Stress-Dependent Optical Extinction in Low-Pressure Chemical Vapor Deposition Silicon Nitride Measured by Nanomechanical Photothermal Sensing.

Understanding optical absorption in silicon nitride is crucial for cutting-edge technologies like photonic integrated circuits, nanomechanical photothermal infrared sensing and spectroscopy, and cavity optomechanics. Yet, the origin of its strong dependence on the film deposition and fabrication process is not fully understood. This Letter leverages nanomechanical photothermal sensing to investigate optical extinction κext at a 632.8 nm wavelength in low-pressure chemical vapor deposition (LPCVD) SiN strings across a wide range of deposition-related tensile stresses (200-850 MPa). Measurements reveal a reduction in κext from 103 to 101 ppm with increasing stress, correlated to variations in Si/N content ratio. Within the band-fluctuations framework, this trend indicates an increase of the energy bandgap with the stress, ultimately reducing absorption. Overall, this study showcases the power and simplicity of nanomechanical photothermal sensing for low absorption measurements, offering a sensitive, scattering-free platform for material analysis in nanophotonics and nanomechanics.

Characterization of Surface Modifications in Oxygen Plasma-Treated Teflon AF1600.

We explore the surface properties of Teflon AF1600 films treated by oxygen plasma with various procedure parameters. Contact angle (CA) measurements, scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron microscopy (XPS) are employed to investigate the wetting behavior, surface topography, and chemical composition, respectively. While the etched thickness reveals a linear relationship to the applied plasma energy, the surface presents various wetting properties and topographies depending on the plasma energy: low advancing and zero receding CA (1 kJ), super high advancing and zero receding CA (2-3 kJ), and super high advancing and high receding CA (≥4.5 kJ) for the wetting behaviors; pillar-like (≤6 kJ) and fiber-like (>6 kJ) nanoscaled structures for the topographies. The results of XPS analysis reveal slight changes in the presence of O- and F-components (<4%) after oxygen plasma treatment. Furthermore, we discuss the applicability of the Wenzel and Cassie-Baxter equations and employ the Friction-Adsorption (FA) model, where no wetting state and structure-related parameters are needed, to describe the CAs on the plasma-treated surfaces. Additionally, we conduct electrowetting experiments on the treated surfaces and find that the experimental results of the advancing CA are in good agreement with the predictions of the FA model.

Polymerized ionic liquid Co-catalysts driving photocatalytic CO2 transformation.

Photocatalytic production of CO from CO2 has the potential for safe and atom-economic production of feedstock chemicals via in situ carbonylation chemistry. We developed novel ionic liquid-based polymeric materials through radical copolymerisation of 1-butyl-3-vinylimidazolium chloride and photocatalytically active Re- and Ru-complexes that serve as the CO2 reduction catalyst and photosensitiser, respectively. The crosslinked polymeric framework allows for the facile immobilisation of molecular organometallic complexes for use as heterogenised catalysts; moreover, the involved imidazolium core units co-catalyze the reduction of CO2 via covalent interaction. The ratio of sensitiser and catalyst was analysed by laser ablation inductively coupled plasma mass spectroscopy (LA-ICP-MS) and set in relation to results from photocatalytic experiments. Ultimately, the heterogenous polymeric framework showed high selectivity for CO formation on photocatalytic CO2 reduction with improved stability to the corresponding homogenous system.

A combined experimental and theoretical study of RuO2/TiO2 heterostructures as a photoelectrocatalyst for hydrogen evolution.

We report a joint experimental and theoretical study of RuO2/TiO2 heterostructures. In the experimental section, mesoporous RuO2/TiO2 heterostructures were prepared by impregnation of mesoporous TiO2 nanoparticles which were synthesized from a new precursor, Na2[Ti(C2O4)3], in an aqueous solution of ruthenium(III) chloride followed by calcination at 300 °C. Using various techniques, the prepared TiO2 and RuO2/TiO2 heterostructures were extensively characterized. The photoelectocatalytic application of the as-prepared heterostructures was then investigated toward the hydrogen evolution reaction (HER). The results illustrated that RuO2 is dispersed uniformly on the TiO2 surface. The loading of RuO2 on TiO2 decreases the band gap energy and extends the absorption edge to the visible light region. This wide absorption extends the photoelectrocatalytic activity of RuO2/TiO2 heterostructures. To obtain a deeper understanding of the increase of the photoelectrocatalytic activity of RuO2/TiO2 heterostructures compared to pure TiO2, theoretical calculations at the density functional theory (DFT) level were performed on some model clusters of pure TiO2 and the RuO2/TiO2 heterostructure. The theoretical results elucidated that the recombination ratio of electron-hole pairs decreases effectively for RuO2/TiO2 compared to pure TiO2.

[Ru(tmphen)3]2[Fe(CN)6] and [Ru(phen)3][Fe(CN)5(NO)] complexes and formation of a heterostructured RuO2-Fe2O3 nanocomposite as an efficient alkaline HER and OER electrocatalyst.

Water electrolysis is one of the most capable processes for supplying clean fuel. Herein, two novel ionic Ru(II)-Fe(II) complexes, [Ru(tmphen)3]2[Fe(CN)6] and [Ru(phen)3][Fe(CN)5(NO)], where tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline and phen = 1,10-phenanthroline, were synthesized and characterized by UV-Vis spectroscopy, elemental analysis, FT-IR, and single-crystal X-ray structural analysis. By thermally decomposing the [Ru(tmphen)3]2[Fe(CN)6] complex at 600 °C for 4 h, a heterostructured RuO2-Fe2O3 nanocomposite was fabricated through a facile one-pot treatment and then characterized by FT-IR, XRD, FT-Raman, UV-Vis (DRS), ICP-OES, FE-SEM, TEM, TGA/DTG, BET, and XPS analyses, which revealed the formation of highly crystalline RuO2-Fe2O3 nanoparticles with an average size of 8-12 nm. The prepared nanocomposite was an efficient heterostructured electrocatalyst for performing water-splitting redox reaction processes, including hydrogen and oxygen evolution reactions (HER and OER) in alkaline solutions. In this regard, RuO2 and Fe2O3 samples were also prepared through thermal decomposition of [Ru(tmphen)3](NO3)2 and K4[Fe(CN)6] precursors, respectively, as control experiments to compare their HER and OER electrocatalytic activity with that of the RuO2-Fe2O3 nanocomposite. Specifically, the RuO2-Fe2O3 nanocomposite exhibited significant electrocatalytic performance, generating 10 mA cm-2 current density at -148 and 292 mV overpotentials, and the Tafel slope results from fitting the LSV curves to the Tafel equation were -43 and 56.08 mV dec-1 for the HER and OER, respectively. Therefore, the heterostructured RuO2-Fe2O3 nanocomposite can be viewed as a bi-functional electrocatalyst for HER and OER because it exploits the synergistic effects of heterostructures and active sites at its interface.

Elucidating the formation and active state of Cu co-catalysts for photocatalytic hydrogen evolution.

The design of active and selective co-catalysts constitutes one of the major challenges in developing heterogeneous photocatalysts for energy conversion applications. This work provides a comprehensive insight into thermally induced bottom-up generation and transformation of a series of promising Cu-based co-catalysts. We demonstrate that the volcano-type HER profile as a function of calcination temperature is independent of the type of the Cu precursor but is affected by changes in oxidation state and location of the copper species. Supported by DFT modeling, our data suggest that low temperature (<200 °C) treatments facilitate electronic communication between the Cu species and TiO2, which allows for a more efficient charge utilization and maximum HER rates. In contrast, higher temperatures (>200 °C) do not affect the Cu oxidation state, but induce a gradual, temperature-dependent surface-to-bulk diffusion of Cu, which results in interstitial, tetra-coordinated Cu+ species. The disappearance of Cu from the surface and the introduction of new defect states is associated with a drop in HER performance. This work examines electronic and structural effects that are in control of the photocatalytic activity and can be transferred to other systems for further advancing photocatalysis.

Peptide-coated silver nanoparticles: synthesis, surface chemistry, and pH-triggered, reversible assembly into particle assemblies.

Simple tripeptides are scaffolds for the synthesis and further assembly of peptide/silver nanoparticle composites. Herein, we further explore peptide-controlled silver nanoparticle assembly processes. Silver nanoparticles with a pH-responsive peptide coating have been synthesized by using a one-step precipitation/coating route. The nature of the peptide/silver interaction and the effect of the peptide on the formation of the silver particles have been studied via UV/Vis, X-ray photoelectron, and surface-enhanced Raman spectroscopies as well as through electron microscopy, small angle X-ray scattering and powder X-ray diffraction with Rietveld refinement. The particles reversibly form aggregates of different sizes in aqueous solution. The state of aggregation can be controlled by the solution pH value. At low pH values, individual particles are present. At neutral pH values, small clusters form and at high pH values, large precipitates are observed.

One-step synthesis and XPS investigations of chiral NHC-Au(0)/Au(i) nanoparticles.

Although N-heterocyclic carbenes (NHCs) have been demonstrated as suitable ligands for the stabilisation of gold nanoparticles (AuNPs) through a variety of methods, the manner in which such AuNPs form is yet to be fully elucidated. We report a simple and fast one-step synthesis of uniform chiral (l/d)-histidin-2-ylidene stabilised gold nanoparticles using the organometallic Au(i) complex as a well defined starting material. The resulting nanoparticles have an average size of 2.35 ± 0.43 nm for the L analog whereas an average size of 2.25 ± 0.39 nm was found for the D analog. X-ray photoelectron spectroscopy analyses reveal the presence of Au(i) and Au(0) in all NHC stabilised AuNPs. In contrast, measured X-ray photoelectron spectra of dodecanethiol protected gold nanoparticles showed only the presence of a Au(0) species. This observation leads us to postulate that AuNPs synthesised from organometallic NHC-Au(i) complexes exhibit a monolayer of Au(i) surrounding a Au(0) core. This work highlights the importance of synthetic method choice for NHC-stabilized AuNPs, as this could determine Au oxidation states and resulting AuNP properties such as catalytic activities and stabilities.

Silver nanoparticle engineering via oligovaline organogels.

l-Valine-based oligopeptides with the chemical structure Z-(l-Val)3-OMe and Z-(l-Val)2-l-Cys(S-Bzl)-OMe form stable organogels in butanol. Both peptides are efficient gelators, but Z-(l-Val)2-l-Cys(S-Bzl)-OMe crystallizes more readily than Z-(l-Val)3-OMe. The two peptides can form mixed fibers, which also gel butanol. The resulting organogels are very similar to oligovaline organogels reported earlier (Mantion and Taubert, Macromol. Biosci., 2007, 7, 208) as they also form highly ordered peptide fibers with a predominant ß-sheet structure and diameters of ca. 100 nm. The fibers can be mineralized with silver nanoparticles using DMF as a reducing agent. The fraction of the sulfur-containing peptide Z-(l-Val)2-l-Cys(S-Bzl)-OMe controls the shape and size of the resulting nanoparticles. At high Z-(l-Val)2-l-Cys(S-Bzl)-OMe content, small spherical particles are distributed all over the fiber. Lower contents of Z-(l-Val)2-l-Cys(S-Bzl)-OMe lead to a size increase of the particles and to more complex shapes like plate-like and raspberry-like silver particles. The interactions between peptide and silver ions or silver particles takes place via a complexation of the silver ions to the sulfur atom of the thioether moiety, and are shown to be the key interaction in controlling particle formation.

Electronic properties of Ag nanoparticle arrays. A Kelvin probe and high resolution XPS study.

The electronic properties of citrate stabilised Ag nanoparticles with sizes ranging from 4 to 35 nm were investigated by the Kelvin probe method and high resolution XPS. Two and three dimensional assemblies of the particles were prepared by electrostatic adsorption from aqueous solution onto poly-l-lysine modified surfaces. The work function of the Ag particles increased from 5.29 +/- 0.05 to 5.53 +/- 0.05 eV as the particle size decreased. These values are approximately 0.8 eV higher than for clean polycrystalline Ag surfaces. The origin of these remarkable high work functions cannot be explained in terms of either citrate induced changes in the surface dipole or image forces in the confined metallic domains. High resolution XPS spectra of the Ag 3d(5/2) core level were characterised by broad bands and a 0.4 eV shift towards lower binding energies for the smallest particles. Comparisons with reported studies on extended Ag surfaces indicate that as-grown particles exhibit partially oxidised surfaces. The behaviour of the work function further suggests that the strength of the Ag-O bonding increases with decreasing particle sizes. These findings are highly relevant to the interpretation of the catalytic properties of Ag nanoparticles.