Giant Flexoelectricity in Bent Semiconductor Thinfilm.

We elucidate the flexoelectricity of semiconductors in the high strain gradient regime, the underlying mechanism of which is less understood. By using the generalized Bloch theorem, we uncover a strong flexoelectric-like effect in bent thinfilms of Si and Ge due to a high-strain-gradient-induced band gap closure. We show that an unusual type-II band alignment is formed between the compressed and elongated sides of the bent film.

Chemistry of the Interaction and Retention of Tc and Tc Species at the FeO(001) Surface.

The pertechnetate ion TcO is a nuclear fission product whose major issue is the high mobility in the environment. Experimentally, it is well known that FeO can reduce TcO to Tc species and retain such products quickly and completely, but the exact nature of the redox process and products is not completely understood. Therefore, we investigated the chemistry of TcO and Tc species at the FeO(001) surface through a hybrid DFT functional (HSE06) method.

TETT-functionalized TiO nanoparticles for DOX loading: a quantum mechanical study at the atomic scale.

In this work, we present a quantum mechanical investigation, based on the self-consistent charge density functional tight-binding (SCC-DFTB) method, of the functionalization with silane-type ligands (TETT) of a spherical TiO nanoparticle of realistic size (2.2 nm containing 700 atoms) to create an efficient nanosystem for simultaneous photodynamic therapy and drug transport. We determine the mechanism of the TETT ligand anchoring and its stability under thermal treatment, through molecular dynamics simulations at 300 K.

Unconventional deformation potential and half-metallicity in zigzag nanoribbons of 2D-Xenes.

Realization of half-metallicity (HM) in low dimensional materials is a fundamental challenge for nano spintronics and a critical component for developing alternative generations of information technology. Using first-principles calculations, we reveal an unconventional deformation potential for zigzag nanoribbons (NRs) of 2D-Xenes. Both the conduction band minimum (CBM) and valence band maximum (VBM) of the edge states have negative deformation potentials.

Twist-driven separation of -type and -type dopants in single-crystalline nanowires.

The distribution of dopants significantly influences the properties of semiconductors, yet effective modulation and separation of -type and -type dopants in homogeneous materials remain challenging, especially for nanostructures. Employing a bond orbital model with supportive atomistic simulations, we show that axial twisting can substantially modulate the radial distribution of dopants in Si nanowires (NWs) such that dopants of smaller sizes than the host atom prefer atomic sites near the NW core, while dopants of larger sizes are prone to staying adjacent to the NW surface. We attribute such distinct behaviors to the twist-induced inhomogeneous shear strain in NW.

Correction: Synthetic 2-D lead tin sulfide nanosheets with tuneable optoelectronic properties from a potentially scalable reaction pathway.

[This corrects the article DOI: 10.1039/C8SC04018D.].

Luminescent Emission of Excited Rydberg Excitons from Monolayer WSe.

We report the experimental observation of radiative recombination from Rydberg excitons in a two-dimensional semiconductor, monolayer WSe, encapsulated in hexagonal boron nitride. Excitonic emission up to the 4 s excited state is directly observed in photoluminescence spectroscopy in an out-of-plane magnetic field up to 31 T. We confirm the progressively larger exciton size for higher energy excited states through diamagnetic shift measurements.

An efficient way to model complex magnetite: Assessment of SCC-DFTB against DFT.

Magnetite has attracted increasing attention in recent years due to its promising and diverse applications in biomedicine. Theoretical modelling can play an important role in understanding magnetite-based nanomaterials at the atomic scale for a deeper insight into the experimental observations. However, calculations based on density functional theory (DFT) are too costly for realistically large models of magnetite nanoparticles.

Synthetic 2-D lead tin sulfide nanosheets with tuneable optoelectronic properties from a potentially scalable reaction pathway.

Solventless thermolysis of molecular precursors followed by liquid phase exfoliation allows access to two-dimensional IV-VI semiconductor nanomaterials hitherto unreachable by a scalable processing pathway. Firstly, the use of metal dithiocarbamate precursors to produce bulk alloys in the series Pb Sn S (0 ≤ ≤ 1) by thermolysis is demonstrated. The bulk powders are characterised by powder X-ray diffraction (pXRD), Raman spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy.

A comparative analysis of symmetric diketopyrrolopyrrole-cored small conjugated molecules with aromatic flanks: From geometry to charge transport.

Diketopyrrolopyrrole (DPP) derivatives are promising compounds for application in organic electronics. Here, we investigate several symmetrical N-unsubstituted and N-methyl substituted DPPs which differ in the heteroatom in the aromatic flanks. The conformational, electronic, and optical properties are characterized for single molecules in vacuum or a solvent.

Theoretical and experimental investigations of Xe NMR chemical shift isotherms in metal-organic frameworks.

The pressure dependence of the 129Xe chemical shift in the metal-organic frameworks (MOFs) UiO-66 and UiO-67 (UiO - University of Oslo) has been investigated using both theory and experiment. The resulting chemical shift isotherms were analyzed with a theoretical approach based on model systems (as proposed by K. Trepte, J.

Curved TiO Nanoparticles in Water: Short (Chemical) and Long (Physical) Range Interfacial Effects.

In most technological applications, nanoparticles are immersed in a liquid environment. Understanding nanoparticles/liquid interfacial effects is extremely relevant. This work provides a clear and detailed picture of the type of chemistry and physics taking place at the prototypical TiO nanoparticles/water interface, which is crucial in photocatalysis and photoelectrochemistry.

Functional thiols as repair and doping agents of defective MoS monolayers.

Recent experimental and theoretical studies indicate that thiols (R-SH) can be used to repair sulfur vacancy defects in MoS monolayers (MLs). This density functional theory study investigates how the thiol repair mechanism process can be used to dope MoS MLs. Fluorinated thiols as well as amine-containing ones are used to p- and n-dope the MoS ML, respectively.

Chemical and Electronic Repair Mechanism of Defects in MoS Monolayers.

Using ab initio density functional theory calculations, we characterize changes in the electronic structure of MoS monolayers introduced by missing or additional adsorbed sulfur atoms. We furthermore identify the chemical and electronic function of substances that have been reported to reduce the adverse effect of sulfur vacancies in quenching photoluminescence and reducing electronic conductance. We find that thiol-group-containing molecules adsorbed at vacancy sites may reinsert missing sulfur atoms.

Toward Activity Origin of Electrocatalytic Hydrogen Evolution Reaction on Carbon-Rich Crystalline Coordination Polymers.

The fundamental understanding of electrocatalytic active sites for hydrogen evolution reaction (HER) is significantly important for the development of metal complex involved carbon electrocatalysts with low kinetic barrier. Here, the MS N (M = Fe, Co, and Ni, x/y are 2/2, 0/4, and 4/0, respectively) active centers are immobilized into ladder-type, highly crystalline coordination polymers as model carbon-rich electrocatalysts for H generation in acid solution. The electrocatalytic HER tests reveal that the coordination of metal, sulfur, and nitrogen synergistically facilitates the hydrogen ad-/desorption on MS N catalysts, leading to enhanced HER kinetics.

Water Multilayers on TiO (101) Anatase Surface: Assessment of a DFTB-Based Method.

A water/(101) anatase TiO interface has been investigated with the DFT-based self-consistent-charge density functional tight-binding theory (SCC-DFTB). By comparison of the computed structural, energetic, and dynamical properties with standard DFT-GGA and experimental data, we assess the accuracy of SCC-DFTB for this prototypical solid-liquid interface. We tested different available SCC-DFTB parameters for Ti-containing compounds and, accordingly, combined them to improve the reliability of the method.

Multilayered intercalation of 1-octanol into Brodie graphite oxide.

Multilayered intercalation of 1-octanol into the structure of Brodie graphite oxide (B-GO) was studied as a function of temperature and pressure. Reversible phase transition with the addition/removal of one layer of 1-octanol was found at 265 K by means of X-ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC). The same transition was observed at ambient temperature upon a pressure increase above 0.

The origin of the measured chemical shift of Xe in UiO-66 and UiO-67 revealed by DFT investigations.

The NMR chemical shift of the xenon isotope Xe inside the metal-organic frameworks (MOFs) UiO-66 and UiO-67 (UiO - University of Oslo) has been investigated both with density functional theory (DFT) and in situ high-pressure Xe NMR measurements. The experiments reveal a decrease of the total chemical shift comparing the larger isoreticular MOF (UiO-67) with the smaller one (UiO-66), even though one may expect an increase due to the higher amount of adsorbed Xe atoms. We are able to calculate contributions to the chemical shift individually.

Molybdenum Carbide-Embedded Nitrogen-Doped Porous Carbon Nanosheets as Electrocatalysts for Water Splitting in Alkaline Media.

Molybdenum carbide (MoC) based catalysts were found to be one of the most promising electrocatalysts for hydrogen evolution reaction (HER) in acid media in comparison with Pt-based catalysts but were seldom investigated in alkaline media, probably due to the limited active sites, poor conductivity, and high energy barrier for water dissociation. In this work, MoC-embedded nitrogen-doped porous carbon nanosheets (MoC@2D-NPCs) were successfully achieved with the help of a convenient interfacial strategy. As a HER electrocatalyst in alkaline solution, MoC@2D-NPC exhibited an extremely low onset potential of ∼0 mV and a current density of 10 mA cm at an overpotential of ∼45 mV, which is much lower than the values of most reported HER electrocatalysts and comparable to the noble metal catalyst Pt.

Tuning quantum electron and phonon transport in two-dimensional materials by strain engineering: a Green's function based study.

Novel two-dimensional (2D) materials show unusual physical properties which combined with strain engineering open up the possibility of new potential device applications in nanoelectronics. In particular, transport properties have been found to be very sensitive to applied strain. In the present work, using a density-functional based tight-binding (DFTB) method in combination with Green's function (GF) approaches, we address the effect of strain engineering of the transport setup (contact-device(scattering)-contact regions) on the electron and phonon transport properties of two-dimensional materials, focusing on hexagonal boron-nitride (hBN), phosphorene, and MoS monolayers.

Immobilizing Molecular Metal Dithiolene-Diamine Complexes on 2D Metal-Organic Frameworks for Electrocatalytic H Production.

Carbon electrocatalysts consisting of metal complexes such as MN or MS are promising alternatives to high-cost Pt catalysts for the hydrogen evolution reaction (HER). However, the exact HER active sites remain elusive. Here, molecular metal dithiolene-diamine (MS N , M=Co and Ni), metal bis(dithiolene) (MS ), and metal bis(diamine) (MN ) complexes were selectively incorporated into carbon-rich 2D metal-organic frameworks (2D MOFs) as model carbon electrocatalysts.

Wafer-sized multifunctional polyimine-based two-dimensional conjugated polymers with high mechanical stiffness.

One of the key challenges in two-dimensional (2D) materials is to go beyond graphene, a prototype 2D polymer (2DP), and to synthesize its organic analogues with structural control at the atomic- or molecular-level. Here we show the successful preparation of porphyrin-containing monolayer and multilayer 2DPs through Schiff-base polycondensation reaction at an air-water and liquid-liquid interface, respectively. Both the monolayer and multilayer 2DPs have crystalline structures as indicated by selected area electron diffraction.

High Conductivity in Molecularly p-Doped Diketopyrrolopyrrole-Based Polymer: The Impact of a High Dopant Strength and Good Structural Order.

[3]-Radialene-based dopant CN6-CP studied herein, with its reduction potential of +0.8 versus Fc/Fc+ and the lowest unoccupied molecular orbital level of -5.87 eV, is the strongest molecular p-dopant reported in the open literature, so far.

Towards an optimal contact metal for CNTFETs.

Downscaling of the contact length Lc of a side-contacted carbon nanotube field-effect transistor (CNTFET) is challenging because of the rapidly increasing contact resistance as Lc falls below 20-50 nm. If in agreement with existing experimental results, theoretical work might answer the question, which metals yield the lowest CNT-metal contact resistance and what physical mechanisms govern the geometry dependence of the contact resistance. However, at the scale of 10 nm, parameter-free models of electron transport become computationally prohibitively expensive.

Screening for high-spin metal organic frameworks (MOFs): density functional theory study on DUT-8(M1,M2) (with Mi = V,…,Cu).

We present a first principles study of low-spin (LS)/high-spin (HS) screening for 3d metal centers in the metal organic framework (MOF) DUT-8(Ni). Various density functional theory (DFT) codes have been used to evaluate numerical and DFT related errors. We compare highly accurate all-electron implementations with the widely used plane wave approach.