MgO Molecules Research Articles

Laser-textured Pd-Au hierarchical superhydrophobic micro-arrays for ultralow SERS detection

Ultra-trace identification of the limited quantity of diluted analyte solutions requires the condensation of target analytes utilizing the superhydrophobic analyte enrichment effect and are extremely desirable for improving the detection sensitivity. Herein, the identification of ultra-trace analyte concentrations employing laser-textured palladium-gold (Pd-Au) hierarchical superhydrophobic micro-arrays as surface-enhanced Raman sensors (SMA-SERS) is reported. The double ns-laser fast scanning strategy produces hierarchically arranged micro-strip and micro-pyramidal arrays over the large surface areas composed of nano-scale inter-particle gaps, enabling the numerous three-dimensional plasmonic hot-spots due to the uniform formation of Au nanoparticles' aggregates/clusters. Under the optimized fabrication parameters, the resultant hybrid SMA-SERS sensors exhibit periodic micro-pyramidal arrays with excellent inherent superhydrophobicity (Contact angle, CA∼171°) and consequently superior SERS performance with uniform (RSD∼10%) signal detectability down to the ∼34.2 fM (3.42×10−14 M) MB molecules utilizing analyte enrichment effect. The accumulation of analytes within the smaller dried spots (Contact diameter, CD∼1.13 mm) results in increased spatial density of analytes and subsequently enables the ultra-low detectability of MGO, DTTCI, PA, AN, adenine, and l-tryp molecules down to ∼3.57 pM, 0.34 fM, 0.31 nM, 0.44 µM, 0.25 nM, and 97.7 nM concentrations, respectively. The multiplexed identification of target (AN and adenine) analytes is explored utilizing serial-deposition of analytes and depict the simultaneous detection of target analytes down to ∼10−7 M (AN) and 10−9 M (adenine) concentrations. The double ns-laser fast scanning strategy provides dual-scale surface roughness in the SMA-SERS substrates and offers ultrahigh sensitivity for the identification of the low amount of analytes utilizing the superhydrophobicity-induced analyte enrichment effect.

Thermal and mechanical characterization of blindex glass powder residue® for the production of ecological coating

The science of materials has great interest in the development of new composites, therefore, this work aims to obtain a new material using the waste produced by the industries themselves and which in many cases produce a serious problem for the environment. For the development of this research, was used the residue in the form of mud resulting from the cutting process in the manufacture of flat glazing. The samples obtained dehydrated for 24 h at a temperature of 100 °C. The samples were pressed using hydraulic press with a capacity of 150 ton/cm2 resulting in proof body's with dimensions in the order of 105 mm long, 52 mm wide and 5.7 mm thick and submitted the process of sintering at different temperatures in ambient atmosphere. The characterizations of proof bodies applying thermal analysis technique (TGA), presented evaporation of surface H2O and to the degradation of the molecules of Na2O, K2O and P2O5 until 100 °C. In the range between 200 °C and 600 °C the curve has a more linear attributed to the thermal degradation of the Al2O3, MgO and Fe2O3 molecules and a thermal stability above 600 °C. The x-ray diffraction analyses (XRD), with the precursor glass powder presented characteristic of a standard amorphous structure and with the powders of sintered proof body's at different temperatures, observed the characteristic peaks of calcite (CaCo3), cristobalite (SiO2), quartz (SiO2) and low silicon oxide (SiO2) crystals. The characterizations using scanning electron microscopy technique (SEM) show a homogeneous distribution of particles with sizes in the order of 30 μm. The mechanical characterizations in the specimens applying bending rupture tests showed range of rupture modules of the 31.92 kgf/cm2 and 55.28 kgf/cm2 to the range temperature between 200 °C and 600 °C. The characterizations and water absorption tests apresented that there is a great advantage in the use of blindex® glass powder residue for the manufacture of a new ecological coating, this material can be applied more abrasively to paving blocks, septic sewer tanks, grease traps, wall building blocks and in the most finished form it can be applied as a tactile floor, internal coatings in the form of tablets for bathroom and kitchen and other finishes to the civil construction sector.

Gas-phase spectra of MgO molecules: a possible connection from gas-phase molecules to planet formation

A more fine-tuned method for probing planet-forming regions, such as protoplanetary discs, could be rovibrational molecular spectroscopy observation of particular premineral molecules instead of more common but ultimately less related volatile organic compounds. Planets are created when grains aggregate, but how molecules form grains is an ongoing topic of discussion in astrophysics and planetary science. Using the spectroscopic data of molecules specifically involved in mineral formation could help to map regions where planet formation is believed to be occurring in order to examine the interplay between gas and dust. Four atoms are frequently associated with planetary formation: Fe, Si, Mg and O. Magnesium, in particular, has been shown to be in higher relative abundance in planet-hosting stars. Magnesium oxide crystals comprise the mineral periclase making it the chemically simplest magnesium-bearing mineral and a natural choice for analysis. The monomer, dimer and trimer forms of (MgO)n with n = 1–3 are analysed in this work using high-level quantum chemical computations known to produce accurate results. Strong vibrational transitions at 12.5, 15.0 and 16.5 μm are indicative of magnesium oxide monomer, dimer and trimer making these wavelengths of particular interest for the observation of protoplanetary discs and even potentially planet-forming regions around stars. If such transitions are observed in emission from the accretion discs or absorptions from stellar spectra, the beginning stages of mineral and, subsequently, rocky body formation could be indicated.

Photolysis of metal oxides as a source of atoms in planetary exospheres

The cross sections of photolysis of LiO, NaO, KO, MgO, and CaO molecules have been calculated by the use of quantum chemistry methods. The maximal values for photolysis cross sections of alkali metal monoxides have the order of 10−17 cm2, and for alkaline earth metal monoxides these values are less on 1–2 orders of the magnitude. The lifetimes of photolysis at 1 astronomical unit are estimated as 5, 3, 60, 70, and 3,000 s for LiO, NaO, KO, MgO, and CaO, respectively. Typical kinetic energies of main peaks of photolysis-generated metal atoms are determined. Impact-produced LiO, NaO, KO, and MgO molecules are destroyed in the lunar and Hermean exospheres almost completely during the first ballistic flight while CaO molecule is more stable against destruction by photolysis. Photolysis-generated metal atoms in planetary exospheres can be detected by performing high-resolution spectral observations of velocity distribution of exospheric metal atoms.

Ab Initio Study of Electronic States of Astrophysically Important Molecules

A study of electronic states of LiO, NaO, KO, MgO, and CaO molecules has been performed. Potential energy curves of the investigated molecules have been constructed within the framework of the XMC-QDPT2 method. Lifetimes and efficiencies of photolysis mechanisms of these monoxides have been estimated within the framework of an analytical model of photolysis. The results obtained show that oxides of the considered elements in the exospheres of the Moon and Mercury are destroyed by solar photons during the first ballistic flight.

First-principles study of the adsorption of MgO molecules on a clean Fe(001) surface

The adsorption of MgO molecules on a Fe(001) surface was studied using density functional theory (DFT) and projector augmented wave methods. The energetically most favored configurations for different adsorption sites considered were identified. The most preferable adsorption geometry is when the MgO molecules are parallel to the surface, with Mg in the interstitial site and O in on-top of the Fe atom. During the adsorption of subsequent MgO molecules in this geometry, a sharp, non-oxidized interface is formed between the MgO adlayer and Fe(001) surface. The adsorption of MgO perpendicular to the surface, with oxygen incorporated in the topmost Fe layer is less probable, but may lead to the formation of the FeO layer when stabilized with an excess of oxygen atoms. Structural, electronic and magnetic properties of both interface types were examined for the MgO coverage from 1/9 to 1 monolayer (ML). Electronic and magnetic properties are sensitive to the MgO coverage. For lower coverage of MgO, clear hybridization between the Fe 3d and O 2p states is shown. The average magnetic moment of the surface Fe atoms is reduced with coverage, achieving 2.78 $\mu_{\rm B}$ for 1 ML of MgO.

Collisional excitation of MgO by He

Using a well-established ab initio methodology to generate the potential energy surface of the MgO–He interacting system and a quantum close-coupling treatment of nuclear motion, we give the rotational (de-)excitation cross-sections and the collision rate coefficients for the first 16 rotational levels of the MgO molecule and He for temperatures ranging from 10 up to 300 K. A clear propensity rule in favour of Δj = 1 rotational transitions is observed. These data are compared with previous works on astrophysical oxygen-bearing diatomic species. This work should be useful for the eventual detection of the key metal-oxide MgO molecule in the circumstellar and interstellar media with current and future high-resolution telescopes.

First principles approach to ionicity of fragments

We develop a first principles approach towards the ionicity of fragments. In contrast to the bond ionicity, the fragment ionicity refers to an electronic property of the constituents of a larger system, which may vary from a single atom to a functional group or a unit cell to a crystal. The fragment ionicity is quantitatively defined in terms of the coefficients of contributing charge states in a superposition of valence configurations of the system. Utilizing the constrained density functional theory-based computations, a practical method to compute the fragment ionicity from valence electron charge densities, suitably decomposed according to the Fragment Hamiltonian (FH) model prescription for those electron densities, is presented for the first time. The adopted approach is illustrated using BeO, MgO and CaO diatomic molecules as simple examples. The results are compared and discussed with respect to the bond ionicity scales of Phillips and Pauling.

Excellent fluoride removal properties of porous hollow MgO microspheres

Porous hollow MgO microspheres were synthesized and characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption–desorption isotherms. The removal properties of the MgO microspheres towards toxic fluoride were investigated, including adsorption kinetics, adsorption isotherms, and influences of pH and coexisting anions. The adsorption capacity was larger than 120 mg g−1 at a pH of 7.0. The effects of anions on fluoride removal were also investigated. The results indicated that phosphate was the greatest competitor of fluoride for adsorptive sites. In addition, the removal mechanism was revealed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The reaction of MgO and water molecules resulted in the formation of Mg(OH)2. The excellent adsorption properties towards fluoride resulted from the surface reaction between the generated Mg(OH)2 and fluoride in solution.

High symmetry Nbn and Tan (n = 12, 15, and 17) clusters: High magnetic moments and the finding of superatoms with doping

Using ab initio calculations, we study Nbn and Tan clusters with n=12, 15, and 17 and find superatoms made of transition metals. Nb12 and Ta12 have an empty cage icosahedral structure. Neutral Ta12 has icosahedral symmetry and 2μB magnetic moments while the cage for Nb12 is slightly distorted and has no magnetic moment. These clusters behave like a divalent superatom. Accordingly an oxygen atom interacts exohedrally on a 3-fold site of the icosahedral cage like an MgO molecule and leaves the cage intact while Fe, Ru, and Os atoms can be endohedrally doped in Ta12 to produce electronically closed shell clusters with large highest occupied-lowest unoccupied molecular orbital (HOMO–LUMO) gap. Also isoelectronic Co@X12 and Rh@X12 (X=Nb and Ta) cations have a large HOMO–LUMO gap of up to about 1eV. In these cases the magnetic moment is quenched. On the other hand doping with Ni leaves the magnetic behavior of Ta12 the same. Further anions of Nb15 and Ta15 have a closed electronic shell structure and a singlet ground state with a large HOMO–LUMO gap. We show that isoelectronic Nb14Mo, Nb14W, Ta14Mo, Ta14W, Nb14Mn+, Nb14Re+, Ta14Mn+, and Ta14Re+ all have a large HOMO–LUMO gap of up to about 1.0eV and are magic clusters. Most interestingly Ta17 has a tetrahedrally symmetric Z16 Frank–Kasper polyhedral structure with a large magnetic moment of 5μB. On the other hand the magnetic moment on Nb17 cluster is 1μB. The magnetic moment on Ta17 is surprisingly large and it is counter intuitive as normally the magnetic moments decrease as one goes down in a column in the periodic table but some tantalum clusters behave differently. Doping of the n=17 clusters with Zr at the center leaves Zr@Ta16 magnetic with 2μB and 6μB magnetic moments nearly degenerate while Zr@Nb16 has zero magnetic moment.

Kinetic Monte-Carlo simulation of the homoepitaxial growth of MgO{001} thin films by molecular deposition

A lattice-based kinetic Monte-Carlo (KMC) code has been developed to investigate the MgO{001} crystal growth from deposition of MgO molecules, as a prototypical case of the growth of oxide thin films. The KMC approach has been designed on the basis of an extensive database including all possible diffusion mechanisms. The corresponding activation energies have been computed through first-principles calculations at zero temperature or from Arrhenius plots of the frequencies obtained by molecular dynamics simulations with empirical potentials. Crystal growth occurs layer by layer, as experimentally observed, and the diffusion of admolecules leads to a high capacity of nucleation, which is enhanced by vacancy diffusion. We have characterized the growth through surface roughness, size distribution and density of the islands, and filling ratios of the growing layers. Moreover, we have analysed the influence of each elementary mechanism on the growth. The best quality of the deposited layers is reached for temperatures larger than 700K and for pressures smaller than 0.1Torr. For these conditions, the simulated surface roughness is fully consistent with available experimental results.

THEORETICAL CHARACTERS OF MgX (X = Te, Se, S AND O) CLUSTERS

At DFT/B3LYP/LANL2DZ theoretical level, a series of MgX clusters with Mg3X3 hexagon, Mg4X4-t tetrahedron and Mg4X4-o octagon conformations are investigated. Their wavelengths of absorption spectra are calculated with time-dependent Density Functional Theory (TDDFT) using water as solvent. Firstly, the lowest vibrational frequencies, bond lengths, Dipole Moment and Raman spectra of them present regular change. Dipole Moment result shows that different clusters have different charges. From Raman spectra, we have discovered that they correlate with the conformation and variety of clusters. Conformations of MgO clusters have different optimizing characters with MgS , MgSe and MgTe molecules. Secondly, through Molecular Orbital and Nature Bond Orbital (NBO) analysis, we have found that all these clusters are materials with wider gaps. MgTe structures have stronger bonding. Besides, MgO have different transition from the other clusters. The order of wavelengths of absorption spectra is MgTe > MgSe > MgS . In a word, except MgO molecules, these clusters have similar or regular characters. These results are significant for experimental study of MgX nanocrystals.

Electronic states of MgO: Spectroscopy, predissociation, and cold atomic Mg and O production

We used multiconfigurational methods and a large basis set to compute the potential energy curves of the valence and valence-Rydberg electronic states of MgO molecule. New bound electronic states are found. Using these highly correlated wave functions, we evaluated their mutual spin-orbit couplings and transition moment integrals. For the bound electronic states of MgO, we deduced an accurate set of spectroscopic constants that agree remarkably well with experimental results. Moreover, our potentials, transition moments, and spin-orbit coupling evolutions are incorporated into Fermi golden rule calculations to deduce the radiative lifetimes of MgO(B (1)Σ(+)) rovibrational levels and the natural lifetimes of MgO(A (1)Π) vibrational levels, where a good agreement is found with experimental values. Finally, we suggest new routes for the production of cold Mg and O atoms and cold MgO molecules.

Formation and Characterization of Magnesium Bisozonide and Carbonyl Complexes in Solid Argon

The reactions of magnesium atoms with dioxygen and dioxygen/carbon monoxide mixture have been investigated by matrix isolation infrared absorption spectroscopy. Magnesium atoms react with dioxygen in solid argon to form the inserted MgO(2) molecules under UV excitation, which were previously characterized. Annealing allows the dioxygen molecules to diffuse and to react with MgO(2) and form the magnesium bisozonide complex, Mg(O(3))(2), which is proposed to be coordinated by two argon atoms in solid argon matrix. The Mg(O(3))(2)(Ar)(2) complex is characterized to have two equivalent side-on bonded ozonide ligands with a D(2h) symmetry. The coordinated argon atoms can be replaced by carbon monoxide to give the magnesium bisozonide dicarbonyl complex, Mg(O(3))(2)(CO)(2), a neutral magnesium carbonyl complex with CO binding to the Mg(2+) center.

Study on structure characteristics of MgO molecule under external electric field

The influence of external electric field ranging from -003 to 003 a.u. on the equilibrium geometry, HOMO energy level, LUMO energy level, energy gap, harmonic frequency and infrared intensity of MgO ground state molecule is investigated by employing the density functional methods （B3LYP） with basis sets 6-311+G（2DF）. The results show that the LUMO energy level, energy gap and harmonic frequency decrease, but the total energy increases with increasing external field. The bond length is proved firstly decreasing, then increasing, however, the HOMO energy level is proved firstly increasing, then decreasing with increasing external field. The maximum of HOMO energy level and minimum of bond length are -021765 a.u. at F=001 a.u. and 017397 nm at F=002 a.u, respectively. The external electric field has effect on excitation energies, oscillator strengths and the position and intensity of infrared spectrum.

Deposition process of MgO thin film on MgO（001） surface simulated by molecular dynamics

Molecular dynamics is used to simulate the deposition process of MgO molecules on MgO（001） surface，and substrate temperature and molecular incident energy are discussed in terms of their effects on the diffusivity of MgO molecules and the substrate surface coverage ratio. The simulated results show that with the substrate temperature increasing， vacant sites in MgO film decrease, owing to the increase in diffusivity of the deposited molecules on the substrate. At low temperatures， the substrate surface coverage ratio increases with molecular incident energy increasing. At high temperatures， the surface coverage ratio reaches the maximum at an incident energy of 3.0 eV， and then it decreases with the increase of incident energy.

Primary nucleation processes in binary oxide growth: The case of MgO

The smallest forms of stoichiometric and non-stoichiometric MgO clusters appearing on the MgO(0 0 1) surface during the growth under atomic and/or molecular deposition are investigated from first-principles and empiric potentials. The basic entities (MgO molecule and (MgO) 2 cluster) result from a very exoenergetic and spontaneous redox reaction that involves directly the deposited species (Mg and O atoms, O 2 molecule). The stoichiometric clusters, resulting from the agglomeration of MgO molecules, are very stable under non-polar forms. Their formation energy is modelized, down to very small sizes, within an independent defect model. We point out the specificity of such clusters in the framework of the classical nucleation theory. The high-energy polar isomers are associated to destabilizing macroscopic electric fields and dipoles. These forms may nevertheless be strongly stabilized by incorporating extra Mg adatoms that give part of their valence shell to the cluster and decrease the total dipole in this way, illustrating the delicate coupling between chemistry and electrostatics in growth processes of oxides. Based on these considerations, we propose a scenario describing MgO growth both in the step-flow and in the nucleation regime.

Microwave spectroscopy of MgO in the a 3Π and X 1Σ states

Pure rotational transitions of MgO in the a 3Π i state and the ground X 1Σ + state (v=1–3) were observed in the 210–400 GHz region. The MgO molecule was produced by a DC discharge in a mixture of Mg vapor and N 2O. A simultaneous deperturbation analysis for the X 1Σ +, a 3Π, and A 1Π states was carried out for the observed transition frequencies including previous high-resolution data, where the energy levels were calculated by diagonalizing the energy matrix including the spin–orbit and orbit–rotation interactions among three electronic states with vibrational levels up to v=9. A centrifugal term of the spin–orbit interaction between the a 3Π i and X 1Σ + states was newly introduced to improve quality of the fitting, to explain the observed Λ-type doubling of the a 3Π i state.

Spectroscopic characterization of the F 1Π 1 ‘Rydberg’ state of the MgO molecule

The F 1Π 1 ‘Rydberg’ state of 24Mg 16O has been characterized by two-color Resonance-Enhanced Two-Photon Ionization (R2PI) spectroscopy in the 37 000–39 000 cm −1 region. Several rotationally resolved bands, assigned to 24Mg 16O(F 1Π 1 ← X 1Σ +) vibronic transitions, have been analyzed to yield spectroscopic constants for the F 1Π 1 state. Consistent with the ab initio calculations of Peyerimhoff and co-workers, the F 1Π 1 state appears to have mixed Rydberg–valence character.

A new source for vibrationally excited and rotationally cold metal-oxide molecules: spectroscopic characterization of the low-lying a [formula omitted] metastable excited state of the MgO molecule

Several ν=0–4 series of hot bands in the 36 000–39 000 cm −1 spectral region have been recorded from the MgO(a 3 Π 2 ) metastable state (produced by the products of laser vaporization of a magnesium rod reacting with N 2O) to higher-lying MgO( 3 Π 2 ) vibronic levels, and have been rotationally resolved. From the analysis of the spectra, rotational and vibrational spectroscopic constants for this interesting low-lying MgO(a 3 Π 2 ) excited state, which formally has Mg +O − ‘open-shell’ character, have been determined.