Gas-solid interfacial charge transfer in volatile organic compound detection by CuCrO2nanoparticles.

Nanostructured metal oxide semiconductors have received great attention used as the chemiresistive layer of gas sensor to detect the volatile organic compound recently. As indispensable complementary parts for dominative n-type semiconductors, the p-type metal oxides based gas sensors fail to be studied sufficiently, which hampers their practical applications. In this work, the p-type delafossite CuCrO2nanoparticles were synthesized, characterized, and tested for gas sensing, followed by the first principles calculations to simulate the generation of chemiresistive signal. The hydrothermal synthesis time of CuCrO2nanoparticles is optimized as 24 h with a higher proportion of oxygen vacancies but a smaller size, which is confirmed by the microscopy and spectrum characterization and allows for a prevailing gas sensitivity. Meanwhile, this CuCrO2gas sensor is proven to perform a higher selectivity to n-propanol and a low detection limit of 1 ppm. The adsorption sites and charge variations of dehydrogenation at the gas-solid interface predicted by the theoretical analysis are claimed to be crucial to such selectivity. It is an innovative approach to understand the chemiresistive gas sensing by evaluating the preference of charge transfer between the sensor and target gaseous molecule, which provides a new route to precisely design and develop the advanced sensing devices for the diverse applications.

Replacing the cyano (-C[triple bond, length as m-dash]N) group to design environmentally friendly fused-ring electron acceptors.

The cyano-group (-C[triple bond, length as m-dash]N) is an electron-withdrawing group, which has been widely used to construct high-performance fused-ring electron acceptors (FREAs). Benefiting from these FREAs, the power conversion efficiency of organic solar cells has recently exceeded 18%. However, malononitrile is a highly toxic substance used to introduce -C[triple bond, length as m-dash]N during the synthesis of these FREAs. Therefore, the synthesis processes of most high-performance FREAs are typically harmful to the environment. Our previous work demonstrated that the electron-withdrawing ability of -C[triple bond, length as m-dash]N is necessary for FREAs. Thus, the use of other electron-withdrawing groups instead of -C[triple bond, length as m-dash]N to design environmentally friendly FREAs is feasible. We utilized seven electron-withdrawing groups, namely, -C[double bond, length as m-dash]NH, -N[double bond, length as m-dash]O, -CH[double bond, length as m-dash]O, -CO-CH3, -CO-OH, -CO-Cl, and -CO-Br, to replace -C[triple bond, length as m-dash]N in the commonly used acceptor Y6 to design new FREAs (Y6-CNH, Y6-NO, Y6-CHO, Y6-COCH3, Y6-COOH, Y6-COCl, and Y6-COBr). Multi-scale theoretical calculation methods were used to investigate the photoelectronic properties of these new FREAs, including energy level, absorption spectrum, exciton binding energy, and electron mobility. The results showed that Y6-CNH, Y6-COCH3 and Y6-COOH are unsuitable for use as acceptor materials because of their high frontier molecular orbital energy level and weak electron affinity. The strong absorption intensity and weak exciton binding energy of Y6-CHO, Y6-COCl, and Y6-COBr indicated that they can absorb more solar energy than Y6 and excitons are easier to separate into free charges. The electron mobility of Y6-CHO (3.53 × 10-4 cm2 V-1 s-1) was found to be approximately 28 times that of Y6-COCl (1.24 × 10-5 cm2 V-1 s-1) and Y6-COBr (1.28 × 10-5 cm2 V-1 s-1). The possible synthetic routes to Y6-CHO are environmentally friendly. Therefore, -CH[double bond, length as m-dash]O is the most suitable electron-withdrawing group for constructing high-performance environmentally friendly FREAs. This work can provide a new molecular design perspective in experimental science for developing high-performance environmentally friendly FREAs.

Detecting Air Pollutant Molecules Using Tube-Shaped Single Electron Transistor.

An air pollution detector is proposed based on a tube-shaped single-electron transistor (SET) sensor. By monitoring the flow control component of the detector, each air pollutant molecule can be placed at the center of a SET nanopore and is treated as an island of the SET device in the same framework. Electron transport in the SET was incoherent, and the performances of the SET were sensitive at the single molecule level. Employing first-principles calculations, electronic features of an air pollutant molecule within a tube-shaped SET environment were found to be independent of the molecule rotational orientations with respect to axis of symmetry, unlike the electronic features in a conventional SET environment. Charge stability diagrams of the island molecules were demonstrated to be distinct for each molecule, and thus they can serve as electronic fingerprints for detection. Using the same setup, quantification of the air pollutant can be realized at room temperature as well. The results presented herein may help provide guidance for the identification and quantification of various types of air pollutants at the molecular level by treating the molecule as the island of the SET component in the proposed detector.

Size modulation electronic and optical properties of phosphorene nanoribbons: DFT-BOLS approximation.

DFT and BOLS approximations were carried out to study the electronic and optical properties of different sizes of black phosphorus nanoribbons (PNRs) with either zigzag- or armchair-terminated edges. PNRs exhibit a nearly direct bandgap, the size of which is strongly increased because of quantum effects. Meanwhile, the bandgap energies of these two kinds of edge PNRs reveal an excellent size dependency. We reconcile the size-dependence of the bandgap energy shifts for PNRs with respect to stimulated bond relaxation, and quantification of the bond length, the bond strength, and the bond nature index. Our calculations suggest that atomic under-coordination shortens the length and increases the stiffness of the P-P bond, which widens the bandgap.

Skin Bond Electron Relaxation Dynamics of Germanium Manipulated by Interactions with H2 , O2 , H2 O, H2 O2 , HF, and Au.

Although germanium performs amazingly well at sites surrounding hetero-coordinated impurities and under-coordinated defects or skins with unusual properties, having important impact on electronic and optical devices, understanding the behavior of the local bonds and electrons at such sites remains a great challenge. Here we show that a combination of density functional theory calculations, zone-resolved X-ray photoelectron spectroscopy, and bond order length strength correlation mechanism has enabled us to clarify the physical origin of the Ge 3d core-level shift for the under-coordinated (111) and (100) skin with and without hetero-coordinated H2 , O2 , H2 O, H2 O2 , HF impurities. The Ge 3d level shifts from 27.579 (for an isolated atom) by 1.381 to 28.960 eV upon bulk formation. Atomic under-coordination shifts the binding energy further to 29.823 eV for the (001) and to 29.713 eV for the (111) monolayer skin. Addition of O2 , HF, H2 O, H2 O2 and Au impurities results in quantum entrapment by different amounts, but H adsorption leads to polarization.

Electronic binding energy and thermal relaxation of Li and LiNa atomic alloying clusters.

We examined the effects of atomic hetero- and under-coordination on the relaxation of the interatomic bonding and electronic binding energy of Li and LiNa cluster alloying using a combination of the bond-order-length-strength correlation and density functional theory calculations. We found that bond nature alteration by heterocoordination, bond relaxation by thermal excitation and atomic coordination contribute intrinsically to the core-level energy shifts with resolution of the binding energy at the atomic sites of terrace edges, facets, and bulk of the LiNa alloy nanoclusters. Our strategies may simplify the complexity of core electron binding energies in analyzing the experimental data of the irregularly coordinating atoms.

Coordination-Resolved Spectrometrics of Local Bonding and Electronic Dynamics of Au Atomic Clusters, Solid Skins, and Oxidized Foils.

By using combination of bond-order-length-strength (BOLS) correlation, the tight-binding (TB) approach, and zone-selective photoelectron spectroscopy (ZPS), we were able to resolve local bond relaxation and the associated 4f7/2 core-level shift of Au atomic clusters, Au(100, 110, 111) skins, and Au foils exposed to ozone for different lengths of time. In addition to quantitative information, such as local bond length, bond energy, binding-energy density, and atomic cohesive energy, the results confirm our predictions that bond-order deficiency shortens and stiffens the bond between undercoordinated atoms, which results in local densification and quantum entrapment of bonding electrons. The entrapment perturbs the Hamiltonian, and hence, shifts the core-level energy accordingly. ZPS also confirms that oxidation enhances the effect of atomic undercoordination on the positive 4f7/2 energy shift, with the associated valence electron polarization contributing to the catalytic ability of undercoordinated Au atoms.

Atomistic bond relaxation, energy entrapment, and electron polarization of the RbN and CsN clusters (N ≤ 58).

We systematically examined the effect of atomic undercoordination on the performance of bonds and electrons of Rb and Cs atomic clusters and their solid skins using a combination of photoelectron spectrometric analysis and density functional theory calculations. Results show that atomic coordination number reduction shortens the bonds by up to 30% for the Rb13 and Cs13 clusters, which densifies the local electrons and entraps their binding energies. Consistency between predictions and observations revealed that the Rb 4p level shifts from 13.654 eV for an isolated atom to a bulk value of 14.940 eV and the Cs 5p level shifts from 10.284 to 11.830 eV upon bulk formation. Such core-electron densification and entrapment polarize the valence charge from the inner to the outermost layer of skins, which perturbs the local Hamiltonian and hence dictates the unusual behavior of the Rb and Cs solid skins and nanocrystals.

Organic molecule functionalized lead sulfide hybrid system for energy storage and field dependent polarization performances.

A wet chemical route is reported for synthesising organic molecule stabilized lead sulfide nanoparticles. The dielectric capacitance, energy storage performances and field-driven polarization of the organic-inorganic hybrid system are investigated in the form of a device under varying temperature and frequency conditions. The structural analysis confirmed the formation of the monoclinic phase of lead sulfide within the organic network. The band structure of lead sulfide was obtained by density functional theory calculation that supported the semiconductor nature of the material with a direct band gap of 2.27 eV. The dielectric performance of the lead sulfide originated due to the dipolar and the space charge polarization. The energy storage ability of the material was investigated under DC-bias conditions, and the device exhibited the power density values 30 W/g and 340 W/g at 100 Hz and 10 kHz, respectively. The electric field-induced polarization study exhibited a fatigue-free behaviour of the device for 103 cycles with a stable dielectric strength. The study revealed that the lead sulfide-based system has potential in energy storage applications.

Crystalline-to-Amorphous Phase Transformation in CuO Nanowires for Gaseous Ionization and Sensing Application.

We report a dramatic reduction of operation voltage of a CuO nanowire-based ionization gas sensor due to the crystalline-to-amorphous phase transformation. The structural change is attributed to the ion bombardment and heating effect during the initial discharge, which brings about the formation of abundant nanocrystallites and surface states favoring gaseous ionization. The gas-sensing properties of the CuO nanowire sensor are confirmed by differentiating various types or concentrations of volatile organic compounds diluted in nitrogen, with a low detection limit at the ppm level. Moreover, a sensing mechanism is proposed on the basis of charge redistribution by electron-gas collision related to the specific ionization energy. The insightful study of the electrode microstructure delivers an exploratory investigation to the effect of gas ionization toward the discharge system, which provides new approaches to develop advanced ionization gas sensors.

Atomic Bonding and Electronic Binding Energy of Two-Dimensional Bi/Li(110) Heterojunctions via BOLS-BB Model.

Combining the bond-order-length-strength (BOLS) and atomic bonding and electronic model (BB model) with density functional theory (DFT) calculations, we studied the atomic bonding and electronic binding energy behavior of Bi atoms adsorbed on the Li(110) surface. We found that the Bi atoms adsorbed on the Li(110) surface form two-dimensional (2D) geometric structures, including letter-, hexagon-, galaxy-, crown-, field-, and cobweb-shaped structures. Thus, we obtained the following quantitative information: (i) the field-shaped structure can be considered the bulk structure; (ii) the field-shaped structure of Bi atom formation has a 5d energy level of 22.727 eV, and in the letter shape structure, this energy is shifted to values greater than 0.342 eV; and (iii) the Bi/Li(110) heterojunction transfers charge from the inner Li atomic layer to the outermost Bi atomic layer. In addition, we analyzed the bonding and electronic dynamics involved in the formation of the Bi/Li(110) heterojunctions using residual density of states. This work provides a theoretical reference for the fine tuning of binding energies and chemical bonding at the interfaces of 2D metallic materials.

Functionalizing triptycene to create 3D high-performance non-fullerene acceptors.

Non-fullerene acceptors have been widely investigated for organic solar cells (OSCs). In particular, fused-ring electron acceptors (FREAs), composed of two strongly electron-withdrawing end groups connected by a planar fused-ring core, have been successfully applied to develop high-performance OSCs (>16%). In this work, we proposed two novel 3D FREAs named BFT-3D and BFTT-3D, which can reduce the formation of crystalline domains and increase the interface with donors to promote exciton separation. These 3D FREAs consist of three strongly electron-withdrawing end groups linked by a central triptycene hub to form a three-bladed propeller nanostructure. In comparison with high-performance FREA (ITOIC-2F), these FREAs have stronger absorption intensity and smaller exciton binding energy. These findings demonstrated that these three-bladed propeller-shaped FREAs can absorb abundant energy from sunlight to generate excitons, easily separate excitons to free electrons and holes, and reduce the recombination of excitons. In addition, the electron mobility of BFT-3D (8.4 × 10-4 cm2 V-1 s-1) is higher than that of BFTT-3D (1.0 × 10-4 cm2 V-1 s-1), which indicated that the appropriate 3D core structure was conducive to the electron mobility of the three-bladed propeller-shaped FREAs. It can effectively improve the current density to enhance the performance of OSCs. These findings will provide new perspectives for experimental scientists to synthesize high-performance FREAs.

Understanding atomic bonding and electronic distributions of a DNA molecule using DFT calculation and BOLS-BC model.

Deoxyribonucleic acid (DNA) is an important molecule that has been extensively researched, mainly due to its structure and function. Herein, we investigated the electronic behavior of the DNA molecule containing 1008 atoms using density functional theory. The bond-charge (BC) model shows the relationship between charge density and atomic strain. Besides, the model mentioned above is combined with the bond-order-length-strength (BOLS) notion to calculate the atomic cohesive energy, the bond energy, and the local bond strain of the DNA chain. Using the BOLS-BC model, we were able to obtain information on the bonding features of the DNA chain and better comprehend the associated properties of electrons in biological systems. Consequently, this report functions as a theoretical reference for the precise regulation of the electrons and the bonding states of biological systems.

Construction of ultra-stable trinickel disulphide (Ni3S2)/polyaniline (PANI) electrodes based on carbon fibers for high performance flexible asymmetric supercapacitors.

Highly flexible supercapacitors (SCs) have attracted significant attention in modern electronics. However, it has been found that flexible, metal sulfide-based electrodes usually suffer from corrosion, instability and low conductivity, which significantly limits their large scale application. Herein, we report on an electrode comprised of highly stable, free-standing carbon fiber/trinickel disulphide covered with polyaniline (CF/Ni3S2@PANI). This electrode was prepared and then employed in a high-performance of flexible asymmetric SCs (FASC). The coating layer of polyaniline served as both a protector and conducting shell for the Ni3S2 due to the nature of the highly stable N-Ni bonds that formed between the polyaniline and Ni3S2. In addition, the lightweight carbon fiber support served as both a current collector and flexible support. The prepared CF/Ni3S2@PANI electrode exhibited a significantly enhanced specific capacity (715.3 F·g-1 at 1 A·g-1) compared with the carbon fiber/Ni3S2 electrode (318 F·g-1 at 1 A·g-1). More importantly, the assembled FASC device delivered an impressive energy density of 35.7 Wh·kg-1 at a power density of 850 W·kg-1. The FASC device benefited from the interconnected flexible microstructure and the stable bond bridges, so that it could be bent into various angles without noticeably impairing its performance. This effective protective strategy may further inspire the design and manufacture of metallic oxide or sulfide electrode with ultrahigh-stability interbond bridges for high-performance flexible supercapacitors.

Electronic structure of two-dimensional In and Bi metal on BN nanosheets.

The electronic structures of two-dimensional (2D) indium (In) and bismuth (Bi) metal on BN nanosheets are systematically studied using hybrid density functional theory (DFT). We found that 2D In and Bi metal effectively modulate the band gap of a BN nanosheet. We also found that the indirect band gap of the 2D In and Bi metal electronic structures are 0.70 and 0.09 eV, respectively. This modulation originates from the charge transfer between the 2D metal and BN nanosheet interfaces, as well as from the electron redistribution of the In/BN and Bi/BN heterojunctions of the s and p orbitals. Our results provide an insight into 2D In/BN and Bi/BN heterojunctions, which should be useful in the design of 2D In and Bi metal-semiconductor-based devices.

The Band-Gap Modulation of Graphyne Nanoribbons by Edge Quantum Entrapment.

Using ab initio calculation coupled with the bond-order-length-strength (BOLS) approximation, we investigate the configurations and electronic properties of (α, ß)-graphyne nanoribbons (GYNRs) with armchair (AGYNRs) and zigzag (ZGYNRs) edges. Our investigation shows that the armchair-edged ß-GYNRs and all α-GYNRs are semiconductors with suitable band-gaps, and that their band-gaps increase as the widths of nanoribbons decrease; on the other hand, zigzag-edged ß-GYNRs appear to be zero-band-gap materials. Observation results suggest that (i) atomic undercoordination shortens and stiffens the C-C bond, which contributes to the Hamiltonian and hence widens the band-gap intrinsically; (ii) zigzag-edged ß-GYNRs lack a band-gap due to the edge-undercoordinated atoms lacking the energy to open the ß-graphyne gap; and (iii) the edge-undercoordination of atoms occurs during charge entrapment.