  We are motivated by the recent measurements of dust opacity indices beta
around young stellar objects (YSOs), which suggest that efficient grain growth
may have occurred earlier than the Class I stage. The present work makes use of
abundant archival interferometric observations at submillimeter,millimeter, and
centimeter wavelength bands to examine grain growth signatures in the dense
inner regions (<1000 AU) of nine Class 0 YSOs. A systematic data analysis is
performed to derive dust temperatures, optical depths, and dust opacity indices
based on single-component modified black body fittings to the spectral energy
distributions (SEDs). The fitted dust opacity indices (beta) are in a wide
range of 0.3 to 2.0 when single-component SED fitting is adopted. Four out of
the nine observed sources show beta lower than 1.7, the typical value of the
interstellar dust. Low dust opacity index (or spectral index) values may be
explained by the effect of dust grain growth, which makes beta<1.7.
Alternatively, the very small observed values of beta may be interpreted by the
presence of deeply embedded hot inner disks, which only significantly
contribute to the observed fluxes at long wavelength bands. This possibility
can be tested by the higher angular resolution imaging observations of ALMA, or
more detailed sampling of SEDs in the millimeter and centimeter bands. The beta
values of the remaining five sources are close to or consistent with 1.7,
indicating that grain growth would start to significantly reduce the values of
beta no earlier than the late-Class 0 stage for these YSOs.
