An arrangement of self-assembled GaN nanowires (NWs) grown by plasma-assisted molecular beam epitaxy on a Si(111) substrate is studied as a function of the temperature at which the substrate is nitridized before GaN growth. We show that the NWs grow with the c-axis perpendicular to the substrate surface independently of nitridation temperature with only a slight improvement in tilt coherency for high nitridation temperatures. A much larger influence of the substrate nitridation process on the in-plane arrangement of NWs is found. For high (850 °C) and medium (450 °C) nitridation temperatures angular twist distributions are relatively narrow and NWs are epitaxially aligned to the substrate in the same way as commonly observed in GaN on Si(111) planar layers with an AlN buffer. However, if the substrate is nitridized at low temperature (~150 °C) the epitaxial relationship with the substrate is lost and an almost random in-plane orientation of GaN NWs is observed. These results are correlated with a microstructure of silicon nitride film created on the substrate as the result of the nitridation procedure.

We present angle resolved photoemission spectroscopy measurements of the surface states on in-situ grown (111) oriented films of Pb1−xSnxSe, a three dimensional topological crystalline insulator. We observe surface states with Dirac-like dispersion atΓ andM in the surface Brillouin zone, supporting recent theoretical predictions for this family of materials. We study the parallel dispersion isotropy and Dirac-point binding energy of the surface states, and perform tight-binding calculations to support our findings. The relative simplicity of the growth technique is encouraging, and suggests a clear path for future investigations into the role of strain, vicinality and alternative surface orientations in (Pb,Sn)Se compounds.

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The growth mode and structural and optical properties of novel type of inclined GaN nanowires (NWs) grown by plasma-assisted MBE on Si(001) substrate were investigated. We show that due to a specific nucleation mechanism the NWs grow epitaxially on the Si substrate without any Si(x)N(y) interlayer, first in the form of zinc-blende islands and then as double wurtzite GaN nanorods with Ga-polarity. X-ray measurements show that orientation of these nanowires is epitaxially linked to the symmetry of the substrate so that [0001] axis of w-GaN nanowire is directed along the [111]Si axis. This is different from commonly observed behavior of self-induced GaN NWs that are N-polar and grow perpendicularly to the surface of nitridized silicon substrate independently on its orientation. The inclined NWs exhibit bright luminescence of bulk donor-bound excitons (D(0)X) at 3.472 eV and exciton-related peak at 3.46 eV having a long lifetime (0.7 ns at 4 K) and observable up to 50 K.

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One-dimensional (1D) ZnO nanostructures have been widely studied because of their electronic and optoelectronic applications. This report discusses the morphology, optical, electrical and sensory properties of polycrystalline ZnO nanofibers (NFs). We observed that the electrospun ceramic NFs interband emission increases with the nanocrystal size, consistent with decreasing of the surface-to-volume ratio. The observation is novel for the electrospun ceramic NFs. The chemical composition and structural characterization reveal that the NFs consist of ZnO wurzite nanocrystals, whose mean diameters increase from 7 to 22 nm with calcination temperature. Emission properties are studied by cathodo-and photoluminescence. The NFs are applied to construct light, gas and liquid sensors. We find an increase of the NFs conductivity by three orders of magnitude under UV illumination as a result of desorption of molecular oxygen from the nanocrystal surface. We study the influence of oxygen on NF conductivity by purging the NFs with air or nitrogen. We show that the flow of nitrogen removes the oxygen resulting in an important increase of the conductivity. Also, we study the dynamics of this process with and without UV illumination. We show sensitivity of the NFs to liquid environment by studying the conductivity of NFs immersed in water and ethanol and find an increased conductivity with respect to a dry air environment. These light-and environmental-sensitive ZnO NFs have useful optical and electronic properties for building high-performance sensors.

MnBi2Te4/(Bi2Te3)n materials system has recently generated strong interest as a natural platform for realization of the quantum anomalous Hall (QAH) state. The system is magnetically much better ordered than substitutionally doped materials, however, the detrimental effects of certain disorders are becoming increasingly acknowledged. Here, from compiling structural, compositional, and magnetic metrics of disorder in ferromagnetic MnBi2Te4/(Bi2Te3)n it is found that migration of Mn between MnBi2Te4 septuple layers (SLs) and otherwise non-magnetic Bi2Te3 quintuple layers (QLs) has systemic consequences - it induces ferromagnetic coupling of Mn-depleted SLs with Mn-doped QLs, seen in ferromagnetic resonance as an acoustic and optical resonance mode of the two coupled spin subsystems. Even for a large SL separation (n ≳ 4 QLs) the structure cannot be considered as a stack of uncoupled two-dimensional layers. Angle-resolved photoemission spectroscopy and density functional theory studies show that Mn disorder within an SL causes delocalization of electron wave functions and a change of the surface band structure as compared to the ideal MnBi2Te4/(Bi2Te3)n. These findings highlight the critical importance of inter- and intra-SL disorder towards achieving new QAH platforms as well as exploring novel axion physics in intrinsic topological magnets.