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We present two-dimensional arrays of silver nanoparticles embedded in amorphous silicon, fabricated by a sequential Si∕Ag∕Si electron-beam evaporation process. The particle arrays exhibit surface plasmon resonance spectra in the near-infrared (0.9eV), with tails extending below 0.5eV. The data are compared with calculations that take into account measured particle size, shape anisotropy, and separation. It is concluded that the large redshift is mainly due to the high refractive index of the matrix, with shape anisotropy and interparticle coupling contributing several tenths of an electron volt. This work enables plasmon-related applications at the telecommunication wavelength of 1.5μm(0.8eV).

The authors have realized NbN ͑100͒ nanofilms on a 3C-SiC ͑100͒/Si͑100͒ substrate by dc reactive magnetron sputtering at 800°C. High-resolution transmission electron microscopy ͑HRTEM͒ is used to characterize the films, showing a monocrystalline structure and confirming epitaxial growth on the 3C-SiC layer. A film ranging in thickness from 3.4 to 4.1 nm shows a superconducting transition temperature of 11.8 K, which is the highest reported for NbN films of comparable thickness. The NbN nano-films on 3C-SiC offer a promising alternative to improve terahertz detectors. For comparison, NbN nanofilms grown directly on Si substrates are also studied by HRTEM. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2766963͔The ability to grow superconducting NbN films of several nanometer thick is of significant importance to the development of modern photon detector technology. Superconducting hot electron bolometer ͑HEB͒ mixers based on such nanofilms are the only sensitive heterodyne detectors for high-resolution spectroscopy at frequencies between 1.5 and 6 THz.1-4 These detectors will be used on the Herschel space telescope 5 and are required in various future conceptual space missions. 6 Another type of detector, the superconducting single photon detector ͑SSPD͒, 7 is based on similar films and is ultrafast and sensitive for the detection of both visible and infrared photons. SSPDs can perform high speed photon counting which has many applications, for example, optical communications and quantum information.To date, HEB mixers are based on ultrathin NbN films grown primarily on substrates such as Si with its native oxide, 2-4 MgO, 8 and Si with a buffering MgO film. 9 SSPDs are based on NbN films grown on sapphire substrates. For films with an intended thickness of 3.5 nm ͑not directly measured͒, the highest superconducting transition temperatures ͑T c ͒ are reported to be 9.5-11 K.9 Among them, NbN films on MgO, MgO buffer layers and sapphire substrates have higher T c than NbN films on Si substrates. These substrates allow for epitaxial growth of the NbN films, 8-10 resulting in a monocrystalline structure. For HEB mixers, Si is a preferred substrate because of its low loss at terahertz frequencies, well-established processing technology, and inherent reliability. However, the drawback to using Si in this case is the limited intermediate frequency bandwidth, which is set by the thermal time constant.In this letter, we demonstrate superconducting NbN nanofilms on a 3C-SiC buffered Si substrate. The films were characterized by high-resolution transmission electron microscopy ͑HRTEM͒. In addition, the superconducting properties were measured.The 3C-SiC buffer layers were heteroepitaxially grown on Si ͑100͒ substrates by atmospheric pressure chemical vapor deposition at 1280°C using a process described in detail elsewhere.11 To ensure reasonably good crystal quality near the top surface of the 3C-SiC layer given its lattice mismatch with Si, we choose a thickness of 1 m for 3C-SiC layer. As reported previously, 11 t...

Experimental studies of size-related effects in silicon nanocrystals are reported. We present investigations carried out on nanocrystals prepared from single-crystal Si:P wafer by ball milling. The average final grain dimension varied depending on the way of preparation in the range between 70 and 230 nm. The ball milling was followed by sedimentation and selection of the smallest grains. The initial grain size distribution was measured by scanning electron microscopy. Further reduction in size was achieved by oxidation at 1000°C which creates a silicon dioxide layer around a silicon core. The oxidation process was monitored by transmission electron microscopy and the growth speed of SiO 2 was estimated in order to model the grain size of nanocrystals. Crystallinity of silicon grains was confirmed by x-ray diffraction and by transmission electron microscopy using a bright/dark field method and selected area diffraction pattern. In the silicon nanocrystals the electron energy levels are shifted which was observed separately for conduction band, valence band and energy band gap. Electron paramagnetic resonance was applied to investigate variation of the conduction band minimum by monitoring its influence on the hyperfine interaction of phosphorus shallow donor. On the basis of these results an explicit expression for conduction band upshift as a function of average grain size has been derived. Information about the downshift of the valence band was obtained from measurements on a photoluminescence band related to a deep to shallow level transition. A perturbation of a few meV for grain sizes of the order about 100 nm has been observed. Internal consistency of these findings has been examined by investigation of the photoluminescence band due to an electron-hole recombination whose energy is directly related to the band gap of silicon.

High critical current-density ͑10 to 420 kA/ cm 2 ͒ superconductor-insulator-superconductor tunnel junctions with aluminum nitride barriers have been realized using a remote nitrogen plasma from an inductively coupled plasma source operated in a pressure range of 10 −3 -10 −1 mbar. We find a much better reproducibility and control compared to previous work. From the current-voltage characteristics and cross-sectional transmission electron microscopy images it is inferred that, compared to the commonly used AlO x barriers, the polycrystalline AlN barriers are much more uniform in transmissivity, leading to a better quality at high critical current densities.

Solar cell using profiled poly-Si:H by HWCVD as i-layer in the configuration SS/n-µSi:H(PECVD)/i-poly-Si:H(HWCVD)/p-µc-Si:H(PECVD)/ITO showed 3.7% efficiency. A current of 23.6 mA/cm2 was generated in only 1.5 µm thick poly-Si:H i-layer grown at ∼5Å/s. TFTs made with the poly-Si:H films (grown at ≥ 9Å/s) exhibited remarkable stability to long duration of 23 hours of gate bias stress of ∼lMV/cm. A saturation mobility of 1.5 cm2/Vs for the TFT has been achieved. Films made at low hydrogen dilution (Poly2) showed device quality (purely intrinsic nature, ambipolar diffusion length of 568 nm, only (220) oriented growth and low ESR defect density of <1017/cm3with complete absence of signal due to conduction electrons) but with an incubation phase of amorphous initial growth, whereas the films made at high hydrogen dilution (Polyl) had a polycrystalline initial growth, though with higher defect density, incorporated oxygen and randomly oriented grains. Poly2 films are compact and hydrogen bonding is at compact Si-H sites manifested as 2000 cm−1IR vibration and high temperature hydrogen evolution peak. Exchange interaction of spins and spin pairing are observed while increasing defects in such a compact structure. A new approach has been used to integrate these two regimes of growth to make profiled poly-Si:H layers. The new layers show good electronic properties as well as complete elimination of incubation phase.

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