Stable Planar Structure Research Articles

Rich essential properties of silicon-substituted graphene nanoribbons: a comprehensive computational study.

The diverse structural, electronic, and magnetic properties of silicon (Si)-substituted armchair and zigzag graphene nanoribbons (AGNRs and ZGNRs) were investigated using spin-polarized density functional theory (DFT) calculations. Pristine AGNRs belong to a nonmagnetic semiconductor with a direct bandgap of 1.63/1.92 eV determined by PBE/HSE06 functionals. Under various Si substitutions, nonmagnetic bandgaps were tuned at 1.49/1.87, 1.06/1.84, 0.81/1.45, 1.04/1.71, 0.89/1.05, and 2.38/3.0 eV (PBE/HSE06) in the single Si edge-, single Si non-edge-, double Si ortho-, double Si meta-, double Si para-, and 100% Si-substituted AGNR configurations, respectively. Meanwhile, pristine ZGNRs displayed antiferromagnetic semiconducting behavior with a spin degenerate bandgap of 0.52/0.81 eV (PBE/HSE06) and becomes a ferromagnetic semimetal in the single Si configurations or an unusual ferromagnetic semiconductor in the 100% Si configuration. Under the developed first-principles theoretical framework, the formation of quasi π (C-2pz and Si-3pz) and quasi σ (C-2s, -2pxy and Si-3s and -3pxy) bands was identified in the Si-substituted configurations. These quasi π and quasi σ bands showed weak separation, resulting in weak quasi sp2 hybridization in Si-C bonds, in which the identified hybridization mechanism was a strong evidence for the formation of stable planar 1D structures in the Si-substituted configurations. Our complete revelation of the essential properties of Si-substituted GNRs can provide a complete understanding of their chemically doped 1D materials for various practical applications.

A DFT insight into magnetic, optoelectronic and thermoelectric properties of h-Zn1-xCuxS monolayer

In this study, we used the density functional theory (DFT) method to analyze the effect of Cu insertion on the structural stability, electronic, magnetic, optical and thermoelectric properties of the hexagonal ZnS monolayer (h-ZnS-2D). Our findings show that Cu replaces zinc sites by giving a stable planar structure in Ferromagnetic (FM) phase with slight decrease in the lattice parameter. A p-type semiconductor with a direct band gap that decreases with increasing Cu concentration was obtained. The half-metallic character found for low Cu concentrations let consider the h-Zn1-xCuxS-2D for potential applications in spintronic devices. The optical properties show that the h-Zn1-xCuxS-2D monolayers have high absorption and low transmittance in the UV range. The improved figure of merit of h-Zn1-xCuxS-2D due to increased electrical conductivity and decreased thermal conductivity with Cu content, makes these nanostructures a promising absorber for thin-film solar cells and suitable for solar thermal energy conversion technologies.

First-Principles Insight into a B4C3 Monolayer as a Promising Biosensor for Exhaled Breath Analysis.

Nanomaterial-based room temperature gas sensors are used as a screening tool for diagnosing various diseases through breath analysis. The stable planar structure of boron carbide (B4C3) is utilized as a base material for adsorption of human breath exhaled VOCs, namely formaldehyde, methanol, acetone, toluene along, with interfering gases of carbon dioxide and water. The adsorption energy, charge density, density of states, energy band gap variation, recovery time, sensitivity, and work function of adsorbed molecules on pristine B4C3 are analyzed by density functional theory. The computed adsorption energies of VOC are in the range of − 0.176 to − 0.238 eV, and a larger interaction distance validate the physisorption behavior of these VOCs biomarkers on pristine boron carbide monolayer. Minute changes are determined from the electronic band structure of all adsorbed systems conserving the semiconducting nature of the B4C3 monolayer. The band gap variation upon adsorption of VOCs and interfering gases is examined between 0.05 and 0.52%. The 13.63 × 10–9 s recovery time of methanol is slower among VOCs, and 0.556 × 10–9 s of carbon dioxide (CO2) is faster for desorption. The results reveal that boron carbide can be utilized as a biosensor at room temperature for the analysis of exhaled VOCs from human breath.Graphical abstract

The Creation of True Two-Dimensional Silicon Carbide.

This paper reports the successful synthesis of true two-dimensional silicon carbide using a top-down synthesis approach. Theoretical studies have predicted that 2D SiC has a stable planar structure and is a direct band gap semiconducting material. Experimentally, however, the growth of 2D SiC has challenged scientists for decades because bulk silicon carbide is not a van der Waals layered material. Adjacent atoms of SiC bond together via covalent sp3 hybridization, which is much stronger than van der Waals bonding in layered materials. Additionally, bulk SiC exists in more than 250 polytypes, further complicating the synthesis process, and making the selection of the SiC precursor polytype extremely important. This work demonstrates, for the first time, the successful isolation of 2D SiC from hexagonal SiC via a wet exfoliation method. Unlike many other 2D materials such as silicene that suffer from environmental instability, the created 2D SiC nanosheets are environmentally stable, and show no sign of degradation. 2D SiC also shows interesting Raman behavior, different from that of the bulk SiC. Our results suggest a strong correlation between the thickness of the nanosheets and the intensity of the longitudinal optical (LO) Raman mode. Furthermore, the created 2D SiC shows visible-light emission, indicating its potential applications for light-emitting devices and integrated microelectronics circuits. We anticipate that this work will cause disruptive impact across various technological fields, ranging from optoelectronics and spintronics to electronics and energy applications.

Enhanced efficiency and stability of planar perovskite solar cells using SnO2:InCl3 electron transport layer through synergetic doping and passivation approaches

There are many defect states at the interface between SnO2 and perovskite due to the preparation process and the lattice mismatch. These defects will trap photo-generated carriers, resulting in low carrier extraction efficiency and loss of device stability. Many researches are underway to further improve the performance of perovskite solar cells (PSCs) based on SnO2 electron transport layer (ETL), including doping of ETL and effective passivation of interface defects. Here, the SnO2:InCl3 ETL is used in planar perovskite solar cells to simultaneously dope ETL and passivate the defects at the ETL/perovskite interface. First, Cl ions can passivate the defects on the SnO2 surface, and part of the chloride ions can also diffuse into the perovskite to passivate the grain boundaries. Additionally, In ions themselves are suitable dopants and can provide better doping performance for SnO2. The result shows that the simultaneous ETL doping and interface passivation result in a significant increase of PCE from 19.1% to 20.8% due to the enhancement of short-circuit current density. This method expands the ETL/perovskite interface optimization work by using anions and cations for passivation and doping, respectively, and has some inspiration for the delivery of high efficiency and stable planar structure PSCs based on SnO2 ETL.

Improving the power conversion efficiency of perovskite solar cells by adding carbon quantum dots

High-quality perovskite films are the key factor in manufacturing high-performance devices. In this work, we for the first time use carbon quantum dots (CQDs) as additive in the methylammonium iodide solution for high-quality CH3NH3PbI3 (MAPbI3) films. Appropriate concentration of CQDs (0.04 mg ml−1) can passivate the crystal defects, improve the crystallinity, increase the grain size and reduce the grain boundary of MAPbI3 film. Various characterization results show that CQDs additive can reduce trap-state density, decrease carrier recombination and improve photoelectric performance. Compared with the pristine device, the average power conversion efficiency (PCE) of CQD-modified MAPbI3 device was increased from 15.8 ± 0.37% to 18.81 ± 0.45%, and the maximum PCE of champion device was increased from 16.21 to 19.17%. In this study, we propose a simple method for the preparation of stable and efficient inverted planar structure perovskite solar cells using CQD additives in a two-step spin-coated deposition method.

Deformed lying helix transition and lasing effect in cholesteric LC layers at spatially periodic boundary conditions

ABSTRACTThe field-induced orientational transition in layers of cholesteric liquid crystals with spatially periodic modulation of the surface anchoring is studied by numerical simulations and experimentally. The modulation of the surface anchoring is implemented using high-resolution focused ion-beam treatment of a polymer film providing planar alignment conditions. A specific feature of the orientational transition is that the thermodynamically stable initial planar structure with the helix axis along the normal to the layer transforms under an electric field into an equilibrium structure with a deformed lying helix (DLH) in the plane of the layer. For such a transition to occur the natural pitch of the cholesteric helix must be substantially less than the anchoring modulation period. The appearance of the DLH with a pitch corresponding to the anchoring modulation period results in strongly enhanced first-order diffraction efficiency. The orientational DLH transition is characterised by a rather narrow driving voltage range with a pronounced hysteresis. The waveguide lasing effect with characteristic of the deformed helix spectral modes is demonstrated in a range of the DLH transition.

First-principle prediction of the existence of C64-graphyne and (BN)64

By using of the first-principles calculations based on density functional theory, a novel monolayer planar structure named C64-graphyne is predicted. Tetratomic and hexatomic rings, as well as CC triple bonds exist in this new stable structure with the lattice parameter of 9.291 Å. The carbon hexatomic ring in C64-graphyne contains two quite distinct CC bonds, which is known as cyclohexatriene. Its electronic band structures show a semiconductor nature with a narrow direct band gap of 0.35 eV. Interestingly, by substituting a carbon atom with one nitrogen atom either in the hexatomic ring or in the chain of C64-graphyne, two stable planar structures are obtained. Such doping with nitrogen atom induced metallic properties in this monolayer structure. Further investigation shows that the alternating substitution of boron and nitrogen atoms for all carbon atoms in C64-graphyne also induced a new stable structure, the (BN)64 structure. The electronic studies proved its insulator property with the band gap of 4.08 eV.

Ab initio study of the structural, electronic, magnetic, and optical properties of silicene nanoribbons

We present first-principles calculations of structural, electronic, magnetic, and optical properties of zigzag-oriented silicene nanoribbons, which, being endowed with spin-polarized edge states, are promising candidates as building blocks of future spintronic devices. The minimal width for a structurally stable planar structure having zigzag edges corresponds to a 4-chain ribbon, whose ground state presents antiferromagnetically coupled spin-polarized edges, and a lattice parameter along the nanoribbon axis contracted ($\ensuremath{\sim}5%$) with respect to the bulk value. Starting from the dependence of structural and electronic properties on the ribbon width, we present theoretical predictions for the optical spectra of narrow nanoribbons, in which excitonic effects are relevant due to the confinement in a quasi-one-dimensional structure. Especially for light polarized parallel to the ribbon axis, we find significant differences in the position of optical absorption peaks of ribbons with ferro- or antiferromagnetically coupled edges, showing that optical spectra can be used as a fingerprint of the magnetic coupling of electronic edge states.

The symmetry breaking phenomenon in heteronine analogues due to the pseudo Jahn-Teller effect.

The pseudo Jahn-Teller effect (PJTE) is employed in C8AH8 (A = O, S, Se, Te), and C8EH8 + 1 (E = N, P, As, Sb) with planar configurations to show symmetry breaking phenomena (SBP) in heteronine analogues, and to explain why molecules with (C2v) high-symmetry configurations cannot maintain planarity and pucker to their (C2) and (Cs) lower-symmetry structures, respectively. To investigate this phenomenon, geometry optimization and frequency calculations through the density functional B3LYP method using the cc-pVTZ basis set (for Te, and Sb cc-pVTZ-PP) were carried out for all compounds in the series. The state average-complete active space self-consistent field wave-function method was employed to calculate the electronic ground and several low-lying excited states to specify the adiabatic potential energy surface along the a2 and b1 puckering nuclear displacements. The PJTE (A1 + A2 + A1') a2 and (A1 + B1 + A1') b1 problems were formulated as the effects originating via the PJTE theorem. Moreover, replacing hydrogen atoms in C8NH9, a stable planar structure, with fluorine ligands demonstrated that SBP occur from C2v to C2 symmetry. Furthermore, thermochemical calculations via B3LY/cc-pVTZ illustrated that the planarity of the C8E ring is restored in C8EH8- (E = P, As, Sb) anions ,with the change in free energy corresponding to spontaneous deprotonation reactions as 23.67kJmol-1, 21.88kJmol-1, and 16.57kJmol-1, respectively. In fact, despite C8EH8 + 1 having a donor electron-pair and potentially being Lewis base compounds, it acts as a Bronsted-Lowry acid releasing a H+ proton instead in this case.

Optical properties of shortest-width zig-zag silicene nano-ribbons: Effects of local fields

Abstract We have computed from first principles the structural, magnetic and optical properties of zig-zag oriented silicene nanoribbons. The minimal width for structurally stable planar structure having zig-zag edges corresponds to a 4-chains ribbon. Its ground state presents reconstructed and spin polarized edges, coupled antiferromagnetically. For this state, and for the corresponding excited state with ferromagnetically coupled edges, we computed the optical absorption spectra within the independent particle approximation, including local field effect corrections, for light polarized in the directions parallel and perpendicular to the ribbon axis. For the “parallel” light polarization the inclusion of local fields effects is limited to a slight reduction of the intensity of the main peak in the infrared region, as well as that of some minor peaks in the visible-ultraviolet structure. Conversely, the computed optical spectrum for light polarized perpendicularly to the ribbon axis shows that the short-width zig-zag nanoribbons are basically transparent in the infrared and visible region, because of the effect of electronic confinement combined with local fields.

Predicting the structural and electronic properties of two-dimensional single layer boron nitride sheets

Three two-dimensional (2D) single layer boron nitride sheets have been predicted based on the first-principles calculations. These 2D boron nitride sheets are comprised of equivalent boron atoms and nitride atoms with sp2 and sp bond hybridization. The geometry optimization reflects that they all possess stable planar crystal structures with the space group P6¯2m (D3h3) symmetry. The charge density distribution manifests that the B–N bonds in these boron nitride sheets are covalent in nature but with ionic characteristics. The tunable band gaps indicate their potential applications in nanoscale electronic and optoelectronic devices by changing the length of sp-bonded BN linkages.

Stabilization of planar tetra-coordinate silicon in a 2D-layered extended system and design of a high-capacity anode material for Li-ion batteries.

Stabilization of planar tetra-coordinate silicon (ptSi) was achieved in compounds and 2D-layered extended systems, in which single molecular ptSi in C12H8Si captures four additional electrons to maintain a stable planar structure while the extending conjugate interactions are responsible for the stabilization of ptSi in the 2D sheet. Based on the ptSi SiC12 building block, a SiC8 siligraphene 2D sheet was constructed, and each of its ptSi could accommodate six lithium atoms. The electronic and lithium-storage properties of the ptSi 2D network were explored using first-principles calculations and ab initio molecular dynamics (AIMD) simulations. The newly designed 2D SiC8 sheet has high thermal and dynamic stability, good electronic conductivity, strong lithium-storage ability, a large theoretical capacity of 1297 mA h g-1, and facile surface diffusion of Li and Li+. The predicted relatively high average cell voltages from 2.24 to 2.47 V are fairly stable as the lithium content varies. These unique properties of the 2D SiC8 sheet with ptSi make it quite appealing as a novel anode material for high-performance Li-ion batteries (LIBs).

The bonding picture in hypervalent XF3 (X = Cl, Br, I, At) fluorides revisited with quantum chemical topology.

Hypervalent XF3 (X = Cl, Br, I, At) fluorides exhibit T-shaped C2V equilibrium structures with the heavier of them, AtF3 , also revealing an almost isoenergetic planar D3h structure. Factors explaining this behavior based on simple "chemical intuition" are currently missing. In this work, we combine non-relativistic (ClF3 ), scalar-relativistic and two-component (X = Br - At) density functional theory calculations, and bonding analyses based on the electron localization function and the quantum theory of atoms in molecules. Typical signatures of charge-shift bonding have been identified at the bent T-shaped structures of ClF3 and BrF3 , while the bonds of the other structures exhibit a dominant ionic character. With the aim of explaining the D3h structure of AtF3 , we extend the multipole expansion analysis to the framework of two-component single-reference calculations. This methodological advance enables us to rationalize the relative stability of the T-shaped C2v and the planar D3h structures: the Coulomb repulsions between the two lone-pairs of the central atom and between each lone-pair and each fluorine ligand are found significantly larger at the D3h structures than at the C2v ones for X = Cl - I, but not with X = At. This comes with the increasing stabilization, along the XF3 series, of the planar D3h structure with respect to the global T-shaped C2v minima. Hence, we show that the careful use of principles that are at the heart of the valence shell electron pair repulsion model provides reasonable justifications for stable planar D3h structures in AX3 E2 systems. © 2017 Wiley Periodicals, Inc.

A computational study of beryllium-bonded H2Be⋯FNgH/FKrCl (Ng = Ar, Kr) dyads and their intermolecular interactions with the model nucleophiles F−, NH3 and NCH

An MP2/6-311++G(2d,2p) computational study of the beryllium-bonded dimers formed between FNgH/FKrCl noble-gas molecules and the BeH2 molecule predicted energetically stable planar structures. It was also found that the vacant 2p orbital of Be (perpendicular to the plane of the dyads) allows for strong electrostatic binding to several model nucleophiles Y (= F−, NH3 and NCH) to produce energetically stable non-planar Y⋯BeH2⋯FNgH/FKrCl triads. The beryllium bond is weakened by the interaction of the nucleophile but remains strongly-bound. A many-body interaction energy analysis and a charge-partitioning natural bond orbital (NBO) analysis are consistent with this finding. Attachment of the nucleophile Y to the H (or Cl) atom to form BeH2⋯FNgH/FKrCl⋯Y triads appears to destabilize the interaction since no local minima were obtained for these complexes.

Computational studies of stable hexanuclear CulAgmAun(l + m + n = 6;l,m,n > 0) clusters

A DFT study was carried out on the ground state structures of ternary CulAgmAun (l + m + n = 6) clusters, with the aim of investigating changes of thermal and kinetic stabilities as an effect of composition, as well as the composition dependence of the electrostatic potential, of stable planar structures. DFT optimizations were performed using the PBE functional and the SDD basis set. All the optimized structures adopt planar geometries with bent triangular structures. Calculated binding energy values are in the range 1.5–1.9 eV/atom, which shows their thermal stability. The predicted HOMO-LUMO energy gap values are in the semiconductor region, providing a qualitative indication of a moderate kinetic stability. NBO analyses indicate the existence of two mechanisms promoting planar structural stability, one due to bonding-antibonding orbital interaction, and the other one due to the well-known spd hybridization. Wiberg indices were obtained showing interatomic bonding. Electrostatic potential calculations show the existence of nucleophilic attack regions preferentially around silver and copper atoms located at the vertices while electrophilic attack regions are found in the vicinity of gold atoms over the cluster plane. Apparently, charge transfer occurs toward gold from silver and copper atoms when the concentration is favorable in the proximity of gold atoms. In particular, if the small ternary clusters discussed here contain only one gold atom, then a high electron density is observed at the site of this gold atom. © 2016 Wiley Periodicals, Inc.

P-i-n/n-i-p type planar hybrid structure of highly efficient perovskite solar cells towards improved air stability: synthetic strategies and the role of p-type hole transport layer (HTL) and n-type electron transport layer (ETL) metal oxides

There has been fast recent progress in perovskite solar cells (PSCs) towards low cost photovoltaic technology. Organometal mixed halide (MAPbX or FAPbX) perovskites are the most promising light absorbing material sandwiched between the electron transport layer (ETL) and hole transport layer (HTL). These two layers play a critical role in boosting the power conversion efficiency (PCE) and maintaining air stability. However, the device stability is a serious issue in regular as well as p-i-n inverted type perovskite solar cells. This mini-review briefly outlines the state-of-art of p-i-n/n-i-p type planar hybrid perovskite solar cells using MAPbX/FAPbX perovskite absorbing layers. Later, we will focus on recent trends, progress and further opportunities in exploring the air stable hybrid planar structure PSCs.

Abstract 3038: G quadruplex stabilization induces mitophagy in S. cerevisiae

Abstract G-quadruplex (G4) DNA structures are stable planar structures held together by multiple G-G base pairs. G4 structures are thought to affect transcription and other chromosomal processes but their presence in vivo is also expected to slow replication fork progression. Previous work from our lab demonstrates that the S. cerevisiae Pif1 5′ to 3′ DNA helicase is a particularly potent unwinder of G4 structures in vitro1. In addition, cells lacking the Pif1 helicase exhibit replication fork slowing and DNA breakage at G4 motifs, chromosomal sequences that form intra-molecular G4 structures in vitro1,2. In addition, treating yeast in vivo with the G4 stabilizing drug PhenDC3 increases G4-mediated genome instability3. We treated a collection of 4,783 S. cerevisiae strains that each contained a single gene deletion with PhenDC3 to search for genes that are sensitive or resistant to PhenDC3. We will discuss results showing that several yeast genes that affect maintenance of mitochondrial DNA and autophagy induction are hypersensitive to PhenDC3. Using fluorescent microscopy and immunoblotting, we further demonstrate that treatment of wild type S. cerevisiae cells with PhenDC3 induces autophagy, and more specifically, mitophagy. Moreover, cells lacking Pif1 are themselves activated for autophagy. Reference: 1 Paeschke, K. et al. Pif1 family helicases suppress genome instability at G-quadruplex motifs. Nature 497, 458-+, doi:10.1038/nature12149 (2013). 2 Paeschke, K., Capra, J. A. & Zakian, V. A. DNA replication through G-quadruplex motifs is promoted by the Saccharomyces cerevisiae Pif1 DNA helicase. Cell 145, 678-691, doi:10.1016/j.cell.2011.04.015 (2011). 3 Piazza, A. et al. Genetic instability triggered by G-quadruplex interacting Phen-DC compounds in Saccharomyces cerevisiae. Nucleic Acids Res 38, 4337-4348, doi:10.1093/nar/gkq136 (2010). Citation Format: Jennifer Stundon. G quadruplex stabilization induces mitophagy in S. cerevisiae. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3038. doi:10.1158/1538-7445.AM2015-3038

An RNA-binding Protein, Lin28, Recognizes and Remodels G-quartets in the MicroRNAs (miRNAs) and mRNAs It Regulates

Lin28 is an evolutionarily conserved RNA-binding protein that inhibits processing of pre-let-7 microRNAs (miRNAs) and regulates translation of mRNAs that control developmental timing, pluripotency, metabolism, and tumorigenesis. The RNA features that mediate Lin28 binding to the terminal loops of let-7 pre-miRNAs and to Lin28-responsive elements (LREs) in mRNAs are not well defined. Here we show that Lin28 target datasets are enriched for RNA sequences predicted to contain stable planar structures of 4 guanines known as G-quartets (G4s). The imino NMR spectra of pre-let-7 loops and LREs contain resonances characteristic of G4 hydrogen bonds. These sequences bind to a G4-binding fluorescent dye, N-methyl-mesoporphyrin IX (NMM). Mutations and truncations in the RNA sequence that prevent G4 formation also prevent Lin28 binding. The addition of Lin28 to a pre-let-7 loop or an LRE reduces G4 resonance intensity and NMM binding, suggesting that Lin28 may function to remodel G4s. Further, we show that NMM inhibits Lin28 binding. Incubation of a human embryonal carcinoma cell line with NMM reduces its stem cell traits. In particular it increases mature let-7 levels, decreases OCT4, HMGA1, CCNB1, CDK4, and Lin28A protein, decreases sphere formation, and inhibits colony formation. Our results suggest a previously unknown structural feature of Lin28 targets and a new strategy for manipulating Lin28 function.

AlSi2P nanotubes: a theoretical study

The geometry, stability, and structural properties of single-walled AlSi2P nanotubes were investigated by the first-principles density functional calculations. Considering different arrangements of AlP and SiSi units, three types of zigzag (ZZ-1, ZZ-2, and ZZ-3) (n, 0), n = 3, 4, and 5, and two types of armchair (AC-1 and AC-2) (n, n) AlSi2P nanotubes, n = 4, 5, and 6, were constructed. The present calculations show that, in general, there is a tendency toward the formation of alternate –Si–Si– and –Al–P– chains in the most stable AlSi2P nanotubes. Due to the high tendency of P and Si atoms to adopt sp 3 hybridization, silicon and phosphorus atoms somewhat pop outward, while Al atoms prefer stable sp 2 hybridization and form planar structure on the tube surface. Such structural features in the optimized geometry of the AlSi2P nanotubes lead to amazing structures such as the periodic bamboo-like structure of the ZZ-1(n, 0) AlSi2P nanotubes and “polygonal” cross section in the ZZ-3(n, 0) and AC-1(n, n) AlSi2P nanotubes. It is expected that the high point charges calculated on Al atoms, ranging from +0.839 to +1.021, and P atoms, ranging from −0.561 to −0.949, establish an overall charge transfer on the surface of nanotubes. AlSi2P nanotubes