Raman modes in porous GaP under hydrostatic pressure

Bulk and free-standing porous membranes of GaP have been characterised by R aman spectroscopy under hydrostatic pressure, with emphasis to the Frohlich surface vibration mode. Under compression, an increase in the frequency ga p between the Frohlich mode and the LO phonon has been observed, which is a ttributed to pressure-induced changes in the anharmonicity of the surface-r elated modes and, possibly, to the relative increase of the dielectric cons tant of the surrounding effective medium, through better wetting under comp ression.