Characterization and Solid-State UV-Vis Investigations of Photoelectrocatalytically Active La5Cl7[TeO3]4, a Mixed Anion Compound with Alternating 2D Layers of Oxygen and Chlorine.

An oxide chloride, La5Cl7[TeO3]4, was synthesized using the conventional high-temperature solid-state synthesis technique in an inert atmosphere. This compound possesses a novel crystal structure that can be described with the triclinic space group P1̅ (No. 2) and unit cell parameters: a = 7.2634(3) Å, b = 8.1241(3) Å, c = 9.1993(3) Å, α = 79.373(1)°, ß = 83.599(1)°, and γ = 82.511(1)°. The preference of Te(IV) to coordinate to oxygen and direct its lone pair toward the lower charged chlorine results in 2D layers of both oxygen and chlorine, alternating along the crystallographic b-direction. Homoleptic coordination, solely to oxygen, and heteroleptic coordination to oxygen and chlorine are observed for lanthanum, forming layers connected through edge-sharing polyhedra. In the crystal structure, two distinct tellurium positions are observed, with three close Te-O distances, emphasizing an active lone pair. The compound has been investigated by solid-state UV-vis measurements, and a band gap of 3.44 eV has been determined by DFT calculations. Detailed photoelectrochemical measurements clearly indicate that the title compound is photoelectrocatalytically active, showing an n-type behavior. Raman spectroscopy confirms that complex tellurite ions are present in the crystal structure; several observed bands can be assigned to Te-O stretching, reflecting the relatively low crystallographic symmetry of the title compound.

Towards bone regeneration: Understanding the nucleating ability of proline-rich peptides in biomineralisation.

Obtaining rapid mineralisation is a challenge in current bone graft materials, which has been attributed to the difficulty of guiding the biological processes towards osteogenesis. Amelogenin, a key protein in enamel formation, inspired the design of two intrinsically disordered peptides (P2 and P6) that enhance in vivo bone formation, but the process is not fully understood. In this study, we have elucidated the mechanism by which these peptides induce improved mineralisation. Our molecular dynamics analysis demonstrated that in an aqueous environment, P2 and P6 fold to interact with the surrounding Ca2+, PO43- and OH- ions, which can lead to apatite nucleation. Although P2 has a less stable backbone, it folds to a stable structure that allows for the nucleation of larger calcium phosphate aggregates than P6. These results were validated experimentally in a concentrated simulated body fluid solution, where the peptide solutions accelerated the mineralisation process compared to the control and yielded mineral structures mimicking the amorphous calcium phosphate crystals that can be found in lamella bone. A pH drop for the peptide groups suggests depletion of calcium and phosphate, a prerequisite for intrinsic osteoinduction, while S/TEM and SEM suggested that the peptide regulated the mineral nucleation into lamella flakes. Evidently, the peptides accelerate and guide mineral formation, elucidating the mechanism for how these peptides can improve the efficacy of P2 or P6 containing devices for bone regeneration. The work also demonstrates how experimental mineralisation study coupled with molecular dynamics is a valid method for understanding and predicting in vivo performance prior to animal trials.

X-ray and Neutron Diffraction Studies of SrTe2FeO6Cl, an Oxide Chloride with Rare Anion Ordering.

The oxychloride SrTe2FeO6Cl is obtained by high-temperature solid-state synthesis under inert conditions in closed reaction vessels. The compound crystallizes in a novel monoclinic crystal structure that is described in the space group P121/n1 (No. 14). The unit cell parameters, a = 10.2604(1) Å, b = 5.34556(5) Å, c = 26.6851(3) Å, and ß = 93.6853(4)°, and atomic parameters were determined from synchrotron diffraction data, starting from a model that was obtained from single-crystal X-ray diffraction data. The anion lattice exhibits a rare ordering of oxide and chloride ions: one-dimensional zig-zag ladders of chlorine (squarelike motif) are surrounded by an oxygen matrix. Two different iron sites coordinated solely to oxygen are present in the structure, one octahedral and one square pyramidal, both distorted. Similarly, two different strontium coordinations are present; the first homoleptic coordinated to eight oxygen atoms and the second heteroleptic coordinated to four oxygen and four chlorine atoms in a fac-like manner. The lone pair of Te(IV) is directed toward the larger chlorine atoms. Magnetic susceptibility measurements confirm that Fe is +3 (d5) in the high-spin electronic configuration, exhibiting an almost ideal spin-only moment, µeff = 5.65 µB Fe-1. The slightly negative Weiss constant (θCW = -39 K) suggests dominating antiparallel spin-to-spin coupling in the paramagnetic temperature range, agreeing with an observed long-range antiferromagnetic spin ordering below Néel temperature, TN ∼ 13 K, and a broad second order-like anomaly in the specific heat measurement data. Low-temperature neutron diffraction data reveal that the antiferromagnetic ordered phase is C-type, with a k-vector (1/2, 1/2, 0) and ordered moment of 4.14(7) µB. The spin structure can be described as antiferromagnetic ordered layers stacked along the a-axis, forming layers of squares that alternate along the c-axis.

A CMOS Multi-Electrode Array for Four-Electrode Bioimpedance Measurements.

This work demonstrates how a multi-electrode array (MEA) dedicated to four-electrode bioimpedance measurements can be implemented on a complementary metal-oxide-semiconductor (CMOS) chip. As a proof of concept, an 8 × 8 pixel array along with dedicated amplifiers was designed and fabricated in the TSMC 180 nm process. Each pixel in the array contains a circular current carrying (CC) electrode that can act as a current source or sink. In order to measure a differential voltage between the pixels, each CC electrode is surrounded by a ring shaped pick up (PU) electrode. The differential voltages can be measured by an on-board instrumentation amplifier, while the currents can be measured with an on-bard transimpedance amplifier. Openings in the passivation layer exposed the aluminum top metal layer, and a metal stack of zinc, nickel and gold was deposited in an electroless plating process. The chips were then wire bonded to a ceramic package and prepared for wet experiments by encapsulating the bonding wires and pads in the photoresist SU-8. Measurements in liquids with different conductivities were performed to demonstrate the functionality of the chip.

Aromatic sensitizers in luminescent hybrid films.

Atomic layer deposition offers a unique set of design possibilities due to the vast range of metal and organic precursors that can be used and combined. In this work, we have combined lanthanides with aromatic aids as strongly absorbing sensitizers to form highly luminescent thin films. Terephthalic acid is used as a base sensitizer, absorbing shorter wavelengths than 300 nm. The absorption range is extended towards the near-UV and blue range by increasing the aromatic system and adding functional groups that have strong red-shifting effects. While terbium and europium provide green and red emission, yttrium allows emission from the sensitizer itself spanning the whole color range from purple, blue and green to red. Many organic dye molecules show very high luminescence quantum yields and several of the molecules and materials investigated in this work show bright luminescence.

Photoactive Zr-aromatic hybrid thin films made by molecular layer deposition.

The principle of antimicrobial photodynamic therapy (PDT) is appealing because it can be controlled by an external light source and possibly the use of durable materials. However, to utilise such surfaces requires a process for their production that allows for coating on even complex geometries. We have therefore explored the ability of the emerging molecular layer deposition (MLD) technique to produce and tune PDT active materials. This study demonstrates how the type of aromatic ligand influences the optical and antimicrobial properties of photoactive Zr-organic hybrid thin films made by MLD. The three aromatic dicarboxylic acids: 2,5-dihydroxy-1,4-benzenedicarboxylic acid, 2-amino-1,4-benzenedicarboxylic acid and 2,6-naphthalenedicarboxylic acid have been combined with ZrCl4 to produce hybrid coatings. The first system has not been previously described by MLD and is therefore more thoroughly investigated using in situ quartz crystal microbalance (QCM), Fourier transform infrared (FTIR) and UV-Vis spectroscopy. The antibacterial phototoxic effects of Zr-organic hybrids have been explored in the Staphylococcus aureus bacteria model using a UVA/blue light source. Films based on the 2,6-naphthalenedicarboxylic acid linker significantly reduced the number of viable bacteria by 99.9%, while no apparent activity was observed for the two other photoactive systems. Our work thus provides evidence that the MLD technique is a suitable tool to produce high-quality novel materials for possible applications in antimicrobial PDT, however it requires a careful selection of aromatic ligands used to construct photoactive materials.

Avoiding water reservoir effects in ALD of functional complex alkali oxides by using O3 as the oxygen source.

Toxic Pb-containing piezo-, pyro- and ferroelectrics continue to dominate the market even though they were banned from use in consumer products more than a decade ago. There is a strong need for sustainable alternatives, but the lack of facile synthesis routes for thin films exhibiting suitable functional properties have limited the transition from Pb workhorse materials like Pb(Zr,Ti)O3 and Pb(Mg,Nb)O3 - PbTiO3. Atomic layer deposition has proven capable of the deposition of possible successors, such as LiNbO3, (K,Na)NbO3 and K(Ta,Nb)O3, albeit with limited control due to water reservoir effects resulting from the hygroscopicity of intermediate products. In this article, we show that replacing H2O with O3 in the deposition of complex alkali oxides provides an alternative and much more controlled process. We exemplify this by deposition of crystalline K(Ta,Nb)O3 with high compositional control and over a larger composition range than previously reported. This opens new doors to a simplified synthesis of polar functional lead-free alternatives.

Utilizing Zirconium MOF-functionalized Fiber Substrates Prepared by Molecular Layer Deposition for Toxic Gas Capture and Chemical Warfare Agent Degradation.

Metal-organic frameworks (MOFs) are a class of porous organic-inorganic solids extensively explored for numerous applications owing to their catalytic activity and high surface area. In this work MOF thin films deposited in a one-step, molecular layer deposition (MLD), an all-gas-phase process, on glass wool fibers are characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and their capabilities towards toxic industrial chemical (TIC) capture and chemical warfare agents (CWA) degradation are investigated. It is shown that despite low volume of the active material used, MOFs thin films are capable of removal of harmful gaseous chemicals from air stream and CWA from neutral aqueous environment. The results confirm that the MLD-deposited MOF thin films, amorphous and crystalline, are suitable materials for use in air filtration, decontamination, and physical protection against CWA and TIC.

Molecular layer deposition of photoactive metal-naphthalene hybrid thin films.

We here report on photoactive organic-inorganic hybrid thin films prepared by the molecular layer deposition (MLD) method. The new series of hybrid films deposited using 2,6-naphthalenedicarboxylic acid (2,6-NDC) and either hafnium chloride (HfCl4), yttrium tetramethylheptanedionate (Y(thd)3) or titanium chloride (TiCl4) were compared with the known zirconium chloride (ZrCl4) based system. All metal-naphthalene films are amorphous as-deposited and show self-saturating growth as expected for an ideal MLD process with varied growth rates depending on the choice of metal precursor. The growth was studied in situ using quartz crystal microbalance (QCM) and the films were further characterised using spectroscopic ellipsometry (SE), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and UV-Vis and photoluminescence (PL) spectroscopy to obtain information on their physicochemical properties. The hybrid thin films display intense blue photoluminescence, except for the Ti-organic complex in which titanium clusters were found to be an effective PL quencher for the organic linker. We demonstrate how the optical properties of the films depend on the choice of metal component to make a foundation for further studies on these types of organic-inorganic hybrid materials for applications as photoactive agents.

Quinizarin: a large aromatic molecule well suited for atomic layer deposition.

Atomic layer deposition (ALD) is a remarkable synthesis tool due to the vast array of materials that can be deposited and the complexity of structures that can be designed. The low-temperature layer-by-layer approach even allows organic and inorganic components to be combined as hybrid or composite materials. The technique is then called molecular layer deposition (MLD). This opens the door for deposition of advanced optical materials using highly absorbing aromatic molecules. Unfortunately, most large aromatic molecules are difficult to sublime or have insufficient reactivity. This is a major barrier for ALD when designing with the use of organic components for dye-sensitized solar cells, luminescence, visible light photochemistry, chemical sensors and organic electronics. In this work, we introduce a well-known orange dye molecule, quinizarin. This molecule has a large conjugated aromatic system with strong absorption of visible light and shows strong luminescence both in solutions and as a complex together with aluminium ions. Interestingly, quinizarin also shows surprisingly good properties for film deposition due to reactive -OH groups and low sublimation temperature (130 °C). Strongly coloured pink hybrid films were deposited with trimethylaluminium and quinizarin at 175 °C with a growth rate of 0.28 nm per cycle. These films were not luminescent although their optical absorption spectra are similar to those of the corresponding solution. An attempt was made to dilute quinizarin through partial replacement with pentaerythritol as a multilayer structure or simultaneous co-pulsing, although this also did not produce luminescent films. The low sublimation temperature, good reactivity and large conjugated system of quinizarin open the way for exploration of solid-state hybrid and organic films based on this molecule along many different technological pathways.

Understanding KOtBu in atomic layer deposition - in situ mechanistic studies of the KNbO3 growth process.

Functional coatings based on alkali metals have become increasingly attractive in the current shift towards sustainable technologies. While lithium-based compounds have a natural impact on batteries, other alkali metal compounds are important as replacements for toxic materials in a range of electronic devices. This is especially true for potassium, being a major component in e.g. KxNa1-xNbO3 (KNN) and KTaxNb1-xO3 (KTN), with hope to replace Pb(ZrxTi1-x)O3 (PZT) in piezo-/ferroelectric and electrooptic devices. ALD facilitates functional conformal coatings at deposition temperatures far below what is reported using other techniques and with excellent compositional control. The ALD growth of potassium-containing films using KOtBu has, however, been unpredictable. Untraditional response to the pulse composition and precursor dose, severe reproducibility issues, and very high growth per cycle are some of the puzzling features of these processes. In this article, we shed light on the growth behavior of KOtBu in ALD by in situ quartz crystal microbalance and Fourier transform infrared spectroscopy studies. We study the precursor's behavior in the technologically interesting KNbO3-process, showing how the potassium precursor strongly affects the growth of other cation precursors. We show that the strong hygroscopic nature of the intermediary potassium species has far-reaching implications throughout the growth. This helps not only to enhance the understanding of alkali metal containing compounds' growth in ALD, but also to provide the means to control the growth of novel sustainable technological materials.

A foundation for complex oxide electronics -low temperature perovskite epitaxy.

As traditional silicon technology is moving fast towards its fundamental limits, all-oxide electronics is emerging as a challenger offering principally different electronic behavior and switching mechanisms. This technology can be utilized to fabricate devices with enhanced and exotic functionality. One of the challenges for integration of complex oxides in electronics is the availability of appreciable low-temperature synthesis routes. Herein we provide a fundamental extension of the materials toolbox for oxide electronics by reporting a facile route for deposition of highly electrically conductive thin films of LaNiO3 by atomic layer deposition at low temperatures. The films grow epitaxial on SrTiO3 and LaAlO3 as deposited at 225 °C, with no annealing required to obtain the attractive electronic properties. The films exhibit resistivity below 100 µΩ cm with carrier densities as high as 3.6 · 1022 cm-3. This marks an important step in the realization of all-oxide electronics for emerging technological devices.

Solar-driven plasmonic heterostructure Ti/TiO2-x with gradient doping for sustainable plasmon-enhanced catalysis.

Plasmon-enhanced harvesting of photons has contributed to the photochemical conversion and storage of solar energy. However, high dependence on noble metals and weak coupling in heterostructures constrain the progress towards sustainable plasmonic enhancement. Here earth-abundant Ti is studied to achieve the plasmonic enhancement of catalytic activity in a solar-driven heterostructure Ti/TiO2-x. The heterostructure was fabricated by engineering an intense coupling of a surface-etched Ti metal and a gradient-based TiO2-x dielectric via diffusion doping. Ti/TiO2-x exhibits a highly resonant light absorption band associated with surface plasmon resonances that exhibit strong near-field enhancement (NFE) and hot electron injection effects. In a photoelectrochemical system, intense interaction of the resonant plasmons with a vicinal TiO2-x dielectric accelerates the transfer of solar energy to charge carriers for plasmon-enhanced water splitting reactions. Moreover, the plasmonic Ti/TiO2-x structure presents sustained enhanced redox activities over 100 h. The intense coupling by gradient doping offers an effective approach to enable the plasmon resonances of Ti excited by visible light. The Ti-based plasmonic heterostructure potentially opens an alternative avenue towards sustainable plasmon-enhanced catalysis.

Single-step approach to sensitized luminescence through bulk-embedded organics in crystalline fluorides.

Luminescent materials enable warm white LEDs, molecular tagging, enhanced optoelectronics and can improve energy harvesting. With the recent development of multi-step processes like down- and upconversion and the difficulty in sensitizing these, it is clear that optimizing all properties simultaneously is not possible within a single material class. In this work, we have utilized the layer-by-layer approach of atomic layer deposition to combine broad absorption from an aromatic molecule with the high emission yields of crystalline multi-layer lanthanide fluorides in a single-step nanocomposite process. This approach results in complete energy transfer from the organic molecule while providing inorganic fluoride-like lanthanide luminescence. Sm3+ is easily quenched by organic sensitizers, but in our case we obtain strong fluoride-like Sm3+ emission sensitized by strong UV absorption of terephthalic acid. This design allows combinations of otherwise incompatible species, both with respect to normally incompatible synthesis requirements and in controlling energy transfer and quenching routes.

Atomic Layer Deposition of GdCoO3 and Gd0.9Ca0.1CoO3.

Thin films of the catalytically interesting ternary and quaternary perovskites GdCoO3 and Gd0.9Ca0.1CoO3 are fabricated by atomic layer deposition using metal ß-diketonates and ozone as precursors. The resulting thin films are amorphous as deposited and become single-oriented crystalline on LaAlO3(100) and YAlO3(100/010) after post-annealing at 650 °C in air. The crystal orientations of the films are tunable by choice and the orientation of the substrate, mitigated through the interface via solid face epitaxy upon annealing. The films exhibit no sign of Co2+. Additionally, high-aspect-ratio Si(100) substrates were used to document the suitability of the developed process for the preparation of coatings on more complex, high-surface-area structures. We believe that coatings of GdCoO3 and Gd1-xCaxCoO3 may find applications within oxidation catalysis.

Phase and Orientation Control of NiTiO3 Thin Films.

Subtle changes in the atomic arrangement of NiTiO3 in the ilmenite structure affects its symmetry and properties. At high temperatures, the cations are randomly distributed throughout the structure, resulting in the corundum structure with R-3c symmetry. Upon cooling, the cations order in alternating layers along the crystallographic c axis, resulting in the ilmenite structure with R-3 symmetry. Related to this is the R3c symmetry, where the cations alternate both perpendicularly and along the c axis. NiTiO3 with the latter structure is highly interesting as it exhibits ferroelectric properties. The close relationship between structure and properties for ilmenite-related structures emphasizes the importance of being able to control the symmetry during synthesis. We show that the orientation and symmetry of thin films of NiTiO3 formed by atomic layer deposition (ALD) can be controlled by choice of substrate. The disordered phase (R-3c), previously only observed at elevated temperatures, have been deposited at 250 °C on α-Al2O3 substrates, while post-deposition annealing at moderate temperatures (650 °C) induces ordering (R-3). We have in addition explored the symmetry and epitaxial orientation obtained when deposited on substrates of LaAlO3(100), SrTiO3(100) and MgO(100). The presented work demonstrates the possibilities of ALD to form metastable phases through choice of substrates.

Chemical Uniformity in Ferroelectric K x Na1- x NbO3 Thin Films.

Potassium sodium niobate (KNN) has long been considered a viable candidate for replacing lead-based materials in piezo- and ferroelectric devices. The introduction of KNN on an industrial scale is highly awaited; however, processing challenges still remain to be solved. The main obstacle is lack of reproducible growth of uniform boules or thin films at temperatures that facilitate monolithic device integration. Herein, atomic layer deposition (ALD) of KNN thin films, exhibiting high chemical uniformity over large areas, is reported. The cation composition can be controlled at a 1% level, enabling fine-tuning of the film stoichiometry across the morphotropic phase boundaries of the KNbO3-NaNbO3 solid solution. The films are obtained as highly oriented on Pt (111)||Si (100)-substrates after annealing at temperatures as low as 550 °C. They exhibit converse piezoelectric effects with magnitudes in accordance with literature. It is believed that the successful development of the described ALD process represents a major step toward achieving lead-free piezo- and ferroelectrics on an industrial scale.

Sensors for optical thermometry based on luminescence from layered YVO4: Ln3+ (Ln = Nd, Sm, Eu, Dy, Ho, Er, Tm, Yb) thin films made by atomic layer deposition.

Below the Earth's crust, temperatures may reach beyond 600 K, impeding the batteries used to power conventional thermometers. Fluorescence intensity ratio based temperature probes can be used with optical fibers that can withstand these conditions. However, the probes tend to exhibit narrow operating ranges and poor sensitivity above 400 K. In this study, we have investigated single and dual layered YVO4: Ln3+ (Ln = Nd, Sm, Eu, Dy, Ho, Er, Tm, Yb) thin films (100-150 nm) for use in fluorescence intensity ratio based temperature sensors in the 300-850 K range. The type of lanthanide emission can be fine-tuned by adjusting the thickness of each layer, and the layered structure allows for emission from otherwise incompatible lanthanide pairs. This novel multi-layered approach enables high sensitivity over a broad temperature range. The highest relative sensitivity was achieved for a dual layered YVO4: Eu3+/YVO4: Dy3+ sample, exhibiting a maximum sensitivity of 3.6% K-1 at 640 K. The films were successfully deposited on all tested substrates (silicon, iron, aluminum, glass, quartz, and steel), and can be applied homogenously to most surfaces without the use of binders. The films are unaffected by water, enabling non-contact temperature sensing in water, where IR thermometers are not an option.

Biocompatible organic-inorganic hybrid materials based on nucleobases and titanium developed by molecular layer deposition.

We have constructed thin films of organic-inorganic hybrid character by combining titanium tetra-isopropoxide (TTIP) and the nucleobases thymine, uracil or adenine using the molecular layer deposition (MLD) approach. Such materials have potential as bioactive coatings, and the bioactivity of these films is described in our recent work [Momtazi, L.; Dartt, D. A.; Nilsen, O.; Eidet, J. R. J. Biomed. Mater. Res., Part A 2018, 106, 3090-3098. doi:10.1002/jbm.a.36499]. The growth was followed by in situ quartz crystal microbalance (QCM) measurements and all systems exhibited atomic layer deposition (ALD) type of growth. The adenine system has an ALD temperature window between 250 and 300 °C, while an overall reduction in growth rate with increasing temperature was observed for the uracil and thymine systems. The bonding modes of the films have been further characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction, confirming the hybrid nature of the as-deposited films with an amorphous structure where partial inclusion of the TTIP molecule occurs during growth. The films are highly hydrophilic, while the nucleobases do leach in water providing an amorphous structure mainly of TiO2 with reduced density and index of refraction.

Molecular layer deposition builds biocompatible substrates for epithelial cells.

The demand for novel biocompatible materials as surface coating in the field of regenerative medicine is high. We explored molecular layer deposition (MLD) technique for building surface coatings and introduced a new group of substrates consisting of amino acids, or nucleobases, and the biocompatible metal titanium. The substrates were built from titanium tetraisopropoxide (TTIP) with l-lysine, glycine, l-aspartic acid, l-arginine, thymine, uracil, and adenine. Substrates based on zirconium chloride and terephthalic acid were also included. Titanium oxide (TiO2 ) substrates made by atomic layer deposition and uncoated cover slips served as controls. Rat conjunctival epithelial goblet cells were grown in RPMI 1640 and RT-PCR, immunofluorescence, cell attachment, proliferation, and viability were analyzed. Cells cultured on MLD and uncoated substrates were proliferating (positive for Ki67). Cell attachment after 3 h of culture on MLD substrates was similar to uncoated coverslips (p > 0.05). Compared to uncoated coverslips, cell proliferation assayed with alamarBlue® after 4 days was significantly higher on all MLD substrates (p < 0.05), whereas terephthalic acid-containing MLD substrates reduced proliferation (p < 0.01). Viability assessed by LIVE/DEAD® was high (>85%) for all substrates after 5 days. The novel MLD technique is promising for building biocompatible substrates that direct epithelial cell growth. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 3090-3098, 2018.