International audienceStructural and electronic properties of epitaxial graphene on 3C-SiC(111) pseudosubstrate epilayers on silicon was investigated in detail by scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), scanning transmission electron microscopy (STEM), and synchrotron angle-resolved photoemission spectroscopy (ARPES). The graphitization process has been observed by distinct features in the atomically resolved STM images and abrupt interface with the number of stacked-graphene layer has been revealed in STEM image. Two different types of carbon atom networks, honeycomb and one sublattice, were atomically resolved by STM. Electronic properties and band structures of the epitaxial graphene are examined with angle-resolved photoemission spectroscopy, showing linear band dispersion K point of the Brillouin zone, with Dirac point about 500 meV below the Fermi level (E-F). These findings are of relevance for various potential applications based on graphene-SiC/Si(111) structures

Articles you may be interested inSize, shape, composition, and electronic properties of InAs/GaAs quantum dots by scanning tunneling microscopy and spectroscopy

A pulsed metal-organic chemical vapor deposition technique is developed for the growth of high-quality AlN/GaN superlattices ͑SLs͒ with intersubband ͑ISB͒ transitions at optical communications wavelengths. Tunability of the AlN and GaN layers is demonstrated. Indium is shown to improve SL surface and structural quality. Capping thickness is shown to be crucial for ISB transition characteristics. Effects of barrier-and well-doping on the ISB absorption are reported.

The optical properties of single InAsP/InP quantum dots are investigated by spectrally-resolved and time-resolved photoluminescence measurements as a function of excitation power. In the shortwavelength region (below 1.45 µm), the spectra display sharp distinct peaks resulting from the discrete electron-hole states in the dots, while in the long-wavelength range (above 1.45 µm), these sharp peaks lie on a broad spectral background. In both regions, cascade emission observed by time-resolved photoluminescence confirms that the quantum dots possess discrete exciton and multiexciton states. Single photon emission is reported for the dots emitting at 1.3 µm through antibunching measurements. INTRODUCTIONThe three-dimensional confinement of electrons and holes in semiconductor quantum dots gives rise to discrete electron-hole states and sharp absorption and emission lines, analogous to those in atomic systems [1]. These features have been exploited to produce quantum states of light, such as single photons [2, 3], indistinguishable photons [4, 5, 40] and entangled photon pairs [7][8][9] that may be used in quantum communication protocols, such as quantum key distribution or quantum relays based on quantum teleportation [10][11][12][13]. At the same time, quantum dots have been used as gain media in photonic crystal nanolasers [14]. However, for highly-excited quantum dots placed inside photonic crystal nanocavities, it was found that the simple "artificial atom" model of the quantum dot, which successfully described the emission of one or two photons by the quantum dot in free space, could not adequately explain the emission of light by the dot into an apparently non-resonant nanocavity [15]. This cavity feeding required explicit consideration of multiply-excited states emitting into a broad quasicontinuum [16].To date most such photon sources and nanolasers have been fabricated with quantum dots embedded in a GaAs matrix and thus emitting around 920 nm, while prospective applications require sources operating in the telecommunications wavelength range, particularly in the Oand C-bands, around 1.3 µm and 1.5 µm respectively. InAs/InP quantum dots can emit in these wavelength bands and are well suited as active media in semiconductor optical amplifiers or ridge laser systems useful for telecommunications applications [17]. However, attempts to grow such dots by Molecular Beam Epitaxy (MBE) did not give the desired results, as growth on (001)-InP substrate generally leads to the formation of quantum dashes or quantum wires [18, 19], while growth on a (311)-InP oriented substrate [20] is not compatible with the standard processes used in the fabrication of photonic devices such as microcavities. Use of Metal-Organic Chemical Vapor Deposition (MOCVD), on the other hand, has made it possible to grow small InAsP/InP islands on a (100)-InP oriented substrate, as it allows for the spontaneous formation of a twodimensional wetting layer on which small islands can grow [21][22][23], while their spectral distribution [24] o...

Real-world sensory-processing applications require compact, low-latency, and low-power computing systems. Enabled by their in-memory event-driven computing abilities, hybrid memristive-Complementary Metal-Oxide Semiconductor neuromorphic architectures provide an ideal hardware substrate for such tasks. To demonstrate the full potential of such systems, we propose and experimentally demonstrate an end-to-end sensory processing solution for a real-world object localization application. Drawing inspiration from the barn owl’s neuroanatomy, we developed a bio-inspired, event-driven object localization system that couples state-of-the-art piezoelectric micromachined ultrasound transducer sensors to a neuromorphic resistive memories-based computational map. We present measurement results from the fabricated system comprising resistive memories-based coincidence detectors, delay line circuits, and a full-custom ultrasound sensor. We use these experimental results to calibrate our system-level simulations. These simulations are then used to estimate the angular resolution and energy efficiency of the object localization model. The results reveal the potential of our approach, evaluated in orders of magnitude greater energy efficiency than a microcontroller performing the same task.