We report a catalyst-free epitaxial growth of silicon nanowires on polyhedral facets of mother Si nanoparticles by thermal evaporation process. Single silicon nanowires and octopuslike silicon nanowires (OSNWs) were synthesized under different temperatures. The OSNWs have several directions including ⟨112⟩, ⟨110⟩, and the unusual directions of ⟨100⟩ and ⟨111⟩. A catalyst-free temperature-dependent epitaxial growth model was suggested. Using the Wulff theory and first principle calculations, these growth directions can be explained by the preferential selection of temperature-dependent surface energies. It thus revealed an important but simple growth model in which the growth directions could be delicately controlled through only determining temperature and substrate orientation.

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In this paper, a metasurface antenna with ultrabroadband radar cross section (RCS) reduction was systematically presented and evaluated based on the spoof surface plasmon polariton (SSPP) and transmission. A circular metasurface consisted of twelve gradually increasing two-sided metallic grooves and an ultra-thin dielectric substrate. The evolutions of the dispersion characteristic and near electric-field distributions were adequately demonstrated based on SSPP in simulation. Furthermore, the SSPP metasurface had been loaded on a common waveguide slot antenna. The simulation and laboratory measurements were performed to characterize RCS reduction, radiation patterns and scattering performance. A prototype of metasurface antenna has been fabricated and measured to demonstrate the characteristics. Experimental data were carried out to verify the simulation results and the measured results showed that the metasurface antenna exhibited ultra-wideband RCS reduction from 1 GHz to 10 GHz.

We study the electronic structures of TiO2/Ti4O7 and Ta2O5/TaO2 interfaces using the screened exchange (sX-LDA) functional. Both of these bilayer structures are useful infrastructures for high performance RRAMs. We find that the system Fermi energies of both interfaces are just above the conduction band edge of the corresponding stoichiometric oxides. According to the charge transition levels of the oxygen vacancies, the oxygen vacancies are stabilized at the -2 charged state in both Ta2O5 and TiO2. We propose to introduce interfacial dopants to shift the system Fermi energies downward so that the +2 charged oxygen vacancy can be stable, which is important for the controlled resistive switching under the electrical field. Several dipole models are presented to account for the ability of Fermi level shift due to the interfacial dopants. IntroductionMetal oxides have been widely used in the emerging nonvolatile memory technologies like the resistive random access memory (RRAM) [1,2] and the memristor [3][4][5]. Both of these devices are characterized by the reversible resistance switching (RS) which is commonly due to the growth and rupture of the conducting filaments (CFs) consisting of charged oxygen vacancies (Ov) [6][7][8]. Numerous reports have been published on metal oxides operating through this RS mechanism like TiO2 [9,10], Ta2O5 [11], SrTiO3 [12], NiO [13,14], and so on. Among various oxide candidates, TiO2 demonstrates both unipolar [9,10] and bipolar [15,16] RS. Transmission electron microscopy of the unipolar RS TiO2 has suggested that the CFs in unipolar switching are composed of Magneli phase Ti4O7 [10]. Recently, real time identification of the evolution of Ti4O7 CFs in TiO2 has been reported [17]. However, the problem of TiO2 is the co-existence of more than one stable substoichiometric Magneli phases which is unfavorable for long device endurance [18]. On the other hand, Ta2O5 keeps the longest endurance record among these oxides [11] and it operates in a bipolar manner. The long endurance of Ta2O5 based devices is partly attributed to only one stable substoichiometric phase, Ta, under 1000°C [18] despite of large amount of metastable substoichiometric phases such as TaO2. The in situ observation of CFs in Ta2O5 has recently been reported [19].One of the biggest challenges of these oxide based devices is the requirement for the electroforming process [20,21]. This could induce physical damages to the device due to oxygen gas release [22]. Besides, wide variance of device properties depends on the details of the electroforming which are yet to be understood. Therefore, it is essential to achieve electroforming free RS so as to eliminate the device variance for applicable computer circuits [20,21].

The numerical study of plasmon resonances as optical means for light delivery in thermally assisted magnetic recording is reported. The analysis of two distinct designs is performed. In these designs, the plasmon resonances in metallic nanoparticles and perforated metallic nanofilms are used, respectively. The specific plasmon modes that create the strongest and well-localized (on nanoscale) optical fields have been identified. The issues of coupling of incident laser radiation to these plasmon modes as well as the sharpness of plasmon resonances are discussed.