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Expitaxial films of 2 on Si(111) were investigated by low-energy electron diffraction. Films of approximately 12 Å thickness were prepared by simultaneous deposition of Co and Si and subsequent annealing. The films were found to crystallize in 2 structure in (111) orientation. Two (1×1) phases of different stoichiometry exist. The surface phase that contains more Co is found to be a 2(111) bulklike structure terminated by a Si-Co-Si trilayer. The Si-rich phase is terminated by an additional nonrotated silicon bilayer with the lower silicon atoms bound to cobalt in the first 2 layer. Consequently, these cobalt atoms have an eightfold coordination. Due to the lattice mismatch the silicide films are expanded by 0.5% in the lateral direction and contracted by 1.4% in the vertical direction. [ABSTRACT FROM AUTHOR]

The interface structure of ultrathin CoSi[sub 2] films grown on Si(111) was investigated by quantitative low-energy electron diffraction. Codeposition of the elements leads to a film composed of domains with two and three Si-Co-Si trilayers in CaF[sub 2] structure. As within the film, Co atoms at the interface are eightfold coordinated. The lateral unit cells of the film and substrate are mutually rotated by 60° (B-type orientation). The interfacial trilayer is substantially distorted, its distance to the substrate expanded, and its sublayer spacings considerably modified from the bulk. Also, the substrate's top spacing is expanded. The results compare almost quantitatively with recent density-functional calculations. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Optoelectronic devices based on organic semiconductor materials are on the rise for sensing applications due to their integrability with a variety of substrates - including flexible substrates for wearables. For sensing applications often narrowband absorption is desired with suppression of light at other wavelengths. Here, we investigate narrowband absorption enhancement of organic photodetectors (OPD) with an integrated lateral nanostructure. We show with finite-element simulations, that resonant excitation of low absorbing wavelength regimes allow for up to 3 times the absolute absorption at wavelengths on resonance compared to wavelengths off resonance. We present experimental results for CuPc/C 60 OPDs fabricated on grating nanostructures with periods of 350 nm and 400 nm and a grating depth of 140 nm as well as a grating period of 370 nm and grating depths of 30 nm. Angle-resolved transmission spectra clearly show the optical resonance effects. In order to evaluate the electrical resonance effects a measurement system is introduced based on angular laser excitation. An angular resolution of 0.1° is achieved in the analysis of the OPD photocurrent response. Using the measurement setup an increase of the photocurrent by up to 50% is observed for the TE-resonance. It is demonstrated that the resonance wavelength is tuned simply by adjusting the grating period without changes in the layer thicknesses. This opens up new opportunities in realizing pixels of different wavelength response next to each other employing a single active stack design.

Photonic crystal slabs (PCS) are a promising platform for optical biosensing. Yet, flexible applications based on PCS for biosensing have been limited, as the mechanical properties influence the optical ones. Here, we show the suppression of the mechanochromism effect for flexible PCS. We obtained flexible photonic crystal slabs by sputtering of a dielectric 100 nm Nb 2 O 5 high refractive index layer onto a flexible nanostructured polydimethylsiloxane (PDMS) substrate with 370 nm grating period. The PCS exhibit a guided mode resonance at around 650 nm. We demonstrate that these flexible photonic crystal slabs show less than 0.5 nm resonance shift for 4% strain and call them stabilized PCS (sPCS). We compare this to a resonance shift of ∼21 nm for ∼4% strain of a flexible photonic crystal with a flexible nanoparticle high index layer (mechanochromatic PCS, mPCS). This high resonance shift is expected from the Bragg equations, where 4% grating period change correspond to approximately 4% change of the resonance wavelength (i.e., ∼26 nm at a resonance wavelength of 650 nm), if changes in the mode effective refractive index are neglected. In a stretch series we obtain color-to-strain dependencies of 4.79 nm/% strain for mPCS and 0.11 nm/% strain for our stabilized sPCS. We analyze the suppression of the mechanochromism with detailed microscopy results. We observe that fissures and fractures form in the rigid waveguiding layer of the sPCS upon mechanical stress. An algorithm based on Holistically-Nested Edge Detection (HED) is used for automated counting of cracks. Rigid photonic crystal cells with sizes on the order of 10 µm to 100 µm are formed that explain the stable optical properties. Even more stable optical properties with less than 0.03 nm wavelength shift per 1% strain are demonstrated for sPCS with an additional dielectric 100 nm SiO 2 low index layer beneath the Nb 2 O 5 waveguide layer decoupling the waveguide further from the flexible PDMS substrate.