  We have observed new combination modes in the range from 1650 - 2300 cm-1 in
single-(SLG), bi-, few-layer and incommensurate bilayer graphene (IBLG) on
silicon dioxide substrates. The M band at ~1750 cm-1 is suppressed for both SLG
and IBLG. A peak at ~1860 cm-1 (iTALO-) is observed due to a combination of the
iTA and LO phonons. The intensity of this peak decreases with increasing number
of layers and this peak is absent in bulk graphite. Two previously unidentified
modes at ~1880 cm-1 (iTALO+) and ~2220 cm-1 (iTOTA) in SLG are tentatively
assigned as combination modes around the K point of the graphene Brillouin
zone. The peak frequencies of the iTALO+ (iTOTA) modes are observed to increase
(decrease) linearly with increasing graphene layers.
