Increasing the Strain Resistance of Si/SiO2 Interfaces for Flexible Electronics.

Understanding the changes that occur in the micro-mechanical properties of semiconductor materials is of utmost importance for the design of new flexible electronic devices, especially to control the properties of newly designed materials. In this work, we present the design, fabrication, and application of a novel tensile-testing device coupled to FTIR measurements that enables in situ atomic investigations of samples under uniaxial tensile load. The device allows for mechanical studies of rectangular samples with dimensions of 30 mm × 10 mm × 0.5 mm. By recording the alternation in dipole moments, the investigation of fracture mechanisms becomes feasible. Our results show that thermally treated SiO2 on silicon wafers has a higher strain resistance and breaking force than the SiO2 native oxide. The FTIR spectra of the samples during the unloading step indicate that for the native oxide sample, the fracture happened following the propagation of cracks from the surface into the silicon wafer. On the contrary, for the thermally treated samples, the crack growth starts from the deepest region of the oxide and propagates along the interface due to the change in the interface properties and redistribution of the applied stress. Finally, density functional theory calculations of model surfaces were conducted in order to unravel the differences in optic and electronic properties of the interfaces with and without applied stress.

Inverse Vulcanization of Styrylethyltrimethoxysilane-Coated Surfaces, Particles, and Crosslinked Materials.

Sulfur as a side product of natural gas and oil refining is an underused resource. Converting landfilled sulfur waste into materials merges the ecological imperative of resource efficiency with economic considerations. A strategy to convert sulfur into polymeric materials is the inverse vulcanization reaction of sulfur with alkenes. However, the materials formed are of limited applicability, because they need to be cured at high temperatures (>130 °C) for many hours. Herein, we report the reaction of elemental sulfur with styrylethyltrimethoxysilane. Marrying the inverse vulcanization and silane chemistry yielded high sulfur content polysilanes, which could be cured via room temperature polycondensation to obtain coated surfaces, particles, and crosslinked materials. The polycondensation was triggered by hydrolysis of poly(sulfur-r-styrylethyltrimethoxysilane) (poly(Sn -r-StyTMS) under mild conditions (HCl, pH 4). For the first time, an inverse vulcanization polymer could be conveniently coated and mildly cured via post-polycondensation. Silica microparticles coated with the high sulfur content polymer could improve their Hg2+ ion remediation capability.

Light-Switchable One-Dimensional Photonic Crystals Based on MOFs with Photomodulatable Refractive Index.

Photonic crystals are solids with regular structures having periodicities comparable to the wavelength of light. Here, we showcase the photomodulation of the refractive index of a crystalline material and present a quasi-one-dimensional photonic crystal with remote-controllable optical properties. The photonic material is composed of layers of TiO2 and films of a nanoporous metal-organic framework (MOF) with azobenzene side groups. While the rigid MOF lattice is unaffected, the optical density is reversibly modified by the light-induced trans-cis-azobenzene isomerization. Spectroscopic ellipsometry and precise DFT calculations show the optical-density change results from the different orbital localizations of the azobenzene isomers and their tremendously different oscillator strengths. The photomodulation of the MOF refractive index controls the optical properties of the quasi-one-dimensional photonic crystal with Bragg reflexes reversibly shifted by more than 4 nm. This study may path the way to photoswitchable photonic materials applied in advanced, tunable optical components and lens coatings and in light-based information processing.

In-situ-Investigation of Enzyme Immobilization on Polymer Brushes.

Herein, we report on the use of a combined setup of quartz-crystal microbalance, with dissipation monitoring and spectroscopic ellipsometry, to comprehensively investigate the covalent immobilization of an enzyme to a polymer layer. All steps of the covalent reaction of the model enzyme glucose oxidase with the poly(acrylic acid) brush by carbodiimide chemistry, were monitored in-situ. Data were analyzed using optical and viscoelastic modeling. A nearly complete collapse of the polymer chains was found upon activation of the carboxylic acid groups with N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide and N-Hydroxysuccinimide. The reaction with the amine groups of the enzyme occurs simultaneously with re-hydration of the polymer layer. Significantly more enzyme was immobilized on the surface compared to physical adsorption at similar conditions, at the same pH. It was found that the pH responsive swelling behavior was almost not affected by the presence of the enzyme.

Enzyme Immobilization in Polyelectrolyte Brushes: High Loading and Enhanced Activity Compared to Monolayers.

Catalysis by enzymes on surfaces has many applications. However, strategies for efficient enzyme immobilization with preserved activity are still in need of further development. In this work, we investigate polyelectrolyte brushes prepared by both grafting-to and grafting-from with the aim to achieve high catalytic activity. For comparison, self-assembled monolayers that bind enzymes with the same chemical interactions are included. We use the model enzyme glucose oxidase and two kinds of polymers: anionic poly(acrylic acid) and cationic poly(diethylamino)methyl methacrylate. Surface plasmon resonance and spectroscopic ellipsometry are used for accurate quantification of surface coverage. Besides binding more enzymes, the "3D-like" brush environment enhances the specific activity compared to immobilization on self-assembled monolayers. For grafting-from brushes, multilayers of enzymes were spontaneously and irreversibly immobilized without conjugation chemistry. When the pH was between the pI of the enzyme and the p Ka of the polymer, binding was considerable (thousands of ng/cm2 or up to 50% of the polymer mass), even at physiological ionic strength. However, binding was observed also when the brushes were neutrally charged. For acidic brushes (both grafting-to and grafting-from), the activity was higher for covalent immobilization compared to noncovalent. For grafting-from brushes, a fully preserved specific activity compared to enzymes in the liquid bulk was achieved, both with covalent (acidic brush) and noncovalent (basic brush) immobilization. Catalytic activity of hundreds of pmol cm-2 s-1 was easily obtained for polybasic brushes only tens of nanometers in dry thickness. This study provides new insights for designing functional interfaces based on enzymatic catalysis.

Preexisting epiretinal membrane is associated with pseudophakic cystoid macular edema.

PURPOSE: The purpose of the present study was to evaluate whether preexisting epiretinal membrane (ERM) is a significant risk factor for developing pseudophakic cystoid macular edema (PCME). METHODS: Two hundred four consecutive eyes and 153 consecutive eyes without preexisting epiretinal membranes were retrospectively compared regarding PCME development following phacoemulsification with posterior chamber lens implantation. Patients with vascular retinal diseases, uveitis, trauma, neovascular macular degeneration, chronic inflammatory conditions, diabetic retinopathy, endophthalmitis, eventful cataract surgery, and combination of cataract surgery and vitrectomy during the observation period were excluded. Macular examination was performed using spectral-domain optical coherence tomography (SD-OCT) before as well as at 4, 8, 12, 16, 24, and 36 weeks after cataract surgery. Univariate and multivariate logistic regression analyses were calculated. RESULTS: PCME occurred in 32 of 204 eyes with preexisting ERM (15.7%), whereas 9 of 153 eyes without preexisting ERM (5.9%) developed PCME. The risk of PCME was significantly increased in eyes with ERM (p = 0.007). By multivariate logistic regression analysis, factors predictive of PCME included the history of previous pars plana vitrectomy for retinal detachment (odds ratio (OR) 3.619 [95% confidence interval (CI) 1.242 to 10.258]; p = 0.016) as well as the preexistence of ERM (OR 3.885 [95% CI 1.162 to 17.762]; p = 0.04). CONCLUSION: Preexisting ERM seems to be associated with an increased risk of PCME following cataract surgery. Therefore, this risk should be considered in surgery planning, preoperative medication, and follow-up care after surgery.

Salt Sensitivity of the Thermoresponsive Behavior of PNIPAAm Brushes.

We report investigations on the salt sensitivity of the thermoresponsive behavior of PNIPAAm brushes applying the quartz crystal microbalance coupled with spectroscopic ellipsometry technique. This approach enables a detailed study of the optical and mechanical behavior of the polymer coatings. Additional conclusions can be drawn from the difference between both techniques due to a difference in the contrast mechanism of both methods. A linear shift of the phase-transition temperature to lower temperatures with the addition of sodium chloride was found, similar to the behavior of free polymer chains in solution. The thermal hysteresis was found to be decreased by the addition of sodium chloride to the solution, hinting to the interaction of the ions with the amide groups of the polymer, whereby the formation of hydrogen bonds is hindered. The results of this study are of relevance to the application of PNIPAAm brushes in biological fluids and demonstrate the additional potential of the ion sensitivity besides the better known thermosensitivity.

Defects as Color Centers: The Apparent Color of Metal-Organic Frameworks Containing Cu2+-Based Paddle-Wheel Units.

As in the case of other semiconducting materials, optical and electronic properties of metal-organic frameworks (MOFs) depend critically on defect densities and defect types. We demonstrate here that, in addition to the influence of imperfections on MOF chemical properties like guest binding energies and catalytic activity, the optical properties of these crystalline molecular solids also crucially depend on deviations from the perfect crystalline structure. By recording UV-vis absorption spectra for MOF thin films of particularly high quality, we demonstrate that low-defect samples of an important MOF, HKUST-1, are virtually colorless. Electronic structure calculations of the excited states by employing complete active space self-consistent field (CASSCF) calculations show that the d-d excitations in defects result in the typical green color of the MOF material synthesized by conventional methods.

Bioinstructive Coatings for Hematopoietic Stem Cell Expansion Based on Chemical Vapor Deposition Copolymerization.

We report the chemical vapor deposition (CVD) of dual-functional polymer films for the specific and orthogonal immobilization of two biomolecules (notch ligand delta-like 1 (DLL1) and an RGD-peptide) that govern the fate of hematopoietic stem and progenitor cells. The composition of the CVD polymer and thus the biomolecule ratio can be tailored to investigate and optimize the influence of the relative surface concentrations of biomolecules on stem cell behavior. Prior to cell experiments, all surfaces were characterized by infrared reflection adsorption spectroscopy, time-of-flight secondary ion mass spectrometry, and X-ray photoelectron spectroscopy to confirm the presence of both biomolecules. In a proof-of-principle stem cell culture study, we show that all polymer surfaces are cytocompatible and that the proliferation of the hematopoietic stem and progenitor cells is predominantly influenced by the surface concentration of immobilized DLL1.

Nanotopographical control of surfaces using chemical vapor deposition processes.

In recent years much work has been conducted in order to create patterned and structured polymer coatings using vapor deposition techniques - not only via post-deposition treatment, but also directly during the deposition process. Two-dimensional and three-dimensional structures can be achieved via various vapor deposition strategies, for instance, using masks, exploiting surface properties that lead to spatially selective deposition, via the use of additional porogens or by employing oblique angle polymerization deposition. Here, we provide a concise review of these studies.

Combined Ab Interno Glaucoma Surgery Does not Increase the Risk of Pseudophakic Cystoid Macular Edema in Uncomplicated Eyes.

PURPOSE: To assess the risk of pseudophakic cystoid macular edema (PCME) following cataract surgery (bimanual phacoemulsification with posterior chamber lens implantation) combined with ab interno glaucoma surgery (trabecular aspiration or ab interno trabeculotomy) compared with solely cataract extraction. PATIENTS AND METHODS: In total, 360 consecutive eyes of 180 patients with age-related cataract, and thereof 162 with coexistent glaucoma, who underwent sole cataract surgery or in combination with ab interno glaucoma surgery (trabecular aspiration or ab interno trabeculotomy) were compared retrospectively regarding PCME development. Patients with known risk factors of PCME were excluded. Macular examination was performed using spectral-domain optical coherence tomography before and at 4, 8, 12, 16, 24, 36, and 48 weeks after surgery. Main outcome measure was the incidence of PCME. RESULTS: In total, 126 eyes (35%) underwent cataract surgery combined with ab interno glaucoma surgery (96 trabecular aspiration (76.2%), 30 ab interno trabeculotomy (23.8%), and 234 eyes (65%) received cataract surgery alone. PCME overall occurred in 23 eyes (6.4%). Following combined trabecular aspiration 5 eyes (5.2%) developed PCME, following ab interno trabeculotomy 2 eyes (6.7%), and following sole cataract surgery 16 eyes (6.8%), reaching no significant difference (P=0.676). Risk of PCME in fellow eye was significantly increased (P=0.025; odds ratio 7.177; 95% confidence interval, 5.667-8.687). CONCLUSIONS: Additional ab interno glaucoma surgery combined with phacoemulsification does not seem to increase the risk of PCME in uncomplicated eyes. However, in patients with history of PCME a significantly increased risk of PCME in fellow eye should be taken into account.

Impact of allergy and atopy on the risk of pseudophakic cystoid macular edema.

PURPOSE: To assess the risk of pseudophakic cystoid macular edema (PCME) following cataract surgery in patients with allergies and/or atopic disorders. PATIENTS AND METHODS: Medical records of 3,850 consecutive eyes that underwent cataract surgery were retrospectively reviewed for prevalence of allergies and atopic status and development of PCME. Patients with any known risk factors for PCME were excluded. Macular examination was performed using spectral-domain optical coherence tomography (SD-OCT) before and at 4, 8, 12, 16, 24, and 36 weeks after surgery. If both eyes in one patient underwent cataract surgery, one eye was randomly selected. Odds ratios and confidence intervals were estimated. RESULTS: Out of 240 patients enrolled in this series, 65 patients (27.1 %) showed positive allergic status, 19 patients (7.9 %) suffered from atopic syndromes, and 11 (4.6 %) showed both (allergies and atopic diseases). PCME occurred in eight patients (12.3 %) of the allergy cohort, whereas no patient (0 %) of the atopy cohort developed PCME. The risk of PCME was comparable in patients with allergies or atopic diseases to patients without allergies or atopy (allergy: p = 0.635; odds ratio (OR) 1.303, 95 % confidence interval (CI) 0.461-3.398; atopy: p = 0.234; OR 0.000, 95 % CI 0-1.815). CONCLUSION: Positive status of allergy or atopy does not seem to increase the risk of PCME. Therefore, postoperative treatment after cataract surgery does not have to be modified in allergic or atopic patients.

Adsorption of enzymes to stimuli-responsive polymer brushes: Influence of brush conformation on adsorbed amount and biocatalytic activity.

Polyelectrolyte brushes can be utilized to immobilize enzymes on macroscopic surfaces. This report investigates the influence of the pH value of the surrounding medium on the amount and the activity of enzymes adsorbed to poly(2-vinylpyridine) and poly(acrylic acid) brushes, as well as the creation of thermoresponsive biocatalytically active coatings via the adsorption of enzymes onto a mixed brush consisting of a polyelectrolyte and temperature-sensitive poly(N-isopropylacryl amide). Spectroscopic ellipsometry and attenuated total reflection-Fourier transform infrared spectroscopy are used to monitor the adsorption process. Additionally, infrared spectra are evaluated in terms of the secondary structure of the enzymes. Glucose oxidase is used as a model enzyme, where the enzymatic activity is measured after different adsorption conditions. Poly(acrylic acid) brushes generally adsorb larger amounts of enzyme, while less glucose oxidase is found on poly(2-vinylpyridine), which however exhibits higher specific activity. This difference in activity could be attributed to a difference in secondary structure of the adsorbed enzyme. For glucose oxidase adsorbed to mixed brushes, switching of enzymatic activity between an active state at 20°C and a less active state at 40°C as compared to the free enzyme in solution is observed. However, this switching is strongly depending on pH in mixed brushes of poly(acrylic acid) and poly(N-isopropylacryl amide) due to interactions between the polymers.

Combined QCM-D/GE as a tool to characterize stimuli-responsive swelling of and protein adsorption on polymer brushes grafted onto 3D-nanostructures.

A combined setup of quartz crystal microbalance and generalized ellipsometry can be used to comprehensively investigate complex functional coatings comprising stimuli-responsive polymer brushes and 3D nanostructures in a dynamic, noninvasive in situ measurement. While the quartz crystal microbalance detects the overall change in areal mass, for instance, during a swelling or adsorption process, the generalized ellipsometry data can be evaluated in terms of a layered model to distinguish between processes occurring within the intercolumnar space or on top of the anisotropic nanocolumns. Silicon films with anisotropic nanocolumnar morphology were prepared by the glancing angle deposition technique and further functionalized by grafting of poly-(acrylic acid) or poly-(N- isopropylacrylamide) chains. Investigations of the thermoresponsive swelling of the poly-(N-isopropylacrylamide) brush on the Si nanocolumns proved the successful preparation of a stimuli-responsive coating. Furthermore, the potential of these novel coatings in the field of biotechnology was explored by investigation of the adsorption of the model protein bovine serum albumin. Adsorption, retention, and desorption triggered by a change in the pH value is observed using poly-(acrylic acid) functionalized nanostructures, although generalized ellipsometry data revealed that this process occurs only on top of the nanostructures. Poly-(N-isopropylacrylamide) is found to render the nanostructures non-fouling properties.