Recently, the first synthesis of a freestanding monolayer amorphous carbon (MAC) was reported. MAC is a pure carbon structure composed of randomly distributed five, six, seven, and eight atom rings. ...MAC is structurally very stable and highly fracture resistant. Its electronic properties are similar to those of boron nitride. In this work, we have investigated the mechanical properties and thermal stability of MAC models using fully atomistic reactive molecular dynamics simulations. For comparison purposes, the results are contrasted against pristine graphene (PG) models of similar dimensions. Our results show that MAC and PG exhibit distinct mechanical behavior and fracture dynamics patterns. While PG, after a critical strain threshold, goes directly from elastic to brittle regimes, MAC shows different elastic stages between these two regimes. MAC is thermally stable up to 5368 K, which is close to the melting point of PG (5643 K). These exceptional physical properties make MAC-based materials promising candidates for new technologies, such as flexible electronics.
Plasmodium sporozoites actively migrate in the dermis and enter blood vessels to infect the liver. Despite their importance for malaria infection, little is known about these cutaneous processes. We ...combine intravital imaging in a rodent malaria model and statistical methods to unveil the parasite strategy to reach the bloodstream. We determine that sporozoites display a high-motility mode with a superdiffusive Lévy-like pattern known to optimize the location of scarce targets. When encountering blood vessels, sporozoites frequently switch to a subdiffusive low-motility behavior associated with probing for intravasation hotspots, marked by the presence of pericytes. Hence, sporozoites present anomalous diffusive motility, alternating between superdiffusive tissue exploration and subdiffusive local vessel exploitation, thus optimizing the sequential tasks of seeking blood vessels and pericyte-associated sites of privileged intravasation.
Abstract Schwarzites are porous (spongy‐like) carbon allotropes with negative Gaussian curvatures. They are proposed by Mackay and Terrones inspired by the works of the German mathematician Hermann ...Schwarz on Triply‐Periodic Minimal Surfaces (TPMS). This review presents and discusses the history of schwarzites and their place among curved carbon nanomaterials. The main works on schwarzites are summarized and are available in the literature. Their unique structural, electronic, thermal, and mechanical properties are discussed. Although the synthesis of carbon‐based schwarzites remains elusive, recent advances in the synthesis of zeolite‐templates nanomaterials have brought them closer to reality. Atomic‐based models of schwarzites are translated into macroscale ones that are 3D‐printed. These 3D‐printed models are exploited in many real‐world applications, including water remediation and biomedical ones.
Laser ablation synthesis in solution (LASiS) was used to synthesize quantum dots (QDs) of manganese telluride (MnTe). Size-tuneable QDs exhibit physicochemical property variation in the bandgap, ...optical, electrical, and magnetic properties. The size of QDs was fine-tuned with varying power and time duration of laser ablation. The characteristics of MnTe QDs were investigated using basic structural and morphological characterizations. The observed bandgap opening in the material is due to the quantum confinement effect, which led to increased energy band separation, as predicted from DFT simulations. The magnetic property of the synthesized MnTe QD catalysts influences the degradation process, with the process following pseudo-first-order kinetics. The photocatalytic dye degradation was studied using UV–visible spectroscopy. MnTe QDs were able to photodegrade methylene blue reagent up to 93.4% in 60 min under an external magnetic field. The magnetic field-induced MnTe QDs showed enhanced photocatalytic degradation efficiency with increased apparent rate kinetics up to ten times (0.0453 min
−1
) compared to just sunlight exposure (0.00456 min
−1
).
Graphical Abstract
(a) HAADF-STEM of the synthesized MnTe QD dispersed, (b) SEM image of the same, (c) relative concentration of the samples with and without magnetic fields, inset: photo degraded samples on exposure of magnetic fields and (d) schematic representation of the photocatalytic dye-degradation.
A thorough investigation of local structure, influencing the macroscopic properties of the solid, is of potential interest. We investigated the local structure of GaN nanowires (NWs) with different ...native defect concentrations synthesized by the chemical vapor deposition technique. Extended X-ray absorption fine structure (EXAFS) analysis and semiempirical and density functional theory (DFT) calculations were used to address the effect of dopant incorporation along with other defects on the coordination number and bond length values. The decrease of the bond length values along preferential crystal axes in the local tetrahedral structure of GaN emphasizes the preferred lattice site for oxygen doping. The preferential bond length contraction is corroborated by the simulations. We have also studied the impact on the local atomic configuration of GaN NWs with Al incorporation. Al x Ga1–x N NWs are synthesized via novel ion beam techniques of ion beam mixing and post-irradiation diffusion process. The change in the local tetrahedral structure of GaN with Al incorporation is investigated by EXAFS analysis. The analysis provides a clear understanding of choosing a suitable process for ternary III-nitride random alloy formation. The study of the local structure with the EXAFS analysis is corroborated with the observed macroscopic properties studied using Raman spectroscopy.
Van der Waals (vdW) heterostructures that pair materials with diverse properties enable various quantum phenomena. However, the direct growth of vdW heterostructures is challenging. Modification of ...the surface layer of quantum materials to introduce new properties is an alternative process akin to solid state reaction. Here, vapor deposited transition metals (TMs), Cr and Mn, are reacted with Bi2Se3 with the goal to transform the surface layer to XBi2Se4 (X = Cr, Mn). Experiments and ab initio MD simulations demonstrate that the TMs have a high selenium affinity driving Se diffusion toward the TM. For monolayer Cr, the surface Bi2Se3 is reduced to Bi2‐layer and a stable (pseudo) 2D Cr1+δSe2 layer is formed. In contrast, monolayer Mn can transform upon mild annealing into MnBi2Se4. This phase only forms for a precise amount of initial Mn deposition. Sub‐monolayer amounts dissolve into the bulk, and multilayers form stable MnSe adlayers. This study highlights the delicate energy balance between adlayers and desired surface modified layers that governs the interface reactions and that the formation of stable adlayers can prevent the reaction with the substrate. The success of obtaining MnBi2Se4 points toward an approach for the engineering of other multicomponent vdW materials by surface reactions.
Solid state reaction of Cr and Mn with Bi2Se3 surface is investigated. Cr reacts with Se to form a 2D Cr1+δSe2 adlayer while reducing Bi2Se3 to Bi2. In contrast, precisely controlled monolayer amounts of Mn transforms the surface layer to MnBi2Se4. The different interface reactions are due to varying stability of the monolayer selenides and the mixed bismuth selenide phases.
Transition-metal tellurides (TMTs) are promising materials for “post-graphene age” nanoelectronics and energy storage applications owing to their industry-standard compatibility, high electron ...mobility, large spin–orbit coupling (SOC), etc. However, tellurium (Te) having a larger ionic radius (Z = 52) and broader d-bands endows TMTs with semimetallic nature, restricting their application in photonic and optoelectronic domains. In this work, we report the optical properties of the quantum-confined semiconducting phase of cobalt ditelluride (CoTe2) for the first time, exhibiting excellent two-color band photoabsorption attributes covering the UV–visible and near-infrared regions. Furthermore, novel excitonic resonances (X) of size-varying CoTe2 nanocrystals and quantum dots (QDs) are indicated by their temperature-dependent emission characteristics, which are attributed to the splitting of band edge states via confinement. On the other hand, the sudden rupture of the large-area CoTe2 nanosheets via ultrasonication incorporates Co vacancy-mediated localized trap states within the band gap, which is attributed to the superior room-temperature photoluminescence (PL) quantum yield of QDs and further corroborated using Raman analysis and atomistic density functional theory (DFT) simulations. Most interestingly, the excitonic peak of CoTe2 QDs reveals a unique positive-to-negative thermal quenching transition phenomenon, owing to the thermal activation of nonradiative surface trap states. These results introduce an exciting approach for the defect-mediated color-saturated light emission that paves the way for solution-processed telluride-based QD light-emitting diodes.
Atomic Adsorption on Nitrogenated Holey Graphene Tromer, Raphael M; da Luz, Marcos G. E; Ferreira, Mauro S ...
Journal of physical chemistry. C,
02/2017, Letnik:
121, Številka:
5
Journal Article
Recenzirano
Two-dimensional (2D) crystals with C2N stoichiometry have recently been synthesized. This novel material, dubbed nitrogenated holey graphene (NHG), is a semiconductor unlike pristine graphene. For ...any novel material, it is fundamental to understand the behaviors of different adatoms on its surface, a process responsible for a rich phenomenology. In this work, we employed first-principles calculations and a hybrid quantum mechanics/molecular mechanics method to investigate the adsorption of H, B, and O on NHG sheets. The adsorption of H atoms could prove important for applications in hydrogen storage and gas sensors, whereas the adsorption of O in any new material is important to understand its oxidation process. Both N and B are common dopants in carbon-based systems, such as in BNC structures. We found that H and B prefer to adsorb on top of a nitrogen atom, whereas O prefers to adsorb on top of a carbon–carbon bond. The electronic structure of NHG also changes as a result of the presence of adatoms, with the appearance of midgap states close to the Fermi level. In the case of NHG + H and NHG + B, we observed the appearance of a finite magnetic moment, related to the midgap states, which could give rise to a magnetoresistance effect. Our results provide insight into the adsorption of impurities on this novel 2D carbon-based material, with potential for applications in novel electronic devices.
Pentadiamond is a recently proposed new carbon allotrope consisting of a network of pentagonal rings where both sp2 and sp3 hybridization are present. In this work we investigated the mechanical and ...electronic properties, as well as, the thermal stability of pentadiamond using DFT and fully atomistic reactive molecular dynamics (MD) simulations. We also investigated its properties beyond the elastic regime for three different deformation modes: compression, tensile and shear. The behavior of pentadiamond under compressive deformation showed strong fluctuations in the atomic positions which are responsible for the strain softening at strains beyond the linear regime, which characterizes the plastic flow. As we increase temperature, as expected, Young's modulus values decrease, but this variation (up to 300 K) is smaller than 10% (from 347.5 to 313.6 GPa), but the fracture strain is very sensitive, varying from ∼44% at 1 K to ∼5% at 300 K.
•The mechanical response of diamond, schwarzite and pentadiamond were investigated.•The compressive behavior of pentadiamond presents strong fluctuations after yield strain, indicating a plastic flow.•D688 schwarzite exhibits a cubic-to-triclinic transition under mechanical compression.•As we increase the temperature, Young’s modulus values decrease, but this variation (up to 300 K) is smaller then 10% (from 347.5 to 313.6 GPa.•Fracture strain is very sensitive to temperature, varying from ~44% at 1 K to ~5% at 300 K.
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