  Capacitively coupled radio-frequency (CCRF) CF_4 plasmas have been found to
exhibit a self-organized striated structure at operating conditions, where the
plasma is strongly electronegative and the ion-ion plasma in the bulk region
(largely composed of CF_3^+ and F^- ions) resonates with the excitation
frequency. In this work we explore the effects of the gas pressure, the RF
voltage, and the electrode gap on this striated structure by Phase Resolved
Optical Emission Spectroscopy and Particle-In-Cell/Monte Carlo Collisions
simulations. The measured electronic excitation patterns at different external
parameters show a good general agreement with the spatio-temporal plots of the
ionization rate obtained from the simulations. For a fixed driving frequency
the minima of the CF_3^+ and F^- ion densities (between the density peaks in
the bulk) are comparable and independent of other external parameters. However,
the ion density maxima generally increase as a function of the pressure or RF
voltage, leading to the enhanced spatial modulation of plasma parameters. The
striation gap (defined as the distance between two ion density peaks) is
approximately inversely proportional to the pressure, while it exhibits a weak
dependence on the RF voltage and the electrode gap. A transition between the
striated and non-striated modes can be observed by changing either the pressure
or the RF voltage; for 13.56 MHz and 18 MHz driving frequencies we present a
phase diagram as a function of the pressure and voltage amplitude parameters.
