Electron Work Function Research Articles

C6N7 monolayer as an innovative sensor and scavenger for NO, H2S and SO2: A first-principles study

The adsorption, electronic, gas-sensing and capture properties of molecules (NO, H2S, SO2, NO2, NH3, N2, CO, CH4, CO2, and H2O) on the C6N7 monolayer were systematically studied to explore the possibilities of C6N7-based toxic gas sensor and scavenger by using first-principles methods. We found only NO, H2S, and SO2 are adsorbed on the monolayer with large adsorption energy (ranging of -0.853∼-0.931 eV), meanwhile the other molecules are all weakly physisorbed on the monolayer with Ead of -0.193∼-0.547 eV. The NO and H2S adsorption could remarkably affect the electronic properties and work function (Φ) of the C6N7 monolayer, indicating it is highly sensitive and selective towards NO and H2S. The recovery time (τ) of NO and H2S was predicted respectively to be 25 and 1.9 s at 350 K, while the τ of the other molecules was too short to make the sensor device be difficult to measure these gases. The C6N7 monolayer can be promising resistance-type (Φ-type) gas sensors for H2S and NO detection at 350 K. However, the presence of humidity effects the gas sensing of C6N7-based resistance-type sensor, so that it should operate in a dry environment, but as Φ-type sensor can operate regardless of the existence of humidity and concentrations. In addition, the high adsorption capacity and desired recovery time of the C6N7 monolayer make it be an optimal scavenger for toxic gases.

DFT study of the adsorption of simple organic sulfur gases on g-C3N4; periodic and non-periodic approaches

In the present work, the adsorption of some simple organic sulfur gases (CS2, OCS, and CH3SH) on the g-C3N4 was studied using periodic and non-periodic density functional theory (DFT). PBE-D3/DNP and B3LYP-D3/6-31G(d) levels of theory were employed for periodic and non-periodic calculations, respectively. The calculated CS2, OCS, and CH3SH adsorption energies were obtained to be −4.35, −5.82, and −8.58 Kcal/mol. The interactions of simple organic sulfur gases with g-C3N4 were characterized by NBO second-order perturbation theory and quantum theory of atom in molecule (QTAIM). The bandgap energies and work function of g-C3N4 and its complexes with simple organic sulfur gases were extracted from their band structures. The CS2 and OCS adsorptions didn’t significantly alter the bandgap and work function of g-C3N4. Therefore, g-C3N4 is not a proper sensor for detecting CS2 and OCS. The bandgap and work function of g-C3N4 were averagely changed by 18% and 2.7%, respectively, after CH3SH adsorption. Accordingly, g-C3N4 may use as a suitable sensor for detecting CH3SH based on electronic conductivity and work function.

Critical influence of phase transition on the hydrogen evolution reaction activity of Heusler alloys

Unraveling structure-property relationships is of critical importance for designing superior catalysts. Heusler alloys are a family of materials whose atomic packing structure may change with a change in the external field, for example, temperature, magnetic field, and/or stress, and are ideal models for studying the structure-property relationship. In this study, a series of Ni–Mn–Sn–Co Heusler alloys with controlled phases and compositions, including the tetragonal martensite phase (Ni46Mn36Sn11Co7, labeled Co7), cubic austenite phase (Ni42Mn43Sn10Co5, labeled Co5), and tetragonal/cubic mixing phase (Ni46Mn38Sn12Co4, labeled Co4) were investigated. The alloys with the martensitic phase exhibited superior catalytic activity toward hydrogen evolution reaction (HER) than those with the austenitic phase. At an overpotential of 350 mV, the HER current density of the martensite phase of the Co7 sample was almost 2 times higher than that of the austenite phase of the Co5 sample. In-situ temperature-dependent catalytic measurements for the Co4 alloy suggest that the catalytic activity decreases significantly when phase transformation from martensite to austenite occurs. The efficient electron transfer kinetics and low electron work function are responsible for the high activity of the martensite phase, according to Tafel and work function analyses. These results provide a promising strategy for the development of high-performance Heusler alloys by controlling their phase structures and phase transitions.

Molybdenum Carbide MXenes as Efficient Nanosensors toward Selected Chemical Warfare Agents

There has been budding demand for the fast, reliable, inexpensive, non-invasive, sensitive, and compact sensors with low power consumption in various fields, such as defense, chemical sensing, healthcare, and safe environmental monitoring units. Particularly, efficient detection of chemical warfare agents (CWAs) is of great importance for human safety and security. Inspired by this, we explored molybdenum carbide MXenes (Mo2CTx; Tx = O, F, and S) as efficient sensors toward selected CWAs, such as arsine (AsH3), mustard gas (C4H8Cl2S), cyanogen chloride (NCCl), and phosgene (COCl2) both in aqueous and non-aqueous media. Our calculations based on van der Waals-corrected density functional theory (DFT) revealed that the CWAs bind with Mo2CF2, and Mo2CS2 monolayers under strong chemisorption with binding energies in the range of −2.33 to −4.05 eV, whereas Mo2CO2 resulted in comparatively weak bindings of −0.29 to −0.58 eV. We further reported the variations in the electronic properties, electrostatic potentials, and work functions of Mo2CTx upon the adsorption of CWAs, which authenticated an efficient sensing mechanism toward CWA detection. Statistical thermodynamic analysis was applied to explore the sensing properties of Mo2CTx at various temperatures and pressures. These findings will pave the way to an innovative class of low-cost reusable sensors for the sensitive and selective detection of highly toxic CWAs in air as well as in aqueous media.

Corrosion behavior of Al-6.8Zn-2.2Mg-Sc-Zr alloy with high resistance to intergranular corrosion

A high-strength and anti-intergranular corrosion (IGC) Al-6.8Zn-2.2 Mg-Sc-Zr alloy (AS alloy) was designed, and the effects of Sc addition and Cu removal on the microstructure, mechanical properties and corrosion behavior were systematically investigated. Based on transmission electron microscopy (TEM) and Kelvin probe force microscopy (KPFM) techniques, the underlying causes of IGC and exfoliation corrosion (EXCO) of the AS alloy were investigated, and the corrosion mechanism of AS alloy was finally obtained. The AS alloy exhibits excellent mechanical properties with a tensile strength of 601 MPa in the peak-ageing condition at 120 °C, which comes from the pinning effect of Al3(Sc, Zr) dispersions. Moreover, AS alloys of T6 and T74 conditions show outstanding IGC and EXCO resistance. On the one hand, the fine, near-ellipsoidal grains in AS alloy alleviate the peeling stress caused by IGC products by blocking the formation of wedge-shaped gaps along GBs, which then bring about improved EXCO resistance. On the other hand, the removal of Cu from the traditional Al-Zn-Mg-Cu alloy avoids the segregation of Cu into GBs and thereafter reduces the fluctuations of the potential and the electron work function (EWF) across the GBs; the addition of Sc induces the high fraction of LAGBs and thus weakens the solutes' segregation at GBs, which can be beneficial for smoothing the fluctuation of corrosion potential (Ecorr) to enhance the IGC resistance.

Prediction of band edge potentials and reaction products in photocatalytic copper and iron sulfides.

The prediction of band edge potentials in photocatalytic materials is an important but challenging task. In contrast, bandgaps can be easily determined through absorption spectra. Here, we present two simple theoretical approaches for the determination of band edge potentials which are based on the electron negativity and work function of each constituent atom. We use these approaches to determine band edge potentials in semiconducting metallic oxides and sulfides, such as titanium dioxide (TiO2), chalcopyrite (CuFeS2), pyrite (FeS2), covellite (CuS), and chalcocite (Cu2S) with respect to an absolute scale (eV) and an electrochemical scale (V). Until now, there is little information on iron and copper sulfides referring to these thermodynamic parameters.TiO2 (Titania p25) was used as reference semiconductor to validate the calculation procedures using experimental values by X-ray diffraction analysis (XRD), diffuse reflectance spectrometry (DRS), and electron paramagnetic resonance spectroscopy (EPR). The production of key chemical species such as reactive oxygen species (ROS) and reactive sulfur species (RSS) has been theoretically and experimentally determined by EPR.

Metalloporphyrin reduced C70 fullerenes as adsorbents and detectors of ethenone; A DFT, NBO, and TD-DFT study

In the present work, the structure and electronic properties of Ti-, Cr-, Fe-, Ni-, Zn-, and Cu-inserted in porphyrin-reduced C70 fullerenes (TM-PIC70Fs) and their interactions with the ethenone were studied using DFT, NBO, and TD-DFT at CAM-B3LYP/6-31G(d) level of theory. 2.89–3.83 and 4.02–4.56 eV were obtained for the HOMO-LUMO gap energies and work functions of TM-PIC70Fs, respectively, compared with 3.76 and 4.54 eV for PIC70F. Among considered TM-PIC70Fs, the adsorption of the ethenone on Ti-PIC70F appreciably changed the HOMO-LUMO energy gap and work function. Consequently, Ti-PIC70F may be used as the ethenone's electronic conductivity and work function types sensor. According to calculated UV–visible spectra, the ethenone adsorption may change the color of Fe- and Ti-PIC70Fs. Therefore, they can be used as color-changing sensors of ethenone. In addition, Ti-, Cr-, Fe-, and Zn-PIC70Fs can be employed as suitable adsorbents of ethenone. Among proper sensors and adsorbents of ethenone, Cr-, Fe-, and Zn-PIC70Fs may be recovered and reused.

Preparation and properties of in situ formed TiCx/high chromium white iron composite with honeycomb structure

The well-formed porous Ti3AlC2 preform with honeycomb structure using mold forming method, and TiCx/high chromium white iron (TiCx/HCWI) composite with fine TiCx framework formed by porous Ti3AlC2 preform in situ decomposition using pressureless infiltration method were successfully prepared, respectively. The HCWI composite with fine in situ TiCx framework exhibited excellent properties. The transition zone between framework and HCWI with the highest hardness, the minimum friction coefficient, wear depth and electronic work function (EWF) may protect the whole sample during wear.

Optoelectronic Properties of In0.87Ga0.13As0.25P0.75(001)β2(2×4) Surface: A First-Principles Study.

InGaAsP photocathode surface affects the absorption, transport and escape of photons, and has a great influence on quantum efficiency. In order to study InGaAsP photocathode surface, the electronic structure, work function, formation energy, Mulliken population and optical properties of In0.87Ga0.13As0.25P0.75(001)β2(2×4) reconstruction surface were calculated from first principles. Results show that stabilized the In0.87Ga0.13As0.25P0.75(001)β2(2×4) surface is conducive to the escape of low-energy photoelectrons. The narrow bandgap and emerging energy levels of the reconstruction surface make the electron transition easier. Under the action of the dipole moment, the electrons transfer from inner layers to the surface during the surface formation process. By contrast to the bulk, the surface absorption coefficient and reflectivity considerably decrease, and the high-reflection range becomes narrower as the falling edge redshifts. On the contrary, the surface transmissivity increases, which is conducive for the photons passing through the surface into the bulk to excite more photoelectrons. Meanwhile, the higher absorption coefficient of surface in low-energy side is favorable for long-wave absorption. The dielectric function peaks of the surface move toward the low-energy side and peak values decrease.

Influence of solution-hardening on the mechanical properties and wear resistance of copper alloys

Solid-solution hardening can increase the wear resistance of metals, involving two factors: the solute 1) pins dislocations, leading to increased hardness of the metals; 2) influences the atomic bond strength and thus Young's modulus, which also affects the resistance to dislocation generation and movement. Solute atoms generally increase hardness of the host metal but may increase or decrease its Young's modulus, which is related to the solute's electron work function (EWF). In this study, Cu (EWF = 4.65 eV) was hardened by solutes, Ni (EWF = 5.15 eV), and Mn (EWF = 4.1 eV), respectively. CuNi (10, 30, 60, 80 wt% Ni) and CuMn (2, 4, 6, 8 wt% Mn) alloys were prepared using an arc furnace. It is demonstrated that with Ni addition, both hardness and Young's modulus increased, while Mn addition led to a decrease in Young's modulus though the hardness was increased. As a result, the effect of Ni on the wear resistance of Cu is underestimated when predicted using the classic Archard equation, while that of Mn is overestimated. Such an issue of under- or over-estimation can be corrected using a wearing energy model, which takes into account the influence of Young's modulus on the wear resistance. The wearing energy model is a modified form of Archard equation, established by including wearing energy consumption via the relationships among atomic bond strength, Young's modulus, and EWF. Density functional theory (DFT) calculations on CuMn and CuNi alloys systems confirm a stronger metallic bond in CuNi with higher overall EWF, compared with that in CuMn showing a lower overall EWF.

Structural and physical properties of hydroxyapatite modified by Sr/Ca substitutions

The structural and physical properties of hydroxyapatite with the substitutions of Sr/Ca were studied by density functional theory calculations using Quantum ESPRESSO. The calculation of the lattice constants upon substitution of Sr/Ca in HAP was compared with the experimental data and showed similar increase in these parameters after the Sr/Ca substitutions. The changes in the band gap ΔE g and the electron work function Δϕ after Sr/Ca substitutions were estimated. The changes in the polarization and piezoelectric properties upon Sr/Ca substitution were calculated using the new quantum-chemical semi-empirical PM7, PM6-D3H4 (MOPAC) calculations.

High-entropy carbides designed to resist cavitation erosion-corrosion in an acidic environment: Surface engineering guided by first-principles calculations and experiments

In this study, the influence of chemical composition on phase stability, mechanical and electronic properties of (TixZr0.2Nb0.2Ta0.2Mo0.4-x)C (x = 0.3, 0.2, 0.1) high entropy carbide ceramics (HECCs) were first explored by first-principles calculations. The results showed that the composition (Ti0.3Zr0.2Nb0.2Ta0.2Mo0.1)C has higher values of electron work function (EWF) value and theoretical hardness than that of the other HECCs with lower Ti concentrations. Following this investigation, a (Ti0.3Zr0.2Nb0.2Ta0.2Mo0.1)C HECC coating was deposited onto a commercially pure titanium substrate by a reactive-sputtering method. The as-prepared HECC coating had a uniform thickness of ∼17 μm and consisted of equiaxed nanocrystals with a mean diameter of ∼7 nm. The cavitation erosion-corrosion behavior of the HECC coating was studied by combining electrochemical impedance spectroscopy (EIS) and electrochemical noise (EN) measurements in a 0.05 M H2SO4 solution. The EIS results revealed that with increasing time of cavitation exposure, the resistance value of the HECC coating was an order of magnitude larger than that for uncoated CP-Ti for a given cavitation time. EN analysis indicated that under cavitation conditions, uncoated CP-Ti was more vulnerable to localized corrosive attack than the HECC coating in an acidic environment.

Accelerated radical generation from visible light driven peroxymonosulfate activation by Bi2MoO6/doped gCN S-scheme heterojunction towards Amoxicillin mineralization: Elucidation of the degradation mechanism

A novel S-scheme photocatalyst Bi2MoO6 @doped gCN (BMO@CN) was prepared through a facile microwave (MW) assisted hydrothermal process and further employed to degrade Amoxicillin (AMOX), by peroxymonosulfate (PMS) activation with visible light (Vis) irradiation. The reduction in electronic work functions of the primary components and strong PMS dissociation generate abundant electron/hole (e-/h+) pairs and SO4*−,*OH,O2*−reactive species, inducing remarkable degeneration capacity. Optimized doping of Bi2MoO6 on doped gCN (upto 10 wt%) generates excellent heterojunction interface with facile charge delocalization and e-/h+ separation, as a combined effect of induced polarization, layered hierarchical structure oriented visible light harvesting and formation of S-scheme configuration. The synergistic action of 0.25 g/L BMO(10)@CN and 1.75 g/L PMS dosage can degrade 99.9% of AMOX in less than 30 min of Vis irradiation, with a rate constant (kobs) of 0.176 min−1. The mechanism of charge transfer, heterojunction formation and the AMOX degradation pathway was thoroughly demonstrated. The catalyst/PMS pair showed a remarkable capacity to remediate AMOX-contaminated real-water matrix. The catalyst removed 90.1% of AMOX after five regeneration cycles. Overall, the focus of this study is on the synthesis, illustration and applicability of n-n type S-scheme heterojunction photocatalyst to the photodegradation and mineralization of typical emerging pollutants in the water matrix.

The impact of surface scratches on the corrosion behavior of nanocrystalline high entropy alloy coatings: Electrochemical experiments and first-principles study

To prolong the service life of engineering components used in aggressive environments, a TiZrHfMoW refractory high entropy alloy (RHEA) coating was prepared onto a titanium alloy substrate. Various electrochemical analytical techniques were used to evaluate the corrosion resistance of the scratched RHEA coating in a 3.5 wt.% NaCl solution. The electrochemical corrosion tests indicate that the scratched RHEA coating exhibits a higher electrochemical stability and a lower corrosion rate than the bare titanium alloy. The effects of the localized plastic deformation on the corrosion behavior for the RHEA coating was investigated. A slab model for the RHEA surface was proposed for the first-principles calculation to explored the change of the electron work function (EWF) as a function of external stress. The influence of the constituent elements in the RHEA on the mechanical properties and the electron work function was study to uncover the mechanism underlying the high scratch corrosion resistance of the RHEA coating and provide guidance for the composition design of refractory high entropy alloy.

Enhancing the Catalytic Activity of Mo(110) Surface via Its Alloying with Submonolayer to Multilayer Boron Films and Oxidation of the Alloy: A Case of (CO + O2) to CO2 Conversion

In-situ formation of boron thin films on the Mo(110) surface, as well as the formation of the molybdenum boride and its oxide and the trends of carbon monoxide catalytic oxidation on the substrates formed, have been studied in an ultra-high vacuum (UHV) by a set of surface-sensitive characterization techniques: Auger and X-ray photoelectron spectroscopy (AES, XPS), low-energy ion scattering (LEIS), reflection-absorption infrared spectroscopy (RAIRS), temperature-programmed desorption (TPD), electron energy loss spectroscopy (EELS) and work function measurements using the Anderson method. The boron deposited at Mo(110) via electron-beam deposition at a substrate temperature of 300 K grows as a 2D layer, at least in submonolayer coverage. Such a film is bound to the Mo(110) via polarized chemisorption bonds, dramatically changing the charge density at the substrate surface manifested by the Mo(110) surface plasmon damping. Upon annealing of the B-Mo(110) system, the boron diffuses into the Mo(110) bulk following a two-mode regime: (1) quite easy dissolution, starting at a temperature of about 450 K with an activation energy of 0.4 eV; and (2) formation of molybdenum boride at a temperature higher than 700 K with M-B interatomic bonding energy of 3.8 eV. The feature of the formed molybdenum boride is that there is quite notable carbon monoxide oxidation activity on its surface. A further dramatic increase of such an activity is achieved when the molybdenum boride is oxidized. The latter is attributed to more activated states of molecular orbitals of coadsorbed carbon monoxide and oxygen due to their enhanced interaction with both boron and oxygen species for MoxByOz ternary compound, compared to only boron for the Mox'By' double alloy.

Model Metallic Glasses for Superior Electrocatalytic Performance in a Hydrogen Oxidation Reaction

Metallic glasses or amorphous alloys, with their excellent chemical stability, disordered atomic arrangement, and ability for thermoplastic nanostructuring, show promising performance toward a range of electrocatalytic reactions in proton-exchange membrane fuel cells. However, there are knowledge gaps and a distinct lack of understanding of the role of amorphous alloy chemistry in determining their catalytic activity. Here, we demonstrate the influence of alloy chemistry and the associated electronic structure on the hydrogen oxidation reaction (HOR) activity of a systematic series of Pt42.5-xPdxCu27Ni9.5P21 bulk metallic glasses (BMGs) with x = 0 to 42.5 at%. The HOR activity and electrochemical active surface area as a function of composition were in the form of volcano plots, with a peak around equal proportion of Pt and Pd. The lower relative electron work function and higher binding energy of the Pt core level explain the reduced charge-transfer resistance and improved electrocatalytic activity due to weakened chemisorption of protons in the mid-range composition. Density functional theory calculations show the lower free energy change and higher hydrogen adsorption density for these Pt42.5-xPdxCu27Ni9.5P21 BMGs, suggesting a synergistic effect from the presence of both noble metals, Pt and Pd.

Creation of Gases with Interplanetary Oxygen Concentration at Atmospheric Pressure by Nanoparticle Aerosol Scavengers: Implications for Metal Processing from nm to mm Range

A gas purification setup (GPS) is presented that is capable of producing ultrapure inert gases, such as nitrogen, at ambient pressure with residual oxygen concentrations of 10–13 ppm and below. The GPS relies on the interaction of metallic aerosol nanoparticles that capture residual oxygen, resulting in metal oxide particle formation. The finally reached residual oxygen level can be illustrated by the 6.8 billion years needed for the creation of one monolayer of oxygen on a substrate. Consequently, the processing of oxygen-affine materials of any size may be shifted from vacuum processes toward machining steps at atmospheric pressure, maintaining an oxygen-free environment in the future. As an outlook, the presented work includes measurements of the electron work function of nanoparticles under purified (10–13 ppm-level) and unpurified process gas (100 ppm-level), pointing at the strong influence of residual oxygen on nanostructured materials with reference to copper nanoparticles. Future syntheses and applications of nanoscaled structures will be inspired by the opportunity to work with true inert gases at ambient pressure, which has been inaccessible so far.

Enhanced secondary electron emission properties of Zn doped MgO thin films prepared by aerosol assisted chemical vapor deposition

In this study Zn doping was applied to MgO thin films in order to improve the secondary electron emission (SEE) property via relieving the surface charging and modifying the electron structure of MgO. MgO and Mg1-xZnxO thin films (the Zn doping proportion x is within 11 at.%) were prepared on Si substrates by a simple, cost effective aerosol assisted chemical vapor deposition method followed by annealing at elevated temperature. The surface morphology and microstructure of the Mg1-xZnxO films were characterized. Secondary electron yield (δ) as a function of primary electron energy the films was examined. First principles calculation based on the density functional theory was introduced to evaluate the electronic structure and work function of Mg1-xZnxO crystals. SEE testing results revealed that δ of the MgO film is effectively improved by Zn doping of proper concentration. The undoped MgO film with relatively smooth surface exhibits a maximum secondary electron yield (δm) of 5.1 at Ep of 750 eV. The δm of the Mg1-xZnxO film (x = 0.09) is 7.0 at Ep = 1500 eV, which is 34.6% higher than that of the MgO film prepared under identical method. Improvement of δ of the Mg1-xZnxO films with x < 0.1 is probably due to the unique surface morphology with protrusions and sharp edges and the increase of electrical conductivities of the films. Another factor contributing to the δ increase is the decrease of work function due to Zn doping, which is confirmed by first-principles calculation of Mg1-xZnxO crystals.

Defect Engineering of Green Phosphorene Nanosheets for Detecting Volatile Organic Compounds: A Computational Approach

The high performance of chemical gas detection has become an essential factor for monitoring biotoxin volatile organic compounds (VOCs). Here, using first-principles modeling, defect engineering of green phosphorene (GreenP) with heteroatom substitution and vacancy formation was proposed to obtain high sensing ability and reusability of gas sensing materials for VOC gases. Our computations suggest that pristine and S- and C-doped GreenP weakly adsorbs the VOC gases with small charge transfer, leading to almost no change in the electronic properties. Although mono- and di-vacancy GreenP substantially improves the adsorption strength, the electronic structure exhibits negligible changes upon adsorption, resulting in low sensitivity. Remarkably, Si doping improves the adsorption of carbonyl-containing compounds, including acetone, propanal, and formaldehyde, and yields major changes in the electronic properties and work function, which promote sensitivity and selectivity. In addition, their adsorption energies are moderately strong, which also allow for fast desorption at elevated temperature, resulting in high reusability. From the computational viewpoints, we proposed Si-doped GreenP as a promising candidate for gas sensing material for VOC detection.

Choice of material for cumulative lattices to accelerate thermal diffusion chromium plating processes

The results of thermal diffusion chromium plating of samples of steel X35CrNi2-3 in technological filling containing oxide-emitters of oxygen anions, which create a thermionic field upon heating, are presented. The use of cumulative gratings made of Cr20Ni80 nichrome, cobalt and tantalum makes it possible to increase the depth of chromium diffusion by 1.4—1.8 times. It has been established that the efficiency of the cumulative grating during thermal diffusion chromium plating depends on the work function of electrons from the grating material. The results obtained are experimental confirmation of the hypothesis about the mechanism of acceleration of chromium diffusion during thermal diffusion chromium plating and confirm not only the acceleration in the conical holes of the lattice of the main diffusion flow created in the technological backfill, but also the occurrence of an additional electron flow from their walls.