Twisted bilayer graphene (tBLG) devices with ion gel gate dielectrics are studied using Raman spectroscopy in the twist angle regime where a resonantly enhanced G band can be observed. We observe prominent splitting and intensity quenching on the G Raman band when the carrier density is tuned away from charge neutrality. This G peak splitting is attributed to asymmetric charge doping in the two graphene layers, which reveals individual phonon selfenergy renormalization of the two weakly-coupled layers of graphene. We estimate the effective interlayer capacitance at low doping density of tBLG using an interlayer screening model. The anomalous intensity quenching of both G peaks is ascribed to the suppression of resonant 2 interband transitions between the two saddle points (van Hove singularities), that are displaced in the momentum space by gate-tuning. In addition, we observe a softening (hardening) of the R Raman band, a superlattice-induced phonon mode in tBLG, in electron (hole) doping. Our results demonstrate that gate modulation can be used to control the optoelectronic and vibrational properties in tBLG devices. TEXT:Recently there has been growing interest in two-dimensional (2D) van der Waals (vdW) materials and structures in which interlayer interaction can significantly affect these systems' properties and functionalities. [1][2][3][4][5][6][7][8][9] Twisted bilayer graphene (tBLG), in which the two graphene layers are stacked with a twist angle () and coupled by vdW force, has been demonstrated to show new physical (electronic, vibrational, and optical) properties through changed interlayer interaction at different twist angles. [10][11][12][13][14][15] Angle-resolved photoemission spectroscopy measurement has shown that tBLG exhibits weak interlayer coupling as revealed by the presence of van Hove singularities (VHSs) in the density of states at the overlap (saddle point) of two single layer graphene (SLG) Dirac cones. 13 Furthermore, low-energy, -dependent VHSs and superlattice Dirac cones have been observed by scanning tunneling microscopy and spectroscopy. [16][17][18] Optical spectroscopy has been exploited to study the optical and vibrational properties associated with the low-energy VHSs of tBLG. [19][20][21][22][23][24][25][26][27] These studies have demonstrated that tBLG is a prototype system to explore the influence of interlayer interaction in 2D layered materials. 3Raman spectroscopy is a sensitive probe of the unique electronic and phonon band structures of tBLG through resonance enhancement and superlattice induced Raman processes.Raman intensities from G and double-resonant (DR) ZO' L (fundamental layer-breathing vibration) bands display large resonance enhancements when the excitation photon energy equals to the inter-VHS energy (E VHS ; the energy difference between the saddle points in the conduction and valence bands). [19][20][21][22]27 The twist angle at which E VHS equals the excitation photon energy is called the critical angle  c . For 532 nm laser excitation, ...

NbSe 3 exhibits remarkable anisotropy in most of its physical properties and has been a model system for studies of quasi-one-dimensional charge-density-wave (CDW) phenomena.Herein, we report the synthesis, characterization, and electrical transport of single-crystalline NbSe 3 nanoribbons by a facile one-step vapour transport process involving the transport of selenium powder onto a niobium foil substrate. Our investigations aid the understanding of the CDW nature of NbSe 3 and the growth process of the material. They also indicate that NbSe 3 nanoribbons have enhanced CDW properties compared to those of the bulk phase due to size confinement effects, thus expanding the search for new mesoscopic phenomena at the nanoscale level. Single nanoribbon measurements on the electrical resistance as a function of temperature show charge-density wave transitions at 59 K and 141 K. We also demonstrate significant enhancement in the depinning effect and sliding regimes mainly attributed to finite size effects.