Group VI Elements Research Articles

Photoluminescence properties of SnO2 nanoparticles doped with group VI elements (Cr, Mo, W) synthesized by pulsed laser ablation in liquid

Tin oxide nanoparticles (SnO2 NPs), both pure and doped with Group VI (G6) metal ions (Cr+3, Mo+5, and W+6), were synthesized using pulsed laser ablation in liquid. This study aimed to investigate the effect of G6 doping on the electronic properties of SnO2 NPs, with an emphasis on enhancing their photoluminescence for optoelectronic applications. Transmission electron microscopy revealed well-crystallized samples with diameters of 3–6 nm, indicating quantum-confinement effects. The optical band gap, determined by UV–Vis spectroscopy, was reduced from 5.1 eV (undoped) to 4.9 eV (Cr-doped) due to defect states, while increasing to 5.3 eV and 5.7 eV for Mo- and W-doped SnO2, respectively, due to the Moss-Burstein effect. The photoluminescence spectra exhibited a redshift, with strong red emission around 700 nm, which was up to 90 % more intense than that of the undoped SnO2. This enhancement was attributed to the 2E→4A2 transition and increased defect states.

Structural analysis of molybdate binding protein ModA from Klebsiella pneumoniae

Klebsiella pneumoniae, a facultative anaerobe, relies on acquiring molybdenum to sustain growth in anaerobic conditions, a crucial factor for the pathogen to establish infections within host environments. Molybdenum plays a critical role in pathogenesis as it forms an essential component of cofactors for molybdoenzymes. K. pneumoniae utilizes the ABC (ATP-Binding-Cassette) transporter encoded by the modABC operon for uptake of the group VI elements molybdenum and tungsten. In this study, we determined the X-ray crystal structures of both the molybdenum-free and molybdenum-bound substrate-binding protein (SBP) ModA from Klebsiella pneumoniae to 2.00 Å and 1.77 Å resolution respectively. ModA crystallizes in the space group P222 with a single monomer in one asymmetric unit. The purified protein remained soluble and specifically bound molybdate and tungstate with Kd values of 6.3 nM and 5.2 nM, respectively. Tungstate competes with molybdate by binding to ModA, resulting in enhanced antimicrobial activity. These data provide a starting point for structural and functional analyses of molybdate transport in K. pneumoniae.

The effect of intrinsic electric field on electronic structures: The case of polar Janus group-III monochalcogenides and their van der Waals heterostructures

Electrostatic control and van der Waals integration are useful methods for 2D materials to help modulate their properties. Here, we constructed nine types of monolayer and multilayer Janus structures based on group-III monochalcogenides and investigated their atomic and electronic structures from first-principles calculations. We found the existence of an intrinsic electric field at Janus structures by comparing their average vacuum electron potentials at two surfaces. Careful charge analyses reveal that the electric field at monolayer Janus structures is mainly due to the dipole of the bond that connects group-III elements of weaker negativity and group-VI elements of stronger negativity. The E-filed at multilayer Janus structures maintains owing to the superposition of dipole at each layer when layer numbers (LN) are not very large, and the electric field starts to reduce when LN is large enough and obvious charge transfer happens between two surfaces of Janus multilayers. Electronic structure calculations at Janus structures demonstrate that the electric field can hardly modulate the charge density population in the monolayer case, while the electric field will significantly bend the bands in multilayer cases and make the charge density of the valence band maximum and the conduction band minimum always located at two separating surfaces, which promotes electron–hole to separate. Furthermore, we investigated the band alignment of isolated monolayer pristine group-III monochalcogenides and isolated Janus group-III monochalcogenides of monolayer, bilayer, and trilayer, and constructed van der Waals (vdW) heterostructures with one pristine monolayer and one Janus monolayer. The results show that the surface termination of Janus structures at the interface can significantly influence the band offset and electronic structures of vdW heterostructures. These results can not only provide a new understanding of the intrinsic electric field of monolayer and multilayer 2D Janus structures but also give a guide that uses electrostatic to modulate the properties of group-III monochalcogenides and other 2D materials.

Extrinsic n-type doping of Cd3As2 thin films

Cd3As2 provides an excellent platform for studying the physics of three-dimensional Dirac semimetals due to its stability as well as its compatibility with thin film growth. Crystals made using both bulk and thin film synthesis are unintentionally doped n-type, and other than introducing Zn to reduce the carrier concentration, no efforts have been reported to alter this intrinsic doping without major changes to the band structure. Here, group VI elements Te and Se are introduced during epitaxy to increase the electron concentration of the films. Starting from an unintentionally doped electron concentration of 1–2 × 1017 cm−3, concentrations of up to 3 × 1018 cm−3 are achieved. Analysis of Shubnikov–de Haas oscillations reveals good agreement in calculated effective mass and Fermi velocity of highly doped films with unintentionally doped single crystals with similar electron concentrations. The density functional theory is also performed to study the effects of group VI substitutions and confirms no strong perturbations in the electronic structure. This work ultimately demonstrates tunability in the carrier concentration using extrinsic dopants without substantial changes in the band structure, allowing for intentional design of Fermi-level position for device applications.

Anharmonicity in bcc refractory elements: A detailed ab initio analysis

Explicit anharmonicity, defined as the vibrational contribution beyond the quasiharmonic approximation, is qualitatively different between the group V and group VI bcc refractory elements. Group V elements show a small and mostly negative anharmonic entropy, whereas group VI elements have a large positive anharmonic entropy, strongly increasing with temperature. Here, we explain this difference utilizing highly accurate anharmonic free energies and entropies from ab initio calculations for Nb and Ta (group V), and Mo and W (group VI). The numerically calculated entropies are in agreement with prior experimental data. The difference in behavior between the two sets of elements arises not from their high-temperature behavior but rather from the $0\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ quasiharmonic reference state. We understand this by analyzing the $0\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and the high-temperature phonon density of states and the electronic density of states. The qualitative difference disappears when the anharmonicity is instead referenced with a high-temperature effective harmonic potential. However, even for an optimized effective harmonic reference, the remaining effective anharmonicity is significant. The reason is that the anharmonicity in the bcc systems---carried by asymmetric distributions in the nearest neighbors---can never be accounted for by a harmonically restricted potential.

First principles study of 2D ring-Te and its electrical contact with a topological Dirac semimetal.

In recent years, researchers have manifested their interest in two-dimensional (2D) mono-elemental materials of group-VI elements because of their excellent optoelectronic, photovoltaic and thermoelectric properties. Despite the intensive recent research efforts, there is still a possibility of novel 2D allotropes of these elements due to their multivalency nature. Here, we have predicted a novel 2D allotrope of tellurium (ring-Te) using density functional theory. Its stability is confirmed by phonon and ab initio molecular dynamics simulations. Ring-Te has an indirect band gap of 0.69 eV (1.16 eV) at the PBE (HSE06) level of theories and undergoes an indirect-direct band gap transition under tensile strain. The higher carrier mobility of holes (∼103 cm2 V-1 s-1), good UV-visible light absorption ability and low exciton binding (∼0.35 eV) of ring-Te give rise to its potential applications in optoelectronic devices. Furthermore, the electrical contact of ring-Te with a topological Dirac semimetal (sq-Te) under the influence of an electric field shows that the Schottky barriers and contact types can undergo transition from p-type to n-type Schottky contact and then to ohmic contact at a higher electric field. Our study provides an insight into the physics of designing high-performance electrical coupled devices composed of 2D semiconductors and topological semimetals.

Theoretical design and electronic properties study of two-dimensional Si2S

The zero band gap and air instability seriously of silicene limit its application in logic devices. By introducing the group VI elements, the band gap and stability of silicene will be adjusted. In this research, we propose a new two-dimensional material, Si2S. Si2S has excellent dynamic stability and thermal stability. AIMD simulations show that Si2S can maintain structural integrity at a temperature of 600 K. Si2S has an indirect band gap of 1.93 eV. The indirect band gap can be transformed into a direct band gap under the uniaxial strain along x direction or biaxial strain. The calculated carrier mobility of Si2S is anisotropic and the highest carrier mobility of Si2S is 182.72 cm2 V−1 S−1. The band gap and carrier mobility of Si2S are comparable with that of monolayer MoS2, which makes it promising to be used in the field of nanoelectronics.

Stability, optoelectronic and thermal properties of two-dimensional Janus α-Te2S

Motivated by recent progress in the two-dimensional (2D) materials of group VI elements and their experimental fabrication, we have investigated the stability, optoelectronic and thermal properties of Janus α-Te2S monolayer using first-principles calculations. The phonon dispersion and MD simulations confirm its dynamical and thermal stability. The moderate band gap (∼1.5 eV), ultrahigh carrier mobility (∼103 cm2 V−1 s−1), small exciton binding energy (0.26 eV), broad optical absorption range and charge carrier separation ability due to potential difference (ΔV = 1.07 eV) on two surfaces of Janus α-Te2S monolayer makes it a promising candidate for solar energy conversion. We propose various type-II heterostructures consisting of Janus α-Te2S and other transition metal dichalcogenides for solar cell applications. The calculated power conversion efficiencies of the proposed heterostructures, i.e. α-Te2S/T-PdS2, α-Te2S/BP and α-Te2S/H-MoS2 are ∼21%, ∼19% and 18%, respectively. Also, the ultralow value of lattice thermal conductivity (1.16 W m−1 K−1) of Janus α-Te2S makes it a promising material for the fabrication of next-generation thermal energy conversion devices.

Selenourea and thiourea derivatives of chiral and achiral enetetramines: Synthesis, characterization and enzyme inhibitory properties

A series of chiral and achiral cyclic seleno- and thiourea compounds bearing benzyl groups on N-atoms were prepared from enetetramines and appropriate Group VI elements in good yields. All the synthesized compounds were characterized by elemental analysis, FT-IR, 1H NMR and 13C NMR spectroscopy, and the molecular and crystal structures of (R,R)-4b and (R,R)-5b were confirmed by the single-crystal X-ray diffraction method. These assayed for their activities against metabolic enzymes acetylcholinesterase, butyrylcholinesterase, and α-glycosidase. These selenourea and thiourea derivatives of chiral and achiral enetetramines effectively inhibit AChE and BChE with IC50 values in the range of 3.32–11.36 and 1.47–9.73 µM, respectively. Also, these compounds inhibited α-glycosidase enzyme with IC50 values varying between 1.37 and 8.53 µM. The results indicated that all the synthesized compounds exhibited excellent inhibitory activities against mentioned enzymes as compared with standard inhibitors. Representatively, the most potent compound against α-glycosidase enzyme, (S,S)-5b, was 12-times more potent than standard inhibitor acarbose; 7b and 8a as most potent compounds against cholinesterase enzymes, were around 5 and 13-times more potent than standard inhibitor tacrine against achethylcholinesterase (AChE) and butyrylcholinesterase (BChE), respectively.

Prospects for n-type conductivity in cubic boron nitride

Cubic boron nitride is an ultrawide-bandgap semiconductor with potential applications in high-power electronics, ultraviolet optoelectronics, and quantum information science. Many of those applications are predicated on the ability to control doping. Using hybrid-functional first-principles calculations, we systematically explore potential donors including group-IV (C, Si, and Ge) and group-VI (O, S, and Se) elements, as well as Li and F. We also address the role of compensation either by substitution on the wrong site or due to native point defects. We identify SiB and ON as promising dopants, as they have the lowest formation energies and do not suffer from self-compensation. However, compensation by boron vacancies, which act as deep acceptors, poses a challenge. We discuss strategies to mitigate these effects.

Formation of complexes consisting of impurity Mn atoms and group VI elements in the crystal lattice of silicon

Formation of complexes of impurity Mn atoms with impurity atoms of group VI elements (S, Se, Te) in the silicon crystal lattice has been studied. It has been experimentally found that formation of electrically neutral molecules with an ionic-covalent bond between Mn atoms and group VI elements takes place, which possibly leads to formation of new Si2BVI++Mn binary unit cells in the silicon crystal lattice. It has been shown that in the samples Si<S, Mn>, Si<Se, Mn> and Si<Te, Mn>, an intense complex formation occurs at the temperatures 1100, 820 and 650°C, respectively.

Electrical and Optical Properties of CNTs Additives Chalcogenide Glasses

Glasses have been used as the most versatile engineering materials for more than five decades. Chalcos is a Greek word which means ore former and glasses prepared by particular chalcogenide of group VI element of the periodic table or by their compounds have been known for more than 50 years as an optical material. The primary objective is to provide up to date description of the development in the field of optical and electrical properties of MWCNTs additive chalcogenide glasses. An extensive survey of relevant literature was carried out using sophisticated libraries, virtual media, different research laboratories, internet and also by personal contact with the senior researcher of this field. The exponential increase in D.C. conductivity was observed on increasing the CNT concentration. Inter nanotube connections increase which results in modification of chemical bond formation with increased CNT concentration. It has been observed that the optical band gap of CNT doped chalcogenide glass increases which may be attributed to the fact that CNT added to to the glasses retards the motion of charge carriers and may raise the optical bandgap. The electrical and optical properties of CNT additives chalcogenide glasses have been reviewed. Several applications based on CNT doped glasses have also been discussed, including the development of ionic memories, sensors, optical waveguides, holography, solid-state batteries, optical, and non-linear optical devices.

Superconducting incommensurate host-guest phases in compressed elemental sulfur

We use Density Functional Theory (DFT) and structure searching methods to show that the ground state of elemental sulfur is a Barium-IVa type incommensurate host-guest (HG) phase between $386$-$679$ GPa, becoming the first group-VI element predicted to possess such a structure. Within the HG phase, sulfur undergoes a series of transitions in which adjacent guest chains are not aligned but rather offset by different amounts, which can be described as a rearrangement of the stacking order of the chains. We show that these chain rearrangements are intimately coupled to modulations of the host and guest atoms which prove crucial to stabilising the HG structure. Unlike the high-pressure HG phases of other elements, sulfur does not exhibit interstitial charge localisation, and instead features strongly localised `voids' that are depleted of electronic charge. Prior to adopting the HG structure, we predict that sulfur possesses an orthorhombic structure of $Fdd2$ symmetry. We calculate the superconducting critical temperatures of these newly discovered phases, and show that $T_c$ is expected to peak between $24.8$ and $28.2$ K at $271$ GPa.

First principles computation of composition dependent elastic constants of omega in titanium alloys: implications on mechanical behavior

For decades the poor mechanical properties of Ti alloys were attributed to the intrinsic brittleness of the hexagonal ω-phase that has fewer than 5-independent slip systems. We contradict this conventional wisdom by coupling first-principles and cluster expansion calculations with experiments. We show that the elastic properties of the ω-phase can be systematically varied as a function of its composition to enhance both the ductility and strength of the Ti-alloy. Studies with five prototypical β-stabilizer solutes (Nb, Ta, V, Mo, and W) show that increasing β-stabilizer concentration destabilizes the ω-phase, in agreement with experiments. The Young’s modulus of ω-phase also decreased at larger concentration of β-stabilizers. Within the region of ω-phase stability, addition of Nb, Ta, and V (Group-V elements) decreased Young’s modulus more steeply compared to Mo and W (Group-VI elements) additions. The higher values of Young’s modulus of Ti–W and Ti–Mo binaries is related to the stronger stabilization of ω-phase due to the higher number of valence electrons. Density of states (DOS) calculations also revealed a stronger covalent bonding in the ω-phase compared to a metallic bonding in β-phase, and indicate that alloying is a promising route to enhance the ω-phase’s ductility. Overall, the mechanical properties of ω-phase predicted by our calculations agree well with the available experiments. Importantly, our study reveals that ω precipitates are not intrinsically embrittling and detrimental, and that we can create Ti-alloys with both good ductility and strength by tailoring ω precipitates' composition instead of completely eliminating them.

A design of TiZr-rich body-centered cubic structured multi-principal element alloys with outstanding tensile strength and ductility

Body-centered cubic (BCC) multi-principal element alloys (MPEAs) have drawn extensive attention for their interesting structures and good mechanical properties. However, most BCC MPEAs lack ductility at room temperature. Decreasing the valence electron concentration (VEC) value is an effective approach to design the BCC MPEAs with intrinsic ductility. Three TiZr-rich MPEAs (Ti 45 Zr 45 Nb 5 Ta 5 , Ti 45 Zr 45 Nb 5 Mo 5, and Ti 42.5 Zr 42.5 Nb 5 Mo 5 Ta 5 ) were designed in this paper, by controlling their VEC through restricting the contents of group V (Nb, Ta) and group VI (Mo) elements into 5 at.%. These alloys all possessed BCC structure, low elastic modulus (56–74 GPa), and intrinsic ductility in the as-cast status. Among the three MPEAs, Ti 42.5 Zr 42.5 Nb 5 Mo 5 Ta 5 exhibited the finest microstructure, as well as the highest tensile yield strength (~907 MPa) and elongation (~14.9%). The theoretical calculation indicates that the high strength of Ti 42.5 Zr 42.5 Nb 5 Mo 5 Ta 5 alloy was dominantly attributed to solid solution strengthening. The results also show that Mo element possesses a stronger solution strengthening effect than Ta, as it has a wide difference of shear modulus compared to the other constituent elements.

Characterization of Shock Wave Damages in Explosion Welded Mo/Cu Clads

The shock wave damage during explosive welding has not been reported in a flyer Mo plate of the Mo/Cu clads. However, it would be an inevitable problem in group VI elements. This study was aimed to characterize the shock wave damage in the Mo plate, that is less brittle than a W plate, of explosive welded Mo/Cu clads. Cladding at low horizontal collision velocities leading to high collision angles was expected to enhance the shock wave damage, and the clads resulted in less elongation in bending tests. On the other hand, in the clads obtained at high horizontal collision velocities (HCVs) with low collision angles, their bending elongation increased significantly. The shock wave damage penetrated from the surface of a Mo plate to the Mo/Cu interface, and thus reducing thickness of a Mo plate of bending specimens increased bending plastic strain. The shock wave damage is associated with kinetic energy imparted to the flyer Mo plate, and thus loss of kinetic energy due to formation of an intermediate layer at the interface and reducing thickness of a flyer Mo plate would be very helpful for decrease of shock wave damage.

Incorporating highly basic polyoxometalate anions comprising Nb or Ta into nanoscale reaction fields of porous ionic crystals.

Polyoxometalates (POMs) are oxide cluster anions composed of high-valence early transition metals and are widely used as catalysts. Yet base catalysis of POMs remains an ongoing challenge; group V (V, Nb, and Ta) elements form more negatively charged POMs than group VI (Mo and W) elements, and in particular, polyoxoniobates and polyoxotantalates are known to show strong basicity in solution due to the highly negative surface oxygen atoms. Herein, we report for the first time porous ionic crystals (PICs) comprising Nb or Ta. The PICs are composed of Dawson-type Nb/W or Ta/W mixed-addenda POMs with oxo-centered trinuclear CrIII carboxylates and potassium ions as counter cations to control the crystal structure. Among the PICs, those with Nb or Ta tri-substituted POMs exhibit the highest yield (78-82%) and selectivity (99%) towards the Knoevenagel condensation of benzaldehyde and ethyl cyanoacetate (353 K, 6 h), which is a typical base-catalyzed reaction, as reusable solid catalysts, and they can also catalyze the reaction of other active methylene compounds. A detailed investigation into the crystal structures together with DFT calculations and in situ IR spectroscopy with methanol as a basic probe molecule shows that the exposure of [Nb3O13] or [Ta3O13] units with highly negative surface oxygen atoms to the pore surface of PICs is crucial to the catalytic performance. These findings based on the composition-structure-function relationships show that Nb- and Ta-containing PICs can serve as platforms for rational designing of heterogeneous base catalysts.

Bonding, structure, and mechanical stability of 2D materials: the predictive power of the periodic table.

This tutorial review describes the ongoing effort to convert main-group elements of the periodic table and their combinations into stable 2D materials, which is sometimes called modern 'alchemy'. Theory is successfully approaching this goal, whereas experimental verification is lagging far behind in the synergistic interplay between theory and experiment. The data collected here gives a clear picture of the bonding, structure, and mechanical performance of the main-group elements and their binary compounds. This ranges from group II elements, with two valence electrons, to group VI elements with six valence electrons, which form not only 1D structures but also, owing to their variable oxidation states, low-symmetry 2D networks. Outside of these main groups reviewed here, predominantly ionic bonding may be observed, for example in group II-VII compounds. Besides high-symmetry graphene with its shortest and strongest bonds and outstanding mechanical properties, low-symmetry 2D structures such as various borophene and tellurene phases with intriguing properties are receiving increasing attention. The comprehensive discussion of data also includes bonding and structure of few-layer assemblies, because the electronic properties, e.g., the band gap, of these heterostructures vary with interlayer layer separation and interaction energy. The available data allows the identification of general relationships between bonding, structure, and mechanical stability. This enables the extraction of periodic trends and fundamental rules governing the 2D world, which help to clear up deviating results and to estimate unknown properties. For example, the observed change of the bond length by a factor of two alters the cohesive energy by a factor of four and the extremely sensitive Young's modulus and ultimate strength by more than a factor of 60. Since the stiffness and strength decrease with increasing atom size on going down the columns of the periodic table, it is important to look for suitable allotropes of elements and binaries in the upper rows of the periodic table when mechanical stability and robustness are issues. On the other hand, the heavy compounds are of particular interest because of their low-symmetry structures with exotic electronic properties.

Lithium and Sodium Adsorption on Monolayer Tellurene

A new family of two-dimensional (2D) materials, tellurene, composed only by group-VI element tellurium, were recently predicted theoretically and verified experimentally. The most stable phase of m...

(Invited) Photocatalytic H2 Evolution with Anisotropic-Shaped ZnSe-AgInSe2 Solid Solution Nanorods

Semiconductor nanocrystals (NCs) exhibit unique size- and structure-dependent physicochemical properties different from bulk materials, due to the quantum size effect. Among various kinds of metal chalcogenide semiconductors, group I-III-VI-based NCs, such as CuInS2 and AgInS2, have attracted intense attention to develop high-quality NCs, because these materials contain no toxic elements and have large absorption coefficients. Recently we have successfully prepared anisotropic-shaped NCs of ZnS-AgInS2 solid solution, the Eg of which was tunable in the visible wavelength region [1, 2]. Their photocatalytic H2 evolution activity was controlled by the chemical composition, shape, and size of NCs. On the other hand, the near-IR responsivity seems necessary for NCs to efficiently utilize solar light in photocatalytic reactions. In general, the Eg of I-III-VI semiconductor decreases with use of Se as a group VI element in place of S. Thus, in this study, we prepare rod-shaped NCs composed of less-toxic ZnSe-AgInSe2 solid solution ((AgIn)xZn2(1-x)Se2, ZAISe(x)) and report their higher photocatalytic activity for H2 evolution than that of spherical ones.Rod-shaped ZAISe(x) NCs with different x values were synthesized by thermal decomposition of corresponding metal acetates and selenourea in a mixture solution of oleylamine and dodecanethiol at 250 oC. The chemical composition of resulting NCs, that is, x value, could be controlled by varying the fraction of Zn(OAc)2 in metal precursors, in which the NCs had almost stoichiometric composition. The length of nanorods decreased from ca. 116 to 8.2 nm with an increase in the x value, while the width of nanorods increased from ca. 3.7 to 6.9 nm. The absorption onset of ZAISe(x) NCs was blue-shifted from ca. 900 to 500 nm with a decrease in the x value, that is, with an increase in the Zn fraction.The photocatalytic activity of ZAISe(x) NCs was investigated for H2 evolution as a model reaction. The ligands modified on the nanocrystal surface were changed from dodecanethiol to mercaptopropionic acid to improve the dispersibility of NCs in an aqueous solution. The irradiation to ZAISe(x) NCs suspended in an aqueous solution containing Na2S and Na2SO3 as hole scavengers was carried out using Xe lamp light (λ> 350 nm). With the elapse of light irradiation, the amount of H2 evolved linearly increased, regardless of kinds of ZAISe(x) NCs. The H2 evolution rate was remarkably dependent on the composition of ZAISe(x) NCs: A volcano-type dependence was observed between the H2 evolution rate and the Eg of ZAISe(x) NCs. The highest photocatalytic activity was obtained for rod-shaped ZAISe(0.5) NCs with Eg of 1.65 eV. This behavior can be explained by the changes in both the electronic energy structure of ZAISe NCs and the amount of photon absorption with the chemical composition. Furthermore, the rod-shaped ZAISe(x) NCs exhibited a higher photocatalytic activity than that of spherical ones with similar Eg. References Kameyama, T. Takahashi, T. Machida, Y. Kamiya, T. Yamamoto, S. Kuwabata, and T. Torimoto, J. Phys. Chem. C, 2015, 119, 24740-24749.Torimoto, Y. Kamiya, T. Kameyama, H. Nishi, T. Uematsu, S. Kuwabata, and T. Shibayama, ACS Appl. Mater. Interfaces 2016 , 8, 27151-27161.