Small-angle neutron scattering by surface imperfections in amorphous alloys

Small-angle neutron scattering experiments have been performed on amorphous ${\mathrm{Pd}}_{80}$ ${\mathrm{Si}}_{20}$ alloys. It is shown that the small-angle signal varies over more than one decade with surface treatment. For each of the three samples studied (as quenched, mechanically polished, and chemically etched), the method of contrast variation has been applied by immersing the samples in a ${\mathrm{CD}}_3$ ${\mathrm{O}\mathrm{D}/\mathrm{C}\mathrm{H}}_3$OH solution. In each case, the intensity of the small-angle scattering goes through a minimum as a function of D/H ratio. This clearly indicates that surface state (rugosity, oxide layer, chemical composition, or structure) is the most important factor determining the appearance of a small-angle scattering signal in amorphous alloys.