Zero-dimensional lead-free organic–inorganic hybrid metal halides have drawn attention as a result of their local metal ion confinement structure and photoelectric properties. Herein, a lead-free compound of (Gua)3Cu2I5 (Gua = guanidine) with a different metal ion confinement has been discovered, which possesses a unique [Cu2I5]3– face-sharing tetrahedral dimer structure. First-principles calculation demonstrates the inherent nature of a direct band gap for (Gua)3Cu2I5, and its band gap of ∼2.98 eV was determined by experiments. Worthy of note is that (Gua)3Cu2I5 exhibits a highly efficient cool-white emission peaking at 481 nm, a full-width at half-maximum of 125 nm, a large Stokes shift, and a photoluminescence quantum efficiency of 96%, originating from self-trapped exciton emission. More importantly, (Gua)3Cu2I5 single crystals have a reversible thermoinduced luminescence characteristic due to a structural transition scaled by the electron–phonon coupling coefficients, which can be converted back and forth between cool-white and yellow color emission by heating or cooling treatment within a short time. In brief, as-synthesized (Gua)3Cu2I5 shows great potential for application both in single-component white solid-state lighting and sensitive temperature scaling.
Single crystalline h-MoO 3 nano-and microrods were successfully synthesized using modified liquid-phase processes with concentrated HNO 3 and H 2 SO 4 . Their X-ray powder diffraction (XRD) data were unambiguously indexed based on a hexagonal structure with the lattice constants a ≈ 10.57 and c ≈ 3.72 A ˚instead of a = 10.53 and c = 14.98 A ˚(JCPDS 21-0569) usually adopted. Rietveld refinements of the XRD data were pioneeringly performed based on the (Na 3 2H 2 O)Mo 5.33 -[H 4.5 ] 0.67 O 18 structure with the space group of P6 3 /m regardless of H þ and Na þ . Nanorods synthesized under different conditions show different sizes and aspect ratios. Annealing at 300 °C for 3 h significantly improves the crystallinity and phase purity of as-synthesized h-MoO 3 rods, which is evidenced by sharpening of peaks in micro-Raman spectra with no shift. An irreversible transition from h-MoO 3 to R-MoO 3 occurring between 413 and 436 °C can be triggered by irradiation of either electrons or laser with high energies or powers as well. The turning points on both differential thermal analysis (DTA) and thermogravimetry (TG) curves show presence of water molecules interacted differently with the lattice which escape at different temperatures. h-MoO 3 rods reduce the temperatures of soot oxidation to 482-490 °C, much higher than its structural transition temperatures. This makes it simply suitable for catalyzing reactions taking place at temperatures lower than the transition temperatures, say, as the catalyst of the selective oxidation of methanol.
Beyond the demonstration of single-molecule (or singleatom) and organic-thin-film transistors, [1±4] a reliable electrode contact remains one of the most critical challenges in the development of molecular and organic electronics. Except for the tip of a scanning tunneling microscope, [5±7] more practical connections often involve a metal/ insulator(semiconductor)/metal thin-film structure, either through a gate thin-film dielectric assembly below the source±drain, [1±4] or a insulating thin-film separator which runs parallel to the molecular path. [8,9] To achieve practical applications, not only does one need ohmic contacts so that any nonlinearity can be correctly attributed, but also a much more insulating medium to minimize the influence from the surroundings.[10] However, one often encounters unexpected current±voltage characteristics which do not arise from the given atoms or molecules. For example, negative differential resistance (NDR) [11±15] and the memory effect (hysteresis) [16±21] were found not only in singlemolecule devices, but also in organic thin-film transistors, organic light-emitting devices, and metal/inorganic insulator/ metal systems.[22±26] Despite many years of effort, the precise origin of the phenomena remains unknown, which has become a major obstacle in the research and development of new electronic devices. In this report, we try to reveal the origin of such phenomena, based on new experiment results from various metals and both organic and polymeric thin films. The answer is surprisingly found to be two-dimensional (2D) single-electron tunneling due to nanometer-sized metal islands, which were manifested unexpectedly through a wellknown process where some nuclei were blocked from further growth by the sealing of electrode outside crevices. The results not only provide a satisfactory explanation of the anomalous phenomena, but also open a new door to the construction and fabrication of molecular electronic and memory devices.The widespread nature of the phenomena is shown by its easy duplication, using any metal electrode and any organic or inorganic thin-film insulator, or even semiconductors, since the anomalous current is usually several orders of magnitude higher than that of the nominal conductance. The typical current±voltage (I±V) curve showing NDR and a memory effect has two distinctive features. One is a local current maximum (when V = V max ), followed by a region of NDR. The other feature is the dual states for V < V max , where the ªonº state is obtained by reaching the V max first, and the ªoffº state is recovered by visiting a voltage beyond NDR before rapidly setting back to zero.[21] In addition, there are intermediate states available, [21,22] and the phenomena could be removed by exposure to oxygen gas. [13] Many models have been proposed, but so far none offers a satisfactory explanation. The arbitrary choice of metals and insulators of various energies immediately rejects any speculation related to, for example, a particular type of insulating or semiconduc...
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