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The stability of perovskite solar cells (PSCs) is greatly affected by the interface between the perovskite active layer and the hole transport material (HTM). The rational design of HTMs with effective anchoring to the perovskite surface is an emerging elegant strategy to promote compact and ordered interfaces that lead to highly efficient and stable PSCs. Herein, we propose two fluorene-based HTM molecular architectures (SCF1 and SCF2) derived from the popular yet expensive Spiro-OMeTAD. Their employment as dopant-free HTMs in standard triple-cation CsFAMA PSCs leads to superior device stability, with a T80 lifetime well above 1 year (431 days). Our combined theoretical and experimental study of the CsFAMA|HTM interface reveals that the improved adhesion of the SCF-HTMs to the perovskite layer is the key to minimize the non-radiative recombination, reduce the hole trap density, and enhance the long-term stability of the corresponding devices. The simplified structures of SCF1 and SCF2, obtained by removing the orthogonal fragment of the Spiro-OMeTAD scaffold, show a lower molecular distortion than Spiro-OMeTAD, thus promoting a favorable electronic interaction between the SCF-HTMs and the perovskite. This study provides useful design criteria for achieving highly stable PSCs including dopant-free HTMs with optimized adhesion to the perovskite surface.

Perovskite-inspired Cu2AgBiI6 (CABI) absorber has recently gained increased popularity due to its low toxicity, intrinsic air stability, and wide bandgap ≈ 2 eV, which makes it ideal for indoor photovoltaics (IPVs). However, the considerable presence of both intrinsic and surface defects is responsible of the still modest indoor power conversion efficiency (PCE(i)) of CABI- based IPVs, with the short-circuit current density (JSC) being nearly half of the theoretical limit. Herein, we introduce antimony (III) (Sb3+) into the octahedral lattice sites of CABI structure, leading to CABI-Sb with substantially larger crystalline domains than CABI. The alloying of Sb3+ with bismuth (III) (Bi3+) induces changes in the local structural symmetry, in turn causing a remarkably increased formation energy of intrinsic defects. This accounts for the overall reduced defect density in CABI-Sb. CABI-Sb IPVs feature an outstanding PCE(i) of nearly 10% (9.53%) at 1000 lux, which represents an almost double PCE(i) compared to that of CABI devices (5.52%) mainly due to an improvement in JSC. This work will promote future compositional design studies to reduce the intrinsic defect tolerance of next-generation wide- bandgap absorbers for high-performance and stable IPVs.

Antimony-based perovskite-inspired materials (PIMs) are solution-processable halide absorbers with interesting optoelectronic properties, low toxicity, and good intrinsic stability. Their bandgaps around 2 eV make them particularly suited for indoor photovoltaics (IPVs). Yet, so far only the fully inorganic Cs3Sb2ClxI9−x composition has been employed as a light-harvesting layer in IPVs. Herein, the first triple-cation Sb-based PIM (CsMAFA-Sb) in which the A-site of the A3Sb2X9 structure consists of inorganic cesium alloyed with organic methylammonium (MA) and formamidinium (FA) cations is introduced. Simultaneously, the X-site is tuned to guarantee a 2D structure while keeping the bandgap nearly unchanged. The presence of three A-site cations is essential to reduce the trap-assisted recombination pathways and achieve high performance in both outdoor and indoor photovoltaics. The external quantum efficiency peak of 77% and the indoor power conversion efficiency of 6.4% are the highest values ever reported for pnictohalide-based photovoltaics. Upon doping of the P3HT hole-transport layer with F4-TCNQ, the power conversion efficiency of CsMAFA-Sb devices is fully retained compared to the initial value after nearly 150 days of storage in dry air. This work provides an effective compositional strategy to inspire new perspectives in the PIM design for IPVs with competitive performance and air stability. publishedVersion

Titanium dioxide (TiO2) can protect photoelectrochemical (PEC) devices from corrosion, but the fabrication of high-quality TiO2 coatings providing long-term stability has remained challenging. Here, we compare the influence of Si wafer cleaning and postdeposition annealing temperature on the performance of TiO2/n+-Si photoanodes grown by atomic layer deposition (ALD) using tetrakis(dimethylamido)titanium (TDMAT) and H2O as precursors at a growth temperature of 100 °C. We show that removal of native Si oxide before ALD does not improve the TiO2 coating performance under alkaline PEC water splitting conditions if excessive postdeposition annealing is needed to induce crystallization. The as-deposited TiO2 coatings were amorphous and subject to photocorrosion. However, the TiO2 coatings were found to be stable over a time period of 10 h after heat treatment at 400 °C that induced crystallization of amorphous TiO2 into anatase TiO2. No interfacial Si oxide formed during the ALD growth, but during the heat treatment, the thickness of interfacial Si oxide increased to 1.8 nm for all of the samples. Increasing the ALD growth temperature to 150 °C enabled crystallization at 300 °C, which resulted in reduced growth of interfacial Si oxide followed by a 70 mV improvement in the photocurrent onset potential. publishedVersion

The physicochemical properties of titanium dioxide (TiO2) depend strongly on the crystal structure. Compared to anatase, rutile TiO2 has a smaller bandgap, a higher dielectric constant, and a higher refractive index, which are desired properties for TiO2 thin films in many photonic applications. Unfortunately, the fabrication of rutile thin films usually requires temperatures that are too high (>400 °C, often even 600-800 °C) for applications involving, e.g., temperature-sensitive substrate materials. Here, we demonstrate atomic layer deposition (ALD)-based fabrication of anatase and rutile TiO2 thin films mediated by precursor traces and oxide defects, which are controlled by the ALD growth temperature when using tetrakis(dimethylamido)titanium(IV) (TDMAT) and water as precursors. Nitrogen traces within amorphous titania grown at 100 °C inhibit the crystal nucleation until 375 °C and stabilize the anatase phase. In contrast, a higher growth temperature (200 °C) leads to a low nitrogen concentration, a high degree of oxide defects, and high mass density facilitating direct amorphous to rutile crystal nucleation at an exceptionally low post deposition annealing (PDA) temperature of 250 °C. The mixed-phase (rutile-brookite) TiO2 thin film with rutile as the primary phase forms upon the PDA at 250-500 °C that allows utilization in broad range of TiO2 thin film applications. publishedVersion

Simultaneous poisoning of sulfur + phosphorus on a platinum-based diesel oxidation catalyst was studied to gain a deeper understanding on the catalyst deactivation. Compared to a single poisoning (sulfur or phosphorus), the simultaneous poisoning had a severe effect on the catalyst activation: light-off temperature for 90% conversion of propene was not reached, this of carbon monoxide was much higher than expected, and the maximum conversion of nitrogen monoxide collapsed. With very comprehensive structural characterization by various methods (e.g. STEM-EDS, XPS, DRIFTS) used, we achieved to conclude an explanation for this. In the case of the S + P-poisoning of the catalyst, formed aluminum phosphate was found to block adsorption sites for sulfur species on alumina and sulfur adsorbs mainly on cerium oxides. In addition, sulfur species remain with and in the vicinity of the platinum particles blocking active sites. publishedVersion

Hierarchical surfaces that aid in the droplet nucleation, growth, and removal is highly desirable for fog and moisture harvesting applications. Taking inspiration from the unique architecture of leaf skeletons, we present a multiscale surface capable of rapidly nucleating, growing, and directional transport of the water droplets. Copper oxide microtufts were fabricated onto the Ficus religiosa leaf skeletons via electroplating and chemical oxidation techniques. The fabricated surfaces with microtufts had high wettability and very good fog harvesting ability. CuO surfaces tend to become hydrophobic over time because of the adsorption of the airborne species. The surfaces were efficient in fog harvesting even when the hydrophobic coating is present. The overall water collection efficiencies were determined, and the role of the microtufts, fractal structures, and the orientation of leaf veins was investigated. Compared to the planar control surfaces, the noncoated and hydrophobic layer-coated copper oxide microtufts on the leaf skeletons displayed a significant increase in the fog harvesting efficiency. For superhydrophilic skeleton surfaces, the water collection rate was also observed to slightly vary with the vein orientation. The CuO microtufts along with high surface area fractals allowed an effective and sustainable way to capture and transport water. The study is expected to provide valuable insights into the design and fabrication of sustainable and efficient fog harvesting systems. publishedVersion

In the study of the electrophysiological activity of cultured cells, the integrity of the electrical insulation layer is crucial in ensuring the reliability of microelectrode array (MEA) sensor measurements. The materials used are required to withstand the challenging culture conditions for up to several months. The commonly used silicon nitride (SiN) has been reported to corrode in cell cultures with very little attention in the scientific community. Herein, we show that plasma-enhanced chemical vapor deposited (PECVD) SiN is subject to substantial wear when in contact with different culture media, with the corrosion rate depending on the deposition temperature and media type. A chemically stable insulator is proposed and demonstrated as an alternative for SiN using thermally annealed atomic layer deposited (ALD) titanium dioxide (TiO2) as a transparent protective layer for SiN. Electrochemical impedance spectroscopy (EIS) was successfully applied to periodically assess the integrity and thickness of the insulation layers in two different media, with profilometer measurements performed as an endpoint analysis to confirm the actual change in thickness in four solutions. ALD TiO2 not only prevented insulator corrosion but also showed excellent cytocompatibility during a four-week culture with human embryonic stem cell (hESC)-derived neurons. The results here underline the need for addressing the corrosion of SiN insulation in MEA sensors. We believe that the integrity and results of cellular measurements can be compromised, especially when reusing MEAs. We propose the ALD TiO2 protected insulator as a viable solution for this problem, as it increases reliability, particularly during extended cell cultures. publishedVersion

Lead-free perovskite-inspired materials (PIMs) are gaining attention in optoelectronics due to their low toxicity and inherent air stability. Their wide bandgaps (≈2 eV) make them ideal for indoor light harvesting. However, the investigation of PIMs for indoor photovoltaics (IPVs) is still in its infancy. Herein, the IPV potential of a quaternary PIM, Cu2AgBiI6 (CABI), is demonstrated upon controlling the film crystallization dynamics via additive engineering. The addition of 1.5 vol% hydroiodic acid (HI) leads to films with improved surface coverage and large crystalline domains. The morphologically-enhanced CABI+HI absorber leads to photovoltaic cells with a power conversion efficiency of 1.3% under 1 sun illumination—the highest efficiency ever reported for CABI cells and of 4.7% under indoor white light-emitting diode lighting—that is, within the same range of commercial IPVs. This work highlights the great potential of CABI for IPVs and paves the way for future performance improvements through effective passivation strategies. publishedVersion

Cesium lead iodide (CsPbI3) perovskite nanocrystals (NCs) suffer from a known transformation at room temperature from their red-emitting (black) to non-emitting (yellow) phase, induced by the tilting of PbI6 octahedra. While the reported attempts to stabilize CsPbI3 NCs mainly involve Pb2+-site doping as well as compositional and/or NC surface engineering, the black phase stability in relation only to the variation of the reaction temperature of CsPbI3 NCs is surprisingly overlooked. We report a holistic study of the phase stability of CsPbI3 NCs, encompassing dispersions, films, and even devices by tuning the hot-injection temperature between 120-170 °C. Our findings suggest that the transition from the black to the yellow phase occurs after over a month for NCs synthesized at 150 °C (150@NCs). Structural refinement studies attribute the enhanced stability of 150@NCs to their observed lowest octahedral distortion. The 150@NCs also lead to stable unencapsulated solar cells with unchanged performance upon 26 days of shelf storage in dry air. Our study underlines the importance of scrutinizing synthesis parameters for designing stable perovskite NCs towards long-lasting optoelectronic devices. publishedVersion

Colloidal lead‐free perovskite nanocrystals have recently received extensive attention because of their facile synthesis, the outstanding size‐tunable optoelectronic properties, and less or no toxicity in their commercial applications. Tin (Sn) has so far led to the most efficient lead‐free solar cells, yet showing highly unstable characteristics in ambient conditions. Here, we propose the synthesis of all‐inorganic mixture Sn‐Ge perovskite nanocrystals, demonstrating the role of Ge2+ in stabilizing Sn2+ cation while enhancing the optical and photophysical properties. The partial replacement of Sn atoms by Ge atoms in the nanostructures effectively fills the high density of Sn vacancies, reducing the surface traps and leading to a longer excitonic lifetime and increased photoluminescence quantum yield. The resultant Sn‐Ge nanocrystals‐based devices show the highest efficiency of 4.9 %, enhanced by nearly 60 % compared to that of pure Sn nanocrystals‐based devices., CsSn0.6Ge0.4I3 nanocrystals have been synthesized for the first time by a B‐site co‐alloying strategy. The introduction of Ge effectively decreases the high density of intrinsic Sn defects, resulting in an extended excitonic lifetime and enhanced solar cell performance. The stability of the new nanocrystals also improves owing to the effective protection of Sn2+ against oxidation.

Lead-based halide perovskite nanocrystals (NCs) are recognized as emerging emissive materials with superior photoluminescence (PL) properties. However, the toxicity of lead and the swift chemical decomposition under atmospheric moisture severely hinder their commercialization process. Herein, we report the first colloidal synthesis of lead-free Cs4CuIn2Cl12 layered double perovskite NCs via a facile moisture-assisted hot-injection method stemming from relatively nontoxic precursors. Although moisture is typically detrimental to NC synthesis, we demonstrate that the presence of water molecules in Cs4CuIn2Cl12 synthesis enhances the PL quantum yield (mainly in the near-UV range), induces a morphological transformation from 3D nanocubes to 2D nanoplatelets, and converts the dark transitions to radiative transitions for the observed self-trapped exciton relaxation. This work paves the way for further studies on the moisture-assisted synthesis of novel lead-free halide perovskite NCs for a wide range of applications. publishedVersion

Amorphous titania (am.-TiO2) has gained wide interest in the field of photocatalysis, thanks to exceptional disorder-mediated optical and electrical properties compared to crystalline TiO2. Here, we study the effects of intrinsic Ti3+ and nitrogen defects in am.-TiO2 thin films via the atomic layer deposition (ALD) chemistry of tetrakis(dimethylamido)titanium(IV) (TDMAT) and H2O precursors at growth temperatures of 100–200 °C. X-ray photoelectron spectroscopy (XPS) and computational analysis allow us to identify structural disorder-induced penta- and heptacoordinated Ti4+ ions (Ti5/7c4+), which are related to the formation of Ti3+ defects in am.-TiO2. The Ti3+-rich ALD-grown am.-TiO2 has stoichiometric composition, which is explained by the formation of interstitial peroxo species with oxygen vacancies. The occupation of Ti3+ 3d in-gap states increases with the ALD growth temperature, inducing both visible-light absorption and electrical conductivity via the polaron hopping mechanism. At 200 °C, the in-gap states become fully occupied extending the lifetime of photoexcited charge carriers from the picosecond to the nanosecond time domain. Nitrogen traces from the TDMAT precursor had no effect on optical properties and only little on charge transfer properties. These results provide insights into the charge transfer properties of ALD-grown am.-TiO2 that are essential to the performance of protective photoelectrode coatings in photoelectrochemical solar fuel reactors. publishedVersion

Dip catalysts are attracting interest in both academia and industry for catalyzing important chemical reactions. These provide excellent stability, better recoverability, recyclability, and easy scale-up. Using the unique microstructures of leaf skeletons, we present a fractal-like hierarchical surface that can be used as a versatile and efficient dip catalyst. Copper oxide microcactuses with nanoscalar features were fabricated onto the Bauhinia racemosa leaf skeletons via a combination of physical vapor deposition, electroplating, and chemical oxidation methods. The coated leaf skeletons have a very high surface area, and the three-dimensional (3D) morphology allows the reactants to encounter the catalytic sites efficiently and move around the reaction mixture swiftly. The fabricated bioinspired leaf skeleton-based dip catalyst was characterized and demonstrated to be very efficient for alcohol dehydrogenation reaction, examined under different experimental conditions. A ceramic 3D-printed catalyst holder was designed to hold the catalysts to avoid any damage caused by the magnetic bars during the reactions. The performance is determined using the reaction yields, and the efficiencies are correlated with microcactus-like structures composed of CuO and the 3D fractal-like shape provided by the leaf skeleton. This strategy can be applied to fabricate other dip catalysts using different materials and designs, suitable for catalyzing numerous other chemical reactions. publishedVersion

Atomic layer deposited (ALD) TiO2 thin films have a wide range of applications in photonics which are, however, limited by the chemical instability of the amorphous as-deposited TiO2. Post-deposition annealing is required for improving the performance by inducing phase transitions and oxide defects. ALD precursor traces remaining in the TiO2 film affect the thermally-induced processes but the understanding of the effect of growth temperature on precursor traces in the film as well as on the thermally-induced processes is weak. In this study 30 nm ALD TiO2 was grown on Si wafer from tetrakis(dimethylamido)titanium and water at 100–200 °C. TiO2 was subsequently annealed in vacuum at 200–500 °C. Increasing the growth temperature decreased the amount of N bearing precursor traces and thus makes the TiO2 more easily reducible. The reduction takes place simultaneously with the crystallization and formation of O1− defects. Vacuum annealing of TiO2 with less than 0.3 at% of N results in nanocrystalline rutile whereas samples with more N containing traces crystallized as microcrystalline anatase. Nanocrystalline rutile TiO2 was chemically stable and resistant to the dissolution at the grain boundaries under alkaline conditions making it a suitable material for protective photoelectrode coatings used in artificial photosynthesis. publishedVersion

TiO2 inverse opal (IO) structure surfaces were functionalized with a sub-monolayer amount of Cu by atomic layer deposition (ALD) and tested for photocatalytic and antimicrobial applications. Decomposition of acetylene (C2H2) into CO2 and reduction of CO2 into CH4 were tested in the gas phase and photodegradation of methylene blue (MB) was tested in the liquid phase. Antimicrobial activity was tested against Gram-positive Staphylococcus aureus (S. aureus) bacteria. ALD Cu without any post-deposition heat treatment (HT) decreased the photo degradation rate of both C2H2 and MB but improved the activity towards CO2 reduction. ALD Cu increased MB photodegradation rate and antimicrobial activity only after HT at 550 °C, which was linked to the improved chemical stability Cu after the HT. The same HT decreased the activity towards CO2 reduction and decomposition of C2H2. The HT induced desorption of loosely bound ALD Cu+/2+ from the TiO2 IO surface and the remaining Cu+/2+ was reduced to Cu+. The photocatalytic and antimicrobial activity of TiO2 IO can be tailored by the addition of a sub-monolayer amounts of Cu with performance depending on the targeted reaction. publishedVersion

Several passivation techniques are developed and compared in terms of their ability to preserve the optical properties of close-to-surface InAs/GaAs quantum dots (QDs). In particular, the influence of N-passivation by hydrazine chemical treatment, N-passivation by hydrazine followed by atomic layer deposition (ALD) of AlO x and use of AlN x deposited by plasma-enhanced ALD are reported. The effectiveness of the passivation is benchmarked by measuring the emission linewidths and decay rates of photo-carriers for the near-surface QDs. All three passivation mechanisms resulted in reducing the oxidation of Ga and As atoms at the GaAs surface and consequently in enhancing the room-temperature photoluminescence (PL) intensity. However, long-term stability of the passivation effect is exhibited only by the hydrazine + AlO x process and more significantly by the AlN x method. Moreover, in contrast to the results obtained from hydrazine-based methods, the AlN x passivation strongly reduces the spectral diffusion of the QD exciton lines caused by charge fluctuations at the GaAs surface. The AlN x passivation is found to reduce the surface recombination velocity by three orders of magnitude (corresponding to an increase of room-temperature PL signal by ∼1030 times). The reduction of surface recombination velocity is demonstrated on surface-sensitive GaAs (100) and the passivating effect is stable for more than one year. This effective method of passivation, coupled with its stability in time, is extremely promising for practical device applications such as quantum light sources based on InAs/GaAs QDs positioned in small-volume photonic cavities and hence in the proximity of GaAs-air interface.

Titanium dioxide (TiO2) thin films are widely employed for photocatalytic and photovoltaic applications where the long lifetime of charge carriers is a paramount requirement for the device efficiency. To ensure the long lifetime, a high temperature treatment is used which restricts the applicability of TiO2 in devices incorporating organic or polymer components. In this study, we exploited low temperature (100&ndash, 150 &deg, C) atomic layer deposition (ALD) of 30 nm TiO2 thin films from tetrakis(dimethylamido)titanium. The deposition was followed by a heat treatment in air to find the minimum temperature requirements for the film fabrication without compromising the carrier lifetime. Femto-to nanosecond transient absorption spectroscopy was used to determine the lifetimes, and grazing incidence X-ray diffraction was employed for structural analysis. The optimal result was obtained for the TiO2 thin films grown at 150 &deg, C and heat-treated at as low as 300 &deg, C. The deposited thin films were amorphous and crystallized into anatase phase upon heat treatment at 300&ndash, 500 &deg, C. The average carrier lifetime for amorphous TiO2 is few picoseconds but increases to &gt, 400 ps upon crystallization at 500 &deg, C. The samples deposited at 100 &deg, C were also crystallized as anatase but the carrier lifetime was &lt, 100 ps.

As the Earth's atmosphere contains an abundant amount of water as vapors, a device which can capture a fraction of this water could be a cost-effective and practical way of solving the water crisis. There are many biological surfaces found in nature which display unique wettability due to the presence of hierarchical micro-nanostructures and play a major role in water deposition. Inspired by these biological microstructures, we present a large scale, facile and cost-effective method to fabricate water-harvesting functional surfaces consisting of high-density copper oxide nanoneedles. A controlled chemical oxidation approach on copper surfaces was employed to fabricate nanoneedles with controlled morphology, assisted by bisulfate ion adsorption on the surface. The fabricated surfaces with nanoneedles displayed high wettability and excellent fog harvesting capability. Furthermore, when the fabricated nanoneedles were subjected to hydrophobic coating, these were able to rapidly generate and shed coalesced droplets leading to further increase in fog harvesting efficiency. Overall, ∼99% and ∼150% increase in fog harvesting efficiency was achieved with non-coated and hydrophobic layer coated copper oxide nanoneedle surfaces respectively when compared to the control surfaces. As the transport of the harvested water is very important in any fog collection system, hydrophilic channels inspired by leaf veins were made on the surfaces via a milling technique which allowed an effective and sustainable way to transport the captured water and further enhanced the water collection efficiency by ∼9%. The system presented in this study can provide valuable insights towards the design and fabrication of fog harvesting systems, adaptable to arid or semi-arid environmental conditions. publishedVersion

This work aims to quantify the effect of a diamond-like carbon coating (DLC) treatment of aramid fibres and to reveal the conversion of a fibre-level performance leap on the macroscale mechanical behaviour. The DLC-based coating is applied directly to the reinforcement and laminates are infused with an epoxy matrix. After characterisation of the coated surfaces, the performance of the composite is analysed via interlaminar shear testing, fatigue testing and damage tolerance testing, microbond tests, and 3D finite element simulation using a cohesive zone model of the interface. The results show that the coating treatment improves the fatigue life and the S-N curve slope for the laminates, while the residual strength after impact damage and environmental conditioning (water immersion at 60 °C) remains high. The scaling factor to convert the performance on macroscale was determined to be 0.17–0.39 for the DLC-based fibre treatment. publishedVersion

Amorphous titanium dioxide (a-TiO2) combined with an electrocatalyst has shown to be a promising coating for stabilizing traditional semiconductor materials used in artificial photosynthesis for efficient photoelectrochemical solar-to-fuel energy conversion. In this study we report a detailed analysis of two methods of modifying an undoped thin film of atomic layer deposited (ALD) a-TiO2 without an electrocatalyst to affect its performance in water splitting reaction as a protective photoelectrode coating. The methods are high-temperature annealing in ultrahigh vacuum and atomic hydrogen exposure. A key feature in both methods is that they preserve the amorphous structure of the film. Special attention is paid to the changes in the molecular and electronic structure of a-TiO2 induced by these treatments. On the basis of the photoelectrochemical results, the a-TiO2 is susceptible to photocorrosion but significant improvement in stability is achieved after heat treatment in vacuum at temperatures above 500 °C. On the other hand, the hydrogen treatment does not increase the stability despite the ostensibly similar reduction of a-TiO2. The surface analysis allows us to interpret the improved stability to the thermally induced formation of O- species within a-TiO2 that are essentially electronic defects in the anionic framework. publishedVersion

Iron and titanium oxides have attracted substantial attention in photoelectrochemical water splitting applications. However, both materials suffer from intrinsic limitations that constrain the final device performance. In order to overcome the limitations of the two materials alone, their combination has been proposed as a solution to the problems. Here we report on the fabrication of an atomic layer deposited (ALD) Fe2O3 coating on porous ALD-TiO2. Our results show that successful implementation requires complete mixing of the TiO2 and Fe2O3 layers via annealing resulting in the formation of a photoactive iron titanium oxide on the surface. Moreover, we found that incomplete mixing leads to crystallization of Fe2O3 to hematite that is detrimental to the photoelectrochemical performance. IPCE and transient photocurrent measurements performed using UV and visible light excitation confirmed that the iron titanium oxide extends the photocurrent generation to the visible range. These measurements were complemented by transient absorption spectroscopy (TAS), which revealed a new band absent in pristine hematite or anatase TiO2 that we assign to charge transfer within the structure. Taken together, these results provide design guidelines to be considered when aiming to combine TiO2 and Fe2O3 for photoelectrochemical applications.

Self-assembling organic molecule-metal interfaces exhibiting free-electron like (FEL) states offers an attractive bottom-up approach to fabricating materials for molecular electronics. Accomplishing this, however, requires detailed understanding of the fundamental driving mechanisms behind the self-assembly process. For instance, it is still unresolved as to why the adsorption of glycine ([NH2(CH2)COOH]) on isotropic Cu(100) single crystal surface leads, via deprotonation and self-assembly, to a glycinate ([NH2(CH2)COO−]) layer that exhibits anisotropic FEL behavior. Here, we report on bias-dependent scanning tunneling microscopy (STM) experiments and density functional theory (DFT) calculations for glycine adsorption on Cu(100) single crystal surface. We find that after physical vapor deposition (PVD) of glycine on Cu(100), glycinate self-assembles into an overlayer exhibiting c(2x4) and p(2x4) symmetries with non-identical adsorption sites. Our findings underscore the intricacy of electrical conductivity in nanomolecular organic overlayers and the critical role the structural anisotropy at molecule-metal interface plays in the fabrication of materials for molecular electronics. acceptedVersion

Novel monoisomeric perylene imide derivatives with terpyridinyl and pyrrolidinyl substituents were synthesized and deposited onto solid substrates, such as a thin film of Al2 O3 and mesoporous TiO2 nanoparticle layer, by using a simple dip-by-dip method. Arrays of up to 33 layers were built on Al2 O3 . In the case of mesoporous TiO2 , the interstitial volume between the particles was filled up with dye assemblies. Deposition could produce either layers of microcrystals or molecular layers if an appropriate washing procedure was used. The resultant arrays were studied by means of scanning electron microscopy, X-ray photoelectron spectroscopy measurements, and UV/Vis absorption.

Atomic layer deposited (ALD) TiO2 is an attractive material for improving the photoactivity and chemical stability of semiconductor electrodes in artificial photosynthesis. Using photoelectrochemical (PEC) measurements, we show that an interfacial, topographically microstructured TiSi2 layer inside the TiO2/Si heterojunction improves the charge carrier separation and shifts the water dissociation onset potential to more negative values. These observations are correlated with the X-ray photoelectron spectroscopy (XPS) and ultra-violet photoelectron spectroscopy (UPS) measurements, which reveal an increased band bending due to the TiSi2 interlayer. Combined with the UV–Vis absorption results, the photoelectron spectroscopy measurements allow the reconstruction of the complete energy band diagram for the TiO2/TiSi2/Si heterojunction and the calculation of the valence and conduction band offsets. The energy band alignment and improvements in PEC results reveal that the charge transfer across the heterojunction follows a Z-scheme model, where the metal-like TiSi2 islands act as recombination centers at the interface. acceptedVersion

We investigate the fluorescence characteristics of a purely Ce-doped silica fiber and demonstrate broad-bandwidth fluorescence across the visible and near-infrared. The Ce-doped fiber is fabricated using standard modified chemical vapor deposition technology. Trace metal analysis by inductively coupled plasma mass spectrometry confirmed the purity of Ce-doping. The Ce valence state of 3+ was revealed by X-ray photoelectron spectroscopy. The optimum pump wavelength for the broadest luminescence from a fiber is scanned between 405 nm to 440 nm wavelength of diode lasers operating under continuous-wave regime. The strongest pump absorption is observed at the wavelength of 405 nm. Variation of pump power and fiber length results in the demonstration of broad-bandwidth fluorescence with spectral widths up to 301 nm (at -10 dB). The measured fluorescence spectra cover the wavelength range from ∼458 nm to ∼819 nm with spectral power densities of up to 2.4 nW/nm. publishedVersion

Funding Information: All the co‐authors acknowledge Dr. Ayodele Fatona with gratitude for the assistance with TGA measurements. This work was supported by the Academy of Finland (Decision Nos. 141481, 286713, and 309920). T.O. was partially supported through a Natural Sciences and Engineering Research Council of Canada Undergraduate Student Research Award (NSERC‐USRA). J.M.M. and E.D.C. are recipients of Early Researcher Awards from the Ontario Ministry of Research and Innovation and J.M.M. holds the Tier 2 Canada Research Chair in Micro‐ and Nanostructured Materials. Funding from NSERC through Discovery Grants to J.M.M. and E.D.C. is gratefully acknowledged. This research made use of instrumentation in the Canadian Centre for Electron Microscopy and Biointerfaces Institute at McMaster University. This work is part of the Academy of Finland Flagship Programme, Photonics Research, and Innovation (PREIN) (Decision No. 320 165). Publisher Copyright: © 2021 The Authors. Advanced Materials Interfaces published by Wiley-VCH GmbH Copyright: Copyright 2021 Elsevier B.V., All rights reserved. A key challenge in the development of materials for applications in the fields of opto- and nanoelectronics, catalysis, separation, and energy conversion is the ability to fabricate 3D inorganic semiconductive nanostructures in a precisely-controlled and cost-effective manner. This work describes the fabrication of 3D nanostructured TiO2 monoliths by coating ultraporous cross-linked cellulose nanocrystal (CNC) aerogel templates with TiO2 layers of controlled thickness via atomic layer deposition (ALD). Following calcination, the resulting hollow inorganic ultraporous 3D networks form the thinnest self-supporting semiconductive structure (7 nm) fabricated directly on a conductive substrate. The CNC-templated ALD–TiO2 electrodes are applied toward photoelectrochemical water splitting. The results show that a TiO2 coating as thin as 15 nm produces a maximum water splitting efficiency, resulting in materials savings and reduced fabrication time.

Thin organic coatings (TOC) or paints on hot dip galvanized steel (HDGS) improve the corrosion properties and create visually pleasing surfaces. Delamination of these coatings leads to corrosion and peeling of the paints. Hence, a novel method for improved adhesion and corrosion properties for HDGS surfaces is introduced. It is shown how the fabrication of a nanomolecular silane film as an interfacial layer between the HDGS and TOC or paint improves the corrosion properties of HDGS in different pH regimes. Understanding the corrosion behavior of ultra-thin silane layers under differing pH is crucial, as subsequent coatings have different pHs. By varying the silanization parameters, two different nanomolecular surface structures of aminopropyl trimethoxysilane (APS) on HDGS were fabricated: well-ordered monolayers with approximately 1 nm thickness and highly clustered APS films with a thickness in the range of 5 nm to 8 nm. To verify the nanomolecular APS structures, photoelectron spectroscopy and contact ...

The preparation of weblike titanium dioxide thin films by atomic layer deposition on cellulose biotemplates is reported. The method produces a TiO2 web, which is flexible and transferable from the deposition substrate to that of the end application. Removal of the cellulose template by calcination converts the amorphous titania to crystalline anatase and gives the structure a hollow morphology. The TiO2 webs are thoroughly characterized using electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy to give new insight into manufacturing of porous titanium dioxide structures by means of template-based methods. Functionality and integrity of the TiO2 hollow weblike thin films were successfully confirmed by applying them as electrodes in dye-sensitized solar cells.

Surface segregation and oxide formation anisotropy on Ti-Nb stabilized ferritic stainless steel (EN 1.4521) were studied by XPS and Electron Backscatter Diffraction. Competitive surface segregation of Si, Nb and Ti was initiated at ∼550. °C, and segregation was favored to the open surface sites of 〈111〉 oriented grains. Furthermore, the surface segregation of Cr was strongly limited at the locations of stable Ti(CN)- and (NbTi)C-type precipitates. Consequently, the oxidation resistance of stainless steels can be enhanced cost-efficiently, without alloy additions, by optimizing the microstructure to facilitate the fast and uniform growth of protective oxide scale. acceptedVersion

Area selective deposition (ASD) is an emerging method for the patterning of electronic devices as it can significantly reduce processing steps in the industry. A potential ASD methodology uses infiltration of metal precursors into patterned polymer materials. The work presented within demonstrates this potential by examining hydroxy terminated poly(2-vinylpyridine) (P2VP-OH) as the ‘receiving’ polymer and trimethylaluminium (TMA) and H2O as the material precursors in a conventional atomic layer deposition (ALD) process. Fundamental understanding of the surface process was achieved using X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX) mapping via transmission electron microscopy (TEM). The resulting analysis confirms aluminium inclusion within the polymer film. Spectroscopic and microscopic characterisation show metal infiltration throughout the polymer to the underlying silicon dioxide interface. Exposing the infiltrated film to an oxygen plasma results in the removal of the organic component and resultant fabrication of a sub 5 nm aluminium oxide layer. acceptedVersion

Visually black, electrically leaky, amorphous titania (am-TiO2) thin films were grown by atomic layer deposition (ALD) for photocatalytic applications. Broad spectral absorbance in the visible range and exceptional conductivity are attributed to trapped Ti3+ in the film. Oxidation of Ti3+ upon heat treatment leads to a drop in conductivity, a color change from black to white, and crystallization of am-TiO2. ALD-grown black TiO2, without any heat treatment, is subject to dissolution in alkaline photoelectrochemical conditions. The best photocatalytic activity for solar water splitting is obtained for completely crystalline white TiO2.

Visually black, electrically leaky, amorphous titania (am-TiO2) thin films were grown by atomic layer deposition (ALD) for photocatalytic applications. Broad spectral absorbance in the visible range and exceptional conductivity are attributed to trapped Ti3+ in the film. Oxidation of Ti3+ upon heat treatment leads to a drop in conductivity, a color change from black to white, and crystallization of am-TiO2. ALD-grown black TiO2, without any heat treatment, is subject to dissolution in alkaline photoelectrochemical conditions. The best photocatalytic activity for solar water splitting is obtained for completely crystalline white TiO2. publishedVersion

We employ atomic layer deposition to prepare 50 nm thick hematite photoanodes followed by passivating them with a 0.5 nm thick Ta2O5-overlayer and compare them with samples uniformly doped with the same amount of tantalum. We observe a three-fold improvement in photocurrent with the same onset voltage using Ta-overlayer hematite photoanodes, while electrochemical impedance spectroscopy under visible light irradiation shows a decreased amount of surface states under water splitting conditions. The Tadoped samples have an even higher increase in photocurrent along with a 0.15 V cathodic shift in the onset voltage and decreased resistivity. However, the surface state capacitance for the Ta-doped sample is twice that of the reference photoanode, which implies a larger amount of surface hole accumulation. We further utilize transient absorption spectroscopy in the sub-millisecond to second timescale under operating conditions to show that electron trapping in both Ta2O5-passivated and Ta-doped samples is markedly reduced. Ultrafast transient absorption spectroscopy in the sub-picosecond to nanosecond timescale shows faster charge carrier dynamics and reduced recombination in the Ta-doped hematite photoanode resulting in the increased photoelectrochemical performance when compared with the Ta2O5-overlayer sample. Our results show that passivation does not affect the poor charge carrier dynamics intrinsic to hematite based photoanodes. The Ta-doping strategy results in more efficient electron extraction, solving the electron trapping issue and leading to increased performance over the surface passivation strategy. Funding Agencies|Finnish Cultural Foundation; Jenny and Antti Wihuri Foundation; Academy of Finland [141481, 286713, 309920]; Finnish Centre of Excellence in Atomic Layer Deposition

We address the thermal management of flip-chip semiconductor disk lasers (SDLs) emitting at wavelengths 1.3–1.6 μm. The emphasis of the study is on fabricating thin SDL structures with high thermal conductance. An essential part of this task is to use GaAs-based materials in the distributed Bragg reflector (DBR), because they can provide a combination of high thermal conductivity and high refractive index contrast. Furthermore, the reflectivity of the GaAs-based DBR should preferably be enhanced using a thin dielectric layer and a highly reflecting metal layer. Such a configuration enables very thin mirror structures with a reduced number of DBR layer pairs without compromising the reflectivity. The concept is demonstrated experimentally with a 1.32-μm flip-chip SDL, where the GaAs-based DBR is finished with a thin Al2O3 layer and a highly reflective Al layer. In addition, the design principles, thermal management, and the development issues related to semiconductor–dielectric–metal mirrors in 1.3–1.6-μm flip-chip SDLs are discussed.

We report high-power 1180-nm GaInNAs distributed Bragg reflector laser diodes with and without a tapered amplifying section. The untapered and tapered components reached room temperature output powers of 655 mW and 4.04 W, respectively. The diodes exhibited narrow linewidth emission with side-mode suppression ratios in the range of 50 dB for a broad range of operating current, extending up to 2 A for the untapered component and 10 A for the tapered component. The high output power is rendered possible by the use of a high quality GaInNAs-based quantum well gain region, which allows for lower strain and better carrier confinement compared with traditional GaInAs quantum wells. The development opens new opportunities for the power scaling of frequency-doubled lasers with emission at yellow–orange wavelengths. publishedVersion

Amorphous titanium dioxide (a-TiO

In in vitro live-cell imaging, it would be beneficial to grow and assess human embryonic stem cell-derived retinal pigment epithelial (hESC-RPE) cells on thin, transparent, rigid surfaces such as cover glasses. In this study, we assessed how the silanization of glass with 3-aminopropyltriethoxysilane (APTES), 3-(trimethoxysilyl)propyl methacrylate (MAPTMS), or polymer-ceramic material Ormocomp affects the surface properties, protein binding, and maturation of hESC-RPE cells. The surface properties were studied by contact angle measurements, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and a protein binding assay. The cell adherence and proliferation were evaluated by culturing hESCRPE cells on collagen IV-coated untreated or silanized surfaces for 42 days. The Ormocomp treatment significantly increased the hydrophobicity and roughness of glass surfaces compared to the APTES and MAPTMS treatments. The XPS results indicated that the Ormocomp treatment changes the chemical composition of the glass surface by increasing the carbon content and the number of C-O/═O bonds. The protein-binding test confirmed that the Ormocomp-treated surfaces bound more collagen IV than did APTES- or MAPTMS-treated surfaces. All of the silane treatments increased the number of cells: after 42 days of culture, Ormocomp had 0.38, APTES had 0.16, MAPTMS had 0.19, and untreated glass had only 0.062, all presented as million cells cm(-2). There were no differences in cell numbers compared to smoother to rougher Ormocomp surfaces, suggesting that the surface chemistry and, more specifically, the collagen binding in combination with Ormocomp are beneficial to hESC-RPE cell culture. This study clearly demonstrates that Ormocomp treatment combined with collagen coating significantly increases hESC-RPE cell attachment compared to commonly used silanizing agents APTES and MAPTMS. Ormocomp silanization could thus enable the use of microscopic live cell imaging methods for hESC-RPE cells.

A versatile and economic method of preparing covalently-bound and uniform bifunctional silane monolayers on stainless steel is presented. Stainless steel is first electrochemically hydroxylated to enable the formation of a bifunctional overlayer via simultaneous liquid-phase deposition of two organofunctional silanes: (3-aminopropyl)trimethoxysilane (APS) and (3-mercaptopropyl)trimethoxysilane (MPS). The chemical composition, in-depth distribution, molecular orientation and chemical bonds in APS, MPS and APS/MPS layers over a range of APS/MPS mixing ratios are studied with synchrotron radiation mediated photoelectron spectroscopy (SR-PES), conventional X-ray photoelectron spectroscopy (XPS) and energy filtered X-ray photoemission electron microscopy (EF-XPEEM). Inelastic electron energy-loss background (IEEB) analysis is employed to determine the surface morphology of the silanized samples. Coadsorption is shown to produce a covalently-bound and highly ordered monolayer with a controllable MPS surface concentration within APS matrix. The results show evidence of strong synergistic effects during simultaneous adsorption of MPS and APS from liquid phase. While the uptake of MPS alone is low, the coadsorption of MPS and APS strongly enhances both the uptake of MPS and ordering in the APS/MPS overlayer. Results from PES, EF-XPEEM and IEEB analysis reveal that the surface is predominantly covered by a well-ordered APS/MPS monolayer with only slight degree of clustering. Clustering is attributed to different hydrolysis rates in solution and structural irregularities on the substrate. Our results conclusively invalidate the assumption that APS/MPS ratio in a deposited overlayer should correlate linearly with the mixing ratio in solution. The reported insights into the chemical bonds, molecular orientation and morphology in APS/MPS overlayers facilitate site-selective coupling of functional molecules to amino and thiol groups with controllable spatial distribution and, in general, knowledge-based development of novel surface functionalities for stainless steel and other metal (alloy) oxides.

The most commonly used hole transporting layer (HTL) in conventional polymer solar cells is poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) PEDOT:PSS. The acidic nature of this HTL is responsible for etching of the indium tin oxide (ITO) layer which is the anode in polymer solar cells and leads to degradation of efficiency in polymer solar cells in the long run. In this article we explored the effect of plasma treated Ag as an intermediate layer between ITO and PEDOT:PSS for over one month period. It was found that the devices with plasma treated Ag as an intermediate layer with thickness of 5 nm resulted in only 30% degradation over one month and did not decrease the initial power conversion efficiency (PCE) compared to the cell without the anode modification, whereas the devices without the intermediate layer, degraded up to 66% of the initial PCE. The mechanism was analyzed using XPS measurements and found out that indium from ITO etches out and diffuses to the subsequent polymer layer. Further, the experiment revealed that the presence of plasma treated Ag layer restricted the rapid indium diffusion, which accounted to enhanced device stability.

In this work, controlled anodic oxidation is reported for ultra-thin (3 nm thick) titanium layers on indium tin oxide (ITO) coated glass substrates. A physical explanation is also provided for the origin of the delamination process of the Ti during the anodic oxidation. The properties of the fabricated layers are studied using electrochemical impedance spectroscopy (EIS) and X-ray Photoelectron Spectroscopy (XPS). In addition, one intriguing application is demonstrated for the anodized layers: their use as an interfacial barrier in organic diodes. Diodes containing an electrochemically fabricated TiO2 barrier layer exhibit clear room temperature negative differential resistance (NDR) and a peak-to-valley current ratio (PVCR) of 3.6. The reference diodes without the TiO2 layer show normal diode characteristics with no observable NDR. The NDR diodes have potential applications as memory elements for large-area electronics.

Highly mobile twin boundaries allow straining of the 10M Ni–Mn–Ga martensite single crystals with low as 0.15 MPa uniaxial stresses. This is clearly lower than what is possible to magnetically generate in this structure. Therefore, this material can be used for magnetically controlled actuation. In cyclic deformation occurring by twin variant reorientation, fatigue life up to 2 × 10 9 cycles has been demonstrated without decrease of the magnetic-field-induced strain or without failure of the specimen. However, the actuation behavior can be strongly impaired by unfavorable twin variant configuration or surface constraints which decrease the twin mobility and increase the twinning stress. In the present work, the surface properties of the 10M Ni–Mn–Ga are studied in details. The existence of an ultra-thin surface layer having chemical composition different from the bulk crystal is established with the XPS analysis. The influence of this layer on the nano-mechanical properties of the surface is investigated using instrumented nanoindentation both on electropolished crystals and crystals where surface deformation has been introduced by mechanical polishing. The results show that the surface layer appears both in the electropolished and mechanically polished surface. However, the nano-mechanical properties of the surface are distinctly different in the two cases. In the case of electropolished surface essentially elastic loading occurs first followed by a notable pop-in of the indenter, while in the case of mechanically polished surface minor or no pop-in is observed. This behavior is attributed to the differences of the initiation of plastic deformation in the two types of surfaces. The contribution of the layer to the performance and actuation properties of the material is discussed. © 2012 Elsevier B.V. All rights reserved.