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The scope of impact that the coronavirus SARS-CoV-2 has had and continues to have on life, society, and the world as we know it will be debated for years to come. One thing is for certain, scientists, engineers, clinicians, and researchers around the globe rallied to heed the call for innovation, particularly in the field of materials science. In this special issue of MRS Bulletin, we feature six articles, two of which showcase primary consumable materials research and development, along with four review articles highlighting materials innovation over the last 18 months in diagnostics, prevention, and treatment of SARS-CoV-2 infection. Graphic abstract

Gold nanoparticles play an important role in plasmonic arrays, including, but not limited to, photovoltaic, biomedical, sensing, optical, and catalytic applications. For plasmonic arrays, control o...

Copper-doped beryllium spheres are an attractive ablator for inertial confinement fusion experiments. Beryllium spheres are made by sputtering beryllium onto spherical plastic mandrels which must t...

Solid-state diffusional dewetting is utilized to produce randomly oriented ensembles of nanoparticles on large scales, which then function as dry etching masks for generation of durable metasurfaces for antireflective and metaoptics applications.

Carbon nanotubes (CNTs) possess exceptional mechanical properties, surpassing stiffness and strength metrics of common materials such as steel alloys by 100 × at the nanoscale. However, when myriads of individual CNTs are bundled together into macroscopic ensembles like fibers or sheets, the result is a 100-fold drop in strength compared to its individual components. Here we present a general strategy aimed to close this gap in property scaling. By using vapor-phase polymerization of a crosslinkable polymer, we reinforced the weak interlinkages among individual CNTs within both yarns and sheets to promote a better transference of mechanical load across the structure. After the treatment, dry-spun, low-density 2.3 μm thin yarns increased their elastic moduli by at least 300%, and free-standing CNT sheets exhibited a 10 × boost. In-situ synchrotron small-angle X-ray scattering revealed that polymer-reinforced yarns undergo limited CNT bundle rearrangement when subjected to tensile loads compared to pristine yarns. This evidence supports the hypothesis that the polymer hinders CNTs slippage, the root cause of the poor scaling of mechanical properties in these materials. While we demonstrated this reinforcement method for CNT structures, it is not specific to CNTs and could be used in a wide variety of other hierarchical nanostructured ensembles.

Reuse of filtering facepiece respirators (FFRs, commonly referred to as N95s) normally meant for single use has become common in healthcare facilities due to shortages caused by the COVID-19 pandemic. Here, we report that murine hepatitis coronavirus initially seeded on FFR filter material is inactivated (6 order of magnitude reduction as measured by median tissue culture infective dose, TCID50) after dry heating at 75°C for 30 min. We also find that the quantitative fit of FFRs after heat treatment at this temperature, under dry conditions or at 90% relative humidity, is not affected by single or 10 heating cycles. Previous studies have reported that the filtration efficiency of FFRs is not negatively impacted by these heating conditions. These results suggest that thermal inactivation of coronaviruses is a potentially rapid and widely deployable method to reuse N95 FFRs in emergency situations where reusing FFRs is a necessity and broad-spectrum sterilization is unavailable. However, we also observe that a radiative heat source (e.g. an exposed heating element) results in rapid qualitative degradation of the FFR. Finally, we discuss differences in the results reported here and other recent studies investigating heat as a means to recycle FFRs. These differences suggest that while our repeated decontamination cycles do not affect FFR fit, overall wear time and the number of donning/doffing cycles are important factors that likely degrade FFR fit and must be investigated further.

We present a method for producing spatially patterned glass engraved meta-surfaces, which is scalable, has high mechanical stability and high laser damage durability, and thus promising for ultra-thin optics implementation for high-power lasers. The process is based on laser raster-scan of a thin metal film on a glass, followed by dry-etching and removal of the metal mask. We present fabricated structures, characterization of their optical performance, mechanical stability and laser damage performance.

SummaryRe-use of filtering facepiece respirators (FFRs, commonly referred to as N95s) normally meant for single use only is becoming common in healthcare facilities due to shortages caused by the COVID19 pandemic. Here we report that mouse hepatitis virus (MHV) initially seeded on FFR filter material is inactivated (6 log reduction as measured by 50% tissue culture infective dose (TCID50)) after dry heating at 75 ºC for 30 minutes. We also find that the quantitative fit of FFRs after heat treatment at this temperature, under dry conditions or at 90% relative humidity, is not affected by single or ten heating cycles. Previous studies have reported that the filtration efficiency of FFR filters is not negatively impacted by these heating conditions. These results suggest that thermal inactivation of coronaviruses is a potentially rapid and widely deployable method to re-use N95 FFRs in emergency situations where re-using FFRs is a necessity and broad-spectrum sterilization is unavailable. However, we also found that a heat source that emits radiation (e.g., an exposed heating element) results in rapid qualitative degradation of the FFR. Finally, we discuss differences in the results reported here and other recent studies investing heat as a means to recycle FFRs and suggest that overall wear time and donning/doffing cycles are important factors that need to be considered.

We present a simple and scalable method for the production of optics with incorporated metasurfaces, resulting in durable all-dielectric based meta-optics. The scalability and robustness of this method overcome limitations imposed by current technology when fabricating metasurfaces for high power laser applications, while the simplicity of the fabrication process makes it an exciting technique for metasurface generation. This talk will describe the method, show resultant fabricated metasurfaces and the sensitivity introduced by processing parameters – i.e. control over generated surfaces, and discuss the laser damage performance of these engineered large-scale metasurfaces.

Experiments and analysis in the 2 years since the 2015 Target Fabrication Meeting have resulted in further evolution of the requirements for high-performance layered implosions. This paper is a status update on the experimental program and supporting modeling, with emphasis on the implications for fabrication requirements. Previous work on the capsule support has continued, with various other support options being explored in experiments and modeling. Work also continues on ablator composition nonuniformities, with important new results from CH experiments on Omega, and the first three-dimensional X-ray transmission measurements of Be capsules on the National Ignition Facility. Work on hohlraums continues to include near-vacuum hohlraums and U hohlraums without a gold lining. Overall, the understanding that has been achieved, along with the progress in fabrication technology, represents good continuing progress toward the goal of fusion in the laboratory.

We report two examples of initiated chemical vapor deposition (iCVD) polymers being developed for use in laser targets for high peak-power laser systems. First, we show that iCVD poly(divinylbenzene) is more photo-oxidatively stable than the plasma polymers currently used in laser targets. Thick layers (10–12 μm) of this highly crosslinked polymer can be deposited with near-zero intrinsic film stress. Second, we show that iCVD epoxy polymers can be crosslinked after deposition to form thin adhesive layers for assembling precision laser targets. The bondlines can be made as thin as ~ 1 μm, approximately a factor of 2 thinner than achievable using viscous resin-based adhesives. These bonds can withstand downstream coining and stamping processes.

Although closely related to polystyrene, poly(divinylbenzene) (PDVB) has found limited utility due to the difficulties associated with its synthesis. As a highly cross-linked polymer, PDVB is infusible and insoluble and thus nearly impossible to shape into films by either melt or solvent-based processes. Here, we report the initiated chemical vapor deposition (iCVD) of nearly stress-free, highly transparent, free-standing films of PDVB up to 25 μm thick. Films initially grow under tensile intrinsic stress but become more compressive with thickness and eventually converge to zero-stress values once they reach ≥10 μm in thickness. Upon initial heating, the evaporative loss of unreacted monomer left in the polymer matrix induces between 35 and 45 MPa of tensile stress in the films. Afterward, subsequent heating cycles induce reversible stress and film expansion behaviors. We estimate the degree of cross-linking to be 44%, resulting in high thermal stability (up to 300 °C) and mechanical stiffness (Young's modulus of 5.2 GPa). The low stress combined with high cross-linking makes iCVD PDVB an excellent candidate for protective coatings in harsh environments.

A key challenge for metasurface research is locally controlling at will the nanoscale geometric features on meter-scale apertures. Such a technology is expected to enable large aperture meta-optics and revolutionize fields such as long-range imaging, lasers, laser detection and ranging (LADAR), and optical communications. Furthermore, these applications are often more sensitive to light-induced and environmental degradation, which constrains the possible materials and fabrication process. Here, we present a relatively simple and scalable method to fabricate a substrate-engraved metasurface with locally printed index determined by induced illumination, which, therefore, addresses both the challenges of scalability and durability. In this process, a thin metal film is deposited onto a substrate and transformed into a mask via local laser-induced dewetting into nanoparticles. The substrate is then dry-etched through this mask, and selective mask removal finally reveals the metasurface. We show that masking by the local nanoparticle distribution, and, therefore, the local index, is dependent on the local light-induced dewetting temperature. We demonstrate printing of a free-form pattern engraved into a fused silica glass substrate using a laser raster scan. Large-scale spatially controlled engraving of metasurfaces has implications on other technological fields beyond optics, such as surface fluidics, acoustics, and thermomechanics.

We explored templating effects of various materials for hydrogen (H2 and D2) solidification by measuring the degree of supercooling required for liquid hydrogen to solidify below each triple point....

Experiments and analysis in the 3 years since the 2012 Target Fabrication Meeting have resulted in significant improvement in understanding of the requirements for high-performance layered implosio...

Complex and precise research targets are required for the inertial confinement fusion (ICF) experiments conducted at the National Ignition Facility. During the National Ignition Campaign (NIC) the ...

Amorphous hydrogenated carbon (a-C:H), a polymer-like network typically synthesized by plasma chemical vapor deposition, has long been known to exhibit optical absorption of visible light (λ > 400 nm). Here, we report that this absorption is accompanied by rapid photo-oxidation (within minutes) that behaves in most respects like classic polymer photo-oxidation with the exception that it occurs under visible light illumination rather than ultraviolet illumination. Lower plasma power during deposition produces a-C:H that is less crosslinked, is less absorptive, has longer photoluminescence lifetimes, and has a slower photo-oxidative degradation than a-C:H deposited at higher plasma power. The optical gap of the material deposited here is ∼2.5 eV, and we correspondingly observe photo-oxidation at photon energies of 2.7 and 3.1 eV. A reduced photo-oxidative response is observed at sub-gap energies, suggesting that defect states or absorption tails enable absorption at lower energies. The photo-oxidation depends on both the total accumulated dose as well as the intensity of the illumination, suggesting either a transport limitation of O2 in the a-C:H or a complex reaction pathway. Under typical laboratory lighting conditions, plasma CVD a-C:H continues to photo-oxidize for more than 20 weeks, demonstrating that any characterization of the long-term behavior of a-C:H under use conditions requires control of not only atmospheric conditions but also ambient lighting environment.

A critical component for all high-power laser systems that is particularly susceptible to laser damage is the antireflective coating, which maximizes energy transmission and minimizes scattered and stray light. We demonstrate the ability to generate substrate-engraved nanostructured surfaces (NS) for scalable and designable antireflective (AR) coatings that are monolithic to the substrate and can handle peak power levels comparable to the bulk material. Experimentally measured reflectance from these fabricated structures has validated our effective index theory-based transmission matrix model, demonstrating the designability of the AR properties. Upon exposure to sufficiently high fluences, a new mode of damage, nanostructured surface damage, has been observed and is likely the result of thermally driven material reflow accompanied by plasma initiation on the nanostructured surface. At 1053 nm, nanostructured surface damage onsets at 39 J / c m 2 with sample cleaning and 74 J / c m 2 after laser conditioning—very close to the reference substrate at 81 J / c m 2 . At 351 nm we show damage onset of 30 J / c m 2 , with reference substrate material damage onset of 47 J / c m 2 . Therefore, damage is close to the bulk material and represents an improvement with respect to other methods. The nanostructured surfaces were found to be mechanically durable and able to withstand cleaning procedures with sonication. Under normal incidence mechanical testing with a 200 µm radius indenter tip, the AR performance of these nanostructured surfaces was minimally impacted at pressures orders of magnitude higher than an average fingerprint pressure—indicating that incidental handling contact will not affect NS structures. Mechanical damage is attributed to plastic compression, not fracturing of the NS features. We demonstrate for the first time, to the best of our knowledge, that NS AR coatings, despite being rich in etched surface features, can tolerate laser fluences comparable to unprocessed optical surfaces. Furthermore, laser-damage features of NS indicate a unique non-growing failure mode whereby following absorption the featureless damage site does not precipitate future damage growth, reducing considerably the burdens for managing optics processing in high-power laser systems.

Absorbing defects such as fractures and contaminants are a leading cause of surface damage in nanosecond pulsed lasers. Etching such defects has proven to be a powerful technique for increasing the laser damage threshold of fused silica, but to date no etching process has been reported for potassium dihydrogen phosphate (KH2PO4 or KDP) or its deuterated analog (DKDP). We show that physical dissolution in water is a viable strategy for etching DKDP surfaces but surface-redeposited byproducts can serve as laser damage precursors. We use a water-in-oil microemulsion to etch engineered surface fractures in DKDP. Etching widens surface fractures laterally and decreases their optical activity, as measured by photoluminescence. The removal of 1 μm of the surface of a DKDP crystal increases the laser damage threshold (λ = 355 nm, 7 ns) of the engineered surface fractures by 2-4 J/cm2 (15-30%).

The U.S. indirect drive inertial confinement fusion (ICF) program uses glow discharge polymer (GDP) as one of the ablator materials for the ICF experiments at the National Ignition Facility (NIF). The performance of those implosions may be adversely affected by photoactivated uptake of oxygen impurities in the surface of the GDP ablator. These impurities can induce significant perturbations in the shock waves generated in the ablator. These perturbed shocks generate mass modulations that are amplified by Rayleigh-Taylor (RT) instability and reduce the performance of the implosions. Here we report on experiments that provide a quantitative connection between photoactivated oxygen uptake in GDP samples and modulations in shock velocities in the samples. The observed shock nonuniformity confirms the hypothesis that irregular oxygenation is a competent seed for the RT and can have a significant effect on NIF GDP implosions.

Hypothesis The dynamic nature of the oil-water interface allows for sequestration of material within the dispersed domains of a microemulsion. Microstructural changes should therefore change the dissolution rate of a solid surface in a microemulsion. We hypothesize that microstructural changes due to formulation and cavitation in an acoustic field will enable control over solid dissolution rates. Experiments Water-in-oil microemulsions were formulated using cyclohexane, water, Triton X-100, and hexanol. The microstructure and solvation properties of Winsor Type IV formulations were characterized. Dissolution rates of KH2PO4 (KDP), were measured. A kinetic analysis isolated the effect of the microstructure, and rate enhancements due to cavitation effects on the microstructure were characterized by measuring dissolution rates in an ultrasonic field. Findings Dispersed aqueous domains of 2–6 nm radius dissolve a solid block of KDP at 0–10 nm/min. Dissolution rate is governed not by the domain-surface collision frequency but rather by a dissolution probability per domain-surface encounter. Higher probabilities are correlated with larger domains. Rapid and reversible dissolution rate increases of up to 270× were observed under ultrasonic conditions, with

Plasma polymers are often limited by their susceptibility to spontaneous and photo-oxidation. We show that the unusual photoluminescence (PL) behavior of a plasma polymer of trans-2-butene is correlated with its photoluminescence strength. These photo-processes occur under blue light illumination (λ=405 nm), distinguishing them from traditional ultraviolet degradation of polymers. These photo-active defects are likely formed during the plasma deposition process and we show that a polymer synthesized using initiated (i)CVD, non-plasma method, has 1000× lower PL signal and enhanced photo-stability. In conclusion, non-plasma methods such as iCVD may therefore be a route to overcoming material aging issues that limit the adoption of plasma polymers.

In a series of studies related to laser-induced damage of optical materials and deposition of plastics, we discovered a broadly emitting photoluminescence with fast lifetimes that we termed quasicontinuum photoluminescence (QC-PL). Here, we suggest that a high density of optically active defects leads to QC-PL, where interactions between defects affect the temporal and spectral characteristics of both excitation and emission. We develop a model that predicts the temporal characteristics of QC-PL, based on energy transfer interactions between high densities of defects. Our model does not explain all spectral broadening and redshifts found in QC-PL, since we do not model spectral changes in defects due to proximity to other defects. However, we do provide an example of a well-defined system that exhibits the QC-PL characteristics of a distribution in shortened lifetimes and broadened, redshifted energy levels: an organic chromophore (fluorescein) that has been dried rapidly on a fused silica surface. Recently, we showed that regions of fused silica exposed to up to 1 billion high-fluence laser shots at 351 rm nm at subdamage fluences exhibit significant transmission losses at the surface. Here, we find that these laser-exposed regions also exhibit QC-PL. Increases in the density of induced defects on these laser-exposed surfaces, as measured by the local transmission loss, lead to decreases in the observed lifetime and redshifts in the spectrum of the QC-PL, consistent with our explanation for QC-PL. We have found QC-PL in an increasing variety of situations and materials, and we believe it is a phenomenon commonly found on surfaces and nanostructured materials.

We have demonstrated the world's highest average power, fully diode-pumped, petawatt-class peak power laser, the High-repetition-rate Advanced Petawatt Laser System (HAPLS) [1-3]. These first commissioning results at 16J (stretched) at 3%Hz fully validate projected performance of 30J/30fs (>1PW) at 10Hz. The laser has been operated at this intermediate level at Lawrence Livermore National Laboratory to demonstrate integrated performance of all subsystems and provide benchmarking data to laser performance models before further increasing energy and peak power. Data was obtained during multiple campaigns, exceeding several hours of run time, and a snapshot of 60min of data is shown in Fig. 1. The average pump laser 1ω (1053nm) energy was 97J with an rms stability of 0.7%, 2ω (527nm) energy at the Ti:sapphire power amplifier was 62J, and the average stretched short pulse energy was 16J. A full-aperture diagnostic suite allows simultaneous, single-shot measurement of energy, spectrum, beam quality, and pulse duration at full repetition rate. Single-shot SPIDER retrieved pulse shapes (Fig. 1 inset) with an average pulse duration over 12000 consecutive shots of 28.6fs (rms=1.4fs). The mean pulse duration is consistent with the measured spectral bandwidth and is ∼1.2× the transform limit. All results shown are raw data without filtering or averaging, demonstrating the exceptional pulse characteristics, repeatability, and stability of the entire laser system.

Various ceria and colloidal silica polishing slurries were used to polish fused silica glass workpieces on a polyurethane pad. Characterization of the slurries’ particle size distribution (PSD) (using both ensemble light scattering and single particle counting techniques) and of the polished workpiece surface (using atomic force microscopy) was performed. The results show the final workpiece surface roughness is quantitatively correlated with the logarithmic slope of the distribution function for the largest particles at the exponential tail end of the PSD. Using the measured PSD, fraction of pad area making contact, and mechanical properties of the workpiece, slurry, and pad as input parameters, an Ensemble Hertzian Gap (EHG) polishing model was formulated to estimate each particle’s penetration, load, and contact zone. The model is based on multiple Hertzian contact of slurry particles at the workpiece–pad interface in which the effective interface gap is determined through an elastic load balance. Separately, ceria particle static contact and single pass sliding experiments were performed showing ~1-nm depth removal per pass (i.e., a plastic type removal). Also, nanoindentation measurements on fused silica were made to estimate the critical load at which plastic type removal starts to occur (Pcrit~5 3 10 � 5 N). Next the EHG model was extended to create simulated polished surfaces using the Monte Carlo method where each particle (with the calculated characteristics described above) slides and removes material from the silica surface in random directions. The polishing simulation utilized a constant depth removal mechanism (i.e., not scaling with particle size) of the elastic deformation zone cross section between the particle and silica surface, which was either 0.04 nm (for chemical removal) at low loads ( Pcrit). The simulated surfaces quantitatively compare well with the measured rms roughness, power spectra, surface texture, absolute thickness material removal rate, and load dependence of removal rate.

Capsule ablators are precision hollow spheres used in inertial confinement fusion targets used in high-peak-power laser systems such as the National Ignition Facility. These capsules have high surf...

Gold nanorods (GNRs) stabilized with cetyltrimethylammonium bromide (CTAB) and GNR functionalized via a ligand exchange method with either thiolated polyethylene glycol (PEG(5000)) or mercaptohexadecanoic acid (MHDA) were investigated for their stability in biological media and subsequent toxicological effects to HaCaT cells. GNR-PEG and GNR-MHDA exhibited minimal effects on cell proliferation, whereas GNR-CTAB reduced cell proliferation significantly due to the inherent toxicity of the cationic surfactant to cells. Cell uptake studies indicated relatively low uptake for GNR-PEG and high uptake for GNR-MHDA. Reverse transcriptase polymerase chain reaction (RT-PCR) revealed that GNR-PEG induced less significant and unique changes in the transcription levels of 84 genes related to stress and toxicity compared to GNR-MHDA. The results demonstrate that, although cell proliferation was not affected by both particles, there is a significant difference in gene expression in GNR-MHDA exposed cells, suggesting long-term implications for chronic exposure.

Despite the extensive work done to characterize and improve the smoothness of ablator materials used in inertial confinement fusion (ICF), features indicative of seeded instability growth in these materials are still observed. A two-dimensional imaging velocimetry technique has been used on Omega to measure the velocity non-uniformities of shock fronts launched by indirect drive in the three ablator materials of current interest, glow-discharge polymer, beryllium, and high-density carbon ablators. Observed features are deviations from shock front planarity with amplitudes of a few tens of nanometers, local velocity variations of a few tens of m/s, and transverse spatial scales ranging from 5 to 200 μm. These data will help develop a full understanding of the effects of surface topography, dynamic material response, and internal heterogeneities on the stability of ICF capsules. For all three ablators, we have quantified perturbations at amplitudes that can dominate conventional surface roughness seeds to hydrodynamic instability.Despite the extensive work done to characterize and improve the smoothness of ablator materials used in inertial confinement fusion (ICF), features indicative of seeded instability growth in these materials are still observed. A two-dimensional imaging velocimetry technique has been used on Omega to measure the velocity non-uniformities of shock fronts launched by indirect drive in the three ablator materials of current interest, glow-discharge polymer, beryllium, and high-density carbon ablators. Observed features are deviations from shock front planarity with amplitudes of a few tens of nanometers, local velocity variations of a few tens of m/s, and transverse spatial scales ranging from 5 to 200 μm. These data will help develop a full understanding of the effects of surface topography, dynamic material response, and internal heterogeneities on the stability of ICF capsules. For all three ablators, we have quantified perturbations at amplitudes that can dominate conventional surface roughness seeds to h...

Chemical Vapor Deposition (CVD) methods significantly augment the capabilities of traditional surface modification techniques for designing polymeric surfaces. In CVD polymerization, the monomer(s) are delivered to the surface through the vapor phase and then undergo simultaneous polymerization and thin film formation. By eliminating the need to dissolve macromolecules, CVD enables insoluble polymers to be coated and prevents solvent damage to the substrate. Since de-wetting and surface tension effects are absent, CVD coatings conform to the geometry of the underlying substrate. Hence, CVD polymers can be readily applied to virtually any substrate: organic, inorganic, rigid, flexible, planar, three-dimensional, dense, or porous. CVD methods integrate readily with other vacuum processes used to fabricate patterned surfaces and devices. CVD film growth proceeds from the substrate up, allowing for interfacial engineering, real-time monitoring, thickness control, and the synthesis of films with graded composition. This article focuses on two CVD polymerization methods that closely translate solution chemistry to vapor deposition; initiated CVD and oxidative CVD. The basic concepts underlying these methods and the resultant advantages over other thin film coating techniques are described, along with selected applications where CVD polymers are an enabling technology., Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Contract DAAD-19-02-D-0002)

Bifunctional surfaces are micropatterned using a self-aligned, dual-purpose lithographic mask and pairs of conformally deposited iCVD polymers. A first layer is deposited, then physically masked and etched in oxygen plasma. A second layer is deposited with the mask still in place. Lift-off reveals the micropatterned surface. The thicknesses of the two layers are independently controlled so that the resultant surface displays both chemical and topographical contrast. The patterning scheme is independent of the polymers used and order of deposition. We use this scheme to create surfaces that spatially confine microcondensation, as well as chemical functionality. We also demonstrate microwells whose depth can be altered in response to a water stimulus.

Chemical vapor deposition (CVD) polymerization utilizes the delivery of vapor-phase monomers to form chemically well-defined polymeric films directly on the surface of a substrate. CVD polymers are desirable as conformal surface modification layers exhibiting strong retention of organic functional groups, and, in some cases, are responsive to external stimuli. Traditional wet-chemical chain- and step-growth mechanisms guide the development of new heterogeneous CVD polymerization techniques. Commonality with inorganic CVD methods facilitates the fabrication of hybrid devices. CVD polymers bridge microfabrication technology with chemical, biological, and nanoparticle systems and assembly. Robust interfaces can be achieved through covalent grafting enabling high-resolution (60 nm) patterning, even on flexible substrates. Utilizing only low-energy input to drive selective chemistry, modest vacuum, and room-temperature substrates, CVD polymerization is compatible with thermally sensitive substrates, such as paper, textiles, and plastics. CVD methods are particularly valuable for insoluble and infusible films, including fluoropolymers, electrically conductive polymers, and controllably crosslinked networks and for the potential to reduce environmental, health, and safety impacts associated with solvents. Quantitative models aid the development of large-area and roll-to-roll CVD polymer reactors. Relevant background, fundamental principles, and selected applications are reviewed.

Smooth surfaces with compositional heterogeneities at a molecular-length scale are presented with the goal of disrupting surface-protein interactions. These surfaces are synthesized by utilizing photoinitiated chemical vapor deposition (piCVD) to deposit thin films of random copolymers consisting of highly hydrophilic and highly hydrophobic comonomers. Swellability, wettability, and surface roughness could be systematically controlled by tuning the copolymer composition. The surface composition was dynamic, and the surface reconstructed based on the hydration state of the film. Proteins adsorbed to the copolymer films less readily than to either of the respective homopolymers, indicating a synergistic effect resulting from the random copolymer presenting molecular-scale compositional heterogeneity. These results provide direct evidence that protein adsorption can be disrupted by such surfaces and a simple analytical model suggests that the heterogeneities occur over areas encompassing 4-5 repeat units of the polymer. The synthetic method used to create these films can be used to coat arbitrary geometries, enabling practical utility in a number of applications.

Colloidal lithography, a popular inexpensive alternative to conventional lithography, uses two−dimensional self-assembled monolayer arrays of colloidal nanoparticles as a lithographic template. Combined with initiated chemical vapor deposition (iCVD), which offers unprecedented opportunity for producing grafted polymeric layers, this work demonstrates a generic “bottom-up” process as an inexpensive, simple, and environmentally friendly technique for creating robust well-ordered arrays of functional patterned polymeric nanostructures up to 500 nm in height. These grafted “nanobowl” patterns are produced for a broad material set of functional organic, fluorinated, and silicon containing polymers. These polymers fully retain the organic functionality of their monomeric precursors, are free of wetting defects, and are robustly tethered to the underlying substrate as shown by their ability to withstand aggressive solvent. Furthermore, using this method we pattern a novel low dielectric constant polymer down to...

Colloidal lithography, a popular inexpensive alternative to conventional lithography, uses two-dimensional self-assembled monolayer arrays of colloidal nanoparticles as a lithographic template. Combined with initiated chemical vapor deposition (iCVD), which offers unprecedented opportunity for producing grafted polymeric layers, this work demonstrates a generic "bottom-up" process as an inexpensive, simple, and environmentally friendly technique for creating robust well-ordered arrays of functional patterned polymeric nanostructures up to 500 nm in height. These grafted "nanobowl" patterns are produced for a broad material set of functional organic, fluorinated, and silicon containing polymers. These polymers fully retain the organic functionality of their monomeric precursors, are free of wetting defects, and are robustly tethered to the underlying substrate as shown by their ability to withstand aggressive solvent. Furthermore, using this method we pattern a novel low dielectric constant polymer down to 25 nm without the need for environmentally harmful solvents.

Several property requirements have led to the modification of hydrogels by incorporating functional groups. The current work seeks to achieve graded functional group incorporation into hydrogel thin films using the one-step technique of photoinitiated CVD (piCVD). The functional group pentafluorophenylmethacrylate (PFM) is copolymerized with hydroxyethyl methacrylate (HEMA). Because PFM reacts easily with amine groups, the incorporation of PFM results in a platform for subsequent functionalization. The graded copolymer confines the PFM to the near surface region (∼20 nm) allowing the control of the hydrogel film properties independently of the surface reactivity. Although homogeneous incorporation of PFM in the hydrogel matrix inhibits swelling, the swollen water content of pure pHEMA is nearly preserved in the graded copolymer. FTIR spectroscopy shows that the absorption peaks corresponding to the fluorinated phenyl ring in the graded copolymer disappear after functionalization with O,O-bis (2-aminoethyl...

Initiated (i)CVD is used to deposit thin films of poly(cyclohexylmethacrylate) (pCHMA) in microtrenches of depth 7 µm and widths 1-5 µm. By changing the fractional saturation of the monomer vapor, step coverage of 0.85 is achieved for the highest aspect ratio trench studied while maintaining a deposition rate of 15 nm min−1. An analytical model for determining the sticking probability of the initiating radical (CH3)3CO· is developed, and is experimentally shown to be a function of the fractional saturation of the monomer vapor. For the conditions studied, the sticking probability is in the range 1.1 × 10−2–5.0 × 10−2. These results suggest that iCVD proceeds via the reaction of a vapor-phase initiating radical with a surface-adsorbed monomer.

Vapor-phase deposition and characterization of covalently bound polymer coatings using type II surface photoinitiation of the monomers (dimethylamino)methyl styrene (DMAMS) and (diethylamino)ethyl ...

This procedure describes a method for the fabrication of large-area and ultrathin free-standing polymer films. Typically, ultrathin films are prepared using either sacrificial layers, which may damage the film or affect its mechanical properties, or they are made on freshly cleaved mica, a substrate that is difficult to scale. Further, the size of ultrathin film is typically limited to a few square millimeters. In this method, we modify a surface with a polyelectrolyte that alters the strength of adhesion between polymer and deposition substrate. The polyelectrolyte can be shown to remain on the wafer using spectroscopy, and a treated wafer can be used to produce multiple films, indicating that at best minimal amounts of the polyelectrolyte are added to the film. The process has thus far been shown to be limited in scalability only by the size of the coating equipment, and is expected to be readily scalable to industrial processes. In this study, the protocol for making the solutions, preparing the deposition surface, and producing the films is described.

Increases in the laser damage threshold of fused silica have been driven by the successive elimination of near-surface damage precursors such as polishing residue, fractures, and inorganic salts. In this work, we show that trace impurities in ultrapure water used to process fused silica optics may be responsible for the formation of carbonaceous deposits. We use surrogate materials to show that organic compounds precipitated onto fused silica surfaces form discrete damage precursors. Following a standard etching process, solvent-free oxidative decomposition using oxygen plasma or high-temperature thermal treatments in air reduced the total density of damage precursors to as low as

When used with 1.06-mm beryllium (Be) capsules on the National Ignition Facility, gold hohlraums with the inner diameter of 5.75 mm and helium gas fill density of 1.6 mg/cm3 exhibit significant drive degradation due to laser energy backscatter (of order 14%–17%) and “missing” X-ray drive energy (about 32% during the main pulse). Also, hard to simulate cross-beam energy transfer (CBET) must be used to control the implosion symmetry. Larger, 6.72-mm hohlraums with fill densities ≤0.6 mg/cm3 generally offer improved drive efficiency, reduced hot-electron preheat, and better control of the implosion symmetry without CBET. Recently, we carried out an exploratory campaign to evaluate performance of 1.06-mm Be capsules in such hohlraums and determine optimal hohlraum parameters. Specifically, we performed a hohlraum fill-density scan with a three-shock, 9.5-ns laser pulse and found that an appropriate axial laser repointing and azimuthal outer-quad splitting resulted in significantly improved hohlraum energetics...

Controlling laser damage is essential for reliable and cost-effective operation of high energy laser systems. We will review important optical damage precursors in silica up to UV fluences as high as 45J/cm2 (3ns) along with studies of the damage mechanisms involved and processes to mitigate damage precursors. We have found that silica surface damage is initiated by nano-scale precursor absorption followed by thermal coupling to the silica lattice and formation of a laser-supported absorption front. Residual polishing compound and defect layers on fracture surfaces are primarily responsible for optic damage below about 10J/cm2; they can be mitigated by an optimized oxide etch processes. At fluences above about 10J/cm2, precipitates of trace impurities are responsible for damage; they can be mitigated by eliminating the chances of impurity precipitation following wet chemical processing. Using these approaches, silica damage densities can be reduced by many orders of magnitude allowing large increases in the maximum operating fluences these optics see.

Free-standing polymer thin films are typically fabricated using a sacrificial underlayer (between the film and its deposition substrate) or overlayer (on top of the film to assist peeling) in order to facilitate removal of the thin film from its deposition substrate. We show the direct delamination of extraordinarily thin (as thin as 8 nm) films of poly(vinyl formal) (PVF), polystyrene, and poly(methyl methacrylate). Large (up to 13 cm diameter) films of PVF could be captured on wire supports to produce free-standing films. By modifying the substrate to lower the interfacial energy resisting film-substrate separation, the conditions for spontaneous delamination are satisfied even for very thin films. The substrate modification is based on the electrostatic adsorption of a cationic polyelectrolyte. Eliminating the use of sacrificial materials and instead relying on naturally self-limiting adsorption makes this method suitable for large areas. We have observed delamination of films with aspect ratios (ratio of lateral dimension between supports to thickness) of 10(7) and have captured dry, free-standing films with aspect ratios10(6). Films with an aspect ratio of 10(5) can bear loads up to 10(6) times the mass of the film itself. The presence of the adsorbed layer can be observed using X-ray photoelectron spectroscopy, and this layer is persistent through multiple uses. In the system studied, elimination of sacrificial materials leads to an enhancement in the failure strength of the free-standing thin film. The robustness, persistence, and the self-optimizing nature distinguish this method from various fabrication methods utilizing sacrificial materials and make it a potentially scalable process for the fabrication of ultrathin free-standing or transferrable films for filtration, MEMS, or tissue engineering applications.