Simulations of an OSNR-limited all-optical wavelength conversion scheme

We present simulations of a scheme to perform wavelength conversion of signals that eliminates phase-noise transfer from the pump to the converted signal. Nondegenerate four-wave mixing in a semiconductor optical amplifier is used to convert the signal to a new wavelength; and if an optical comb generator is used as the multiple-pump source, then the signal can be converted without incurring any phase-noise transfer from the pumps. We highlight the capabilities of this scheme by simulating the conversion of 16-QAM signals at 10 Gbaud and showing that errors due to phase-noise accumulation are eliminated thus enabling conversion whose only impairment would be the total additive optical noise

Plasma-enhanced atomic layer deposition of nanostructured gold near room temperature

A plasma-enhanced atomic layer deposition (PE-ALD) process to deposit metallic gold is reported, using the previously reported Me3Au(PMe3) precursor with H-2 plasma as the reactant. The process has a deposition window from 50 to 120 degrees C with a growth rate of 0.030 +/- 0.002 nm per cycle on gold seed layers, and it shows saturating behavior for both the precursor and reactant exposure. X-ray photoelectron spectroscopy measurements show that the gold films deposited at 120 degrees C are of higher purity than the previously reported ones (<1 at. % carbon and oxygen impurities and <0.1 at. % phosphorous). A low resistivity value was obtained (5.9 +/- 0.3 mu Omega/cm), and X-ray diffraction measurements confirm that films deposited at 50 and 120 degrees C are polycrystalline. The process forms gold nanoparticles on oxide surfaces, which coalesce into wormlike nanostructures during deposition. Nanostructures grown at 120 degrees C are evaluated as substrates for free-space surface-enhanced Raman spectroscopy (SERS) and exhibit an excellent enhancement factor that is without optimization, only one order of magnitude weaker than state-of-the-art gold nanodome substrates. The reported gold PE-ALD process therefore offers a deposition method to create SERS substrates that are template-free and does not require lithography. Using this process, it is possible to deposit nanostructured gold layers at low temperatures on complex three-dimensional (3D) substrates, opening up opportunities for the application of gold ALD in flexible electronics, heterogeneous catalysis, or the preparation of 3D SERS substrates

Sobre a Faixa de Pedestres

The interference colors resulting from thin films of Al 2O 3 deposited by atomic layer deposition (ALD) on silicon have been rigorously analyzed using a recently developed robotic gonioreflectometer. A series of eleven increasingly thick films was deposited, up to 1613 Å, and their reflectance values obtained for the visible spectrum. A comparison of these values with the predictions of computer simulations employing Fresnel equations has revealed that while there was generally good agreement between predicted and measured spectra, there are some spectral regions that exhibit large deviations from predicted reflectances, typically at near-normal measurement angles and shorter wavelengths. The effect of these discrepancies on color appearance was investigated in the CIE L*a*b* color space for the daylight illuminant D65. Large iridescence is both predicted and measured for most film thicknesses. Chroma and hue differences as large as 20 CIELAB units between the predicted and the measured color centers were obtained. Simulation also predicts larger iridescence than what is actually measured. A likely cause for the observed discrepancies is that the dielectric constants of the ALD films deviate from the literature values for the bulk material

Volatile and thermally stable polymeric tin trifluoroacetates

Tin trifluoroacetates are effective vapor phase single-source precursors for F-doped SnO2, but their structures have been poorly understood for decades. Here we undertook a comprehensive structural analysis of these compounds in both the solid and gas phases through a combined single-crystal X-ray crystallography, gas phase electron diffraction, and density functional theory investigation. Tin(II) bis(trifluoroacetate) (1) thermally decomposes into a 1:1 mixture of 1 and ditin(II) μ-oxybis(μ-trifluoroacetate) (2) during sublimation, which then polymerize into hexatin(II)-di-μ3-oxyoctakis(μ-trifluoroacetate) (3) upon solidification. Reversible depolymerization occurred readily upon heating, making 3 a useful vapor phase precursor itself. Tin(IV) tetrakis(trifluoroacetate) (5) was also found to be polymeric in the solid state, but it evaporated as a monomer over 130 °C lower than 3. This counterintuitive improvement in volatility by polymerization was possibly due to the large entropy change during sublimation, which offers a strategic new design feature for vapor phase deposition precursors

Gold nanowire electrodes in array: Simulation study and experiments

Recent developments in nanofabrication have enabled fabrication of robust and reproducible nanoelectrodes with enhanced performance, when compared to microelectrodes. A hybrid electron beam/photolithography technique is shown that permits gold nanowire array electrodes to be routinely fabricated at reasonable cost. Fabricated devices include twelve gold nanowire working electrode arrays, an on-chip gold counter electrode and an on-chip platinum pseudo reference electrode. Using potential sweep techniques, these nanowires exhibit measurable currents in the nanoAmpere regime and display steady-state voltammograms even at very high scan rates (5000 mV.s-1) indicative of fast analyte mass transport to the electrode. Nanowire electrode arrays offer the potential for enhancements in electroanalysis including: increased signal to noise ratio and increased sensitivity while also allowing quantitative detection at much lower concentrations. However, to achieve this goal a full understanding of the diffusion profiles existing at nanowire arrays is required. To this end, we simulate the effects of altering inter-electrode separations on analyte diffusion for a range of scan rates at nanowire electrode arrays, and perform the corresponding experiments. We show that arrays with diffusionally independent concentration profiles demonstrate superior electrochemical performance compared to arrays with overlapping diffusion profiles when employing sweep voltammetric techniques. By contrast, we show that arrays with diffusionally overlapping profiles exhibit enhanced performance when employing step voltammetric techniques

Anisotropic effective permittivity of an ultrathin gold coating on optical fiber in air, water and saline solutions

The optical properties of an ultrathin discontinuous gold film in different dielectric surroundings are investigated experimentally by measuring the polarization-dependent wavelength shifts and amplitudes of the cladding mode resonances of a tilted fiber Bragg grating. The gold film was prepared by electron-beam evaporation and had an average thickness of 5.5 nm ( ± 1 nm). Scanning electron imaging was used to determine that the film is actually formed of individual particles with average lateral dimensions of 28 nm ( ± 8 nm). The complex refractive indices of the equivalent uniform film in air at a wavelength of 1570 nm were calculated from the measurements to be 4.84-i0.74 and 3.97-i0.85 for TM and TE polarizations respectively (compared to the value for bulk gold: 0.54-i10.9). Additionally, changes in the birefringence and dichroism of the films were measured as a function of the surrounding medium, in air, water and a saturated NaCl (salt) solution. These results show that the film has stronger dielectric behavior for TM light than for TE, a trend that increases with increasing surrounding index. Finally, the experimental results are compared to predictions from two widely used effective medium approximations, the generalized Maxwell-Garnett and Bruggeman theories for gold particles in a surrounding matrix. It is found that both of these methods fail to predict the observed behavior for the film considered

Deposition of copper by plasma-enhanced atomic layer deposition using a novel N-Heterocyclic carbene precursor

Two novel N-heterocyclic carbene (NHC)-containing copper(I) amides are reported as atomic layer deposition (ALD) precursors. 1,3-Diisopropyl-imidazolin-2-ylidene copper hexamethyldisilazide (1) and 4,5-dimethyl-1,3-diisopropyl-imidazol-2-ylidene copper hexamethyldisilazide (2) were synthesized and structurally characterized. The thermal behavior of both compounds was studied by thermogravimetric analysis (TGA), and they were both found to be reasonably volatile compounds. Compound 1 had no residual mass in the TGA and showed long-term stability at temperatures as high as 130 °C, while 2 had a residual mass of 7.4%. Copper metal with good resistivity was deposited using 1 by plasma-enhanced atomic layer deposition. The precursor demonstrated self-limiting behavior indicative of ALD, and gave a growth rate of 0.2 Å/cycle. Compound 2 was unsuccessful as an ALD precursor under similar conditions. Density functional theory calculations showed that both compounds adsorb dissociatively onto a growing copper film as long as there is some atomic roughness, via cleavage of the Cu-carbene bond

Atomic Layer Deposition of PbS Thin Films at Low Temperatures

doi: 10.1021/acs.chemmater.0c01887Atomic layer deposition (ALD) is a viable method for depositing functional, passivating, and encapsulating layers on top of halide perovskites. Studies in that area have only focused on metal oxides, despite a great number of materials that can be made with ALD. This work demonstrates that, in addition to oxides, other ALD processes can be compatible with the perovskites. We describe two new ALD processes for lead sulfide. These processes operate at low deposition temperatures (45-155 degrees C) that have been inaccessible to previous ALD PbS processes. Our processes rely on volatile and reactive lead precursors Pb(dbda) (dbda = rac-N-2,N-3-di-tertbutylbutane-2,3-diamide) and Pb(btsa)(2) (btsa = bis(trimethylsilyl)amide) as well as H2S. These precursors produce high quality PbS thin films that are uniform, crystalline, and pure. The films exhibit p- type conductivity and good mobilities of 10-70 cm(2) V-1 s(-1). Low deposition temperatures enable direct ALD of PbS onto a halide perovskite CH3NH3PbI3 (MAPI) without its decomposition. The stability of MAPI in ambient air is greatly improved by capping with ALD PbS. More generally, these new processes offer valuable alternatives for PbS-based devices, and we hope that this study will inspire more studies on ALD of non-oxides on halide perovskites.Peer reviewe

Atomic layer deposition of Cu with a carbene-stabilized Cu (i) silylamide

The metal–organic Cu(I) complex 1,3-diisopropyl-imidazolin-2-ylidene copper hexamethyl disilazide has been tested as a novel oxygen-free precursor for atomic layer deposition of Cu with molecular hydrogen. Being a strong Lewis base, the carbene stabilizes the metal centre to form a monomeric compound that can be vaporised and transported without visible degradation. A significant substrate dependence of the growth process not only with respect to the film material but also to the structure of the films was observed. On Pd surfaces continuous films are grown and no phase boundary can be observed between the Cu film and the Pd, while island growth is observed on Ru substrates, which as a consequence requires thicker films in order to achieve a fully coalesced layer. Island growth is also observed for ultra-thin (<10 nm) Pd layers on Si substrates. Possible explanations for the different growth modes observed are discussed