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.
翻译:在二氧化硅基质上,我们观察到了1650-2300厘米-1的单(SLG)新组合模式,双层、几层和不相配双层双层平方块(IBLG)在二氧化硅基子上。SLG和IBLG的M波段为~1750厘米-1被抑制。由于iTA和LO phoonons的结合,观测到了一个峰值为~1860厘米-1(iTALO-)的峰值。这一峰值的强度随着层数的增加而下降,而散状石墨则没有出现这一峰值的强度。在SLG的~1880厘米-1(iTALO+)和~22厘米-1(iTOTA)两种先前不明的波段暂时被分配为图示 Brillouin区K点周围的组合模式。观察到,iTALO+(iTOTA)模式的峰值频率随着石墨层的增加而线性增加(减少)。