successfully applied to the growth of AGNRs 11-13 and related structures [14][15][16] . Here, we describe the successful bottom-up synthesis of ZGNRs, which are fabricated by the surface-assisted colligation and cyclodehydrogenation of specifically designed precursor monomers including carbon groups that yield atomically precise zigzag edges. Using scanning tunnelling spectroscopy we prove the existence of edge-localized states with large energy splittings. We expect that the availability of ZGNRs will finally allow the characterization of their predicted spin-related properties such as spin confinement 17 and filtering 18,19 , and ultimately add the spin degree of freedom to graphene-based circuitry.To explore the fundamental electronic and magnetic properties related to zigzag edges and to realize specific carbon nanostructures for the controlled manipulation of their spin states,ZGNRs with atomically precise edges are required. For GNRs with armchair edges, it was demonstrated that atomic precision can indeed be achieved by a bottom-up approach based on the surface-assisted polymerization and subsequent cyclodehydrogenation of specifically designed oligophenylene precursor monomers 11 . The on-surface synthesis has been applied by many groups to fabricate a number of different AGNR structures [11][12][13] , N-doped AGNRs 14,15 as well as AGNR heterostructures 15,16 . It is, however, not directly suited forZGNRs since polymerization of monomers via aryl-aryl coupling does not take place along the zigzag but along the armchair direction (Fig. 1a). In addition, dehydrogenative cyclization of phenyl subgroups is not sufficient to form pure zigzag edges, thus calling for a totally new chemical design. Thereby, additional carbon functions must be placed at the edges of the monomers to complete the tiling toolbox needed for the bottom-up fabrication of arbitrary GNR structures.Here, we report a bottom-up fabrication approach to ZGNRs. In our unique protocol, surfaceassisted polymerization and subsequent cyclization of suitably designed molecular precursors carrying the full structural information of the final ZGNR afford atomic precision with respect to ribbon width and edge morphology. The groundbreaking idea depends upon the choice of a unique U-shaped monomer as 1 shown in Fig. 1b. With two halogen functions for thermally induced aryl-aryl-coupling at the R 1 positions, it allows the polymerization toward a snake-like polymer. It is the beauty of this design that additional phenyl groups at the R 2 position fill the holes in the interior of the undulating polymer. The crucial precursor is monomer 1a which carries two additional methyl groups. In such a case, apart from the 3 polymerization and planarization, an oxidative ring closure including the methyl groups is expected which would then establish two new six-membered rings together with the zigzag edge structure. To our delight, this concept could indeed be synthetically realized under reaction monitoring and structure proof by scanning tunneling microscopy (S...

into visible light that are further captured and converted into electrical signals by a following photomultiplier. [7][8][9][10][11] Scintillators have been actively utilized for radiation detection applications in many fields, like nondestructive inspection, medical imaging, and space exploration. Scintillator-based X-ray detectors are advantageous in terms of cost and stability than direct X-ray detectors (a-Se), and the current market of X-ray detectors is dominated by scintillators.The light yield of scintillators, as one of the most important figures of merit, determines the X-ray conversion efficiency and detection contrast. Liu and co-workers reported the good X-ray imaging properties from CsPbBr 3 nanocrystals [8] and Zhang et al. evaluated the light yield for CsPbBr 3 nanocrystals as 21 000 photons per MeV. [11] Such value is still much lower than traditional scintillators like Lu 1.8 Y 0.2 SiO 5 -Ce (LYSO, 33 200 photons per MeV), [12] CsI-Tl (54 000 photons per MeV) [12] and Gd 2 O 2 S-Tb (GOS, 60 000 photons per MeV) [13] etc. The major reason is that the small Stokes shift and the self-absorption effect for lead halide perovskites would severely restrict the light outcoupling efficiency in films and crystals, which require large thickness for complete X-ray attenuations. For scintillators, large Stokes shift and high photoluminescence efficiency are required to obtain high scintillation light yield. The recently emerged self-trapped exciton emissions from low dimensional perovskites exhibit large stokes shift and high PLQY, and may provide efficient X-ray scintillations, but have scarcely been studied. [14][15][16] Another severe issue restricting the applications of lead halide perovskite scintillators is the toxicity of lead element. The ionic nature of halide perovskites and high solubility in water may seriously harm the human health as well as the environment. It is thus of great significance to find lead-free perovskites or halide scintillators.Here we present 1D structured Rb 2 CuBr 3 as one new member of scintillators with exceptionally high light yield. Rb 2 CuBr 3 is obtained by direct reaction between RbBr and CuBr with phase-purity, high quality, and good stability. Its 1D crystal structure and soft crystal lattice facilitate the formation of self-trapped exciton, which emits at 385 nm with a large Stokes shift of 85 nm (0.91 eV) and 98.6% photoluminescence quantum yield. The high emission efficiency, large Stokes shift, strong X-ray attenuation, and good spectrum matching with the photomultiplier tube (PMT) or silicon photomultiplier Scintillators are widely utilized for radiation detections in many fields, such as nondestructive inspection, medical imaging, and space exploration. Lead halide perovskite scintillators have recently received extensive research attention owing to their tunable emission wavelength, low detection limit, and ease of fabrication. However, the low light yields toward X-ray irradiation and the lead toxicity of these perovskites severely restricts their practical ...

X-ray detectors are broadly utilized in medical imaging and product inspection. Halide perovskites recently demonstrate excellent performance for direct X-ray detection. However, ionic migration causes large noise and baseline drift, limiting the detection and imaging performance. Here we largely eliminate the ionic migration in cesium silver bismuth bromide (Cs 2 AgBiBr 6 ) polycrystalline wafers by introducing bismuth oxybromide (BiOBr) as heteroepitaxial passivation layers. Good lattice match between BiOBr and Cs 2 AgBiBr 6 enables complete defect passivation and suppressed ionic migration. The detector hence achieves outstanding balanced performance with a signal drifting one order of magnitude lower than all previous studies, low noise (1/ f noise free), a high sensitivity of 250 µC Gy air −1 cm –2 , and a spatial resolution of 4.9 lp mm −1 . The wafer area could be easily scaled up by the isostatic-pressing method, together with the heteroepitaxial passivation, strengthens the competitiveness of Cs 2 AgBiBr 6 -based X-ray detectors as next-generation X-ray imaging flat panels.