Interstitial Species Research Articles

A study on the evolution of hydrothermally synthesized MoS2 on thermal annealing and development of novel MoS2-MoO3 hybrid nanostructure for supercapacitor applications

The electrochemical capacitor also known as supercapacitor is a high-performance energy storage device with exceptional properties. We report the evolution of structural, morphological, optical, and thermal properties of MoS2 on thermal annealing along with its supercapacitor study. The pristine MoS2 is synthesized via the hydrothermal method at 200 °C and the material is annealed in the presence of air at 250 °C, 300 °C, and 350 °C. The 300 °C annealed sample has shown a hybrid MoO3-xMoS2-y phase characterized by morphology of mixed flower-like and nano brick-like structures, marking the first time report of this novel formation. The evolution of the novel MoO3-xMoS2-y phase can be attributed to the intervention of lattice and interstitial oxygen species during synthesis. Electrochemical analysis is employed to study the supercapacitor nature of the materials. The electrochemical study revealed that the hybrid structure has a higher charge storage capacity than MoS2 or MoO3. The calculated specific capacitance from the galvanostatic charge-discharge curve of MoO3-xMoS2-y in 0.1 M NaOH is observed to be 1.71 mF/cm2, five times greater than other samples. Furthermore, the capacitor behavior of MoO3-xMoS2-y is studied in different electrolytes such as KOH, NaOH, and Na2SO4 at a concentration of 3 M. The intercalation-assisted faradaic process is observed to be the major charge storage mechanism of the hybrid structure. Developing novel nanostructures with distinct properties is crucial for advancing supercapacitors to achieve optimal performance.

Phascolion kamchatikus sp. nov., the first interstitial sipunculan (Sipuncula, Phascolionidae) from the Pacific Ocean

A new species of meiobenthic sipunculan, Phascolion kamchatikus sp. nov. collected from coarse sand and shell hash in shallow waters in the northwestern Pacific, is described and illustrated using light and electron microscopy. This new species is well distinguished from all other congeners by a unique combination of main taxonomic characters. This is the only sipunculan having only two primary tentacles in both juvenile and sexually mature worms. There are no hooks and holdfast papillae in the adult stages. Because of the presence of three nearly equal in size retractor muscles forming a retractor column divided for most of its length, this species is assigned to the subgenus Isomya of the genus Phascolion. Unlike most other species of the genus Phascolion, P. kamchatikus sp. nov. has an interstitial mode of life moving among the coarse sand grains and shell hash accumulated between rocks and stones in shallow water areas alongside the Pacific coast of Kamchatka, Aleutian Islands and Alaska Peninsula. Phascolion kamchatikus sp. nov. constitutes the only third interstitial species of the phylum Sipuncula. This is also the ninth species of Phascolion in the northwestern Pacific and the first interstitial representative of this genus in the Pacific Ocean.

Predictive Modeling of Nanocrystal Orientation in Superlattices: Insights from Ligand Entropy.

The self-assembly of nanocrystals (NCs) into close-packed, ordered superlattices (SLs) is of broad, engineering interest. The coherent orientation of polyhedral nanocrystals within NC SLs enhances electronic, magnetic, and vibrational coupling, leading to a variety of emergent phenomena. Here, we show that coherent orientation of polyhedral NCs in many SLs can be understood simply by considering its effect on the conformational entropy of surface ligands. We report the predicted nanocrystal orientations and entropic driving force to orient for a broad range of nanocrystal shapes and superlattice unit cells, and we show that ligand entropy is sufficient to reproduce a host of reported experimental and computational observations. We additionally use this framework to predict the expected distribution of interstitial species such as solvent or unbound ligands in an oriented NC SL. This work offers intuition for understanding the orientation of NCs in superlattices and a future framework for analyzing multinary structures.

Efficient determination of free energies of non-ideal solid solutions via hybrid Monte Carlo simulations

Predicting the phase diagram of solid solutions is crucial for understanding their physical behavior under various conditions and at different compositions. However, conventional sampling methods face challenges in efficiently addressing configurational and vibrational disorder for substitutional solid solutions. Additionally, a persistent obstacle has been the lack of a robust theoretical approach for determining the free energy of interstitial solid solutions characterized by the fluid-like diffusion of interstitial species. The method presented in this paper overcomes both hurdles by coupling thermodynamic integration with hybrid Monte Carlo algorithms. We validate the accuracy of the method by computing the free energies of iron alloys described by a Lennard-Jones potential. We also showcase its efficiency by determining the phase diagram of the MgO-CaO system, described by a machine-learning interatomic potential. The high efficiencies achieved with this method pave the way to the determination of the free energies of solid solutions with ab initio accuracy.

Spatially-resolved cluster dynamics modeling of irradiation growth

We develop here a spatially resolved, three-dimensional continuum model coupling cluster dynamics (SR-CD) and crystal plasticity to investigate irradiation growth in zirconium. The model uses scale separation to divide the population of the irradiation cluster into mobile and immobile families. Small interstitial and vacancy clusters are modeled using anisotropic reaction–diffusion equations. Among the immobile clusters, an atomistically-informed vacancy cluster to vacancy loop transition is taken into account. The coupling between the evolution equation of CD and the plastic deformation of the material is two-fold, with stress-informed bias factors and local inelastic strains computed from the evolution of the evolving cluster population. The numerical implementation of the model utilizes the finite element method to analyze both single-crystal and polycrystalline samples. The growth strains that are computed align well with the experimental data provided by Carpenter for single-crystal Zr. Furthermore, the transformation of a vacancy cluster into a complete vacancy loop, occurring at a size of 14 nm, is in agreement with experimental observations and atomistic simulations. The density, size, and growth rate of the dislocation loops, denoted as 〈c〉 and 〈a〉, also exhibit good agreement with transmission electron microscopy (TEM) analysis of irradiated Zr and its alloys. Our findings demonstrate that there is a spatial correlation between the growth of these dislocation loops and growth strains, significantly influenced by the crystal size. To explain the expansion of the 〈a〉 axis and the contraction of the 〈c〉 axis in irradiated Zr, it is necessary to consider the diffusion anisotropy difference (DAD) of mobile interstitial species. We show that the PWR Kearns parameters, specifically fr = 0.63, ft = 0.32, fa = 0.05, confer enhanced irradiation resistance to Zr along the principal directions when compared to single crystals. Additionally, reducing the grain size to nanograins further enhances the resistance to irradiation-induced growth, particularly along the direction with the highest volume fraction of basal poles [0001].

Three new interstitial species of the genus Neonesidea (Bairdioidea: Podocopida: Ostracoda) from the infralittoral zone in Japan.

This study is the first to report on interstitial species of the genus Neonesidea: Neonesidea arenalocus sp. nov. from the Pacific coast of central Japan, Neonesidea alyamanai sp. nov. from the Pacific coast of south-western Japan, and Neonesidea alwakasaensis sp. nov. from the Sea of Japan coast of western Japan. All three species share a smaller carapace size than that of the epiphytic Neonesidea species; in particular, the carapace width and valve thickness are significantly less. Furthermore, the terminal claws on the walking legs are more linear than those of the epiphytic Neonesidea species. However, these three new species share a feature in the apical portion of the terminal claw on the males second antennae and asymmetric brush-shaped organs, which are common to this genus. In addition, the results of our field survey indicate that all three new species occur in coarse-grained sediments (coarse sand to pebbles) in the upper infralittoral zone, particularly on Miho-Masaki Beach, which contains an optimum zone for N. arenalocus sp. nov.

Does atp8 exist in the mitochondrial genome of Proseriata (Metazoa: Platyhelminthes)?

The adenosine triphosphate (ATP) synthase F0 subunit 8 gene (atp8) had been believed to be absent in mitochondrial genomes of platyhelminths until the late 2010s, since when multiple lines of emergent evidence have suggested that this gene is actually present, albeit in highly derived forms, throughout the entire phylum except for the parasitic Neodermata (tapeworms, flukes, and their kin). Of about 11 non-parasitic (turbellarian) major platyhelminth subtaxa, the existence of atp8 has hitherto been documented in five (Catenulida, Macrostomorpha, Polycladida, Rhabdocoela, and Tricladida), while it remains open in the remaining six (Prorhynchida, Gnosonesmida, Proseriata, Fecampiida, Prolecithophora, and Bothrioplanida). Here we report the mitochondrial genome sequence of an undetermined marine interstitial turbellarian species in the genus NematoplanaMeixner, 1938 as the first representative of Proseriata. This circular genome comprises 16,106 bp (but potentially 18,812–19,277 bp when unresolved, non-coding tandem repeats are considered) and includes 38 genes, viz. 23 transfer RNA genes, 13 protein-coding genes (including the putative atp8), and two ribosomal RNA genes. The putative atp8 in Nematoplana sp. was not annotated by a standard automated procedure but was detected by manual inspection. If it encodes a translated product, it consists of 156 bp, with the potential 52-amino-acid-residue product beginning with MPHV, instead of the metazoan-canonical MPQL, and containing a single putative transmembrane region expanding from the 7th to the 29th amino-acid positions. While our finding seemingly strengthens the hypothesis that atp8 is in the ground pattern of flatworm mitochondrial genomes, whether the putative atp8 in flatworms is actually transcribed and translated to form a functional ATP synthetase F0 subunit should be tested in future studies.

Enhanced photocatalytic toluene oxidation on CN species modified TiO2: Nitrogen doping state and anti-inactivation mechanism

The photocatalytic oxidation of toluene is limited by low mineralization and inactivation. Cheap carbon and nitrogen (CN) species on TiO2 provides an efficient strategy. CN species from the urea calcination in situ formed on TiO2 were denoted as UTx (x = 0.5, 1, 2), and UT1 photocatalyst had the best performance of ca. 90% conversion and 85% mineralization of toluene in light (λ ≥ 400 nm, RH= 20%), with keeping for at least 720 min. The excellent activity of UT1 photocatalyst was resulted from the observed interstitial nitrogen and CN species with triple bonds. Because easily forming interstitial nitrogen resulted in isolated states and more negative VBM to generate hydroxyl radicals, and CN species with triple bonds was beneficial for transferring electrons and opening benzene rings. Therefore, quinone intermediates on UT1 were oxidized to 3-hydroxyglutaric dialdehyde and deeply mineralized, while more accumulated benzaldehyde on TiO2 led to poorer stability.

Theama japonica sp. nov., an Interstitial Polyclad Flatworm Showing a Wide Distribution along Japanese Coasts.

We establish a new interstitial polyclad species, Theama japonica sp. nov., based on specimens collected from coarse-sandy habitats in three Japanese main islands (Hokkaido, Honshu, and Shikoku) along the coasts of the Pacific Ocean and the Sea of Japan. Theama japonica is characterized by i) two pairs of cerebral eyespots and four to six precerebral eyespots; ii) eosinophilic secretion glands distributed in the distal half of the inner ventral part of the prostatic vesicle; iii) a conical penis papilla, bent up dorsally, with a sclerotized inner wall; iv) the prostatic sheath with an inner angular fold on the dorso-distal side; and v) the external cilia longer dorsally than ventrally. Partial sequences of the cytochrome c oxidase subunit I (COI) gene from 20 specimens collected at eight localities along Japanese coasts represented 19 haplotypes. The uncorrected p-distances among these COI haplotypes fell within intraspecific variations observed in other polyclads. A network analysis based on these COI haplotypes suggested a geographically non-cohesive genetic structure of the species, possibly indicating the species' high dispersibility. Molecular phylogenetic analyses based on a concatenated dataset of 18S and 28S rDNA sequences showed T. japonica formed a clade with other Theama species. The resulting tree also indicates that our new species is more closely related to Theama sp. from Colombia than species from Panama and Croatia.

How climate-driven changes in disturbance frequency affect the recovery of intertidal mussel beds

Community and population recovery from disturbance depends on the intensity, spatial scales, and frequency of disturbance events. Moreover, foundation species, like bed-forming mussels in rocky intertidal shores, are especially prone to disturbance associated with extreme climatic events. The aim of the present study was to experimentally evaluate how the frequency of physical disturbances that generate gaps in beds of the mussel Brachidontes rodriguezii affects mussel recolonization and the succession process on two rocky shore sites of the Southwestern Atlantic. Experimental disturbances (removal of mussels and other forms of biotic cover) were applied to small plots (14 cm × 14 cm) at three different frequencies over two years: 1) only at the beginning of the experiment (i.e., 1× removal frequency), 2) at the beginning of the experiment and 12 months later (2× removal frequency) and, 3) at the beginning of the experiment and 6, 12, and 18 later (4× removal frequency). Unmanipulated areas were maintained as controls. Before applying the experimental disturbance, we measured the abundance of all organisms present in all plots, obtaining data every 6 months. The data were analyzed considering two factors associated with the disturbance frequency: the time since the last removal and the number of removals on the same plot. Our results indicate that increases in disturbance frequencies were sufficient to maintain mussel bed recovery below control levels and increased the cover of crustose algae at the end of the two-year experimental period in one of the rocky shores studied. The decreases observed in the mussel recovery rates under increased disturbance scenarios are expected to have cascading consequences on rocky shore biodiversity, such as reductions in the overall abundance of interstitial invertebrate species that depend on mussel bed habitats and increases in the abundance of sessile organisms that preferentially occur in gaps and are otherwise excluded by mussels, such as the non-native barnacle Balanus glandula.

Community assembly and co-occurrence network complexity of interstitial microbial communities in the Arctic (investigation of ciliates in the White Sea intertidal zone)

Arctic coastal ecosystems play a major role in global environmental system and have been altered significantly by climate changes. To better understanding the response of marine coastal ecosystems towards rapid Arctic climate changes, we examined the variation in diversity and community structure and provided insights into the co-occurrence network and community assembly of interstitial ciliates in the Kandalaksha Gulf of the White Sea from 2009 to 2019. Co-occurrence networks analysis indicated considerably high ration of positive correlations within a community that indicated low competition between interstitial ciliate species. Furthermore, we found that contribution of stochastic processes to the ciliate community assembly was insignificant. Compare with earlier data from the same ecosystem obtained in 1980s–1990s, the role of competitive factors is decreasing, and communities are becoming more spatially and temporally homogeneous. This community simplification is likely due to the response of the entire intertidal ecosystem to global climate change in Arctic.

Reversible shifts between interstitial and epibenthic habitats in evolutionary history: Molecular phylogeny of the marine flatworm family Boniniidae (Platyhelminthes: Polycladida: Cotylea) with descriptions of two new species.

Tiny animals in various metazoan phyla inhabit the interstices between sand and/or gravel grains, and adaptive traits in their body plan, such as simplification and size reduction, have attracted research attention. Several possible explanations of how such animals colonized interstitial habitats have been proposed, but their adaptation to this environment has generally been regarded as irreversible. However, the actual evolutionary transitions are not well understood in almost all taxa. In the present study, we show reversible evolutionary shifts from interstitial to epibenthic habitats in the lineage of the polyclad flatworm genus Boninia. In addition, we establish two new species of this genus found from different microhabitats on a single beach in Okinawa Island, Japan: (i) the interstitial species Boninia uru sp. nov. from gravelly sediments and (ii) the epibenthic species Boninia yambarensis sp. nov. from rock undersurfaces. Our observations suggest that rigid microhabitat segregation exists between these two species. Molecular phylogenetic analyses based on the partial 18S and 28S rDNA sequences of the new Boninia species and four other congeners, for which molecular sequences were available in public databases [Boninia antillara (epibenthic), Boninia divae (epibenthic), Boninia neotethydis (interstitial), and an unidentified Boninia sp. (habitat indeterminate)], revealed that the two interstitial species (B. neotethydis and B. uru sp. nov.) were not monophyletic among the three epibenthic species. According to ancestral state reconstruction analysis, the last common ancestor of the analyzed Boninia species inhabited interstitial realms, and a shift to the epibenthic environment occurred at least once. Such an "interstitial to noninterstitial" evolutionary route seems to be rare among Animalia; to date, it has been reported only in acochlidian slugs in the clade Hedylopsacea. Our phylogenetic tree also showed that the sympatric B. uru sp. nov. and B. yambarensis sp. nov. were not in a sister relationship, indicating that they colonized the same beach independently rather than descended in situ from a common ancestor that migrated and settled at the beach.

Notes on morphology and ecology of an elusive water flea Rhynchotalona latens (Sarmaja-Korjonen, Hakojärvi & Korhola, 2000) (Crustacea: Cladocera)

Very rare North European water flea Rhynchotalona latens (Sarmaja-Korjonen, Hakojärvi & Korhola, 2000) (Crustacea: Cladocera), found mostly as remains during subfossil studies, was found in North Karelia, Russia. The species inhabits waterlogged Sphagnum mosses at lake margins, but is not present in littoral zones of the lakes. Morphology of thoracic limbs of R. latens was studied for the first time; SEM studies of the species were conducted for the first time. Our data suggests that R. latens is a specialized interstitial moss-dwelling species, only accidentally found in open water, which explains its rarity in samples taken by standard sampling methods. Presence of R. latens subfossil remains in sediments specifically indicate presence of Sphagnum at the lake coast, typical for acid oligotrophic or dystrophiс lakes.

(Invited) Atomistic Insights on Prussian Blue Analogues for Aqueous Electrochemical Separations

Prussian blue analogues (PBAs) containing metal centers bridged by cyanide ligands exhibit one of the simplest structures among metal organic frameworks, which lends them to facile and reversible insertion of monovalent cations. Such a property has motivated their use in aqueous electrochemical separations, including our most recent demonstration of brackish water desalination with only 25% more energy consumption than thermodynamic minimum.1 Despite their selectivity bias toward cations of small hydrated radius being known for 36 years,2 the microscopic mechanisms responsible for such bias that could be used to inform the rational design of future materials are not well understood.Accordingly, we report on our recent efforts3,4 to uncover the interactions between inserted cations, interstitial water, and PBA lattices that produce selectivity bias. To understand the interplay between structural distortion, bonding, and water uptake from contacting electrolyte we use a first-principles approach that combines machine learning with density functional theory and grand potential analysis to explore the potential energy landscapes of disordered arrangements of interstitial species in nickel hexacyanoferrate PBA. Here, a competition for dative bonds of acidic interstitial cations between basic oxygen in interstitial water and basic cyanide ligands is shown to result in complexation between cations and water that deviate fundamentally from bulk hydration in pure water, despite the common attribution of PBA selectivity to purely steric effects of cation hydration. Van der Waals interactions are further shown to enhance the formation of water clusters and extended hydrogen-bonded networks within the PBA host, depending on the bare ionic radius of inserted cations. Grand potential analysis is performed to ultimately produce previously observed selectivity bias (Cs+ > K+ > Na+) and to determine the equilibrium hydration degree of the PBA in both reduced and oxidized forms. This analysis shows that small (Na+) and moderately sized (K+) cations require two to four water molecules per formula unit in both reduced and oxidized forms of the PBA, while large cations (Cs+) exhibit much smaller hydration levels in oxidized form and exhibit no hydration in reduced form. References Reale, E. R., Regenwetter, L., Agrawal, A., Dardón, B., Dicola, N., Sanagala, S. & Smith, K. C. Low porosity, high areal-capacity Prussian blue analogue electrodes enhance salt removal and thermodynamic efficiency in symmetric Faradaic deionization with automated fluid control. Water Res. X 13, 100116 (2021).Ikeshoji, T. Separation of Alkali Metal Ions by Intercalation into a Prussian Blue Electrode. J. Electrochem. Soc. 133, 2108 (1986).Liu, S. & Smith, K. C. Linking the polyatomic structure of interstitial H2O and cations to bonding within Prussian blue analogues ab initio using gradient-boosted machine learning. Phys. Rev. Mater. 5, 035003 (2021).Liu, S. & Smith, K. C. Effects of interstitial water and alkali cations on the expansion, intercalation potential, and orbital coupling of nickel hexacyanoferrate from first principles. J. Appl. Phys. 131, 105101 (2022).

Two species of the genus Anchistrocheles (Bairdioidea: Ostracoda: Crustacea) from Japan and their developmental characteristics for adaptation to interstitial environments

A new species and an already known species of the genus Anchistrocheles Brady & Norman, 1889 from the Pacific coast of Japan, are described in detail using scanning electron microscopy of the carapaces and soft-part anatomy of the appendages. The new species, Anchistrocheles hayatotanakai sp. nov., is only the second to be described in the genus Anchistrocheles from Japan, and this study is also the first to describe the appendages of A. yamaguchii Yajima, 1987, previously only known as a fossil from Pleistocene strata of the Atsumi Formation in central Japan. The two species are considered to be closely related because they share many common characters in their appendages, but they are distinguishable from each other based on the male and female copulatory organs, furcal chaetotaxy, brush-shaped organs, number of lateral pore systems, and outlines of the carapaces in dorsal view. Ontogenetic changes of carapace sizes were compared between three interstitial species (Anchistrocheles hayatotanakai sp. nov., A. yamaguchii, and Neonesidea sp. I) and an epifaunal species (N. sp. S). The reduction in carapace width was found to be the primary reason for the reduction in the cross-sectional area and is probably related to the adaptation to interstitial environments. The brush-shaped organs located between the 6th pair of limbs are also shown. This study is the first to report the anatomically precise position of these organs.

Revealing the influence of carbon on shear-coupled grain boundary migrationin α-iron via molecular dynamics simulations

Shear-coupled grain boundary (GB) migration is of importance theoretically on the mechanisms of GB behaviors and application oriented on the development of novel processing methods by plastic deformation. We demonstrate via molecular dynamics simulations that the interstitial species carbon may affect the shear-coupled migration in α-iron strongly. The impact of carbon selectively takes effect depending on the variety of grain boundaries. Specifically, the coupling factor of the Σ9(221) GB is increased in the presence of carbon. While the carbon effect is inactive for the Σ17(223) GB. The influence of carbon is revealed to be connected with the disconnection modes of grain boundaries. The results of the work implicate correlations between the carbon enrichment and the final microstructure after severe plastic deformation.

Environmental stability and long-term variability of harpacticoid copepod assemblages

Harpacticoid copepods of the Chernaya Bay (White Sea) intertidal zone were collected in 45 surveys carried out from spring to autumn over a 25-year period (1996–2020) at three sites that differed in sediment properties. There were no significant long-term trends or seasonal cycles in total abundance. Regarding the species composition, the differences between sites were the most important source of variability over the whole period while the fine-scale (within-habitat) variability was low. Epibenthic species prevailed in fine silty sand, both burrowing and epibenthic species prevailed in medium sand, and interstitial and burrowing species prevailed in coarse sand. A comparison of the data on harpacticoid assemblages from a number of geographically remote loci corroborated the generality of this pattern. In a temporal dimension, the structure of each community was stable until the early 2000s, when the proportion of epibenthic, burrowing and interstitial species changed following changes in sediment properties (increasing siltation at sandy sites and decreasing siltation at the silty site). At each site, there was an increasing long-term trend in diversity (both in total richness and in expected species number). This increase was particularly apparent at sandy sites because of the appearance of epibenthic species. We suggest that sediment composition is the key factor determining the composition of harpacticoid assemblages in space and time. The “ecomorphological profile”, i.e., the proportion of species with different lifestyle and morphological traits, is a useful and informative indicator for describing and typifying these assemblages.

The effect of riparian pool‐riffles on the hydrochemistry of hyporheic habitats: The River Esk, Yorkshire, UK

AbstractEuropean Union Water Framework Directive (WFD) (2000/60/EC) waterbody statuses are often derived from the assemblage of mixed‐taxon organisms found within bed sediments. Yet no routine water chemistry samples are taken from riverbed substrate, despite many interstitial species being dependant on specific physicochemical conditions. This paper examines water and nutrient exchanges between stream and substrate, the hyporheic zone, and the consequent alteration to the chemistry of interstitial and in‐stream waters, which in turn leads to small‐scale but significant changes in habitat. Bed topography, principally a pool‐riffle sequence, was surveyed and hydraulically sampled to examine the hyporheic flow pathways generated between the stream, substrate, and groundwater—creating an ecotone. Hyporheic zone, in‐stream and groundwater hydrochemistry, and hydraulic measures were assessed at a braided woodland river reach using a dense monitoring approach. The findings demonstrate that through a 23‐m pool‐riffle sequence, where water infiltrates at the riffle‐head and subsequently exfiltrates at the riffle‐tail, there is a 5% reduction in mean in‐stream nitrate‐N and a 73% reduction in hyporheic zone concentration. When calcium‐enriched riffle‐tail exfiltrate meets riffle‐runoff water that is turbulently oxygenated from riffle‐flow, an interstitial redoxcline is created. Dissolved oxygen nocturnally drops, with photosynthetic rate reduction, which causes hyporheic nitrate‐N to double its daytime concentration. The results are related to the Yorkshire River Esk freshwater pearl mussels, Margaritifera margaritifera Linnaeus (1758), a declining endangered species. At present, scant monitoring of interstitial hydrochemistry and diurnal change across stream and substrate occurs.

Tunable Ti3+-Mediated Charge Carrier Dynamics of Atomic Layer Deposition-Grown Amorphous TiO2

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.

Insertion and diffusion of N and C in [formula omitted]–TiAl: Theoretical study and comparison with O

Nitrogen and carbon play an important role in the oxidation of Ti-Al intermetallic alloys in air. The insertion and diffusion of these elements in the γ-TiAl phase are investigated by first-principle computations. The accommodation of C and N atoms in several likely interstitial positions has been evaluated using density functional theory (DFT) calculations. The results show that both carbon and nitrogen prefer Ti-rich environments. Then, considering the possible jumps among the stable and metastable interstitial sites, the diffusion coefficients have also been obtained from ab initio calculations. According to the Transitional State Theory, in order to compute atomic jump rates, diffusion energy barriers and vibrational modes need to be known. Herein, barrier energies are obtained using the Climbing Image Nudged Elastic Band method. Vibrational properties are computed using the finite displacement method. Finally, diffusion coefficients are obtained solving the transport equation in the infinite time limit, using an analytical approach. The obtained results are compared to the diffusion of oxygen in γ-TiAl, investigated in previous studies. An anisotropic diffusion is obtained for all the interstitial species.