Ir Surface Research Articles

Heteroepitaxy of single crystal diamond on Ir buffered KTaO3 (001) substrates

The heteroepitaxy of a single crystal diamond has been carried out in the KTaO3 substrate using Ir as a buffer layer. KTaO3 has a perovskite lattice structure and displays a face-centered cubic structure. Its lattice constant is 3.98 Å, which is only 3% mismatched with the lattice constant of Ir of 3.84 Å, and also, its thermal expansion coefficient is 4.031 × 10−6/K, which is nearly close to that of diamond 3.85 × 10−6/K (at 1223 K), making it to be regarded as an alternate substrate of the heteroepitaxy of a single crystal diamond. The magnetron sputtering technique was used to deposit Ir thin films with a high orientation in the (001) direction on a KTaO3 (001) substrate. Thereafter, bias enhanced nucleation on Ir surface was grown by direct current chemical vapor deposition (CVD) methods. At last, a single crystal diamond with a size of 10 × 10 × 0.78 mm3 has been grown, whose (004) rocking curve FWHM is 183 arc sec, which testifies to the excellent crystalline quality of the heteroepitaxial diamond film.

The trapping of methane on Ir(111): A first-principles quantum study.

We implement a fully quantum mechanical study of methane trapping on Ir(111), where the phonons, the molecule-surface interaction, and the molecule-phonon coupling are all computed from first-principles. We find that both the surface corrugation and the phonon coupling vary strongly with molecular orientation and that there is a "chemical" aspect to this due to the catalytic nature of the metal. For example, molecules with reactive orientations can approach close to surface sites with low barriers to dissociation. Moreover, lattice motion can lower the barrier to dissociation, leading to unusual behavior for the phonon coupling. We find good agreement with experiment and two recent classical studies if we average our potential energy surface over several orientations of the molecule. We also find reasonable agreement with a recent study of methane diffraction, although we show that diffraction does not play a major role in trapping on the smooth Ir(111) surface and that trapping obeys normal energy scaling, consistent with experiment. We show that the trapping probability can be sensitive to the temperature at both high and low incidence energies. Relaxation and desorption of trapped particles are examined.

Trends of higher-order exchange interactions in transition metal trilayers

We present a systematic study of higher-order exchange interactions beyond the pair-wise Heisenberg exchange in transition-metal trilayers based on density functional theory calculations. We show that these terms can play an important role in magnetic trilayers composed of a single hexagonal Fe or Co atomic layer sandwiched between $4d$ and $5d$ transition-metal layers. We study the dependence of the biquadratic and the three-site and four-site four spin interaction on the band filling of the $4d$ and $5d$ layers as well as the stacking sequence, i.e. fcc vs. hcp stacking. Our calculations reveal relatively small higher-order interactions for Co based trilayers. For Fe based trilayers with a Rh or Ir layer the higher-order terms can be on the same order of magnitude as pair-wise Heisenberg exchange. The trends obtained for freestanding trilayers are used to understand the higher-order interactions in ultrathin film systems on surfaces that are experimentally accessible. It is shown that hcp Rh/Fe/Ir(111) and hcp-Rh/Fe/Rh(111) exhibit the largest values for the biquadratic and the three-site four spin interaction of all systems under study. We further demonstrate that the three-site four spin interaction is responsible for the experimentally observed change of the magnetic ground state of Rh/Fe/Ir(111) from a spin spiral (single-Q) for fcc-Rh to a 2Q state for hcp-Rh. We find similar trends for Rh/Fe/Rh(111), i.e. replacing the Ir surface by the isoelectronic Rh surface. For Rh/Co/Ir(111), we obtain a negative value for the four-site four spin interaction which will lead to a reduced stability of magnetic skyrmions which are metastable in this film at zero magnetic field. In contrast, for Pd/Fe/Ir(111), the four-site four spin interaction is positive which leads to an enhanced stability of skyrmions.

Reconstruction of a 2D layer of KBr on Ir(111) and electromechanical alteration by graphene.

A novel reconstruction of a two-dimensional layer of KBr on an Ir(111) surface is observed by high-resolution noncontact atomic force microscopy and verified by density functional theory (DFT). The observed KBr structure is oriented along the main directions of the Ir(111) surface, but forms a characteristic double-line pattern. Comprehensive calculations by DFT, taking into account the observed periodicities, resulted in a new low-energy reconstruction. However, it is fully relaxed into a common cubic structure when a monolayer of graphene is located between substrate and KBr. By using Kelvin probe force microscopy, the work functions of the reconstructed and the cubic configuration of KBr were measured and indicate, in accordance with the DFT calculations, a difference of nearly 900 meV. The difference is due to the strong interaction and local charge displacement of the K+/Br− ions and the Ir(111) surface, which are reduced by the decoupling effect of graphene, thus yielding different electrical and mechanical properties of the top KBr layer.

Influence of surface tension on the characteristics of FTIR spectra on the example of saliva

The aim of this work was to test the hypothesis about the effect of surface tension of biological fluids on the characteristics of IR spectra using saliva as an example. The study involved 100 volunteers without clinically significant diseases. Saliva samples were collected from all participants, a parallel determination of surface tension, biochemical composition was carried out, and IR spectra were obtained. Comparison of the results was carried out using cluster analysis, principal component analysis and correlation analysis. The existence of a relationship between the characteristics of absorption bands in IR spectra and surface tension has been established using saliva as an example. It is shown that, first, a change in the surface tension affects the shift of the absorption bands in the spectra, while the intensity and area of ​​the corresponding absorption bands change to a lesser extent. Combinations of the characteristics of the IR spectra have been revealed that provide the maximum correlation relationship with both the total volumetric content of surfactants and their adsorption activity. Correlations with total surfactant content include absorption band characteristics corresponding to proteins, lipids and phospholipids. Whereas the adsorption activity of surfactants correlates mainly with the absorption bands of proteins in saliva. The revealed patterns are substantiated taking into account the biochemical composition of saliva, depending on the surface tension.

Structural and spectroscopic studies, DFT calculations, thermal characterization and antimicrobial activity of cobalt(II) organic-inorganic hybrid material with benzamidinium cation

An organic-inorganic hybrid compound bis(benzamidinium)tetrachlorocobaltate(II) monohydrate, (C7H9N2)2[CoCl4]·H2O, was synthesized by slow evaporation at room temperature and characterized by powder and single-crystal X-ray diffraction (XRD), IR, UV-vis spectroscopies, and Hirshfeld surface analysis. Single-crystal X-ray diffraction analysis indicates that the structure consists of a succession of mixed layers formed by organic cations, inorganic anions and water molecules parallel to the (ab) plane and propagate according to the c-axis. The structure is stabilized by N-H···Cl, N-H···O, O-H···Cl hydrogen bonds, Cl···Cl and π-π interactions. The powder XRD analysis confirms the phase purity of the crystalline sample, while the composition of our phase was verified by semi-quantitative analysis EDX. The DFT calculations were performed using the B3LYP functional and 6-311 + G(2d,2p) basis set for H, C, N, Cl and LANL2DZ for Co. Comprehensive experimental and theoretical structural studies on the compound were carried out through IR and UV-visible spectroscopies. The thermal stability of the three-dimensional (3-D) network of this compound was also discussed. The in vitro antibacterial activity of the compound against different bacterial strains was evaluated. Hirshfeld surface analysis was used to show surface contours and 2-D fingerprint plots have been used to analyze intermolecular interactions.

Nonoxidative Conversion of Methane, Ethane, and Ethylene on Flat Ir(111) and Stepped Ir(211) Surfaces

The mechanisms of iridium-catalyzed nonoxidative conversion of light hydrocarbons have been computed on flat Ir(111) and stepped Ir(211) surfaces under given conditions. On Ir(111), CH4 dissociatio...

A novel fluorescent strategy based on double modifications of metal organic framework material CAU-10-NH2 for low background and high sensitivity determination of H2S

Hydrogen sulfide is typical metabolic marker and environmental pollutant which is worthwhile to determine. Herein, a low background and high sensitivity fluorescent strategy based on double modifications of metal organic framework material CAU-10-NH2 is proposed for the determination of hydrogen sulfide. Firstly, a functional monomer 3,5-diaminobenzoic acid is employed to modify on the CAU-10-NH2, the product CAU-10-NH-dAba has strong fluorescent performance at 412 nm under an excitation wavelength of 320 nm. Subsequently, it is further modified by the azide group to form CAU-10-NH-dAba-N3. This azidation inhibits the fluorescent signal. However, in the presence of hydrogen sulfide, the azide group is specifically reduced to amidogen, and results in the recovery of the fluorescence. The CAU-10-NH-DABA-N3 was characterized by solid state NMR, XPS, fluorescence, IR, XRD, SEM and specific surface area. After the optimization of pH value, temperature and interaction time, the detection results of hydrogen sulfide demonstrate the linear range of this strategy is from 20 to 140 nM with a detection limit of 1.51 nM, which is significantly better than that of the CAU-10-NH2 merely modified by 3,5-dinitrobenzoic acid. Meanwhile, the satisfactory assay results of hydrogen sulfide in serum sample and Pearl river water suggest a potential application prospect of this strategy in clinical diagnosis and environment monitoring.

H2O decomposition on Ir (1 1 1) surface with high-reactivity at room temperature: A first-principles study

H2O decomposition by chemical catalyst with low energy-cost is accepted as a promising method to produce hydrogen with high-purity and no carbon monoxide. In this paper, we studied the decomposing behavior of H2O molecule on the clean and O-covered Ir (111) surface in order to explore its potential as a novel chemical catalyst for this purpose. Results indicated that the pre-adsorbed O atom can exert a prominent promotion impact for Ir (111) surface upon H2O and OH dehydrogenations, boosting their Ead and lowering the Ebar simultaneously. Given the small Ebar of 0.40 eV for H2O dehydrogenation and of 0.76 eV for OH dehydrogenation on the O-covered Ir (111) surface, we are hopeful that the H2O decomposition into separate atoms could be realized on such surface at room temperature.

Electrochemically Decorated Iridium Electrodes with WS3−x Toward Improved Oxygen Evolution Electrocatalyst Stability in Acidic Electrolytes

AbstractIridium‐based oxides, currently the state‐of‐the‐art oxygen evolution reaction (OER) electrocatalysts in acidic electrolytes, are cost‐intensive materials which undergo significant corrosion under long‐term OER operation. Thus, numerous researchers have devoted their efforts to mitigate iridium corrosion by decoration with corrosion‐resistant metal oxides and/or supports to maximize OER catalyst durability whilst retaining high activity. Herein a one‐step, facile electrochemical route to obtain improved IrOx thin film OER stability in acid by decorating with amorphous tungsten sulphide (WS3−x) upon electrochemical decomposition of a [WS4]2− aqueous precursor is proposed. The rationale behind applying such WS3−x decoration stems from the generation of a tungsten oxide phase, a well‐known corrosion‐resistant photoactive OER catalyst. The study demonstrates the viability of the proposed WS3−x decoration, allowing the tailoring of experimental parameters responsible for WS3−x nanoparticle size and surface coverage. OER stability tests coupled by ex situ SEM and XPS corroborate the beneficial effect of WS3−x decoration, yielding improved OER specific activity metrics along with minimized Ir surface roughening, a characteristic of electrodissolution. Iridium decoration with electrodeposited, corrosion‐resistant oxides is consequently shown to be a promising route to maximize OER stabilities.

Virtues of Ir(1 0 0) substrate on diamond epitaxial growth: First-principle calculation and XPS study

The heteroepitaxial growth of single crystal diamond requires substrate of high quality, and Ir(100) is an ideal substrate which can meet the standard perfectly. However, the reason of its outstanding performance still remains unclear. In this paper, the interaction mechanism between carbon atoms and Ir (100) surface at the initial stage of nucleation and its uniqueness caused by distinctive energy changes compared with (100) faces of Cu and Ni are explained by first-principle calculation, which acts as a dominating factor in the transformation from epitaxial films to single crystal wafers. The energy driving force of the dissolution-precipitation process is described, which can completely accord with bias-enhanced nucleation(BEN) method to illustrate the effect of voltage on diamond nucleation. The precipitation of carbon atoms and appearance of primary nuclei with the increase of carbon concentration are discussed, which can effectively explain the special phenomenon of the “domain” formation. A carbon-rich pre-treatment before primary nucleation on Ir (100) surface shows that the initial nucleation process can form supersaturated solid solution of carbon in Ir (100), which can greatly accelerate the subsequent dissolution-precipitation circulation.

Density functional theory insights into the bonding of CH3OH and CH3O with Ir(111) surface

Introduction: Understanding the adsorption characteristics of CH3OH and CH3O on the noble metal surfaces is essential for designing better catalysts for the on-board production of hydrogen from CH3OH. This study aims to provide insights into the adsorption behavior of these molecules on Ir(111) surface.
 Methods: The adsorption structure, the adsorption energy, and the bonding mechanism of CH3OH and CH3O with Ir(111) surface were investigated by means of the density functional theory (DFT) calculations and the Bader charge analysis.
 Results: The DFT results show that the adsorption of CH3OH and CH3O is driven by the formation of Ir–O bond at the top site of the surface by the overlap of O-2p and Ir-5d orbitals. The overlap of these orbitals is greater in the absorption of CH3O, resulting in stronger adsorption energy of CH3O (2.23 eV vs. 0.32 eV). In agreement with the adsorption strength, the charge transfer from CH3O to the surface is significantly larger than from CH3OH (0.386 e vs. 0.073 e).
 Conclusion: Although driven by the same adsorption bond, the difference in the molecular characteristics leads to a marked difference in the absorption strength of CH3OH and CH3O on Ir(111) surface.

Regulating Star Formation in Nearby Dusty Galaxies: Low Photoelectric Efficiencies in the Most Compact Systems

Abstract Star formation in galaxies is regulated by heating and cooling in the interstellar medium (ISM). In particular, the processing of molecular gas into stars will depend strongly on the ratio of gas heating to gas cooling in the neutral gas around sites of recent star formation. In this work, we combine mid-infrared (mid-IR) observations of polycyclic aromatic hydrocarbons (PAHs), the dominant heating mechanism of gas in the ISM, with [C ii], [O i], and [Si ii] fine-structure emission, the strongest cooling channels in dense, neutral gas. The ratio of IR cooling line emission to PAH emission measures the photoelectric efficiency, a property of the ISM which dictates how much energy carried by ultraviolet photons gets transferred into the gas. We find that star-forming, IR-luminous galaxies in the Great Observatories All-Sky LIRG Survey with high IR surface densities have low photoelectric efficiencies. These systems also have, on average, higher ratios of radiation field strength to gas densities, and larger average dust grain size distributions. The data support a scenario in which the most compact galaxies have more young star-forming regions per unit area that exhibit less efficient gas heating. These conditions may be more common at high z, and may help explain the higher star formation rates at cosmic noon. We make predictions on how this can be investigated with the James Webb Space Telescope.

Highly Efficient Ir-CoOx Hybrid Nanostructures for the Selective Hydrogenation of Furfural to Furfuryl Alcohol.

Decoration of noble metals with transition-metal oxides has been intensively studied for heterogeneous catalysis. However, controllable syntheses of metal-metal oxide heterostructures are difficult, and elucidation of such interfaces is still challenging. In this work, supported IrCo alloy nanoparticles are transformed into supported Ir-CoOx close-contact nanostructures by in situ calcination and following selective reduction. Relative to Ir/Al2O3, Ir-CoOx/Al2O3 shows greatly enhanced activities for the hydrogenation of furfural derivatives to the corresponding furfuryl alcohol derivatives with more than 99% selectivity and demonstrates significantly improved activities and selectivity for hydrogenations of α,β-unsaturated aldehydes to α,β-unsaturated alcohols. The modification of Ir surfaces with CoOx prevents Ir nanoparticles from growing, achieving high thermal and catalytic stabilities. Theoretic calculation suggests that the better catalytic performance of Ir-CoOx/Al2O3 is ascribed to the Ir-CoOx interaction, which promotes the absorption of furfural as well as desorption of furfuryl alcohol, resulting in enhanced catalytic activities.

Friedel Oscillations Induced by Magnetic Skyrmions: From Scattering Properties to All-Electrical Detection.

Magnetic skyrmions are spin swirling solitonic defects that can play a major role in information technology. Their future in applications and devices hinges on their efficient manipulation and detection. Here, we explore from ab-initio their nature as magnetic inhomongeities in an otherwise unperturbed magnetic material, Fe layer covered by a thin Pd film and deposited on top of Ir(111) surface. The presence of skyrmions triggers scattering processes, from which Friedel oscillations emerge. The latter mediate interactions among skyrmions or between skyrmions and other potential surrounding defects. In contrast to their wavelengths, the amplitude of the oscillations depends strongly on the size of the skyrmion. The analogy with the scattering-off atomic defects enables the assignment of an effective scattering potential and a phase shift to the skyrmionic particles, which can be useful to predict their behavior on the basis of simple scattering frameworks. The induced charge ripples can be utilized for a noninvasive all-electrical detection of skyrmions located on a surface or even if buried a few nanometers away from the detecting electrode.

Magnetic response and electronic states of well defined Graphene/Fe/Ir(111) heterostructure

We investigate a well defined heterostructure constituted by magnetic Fe layers sandwiched between graphene (Gr) and Ir(111). The challenging task to avoid Fe-C solubility and Fe-Ir intermixing has been achieved with atomic controlled Fe intercalation at moderate temperature below 500 K. Upon intercalation of a single ordered Fe layer in registry with the Ir substrate, an intermixing of the Gr bands and Fe $d$ states breaks the symmetry of the Dirac cone, with a downshift in energy of the apex by about 3 eV, and well-localized Fe intermixed states induced in the energy region just below the Fermi level. First principles electronic structure calculations show a large spin splitting of the Fe states, resulting in a majority spin channel almost fully occupied and strongly hybridized with Gr $\ensuremath{\pi}$ states. X-ray magnetic circular dichroism on the Gr/Fe/Ir heterostructure reveals an ordered spin configuration with a ferromagnetic response of Fe layer(s), with enhanced spin and orbital configurations with respect to the bcc-Fe bulk values. The magnetization switches from a perpendicular easy magnetization axis when the Fe single layer is lattice matched with the Ir(111) surface to a parallel one when the Fe thin film is almost commensurate with graphene.

First principles study of atomic adsorption on (111) and (100) surfaces of iridium

We have investigated the adsorption of nine different adatoms on the (111) and (100) surfaces of Iridium (Ir) using first principles density functional theory. The study explores surface functionalization of Ir which would provide important information for further study of its functionality in catalysis and other surface applications. The adsorption energy, stable geometry, density of states and magnetic moment are some of the physical quantities of our interest. The study reveals that the three-/four-fold hollow site is energetically the most favorable adsorption site on the (111)/(100) surface of Ir. The investigation on a wide range of coverages (from 0.04 to 1 monolayer) reveals the strong coverage dependence of adsorption energy of the adsorbate atoms. The adsorption energy is found to increase as the coverage increases, implying a repulsive interaction between the adsorbates. Strong hybridization between the adsorbates and the substrate electronic states is revealed to impact the adsorption, while the magnetic moment of the adsorbates is found to be suppressed. The Bader analysis reveals significant amount of charge transfers between the adsorbate atoms and the substrate. The binding of adsorbate atoms on the (100) surface is observed to be moderately stronger as compared to that on the (111) surface.

Kinetic and mechanistic analysis of NH3 decomposition on Ru(0001), Ru(111) and Ir(111) surfaces.

We investigated the catalytic NH3 decomposition on Ru and Ir metal surfaces using density functional theory. The reaction mechanisms were unraveled on both metals, considering that, on the nano-scale, Ru particles may also present an fcc structure, hence, leading to three energy profiles. We implemented thermodynamic and kinetic parameters obtained from DFT into microkinetic simulations. Batch reactor simulations suggest that hydrogen generation starts at 400 K, 425 K and 600 K on Ru(111), Ru(0001) and Ir(111) surfaces, respectively, in excellent agreement with experiments. During the reaction, the main surface species on Ru are NH, N and H, whereas on Ir(111), it is mainly NH. The rate-determining step for all surfaces is the formation of molecular nitrogen. We also performed temperature-programmed reaction simulations and inspected the desorption spectra of N2 and H2 as a function of temperature, which highlighted the importance of N coverage on the desorption rate.

Towards bridging the structure gap in heterogeneous catalysis: the impact of defects in dissociative chemisorption of methane on Ir surfaces

A quantitative understanding of the role played by defect sites in heterogeneous catalysis is of great importance in designing new and more effective catalysts. In this work, we report a detailed dynamic study of a key step in methane steam reforming under experimentally relevant conditions on a new high-dimensional potential energy surface determined from first principles data with the aid of machine learning, with which the interactions of CH4 with both the flat Ir(111) and stepped Ir(332) surfaces are described. In particular, we argue based on our simulations that the experimentally observed "negatively activated" dissociative chemisorption of methane on Ir surfaces could be due to a combined effect of defects and high substrate temperature, which lowers the reaction barrier relative to that on terraces. Furthermore, a model based on dynamic information of trapping and reaction channels is proposed, which allows a quantitative prediction of the initial sticking probability for different defect densities, thus helping to close the so-called structure gap in heterogeneous catalysis.

Time-of-flight measurements of the low-energy scattering of CH4 from Ir(111).

We have measured high-resolution time-of-flight (TOF) spectra of methane scattered from an Ir(111) surface at an incident energy of 81 meV. The angular distributions of scattered CH4 reveal the presence of a sharp and intense specular peak in addition to sharp features corresponding to rotationally inelastic diffraction (RID) peaks along the two main symmetry directions of Ir(111). TOF spectra have been recorded at several RID positions for the two high-symmetry directions. The data show that the scattering dynamics of CH4 is more complex than the one reported for H2/D2, where energy losses in TOF correspond to the expected excitation/deexcitation RID energy transitions. For CH4, this is the case only for RID peaks showing up far from the specular peak, whereas those appearing close to the specular position present different behaviors, depending on the incident direction. The results are compared with Ne scattering TOF data, which allows to assess the relevance of multiphonon scattering in the energy-exchange process. Finally, we report experimental evidence of selective adsorption resonances detected with CH4 beams. This will allow characterizing the CH4-metal surface physisorption well by measuring angular distributions with CH4 beams.