Michael J. Eller

Nanoscopic Cylindrical Dual Concentric and Lengthwise Block Brush Terpolymers as Covalent Preassembled High-Resolution and High-Sensitivity Negative-Tone Photoresist Materials

We describe a high-resolution, high-sensitivity negative-tone photoresist technique that relies on bottom-up preassembly of differential polymer components within cylindrical polymer brush architectures that are designed to align vertically on a substrate and allow for top-down single-molecule line-width imaging. By applying cylindrical diblock brush terpolymers (DBTs) with a high degree of control over the synthetic chemistry, we achieved large areas of vertical alignment of the polymers within thin films without the need for supramolecular assembly processes, as required for linear block copolymer lithography. The specially designed chemical compositions and tuned concentric and lengthwise dimensions of the DBTs enabled high-sensitivity electron-beam lithography of patterns with widths of only a few DBTs (sub-30 nm line-width resolution). The high sensitivity of the brush polymer resists further facilitated the generation of latent images without postexposure baking, providing a practical approach for controlling acid reaction/diffusion processes in photolithography.

Noradrenaline-functionalized hyperbranched fluoropolymer-poly(ethylene glycol) cross-linked networks as dual-mode, anti-biofouling coatings.

The strategy of decorating antibiofouling hyperbranched fluoropolymer-poly(ethylene glycol) (HBFP-PEG) networks with a settlement sensory deterrent, noradrenaline (NA), and the results of biofouling assays are presented. This example of a dual-mode surface, which combines both passive and active modes of antibiofouling, works in synergy to improve the overall antibiofouling efficiency against barnacle cyprids. The HBFP-PEG polymer surface, prior to modification with NA, was analyzed by atomic force microscopy, and a significant distribution of topographical features was observed, with a nanoscopic roughness measurement of 110 ± 8 nm. NA attachment to the surface was probed by secondary ion mass spectrometry to quantify the extent of polymer chain-end substitution with NA, where a 3- to 4-fold increase in intensity for a fragment ion associated with NA was observed and 39% of the available sites for attachment were substituted. Cytoskeletal assays confirmed the activity of tethered NA on adhering oyster hemocytes. Settlement assays showed deterrence toward barnacle cyprid settlement, while not compromising the passive biofouling resistance of the surface. This robust strategy demonstrates a methodology for the incorporation of actively antibiofouling moieties onto a passively antibiofouling network.

Targeted surface nanocomplexity: two-dimensional control over the composition, physical properties and anti-biofouling performance of hyperbranched fluoropolymer–poly(ethylene glycol) amphiphilic crosslinked networks

A two-dimensional array of amphiphilic crosslinked networks was prepared by systematic alteration of both the composition of hyperbranched fluoropolymers (HBFPs) and the relative stoichiometries upon crosslinking with poly(ethylene glycol) (PEG). Results of physicochemical, mechanical, surface and biofouling assessment are described in full. The materials were designed to present complex surface topographies, morphologies, and chemical features over nano- and microscopic dimensions to explicitly inhibit microorganism settlement and adhesion. A multi-dimensional, tunable matrix was generated to understand and optimize the composition–structure–property relationships. The thermal properties of the crosslinked networks were analyzed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), where the onset of thermal degradation, overall thermal stability and phase transition temperatures could be controlled based on the formulation. Investigation of the mechanical properties of the coatings in the water-swollen state found that the Youngs modulus, ranging between 10.0 and 121 MPa, was dependent on both the wt% of PEG crosslinker and chemical composition of the HBFP. This result, on average, gives Youngs moduli an order of magnitude larger than that previously reported for HBFP–PEG networks. Use of atomic force microscopy (AFM) provided insight into the nanoscale topography of the networks. Interestingly, it was observed that for all networks, surface roughness increased with water swelling going from an average of 115 ± 49 nm (dry) to 214 ± 106 nm (swelled) RMS roughness. Probing the surface chemistry by optical tensiometry revealed an increase in the static water contact angle by as much as 40° after water swelling. These two findings display a counter-intuitive increase of the surface hydrophobicity. Secondary ion mass spectrometry (SIMS) confirmed migration of hydrophobic fluorocarbon units to the surface by quantifying a 24% increase in fluorine species ejected from a dry versus water-swollen surface. Selected formulations of HBFP–PEG that demonstrated complex surface features and an overall high mechanical strength were tested in biological assays and all surfaces (3 formulations × 12 replicates) completely resisted the settlement of barnacle cyprids (Balanus amphitrite). Diatoms (Navicula incerta) were two- to three-times more easily removed from the HBFP–PEG surfaces compared to a homogeneous polydimethylsiloxane elastomer (PDMSe) standard surface. In contrast, algal spores (Ulva linza) were able to colonize the surfaces and were more difficult to remove in comparison to the PDMSe standard, pointing to the challenges associated with the development of a single material that is capable of broad anti-biofouling performance.

Analysis of Native Biological Surfaces Using a 100 kV Massive Gold Cluster Source

In the present work, the advantages of a new, 100 kV platform equipped with a massive gold cluster source for the analysis of native biological surfaces are shown. Inspection of the molecular ion emission as a function of projectile size demonstrates a secondary ion yield increase of ~100× for 520 keV Au(400)(4+) as compared to 130 keV Au(3)(1+) and 43 keV C(60). In particular, yields of tens of percent of molecular ions per projectile impact for the most abundant components can be observed with the 520 keV Au(400)(4+) probe. A comparison between 520 keV Au(400)(4+) time-of-flight-secondary ion mass spectrometry (TOF-SIMS) and matrix assisted laser desorption ionization-mass spectrometry (MALDI-MS) data showed a similar pattern and similar relative intensities of lipid components across a rat brain sagittal section. The abundant secondary ion yield of analyte-specific ions makes 520 keV Au(400)(4+) projectiles an attractive probe for submicrometer molecular mapping of native surfaces.

Directing Self-Assembly of Nanoscopic Cylindrical Diblock Brush Terpolymers into Films with Desired Spatial Orientations: Expansion of Chemical Composition Scope

Diblock brush terpolymers (DBTs) with different fluorinated methacrylate-based block segments are synthesized through sequential ring-opening metathesis polymerizations and are used to prepare polymer thin films with predictable film thicknesses. These DBTs exhibit preferable substrate vertical alignments within the films, induced by the relatively lower surface energy of the fluorinated structural components, together with the overall cylindrical morphology of the brush architecture.

Quantitative Label-Free Characterization of Avidin-Biotin Assemblies on Silanized Glass

In this study, a time-of-flight secondary ion mass spectrometer TOF-SIMS, operating in the event-by-event bombardment/detection mode was used to characterize avidin-biotin assemblies on silane-modified glass substrates. SIMS was used to analyze several variants of the biointerface, including avidin physically adsorbed on a monofunctional acryl silane surface and covalently attached on monofunctional (amine terminated) and bifunctional (amine and acryl terminated) silanes. The goal of these studies was to determine density of avidin and biotin layers chemically or physically adsorbed on silanized glass substrate. An individual impact of a C(60) projectile used in this study creates a hemispherical crater (∼10 nm in diameter) and emits large numbers of secondary ions from the same nanovolume. Thus, a single impact enables one to unfold distinct secondary ions that span the thickness of the assembled film. This method was used to monitor the presence of glass, silane, and protein ions and to estimate the thickness and density of the avidin layer. In addition, we employed the double coincidence mass spectrometry approach to identify ions coemitted from a specific stratum of the biointerface. This approach was used to determine density of biotin and avidin immobilization while eliminating interferences from isobaric ions that originated from other constituents on the surface. Overall, novel TOF-SIMS quantitative approaches employed here were useful for examining complex biointerfaces and determining both lateral and in depth composition of the film.

SIMS instrumentation and methodology for mapping of co-localized molecules.

We describe an innovative mode for localizing surface molecules. In this methodology, individual C60 impacts at 50 keV are localized using an electron emission microscope, EEM, synchronized with a time-of-flight mass spectrometer for the detection of the concurrently emitted secondary ions. The instrumentation and methodologies for generating ion maps are presented. The performance of the localization scheme depends on the characteristics of the electron emission, those of the EEM and of the software solutions for image analysis. Using 50 keV C60 projectiles, analyte specific maps and maps of co-emitted species have been obtained. The individual impact sites were localized within 1-2 μm. A distinctive feature of recording individual impacts is the ability to identify co-emitted ions which originate from molecules co-located within ~10 nm.

Bottom-up/top-down, high-resolution, high-throughput lithography using vertically assembled block bottle brush polymers

Abstract. We describe a novel deterministic bottom-up/top-down approach to sub-30-nm photolithography using a film composed of assembled block brush polymers of highly uniform composition and chain length. The polymer architecture consists of a rigid backbone of polymerized norbornene, each linked to flexible short side brush chains. The resultant bottle brush topology has a cylindrical shape with short brush chains arranged concentrically around the backbone, in which the cylinder radius is determined by the number of monomers within the brush fragment, while the cylinder length is determined by the degree of backbone polymerization. The modularity of the synthetic system allows a wide diversity of lithographically useful monomers, sequencing, dimension, and property variation. Sequential grafting of presynthesized blocks allows for facile formation of either concentric or lengthwise block copolymers. Placement of brush chains of different compositions along different regions of the cylinder, along with variation of the relative concentric and lengthwise dimensions, provides mechanisms to align and control placement of the cylinders. These polymers are compatible with photoacid generators and crosslinker functionality. Our results are consistent with a model that the bottle brush polymers assemble (bottom-up) in the film to yield a forest of vertically arranged cylindrical block brush polymers, with the film thickness determined by the coherence lengths of the cylinders. Subsequent imaging via electron beam (e-beam) or optical radiation yields a (top-down) mechanism for acid catalyzed crosslinking of adjacent cylinders. Uncrosslinked cylinders are removed in developer to yield negative photoresist patterns. Exposure doses are very low and throughputs are amenable to the requirements of extreme ultraviolet lithography. The limiting resolution with e-beam exposure is potentially about two cylinder diameters width (<8  nm), with the smallest observed patterns approaching 10 nm.

The collision of a hypervelocity massive projectile with free-standing graphene: Investigation of secondary ion emission and projectile fragmentation

We present here the study of the individual hypervelocity massive projectiles (440-540 keV, 33-36 km/s Au4004+ cluster) impact on 1-layer free-standing graphene. The secondary ions were detected and recorded separately from each individual impact in the transmission direction using a time-of-flight mass spectrometer. We observed C1-10± ions emitted from graphene, the projectiles which penetrated the graphene, and the Au1-3± fragment ions in mass spectra. During the projectile-graphene interaction, the projectile loses ∼15% of its initial kinetic energy (∼0.18 keV/atom, 72 keV/projectile). The Au projectiles are neutralized when approaching the graphene and then partially ionized again via electron tunneling from the hot rims of the holes on graphene, obtaining positive and negative charges. The projectile reaches an internal energy of ∼450-500 eV (∼4400-4900 K) after the impact and then undergoes a ∼90-100 step fragmentation with the ejection of Au1 atoms in the experimental time range of ∼0.1 μs.

Bottom-up/top-down high resolution, high throughput lithography using vertically assembled block bottle brush polymers

We describe a novel deterministic bottom-up / top-down approach to sub-30 nm photolithography using a film composed of assembled block brush polymers of highly uniform composition and chain length. The polymer architecture consists of a rigid backbone of polymerized norbornene, each linked to flexible short side brush chains. The resultant ‘bottle brush’ topology has a cylindrical shape with short brush chains arranged concentrically around the backbone, in which the cylinder radius is determined by the number of monomers within the brush fragment, while the cylinder length is determined by the degree of backbone polymerization. The modularity of the synthetic system allows a wide diversity of lithographically useful monomers, sequencing, dimension and property variation. Sequential grafting of pre-synthesized blocks allows for facile formation of either concentric or lengthwise block copolymers. Placement of brush chains of different compositions along different regions of the cylinder, along with variation of the relative concentric and lengthwise dimensions, provides mechanisms to align and control placement of the cylinders. These polymers are compatible with photoacid generators (PAGs) and crosslinker functionality. Our results are consistent with a model that the bottle brush polymers assemble (bottom-up) in the film to yield a ‘forest’ of vertically arranged cylindrical block brush polymers, with the film thickness determined by the coherence lengths of the cylinders. Subsequent imaging via electron beam (EB or ebeam) or optical radiation yields a (top-down) mechanism for acid catalyzed crosslinking of adjacent cylinders. Uncrosslinked cylinders are removed in developer to yield negative photoresist patterns. Exposure doses are very low and throughputs are amenable to the requirements of Extreme Ultraviolet (EUV) lithography. The limiting resolution with ebeam exposure is potentially about two cylinder diameters width (< 8 nm), with the smallest observed patterns approaching 10 nm.