Charge transport across metal/molecular (alkyl) monolayer-Si junctions is dominated by the LUMO level

We compare the charge transport characteristics of heavy doped p- and n-Si-alkyl chain/Hg junctions. Photoelectron spectroscopy (UPS, IPES and XPS) results for the molecule-Si band alignment at equilibrium show the Fermi level to LUMO energy difference to be much smaller than the corresponding Fermi level to HOMO one. This result supports the conclusion we reach, based on negative differential resistance in an analogous semiconductor-inorganic insulator/metal junction, that for both p- and n-type junctions the energy difference between the Fermi level and LUMO, i.e., electron tunneling, controls charge transport. The Fermi level-LUMO energy difference, experimentally determined by IPES, agrees with the non-resonant tunneling barrier height deduced from the exponential length-attenuation of the current

Простір публічних комунікацій сучасних релігійних організацій

Porous aluminum oxide (PAO) is a nanoporous material used for various (bio)­technological applications, and tailoring its surface properties via covalent modification is a way to expand and refine its application. Specific and complex chemical modification of the PAO surface requires a stepwise approach in which a secondary reaction on a stable initial modification is necessary to achieve the desired terminal molecular architecture and reactivity. We here show that the straightforward initial modification of the bare PAO surface with bromo-terminated phosphonic acid allows for the subsequent preparation of PAO with a wide scope of terminal reactive groups, making it suitable for (bio)­functionalization. Starting from the initial bromo-terminated PAO, we prepared PAO surfaces presenting various terminal functional groups, such as azide, alkyne, alkene, thiol, isothiocyanate, and <i>N</i>-hydroxysuccinimide (NHS). We also show that this wide scope of easily accessible tailored reactive PAO surfaces can be used for subsequent modification with (bio)­molecules, including carbohydrate derivatives and fluorescently labeled proteins

Zwitterionic dendrimer – Polymer hybrid copolymers for self-assembling antifouling coatings

In this work, we show two different routes to synthesize polymer-dendrimer hybrids by the coupling of poly(L-lysine) and zwitterionic dendrimers (ZIDs). Poly(L-lysine) (PLL) is used because of its advantageous self-assembly properties onto silicon oxide by charged-based interactions between the lysine groups and the negatively charged surface, whilst the coupled ZIDs provide antifouling properties. The first route yields network-like structures in which PLL and ZIDs are crosslinked by multiple amide bonds. By using different ratios of PLL and ZID, we vary the size of the formed networks. A more defined, linear PLL-ZID macromolecule is formed via coupling of multiple ZIDs to PLL in a controlled way by a copper-catalyzed azide/alkyne cycloaddition (CuAAC) “click” reaction. Following synthesis and characterization of the two different types of PLL-ZID macromolecules, they are self-assembled on silicon oxide surfaces from aqueous solutions in a single step, to form thin, hydrophilic coatings. Their potential use as antifouling coatings is tested by fluorescence microscopy and quartz crystal microbalance (QCM) with foulants such a single proteins and diluted human serum. Finally, by performing an on-surface biofunctionalization step by biotin we demonstrate it is possible to use these polymer-dendrimer hybrids for selective detection of target analytes (here: streptavidin), while the underlying coating maintains its antifouling properties. This method presents a new, straightforward approach for the manufacturing of PLL-ZID based coatings that can be pre-synthesized partly or fully and applied as coating in a single self-assembly step. Both steps can take place in aqueous solution and under ambient conditions, and result in stable coatings that not only display antifouling properties but also maintain the possibility of further functionalization

Design, Synthesis, and Characterization of Fully Zwitterionic, Functionalized Dendrimers

Dendrimers are interesting candidates for various applications because of the high level of control over their architecture, the presence of internal cavities, and the possibility for multivalent interactions. More specifically, zwitterionic dendrimers modified with an equal number of oppositely charged groups have found use in in vivo biomedical applications. However, the design and control over the synthesis of these dendrimers remains challenging, in particular with respect to achieving full modification of the dendrimer. In this work, we show the design and subsequent synthesis of dendrimers that are highly charged while having zero net charge, that is zwitterionic dendrimers that are potential candidates for biomedical applications. First, we designed and fully optimized the synthesis of charge-neutral carboxybetaine and sulfobetaine zwitterionic dendrimers. Following their synthesis, the various zwitterionic dendrimers were extensively characterized. In this study, we also report for the first time the use of X-ray photoelectron spectroscopy as an easy-to-use and quantitative tool for the compositional analysis of this type of macromolecules that can complement techniques such as nuclear magnetic resonance and gel permeation chromatography. Finally, we designed and synthesized zwitterionic dendrimers that contain a variable number of alkyne and azide groups that allow straightforward (bio)functionalization via click chemistry.</p

Light-Activated Electroactive Molecule-Based Memory Microcells Confined on a Silicon Surface

International audienceUltrahigh-capacity molecular AND gates provide the potential for the next-generation dynamic random access memory. The ferrocene-terminated monolayer on oxide-free silicon system allows a highly stable and independent switching with both light and potential, yielding precisely such an AND gate

PLL-Poly(HPMA) Bottlebrush-Based Antifouling Coatings: Three Grafting Routes

In this work, we compare three routes to prepare antifouling coatings that consist of poly(l-lysine)-poly(N-(2-hydroxypropyl)methacrylamide) bottlebrushes. The poly(l-lysine) (PLL) backbone is self-assembled onto the surface by charged-based interactions between the lysine groups and the negatively charged silicon oxide surface, whereas the poly(N-(2-hydroxypropyl)methacrylamide) [poly(HPMA)] side chains, grown by reversible addition-fragmentation chain-transfer (RAFT) polymerization, provide antifouling properties to the surface. First, the PLL-poly(HPMA) coatings are synthesized in a bottom-up fashion through a grafting-from approach. In this route, the PLL is self-assembled onto a surface, after which a polymerization agent is immobilized, and finally HPMA is polymerized from the surface. In the second explored route, the PLL is modified in solution by a RAFT agent to create a macroinitiator. After self-assembly of this macroinitiator onto the surface, poly(HPMA) is polymerized from the surface by RAFT. In the third and last route, the whole PLL-poly(HPMA) bottlebrush is initially synthesized in solution. To this end, HPMA is polymerized from the macroinitiator in solution and the PLL-poly(HPMA) bottlebrush is then self-assembled onto the surface in just one step (grafting-to approach). Additionally, in this third route, we also design and synthesize a bottlebrush polymer with a PLL backbone and poly(HPMA) side chains, with the latter containing 5% carboxybetaine (CB) monomers that eventually allow for additional (bio)functionalization in solution or after surface immobilization. These three routes are evaluated in terms of ease of synthesis, scalability, ease of characterization, and a preliminary investigation of their antifouling performance. All three coating procedures result in coatings that show antifouling properties in single-protein antifouling tests. This method thus presents a new, simple, versatile, and highly scalable approach for the manufacturing of PLL-based bottlebrush coatings that can be synthesized partly or completely on the surface or in solution, depending on the desired production process and/or application.</p

Organic Monolayers from 1‑Alkynes Covalently Attached to Chromium Nitride: Alkyl and Fluoroalkyl Termination

Strategies to modify chromium nitride (CrN) surfaces are important because of the increasing applications of these materials in various areas such as hybrid electronics, medical implants, diffusion barrier layers, corrosion inhibition, and wettability control. The present work presents the first surface immobilization of alkyl and perfluoro-alkyl (from C₆ to C₁₈) chains onto CrN substrates using appropriately functionalized 1-alkynes, yielding covalently bound, high-density organic monolayers with excellent hydrophobic properties and a high degree of short-range order. The obtained monolayers were characterized in detail by water contact angle, X-ray photoelectron spectroscopy (XPS), ellipsometry, and infrared reflection absorption spectroscopy (IRRAS)