We report on the first dark-matter (DM) search results from PandaX-I, a low threshold dualphase xenon experiment operating at the China JinPing Underground Laboratory. In the 37-kg liquid xenon target with 17.4 live-days of exposure, no DM particle candidate event was found. This result sets a stringent limit for low-mass DM particles and disfavors the interpretation of previously-reported positive experimental results. The minimum upper limit, 3.7 × 10 −44 cm 2 , for the spin-independent isoscalar DM-particle-nucleon scattering cross section is obtained at a DMparticle mass of 49 GeV/c 2 at 90% confidence level.PACS numbers: 95.35.+d, 95.55.Vj

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The dislocation multiplication and movement mechanism in GaN single crystals has been studied using nanoindentation and cathodoluminescence. Dislocation loops can multiply and move from plane to plane by cross-slip, thus producing a wide plastic deformation in GaN during indentation. This mechanism is further supported by the remarkable movement of indentation induced dislocations during annealing. Furthermore, the so-called pop-in events, in which the indenter suddenly enters deeper into the material without the application of any additional force, can be better understood by considering the cross-slip mechanism.

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Rubrene is a nonplanar molecule, it is recognized that only amorphous rubrene films can be obtained on such substrates as Au, SiO 2 , and Al 2 O 3 by organic molecular beam deposition or ordinary vacuum evaporation. In this work, rubrene organic single crystals with very smooth surfaces were used as substrates. Well-ordered rubrene thin films were obtained by ordinary vacuum evaporation, and the substate temperature is room temperature. Two-dimensional nucleation-monolayer by monolayer growth and homoepitaxy was demonstrated when the deposition rate was kept at 0.2 nm/min. Furthermore, when the deposition rate was increased to 0.6 nm/min, two-dimensional hexagons were observed in the growth process of rubrene thin films and are similar to the twodimensional islands with regular shapes observed in homoepitaxy growth of inorganic thin films.

Elasto-plastic mechanical deformation behaviors of c-plane (0001) and nonpolar GaN single crystals are studied using nanoindentation, cathodoluminescence, and transmission electron microscopy. Nanoindentation tests show that c-plane GaN is less susceptible to plastic deformation and has higher hardness and Young's modulus than the nonpolar GaN. Cathodoluminescence and transmission electron microscopy characterizations of indent-induced plastic deformation reveal that there are two primary slip systems for the c-plane GaN, while there is only one most favorable slip system for the nonplane GaN. We suggest that the anisotropic elasto-plastic mechanical properties of GaN are relative to its anisotropic plastic deformation behavior.PACS: 62.20.fq; 81.05.Ea; 61.72.Lk.

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