Monolayer State Research Articles

In Pursuit of Authenticity: Induced Pluripotent Stem Cell-Derived Retinal Pigment Epithelium for Clinical Applications.

The retinal pigment epithelium (RPE) is essential for maintaining visual function. RPE derived from human induced pluripotent stem cells (iPSC-RPE) offer a promising cell-based transplantation therapy for slowing or rescuing RPE-induced visual function loss. For effective treatment, iPSC-RPE must recapitulate the physiology of native human RPE. A set of physiologically relevant functional assays are provided that assess the polarized functional activity and maturation state of the intact RPE monolayer. The present data show that donor-to-donor variability exceeds the tissue-to-tissue variability for a given donor and provides, for the first time, criteria necessary to identify iPSC-RPE most suitable for clinical application.

Atomic defect states in monolayers of MoS2 and WS2

The influence of atomic vacancy defects at different concentrations on electronic properties of MoS2 and WS2 monolayers is studied by means of Slater–Koster tight-binding model with non-orthogonal sp3d5 orbitals and including the spin–orbit coupling. The presence of vacancy defects induces localized states in the bandgap of pristine MoS2 and WS2, which have potential to modify the electronic structure of the systems, depending on the type and concentration of the defects. It is shown that although the contribution of metal (Mo or W) d orbitals is dominant in the formation of midgap states, the sulphur p and d orbitals have also considerable contribution in the localized states, when metal defects are introduced. Our results suggest that Mo and W defects can turn the monolayers into p-type semiconductors, while the sulphur defects make the system a n-type semiconductor, in agreement with ab initio results and experimental observations.

Magnetism from 2p states in K-doped ZnO monolayer: A density functional study

Using density-functional–based methods, we have studied 2p-based magnetic moments and magnetic coupling in potassium (K)-doped ZnO monolayer. We find that the substitution of a K atom at a Zn site in a ZnO monolayer induces a magnetic moment of per cell mainly originating from the O-2p states and has much lower formation energy than a magnetic Zn vacancy. A half-metallic electronic property and long-range ferromagnetic coupling between the magnetic moments are obtained based on the generalized gradient approximation (GGA) calculations, which is explained by a double-exchange–like mechanism. Moreover, with stronger correlation correction on 2p states, the structure of the substitutional K impurity undergoes a Jahn-Teller–like distortion. Incorporating magnetism into a two-dimensional ZnO monolayer will promote its application in nanodevices.

Manipulating interface states in monolayer–bilayer graphene planar junctions

We report on transport properties of monolayer–bilayer graphene planar junctions in a magnetic field. Due to its unique geometry, the edge and interface states can be independently manipulated by either interlayer potential or Zeeman field, and the conductance exhibits interesting quantized behaviors. In the hybrid graphene junction, the quantum Hall (QH) conductance is no longer antisymmetric with respect to the charge neutrality point. When the Zeeman field is considered, a quantum spin Hall (QSH) phase is found in the monolayer region while the weak-QSH phase stays in the bilayer region. In the presence of both interlayer potential and Zeeman field, the bilayer region hosts a QSH phase, whereas the monolayer region is still in a QH phase, leading to a spin-polarized current in the interface. In particular, the QSH phase remains robust against the disorder.

Computational Study of Quasi-2D Liquid State in Free Standing Platinum, Silver, Gold, and Copper Monolayers.

Recently, freestanding atomically thick Fe metal patches up to 10 atoms wide have been fabricated experimentally in tiny pores in graphene. This concept can be extended conceptually to extended freestanding monolayers. We have therefore performed ab initio molecular dynamics simulations to evaluate the early melting stages of platinum, silver, gold, and copper freestanding metal monolayers. Our calculations show that all four freestanding monolayers will form quasi-2D liquid layers with significant out-of-plane motion and diffusion in the plane. Remarkably, we observe a 4% reduction in the Pt most likely bond length as the system enters the liquid state at 2400 K (and a lower effective spring constant), compared to the system at 1200 and 1800 K. We attribute this to the reduced average number of bonds per atom in the Pt liquid state. We used the highly accurate and reliable Density Functional Theory (DFT-D) method that includes dispersion corrections. These liquid states are found at temperatures of 2400 K, 1050 K, 1600 K, and 1400 K for platinum, silver, gold, and copper respectively. The pair correlation function drops in the liquid state, while the bond orientation order parameter is reduced to a lesser degree. Movies of the simulations can be viewed online (see Supplementary Material).

Probing the electronic states and impurity effects in black phosphorus vertical heterostructures

AbstactAtomically thin black phosphorus (BP) is a promising two-dimensional material for fabricating electronic and optoelectronic nano-devices with high mobility and tunable bandgap structures. However, the charge-carrier mobility in few-layer phosphorene (monolayer BP) is mainly limited by the presence of impurity and disorders. In this study, we demonstrate that vertical BP heterostructure devices offer great advantages in probing the electron states of monolayer and few-layer phosphorene at temperatures down to 2 K through capacitance spectroscopy. Electronic states in the conduction and valence bands of phosphorene are accessible over a wide range of temperature and frequency. Exponential band tails have been determined to be related to disorders. Unusual phenomena such as the large temperature-dependence of the electron state population in few-layer phosphorene have been observed and systematically studied. By combining the first-principles calculation, we identified that the thermal excitation of charge trap states and oxidation-induced defect states were the main reasons for this large temperature dependence of the electron state population and degradation of the on-off ratio in phosphorene field-effect transistors.

Two-Dimensional π-Conjugated Covalent-Organic Frameworks as Quantum Anomalous Hall Topological Insulators.

The quantum anomalous Hall (QAH) insulator is a novel topological state of matter characterized by a nonzero quantized Hall conductivity without an external magnetic field. Using first-principles calculations, we predict the QAH state in monolayers of covalent-organic frameworks based on the newly synthesized X_{3}(C_{18}H_{12}N_{6})_{2} structure where X represents 5d transition metal elements Ta, Re, and Ir. The π conjugation between X d_{xz} and d_{yz} orbitals, mediated by N p_{z} and C p_{z} orbitals, gives rise to a massive Dirac spectrum in momentum space with a band gap of up to 24meV due to strong spin-orbit coupling. We show that the QAH state can appear by chemically engineering the exchange field and the Fermi level in the monolayer structure, resulting in nonzero Chern numbers. Our results suggest a reliable pathway toward the realization of a QAH phase at temperatures between 100K and room temperature in covalent-organic frameworks.

The effects of cysplatin on human adipose tissue derived mesenchymal stromal cells under different oxygen levels

To evaluate the damaging effects of cisplatin on MMSCs from adipose tissue in a phase of active proliferation and the state of the monolayer, this was exposed at standard (20%) and reduced to 1% and 5% level of oxygen. The effect of cisplatin was detected on monolayer cultures in the active growth phase after 2 passages. Profile surface markers of MMSC was determined by flow cytometry. MMSCs viability after incubation with cisplatin was detected by the number of apoptotic and necrotic cells using ANNEXIN V-FITC--PI Kit (Immunotech, France). Standard culture conditions (~20% O₂) were created in a CO₂ incubator (Sanyo, Japan), 5% O₂--using multigas incubator (Sanyo, Japan), 1% O₂--using an airtight chamber (Stemcell Technologies, USA). Incubation of MMSC monolayer with cisplatin at a concentration of 10 ug/ml for 72 hours leads to death of half of the cells in the culture. Cisplatin increased thefracture of PI⁺-cell, and PI⁺/Ann⁺-cells under all culture conditions. The short-term exposure with cisplatin (24 and 48 hours) did not cause the damaging effect. Effects of cisplatin on the MMSC in the growth phase for 48 hours led to accumulation of Ann⁺-cells and PI⁺/Ann⁺-cells under all culture conditions. However, minimal noci-influence of cisplatin was observed in a culture under hypoxic conditions (1% O₂). These data suggest that MMSC monolayer dies primarily through necrosis, whereas MMSCs in the growth phase in response to cisplatin treatment dies by apoptosis, regardless the oxygen tension.

The Effect of Ovine Secreted Soluble Factors on Human Dermal Papilla Cell Aggregation.

Context:In androgenetic alopecia, follicular miniaturization and dynamic changes to the hair cycle produce patterned baldness. The most effective treatment for baldness is hair transplantation surgery. The major limitation to hair transplantation is the availability of donor hair from the relatively unaffected occipital scalp. Hair induction with in vitro expansion of donor follicle populations has the potential to overcome this. The major obstacle to this is that in vitro expansion of human dermal papilla cell (DPC) colonies is associated with irreversible loss of aggregative behavior and hair follicle-inductive potential. In contrast, cultured ovine DPCs maintain these properties after extensive proliferation.Aims:To determine whether aggregating ovine DPC secrete factors that enhance the aggregative behavior or inductive potential of human DPC.Subjects and Methods:Fluorescently-labelled ovine DPC were mixed in culture with human DPC at passage number seven-nine, which had lost their aggregative behavior. The effects of different culture substrates and medium compositions on aggregative behavior were determined. Ovine and human papilla cells were co-cultured, separated by a permeable membrane to determine whether the ovine cells secrete soluble factors that affect human papilla cells.Results:In direct co-culture experiments, well-formed aggregates were produced by 90:10 human:ovine and 50:50 human:ovine DPC mixtures. In contrast, unmixed human DPC remained in a monolayer state after 18 days. Both human and ovine DPC had a higher tendency to aggregate in medium containing 20% (v/v) lamb serum (LS) compared to 10% (v/v) fetal calf serum (FCS). In co-culture experiments separated with permeable membrane, the human DPC aggregates were bigger and more rapidly formed with the addition of ovine secreted soluble factors.Conclusions:Soluble factors secreted by ovine DPC and present in LS increase the aggregative behavior of human DPC. These molecules might improve follicle inductiveness of human DPCs for the purpose of hair replacement therapy.

Strain tuning of the charge density wave in monolayer and bilayer 1T-TaS2.

Using first-principles calculations, we investigate the strain effects on the charge density wave states of monolayer and bilayer 1T-TaS2. The modified stability of the charge density wave in the monolayer is understood in terms of the strain dependent electron localization, which determines the distortion amplitude. On the other hand, in the bilayer, the effect of strain on the interlayer interaction is also crucial. The rich phase diagram under strain opens new venues for applications of 1T-TaS2. We interpret the experimentally observed insulating state of bulk 1T-TaS2 as inherited from the monolayer by effective interlayer decoupling.

Using dark states for exciton storage in transition-metal dichalcogenides

We explore the possibility of storing excitons in excitonic dark states in monolayer semiconducting transition-metal dichalcogenides. In addition to being optically inactive, these dark states require the electron and hole to be spatially separated, thus inhibiting electron/hole recombination and allowing exciton lifetimes to be extended. Based on an atomistic exciton model, we derive transition matrix elements and an approximate selection rule showing that excitons could be transitioned into and out of dark states using a pulsed infrared laser. For illustration, we also present exciton population scenarios based on a population analysis for different recombination decay constants. Longer exciton lifetimes could make these materials candidates for applications in energy management and quantum information processing.

Ultra-large scale synthesis of Co–Ni layered double hydroxides monolayer nanosheets by a solvent-free bottom-up strategy

Monolayer nanosheets of Co–Ni layered double hydroxides (LDHs) were synthesized by an ultra-large scale strategy under very moderate condition. The simple grinding of nickel nitrate hexahydrate and cobalt nitrate hexahydrate in morpholine at room temperature produced monolayer nanosheets. At least 40 g monolayer nanosheets can be produced in one batch. The capacity for the production of nanosheets is only limited by the facility used in the laboratory. The formation of monolayered hydroxide is attributed to the complete consumption of water in the water-deficient environment by the hydrolysis reaction between water and morpholine. The water consumption would consequently eliminate the possibility of interlayer hydrogen-bonding, avoiding the stacking of already produced monolayers. Because of the monolayer state of LDHs and the synergistic effect of cobalt ions in LDHs, the nanosheets presented high electrochemical performance.

分子レベル構造制御によるAu(111)上DNTT単分子膜の電子状態の変調

分子レベル構造制御によるAu(111)上DNTT単分子膜の電子状態の変調

Low-dimensional ScO2 with tunable electronic and magnetic properties: first-principles studies

Transition metal dichalcogenides (TMDs) have attracted extensive attention due to their appealing properties for device applications. In this work, we explored the structure stability, electronic structure and magnetism of low-dimensional scandium dioxides, ScO2, by using the first-principles calculations. The results demonstrate that bulk ScO2, monolayers and nanoribbons (NRs) are thermodynamically stable, implying a high possibility of fabricating ScO2 nanocrystals in experiments. Despite the metallic characteristics of bulk ScO2, low-dimensional ScO2 possesses various electronic behaviors that can be further modulated by crystal structure and dimensionality. The results also show that the ground states of ScO2 monolayers and NRs are ferromagnetic (FM) with about 1 μB per ScO2 formula. Our studies expand a new realm in low-dimensional TMDs, with tunable electronic and magnetic properties.

Influence of alkaline phosphatase on phase state of the SM monolayers at the air-water interface

Abstract The Langmuir monolayer is a most suitable model membrane system to study the interfacial interaction between protein and lipid. The surface pressure-area per molecule isotherms of the SM monolayer in the presence of different amount of alkaline phosphatase have been studied in this work. The compression modulus and the interfacial mixing ratio of protein/lipid have been calculated. The different amount of alkaline phosphatase has an influence on the phase transition of SM monolayer at the air–water interface. A coexist state of liquid expanded and liquid condensed is due to the presence of alkaline phosphatase. The process of phase transition from liquid expanded state to coexist state is longer in the presence of more amount of protein. The emergence of coexistence phase state reflects the interaction of the protein and the SM monolayer. The interfacial mixing ratio at the liquid expanded state is higher than that of the coexist state of liquid expanded and liquid condensed. The images of SEM and AFM also shown the microstructure of SM monolayers at two phase states in the presence of alkaline phosphatase.

Topological superconducting states in monolayerFeSe/SrTiO3

The monolayer FeSe with a thickness of one unit cell grown on a single-crystal SrTiO$_{3}$ substrate (FeSe/STO) exhibits striking high-temperature superconductivity with transition temperature $T_{c}$ over 65K reported by recent experimental measurements. In this work, through analyzing the distinctive electronic structure, and providing systematic classification of the pairing symmetry , we find that both $s$-and $p$-wave pairing with odd parity give rise to topological superconducting states in monolayer FeSe, and the exotic properties of $s$-wave topological superconducting states have close relations with the unique non-symmorphic lattice structure which induces the orbital-momentum locking. Our results indicate that the monolayer FeSe could be in the topological nontrivial $s$-wave superconducting states if the relevant effective pairing interactions are dominant in comparison with other candidates.

Vacancy and Doping States in Monolayer and bulk Black Phosphorus.

The atomic geometries and transition levels of point defects and substitutional dopants in few-layer and bulk black phosphorus are calculated. The vacancy is found to reconstruct in monolayer P to leave a single dangling bond, giving a negative U defect with a +/− transition level at 0.24 eV above the valence band edge. The V− state forms an unusual 4-fold coordinated site. In few-layer and bulk black P, the defect becomes a positive U site. The divacancy is much more stable than the monovacancy, and it reconstructs to give no deep gap states. Substitutional dopants such as C, Si, O or S do not give rise to shallow donor or acceptor states but instead reconstruct to form non-doping sites analogous to DX or AX centers in GaAs. Impurities on black P adopt the 8-N rule of bonding, as in amorphous semiconductors, rather than simple substitutional geometries seen in tetrahedral semiconductors.

Detailed Analysis of the Surface Area and Elasticity in the Saturated 1,2-Diacylphosphatidylcholine/Cholesterol Binary Monolayer System.

The surface pressure-area (π-A) isotherms of DMPC, DPPC, and DSPC/cholesterol binary monolayers were systematically measured with great care to gain insight into the lateral molecular packing in these binary monolayer systems. The average molecular area A and the area elastic modulus C(s)⁻¹ at a given surface pressure were calculated as a function of cholesterol mole fraction x(chol). As a result, data reliable enough for the analysis of detailed phase behavior were obtained. We identified several characteristic phase regions and assigned the phase state in each region on the basis of the deviation of A(x(chol)) and C(s)⁻¹(x(chol)) from ideal additivity. We also estimated the partial molecular areas of DMPC, DPPC, DSPC, and cholesterol in the single-phase regions, where C(s)⁻¹(x(chol)) values fell on an ideal additivity curve. We found that the addition of cholesterol induces the formation of a highly condensed phase where the diacylphosphatidylcholine (diacyl PC) molecule has a surface area even smaller than that in the solid phase, irrespective of the surface pressure and the chain length of diacyl PC. Here, we call the cholesterol-induced condensed phase the CC phase. Furthermore, we demonstrated that the basic features of A(x(chol)) and C(s)⁻¹(x(chol)) profiles can be explained semiquantitatively by assuming the state of vicinity lipids surrounding sparsely distributed cholesterol molecules in the low x(chol) region as a third state of the diacyl PC molecule in addition to the states in the pure diacyl PC monolayer and in the CC phase.

Adsorbed film of n-tetradecylphosphocholine at the tetradecane/water interface studied by interfacial tensiometry and X-ray reflection

Abstract The adsorbed film of n-tetradecylphosphocholine (C14PC) at the tetradecane (C14)/aqueous solution (W) interface was studied by interfacial tensiometry and X-ray reflection (XR). The interfacial tension γ was measured as a function of molality m C 14 PC and temperature T under atmospheric pressure. The interfacial density of C14PC Γ C 14 PC H increases with increasing m C 14 PC and converges into 3 μmol m−2 (first saturation) at m C 14 PC ≈ 0.08 mmol kg − 1 and into 4.2 μmol m−2 (second saturation) at the critical micelle concentration (CMC). The electron density profile determined by XR indicated that C14PC molecules form monolayer with relatively loose packing at the first saturation. In the second saturation, on the other hand, the molecules form bilayer in which charge separated phosphocholine groups take upside-down arrangement to interact attractively between neighbors. The positive entropy changes associated with adsorption both from monomeric and from micellar states result from that the contribution of dehydration around C14PC molecules, especially around PC groups, by the adsorption from aqueous solution overcomes that of a comparatively ordered molecular orientation at the interface. By comparing the results at the C14/W interface with those at the Air (A)/W one, it was shown that in the monolayer and bilayer states, hydrophobic chains of C14PC molecules are more ordered at the C14/W than at the A/W interface because of attractive interaction between C14PC and C14 molecules. This leads to smaller value of the partial molar entropy and energy changes associated with the adsorption at the C14/W than at the A/W interface. Furthermore the entropy of micelle formation changes from positive to negative with increasing T, suggesting that the entropy gain due to the dehydration exceeds the entropy loss by the aggregation at low temperatures, while the gain is less than the loss at high temperature.

Hydration state inside HeLa cell monolayer investigated with terahertz spectroscopy

The hydration state in living cells is believed to be associated with various cellular activities. Nevertheless, in vivo characterization of intracellular hydration state under physiological condition has not been well documented to date. In this study, the hydration state of an intact HeLa cell monolayer was investigated by terahertz time-domain attenuated total reflection spectroscopy. Combined with the extended theory of Onsager, we found 23.8 ± 7.4% of HeLa intracellular water was hydrated to biomolecules (corresponding to 1.25 g H2O/g solute); exhibiting slower relaxation dynamics than bulk water.