Electron Orbital Overlap Research Articles

New insights into the adsorption of Fe on Ti(CxN1−x) surface: First-principles study

The present study systematically investigates the adsorption behavior of Fe atoms on the titanium carbonitride (Ti(CxN1−x)) surface during the initial stage of austenite nucleation. The results indicate that the formation energy of TiN is lower than that of TiC, suggesting that TiN is more likely to form. However, it is observed that the TiN content in the steel is so little. The C-Top site of TiC exhibits the highest adsorption capacity for Fe atoms. For the various stacking models evaluated for Ti(CxN1−x), the CNNC model exhibits the most favorable adsorption performance for Fe atoms in Ti(C0.5N0.5). Furthermore, TiC exhibits superior adsorption performance as compared to TiN, which is attributed to its shorter bond length and higher electron orbital overlap. When the Fe atoms adsorb on the TiC(001) surface, covalent bonds are formed among C, Ti, and Fe atoms, revealing the presence of metal bonds.

Thickness-Dependent Dielectric Screening in Few-Layer Phosphorus.

The dielectric screening plays a critical role in determining the fundamental electronic properties in semiconductor devices. In this work, we report a noncontact and spatially resolved method, based on Kelvin probe force microscopy (KPFM), to obtain the inherent dielectric screening of black phosphorus (BP) and violet phosphorus (VP) as a function of the thickness. Interestingly, the dielectric constant of VP and BP flakes increases monotonically and then saturates to the bulk value, which is consistent with our first-principles calculations. The dielectric screening in VP has a much weaker dependence on the number of layers. This could be ascribed to a strong electron orbital overlap between two adjacent layers of VP, resulting in a strong interlayer coupling. The findings of our work are significant both for fundamental studies of dielectric screening and for more technical applications in nanoelectronic devices based on layered 2D materials.

Modulating Pt nanozyme by using isolated cobalt atoms to enhance catalytic activity for alleviating osteoarthritis

Combining the synergistic effect of single-atom catalysts and nanoparticles (NPs) to improve the catalytic activity may be promising in the design of nanozymes, although it only applies in the field of electrocatalysis. Herein, we designed a polyatomic SOD and CAT-mimicking Pt/Co-SA-NSG nanozyme composed of ultrafine Pt NPs and Co-SA-NSG with atomically dispersed Co and N, S co-doped graphene for OA treatment. Results demonstrated the Pt/Co-SA-NSG nanozyme has dual active centers containing Co-N4 and Pt and effective scavenging effect of reactive oxygen species (ROS), possibly due to that the electron orbital overlap between Co single atoms and Pt NPs enhanced the electron transport interaction to increase the adsorption energy of free radicals and reduce the reaction energy. Based on the H2O2 induced chondrocytes and OA joint model, Pt/Co-SA-NSG nanozyme exhibited biosafety, high photothermal conversion performance (54.56%), excellent SOD and CAT-like enzyme activities, and ROS scavenging ability. Particularly, in combination with NIR II irradiation therapy, Pt/Co-SA-NSG nanozyme could greatly relieved the OA progression with a Pelletier Score reduction of 54.54%. Mechanistically, the Pt/Co-SA-NSG nanozyme can restore mitochondrial function, thereby regulate ATP level, so as to reduce inflammatory factors level and increase antioxidant factors level. This novel nanozyme was expected to guide the design and activity enhancement of other nanozymes in the future.

A UV-Responsive Multifunctional Photoelectric Device Based on Discotic Columnar Nanostructures and Molecular Motors.

Orientation control of ordered materials would not only produce new physical phenomenon but also facilitate the development of fancy devices. Discotic liquid crystals (DLCs) form 1D charge transport pathway by self-organizing into columnar nanostructures via π-π stacking. However, controlling the electrical properties in such nanostructures with some direct and instant way is a formidable task for their high viscosity and insensitivity to external stimuli. Herein, the arbitrary control over electrical conductivity of such columnar nanostructures is achieved with UV light by incorporating DLCs with molecular motors. Highly ordered DLC microstripe arrays are generated on desired substrate through a capillary bridge dewetting strategy. The conductivity of the microstripes could be continuously modulated by 365 nm light due to the influence of molecular motion under UV irradiation on the electron orbital overlap of columnar nanostructures. This is so because the disorder degree of the DLC molecules is associated with the intensity of UV light and the doping concentration of molecular motors. Moreover, the device shows memory effect and reversible conductivity change. The DLC microstripe arrays are very promising for the applications in UV detectors, memory devices, optical switches, and so on.

Performance analysis of a substrate-engineered monolayer MoS2 field-effect transistor

We investigate the impact of different substrates on the performance of a monolayer MoS2 field-effect transistor (FET) by calculating the interface charge density between the MoS2 layer and the substrate using first-principle calculations based on density functional theory to provide details about the overlap of electron orbitals at the interface. The electrical characteristics of the monolayer MoS2 FET are determined by using the extracted interface charge density in numerical simulations. The electron transport behavior of the monolayer MoS2 FET is modeled using the nonequilibrium Green’s function with mode space (NEGF_MS) approach. We study and compare the performance of monolayer MoS2 FETs on different substrates, viz. SiO2, HfSiO4, Si3N4, HfO2, and h-BN. The results reveal that the monolayer MoS2 FET on the h-BN/Si substrate exhibits an on-current of 548 µA/µm and a subthreshold swing of 65 mV/dec.

Theoretical study on the interaction of heptafluoro-iso-butyronitrile decomposition products with Al (1 1 1)

ABSTRACTSeeking environmentally friendly gas-insulated medium has become a research hotspot in recent years. At present, C3F7CN (Heptafluoro-iso-butyronitrile) is considered to be a potential SF6 environment-friendly alternative gas and some achievements have been made in the study of its insulation and decomposition characteristics, but there are few reports on the compatibility between its characteristic decomposition products and materials. The investigation of compatibility between gas-insulated medium and material is an important part of evaluating its comprehensive performance. In this paper, we investigated the interaction between C2F5CN, CF3CN, COF2 and CF4 with the aluminium widely used in electrical equipment. It was found that the interaction between C2F5CN, CF3CN and Al (1 1 1) surface is strong. There are obvious charge transfer and electron orbital overlap between the C atom, N atom in CN group and Al (1 1 1). The interaction between COF2, CF4 and Al (1 1 1) surface is weak and van der Waal’s forces play the major role. Relevant results reveal the characteristics of C3F7CN decomposition products and provide theoretical guidance for evaluating the material compatibility between C3F7CN decomposition products and aluminium.

Quantifying the critical thickness of electron hybridization in spintronics materials

In the rapidly growing field of spintronics, simultaneous control of electronic and magnetic properties is essential, and the perspective of building novel phases is directly linked to the control of tuning parameters, for example, thickness and doping. Looking at the relevant effects in interface-driven spintronics, the reduced symmetry at a surface and interface corresponds to a severe modification of the overlap of electron orbitals, that is, to a change of electron hybridization. Here we report a chemically and magnetically sensitive depth-dependent analysis of two paradigmatic systems, namely La1−xSrxMnO3 and (Ga,Mn)As. Supported by cluster calculations, we find a crossover between surface and bulk in the electron hybridization/correlation and we identify a spectroscopic fingerprint of bulk metallic character and ferromagnetism versus depth. The critical thickness and the gradient of hybridization are measured, setting an intrinsic limit of 3 and 10 unit cells from the surface, respectively, for (Ga,Mn)As and La1−xSrxMnO3, for fully restoring bulk properties.

Graphene-wrapped TiO2nanofibers with effective interfacial coupling as ultrafast electron transfer bridges in novel photoanodes

For TiO2-based photoanodes, the interfacial coupling between TiO2 and conductive materials (e.g., carbon) plays a vital role in determining the electron transfer efficiency and thus photoelectrical performance. In this paper, we describe a facile approach to effectively engineering the interfacial coupling between reduced graphene oxide (RGO) and TiO2 in well-designed one-dimensional (1D) RGO-wrapped TiO2 nanofibers, which act as ultrafast electron transfer bridges when implanted in photoanodes. The 3–5 nm RGO nanoshells were hybridized with TiO2 nanofibers as an electron donor component via d–π electron orbital overlap between C and Ti atoms, by adopting a thermal reduction at 450 °C. Remarkable photoelectric improvement, in terms of high photocurrent density by 2.2-fold and ultralow charge transfer resistance (Rct) by 0.2-fold, is ascribed to the interfacial charge transfer. Completely reduced RGO in RGO/TiO2 nanofibers was not necessary at the expense of their hydrophilicity, as it led to unexpected isolation in the photoanodes. The thermal reduction temperature of RGO/TiO2 nanofibers was found to be critical, and a maximal photocurrent density could be achieved by 2.7-fold at 530 °C. An excess of RGO/TiO2 nanofibers of more than 5 wt% had a degrading effect on the photoelectrical activity, largely due to the light-block effect and isolation in the matrix. This strategy provides new insight for tuning the intrinsic chemical and/or physical properties of well-designed semiconductor nanostructures with promising photoactivities in highly efficient photovoltaic devices.

Tuning charge transport in solution-sheared organic semiconductors using lattice strain

Circuits based on organic semiconductors are being actively explored for flexible, transparent and low-cost electronic applications. But to realize such applications, the charge carrier mobilities of solution-processed organic semiconductors must be improved. For inorganic semiconductors, a general method of increasing charge carrier mobility is to introduce strain within the crystal lattice. Here we describe a solution-processing technique for organic semiconductors in which lattice strain is used to increase charge carrier mobilities by introducing greater electron orbital overlap between the component molecules. For organic semiconductors, the spacing between cofacially stacked, conjugated backbones (the π-π stacking distance) greatly influences electron orbital overlap and therefore mobility. Using our method to incrementally introduce lattice strain, we alter the π-π stacking distance of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) from 3.33 Å to 3.08 Å. We believe that 3.08 Å is the shortest π-π stacking distance that has been achieved in an organic semiconductor crystal lattice (although a π-π distance of 3.04 Å has been achieved through intramolecular bonding). The positive charge carrier (hole) mobility in TIPS-pentacene transistors increased from 0.8 cm(2) V(-1) s(-1) for unstrained films to a high mobility of 4.6 cm(2) V(-1) s(-1) for a strained film. Using solution processing to modify molecular packing through lattice strain should aid the development of high-performance, low-cost organic semiconducting devices.

Lattice-scale imaging of mica and clay (001) surfaces by atomic force microscopy using net attractive forces

The force between a sample and the tip during an AFM experiment consists of both attractive and repulsive components. In air, attraction is a combination of capillary adhesion from adsorbed water and attraction from van der Waals and Coulombic interactions. Opposing these attractive components is the repulsive force resulting from overlap of electron orbitals at the point of tip-sample contact. If the tip is very sharp, this Pauli-exclusion force is localized enough to obtain atomic- and lattice-scale resolution. In air, repulsive contact is present even while scanning with a net attractive force, as indicated by atomic- or lattice-scale resolution in the attractive-imaging mode. In this paper, we present lattice-scale images of mica and clay (001) surfaces that were obtained in air with a net attractive force on the cantilever. These images demonstrate that contact forces at the point of tip-sample contact oppose the capillary forces acting on the AFM tip in air.

Polymer LEDSs

Traditionally, polymers have been known for their flexibility and ease of processing, but not for their electrical properties. Then it was found that polymers could be grown in such a way that they demonstrated semi-conducting properties. This arises from overlap of electron orbitals along the polymer chain, forming a valence and a conduction band, analogous to how these form in silicon. Such materials, termed “conjugated” polymers, are extremely attractive in that they combine semiconductor properties with the advantages of processing and the mechanical properties associated with polymers. Thin-film structures can be fabricated from these polymers, including semiconductor devices such as field-effect transistors which can be prepared over large areas. Recently we have found that conjugated polymers, with improved purity, and which show very strong photoluminescence, can form the “active” or electroluminescent layer in light-emitting diodes (LEDs). Materials processing and device growing has now reached a stage where control of the colour of light emitted and levels of efficiency are acceptable for display applications, such as instrument panels and pixellated flat-screen displays.

An X-ray spectroscopic study of Co-Al alloys

The X-ray K absorption spectrum of cobalt is studied for the pure metal and also for three of its alloys in the Co-Al phase with 45, 50 and 60 atomic per cent of cobalt. Each spectrum shows a main edge (K discontinuity) and associated fine structure, extending up to 250 eV for the pure metal and 180 eV for the alloys. The main edges in the alloys are interpreted on the basis of Carter's model (1971), which is concerned with the overlap of electron orbitals and with the defect structure of the phase. Application of the Lytle theory (1966) in order to explain the fine structure shows that the Lytle plots for the 50 at.% alloy and the pure metal pass through the origin while those for the 45 and 60 at.%Co alloys do not. This may be because the 50 at.% alloy and the pure metal are perfectly ordered structures, CsCl-type and HCP respectively, whereas the 45 and 60 at.%Co alloys have defect structure, with Al vacancies and substitutional Co respectively.

Pressure-induced phase transformations in the B1 Ag-halides

The structures which form with pressure from the Ag-halides in the B1-type have been investigated using X-ray powder diffraction techniques. It is proposed that AgCl transforms to a cinnabar (B9) type structure with c = 7.02 A ̊ , a = 4.06 A ̊ and c a = 1.73 and a ΔV V 0 at the transition of 8 per cent. This structure is stabilized due to overlap of electron orbitals resulting in the formation of two highly covalent collinear-bonds. AgBr transforms to the same structure with a volume change of the same magnitude, but at a slightly lower pressure. The structure to which Bl-Agl transforms at 97 kbar is suggested to be tetragonal with a = 5.611 A ̊ , c = 5.020 A ̊ with Δ V V 0 at the transition approximately 13 per cent. Electrical conductivity measurements indicate that this transformation also involves a significant change to more covalent bonding.