Plasma-Etched Pattern Transfer of Sub-10 nm Structures Using a Metal-Organic Resist and Helium Ion Beam Lithography.

Field-emission devices are promising candidates to replace silicon fin field-effect transistors as next-generation nanoelectronic components. For these devices to be adopted, nanoscale field emitters with nanoscale gaps between them need to be fabricated, requiring the transfer of, for example, sub-10 nm patterns with a sub-20 nm pitch to substrates like silicon and tungsten. New resist materials must therefore be developed that exhibit the properties of sub-10 nm resolution and high dry etch resistance. A negative tone, metal-organic resist is presented here. It can be patterned to produce sub-10 nm features when exposed to helium ion beam lithography at line doses on the order of tens of picocoulombs per centimeter. The resist was used to create 5 nm wide, continuous, discrete lines spaced on a 16 nm pitch in silicon and 6 nm wide lines on an 18 nm pitch in tungsten, with line edge roughness of 3 nm. After the lithographic exposure, the resist demonstrates high resistance to silicon and tungsten dry etch conditions (SF6 and C4F8 plasma), allowing the pattern to be transferred to the underlying substrates. The resist's etch selectivity for silicon and tungsten was measured to be 6.2:1 and 5.6:1, respectively; this allowed 3 to 4 nm thick resist films to yield structures that were 21 and 19 nm tall, respectively, while both maintained a sub-10 nm width on a sub-20 nm pitch.

Comment on: Synthesis of New Azo Compounds Based on N-(4-Hydroxyphenyl)maleimide and N-(4-Methylphenyl)maleimide. Molecules 2010, 15, 7498-7508.

The synthesis of (E)-phenylazo-3-N-(4-hydroxyphenyl)maleimide (1) using a procedure previously reported in Molecules is deemed to be erroneous. A detailed re-investigation of the earlier work suggests that the spectral data for key intermediates and the final product, (1), was mis-assigned. We conclude that compound (1) was not synthesized, but rather an unusual ring opening reaction of the maleimide unit of the starting material, N-(4-hydroxyphenyl)maleimide (2) leading to the generation of (Z)-4-((4-hydroxyphenyl)amino)-4-oxobut-2-enoic acid, (3) was observed instead. Examination of the original experimental data reveals systematic errors in the reporting of all of the combustion microanalytical data. Overall, the present investigation suggests that errors in the interpretation of spectral data, falsification of analytical data and selective editing of experimental results raise questions over the veracity of the work presented in the original paper.

Use of Supramolecular Assemblies as Lithographic Resists.

A new resist material for electron beam lithography has been created that is based on a supramolecular assembly. Initial studies revealed that with this supramolecular approach, high-resolution structures can be written that show unprecedented selectivity when exposed to etching conditions involving plasmas.

Submicron Patterning of Polymer Brushes: An Unexpected Discovery from Inkjet Printing of Polyelectrolyte Macroinitiators.

Using an electrostatic-based super inkjet printer we report the high-resolution deposition of polyelectrolyte macroinitiators and subsequent polymer brush growth using SI-ARGET-ATRP. We go on to demonstrate for the first time a submicron patterning phenomenon through the addition of either a like charged polyelectrolyte homopolymer or through careful control of ionic strength. As a result patterning of polymer brushes down to ca. 300 nm is reported. We present a possible mechanistic model and consider how this may be applied to other polyelectrolyte-based systems as a general method for submicron patterning.

Non-linear, cata-Condensed, Polycyclic Aromatic Hydrocarbon Materials: A Generic Approach and Physical Properties.

A generic approach to the regiospecific synthesis of halogenated polycyclic aromatics is made possible by the one- or two-directional benzannulation reactions of readily available (ortho-allylaryl)trichloroacetates (the "BHQ" reaction). Palladium-catalysed cross-coupling reactions of the so-formed haloaromatics enable the synthesis of functionalised polycyclic aromatic hydrocarbons (PAHs) with surgical precision. Overall, this new methodology enables the facile mining of chemical space in search of new electronic functional materials.

Semiconductor Deposition via Laser Printing of a Bespoke Toner Containing Metal Xanthate Complexes.

A methodology to use laser printing, a form of electrophotography, to print metal chalcogenide complexes on paper, is described. After fusing the toner to paper, a heating step is used to cause the printed metal xanthate complexes to thermolyze within the toner and form three target metal chalcogenides: CuS, SnS, and ZnS. To achieve this, we synthesize a poly(styrene-co-n-butyl acrylate) thermopolymer that emulates the thermal properties of a commercial toner and is also solution processable with the metal xanthate complexes used: [Zn(S2COEt)2], [Cu(S2COEt)·(PPh3)2], and [Sn(S2COEt)2]. We demonstrate through energy dispersive X-ray mapping that the toner is deposited following printing and that thermolysis of the metal xanthate complexes occurs in the fused toner, demonstrating the first example of laser printing of inorganic complexes and, in turn, semiconductors.

Segregation in like-charged polyelectrolyte-surfactant mixtures can be precisely tuned via manipulation of the surfactant mass ratio.

In this study, we consider segregative phase separation in aqueous mixtures of quaternary ammonium surfactants didecyldimethylammonium chloride (DDQ) and alkyl (C12, 70%; C14 30%) dimethyl benzyl ammonium chloride (BAC) upon the addition of poly(diallyldimethylammonium) chloride (pDADMAC) as a function of both concentration and molecular weight. The nature of the surfactant type is dominant in determining the concentration at which separation into an upper essentially surfactant-rich phase and lower polyelectrolyte-rich phase is observed. However, for high-molecular-weight pDADMAC there is a clear indication of an additional depletion flocculation effect. When the BAC/DDQ ratio is tuned, the segregative phase separation point can be precisely controlled. We propose a phase separation mechanism for like-charged quaternary ammonium polyelectrolyte/surfactant/water mixtures induced by a reduction in the ionic atmosphere around the surfactant headgroup and possible ion pair formation. An additional polyelectrolyte-induced depletion flocculation effect was also observed.

An Approach to the Synthesis of Functionalized Polycyclic Aromatic Hydrocarbons.

The application of a new benzannulation reaction for the regiocontrolled synthesis of functionalized chrysenes is reported. The initial benzannulation and the subsequent halogen displacement reactions are both highly regiospecific, which thereby enables the regiocontrolled synthesis of a variety of 4,10-disubstituted chrysenes from commercially available 1,5-dihydroxynaphthalene.

Hall-effect measurements probing the degree of charge-carrier delocalization in solution-processed crystalline molecular semiconductors.

Intramolecular structure and intermolecular packing in crystalline molecular semiconductors should have profound effects on the charge-carrier wave function, but simple drift mobility measurements are not very sensitive to this. Here we show that differences in the Hall resistance of two soluble pentacene derivatives can be explained with different degrees of carrier delocalization being limited by thermal lattice fluctuations. A combination of Hall measurements, optical spectroscopy, and theoretical simulations provides a powerful probe of structure-property relationships at a molecular level.

Flow-induced polymer degradation during ink-jet printing.

We report for the first time evidence of flow-induced polymer degradation during inkjet printing for both poly(methyl methacrylate) (PMMA) and polystyrene (PS) in good solvent. This has significance for the deposition of functional and biological materials. Polymers having Mw either less than 100 kDa or greater than approximately 1,000 kDa show no evidence of molecular weight degradation. The lower boundary condition is a consequence of low Deborah Number De imposed by the printhead geometry and the upper boundary condition due to visco-elastic damping. For intermediate molecular weights the effect is greatest at high elongational strain rate and low solution concentration with higher polydispersity polymers being most sensitive to molecular weight degradation. For low polydispersity samples, PDi ≤ 1.3, chain breakage is essentially centro-symmetric induced either by turbulance or overstretching when the strain rate increases well beyond a critical value, that is the stretching rate is high enough to exceed the rate of relaxation. For higher polydispersity samples chain breakage is consistent with almost random scission along the chain, inferring that the forces required to break the chain are additionally transmitted either by valence bonds, i.e. network chains and junctions or discrete entanglements rather than solely by hydrodynamic interaction.

A rich gallery of carbon dots based photoluminescent suspensions and powders derived by citric acid/urea.

In this study we demonstrate simple guidelines to generate a diverse range of fluorescent materials in both liquid and solid state by focusing on the most popular C-dots precursors, i.e. the binary systems of citric acid and urea. The pyrolytic treatment of those precursors combined with standard size separation techniques (dialysis and filtration), leads to four distinct families of photoluminescent materials in which the emissive signal predominantly arises from C-dots with embedded fluorophores, cyanuric acid-rich C-dots, a blend of molecular fluorophores and a mixture of C-dots with unbound molecular fluorophores, respectively. Within each one of those families the chemical composition and the optical properties of their members can be fine-tuned by adjusting the molar ratio of the reactants. Apart from generating a variety of aqueous dispersions, our approach leads to highly fluorescent powders derived from precursors comprising excessive amounts of urea that is consumed for the build-up of the carbogenic cores, the molecular fluorophores and the solid diluent matrix that suppresses self-quenching effects.

Textile materials inspired by structural colour in nature.

The concept of mimicking structural colour in nature as an alternative to traditional textile coloration techniques would reduce dependency on dyes, pigments and vast quantities of water in the textile supply chain. Structural colours originate from the physical interaction of light with nanoscale structures. This is exhibited in the bodies and wings of certain species of butterfly, beetles and plants. The angular optical effects of the Chrysina gloriosa beetle result from the periodicity due to the cholesteric liquid crystal (CLC) structure adopted by the cells in their exoskeleton. The optical properties of CLCs makes promising applications for optical sensors and anti-counterfeit materials. Application using inkjet printing technology enables designs to be tuned to meet product requirements, and with a hydrophobic treatment challenges associated with a rough surface such as textiles are overcome. Here we report inkjet printing CLC solutions onto hydrophobic pre-treated textiles. CIE L*a*b* values demonstrate the resultant colourful films display a greater degree of colour compared to those on untreated textiles.

Aqueous gels of mixtures of ionic surfactant SDS with pluronic copolymers P123 or F127.

Gel diagrams based on tube inversion and oscillatory rheometry are reported for Pluronic copolymers F127 (E(98)P(67)E(98)) and P123 (E(21)P(67)E(21)) in mixtures with anionic surfactant sodium dodecyl sulfate (SDS). Total concentrations (c, SDS+copolymer) were as high as 50 wt % with mole ratios SDS/copolymer (mr) in the ranges 1-5 (F127) and 1-7 (P123). Temperatures were as high as 90 degrees C. Determination of the temperature dependences of the dynamic moduli served to confirm the gel boundaries from tube inversion and to reveal the high elastic moduli of the gels, e.g., compared at comparable positions in the gel phase, a 50 wt % SDS/P123 with mr = 7 had G' three times that of a corresponding gel of P123 alone. Small-angle X-ray scattering (SAXS) was used to show that the structures of all the SDS/F127 gels were bcc and that the structures of the SDS/P123 gels with mr = 1 were either fcc (c = 30 wt %) or hex (c = 40 wt %). Assignment of structures to SDS/P123 gels with values of mr in the range 3-7 was more difficult, as high-order scattering peaks could be very weak, and at the higher values of c and mr, the SAXS peaks included multiple reflections.

Additional supra-self-assembly of human serum albumin under amyloid-like-forming solution conditions.

Protein aggregation has a multitude of consequences ranging from affecting protein expression to its implication in different diseases. Of recent interest is the specific form of aggregation leading to the formation of amyloid fibrils, structures associated with diseases such as Alzheimer's disease. These fibrils can further associate in other more complex structures such as fibrillar gels, plaques, or spherulitic structures. In the present work, we describe the physical and structural properties of additional supraself-assembled structures of human serum albumin under solution conditions in which amyloid-like fibrils are formed. We have detected the formation of ordered aggregates of amyloid fibrils, i.e., spherulites which possess a radial arrangement of the fibrils around a disorganized protein core and sizes of several micrometers by means of polarized optical microscopy, laser confocal microscopy, and transmission electron microscopy. These spherulites are detected both in solution and embedded in an isotropic matrix of fibrillar gels. In this regard, we have also noted the formation of protein gels when the protein concentration and/or ionic strength exceds a threshold value (the gelation point) as observed by rheometry. Fibrillar gels are formed through intermolecular nonspecific association of amyloid fibrils at a pH far away from the isolectric point of the protein where protein molecules seem to display a "solid-like" behavior due to the existence of non-DLVO (Derjaguin-Landau-Verwey-Overbeck) intermolecular repulsive forces. As the solution ionic strength increases, a coarsening of this type of gel is observed by environmental scanning microscopy. In contrast, at pH close to the protein isoelectric point, particulate gels are formed due to a faster aggregation process, which does not allow substantial structural reorganization to enable the formation of ordered structures. This behavior also additionally corroborates that the existence of particulates might also be a generic property of all polypeptide chains as amyloid fibril formation under suitable conditions.

High performance, acene-based organic thin film transistors.

1,4,8,11-Methyl-substituted 6,13-triethylsilylethynylpentacene shows extended pi-pi overlap when deposited from solution, yielding organic thin film transistors with high and reproducible hole mobility with negligible hysteresis.

All Inkjet-Printed Graphene-Silver Composite Ink on Textiles for Highly Conductive Wearable Electronics Applications.

Inkjet-printed wearable electronic textiles (e-textiles) are considered to be very promising due to excellent processing and environmental benefits offered by digital fabrication technique. Inkjet-printing of conductive metallic inks such as silver (Ag) nanoparticles (NPs) are well-established and that of graphene-based inks is of great interest due to multi-functional properties of graphene. However, poor ink stability at higher graphene concentration and the cost associated with the higher Ag loading in metal inks have limited their wider use. Moreover, graphene-based e-textiles reported so far are mainly based on graphene derivatives such as graphene oxide (GO) or reduced graphene oxide (rGO), which suffers from poor electrical conductivity. Here we report inkjet printing of highly conductive and cost-effective graphene-Ag composite ink for wearable e-textiles applications. The composite inks were formulated, characterised and inkjet-printed onto PEL paper first and then sintered at 150 °C for 1 hr. The sheet resistance of the printed patterns is found to be in the range of ~0.08-4.74 Ω/sq depending on the number of print layers and the graphene-Ag ratio in the formulation. The optimised composite ink was then successfully printed onto surface pre-treated (by inkjet printing) cotton fabrics in order to produce all-inkjet-printed highly conductive and cost-effective electronic textiles.

Layer by Layer Antimicrobial Coatings Based on Nafion, Lysozyme, and Chitosan.

The study focuses on the development of a new family of layer-by-layer coatings comprising Nafion, lysozyme and chitosan to address challenges related to microbial contamination. Circular dichroism was employed to gain insights on the interactions of the building blocks at the molecular level. Quartz crystal microbalance tests were used to monitor in real time the build-up of multilayer coatings, while atomic force microscopy, contact angle and surface zeta potential measurements were performed to assess the surface characteristics of the multilayer assemblies. Remarkably, the nanocoated surfaces show almost 100% reduction in the population of both Escherichia coli and Staphylococcus aureus. The study suggests that Nafion based synergistic platforms can offer an effective line of defence against bacteria, facilitating antimicrobial mechanisms that go beyond the concept of exclusion zone.

Initial Studies Directed toward the Rational Design of Aqueous Graphene Dispersants.

This study presents preliminary experimental data suggesting that sodium 4-(pyrene-1-yl)butane-1-sulfonate (PBSA), 5, an analogue of sodium pyrene-1-sulfonate (PSA), 1, enhances the stability of aqueous reduced graphene oxide (RGO) graphene dispersions. We find that RGO and exfoliated graphene dispersions prepared in the presence of 5 are approximately double the concentration of those made with commercially available PSA, 1. Quantum mechanical and molecular dynamics simulations provide key insights into the behavior of these molecules on the graphene surface. The seemingly obvious introduction of a polar sulfonate head group linked via an appropriate alkyl spacer to the aromatic core results in both more efficient binding of 5 to the graphene surface and more efficient solvation of the polar head group by bulk solvent (water). Overall, this improves the stabilization of the graphene flakes by disfavoring dissociation of the stabilizer from the graphene surface and inhibiting reaggregation by electrostatic and steric repulsion. These insights are currently the subject of further investigations in an attempt to develop a rational approach to the design of more effective dispersing agents for rGO and graphene in aqueous solution.

An Exploration of Behind-the-Ear ECG Signals From a Single Ear Using Inkjet Printed Conformal Tattoo Electrodes.

Wearable sensors placed behind-the-ear are emerging as being very promising for unobtrusive long term monitoring. Factors such as gait, electroencephalography (EEG), and ballistocardiography (BCG) can all be measured from behind-the-ear in a socially acceptable hearing aid based form factor. Previous works have investigated the recording of electrocardiography (ECG) from the ear, but generally with one electrode placed some distance away from the ear itself. This paper uses recently introduced tattoo electrodes to investigate whether ECG components can indeed be measured from behind a single ear. Compared to a reference photophelsmography (PPG) device we show that the fundamental heart beat frequency is present in behind-the-ear ECG only in half of the cases considered. In contrast the second harmonic is present in all records and could allow the extraction of heart rate to within a few beats-per-minute accuracy. Further signal processing work is required to allow the automated extraction of this, particularly when working with short time windows of data, but our results characterize the signal and demonstrate the principle of behind-the-ear ECG collected from a single ear.

Block copolymers for drug solubilisation: relative hydrophobicities of polyether and polyester micelle-core-forming blocks.

Published values of the critical micelle concentration are tabulated for diblock copolymers E(m)P(n), E(m)B(n), E(m)S(n), E(m)L(n), E(m)VL(n) and E(m)CL(n), where E denotes a chain unit derived from ethylene oxide, P from propylene oxide, B from 1,2-butylene oxide, S from styrene oxide, L from dl-lactide, VL from gamma-valerolactone and CL from epsilon-caprolactone, and the subscripts denote average chain lengths. Noting that log(cmc/moldm(-3) is proportional to the standard Gibbs energy of micellisation, the dependence of this quantity on hydrophobic block length (n) is explored for a given E-block length. Superposition of data allows ranking of the hydrophobicities of the chain units. The ratios relative to the least hydrophobic unit are: P : L : B : VL : S : CL = 1 : 4 : 6 : 10 : 12 : 12 Transitions in the slope of log(cmc) versus n are assigned to changes in the unimer-micelle equilibrium and related to the formation of unimolecular micelles and, at high values of n, to the completion of that process. The formation transition is seen in the plots for all the copolymers except the least hydrophobic, E(m)P(n). The completion transition is seen in the plots for E(m)CL(n) and E(m)L(n) copolymers, as these alone include results for copolymers with very lengthy hydrophobic blocks.