Covalent molecular assembly of oligoimide ultrathin films in supercritical and liquid solvent media

Sequence-controlled molecular layers on surfaces by thiol–ene chemistry: synthesis and multitechnique characterization

Silicon surfaces were functionalized by thiol–ene chemistry using sequential reactions of different α,ω-dienes and α,ω-dithiols bearing marker moieties.

Application of Organophosphonic Acids by One-Step Supercritical CO2 on 1D and 2D Semiconductors: Toward Enhanced Electrical and Sensing Performances

Formation of dense monolayers with proven atmospheric stability using simple fabrication conditions remains a major challenge for potential applications such as (bio)sensors, solar cells, surfaces for growth of biological cells, and molecular, organic, and plastic electronics. Here, we demonstrate a single-step modification of organophosphonic acids (OPA) on 1D and 2D structures using supercritical carbon dioxide (SCCO2) as a processing medium, with high stability and significantly shorter processing times than those obtained by the conventional physisorption-chemisorption method (2.5 h vs 48-60 h).The advantages of this approach in terms of stability and atmospheric resistivity are demonstrated on various 2D materials, such as indium-tin-oxide (ITO) and 2D Si surfaces. The advantage of the reported approach on electronic and sensing devices is demonstrated by Si nanowire field effect transistors (SiNW FETs), which have shown a few orders of magnitude higher electrical and sensing performances, compared with devices obtained by conventional approaches. The compatibility of the reported approach with various materials and its simple implementation with a single reactor makes it easily scalable for various applications.

Imprinting of metal receptors into multilayer polyelectrolyte films: fabrication and applications in marine antifouling

Polymeric films constructed using the layer-by-layer (LbL) fabrication process were employed as a platform for metal ion immobilization and applied as a marine antifouling coating. The novel Cu2+ ion imprinting process described is based on the use of metal ion templates and LbL multilayer covalent cross-linking. Custom synthesized, peptide mimicking polycations composed of histidine grafted poly(allylamine) (PAH) to bind metal ions, and methyl ester containing polyanions for convenient cross-linking were used in the fabrication process. Two methods of LbL film formation have been investigated using alternate polyelectrolyte deposition namely non-imprinted LbLA, and imprinted LbLB. Both LbL films were cross linked at mild temperature to yield covalent bridging of the layers for improved stability in a sea water environment. A comparative study of the non-imprinted LbLA films and imprinted LbLB films for Cu2+ ion binding capacity, leaching rate and stability of the films was performed. The results reveal that the imprinted films possess enhanced affinity to retain metal ions due to the preorganization of imidazole bearing histidine receptors. As a result the binding capacity of the films for Cu2+ could be improved by seven fold. Antifouling properties of the resulting materials in a marine environment have been demonstrated against the settlement of barnacle larvae, indicating that controlled release of Cu ions was achieved.

Stable Organic Monolayers on Oxide-Free Silicon/Germanium in a Supercritical Medium: A New Route to Molecular Electronics

Oxide-free Si and Ge surfaces have been passivated and modified with organic molecules by forming covalent bonds between the surfaces and reactive end groups of linear alkanes and aromatic species using single-step deposition in supercritical carbon dioxide (SCCO2). The process is suitable for large-scale manufacturing due to short processing times, simplicity, and high resistance to oxidation. It also allows the formation of monolayers with varying reactive terminal groups, thus enabling formation of nanostructures engineered at the molecular level. Ballistic electron emission microscopy (BEEM) spectra performed on the organic monolayer on oxide-free silicon capped by a thin gold layer reveals for the first time an increase in transmission of the ballistic current through the interface of up to three times compared to a control device, in contrast to similar studies reported in the literature suggestive of oxide-free passivation in SCCO2. The SCCO2 process combined with the preliminary BEEM results opens up new avenues for interface engineering, leading to molecular electronic devices.

Nanopatterned monolayers of an adsorbed chromophore

A simple lift-off process was developed to rapidly fabricate nanopatterned photofunctional surfaces. Dye molecules of a perylene derivative (PDID) were adsorbed irreversibly on clean silicon through the holes of an electron-beam lithographied polymer mask. The subsequent removal of the mask in a proper solvent results in PDID nanosized regions of width as small as 30 nm for stripes and of diameter as small as 120 nm for dots. Numerical analyses of atomic force microscopy and laser-scanning confocal microscopy images show that the dye molecules are confined to the regions defined by the lithographic process, with the integrated fluorescence intensity being essentially proportional to the size of the nanofeatures. This demonstrates that a simple organic lift-off process compatible with clean-room technology, and not involving any chemical step, is able to produce photofunctional nanopatterned surfaces, even though the dye is not chemically bonded to the silicon surface.

Tribological properties of nanoparticle-laden ultrathin films formed by covalent molecular assembly

The tribological properties of ultrathin films containing nanoparticles encapsulated in immobilized dendrimers are investigated. The films were formed by covalent molecular assembly in supercritical carbon dioxide, and the Au nanoparticles were formed in aqueous solution. End-capping of the terminal amine groups of the dendrimer by fluorinated species resulted in a reduction in the size of the nanoparticles formed. The resulting film structure displayed a lower coefficient of friction when the nanoparticles were formed after fluorination. The observed improvement in the tribological properties is attributed to the reduction in agglomeration of the nanoparticles due to the presence of the fluorine moieties.

Covalent molecular assembly of multilayer dendrimer ultrathin films in supercritical medium

Ultrathin films containing dendrimers are fabricated on amine- and anhydride-derivatized silicon dioxide surface through alternate layer-by-layer (LbL) assembly of pyromellitic dianhydride (PMDA) and poly(amidoamine) (PAMAM) dendrimer in supercritical carbon dioxide (SCCO2) with interlayer linkage established by covalent bonds. X-ray photoelectron and UV-visible absorption spectroscopies, atomic force microscopy (AFM), and ellipsometry were employed to study the interfacial chemistry, growth, morphology, and thickness of the assembled film. XPS analysis suggests that the PMDA/PAMAM interlayer covalent bond is established to completion, and functional surfaces for immobilization of the next layer are available after deposition of each layer. UV-visible absorption and ellipsometry revealed layer-by-layer growth of the film. The functional property film as a porous matrix was manifested in the reduction of the refractive index upon introduction of the dendrimer.

Covalent molecular assembly in supercritical carbon dioxide: a comparative study between amine- and anhydride-derivatized surfaces

Layer-by-layer covalent assembly of an oligoimide on an anhydride- derivatized silicon dioxide surface is investigated using supercritical carbon dioxide (SCCO2) as the depositing medium. The deposited films were characterized by X-ray photoelectron spectroscopy (XPS), ellipsometry (VASE), UV-visible spectroscopy, electrochemical impedance spectroscopy, nano indentation, and atomic force microscopy (AFM) and the properties of the films compared with those of an oligoimide deposited on amine-derivatized surfaces. Films formed on the anhydride surface are more uniform and stable possibly because the silane precursor for the anhydride is anchored to the surface through two (-Si-O-Si-) tripods. XPS results indicate that the interfacial reaction resulting in amide formation is almost complete in the case of the anhydride, but not in the case of the amine. We infer that the twin tripods linking the anhydride group to the surface may have improved the accessibility of the functional groups for immobilization of the next layer, thereby contributing to the better quality.