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Chemistry - a European journal 27(38), 9791-9800 (2021). doi:10.1002/chem.202101126, Multilayered heterostructures comprising of In$_2$O$_3$, SnO$_2$, and Al$_2$O$_3$ 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 Al$_2$O$_3$ 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 In$_2$O$_3$/SnO$_2$/Al$_2$O$_3$ are incorporated into TFT devices, exhibiting a saturation field-effect mobility ($μ_{sat}$) of 2.0 cm$^2$⋅ V$^{−1}$ s$^{−1}$, a threshold-voltage (V$_{th}$) of 8.6 V, a high current on/off ratio (I$_{On}$/I$_{Off}$) of 1.0×10$^7$, 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)., Published by Wiley-VCH, Weinheim

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 m$^{2}$ 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 CO$_{2}$ 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 m$^{2}$ g$^{-1}$ shows an adsorption of 6.05 mmol g$^{-1}$ CO$_{2}$ at 30 bar. From the comparison with the pristine materials ZIF-8 and VACNT alone the observed overall CO$_{2}$ 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.

This study examined the influence of graphene oxide (GO) dosage on the properties and microstructure of cement pastes against hydrochloric acid (HCl) attack. The mass loss (and sectional area loss)...

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−1s−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., Thin‐film transistors: Zinc oxide layers can be obtained conveniently through the oxidation of sputter‐deposited thin films of zinc metal at temperatures between 250 and 450 °C. Positron annihilation studies hint at vacancy clusters rather than isolated point defects as the dominating feature in the defect chemistry of these films. This allows the description of the influence of annealing temperature on the resulting electronic performance of the semiconducting layers in thin‐film transistors.

Titanium diselenide (TiSe2) is the least studied member of the transition metal dichalcogenide family due to a lack of available synthesis methodology, controlled bandgap engineering, and rapid characterization of layers. In this paper, we report the chemical exfoliation of TiSe2 platelets synthesized by the chemical vapor transport route in ortho-dichlorobenzene (o-DCB) functionalized with oleylamine (OLA), for the first time to the best of our knowledge. It is found that the addition of OLA supports the formation of a stable dispersion of a large area of the TiSe2 sheets due to surface capping with the OLA molecules indicating the importance of the ligand in dispersion behavior. The X-ray diffraction pattern confirms the hexagonal structure of the TiSe2 platelets with the space group P3[combining macron]m1 while Raman spectroscopy reveals that two modes of vibration i.e. A1g and E2g exist with layered structures having dimensions in micrometers as confirmed by scanning electron microscopy. Fourier transform infrared spectroscopy confirms the successful functionalization of chemically exfoliated TiSe2 nanosheets. Field-emission scanning electron microscopy reveals that exfoliated TiSe2 has a thickness of 15-55 nm whereas high-resolution transmission electron microscopy indicates thicker sheets for ligand-free exfoliated TiSe2 which are crystalline. Atomic force microscopy confirms the formation of nanosheets. UV-Visible, photoluminescence, and time-resolved PL spectroscopy showed an enhanced effect and better average lifetime of excitation for the exfoliated sheets with OLA than those without OLA. The C-V studies reveal that with increasing scan rate, the corresponding current also increases. The present study offers the possibility of their utilization in optoelectronics, advanced low-power electronics, voltage-controlled oscillators, ultra-fast electronics, and electrochemical devices.

All-solid-state lithium-ion batteries (ASSLIBs) are promising alternatives to conventional organic electrolyte-based batteries due to their higher safety and higher energy densities. Despite advantages, ASSLIBs suffer from issues like high charge transfer resistances due to the brittleness of the inorganic solid electrolyte and chemical instabilities at the lithium/electrolyte interface. Within this work, we investigate composite electrolytes based on garnet-type Li6.4La3Zr1.4Ta0.6O12 (LLZTO), polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl) imide (LiTSFI), prepared via a solvent free cryo-milling approach in contrast to conventional solvent mediated synthesis. Compositions ranging from polymer-rich to garnet-rich systems are investigated via X-ray diffraction, Raman spectroscopy and Fourier transform infrared spectroscopy (FT-IR) in order to determine the compatibility of the cryo-milling process towards membrane fabrication along with the possible chemical interactions between the composite membrane components. Electrochemical impedance spectroscopy (EIS) is used to study the role of ceramic to Polymer weight fraction on ionic conductivity. It is shown that the addition of succinonitrile (SCN) to the garnet-rich composite electrolytes can significantly improve the ionic conductivity compared to the SCN free composite electrolytes.

Self-organized porous anodic alumina (PAA) layers have been previously suggested as effective surface-enhanced Raman scattering (SERS) substrates, which exhibit high enhancement factors when coated...

Porous hexagonal ordered anodic alumina (PAOX) is a long-known porous oxide material. Despite its straightforward experimental approach, a precise understanding of the microscopic processes that le...

Surface-enhanced Raman spectroscopy (SERS) represents an important spectroscopic technique with applications in many fields due to its ability to determine structural information of the analyte wit...

Fabrication of dielectric yttrium aluminium oxide YAlxOy thin films utilizing nitro functionalized malonato complexes of aluminium Al-DEM-NO21 and yttrium Y-DEM-NO22 is described. Their controlled thermal conversion under moderate conditions into amorphous ternary yttrium aluminium oxide dielectric thin films with a very low surface roughness (RRMS < 0.2 nm) was accomplished. Capacitor devices composed of YAlxOy exhibit excellent dielectric properties at a processing temperature of 350 °C. It was possible to systematically modulate their significant performance parameters such as dielectric constant, leakage current density and breakdown voltage according to the amount of yttrium rare earth metal incorporation which showed an optimum at 30 mol% yttrium incorporation. The yttrium inclusion into the amorphous AlxOy lattice reduces the formation of carbonate species in comparison to yttrium free pristine AlxOy dielectric thin films. Finally, a solution-processed thin-film transistor (TFT) with YAlxOy (30 mol% – Y content) as the dielectric and indium zinc oxide (IZO) as the semiconductor exhibits good TFT characteristics with a saturation mobility (μsat) of 2.6 cm2 V−1 s−1, an on-voltage (Von) of −1.1 V, a threshold voltage (Vth) of 12.4 V and an on/off current ratio (Ion/off) of 1.8 × 107. As an alternative to a necessary thermal annealing step deep UV irradiation at 160 nm allows the implementation of low-temperature (150 °C) solution processing of a yttrium free pure AlxOy dielectric, which exhibits excellent dielectric performance parameters. It displays an areal capacity of 153 nF cm−2, a leakage current density of 1.7 × 10−9 A cm−2 at 1 MV cm−1 and a breakdown voltage of 4.1 MV cm−1.

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., Crystal shape: Doping is an effective way to control crystal shape in mineralization processes. Studying the synthesis of single‐crystalline hexagonal platelets of Co‐doped ZnO with advanced high‐resolution transmission electron microscopy (HRTEM) techniques can hereby provide an instructive insight into the details of the formation mechanism.

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.

Today's energy problems, caused by the irrational consumption of fossil fuels and, as a result, terrible environmental consequences, require the global population to quickly introduce clean energy sources. Electrochemical power sources, which include the fuel cell, provide the technological basis for electrical energy production. While proton exchange membrane fuel cells (PEMFC) rely on platinum based catalysts, obtaining stable and earth abundant catalytic materials for the oxygen reduction reaction (ORR) is an important step towards large scale integration. Our work focusses on FeNC noble-metal free catalysts in PEMFC conditions. The reaction conditions are much more complex in comparison to half cells, as transport processes and e.g. carbon oxidation affect the performance data. Thus, it turns out to be extremely difficult to determine the most important factors affecting the catalytic activity and stability of the material and to optimize the structure of the membrane-electrode assembly as several factors are overlaying each other: For example, the pyrolysis temperature affects the surface area, degree of graphitization and iron-related composition as well as extent of surface functional groups [1]. The metal loading, pyrolysis temperature and a use of possible precursor templates effects the structure, surface area as well as ORR activity and selectivity of catalysts [2], [3]. In our recent work, it was shown that in contrast to the electrochemical characteristics observed in rotating disc electrode (RDE) measurements, the best performing catalyst was prepared at the highest investigated temperature for both FC activity and stability [1]. In contrast, the dwell time had only a limited impact at low pyrolysis temperature, whereas a variation from 30 min to 90 min gave significant destruction of molecular FeNx moieties for the high temperature pyrolysis. [1] To gain further insights on the effect of preparation parameters on FC performance and in specific stability, we coupled a quadrupole mas-spectrometer to the cathode exhaust to follow possible release of CO2 depending on the applied conditions. The data are interpreted together with the structural characterization of the materials. We will discuss how the dwell time and pyrolysis temperature effected on morphology changes of the catalyst and to what extent this impacts the FC activity and short-term stability. Acknowledgements A.O. would like to thank you the TU Darmstadt for the Future talent scholarship, UIK gratefully acknowledges financial support by the BMBF young research group StRedO (03XP0092), and we thank Y. Ostroverkh, and Z. L. Müller, for the consultation and assistance with the fuel cell setup. [1] J. Scharf, M. Kübler, V. Gridin, W.D.Z. Wallace, L. Ni, S.D. Paul, U.I. Kramm, Relation between half-cell and fuel cell activity and stability of FeNC catalysts for the oxygen reduction reaction, (2022) SusMat, accepted (doi: 10.1002/sus2.84). [2] P.Theis, W.D. Z. Wallace, L. Ni, M. Kübler, A. Schlander, R. W. Stark, N. Weidler, M, Gallei, U. I. Kramm. Systematic study of precursor effects on structure and oxygen reaction activity of FeNC catalysts, (2021) Philos. Trans. Royal Soc. A PHILOS T R SOC A, (doi: 10.6084/m9.figshare.c.5506708). [3] P. Boldrin, D. Malko, A. Mehmood, U. I. Kramm, S. Wagner, S. Paul, N. Weidler, A. Kucernak. Deactivation, reactivation and super-activation of Fe-N/C oxygen reduction electrocatalysts: Gas sorption, physical and electrochemical investigation using NO and O2., (2021) Appl. Catal. B, Vol. 292, 120169, (doi: 10.1016/j.apcatb.2021.120169).

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.

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 YxOy based TFT was fabricated employing the precursor Y-DEM-NO21. The device exhibits decent TFT characteristics with a saturation mobility (μsat) of 2.1 cm² V⁻¹ s⁻¹, a threshold voltage (Vth) of 6.9 V and an on/off current ratio (Ion/off) of 7.6 × 10⁵.

Amorphous aluminium oxide thin films are accessible by a molecular single source precursor approach employing the coordination compound tris[(diethyl-2-nitromalonato)]aluminium(III) (Al-DEM-NO2). The precursor decomposes by thermal combustion under oxygen without the need of an additional additive into amorphous aluminium oxide films at 350 °C with a very low surface roughness of about 0.3 nm. Solution processing of the precursor results in the formation of smooth, dense and crack-free films, which are converted into amorphous AlxOy thin films after further calcination. Amorphous AlxOy thin films integrated within a capacitor device exhibit dielectric behavior in the temperature range between 200 and 350 °C, with areal capacity values between 41 and 86 nF cm−2 and leakage current densities ranging from 1.7 × 10−7 to 8.9 × 10−10 A cm−2 (at 1 MV cm−1) whereas breakdown voltages increase from 1.82 to 2.79 MV cm−1 in the temperature regime from 200 to 350 °C. The increase in performance at higher temperatures can be attributed to the stepwise conversion of the intermediate aluminium oxo–hydroxy species into aluminium oxide which is confirmed by X-ray photoelectron spectroscopy (XPS).

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., Coated metallic pigments: Solution based synthesis using molecular urea‐nitrate precursors allow low temperature metal oxide (Fe, Cu) thin film formation on aluminum pigments. The densely coated aluminum pigments display a good optical performance in regard of gloss and flop indices and an exceptional hiding power.

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.

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.

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.

Owing to their high stability against corrosive gases, carbon-based adsorbents are preferentially used for the adsorptive removal of SO2. In the present study, SO2 adsorption on different carbon nanomaterials namely carbon nanohorns (CNHs), multiwalled carbon nanotubes (MWNTs), single-walled carbon nanotubes (SWNTs) and vertically aligned carbon nanotubes (VACNTs) are investigated and compared against the adsorption characteristics of activated carbon and graphene oxide (GO). A comprehensive overview of the adsorption behavior of this family of carbon adsorbents is given for the first time. The relative influence of surface area and functional groups on the SO2 adsorption characteristics is discussed. The isosteric heat of adsorption values are calculated to quantify the nature of the interaction between the SO2 molecule and the adsorbent. Most importantly, while chemisorption is found to dominate the adsorption behavior in activated carbon, SO2 adsorption on carbon nanomaterials occurs by a physisorption mechanism.

Films consisting of nanocrystalline ZnO were deposited on ITO/glass electrodes using an electrophoretic process. The microwave-assisted thermolysis of zinc alkyl-acetoacetates resulted in the formation of stable dispersions for the electrophoretic deposition procedure. Uniform and smooth coatings could be achieved by starting the electrophoresis at lower voltages first and increasing to higher voltages at later stages of the deposition. The ZnO/ITO double layers were integrated in metal oxide semiconductor (MOS) capacitors by completing the set-up with a spin-coated PMMA dielectric layer and gold contacts. The MOS capacitors showed IV curves with a region of negative differential resistance, indicating charge trapping, both in the ZnO grains and at the ZnO/PMMA interface. Doppler broadening positron annihilation (DB-PAS) and positron annihilation life time spectroscopy (PALS) were employed to characterize the point defects and void space within the deposited ZnO layer which allowed to give insight into the bulk composition of the film composition. PALS revealed the presence of micropores in the range of 0.5 to 1.5 nm.

Multi-layer heterostructure oxide semiconductors employing a layer-by-layer deposition of alternating indium oxide and zinc oxide thin films generated via atomic layer deposition (ALD) are investigated for their feasibility into high performance thin film transistors (TFT). The successful deposition of uniform film thickness across the alternating indium oxide and zinc oxide deposition at 200 °C is achieved using trimethyl indium (TMI), diethyl zinc (DEZ) and water as oxidizing agent. The as-prepared polycrystalline material shows a conductive behaviour which upon additional mild annealing between 250–300 °C demonstrates a high TFT device performance. In addition, insights into the dependency of the defect passivation gradient within the multilayer upon thermal annealing of the oxide stack are presented. Studies towards an optimised film thickness result in a high device performance in enhancement mode with a saturation field-effect mobility (μsat.) of 6.5 cm2 V−1 s−1 and an on/off ratio (Ion/off) of 4.6 × 107 using a deliberately large width to length channel ratio (W/L = 500). The TFT performance turned out to be dependent on the position of the individual oxide layers within the stack and the number of heterostructure stacks. These findings on the influence of semiconductor stack formation allow for a better understanding on the formation of the active semiconductor channel and serve towards the applicability of ALD based heterostructure metal oxide semiconductors in next generation electronics.

Molybdenum(vi) oxide (MoO3) nanorod arrays were synthesized employing a template-assisted method. A polycarbonate membrane as a template was vacuum infiltrated with an aqueous solution of ammonium heptamolybdate. Template removal by oxygen plasma etching and calcination leads to the formation of highly crystalline 3D MoO3 nanorod arrays as a negative replica of the template. By applying sucrose as the carbon precursor, the mantling of the MoO3 nanorods with a thin carbon coating is obtained. Simultaneously, the direct and binder-free contact between the 3D MoOx nanorod arrays and the current collector resulting from the carbon coating could be achieved and leads to high capacities of up to 1376, 783, 856, 804 and 324 mA h g-1 for cycles 1, 2, 20, 50 and 200 as well as a coulombic efficiency of 99% for such 3D MoOx/C composite electrodes. The cycling performance of this 3D MoOx/C composite material is even more impressive, when comparing the determined experimental capacities with the theoretical capacities of graphite (372 mA h g-1) and MoO2 (838 mA h g-1). Additionally, MoO3 nanorod array electrodes without such an encapsulating carbon coating show an average capacity of only 175 mA h g-1 between cycles 20 and 200. Thus, the carbon coating of the MoO3 nanorod array can increase the electrochemical performance of a lithium-ion cell compared to conventional carbon additives when using MoO3 as the active anode material. This emphasizes the positive effects of the intimate and efficient electron transport and large surface area of the electrode material based on a minimal footprint architecture in Li-ion cells.

As an adsorbent, carbon nanotubes integrate the advantages of activated carbon with a robust sp2 carbon framework and a defined pore structure. Due to the presence of multiple adsorption sites, vertically aligned carbon nanotubes (VACNTs) exhibit excellent adsorption characteristics at high pressures (∼30 bar). However, it is known that a large fraction of the as-synthesized VACNTs are closed and are inaccessible for the adsorptive. In the present study, we employ a high temperature CO2 treatment process to open the VACNTs under controlled conditions without altering their alignment. Opening of the CNTs is confirmed by TEM and N2 adsorption measurements and subsequently the surface area of the opened VACNTs increases by 60%. Consequently, a so far unreported adsorption step, corresponding to adsorption in the interior of the CNTs is observed in the N2 adsorption isotherm. High pressure adsorption studies on these opened VACNTs revealed a dramatic increase of more than 140% in CO2 adsorption compared to as-prepared VACNTs, which is almost double that of zeolite 13X and is at par with certain metal-organic frameworks.