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Multi-layer graphene with rhombohedral stacking is a promising carbon phase possibly displaying correlated states like magnetism or superconductivity due to the occurrence of a flat surface band at the Fermi level. Recently, flakes of thickness up to 17 layers were tentatively attributed ABC sequences although the Raman fingerprint of rhombohedral multilayer graphene is currently unknown and the 2D resonant Raman spectrum of Bernal graphite not understood. We provide a first principles description of the 2D Raman peak in three and four layers graphene (all stackings) as well as in Bernal, rhombohedral and an alternation of Bernal and rhombohedral graphite. We give practical prescriptions to identify long range sequences of ABC multi-layer graphene. Our work is a prerequisite to experimental non-destructive identification and synthesis of rhombohedral graphite.Bernal graphite [1] with AB stacked graphene is the most stable form of graphite. Recently, however, rhombohedral stacked multi-layers graphene (RMG) with ABC stacking, see Fig. 1 (a), attracted an increasing attention as theoretical calculations suggest the occurrence of a dispersionless electronic band (bandwith smaller than 2 meV) at the Fermi level [2, 3]. This flat band with extremely large effective mass, constitutes a very promising candidate for highly correlated states of matter such as magnetism [4] or room-temperature superconductivity [5].As ABC-stacked graphite is metastable [6], the synthesis of long sequences of ABC graphene layers is a real challenge. For a random sequence of N graphene layers stacked along the c axis, a purely statistical argument states that the probability to obtain N layers with ABC order is 1/2 N −1 . In reality the probability is even lower as all stackings are not equally probable as energetics favour the Bernal one with respect to the others. This explains why three and four layer graphene flakes with ABC-stacking are systematically found [7-9], while it is highly unprobable to obtain long range ABC-stacking order. Recently, it has been suggested that pentalayers graphene with rhombohedral stacking can be grown epitaxially on 3C-SiC(111) [10]. Finally, Henni et al. [11] were able to isolate multilayer graphene flakes with ABC sequences exceeding 17 graphene sheets. However, while for three and four ABC stacked graphene layers an optical signature exists [7, 8], a clear fingerprint of long-range rombohedral order is lacking.Raman spectroscopy, and in particular the 2D double resonant Raman peak, has proven to be a very powerful technique to investigate structural and physical properties of graphene flakes. It can be used to count the number of layers [12], detect charged impurities [13], measure the strain-induced deformation of the electronic structure [14,15], measure the phonon dispersion [16,17] and many other properties (for a review see [18]). However, despite its crucial importance, the theoretical understanding of Figure 1. (a) Crystal structure of Bernal (ABA) and rhombohedral (ABC) stacked multilayer graphen...

Ultrathin semiconductor nanocrystals (NCs) with at least one dimension below their excitonBohr radius receive a rapidly increasing attention due to their unique physicochemical properties such as strong quantum confinement, large surface-to-volume ratio, and giant oscillator strength. These superior properties highly depend on the shape and crystal phase of semiconductor NCs. Slight changes in the shape and phase of NCs can cause significant changes in their properties. Therefore, it is crucial to controllably synthesize semiconductor NCs. Here, we demonstrate not only the synthesis of robust welldefined ultrathin ZnS nanoplatelets (NPLs) with excitonic absorption and emission, but also the precise shape and phase control of ZnS NCs based on a soft template strategy. The key feature of our approach is the tuning of the sulfur precursor amount, resulting in a simultaneous shape/phase transformation between wurtzite (WZ) ZnS NPLs and zinc blende (ZB) ZnS nanorods (NRs) at moderate temperatures (150 °C). UV-vis absorption and photoluminescence (PL) spectra reveal very distinct optical properties betweenWZ-ZnS NPLs and ZB-ZnS NRs. UV-vis absorption spectra of WZ-ZnS NPLs clearly exhibit a sharp excitonic peak that is not observed in ZB-ZnS NRs. Besides, the PL characterization shows that WZ-ZnS NPLs have a narrow excitonic emission peak (292 nm), while the ZB-ZnS NRs exhibit a broad collective emission band consisting of four emission peaks (335, 359, 395, and 468 nm). The appearance of excitonic features in the absorption spectra of ZnS NPLs is explained by interband electronic transitions, which is simulated in the framework of density functional theory (DFT). The presented simple and effective synthetic strategy opens a new path to synthesize further NCs with shape and phase control for advanced applications in electronics and photonics.