned to silicon dangling bonds on the basis of measured binding energies and photoemitted intensity changes between horizontal and vertical light polarisations. Three surface states ($S_1$, $S_2$ and $S_4$), observed in the Si(110)`$16\times2$' reconstruction, were assigned to Si atoms present at the edges of the corrugated terrace structure. Only one of the four surface states, $S_3$, was observed in both the Si(110)`$16\times2$' and $1\times1$ band maps and consequently attributed to the pervasive Si zigzag chains that are components of both the Si(110)`$16\times2$' and $1\times1$ surfaces. A state in the bulk-band region was attributed to an in-plane bond. All data were consistent with the adatom-buckling model of the Si(110)`$16\times2$' surface. Spin polarisation data were measured with optimised and fully characterised VLEED polarimeters allowing polarisation measurements with a precision of better than 1\%. Room temperature measurements of $P_y$ and $P_z$ for the Si(110)`$16\times2$' surface gave, as anticipated, zero polarisation but longitudinal polarisation measurements, $P_x$, for $S_3$ at a higher resolution and lower temperature gave a very small average polarisation of $2.8\pm 1.9\%$. An upper limit of $\sim3\%$ may thus be taken for the longitudinal polarisation.