4s Band Research Articles

One-Step Theory View on Photoelectron Diffraction: Application to Graphene.

Diffraction of photoelectrons emitted from the core 1s and valence band of monolayer and bilayer graphene is studied within the one-step theory of photoemission. The energy-dependent angular distribution of the photoelectrons is compared to the simulated electron reflection pattern of a low-energy electron diffraction experiment in the kinetic energy range up to about 55 eV, and the implications for the structure determination are discussed. Constant energy contours due to scattering resonances are well visible in photoelectron diffraction, and their experimental shape is well reproduced. The example of the bilayer graphene is used to reveal the effect of the scattering by the subsurface layer. The photoemission and LEED patterns are shown to contain essentially the same information about the long-range order. The diffraction patterns of C 1s and valence band photoelectrons bear similar anisotropy and are equally suitable for diffraction analysis.

Strain effect on the intraband absorption coefficient for spherical CdSe/CdS/ZnSe core–shell–shell quantum dots

In this work, we theoretically calculated the intraband absorption coefficient (IAC) between the 1s and 1p conduction band states for a spherical core/shell/shell quantum dot (CSS-QD) as function of inner and outer shells’ sizes with and without the presence of strain effect. The electronic structure for the system is computed in the effective mass approximation framework and the strain effect is considered on the continuum elasticity model. We found out that as we compared the strained and the unstrained system, the former causes that the IAC undergoes a small redshift. A similar behavior occurs as the inner and outer shell size increase. The results show that the strain effect is an important factor that will be considered in these nanostructure type. The incorporation of inner and outer shells allowed us to extend some fractions of eV into the absorption spectrum that could be interesting as a mechanism to control the IAC device design.

Collisional and transport parameters of Cu in the warm dense matter regime calculated using the average atom model

Collisional and transport parameters for Cu are computed using the average atom model. Transition metals such as copper are difficult to model within the framework of the average atom model due to the presence of a narrow band of 3d electrons that mix and hybridize with the broad 4s band of nearly-free electrons. With electron temperature increasing, the 3d electrons play a key role in the thermodynamics and transport properties of Cu (Lin et al 2008 Phys. Rev. B 77 075133), as well as the stability of the lattice (Loboda et al 2011 High Energy Density Phys. 7 361). In this work, the average atom model was used to track the average energy of the 3d band and its evolution with electron temperature. At room temperature, its center is at ∼6 electron volts (eV), a few electron-volts below the Fermi energy, and with electron temperature increasing it sinks relative to it. At electron temperature of about 8 eV the 3d electrons leave the conduction band and become bound. A long-standing problem related to the average ion charge observed by conduction band electrons is addressed and successfully resolved. A work-around has been found that predicts the correct average ion charge, , by formally introducing a third group of electrons: quasi-bound electrons. Benchmarking with published data is made that shows good agreement.

An In Situ Film-to-Film Transformation Approach toward Highly Crystalline Covalent Organic Framework Films

An In Situ Film-to-Film Transformation Approach toward Highly Crystalline Covalent Organic Framework Films

Effect of Silane A-174 Modifications in the Structure, Chemistry, and Compressive Strength of PLA-HAP and PLA-β-TCP Biocomposites: Toward the Design of Polymer–Ceramic Implants with High Performance

The effect of silane A-174 (3-(trimethoxysilyl)propyl methacrylate (methacryloxypropyl trimethoxysilane)) modifications of the ceramic surface on the structural characteristics and mechanical performance of hydroxyapatite (HAP)–polylactic acid (PLA) and β-tricalcium phosphate (β-TCP)–PLA composite systems was investigated employing a combination of Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), compressive strength measurements, and statistical models constructed via projection to latent structures (PLS) analysis. The composites were synthesized by solvent casting method at ambient conditions employing ceramic/PLA ratios of 60/40 and 50/50, and silane A-174 percentages of 0, 1, and 3 wt %. Peak positions of O 1s, Ca 2p, P 2p, Si 2p, and C 1s in XP spectra of ceramics, surface-modified ceramics, and the corresponding composites and compressive strength values were used as the predictors and response variables in PLS models. It was found that Ca 2p, P 2p, and Si 2p binding energies of the ceramic component employed in composite synthesis played the most significant role in determining compressive strength. PLA-HAP composite with a ceramic/PLA ratio of 50/50, synthesized employing 3 wt % silane A-174 treated HAP (HAP50PLA50Si3), resulted in enhancement of the compressive strength up to 365 MPa, which is the highest compressive strength value reported in the literature to the best of our knowledge. Additional P 2p, Ca 2p, and C 1s features positioned at 129.64, 350.08, and 280.74 eV in the XP spectra of this specimen together with significant shifts of Si 2p and C 1s bands toward lower binding energies and polymer-bridge-like surface characteristics signaled improved polymer–ceramic interaction in this composite. Attaining mechanical performance comparable with and even higher than that of cortical bone upon silane A-174 modifications might provide opportunities for clinical applications toward developing bioresorbable PLA-HAP-based implants that can be employed in load-bearing applications such as knee and hip replacements.

Anomalous magnetic behaviour of Bi based tetradymites

This work investigates the magnetic properties of the Bi-based bulk Bi2(Se1−xTex)3 tetradymites. The samples were prepared using the melting technique, and all composites are crystallised in the R3m Rhombohedral structure. The lattice cell volume increases monotonically with the Te introduction due to the larger size of Te in comparison with Se. The electrical resistivity data show a metal–semiconductor transition at a certain temperature (Tm) that arises from the overlapping between the 6p and 6s bands. The metal-like behaviour below Tm is in correspondence with the semiconducting degeneracy state, and the empirical analysis has confirmed the metal characteristic scattering mechanisms. The resistivity of the pristine Bi2Se3 compound decreases with the low Te doping level, then increases monotonically with the further Te amounts. This behaviour can be attributed to grain size effect and the change in carriers concentration and mobility. The magnetic measurements have shown the non-pure diamagnetism for the Bi2(Se1−xTex)3 composites, in disagreement with several studies, and show the coexistence of a paramagnetic component. This paramagnetic component arises from the orbital magnetisation, where, the electrons abundance (due to Te and the electron source defects) bends the electronic band, forming 2-dimensional electron gas state that leads to the spin-orbital magnetisation (the source of orbital magnetisation).

Plasma Nitriding of TiO2 Nanotubes: N-Doping in Situ Investigations Using XPS.

The nitrogen doping of titanium dioxide nanotubes (TiO2 NTs) was investigated as a result of well-controlled plasma nitriding of TiO2 NTs at a low temperature. This way of nitrogen doping is proposed as an alternative to chemical/electrochemical methods. The plasma nitriding process was performed in a preparation chamber connected to an X-ray photoelectron spectroscopy (XPS) spectrometer, and the nitrogen-doped TiO2 NTs were next investigated in situ by XPS in the same ultrahigh vacuum (UHV) system. The collected high-resolution (HR) XPS spectra of N 1s, Ti 2p, O 1s, C 1s, and valence band (VB) revealed the formation of chemical bonds between titanium, nitrogen, and oxygen atoms as substitutional or interstitial species. Moreover, the results provided a characterization of the electronic states of N–TiO2 NTs generated by various plasma nitriding and annealing treatments. The VB XPS spectrum showed a reduction in the TiO2 band gap of about 0.6 eV for optimal nitriding and heat-treated conditions. The TiO2 NTs annealed at 450 or 650 °C in air (ex situ) and nitrided under UHV conditions were used as reference materials to check the formation of Ti–N bonds in the TiO2 lattice with a well-defined structure (anatase or a mixture of anatase and rutile). Scanning electron microscopy microscopic observations of the received materials were used to evaluate the morphology of the TiO2 NTs after each step of the nitriding and annealing treatments.

ZnCl2 Enabled Synthesis of Highly Crystalline and Emissive Carbon Dots with Exceptional Capability to Generate O2⋅–

Summary Highly crystalline and emissive carbon dots (CDs) are firstly synthesized via an ionothermal method in organic solvents. In contrast to well-established approaches, ZnCl2 is utilized as the pyrolysis-promoting agent to prepare emissive CDs with tunable wavelengths, directly by carbonization from different O and N precursors under a mild reaction condition at 210°C. More than 50% synthetic yield and 39% photoluminescent quantum yield (blue CD) are obtained. XAFS measurements, in conjunction with TEM, HAADF-STEM, UPS, and ESR analyses, allow us to obtain energy diagram configuration and confirm the luminescent nature of these hard-core structured CDs. Importantly, the resulting CDs exhibit excellent capability to photogenerate superoxide radical anion (O2⋅–), which can be exemplified by both photodynamic therapy and photooxidative cyclization synthesis of tetrahydroquinolines. Representative pharmaceutical mifepristone can be derivatized in 90% yield within 10 min of irradiation of the CDs in an elegant flow reactor.

Hole and Electron Doping of the 4d Transition-Metal Oxyhydride LaSr3 NiRuO4 H4.

Hole or electron doping of phases prepared by topochemical reactions (e.g. anion deintercalation or anion-exchange) is extremely challenging as these low-temperature conversion reactions are typically very sensitive to the electron counts of precursor phases. Herein we report the successful hole and electron doping of the transition-metal oxyhydride LaSr3 NiRuO4 H4 by first preparing precursors in the range Lax Sr4-x NiRuO8 0.5<x<1.4 and then converting into the corresponding Lax Sr4-x NiRuO4 H4 phases. This is particularly noteworthy as the (Ni/Ru)H2 sheets in the Lax Sr4-x NiRuO4 H4 phases are structurally analogous to the CuO2 sheets in cuprate superconductors and hole doping (Ni1+/2+ , Ru2+ ) or electron doping (Ni2+ , Ru1+/2+ ) yields materials with partial occupancy in Ni/Ru -H 1s bands which are analogous to the partially occupied Cu -O 2p bands present in the CuO2 sheets of doped superconducting cuprates.

Hole and Electron Doping of the 4d Transition‐Metal Oxyhydride LaSr3NiRuO4H4

AbstractHole or electron doping of phases prepared by topochemical reactions (e.g. anion deintercalation or anion‐exchange) is extremely challenging as these low‐temperature conversion reactions are typically very sensitive to the electron counts of precursor phases. Herein we report the successful hole and electron doping of the transition‐metal oxyhydride LaSr3NiRuO4H4 by first preparing precursors in the range LaxSr4−xNiRuO8 0.5&lt;x&lt;1.4 and then converting into the corresponding LaxSr4−xNiRuO4H4 phases. This is particularly noteworthy as the (Ni/Ru)H2 sheets in the LaxSr4−xNiRuO4H4 phases are structurally analogous to the CuO2 sheets in cuprate superconductors and hole doping (Ni1+/2+, Ru2+) or electron doping (Ni2+, Ru1+/2+) yields materials with partial occupancy in Ni/Ru –H 1s bands which are analogous to the partially occupied Cu –O 2p bands present in the CuO2 sheets of doped superconducting cuprates.

Nitrogen gas (N2), by near-ambient pressure XPS

Near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., at ca. 2500 Pa, or even higher in some cases. With NAP-XPS, XPS can probe moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. In this submission, we show NAP-XPS survey and narrow scans from nitrogen gas (N2), a material that could not be analyzed at moderate pressures by conventional approaches. Nitrogen gas is an important reference material for NAP-XPS because residual N2 from the air and/or venting produces an N 1s signal in many NAP-XPS spectra. Nitrogen gas may also be deliberately employed as the gaseous background for NAP-XPS experiments. The survey spectrum of N2 gas contains N 1s, N 2s, N KLL (Auger), and valence band signals. This submission is part of a series of articles on NAP-XPS that has been submitted to Surface Science Spectra.

Preparation and characterization of copper oxide nanoparticles decorated carbon nanoparticles using laser ablation in liquid

Carbon nanoparticles CNPs ecorated by copper oxide nano-sized particles would be successfully equipped using technique named pulsed laser ablation in liquid. The XRD pattern proved the presence of phases assigned to carbon and different phases of copper oxide. The chemical structure of the as-prepared nanoparticles samples was decided by Energy Dispersive Spectrum (EDS) measurement. EDS analysis results show the contents of Carbon, Oxygen and Copper in the final product. These nanoparticles were spherical shaped with a size distribution 10 to 80 nm or carbon nanoparticles and 5 to 50 nm for carbon decorated copper oxide nanoparticles, according to Transmission Electron Microscopy (TEM) images and particle-size distribution histogram. It was found that after doping with copper oxide, nanoparticles become smaller and more regular in shape. Optical absorption spectra of prepared nanoparticles were measured using UV–VIS spectroscopy. The absorption spectrum of carbon nanoparticles without doping indicates absorption peak at about 228 nm. After doping with copper oxide, absorption shows appearance of new absorption peak at about (254-264) nm, which is referred to the movement of the charge between 2p and 4s band of Cu2+ ions.

Self-Assembly of Metal Oxide Nanoparticles in Liquid Metal toward Nucleation Control for Graphene Single-Crystal Arrays

Summary We have achieved the spontaneous assembly of alumina nanoparticles on a liquid metal surface and further synthesized a very-large-scale graphene single-crystal array. The effective electrical field established as a result of the electrical charge of the alumina nanoparticles in the liquid metal ensures the ordered self-assembly of the alumina islands and lays the foundation for precise spatial control of graphene nucleation, leading to the formation of graphene single-crystal arrays. In addition, controlling the density of the alumina in the liquid metal can precisely tune the periodicity of the arrays. This simple strategy, which is unlike the usual solid/aqueous solution system, opens up new territory for nanoparticle assembly. Focusing on the origin of the nanoparticle interaction that drives the self-assembly of ordered structure in the liquid metal system is a promising avenue for triggering more interesting applications.

Internal photoemission for photovoltaic using p-type Schottky barrier: Band structure dependence and theoretical efficiency limits

Solar energy conversion via internal photoemission (IPE) across a planar p-type Schottky junction is quantified for aluminum (Al) and copper (Cu) in the framework of direct transitions with non-constant matrix elements. Transition probabilities and k-resolved group velocities are obtained based on pseudo-wavefunction expansions and realistic band structures using the pseudopotential method. The k-resolved number of direct transitions, hole photocurrent density, quantum yield (QY), and the power conversion efficiency (PCE) under AM1.5G solar irradiance are subsequently calculated and analyzed. For Al, the parabolic and “parallel-band” effect along the U-W-K path significantly enhances the transition rate with final energies of holes mainly within 1.41 eV below the Fermi energy. For Cu, d-state hot holes mostly generated near the upper edge of 3d bands dominate the hole photocurrent and are weekly (strongly) dependent on the barrier height (metal film thickness). Hot holes produced in the 4s band behave just oppositely to their d-state counterparts. Non-constant matrix elements are shown to be necessary for calculations of transitions due to time-harmonic perturbation in Cu. Compared with Cu, Al-based IPE in p-type Schottky shows the highest PCE (QY) up to about 0.2673% (5.2410%) at ΦB = 0.95 eV (0.5 eV) and a film thickness of 11 nm (20 nm). It is predicted that metals with relatively dispersionless d bands (such as Cu) in most cases do not outperform metals with photon-accessible parallel bands (such as Al) in photon energy conversion using a planar p-type Schottky junction.

On the consequences of the stereochemical activity of the Bi(iii) 6s2 lone pair in cyclen-based complexes. The [Bi(DO3A)] case.

We report a detailed study of the structure of the [Bi(DO3A)] complex both in the solid state and in solution. The X-ray crystal structure of [Bi(DO3A)] evidences the octa-coordination of the Bi(iii) ion, which is directly coordinated to the four nitrogen atoms of the cyclen unit and three oxygen atoms of the carboxylate groups. The octa-coordination is completed by an oxygen atom of a neighboring carboxylate group, which bridges Bi(iii) ions thanks to μ2-η1:η1 coordination, resulting in the formation of a coordination polymer. The Bi(iii) ion presents a twisted-square antiprismatic (TSAP) coordination geometry associated with the Δ(δδδδ)/Λ(λλλλ) enantiomeric pair. A computational DFT study indicates that the 6s2 lone pair of Bi(iii) is stereochemically active in [Bi(DO3A)] and most of the cyclen-based complexes reported in the literature. Depending on the spatial arrangement of the donor atoms of the ligand the lone pair points in different directions, so that Bi(iii) can easily accommodate different coordination environments. In solution the [Bi(DO3A)] complex exists as a monomeric complex, as demonstrated by DOSY measurements. The stability constant of the [Bi(DO3A)] complex, determined by using batch spectrophotometric titrations, was found to be rather high (log K = 26.85(5)). The complex presents characteristic absorption in the UV spectrum at 299 nm (ε = 8770 M-1 cm-1) that was attributed to the Bi(iii)-centered 6p ← 6s band on the basis of TDDFT calculations. Spectrophotometric titrations reveal weak binding of different anions to the [Bi(DO3A)] complex, with association constants of K11 = 3.55(8), 3.09(7), 6.2(1) and 2.19(5) for Cl-, Br-, I- and N3-, respectively.

Ce in the +4 oxidation state: Anion photoelectron spectroscopy and photodissociation of small CexOyHz- molecules.

The anion photoelectron (PE) spectra of a range of small mono-cerium molecular species, along with the Ce2O4- and Ce3O6- stoichiometric clusters, are presented and analyzed with the support of density functional theory calculations. A common attribute of all of the neutral species is that the Ce centers in both the molecules and clusters are in the +4 oxidation state. In bulk ceria (CeO2), an unoccupied, narrow 4f band lies between the conventional valence (predominantly O 2p) and conduction (Ce 5d) bands. Within the CeO2-, CeO3H2-, and Ce(OH)4- series, the PE spectra and computational results suggest that the Ce 6s-based molecular orbital is the singly occupied HOMO in CeO2- but becomes destabilized as the Ce 4f-local orbital becomes stabilized with increasing coordination. CeO3-, a hyperoxide, undergoes photodissociation with 3.49 eV photon energy to form the stoichiometric neutral CeO2 and O-. In the CeO2-, Ce2O4- ,and Ce3O6- stoichiometric cluster series, the 6s destabilization with 4f stabilization is associated with increasing cluster size, suggesting that a bulk-like band structure may be realized with fairly small cluster sizes. The destabilization of the 6s-based molecular orbitals can be rationalized by their diffuse size relative to Ce-O bond lengths in a crystal structure, suggesting that 6s bands in the bulk may be relegated to the surface.

Super-hydrophilic anatase TiO2 thin film in-situ deposited by DC magnetron sputtering

The present work shows in-situ polycrystalline anatase TiO2 without annealing under the deposition condition of affluent oxygen partial pressure (≥5.67, PO2/PAr) by DC magnetron sputtering. The films tended to grow from the early random orientation to A(211) oriented polycrystalline as deposition time increases. As the oxygen gas flow rate was high, A(211) facet grew more. Therefore, oxygen partial pressure and the deposition time/thickness can be considered as the key parameters that promote the growth of A(211) facet. The study focus was the hydrophilicity due to A(211) facet measured in dark after initial one time UV exposure. The contact angle relaxation of super-hydrophilic TiO2 films was influenced by the humidity for dark storage time. The contact angle was measured after 24h from the initial UV irradiation. The measured contact angle decreased somewhat linearly with the increase of the XRD intensity ratio of A(211)/A(101) up to 50%. When it was higher than 50%, the angle saturated. XPS analysis showed that the higher the XRD intensity ratio of A(211)/A(101), the larger the area of O 1s (OH) band related to the dissociative adsorption of water. The relative amount of the surface hydroxyl group was found to be inversely proportional to the contact angle. ATR-FTIR spectra also showed that the water is adsorbed more on the formation of A(211) facet on the TiO2 surface. In summary, A(211) oriented TiO2 grains lead to dissociative adsorption of water and show better superhydrophilicity due to a sufficient amount of surface hydroxyl groups.

Antibacterial efficiency of magnetron sputtered TiO2 on poly(methyl methacrylate)

Titanium dioxide (TiO2) particles were deposited on poly(methyl methacrylate) (PMMA) by magnetron sputtering of Ti at varying O2/Ar flow rate ratio and at varying discharge current using a Compact Planar Magnetron (CPM) sputtering device. The deposited TiO2 on PMMA samples were characterized using X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The samples were tested for their photoinduced hydrophilicity, and antibacterial activity against Escherichia coli (E.coli). XPS, FTIR and EDX analyses confirmed the presence of TiO2 on the surface of PMMA. XPS spectra revealed the presence of Ti 2p and O 1s bands on the surface of the samples and the EDX spectra showed that the elemental ratio of Ti and O ranged from 26 to 30% and 69 to 73%, respectively. SEM showed that the deposited TiO2 was relatively smooth with micro islands of titanium at the surface. Photoinduced hydrophilicity was observed for all samples after 10min of UV irradiation; this was seen from the reduction of the water contact angles on the UV irradiated samples from 66° to as low as <5°. Antibacterial tests showed that all TiO2-deposited PMMA samples exhibited antibacterial efficiency of 70% to 80%.

Angle-Resolved and Resonant Photoemission Study of the Valence Bands of &amp;lt;i&amp;gt;α&amp;lt;/i&amp;gt;-La(0001) on W(110)

We report a photoelectron spectroscopic study of the valence bands of double hexagonal-close-packed (dhcp) α-La(0001) films epitaxially grown on W(110) at room temperature. The La 5d photoemission cross section in the photon energy region from 20 eV to 130 eV was obtained and the valence-band structure of α-La was determined. Except for 4f-related structures, the valence-band structures of dhcp α-La and dhcp β-Ce were found to resemble each other. From the band structure, the crystal structure of the La film was confirmed. No evidence for the existence of a 5d-like surface state near the Fermi energy at the point of the surface Brillouin zone was obtained and a 6s band bottom was identified.

Comparative study of optical and magneto‐optical properties of normal, disordered, and inverse spinel‐type oxides

Abstract, , , , and thin films were fabricated by pulsed laser deposition at high and low temperatures resulting in crystalline single‐phase normal, inverse, as well as disordered spinel oxide thin films with smooth surface morphology. The dielectric function, determined by spectroscopic ellipsometry in a wide spectral range from 0.5 to 8.5 eV, is compared with the magneto‐optical response of the dielectric tensor, investigated by magneto‐optical Kerr effect spectroscopy in the spectral range from 1.7 to 5.5 eV with an applied magnetic field of 1.7 T. Crystal field, inter‐valence, and inter‐sublattice charge transfer transitions, and transitions from to metal cation 3d or 4s bands are identified in both the principal diagonal elements and the magneto‐optically active off‐diagonal elements of the dielectric tensor. Depending on the degree of cation disorder, resulting in local symmetry distortion, the magneto‐optical response is found to be strongest for high crystal quality inverse spinels and for disordered normal spinel structure, contrary to the first principle studies of and . The results presented provide a basis for deeper understanding of light–matter interaction in this material system that is of vital importance for device‐related phenomena and engineering.