Toward a Metal Anode-Free Zinc-Air Battery for Next-Generation Energy Storage.

Rechargeable aqueous zinc-air batteries (ZABs) promise high energy density and safety. However, the use of conventional zinc anodes affects the energy output from the battery, so that the theoretical energy density is not achievable under operation conditions. A large portion of the zinc is shielded by anode passivation during the discharge process and remains electrochemically unused, making the operation of rechargeable ZABs inefficient up to date. In a metal anode-free ZAB, there is no unnecessary excess zinc if the zinc reservoir can be precisely adjusted by electrodeposition of zinc from the electrolyte. In this respect, an anode-free battery uses the electrolyte offering a dual-mode functionality not only providing ionic conductivity but also being the source of zinc. In addition, it is shown that a defined porous anode architecture is crucial for high rechargeability in this new type of ZAB. 3D-spatially arranged carbon nanotubes as geometrically defined host structures allow a homogeneous zinc deposition from the electrolyte. Together with carbon nanohorns as an active 2e- catalyst on the cathode side, the rechargeability of this new concept reaches up to 92%.

Comment on Pashchanka, M. Conceptual Progress for Explaining and Predicting Self-Organization on Anodized Aluminum Surfaces. Nanomaterials 2021, 11, 2271.

In the review article "Conceptual Progress for Explaining and Predicting Self-Organization on Anodized Aluminum Surfaces" [...].

[Conspiracy as a surrogate for religion? Religiosity, spirituality, and affinity towards conspiracy myths in times of crisis]. / Verschwörung als Ersatzreligion? Religiosität, Spiritualität und Verschwörungsaffinität in Zeiten gesellschaftlicher Krisen.

In times of crisis, alternative interpretations of the world that challenge the public sphere gain impact. During the COVID-19 pandemic, such narratives spread in the form of conspiracy myths. They give explanations for complex questions by assuming that social events are planned and controlled by secret elites. Moreover, they are often based on pseudo-transcendental explanations that defy scrutiny but fill fateful events with meaning. In this context, the question arises whether conspiracy myths contain religious or spiritual elements. In this study, we use a representative population survey conducted in April 2022 in German- and French-speaking Switzerland (n = 1221) to examine the relationship between spirituality, religiosity, and affinity toward conspiracy myths. The results show that emotional concern during the COVID-19 pandemic is an important predictor related to conspiracy affinity. The more negative the emotional concern, the higher the affinity towards conspiracy myths. Conversely, positive emotions during the pandemic negatively affect conspiracy affinity. While religious affiliations and religiosity hardly influence conspiracy affinity, spirituality turns out to be the most important predictor in our study. We conclude that in secularized societies spirituality without involvement in traditional religious communities can result in an increased openness to conspiracy myths as a surrogate for religion.

Results from Canton Grisons of Switzerland suggest repetitive testing reduces SARS-CoV-2 incidence (February-March 2021).

In February 2021, in response to emergence of more transmissible SARS-CoV-2 virus variants, the Canton Grisons launched a unique RNA mass testing program targeting the labour force in local businesses. Employees were offered weekly tests free of charge and on a voluntary basis. If tested positive, they were required to self-isolate for ten days and their contacts were subjected to daily testing at work. Thereby, the quarantine of contact persons could be waved.Here, we evaluate the effects of the testing program on the tested cohorts. We examined 121,364 test results from 27,514 participants during February-March 2021. By distinguishing different cohorts of employees, we observe a noticeable decrease in the test positivity rate and a statistically significant reduction in the associated incidence rate over the considered period. The reduction in the latter ranges between 18 and 50%. The variability is partly explained by different exposures to exogenous infection sources (e.g., contacts with visiting tourists or cross-border commuters). Our analysis provides the first empirical evidence that applying repetitive mass testing to a real population over an extended period of time can prevent spread of COVID-19 pandemic. However, to overcome logistic, uptake, and adherence challenges it is important that the program is carefully designed and that disease incursion from the population outside of the program is considered and controlled.

Gas phase synthesis and adsorption properties of a 3D ZIF-8 CNT composite.

The metal organic framework structure ZIF-8 has been grown directly on vertically aligned carbon nano tubes (VACNT) by a solid vapour transformation of a ZnO@VACNT composite with gaseous 2-methylimidazole. The ZnO@VACNT composite was synthesised by atomic layer deposition (ALD) using diethylzinc and water as precursors resulting in a homogeneous distribution of crystalline ZnO particles with an average size of 13 nm within the 3D VACNT host structure. The ZnO@VACNT composite was transformed to ZIF-8 by reaction with 2-methyl-imidazole (Hmim) while maintaining the 3D VACNT structure employing a solid vapour transformation reaction. Reaction time and temperature were identified as key parameters to control the generated surface area and the degree of conversion of the nanoscaled ZnO particles. 80 °C and 72 h were found to be sufficient for a complete conversion while longer reaction times result in even higher surface areas of the formed ZIF-8@VACNT composite. Surface areas of up to 1569 m2 g-1 could be achieved. Temperatures below 80 °C led to an incomplete conversion even under longer reaction times of up to 6 weeks. Finally, the CO2 adsorption properties of the ZIF-8@VACNT composite were evaluated. A composite with a 27 w% content of CNTs and a surface area of 1277 m2 g-1 shows an adsorption of 6.05 mmol g-1 CO2 at 30 bar. From the comparison with the pristine materials ZIF-8 and VACNT alone the observed overall CO2 adsorption behaviour of the composite is a combination of the behaviour of the individual components, ZIF-8 and VACNTs. Namely the typical steep rise of the ZIF-8 in the low-pressure regime with a nearly linear steady progression in the medium pressure size regime, the latter typical for VACNTs, proves that the combination of both components leads to enhanced adsorption properties of the ZIF-8@VACNT composite compared to the sole components ZIF-8 and VACNTs.

Indicators for implementation outcome monitoring of reporting and learning systems in hospitals: an underestimated need for patient safety.

OBJECTIVE: We aimed to investigate the perception of the implementation success of reporting and learning systems in German hospitals, the perceived relevance of the implementation outcomes and whether and how these implementation outcomes are monitored. An reporting and learning system is a tool used worldwide for patient safety that identifies and analyses critical events, errors, risks and near misses in healthcare. METHODS: A pretested exploratory cross-sectional online survey was conducted with reporting and learning system experts from 51 acute care hospitals. For communicative validation, the results were discussed in person in an expert panel discussion (N=23). RESULTS: Fifty-three per cent (n=27) of the participants (N=51) of the online survey perceived that their reporting and learning system was being comprehensively and successfully implemented. However, no service or patient outcomes were reported to ultimately capture the concept of implementation success. Most of the participants reported a (high) relevance of the implementation outcomes' acceptability and sustainability. In total, 44 measures were provided to monitor implementation outcomes. However, most of the quantitative measures were based on the (relative) number of entered reports. Qualitative measures were reported in relation to the 'quality of the report'. In general, the measures were poorly specified. CONCLUSION: There is an underestimated need to develop validated 'implementation patient safety indicator(s) (sets)' to monitor implementation outcomes of reporting and learning systems. We also identified a potential need to facilitate awareness of the concept of implementation success and its relevance for patient safety. Drafts of indicators that could be used as a starting point for the further development of 'implementation patient safety indicators' were provided.

Conductive Geopolymers as Low-Cost Electrode Materials for Microbial Fuel Cells.

Geopolymer (GP) inorganic binders have a superior acid resistance compared to conventional cement (e.g., Portland cement, PC) binders, have better microbial compatibility, and are suitable for introducing electrically conductive additives to improve electron and ion transfer properties. In this study, GP-graphite (GPG) composites and PC-graphite (PCG) composites with a graphite content of 1-10 vol % were prepared and characterized. The electrical conductivity percolation threshold of the GPG and PCG composites was around 7 and 8 vol %, respectively. GPG and PCG composites with a graphite content of 8 to 10 vol % were selected as anode electrodes for the electrochemical analysis in two-chamber polarized microbial fuel cells (MFCs). Graphite electrodes were used as the positive control reference material. Geobacter sulfurreducens was used as a biofilm-forming and electroactive model organism for MFC experiments. Compared to the conventional graphite anodes, the anode-respiring biofilms resulted in equal current production on GPG composite anodes, whereas the PCG composites showed a very poor performance. The largest mean value of the measured current densities of a GPG composite used as anodes in MFCs was 380.4 µA cm-2 with a standard deviation of 129.5 µA cm-2. Overall, the best results were obtained with electrodes having a relatively low Ohmic resistance, that is, GPG composites and graphite. The very first approach employing sustainable GPs as a low-cost electrode binder material in an MFC showed promising results with the potential to greatly reduce the production costs of MFCs, which would also increase the feasibility of MFC large-scale applications.

Solution synthesis and dielectric properties of alumina thin films: understanding the role of the organic additive in film formation.

Alumina thin films are synthesized by combustion synthesis of mixtures of aluminium nitrate (ALN) and methylcarbazate (MCZ). The interdependence of the ratio of oxidizer and reducing agent on composition, microstructure and electronic properties of the resulting oxide layers is investigated. The dielectric and insulating behaviour is improved by addition of different amounts of MCZ (MCZ : ALN = 0.67 or 2.5). In this way films (thickness ∼140 nm) with a dielectric constant κ of 9.7 and a dielectric loss tan δ below 0.015 can be achieved. Medium concentrations of MCZ (MCZ : ALN = 1.0 or 1.5) lead to films with lower performance, though. Our studies indicate two opposing effects of the organic additive. Removal of organic residues during film formation as combustion gases is potentially detrimental. Larger amounts of MCZ, however, cause condensation reactions in the precusor mixture, which improve the microstructure. The porosity of the films can be sucessfully analyzed by positron annihilation liftetime studies. In this way the impact of the organic ligand sphere on the resulting microstructure can be quantified. Samples prepared from ALN alone exhibit mesopores and also larger micropores. In contrast, the formation of mesopores can be inhibited by addition of MCZ.

Atomic Layer Deposition of Ternary Indium/Tin/Aluminum Oxide Thin Films, Their Characterization and Transistor Performance under Illumination.

Multilayered heterostructures comprising of In2 O3 , SnO2 , and Al2 O3 were studied for their application in thin-film transistors (TFT). The compositional influence of tin oxide on the properties of the thin-film, as well as on the TFT characteristics is investigated. The heterostructures are fabricated by atomic layer deposition (ALD) at 200 °C, employing trimethylindium (TMI), tetrakis(dimethylamino)tin (TDMASn), trimethylaluminum (TMA), and water as precursors. After post-deposition annealing at 400 °C the thin-films are found to be amorphous, however, they show a discrete layer structure of the individual oxides of uniform film thickness and high optical transparency in the visible region. Incorporation of only two monolayers of Al2 O3 in the active semiconducting layer the formation of oxygen vacancies can be effectively suppressed, resulting in an improved semiconducting and switching behavior. The heterostacks comprising of In2 O3 /SnO2 /Al2 O3 are incorporated into TFT devices, exhibiting a saturation field-effect mobility (µsat ) of 2.0 cm2 ⋅ V-1 s-1 , a threshold-voltage (Vth ) of 8.6 V, a high current on/off ratio (IOn /IOff ) of 1.0×107 , and a subthreshold swing (SS) of 485 mV ⋅ dec-1 . The stability of the TFT under illumination is also altered to a significant extent. A change in the transfer characteristic towards conductive behavior is evident when illuminated with light of an energy of 3.1 eV (400 nm).

Zinc Oxide Defect Microstructure and Surface Chemistry Derived from Oxidation of Metallic Zinc. Thin Film Transistor and Sensoric Behaviour of ZnO Films and Rods.

Invited for the cover of this issue is Jörg J. Schneider and co-workers at Technical University Darmstadt, Helmholtz-Zentrum Dresden-Rossendorf and KIT Karlsruhe. The image depicts the application of high energy generated electron/positron couples which are able to detect defects sites in semiconducting zinc oxide thin films. Read the full text of the article at 10.1002/chem.202004270.

Zinc Oxide Defect Microstructure and Surface Chemistry Derived from Oxidation of Metallic Zinc: Thin-Film Transistor and Sensor Behavior of ZnO Films and Rods.

Zinc oxide thin films are fabricated by controlled oxidation of sputtered zinc metal films on a hotplate in air at temperatures between 250 and 450 °C. The nanocrystalline films possess high relative densities and show preferential growth in (100) orientation. Integration in thin-film transistors reveals moderate charge carrier mobilities as high as 0.2 cm2 V-1 s-1 . The semiconducting properties depend on the calcination temperature, whereby the best performance is achieved at 450 °C. The defect structure of the thin ZnO film can be tracked by Doppler-broadening positron annihilation spectroscopy as well as positron lifetime studies. Comparably long positron lifetimes suggest interaction of zinc vacancies (VZn ) with one or more oxygen vacancies (VO ) in larger structural entities. Such VO -VZn defect clusters act as shallow acceptors, and thus, reduce the overall electron conductivity of the film. The concentration of these defect clusters decreases at higher calcination temperatures as indicated by changes in the S and W parameters. Such zinc oxide films obtained by conversion of metallic zinc can also be used as seed layers for solution deposition of zinc oxide nanowires employing a mild microwave-assisted process. The functionality of the obtained nanowire arrays is tested in a UV sensor device. The best results with respect to sensor sensitivity are achieved with thinner seed layers for device construction.

Can top-down effects of cypriniform fish be used to mitigate eutrophication effects in medium-sized European rivers?

Eutrophication seriously threatens the ecological quality and biodiversity of running waters. In nutrient-enriched streams and shallow rivers, eutrophication leads to excessive periphyton growth and, in turn, biological clogging, oxygen depletion in the hyporheic zone and finally a reduction in the hyporheic habitat quality. Top-down control of the food-web by manipulating fish stocks, similar to the biomanipulation successfully applied in lakes, offers a promising approach to mitigating the effects of eutrophication in shallow rivers, especially those in which major reductions in nutrient input are not feasible. We conducted a reach-scale experiment over 4 years in a medium-sized eutrophic river to assess whether the top-down effects of two important large European cypriniform fish species, herbivorous common nase (Chondrostoma nasus) and omnivorous European chub (Squalius cephalus), would mitigate the effects of eutrophication. The enhancement of fish stocks was expected to reduce biological clogging, via the top-down control of periphyton by benthic grazing and enhanced bioturbation, thus increasing oxygen availability in the hyporheic zone as well as water exchange between the surface water and the hyporheic zone. As expected, enhancing the stocks of nase and chub increased both oxygen availability and vertical exchange flux of water in the upper layer of the hyporheic zone. However, periphyton biomass (chlorophyll a) was significantly reduced only in deeper pool habitat. Thus, while experimental biomanipulation in a shallow river significantly mitigated the effects of eutrophication in the hyporheic zone, top-down effects on periphyton biomass were rather small. Overall, to our knowledge, our results provide first evidence that the biomanipulation achieved by enhancing herbivorous and omnivorous fish stocks has the potential to mitigate the effects of eutrophication in medium-sized European rivers.

Environmentally Benign Solution-Based Procedure for the Fabrication of Metal Oxide Coatings on Metallic Pigments.

Aluminum pigments were coated with Fe2O3 and CuO by solution-based thermal decomposition of the urea nitrate compounds hexakisureairon(III)nitrate and tetrakisureacopper(II)nitrate. The deposition process was optimized to obtain homogeneously coated aluminum pigments. The growth of the surface coatings was controlled by investigation with scanning electron microscopy, energy dispersive X-ray spectroscopy and static light scattering as well as infrared, X-ray diffraction and thermogravimetric analysis. The iron precursor showed an incomplete decomposition in solution, incorporating traces of urea molecules inside the coatings while the copper precursor showed complete dissociation accompanied by in situ formation of amine complexes. The amount of organic residues resulting from ligand fragments in the final oxide coatings could be reduced to 22 % for the iron oxide and 12 % for the copper oxide by further temperature treatment in solution (259 °C). Colorimetric investigations of the obtained pigments revealed an excellent hiding power, outperforming the pigments used in current state-of-the-art formulations.

A 3D-polyphenylalanine network inside porous alumina: Synthesis and characterization of an inorganic-organic composite membrane.

Surface functionalization of porous materials allows for the introduction of additional functionality coupled with high mechanical stability of functionalized inner pores. Herein, we investigate the surface-initiated ring-opening polymerization (SI-ROP) of phenylalanine-N-carboxyanhydride (PA-NCA) in porous alumina membranes (ALOX-membranes) with respect to different solvent mixtures (tetrahydrofuran (THF) and dichloromethane (DCM)). It was found that increasing the volume fraction of DCM leads to an increasing amount of fibrillar polymer structures within the porous ALOX-membrane. A three-dimensional fibrillar network with intrinsic porosity was formed in DCM, whereas in THF, a dense and smooth polypeptide film was observed. A post-treatment with a mixture of chloroform and dichloroacetic acid leads to rearrangement of the morphology of the grafted polymer films. The analysis by scanning electron microscopy (SEM), near-infrared spectroscopy (NIR) and contact angle measurements (CA) reveals a change in morphology of the grafted polymer films, which is due to the rearrangement of the secondary structure of the polypeptides. No significant loss of the surface-grafted polypeptides was determined by thermogravimetric (TG) measurements, which indicates that the change in morphology of the polymer films is solely a result of a conformational change of the surface-grafted polypeptides. Furthermore, adsorption of a test analyte (chloroanilic acid) was investigated with respect to different polymer functionalization schemes for reversed-phase solid phase extraction applications. The adsorption capability of the functionalized composite membrane was increased from 16.7% to 38.1% compared to the native ALOX-membrane.

Synthesis and Assembly of Zinc Oxide Microcrystals by a Low-Temperature Dissolution-Reprecipitation Process: Lessons Learned About Twin Formation in Heterogeneous Reactions.

Cobalt-doped zinc oxide single crystals with the shape of hexagonal platelets were synthesized by thermohydrolysis of zinc acetate, cobalt acetate, and hexamethylenetetramine (HMTA) in mixtures of ethanol and water. The mineralization proceeds by a low-temperature dissolution-reprecipitation process from the liquid phase by the formation of basic cobalt zinc salts as intermediates. The crystal shape as well as twin formation of the resulting oxide phase can be influenced by careful choice of the solvent mixture and the amount of doping. An understanding of the course of the reaction was achieved by comprehensive employment of analytical techniques (i.e., SEM, XRD, IR) including an in-depth HRTEM study of precipitates from various reaction stages. In addition, EPR as well as UV/Vis spectroscopic measurements provide information about the insertion of the cobalt dopant into the zincite lattice. The Langmuir-Blodgett (LB) technique is shown to be suitable for depositing coatings of the platelets on glass substrates functionalized with polyelectrolyte multilayers and hence is applied for the formation of monolayers containing domains with ordered tessellation. No major differences are found between deposits on substrates with anionic or cationic surface modification. The adherence to the substrates is sufficient to determine the absolute orientation of the deposited polar single crystals by piezoresponse force microscopy (PFM) and Kelvin probe force microscopy (KPFM) studies.

Photothermal catalytic properties of layered titanium chalcogenide nanomaterials.

The search for novel photocatalysts that make use of almost the entire solar spectrum remains an ongoing task to achieve high efficiency in energy conversion. While titanium chalcogenides offer a variety of phase compositions with different photophysical properties, their photocatalytic performance in pollutant degradation has not been investigated to date. In contrast to the model photocatalyst titanium dioxide, titanium chalcogenides possess small band gaps which make them eligible to absorb light in the visible range up to the near-infrared region, thus making them interesting candidates for photocatalysis. Herein titanium chalcogenide-based photocatalysts are synthesized by the chemical vapor transport (CVT) method and studied for their photocatalytic activity towards pollutant degradation. A series of titanium chalcogenides TiXn (X = S, n = 1-3; X = Se, n = 2; X = Te, n = 1) have been characterized by a variety of physico-chemical methods. Due to the expected non-stoichiometry of some titanium sulfides, they offer a large number of defect states which make them interesting candidates for photocatalysis. Thus, these titanium-chalcogenides were systematically studied for the photocatalytic degradation of pollutants using methyl orange dye as the test pollutant under simulated sunlight. Particularly TiS and TiS3 show high photocatalytic and thermocatalytic activity, outperforming the activity of titanium dioxide (pure anatase). By controlling the ratios of titanium and chalcogen elements and the specific reaction conditions, a variety of titanium chalcogenides with different compositions and phases showing a high photocatalytic activity can be accessed. Furthermore, it is found that the formation of a titanium dioxide passivation layer during photocatalysis results in a titanium oxide/titanium sulfide heterostructure. This allows further enhancement of the photocatalytic and thermocatalytic activity compared to the bare Ti-chalcogenides.

Synthesis, oxide formation, properties and thin film transistor properties of yttrium and aluminium oxide thin films employing a molecular-based precursor route.

Combustion synthesis of dielectric yttrium oxide and aluminium oxide thin films is possible by introducing a molecular single-source precursor approach employing a newly designed nitro functionalized malonato complex of yttrium (Y-DEM-NO21) as well as defined urea nitrate coordination compounds of yttrium (Y-UN 2) and aluminium (Al-UN 3). All new precursor compounds were extensively characterized by spectroscopic techniques (NMR/IR) as well as by single-crystal structure analysis for both urea nitrate coordination compounds. The thermal decomposition of the precursors 1-3 was studied by means of differential scanning calorimetry (DSC) and thermogravimetry coupled with mass spectrometry and infrared spectroscopy (TG-MS/IR). As a result, a controlled thermal conversion of the precursors into dielectric thin films could be achieved. These oxidic thin films integrated within capacitor devices are exhibiting excellent dielectric behaviour in the temperature range between 250 and 350 °C, with areal capacity values up to 250 nF cm-2, leakage current densities below 1.0 × 10-9 A cm-2 (at 1 MV cm-1) and breakdown voltages above 2 MV cm-1. Thereby the increase in performance at higher temperatures can be attributed to the gradual conversion of the intermediate hydroxy species into the respective metal oxide which is confirmed by X-ray photoelectron spectroscopy (XPS). Finally, a solution-processed Y x O y based TFT was fabricated employing the precursor Y-DEM-NO21. The device exhibits decent TFT characteristics with a saturation mobility (µ sat) of 2.1 cm2 V-1 s-1, a threshold voltage (V th) of 6.9 V and an on/off current ratio (I on/off) of 7.6 × 105.

New Approaches to Respiratory Assist: Bioengineering an Ambulatory, Miniaturized Bioartificial Lung.

Although state-of-the-art treatments of respiratory failure clearly have made some progress in terms of survival in patients suffering from severe respiratory system disorders, such as acute respiratory distress syndrome (ARDS), they failed to significantly improve the quality of life in patients with acute or chronic lung failure, including severe acute exacerbations of chronic obstructive pulmonary disease or ARDS as well. Limitations of standard treatment modalities, which largely rely on conventional mechanical ventilation, emphasize the urgent, unmet clinical need for developing novel (bio)artificial respiratory assist devices that provide extracorporeal gas exchange with a focus on direct extracorporeal CO2 removal from the blood. In this review, we discuss some of the novel concepts and critical prerequisites for such respiratory lung assist devices that can be used with an adequate safety profile, in the intensive care setting, as well as for long-term domiciliary therapy in patients with chronic ventilatory failure. Specifically, we describe some of the pivotal steps, such as device miniaturization, passivation of the blood-contacting surfaces by chemical surface modifications, or endothelial cell seeding, all of which are required for converting current lung assist devices into ambulatory lung assist device for long-term use in critically ill patients. Finally, we also discuss some of the risks and challenges for the long-term use of ambulatory miniaturized bioartificial lungs.

Tungsten oxide nanorod architectures as 3D anodes in binder-free lithium-ion batteries.

Tungsten oxide nanorods were synthesized using a template assisted process. A polycarbonate membrane (pore diameter 100 nm) was vacuum infiltrated by an aqueous solution of ammonium paratungstate ((NH4)10H2W12O42·xH2O) and yielded crystalline 3D oriented WO3 nanorod arrays after template etching and calcination. By coating the nanorod arrays with carbon, a binder-free 3D WO3/C composite electrode could be fabricated, allowing capacities up to 1149, 811, 699, 559 and 253 mA h g-1 for cycles 1, 2, 20, 50 and 200 as well as a coulombic efficiency of around 99%. Moreover, as prepared WO3 nanorod structures without that specific type of carbon coating deliver capacities in a range of 200-250 mA h g-1 after 20 cycles. Finally, a full cell lithium ion battery system is fabricated. It consists of LiCoO2 nanoparticles as cathode and binder-free carbon coated 3D WO3 composite material as anode. Pre-lithiation of this 3D WO3/C composite material as pre-conditioning before full cell assembly leads to a cell capacity of almost twice of that without pre-lithiation. Discharge capacities of 111, 91, 41 and 23 mA h g-1 can be obtained for cycles 2, 20, 100 and 200 with a coulombic efficiency of around 99% in the case of the pre-lithiated 3D WO3/C composite anode.

Controlling surface morphology and sensitivity of granular and porous silver films for surface-enhanced Raman scattering, SERS.

The design of efficient substrates for surface-enhanced Raman spectroscopy (SERS) for large-scale fabrication at low cost is an important issue in further enhancing the use of SERS for routine chemical analysis. Here, we systematically investigate the effect of different radio frequency (rf) plasmas (argon, hydrogen, nitrogen, air and oxygen plasma) as well as combinations of these plasmas on the surface morphology of thin silver films. It was found that different surface structures and different degrees of surface roughness could be obtained by a systematic variation of the plasma type and condition as well as plasma power and treatment time. The differently roughened silver surfaces act as efficient SERS substrates showing greater enhancement factors compared to as prepared, sputtered, but untreated silver films when using rhodamine B as Raman probe molecule. The obtained roughened silver films were fully characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron (XPS and Auger) and ultraviolet-visible spectroscopy (UV-vis) as well as contact angle measurements. It was found that different morphologies of the roughened Ag films could be obtained under controlled conditions. These silver films show a broad range of tunable SERS enhancement factors ranging from 1.93 × 102 to 2.35 × 105 using rhodamine B as probe molecule. The main factors that control the enhancement are the plasma gas used and the plasma conditions, i.e., pressure, power and treatment time. Altogether this work shows for the first time the effectiveness of a plasma treatment for surface roughening of silver thin films and its profound influence on the interface-controlled SERS enhancement effect. The method can be used for low-cost, large-scale production of SERS substrates.