Adherent carbon film deposition by cathodic arc with implantation

A method of improving the adhesion of carbon thin films deposited using a cathodic vacuum arc by the use of implantation at energies up to 20 keV is described. A detailed analysis of carbon films deposited onto silicon in this way is carried out using complementary techniques of transmission electron microscopy and x-ray photoelectron spectroscopy (XPS) is presented. This analysis shows that an amorphous mixing layer consisting of carbon and silicon is formed between the grown pure carbon film and the crystalline silicon substrate. In the mixing layer, it is shown that some chemical bonding occurs between carbon and silicon. Damage to the underlying crystalline silicon substrate is observed and believed to be caused by interstitial implanted carbon atoms which XPS shows are not bonded to the silicon. The effectiveness of this technique is confirmed by scratch testing and by analysis with scanning electron microscopy which shows failure of the silicon substrate occurs before delamination of the carbon film

Synthesis and characterisation of alpha-carboxynitrobenzyl photocaged l-aspartates for applications in time-resolved structural biology

We report a new synthetic route to a series of α-carboxynitrobenzyl photocaged ⌊-aspartates for application in time-resolved structural biology. The resulting compounds were characterised in terms of UV/Vis absorption properties, aqueous solubility and stability, and photocleavage rates (τ = μs to ms) and quantum yields (φ = 0.05 to 0.14)

Spectral focusing of broadband silver electroluminescence in nanoscopic FRET-LEDs

Few inventions have shaped the world like the incandescent bulb. Edison used thermal radiation from ohmically heated conductors, but some noble metals also exhibit ‘cold’ electroluminescence in percolation films1,2, tunnel diodes3, electromigrated nanoparticle aggregates4,5, optical antennas6 or scanning tunnelling microscopy7,8,9. The origin of this radiation, which is spectrally broad and depends on applied bias, is controversial given the low radiative yields of electronic transitions. Nanoparticle electroluminescence is particularly intriguing because it involves localized surface-plasmon resonances with large dipole moments. Such plasmons enable very efficient non-radiative fluorescence resonance energy transfer (FRET) coupling to proximal resonant dipole transitions. Here, we demonstrate nanoscopic FRET–light-emitting diodes which exploit the opposite process, energy transfer from silver nanoparticles to exfoliated monolayers of transition-metal dichalcogenides10. In diffraction-limited hotspots showing pronounced photon bunching, broadband silver electroluminescence is focused into the narrow excitonic resonance of the atomically thin overlayer. Such devices may offer alternatives to conventional nano-light-emitting diodes11 in on-chip optical interconnects

General Management: BEC 322 & 322E

General Management: BEC 322 & 322E, examination November 2010

Business Management: BEC 111 E & BEC 111

Business Management BEC 111 E & BEC 111, main examination June 2012

Primal Heuristics for Branch-and-Price Algorithms

In this paper, we present several primal heuristics which we implemented in the branch-and-price solver GCG based on the SCIP framework. This involves new heuristics as well as heuristics from the literature that make use of the reformulation yielded by the Dantzig-Wolfe decomposition. We give short descriptions of those heuristics and briefly discuss computational results. Furthermore, we give an outlook on current and further development

Linearly Polarized Electroluminescence from MoS 2 Monolayers Deposited on Metal Nanoparticles: Toward Tunable Room‐Temperature Single‐Photon Sources

Break junctions in noble-metal films can exhibit electroluminescence (EL) through inelastic electron tunneling. The EL spectrum can be tuned by depositing a single-layer crystal of a transition-metal dichalcogenide (TMDC) on top. Whereas the emission from the gaps between silver or gold nanoparticles formed in the break junction is spectrally broad, the hybrid metal/TMDC structure shows distinct luminescence from the TMDC material. The EL from individual hotspots is found to be linearly polarized, with a polarization axis apparently oriented randomly. Surprisingly, the degree of polarization is retained in the EL from the TMDC monolayer at room temperature. In analogy to polarized photoluminescence experiments, such polarized EL can be interpreted as a signature of valley-selective transitions, suggesting that spin-flip transitions and dephasing for excitons in the K valleys are of limited importance. However, polarized EL may also originate from the metal nanoparticles formed under electromigration which constitute optical antenna structures. Such antennae can apparently change over time since jumps in the polarization are observed in bare silver-nanoparticle films. Remarkably, photon-correlation spectroscopy reveals that gold-nanoparticle films exhibit signatures of deterministic single-photon emission in the EL, suggesting a route to designing room-temperature polarized single-photon sources with tunable photon energy through the choice of TMDC overlayer