A magnetron discharge with a zirconium cathode is operated in an argon/oxygen gas mixture. The magnetron is operated in pulsed mode with repetition frequencies of 0.5–5 kHz and in radiofrequency mode. Positively charged atomic O+, Ar+, and Zr+ and molecular O2+, ArO+, Ar2+, ZrO+ and ZrO2+ are observed. Negatively charged O− ions sputtered from the magnetron’s cathode are investigated in some detail. The intensity of negatively charged O− is strongly influenced by the repetition rate. Formation of excited Ar, Ar+, Zr, and Zr+ species is influenced by target poisoning. Target poisoning reduces the deposition rate by one order of magnitude. Zirconium dioxide films are either deposited at room temperature followed by post-deposition annealing or on heated Si substrates. Deposited films are characterised by means of X-ray diffractometry (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy, infrared ellipsometry, and spectroscopic optical ellipsometry. XRD confirms the monoclinic lattice phase of the films. The ultra-wide bandgap of the deposited zirconia films is confirmed by spectroscopic ellipsometry measurements. Two direct optical bandgaps at 5.25 eV and 6.1 eV are extracted from the measurements.

Understanding charge transport mechanisms are crucial when making ultrathin layer-by-layer (LbL) films with high electrical conductivity. We investigate the influence of the relative humidity (RH), and thus, the water content of the films. We study polyelectrolyte multilayers made from PEDOT:PSS (poly-3,4-ethylenedioxythiophen:poly styrenesulfonate) and carbon nanotubes (CNTs) as polyanion layers. All films investigated showed the highest conductivity at RH ≈ 40%. At RH ≤ 20%, UV/vis/IR absorption measurements of PEDOT:PSS films are typical for strongly charged PEDOT (as found in spin-coated PEDOT:PSS films), the direct current (DC) conductivity is low (103-104 S/m). The conductivity increases by up to 2 orders of magnitude when RH = 40% (≈2.5 × 105 S/m), with absorption typical for moderately charged PEDOT. On further increase of the RH, the conductivity decays exponentially, consistent with charge carrier transport mechanisms by tunneling through nonconductive polymers. The influence of the RH on LbL films made of CNTs is similar, yet the electrical conductivity is lower, and the effects are weaker. By changing the RH between 10 and 40%, the DC electrical conductivity of PDADMA/PEDOT:PSS LbL films could be reversibly changed by 2 orders of magnitude.

Inspired by diblock copolymer self-assembly, we study lipopolymer monolayers at the air/water interface. We investigated DSPE-PEG1000 (DSPE-EO22) monolayers with alkyl chains in the liquid-condensed phase in dependence of the molecular area. Due to its conformational entropy, the moderately hydrophilic PEG has a larger area requirement than the alkyl chains in all-trans conformation. Small-angle grazing incidence X-ray diffraction (GID) measurements identified a hexagonal superstructure. The ordered alkyl chains form hydrophobic domains that are embedded in dissolved PEG. These domains consist of the alkyl chains of ≈200 PEGylated lipid molecules. During monolayer compression, the number of alkyl chains in a domain remains constant, while their area fraction increases. At an area fraction of 50%, a transition to a lamellar superstructure occurs. During this transition, the alkyl chain domains merge. This transition is attributed to the entropy loss of the laterally compressed PEG chains. Wide-angle GID reveals that the alkyl chains in the liquid-condensed phase possess the same small cross-sectional area (19.75 Å2) as those in DSPE monolayers, indicating that PEG has little influence on the liquid-condensed phase. The hexagonal superstructure was confirmed with AFM images.

The spontaneous formation of polyelectrolyte multilayers or polyelectrolyte complexes depends on the (inter)diffusion of polyelectrolytes. We investigate the transport of polyelectrolytes and extrinsic sites-charged polyelectrolyte repeat units balanced by counterions-during multilayer buildup. We determine the vertical diffusion coefficient D-PSS of polystyrenesulfonate (PSS) repeat units in polyelectrolyte multilayer films from poly(diallyldimethylammonium) (PDADMA) and PSS using a quartz crystal microbalance with dissipation (QCM-D) and analyzing the observed film growth. Varying the NaCl concentration c(NaCl) results in DPSS=(4.3 +/- 1.4).10-20m(2)/(s).e alpha.cNaCl. As known from the free volume model, the prefactor is constant. For site diffusion, the exponent is also constant (alpha = 4.9 M-1). For polymer diffusion, however, alpha increases linearly with M-PSS, the molecular weight of PSS. The results for site diffusion quantitatively agree with those of Fares and Schlenoff (J. Am. Chem. Soc., 2017, 139(41), 14656-14667). For M-PDADMA = 117 kDa, polymer diffusion dominates when M-PSS < 65 kDa; at larger M-PSS, site diffusion determines multilayer buildup. To describe polymer diffusion, we use D-PSS = B . M-PSS(-gamma). B increases exponentially with c(NaCl), while gamma increases linearly with c(NaCl). We compare these results with polymer diffusion observed by neutron reflectivity and discuss other parameters that influence site and polymer diffusion, such as the type of monovalent ion, the molecular weight of the oppositely charged polyelectrolyte, and the type of polyelectrolyte.

Electrically conductive films of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) are usually formed by spin coating of aqueous dispersions with PEDOT:PSS nanoparticles. To better understand the film formation, the adsorption conditions are investigated using dip coating and a flow cell with different flow rates. Multilayer films are formed by sequential adsorption of oppositely charged macromolecules or nanoparticles. PEDOT:PSS serves as polyanion, and PDADMA is the polycation. In the dip coating process, the first layer consists of a approximate to 70 nm thick PEDOT:PSS nanoparticle monolayer. Subsequent PDADMA/PEDOT:PSS bilayers have a constant thickness (9.5 nm). Using the flow cell (0.2 mL/min) for film preparation led to constant PDADMA/PEDOT:PSS bilayer thickness (7.5 nm). PEDOT:PSS nanoparticle monolayers were only observed after PEDOT:PSS adsorption when the washing step was omitted. The electrical conductivity is independent of the number of deposition cycles for both preparation methods. Films prepared by dip coating show low conductivity (26 kS/m) and high surface roughness, whereas films prepared by flow cell show high conductivity (230 kS/m) and low roughness (2-4 nm). We propose that the adsorption in a flow cell leads to a flat orientation of the PEDOT molecules, which increases charge carrier mobility. It is hoped that a better understanding of the relationship between adsorption conditions and carrier mobility will further improve electrical conductivity.

Polyethylene (PE) is the most commonly used plastic type in the world, contributing significantly to the plastic waste crisis. Microbial degradation of PE in natural environments is unlikely due to its inert saturated carbon-carbon backbones, which are difficult to break down by enzymes, challenging the development of a biocatalytic recycling method for PE waste. Here, we demonstrated the depolymerization of low-molecular-weight (LMW) PE using an enzyme cascade that included a catalase-peroxidase, an alcohol dehydrogenase, a Baeyer Villiger monooxygenase, and a lipase after the polymer was chemically pretreated with m- chloroperoxybenzoic acid ( m CPBA) and ultrasonication. In a preparative experiment with gram-scale pretreated polymers, GC-MS and weight loss determinations confirmed ~27 % polymer conversion including the formation of medium-size functionalized molecules such as ω-hydroxycarboxylic acids and α,ω-carboxylic acids. Additional analyses of LMWPE-nanoparticles using AFM showed that enzymatic depolymerization reduced the sizes of these m CPBA- and enzyme-treated LMWPE-nanoparticles. This multi-enzyme catalytic concept with distinct chemical steps represents a unique starting point for future development of bio-based recycling methods for polyolefin waste.

Tidal breathing is associated with a 30% change of the surfactant-covered alveolar surface occurring about 16 times per minute. To model this highly dynamic process, erucic acid monolayers at the air-water interface were compressed fast. Brewster angle microscopy imaged the fractal liquid-condensed (LC) domains and quantified the surface flow in size, direction, and duration. Radial branch distribution of the domains has a minimum in the flow direction, as was shown with directionality histograms. The fast Fourier transform of the domains shows a preferential growth perpendicular to the flow direction. Additionally, at the beginning of the flow, the downstream side of the domain grows faster than the upstream side. Surface flows act on the mm to cm scale, cause an anisotropic flow in the liquid expanded phase surrounding the LC domain, and affect the overall domain shape. On the μm-scale, the dendritic or seaweed domains' branches were only slightly disturbed. These results may help to understand pulmonary surfactant layers.

In this study, thin films of CuFeO2 were prepared using radio frequency reactive sputtering (RF) and reactive high-power impulse magnetron sputtering combined with electron cyclotron wave resonance plasma (HiPIMS-ECWR). The plasma was characterized using an RF ion probe. Plasma density, tail electron energy, and electron temperature were extracted from the measured data. The films were deposited on fluorine-doped tin oxide-coated glass and quartz glass, with the substrates being heated during the deposition process. The final delafossite CuFeO2 structure was formed after annealing in an argon gas flow at 550–600 °C. The ideal deposition conditions were found to be with a stoichiometric ratio of Cu:Fe = 1:1, which was the optimal condition for creating the delafossite CuFeO2 structure. The measured optical bandgap of CuFeO2 was 1.4 eV. The deposited CuFeO2 films were subjected to photoelectrochemical measurements in the cathodic region to investigate their potential application in solar photocatalytic water splitting. The films showed photocatalytic activity, with a photocurrent density of around 70 μA/cm2 (under an incident light irradiation of 62 mW/cm2, AM 1.5 G). The electrochemical properties of the layers were studied using open circuit potential, linear voltammetry, and chronoamperometry. The surface morphology and chemical composition of the layers were analyzed by atomic force microscopy and energy-dispersive x-ray spectroscopy, respectively. The crystalline structure was determined using XRD and Raman spectroscopy. The results of these methods are presented and discussed in this article.

For engineering and biomedical applications, nanometer-thin films with high electrical conductivity in aqueous solutions are desirable. Multilayers of polydimethyldiallylammonium chloride (PDADMA) and oxidized carbon nanotubes (CNTs) were built using the layer-by-layer technique. CNTs with a low linear charge density were used. The surface coverage of the CNTs was monitored with optical absorption. The film thickness and the surface coverage of the CNTs increased linearly with the number of CNT/PDADMA bilayers deposited. On immersion into aqueous solutions, the film thickness decreased or remained constant. This finding is attributed to the hydrophobic character of the CNTs and the backbone of PDADMA. The films showed ohmic behavior, both in air and in solutions. The electrical conductivity was 0.95 x 10(4) S/m in air and increased to 1.36 x 10(4) S/m in solution, provided the thickness of the CNT/PDADMA bilayers was as low as 1.9 nm. We suggest that high electrical conductivity can be achieved by flat adsorption of the CNTs.

The self-patterning of thin films is relevant for both fundamental research and applications. We investigate polyelec-t r o l y t e multilayer films made from poly-(diallyldimethylammonium) chloride and poly(styrene sulfonate) sodium salt (PDADMA/PSS). Various PSS with low molecular weight were used. First, the film thickness increases exponentially with the number of deposited PDADMA/PSS bilayers. The separation and height of the pillar-like domains increase significantly with each deposited PDADMA/PSS bilayer, as AFM images show. After the exponential growth regime, either a parabolic (and then a linear) or a linear growth regime follows, depending on the PSS molecular weight. The domain separation changes less and correlates with the vertical growth regimes. The domain separation varies between 70 and 750 nm and always exceeds the domain height. PSS-terminated films show the same domain distance in water and air. However, when PDADMA-terminated films are dried, the domain distance in air increases while the domain height decreases, causing a reduction in total area. In the air, the surface energy is greater than in water and a highly textured surface costs a lot of energy. We propose that the changed surface pattern is attributable to energy minimization. Furthermore, the domains are stable when exposed to 1 M NaCl solution but shrink enormously in 2 M NaCl, while their separation increases slightly. Under certain conditions, 50 nm broad filaments consisting of PDADMA/PSS complexes are observed. We suggest that these complexes diffuse between the domains and adjust their separation.

Molecular surface gradients can constitute electric field landscapes and serve to control local cell adhesion and migration. Cellular responses to electric field landscapes may allow the discovery of routes to improve osseointegration of implants. Flat molecule aggregate landscapes of amine- or carboxyl-teminated dendrimers, amine-containing protein and polyelectrolytes were prepared on glass to provide lateral electric field gradients through their differing zeta potentials compared to the glass substrate. The local as well as the mesoscopic morphological responses of adhered osteoblasts (MG-63) with respect to the stripes were studied by means of Scanning Ion Conductance Microscopy (SICM) and Fluorescence Microscopy, in situ. A distinct spindle shape oriented parallel to the surface pattern as well as a preferential adhesion of the cells on the glass site have been observed at a stripe and spacing width of 20 μm. Excessive ruffling is observed at the spindle poles, where the cells extend. To explain this effect of material preference and electro-deformation, we put forward a retraction mechanism, a localized form of double-sided cathodic taxis.

The practical applicability of ultrathin films, which offer interesting and novel functionalities, is often hampered by difficulties in large-area deposition while maintaining homogeneous film properties. Here, we induce a breakup after forced wetting to produce the ultrathin film [Runde, S. et al. Adv. Mater. Interfaces 2018, 5(16), 1800323] and apply this deposition method to selected liquid metals and alloys to produce electrically conductive films at ambient conditions on wafer-scaled areas. In addition to ultrathin monolayers, vertically stacked and heterostructured multilayers of metal and metal hydroxide can be built by repeating the deposition method. Structural analysis using X-ray reflectometry shows that the multilayer thickness is proportional to the number of deposition cycles, yielding a single layer thickness between 2.9 and 5.2 nm, depending on the material used. Every single layer consists of a complex heterostructure composed of a nanometer-thin metallic core surrounded by stabilizing metal (hydr)oxide skin layers. The crystallinity of the layers within the films was investigated with grazing incidence X-ray diffraction; X-ray amorphous materials were Ga, GaIn(1:1), and GaInSn(7:2:1), which also showed low optical absorbance and low electrical resistivity. Films made from InSn(1:1)- and Bi-containing alloys showed weak diffraction peaks, indicating partial crystallization. The electrical conductivity of all multilayers increases with the number of deposition cycles, allowing to fine-tune the sheet resistance. The preparation of ultrathin multilayers of metallic materials at the centimeter scale is attributed to the low melting temperature combined with the high surface tension and wettability of the liquid metals.

Copper tungsten oxide films are deposited with the help of reactive high power impulse magnetron sputtering (HiPIMS) in an argon/oxygen gas mixture. Two magnetrons, one equipped with a tungsten target and the other with a copper target, are employed. The HiPIMS discharge is operated with a repetition frequency of f=100 Hz. Pulse widths of 100 and 20 μs separated by 25 μs are chosen for the tungsten and copper target, respectively. Films deposited on two different glass substrates [soda lime glass and fluorine doped tin oxide (FTO) coated glass] are characterized by energy dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, x-ray diffraction, Raman spectroscopy, and ellipsometry. Photoelectrochemical activity was investigated by linear voltammetry. The composition and crystal structure of as-deposited and annealed films are found to depend on the deposition conditions. Annealed films deposited on FTO glass are composed of WO3 and CuWO4 or Cu2WO4 crystal phases. Films deposited on soda lime glass are subject to sodium diffusion into the films during annealing and the formation of Na2W2O7 and Na2W4O13 phases.

For biological and engineering applications, nm-thin films with high electrical conductivity and tunable sheet resistance are desirable. Multilayers of polydimethyldiallylammonium chloride (PDADMA) with two different molecular weights (322 and 44.3 kDa) and oxidized carbon nanotubes (CNTs) were constructed using the layer-by-layer technique. The surface coverage of the CNTs was monitored with a selected visible near infrared absorption peak. Both the film thickness and the surface coverage of the CNTs increased linearly with the number of CNT/PDADMA bilayers deposited (film thickness up to 80 nm). Atomic force microscopy images showed a predominantly surface-parallel orientation of CNTs. Ohmic behavior with constant electrical conductivity of each CNT/PDADMA film and conductivity up to 4. 10(3) S/m was found. A change in PDADMA molecular weight by almost a factor of ten has no effect on the film thickness and electrical conductivity, only the film/air roughness is reduced. However, increasing CNT concentration in the deposition dispersion from 0.15 up to 0.25 mg/ml results in an increased thickness of a CNT/PDADMA bilayer (by a factor of three). The increased bilayer thickness is accompanied by a decreased electrical conductivity (by a factor of four). The decreased conductivity is attributed to the increased monomer/CNT ratio.

Tungsten oxide films are deposited with the help of reactive magnetron sputtering in an argon/oxygen gas mixture. Films are deposited on different substrates, in particular, on soda lime glass, fluorine-doped tin oxide coated glass, silicon (Si), and quartz (SiO2). Thin films from three different discharge modes, in particular, high power impulse magnetron sputtering, midfrequency magnetron sputtering, and radiofrequency magnetron sputtering, are compared. Deposited films are characterized by x-ray diffraction, Raman spectroscopy, and spectroscopic ellipsometry. Composition, crystal structure, and optical properties of as-deposited and annealed films are found to depend on the deposition mode and on the substrate.

The lateral movement in lipid membranes depends on their diffusion constant within the membrane. However, when the flux of the subphase is high, the convective flow beneath the membrane also influences lipid movement. Lipid monolayers of an unsaturated fatty acid at the water–air interface serve as model membranes. The formation of domains in the liquid/condensed coexistence region is investigated. The dimension of the domains is fractal, and they grow with a constant growth velocity. Increasing the compression speed of the monolayer induces a transition from seaweed growth to dendritic growth. Seaweed domains have broad tips and wide and variable side branch spacing. In contrast, dendritic domains have a higher fractal dimension, narrower tips, and small, well-defined side branch spacing. Additionally, the growth velocity is markedly larger for dendritic than seaweed growth. The domains’ growth velocity increases and the tip radius decreases with increasing supersaturation in the liquid/condensed coexistence region. Implications for membranes are discussed.

Lipid rafts are discrete, heterogeneous domains of phospholipids, sphingolipids, and sterols that are present in the cell membrane. They are responsible for conducting cell signaling and maintaining lipid-protein functionality. Redox-stress-induced modifications to any of their components can severely alter the mechanics and dynamics of the membrane causing impairment to the lipid-protein functionality. Here, we report on the effect of sphingomyelin (SM) in controlling membrane permeability and its role as a regulatory lipid in the presence of nitric oxide (NO). Force spectroscopy and atomic force microscopy imaging of raft-like phases (referring here to the coexistence of "liquid-ordered" and "liquid-disordered" phases in model bilayer membranes) prepared from lipids: 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC):SM:cholesterol (CH) (at three ratios) showed that the adhesion forces to pull the tip out of the membrane increased with increasing SM concentration, indicating decreased membrane permeability. However, in the presence of NO radical (1 and 5 μM), the adhesion forces decreased depending on SM concentration. The membrane was found to be stable at the ratio POPC:SM:CH (2:1:1) even when exposed to 1 μM NO. We believe that this is a critical ratio needed by the raft-like phases to maintain homeostasis under stress conditions. The stability could be due to an interplay existing between SM and CH. However, at 5 μM NO, membrane deteriorations were detected. For POPC:SM:CH (2:2:1) ratio, NO displayed a pro-oxidant behavior and damaged the membrane at both radical concentrations. These changes were reflected by the differences in the height profiles of the raft-like phases observed by atomic force microscopy imaging. Malondialdehyde (a peroxidation product) detection suggests that lipids may have undergone lipid nitroxidation. The changes were instantaneous and independent of radical concentration and incubation time. Our study underlines the need for identifying appropriate ratios in the lipid rafts of the cell membranes to withstand redox imbalances caused by radicals such as NO.

Surface charges at the cell–biomaterial interface are known to determine cellular functions. Previous findings on cell signaling indicate that osteoblastic cells favor certain moderately positive surface charges, whereas highly positive charges are not tolerated. In this study, we aimed to gain deeper insights into the influence exerted by surface charges on the actin cytoskeleton and the cell shape. We analyzed surfaces with a negative, moderately positive, and highly positive zeta (ζ) potential: titanium (Ti), Ti with plasma polymerized allylamine (PPAAm), and Ti with a polydiallyldimethylammonium chloride (PDADMA) multilayer, respectively. We used the software FilaQuant for automatic actin filament quantification of osteoblastic MG-63s, analyzed the cell edge height with scanning ion conductance microscopy (SICM), and described the cellular shape via a mathematical vertex model. A significant enhancement of actin filament formation was achieved on moderately positive (+7 mV) compared with negative ζ-potentials (−87 mV). A hampered cell spreading was reflected in a diminished actin filament number and length on highly positively charged surfaces (+50 mV). Mathematical simulations suggested that in these cells, cortical tension forces dominate the cell–substrate adhesion forces. Our findings present new insights into the impact of surface charges on the overall cell shape and even intracellular structures.

Layer-by-layer (LbL) assembly is a widely used tool for engineering materials and coatings, but the dynamics of the constituent polymer chains remain poorly understood. Using neutron reflectivity, the vertical diffusion of polyanion poly(styrene sulfonate) (PSS) (M-w(PSS) = 75.6 kDa) within PSS/poly(diallyldimethylammonium) (PDADMA) (M-w(PDADMA) = 72.1 kDa) multilayers is probed, while the annealing temperature and salt concentration were varied. Only one fraction of PSS was mobile, and the other PSS molecules were assigned to a second, almost immobile fraction, with the respective diffusion constants D-PSS,D-fast and D-PSS,D-slow differing by about two orders of magnitude. The model with the two different mobile fractions is the simplest one that describes the time dependence of the scattering length density profiles. The relationship between the diffusion constants and the annealing temperature can be described using the Arrhenius equation. From this, the activation energies could be determined. Conditions for Fickian diffusion and for the formation of different mobile fractions are discussed.

In the eye lens cell membrane, the lipid composition changes during the aging process: the proportion of sphingomyelins (SM) increases, that of phosphatidylcholines decreases. To investigate the protective role of the SMs in the lens cell membrane against oxidative damage, analytical techniques such as electrochemistry, high-resolution mass spectrometry (HR-MS), and atomic force microscopy (AFM) were applied. Supported lipid bilayers (SLB) were prepared to mimic the lens cell membrane with different fractions of PLPC/SM (PLPC: 1-palmitoyl-2-linoleoyl-sn-glycero-3-phosphocholine). The SLBs were treated with cold physical plasma. A protective effect of 30% and 44% in the presence of 25%, and 75% SM in the bilayer was observed, respectively. PLPC and SM oxidation products were determined via HR-MS for SLBs after plasma treatment. The yield of fragments gradually decreased as the SM ratio increased. Topographic images obtained by AFM of PLPC-bilayers showed SLB degradation and pore formation after plasma treatment, no degradation was observed in PLPC/SM bilayers. The results of all techniques confirm the protective role of SM in the membrane against oxidative damage and support the idea that the SM content in lens cell membrane is increased during aging in the absence of effective antioxidant systems to protect the eye from oxidative damage and to prolong lens transparency.